PATENT DOCUMENT

Publication Number: US-11144158-B2
Application Number: US-201815988991-A
Country: US
Kind Code: B2

Title: Differential acoustic touch and force sensing

Abstract:
Acoustic touch and/or force sensing system architectures and methods for acoustic touch and/or force sensing can be used to detect a position of an object touching a surface and an amount of force applied to the surface by the object. The position and/or an applied force can be determined using time-of-flight (TOF) techniques, for example. Acoustic touch sensing can utilize transducers (e.g., piezoelectric) to simultaneously transmit ultrasonic waves along a surface and through a thickness of a deformable material. The location of the object and the applied force can be determined based on the amount of time elapsing between the transmission of the waves and receipt of the reflected waves. In some examples, an acoustic touch sensing system can be insensitive to water contact on the device surface, and thus acoustic touch sensing can be used for touch sensing in devices that may become wet or fully submerged in water.

Claims:
What is claimed is: 
     
       1. An acoustic touch sensing system, comprising:
 a transducer; 
 a differential electrode configuration coupled to the transducer; and 
 an amplifier coupled to at least one electrode of the differential electrode configuration, 
 wherein the amplifier and the differential electrode configuration are configured to perform a differential measurement to sense a touch signal at one or more spatial modulation frequencies corresponding to the differential electrode configuration and reject a spatial common mode signal having a common spatial characteristic relative to the differential electrode configuration. 
 
     
     
       2. The acoustic touch sensing system of  claim 1 , wherein the differential electrode configuration is configured with an alternating pattern of electrodes. 
     
     
       3. The acoustic touch sensing system of  claim 2 , wherein the alternating pattern of electrodes has a pitch corresponding to a first spatial frequency. 
     
     
       4. The acoustic touch sensing system of  claim 1 , further comprising switching circuitry configured to:
 group two or more electrodes of the differential electrode configuration in a first grouping configuration having a first pitch; and 
 group two or more electrodes of the differential electrode configuration in a second grouping configuration having a second pitch, different from the first pitch. 
 
     
     
       5. The acoustic touch sensing system of  claim 1 , further comprising switching circuitry configured to:
 group four or more electrodes of the differential electrode configuration in a first grouping configuration having a first pitch and a first spatial phase; and 
 group the four or more electrodes of the differential electrode configuration in a second grouping configuration having the first pitch and a second spatial phase, different from the first spatial phase. 
 
     
     
       6. The acoustic touch sensing system of  claim 5 , further comprising switching circuitry configured to:
 group the four or more electrodes of the differential electrode configuration in a third grouping configuration having a second pitch, different from the first pitch. 
 
     
     
       7. The acoustic touch sensing system of  claim 6 , wherein the first pitch corresponds to a first spatial frequency, and the second pitch corresponds to a second spatial frequency, different from the first spatial frequency. 
     
     
       8. The acoustic touch sensing system of  claim 1 , further comprising switching circuitry configured to:
 couple the differential electrode configuration to drive circuitry configured to drive the transducer to produce an acoustic wave during a drive phase; and 
 couple the differential electrode configuration to sense circuitry configured to receive electrical signals from the transducer during a sensing phase. 
 
     
     
       9. The acoustic touch sensing system of  claim 8 , further comprising:
 a first electrode and a second electrode disposed on a first side of the transducer; and 
 a third electrode disposed on the second side of the transducer; 
 wherein:
 the first electrode and the second electrode are coupled together during the drive mode; and 
 the first electrode and the second electrode are coupled differentially to the sense circuitry during the sensing mode. 
 
 
     
     
       10. The acoustic touch sensing system of  claim 9 , wherein the third electrode is grounded during the sensing mode and the third electrode is differentially driven with the coupled first and second electrode in the driving mode. 
     
     
       11. The acoustic touch sensing system of  claim 9 , wherein the third electrode is floating during the sensing mode and the third electrode is differentially driven with the coupled first and second electrode in the driving mode. 
     
     
       12. A method comprising:
 transmitting an acoustic wave from a transducer; 
 receiving a reflected acoustic wave at a differential electrode configuration coupled to the transducer using an amplifier coupled to at least one electrode of the differential electrode configuration; and 
 compensating for a spatial common mode signal having a common spatial characteristic relative to the differential electrode configuration using the received signal from the differential electrode configuration, wherein compensating comprises performing a differential measurement to sense a touch signal at one or more spatial modulation frequencies corresponding to the differential electrode configuration and rejecting the spatial common mode signal having the common spatial characteristic relative to the differential electrode configuration. 
 
     
     
       13. The method of  claim 12 , wherein the differential electrode configuration is configured with an alternating pattern of electrodes. 
     
     
       14. The method of  claim 12 , wherein the alternating pattern of electrodes has a pitch corresponding to a first spatial frequency. 
     
     
       15. The method of  claim 12 , further comprising:
 grouping two or more electrodes of the differential electrode configuration in a first grouping configuration having a first pitch; and 
 grouping two or more electrodes of the differential electrode configuration in a second grouping configuration having a second pitch, different from the first pitch. 
 
     
     
       16. The method of  claim 12 , further comprising:
 grouping four or more electrodes of the differential electrode configuration in a first grouping configuration having a first pitch and a first spatial phase; and 
 grouping four or more electrodes of the differential electrode configuration in a second grouping configuration having the first pitch and a second spatial phase, different from the first spatial phase. 
 
     
     
       17. The method of  claim 12 , wherein compensating for the spatial common mode signal using the received signal from the differential electrode configuration includes floating an electrode that is common to the differential electrode configuration. 
     
     
       18. The method of  claim 12 , wherein compensating for the spatial common mode signal using the received signal from the differential electrode configuration includes inputting a pair of outputs of the differential electrode configuration to a common-mode feedback circuit. 
     
     
       19. A non-transitory computer-readable storage medium having stored therein instructions, which when executed by a processor cause the processor to perform a method comprising:
 coupling a differential electrode configuration to drive circuitry configured to drive a transducer to produce an acoustic wave during a drive phase; and 
 coupling the differential electrode configuration to sense circuitry configured to receive electrical signals from the transducer during a sensing phase, 
 wherein the differential electrode configuration is coupled to the transducer and wherein the differential electrode configuration and the sensing circuitry are configured to perform a differential measurement to sense a touch signal at one or more spatial modulation frequencies corresponding to the differential electrode configuration and reject a spatial common mode signal from a received acoustic wave having a common spatial characteristic relative to the differential electrode configuration. 
 
     
     
       20. The non-transitory computer-readable storage medium of  claim 19 , wherein the sensing phase comprises a touch sensing phase and a force sensing phase. 
     
     
       21. The non-transitory computer-readable storage medium of  claim 20 , wherein the touch sensing phase comprises an in-phase touch sensing phase and a quadrature touch sensing phase, wherein coupling the differential electrode configuration to the sense circuitry during the in-phase touch sensing phase comprises coupling the differential electrode configuration to the sense circuitry in a first electrode grouping and coupling the differential electrode configuration to the sense circuitry during the quadrature touch sensing phase comprises coupling the differential electrode configuration to the sense circuitry in a second electrode grouping, different from the first electrode grouping. 
     
     
       22. The non-transitory computer-readable storage medium of  claim 19 , wherein the sensing phase comprises concurrently capturing an in-phase touch measurement, a quadrature touch measurement, and a force measurement. 
     
     
       23. The non-transitory computer-readable storage medium of  claim 22 , wherein concurrently capturing comprises, concurrently receiving at least four signals from at least four of the electrodes of the differential electrode configuration at four sensing circuits and concurrently combining the at least four differential signals in different combinations to produce the in-phase touch measurement, quadrature touch measurement, and force measurement.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application Ser. No. 62/510,493, filed May 24, 2017, U.S. Provisional Application Ser. No. 62/510,513, filed May 24, 2017, U.S. Provisional Application Ser. No. 62/561,578, filed Sep. 21, 2017 and U.S. Provisional Application Ser. No. 62/561,609, filed Sep. 21, 2017, the contents of which are hereby incorporated herein by reference in their entirety for all purposes. 
    
    
     FIELD OF THE DISCLOSURE 
     This relates generally to touch and/or force sensing systems, and more particularly, to integrated acoustic touch and force sensing systems and methods for acoustic touch and force sensing. 
     BACKGROUND OF THE DISCLOSURE 
     Many types of input devices are presently available for performing operations in a computing system, such as buttons or keys, mice, trackballs, joysticks, touch sensor panels, touch screens and the like. Touch screens, in particular, are becoming increasingly popular because of their ease and versatility of operation as well as their declining price. Touch screens can include a touch sensor panel, which can be a clear panel with a touch-sensitive surface, and a display device such as a liquid crystal display (LCD) that can be positioned partially or fully behind the panel so that the touch-sensitive surface can cover at least a portion of the viewable area of the display device. Touch screens can allow a user to perform various functions by touching the touch sensor panel using a finger, stylus or other object at a location often dictated by a user interface (UI) being displayed by the display device. In general, touch screens can recognize a touch and the position of the touch on the touch sensor panel, and the computing system can then interpret the touch in accordance with the display appearing at the time of the touch, and thereafter can perform one or more actions based on the touch. In the case of some touch sensing systems, a physical touch on the display is not needed to detect a touch. For example, in some capacitive-type touch sensing systems, fringing electrical fields used to detect touch can extend beyond the surface of the display, and objects approaching near the surface may be detected near the surface without actually touching the surface. Capacitive-type touch sensing systems, however, can experience reduced performance due to conductive, electrically-floating objects (e.g., water droplets) in contact with the touch-sensitive surface. 
     SUMMARY 
     This relates to acoustic touch and/or force sensing systems and methods for acoustic touch and/or force sensing. The position of an object touching a surface can be determined using time-of-flight (TOF) techniques, for example. Acoustic touch and/or force sensing can utilize transducers, such as piezoelectric transducers, to transmit ultrasonic waves along a surface and/or through the thickness of one or more materials (e.g., a thickness of an electronic device housing). As the wave propagates along the surface and/or through the thickness of the one or more materials, an object (e.g., finger, stylus, etc.) in contact with the surface can interact with the transmitted wave, causing a reflection of at least a portion of the transmitted wave. Portions of the transmitted wave energy after interaction with the object can be measured to determine the touch location of the object on the surface of the device. For example, one or more transducers (e.g., acoustic transducers) coupled to a surface of a device can be configured to transmit an acoustic wave along the surface and/or through the thickness of the one or more materials and can receive a portion of the wave reflected back when the acoustic wave encounters a finger or other object touching the surface. The location of the object can be determined, for example, based on the amount of time elapsing between the transmission of the wave and the detection of the reflected wave. Acoustic touch sensing can be used instead of, or in conjunction with, other touch sensing techniques, such as resistive, optical, and/or capacitive touch sensing. In some examples, the acoustic touch sensing techniques described herein can be used on a metal housing surface of a device, which may be unsuitable for capacitive or resistive touch sensing due to interference (e.g., of the housing with the capacitive or resistive sensors housed in the metal housing). In some examples, the acoustic touch sensing techniques described herein can be used on a glass surface of a display or touch screen. In some examples, an acoustic touch sensing system can be configured to be insensitive to contact on the device surface by water, and thus acoustic touch sensing can be used for touch sensing in devices that may become wet or fully submerged in water. 
     Additionally or alternatively, a force applied by the object on the surface can also be determined using TOF techniques. For example, one or more transducers can transmit ultrasonic waves through the thickness of a deformable material, and reflected waves from the opposite edge of the deformable material can be measured to determine a TOF or a change in TOF. The TOF, or change in TOF (ΔTOF), can correspond to the thickness of the deformable material (or changes in thickness) due to force applied to the surface. Thus, the TOF or change in TOF (or the thickness or change in thickness) can be used to determine the applied force. In some examples, using acoustic touch and force sensing can reduce the complexity of the touch and force sensing system by reducing the sensing hardware requirements (e.g., transducers, sensing circuitry/controllers, etc. can be integrated/shared). 
     The present disclosure is primarily directed to timing and switching schemes for acoustic touch sensing as described with regard to  FIGS. 19A-36B  below.  FIGS. 1A-18C  provide context to the timing and switching schemes as well as several exemplary configurations illustrating touch and force sensing systems according to examples of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1E  illustrate exemplary systems with touch screens that can include acoustic sensors for detecting contact between an object and a surface of the system according to examples of the disclosure. 
         FIG. 2  illustrates an exemplary block diagram of an electronic device including an acoustic touch and/or force sensing system according to examples of the disclosure. 
         FIG. 3A  illustrates an exemplary process for acoustic touch and/or force sensing of an object in contact with a touch and/or force sensitive surface according to examples of the disclosure. 
         FIG. 3B  illustrates an exemplary system, which can perform an exemplary process for acoustic touch and/or force sensing of an object in contact with a touch and/or force sensitive surface, according to examples of the disclosure. 
         FIG. 3C  illustrates a transducer without pixelated electrodes according to examples of the disclosure. 
         FIG. 4  illustrates an exemplary configuration of an acoustic touch and/or force sensing circuit according to examples of the disclosure. 
         FIGS. 5A-5C  illustrate exemplary system configurations and timing diagrams for acoustic touch sensing to determine position using time-of-flight measurements according to examples of the disclosure. 
         FIGS. 6A-6D  illustrate exemplary system configurations and timing diagrams for acoustic force sensing to determine an amount of applied force using a time-of-flight measurement according to examples of the disclosure. 
         FIG. 7  illustrates a timing diagram for acoustic touch and force sensing according to examples of the disclosure. 
         FIGS. 8A-8C  illustrate an exemplary cover glass ringing effect and exemplary mitigations for the ringing effect according to examples of the disclosure. 
         FIG. 9A  illustrates a representation of spatial and temporal distribution of energy received by a transducer due to the ringing effect described in  FIG. 8A . 
         FIG. 9B  illustrates a representation of spatial and temporal distribution of energy received by a transducer during a touch sensing operation. 
         FIG. 9C  illustrates a spatial differential electrode configuration for transducer electrodes alongside the spatial and temporal distribution of energy due to the ringing effect according to examples of the disclosure. 
         FIG. 9D  illustrates the spatial differential electrode configuration for transducer electrodes alongside the representation of spatial and temporal distribution of energy of a touch sensing signal according to examples of the disclosure. 
         FIGS. 10A-10B  illustrate exemplary spatial differential force sensing configurations according to examples of the disclosure. 
         FIGS. 11A-11E  illustrate electrode arrangement grouping patterns for single-sided spatial differential electrode configurations according to examples of the disclosure. 
         FIG. 12A  illustrates an exemplary configuration for a spatial differential electrode configuration having differential electrodes on both sides of a transducer according to examples of the disclosure. 
         FIG. 12B  illustrates an exemplary connection pattern for performing acoustic wave transmission, touch measurement, and force measurements. 
         FIGS. 13A and 13B  illustrated exemplary configurations and groupings for double sided differential electrode configurations according to examples of the disclosure. 
         FIGS. 14A-14F  illustrate exemplary amplifier configurations for performing differential sensing according to examples of the disclosure. 
         FIGS. 15A-15C  illustrate a spatial null phenomenon that can be associated with spatial differential electrode configurations according to examples of the disclosure. 
         FIGS. 16A-16D  illustrate an exemplary quadrature spatial differential electrode configuration according to examples of the disclosure. 
         FIGS. 17A-17C  illustrates a first exemplary spatial electrode configuration for performing quadrature spatial differential measurements of touch signals on cover glass and force sensing using a shared set of electrodes according to examples of the disclosure. 
         FIGS. 18A-18C  illustrates a second exemplary spatial electrode configuration for performing quadrature spatial differential measurements of touch signals on cover glass and force sensing using a shared set of electrodes according to examples of the disclosure. 
         FIGS. 19A-20B  illustrate exemplary timing diagrams for acoustic touch and force sensing according to examples of the disclosure. 
         FIGS. 21-27  illustrate exemplary switching configurations for acoustic touch and force sensing systems according to examples of the disclosure. 
         FIGS. 28A-30B  illustrate exemplary timing diagrams for acoustic touch and force sensing according to examples of the disclosure. 
         FIGS. 31A-34  illustrate exemplary switching configurations for quadrature acoustic touch and force sensing systems according to examples of the disclosure. 
         FIGS. 35A-36B  illustrate exemplary transmitter configurations for acoustic touch and force sensing systems according to examples of the disclosure. 
         FIGS. 37A-37Q  illustrate exemplary transducers according to examples of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description of various examples, reference is made to the accompanying drawings which form a part hereof, and in which it is shown by way of illustration specific examples that can be practiced. It is to be understood that other examples can be used and structural changes can be made without departing from the scope of the various examples. 
     This relates to acoustic touch and/or force sensing systems and methods for acoustic touch and/or force sensing. The position of an object touching a surface can be determined using time-of-flight (TOF) techniques, for example. Acoustic touch and/or force sensing can utilize transducers, such as piezoelectric transducers, to transmit ultrasonic waves along a surface and/or through the thickness of one or more materials (e.g., a thickness of an electronic device housing). As the wave propagates along the surface and/or through the thickness of the one or more materials, an object (e.g., finger, stylus, etc.) in contact with the surface can interact with the transmitted wave, causing a reflection of at least a portion of the transmitted wave. Portions of the transmitted wave energy after interaction with the object can be measured to determine the touch location of the object on the surface of the device. For example, one or more transducers (e.g., acoustic transducers) coupled to a surface of a device can be configured to transmit an acoustic wave along the surface and/or through the thickness of the one or more materials and can receive a portion of the wave reflected back when the acoustic wave encounters a finger or other object touching the surface. The location of the object can be determined, for example, based on the amount of time elapsing between the transmission of the wave and the detection of the reflected wave. Acoustic touch sensing can be used instead of, or in conjunction with, other touch sensing techniques, such as resistive, optical, and/or capacitive touch sensing. In some examples, the acoustic touch sensing techniques described herein can be used on a metal housing surface of a device, which may be unsuitable for capacitive or resistive touch sensing due to interference (e.g., of the housing with the capacitive or resistive sensors housed in the metal housing). In some examples, the acoustic touch sensing techniques described herein can be used on a glass surface of a display or touch screen. In some examples, an acoustic touch sensing system can be configured to be insensitive to contact on the device surface by water, and thus acoustic touch sensing can be used for touch sensing in devices that may become wet or fully submerged in water. 
     Additionally or alternatively, a force applied by the object on the surface can also be determined using TOF techniques. For example, one or more transducers can transmit ultrasonic waves through the thickness of a deformable material, and reflected waves from the opposite edge of the deformable material can be measured to determine a TOF or a change in TOF. The TOF, or change in TOF (ΔTOF), can correspond to the thickness of the deformable material (or changes in thickness) due to force applied to the surface. Thus, the TOF or change in TOF (or the thickness or change in thickness) can be used to determine the applied force. In some examples, using acoustic touch and force sensing can reduce the complexity of the touch and force sensing system by reducing the sensing hardware requirements (e.g., transducers, sensing circuitry/controllers, etc. can be integrated/shared). 
     The present disclosure is primarily directed to timing and switching schemes for acoustic touch sensing as described with regard to  FIGS. 19A-36B  below.  FIGS. 1A-18C  provide context to the timing and switching schemes as well as several exemplary configurations illustrating touch and force sensing systems according to examples of the disclosure. 
       FIGS. 1A-1E  illustrate exemplary systems with touch screens that can include acoustic sensors for detecting contact between an object (e.g., a finger or stylus) and a surface of the system according to examples of the disclosure. Detecting contact can include detecting a location of contact and/or an amount of force applied to a touch-sensitive surface.  FIG. 1A  illustrates an exemplary mobile telephone  136  that includes a touch screen  124  and can include an acoustic touch and/or force sensing system according to examples of the disclosure.  FIG. 1B  illustrates an example digital media player  140  that includes a touch screen  126  and can include an acoustic touch and/or force sensing system according to examples of the disclosure.  FIG. 1C  illustrates an example personal computer  144  that includes a touch screen  128  and a track pad  146 , and can include an acoustic touch and/or force sensing system according to examples of the disclosure.  FIG. 1D  illustrates an example tablet computing device  148  that includes a touch screen  130  and can include an acoustic touch and/or force sensing system according to examples of the disclosure.  FIG. 1E  illustrates an example wearable device  150  (e.g., a watch) that includes a touch screen  152  and can include an acoustic touch and/or force sensing system according to examples of the disclosure. Wearable device  150  can be coupled to a user via strap  154  or any other suitable fastener. It should be understood that the example devices illustrated in  FIGS. 1A-1E  are provided by way of example, and other types of devices can include an acoustic touch and/or force sensing system for detecting contact between an object and a surface of the device. Additionally, although the devices illustrated in  FIGS. 1A-1E  include touch screens, in some examples, the devices may have a non-touch-sensitive display. 
     Acoustic sensors can be incorporated in the above described systems to add acoustic touch and/or force sensing capabilities to a surface of the system. For example, in some examples, a touch screen (e.g., capacitive, resistive, etc.) can be augmented with acoustic sensors to provide a touch and/or force sensing capability for use in wet environments or under conditions where the device may get wet (e.g., exercise, swimming, rain, washing hands). In some examples, an otherwise non-touch sensitive display screen can be augmented with acoustic sensors to provide a touch and/or force sensing capability. In such examples, a touch screen can be implemented without the stack-up required for a capacitive touch screen. In some examples, the acoustic sensors can be used to provide touch and/or force sensing capability for a non-display surface. For example, the acoustic sensors can be used to provide touch sensing capabilities for a track pad  146 , a button, a scroll wheel, part or all of the housing or any other surfaces of the device (e.g., on the front, rear or sides). 
       FIG. 2  illustrates an exemplary block diagram of an electronic device including an acoustic touch and/or force sensing system according to examples of the disclosure. In some examples, housing  202  of device  200  (e.g., corresponding to devices  136 ,  140 ,  144 ,  148 , and  150  above) can be coupled (e.g., mechanically) with one or more acoustic transducers  204 . In some examples, transducers  204  can be piezoelectric transducers, which can be made to vibrate by the application of electrical signals when acting as a transmitter, and generate electrical signals based on detected vibrations when acting as a receiver. In some examples, transducers  204  can be formed from a piezoelectric ceramic material (e.g., PZT or KNN) or a piezoelectric plastic material (e.g., PVDF or PLLA). Similarly, transducers  204  can produce electrical energy as an output when vibrated. In some examples, transducers  204  can be bonded to housing  202  by a bonding agent (e.g., a thin layer of stiff epoxy). In some examples, transducers  204  can be deposited on one or more surfaces (e.g., a cover glass of touch screen  208  and/or a deformable material as described in more detail below) through processes such as deposition, lithography, or the like. In some examples, transducers  204  can be bonded to the one or more surfaces using electrically conductive or non-conductive bonding materials. When electrical energy is applied to transducers  204  it can cause the transducers to vibrate, the one or more surfaces in contact with the transducers can also be caused to vibrate, and the vibrations of the molecules of the surface material can propagate as an acoustic wave through the one or more surfaces/materials. In some examples, vibration of transducers  204  can be used to produce ultrasonic acoustic waves at a selected frequency over a broad frequency range (e.g., 500 kHz-10 MHz) in the medium of the surface of the electronic device which can be metal, plastic, glass, wood, or the like. It should be understood that other frequencies outside of the exemplary range above can be used while remaining within the scope of the present disclosure. 
     In some examples, transducers  204  can be partially or completely disposed on (or coupled to) a portion of a touch screen  208 . For example, touch screen  208  (e.g., capacitive) may include a glass panel (cover glass) or a plastic cover, and a display region of the touch screen may be surrounded by a non-display region (e.g., a black border region surrounding the periphery of the display region of touch screen  208 ). In some examples, transducers  204  can be disposed partially or completely in the black mask region of touch screen  208  (e.g., on the back side of the glass panel behind the black mask) such that the transducers are not visible (or are only partially visible) to a user. In some examples, transducers  204  can be partially or completely disposed on (or coupled to) a portion of a deformable material (not shown). In some examples, the deformable material can be disposed between touch screen  208  and a rigid material (e.g., a portion of housing  202 ). In some examples, the deformable material can be silicone, rubber or polyethylene. In some examples, the deformable material can also be used for water sealing of the device. 
     Device  200  can further include acoustic touch and/or force sensing circuitry  206 , which can include circuitry for driving electrical signals to stimulate vibration of transducers  204  (e.g., transmit circuitry), as well as circuitry for sensing electrical signals output by transducers  204  when the transducer is stimulated by received acoustic energy (e.g., receive circuitry). In some examples, timing operations for acoustic touch and/or force sensing circuitry  206  can optionally be provided by a separate acoustic touch and/or force sensing controller  210  that can control timing of and other operations by acoustic touch and/or force sensing circuitry  206 . In some examples, touch and/or force sensing controller  210  can be coupled between acoustic touch and/or force sensing circuitry  206  and host processor  214 . In some examples, controller functions can be integrated with acoustic touch and/or force sensing circuitry  206  (e.g., on a single integrated circuit). In particular, examples integrating touch and force sensing circuitry and controller functionality into a single integrated circuit can reduce the number of transducers (sensor elements) and electronic chipsets for a touch and force sensing device. Output data from acoustic touch and/or force sensing circuitry  206  can be output to a host processor  214  for further processing to determine a location of and a force applied by an object contacting the device as will be described in more detail below. In some examples, the processing for determining the location of and a force applied by the contacting object can be performed by acoustic touch and/or force sensing circuitry  206 , acoustic touch and/or force sensing controller  210  or a separate sub-processor of device  200  (not shown). 
     In addition to acoustic touch and/or force sensing, device  200  can include additional touch circuitry  212  and optionally a touch controller (not shown) that can be coupled to the touch screen  208 . In examples including a touch controller, the touch controller can be disposed between touch circuitry  212  and host processor  214 . Touch circuitry  212  can, for example, be capacitive or resistive touch sensing circuitry, and can be used to detect contact and/or hovering of objects (e.g., fingers, styli) in contact with and/or in proximity to touch screen  208 , particularly in the display region of the touch screen. Thus, device  200  can include multiple types of sensing circuitry (e.g., touch circuitry  212  and acoustic touch and/or force sensing circuitry  206 ) for detecting objects (and their positions and/or applied force) in different regions of the device and/or for different purposes, as will be described in more detail below. Although described herein as including a touch screen, it should be understood that touch circuitry  212  can be omitted, and in some examples, touch screen  208  can be replaced by an otherwise non-touch-sensitive display (e.g., but-for the acoustic sensors). 
     Host processor  214  can receive acoustic or other touch outputs (e.g., capacitive) and/or force outputs and perform actions based on the touch outputs and/or force outputs. Host processor  214  can also be connected to program storage  216  and touch screen  208 . Host processor  214  can, for example, communicate with touch screen  208  to generate an image on touch screen  208 , such as an image of a user interface (UI), and can use touch sensing circuitry  212  and/or acoustic touch and/or force sensing circuitry  206  (and, in some examples, their respective controllers) to detect a touch on or near touch screen  208  and/or an applied force, such as a touch input and/or force input to the displayed UI. The touch input and/or force input can be used by computer programs stored in program storage  216  to perform actions that can include, but are not limited to, moving an object such as a cursor or pointer, scrolling or panning, adjusting control settings, opening a file or document, viewing a menu, making a selection, executing instructions, operating a peripheral device connected to the host device, answering a telephone call, placing a telephone call, terminating a telephone call, changing the volume or audio settings, storing information related to telephone communications such as addresses, frequently dialed numbers, received calls, missed calls, logging onto a computer or a computer network, permitting authorized individuals access to restricted areas of the computer or computer network, loading a user profile associated with a user&#39;s preferred arrangement of the computer desktop, permitting access to web content, launching a particular program, encrypting or decoding a message, and/or the like. Host processor  214  can also perform additional functions that may not be related to touch and/or force processing. 
     Note that one or more of the functions described herein can be performed by firmware stored in memory and executed by touch circuitry  212  and/or acoustic touch and/or force sensing circuitry  206  (or their respective controllers), or stored in program storage  216  and executed by host processor  214 . The firmware can also be stored and/or transported within any non-transitory computer-readable storage medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this document, a “non-transitory computer-readable storage medium” can be any medium (excluding a signal) that can contain or store the program for use by or in connection with the instruction execution system, apparatus, or device. The non-transitory computer readable medium storage can include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus or device, a portable computer diskette (magnetic), a random access memory (RAM) (magnetic), a read-only memory (ROM) (magnetic), an erasable programmable read-only memory (EPROM) (magnetic), a portable optical disc such a CD, CD-R, CD-RW, DVD, DVD-R, or DVD-RW, or flash memory such as compact flash cards, secured digital cards, USB memory devices, memory sticks, and the like. 
     The firmware can also be propagated within any transport medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this document, a “transport medium” can be any medium that can communicate, propagate or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The transport readable medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic or infrared wired or wireless propagation medium. 
     It is to be understood that device  200  is not limited to the components and configuration of  FIG. 2 , but can include other or additional components in multiple configurations according to various examples. Additionally, the components of device  200  can be included within a single device, or can be distributed between multiple devices. Additionally, it should be understood that the connections between the components is exemplary and different unidirectional or bidirectional connections can be included between the components depending on the implementation, irrespective of the arrows shown in the configuration of  FIG. 2 . 
       FIG. 3A  illustrates an exemplary process  300  for acoustic touch and/or force sensing of an object in contact with a touch and/or force sensitive surface according to examples of the disclosure.  FIG. 3B  illustrates an exemplary system  310 , which can perform an exemplary process  300  for acoustic touch and/or force sensing of an object in contact with a touch and/or force sensitive surface, according to examples of the disclosure. At  302 , acoustic energy can be transmitted (e.g., by one or more transducers  204 ) along a surface and/or through the thickness of a material in the form of an ultrasonic wave, for example. For example, as illustrated in  FIG. 3B , transducer  314  can generate a transmit ultrasonic wave  322  in cover glass  312  (or other material capable of propagating an ultrasonic wave). In some examples, the wave can propagate as a compressive wave, a guided wave such as a shear horizontal wave, a Rayleigh wave, a Lamb wave, a Love wave, a Stoneley wave, or a surface acoustic wave. Other propagation modes for the transmitted acoustic energy can also exist based on the properties of the surface material, geometry and the manner of energy transmission from the transducers to the surface of the device. In some examples, the surface can be formed from glass, plastic, or sapphire crystal (e.g., touch screen  208 , cover glass  312 ) or the surface can be formed from metal, ceramics, plastic, or wood (e.g., housing  202 ). Transmitted energy can propagate along the surface (e.g., cover glass  312 ) and/or through the thickness until a discontinuity in the surface is reached (e.g., an object, such as a finger  320 , in contact with the surface), which can cause a portion of the energy to reflect. In some examples, a discontinuity can occur at edges (e.g., edge  330 ) of the surface material (e.g., when the ultrasonic wave propagates to the edge of the surface opposite the transducer). When the transmitted energy reaches one of the discontinuities described above, some of the energy can be reflected, and a portion of the reflected energy (e.g., object-reflected wave  326 , edge-reflected wave  328 ) can be directed to one or more transducers (e.g., transducers  204 ,  314 ). In some examples, water or other fluids in contact with the surface of the device (e.g., device  200 ) will not act as a discontinuity to the acoustic waves, and thus the acoustic touch sensing process can be effective for detecting the presence of an object (e.g., a user&#39;s finger) even in the presence of water drops (or other low-viscosity fluids) on the surface of the device or even while the device is fully submerged. 
     At  304 , returning acoustic energy can be received, and the acoustic energy can be converted to an electrical signal by one or more transducers (e.g., transducers  204 ). For example, as illustrated in  FIG. 3B , object-reflected wave  326  and edge-reflected wave  328  can be received by transducer  314  and converted into an electrical signal. 
     At  306 , the acoustic sensing system can determine whether one or more objects is contacting the surface of the device, and can further detect the position of one or more objects based on the received acoustic energy. In some examples, a distance of the object from the transmission source (e.g., transducers  204 ) can be determined from a time-of-flight between transmission and reception of reflected energy, and a propagation rate of the ultrasonic wave through the material. In some examples, baseline reflected energy from one or more intentionally included discontinuities (e.g., edges) can be compared to a measured value of reflected energy corresponding to the one or more discontinuities. The baseline reflected energy can be determined during a measurement when no object (e.g., finger) is in contact with the surface. Deviations of the reflected energy from the baseline can be correlated with a presence of an object touching the surface. 
     Although process  300 , as described above, generally refers to reflected waves received by the same transducer(s) that transmitted the waves, in some examples, the transmitter and receiver functions can be separated such that the transmission of acoustic energy at  302  and receiving acoustic energy at  304  may occur at different co-located transducers (e.g., one transducer in a transmit configuration and one transducer in a receive configuration). In some examples, the acoustic energy can be transmitted along and/or through the surface (e.g., cover glass  312 ) by one or more transducers (e.g., transducer  314 ) and received on an opposite edge (e.g., edge  330 ) of the surface by one or more additional transducers (not shown). The attenuation of the received acoustic energy can be used to detect the presence of and/or identify the position of one or more objects (e.g., finger  320 ) on the surface (e.g., cover glass  312 ). Exemplary device configurations and measurement timing examples that can be used to implement process  300  will be described in further detail below. In some examples, the transmitted acoustic energy from transducer  314  can be received at the transmitting transducer and also received at one or more other non-transmitting transducers located in different positions (e.g., at different edges of the surface (e.g., cover glass  312 ). Energy can reflect from one or more objects at multiple angles, and the energy received at all of the receiving transducers can be used to determine the position of the one or more objects. In some examples, the non-transmitting transducers can be free of artifacts that can be associated with transmitting acoustic energy (e.g., ringing). 
     In some examples, the acoustic energy transmitted and received through a deformable material can be used to determine changes in the thickness of the deformable material and/or an applied force. For example, at  302 , acoustic energy can be transmitted (e.g., by transducer  314 ) through the thickness of deformable material  316  in the form of a transmit ultrasonic wave  324 . Transmitted energy can propagate through the deformable material  316  until it reaches a discontinuity at the rigid material  318  (e.g., at the opposite edge of the deformable material  316 ). When the transmitted energy reaches the discontinuity, some of the energy can be reflected, and a portion of the reflected energy can be directed back to transducer  314 . At  304 , returning acoustic energy can be received, and the acoustic energy can be converted to an electrical signal by transducers  314 . At  306 , the acoustic sensing system can determine an amount of force applied by one or more objects contacting the surface (e.g., cover glass  312 ) based on the received acoustic energy. In some examples, a thickness of deformable material  316  can be determined from a time-of-flight between transmission and reception of reflected energy, and a propagation rate of the ultrasonic wave through the material. Changes in the thickness of the deformable material (or the time-of-flight through the deformable material) can be used to determine an amount of applied force, as described in more detail below. 
       FIG. 4  illustrates an exemplary configuration of an acoustic touch and/or force sensing circuit  400  according to examples of the disclosure. Acoustic touch and/or force sensing circuit  400  can include transmit circuitry (also referred to herein as Tx circuitry or transmitter)  402 , switching circuitry  404 , receive circuitry (also referred to herein as Rx circuitry or receiver)  408  and input/output (I/O) circuit  420  (which together can correspond to acoustic touch and/or force sensing circuitry  206 ) and acoustic scan control logic  422  (which can correspond to acoustic touch and/or force sensing controller  210 ). Transmitter  402 , switching circuitry  404 , receiver  408 , I/O circuit  420  and/or acoustic scan control logic  422  can be implemented in an application specific integrated circuit (ASIC) in some examples. In some examples, acoustic touch and/or force sensing circuit  400  can also optionally include transducers  406  (which can correspond to transducers  204 ). 
     In some examples, a transmitter  402  can generate an electrical signal for stimulating movement of one or more of a plurality of transducers  406 . In some examples, the transmitted signal can be a differential signal, and in some examples, the transmitted signal can be a single-ended signal. In some examples, transmitter  402  can be a simple buffer, and the transmitted signal can be a pulse (or burst of pulses at a particular frequency). In some examples, transmitter  402  can include a digital-to-analog converter (DAC)  402 A and an optional filter  402 B that can be optionally used to smooth a quantized output of DAC  402 A. In some examples, characteristics of the transducer itself can provide a filtering property and filter  402 B can be omitted. DAC  402 A can be used to generate transmit waveform (e.g., any transmit waveform suitable for the touch and/or force sensing operations discussed herein). In some examples, the transmit waveform output can be pre-distorted to equalize the channel. In some examples, the characteristics of each channel, such as the properties of the surface material (and/or deformable material) coupled to transducers  406 , the discontinuities in the surface material and/or deformable material, and the reflection characteristics of an edge of the device or deformable material can be measured and stored. In some examples, the channel characteristics can be measured as a manufacturing step (or factory calibration step), and in other examples the characteristics can be measured as a periodic calibration step (i.e., once a month, once a year, etc. depending on how quickly the channel characteristics are expected to change). In some examples, the channel characteristics can be converted to a transfer function of the channel, and the transmit waveform can be configured using the inverse of the channel transfer function such that the returning signal is equalized (e.g., returning signal can be detected as a pulse or a burst of pulses despite the transmitted waveform having a seemingly arbitrary waveform). In some examples, a single differential pulse can be used as a transmit waveform. For example, a bipolar square pulse (where the voltage applied to the transducer can be both positive and negative) can be used as the transmit waveform, and the bipolar square pulse can be implemented using a single-ended or differential implementation. 
     Switching circuitry  404  can include multiplexers (MUXs) and/or demultiplexers (DEMUXs) that can be used to selectively couple transmitter  402  and/or receiver  408  to one of transducers  406  that can be the active transducer for a particular measurement step in a measurement cycle. In a differential implementation, switching circuitry  404  can include two MUXs and two DEMUXs. In some examples, a DEMUX can have a ground connection, and the non-selected DEMUX outputs can be shorted, open, or grounded. In some examples, the same transducer  406  can be coupled to transmitter  402  by switching circuitry  404  (e.g., DEMUXs) during the drive mode and coupled to receiver  408  by switching circuitry  404  (e.g., MUXs) during the receive mode. Thus, in some examples, a single transducer  406  can be used both for transmitting and receiving acoustic energy. In some examples, a first transducer can be coupled to transmitter  402  by switching circuitry  404  (e.g. DEMUXs) and a second transducer can be coupled by switching circuitry  404  (e.g., MUXs) to receiver  408 . For example, the transmitting transducer and the receiving transducer can be discrete piezoelectric elements, where the transmitting transducer can be designed for being driven by higher voltages (or currents) to produce sufficient motion in transducer  406  to generate an acoustic wave in the surface of a device (e.g., device  200  above), and the receiving transducer can be designed for receiving smaller amplitude reflected energy. In such a configuration, the transmit-side circuitry (e.g., transmitter  402  and DEMUXs of switching circuitry  404 ) can be optionally implemented on a high voltage circuit, and the receive-side circuitry (e.g., receiver  408  and MUXs of switching circuitry  404 ) can be optionally implemented on a separate low voltage circuit. In some examples, switching circuitry  404  (MUXs and DEMUXs) can also be implemented on the high voltage circuit to properly isolate the remaining receive-side circuitry (e.g., receiver  408 ) during transmission operations by transmit side circuitry. Additionally or alternatively, in some examples, the transmit circuit can include an energy recovery architecture that can be used to recover some of the energy required for charging and discharging the transducer. It should be understood that for a single-ended implementation, switching circuitry  404  can include a single DEMUX and MUX. In such a configuration, transmitter  402  and receiver  408  can be single-ended as well. Differential implementations, however, can provide improved noise suppression over a single-ended implementation. 
     Receiver  408  can include an amplifier  410  such as a low-noise amplifier (LNA) configured to sense the transducer. Receiver  408  can also include a gain and offset correction circuit  412 . The gain and offset correction circuit can include a programmable gain amplifier (PGA) configured to apply gain to increase (or in some cases decrease) the amplitude of the signals received from LNA. The PGA can also be configured to filter (e.g., low pass) the signals received from the LNA to remove high frequency components. Additionally, the PGA circuit can also be configured to perform baselining (offset correction). 
     In some examples, the output of gain and offset correction circuit  412  can optionally be coupled to one or more analog processing circuits. In some examples, the output of gain and offset correction circuit  412  can be coupled to a demodulation circuit  414  configured to demodulate the received signals (e.g., by I/Q demodulation). In some examples, the output of the gain and offset correction circuit  412  can be coupled to an envelope detection circuit  415  configured to perform envelope detection on the received signals. In some examples, the output of gain and offset correction circuit  412  can be filtered at filter  416 . In some examples, these blocks/circuits can be placed in a different order. In some examples, the processing of one or more of these analog processing circuits can be performed in the digital domain. 
     The received signals, whether raw or processed by one or more of demodulation circuit  414 , envelope detection circuit  415  or filter  416 , can be passed to an analog-to-digital converter (ADC)  418  for conversion to a digital signal. In some examples, an input/output (I/O) circuit  420  can be used to transmit received data for processing. In some examples, the output of I/O circuit  420  can be transferred to a host processor of the device, or to an auxiliary processor (sub-processor) separate from the host processor. For example, as illustrated, the output of I/O circuit  420  can be coupled to a processor system-on-chip (SoC)  430 , which can include one or more processors. In some examples, processor SoC  430  can include a host processor  432  (e.g., an active mode processor) and an auxiliary processor  434  (e.g., a low power processor). In some examples, some digital signal processing can be performed (e.g., by acoustic touch and/or force sensing circuit  400 ) before transmitting the data to other processors in the system (e.g., processor SoC  430 ). In some examples, the I/O circuit  420  is not only used for data transfer to processor SoC  430  (e.g., host processor  432 ), but also is used for writing the control registers and/or firmware download from processor SoC  430 . 
     The components of receiver circuitry  408  described above can be implemented to detect touch (e.g., presence and location of a touch on a surface). In some examples, receiver  408  can also include a force detection circuit  424  to detect applied force (e.g., of the touch on the surface). In some examples, the force detection circuit  424  can include the same or similar components as described above (e.g., amplifier, gain and offset correction, etc.). In some examples, the function of force detection circuit  424  can be performed using the same components described above that are used to determine time-of-flight for touch detection. In some examples, a low-power time gating circuit can be used to determine time-of-flight for force detection. Data from force sensing circuit  424  can be transferred to I/O circuit  420  and/or processor SoC  430  for further processing of force data in a similar manner as described above for touch data. In some examples the same circuitry for touch detection can be used to detect force. 
     A control circuit, acoustic scan control circuit  422 , can be used to control timing and operations of the circuitry of acoustic touch and/or force sensing circuit  400 . Acoustic scan control circuit  422  can be implemented in hardware, firmware, software or a combination thereof. In some examples, acoustic scan control circuit  422  can include digital logic and timing control. Digital logic can provide the various components of acoustic touch and/or sensing circuit  400  with control signals. A timing control circuit can generate timing signals for acoustic touch and/or sensing circuit  400  and generally sequence the operations of acoustic touch and/or force sensing circuit  400 . In some examples, the acoustic touch and/or force sensing circuit  400  can receive a master clock signal from an external source (e.g., clock from the host processor, crystal oscillator, ring oscillator, RC oscillator, or other high-performance oscillator). In some examples, an on-chip oscillator can be used to generate the clock. In some examples, a master clock signal can be generated by an on-chip phase locked loop (PLL), included as part of acoustic touch and/or force sensing circuit  400 , using an external clock as the input. In some examples, a master clock signal can be routed to the acoustic touch sensing circuit from processor SoC  430 . The appropriate master clock source can be determined based on a tradeoff between area, thickness of the stack-up, power and electromagnetic interference. 
     It is to be understood that the configuration of  FIG. 4  is not limited to the components and configuration of  FIG. 4 , but can include other or additional components (e.g., memory, signal processor, etc.) in multiple configurations according to various examples. Additionally, some or all of the components illustrated in  FIG. 4  can be included in a single circuit, or can be divided among multiple circuits while remaining within the scope of the examples of the disclosure. 
     As described herein, various acoustic sensing techniques can be used to determine the position of an object touching a surface and/or its applied force on the surface. In some examples, one or more time-of-flight measurements can be performed using one or more acoustic transducers to determine boundaries of the position of the contacting object.  FIGS. 5A-5C  illustrate exemplary system configurations and timing diagrams for acoustic touch sensing to determine position using time-of-flight measurements according to examples of the disclosure.  FIG. 5A  illustrates an exemplary acoustic touch sensing system configuration using four acoustic transducers  502 A-D mounted along (or otherwise coupled to) four edges of a surface  500  (e.g., corresponding to cover glass  312 ). Transducers  502 A-D can be configured to generate acoustic waves (e.g., shear horizontal waves) and to receive the reflected acoustic waves. Propagation of shear horizontal waves can be unaffected by water on surface  500  because low viscosity fluids and gases (such as water and air) have a very low shear modulus, and therefore do not perturb the boundary conditions that affect wave propagation. Shear horizontal waves can be highly directional waves such that the active detection region (or active area)  504  can be effectively defined based on the position and dimensions of the acoustic transducers  502 A-D. It should be understood, however, that active area can change based on the directionality property of the acoustic waves and the size and placement of acoustic transducers  502 A-D. Additionally, it should be understood that although illustrated as transmit and receive transducers (i.e., transceivers), in some examples, the transmit and receive functions can be divided (e.g., between two transducers in proximity to one another, rather than one transmit and receive transducer). 
     The position of a touch  506  from an object in contact with surface  500  can be determined by calculating TOF measurements in a measurement cycle using each of acoustic transducers  502 A-D. For example, in a first measurement step of the measurement cycle, acoustic transducer  502 A can transmit an acoustic wave and receive reflections from the acoustic wave. When no object is present, the received reflection can be the reflection from the acoustic wave reaching the opposite edge of surface  500 . However, when an object is touching surface  500  (e.g., corresponding to touch  506 ), a reflection corresponding to the object can be received before receiving the reflection from the opposite edge. Based on the received reflection corresponding to the object received at transducer  502 A, the system can determine a distance to the edge (e.g., leading edge) of touch  506 , marked by boundary line  510 A. Similar measurements can be performed by transducers  502 B,  502 C and  502 D to determine a distance to the remaining edges of touch  506 , indicated by boundary lines  510 B,  510 C and  510 D. Taken together, the measured distances as represented by boundary lines  510 A- 510 D can form a bounding box  508 . In some examples, based on the bounding box, the acoustic touch sensing system can determine the area of the touch (e.g., the area of the bounding box). Based on the bounding box, the acoustic touch sensing system can determine position of touch  506  (e.g., based on a centroid and/or area of the bounding box). 
     The acoustic touch sensing scan described with reference to  FIG. 5A  can correspond to the acoustic touch detection described above with reference to  FIGS. 3A and 3B . Acoustic waves transmitted and received along or through cover glass  312  can be used to determine the position/location of an object touching the surface of cover glass  312 . 
       FIG. 5B  illustrates an exemplary timing diagram  560  for an acoustic touch sensing scan described in  FIG. 5A  according to examples of the disclosure. As illustrated in  FIG. 5B , each of the transducers can transmit acoustic waves and then receive reflected waves in a series of measurement steps. For example, from t 0  to t 1  a first transducer (e.g., acoustic transducer  502 A) can be stimulated, and reflections at the first transducer can be received from t 1  to t 2 . From t 2  to t 3  a second transducer (e.g., acoustic transducer  502 B) can be stimulated, and reflections at the second transducer can be received from t 3  to t 4 . From t 4  to t 5  a third transducer (e.g., acoustic transducer  502 C) can be stimulated, and reflections at the third transducer can be received from t 5  to t 6 . From t 6  to t 7  a fourth transducer (e.g., acoustic transducer  502 D) can be stimulated, and reflections at the fourth transducer can be received from t 7  to t 8 . Although the transmit (Tx) and receive (Rx) functions are shown back-to-back in  FIG. 5B  for each transducer, in some examples, gaps can be included between Tx and Rx functions for a transducer (e.g., to minimize capturing portions of the transmitted wave at the receiver), and or between the Tx/Rx functions of two different transducers (such that acoustic energy and the transients caused by multiple reflections from a scan by one transducer does not impact a scan by a second transducer). In some examples, unused transducers can be grounded (e.g., by multiplexers/demultiplexers in switching circuitry  404 ). 
     The distance between an object touching the surface and a transducer can be calculated based on TOF principles. The acoustic energy received by transducers can be used to determine a timing parameter indicative of a leading edge of a touch. The propagation rate of the acoustic wave through the material forming the surface can be a known relationship between distance and time. Taken together, the known relationship between distance and time and the timing parameter can be used to determine distance.  FIG. 5C  illustrates an exemplary timing diagram according to examples of the disclosure.  FIG. 5C  illustrates the transducer energy output versus time. Signal  550  can correspond to the acoustic energy at the transducer from the generation of the acoustic wave at a first edge of the surface. Signal  552  can correspond to the acoustic energy at the transducer received from the wave reflected off of a second edge opposite the first edge of the surface. Due to the known distance across the surface from the first edge to the opposite second edge and the known or measured propagation rate of the acoustic signal, the reflection off of the opposite edge of the surface occurs at a known time. Additionally, one or more objects (e.g., fingers) touching the surface can cause reflections of energy in the time between the generation of the wave and the edge reflection (i.e., between signals  550  and  552 ). For example, signals  554  and  556  can correspond to reflections of two objects touching the surface (or a leading and trailing edge of one object). It should be understood that signals  550 - 556  are exemplary and the actual shape of the energy received can be different in practice. 
     In some examples, the timing parameter can be a moment in time that can be derived from the reflected energy. For example, the time can refer to that time at which a threshold amplitude of a packet of the reflected energy is detected. In some examples, rather than a threshold amplitude, a threshold energy of the packet of reflected energy can be detected, and the time can refer to that time at which a threshold energy of the packet is detected. The threshold amplitude or threshold energy can indicate the leading edge of the object in contact with the surface. In some examples, the timing parameter can be a time range rather than a point in time. To improve the resolution of a TOF-based sensing scheme, the frequency of the ultrasonic wave and sampling rate of the receivers can be increased (e.g., so that receipt of the reflected wave can be localized to a narrower peak that can be more accurately correlated with a moment in time). 
     In some examples (e.g., as illustrated in  FIG. 5B ), transducers  502 A-D can operate in a time multiplexed manner, such that each transducer transmits and receives an acoustic wave at a different time during a measurement cycle so that the waves from one transducer do not interfere with waves from another transducer. In other examples, the transducers can operate in parallel or partially in parallel in time. The signals from the respective transducers can then be distinguished based on different characteristics of the signals (e.g., different frequencies, phases and/or amplitudes). 
     Although four transducers are illustrated in  FIG. 5A , in some examples, fewer transducers can be used. For example, when using an input object with known dimensions (e.g., stylus or a size-characterized finger or target), as few as two transducers mounted along two perpendicular edges can be used. Based on the known dimensions of an object, a bounding box  518  can be formed by adding the known dimensions of the object to the first and second distances, for example. Additionally, although  FIG. 5A  illustrates detection of a single object (e.g., single touch), in some examples, the acoustic touch sensing system can use more transducers and be configured to detect multiple touches (e.g., by replacing each of transducers  502 A-D with multiple smaller transducers). 
     TOF schemes described with reference to  FIGS. 5A-5C  can provide for touch sensing capability using a limited number of transducers (e.g., as compared with a number of electrodes/touch nodes of a capacitive touch sensing system) which can simplify the transmitting and receiving electronics, and can reduce time and memory requirements for processing. Although  FIGS. 5A-5C  discuss using a bounding box based on TOF measurements to determine position of an object, in other examples, different methods can be used, including applying matched filtering to a known transmitted ultrasonic pulse shape, and using a center of mass calculation on the filtered output (e.g., instead of a centroid). 
     In some examples, a time-of-flight measurement can be performed using one or more acoustic transducers to determine an amount of force applied by an object touching a surface.  FIGS. 6A-6D  illustrate exemplary system configurations and timing diagrams for acoustic force sensing to determine an amount of applied force using a time-of-flight measurement according to examples of the disclosure.  FIG. 6A  illustrates an exemplary acoustic force sensing system stack-up  600  including a deformable material  604  in between two rigid surfaces. One of the rigid surfaces can be a cover glass  601  (e.g., corresponding to cover glass  312 ). The second of the rigid surfaces can be a portion of a device housing, for example (e.g., corresponding to housing  202 ). An acoustic transducer  602  (e.g., corresponding to transducer  314 ) can mounted to (or otherwise coupled to) the deformable material  604 . For example, as illustrated in  FIG. 6A , transducer  602  can be disposed between cover glass  601  and deformable material  604 . Transducer  602  can be configured to generate acoustic waves (e.g., shear horizontal waves) and to receive the reflected acoustic waves from the discontinuity at the edge between deformable material  604  and rigid material  606 . It should be understood that although illustrated as transmit and receive transducers (i.e., transceivers), in some examples, the transmit and receive functions can be divided (e.g., between two transducers in proximity to one another, rather than one transmit and receive transducer). Shear horizontal waves can be highly directional waves such that the time of flight can be effectively measure the thickness of the deformable material. A baseline thickness (or time-of-flight) can be determined for a no-force condition, such that changes in thickness (Δd) (or time-of-flight) can be measured. Changes in thickness or time-of-flight can correspond to amount of applied force. 
     For example, plot  630  of  FIG. 6D  illustrates an exemplary relationship between time-of-flight (or thickness) and applied force according to examples of the disclosure. For example, in a steady state condition, where there is no change in time-of-flight across the deformable material  604 , the applied force can be zero. As the time-of flight varies (e.g., decreases), the applied force can vary as well (e.g., increase). Plot  630  illustrates a linear relationship between TOF and force, but in some examples, the relationship can be non-linear. The relationship between TOF and applied force can be empirically determined (e.g., at calibration) using a correlation. In some examples, the calibration can include linearizing the inferred applied force and normalizing the measurements (e.g., removing gain and offset errors). In some examples, the Young&#39;s modulus of the deformable material can be selected below a threshold to allow a small applied force to introduce a detectable normal deformation. 
       FIG. 6B  illustrates another exemplary acoustic force sensing system stack-up  610  including a deformable material  614  in between two rigid surfaces (e.g., between cover glass  611  and rigid material  618 ). An acoustic transducer  612  can mounted to (or otherwise coupled to) one side of deformable material  614 , and a second acoustic transducer  616  can be mounted to (or otherwise coupled to) a second side (opposite the first side) of deformable material  614 . For example, as illustrated in  FIG. 6B , transducer  612  can be disposed between cover glass  611  and deformable material  614  and transducer  616  can be disposed between rigid material  618  and deformable material  614 . Transducer  612  can be configured to generate acoustic waves (e.g., shear horizontal waves) and transducer  616  can be configured to receive the acoustic waves. The configuration of transducers in stack-up  610  can be referred to as a “pitch-catch” configuration in which one transducer on one side of a material transmits acoustic waves to a second transducer on an opposite side, rather than relying on a reflected acoustic wave. The time-of-flight between the time of transmission and the time of receipt of the acoustic wave can be measured to determine the amount of applied force in a similar manner as discussed above with respect to  FIG. 6D . 
       FIG. 6C  illustrates an exemplary timing diagram  640  according to examples of the disclosure.  FIG. 6C  illustrates the transducer energy output versus time. Signal  620  can correspond to the acoustic energy at transducer  602  from the generation of the acoustic wave at a first edge of the deformable material  604 . Signal  622  can correspond to the acoustic energy at transducer  602  received from a first wave reflected off of a second edge, opposite the first edge, of the deformable material  604 . Due to the known distance across the surface from the first edge to the opposite, second edge (under steady-state) and the known or measured propagation rate of the acoustic signal, the reflection off of the opposite edge of the surface occurs at a known time. In some examples, rather than using the first reflection, a different reflection of the acoustic energy can be used to determine time of flight. For example, signal  624  can refer to the acoustic energy at transducer  602  received from a second wave reflected off of the second edge of deformable material  604  (e.g., signal  622  can reflect off of the first side of  604  deformable material and reflect a second time off of the second edge of deformable material  604 ). In some examples, signal  626  can correspond to an integer number reflection after repeated reflections between the two edges of deformable material  604 . It should be understood that signals  620 - 626  are exemplary and the actual shape of the energy received can be different in practice. In some examples, the choice of which reflection to use for the time-of-flight calculation for force sensing can be a function of the thickness of the material and the frequency of the transmitted wave. 
     In some examples, rather than using time-of-flight measurements to determine thickness of the deformable material, other methods can be used. For example, transducer  602  can stimulate the deformable material  604  with ultrasonic waves at a resonant frequency. As the deformable material  604  changes in thickness due to applied force, the resonant frequency can shift. The change in resonant frequency can be measured to determine the applied force. Using a resonant frequency can result in better signal-to-noise ratio (SNR) performance and better accuracy as compared with the time-of-flight method. 
     As described above with reference to  FIGS. 3A-3B , in some examples acoustic touch and force sensing can both be performed. In some examples, the two operations can be time-multiplexed. Transducers  502 A-D (e.g., one of which can correspond to transducer  314 ) can generate transmit waveforms and receive reflections to determine a location/position of touch on a surface (e.g., cover glass  312 ) as described with reference to timing diagram  560  during an acoustic touch sensing phase. Transducer  602  (e.g., corresponding to transducer  314 ) can generate a transmit waveform and receive a reflection to determine an amount of force applied to the surface (e.g., cover glass  312 ) as described with reference to timing diagram  640  during an acoustic force sensing phase. 
     In some examples, the acoustic touch and force sensing can be performed using transmit waveforms generated at the same time.  FIG. 7  illustrates a timing diagram  700  for acoustic touch and force sensing according to examples of the disclosure. Signal  702  can correspond to a transmit waveform generated by a transducer (e.g., transducer  314 ) to simultaneously propagate in deformable material  316  and in cover glass  312 . Signal  704  can correspond to a reflection (e.g., a first reflection) from the boundary between deformable material  316  and rigid material  318 . Signal  706  can correspond to a reflection from an object (e.g., a finger) on the surface of cover glass  312 . Signal  708  can correspond to a reflection from the opposite edge of cover glass  312 . Based on the timing of signal  704 , the acoustic touch and force sensing circuitry can measure a time-of-flight across the deformable material. Based on the timing of signals  706  and/or  708 , the acoustic touch and force sensing circuitry can measure the time-of-flight along the surface of cover glass  312  to an object (or an edge when no object is contacting the cover glass). The time-of-flight measurements for touch can be repeated for each transducer  502 A-D (e.g., four times) to determine the location/position of the object. The time-of-flight measurements can optionally be repeated (e.g., for each of transducers  502 A-D) to measure force applied to the cover glass  312 . In some examples, an average force measurement can be determined from repeated force measurements. In some examples, the repeated measurements can indicate relative force applied to different edges of the cover glass. In some examples, the measurements and different edges of the cover glass can be combined to determine an applied force. 
     Performing acoustic touch and force sensing using one or more shared transducers can provide for both touch and force information with one set of ultrasonic transducers (e.g.,  502 A-D) and one sensing circuit (e.g., acoustic touch and/or force sensing circuit  400 ). As a result, the touch and force sensing systems can potentially be reduced in size, in complexity and in power consumption. 
     Performance of ultrasonic touch and force sensing using ultrasonic waves transmitted into deformable material  316  and cover glass  312  at the same time can depend, in some examples, on the separation between the transmitted ultrasonic waves for touch and for force. For example,  FIG. 7  illustrates signals  704  and  706  corresponding to force and touch reflections, respectively, that can be well separated in time (e.g., such that the force reflections arrive in a dead zone for touch reflections). In practice, an integration of acoustic touch and force sensing can subject each measurement (touch/force) to noise/interference from the other measurement (force/touch). 
     In some examples, interference between ultrasonic waves in the deformable material and the cover glass can be reduced or eliminated based on the design of the deformable material. For example, the deformable material can be selected to have an ultrasonic attenuation property above a threshold, such that the signal in the deformable material can be damped before reflections in the cover glass are received. In some examples, the thickness of the deformable material can be selected to allow for one or more reflections through the deformable material to be received before reflections from the cover glass. In some examples, the reflection (e.g., first, second, nth) through the deformable material can be selected such that the reflection of interest occurs between reflections from the cover glass can be received. In some examples, an absorbent material can be coupled to the deformable material to further dampen ringing of ultrasonic signals in the deformable material. 
       FIG. 8A  illustrates an exemplary cover glass and a ringing effect that can occur in the cover glass. The cover glass  802  can correspond to cover glass  601  and  611  in  FIGS. 6A and 6B . Transducer  804  can be configured to generate acoustic waves (e.g., shear horizontal waves) and to determine position of a touch from an object in contact with cover glass  802  as described in connection with  FIGS. 5A-5C  above. The generated acoustic wave can travel initially in the z-axis direction, reflect from the curved bezel of the cover glass  802 , and reflect in the direction of transmitted acoustic wave  808 A along the x-axis direction. The transmitted acoustic wave  808 A can correspond to the transmit wave propagation  322  described in connection with  FIG. 3B  above. An edge reflected wave  808 B can correspond to the edge reflected wave  328  described in connection with  FIG. 3B  above. Another portion of the acoustic wave generated by transducer  804  can undergo a series of reflections within the edge area of the cover glass  802  as illustrated by reflecting energy  806 A- 806 D. These reflections can exhibit similar timing characteristics to the multiple reflections described in  FIG. 6C , while the timing between reflections can depend on at least the material properties of the cover glass  802 , the geometry of the edge area of the cover glass, and the frequency and mode of the transmitted wave. These multiple reflections  806 A- 806 D can be referred to as a ringing signal in the bezel. As illustrated in  FIG. 6C , each subsequent reflection can be attenuated such that the ringing can eventually die down. In some examples, the initial reflected energy in the ringing signals in the bezel can have significantly more energy (e.g., several orders of magnitude more energy) than signals due to reflections from an object (e.g., a finger) contacting the cover glass  802 . In some examples, the energy in the ringing can continue to be high long enough to interfere with reflected energy signals received from objects touching the cover glass. The ringing signals in the bezel can also interfere with the operation of the force sensor functionality described in  FIGS. 6A-6C  if the ringing signals occur during the Rx time window of the force sensing operation. 
       FIGS. 8B and 8C  illustrate exemplary mitigation techniques for reducing effects of the ringing illustrated in  FIG. 8A . As illustrated in  FIG. 8B , the shape of the edge of the cover glass  802  can be designed to reduce the relative amount of reflected energy  806 B that returns toward the transducer  804 , and increasing the relative amount of transmitted energy  808 A. For example, a 45-degree angle at the edge of cover glass  802  can behave essentially as a flat mirror that produces a consistent angle of reflection of 90 degrees. It should be understood that flattening even a portion of the edge of cover glass  802  can result in reduced ringing amplitude and that it is not necessary to make the edge of the cover glass completely flat. Many other cover glass edge shapes are possible and the shape illustrated in  FIGS. 8B and 8C  are for illustration purposes only.  FIG. 8C  illustrates the addition of a dampening material  810  can also be added somewhere on the cover glass near where the ringing energy occurs to absorb the ringing energy and cause the ringing to attenuate more quickly. As shown in  FIG. 8C , the dampening material can be combined with the cover glass edge shape of  FIG. 8B  to significantly improve the ringing performance of the device. 
       FIG. 9A  illustrates a representation of spatial and temporal distribution of energy received by a transducer  902  due to the ringing effect described in  FIG. 8A . In the illustrated example, the y-axis represents a position of received acoustic energy that can be received by a transducer  902  positioned at one edge of the electronic device (e.g., transducer  314  above). In  FIG. 9A , the width of each of the bars  906 A- 906 N can represent an amount of signal (e.g., amount of energy) received by transducer  902  at a particular position in the y-axis direction. An acoustic wave can be generated by the transducer  902  at time=0. The illustrated bars  906 A- 906 N can represent a signal received by the transducer  902 , and can correspond to the gradually dampening bezel ringing signal as described in  FIG. 8A  and/or the multiple reflections in the force sensor described in  FIG. 6C  above. For example, when compared to  FIG. 6C , the widest bar  906 A can correspond to the first reflection  622  having the largest amplitude. The appearance of each reflection  906 A- 906 N as a continuous bar in the y-axis direction illustrates that the ringing signal is approximately spatially uniform across the entire length of the transducer  902 . Over time, the energy of the ringing signal can diminish, as illustrated by bar  906 N. The amount of time for the ringing to diminish and the total energy in each of the ringing signals can be mitigated by the techniques described in  FIG. 8B-8C  above. 
       FIG. 9B  illustrates a representation of spatial and temporal distribution of energy received by a transducer  902  during a touch sensing operation. In  FIG. 9B , the received signal pattern represented by  908 A- 908 F can correspond to signals reflected by an object in contact with a cover glass as described above in connection with  FIG. 3B . In some examples, the spacing of the received energy  908 A- 908 F can be affected by ridges in a user&#39;s fingers, orientation of the finger, and the like. The first received energy returning from the object can be represented by  908 A- 908 C, which can all occur at the same time on the time axis. Unlike the ringing energy illustrated in  FIG. 9A , the received signal caused by an object can be non-uniform along the position axis, as shown by the three discrete received signal segments  908 A- 908 C. In some examples, the position of the received signal segments  908 A- 908 C can be used to determine the position of the object in the y-axis direction, and the time of flight can be used to determine the position of the object in the x-axis direction. Spaces of no received energy occurring between received signal segments  908 A- 908 C can be caused by characteristics of the object, e.g., fingerprints of a user. Although a relatively simple pattern is illustrated for the received signal segments  908 A- 908 F, it should be understood that an actual received energy pattern due to an object can be significantly more complex. The pattern shown is merely for illustrative purposes, and is illustrated to show that there can be a spatial modulation in the received signal from an object. The spatial modulation can vary based on, for example, individual fingerprint patterns, orientation of a finger relative to the acoustic wave propagation direction, amount of force being applied to the cover glass, and the like. The position of each received signal segment  906 A- 906 F on the time axis can correspond to the round trip TOF for transmitted acoustic energy from the transducer  902  to return to the transducer after being reflected. Furthermore, the amount of time between the first received signal  906 A- 906 C and the final received signal  908 D- 908 F can be indicative of the size of the object contacting the cover glass. It is important to note that the ringing signal illustrated in  FIG. 9A  can be occurring simultaneously to the signal returning from the object  906 A- 906 F. The amount of received signal  908 A- 908 F from the object can appear relatively small compared to the amount of received signal caused by the ringing  906 A- 906 N. As will be discussed further below, the spatial modulation of the received signal from an object  908 A- 908 F can be used to differentiate between received signal from an object and received signal caused by the ringing. 
       FIG. 9C  illustrates a spatial differential electrode configuration for transducer electrodes alongside the spatial and temporal distribution of energy received by a transducer  902  due to the ringing effect described in  FIGS. 8A and 9A . Although not shown in the figures above, a pair of electrodes can be disposed on opposing sides of the transducer that can be used to both drive the transducer  902  and to receive electrical signals generated by the transducer. In the simplest configuration, one of the two electrodes can act as a common electrode, and the second of the two electrodes act as both the drive and sense electrode for the transducer.  FIG. 9C  illustrates two patterned electrodes  903 A- 903 B disposed on a same side of the transducer  902 . The patterned electrodes  903 A- 903 B are shown with an alternating repeating pattern where each electrode  903 A and  903 B occupies half of the surface of the transducer  902 . In some examples, the received signal at each of these electrodes can be subtracted to remove the effects of the ringing signals  906 A- 906 N. Because of the spatially uniform nature of the ringing signals (e.g., a solid bar across the entire y-axis), the signal due to ringing that is received by each of the electrodes  903 A and  903 B can be approximately equal. Thus, in some examples, the ringing signal can be canceled after subtracting the signal values of the two electrodes  903 A and  903 B. Signals such as the illustrated ringing signal that have a spatially uniform characteristic can be referred to as common mode signals relative to the electrode pattern  903 A and  903 B. As mentioned above, the illustrated ringing signal can correspond to ringing in an edge or bezel area of a cover glass as shown in  FIG. 9A , ringing from the back edge of the cover glass, ringing in a force sensor such as the ringing shown in  FIG. 6C , or any other spatially uniform (e.g., common mode) signal relative to the electrode pattern. 
       FIG. 9D  illustrates the spatial differential electrode configuration for transducer electrodes alongside the representation of spatial and temporal distribution of a touch sensing signal corresponding to the touch sensing operation shown in  FIG. 9B . As explained above, the received signal segments  908 A- 908 F can return with a spatial modulation pattern that can correspond to characteristics of the object contacting the cover glass. The electrode pattern for electrodes  903 A- 903 B can be selected to correspond to a particular spatial modulation frequency. In some examples, by leveraging known spatial modulation characteristics expected in the received signal, the electrode pattern  903 A- 903 B can be designed to be appropriately sensitive to the received signal. In the illustrated pattern of received signal segments  908 A- 908 F, the electrodes  903 A and  903 B can each receive a different amount of reflected energy because of the pattern. For example, signal segments  908 A and  908 B may primarily be received by electrode  903 A, thus causing a difference in the signal on electrodes  903 A and  903 B. In some examples, by subtracting the signals received by the two electrodes  903 A/ 903 B a differential touch signal based on the energy reflected by the object can be produced. At the same time, because the electrodes  903 A and  903 B can receive the same signals from the ringing  906 A- 906 N, the ringing component of received signal can be canceled. In some examples, this scheme can be more effective in reducing the impact of ringing on the detecting touch sensing output than the mitigation measures illustrated in  FIGS. 8B and 8C . Alternatively, the combined effect of the spatial differential electrode configuration and the mitigation measures illustrated in  FIGS. 8B and 8C  can be used to maximize signal to noise ratio values of the acoustic touch sensing system. 
     As can be seen in the configuration of electrodes  903 A and  903 B in  FIGS. 9C-9D , the electrodes can form a repeating pattern with a certain pitch along the y-axis direction. The pitch of the electrodes can have a corresponding spatial frequency to which differential measurement of the electrodes  903 A and  903 B can be responsive. In other words, the electrodes  903 A and  903 B can be designed to be tuned to a particular spatial frequency. For example, ridges on a human finger can produce a spatial frequency within a particular range of frequencies that can correspond to the typical spacing of ridges that form a fingerprint. A typical range of fingerprint ridge spacing can be between 200 μm and 700 μm. Accordingly, the spacing or pitch of the electrodes  903 A and  903 B being used for touch measurement can be tuned to an appropriate spatial frequency that lies within the range of spatial frequencies expected to be produced by a human finger. In addition, as will be discussed in more detail below, multiple electrode patterns of different pitch, electrode patterns with a configurable pitch, or a combination of both can be used to selectively tune the sensitivity of a differential measurement to a plurality of spatial frequencies. 
       FIGS. 10A-10B  illustrate exemplary spatial differential force sensing configurations according to examples of the disclosure. As discussed immediately above, the pitch of electrodes  1003 A and  1003 B can determine a spatial frequency sensitivity for differential measurements of the transducer  1010 . As also described above, the spatial frequencies produced by fingerprint ridges can be used to perform touch measurement with an appropriately tuned electrode configuration. As a reminder, the force measurement described in  FIGS. 3 and 6A-6C  utilize a deformable material (e.g.,  316  and  614 ) with a uniform physical characteristic. Unlike the signals reflected from a fingerprint, a uniform deformable material as described above may produce only a DC or common mode spatial frequency as a result of reflected energy. 
       FIG. 10A  illustrates a first deformable material configuration for introducing a spatial frequency into the deformable material comprising first sections  1014 A and second sections  1014 B. In addition,  FIG. 10A  illustrates a corresponding electrode configuration of electrodes  1003 A and  1003 B (which can correspond to electrodes  903 A and  903 B above) that can be tuned to the spatial frequency created by the pattern in the deformable material. In some examples, the electrodes  1003 A and  1003 B can be coupled to one side of transducer  1010 , and a second electrode  1011  can be disposed on the opposite side of the transducer. In some examples, the second electrode  1011  can be connected to ground. In some examples, as will be described in more detail below regarding  FIGS. 14A-14B , the second electrode  1011  can be operated as a floating electrode. Furthermore, as will be described in more detail below, multiple electrodes  1011  can be disposed on the opposite side of the transducer  1010  and connected in different ways. 
     In some examples, a spatial frequency associated with the deformable material  1014  can be introduced by varying the thickness of the deformable material between the first sections  1014 A and  1014 B as shown in  FIG. 10 . In some examples, the difference in thickness of the first sections  1014 A and second sections  1014 B can introduce a difference time of flight based on the different distances traveled by a travelling acoustic wave. In some examples, the thicknesses can be configured to create a half-wavelength difference in round trip time of flight between the first sections  1014 A and the second sections  1014 B. As described above in  FIGS. 9A-9D , the electrodes  1003 A and  1003 B can be read differentially to eliminate the effects of common mode signals such as a ringing signal in a bezel as described in  FIGS. 8A-8C . In some examples, the half-wavelength difference in time of flight in the first sections  1014 A and second sections  1014 B can result effectively in a summation when the differential measurement is performed between the electrodes  1003 A and  1003 B. In some examples, the electrodes  1003 A and  1003 B can also be used for touch detection in addition to force detection. In some examples, the electrodes  1003 A and  1003 B can be grouped together to perform touch sensing measurements. In some examples, electrodes  1003 A and  1003 B can be added together to perform touch detection. In some examples, force detection in the deformable material  1014 A and  1014 B can be performed during a ring-down period of the bezel reflections described above in  FIGS. 8A-8C . During the ring-down period, the differential measurements being performed can cancel out the common mode bezel reflection signals as described above. In some examples, after the ring-down period, the touch sensing operation using combined electrodes  1003 A and  1003 B or the summation of electrodes  1003 A and  1003 B. In some examples, the spatial frequency selected for the deformable material can be selected to be orthogonal to one or more spatial frequencies used for detecting touch in a touch sensing mode. In some examples, an optional isolation material  1012  can be placed between the first sections  1014 A and the second sections  1014 B of the deformable material to prevent interactions between the waves traveling in the separate sections. 
       FIG. 10B  illustrates an alternative configuration for introducing a spatial frequency associated with the deformable material  1014  by varying the speed of sound between the first sections  1014 A and second sections  1014 B of the deformable material. In some examples, the electrodes  1003 A and  1003 B, transducer  1010 , and second electrode  1011  can be configured in the same was as described in  FIG. 10A  above. In some examples, the speed of sound between the first and second sections can be achieved by placing a first material in the first sections  1014 A and a second, different material with a different speed of sound in the second sections  1014 A. In some examples, the differences of speed of sound of the first sections  1014 A and second sections  1014 B can result in different time of flight of acoustic waves travelling in the respective sections. In some examples, the speed of sounds can be selected such that the round trip time of flight difference between the first sections  1014 A and the second sections  1014 B is half-wavelength of the transmitted acoustic wave. In some examples, the speed of sounds can be selected such that the time of flight difference between the first sections  1014 A and second sections  1014 B is equal to multiple wavelengths of the transmitted acoustic wave. For example, one of the materials can be silicone, while the second material can be air. As described above in  FIGS. 9A-9D , the electrodes  1003 A and  1003 B can be read differentially to eliminate the effects of common mode signals such as a ringing signal in a bezel as described in  FIGS. 8A-8C . In some examples, the ½ wavelength difference in time of flight in the first sections  1014 A and second sections  1014 B can result effectively in a summation when the differential measurement is performed between the electrodes  1003 A and  1003 B. In some examples, the electrodes  1003 A and  1003 B can also be used for touch detection in addition to force detection. In some examples, the electrodes  1003 A and  1003 B can be grouped together to perform touch sensing measurements. In some examples, electrodes  1003 A and  1003 B can be added together to perform touch detection. In some examples, force detection in the deformable material  1014 A and  1014 B can be performed during a ring-down period of the bezel reflections described above in  FIGS. 8A-8C . During the ring-down period, the differential measurements being performed can cancel out the common mode bezel reflection signals as described above. In some examples, after the ring-down period, the touch sensing operation using combined electrodes  1003 A and  1003 B or the summation of electrodes  1003 A and  1003 B. In some examples, the spatial frequency selected for the deformable material can be selected to be orthogonal to one or more spatial frequencies used for detecting touch in a touch sensing mode. In some examples, an optional isolation material  1012  can be placed between the first sections  1014 A and the second sections  1014 B of the deformable material to prevent interactions between the waves traveling in the separate sections. 
       FIGS. 11A-11E  illustrate electrode arrangement grouping patterns for single-sided, spatial differential electrode configurations according to examples of the disclosure.  FIGS. 9C-9D  and  FIGS. 10A-10B  both illustrate single-sided differential electrode patterns, and both touch sensing and force sensing operations associated with the single-sided differential electrode patterns have been described above.  FIG. 11A  illustrates an exemplary two-electrode spatial differential electrode configuration according to examples of the disclosure. The alternating two-electrode configuration can include electrodes  1103 A and  1103 B, which can correspond to electrodes  903 A and  903 B in  FIGS. 9C-9D  above and electrodes  1003 A and  1003 B in  FIGS. 10A and 10B  above. Grouping pattern  1105 A illustrates an exemplary differential connection pattern that can be used to perform spatial differential sensing for touch as described above in connection to  FIGS. 9C-9D  or for force as described above in connection to  FIGS. 10A-10B . In some examples, the electrode  1103 A can be coupled to a first terminal (e.g., positive) of a differential amplifier, and the electrode  1103 B can be connected to a second terminal (e.g., negative) of the differential amplifier. It should be understood that the positive/negative connections of the differential amplifier can be reversed without departing from the scope of the present disclosure. The right hand side of each  FIG. 11A-11E  illustrates a finger spatial frequency curve  1107  that can approximate the energy density of various spatial frequencies produced by finger reflections. The bar  1109 A illustrates one possibility for the spatial frequency that can correspond to the pitch of electrodes  1103 A and  1103 B. In the illustrated bar  1109 A, the spatial frequency that corresponds to the pitch of electrodes  1103 A and  1103 B can be placed at the peak of the finger spatial frequency curve to maximize the amount of signal obtained during a touch operation. However, it should be understood from the disclosure above in  FIGS. 10A-10B  that the spatial frequency can be adjusted (e.g., by changing the pitch) to correspond to a spatial frequency of a deformable material pattern (e.g.,  1014 A and  1014 B above) in order to tune the spatial frequency sensitivity to force sensing. It should be understood that the physical metal layers used to form the electrodes  1103 A and  1103 B are fixed once the metal layers are formed into the electrode patterns. Accordingly the physical size of the metal layers that form electrodes themselves cannot be dynamically changed to change the spatial frequency sensitivity. However, as will be described below in connection with  FIGS. 11B-11E ,  13 B and  17 - 20 , the spatial frequency and phase sensitivity can be dynamically configurable by changing electrode groupings as will be described in more detail below. 
       FIG. 11B  illustrates an exemplary four electrode spatial differential electrode configuration according to examples of the disclosure. In some examples, the electrodes  1103 C- 1103 E can be disposed on a single side of a transducer (e.g.,  612 ,  902 , or  1010  above) with a common electrode on the opposite side of the transducer. The electrodes  1103 C- 1103 E can be placed in an alternating and repeating pattern as indicated by the fill patterns corresponding to each electrode. Grouping patterns  1105 B and  1105 C illustrated two exemplary differential connection patterns that can be used to perform spatial differential sensing tuned to multiple spatial frequencies. 
     Grouping pattern  1105 B illustrates an alternating pattern similar to connection pattern  1105 A in  FIG. 11A . This connection pattern can be achieved by combining the outputs of electrodes  1103 C with the outputs of electrode  1103 E and connecting the combined electrode to one terminal of a differential amplifier (e.g., positive). At the same time, the outputs of electrodes  1103 D and  1103 F can be combined and the combined electrode can be connected to the opposite terminal of the differential amplifier (e.g., negative). Grouping pattern  1105 C illustrates a second exemplary pattern can be configured to produce a different effective electrode pitch (and corresponding spatial frequency sensitive) using the same electrodes as pattern  1105 B. In the grouping configuration  1105 C, the electrodes  1103 C and  1103 D can be combined and connected to a first terminal of a differential amplifier (e.g., positive), and electrodes  1103 E and  1103 F can be combined and connected to a second terminal of the differential amplifier (e.g., negative). The pitch of the resulting pattern can be twice as long as the pitch of the pattern resulting from grouping pattern  1105 B. Thus, by switching the electrode configurations between grouping pattern  1105 A and  1105 B, the spatial frequency sensitivity of the spatial differential electrode configuration can be dynamically changed. Bars  1109 B and  1109 C plotted against the finger spatial frequencies curve  1107  illustrate an exemplary set of spatial frequencies that can correspond to the groupings  1105 B and  1105 C respectively. In the illustrated bars, both of the bars fall near the peak of the spatial frequency curve  1107 . However, because the relative sizing of the grouping patterns can change by a factor of two between the two groupings and the resulting ratio of the spatial frequencies corresponding to bars  1109 B and  1109 C can also be 2:1. 
       FIG. 11C  illustrates an exemplary electrode spatial differential electrode configuration with six electrodes respectively according to examples of the disclosure. In some examples, the electrodes  1103 G- 1103 L can be disposed on a single side of a transducer (e.g.,  612 ,  902 , or  1010  above) with a common electrode on the opposite side of the transducer. The electrodes  1103 G- 1103 L can be placed in an alternating and repeating pattern as indicated by the fill patterns corresponding to each electrode. As should be understood based on the descriptions of  FIG. 10B  above, the grouping configurations  1105 D and  1105 E can be connected to terminals of a differential amplifier. The pitch of the illustrated patterns can have a ratio of 3:2, and corresponding bars  1109 D and  1109 E are illustrated along with the finger spatial frequency curve  1107 . Although the difference may appear subtle, in the graphs of  FIG. 11B  and  FIG. 11C , the groupings in  FIG. 11C  show that by reducing the ratio of effective pixel pitch (e.g., from 2:1 to 3:2), the sensed spatial frequencies can be closer together, and in some examples, an increased in amount of signal can be obtained. 
       FIG. 11D-11E  illustrate exemplary electrode spatial differential electrode configuration with eight and twelve electrodes respectively according to examples of the disclosure. As should be understood based on the  FIGS. 11A-11C  above, the electrodes can be grouped into different groupings (e.g.,  1105 F- 1105 H in  FIG. 11D and 1105I-1105M  in  FIG. 11E ) to maximize an amount of signal obtained within the desirable frequency range. For example, the bars  1109 J- 1109 M can correspond to four different spatial frequencies within the finger spatial frequency curve  1107  peak. In some examples, the bar  1109 I, which is shown positioned away from the spatial frequency curve  1107  peak can be used for force sensing. As explained above, the deformable material in  FIGS. 10A-10B  can be configured with a desired spatial frequency, and by placing the desired frequency outside of the finger spatial frequency curve  1107  peak, the touch and force signals have a reduced amount of interference with one another. 
       FIG. 12A  illustrates an exemplary configuration for a spatial differential electrode configuration having differential electrodes on both sides of a transducer  1210  according to examples of the disclosure.  FIG. 12  depicts a flattened view of a cover glass  1202 , transducer  1210 , and a deformable material  1214  that can correspond to the cover glass, transducer, and deformable material components in  FIGS. 3B and 6B . Furthermore the deformable material  1214  is depicted with a jagged border to illustrate that a spatial frequency has been included in the deformable material  1214 . It should be understood that either of the configurations in  FIGS. 10A and 10B  for including a spatial frequency in the deformable material  1214  can be used while remaining within the scope of the present disclosure. The illustrated jagged shape of the deformable material  1214  is merely illustrative of a pitch of the associated spatial frequency.  FIG. 12  illustrates a transducer  1210  having two sets of two electrode differential patterns, electrodes  1203 A and  1203 B on a first side of the transducer, and electrodes  1207 A and  1207 B on a second side of the transducer. As illustrated, the first side electrodes  1203 A/ 1203 B can be disposed between the transducer and the cover glass  1202  and the second side electrodes  1207 A/ 1207 B can be disposed between the transducer and the deformable material  1214 . It should be recognizable that each of the pairs of electrodes  1203 A/ 1203 B and  1207 A/ 1207 B respectively can correspond to a two pixel differential electrode configuration as shown in  FIG. 11A  above. As illustrated the  1207 A/ 1207 B can have a larger electrode size and a corresponding larger electrode pitch, leading each of the electrode pairs to have a different corresponding spatial frequency. Furthermore, in some examples, the pitch of the electrodes  1207 A and  1207 B can be configured to match the spatial frequency associated with the deformable material. 
       FIG. 12B  illustrates an exemplary connection pattern for performing acoustic wave transmission, touch measurement, and force measurements. In an exemplary transmit state an acoustic wave can be transmitted by providing a differential driving signal across the transducer  1210 . This can be accomplished by differentially driving electrodes on one side (e.g.,  1203 A and  1203 B) of the transducer  1210  with a first polarity of a transmit signal and driving electrodes (e.g.,  1207 A and  1207 B) on the opposite side with the opposite polarity of the transmit signal. While the chart illustrates  1203 A/ 1203 B connected to the positive input terminal and  1207 A/ 1207 B connected to the negative input terminal, these polarities can be switched without departing from the scope of the present disclosure. In some examples, a single-sided transmit can be accomplished by driving a set of electrodes on one side of the transducer (e.g., either  1203 A/ 1203 B or  1207 A/ 1207 B) with a transmit signal and coupling the opposite set of electrodes to ground. 
     In a first exemplary force measurement configuration, the electrode  1207 A can be coupled to a first input terminal of a differential amplifier and the electrode  1207 B can be coupled to a second input terminal of a differential amplifier. In the first exemplary force measurement configuration, the electrodes  1203 A and  1203 B can be coupled to ground. In a second exemplary force measurement configuration, one of the electrodes (e.g.,  1207 A or  1207 B) can be coupled to a single-ended amplifier, and the other electrode (e.g.,  1207 B or  1207 A) can be coupled to ground. In the second exemplary force measurement configuration, the electrodes  1203 A and  1203 B can be left floating to create a differential measurement in the charge domain as will be explained in more detail with regard to  FIGS. 14B and 14C  below. 
     In a first exemplary touch measurement configuration, the electrode  1203 A can be coupled to a first input terminal of a differential amplifier and the electrode  1203 B can be coupled to a second input terminal of a differential amplifier. In the first exemplary force measurement configuration, the electrodes  1207 A and  1207 B can be coupled to ground. In a second exemplary force measurement configuration, one of the electrodes (e.g.,  1203 A or  1203 B) can be coupled to a single ended amplifier, and the other electrode (e.g.,  1203 B or  1203 A) can be coupled to ground. In the second exemplary force measurement configuration, the electrodes  1207 A and  1207 B can be left floating to create a differential measurement in the charge domain as will be explained in more detail with regard to  FIGS. 14B and 14C  below. 
       FIGS. 13A and 13B  illustrated exemplary configurations and groupings for double-sided differential electrode configurations according to examples of the disclosure.  FIG. 13A  illustrates a configuration with two electrodes  1303 A and  1303 B on a first (e.g., top) side of the transducer  1310  and two electrodes  1307 A and  1307 B on a second (e.g., bottom) side of the transducer. The electrode pairs can be operated similarly to the two-sided electrode operation described in  FIG. 12  with grouping pattern  1305 A for the electrodes  1303 A and  1303 B and grouping pattern  1313 A for the electrodes  1307 A and  1307 B. In some examples, the top-side electrodes (e.g.,  1303 A and  1303 B) and bottom-side electrodes (e.g.,  1307 A and  1307 B) can have a different pitch, and thus different corresponding spatial frequency sensitivity. The example in  FIG. 13A  shows a ratio of 2:1 between the pitch of the bottom electrodes and the top electrodes. The chart in the right hand side of  FIG. 13A  illustrates a finger spatial frequency curve  1308  that can correspond to the finger spatial frequency curve  1107  in  FIGS. 11A-11E  above. In the particular example of  FIG. 13A , the top electrodes  1303 A/ 1303 B can be designed to sense a spatial frequency  1309 A at the peak of the finger spatial frequency curve  1308 . Furthermore, the bottom electrodes  1307 A/ 1307 B can be designed to sense a spatial frequency  1311 A that can be away from the peak of the finger spatial frequency curve  1308 . Furthermore, the spatial frequency corresponding to  1311 A can be the spatial frequency associated with the deformable material pattern (e.g.,  1204  above) as further described in  FIGS. 10A-10B . 
       FIG. 13B  illustrates a configuration with four electrodes  1303 C- 1303 F on a first (e.g., top) side of transducer  1310  and six electrodes  1307 G- 1307 L on a second side (e.g., bottom of transducer  1310 . The four-electrode configuration can correspond to the electrode configuration illustrated in  FIG. 11B  and the six-electrode configuration can correspond to the electrode configuration illustrated in  FIG. 11C . In some examples, electrode groupings  1305 B,  1305 C,  1313 B, and  1313 C can be used to obtain measurements at four different spatial frequencies. It should be understood that the transmit, force measurement, and touch measurement states described in  FIGS. 12A and 12B  can be implemented with the electrode groupings in an analogous way to the connections in  FIG. 12B . As one example, the force measurement of  FIG. 12B  can be accomplished using pixel grouping  1313 C. In some examples, the electrodes  1307 G,  1307 H, and  1307 I can be grouped together and coupled to a first input terminal of a differential amplifier and the electrodes  1307 J,  1307 K, and  1307 L can be grouped together and coupled to a second terminal of the differential amplifier. The chart in the right hand side of  FIG. 13B  illustrates a finger spatial frequency curve  1308  that can correspond to the finger spatial frequency curve  1107  in  FIGS. 11A-11E  above. In some examples, the spatial frequency for grouping  1313 C can be located at the position of the bar  1311 B, which is at a spatial frequency far from the peak of the finger spatial frequency curve  1308 . In some examples, the spatial frequency associated with  1311 B can be the frequency associated with the deformable material pattern (e.g.,  1204  above), as further described in  FIGS. 10A-10B . The remaining groupings  1305 B,  1305 C, and  1313 B can also be used to produce measurements at additional spatial frequencies as reflected by bars  1309 B- 1309 D, which can all be positioned near the peak of the finger spatial frequency curve  1308  to maximize an amount of signal for touch measurement. 
       FIGS. 14A-14C  illustrate exemplary amplifier configurations for performing differential sensing according to examples of the disclosure.  FIG. 14A  illustrates an exemplary differential amplifier readout connection for a two-pixel electrode pattern  1403 A and  1403 B disposed on a first side of a transducer  1410 . In some examples, a ground electrode  1407  can be disposed on the opposite side of the transducer  1410 . It should be understood from the disclosure above, including  FIGS. 12 and 13 , that the electrode  1407  could be representative of a multiple electrode configuration (e.g., as described in  FIGS. 11A-11E ) where all of the individual electrodes are connected to ground. In some examples, the use of a differential amplifier to read out the signals from electrodes  1403 A and  1403 B can result in a large amount of noise. Furthermore, in some examples, the differential amplifier must be able to accept a large amount of common mode signal at the differential inputs (e.g., from the ringing signal described in  FIGS. 8A-8C . 
       FIG. 14B  illustrates an alternative single-ended amplifier configuration for performing differential sensing according to examples of the disclosure. In the illustrated configuration, one of the two electrodes  1403 A/ 1403 B can be connected to a single ended amplifier  1413 , and the other of the two electrodes  1403 B/ 1403 A can be connected to ground. The electrode on the opposite side  1407  of the transducer  1410  can be floating instead of connected to ground as shown in  FIG. 14A . In addition, an optional grounded shield  1414  can be provided from preventing coupling of signals into the floating electrode  1407  that can get injected into the signal received at the amplifier  1413 . In some examples, when the optional grounded shield  1414  is provided, an insulating layer  1409  can be disposed between the grounded shield and the floating electrode  1407  to electrically isolate the grounded shield from the floating electrode.  FIG. 14C  illustrates an equivalent circuit of the configuration in  FIG. 14B .  FIG. 14C  shows a voltage signal formed between electrode  1403 A and the floating electrode  1407  having a value V CM +V D /2 and a voltage formed between electrode  1403 B (which can be grounded) and the floating electrode having a value V CM −V D /2. V CM  represents a common mode voltage that can be a result of signals that are common to the two electrodes  1403 A and  1403 B such as ringing in the bezel described in  FIGS. 8A-8C  above. V D  represents a differential voltage between the first and second electrode that can result from the electrodes  1043 A and  1403 B receiving different signals due to spatial modulation of the incoming signal (e.g., from a finger) as described above. In some examples, when the electrode  1403 B is grounded and the floating electrode  1407  is at a floating potential, the single ended amplifier sees the voltages in series, with the common mode signal effectively canceling out, and the differential components adding together. The voltage (V A ) at the input of amplifier  1413  can be expressed with the following equations: 
                     V   A     =       (       V   CM     +       V   D     2       )     -     (       V   CM     -       V   D     2       )               (   1   )                   (       V   CM     +       V   D     2       )     -     (       V   CM     -       V   D     2       )       =     V   D             (   2   )               VA   =     V   D             (   3   )               
The equations show that the common mode term can be canceled, and the voltage at the amplifier input can be equal to the differential voltage between the electrodes  1403 A and  1403 B. Thus, a single-ended amplifier can be used to perform the differential measurement, and the amplifier does not need to handle the signal swing of the full common-mode signal, which can be orders of magnitude larger than the differential signal as described in  FIGS. 8A-8C  above. It should be understood from the disclosure above that the single-ended amplifier configuration of  FIGS. 14B and 14C  is not limited to the situation of a two-electrode pattern on one side of the transducer  1410 , but can be extended to any of the single-sided or double-sided electrode patterns described in  FIGS. 11A-11E and 13A-13B  and other electrode patterns capable of performing the differential sensing described throughout the disclosure.
 
       FIG. 14D  illustrates an alternative amplifier configuration for performing differential sensing according to examples of the disclosure. In the illustrated configuration, the two electrodes  1403 A and  1403 B can be connected to a differential amplifier  1412 , instead of the single ended amplifier  1413  of  FIG. 14B . The other components of the configuration illustrated in  FIG. 14D  can be the same as the configuration illustrated in  FIG. 14B . However unlike in the configuration of  FIG. 14B , the signals may not be referenced to a known potential, as the floating electrode  1407  is floating at the time of measurement. In this case, the differential amplifier  1412  may need to be capable of accepting a wider range of input voltage values. In particular, the floating electrode  1407  can be influenced by coupling with nearby objects. As mentioned above, an optional grounded shield  1414  can be used to shield the floating electrode  1407  from coupling with nearby objects. In some examples, when the optional grounded shield  1414  is provided, an insulating layer  1409  can be disposed between the grounded shield and the floating electrode  1407  to electrically isolate the grounded shield from the floating electrode. However, the optional grounded shield  1414  can create a leakage path for charge via capacitive coupling to the floating electrode  1407 . Accordingly, there can be a trade-off between rejecting outside object coupling and common mode rejection in the floating electrode  1407  configuration. In light of these trade-offs, in some examples, a common-mode feedback approach as described in  FIGS. 14E-14F  below can be used as an alternative to the floating electrode configuration for reducing effects of a common-mode signal in during spatial-differential readout according to examples of the disclosure 
       FIGS. 14E-14F  illustrate exemplary amplifier configurations with a common-mode feedback (CMFB) configuration for performing spatial differential sensing according to examples of the disclosure.  FIG. 14E  illustrates an exemplary differential amplifier  1412  readout connection for a two-pixel electrode pattern  1403 A and  1403 B disposed on a first side of a transducer  1410 . In some examples, an electrode  1407  can be disposed on the opposite side of the transducer  1410 . In some examples, the signals from electrodes  1403 A and  1403 B can result include a large common mode signals as described above (e.g., ringing in the bezel as described with reference to  FIGS. 8A-8C  above). These common mode signals can be reduced or eliminated by the CMFB configuration illustrated in  FIG. 14E . For example, the common mode signal from electrodes  1403 A and  1403 B can be sensed by resistors  1414 A and  1414 B, respectfully. In some examples, resistors  1414 A and  1414 B can be the same size or substantially the same size. In some examples, resistors  1414 A and  1414 B can be a generic impedance that can include resistors, capacitors, and/or inductors. The sensed common mode signal (V CM ) (can be coupled to the first terminal (e.g., negative or inverting) of operational amplifier  1416 , and the second terminal (e.g., positive or non-inverting) of operational amplifier  1416  can be coupled to a desired reference voltage  1420  (e.g., ground or any other desired voltage). In some examples, the output of operational amplifier  1416  can be connected to electrode  1407  on one side of the transducer. In some examples, when the second terminal (e.g., positive) of operational amplifier  1416  is coupled to ground, the common mode signal can be eliminated or reduced by the operational amplifier. As discussed above with reference to  FIG. 14C , a voltage signal can be formed between electrode  1403 A and electrode  1407  having a value V CM +V D /2 and a voltage can be formed between electrode  1403 B and electrode  1407  also having a value V CM −V D /2. Because the configuration illustrated in  FIG. 14E  can eliminate V CM , amplifier  1412  can receive only V D —the differential voltage between the first and second electrode that can result from the electrodes  1403 A and  1403 B receiving different signals due to spatial modulation of the incoming signal (e.g., from a finger) as described above. The voltage (V A ) at the input of amplifier  1412  can be expressed with the following equations:
 
 V   A =( V   CM   +V   D /2)−( V   CM   −V   D /2)  (1)
 
 V   A =(0 +V   D /2)−(0 −V   D /2)  (2)
 
 V   A   =V   D /2+ V   D /2  (3)
 
 V   A   =V   D   (4)
 
The equations show that the common mode term can be eliminated or reduced, and the voltage at the input of amplifier  1412  can be made equal to the differential signal component between the electrodes  1403 A and  1403 B (e.g., V D ). Thus, amplifier  1412  does not need to have to be designed to accomodate the voltage range of common-mode signal, which can be orders of magnitude larger than the differential signal as described in  FIGS. 8A-8C  above. It should be understood from the disclosure above, including  FIGS. 12 and 13 , that the electrode  1407  could represent a multiple electrode configuration (e.g., as described in  FIGS. 11A-11E ).
 
       FIG. 14F  illustrates a CMFB configuration for performing differential sensing according to examples of the disclosure. In some examples, resistors  1414 A and  1414 B can reduce the impedance seen at the input of differential amplifier  1412 , and cause errors. In some examples,  1414 A and  1414 B can introduce thermal noise at the input of amplifier  1412  that can be amplified by the differential amplifier  1412 . In the illustrated configuration, buffers  1418 A and  1418 B can be used to isolate resistors  1414 A/ 1414 B from the inputs of differential amplifier  1412 ). This configuration can isolate resistors  1414 A/ 1414 B from amplifier  1412  such that resistors  1414 A/ 1414 B do not interfere with differential amplifier  1412  and the differential amplifier does not see the resistance of the resistors  1414 A/ 1414 B. Moreover, the positive terminal of feedback operational amplifier  1416  can be coupled to ground or a reference voltage source  1420  that can provide any desired reference voltage. The CMFB circuit illustrated in  FIG. 14F  can be used to remove or reduce the common mode signal component from the input to differential amplifier  1412 . Thus, when the CMFB circuit is employed, amplifier  1412  does not need to be able to accept the full common-mode signal swing. 
     It should be understood from the disclosure above that the CMFB configurations of  FIGS. 14E and 14F  are not limited to the situation of a two-electrode pattern on one side of the transducer  1410 , but can be extended to any of the single-sided or double-sided electrode patterns described in  FIGS. 11A-11E and 13A-13B  as well as other electrode patterns capable of performing the differential sensing described throughout the disclosure 
       FIGS. 15A-15C  illustrate a spatial null phenomenon that can be associated with spatial differential electrode configurations according to examples of the disclosure.  FIGS. 16A and 16B  illustrate a single-sided electrode pattern having four electrodes  1603 A- 1603 D that can correspond to the four-electrode pattern illustrated in  FIG. 11B  above, and in particular the grouping  1105 C.  FIG. 15A  illustrates a point source  1520  of acoustic energy. Acoustic energy from the point source  1520  can radiate in a radiating pattern  1522 , and for some point source locations, the point source  1520  can be aligned with the center of one of the segments of an electrode (e.g.,  1503 B).  FIG. 15B  illustrates a point source  1520  aligned between two adjacent segments  1503 A and  1503 B. In some examples, when the point source  1520  is aligned between the two electrodes, equal amounts of signal from the point source can produce equal amounts of signal on each electrode. In some examples, when the two electrodes are sensed differentially, the signal from the point source can be canceled.  FIG. 15C  illustrates a plurality of spatial nulls  1524  that can occur for point source locations that fall on the edge of the alternating electrode pattern of electrodes  1503 A and  1503 B. Although a point source  1520  is described in connection with the figures above, it should be understood that a similar effect can occur as a result of reflections from an object touching the cover glass  1502 , particularly when the contact by the object is centered along one of the spatial nulls  1524 . Furthermore, it should be understood that the same spatial null phenomenon can occur not only at the intersection points between individual electrodes, but also at intersection points of electrode groupings in the various grouping configurations (e.g.,  1105 A- 1105 M,  1305 A- 1305 C, and/or  1313 A- 1313 C). 
       FIGS. 16A-16D  illustrate an exemplary quadrature spatial differential electrode configuration according to examples of the disclosure.  FIG. 16A  depicts a four electrode spatial differential electrode configuration that can correspond to the electrode configuration in  FIG. 11B  and in particular the electrode grouping  1105 C. As illustrated, the electrodes  1603 A and  1603 B are grouped together and can be connected to a first terminal of a differential amplifier, and the electrodes  1603 C and  1603 D are grouped together and can be connected to a second terminal of a differential amplifier. Similar to the illustration in  FIG. 15B , a point source  1620  is illustrated at the intersection between the electrode groups.  FIG. 16B  illustrates corresponding spatial nulls  1624 , and it can be seen that the point source  1620  in  FIG. 16A  can fall within one of the spatial nulls illustrated in  FIG. 16B . In some examples, signal measurements by the first electrode grouping show in  FIGS. 16A-16B  can be referred to as the in-phase component. 
       FIG. 16C  illustrates the same spatial differential electrode configuration with a second grouping having shifted spatial nulls according to examples of the disclosure. In  FIG. 16C , the point source location on the cover glass  1602  is identical to the location in  FIG. 16A . The grouping of the electrodes has the same pitch as the grouping in  FIG. 16A , but the pattern is shifted by 90 degrees (e.g., one quarter of the total pitch) in the spatial domain. As illustrated, electrodes  1603 A and  1603 D are grouped together and can be connected to a first terminal of a differential amplifier, and the electrodes  1603 B and  1603 C are grouped together and can be connected to a second terminal of a differential amplifier. The overall pitch of the electrode grouping is the same as in  FIG. 16A , and thus the spatial frequency corresponding to the grouping remains the same, but the spatial phase is changed. The spatial phase of the grouping is illustrated by the shifted spatial nulls  1626  in  FIG. 16D . In some examples, signal measurements by the second electrode grouping show in  FIGS. 16C-16D  can be referred to as the quadrature component. The position of the spatial nulls  1624  and shifted spatial nulls  1626  can be made non-overlapping, such that any point source  1620  location on the cover glass  1602  can fall outside of a spatial null in at least one of the two electrode configurations. In some examples, the in-phase and quadrature components can be added together to eliminate any signal nulls regardless of the position of the signal source. 
       FIGS. 17A-17C  illustrates a first exemplary spatial electrode configuration for performing quadrature spatial differential measurements of touch signals on cover glass  1702  and force sensing using a shared set of electrodes according to examples of the disclosure. In some examples, an eight-electrode configuration as described in  FIG. 11D  can be used. FIGS.  17 A and  17 B illustrate the in-phase and quadrature electrode grouping configurations described in  FIGS. 16A-16D . In the in-phase configuration, electrodes  1703 A,  1703 B,  1703 E and  1703 F can be grouped together and electrodes  1703 C,  1703 D,  1703 G, and  1703 H can be grouped together. In the quadrature configuration, electrodes  1703 A,  1703 D,  1703 E, and  1703 H can be grouped together and electrodes  1703 B,  1703 C,  1703 F, and  1703 G can be grouped together. In some examples, the deformable material  1714  can include a spatial pattern as described in  FIGS. 10A-10B  having a corresponding spatial frequency. It should be understood that while the jagged shape of the deformable material  1714  in  FIGS. 17A-17C  imply a spatial pattern based on thickness variations of the deformable material, any of the techniques for including a spatial pattern in the deformable material as taught in  FIGS. 10A-10B  can be used. The illustrated jagged shape of the deformable material  1714  is merely illustrative of the pitch of the associated spatial pattern.  FIG. 17C  illustrates an exemplary electrode grouping for performing touch sensing, the electrode grouping being matched to the pitch of the deformable material  1714  spatial pattern. In some examples, the electrodes  1703 A- 1703 D can be grouped together and the electrodes  1703 E- 1703 H can be grouped together and connected to a differential amplifier for performing force sensing using the deformable material as described in  FIGS. 3B, 6A-6B and 10A-10B  above. The electrode grouping of  FIG. 17C  can result in force sensing at a lower spatial frequency than the touch sensing because the spatial pattern of the deformable material  1714  has a larger pitch than the pitch used for touch sensing. 
       FIGS. 18A-18C  illustrate a second exemplary spatial electrode configuration for performing quadrature spatial differential measurements of touch signals on cover glass  1702  and force sensing using a shared set of electrodes according to examples of the disclosure. In some examples, a four-electrode configuration as described in  FIG. 11B  can be used.  FIGS. 18A and 18B  illustrate the in-phase and quadrature electrode grouping configurations described in  FIGS. 16A-16D . In the in-phase configuration, electrodes  1803 A and  1803 B can be grouped together and electrodes  1803 C and  1803 D can be grouped together. In the quadrature configuration, electrodes  1803 A and  1803 D can be grouped together, and electrodes  1803 B and  1803 C can be grouped together. In some examples, the deformable material  1814  can include a spatial pattern as described in  FIGS. 10A-10B  having a corresponding spatial frequency. It should be understood that while the jagged shape of the deformable material  1814  in  FIGS. 18A-18C  imply a spatial pattern based on thickness variations of the deformable material, any of the techniques for including a spatial pattern in the deformable material as taught in  FIGS. 10A-10B  can be used. The illustrated jagged shape of the deformable material  1814  is merely illustrative of the pitch of the associated spatial pattern.  FIG. 18C  illustrates an exemplary electrode grouping for performing touch sensing, the electrode grouping being matched to the pitch of the deformable material  1714  spatial pattern. In some examples, the electrodes  1803 A and  1803 C can be grouped together and the electrodes  1803 B and  1803 D can be grouped and connected to a differential amplifier for performing force sensing using the deformable material as described in  FIGS. 3B, 6A-6B and 10A-10B  above. The electrode grouping of  FIG. 17C  can result in force sensing at a higher spatial frequency than the touch sensing because the spatial pattern of the deformable material  1814  has a smaller pitch than the pitch used for touch sensing. 
     It should be understood that although one set of electrodes is shown in  FIGS. 17A-17C and 18A-18C  for performing both touch sensing and force sensing, the two-sided electrode configurations shown in  FIGS. 12 and 13A-13B  can also be used together with the quadrature touch sensing described in  FIGS. 16A-16D . 
       FIGS. 19A-20B  illustrate exemplary timing diagrams for performing acoustic touch and force sensing according to examples of the disclosure.  FIGS. 19A-20B  can further be understood in conjunction with the various examples of circuitry configurations described with regards to  FIGS. 21-27  below.  FIGS. 19A and 19B  illustrate timing diagrams for a sequential acoustic touch and force sensing mode of operation. Specifically,  FIGS. 19A and 19B  illustrate a frame time  1900  that can correspond to a complete sequence of events for a touch and force sensing operation. In some examples, the frame time  1900  can begin with a touch capture phase  1902  followed by a force capture phase  1904  such that the two phases do not overlap in time. In some examples, the force capture phase  1904  can be followed by the touch capture phase  1902  (e.g., the force capture phase can be performed first). In some examples, touch capture phase  1902  and force capture phase  1904  can be followed by a data transfer period  1906  (e.g., transferring measured touch and force data to be processed off-chip). In some examples, an algorithm period  1908  can be provided for processing touch and force data for an algorithm that can be used to determine information about touch location and force based on the data measured during the touch capture  1902  and force capture  1904 . In some examples, the algorithm  1908  can be performed on separate circuitry or a processor residing on a different chip from the touch and force sense circuitry. In some examples, the frame time can include an idle period  1910  in which no touch and force measurement, data transfer, or algorithm calculations are performed. In some examples, the data transfer period  1906 , the algorithm period  1908 , or both, can be pipelined or interleaved with the detection without departing from the scope of the present disclosure. In some examples, the transducer can be grounded (e.g., by transmitter circuitry that has grounding capability of switches that can selectively couple the transducer&#39;s electrodes to ground) during the idle period  1910 . In some examples, the algorithm to analyze the touch and force data can be performed on the same chip as acoustic touch/force sensing circuit used for the touch and force measurements, and algorithm period  1908  can come before data transfer period  1906 . In such an example, the data being sent during the data transfer period  1906  after the algorithm period can be the algorithm results. Alternatively both the raw measurement data and the algorithm results can be transmitted during the data transfer period  1906  when algorithm period  1908  is performed on the same circuitry as the touch and force sense circuitry. In some examples, each of touch capture phase  1902  and force capture phase  1904  can include driving and sensing a subset of one or more of a group of transducers. For example, the touch capture phase shows sequentially performing measurements on four transducers, XDUCER1, XDUCER2, XDUCER3, XDUCER 4. These four illustrated transducers can correspond to transducers  502 A- 502 D illustrated in  FIG. 5A  above. It should be understood that the timing diagrams illustrated in  FIGS. 19A-19B  can be applied for any number of transducers being used for acoustic touch and force sensing according to examples of the disclosure. Furthermore, the sequence of the detection from multiple transducers can be arranged in a different order from the one illustrated without departing from the scope of the present disclosure. In addition, the sequence of detection of the multiple transducers can be changed in different frames without departing from the scope of the present disclosure. In yet other examples, a subset of the transducers can be sampled in each frame rather than sampling all of the transducers in every frame without departing from the scope of the present disclosure.  FIG. 19A  shows multiple measurements represented by measurement timing slices  1912  that can be used to obtain an average value for touch capture and force capture. For example, eight touch measurements for XDUCER1 can be averaged, followed by eight measurements each for XDUCER2-XDUCER4, and then similarly eight force measurements of each of XDUCER1-XDUCER4 can be performed. For example, each measurement timing slice  1912  can include a transmit (Tx) function  1914  (e.g., driving a signal onto the transducer to produce an acoustic wave) and a receive (Rx) function  1916  (e.g., receiving reflected signals corresponding to respective touch or force measurements). In some examples, the transmit (Tx) and receive (Rx) functions can be followed by a pulse ring down period  1918  (e.g., to allow ringing signals, as described above with reference to  FIG. 8A , to stop). In some examples, the pulse ring down period  1918  can prevent successive measurements from interfering with each other.  FIG. 19A  illustrates eight measurement time slices  1912  for each transducer measurement averaging operation. However, it should be understood that averaging can used with a different number of measurements than eight, (e.g., as long as there are two or more measurements to average) without departing from the scope of the disclosure. Moreover, the number of measurement averages may be different during touch capture phase  1902  and force capture phase  1904  (e.g., measurements from the touch capture phase  1902  can be averaged over more measurements than in the force capture phase  1904 , and vice versa). In some examples, the touch capture phase  1902  can have a longer duration than force capture phase  1904  as illustrated in  FIG. 19B . In some examples, the difference in durations of the touch capture phase  1902  and force capture phase  1904  can relate to the difference in distance that an acoustic wave travels in the touch phase  1902  (e.g., across the cover glass  601  or  611  above) as compared to the distance that an acoustic wave travels in the force phase  1904  (e.g., through the thickness of deformable material  604  or  614  above). To illustrate this point,  FIG. 19B  illustrates an exemplary timing diagram where the respective receive durations (Rx 1 -RxN) for the force phase  1904  measurements are shorter than the respective receive duration (Rx 1 -RxN) for the touch phase  1902  measurements as described immediately above. As a result,  FIG. 19B  illustrates that the total duration for the force phase  1904  can be shorter than the total duration of the touch phase  1902  even when the same total numbers of transmit and receives are performed during each phase. It should be understood that the duration of various phases illustrated in the timing diagrams of  FIGS. 19A-19B , e.g., touch capture  1902 , force capture  1904 , data transfer  1906 , algorithm  1908 , idle  1910 , etc. are not necessarily drawn to scale and are provided for the purposes of illustration. 
     In some examples, force detections for each of the transducers XDUCER1-XDUCER4 can be performed simultaneously to reduce the total duration of force measurements during the force phase  1904 . In such an example, each transducer XDUCER1-XDUCER4 can be provided with a transmit circuit to drive the transducer and an analog front end to receive the force measurement signals (e.g., from reflections in the deformable material  604  or  614  above coupled to each individual transducer e.g.,  502 A- 502 D above). In some examples, a single transmit circuit can be used to sequentially drive each individual transducer XDUCER1-XDUCER4 with a slight time delay between driving each transducer, and then simultaneously capture the force measurement signals at four analog front ends from each of the transducers XDUCER1-XDUCER4 to reduce the time for force detection. 
       FIGS. 20A and 20B  illustrate timing diagrams for a combined acoustic touch and force sensing mode of operation. Specifically, in contrast to the mode of operation illustrated in  FIGS. 19A-19B , in the mode of operation illustrated in  FIGS. 20A and 20B , the touch and force capture phases are combined into a touch and force capture phase  2020 . This can be accomplished by performing a force receive function  2022  and a touch receive function  2024  as illustrated in  FIG. 20B  during a single combined Rx function  2016 . In some examples, the force and touch receive functions can both be performed sequentially after a single transmit (Tx) function  2014  because reflections associated with force measurement can arrive at the transducer and any ringing associated with the force measurement can settle before any reflections associated with touch measurement are received at the transducer (e.g., as described with reference to  FIG. 7  above). In some examples, the timing illustrated in  FIGS. 20A and 20B  can most preferably be used when signals for the force sensing occur during a dead zone for touch signals from touch sensing. For example, if reflections in a deformable material (e.g.,  604  or  614  above) used for force sensing are sufficiently attenuated before reflected touch measurement signals can return to the transducer, then the two operations can be performed sequentially based on a single Tx function  2014 . In other words, depending on the geometries and material properties of the deformable materials (e.g.,  604  or  614  above) and cover glass (e.g.,  601  and  611  above), the signals for touch capture and force capture can be temporally isolated in two distinct time windows (e.g., force receive  2022  and touch receive  2024 ) following a single transmit Tx function  2014 . Similar to the description of  FIG. 19A-19B  above, the frame time shown in  FIGS. 20A-20B  can include data transfer period  2006 , algorithm period  2008 , and idle period  2010 . As noted above, in some examples, the data transfer period  2006 , the algorithm period  2008 , or both, can be pipelined or interleaved with the touch and force detection without departing from the scope of the present disclosure. Similar to the description of  FIG. 19A  above,  FIG. 20A  shows that averaging can be performed for the combined touch and force captures  2020  as illustrated by measurement time slices  2012 . Furthermore, the sequence of the detection from multiple transducers (e.g., XDUCER1, XDUCER2, XDUCER3, and XDUCER4) can be arranged in a different order from the one illustrated without departing from the scope of the present disclosure. In addition the sequence of detection of the multiple transducers can be changed in different frames without departing from the scope of the present disclosure. In yet other examples, a subset of the transducers can be sampled in each frame rather than sampling all of the transducers in every frame without departing from the scope of the present disclosure. As shown in  FIG. 20B , receive period  2016  can include both a force receive  2022  and a touch receive  2024 . As should be understood from the disclosure above, respective force measurements  2024  can be averaged together and respective touch measurements  2022  can also be averaged together. It should be understood that the duration of various phases illustrated in the timing diagrams of  FIGS. 20A-20B , e.g., touch and force capture  2020 , data transfer  2006 , algorithm  2008 , idle  2010 , etc. are not necessarily drawn to scale and are provided for the purposes of illustration. 
       FIG. 21  illustrates an exemplary switching configuration  2100  for an acoustic touch and force sensing system according to examples of the disclosure. Transducer  2102  can include a pair of electrodes (e.g., electrodes  2104  and  2106 ) disposed on opposing sides of the transducer that can be used to both drive transducer  2102  and to receive electrical signals generated by transducer  2102  (e.g., in response to a received acoustic signal). In some examples, one of the two electrodes can act as a common electrode (e.g., electrode  2106 ), and the second of the two electrodes can act as both the drive and sense electrode (e.g., electrode  2104 ) for the transducer. In some examples, a differential drive and sense scheme can be used by differential driving electrodes  2014  and  2016  and differentially receiving from electrodes  2014  and  2016 . Electrode  2104  and electrode  2106  can be connected to touch and force control and readout circuitry  2108  for acoustic touch and force sensing. Touch and force control and readout circuitry  2108  can include analog front end (AFE) amplifier  2112 , the output of which can be connected to sense circuitry  2110 . Outputs from sense circuitry  2110  can be connected to the inputs of transmitter  2114 . In some examples, electrode  2104  and electrode  2106  can be connected to the input terminals of AFE amplifier  2112  via switches  21 S 1  and  21 S 2 , respectively (as indicated by connection labels  21 A and  21 B). In addition, electrode  2104  and electrode  2106  can be connected to the outputs of transmitter  2114  via switches  21 S 3  and  21 S 4 , respectively (as also indicated by connection labels  21 A and  21 B). During a receive (Rx) function, switches  21 S 1  and  21 S 2  can be closed, and switches  21 S 3  and  21 S 4  can be open. The switch configuration during the Rx function can allow the AFE  2112  to receive electrical signals from the electrodes  2104  and  2106  of transducer  2102 . During a transmit (Tx) function switches  21 S 3  and  21 S 4  can be closed, and switches  21 S 1  and  21 S 2  can be open. The switch configuration during the Tx function can allow transmitter  2114  to drive the electrodes  2104  and  2106  of transducer  2102  to generate an acoustic wave. Notably, exemplary switching configuration  2100  is compatible with the modes of operation illustrated in  FIGS. 19A-20B . In some examples, sense circuitry  2110  can include one or more of digital-to-analog converters (DAC)  402 A, filter  402 B, gain and offset correction circuit  412 , demodulation circuit  414 , filter  416 , analog-to-digital converter (ADC)  418 , input/output (I/O) circuit  420 , acoustic scan control circuit  422 , force detection circuit  424 , processor SoC  430 , host processor  432 , auxiliary processor  434 , and/or any other sense circuitry described above with reference to  FIG. 4 . In some examples, sense circuitry  2110  can be on a different chip from the AFE  2112 , transmitter  2114 , and switches  21 S 1 - 21 S 4 . In some examples, inputs of AFE amplifier  2112  can be connected to a first transducer for receiving, and the outputs of transmitter  2114  can be connected to a second transducer, different than the first transducer, for transmitting. In some examples, the touch and force control and readout  2108  can be included on a silicon chip. In some examples, the transmit circuitry can be designed to drive higher voltages (or currents) to produce sufficient motion in the transducer to generate an acoustic wave in the surface of a device, and the receive circuitry can be designed for receiving smaller amplitude reflected energy. Accordingly, in some examples, the transmit circuitry and receive circuitry can be included on different silicon chips to avoid interference with the operation of the receive circuitry by the transmit circuitry. 
       FIG. 22  illustrates an exemplary switching configuration  2200  for an acoustic touch and force sensing system according to examples of the disclosure. Transducer  2202  can include a pair of electrodes (e.g., electrodes  2204 A and  2204 B) disposed on one side of the transducer and a second electrode (e.g., common electrode  2206 ) disposed on the opposite side of the transducer. In some examples, the electrode configuration of transducer  2202  can correspond to the electrode configuration illustrated in  FIGS. 10A-10B and 11A  above. Electrodes  2204 A,  2204 B, and  2206  can be connected to touch and force control and readout circuitry  2208  for acoustic touch and force sensing. Touch and force control and readout circuitry  2208  can include analog front end (AFE) amplifier  2212 , the output of which can be connected to sense circuitry  2210 . Outputs from sense circuitry  2210  can be connected to the inputs of transmitter  2214 . In some examples, electrodes  2204 A and  2204 B can be connected to the input terminals of AFE amplifier  2212  via switches  22 S 1  and  22 S 2 , respectively (as indicated by connection labels  22 A and  22 B). In addition, electrode  2204 A, electrode  2204 B, and electrode  2206  can be connected to the outputs of transmitter  2214  via switches  22 S 3 ,  23 S 4 , and  22 S 5 , respectively (as indicated by connection labels  22 A,  22 B, and  22 C). In the illustrated configuration, electrode  2204 A and electrode  2204 B (both on the same side of transducer  2302 ) can be connected from the same output terminal of transmitter  2214  (as indicated by connection labels  22 A and  22 B). During a receive (Rx) function, switches  22 S 1  and  22 S 2  can be closed, and switches  22 S 3 ,  22 S 4 , and  22 S 5  can be open. In some examples, electrode  2206  can be left floating by the switch configuration during the Rx function, which can correspond to the analog common mode rejection described in  FIGS. 14A-14C  above. The switch configuration during the Rx function can allow the AFE  2212  to receive electrical signals from the electrodes  2204 A and  2204 B of transducer  2202 . During a transmit (Tx) function switches  22 S 3 ,  22 S 4 , and  22 S 5  can be closed, and switches  22 S 1  and  22 S 2  can be open. The switch configuration during the Tx function can allow transmitter  2214  to drive the electrodes  2204 A,  2204 B, and  2206  of transducer  2202  to create a potential across the transducer and generate an acoustic wave. Notably, exemplary switching configuration  2200  is compatible with the modes of operation illustrated in  FIGS. 19A-20B . In some examples, sense circuitry  2210  can include one or more of digital-to-analog converters (DAC)  402 A, filter  402 B, gain and offset correction circuit  412 , demodulation circuit  414 , filter  416 , analog-to-digital converter (ADC)  418 , input/output (I/O) circuit  420 , acoustic scan control circuit  422 , force detection circuit  424 , processor SoC  430 , host processor  432 , auxiliary processor  434 , and/or any other sense circuitry described above with reference to  FIG. 4 . In some examples, sense circuitry  2210  can be on a different chip from AFE  2212 , transmitter  2214 , and switches  22 S 1 - 22 S 5 . In some examples, inputs of AFE amplifier  2212  can be connected to a first transducer for receiving, and the outputs of transmitter  2214  can be connected to a second transducer, different than the first transducer, for transmitting. In some examples, the touch and force control and readout circuitry  2208  can be included on a silicon chip. In some examples, the transmit circuitry can be designed to drive higher voltages (or currents) to produce sufficient motion in the transducer to generate an acoustic wave in the surface of a device, and the receive circuitry can be designed for receiving smaller amplitude reflected energy. Accordingly, in some examples, transmit circuitry and receive circuitry can be included on different silicon chips to avoid interference with the operation of the receive circuitry by the transmit circuitry. 
       FIG. 23  illustrates an exemplary switching configuration  2300  for an acoustic touch and force sensing system according to examples of the disclosure. Transducer  2302  can include a pair of electrodes (e.g., electrodes  2304 A and  2304 B) disposed on one side of the transducer and a second electrode (e.g., common electrode  2306 ) disposed on the opposite side of the transducer. In some examples, the electrode configuration of transducer  2302  can correspond to the electrode configuration illustrated in  FIGS. 10A-10B and 11A  above. Electrodes  2304 A,  2304 B, and  2306  can be connected to touch and force control and readout circuitry  2308  for acoustic touch and force sensing. Touch and force control and readout circuitry  2308  can include analog front end (AFE) amplifiers  2312  and  2314 , the output of which can be connected to sense circuitry  2310 . Outputs from sense circuitry  2310  can be connected to the inputs of transmitter  2316 . In some examples, electrodes  2304 A and electrode  2306  can be connected to the input terminals of AFE amplifier  2312  via switches  23 S 1  and  23 S 2 , respectively (as indicated by connection labels  23 A and  23 C); and electrodes  2304 B and electrode  2306  can be connected to the input terminals of AFE amplifier  2314  via switches  23  S 3  and  23 S 4 , respectively (as indicated by connection labels  23 B and  23 C). In addition, electrodes  2304 A, electrodes  2304 B, and electrode  2306  can be connected to the outputs of transmitter  2316  via switches  23 S 5 ,  23 S 6 , and  23 S 7 , respectively (as indicated by connection labels  23 A,  23 B, and  23 C). It should be understood that, while not illustrated, electrodes  2304 A and  2304 B can represent electrode configurations as described above with reference to  FIGS. 9-14 . In the illustrated configuration, electrodes  2304 A and electrodes  2304 B can be connected from the same output terminal of transmitter  2316  (as indicated by connection labels  23 A and  23 B). During a receive (Rx) function, switches  23 S 1 ,  23 S 2 ,  23 S 3 ,  23 S 4 , and  23 S 7  can be closed, and switches  23  S 5  and  23  S 6  can be open. The switch configuration during the Rx function can allow the AFE  2212  to receive electrical signals from the electrodes  2304 A,  2304 B, and  2306  of transducer  2302 , and allow transmitter  2316  to drive electrode  2306  of transducer  2302  to ground or another reference potential. Accordingly, unlike the configuration in  FIG. 22 , each of the electrodes  2304 A and  2304 B in  FIG. 23  can be read with a common mode signal component included in the measured signal. In some examples, the common mode component can be removed in the digital domain. During a transmit (Tx) function switches  23 S 5 ,  23 S 6 , and  23 S 7  can be closed, and switches  23 S 1 ,  23 S 2 ,  23 S 3 , and  23 S 4  can be open. The switch configuration during the Tx function can allow transmitter  2214  to drive the electrodes  2304 A,  2304 B, and  2306  of transducer  2302  to create a potential across the transducer and generate an acoustic wave. In some examples, the output of switch  23 S 7  can be tied to ground (e.g., common electrode  2306  can be tied to ground as described above with reference to  FIG. 14A ). Notably, exemplary switching configuration  2300  is compatible with the modes of operation illustrated in  FIGS. 19A-20B . In some examples, sense circuitry  2310  can include one or more of digital-to-analog converters (DAC)  402 A, filter  402 B, gain and offset correction circuit  412 , demodulation circuit  414 , filter  416 , analog-to-digital converter (ADC)  418 , input/output (I/O) circuit  420 , acoustic scan control circuit  422 , force detection circuit  424 , processor SoC  430 , host processor  432 , auxiliary processor  434 , and/or any other sense circuitry described above with reference to  FIG. 4 . In some examples, sense circuitry  2310  can be on a different chip from AFE  2312 , AFE  2314 , transmitter  2316 , and switches  23 S 1 - 23 S 7 . In some examples, inputs of AFE amplifiers  2312  and  2314  can be connected to a first transducer for receiving, and the outputs of transmitter  2316  can be connected to a second transducer, different than the first transducer, for transmitting. In some examples, the touch and force control and readout circuitry  2308  can be included on a silicon chip. In some examples, the transmit circuitry can be designed to drive higher voltages (or currents) to produce sufficient motion in the transducer to generate an acoustic wave in the surface of a device, and the receive circuitry can be designed for receiving smaller amplitude reflected energy. Accordingly, in some examples, the transmit circuitry and receive circuitry can be included on different silicon chips to avoid interference with the operation of the receive circuitry by the transmit circuitry. 
       FIG. 24  illustrates an exemplary switching configuration  2400  for an acoustic touch and force sensing system according to examples of the disclosure. Transducer  2402  can include two sets of two electrode differential patterns, electrodes  2404 A and  2404 B on a first side of the transducer and electrodes  2406 C and  2406 D on a second side of the transducer. As illustrated, the first side electrodes  2404 A can be connected (as indicated by connection label  24 A), and first side electrodes  2404 B can be connected (as indicated by connection label  24 B). It should be understood that, electrodes  2404 A,  2404 B,  2406 C, and  2406 D can correspond to the electrode configuration illustrated in  FIG. 13A . It should also be understood that the switching scheme illustrated in  FIG. 24  can be adapted for different numbers of electrodes on opposing sides of the transducer without departing from the scope of the present disclosure. As illustrated electrodes  2406 C/ 2406 D can have a larger electrode size and a corresponding larger electrode pitch, leading each of the electrode pairs to have a different corresponding spatial frequency as described and illustrated in  FIGS. 13A and 13B . In some examples, the spatial frequencies corresponding to electrodes  2404 A/ 2404 B can be higher than the spatial frequencies corresponding electrodes  2406 C/ 2406 D. Electrodes  2404 A,  2404 B,  2406 C, and  2406 D can be connected to touch and force control and readout circuitry  2408  for acoustic touch and force sensing. Touch and force control and readout circuitry  2408  can include analog front end (AFE) amplifier  2412 , the output of which can be connected to sense circuitry  2410 . Outputs from sense circuitry  2410  can be connected to the inputs of transmitter  2414 . In some examples, electrodes  2404 A and electrode  2406 C can both be connected to a first input terminal of AFE amplifier  2412  via switches  24 S 1  and  24 S 2 , respectively (as indicated by connection labels  2404 A and  24 C). Electrodes  2404 B and electrode  2406 D can both be connected to a second input terminal of AFE amplifier  2412  via switches  24 S 3  and  24 S 4 , respectively (as indicated by connection labels  24 B and  24 D). In addition, electrodes  2404 A and electrodes  2404 B can both be connected to a first output terminal of transmitter  2414  via switches  24 S 5  and  24 S 6 , respectively (as indicated by connection labels  24 A and  24 B). Electrodes  2406 C and electrodes  2406 D can both be connected to a second output terminal of transmitter  2414  via switches  24 S 7  and  24 S 8 , respectively (as indicated by connection labels  24 C and  24 D). During a touch receive (Rx) function, switches  24 S 1  and  24 S 3  can be closed, and switches  24 S 2 ,  24 S 4 ,  24 S 5 ,  24 S 6 ,  24 S 7 , and  24 S 8  can be open. The switch configuration during the touch Rx function can allow the AFE  2412  to receive electrical signals from the electrodes  2404 A and  2406 B of transducer  2402 . At the same time, electrodes  2406 C and  2406 D can be left floating for accomplishing a common mode rejection function as described with regard to  FIGS. 14A-14C  above. During a force receive (Rx) function, switches  24 S 2  and  24 S 4  can be closed, and switches  24 S 1 ,  24 S 3 ,  24 S 5 ,  24 S 6 ,  24 S 7 , and  24 S 8  can be open. The switch configuration during the force Rx function can allow the AFE  2412  to receive electrical signals from the electrodes  2406 C and  2406 D of transducer  2402 . At the same time, electrodes  2406 A and  2406 B can be left floating for accomplishing a common mode rejection function as described with regard to  FIGS. 14A-14C  above. During a transmit (Tx) function switches  24 S 5 ,  24 S 6 ,  24 S 7 , and  24 S 8  can be closed, and switches  24 S 1 ,  24 S 2 ,  24 S 3 , and  24 S 4  can be open. The switch configuration during the Tx function can allow transmitter  2414  to drive the electrodes  2404 A and  2404 B (one a first side of the transducer  2402 ) and electrodes  2406 C and  2406 D (on the opposite side of transducer  2402 ) to create a potential across the transducer and generate an acoustic wave. Notably, exemplary switching configuration  2400  is compatible with the modes of operation illustrated in  FIGS. 19A-20B . In some examples, sense circuitry  2410  can include one or more of digital-to-analog converters (DAC)  402 A, filter  402 B, gain and offset correction circuit  412 , demodulation circuit  414 , filter  416 , analog-to-digital converter (ADC)  418 , input/output (I/O) circuit  420 , acoustic scan control circuit  422 , force detection circuit  424 , processor SoC  430 , host processor  432 , auxiliary processor  434 , and/or any other sense circuitry described above with reference to  FIG. 4 . In some examples, sense circuitry  2410  can be on a different chip from AFE  2412 , transmitter  2414 , and switches  24 S 1 - 24 S 8 . In some examples, inputs of AFE amplifier  2412  can be connected to a first transducer for receiving, and the outputs of transmitter  2414  can be connected to a second transducer, different than the first transducer, for transmitting. In some examples, the touch and force control and readout circuitry  2408  can be included on a silicon chip. In some examples, the transmit circuitry can be designed to drive higher voltages (or currents) to produce sufficient motion in the transducer to generate an acoustic wave in the surface of a device, and the receive circuitry can be designed for receiving smaller amplitude reflected energy. Accordingly, in some examples, the transmit circuitry and receive circuitry can be included on different silicon chips to avoid interference with the operation of the receive circuitry by the transmit circuitry. 
       FIG. 25  illustrates an exemplary switching configuration  2500  for an acoustic touch and force sensing system according to examples of the disclosure. Transducer  2502  can include a four spatial differential electrode configuration with electrodes  2504 A- 2504 D disposed on a first side of the transducer and common electrode  2406  disposed on a second side of the transducer. It should be recognizable that the four spatial differential electrode configuration illustrated in  FIG. 25  can correspond to the configuration described above with reference to  FIG. 11B . Electrodes  2504 A,  2504 B,  2504 C,  2504 D, and  2506  can be connected to touch and force control and readout circuitry  2508  for acoustic touch and force sensing. Touch and force control and readout circuitry  2508  can include analog front end (AFE) amplifier  2512 , the output of which can be connected to sense circuitry  2510 . Outputs from sense circuitry  2510  can be connected to the inputs of transmitter  2514 . In some examples, electrodes  2504 A,  2504 B, and  2504 C can be connected to a first input terminal of AFE amplifier  2512  via switches  25 S 1 ,  25 S 2 , and  25 S 3 , respectively (as indicated by connection labels  25 A- 25 C). Electrodes  2504 B,  2504 C, and  2504 D can be connected to a second input terminal of AFE amplifier  2512  via switches  25 S 4 ,  25 S 5 , and  25 S 6 , respectively (as indicated by connection labels  25 B- 25 D). In addition, electrodes  2504 A,  2504 B,  2504 C, and  2504 D can be connected to a first output terminal of transmitter  2514  via switches  25 S 7 ,  25 S 8 ,  25 S 9 , and  25 S 10 , respectively (as indicated by connection labels  25 A- 25 D). Electrode  2506  can be connected to a second output terminal of transmitter  2514  via switch  25 S 11  (as indicated by connection label  25 E). It should be understood that the switch scheme of  FIG. 25  can be adapted to different electrode configurations, including those disclosed in  FIGS. 13A-13B , without departing from the scope of the present disclosure. During a receive (Rx) touch function, switches  25 S 1 ,  25 S 3 ,  25 S 4 , and  25 S 6  can be closed, and switches  25 S 2 ,  25 S 5 ,  25 S 7 ,  25 S 8 ,  25 S 9 ,  25 S 10 , and  25 S 11  can be open. The switch configuration during the touch Rx function can allow the AFE  2512  to receive electrical signals from the electrodes  2504 A and  2504 C at a first terminal of AFE  2512  and to receive electrical signals from electrodes  2504 B and  2504 D at a second terminal of AFE  2512 . In the touch measurement mode, differential measurements are thus taken between adjacent electrodes, which can correspond to a first spatial frequency. During a force receive (Rx) function, switches  25 S 1 ,  25 S 2 ,  25 S 5 , and  25 S 6  can be closed, and switches  25 S 3 ,  25 S 4 ,  25 S 7 ,  25 S 8 ,  25 S 9 ,  25 S 10 , and  25 S 11  can be open. The switch configuration during the force Rx function can allow the AFE  2512  to receive electrical signals from the electrodes  2504 A and  2504 B at a first terminal of AFE  2512  and to receive electrical signals from electrodes  2504 C and  2504 D at a second terminal of AFE  2512 . In some examples, in the force Rx configuration, the electrodes can be measured with a lower pitch because differential measurements are taken between adjacent pairs of electrodes rather than adjacent individual electrodes as shown in the touch Rx configuration above. Thus, the differential measurements in the force Rx configuration can correspond to a second spatial frequency lower than the first spatial frequency. It should be also understood using a lower spatial frequency for the touch Rx and higher spatial frequency for force Rx can also be done without departing from the scope of the present disclosure. In both the force Rx and touch Rx configurations described above, electrodes  2506  can be left floating for accomplishing a common mode rejection function as described with regard to  FIGS. 14A-14C  above. During a transmit (Tx) function switches  25 S 7 ,  25 S 8 ,  25 S 9 ,  25 S 10 , and  25 S 11  can be closed, and switches  25 S 1 ,  25 S 2 ,  25 S 3 ,  25 S 4 ,  25 S 5 , and  25 S 6  can be open. The switch configuration during the Tx function can allow transmitter  2514  to drive the electrodes  2504 A,  2504 B,  2504 C,  2504 D, and  2206  of transducer  2502  to create a potential across the transducer and generate an acoustic wave. Notably, exemplary switching configuration  2500  is compatible with the modes of operation illustrated in  FIGS. 19A-20B . In some examples, sense circuitry  2510  can include one or more of digital-to-analog converters (DAC)  402 A, filter  402 B, gain and offset correction circuit  412 , demodulation circuit  414 , filter  416 , analog-to-digital converter (ADC)  418 , input/output (I/O) circuit  420 , acoustic scan control circuit  422 , force detection circuit  424 , processor SoC  430 , host processor  432 , auxiliary processor  434 , and/or any other sense circuitry described above with reference to  FIG. 4 . In some examples, sense circuitry  2510  can be on a different chip from AFE  2512 , transmitter  2514 , and switches  25 S 1 - 25 S 11 . In some examples, inputs of AFE amplifier  2512  can be connected to a first transducer for receiving, and the outputs of transmitter  2514  can be connected to a second transducer, different than the first transducer, for transmitting. In some examples, the touch and force control and readout circuitry  2508  can be included on a silicon chip. In some examples, the transmit circuitry can be designed to drive higher voltages (or currents) to produce sufficient motion in the transducer to generate an acoustic wave in the surface of a device, and the receive circuitry can be designed for receiving smaller amplitude reflected energy. Accordingly, in some examples, the transmit circuitry and receive circuitry can be included on different silicon chips to avoid interference with the operation of the receive circuitry by the transmit circuitry. In some examples, each of the four electrodes  2504 A,  2504 B,  2504 C, and  2504 D can be separately read by four analog front ends (e.g., as illustrated and described in more detail with regard to  FIGS. 31A-31B  below) to simultaneously measure the signals of each of the four electrodes. 
       FIG. 26  illustrates an exemplary switching configuration  2600  for an acoustic touch and force sensing system according to examples of the disclosure. Transducer  2602  can include two sets of two electrode differential patterns, electrodes  2604 A and  2604 B on a first side of the transducer, and electrodes  2606 C and  2606 D on a second side of the transducer. As illustrated, the first side electrodes  2604 A can be connected (as indicated by connection label  26 A), and first side electrodes  2604 B can be connected (as indicated by connection label  26 B). It should be understood that the switch scheme of  FIG. 25  can be adapted to different electrode configurations, including those disclosed in  FIGS. 13A-13B , without departing from the scope of the present disclosure. As illustrated electrodes  2606 C/ 2606 D can have a larger electrode size and a corresponding larger electrode pitch, leading each of the electrode pairs to have a different corresponding spatial frequencies. In some examples, the spatial frequencies corresponding to electrodes  2604 A/ 2604 B can be higher than the spatial frequency corresponding to electrodes  2606 C/ 2606 D as illustrated in  FIGS. 13A and 13B  above. Electrodes  2604 A,  2604 B,  2606 C, and  2606 D can be connected to touch and force control and readout circuitry  2608  for acoustic touch and force sensing. Touch and force control and readout circuitry  2608  can include analog front end (AFE) amplifiers  2612  and  2614 , the output of which can be connected to sense circuitry  2610 . Outputs from sense circuitry  2610  can be connected to the inputs of transmitter  2616 . In some examples, electrodes  2604 A and  2604 B can be connected to the input terminals of AFE amplifier  2612  via switches  26 S 1  and  26 S 2 , respectively (as indicated by connection labels  26 A- 26 B), and the outputs of electrodes  2604 C and  2604 D can be connected to the input terminals of AFE amplifier  2614  via switches  26 S 3  and  26 S 4 , respectively (as indicated by connection labels  26 C- 26 D). In addition, electrodes  2604 A,  2604 B,  2606 C, and  2606 D can be connected to the outputs of transmitter  2616  via switches  26 S 5 ,  26 S 6 ,  26 S 7 , and  26 S 8 , respectively (as indicated by connection labels  26 A- 26 D). In the illustrated configuration, electrodes  2604 A and  2604 B can be connected from the same output terminal of transmitter  2616  (e.g., a first terminal) (as indicated by connection labels  26 A- 26 B). In the illustrated configuration, electrodes  2606 C and  2606 D can be connected from the same output terminal of transmitter  2616  (e.g., a second terminal, different from the first terminal) (as indicated by connection labels  26 C- 26 D). During a touch receive (Rx) function, switches  26 S 1  and  26 S 2  can be closed, and switches  26 S 3 ,  26 S 4 ,  26 S 5 ,  26 S 6 ,  26 S 7 , and  26 S 8  can be open. The switch configuration during the touch Rx function can allow the touch AFE  2612  to receive electrical signals from the electrodes  2604 A and  2604 B of transducer  2602 . During a force receive (Rx) function, switches  26 S 3  and  26 S 4  can be closed, and switches  26 S 1 ,  26 S 2 ,  26 S 5 ,  26 S 6 ,  26 S 7 , and  26 S 8  can be open. The switch configuration during the force Rx function can allow the force AFE  2614  to receive electrical signals from the electrodes  2606 C and  2606 D of transducer  2602 . As mentioned in various examples above, the electrodes that are not being read (e.g.,  2606 C and  2606 D during the touch Rx and  2606 A and  2606 B during the force Rx) can be left floating to allow for common mode rejection as described above with regard to  FIGS. 14A-14C . During a transmit (Tx) function switches  26 S 5 ,  26 S 6 ,  26 S 7 , and  26 S 8  can be closed, and switches  26 S 1 ,  26 S 2 ,  26 S 3 , and  26 S 4  can be open. The switch configuration during the Tx function can allow transmitter  2616  to drive the electrodes  2604 A,  2604 B,  2606 C, and  2606 D of transducer  2602  to create a potential across the transducer  2602  and generate an acoustic wave. Notably, exemplary switching configuration  2600  is compatible with the modes of operation illustrated in  FIGS. 19A-20B . In some examples, sense circuitry  2610  can include one or more of digital-to-analog converters (DAC)  402 A, filter  402 B, gain and offset correction circuit  412 , demodulation circuit  414 , filter  416 , analog-to-digital converter (ADC)  418 , input/output (I/O) circuit  420 , acoustic scan control circuit  422 , force detection circuit  424 , processor SoC  430 , host processor  432 , auxiliary processor  434 , and/or any other sense circuitry described above with reference to  FIG. 4 . In some examples, sense circuitry  2610  can be on a different chip from touch AFE  2612 , AFE  2614 , transmitter  2616 , and switches  26 S 1 - 21 S 8 . In some examples, inputs of AFE amplifiers  2612  and  2614  can be connected to a first transducer for receiving, and the outputs of transmitter  2616  can be connected to a second transducer, different than the first transducer, for transmitting. In some examples, the touch and force control and readout circuitry  2608  can be included on a silicon chip. In some examples, the transmit circuitry can be designed to drive higher voltages (or currents) to produce sufficient motion in the transducer to generate an acoustic wave in the surface of a device, and the receive circuitry can be designed for receiving smaller amplitude reflected energy. Accordingly, in some examples, the transmit circuitry and receive circuitry can be included on different silicon chips to avoid interference with the operation of the receive circuitry by the transmit circuitry. 
       FIG. 27  illustrates an exemplary switching configuration  2700  for an acoustic touch and force sensing system according to examples of the disclosure. Transducer  2702  can include two sets of two electrode differential patterns, electrodes  2704 A and  2704 B on a first side of the transducer, and electrodes  2706 C and  2706 D on a second side of the transducer. As illustrated, the first side electrodes  2704 A can be connected (as indicated by connection label  27 A), and first side electrodes  2704 B can be connected (as indicated by connection label  27 B). It should be understood that, while not illustrated, electrodes  2704 A,  2704 B,  2706 C, and  2706 D can represent electrode configurations as described above with reference to  FIGS. 9-14 . As illustrated electrodes  2706 C/ 2706 D can have a larger electrode size and a corresponding larger electrode pitch, leading each of the electrode pairs to have a different corresponding spatial frequency. In some examples, the spatial frequencies corresponding to electrodes  2704 A/ 2704 B can be higher than the spatial frequency corresponding to electrodes  2706 C/ 2706 D. Electrodes  2704 A,  2704 B,  2706 C, and  2706 D can be connected to touch and force control and readout circuitry  2708  for acoustic touch and force sensing. Touch and force control and readout circuitry  2708  can include analog front end (AFE) amplifiers  2712  and  2714 , the output of which can be connected to sense circuitry  2710 . The output of sense circuitry  2710  can be connected to the inputs of transmitter  2716 . In some examples, electrodes  2704 A and  2704 C can be connected to the input terminals of AFE amplifier  2712  via switches  27 S 1  and  27 S 2 , respectively (as indicated by connection labels  27 A and  27 C), and electrodes  2704 B and  2704 D can be connected to the input terminals of AFE amplifier  2714  via switches  27 S 3  and  27 S 4 , respectively (as indicated by connection labels  27 B and  27 D). In addition, electrodes  2704 A,  2704 B,  2706 C, and  2706 D can be connected to the outputs of transmitter  2716  via switches  27 S 5 ,  27 S 6 ,  27 S 7 , and  27 S 8 , respectively (as indicated by connection labels  27 A- 27 D). It should be understood that, while not illustrated, electrodes  2704 A and  2704 B can represent electrode configurations as described above with reference to  FIGS. 9-14 . In the illustrated configuration, electrodes  2704 A and  2704 B can be connected from the same output terminal of transmitter  2716  (e.g., a first terminal) (as indicated by connection labels  27 A- 27 B). In the illustrated configuration, electrodes  2706 C and  2706 D can be connected from the same output terminal of transmitter  2716  (e.g., a second terminal, different from the first terminal) (as indicated by connection labels  27 C- 27 D). During a touch receive (Rx) function, switches  27 S 1 ,  27 S 2 ,  27 S 3 ,  27 S 4 ,  27 S 7 , and  27 S 8  can be closed, and switches  27 S 5  and  27 S 6  can be open. The switch configuration during the touch Rx function can allow the AFE  2712  to receive electrical signals from the electrodes  2704 A and  2706 C of transducer  2702 , AFE  2714  to receive electrical signals from the electrodes  2704 B and  2706 D of transducer  2702 , and transmitter  2716  to drive the electrodes  2706 C and  2706 D with a ground or reference potential for single ended measurement of electrodes  2706 A and  2706 B. During a force receive (Rx) function, switches  27 S 1 ,  27 S 2 ,  27 S 3 ,  27 S 4 ,  27 S 5 , and  27 S 6  can be closed, and switches  27 S 7  and  27 S 8  can be open. The switch configuration during the force Rx function can allow the AFE  2714  to receive electrical signals from the electrodes  2704 B and  2706 D of transducer  2702 , AFE  2714  to receive electrical signals from the electrodes  2704 B and  2706 D of transducer  2702 , and transmitter  2716  to drive the electrodes  2704 A and  2704 B of transducer  2702  with ground or another reference potential for single ended measurement of electrodes  2704 C and  2704 D. During a transmit (Tx) function switches  27 S 5 ,  27 S 6 ,  27 S 7 , and  27 S 8  can be closed, and switches  27 S 1 ,  27 S 2 ,  27 S 3 , and  27 S 4  can be open. The switch configuration during the Tx function can allow transmitter  2716  to drive the electrodes  2704 A,  2704 B,  2706 C, and  2706 D of transducer  2702  to create an electric potential across the transducer  2702  and generate an acoustic wave. Notably, exemplary switching configuration  2700  is compatible with the modes of operation illustrated in  FIGS. 19A-20B . In some examples, sense circuitry  2710  can include one or more of digital-to-analog converters (DAC)  402 A, filter  402 B, gain and offset correction circuit  412 , demodulation circuit  414 , filter  416 , analog-to-digital converter (ADC)  418 , input/output (I/O) circuit  420 , acoustic scan control circuit  422 , force detection circuit  424 , processor SoC  430 , host processor  432 , auxiliary processor  434 , and/or any other sense circuitry described above with reference to  FIG. 4 . In some examples, sense circuitry  2710  can be on a different chip from AFE  2712 , AFE  2714 , transmitter  2716 , and switches  27 S 1 - 27 S 8 . In some examples, inputs of AFE amplifiers  2712  and  2714  can be connected to a first transducer for receiving, and the outputs of transmitter  2716  can be connected to a second transducer, different than the first transducer, for transmitting. In some examples, the touch and force control and readout circuitry  2708  can be included on a silicon chip. In some examples, the transmit circuitry can be designed to drive higher voltages (or currents) to produce sufficient motion in the transducer to generate an acoustic wave in the surface of a device, and the receive circuitry can be designed for receiving smaller amplitude reflected energy. Accordingly, in some examples, the transmit circuitry and receive circuitry can be included on different silicon chips to avoid interference with the operation of the receive circuitry by the transmit circuitry. 
     It should be understood that the common electrode described above with reference to  FIGS. 21-23 and 25  (e.g., electrodes  2106 ,  2206 ,  2306 , and  2506 , respectively) can be floating during the receive (Rx) function to cancel out common mode signals (e.g., as described above with reference to electrode  1407  of  FIGS. 14B and 14C ). 
       FIGS. 28A-30B  illustrate exemplary timing diagrams for acoustic touch and force sensing according to examples of the disclosure. As will be discussed in further detail below, the timing diagrams  29 A- 29 B and  30 A- 30 B below closely resemble the timing diagrams  19 A- 19 B and  20 A- 20 B above, respectively. The main difference between these diagrams is that the following timing diagrams are presented with quadrature spatial differential sensing in mind as described with regard to  FIGS. 15A-18C  above, where each touch Rx function includes a measurement of an in-phase touch measurement, and a quadrature touch measurement that can be used to overcome spatial nulls in acoustic differential sensing as described in detail in the disclosure above. 
       FIGS. 28A and 28B  illustrate exemplary timing diagrams for a quadrature acoustic touch and force sensing mode of operation. Specifically, in this mode of operation the touch and force capture phases are combined. In other words, force and touch receive (Rx) functions  2816  can be performed simultaneously (e.g., not sequentially as described with reference to  FIGS. 19A-20B  above). This can be accomplished by including an analog front end (AFE) amplifier for each sensing electrode in an acoustic touch and force sensing system (e.g., as described in further detail below with reference to  FIGS. 31A and 31B ). These simultaneous force and touch receive (Rx) functions  2816  can be performed after a single transmit (Tx) function  2814 . Because force and touch receive (Rx) functions  2816  can be performed simultaneously, the duration of a touch and force capture  2820  in any given frame can be shorter in duration than in the touch and force sensing modes illustrated in  FIGS. 19A-20B . It should be understood that the duration of functions illustrated in the timing diagrams (e.g., data transfer  2808 ) are not necessarily drawn to scale. It should be understood that the duration of various phases illustrated in the timing diagrams of  FIGS. 28A-28B , e.g., touch and force capture  2820 , data transfer  2806 , algorithm  2808 , idle  2810 , etc. are not necessarily drawn to scale and are provided for the purposes of illustration. In some examples, the data transfer period  2806 , the algorithm period  2808 , or both, can be pipelined or interleaved with the detection without departing from the scope of the present disclosure. 
       FIGS. 29A and 29B  illustrate timing diagrams for a quadrature acoustic touch and force sensing mode of operation. Specifically,  FIGS. 29A and 29B  illustrate a touch capture phase  2902  followed by a force capture phase  2904  such that the two phases do not overlap in time. In some examples, the force capture phase  2904  can be followed by the touch capture phase  2902  (e.g., the force capture phase can be performed first). In some examples, the force capture phase  2904  can be shorter in duration than the touch capture phase  2902 . As described above with regard to  FIGS. 19A-19B  each of touch capture phase  2902  and force capture phase  2904  can include multiple measurement time slices  2912  that can be used to obtain multiple repeated measurements for averaging. For example, each measurement timing slice  2912  can include a transmit (Tx) function  2914  (e.g., driving a signal onto the transducer to produce an acoustic wave) and a receive (Rx) function  2916  (e.g., receiving reflected signals corresponding to respective touch or force measurements). As will be described in more detail below regarding  FIGS. 32-34 , a quadrature acoustic touch sensing operation can utilize two separate measurements (e.g., in-phase and quadrature) to eliminate spatial nulls in the touch sensing measurements. In  FIG. 29A , for each transducer XDUCER1-XDUCER4 during the touch capture phase, sixteen measurement time slices  2912  are shown. These sixteen total time slices shown can correspond to an averaging of eight measurements for in-phase measurement and eight measurements for quadrature measurement. Thus, while  FIG. 29A  illustrates sixteen measurement time slices  2912  for touch capture and eight measurement time slices force capture, it should be understood that eight sample averages are being illustrated for both the touch capture and force capture. However, it should be understood that the number of averages can be different from eight (e.g., as long as there are two or more measurements to average) without departing form the scope of the disclosure. Moreover, the number of averages used during touch capture phase  2902  can be different from the number of averages used during the force capture phase  2904 . Furthermore, the sequence of the detection from multiple transducers can be arranged in a different order from the one illustrated without departing from the scope of the present disclosure. In addition, the sequence of detection of the multiple transducers can be changed in different frames without departing from the scope of the present disclosure. In yet other examples, a subset of the transducers can be sampled in each frame rather than sampling all of the transducers in every frame without departing from the scope of the present disclosure. In some examples, the measurement time slices  2912  during the touch capture phase  2902  can have a longer duration than measurement time slices  2912  during the force capture phase  2904  as illustrated in  FIG. 29B . In some examples, the difference in durations of the touch capture phase  2902  and the force capture phase  2904  can relate to the difference in distance that an acoustic wave travels in the touch phase (e.g., across the cover glass  601  or  611  above) as compared to the distance that an acoustic wave travels in the force phase  2904  (e.g., through the thickness of deformable material  604  or  614  above). To illustrate this point,  FIG. 29B  illustrates an exemplary timing diagram where the respective receive durations (Rx 1 -RxN) for the force phase  2904  measurements are shorter than the respective receive duration (Rx 1 -RxN) for the touch phase  2902  measurements as described immediately above. As a result,  FIG. 29B  illustrates that the total duration for the force phase  2904  can be shorter than the total duration of the touch phase  2902  even when the same total numbers of transmit and receives are performed during each phase (e.g., when half as many averages are taken for touch capture  2902  and force capture  2904  in the case of quadrature touch measurements). It should be understood that the duration of various phases illustrated in the timing diagrams of  FIGS. 29A-29B , e.g., touch capture  2902 , force capture  2904 , data transfer  2906 , algorithm  2908 , idle  2910 , etc. are not necessarily drawn to scale and are provided for the purposes of illustration. 
     In some examples, force detections for each of the transducers XDUCER1-XDUCER4 can be performed simultaneously to reduce the total duration of force measurements during the force phase  2904 . In such an example, each transducer XDUCER1-XDUCER4 can be provided with a transmit circuit to drive the transducer and an analog front end to receive the force measurement signals (e.g., from reflections in the deformable material  604  or  614  above coupled to each individual transducer e.g.,  502 A- 502 D above). In some examples, a single transmit circuit can be used to sequentially drive each individual transducer XDUCER1-XDUCER4 with a slight time delay between driving each transducer, and then simultaneously capture the force measurement signals at four analog front ends from each of the transducers XDUCER1-XDUCER4 to reduce the time for force detection. 
       FIGS. 30A and 30B  illustrate timing diagrams for a quadrature acoustic touch and force sensing mode of operation. Specifically, in the mode of operation illustrated in  FIGS. 30A and 30B , the touch and force capture phases are combined into a touch and force capture phase  3020 . This can be accomplished by performing a force receiving function  3022  and a touch receive function  3024  as illustrated in  FIG. 30B  during a single combined Rx function  3016  (e.g., as described above with reference to  FIG. 20B ). In some examples, the force and touch receive functions can be performed after a single transmit (Tx) function  3014  because force reflections arrive at the transducer and any ringing associated with the force measurement can settle before touch reflections associated with touch measurement are received at the transducer (e.g., as described with reference to  FIG. 7  above). In some examples, the timing illustrated in  FIGS. 30A and 30B  can most preferably be used when signals for the force sensing occur during a dead zone for touch signals from touch sensing. In other words, depending on the geometries and material properties of the deformable material (e.g.,  604  or  614  above) and cover glass (e.g.,  601  and  611  above), the signals for touch capture and force capture can be temporally isolated in two distinct time windows (e.g., force receive  3022  and touch receive  3024 ) following a single Tx function  3014 . 
     Similar to the description of  FIGS. 19A-20B and 28A-29B  above,  FIG. 30A  shows that the combined touch and force capture phase  3020  can include multiple measurement time slices  3012  that can be used to obtain multiple measurements for averaging. For example, each measurement timing slice  3012  can include a transmit (Tx) function  2914  (e.g., driving a signal onto the transducer to produce an acoustic wave) and a receive (Rx) function  2916  (e.g., receiving reflected signals corresponding to both touch and force measurements). The sixteen total measurement time slices  3012  shown in  FIG. 30A  can correspond to an averaging of eight measurements for in-phase measurement, eight measurements for quadrature measurement, and sixteen measurements for the force measurement (which can be taken regardless of whether the touch measurement is associated with in-phase or quadrature). As should be understood from the disclosure above, respective force measurements  3024  can be averaged together and respective touch measurements  3022  (grouped by in-phase and quadrature measurements) can also be averaged together. In some examples, the duration of force receive function  3022  can be shorter than touch receive function  3024 . Although  FIG. 30  described averaging of eight measurements for touch and sixteen measurements for force, it should be understood that averaging can used with a different number of measurements than eight, (e.g., as long as there are two or more measurements to average) without departing from the scope of the disclosure. Furthermore, the sequence of the detection from multiple transducers can be arranged in a different order from the one illustrated without departing from the scope of the present disclosure. In addition, the sequence of detection of the multiple transducers can be changed in different frames without departing from the scope of the present disclosure. In yet other examples, a subset of the transducers can be sampled in each frame rather than sampling all of the transducers in every frame without departing from the scope of the present disclosure. It should be understood that the duration of various phases illustrated in the timing diagrams of  FIGS. 30A-30B , e.g., touch and force capture  3020 , data transfer  3006 , algorithm  3008 , idle  3010 , etc. are not necessarily drawn to scale and are provided for the purposes of illustration. In some examples, the data transfer period  3006 , the algorithm period  3008 , or both, can be pipelined or interleaved with the detection without departing from the scope of the present disclosure. 
       FIGS. 31A-31C  illustrate exemplary switching configurations for quadrature acoustic touch and force sensing systems according to examples of the disclosure. Transducer  3102  illustrated in  FIG. 31A  can include a four spatial differential electrode configuration with electrodes  3104 A- 3104 D disposed on a first side of the transducer and common electrode  3106  disposed on a second side of the transducer. It should be recognizable that the four spatial differential electrode configuration illustrated in  FIG. 31  can correspond to the configuration described above with reference to  FIG. 11B . The outputs/inputs of electrodes  3104 A,  3104 B,  3104 C,  3104 D, and  3106  can be connected to touch and force control and readout circuitry  3108 A or  3108 B of either  FIG. 31A or 31B , respectively, for acoustic touch and force sensing. 
     Touch and force control and readout circuitry  3108 A of  FIG. 31A  can include four analog front end (AFE) amplifiers  3112 ,  3116 ,  3120 , and  3124 , the output of which can be connected to sense circuitry  3110 . The output of sense circuitry  3110  can be connected to the inputs of transmitter  3128 . In some examples, electrode  3104 A can be connected to a first input terminal of AFE amplifier  3112  via switch  31 S 1 , the output of electrode  3104 B can be connected to a first input terminal of AFE amplifier  3116  via switch  31 S 2 , the output of electrode  3104 C can be connected to a first input terminal of AFE amplifier  3120  via switch  31 S 3 , and the output of electrode  3104 D can be connected to a first input terminal of AFE amplifier  3124  via switch  31 S 4  (as indicated by connection labels  31 A- 31 D, respectively). The second terminal of AFE amplifiers  3112 ,  3116 ,  3120 , and  3124  can each connected to ground or any desired reference voltage source. In addition, electrodes  3104 A,  3104 B,  3104 C, and  3104 D can be connected to a first output terminal of transmitter  3128  via switches  31 S 5 ,  31 S 6 ,  31 S 7 , and  31 S 8 , respectively (as indicated by connection labels  31 A- 31 D). Electrode  3106  can be connected to a second output terminal of transmitter  3106  via switch  31 S 9  (as indicated by connection  31 E). During a combined touch and force receive (Rx) function, switches  31 S 1 ,  31 S 2 ,  31 S 3 , and  31 S 4  can be closed, and switches  31 S 5 ,  31 S 6 ,  31 S 7 ,  31 S 8 , and  31 S 9  can be open. The switch configuration during the combined touch and force Rx function can allow each AFE  3112 ,  3116 ,  3120 , and  3124  to receive a signal from electrodes  3104 A,  3104 B,  3104 C, and  3104 D, respectively. During a transmit (Tx) function switches  31 S 5 ,  31 S 6 ,  31 S 7 ,  31 S 8 , and  31 S 9  can be closed, and switches  31 S 1 ,  31 S 2 ,  31 S 3 , and  31 S 4  can be open. The switch configuration during the Tx function can allow transmitter  3128  to drive the electrodes  3104 A,  3104 B,  3104 C,  3104 D, and  3106  of transducer  2202  to create an electric potential across transducer  3102  and generate an acoustic wave. Notably, exemplary switching configuration  3100 A is compatible with the mode of operation illustrated in  FIGS. 28A-28B  (e.g., the configuration that allows signals for in-phase touch, quadrature touch, and force to be sensed simultaneously). In some examples, sense circuitry  3110  can include one or more of digital-to-analog converters (DAC)  402 A, filter  402 B, gain and offset correction circuit  412 , demodulation circuit  414 , filter  416 , analog-to-digital converter (ADC)  418 , input/output (I/O) circuit  420 , acoustic scan control circuit  422 , force detection circuit  424 , processor SoC  430 , host processor  432 , auxiliary processor  434 , and/or any other sense circuitry described above with reference to  FIG. 4 . In some examples, sense circuitry  3110  can be on a different chip from AFE  3112 , AFE  3116 , AFE  3120 , AFE  3124 , transmitter  3128 , switches  31 S 1 - 31 S 9 , and sources  3114 ,  3118 ,  3122 , and  3126 . In some examples, inputs of AFE amplifiers  3112 ,  3116 ,  3120 , and  3124  can be connected to a first transducer for receiving, and the outputs of transmitter  3128  can be connected to a second transducer, different than the first transducer, for transmitting. In some examples, the transmit and receive circuitry  3110  can be included on a silicon chip. In some examples, the transmit circuitry can be designed to drive higher voltages (or currents) to produce sufficient motion in the transducer to generate an acoustic wave in the surface of a device, and the receive circuitry can be designed for receiving smaller amplitude reflected energy. Accordingly, in some examples, the transmit circuitry and receive circuitry can be included on different silicon chips to avoid interference with the operation of the receive circuitry by the transmit circuitry. In some examples, common electrode  3106  can be floating during the receive (Rx) function to cancel out common mode signals (e.g., as described above with reference to electrode  1407  of  FIGS. 14B and 14C ). 
     Touch and force control and readout circuitry  3108 B of  FIG. 31B  is configured similarly to touch and force control and readout circuitry  3108 A of  FIG. 31A  with the exception of analog signal combination blocks  3126 ,  3128 , and  3130 . Each of these blocks can include circuitry (e.g., an inverting summer) for combining the signals measured by the AFEs  3112 ,  3116 ,  3120 , and  3124  to generate in-phase touch, quadrature touch, and force measurements. The formula for the electrode combinations is illustrated above each respective block  3126  (e.g., AB-CD),  3128  (e.g., AD-BC), and  3130  (e.g., AC-BD). As illustrated, the outputs of AFE amplifiers  3112  and  3116  can be combined to produce signal AB, the outputs of amplifiers  3112  and  3120  can be combined to produce signal AC, and so-on, to create all of the signal combinations AB, AC, AD, BC, BD, and CD that are used by the analog signal combination blocks  3126 ,  3128 , and  3130  to generate the in-phase touch, quadrature touch, and force measurements simultaneously. The outputs of the AFE amplifiers  3112 ,  3116 ,  3120 , and  3124  are shown with respective connections to the combination blocks to provide the electrode combinations for forming an in-phase touch (Touch I), quadrature touch (Touch Q) and force signal in parallel. In the figure, connections between intersecting lines are indicated by large black dots at the crossing point and lines crossing without large black dots have no connection. It should be understood that the AFE outputs are shown directly driving each of the combination blocks  3126 ,  3128 , and  3130  buffers (not shown) can be placed between the AFEs and each of the combination block inputs. Touch I circuitry  3130  can be configured to determine the difference between force signals AB and CD, and feed that difference to sense circuitry  3110 . Similarly, the outputs of AFE amplifiers  3112  and  3124  can be combined (e.g., AD) and connected to a first input of touch Q circuitry  3132 , and the outputs of AFE amplifiers  3116  and  3120  can be combined (e.g., BC) and connected to a second input of touch Q circuitry  3132 . Touch Q circuitry  3132  can be configured to determine the difference between touch signals AD and BC, and feed that difference to sense circuitry  3110 . In some examples, the functions performed at touch circuitry  3110  and  3112  can be performed simultaneously. The remaining elements of touch and force control and readout circuitry  3108 B can operate as described with reference to touch and force control and readout circuitry  3108 A of  FIG. 31A  above. 
       FIG. 31C  illustrates an exemplary circuit configuration for combination blocks  3126 ,  3128 , and  3130  in  FIG. 31B  above. In particular, the input voltages V A , V B , V C , and V D  as shown in  FIG. 31C  can correspond to the outputs of AFEs  3112 ,  3116 ,  3120 , and  3124 , respectively, and are arranged to match the input order shown connected to combination block  3126  in  31 B above. As shown in  FIG. 31C , resistors all having a value R can be arranged with the operational amplifier  3150  such that the output voltage V out  is equal to (V A +V B )−(V C +V D ). This result corresponds to the output (e.g., AB-CD) for combination block  3126  that can be used for in-phase touch as described above in  FIG. 31B . It should be understood that the same configuration can be used to form the signals output signals AD-BC for quadrature touch and AC-BD for force touch at combination blocks  3128  and  3130 . As shown in  FIG. 31C , the output of the combination blocks can be single ended, although a differential output is shown for blocks  3126 ,  3128 , and  3130  above. Furthermore, the exact configuration shown in  FIG. 31C  can be replaced with alternative circuit configurations that can add and subtract the voltage signals V A , V B , V C , and V D  to produce the in-phase touch, quadrature touch, and force signals without departing from the scope of the present disclosure. The configuration shown in  FIG. 31C  is not limiting and is provided only to provide one example of a combination circuit that can be used to produce the desired signals for the purpose of illustration. 
       FIG. 32  illustrates exemplary switching configuration  3200  for quadrature acoustic touch and force sensing systems according to examples of the disclosure. Transducer  3202  can include a four spatial differential electrode configuration with electrodes  3204 A- 3204 D disposed on a first side of the transducer and electrode  3206  disposed on a second side of the transducer. It should be recognizable that the four spatial differential electrode configuration illustrated in  FIG. 32  can correspond to the configuration described above with reference to  FIG. 11B . Electrodes  3204 A,  3204 B,  3204 C,  3204 D, and  3206  can be connected to touch and force control and readout circuitry  3208  for acoustic touch and force sensing. Touch and force control and readout circuitry  3208  can include analog front end (AFE) amplifier  3212 , the output of which can be connected to sense circuitry  3210 . The output of sense circuitry  3210  can be connected to the inputs of transmitter  3214 . In some examples, electrodes  3204 A,  3204 B,  3204 C, and  3204 D can be connected to a first input terminal of AFE amplifier  3212  via switches  32 S 1 ,  32 S 2 ,  32 S 3 , and  32 S 4 , respectively (as indicated by connection labels  32 A- 32 D). Electrodes  3204 A,  3204 B,  3204 C, and  3204 D can also be connected to a second input terminal of AFE amplifier  3212  via switches  32 S 5 ,  32 S 6 ,  32 S 7 , and  32 S 8 , respectively (also as indicated by connection labels  32 A- 32 D). Similarly, electrodes  3204 A,  3204 B,  3204 C, and  3204 D can be connected to a first output terminal of transmitter  3214  via switches  32 S 9 ,  32 S 10 ,  32 S 11 , and  32 S 12 , respectively (also as indicated by connection labels  32 A- 32 D). Electrode  3206  can be connected to a second output terminal of transmitter  3214  via switch  32 S 13  (as indicated by connection label  32 E). During an in-phase touch receive (Rx) function (Touch-I), switches  32 S 1 ,  32 S 2 ,  32 S 7 , and  32 S 8  can be closed, and switches  32 S 3 ,  32 S 4 ,  32 S 5 ,  32 S 6 ,  32 S 9 ,  32 S 10 ,  32 S 11 ,  32 S 12 , and  32 S 13  can be open. The switch configuration during the in-phase touch Rx function can allow the AFE  3212  to receive combined electrical signals from the electrodes  3204 A and  3204 B at a first terminal of AFE  3212  and to receive combined electrical signals from electrodes  3204 C and  3204 D at a second terminal of AFE  3212 . This can allow sense circuitry  3210  to detect the in-phase touch signal from the electrodes corresponding to a differential measurement of  32 A,  32 B vs.  32 C,  32 D (e.g., as shown in  FIG. 18A  above). During a quadrature touch Rx (Touch-Q) function, switches  32 S 1 ,  32 S 4 ,  32 S 6 , and  32 S 7  can be closed, and switches  32 S 2 ,  32 S 3 ,  32 S 5 ,  32 S 8 ,  32 S 9 ,  32 S 10 ,  32 S 11 ,  32 S 12 , and  32 S 13  can be open. The switch configuration during the quadrature touch Rx function can allow the AFE  3212  to receive combined electrical signals from the electrodes  3204 A and  3204 D at a first input of AFE  3212  and to receive combined electrical signals from electrodes  3204 B and  3204 C at a second terminal of AFE  3212 . This can allow sense circuitry  3210  to detect the quadrature touch signal from the electrodes corresponding to a differential measurement of  32 A,  32 D vs.  32 B,  32 C (e.g., as shown in  FIG. 18B  above). During a force receive (Rx) function, switches  32 S 1 ,  32 S 3 ,  32 S 6 , and  32 S 8  can be closed, and switches  32 S 2 ,  32 S 4 ,  32 S 5 ,  32 S 7 ,  32 S 9 ,  32 S 10 ,  32 S 11 ,  32 S 12 , and  32 S 13  can be open. The switch configuration during the force Rx function can allow the AFE  3212  to receive electrical signals from the electrodes  3204 A and  3204 C at a first terminal of AFE  3212  and to receive electrical signals from electrodes  3204 B and  3204 D at a second terminal of AFE  3212 . This can allow sense circuitry  3210  to detect the force signal from the electrodes corresponding to a differential measurement of  32 A,  32 C vs.  32 B,  32 D (e.g., as illustrated in  FIG. 18C  above). In the arrangement shown in  FIG. 32 , the force Rx function can be associated with a spatial frequency that is twice the spatial frequency of the in-phase touch and quadrature touch Rx functions. During each of the Rx functions, the electrode  3206  can be left floating for performing common mode rejection as described above with regarding to  FIGS. 14A-14C . During a transmit (Tx) function switches  32 S 9 ,  32 S 10 ,  32 S 11 ,  32 S 12 , and  32 S 13  can be closed, and switches  32 S 1 - 31 S 8  can be open. The switch configuration during the Tx function can allow transmitter  3214  to drive the electrodes  3204 A,  3204 B,  3204 C,  3204 D, and  3206  of transducer  3202  to create an electric potential across transducer  3206  and generate an acoustic wave. Notably, exemplary switching configuration  3200  is compatible with the modes of operation illustrated in  FIGS. 29A-30B . In some examples, additional AFE amplifiers can be incorporated to reduce the total time for reading all of the touch and force electrode groupings. For example, a second AFE amplifier can be incorporated such that a first AFE amplifier can be dedicated for touch detection, and the second AFE amplifier can be dedicated for force detection. In some examples, sense circuitry  3210  can include one or more of digital-to-analog converters (DAC)  402 A, filter  402 B, gain and offset correction circuit  412 , demodulation circuit  414 , filter  416 , analog-to-digital converter (ADC)  418 , input/output (I/O) circuit  420 , acoustic scan control circuit  422 , force detection circuit  424 , processor SoC  430 , host processor  432 , auxiliary processor  434 , and/or any other sense circuitry described above with reference to  FIG. 4 . In some examples, sense circuitry  3210  can be on a different chip from AFE  3212 , transmitter  3214 , and switches  32 S 1 - 32 S 13 . In some examples, AFE amplifier  3212  can be connected to a first transducer for receiving, and the outputs of transmitter  3214  can be connected to a second transducer, different than the first transducer, for transmitting. In some examples, the touch and force control and readout circuitry  3208  can be included on a silicon chip. In some examples, the transmit circuitry can be designed to drive higher voltages (or currents) to produce sufficient motion in the transducer to generate an acoustic wave in the surface of a device, and the receive circuitry can be designed for receiving smaller amplitude reflected energy. Accordingly, in some examples, the transmit circuitry and receive circuitry can be included on different silicon chips to avoid interference with the operation of the receive circuitry by the transmit circuitry. 
       FIG. 33  illustrates exemplary switching configuration  3300  for quadrature acoustic touch and force sensing systems according to examples of the disclosure. Transducer  3302  can include a four spatial differential electrode configuration with electrodes  3304 A- 3304 D disposed on a first side of the transducer and electrodes  3306 E and  3306 F disposed on a second side of the transducer. It should be recognizable that the spatial differential electrode configuration illustrated in  FIG. 33  can correspond to the configuration described above with reference to  FIG. 11B  above. Electrodes  3304 A,  3304 B,  3304 C,  3304 D,  3306 E, and  3306 F can be connected to touch and force control and readout circuitry  3308  for acoustic touch and force sensing. Touch and force control and readout circuitry  3308  can include analog front end (AFE) amplifier  3312 , the output of which can be connected to sense circuitry  3310 . Outputs from sense circuitry  3310  can be connected to the inputs of transmitter  3314 . In some examples, electrodes  3304 A,  3304 B,  3304 D, and  3304 E can be connected to a first input terminal of AFE amplifier  3312  via switches  33 S 1 ,  33 S 2 ,  33 S 3 , and  33 S 4 , respectively (as indicated by connection labels  33 A- 33 D). Electrodes  3304 B,  3304 C,  3304 D, and  3304 F can also be connected to a second input terminal of AFE amplifier  3312  via switches  33 S 5 ,  33 S 6 ,  33 S 7 , and  33 S 8 , respectively (as indicated by connection labels  33 B,  33 C,  33 D, and  33 F). In addition, electrodes  3304 A,  3304 B,  3304 C, and  3304 D can be connected to a first output terminal of transmitter  3314  via switches  33 S 9 ,  33 S 10 ,  33 S 11 , and  33 S 12 , respectively (as indicated by connection labels  33 A- 33 D). Electrodes  3306 E and  3306 F can be connected to a second output terminal of transmitter  3314  via switches  33 S 13  and  33 S 14 , respectively (as indicated by connection labels  33 E- 33 F). During an in-phase touch receive (Rx) function (Touch-I), switches  33 S 1 ,  33 S 2 ,  33 S 6 , and  33 S 7  can be closed, and switches  33 S 3 ,  33 S 4 ,  33 S 5 ,  33 S 8 ,  33 S 9 ,  33 S 10 ,  33 S 11 ,  33 S 12 ,  33 S 13 , and  33 S 13  can be open. The switch configuration during the touch I Rx function can allow the AFE  3312  to receive electrical signals from the electrodes  3304 A and  3304 B at a first terminal of AFE  3312  and to receive electrical signals from electrodes  3304 C and  3304 D at a second terminal of AFE  3312 . This can allow sense circuitry  3310  to detect the in-phase touch signal from the electrodes corresponding to a differential measurement of  33 A,  33 B vs.  33 C,  33 D. During a quadrature touch receive (Rx) function (Touch-Q), switches  33 S 1 ,  33 S 3 ,  33 S 5 , and  33 S 6  can be closed, and switches  33 S 2 ,  33 S 4 ,  33 S 7 ,  33 S 8 ,  33 S 9 ,  33 S 10 ,  33 S 11 ,  33 S 12 ,  33 S 13 , and  33 S 14  can be open. The switch configuration during the quadrature touch Rx function can allow the AFE  3312  to receive electrical signals from the electrodes  3304 A and  3304 D at a first terminal of AFE  3312  and to receive electrical signals from electrodes  3304 B and  3304 C at a second terminal of AFE  3312 . This can allow sense circuitry  3310  to detect the quadrature touch signal from the electrodes corresponding to a differential measurement of  33 A,  33 D vs  33 B,  33 C. During a force receive (Rx) function, switches  33 S 4  and  33 S 8  can be closed, and switches  33 S 1 ,  33 S 2 ,  33 S 3 ,  33 S 5 ,  33 A 6 ,  33 S 7 ,  33 S 9 ,  33 S 10 ,  33 S 11 ,  33 S 12 ,  33 S 13 , and  33 S 14  can be open. The switch configuration during the force Rx function can allow the AFE  3312  to receive electrical signals from the electrodes  3304 E and  3304 F. This can allow sense circuitry  3310  to detect the force signal from the electrodes corresponding to a differential measurement of E vs. F. During each of the Rx functions, the electrode opposite side electrodes (e.g., E and F while A, B, C, D are being sensed, or A, B, C, and D while E and F are being sensed) can be left floating for performing common mode rejection as described above with regard to  FIGS. 14A-14C  above. It should be understood from the disclosure above that the pitch of the  3306 E and  3306 F can correspond to a lower spatial frequency (e.g., half of the spatial frequency) for force touch measurements compared to in-phase touch and quadrature touch measurements. During a transmit (Tx) function switches  33 S 9 - 33 S 14  can be closed, and switches  33 S 1 - 33 S 8  can be open. The switch configuration during the Tx function can allow transmitter  3314  to drive the electrodes  3304 A,  3304 B,  3304 C,  3304 D,  3306 E, and  3306 F of transducer  3302  to produce an electric potential across the transducer  3302  and generate an acoustic wave. Notably, exemplary switching configuration  3300  is compatible with the modes of operation illustrated in  FIGS. 29A-30B . In some examples, additional AFE amplifiers can be incorporated to make this configuration compatible with the mode of operation illustrated in  FIGS. 28A and 28B  (e.g., as described with reference to  FIGS. 31A and 31B ). In some examples, a second AFE amplifier can be incorporated such that a first AFE amplifier can be dedicated for touch detection, and the second AFE amplifier can be dedicated for force detection. In some examples, sense circuitry  3310  can include one or more of digital-to-analog converters (DAC)  402 A, filter  402 B, gain and offset correction circuit  412 , demodulation circuit  414 , filter  416 , analog-to-digital converter (ADC)  418 , input/output (I/O) circuit  420 , acoustic scan control circuit  422 , force detection circuit  424 , processor SoC  430 , host processor  432 , auxiliary processor  434 , and/or any other sense circuitry described above with reference to  FIG. 4 . In some examples, sense circuitry  3310  can be on a different chip from AFE  3312 , transmitter  3314 , and switches  33 S 1 - 33 S 14 . In some examples, inputs of AFE amplifier  3312  can be connected to a first transducer for receiving, and the outputs of transmitter  3314  can be connected to a second transducer, different than the first transducer, for transmitting. In some examples, the touch and force control and readout circuitry  3308  can be included on a silicon chip. In some examples, the transmit circuitry can be designed to be driven by higher voltages (or currents) to produce sufficient motion in the transducer to generate an acoustic wave in the surface of a device, and the receive circuitry can be designed for receiving smaller amplitude reflected energy. Accordingly, in some examples, the transmit circuitry and receive circuitry can be included on different silicon chips to avoid interference with the operation of the receive circuitry by the transmit circuitry. 
       FIG. 34  illustrates exemplary switching configuration  3400  for quadrature acoustic touch and force sensing systems according to examples of the disclosure. Transducer  3402  can include a eight spatial differential electrode configuration with electrodes  3404 A,  3404 B,  3404 C,  3404 D,  3404 A 1 ,  3404 B 1 ,  3404 C 1 , and  3404 D 1  disposed on a first side of the transducer and electrode  3406  on a second side of the transducer. Electrodes  3404 A,  3404 B,  3404 C,  3404 D,  3404 A 1 ,  3404 B 1 ,  3404 C 1 ,  3404 D 1 , and  3406  can be connected to touch and force control and readout circuitry  3408  for acoustic touch and force sensing. Touch and force control and readout circuitry  3408  can include analog front end (AFE) amplifier  3412 , the output of which can be connected to sense circuitry  3410 . Outputs from sense circuitry  3410  can be connected to the inputs of transmitter  3414 . In some examples, electrodes  3404 A,  3404 B,  3404 A 1 ,  3404 B 1 ,  3404 C,  3404 C 1 , and  3404 D can be connected to a first input terminal of AFE amplifier  3412  via switches  34 S 1 ,  34 S 2 ,  34 S 3 ,  34 S 4 ,  34 S 5 ,  34 S 6 , and  34 S 7 , respectively (as indicated by connection labels  34 A,  34 B,  34 A 1 ,  34 B 1 ,  34 C,  34 C 1 , and  34 D). Electrodes  3404 C,  3404 D,  3404 C 1 ,  3404 D 1 ,  3404 A,  3404 A 1 , and  3404 B 1  can also be connected to a second input terminal of AFE amplifier  3412  via switches  34 S 8 ,  34 S 9 ,  34 S 10 ,  34 S 11 ,  34 S 12 ,  34 S 13 , and  34 S 14 , respectively (as indicated by connection labels  34 C,  34 D,  34 C 1 ,  34 D 1 ,  34 A,  34 A 1 , and  34 B 1 ). Similarly, electrodes  3404 A,  3404 B,  3404 C,  3404 D,  3404 A 1 ,  3404 B 1 ,  3404 C 1 , and  3404 D 1  can be connected to a first output terminal of transmitter  3314  via switches  34 S 15 ,  34 S 16 ,  34 S 17 ,  34 S 18 ,  34 S 19 ,  34 S 20 ,  34 S 21 , and  34 S 22 , respectively (as indicated by connection labels  34 A,  34 B,  34 C,  34 D,  34 A 1 ,  34 B 1 ,  34 C 1 , and  34 D 1 ). Electrode  3406  can be connected to a second output terminal of transmitter  3314  via switch  33 S 23  (as indicated by connection label  34 E). It should be understood that, while not illustrated, electrodes  3404 A,  3404 B,  3404 C,  3404 D,  3404 A 1 ,  3404 B 1 ,  3404 C 1 , and  3404 D 1  can represent electrode configurations as described above with reference to  FIGS. 17A-17C . During an in-phase touch receive (Rx) function (Touch-I), switches  34 S 1 ,  34 S 2 ,  34 S 3 ,  34 S 4 ,  34 S 8 ,  34 S 9 ,  34 S 10 , and  34 S 11  can be closed, and switches  34 S 5 - 34 S 7 , and  34 S 12 - 34 S 23  can be open. The switch configuration during the in-phase touch Rx function can allow the AFE  3412  to receive electrical signals from the electrodes  3404 A,  3404 B,  3404 A 1 , and  3404 B 1  at a first terminal of AFE  3312  and to receive electrical signals from electrodes  3404 C,  3404 D,  3404 C 1 , and  3404 D 1  at a second terminal of AFE  3412 . This can allow sense circuitry  3410  to detect the in-phase touch signal from the electrodes corresponding to a differential measurement of ABA1B1 and CDC1D1. During a quadrature touch receive (Rx) function (Touch-Q), switches  34 S 2 ,  34 S 4 ,  34 S 5 ,  34 S 6 ,  34 S 9 ,  34 S 11 ,  34 S 12 , and  34 S 13  can be closed, and switches  34 S 1 ,  34 S 3 ,  34 S 7 ,  34 S 8 , and  34 S 14 - 34 S 23  can be open. The switch configuration during the quadrature touch Rx function can allow the AFE  3412  to receive electrical signals from the electrodes  3404 B,  3404 B 1 ,  3404 C, and  3404 C 1  at a first terminal of AFE  3412  and to receive electrical signals from electrodes  3404 A,  3404 A 1 ,  3404 D, and  3404 D 1  at a second terminal of AFE  3412 . This can allow sense circuitry  3410  to detect the quadrature touch signal from the electrodes corresponding to a differential measurement of BCB1C1 vs ADA1D1. During a force receive (Rx) function, switches  34 S 1 ,  34 S 2 ,  34 S 5 ,  34 S 7 ,  34 S 10 ,  34 S 11 ,  34 S 13 , and  34 S 14  can be closed, and switches  34 S 3 ,  34 S 4 ,  34 S 6 ,  34 S 8 ,  34 S 9 ,  34 S 12  and  34 S 15 - 34 S 23  can be open. The switch configuration during the force Rx function can allow the AFE  3412  to receive electrical signals from the electrodes  3404 A,  3404 B,  3404 C, and  3404 D at a first terminal of AFE  3412  and to receive electrical signals from electrodes  3404 A 1 ,  3404 B 1 ,  3404 C 1 , and  3404 D 1  at a second terminal of AFE  3412 . This can allow sense circuitry  3410  to detect the force signal from the electrodes corresponding to a differential measurement of ABCD and A1B1C1D1. During each of the Rx functions, the electrode  3406  can be left floating for performing common mode rejection as described above with regarding to  FIGS. 14A-14C . During a transmit (Tx) function switches  34 S 15 - 34 S 23  can be closed, and switches  34 S 1 - 34 S 14  can be open. The switch configuration during the Tx function can allow transmitter  3414  to drive the electrodes  3404 A,  3404 B,  3404 C,  3404 D,  3404 A 1 ,  3404 B 1 ,  3404 C 1 ,  3404 D 1 , and  3306 E of transducer  3302  to generate an acoustic wave. Notably, exemplary switching configuration  3400  is compatible with the modes of operation illustrated in  FIGS. 29A-30B . Similar to the example illustrated in  FIG. 33  above, the switching scheme illustrated in  FIG. 34  can measure force at a spatial frequency that is half the spatial frequency of the in-phase touch and quadrature touch measurements. However, unlike  FIG. 33  above, differential measurement electrodes  3404 A- 3404 D 1  all can be disposed on one side of the transducer  3406 . This configuration can simplify forming electrical connections to all of the transducer electrodes (e.g.,  3404 A- 3404 D 1  and  3406 ) from one side of transducer. Since electrodes  3404 A- 3404 D 1  are already on one side of the transducer  3402 , only electrode  3406  would need to be routed to the opposite side to achieve the goal of single-sided connections described immediately above. On the other hand, in  FIG. 33  above, both electrodes  3306 E and  3306 F would need to be routed to the opposite side of transducer  3302  to achieve the same result. This benefit comes with a trade-off of more total electrodes on the transducer (nine in  FIG. 34  compared to six in  FIG. 33 ) and correspondingly more switches for connecting to increased number of electrodes. In some examples, additional AFE amplifiers (e.g., eight in total) can be incorporated to make this configuration compatible with the mode of operation illustrated in  FIGS. 28A and 28B  (e.g., as described with reference to  FIGS. 31A and 31B ). In some examples, a second AFE amplifier can be incorporated such that a first AFE amplifier can be dedicated for touch detection, and the second AFE amplifier can be dedicated for force detection. In some examples, sense circuitry  3410  can include one or more of digital-to-analog converters (DAC)  402 A, filter  402 B, gain and offset correction circuit  412 , demodulation circuit  414 , filter  416 , analog-to-digital converter (ADC)  418 , input/output (I/O) circuit  420 , acoustic scan control circuit  422 , force detection circuit  424 , processor SoC  430 , host processor  432 , auxiliary processor  434 , and/or any other sense circuitry described above with reference to  FIG. 4 . In some examples, sense circuitry  3410  can be on a different chip from AFE  3412 , transmitter  3414 , and switches  24 S 1 - 34 S 23 . In some examples, inputs of AFE amplifier  3412  can be connected to a first transducer for receiving, and the outputs of transmitter  3414  can be connected to a second transducer, different than the first transducer, for transmitting. In some examples, the touch and force control and readout circuitry  3408  can be included on a silicon chip. In some examples, the transmit circuitry can be designed to drive higher voltages (or currents) to produce sufficient motion in the transducer to generate an acoustic wave in the surface of a device, and the receive circuitry can be designed for receiving smaller amplitude reflected energy. Accordingly, in some examples, the transmit circuitry and receive circuitry can be included on different silicon chips to avoid interference with the operation of the receive circuitry by the transmit circuitry. 
       FIGS. 35A-35B  illustrate an exemplary transmitter configuration for acoustic touch and force sensing systems according to examples of the disclosure. The exemplary transmitter can represent any of the various Tx blocks described in  FIGS. 21-27 and 31-34  above. It should be understood that the exemplary Tx block is provided only for the purposes of illustration, and that any circuit configuration capable of driving a piezoelectric transducer to produce acoustic waves can be used without departing from the scope of the present disclosure. Specifically,  FIG. 35A  illustrates transmitter  3514  with inputs  3520 A and  3520 B and outputs  3522 A and  3522 B.  FIG. 35B  illustrates a detailed configuration of transmitter  3514  of  FIG. 35A  illustrating a boost converter configuration for providing the Tx drive signal. In the illustration, the boost circuit  3524  can boost the input voltage to a suitable drive voltage for the transistor. In the illustrated voltage boost configuration of  FIG. 35B , a single ended output can be formed as the negative output terminal is connected to ground  3528 . Accordingly, a differential drive for the transducer can be provided using switches to invert the polarity of the drive signals as will be shown in  FIG. 36B  below. 
       FIGS. 36A-36B  illustrate exemplary transmitter configurations for acoustic touch and force sensing systems according to examples of the disclosure. Specifically,  FIG. 36A  repeats the Tx  3614  Tx configuration shown in  FIGS. 31A-31B  and  FIG. 32  for a transducer with four electrodes  36 A- 36 D on one side and one electrode  36 E on the opposite side. As described in  FIGS. 31A-31B  and  FIG. 32 , during the transmit phase for the configuration in  36 A, all of the switches  36 S 5 - 36 S 9  can be closed, and a differential signal can be driven by the differential Tx  3614  across the two sides of a transducer such as  3102  or  3202  above. As described, the switch configuration shown in  FIG. 36A  can be used with a fully differential transmit circuit  3614 , but is provided here primarily as a reference point for the switch configuration shown in  FIG. 36B  that can be used to provide differential drive to the transducer using a single ended boost converter as described in  FIG. 36A  above. 
       FIG. 36B  illustrates a switching configuration for providing a differential drive signal based on a single-ended output Tx configuration such as the exemplary Tx configuration  3514  described in  FIG. 36A . The boost converter  3614 B can be identical to the boost converter described above in  FIG. 35B . Switches  36 S 5 ,  36 S 6 ,  36 S 7 ,  36 S 8 , and  36 S 9  can correspond directly to the switches having the same numbers as shown in  FIG. 36A  above. Thus, when those switches are closed, the positive output of the boost converter  3614 B can be connected to electrodes on one side of the transducer, while ground  3624  can be connected to the opposite side of the transducer. Switches  36 S 10 ,  36 S 11 ,  36 S 12 ,  36 S 13 , and  36 S 14  can provide analogous connections to the switches  36 S 5 - 36 S 9 , but with the opposite polarity. By switching back and forth between these closing switches  36 S 5 - 36 S 9  (while opening the others) and closing switches  36 S 10 - 36 S 14  (while opening the others), a differential drive can be applied to a transducer based on a single ended voltage boost configuration as illustrated in  FIGS. 35B and 36B . More generally, the switching principle illustrated in  FIG. 36B  can be applied to create a differential drive for a transducer from any single ended source having a sufficient output voltage to drive the transducer to produce acoustic waves as described throughout the disclosure. 
       FIGS. 37A-37Q  illustrate exemplary pixelated transducers  3700 A-Q according to examples of the disclosure. As described herein, a pixelated transducer replaces one or both conventional electrodes of a transducer (e.g., first electrode  332  and/or second electrode  334  in  FIG. 3C ) into multiple electrodes. The pixelated transducers  3700 A-M can, for example, include a piezoelectric material  3701  and a plurality of separated electrodes. In some examples (e.g., illustrated in  FIGS. 37H-37N ), an electrode layer on one side of piezoelectric material  3701  can be pixelated (including a plurality of separated electrodes). In some examples (e.g., illustrated in  FIGS. 37A-37G ), a first electrode layer on a first side of piezoelectric material  3701  and a second electrode layer on a second side of piezoelectric material  3701  can be pixelated. In some examples, the pitch of the upper electrodes can be the same as the pitch of the lower electrodes. In some examples, the pitch of the upper electrodes can be different than the pitch of the lower electrodes. In some examples, the transducer can further include an insulating material  3703 , such as an epoxy or another suitable non-conductive material (e.g., plastic, ceramic, etc.). Insulating material  3703  can provide a surface for wraparound or other connections of the electrodes of pixelated transducers  3700 A-M. Additionally, using an insulating material  3703  can reduce noise in the piezoelectric material and maximize the active area of the piezoelectric material  3701 . The various exemplary pixelated transducers  3700 A-M are described below. 
       FIG. 37A  illustrates an exemplary pixelated transducer  3700 A according to examples of the disclosure. Pixelated transducer  3700 A includes first and second pixelated electrode layers (also referred to as upper and lower pixelated layers based on the orientation illustrated in  FIG. 37A ). For example, pixelated transducer  3700 A can include a plurality of upper electrodes  3704  disposed on a first side of the piezoelectric material  3701  (e.g., top side illustrated in  FIG. 37A ) and a plurality of lower electrodes  3706  disposed on a second side of piezoelectric material  3701  (e.g., bottom side illustrated in  FIG. 37A ). In the pixelated arrangement of  FIG. 37A , adjacent upper electrodes  3704  can be separated from one another by gaps  3770 A and adjacent lower electrodes  3706  can also be separated from one another by gaps  3770 A. The lower electrodes  3706  can wrap around from the second side of piezoelectric material  3701  to the first side of piezoelectric material  3701 , for example. The lower electrodes  3706  wrapping around the piezoelectric material  3701  can be separated from corresponding upper electrodes by gaps  3770 B. Wrapping around the lower electrodes  3706  to the first side of the transducer  3700 A can allow for simplified connections between the transducer and a touch and/or force sensing circuit (e.g., via flex circuit, interposer, direct bonding, etc.). 
       FIG. 37B  illustrates another exemplary pixelated transducer  3700 B according to examples of the disclosure. Pixelated transducer  3700 B can correspond to pixelated transducer  3700 A, except pixelated transducer  3700 B can include an insulating material  3703 , which can be used, for example, for bringing the electrodes on the second side of the transducer to the first side of the transducer. The insulating material  3703  can also be used for the connection area between the transducer and the touch and/or force sensing circuit. For example, pixelated transducer  3700 B can include a plurality of upper electrodes  3708  disposed on a first side of the piezoelectric material  3701  and a first side of insulating material  3703  (e.g., top side illustrated in  FIG. 37B ) and a plurality of lower electrodes  3710  disposed on a second side of piezoelectric material  3701  and a second side of insulating material  3703  (e.g., bottom side illustrated in  FIG. 37B ). In the pixelated arrangement of  FIG. 37B , adjacent upper electrodes  3708  can be separated from one another by gaps  3770 A and adjacent lower electrodes  3710  can also be separated from one another by gaps  3770 A. The lower electrodes  3710  can wrap around from the second side of pixelated transducer  3700 B to the first side of the transducer  3700 B. Unlike lower electrodes  3706  of pixelated transducer  3700 A that wrap around piezoelectric material  3701 , lower electrodes  3710  can wrap around insulating material  3703  and can terminate on the first side of insulating material  3703 . Using an insulating material for the wraparound and/or connection can result in improved stimulation and sensing of the transducer. For example, a differential signal applied or received across piezoelectric material  3701  can have different properties when applied to two opposing sides of piezoelectric material  3701  than when the differential signal is applied to or received from three sides of piezoelectric material  3701  (including applying signals to/receiving signals from electrodes on the first side of piezoelectric material  3701  in  FIG. 37A ). The lower electrodes  3710  wrapping around the pixelated transducer  3700 B (e.g., wrapping around the insulating material  3703 ) can be separated from corresponding upper electrodes  3708  by gaps  3770 B. Wrapping around the lower electrodes  3710  from the second side of pixelated transducer  3700 B to the first side of pixelated transducer  3700 B can allow for simplified connections between the transducer and a touch and/or force sensing circuit (e.g., via flex circuit, interposer, direct bonding, etc.). It should be understood that pixelated transducers  3700 A-B can be similarly implemented with upper electrodes wrapping around from a first side of piezoelectric material  3701  to a second side of piezoelectric material  3701  instead of implemented with lower electrodes wrapping around as illustrated in  FIGS. 37A-B . 
       FIG. 37C  illustrates another exemplary pixelated transducer  3700 C according to examples of the disclosure. Pixelated transducer  3700 C can correspond to pixelated transducer  3700 A implemented with both upper electrodes and lower electrodes wrapping around to a common, third side of piezoelectric material  3701  rather than to a first side (or second side) of piezoelectric material  3701 . Connection between pixelated transducer  3700 C and touch and/or force circuitry can be made on the third side of piezoelectric material  3701 . For example, transducer  3700  can include a plurality of upper electrodes  3712  disposed on a first side of the piezoelectric material  3701  (e.g., top side illustrated in  FIG. 37C ) and a plurality of lower electrodes  3714  disposed on a second side of piezoelectric material  3701  (e.g., bottom side illustrated in  FIG. 37C ). In the pixelated arrangement of  FIG. 37C , adjacent upper electrodes  3712  can be separated from one another by one or more gaps  3770 A and adjacent lower electrodes  3714  can also be separated from one another by gaps  3770 A. The upper electrodes  3712  and lower electrodes  3714  can wrap around from the first side (top side) and from the second side (bottom side) of piezoelectric material  3701 , respectively, to a common, third side of piezoelectric material  3701  (e.g., front right side illustrated in  FIG. 37C ). A portion of upper electrodes  3712  and a portion of lower electrodes  3714  wrapping around to the third side of piezoelectric material  3701  can be separated from each other by gaps  3770 B. Wrapping around the upper electrodes  3712  and the lower electrodes  3714  to the third side of piezoelectric material  3701  can allow for simplified connections between the transducer and a touch and/or force sensing circuit (e.g., via flex circuit, interposer, direct bonding, etc.). 
       FIG. 37D  illustrates another exemplary transducer  3700 D according to examples of the disclosure. Pixelated transducer  3700 D can correspond to pixelated transducer  3700 C, except pixelated transducer  3700 D can include an insulating material  3703  for wraparound and/or connection. For example, pixelated transducer  3700 D can include a plurality of upper electrodes  3716  disposed on a first side of piezoelectric material  3701  (e.g., top side illustrated in  FIG. 37D ) and a plurality of lower electrodes  3718  disposed on a second side of piezoelectric material  3701  (e.g., bottom side illustrated in  FIG. 37D ). In the pixelated arrangement of  FIG. 37D , adjacent upper electrodes  3716  can be separated from one another by gaps  3770 A and adjacent lower electrodes  3718  can also be separated from one another by gaps  3770 A. Upper electrodes  3716  can extend from the first side of piezoelectric material  3701  to the first side of the insulating material  3703  and lower electrodes  3718  can extend from the second side of piezoelectric material  3701  to the second side of the insulating material  3703 . The upper electrodes  3716  and lower electrodes  3718  can wrap around from the first side and the second side of transducer  3700 D, respectively, to a common, third side of transducer  3700 D (e.g., front right side illustrated in  FIG. 37D ). Unlike upper electrodes  3712  and lower electrodes  3714  of transducer  3700 C, upper electrodes  3716  and lower electrodes  3718  can wrap around and/or terminate on the common third side of insulting material  3703 , rather than on the piezoelectric material  3701 . Using an insulating material for the wraparound and/or connection can result in improved stimulation and sensing of the transducer as discussed above with respect to  FIG. 37B . The upper electrodes  3716  and lower electrodes  3718  wrapping around the pixelated transducer  3700 D (e.g., by way of the insulating material  3703 ) can be separated from one another by gaps  3770 B. Wrapping around the electrodes  3716  and  3718  from the first and second sides of pixelated transducer  3700 D to the third side of the pixelated transducer  3700 D can allow for simplified connections between the transducer and a touch and/or force sensing circuit (e.g., via flex circuit, interposer, direct bonding, etc.) on the side of pixelated transducer  3700 D. It should be understood that pixelated transducers  3700 C-D can be similarly implemented with upper and lower electrodes wrapping to a common, fourth side of the transducer (e.g., opposite the third side) instead of wrapping around to the common, third side of the transducer as illustrated in  FIGS. 8C-D . 
       FIG. 37E  illustrates another exemplary pixelated transducer  3700 E according to examples of the disclosure. Pixelated transducer  3700 E can correspond to pixelated transducer  3700 C implemented with the upper electrodes and lower electrodes wrapping around to different third and fourth sides of piezoelectric material  3701  rather than to a common third (or fourth) side of piezoelectric material  3701 . For example, transducer  3700 E can include a plurality of upper electrodes  3720  disposed on a first side of the piezoelectric material  3701  (e.g., top side illustrated in  FIG. 37E ) and a plurality of lower electrodes  3722  disposed on a second side of piezoelectric material  3701  (e.g., bottom side illustrated in  FIG. 37E ). In the pixelated arrangement of  FIG. 37E , adjacent upper electrodes  3720  can be separated from one another by gaps  3770 A and adjacent lower electrodes  3722  can also be separated from one another by gaps  3770 A. The upper electrodes  3720  can wrap around from the first side (top side) of piezoelectric material  3701  to a third side of piezoelectric material  3701  (e.g., front right side illustrated in  FIG. 37E ) and lower electrodes  3722  can wrap around from the second side (bottom side) of piezoelectric material  3701  to a fourth side of piezoelectric material  3701  (e.g. back left side illustrated in  FIG. 37E ), for example. The upper electrodes  3720  and lower electrodes  3722  wrapping around the piezoelectric material  3701  can be on mutually exclusive sides of the piezoelectric material, and thereby separated from one another. Connections between the transducer and a touch and/or force sensing circuit (e.g., via flex circuit, interposer, direct bonding, etc.) can be made on the sides of piezoelectric material  3701  rather than on the top or bottom of piezoelectric material  3701 . 
       FIG. 37F  illustrates another exemplary pixelated transducer  3700 F according to examples of the disclosure. Pixelated transducer  3700 F can correspond to pixelated transducer  3700 E, except pixelated transducer  3700 F can include insulating material  3703  disposed on two opposite sides of the piezoelectric material  3701 . For example, pixelated transducer  3700 F can include a plurality of upper electrodes  3724  disposed on a first side of the piezoelectric material  3701  (e.g., top side illustrated in  FIG. 37F ) and a plurality of lower electrodes  3726  disposed on a second side of the piezoelectric material  3701  (e.g., bottom side illustrated in  FIG. 37F ). Pixelated transducer  3700 F can include an insulating material  3703  disposed on a third side of piezoelectric material  3701  and on a fourth side of piezoelectric material  3701 , for example. In the pixelated arrangement of  FIG. 37F , adjacent upper electrodes  3724  can be separated from one another by gaps  3770 A and adjacent lower electrodes  3726  can also be separated from one another by gaps  3770 A. The upper electrodes  3724  can wrap around from the first side (top side) of piezoelectric material  3701  to a third side (e.g., front right side illustrated in  FIG. 37F ) by way of insulating material  3703  and lower electrodes  3726  can wrap around from the second side (bottom side) of piezoelectric material  3701  to a fourth side (e.g., back left side illustrated in  FIG. 37F ) by way of insulating material  3703 . Unlike the electrodes  3720  and  3722  of transducer  3700 E, electrodes  3724  and  3726  can each wrap around insulating material  3703  and can terminate on insulating material  3703 . Using an insulating material for the wraparound connection can result in improved stimulation and sensing of the transducer as described above. Wrapping around the upper electrodes  3724  from the first side to the third side and wrapping around the lower electrodes  3726  from the second side to the fourth side can allow for connections between the transducer and a touch and/or force sensing circuit (e.g., via flex circuit, interposer, direct bonding, etc.) via the sides of pixelated transducer  3700 F. It should be understood that pixelated transducers  3700 E-F can be similarly implemented with upper electrodes wrapping to a fourth side of the transducer and lower electrodes wrapping to a third side of the transducer instead of upper electrodes wrapping to a third side of the transducer and lower electrodes wrapping to a fourth side of the transducer as illustrated in  FIGS. 8E-F . 
       FIG. 37G  illustrates another exemplary pixelated transducer  3700 G according to examples of the disclosure. Pixelated transducer  3700 G can correspond to pixelated transducer  3700 A implemented without a wraparound. For example, transducer  3700 G can include a plurality of upper electrodes  3728  disposed on a first side of the piezoelectric material  3701  (e.g., top side illustrated in  FIG. 37G ) and a plurality of lower electrodes  3730  disposed on a second side of piezoelectric material  3701  (e.g., bottom side illustrated in  FIG. 37G ). In the pixelated arrangement of  FIG. 37G , adjacent upper electrodes  3728  can be separated from one another by one or more gaps  3770 A and adjacent lower electrodes  3730  can also be separated from one another by gaps  3770 A. A connection can be made to touch and/or force circuitry via a flex circuit (which can be bonded to transducer  3700 G by an adhesive (e.g., epoxy). 
       FIG. 37H  illustrates another exemplary pixelated transducer  3700 H according to examples of the disclosure. Pixelated transducer  3700 H can correspond to pixelated transducer  3700 G implemented with pixelated electrodes on one side and a single continuous electrode on the second side. For example, transducer  3700 H can include a plurality of upper electrodes  3732  disposed on a first side of piezoelectric material  3701  (e.g., top side illustrated in  FIG. 37H ) and a lower electrode  3734  disposed on a second side of piezoelectric material  3701  (e.g., bottom side illustrated in  FIG. 37H ). Adjacent upper electrodes  3732  can be separated from one another by gaps  3770 A. It should be understood that although pixelated transducer  3700 H is illustrated with pixelated upper electrodes  3732  and a single lower electrode, a pixelated transducer can similarly be implemented with a single continuous upper electrode and pixelated lower electrodes. 
       FIG. 37I  illustrates another exemplary pixelated transducer  3700 I according to some examples of the disclosure. Pixelated transducer  3700 I can correspond to pixelated transducer  3700 H implemented such that the lower electrode wraps around piezoelectric material  3701  by way of an insulating material  3703  to a first side (e.g., top side) from a second side (e.g., bottom side). In some examples, insulating material  3703  can be omitted and the lower electrode can wrap piezoelectric material  3701 . For example, transducer  3700 I can include a plurality of upper electrodes  3736  disposed on a first side of the transducer  3700 I (e.g., top side illustrated in  FIG. 37I ) and a lower electrode  3738  disposed on a second side of the transducer  3700 I (e.g., bottom side illustrated in  FIG. 37I ). In the pixelated arrangement of  FIG. 37I , the upper electrodes  3736  can be separated from one another by gaps  3770 A. In some examples, the lower electrode  3738  can wrap around from the second side (e.g., bottom side) of the transducer  3700 I to the first side (e.g., top side) of the transducer  3700 I by way of insulating material  3703 . In some examples, a via through the insulating material  3703  can be used instead of the wraparound. Using an insulating material for the wraparound (or via) connection can result in improved stimulation and sensing of the transducer as described above. The lower electrode  3738  wrapping around pixelated transducer  3700 I (e.g., wrapping around the insulating material  3703 ) can leave a gap  3770 B between the lower electrode  3738  and one of the upper electrodes  3738 , for example. Wrapping around the lower electrode  3738  from the second side of the pixelated transducer  3700 I to the first side of the transducer  3700 I can allow for simplified connections between the transducer and a touch and/or force sensing circuit (e.g., via flex circuit, interposer, direct bonding, etc.). It should be understood that pixelated transducer  3700 I can instead be implemented with a single continuous upper electrode wrapping around from a first side of piezoelectric material  3701  to a second side of piezoelectric material  3701  and pixelated lower electrodes. 
       FIG. 37J  illustrates another exemplary pixelated transducer  3700 J according to examples of the disclosure. For example, transducer  3700 J can include a first upper electrode  3740  and a second upper electrode  3742  disposed on a first side of piezoelectric material  3701  (e.g., top side as illustrated in  FIG. 37J ) and a lower electrode  3744  disposed on a second side of piezoelectric material  3701  (e.g., bottom side as illustrated in  FIG. 37J ). The first upper electrode  3740  and the second plurality of upper electrode  3742  can have interlocking shapes separated from one another by gaps  3770 A, for example. 
       FIG. 37K  illustrates another exemplary pixelated transducer  3700 K according to examples of the disclosure. Pixelated transducer  3700 K can correspond to pixelated transducer  3700 J implemented with the lower electrode wrapping around from a second side (e.g., bottom side) of the transducer to a first side (e.g., top side) of the transducer by way of an insulting material  3703 . In some examples, the insulated material  3703  can be omitted. Transducer  3700 K can include a first upper electrode  3746  and a second upper electrode  3748  disposed on a first side of the transducer  3700 K (e.g., top side as illustrated in  FIG. 37K ) and a lower electrode  3750  disposed on a second side of the transducer  3700 K (e.g., bottom side as illustrated in  FIG. 37K ). The first upper electrode  3746  and the second upper electrode  3748  can have interlocking shapes separated by gaps  3770 A, for example. In some examples, lower electrode  3750  can wrap around from the second side (bottom side) of the transducer  3700 K to the first side (top side) of the transducer  3700 K, for example. The lower electrode  3750  wrapping around the transducer  3700 K (e.g., wrapping around the insulating material  3703 ) can be disposed to leave gap  3770 B between lower electrode  3750  and upper electrodes  3746  and  3748 . Using an insulating material for the wraparound and/or connection can result in improved stimulation and sensing of the transducer as described above. Wrapping around lower electrode  3750  to the first side of the pixelated transducer  3700 K from the second side of pixelated transducer  3700 K can allow for simplified connections between the transducer and a touch and/or force sensing circuit (e.g., via flex circuit, interposer, direct bonding, etc.) In some examples, a via through insulating material  3703  can be used instead of a wraparound. Although lower electrodes  3744  and  3750  are illustrated as single continuous electrodes in  FIGS. 8J and 8K , in some examples, lower electrodes  3744  and  3750  can be implemented with pixelated electrodes. It should be understood that pixelated transducers  3700 J and  3700 K can be similarly implemented with a single upper electrode wrapping around to the second side of the transducer from a first side of the transducer and with two interlocking lower electrodes on the second side of the transducer. 
       FIG. 37L  illustrates another exemplary pixelated transducer  3700 L according to examples of the disclosure. Pixelated transducer  3700 L can correspond to pixelated transducer  3700 J implemented with one of the upper electrodes and the lower electrode wrapping around to a common, third side of piezoelectric material  3701 . In some examples the second of the upper electrodes can also wrap around to a fourth side of piezoelectric material, allowing for side connections to the pixelated transducer. For example, transducer  3700  can include a first upper electrode  3752  and a second upper electrode  3754  disposed on a first side of piezoelectric material  3701  (e.g., top side as illustrated in  FIG. 37L ) and a lower electrode  3756  disposed on a second side of piezoelectric material  3701  (e.g., bottom side as illustrated in  FIG. 37L ). The first upper electrode  3752  and the second upper electrode  3754  can have interlocking shapes separated from each other by gaps  3770 A, for example, with the connection between topside portions of the respective upper electrode connected by wrapping to a different side of piezoelectric material  3701 . For example, the portions of second upper electrode  3754  on the first side of piezoelectric material  3701  can wrap around and be connected together on a different side of piezoelectric material  3701  (third side). The portions of first upper electrode  3752  on the first side of piezoelectric material  3701  can wrap around and be connected together on a different side of piezoelectric material  3701  (fourth side). In some examples, the second upper electrode  3754  and the lower electrode  3756  can wrap from the first side (top side) and second side (bottom side), respectively, of the piezoelectric material  3701  to a third, common side of the piezoelectric material  3701  (e.g., a front right side as illustrated in  FIG. 37L ). In some examples, a portion of lower electrode  3756  and a portion of the second upper electrode  3754  wrapping around to the third side of piezoelectric material  3701  can be separated from one another by gap  3770 B. Wrapping the first upper electrode  3752 , second upper electrode  3754  and/or the lower electrode  3756  around the piezoelectric material  3701  to the third and/or fourth side of the piezoelectric material  3701  can allow for simplified connections between the transducer and a touch and/or force sensing circuit (e.g., via flex circuit, interposer, direct bonding, etc.) on the sides of pixelated transducer  3700 L. Although one lower electrode  3756  is illustrated in  FIG. 37L , in some examples, lower electrode  3756  can be implemented with pixelated lower electrodes in a similar manner as the pixelated top electrode in  FIG. 37L . Pixelated transducer  3700 L can also be implemented with wraparounds on an insulating material on one or both sides of the transducer. 
       FIG. 37M  illustrates another exemplary pixelated transducer  3700 M according to examples of the disclosure. Pixelated transducer  3700 M can correspond to pixelated transducer  3700 H implemented upper electrodes connected to touch and/or force sensing circuitry by post-processing connections. For example, pixelated transducer  3700 M can include a plurality of upper electrodes  3758  between a first side of piezoelectric material  3701  (e.g., top side as illustrated in  FIG. 37M ) and a lower electrode  3760  disposed on a second side of the piezoelectric material  3701  (e.g., bottom side as illustrated in  FIG. 37M ). In the pixelated arrangement of  FIG. 37M , the upper electrodes  3758  can be separated from one another by gaps  3770 A. Upper electrodes  3758  can be coupled to routing  3772  by way of vias  3774 . The upper electrodes  3758  and the routing  3772  can be separated by the insulating material  3703 , for example. The post-processing (metal-insulator) can be performed on the transducer wafer and then individual pixelated transducers can be cut. The electrodes, vias and metal routings can be patterned using photolithography, for example. Connecting the upper electrodes  3762  to routing  3772  can allow for simplified connections between the pixelated transducer  3700 M and a touch and/or force sensing circuit (e.g., via flex circuit, interposer, direct bonding, etc.). In some examples, the routing can continue on another surface (e.g., cover glass) before a connection to the touch and/or force sensing circuit. Although one lower electrode  3760  is illustrated, in some examples, lower electrode  3760  can be pixelated in a similar manner as upper electrodes  3758 . 
       FIGS. 37N and 37O  illustrate exploded views of exemplary pixelated transducers  3700 N and  3700 O according to examples of the disclosure. Pixelated transducer  3700 N can correspond to pixelated transducer  3700 H implemented with an insulating material  3703  disposed over the upper electrodes. Electrodes disposed above the insulating material  3703  can be capacitively coupled to upper electrodes for driving and sensing the transducer (e.g., electrodes on a flex circuit can be bonded via an epoxy or other adhesive). Pixelated transducer  8 O can correspond to a non-pixelated transducer  314  of  FIG. 3C  with an insulating material  3703  disposed over the upper electrode. Electrodes disposed above the insulating material  3703  can be capacitively coupled to upper electrodes for driving and/or sensing the transducer in a localized manner to achieve a pixelated effect (e.g., electrodes on a flex circuit can be bonded via an epoxy or other adhesive). In particular, electrodes disposed above insulating material  3703  for pixelated transducer  8 N can be capacitively coupled to upper electrodes for driving and sensing, and electrodes disposed above insulating material  3703  for pixelated transducer  8 O can be capacitively coupled to upper electrodes for common mode driving. 
     Transducer  3700 N can include a plurality of upper electrodes  3762  disposed on a first side of an insulating material  3703  (e.g., top side as illustrated in  FIG. 37N ) and a lower electrode  3764  disposed on a second side of a piezoelectric material  3701  (e.g., bottom side as illustrated in  FIG. 37N ). The plurality of upper electrodes  3762  can be separated from one another by gaps  3770 A. Insulating material  3703  can be disposed on top of the upper electrode layer and multiple electrodes  3766  can be disposed on top of the insulating material  3703 . Electrodes  3766  can, in some examples, correspond in size, shape and relative location to upper electrodes  3762 . In some examples, the plurality of upper electrodes  3762  can be driven or sensed via capacitive coupling between the upper electrodes  3762  and electrodes  3766 . In some examples, electrodes  3766  can be part of a flex circuit to connect the transducer with a touch and/or force sensing circuit. In some examples, post-processing (metal-insulator) can be performed on the transducer wafer to dispose the insulator and patterned mental electrodes on the piezoelectric material. The individual transducers can then be cut from the wafer. In some examples, in order to enable capacitive coupling via insulating material  3703 , the insulating material can be very thin and/or have large dielectric constant for high-efficiency capacitive coupling. The electrodes can be patterned using photolithography, for example. Transducer  3700 O can include a single upper electrode  3768  rather than pixelated upper electrodes  3762 . The single upper electrodes  3766  capacitively coupled to the pixelated electrodes  3766  can result in capacitive coupling therebetween for common mode driving of the pixelated transducer  3700 O. In some examples, upper electrode  3768  of  FIG. 37O  can be removed and electrodes  3766  can be used to drive and sense the transducer using differential driving techniques and spatial differential receiving techniques. 
     Although lower electrode  3764  is illustrated as a single electrode, in some examples, lower electrode  3764  can be pixelated or mimic a pixelated electrode on the second side of the transducer in addition or instead of the electrodes on the first side of the transducer as illustrated in  FIGS. 37N and 37O . 
     The electrodes of transducers described herein (pixelated or not) can, in some examples, correspond to the full area of the side of the piezoelectric material on which it is disposed (e.g., to maximize the active area of the transducer). In some examples, the electrodes can correspond to less than the full area of the side of the piezoelectric material. The electrodes of the pixelated transducers can be patterned using photolithography or dicing, for example. The upper electrodes and lower electrodes can have same or different dimensions or pitch, for example. In some examples, electrodes on the same layer (e.g., the upper electrode layer or the lower electrode layer) can have varying dimensions and/or different sized gaps between each other. Likewise, the gaps between adjacent upper electrodes and the gaps between adjacent lower electrodes can have different sizes. The dimensions and pitch of the electrodes can be tuned to meet the requirements of spatial differential receiving for touch and/or force. 
     Additionally, it should be understood that although a wraparound using an insulating material is illustrated in many of the above examples, (e.g.,  FIGS. 37B, 37D, 37F , etc.), in some examples, electrodes can be brought from one side of the transducer to another side by a via through the insulating material. 
     Although the pixelated electrodes (and wraparounds) in the above illustrations have a generally rectangular shape, the pixelated electrode (and wraparounds) are not limited to this shape.  FIGS. 37P and 37Q  illustrate pixelated transducers with different shaped electrodes according to examples of the disclosure. Pixelated transducer  3700 P of  FIG. 37P  can correspond to the pixelated transducer of  FIG. 37A , for example, however, implemented with different shaped electrodes. For example, upper electrodes  3782  can be partially rectangular like upper electrodes  3704  in  FIG. 37A , but unlike upper electrodes  3704 , upper electrodes  3782  taper and narrow to make space for a wrapped around portion of lower electrode  3784 . Lower electrode  3784  can similarly be partially rectangular and also taper before wrapping around. Adjacent upper electrodes  3782  can be separated from one another by  3770 A. Adjacent lower electrodes  3784  can be separated from one another by  3770 A. Upper electrodes  3782  and corresponding lower electrodes  3784  can be separated from each other by gaps  3770 B. Pixelated transducer  3700 Q of  FIG. 37Q  can correspond to the pixelated transducer of  FIG. 37A , for example, however, implemented with different shaped electrodes. For example, upper electrodes  3786  can be partially rectangular like upper electrodes  3704  in  FIG. 37A , but unlike upper electrodes  3704 , upper electrodes  3782  can narrow to make space for a wrapped around portion of lower electrode  3788 . Lower electrode  3788  can similarly be partially rectangular and also can narrow before wrapping around. Adjacent upper electrodes  3786  can be separated from one another by  3770 A. Adjacent lower electrodes  3788  can be separated from one another by  3770 A. Upper electrodes  3786  and corresponding lower electrodes  3786  can be separated from each other by gaps  3770 B. 
     It should be understood the pixelated transducers  3700 A-Q are exemplary and other configurations are possible. 
     It should further be understood that different pixel groupings, electrode pitches, and spatial frequencies (and frequency ratios) than the examples explicitly described throughout the disclosure above can be used without departing from the scope of the present disclosure. 
     In some exemplary configurations such as general differential receiving, without spatial differential receiving, a transducer can be implemented without pixelated electrodes. For example,  FIG. 3C  illustrates a transducer without pixelated electrodes according to examples of the disclosure. Transducer  314  can include a piezoelectric material  336  with a first electrode  332  on a first side of piezoelectric material  336  (e.g., top side) and a second electrode  334  on a second side of piezoelectric material  336  (e.g., bottom side). The first electrode  332  and second electrode  334  can be stimulated (e.g., differentially) to transmit ultrasonic waves and can be sensed to receive ultrasonic waves for touch and/or force sensing as described herein. In contrast, spatial differential sensing can require at least pixelated electrodes on at least one side of the transducer. In particular, spatial differential sensing can allow for different receiving configurations (e.g., sensing different pixelated electrode or electrode groups) tuned to receive ultrasonic signal contributions tuned to touch reflections and or force reflections. Thus, the tuning of spatial differential receiving can allow for differentiating of touch and force reflections when overlapping with one another and/or improve detection of touch and/or force reflections even when the touch and force reflections do not overlap. 
     Therefore, according to the above, some examples of the disclosure are directed to an acoustic touch sensing system, comprising: a transducer; a differential electrode configuration coupled to the transducer; and an amplifier coupled to at least one electrode of the differential electrode configuration, wherein the differential electrode configuration is configured to reject a spatial common mode signal. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the differential electrode configuration is configured with an alternating pattern of electrodes. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the alternating pattern of electrodes has a pitch corresponding to a first spatial frequency. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the switching circuitry is further configured to: group two or more electrodes of the differential electrode configuration in a first grouping configuration having a first pitch; and group two or more electrodes of the differential electrode configuration in a second grouping configuration having a second pitch, different from the first pitch. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the switching circuitry is further configured to: group four or more electrodes of the differential electrode configuration in a first grouping configuration having a first pitch and a first spatial phase; and group the four or more electrodes of the differential electrode configuration in a second grouping configuration having the first pitch and a second spatial phase, different from the first spatial phase. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the switching circuitry is further configured to: group the four or more electrodes of the differential electrode configuration in a third grouping configuration having a second pitch, different from the first pitch. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first pitch corresponds to a first spatial frequency, and the second pitch corresponds to a second spatial frequency, different from the first spatial frequency. 
     Some examples of the disclosure are directed to a method comprising: transmitting an acoustic wave from a transducer; receiving a reflected acoustic wave at two electrodes arranged in a differential configuration; and compensating for a spatial common mode signal using the received signal from the differential electrode configuration. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the differential electrode configuration is configured with an alternating pattern of electrodes. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the alternating pattern of electrodes has a pitch corresponding to a first spatial frequency. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the method further comprises: grouping two or more electrodes of the differential electrode configuration in a first grouping configuration having a first pitch; and grouping two or more electrodes of the differential electrode configuration in a second grouping configuration having a second pitch, different from the first pitch. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the method further comprises: grouping four or more electrodes of the differential electrode configuration in a first grouping configuration having a first pitch and a first spatial phase; and grouping four or more electrodes of the differential electrode configuration in a second grouping configuration having the first pitch and a second spatial phase, different from the first spatial phase. 
     Some examples of the disclosure are directed to a non-transitory computer-readable storage medium having stored therein instructions, which when executed by a processor cause the processor to perform a method comprising: transmitting an acoustic wave from a transducer; receiving a reflected acoustic wave at two electrodes arranged in a differential configuration; and compensating for a spatial common mode signal using the received signal from the differential electrode configuration. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the differential electrode configuration is configured with an alternating pattern of electrodes. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the alternating pattern of electrodes has a pitch corresponding to a first spatial frequency. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the method further comprises: grouping two or more electrodes of the differential electrode configuration in a first grouping configuration having a first pitch; and grouping two or more electrodes of the differential electrode configuration in a second grouping configuration having a second pitch, different from the first pitch. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the method further comprises: grouping four or more electrodes of the differential electrode configuration in a first grouping configuration having a first pitch and a first spatial phase; and grouping four or more electrodes of the differential electrode configuration in a second grouping configuration having the first pitch and a second spatial phase, different from the first spatial phase. 
     Some examples of the disclosure are directed to An acoustic touch sensing system, comprising: a transducer, a differential electrode configuration coupled to the transducer; switching circuitry configured to: couple the differential electrode configuration to drive circuitry configured to drive the transducer to produce an acoustic wave during a drive phase; and couple the differential electrode configuration to sense circuitry configured to receive electrical signals from the transducer during a sensing phase; and an amplifier coupled to at least two electrode of the differential electrode configuration, wherein the differential electrode configuration is configured to reject a spatial common mode signal. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the acoustic touch sensing system further comprises: a first electrode and a second electrode are disposed on a first side of the transducer; and a third electrode is disposed on the second side of the transducer; wherein: the first electrode are coupled together during the drive mode; and the first electrode and the second electrode are coupled differentially to the sense circuitry during the sensing mode. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the third electrode is grounded during the sensing mode and the third electrode is differentially driven with the coupled first and second electrode in the driving mode. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the third electrode is floating during the sensing mode and the third electrode is differentially driven with the coupled first and second electrode in the driving mode. 
     Some examples of the disclosure are directed to a method comprising: coupling a differential electrode configuration to drive circuitry configured to drive a transducer to produce an acoustic wave during a drive phase and coupling the differential electrode configuration to sense circuitry configured to receive electrical signals from the transducer during a sensing phase, wherein the differential electrode configuration is coupled to the transducer and configured to reject a spatial common mode signal from a received acoustic wave. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the sensing phase comprises a touch sensing phase and a force sensing phase. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the touch sensing phase comprises an in-phase touch sensing phase and a quadrature touch sensing phase, wherein coupling the differential electrode configuration to the sense circuitry during the in-phase touch sensing phase comprises coupling the differential electrode configuration to the sense circuitry in a first electrode grouping and coupling the differential electrode configuration to the sense circuitry during the quadrature touch sensing phase comprises coupling the differential electrode configuration to the sense circuitry in a second electrode grouping, different from the first electrode grouping. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the sensing phase comprises concurrently capturing an in-phase touch measurement, a quadrature touch measurement, and a force measurement. Additionally or alternatively to one or more of the examples disclosed above, in some examples, concurrently capturing comprises, concurrently receiving at least four signals from at least four of the differential electrodes at four sensing circuits and concurrently combining the at least four differential signals in different combinations to produce the in-phase touch measurement, quadrature touch measurement, and force measurement. 
     Some examples of the disclosure are directed to a non-transitory computer-readable storage medium having stored therein instructions, which when executed by a processor cause the processor to perform a method comprising: coupling a differential electrode configuration to drive circuitry configured to drive a transducer to produce an acoustic wave during a drive phase and coupling the differential electrode configuration to sense circuitry configured to receive electrical signals from the transducer during a sensing phase, wherein the differential electrode configuration is coupled to the transducer and configured to reject a spatial common mode signal from a received acoustic wave. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the sensing phase comprises a touch sensing phase and a force sensing phase. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the touch sensing phase comprises an in-phase touch sensing phase and a quadrature touch sensing phase, wherein coupling the differential electrode configuration to the sense circuitry during the in-phase touch sensing phase comprises coupling the differential electrode configuration to the sense circuitry in a first electrode grouping and coupling the differential electrode configuration to the sense circuitry during the quadrature touch sensing phase comprises coupling the differential electrode configuration to the sense circuitry in a second electrode grouping, different from the first electrode grouping. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the sensing phase comprises concurrently capturing an in-phase touch measurement, a quadrature touch measurement, and a force measurement. Additionally or alternatively to one or more of the examples disclosed above, in some examples, concurrently capturing comprises, concurrently receiving at least four signals from at least four of the differential electrodes at four sensing circuits and concurrently combining the at least four differential signals in different combinations to produce the in-phase touch measurement, quadrature touch measurement, and force measurement. 
     Although examples of this disclosure have been fully described with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications are to be understood as being included within the scope of examples of this disclosure as defined by the appended claims.

Metadata:
Filing Date: 20180524
Publication Date: 20211012
Grant Date: 20211012
Priority Date: 20170524
Inventors: YOUSEFPOR, MARDUKE
YEKE YAZDANDOOST, MOHAMMAD
TUCKER, AARON SCOTT
YIP, Marcus
KHAJEH, EHSAN
KING, BRIAN MICHAEL
GOZZINI, GIOVANNI
Assignee: APPLE INC
CPC Classifications: [{"code": "G06F3/043", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F2203/04106", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/04166", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/0436", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/04166", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/0436", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F2203/04105", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F2203/04106", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F2203/04105", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/0436", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F2203/04105", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F2203/04106", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/043", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/04166", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 64401285