PATENT DOCUMENT

Publication Number: US-11086463-B2
Application Number: US-201816134651-A
Country: US
Kind Code: B2

Title: Multi modal touch controller

Abstract:
A multi-modal touch controller configured to operate in different modes. In some examples, the multi-modal touch controller can be operated in a first mode corresponding to a guarded self-capacitance scan. In some examples, the multi-modal touch controller can be operated in a second mode corresponding to offset-compensated mutual capacitance scan. In some examples, the multi-modal controller can be operated in a third mode corresponding to a mutual and self-capacitance scan. The multi-modal touch controller can advantageously allow one touch sensing chipset to be used across different types of guarded touch sensor panels and across different modes of operation.

Claims:
The invention claimed is: 
     
       1. A touch sensing system comprising:
 a first chip operating in a first power domain referenced to a first voltage, the first chip configured to generate and output a first signal in a first mode and a second signal in a second mode, the first signal different than the second signal and the second signal different from the first voltage, wherein the first chip is configured to output the first signal without outputting the second signal in the first mode and configured to output the second signal without outputting the first signal in the second mode; and 
 a second chip configurable to operate in a second power domain referenced to the first signal in the first mode and to operate in the first power domain referenced to the first voltage in the second mode, the second chip including touch sensing circuitry configured to sense touch at one or more touch nodes of a touch sensor panel. 
 
     
     
       2. The touch sensing system of  claim 1 , wherein the first mode is a self-capacitance mode and the second mode is a mutual capacitance mode. 
     
     
       3. The touch sensing system of  claim 1 , wherein the first voltage is a ground voltage of the touch sensing system. 
     
     
       4. The touch sensing system of  claim 1 , wherein the first signal is a guard voltage. 
     
     
       5. The touch sensing system of  claim 1 , wherein the second signal is an offset voltage. 
     
     
       6. The touch sensing system of  claim 1 , further comprising:
 a guard plane associated with the touch sensor panel, the guard plane configured to be driven by the first signal in the first mode and to be driven by the second signal in the second mode. 
 
     
     
       7. The touch sensing system of  claim 1 , wherein the first chip is configured to generate a third signal based on the first signal and the second signal in a third mode;
 wherein the second chip is configurable to operate in the second power domain referenced to the first signal in the third mode. 
 
     
     
       8. The touch sensing system of  claim 7 , wherein the third mode is a mutual capacitance and self-capacitance mode, wherein the touch sensing circuitry comprises first sense amplifiers configured sense touch at one or more first touch nodes of the touch sensor panel in a mutual capacitance configuration and second sense amplifiers configured to sense touch at one or more second touch nodes of the touch sensor panel in a self-capacitance configuration. 
     
     
       9. The touch sensing system of  claim 8 , wherein the touch sensor panel includes row electrodes and column electrodes forming the first touch nodes of the touch sensor panel and wherein the touch sensor panel includes an array of touch node electrodes forming the second touch nodes of the touch sensor panel. 
     
     
       10. The touch sensing system of  claim 7 , further comprising:
 a guard plane associated with the touch sensor panel, wherein the guard plane is configured to be driven by the third signal in the third mode. 
 
     
     
       11. The touch sensing system of  claim 1 , wherein the first chip and the second chip are formed on one integrated circuit, wherein the second chip is isolated in a deep well from the first chip. 
     
     
       12. A method of touch sensing in a touch sensing system including a multi-modal touch controller comprising a first chip operating in a first power domain referenced to a first voltage and a second chip, the method comprising:
 determining a touch sensing mode; 
 in accordance with a determination that the touch sensing mode is a first mode, generating and outputting a first signal from the first chip without outputting a second signal and operating the second chip in a second power domain referenced to the first signal generated in the first chip; and 
 in accordance with a determination that the touch sensing mode is a second mode, generating and outputting the second signal from the first chip without outputting the first signal and operating the second chip in the first power domain referenced to the first voltage; 
 wherein the first signal is different than the second signal and the second signal different from the first voltage. 
 
     
     
       13. The method of  claim 12 , wherein the first mode is a self-capacitance mode and the second mode is a mutual capacitance mode. 
     
     
       14. The method of  claim 12 , wherein the first voltage is a ground voltage of the touch sensing system. 
     
     
       15. The method of  claim 12 , wherein the first signal is a guard voltage. 
     
     
       16. The method of  claim 12 , wherein the second signal is an offset voltage. 
     
     
       17. The method of  claim 12 , further comprising:
 in accordance with a determination that the touch sensing mode is the first mode, driving a guard plane of the touch sensing system with the first signal; and 
 in accordance with a determination that the touch sensing mode is the second mode, driving the guard plane of the touch sensing system with the second signal. 
 
     
     
       18. The method of  claim 12 , further comprising:
 in accordance with a determination that the touch sensing mode is a third mode, operating the second chip in the second power domain referenced to the first signal. 
 
     
     
       19. The method of  claim 18 , further comprising:
 in accordance with a determination that the touch sensing mode is a third mode, generating a third signal in the first chip, wherein the third signal is a superposition of the first signal and a second signal generated in the first chip. 
 
     
     
       20. The method of  claim 19 , further comprising:
 in accordance with a determination that the touch sensing mode is the third mode, driving a guard plane of the touch sensing system with the third signal. 
 
     
     
       21. The method of  claim 18 , wherein the third mode is a mutual capacitance and self-capacitance mode. 
     
     
       22. The method of  claim 21 , further comprising:
 in accordance with a determination that the touch sensing mode is the third mode:
 sensing a first portion of a touch sensor panel of the touch sensing system in a mutual capacitance configuration to measure touch at one or more first touch nodes of the touch sensor panel; and 
 sensing a second portion of the touch sensor panel of the touch sensing system in a self-capacitance configuration to measure touch at one or more second touch nodes of the touch sensor panel. 
 
 
     
     
       23. The method of  claim 22 , wherein the sensing of the first portion of the touch sensor panel and the sensing of the second portion of the touch sensor panel occur at least partially concurrently. 
     
     
       24. A non-transitory computer readable storage medium storing instructions, which when executed by one or more processors of a touch sensing system including a multi-modal touch controller comprising a first chip operating in a first power domain referenced to a first voltage and a second chip, cause the one or more processors to perform a method comprising:
 determining a touch sensing mode; 
 in accordance with a determination that the touch sensing mode is a first mode, generating and outputting a first signal from the first chip without outputting a second signal and operating the second chip in a second power domain referenced to the first signal generated in the first chip; and 
 in accordance with a determination that the touch sensing mode is a second mode, generating and outputting the second signal from the first chip without outputting the first signal and operating the second chip in the first power domain referenced to the first voltage; 
 wherein the first signal is different than the second signal and the second signal different from the first voltage. 
 
     
     
       25. The non-transitory computer readable storage medium of  claim 24 , further comprising:
 in accordance with a determination that the touch sensing mode is the first mode, driving a guard plane of the touch sensing system with the first signal; and 
 in accordance with a determination that the touch sensing mode is the second mode, driving the guard plane of the touch sensing system with the second signal.

Description:
CROSS REFERENCE FOR RELATED APPLICATION 
     This application claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional Patent Application No. 62/566,210, filed Sep. 29, 2017 the contents of which are incorporated herein by reference in their entirety for all purposes. 
    
    
     FIELD OF THE DISCLOSURE 
     This relates generally to touch sensing, and more particularly to touch sensing with a multi-modal touch controller. 
     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 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), light emitting diode (LED) display or organic light emitting diode (OLED) display 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 touch sensor panels can be formed by a matrix of partially or fully transparent or non-transparent conductive plates (e.g., touch electrodes) made of materials such as Indium Tin Oxide (ITO). In some examples, the conductive plates can be formed from other materials including conductive polymers, metal mesh, graphene, nanowires (e.g., silver nanowires) or nanotubes (e.g., carbon nanotubes). It is due in part to their substantial transparency that some capacitive touch sensor panels can be overlaid on a display to form a touch screen, as described above. Some touch screens can be formed by at least partially integrating touch sensing circuitry into a display pixel stackup (i.e., the stacked material layers forming the display pixels). 
     In some cases, parasitic or stray capacitances can exist between the touch electrodes used for sensing touch on the touch sensor panels, and other components of the devices in which the touch sensor panels are included, which can be referenced to a chassis or earth ground. These parasitic or stray capacitances can introduce errors and/or offsets into the touch outputs of the touch sensor panels. Therefore, it can be beneficial to reduce or eliminate such parasitic or stray capacitances. 
     SUMMARY OF THE DISCLOSURE 
     This relates to a multi-modal touch controller configured to operate in different modes. In some examples, the multi-modal touch controller can be operated in a first mode corresponding to a guarded self-capacitance scan. In some examples, the multi-modal touch controller can be operated in a second mode corresponding to offset-compensated mutual capacitance scan. In some examples, the multi-modal controller can be operated in a third mode corresponding to a mutual and self-capacitance scan. The multi-modal touch controller can advantageously allow one touch sensing chipset to be used across different types of guarded touch sensor panels and across different modes of operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1D  illustrate an example mobile telephone, an example media player, an example personal computer and an example tablet computer that can each include an exemplary touch screen according to examples of the disclosure. 
         FIG. 2  is a block diagram of an example computing system that illustrates one implementation of an example self-capacitance touch screen according to examples of the disclosure. 
         FIG. 3A  illustrates an exemplary touch sensor circuit corresponding to a self-capacitance sensing electrode and sensing circuit according to examples of the disclosure. 
         FIG. 3B  illustrates an exemplary touch sensor circuit corresponding to a mutual-capacitance drive and sense line and sensing circuit according to examples of the disclosure. 
         FIG. 4A  illustrates a touch screen with sensing electrodes arranged in rows and columns according to examples of the disclosure. 
         FIG. 4B  illustrates a touch screen with sensing electrodes arranged in a pixelated sensing electrode configuration according to examples of the disclosure. 
         FIGS. 5A-5B  illustrate an exemplary touch sensor panel configuration in which the touch sensing circuitry of the touch sensor panel is included in an electronic chip (e.g., an integrated circuit, etc.) that is referenced to earth or chassis ground according to examples of the disclosure. 
         FIG. 6A  illustrates an exemplary touch sensor panel configuration including various capacitances associated with exemplary touch sensor panel configuration according to examples of the disclosure. 
         FIG. 6B  illustrates an exemplary equivalent circuit diagram of an exemplary touch sensor panel configuration according to examples of the disclosure. 
         FIG. 7A  illustrates an exemplary block diagram of a touch and/or proximity detection system according to examples of the disclosure. 
         FIG. 7B  illustrates an exemplary multi-modal touch controller configuration according to examples of the disclosure. 
         FIG. 8A  illustrates an exemplary scan plan and corresponding configurations for the multi-modal touch controller according to examples of the disclosure. 
         FIG. 8B  describes a process of touch sensing using a multi-modal touch controller according to examples of the disclosure. 
         FIG. 8C  illustrates an exemplary scan plan and corresponding configurations for the multi-modal touch controller according to examples of the disclosure. 
         FIG. 8D  illustrates process of touch sensing using a multi-modal touch controller in a third mode according to examples of the disclosure. 
         FIG. 9A  illustrates an exemplary guard voltage waveform according to examples of the disclosure. 
         FIG. 9B  illustrates an exemplary stimulation voltage waveform according to examples of the disclosure. 
         FIG. 9C  illustrates an exemplary stimulation voltage waveform according to examples of the disclosure. 
         FIG. 10A  illustrates an exemplary voltage generation circuit for a multi-modal touch controller according to examples of the disclosure. 
         FIG. 10B  illustrates an exemplary touch sensor panel configuration using guard voltage referenced touch sensing circuitry according to examples of the disclosure. 
         FIGS. 11A-11B  illustrate exemplary touch sensor panels including a row and column electrode area and a touch node electrode area according to examples of the disclosure. 
         FIG. 12  illustrates an exemplary configuration including multiple guard planes for a touch sensor panel and multiple applied voltages according to examples of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description of 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 disclosed examples. 
     This relates to a multi-modal touch controller configured to operate in different modes. In some examples, the multi-modal touch controller can be operated in a first mode corresponding to a guarded self-capacitance scan. In some examples, the multi-modal touch controller can be operated in a second mode corresponding to offset-compensated mutual capacitance scan. In some examples, the multi-modal controller can be operated in a third mode corresponding to a mutual and self-capacitance scan. The multi-modal touch controller can advantageously allow one touch sensing chipset to be used across different types of guarded touch sensor panels and across different modes of operation. 
       FIGS. 1A-1D  illustrate example systems in which a touch screen according to examples of the disclosure may be implemented.  FIG. 1A  illustrates an example mobile telephone  136  that includes a touch screen  124 .  FIG. 1B  illustrates an example digital media player  140  that includes a touch screen  126 .  FIG. 1C  illustrates an example personal computer  144  that includes a touch screen  128 .  FIG. 1D  illustrates an example tablet computer  148  that includes a touch screen  130 . It is understood that the above touch screens can be implemented in other devices as well, including in wearable devices. Additionally it should be understood that the disclosure herein is not limited to touch screens, but applies as well to touch sensor panels without a corresponding display. 
     In some examples, touch screens  124 ,  126 ,  128  and  130  can be based on self-capacitance. A self-capacitance based touch system can include a matrix of small, individual plates of conductive material that can be referred to as touch node electrodes (as described below with reference to touch screen  220  in  FIG. 2  and with reference to touch screen  402  in  FIG. 4B ). For example, a touch screen can include a plurality of individual touch node electrodes, each touch node electrode identifying or representing a unique location on the touch screen at which touch or proximity (i.e., a touch or proximity event) is to be sensed, and each touch node electrode being electrically isolated from the other touch node electrodes in the touch screen/panel. Such a touch screen can be referred to as a pixelated self-capacitance touch screen, though it is understood that in some examples, the touch node electrodes on the touch screen can be used to perform scans other than self-capacitance scans on the touch screen (e.g., mutual capacitance scans). During operation, a touch node electrode can be stimulated with an AC waveform, and the self-capacitance to ground of the touch node electrode can be measured. As an object approaches the touch node electrode, the self-capacitance to ground of the touch node electrode can change (e.g., increase). This change in the self-capacitance of the touch node electrode can be detected and measured by the touch sensing system to determine the positions of multiple objects when they touch, or come in proximity to, the touch screen. In some examples, the electrodes of a self-capacitance based touch system can be formed from rows and columns of conductive material (as described below with reference to touch screen  400  in  FIG. 4A ), and changes in the self-capacitance to ground of the rows and columns can be detected, similar to above. In some examples, a touch screen can be multi-touch, single touch, projection scan, full-imaging multi-touch, capacitive touch, etc. 
     In some examples, touch screens  124 ,  126 ,  128  and  130  can be based on mutual capacitance. A mutual capacitance based touch system can include drive and sense lines that may cross over each other on different layers, or may be adjacent to each other on the same layer. The crossing or adjacent locations can form touch nodes. During operation, the drive line can be stimulated with an AC waveform and the mutual capacitance of the touch node can be measured. As an object approaches the touch node, the mutual capacitance of the touch node can change (e.g., decrease). This change in the mutual capacitance of the touch node can be detected and measured by the touch sensing system to determine the positions of multiple objects when they touch, or come in proximity to, the touch screen. In some examples, the electrodes of a mutual-capacitance based touch system can be formed from a matrix of small, individual plates of conductive material, and changes in the mutual capacitance between plates of conductive material can be detected, similar to above. 
     In some examples, touch screens  124 ,  126 ,  128  and  130  can be based on mutual capacitance and/or self-capacitance. The electrodes can be arrange as a matrix of small, individual plates of conductive material (e.g., as in touch screen  402  in  FIG. 4B ) or as drive lines and sense lines (e.g., as in touch screen  400  in  FIG. 4B ), or in another pattern. The electrodes can be configurable for mutual capacitance or self-capacitance sensing or a combination of mutual and self-capacitance sensing. For example, in one mode of operation electrodes can be configured to sense mutual capacitance between electrodes and in a different mode of operation electrodes can be configured to sense self-capacitance of electrodes. In some examples, some of the electrodes can be configured to sense mutual capacitance therebetween and some of the electrodes can be configured to sense self-capacitance thereof. 
       FIG. 2  is a block diagram of an example computing system  200  that illustrates one implementation of an example self-capacitance touch screen  220  according to examples of the disclosure. It is understood that computing system  200  can instead include a mutual capacitance touch screen, as described above, though the examples of the disclosure will be described assuming a self-capacitance touch screen is provided. Computing system  200  can be included in, for example, mobile telephone  136 , digital media player  140 , personal computer  144 , tablet computer  148 , or any mobile or non-mobile computing device that includes a touch screen, including a wearable device. Computing system  200  can include a touch sensing system including one or more touch processors  202 , peripherals  204 , a touch controller  206 , and touch sensing circuitry (described in more detail below). Peripherals  204  can include, but are not limited to, random access memory (RAM) or other types of memory or storage, watchdog timers and the like. Touch controller  206  can include, but is not limited to, one or more sense channels  208  and channel scan logic  210 . Channel scan logic  210  can access RAM  212 , autonomously read data from sense channels  208  and provide control for the sense channels. In addition, channel scan logic  210  can control sense channels  208  to generate stimulation signals at various frequencies and phases that can be selectively applied to the touch nodes of touch screen  220 , as described in more detail below. In some examples, touch controller  206 , touch processor  202  and peripherals  204  can be integrated into a single application specific integrated circuit (ASIC), and in some examples can be integrated with touch screen  220  itself. As described in more detail below, in some examples the sense channel and/or other components of touch controller  206  and touch processor  202  can be implemented across multiple power domains. Additionally, as described in more detail below, in some examples a multi-modal touch controller can be configurable to operate with different types of touch sensor panels (e.g., row/column and pixelated) and for different touch sensing modes (e.g., mutual and/or self-capacitance). 
     Touch screen  220  can be used to derive touch information at multiple discrete locations of the touch screen, referred to herein as touch nodes. For example, touch screen  220  can include touch sensing circuitry that can include a capacitive sensing medium having a plurality of electrically isolated touch node electrodes  222  (e.g., a pixelated self-capacitance touch screen). Touch node electrodes  222  can be coupled to sense channels  208  in touch controller  206 , can be driven by stimulation signals from the sense channels through drive/sense interface  225 , and can be sensed by the sense channels through the drive/sense interface as well, as described above. As used herein, an electrical component “coupled to” or “connected to” another electrical component encompasses a direct or indirect connection providing electrical path for communication or operation between the coupled components. Thus, for example, touch node electrodes  222  may be directly connected to sense channels or indirectly connected to sense channels via drive/sense interface  225 , but in either case provided an electrical path for driving and/or sensing the touch node electrodes  222 . Labeling the conductive plates used to detect touch (i.e., touch node electrodes  222 ) as “touch node” electrodes can be particularly useful when touch screen  220  is viewed as capturing an “image” of touch (e.g., a “touch image”). In other words, after touch controller  206  has determined an amount of touch detected at each touch node electrode  222  in touch screen  220 , the pattern of touch node electrodes in the touch screen at which a touch occurred can be thought of as a touch image (e.g., a pattern of fingers touching the touch screen). In such examples, each touch node electrode in a pixelated self-capacitance touch screen can be sensed for the corresponding touch node represented in the touch image. 
     Computing system  200  can also include a host processor  228  for receiving outputs from touch processor  202  and performing actions based on the outputs. For example, host processor  228  can be connected to program storage  232  and a display controller, such as an LCD driver  234  (or an LED display or OLED display driver). The LCD driver  234  can provide voltages on select (e.g., gate) lines to each pixel transistor and can provide data signals along data lines to these same transistors to control the pixel display image as described in more detail below. Host processor  228  can use LCD driver  234  to generate a display image on touch screen  220 , such as a display image of a user interface (UI), and can use touch processor  202  and touch controller  206  to detect a touch on or near touch screen  220 . The touch input can be used by computer programs stored in program storage  232  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  228  can also perform additional functions that may not be related to touch processing. 
     Note that one or more of the functions described herein, including the configuration of switches, can be performed by firmware stored in memory (e.g., one of the peripherals  204  in  FIG. 2 ) and executed by touch processor  202 , or stored in program storage  232  and executed by host processor  228 . 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 signals) that can contain or store the program for use by or in connection with the instruction execution system, apparatus, or device. The computer-readable storage medium 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 medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic or infrared wired or wireless propagation medium. 
       FIG. 3A  illustrates an exemplary touch sensor circuit  300  corresponding to a self-capacitance touch node electrode  302  and sensing circuit  314  according to examples of the disclosure. Touch node electrode  302  can correspond to touch node electrode  222 . Touch node electrode  302  can have an inherent self-capacitance to ground associated with it, and also an additional self-capacitance to ground that is formed when an object, such as finger  305 , is in proximity to or touching the electrode. The total self-capacitance to ground of touch node electrode  302  can be illustrated as capacitance  304 . Touch node electrode  302  can be coupled to sensing circuit  314 . Sensing circuit  314  can include an operational amplifier  308 , feedback resistor  312  and feedback capacitor  310 , although other configurations can be employed. For example, feedback resistor  312  can be replaced by a switched capacitor resistor in order to minimize a parasitic capacitance effect that can be caused by a variable feedback resistor. Touch node electrode  302  can be coupled to the inverting input (−) of operational amplifier  308 . An AC voltage source  306  (Vac) can be coupled to the non-inverting input (+) of operational amplifier  308 . Touch sensor circuit  300  can be configured to sense changes in the total self-capacitance  304  of the touch node electrode  302  induced by a finger or object either touching or in proximity to the touch sensor panel. Output  320  can be used by a processor to determine the presence of a proximity or touch event, or the output can be inputted into a discrete logic network to determine the presence of a proximity or touch event. 
       FIG. 3B  illustrates an exemplary touch sensor circuit  350  corresponding to a mutual-capacitance drive line  322  and sense line  326  and sensing circuit  314  according to examples of the disclosure. Drive line  322  can be stimulated by stimulation signal  306  (e.g., an AC voltage signal). Stimulation signal  306  can be capacitively coupled to sense line  326  through mutual capacitance  324  between drive line  322  and the sense line. When a finger or object  305  approaches the touch node created by the intersection of drive line  322  and sense line  326 , mutual capacitance  324  can be altered. This change in mutual capacitance  324  can be detected to indicate a touch or proximity event at the touch node, as described previously and below. The sense signal coupled onto sense line  326  can be received by sensing circuit  314 . Sensing circuit  314  can include operational amplifier  308  and at least one of a feedback resistor  312  and a feedback capacitor  310 .  FIG. 3B  illustrates a general case in which both resistive and capacitive feedback elements are utilized. The sense signal (referred to as Vin) can be inputted into the inverting input of operational amplifier  308 , and the non-inverting input of the operational amplifier can be coupled to a reference voltage Vref. Operational amplifier  308  can drive its output to voltage Vo to keep Vin substantially equal to Vref, and can therefore maintain Vin constant or virtually grounded. A person of skill in the art would understand that in this context, equal can include deviations of up to 15%. Therefore, the gain of sensing circuit  314  can be mostly a function of the ratio of mutual capacitance  324  and the feedback impedance, comprised of resistor  312  and/or capacitor  310 . The output of sensing circuit  314  Vo can be filtered and heterodyned or homodyned by being fed into multiplier  328 , where Vo can be multiplied with local oscillator  330  to produce Vdetect. Vdetect can be inputted into filter  332 . One skilled in the art will recognize that the placement of filter  332  can be varied; thus, the filter can be placed after multiplier  328 , as illustrated, or two filters can be employed: one before the multiplier and one after the multiplier. In some examples, there can be no filter at all. The direct current (DC) portion of Vdetect can be used to determine if a touch or proximity event has occurred. 
     Referring back to  FIG. 2 , in some examples, touch screen  220  can be an integrated touch screen in which touch sensing circuit elements of the touch sensing system can be integrated into the display pixel stackups of a display. The circuit elements in touch screen  220  can include, for example, elements that can exist in LCD or other displays (LED display, OLED display, etc.), such as one or more pixel transistors (e.g., thin film transistors (TFTs)), gate lines, data lines, pixel electrodes and common electrodes. In a given display pixel, a voltage between a pixel electrode and a common electrode can control a luminance of the display pixel. The voltage on the pixel electrode can be supplied by a data line through a pixel transistor, which can be controlled by a gate line. It is noted that circuit elements are not limited to whole circuit components, such as a whole capacitor, a whole transistor, etc., but can include portions of circuitry, such as only one of the two plates of a parallel plate capacitor. 
       FIG. 4A  illustrates touch screen  400  with touch electrodes  404  and  406  arranged in rows and columns according to examples of the disclosure. Specifically, touch screen  400  can include a plurality of touch electrodes  404  disposed as rows, and a plurality of touch electrodes  406  disposed as columns. Touch electrodes  404  and touch electrodes  406  can be on the same or different material layers on touch screen  400 , and can intersect with each other, as illustrated in  FIG. 4A . In some examples, touch screen  400  can sense the self-capacitance of touch electrodes  404  and  406  to detect touch and/or proximity activity on touch screen  400 , and in some examples, touch screen  400  can sense the mutual capacitance between touch electrodes  404  and  406  to detect touch and/or proximity activity on touch screen  400 . 
       FIG. 4B  illustrates touch screen  402  with touch node electrodes  408  arranged in a pixelated touch node electrode configuration according to examples of the disclosure. Specifically, touch screen  402  can include a plurality of individual touch node electrodes  408 , each touch node electrode identifying or representing a unique location on the touch screen at which touch or proximity (i.e., a touch or proximity event) is to be sensed, and each touch node electrode being electrically isolated from the other touch node electrodes in the touch screen/panel, as previously described. Touch node electrodes  408  can be on the same or different material layers on touch screen  400 . In some examples, touch screen  400  can sense the self-capacitance of touch node electrodes  408  to detect touch and/or proximity activity on touch screen  400 , and in some examples, touch screen  400  can sense the mutual capacitance between touch node electrodes  408  to detect touch and/or proximity activity on touch screen  400 . 
     In some examples, the touch sensing circuitry of a touch screen or touch sensor panel (e.g., touch sensing circuitry as described with reference to  FIGS. 2 and 3A-3B ) can be fabricated in an electronic chip (e.g., an integrated circuit, etc.), and the electronic chip and/or the circuitry included in the electronic chip can operate with respect to a reference voltage provided by the chassis of the electronic device (“chassis ground”) in which the touch screen or touch sensor panel is included (e.g., devices  136 ,  140 ,  144  and  148  in  FIGS. 1A-1D ). In some examples this chassis ground can be a grounding pathway from the chassis through a user operating the electronic device to earth ground. In some examples, this chassis ground can be the same as earth ground. However, in some examples, operating the electronic chip and/or the circuitry included in the electronic chip with respect to chassis or earth ground can result in undesirable touch sensing performance, as will be described in more detail below. 
       FIGS. 5A-5B  illustrate an exemplary touch sensor panel configuration  500  in which the touch sensing circuitry of the touch sensor panel is included in an electronic chip (e.g., an integrated circuit, etc.) that is referenced to earth or chassis ground according to examples of the disclosure. Specifically, in configuration  500  of  FIG. 5A , a touch sensor panel is included in a device (e.g., devices  136 ,  140 ,  144  and  148  in  FIGS. 1A-1D ) having device chassis  502 . Chassis  502  can be grounded to earth ground  506 , or can be grounded to a separate device ground (not illustrated). Chassis  502  can include electronic chip  504 , which can include touch sensing circuitry for sensing touch on the touch sensor panel included in the device of  FIG. 5A . For example, chip  504  can include touch controller  206  and/or touch processor  202  of  FIG. 2  and/or the touch sensing circuits of  FIGS. 3A-3B . Chip  504  and/or the touch sensing circuitry in chip  504  can be referenced to chassis  502  (e.g., referenced to earth ground  506 ). Chip  504  can be coupled, via one or more traces, to touch node electrode  508 , which can be a touch node electrode included in the touch sensor panel of the device of  FIG. 5A . Chip  504  can also be coupled to other touch node electrodes included in the touch sensor panel, though a single touch node electrode  508  is illustrated for ease of description. Chip  504  can measure the self-capacitance of touch node electrode  508  to detect proximity activity at touch node electrode  508 , as discussed with reference to  FIG. 3A . 
       FIG. 5B  illustrates various capacitances associated with proximity detection using touch sensor panel configuration  500  of  FIG. 5A  according to examples of the disclosure. Specifically, finger (or object)  510  can be in proximity to touch node electrode  508 . Finger  510  can be grounded to earth ground  506  through capacitance  512  (e.g., C body ), which can represent a capacitance from finger  510  through a user&#39;s body to earth ground  506 . Capacitance  514  (e.g., C touch ) can represent a capacitance between finger  510  and touch node electrode  508 , and can be the capacitance of interest in determining how close finger  510  is to touch node electrode  508 . Capacitance  514  can be measured by sense circuitry  522  (e.g., as described with reference to  FIG. 3A ) included in chip  504  to determine an amount of touch at touch node electrode  508 . However, because touch node electrode  508  can be included in chassis  502 , which can be grounded to earth ground  506 , parasitic or stray capacitances can exist between touch node electrode  508  and chassis  502  (represented by capacitance  516  (e.g., C p )) and/or between traces that connect touch node electrode  508  to sense circuitry  522  and chassis  502  (represented by capacitance  518  (e.g., C s )). These parasitic or stray capacitances  516  and  518  can also be measured by sense circuitry  522 , and can create an offset (e.g., from zero output signal) in the output signal of sense circuitry  522 , which can reduce the signal to noise ratio and/or the dynamic range of sense circuitry  522 . This, in turn, can reduce the range of touch-related capacitances (e.g., C touch    514 ) that sense circuitry  522  can detect, thus potentially limiting the touch sensing performance of the touch sensor panel in which touch node electrode  508  is included. 
     In order to reduce or eliminate parasitic or stray capacitances that may be measured by sense circuitry in a touch sensing chip of a touch sensor panel, a guard plane can be established between the touch-related components of the touch sensor panel (e.g., touch node electrode  508 , touch sensing chip  504 , etc.) and chassis  502 . The guard plane, including the touch sensing chip (e.g., integrated circuit, etc.), can be referenced to a guard potential that can mirror or be the same as the stimulation signal used to stimulate the touch node electrodes on the touch sensor panel. In this way, the voltages on both sides of the above-described parasitic or stray capacitances can mirror each other, causing those capacitances to fall out of the touch sensing measurements performed by the touch sensing circuitry in the touch sensing chip. As a result, the signal portion (out of sense amplifier  522 ) associated with the undesired stray capacitances can be largely reduced, therefore improving the touch dynamic range and the touch sensing performance of the touch sensor panel. It should be understood that “guard plane” need not refer to a planar element or electrode; rather, the guard planes of the disclosure can be implemented in any number of manners, including being non-planar, being composed of one or more portions of the device that are driven/maintained at a guard potential, and being implemented in different ways in different parts of the device (e.g., as part of a flex circuit in one portion of the device, as part of the touch sensor panel in another portion of the device, etc.). 
       FIG. 6A  illustrates an exemplary touch sensor panel configuration  600  including various capacitances associated with exemplary touch sensor panel configuration  600  according to examples of the disclosure. In the configuration of  FIG. 6A , the touch sensing circuitry of the touch sensor panel is included on an electronic chip (e.g., an integrated circuit, etc.) that is referenced to a guard ground rather than a chassis or earth ground. Specifically, in configuration  600  of  FIG. 6A , touch sensing circuitry in touch sensing chip  604  (also referred to herein as “touch controller”) can be coupled to touch node electrodes in a touch sensor panel by routing traces. As a representative example, touch node electrode  608  in  FIG. 6A  can be coupled to touch sensing circuitry  622  by routing trace  632 . The routing traces can be included on a flex circuit that couples touch sensing chip  604  to touch sensor panel. Touch sensing chip  604  can be disposed or fabricated on guard plane  620 , which can represent a virtual ground plane of touch sensing chip  604  that is different from chassis or earth ground  606 . In particular, stimulation source  626  (“guard source”) can be referenced to chassis or earth ground  606 , and can output a guard voltage (e.g., a guard stimulation signal, such as a square wave) that can establish the voltage at guard plane  620 . In this manner, the guard plane  620  can be referenced to the guard voltage, acting as a guard ground for touch sensing chip  604 . Stimulation source  626  can be included on a chip, separate from touch sensing chip  604 . Because touch sensing chip  604  can be built on guard plane  620 , the circuitry (e.g., touch sensing circuitry) included in touch sensing chip  604  can be referenced to the guard signal, and can be isolated from chassis or earth ground  606  by guard plane  620 . In other words, touch sensing chip  604  and the chip in which guard source  626  is included can operate in different “power domains”: touch sensing chip  604  can operate in the guard power domain, and guard source  626  can operate in the chassis or earth power domain. Guard plane  620  can be any conductive material on which touch sensing chip  604  can be disposed or fabricated (e.g., silver, copper, gold, etc.). For example, touch sensing chip  604  may be assembled on a flex circuit or printed circuit board (PCB), and may be referenced to the flex circuit or PCB ground layer  620  driven by guard source  626 . Guard source can be implemented, for example, using a waveform generator (e.g., generating arbitrary waveforms, such as a square wave, and can be referenced to earth ground  606 ) whose output can be inputted in to a digital-to-analog converter (DAC). Analog output from the DAC can be provided to a linear buffer (e.g., with unity or some other gain) whose output can correspond to the output of guard source  626 . 
     Additionally, a guard plane  624 A can be disposed between touch node electrode  608  and chassis  602  (or, more generally, earth ground  606 ), and guard plane  628 A can be disposed between routing traces that couple touch node electrode  608  to touch sensing chip  604  and chassis  602  (or, more generally, earth ground  606 ). Guard plane  624 A and guard plane  628 A can also be stimulated by the same guard voltage as is guard plane  620 . These guard planes  624 A and  628 A can similarly isolate touch node electrode  608  and traces that couple touch node electrode  608  to touch sensing chip  604  from chassis or earth ground  606 . One or more of guard planes  620 ,  624  and  628  can reduce or eliminate parasitic or stray capacitances that may exist between touch node electrode  608  and chassis or earth ground  606 , as will be described below. Optionally guard plane  624 B and guard plane  628 B, both referenced to the same guard voltage, can be disposed on an opposite side of touch node electrode  608  and routing trace  632 . For example, a flex circuit including routing (e.g., routing trace  632 ) between the touch sensing chip  604  and touch node electrodes (e.g., touch node electrode  608 ) can include guard plane  628 B on top of routing trace  632  and guard plane  628 A on bottom of routing trace  632  to sandwich trace  632  on both sides. The touch sensor panel can also include a guard plane  624 A and guard plane  624 B sandwiching touch node electrode  608  (and similar for other touch node electrodes in the touch sensor panel). Guard plane  624 B can include openings corresponding to touch node electrodes to enable detection of touch activity on the touch sensor panel (or proximity activity) while guarding the routing in the touch sensor panel from stray capacitances that can form due to a touch or other stray capacitances. In some examples, the top and/or bottom guard planes can be positioned completely or partially between one or more touch node electrodes and one or more noise sources, such as a display. This configuration (locating the guard plane(s) between the touch node electrodes and noise source) can provide a shielding effect by receiving capacitively coupled noise and shunting the charge away from the touch node electrodes (providing noise isolation between the display and touch node electrodes). In some examples, the top and/or bottom guard planes can be driven by a guard voltage. In this configuration, with the guard planes and the touch node electrodes driven with the same signals or signals referenced to each other (e.g., at the same frequency, phase and amplitude), parasitic capacitive coupling between the guard plane(s) and the touch node electrodes can be minimized, which further shields the touch node electrodes from capacitively coupled noise. Similarly, while an “interrogated” touch node electrode (e.g., a touch node electrode being driven and sensed in the D/S configuration) is being sensed to determine the occurrence of a touch, other “non-interrogated” touch node electrodes (in the D configuration) can be driven with the same guard signal as the guard plane(s). In this configuration, the interrogated electrode can be surrounded by other touch node electrodes that can also be acting as a shield for the interrogated touch node electrode. As each touch node electrode is interrogated in one or more steps, the guard voltage can be selectively applied to other non-interrogated electrodes. In some examples, the material(s) out of which guard planes  628 A-B are made in the flex circuit can be different than the material(s) out of which guard planes  624 A-B are made in touch sensor panel  630 . For example, guard planes  624 A-B in touch sensor panel can be made of the same material that touch node electrodes  608  are made of (e.g., ITO, or another fully or partially transparent conductor), and guard planes  628 A-B in the flex circuit can be made of a different conductor, such as copper, aluminum, or other conductor that may or may not be transparent. 
     Various capacitances associated with touch and/or proximity detection using touch sensor panel configuration  600  are also shown in  FIG. 6A . Specifically, an object  610  (e.g., a finger) can be in proximity to touch node electrode  608 . Object  610  can be grounded to earth ground  606  through capacitance  612  (e.g., C body ), which can represent a capacitance from object  610  through a user&#39;s body to earth ground  606 . Capacitance  614  (e.g., C touch ) can represent a capacitance between object  610  and touch node electrode  608 , and can be the capacitance of interest in determining how close object  610  is to touch node electrode  608 . Typically, C body    612  can be significantly larger than C touch    614  such that the equivalent series capacitance seen at touch node electrode  608  through object  610  can be approximately C touch    614 . Capacitance  614  can be measured by touch sensing circuitry  622  (e.g., as described with reference to  FIG. 3A ) included in touch sensing chip  604  to determine an amount of touch at touch node electrode  608  based on the sensed touch signal. As shown in  FIG. 6A , touch sensing circuitry  622  can be referenced to guard ground. Although illustrated with the non-inverting input of the sense amplifier coupled to the guard ground, in some example, additional bias voltage referenced to guard ground (not shown) can be included. In some examples, capacitance  616  (e.g., C p ) can be a parasitic capacitance between one or more touch node electrodes  608  and guard plane  624 A. Capacitance  618  (e.g., C s ) can be a stray capacitance between routing trace  632  coupled to touch node electrode  608  and guard plane  628 , for example. In some examples, the impact of capacitances  616  and  618  on a sensed touch signal can be mitigated because guard planes  624 A and  628 A and touch sensing circuitry  622  are all coupled to the virtual ground signal produced by guard source  626 . 
     When guarded, the voltage at touch node electrode  608  and trace  632  can mirror or follow the voltage at guard planes  624 A and  628 A, and thereby capacitances  616  and  618  can be reduced or eliminated from the touch measurements performed by touch sensing circuitry  622 . Without stray capacitances  616  and  618  affecting the touch measurements performed by touch sensing circuitry  622 , the offset in the output signal of sense circuitry  622  (e.g., when no touch is detected at touch node electrode  608 ) can be greatly reduced or eliminated, which can increase the signal to noise ratio and/or the dynamic range of sense circuitry  622 . This, in turn, can improve the ability of touch sensing circuitry  622  to detect a greater range of touch at touch node electrode  608 , and to accurately detect smaller capacitances C touch    614  (and, thus, to accurately detect proximity activity at touch node electrode  608  at larger distances). Additionally, with a near-zero offset output signal from touch sensing circuitry  622 , the effects of drift due to environmental changes (e.g., temperature changes) can be greatly reduced. For example, if the signal out of sense amplifier  622  consumes 50% of its dynamic range due to undesirable/un-guarded stray capacitances in the system, and the analog front end (AFE) gain changes by 10% due to temperature, the sense amplifier  622  output may drift by 5% and the effective signal-to-noise ratio (SNR) can be limited to 26 dB. By reducing the undesirable/un-guarded stray capacitances by 20 dB, the effective SNR can be improved from 26 dB to 46 dB. 
       FIG. 6B  illustrates an exemplary equivalent circuit diagram of an exemplary touch sensor panel configuration  630  according to examples of the disclosure. As described herein, guarding can reduce or eliminate capacitances  616  and  618  from the touch measurements performed by touch sensing circuitry  622 . As a result, the sense amplifier  622  can simply detect C touch    614 , which can appear as a virtual mutual capacitance between object  610  and touch node electrode  608 . Specifically, object  610  can appear to be stimulated (e.g., via C body    612 ) by guard source  626 , and object  610  can have C touch    614  between it and the inverting input of sense circuitry  622 . Changes in C touch    614  can, therefore, be sensed by sense circuitry  622  as changes in the virtual mutual capacitance C touch    614  between object  610  and sense circuitry  622  (e.g., as described with reference to sense circuitry  314  in  FIG. 3B ). As such, the offset in the output signal of sense circuitry  622  (e.g., when no touch is detected at touch node electrode  608 ) can be greatly reduced or eliminated, as described above. As a result, sense circuitry  622  (e.g., the input stage of sense circuitry  622 ) need not support as great a dynamic input range that self-capacitance sense circuitry (e.g., sense circuitry  314  in  FIG. 3A ) might otherwise need to support in circumstances/configurations that do not exhibit the virtual mutual capacitance effect described here. 
     Because the self-capacitance measurements of touch node electrodes in self-capacitance based touch screen configurations can exhibit the virtual mutual capacitance characteristics described above, in some examples, touch sensing chip  604  need not be a chip designed to support self-capacitance measurements (e.g., touch sensing chip  604  may not include sense circuitry  314  as described in  FIG. 3A ). Instead, touch sensing chip  604  may be a mutual capacitance touch sensing chip designed to support mutual capacitance measurements (e.g., touch sensing chip  604  may include sense circuitry  314  as described in  FIG. 3B , but not sense circuitry  314  as described in  FIG. 3A ). In such examples, guard source  626  can be appropriately designed and used with the mutual capacitance touch sensing chip in various configurations of this disclosure (e.g., configuration  600 ) to effectively achieve the guarded self-capacitance functionality of this disclosure despite touch sensing chip  604  being designed as a mutual capacitance touch sensing chip, rather than as a self-capacitance touch sensing chip. For example, referring to  FIG. 3B , stimulation source  306  (e.g., guard source  626 ) can stimulate the guard plane(s) of the disclosure, which can act as the drive electrodes in the virtual mutual capacitance configuration described here. The touch node electrodes of the touch sensor panel can then, in turn, be treated as the sense electrodes in the virtual mutual capacitance configuration described here, and can be coupled to the input of sense amplifier  308  in  FIG. 3B . Touch sensing circuitry  314  in  FIG. 3B  can then sense the mutual capacitance between the guard plane(s) and the touch node electrodes, which can be represented by the circuit configuration of  FIG. 6B . 
     As discussed herein, in some examples, touch sensing circuitry and guard circuitry (e.g., to generate a guard voltage) for a guarded touch sensor panel can be implemented with separate electronic chips or integrated circuits operating in multiple power domains.  FIG. 7A  illustrates an exemplary block diagram of a touch and/or proximity detection system  700  according to examples of the disclosure. In some examples, proximity detection system  700  can include a touch sensor panel  710  (e.g., implemented in touch screen  124 ,  126 ,  128 , or  130 ), chassis or earth ground referenced touch sensing chip  720 , and guard referenced touch sensing chip  730 . Touch sensor panel  710  can include one or more touch node electrodes  712  (such as touch node electrode  608 ) and one or more guard planes  714  (such as guard plane  624 A). In some examples, chassis or earth ground referenced touch sensing chip  720  can include voltage driver  722  (e.g., guard source  626 ), differential amplifiers  728 , and analog-to-digital converters (ADCs)  726 . Guard referenced touch sensing chip  730  can include one or more sense amplifiers  732  configured to be coupled to touch node electrodes  712  of touch sensor panel  710  (e.g., by switching circuitry such as multiplexers  738 ). In some examples, chassis or earth ground referenced touch sensing chip  720  can also include additional components such as a microcontroller (e.g., corresponding to touch processor  202  or touch controller  206 ), memory, filters (e.g., anti-aliasing filters), etc. In some examples, chassis or earth ground referenced touch sensing chip  720  can be referenced to earth or chassis ground  724  and guard referenced touch sensing chip  730  can be referenced to guard ground (e.g., via voltage driver  722 . 
     Chassis or earth ground referenced touch sensing chip  720  can include voltage driver  722  configured to generate a guard voltage. In some examples, voltage driver  722  can be coupled to one or more guard planes  714  of touch sensor panel  710  and ground pin  734  of guard referenced touch sensing chip  730 . In this way, guard referenced touch sensing chip  730  can “float” relative to earth or chassis ground  724 , which can shield one or more components of touch circuitry from noise. For example, earth or chassis ground  724  can become capacitively coupled to a noise source (e.g., noise from display circuitry within the electronic device and/or a noise source external to the electronic device), which can be shielded by guarding. In some examples, chassis or earth ground referenced touch sensing chip  720  can further include one or more touch sensing components for touch sensing, such as differential amplifiers  728  and ADCs  726 . 
     In some examples, one or more guard planes  714  can be located between touch node electrode  712  and display circuitry (not shown) included in an electronic device having touch and/or proximity detection system  700 . Additionally or alternatively, the electronic device can include one or more guard planes in different locations (e.g., on the same layer as the touch node electrodes  712  or on a different layer between the touch node electrodes and a cover material (e.g., a cover glass) of the electronic device). In some examples, one or more guard planes  714  can be coupled to voltage driver  722  of chassis or earth ground referenced touch sensing chip  720  to receive a guard voltage (e.g., guard ground). Touch node electrode  712  can become capacitively coupled to an object proximate to or touching the touch sensor panel  710 , for example. 
     Touch node electrode  712  can be coupled to the inverting input of sense amplifier  732 , allowing sense amplifier  732  to sense one or more touch signals indicative of an object proximate to or touching the touch node electrode, for example. In some examples, each touch node electrode can have a corresponding sense amplifier (e.g., a 1:1 ratio between touch node electrodes and sense amplifiers) to enable simultaneous sensing of each touch node electrode in one scan step. The coupling between each touch node electrode corresponding sense amplifier can be hard wired or via switching circuitry. The switching circuitry can enable touch node electrodes to be stimulated and sensed (D/S configuration), stimulated without being sensed (D configuration) or grounded (G configuration) or otherwise held at a DC voltage. In some examples, the touch node electrodes  712  of touch sensor panel  710  can be coupled to sense amplifiers  732  through multiplexer  738  (or other switching circuitry). The switching capability can, in some examples, allow for fewer sense amplifiers (and thereby less circuitry) to be used to sense a touch sensor panel of a given size (in addition to providing different configurations (D/S, D or G configurations) for touch node electrodes). For example, a touch sensor panel with 1000 touch nodes can be sensed using 50 sense amplifiers in 20 scan steps. During each scan step different touch node electrodes can be coupled to the available sense amplifiers. In some examples, the non-inverting input of sense amplifier  732  can be coupled to virtual ground pin  736  referenced to the guard voltage generated by voltage driver  722 . Although multiplexers  738  are illustrated in guard referenced touch sensing chip  730 , in some examples, they may be implemented separately from guard referenced touch sensing chip  730  (e.g., in a different chip). 
     Although the block diagram of  FIG. 7A  includes only sense amplifiers and multiplexers implemented in the guarded domain, in other examples, a different distribution of touch sensing circuitry between the earth or chassis ground domain and the guarded domain is possible. For example, the differential ADCs and/or single-ended to differential conversion circuitry (e.g., differential amplifier  728 ) can be implemented in the guarded domain rather than the earth or chassis ground domain. The arrangement of  FIG. 7A , however, can reduce the number of components in the guard domain, thereby reducing the components to be powered in the guarded domain (reducing the requirements for the power system for “floating” guard-domain power supplies). Additional details of powering circuitry in a system operating in two power domains are described in U.S. patent application Ser. No. 15/663,271 to Christoph H. KRAH et al. (“TOUCH SENSOR PANEL WITH MULTI-POWER DOMAIN CHIP CONFIGURATION”), which is herein incorporated by reference for all purposes. Additionally, by level shifting analog signals between the guard domain and the earth or chassis ground domain rather than digital signals, the level shifting burden can be reduced and/or interconnections between the two power domains can be reduced. Specifically, the level shifting can be performed on the single-channel analog output of sense amplifiers  732 , rather than on the multi-channel output of ADC  726  (e.g., n bits/channel per ADC output). 
     The level shifting between the guarded domain and the earth or chassis ground domain can be achieved with differential amplifiers  728 . In some examples, the non-inverting inputs of differential amplifiers  728  can be coupled to the guard voltage output by voltage driver  722  and the inverting input can receive the analog output from sense amplifier  732 . In this way, the touch signals from sense amplifiers  732  can be level shifted from the virtual ground domain to the earth or chassis ground domain (e.g., by subtracted the guarded voltage contribution to the touch signal from the touch signal). The differential amplifiers  728  can be referenced to earth or chassis ground  724 . In addition to level shifting, the differential amplifiers  728  can also convert the single-ended output of sense amplifiers  732  to differential signals. Additionally, the ADC can be referenced to earth or chassis ground  724 . The differential ADC  726  can convert the differential output of differential amplifier  728  to a digital signal. Although analog circuitry is shown in  FIG. 7A , additional digital signal processing can be included on the chassis or earth ground referenced touch sensing chip  720  (e.g., touch processor  202 , touch controller  206 ). It should be understood that touch and/or proximity detection system  700  can divide touch signal processing between guard referenced touch sensing chip  730  and chassis or earth ground referenced touch sensing chip  720  in other ways than illustrated in  FIG. 7A . Although illustrated as differential ADCs in  FIG. 7A , it should be understood that a single-ended ADC can be used without single-ended to differential conversion of the output from sense amplifiers. 
     Guard referenced touch sensing chip  730  and chassis or earth ground referenced touch sensing chip  720  can be separate integrated circuit chips as illustrated in  FIG. 7A . In some examples, both guard referenced touch sensing chip  730  and chassis or earth ground referenced touch sensing chip  720  can be implemented on a single integrated circuit chip. For example, the components of guard referenced touch sensing chip  730  can be placed in a deep well (e.g., n-well) to isolate circuitry operating in the guard domain from chassis or earth ground referenced touch sensing chip  720  and its associated circuitry operating in the chassis or earth ground domain. For example, sense amplifier  732  referenced to the guard voltage can be placed in a deep well to be isolated from guard driver  722  referenced to the chassis or earth ground domain. 
     Implementing the sense amplifier  732  (and optionally other circuitry) in a guard domain chip separate from other analog and/or digital circuitry can improve scalability for touch sensor panels of different sizes. For example, a touch and/or proximity detection system can include one chassis or earth ground referenced touch sensing chip  720  and multiple guard referenced touch sensing chips  730 . The chassis or earth ground referenced touch sensing chip  720  can act as a master chip for multiple guard referenced touch sensing chips  730 . Multiplexers (e.g., multiplexer  738 ) or other switching circuitry (e.g., separate from guard referenced touch sensing chips  720 ) can be used to couple some or all of the touch node electrodes of the touch sensor panel to sense amplifiers in the multiple guard referenced touch sensing chips  720 . The number of guard referenced touch sensing chips  720  for a touch sensor panel can be a function of the size of the touch sensor panel and the number of sense channels in each guard referenced touch sensing chip  730 . For example, when using a guard referenced touch sensing chip  730  including 20 sense channels (e.g., 20 sense amplifiers), two guard referenced touch sensing chips  730  can be used for a touch sensor panel including 40 touch node electrodes and ten guard referenced touch sensing chips  730  can be used for a touch sensor panel including 200 touch node electrodes. In some examples, chassis or earth ground referenced touch sensing chip  720  can include the same number of differential amplifiers and ADCs as each of the guard referenced touch sensing chips  730  (or a different number). For example, chassis or earth ground referenced touch sensing chip  720  can include switching circuitry (e.g., analog MUXs) which can be operated to couple the sense amplifiers  732  of guard referenced touch sensing chip  730  to differential amplifiers  728 . Such a configuration can reduce the number of differential amplifiers and ADCs in chassis or earth ground referenced touch sensing chip  720  while maintaining the ability to interface with each of sense channels in guard referenced touch sensing chip  930 . 
     In some examples, the differential amplifiers in the chassis or earth ground referenced touch sensing chip can receive the guard voltage by a trace in the chassis or earth ground referenced touch sensing chip. For example, as illustrated in  FIG. 7A , the guard voltage generated in chassis or earth ground referenced touch sensing chip  720  can be supplied to differential amplifier  728  by a trace within chassis or earth ground referenced touch sensing chip  720 . In some examples, the guard voltage generated in chassis or earth ground referenced touch sensing chip  720  can be supplied to differential amplifier  728  by a routing trace from the guard referenced touch sensing chip  730  to the chassis or earth ground referenced touch sensing chip  720 . This arrangement can reduce phase drift between the guarded voltage supplied to one terminal of the differential amplifier and the touch signal suppled to the second terminal of the differential amplifier (e.g., by providing conductive paths of substantially the same length to carry both the touch signal and the guard signal). In some examples, the guard planes can sandwich the routing carrying touch signals forming a coaxial cable structure (e.g., carrying the guarded voltage to shield the inner conductive path carrying the guarded touch signal from one or more noise sources). The output from the guard referenced touch sensing chips can be transmitted to a master earth or chassis ground referenced touch sensing chip (e.g., with a guard voltage trace that also travels between the guard referenced touch sensing chip to the earth or chassis ground referenced touch sensing chip to reduce phase drift at the differential amplifiers in the earth or chassis ground referenced touch sensing chip. 
       FIG. 7B  illustrates an exemplary multi-modal touch controller configuration according to examples of the disclosure. In some examples, the multi-modal touch controller can be configured to perform guarded self-capacitance scans (in a first mode), offset compensated mutual capacitance scans (in a second mode) or both mutual and self-capacitance scans (in a third mode). 
     In a first mode (guarded self-capacitance mode), the multi-modal touch controller  750  can operate in a similar manner to the description above with respect to  FIG. 7A . For example, the multi-modal touch controller  750  can be used in the first mode with a touch sensor panel  740  having column electrodes  742  and row electrodes  744  (e.g., as shown in touch screen  400 ) or can be used with individual touch node electrodes (e.g., as shown in touch screen  402 ). The touch sensor panel  740  can also include a guard plane  746  (e.g., disposed between the touch node electrodes and the display circuitry). The touch sensor panel can be substantially similar to the touch sensor panel  710  in  FIG. 7A . The operation of multi-mode touch controller  750  can be divided into two touch sensing chips operating in two power domains like in the block diagram of  FIG. 7A . However, unlike  FIG. 7A  which includes some analog touch sensing circuitry in the guarded domain and the remaining analog and digital touch sensing circuitry in the chassis or earth ground domain, touch controller  750  can including analog touch sensing circuitry in a touch sensing chip  762  in the guarded domain and digital touch sensing circuitry in a second touch sensing chip  752  in the chassis or earth ground referenced domain. However, aside from the different distribution of circuitry between the two chips, the operation of touch controller  750  in the first mode can be similar to the operation of chassis or earth ground referenced touch sensing chip  720  and guard referenced touch sensing chip  730 . In particular, MUXs  764  (e.g., corresponding to MUXs  738 ) can couple analog touch sensing circuitry in analog front end (AFE)  766  (e.g., corresponding to sense amplifiers  732 , ADCs  726 , etc.) to touch node electrodes in touch sensor panel  740  (e.g., corresponding to touch sensor panel  740 ) to measure self-capacitances of the touch node electrodes. Touch sensing chip  752  can be referenced to chassis or earth ground and touch sensing chip  762  (including sensing amplifiers) can be referenced to a guard voltage generated by touch sensing chip  752  (e.g., the ground pin  774  of touch sensing chip  762  can be driven at the guard voltage by from guard source  753  in touch sensing chip  752 ). The panel guard  746  can be driven at the guard voltage by guard source  753 . The guard source  753  can be selected for driving the guard ground for touch chip  762  and for driving guard plane  746  via multiplexers  754  and  776  (e.g., by selecting “Mode 0” corresponding to the first mode). The digital touch signal output by AFE  766  in touch sensing chip  762  can be transmitted to touch sensing chip  752  via level shifters  772  to shift the digital touch signals between the two power domains. The digital touch signal can be demodulated by demodulators  756  and the results can be processed by touch processor  758 . It should be understood, however, that as in  FIG. 7A , different distributions of the circuitry between touch sensing chip  752  and  762  are possible. 
     In a second mode (offset-compensated mutual-capacitance mode), touch controller  750  can operate in one power domain, with touch sensing chips  752  and  762  referenced to chassis or earth ground  760  (e.g., by coupling ground pins for touch sensing chips  752  and  762  to the chassis or earth ground  760 ). In some examples, the guard plane  746  can be driven at an offset voltage by the offset source  755  during the second mode. The offset source  755  can be selected for driving guard plane  746  and chassis or earth ground can be selected for driving the ground pin  774  for touch chip  762  via multiplexers  754  and  776  (e.g., by selecting “Mode 1” corresponding to the second mode). The offset voltage can be configured to compensate for (e.g., remove) background components of the sensed touch signal during a mutual capacitance scan. The remaining touch signal (which can be relatively small in magnitude compared with the background touch signal) can be representative of changes in capacitance due to objects touching or in proximity to touch nodes of touch sensor panel  740 . Offset compensation for a mutual capacitance scan can allow for the dynamic range of the sense amplifiers in AFE  766  to be design for and used for the touch signal of interest, rather than for the background mutual capacitance between the column electrodes  742  and row electrodes  744 . 
     In some examples, touch sensing chip  762  can include circuitry for multi-stimulation mutual capacitance measurements and touch sensing chip  752  can include circuitry for demodulation of touch signals from a multi-stimulation mutual capacitance scan. For example, touch sensing chip  762  can include a stimulus generator  768  (e.g., a transmit oscillator, digital logic, digital-to-analog converter (DAC), driver, etc.) configured to generate the stimulation signals to be applied to drive lines of touch sensor panel  740  and a stimulation matrix  770  configured to select stimulation voltages to be applied to different drive lines during different steps of a multi-stimulus mutual capacitance scan (e.g., a memory storing the parameters which can be represented as a matrix according to scan step and drive line). Stimulus voltages Vstim_p and Vstim_n designate, for example, drive signals at zero phase and 180° phase, respectively. Multiplexers  764  (or other switching circuitry) can couple the column electrodes  742  (or the row electrodes  744 ) to the stimulation voltages (generated by the stimulation generator  768  and selected in accordance with the stimulation matrix  770 ) and the row electrodes  744  (or the column electrodes  742 ) to AFEs to sense the mutual capacitance between the column electrodes  742  and row electrodes  746 . Digital touch signals outputted from AFEs  766  can be level shifted by level shifters  772  from touch sensing chip  762  to touch sensing chip  752 . In the second mode where both touch sensing chips  752  and  762  may be referenced to the same chassis or earth ground  760 , the level shifting may simply be a transfer of digital touch signals between the two touch sensing chips. In such examples, the signals may simply bypass the level shifters  772  when touch sensing chips  752  and  762  (e.g., shown by bypass switch in the figure). Although level shifters  772  are illustrated as straddling between touch sensing chips  752  and  762  in  FIG. 7B , it is understood that level shifters  772  can reside in either touch sensing chip  752  and/or in touch sensing chip  762  (or in a different location). The touch signals measured during the multiple steps of the multi-stimulation scan can be demodulated by digital demodulators  756  in touch sensing chip  752 . The demodulation and decoding of the touch signals for touch nodes of touch sensor panel  740  can be based on the stimulation applied during each step (e.g., based on an inverse of the stimulation matrix and the output of the stimulation generator) as represented by stimulation demodulation synthesis circuit  778 . The demodulated touch signals output by digital demodulators  756  can be further processed by the touch processor  758 . Additional details of an exemplary multi-stimulation scan and multi-stimulation touch controller are described in U.S. patent application Ser. No. 11/619,433 to Steven P. HOTELLING et al. (“SIMULTANEOUS SENSING ARRANGEMENT”) and U.S. patent application Ser. No. 12/283,423 to Steven P. HOTELLING et al. (“SINGLE-CHIP MULTI-STIMULUS SENSOR CONTROLLER”), which are herein incorporated by reference for all purposes. The multi-stimulation circuitry (e.g., stimulus generator  768 , stimulus matrix  770 , and stimulation demodulation synthesis circuit  778 ) can be activated during the second mode and deactivated during the first mode. Although a multi-stimulation mutual capacitance scan is described, in some examples, a single stimulation mutual capacitance scan can be implemented instead. 
     As described above, because the self-capacitance measurements of touch node electrodes can exhibit virtual mutual capacitance characteristics, the same touch sensing circuitry (e.g., AFEs) can be used for both mutual capacitance and self-capacitance sensing operations. Each of the AFEs  766  can include a sense amplifier and an analog-to-digital converter (ADC). The AFEs can also include additional components including filters, single-ended to differential conversion circuits, etc. In the first mode of operation, the non-inverting terminal of the sense amplifier can be guard referenced (e.g., as shown in  FIG. 7A ). In the second mode of operation, the non-inverting terminal of the sense amplifier can be chassis or earth ground referenced. 
     In some examples, touch sensing chip  752  can include guard source  753  and offset source  755  to generate the guard voltage and/or offset voltage depending on the mode of operation. The guard voltage or offset voltage can be selectively applied to guard plane  746  using multiplexer  754  and the guard voltage or chassis or earth ground can be selectively applied to touch sensing chip  762  using multiplexer  776  (or other switching circuitry). 
     In some examples, touch sensing chips  752  and  762  can be implemented as separate chips. In some examples, touch sensing chips  752  and  762  can be implement on the same ASIC. Deep N-well isolation can be used to prevent interference between the two sensing chips (in particular for when the two sensing chips  752  and  762  may be operating in different power domains). 
       FIG. 8A  illustrates an exemplary scan plan and corresponding configurations for the multi-modal touch controller according to examples of the disclosure. The exemplary scan plan includes a spectral analysis scan (“SPA”), a multi-step mutual capacitance scan (N-step), a row self-capacitance scan, and a column self-capacitance scan. Each of these scans can be performed using a row-column touch screen of  FIG. 4A . It is understood that the scan plan is exemplary, and in other cases fewer or more scans can be performed (e.g., mutual capacitance scans without self-capacitance scans or self-capacitance scans without mutual capacitance) and the order may be different (e.g., column self-capacitance first then row self-capacitance scans; self-capacitance scans before mutual capacitance scans, etc.). The exemplary scan plan can repeat once per display frame in some examples. During each scan, the touch sensing chip (e.g., touch sensing chip  762 ) can be referenced to a system ground (e.g., chassis or earth ground) or a guard voltage, and the guard plane for the touch sensor panel can be driven with a guard voltage, a voltage offset or a system ground as illustrated by and described above with reference to  FIGS. 7A and 7B . 
     During a SPA scan, for example, the touch sensor panel can be sensed without stimulation. In such examples, the touch sensing chip (e.g., touch sensing chip  762 ) can be referenced to system ground. The guard plane for the touch sensor panel can also be grounded to system ground. During each scan step of the N-step mutual capacitance scan, the touch sensing chip (e.g., touch sensing chip  762 ) can be referenced to system ground. The drive lines of the touch sensor panel can be stimulated, for example, using multi-stimulation schemes by applying different stimulation voltages (e.g., Vstim+ and Vstim− having the same frequency and amplitude, but different phases). To achieve offset compensation, the guard plane for the touch sensor panel can be driven at an offset voltage during the mutual capacitance scan steps. During the row and/or self-capacitance scans, the touch sensing chip can be referenced to the guard voltage and the guard plane for the touch sensor panel can be driven at the guard voltage. Additionally, the stimulation applied to the row electrodes and/or column electrodes can be referenced to the guard voltage. 
     Referring back to the offset compensated mutual capacitance scan, in some examples, the first scan step of the multi-step mutual capacitance scan can be a common mode scan step in which each drive line is stimulated with the same stimulation voltage, Vstim_p (e.g., same frequency, phase and amplitude). In such examples, even without a proximate or touching object, a mutual capacitance proportional to N*Vstim would be detected for each sense line. As a result, for a common mode scan step the Voffset can be drive to −k*N*Vstim to counteract the effect of driving each mutual capacitance, where k can be a scalar compensating for the mismatch between the guard to sense line capacitance and the drive line to sense line capacitance. In some examples, the remaining scan steps of the multi-stimulation mutual capacitance scan can drive an equal number of drive lines with Vstim+ and Vstim− (e.g., same frequency and amplitude, but opposite phases). In such examples, the net offset can already be zero and thus Voffset can be zero or alternatively the guard plane can be grounded to system ground during these scan steps. Driving the guard plane for the panel to counteract the offset effects from driving multiple lines can compensate for the offset voltage from stimulation. The introduction of an offset voltage can increase the headroom of the sense amplifiers because the relevant headroom can be used for the touch signal post-offset compensation. Without offset compensation, the relatively large offset voltage (e.g., when compared with the size of a touch or proximity signal) can use up the bulk of the headroom, as well as reduce the sensitivity of the sensing amplifier to the small signal changes due to touch and/or proximity. Although the example above relies on a common mode mutual capacitance scan step followed by additional mutual capacitance scan steps (e.g., according to a Hadamard matrix), it is understood that other scan schemes are possible that may require different offset voltages at the guard plane (e.g., depending on the stimulation offset to be compensated for). 
       FIG. 8B  describes a process  800  of touch sensing using a multi-modal touch controller according to examples of the disclosure. At  802 , the system can determine the mode of operation for the touch controller. In some examples, the mode of operation can be a single mode of operation for a system and the multi-modal touch controller can be configured to operate according to that single mode of operation upon boot up of the system. Multi-modal touch controller can be used in such a system whether the single mode of operation is a self-capacitance mode or a mutual capacitance mode. In some examples, the mode of operation can change dynamically (e.g., according to a scan plan) and the determination of a touch sensing mode at  802  can be used to dynamically configure the multi-modal touch controller for operation in the desired mode of operation. In accordance with a determination that the mode of operation is a self-capacitance mode, the touch sensing chip (e.g., touch sensing chip  762 ) can be referenced to the guard voltage at  804  and the guard plane of the touch sensor panel can be driven with the guard voltage at  806 . At  808 , the touch node electrodes of the touch sensor panel can be stimulated and/or sensed relative to earth system ground using the guard voltage. In accordance with the determination that the mode of operation is a mutual capacitance mode, the touch sensing chip (e.g., touch sensing chip  762 ) can be referenced to the system ground at  810 , the guard plane of the touch sensor panel can be driven with the offset voltage at  812 , and the touch sensor panel can be stimulated, with reference to system ground (earth or chassis ground), with the multi-stimulation mutual capacitance touch sensing scheme at  814 . In some examples, the multi-stimulation scheme can include two stimulation signals out of phase by 180 degrees (Vstim_p and Vstim_n) and during each scan an equal number of drive lines can be stimulated with either of the two stimulation signals. In such examples, the offset compensation can be zero (and, in some examples, may be omitted). In some examples, the same result can be achieved, but a first scan step of the mutual capacitance scan can be a common mode scan in which a non-zero offset can result. In such examples, an offset can be applied. In some examples, the offset voltage can be at different levels at different times during the mutual capacitance scan (e.g., difference scan steps), depending on the required voltage level to compensate for offsets. 
       FIG. 9A  illustrates an exemplary guard voltage waveform according to examples of the disclosure. The exemplary guard voltage waveform  900  can represent the amplitude of the output of MUX  776 , for example, corresponding to the self-capacitance mode. The output of MUX  776  can be the guard voltage, which may be a trapezoidal periodic wave with amplitude Vguard. The guard voltage can toggle between a high value (GUARD HIGH) and a low value (GUARD LOW). Although illustrated in  FIG. 9A  as toggling between Vguard and system ground, the guard signal can toggle between +/−Vguard centered around system ground in other examples. The self-capacitance scans performed relative to the guard voltage can occur once the output of MUX  776  settles to the Vguard amplitude (rather than during the transitions of the guard voltage). Although the voltage transitions are illustrated in  FIG. 9A  as linear ramps, the transition can be non-linear. 
       FIG. 9B  illustrates an exemplary stimulation voltage waveform according to examples of the disclosure. The exemplary stimulation voltage waveform  920  can represent the amplitude of the drive signals to be applied to the drive lines during a mutual capacitance mode of multi-mode touch controller  750 . At first time period  922  (e.g., corresponding to a first mutual capacitance scan of the touch sensor panel), the drive lines can be stimulated with stimulus according to the scan step (e.g., by stimulus generator  768  in accordance with the stimulation matrix  770 ). The amplitude of Vstim as shown can represent to application of Vstim_p or Vstim_n in multiple scan steps to multiple drive lines. Voffset can be used to counteract the offset according to the scan step. For example, during a first, common mode scan step corresponding to pulse  926 , the offset voltage can be k*N*Vstim. During subsequent scan steps (e.g., corresponding to pulses  928  and  930 ) in which an equal number of drive lines can be stimulated with Vstim_p and Vstim_n, the offset voltage can be zero. In some examples, the offset voltage can be non-zero to account for mismatch between the guard to sense line capacitance and the drive line to sense line capacitance for each scan step. At second time period  924 , a second mutual capacitance scan of the touch sensor panel can occur (or alternatively, additional scan steps of the mutual capacitance scan can occur). 
     As described above, in some examples, the multi-modal touch controller can be configured to operate in a third mode where both mutual and self-capacitance scans can be supported simultaneously. Referring back to  FIG. 7B , in the third mode the touch sensing chip  762  can be referenced to the guard voltage by MUX  776  (“Mode 2”) and the panel guard  746  can be drive by the combination of the guard voltage and the offset voltage by MUX  754 . Referencing touch sensing chip  762  to the guard voltage and the guard plane  746  to the sum of the guard voltage and the offset voltage can achieve the guarding function for self-capacitance scans of a first portion of the touch sensor panel and the offset voltage function for the mutual capacitance scans of a second portion of the touch sensor panel. 
       FIG. 8C  illustrates an exemplary scan plan and corresponding configurations for the multi-modal touch controller according to examples of the disclosure. The exemplary scan plan includes a spectral analysis scan (“SPA”), and an at least partially overlapping multi-step mutual capacitance scan (N-step) and a self-capacitance scan (including one or more steps). The scans can be performed, for example, using a touch sensor panel including both row/column electrodes and touch node electrodes as illustrated in  FIGS. 11A and 11B . It is understood that the scan plan is exemplary, and in other cases fewer or more scans can be performed and the order may be different. The exemplary scan plan can repeat once per display frame in some examples. During each scan, the touch sensing chip (e.g., touch sensing chip  762 ) can be referenced to a system ground (e.g., chassis or earth ground) or a guard voltage, and the guard plane for the touch sensor panel can be driven with a combination of the guard voltage and offset voltage. 
     The SPA scan can operate in the same manner as described above. During the mutual and self-capacitance scan, touch sensing chip (e.g., touch sensing chip  762 ) can be referenced to the guard voltage and the guard plane for the touch sensor panel can be driven at the guard voltage in superposition with the offset voltage. The drive lines of the touch sensor panel can be stimulated, for example, using multi-stimulation schemes by applying different stimulation voltages (e.g., Vstim+ and Vstim− having the same frequency and amplitude, but different phases). In this example, Vstim+ and Vstim− can be referenced to the guard voltage. Driving the guard plane for the touch sensor panel with the guard voltage and the offset voltage during the mutual capacitance scan steps can achieve offset compensation. The touch node electrodes of the touch sensor panel can also be stimulated and sensed at least partially simultaneously. The touch sensing chip can be referenced to the guard voltage and the guard plane can be driven by the guard voltage and offset voltage. 
     In some examples, Voffset can be zero during most scan steps of the mutual capacitance scan, and the self-capacitance scan can be performed during these scan steps so that the guard plane and touch sensing chip are both voltage guard referenced. In some examples, the self-capacitance scan can be performed even during the common mode scan steps of the mutual capacitance scans. In some examples, the guard plane can be divided into two guard planes one corresponding to the touch node electrodes and one corresponding to the row/column electrodes. In such a configuration, the guard plane corresponding to the row/column electrodes can be driven by the superposition of Voffset and the guard voltage, and the guard plane corresponding to the touch node electrodes can be driven by the guard voltage. In some examples, the guard voltage can be used to reference the touch sensing chip and to drive the guard voltage to stimulate the touch node electrodes. In such examples, the offset compensation can be omitted from the mutual capacitance sensing operations. 
       FIG. 8D  illustrates process  850  of touch sensing using a multi-modal touch controller in a third mode according to examples of the disclosure. Process  850  can include the determination of a touch sensing mode at  852 , which can correspond to  802  in process  800 . In other words, process  850  can correspond to another branch added to process  800 . In accordance with a determination that the mode of operation is a mutual and self-capacitance mode, the touch sensing chip (e.g., touch sensing chip  762 ) can be referenced to the guard voltage at  854 , the guard plane of the touch sensor panel can be driven with the superposition of offset voltage at  856 . At  858 , a first portion of the touch sensor panel can be stimulated, relative to earth system ground using the guard voltage, with the multi-stimulation mutual capacitance touch sensing scheme at  858 . At least partially simultaneously, a second portion of the touch sensor panel can be stimulated and sensed with a self-capacitance touch sensing scheme. 
       FIG. 10A  illustrates an exemplary voltage generation circuit for a multi-modal touch controller according to examples of the disclosure. The guard voltage generation circuit  1000  can include guard voltage driver  1002  and an offset voltage driver  1004 . The circuit  1000  can also include switch  1006  and switch  1008  to generate the output voltage to be applied to the guard plane of the touch sensor panel (e.g., output from MUX  754 ). The guard voltage driver  1002  can also be used as a guard voltage reference for a touch sensing chip. During a self-capacitance mode, the guard voltage driver  1002  can provide a suitable guard voltage at output  1010  to be applied to guard plane  1012  of the touch sensor panel. During a mutual capacitance mode, the guard voltage driver  1002  can output the system ground voltage (or alternatively the guard voltage driver  1002  can be disabled and the output  1010  can be switchable coupled to system ground). In some examples, the output of guard voltage driver  1002  can couple to output  1010  via switch  1008  (e.g., with switch  1006  open). In some examples, when switch  1006  is closed and switch  1008  is open, the output  1010  can be the offset voltage (e.g., for a mutual capacitance scan). In some examples, when switch  1006  and switch  1008  are closed, output  1010  can be the sum of the offset voltage and the guard voltage. The sums of the voltages at the output  1010  can substantially follow the time varying behavior (e.g., ramping up or ramping down) of the guard voltage. 
     As described above, the offset voltage driver  1004  can couple to output  1010  via switch  1006  and the guard voltage driver can couple to output  1010  via switch  1008 . In some examples, each switch can be a Schottky diode. In some examples, each of switches  1006  and  1008  can be implemented with a transistor driven by a control voltage that depends on the touch sensing mode. When the offset voltage is not required (e.g., in a self-capacitance mode), switch  1006  can open and the offset voltage driver  1004  may not contribute to voltage output  1010  (and may be disabled). When the offset voltage is required (e.g., in a mutual capacitance mode), switch  1006  can close and the offset voltage driver  1004  can contribute to voltage output  1010 . Likewise, when guarding is required (e.g., in a self-capacitance mode or a mutual and self-capacitance mode), switch  1008  can be closed. When guarding is not required (e.g., in a mutual capacitance mode), switch  1008  can be opened. In some examples, the offset voltage output by offset voltage driver  1004  can be at different voltage levels at different times depending on the offset compensation required (e.g., for a given mutual capacitance scan step). 
     Although an exemplary circuit is shown in  FIG. 10A , other combinations of different components can be used to generate guard voltages and/or offset voltages without departing from the scope of the present disclosure. 
       FIG. 9C  illustrates an exemplary stimulation voltage waveform according to examples of the disclosure. The exemplary stimulation voltage waveform  960  can represent the amplitude of the drive signals applied to drive lines during a mutual and self-capacitance mode of multi-mode touch controller  750 . Stimulation voltage waveform  960  can include elements from the mutual capacitance scan stimulation voltage waveform  920  superimposed over the guard voltage. The stimulation signals generated by touch sensing chip  762  can be referenced to the guard voltage rather to system ground as in a mutual capacitance mode. It should be understood that the guard voltage and superimposed stimulations shown in  FIG. 9C  is representative, and the relative amplitude, frequency, can be different between the guard voltage and the stimulation signals Vstim_p and Vstim_n (depending on the drive line and scan step), though the mutual and self-capacitance scans can avoid the transitions of the guard voltage and/or superimposed stimulation signals. Although the voltage transitions are illustrated as linear ramps or steps, the transition can be non-linear and other stimulation waveforms are possible. 
       FIG. 10B  illustrates an exemplary touch sensor panel configuration using guard voltage referenced touch sensing circuitry according to examples of the disclosure. For example, circuit  1050  can include touch sensing circuitry (e.g., sense amplifier  1020 ), which can be referenced to guard voltage  1068  for sensing touch on the touch sensor panel. Node  1058  of circuit  1050  can correspond to a touch node electrode of the touch sensor panel (or a sense line in a mutual capacitance configuration). A capacitance  1064  can represent a capacitance between a touch object (e.g., a finger of a chassis/earth grounded user) touching or proximate to the touch node electrode. Sense amplifier  1020  can referenced to a guard voltage generated by voltage source  1068 . Voltage source  1062  can represent the bias voltage for sense amplifier  1020  relative to the guard ground of the touch sensing chip (node  1072 ). Capacitance  1066  can represent the capacitive coupling between one or more drive electrodes and the sense electrode (touch node electrode) during a mutual capacitance scan. During a mutual capacitance scan, guard-referenced stimulation can be applied by stimulation voltage source  1070  to drive lines. In this configuration, the stimulation voltage at drive electrodes can be similar to the waveform at time period  966 . 
     Although the touch sensing methods described in this disclosure can be implemented on a touch sensor panel that includes row and column electrodes or touch node electrodes, as shown in  FIGS. 4A and 4B , these touch sensing methods can be additionally or alternatively implemented on exemplary touch sensor panels shown in  FIGS. 11A and 11B  which include both row and column electrodes and individual touch node electrodes. For example, self-capacitance sensing of touch node electrodes can occur while mutual capacitance sensing the row and column electrodes. In other examples, the touch node electrodes and/or the row and column electrodes can be coupled to perform self-capacitance and/or mutual capacitance sensing. 
     In  FIG. 11A , touch sensor panel  1102  can include one or more touch node electrode areas  1104  and one or more row and column electrode areas  1108 . A touch node electrode area  1104  can include a plurality of touch node electrodes  1106 . A row and column electrode area  1108  can include a plurality of row electrodes  1110  and column electrodes  1112 . In one example, as illustrated, the touch sensor panel can be divided in half with one touch node electrode area  1104  and one row and column electrode area  1108 . In other examples, the relative ratio of these areas can be different for the touch sensor panel. In  FIG. 11B , touch sensor panel  1152  can include a plurality of touch node electrodes  1154 , row electrodes  1156  and column electrodes  1158 , where the touch node electrodes can be located in between the row electrodes  1156  and column electrodes  1158 . It should be understood that other arrangements of touch node electrodes and row/column electrodes are possible for a touch sensor panel. For example, a plurality of touch node electrodes can be located in an opening between two rows and two columns. In some examples, one or more touch node electrodes can be located in some openings, but not others in a regular (e.g., every third “opening”) or irregular pattern. In some examples, the touch sensor panel can include patterns incorporating both touch sensor panel  1102  and touch sensor panel  1152 . 
     As described herein, in some examples, the guard plane for a touch sensor panel can be divided into multiple guard planes. For example, a first guard plane can be used corresponding to touch node electrode area  1104  and a second guard plane can be used corresponding to row and column electrode area  1108 . In such examples, the guard planes can be separately driven according to the mode of operation.  FIG. 12  illustrates an exemplary configuration including multiple guard planes for a touch sensor panel and multiple applied voltages according to examples of the disclosure. For example,  FIG. 12  illustrates touch panel guards  1212 - 1218  corresponding to the touch sensor panel (e.g., corresponding to different portions of the touch sensor panel). Each guard plane can be driven by touch sensing chip  1202 , which can be referenced to system ground. 
     Touch sensing chip  1202  can include one or more guard voltage drivers  1204  and one or more offset voltage drivers  1206 . One or more switches  1208 / 1210  can be used to couple one or more of the guard voltage drivers  1204  and/or one or more of the offset voltage drivers  1206  to respective touch panel guard planes  1212 - 1218 . The switches  1208  and  1210  can be controlled to drive the guard planes with the appropriate voltage according to the touch sensing operation applied to the corresponding portion of the touch sensor panel. 
     Therefore, according to the above, some examples of the disclosure are directed to a touch sensing system. The touch sensing system can comprise: a first chip and a second chip. The first chip can be operating in a first power domain referenced to a first voltage. The first chip can be configured to generate a first signal in a first mode and a second signal in a second mode. The first signal can be different than the second signal. The second chip can be configurable to operate in a second power domain referenced to the first signal in the first mode and to operate in the first power domain referenced to the first voltage in the second mode. The second chip can include touch sensing circuitry configured to sense touch at one or more touch nodes of a touch sensor panel. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first mode can be a self-capacitance mode and the second mode can be a mutual capacitance mode. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first voltage can be a ground voltage of the touch sensing system. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first signal can be a guard voltage. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the second signal can be an offset voltage. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the touch sensing system can further comprise a guard plane associated with the touch sensor panel. The guard plane can be configured to be driven by the first signal in the first mode and to be driven by the second signal in the second mode. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first chip can be configured to generate a third signal based on the first signal and the second signal in a third mode. The second chip can be configurable to operate in the second power domain referenced to the first signal in the third mode. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the third mode can be a mutual capacitance and self-capacitance mode. The touch sensing circuitry can comprise first sense amplifiers configured sense touch at one or more first touch nodes of the touch sensor panel in a mutual capacitance configuration and second sense amplifiers configured to sense touch at one or more second touch nodes of the touch sensor panel in a self-capacitance configuration. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the guard plane can be configured to be driven by the third signal in the third mode. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the touch sensor panel can include row electrodes and column electrodes forming the first touch nodes of the touch sensor panel. The touch sensor panel can include an array of touch node electrodes forming the second touch nodes of the touch sensor panel. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first chip and the second chip can be formed on one integrated circuit. The second chip can be isolated in a deep well from the first chip. 
     Some examples of the disclosure are directed to a method of touch sensing in a touch sensing system including a multi-modal touch controller comprising a first chip operating in a first power domain referenced to a first voltage and a second chip. The method can comprise: determining a touch sensing mode; in accordance with a determination that the touch sensing mode is a first mode, the second chip can be operated in a second power domain referenced to the first signal; and in accordance with a determination that the touch sensing mode is a second mode, the second chip can be operated in the first power domain referenced to the first voltage. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first mode can be a self-capacitance mode and the second mode can be a mutual capacitance mode. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first voltage can be a ground voltage of the touch sensing system. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the method can further comprise: in accordance with a determination that the touch sensing mode is the first mode, generating a first signal in the first chip; and in accordance with a determination that the touch sensing mode is the second mode, generating a second signal in the first chip. The first signal can be different than the second signal. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first signal can be a guard voltage. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the second signal can be an offset voltage. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the method can further comprise: in accordance with a determination that the touch sensing mode is the first mode, driving a guard plane of the touch sensing system with the first signal; and in accordance with a determination that the touch sensing mode is the second mode, driving the guard plane of the touch sensing system with the second signal. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the method can further comprise: in accordance with a determination that the touch sensing mode is a third mode, operating the second chip in the second power domain referenced to the first signal. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the method can further comprise: in accordance with a determination that the touch sensing mode is a third mode, generating a third signal in the first chip. Third signal can be a superposition of a first signal and a second signal generated in the first chip. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the method can further comprise: in accordance with a determination that the touch sensing mode is the third mode, driving the guard plane of the touch sensing system with the third signal. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the third mode can be a mutual capacitance and self-capacitance mode. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the method can further comprise in accordance with a determination that the touch sensing mode is the third mode: sensing a first portion of a touch sensor panel of the touch sensing system in a mutual capacitance configuration to measure touch at one or more first touch nodes of the touch sensor panel; and sensing a second portion of the touch sensor panel of the touch sensing system in a self-capacitance configuration to measure touch at one or more second touch nodes of the touch sensor panel. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the sensing of the first portion of the touch sensor panel and the sensing of the second portion of the touch sensor panel can occur at least partially concurrently. Some examples of the disclosure are directed to a non-transitory computer readable storage medium. The non-transitory computer readable storage medium can store instructions, which when executed by one or more processors of a touch sensing system including a multi-modal touch controller comprising a first chip operating in a first power domain referenced to a first voltage and a second chip, can cause the one or more processors to perform any of the above methods. 
     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: 20180918
Publication Date: 20210810
Grant Date: 20210810
Priority Date: 20170929
Inventors: KRAH, CHRISTOPH H.
Assignee: APPLE INC
CPC Classifications: [{"code": "G06F3/0446", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/0446", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/0412", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/041662", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F2203/0381", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F1/1643", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/041662", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F2203/0381", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/041662", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0412", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1643", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0446", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 63794663