PATENT DOCUMENT

Publication Number: US-10990221-B2
Application Number: US-201816134604-A
Country: US
Kind Code: B2

Title: Multi-power domain touch sensing

Abstract:
The disclosure relates to a touch and/or proximity detection system having some components operating in the guard domain and other components operating in the earth or chassis ground domain. A guard chip in the earth or chassis ground domain can include a voltage driver configured to produce a guard signal, for example. In some examples, the guard signal can be coupled to one or more shielding electrodes of a touch screen and to the ground pin of one or more touch sensing chips of the touch and/or proximity detection system. In this way, for example, the touch sensing chips, which can include sense amplifiers coupled to one or more sensing electrodes of the touch screen, can operate in the guard domain. In some examples, the guard chip can further include differential amplifiers and/or ADCs, allowing these components to operate in the earth or chassis ground domain.

Claims:
The invention claimed is: 
     
       1. An electronic device comprising:
 a first chip operating in a first power domain referenced to a first voltage, the first chip comprising:
 an analog-to-digital converter (ADC) referenced to the first voltage and having a first input; 
 a voltage source configured to output a second voltage; and 
 a level shifting circuit referenced to the first voltage and having an output coupled to the first input of the ADC, wherein the level shifting circuit is configured to shift an analog signal from a second power domain referenced to the second voltage to the first power domain; and 
 
 a second chip operating in the second power domain referenced to the second voltage, the second chip comprising:
 a sense amplifier having a first input configured to be coupled to a touch node electrode, having a second input configured to be coupled to the second voltage, and having an output configured to be coupled to the first input of the ADC via the level shifting circuit. 
 
 
     
     
       2. The electronic device of  claim 1 , wherein the first voltage is a chassis ground of the electronic device. 
     
     
       3. The electronic device of  claim 1 ,
 wherein the level shifting circuit comprises a differential amplifier referenced to the first voltage and having a first input configured to be coupled to the output of the sense amplifier, having a second input configured to be coupled to the second voltage, and having an output coupled to the first input of the ADC. 
 
     
     
       4. The electronic device of  claim 3 , further comprising:
 one or more guard electrodes between the first chip and the second chip, the one or more guard electrodes configured to be coupled to the second voltage, wherein the second input of the differential amplifier is configured to be coupled to the one or more guard electrodes between the first chip and the second chip to supply the second voltage. 
 
     
     
       5. The electronic device of  claim 3 , further comprising:
 a first conductive trace carrying the output of the sense amplifier to the first input of the differential amplifier; and 
 a second conductive trace carrying the second voltage to the second input of the differential amplifier, wherein the first conductive trace and the second conductive trace have a same length. 
 
     
     
       6. The electronic device of  claim 5 , further comprising:
 a third conductive trace carrying the second voltage, wherein the second conductive trace and the third conductive trace are routed on opposite sides of the first conductive trace to shield the output of the sense amplifier. 
 
     
     
       7. The electronic device of  claim 3 , wherein:
 the second chip further comprises:
 a plurality of sense amplifiers; and 
 
 the first chip further comprises:
 a plurality of ADCs; and 
 a plurality of differential amplifiers, wherein each sense amplifier is coupled to one of the plurality of differential amplifier and each differential amplifier is coupled to one of the ADCs. 
 
 
     
     
       8. The electronic device 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. 
     
     
       9. The electronic device of  claim 1 , further comprising:
 a touch screen including the touch node electrode, display circuitry and a guard electrode, wherein the guard electrode is disposed between the display circuitry and the touch node electrode, and wherein the guard electrode and touch node electrode are configured to be coupled to the second voltage during touch sensing. 
 
     
     
       10. The electronic device of  claim 1 , wherein the second voltage is a guard voltage. 
     
     
       11. The electronic device of  claim 1 , wherein:
 the first chip further comprises:
 a power supply with a third voltage referenced to the first voltage; and 
 
 the second chip further comprises:
 a voltage regulator referenced to the second voltage, the voltage regulator having an input configured to be coupled to the third voltage and an output configured to generate a fourth voltage referenced to the second voltage to power the sense amplifier. 
 
 
     
     
       12. The electronic device of  claim 11 , wherein the second chip further comprises:
 a capacitor referenced to the second voltage and coupled to the input of the voltage regulator, the capacitor configured to maintain the input to the voltage regulator within a threshold amount of the third voltage during a first state of the second voltage. 
 
     
     
       13. A method of touch sensing with an electronic device including a first chip operating in a first power domain referenced to a first voltage and a second chip operating in a second power domain referenced to a second voltage, the method comprising:
 generating, at the first chip, the second voltage; 
 sensing, at the second chip, an analog touch signal of a touch node electrode; 
 transmitting the analog touch signal from the second chip to the first chip; 
 shifting, at the first chip, the analog touch signal transmitted from the second chip to the first chip from the second power domain to the first power domain; and 
 converting, at the first chip, the analog touch signal in the first power domain to a digital touch signal via an analog-to-digital converter referenced to the first voltage. 
 
     
     
       14. The method of  claim 13 , wherein the first voltage is a chassis ground. 
     
     
       15. The method of  claim 13 ,
 wherein shifting the analog touch signal comprises subtracting, in the first chip, the second voltage from the analog touch signal transmitted from the second chip to generate a first-voltage-referenced analog touch signal. 
 
     
     
       16. The method of  claim 13 , further comprising:
 driving one or more guard electrodes with the second voltage. 
 
     
     
       17. The method of  claim 13 , wherein the second voltage is a virtual ground voltage. 
     
     
       18. The method of  claim 13 , further comprising:
 supplying a third voltage from the first chip to the second chip; and 
 generating, at the second chip, a fourth voltage to power touch sensing circuitry of the second chip. 
 
     
     
       19. The method of  claim 18 , wherein the third voltage is supplied during a first time interval corresponding to a first state of the second voltage and maintained by circuitry in the second chip during a second time interval corresponding to a second state of the second voltage. 
     
     
       20. A non-transitory computer readable storage medium storing instructions, which when executed by an electronic device including a first chip operating in a first power domain referenced to a first voltage, a second chip operating in a second power domain referenced to a second voltage and one or more processors, cause the one or more processors to perform a method comprising:
 generating, at the first chip, the second voltage; 
 sensing, at the second chip, an analog touch signal of a touch node electrode; 
 transmitting the analog touch signal from the second chip to the first chip; 
 shifting, at the first chip, the analog touch signal transmitted from the second chip to the first chip from the second power domain to the first power domain; and 
 converting, at the first chip, the analog touch signal in the first power domain to a digital touch signal via an analog-to-digital converter referenced to the first voltage. 
 
     
     
       21. The non-transitory computer readable storage medium of  claim 20 , wherein the first voltage is a chassis ground and wherein the second voltage is a virtual ground voltage. 
     
     
       22. The non-transitory computer readable storage medium of  claim 20 ,
 wherein shifting the analog touch signal comprises subtracting, in the first chip, the second voltage from the analog touch signal transmitted from the second chip to generate a first-voltage-referenced analog touch signal. 
 
     
     
       23. The non-transitory computer readable storage medium of  claim 20 , the method further comprising:
 driving one or more guard electrodes with the second voltage. 
 
     
     
       24. The non-transitory computer readable storage medium of  claim 20 , the method further comprising:
 supplying a third voltage from the first chip to the second chip; and 
 generating, at the second chip, a fourth voltage to power touch sensing circuitry of the second chip. 
 
     
     
       25. The non-transitory computer readable storage medium of  claim 24 , wherein the third voltage is supplied during a first time interval corresponding to a first state of the second voltage and maintained by circuitry in the second chip during a second time interval corresponding to a second state of the second voltage.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional Patent Application No. 62/566,089, 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 a touch and/or proximity detection device and more particularly to a touch and/or proximity detection device including touch sensing circuitry divided between multiple power domains. 
     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 electric 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 or sensing 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 sensing 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 generally to a touch and/or proximity detection device and more particularly to a proximity detection device including touch sensing circuitry operating across multiple power domains. In some examples, the touch and/or proximity detection device can include guard circuitry referenced to an earth or chassis ground and touch sensing circuitry referenced to guard ground. The guard circuitry can include a voltage driver configured to produce a guard signal, a plurality of differential amplifiers configured to subtract the guard signal from a touch signal, and a plurality of ADCs configured to convert one or more analog touch signals to one or more digital touch signals, for example. The touch sensing circuitry can include a plurality of sense amplifiers referenced to guard ground and configured to sense a signal of a touch node electrode of a touch screen. The touch screen can further include one or more shielding electrodes coupled to the guard signal and configured to mitigate stray capacitance at the touch node electrodes and/or at one or more routing traces coupled to the touch node electrodes. 
    
    
     
       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 touch and/or proximity detection system according to examples of the disclosure. 
         FIG. 7B  illustrates an exemplary process for detecting one or more touching or proximate objects using a touch and/or proximity detection system according to examples of the disclosure. 
         FIG. 8A  illustrates an exemplary power system for a system operating in two power domains according to examples of the disclosure. 
         FIG. 8B  illustrates an exemplary timing diagram for operating an exemplary power system according to examples of the disclosure. 
         FIG. 9A  illustrates an exemplary block diagram of a touch and/or proximity detection system according to examples of the disclosure. 
         FIG. 9B  illustrates an exemplary block diagram of a touch and/or proximity detection system according to examples of the disclosure. 
         FIG. 9C  illustrates an exemplary process of operating a touch and/or proximity detection system 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 generally to a touch and/or proximity detection device and more particularly to a proximity detection device including touch sensing circuitry operating across multiple power domains. In some examples, the touch and/or proximity detection device can include guard circuitry referenced to an earth or chassis ground and touch sensing circuitry referenced to guard ground. The guard circuitry can include a voltage driver configured to produce a guard signal, a plurality of differential amplifiers configured to subtract the guard signal from a touch signal, and a plurality of ADCs configured to convert one or more analog touch signals to one or more digital touch signals, for example. The touch sensing circuitry can include a plurality of sense amplifiers referenced to guard ground and configured to sense a signal of a touch node electrode of a touch screen. The touch screen can further include one or more shielding electrodes coupled to the guard signal and configured to mitigate stray capacitance at the touch node electrodes and/or at one or more routing traces coupled to the touch node electrodes. 
       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 (e.g., a touch node) 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 touch node 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 electrodes arranged as 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. 
     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 plurality of touch node electrodes of 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  (V ac ) 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 V ref . Operational amplifier  308  can drive its output to voltage V o  to keep V in  substantially equal to V ref , and can therefore maintain V in  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 V detect . V detect  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 V detect  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 or trapezoid 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. 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.  7 A illustrates an exemplary touch and/or proximity detection system  700  according to examples of the disclosure. Touch and proximity detection system  700  illustrated in  FIG. 7A  includes guarded touch sensor panel  710 , guard chip  720 , and touch sensing chip  730 . Touch sensor panel  710  (e.g., implemented in touch screen  124 ,  126 ,  128 , or  130 ) 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), for example. In some examples, guard chip  720  can include voltage driver  722  (e.g., guard source  626 ) configured to output a guard voltage signal. Guard chip  720  can be referenced to earth or chassis ground  724  (i.e., guard chip  720  and its internal circuitry can operate in the earth or chassis ground power domain). Touch sensing chip  730  can be referenced to the guard voltage output from guard chip  720 . Touch sensing chip  730  can include various touch sensing circuitry operating in the guarded power domain. The touch sensing circuitry can include sense amplifier  732  referenced to the guard voltage and an analog-to-digital converter (ADC)  740  configured to convert the output of sense amplifier  732  into a digital signal for further processing. As illustrated in  FIG. 7A , ADC  740  can be a differential ADC in which one input can be the output of sense amplifier  732  and the second input can be an inverted version of the output of sense amplifier (e.g., provided by inverter  738 ). For example, inverter  738  can convert a single-ended touch signal to a differential signal, thereby doubling the voltage swing of the touch signal into the ADC. In some examples, ADC  740  can be a single-ended ADC and inverter  738  can be omitted. A differential ADC can have twice the input range as a single-sided ADC in some examples. Touch sensing chip  730  can include additional components not illustrated in  FIG. 7A , 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, touch sensing chip  730  can be referenced to the guard voltage by coupling the ground pin  734  of touch sensing chip  730  to the guard voltage output by the voltage driver  722  of guard chip  720 . 
     As discussed herein, in some examples, the guard voltage output from guard chip  720  can be applied to one or more guard plane(s)  714  of touch sensor panel  710  and to the ground pin of touch sensing chip  730 . In this way, touch sensing chip  730  can “float” relative to earth or chassis ground  724 , which can reduce noise injected into one or more components of touch circuitry. For example, earth or chassis ground  724  can become capacitively coupled to a noise source, such as display circuitry within the electronic device and/or a noise source external to the electronic device. 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, a guard plane  714  can be located between touch node electrodes  712  and display circuitry (not shown) included in an electronic device that includes a 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., as illustrated in  FIG. 6A ), including in the same layer as the touch node electrodes  712  in a layer above the touch node electrodes  712  (e.g., between the layer including the touch node electrodes and a cover material (e.g., a cover glass) of the electronic device), for example. The one or more guard planes  714  can be coupled to and driven by guard chip  720  to shield the touch node electrodes from parasitic or stray capacitances as described herein. 
     Touch node electrodes  712  can be sensed to detect changes in capacitance due to capacitive coupling due to an object proximate to or touching the touch sensor panel, for example. One or more touch node electrodes  712  can be coupled to the inverting input of one or more sense amplifiers  732  of touch sensing circuitry in touch sensing chip  730 , allowing each sense amplifier  732  to sense one or more touch signals indicative of an object proximate to or touching at the touch node corresponding to touch node electrode  712 , for example. Although one sense amplifier  732  is shown in  FIG. 7A , it should be understood that the touch sensing chip can include additional sense amplifiers to allow for sensing multiple touch nodes of the touch sensor panel partially or fully simultaneously (e.g., in parallel). In some examples, the non-inverting input of sense amplifier  732  can be virtually grounded by the guard voltage (e.g., possibly including some additional biasing (not shown)). The output of sense amplifier  732  can be converted to a digital signal at ADC  740  (which can receive both the non-inverted output signal from sense amplifier  732  and the inverted output signal from sense amplifier  732  in differential ADC examples or simply the output signal from sense amplifier  732  in single-ended ADC examples). The ADC can also be referenced to the guard voltage. The ADC can output a digital signal having n bits, which can be transmitted serially or in parallel using n channels. In some examples, touch sensing chip  730  can include a plurality of m sense amplifiers (e.g., similar to sense amplifier  732 ) and ADCs (e.g., similar to ADC  740 ) to simultaneously sense multiple touch node electrodes, thereby creating a system that can efficiently sense touch at a variety of sizes of touch sensor panels (e.g., by scaling m as a function of touch sensor panel size). 
     Guard chip  720  and touch sensing chip  730  can be separate integrated circuit chips as illustrated in  FIG. 7A . In some examples, both guard chip  720  and touch sensing chip  730  can be implemented on a single integrated circuit chip. For example, the components of touch sensing chip  730  can be placed in a deep well (e.g., n-well) to isolate circuitry operating in the guard domain from guard 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. 
     In some examples, an electronic device including touch and/or proximity detection system  700  can further include additional electronic components (e.g., touch processor  202 , host processor  228 , program storage  232 , LCD driver  234  illustrated in  FIG. 2 ) in the earth or chassis ground domain. One or more of these components, such as a touch processor or host processor may receive touch signals from ADC  740  for further processing, for example. In some examples, the touch signal data can be level shifted from the guarded domain to the earth or chassis ground domain prior to further processing. 
       FIG. 7B  illustrates an exemplary process  760  for detecting one or more touching or proximate objects using touch and/or proximity detection system  700  according to examples of the disclosure. Some of process  760  can be executed in the earth or chassis ground domain and some of process  760  can be executed in the guard domain. 
     At  762 , a guard voltage can be generated (e.g., by voltage driver  722  of guard chip  720 ). As described herein, the guard voltage can be used as the ground reference for the touch and/or proximity sensing. At  764 , touch node electrodes of the touch sensor panel (such as touch node electrode  712 ) can be stimulated relative to earth ground using the guard voltage. At  766  one or more guard planes  714  of the touch sensor panel can be stimulated using the guard voltage. The stimulation of the touch node electrodes and the guard planes can occur simultaneously in some examples. In such examples, the guard voltage can be generated and applied to guard planes when necessary for shielding during touch and/or proximity sensing operations, and not be generated or applied when touch and/or proximity sensing does not occur (e.g., during which time the guard ground can be at the same potential as the earth or chassis ground). At  768 , the touch node electrodes can be sensed by touch sensing circuitry (e.g., by sense amplifier  732 ) referenced to the guard voltage. Sensing the touch node electrodes can generate touch signals for each touch node (where the magnitude of the touch signal can indicate the presence or a touching or proximate object). A proximate or touching object, which is grounded to the chassis/earth ground, can capacitively couple to one or more touch node electrodes causing changes in capacitance that can be converted to one or more touch signals by respective sense amplifiers  732 . The touch signal output by a sense amplifier can have an amplitude equal to V guard ·c touch /C fb , where V guard  represents the guard voltage amplitude, C fb  represents the feedback capacitance of sense amplifier  732  and C touch  represents the capacitance between object  610  and touch node electrode  608 . At  770 , the touch signals sensed by the touch sensing circuitry can be converted into a digital touch signal for further processing (e.g., by ADC  740 ). In some examples, the digital touch signal can be generated by single-ended circuitry. In some examples, the digital touch signal can be generated by differential circuitry. In such examples, the touch signal can be inverted (e.g., by inverter  738 ) and supplied to the second input of the differential circuitry along with the touch signal supplied to the first input of the differential circuitry (e.g., to two inputs of a differential ADC).  764 - 770  can be performed by the touch sensing chip  730  operating in the guarded domain. At  772 , the digital touch signals can be level shifted from the guard domain to the earth or chassis ground domain. At  774 , the touch processor can process the digital touch signals to identify the presence of and/or locate one or more objects in contact with or proximate to the touch sensor panel  710 . The processing by the touch processor can be performed in the earth or chassis ground domain. In some examples, rather than level shifting at  772  and processing the touch signals in the earth or chassis ground domain, the touch processor can also be implemented in the guard domain and the leveling shifting can be performed for data to be transferred to a host processor operating in the earth or chassis ground domain. 
     Although process  760  has been described with reference to  FIG. 7B , in some examples, additional or alternative steps are possible. Further, some or all of process  760  can be repeated, omitted, or modified without departing from the scope of the disclosure. 
     It should be understood that touch and/or proximity detection system  700  is one example system that can use guarding to mitigate parasitic or stray capacitances in the system, but different arrangements of components are possible. As mentioned above, the touch sensing chip  720  can include m sense amplifiers. In some examples, to enable parallel processing, each of them sense amplifiers can have m corresponding ADCs. Each ADC can output n bits of data when transmitting the bits of data in parallel, for example. Therefore, in order to level shift all of the digital data for further processing, n×m channels can be level shifted simultaneously. In some examples, it can be advantageous to provide a system that can reduce the amount of data requiring level shifting between operating domains (e.g., to reduce power). Further, operating both the sense amplifier  732  and the ADC  740  (the analog front end (AFE) of each sense channel) in the guard domain can require powering both of these components (and any other AFE components) in the guard domain, as will be discussed below with reference to  FIGS. 8A-8B . Therefore, in some examples, some circuitry illustrated in touch sensing chip  730  can be operated in the earth or chassis ground domain and other circuitry illustrated in touch sensing chip  730  can be operated in the guard domain, as will be described with reference to  FIGS. 9A-9C . 
     As discussed herein, the touch sensing chip  730  operating in the guard domain can be powered by the guard generating chip operating in the chassis or earth ground domain.  FIG. 8A  illustrates an exemplary power system  800  for a system operating in two power domains according to examples of the disclosure. In some examples, power system can include components included in guard chip  820  (e.g., corresponding to guard chip  720 ) and components included in touch sensing chip  830  (e.g., e.g., corresponding to touch sensing chip  730 ). Guard chip  820  can be referenced to earth or chassis ground  824  (e.g., earth or chassis ground domain) and touch sensing chip  830  can be referenced to a guard voltage (e.g., guard domain). For example, guard chip  820  can include voltage driver  822  to generate a guard voltage for guarded referencing. Additionally, guard chip  820  can include different power buses. For example,  FIG. 8A  illustrates a +V high  power bus, a +V low  power bus, a −V high  power bus. Guard chip  820  can also include switching circuitry to selectively couple the voltage buses of guard chip  820  to touch sensing chip  830 . For example,  FIG. 8A  illustrates a first switch SW 1 , a second switch SW 2 , and a third switch SW 3  (one for each of the three buses). In some examples, one or more of the switches SW 1 , SW 2 , and SW 3  can comprise a diode (e.g., a Schottky diode) and can be current limited to limit the inrush current into capacitors Cn when the guard signal is LOW. 
     In some examples, touch sensing chip  830  can include multiple voltage regulators. For example,  FIG. 8A  illustrates a first voltage regulator LDO 1 , a second voltage regulator LDO 2 , a third voltage regulator LDO 3 . Touch sensing chip  830  can also include multiple capacitors and resistors (e.g., a first capacitor C 1 , a second capacitor C 2 , a third capacitor C 3 , a first resistor R 1 , a second resistor R 2 , and a third resistor R 3 ). To power one or more components of touch sensing chip  830  operating in the guard domain, one or more power buses (e.g., +V high , +V low , and −V high ) can be transposed from the earth or chassis ground domain to the guard domain (e.g., thereby creating busses +V′ high , +V′ low , and −V′ high ), for example. In some examples, voltage regulators LDO 1 , LDO 2 , and LDO 3  can be referenced to guard ground by way of pins  832 ,  834 , and  838  to generate power buses +V′ high , +V′ low , and −V′ high  in the guard domain. The inputs of voltage regulators LDO 1 , LDO 2 , and LDO 3  can be switchably coupled to power buses +V high , +V low , and −V high  by way of switches SW 1 , SW 2 , and SW 3 , for example. For example, while switches SW 1 , SW 2 , and SW 3  are closed, LDO 1 , LDO 2 , and LDO 3  can be powered by power buses +V high , +V low , and −V high  and capacitors C 1 , C 2 , and C 3  can accumulate charge. In some examples, while switches SW 1 , SW 2 , and SW 3  are open, capacitors C 1 , C 2 , and C 3  can discharge to continue to power LDO 1 , LDO 2 , and LDO 3 . In this way, capacitors C 1 , C 2 , and C 3  can be configured as flyback capacitors coupled to guard ground at pin  836  through resistors R 1 , R 2 , and R 3 . Resistors R 1 , R 2  and R 3  can be used to limit current from guard source  822  during the LOW phase of the guard signal and/or to keep the guard source stable when loaded with capacitors Cn. Charge current through guard source (e.g., output of a guard buffer) during the guard LOW phase can be also achieved by current limiting the guard buffer of guard source  822 . 
       FIG. 8B  illustrates an exemplary timing diagram  850  for operating power system  800  according to examples of the disclosure. Voltage driver  822  can generate an alternating voltage signal, guard voltage  852 , for example. In some examples, the operation of switches SW 1 , SW 2 , and SW 3  and the charge present on capacitors C 1 , C 2 , and C 3  can be coordinated with the polarity of guard voltage  852 . For example, during a time period from t 0  to t 1 , guard voltage  852  can have a high or positive voltage (guard HIGH) and switch SWn (e.g., SW 1  or SW 2 ) can be open, allowing capacitor Cn (e.g., C 1  or C 2 ) to discharge, where the discharge can provide the power to operate the corresponding LDOs and subsequent circuitry powered by the LDOs. During a time period from t 1  to t 2 , virtual ground  852  can have a low or negative voltage (guard LOW) and switch SWn (e.g., SW 1  or SW 2 ) can be closed, allowing capacitor Cn (e.g., C 1  or C 2 ) to charge for the next transition of guard voltage  852  while the corresponding voltage regulator (e.g., LDO 1  or LDO 2 ) receives power from a respective power bus (e.g., +V high  or +V low ). In some examples, SW 3  and C 3  can operate in a similar but inverted manner (e.g., SW 3  can be open when virtual ground is low or negative and SW 3  can be closed when virtual ground is high or positive) to deliver a negative voltage to LDO 3 . 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. 
     In some examples, the power requirements for touch sensing chip  830  can be reduced, level-shifting requirements can be simplified and/or interconnections can be reduced by moving some components of the AFE from the guarded domain to the chassis or earth ground domain. Reducing the number of powered components in the guarded domain, for example, can reduce the burden of power system  800 , allowing the size of capacitors C 1 , C 2 , and C 3  to be reduced, for example. Additionally, by performing level shifting in the analog domain (e.g., at the output of the sense amplifier), fewer signals are required between the guard referenced touch sensing chip  930  and the chassis or earth ground referenced touch sensing chip  920 .  FIG. 9A  illustrates an exemplary block diagram of a touch and/or proximity detection system  900  according to examples of the disclosure. In some examples, touch and/or proximity detection system  900  can include a touch sensor panel  910 , chassis or earth ground referenced touch sensing chip  920 , and guard referenced touch sensing chip  930 . Touch sensor panel  910  can include one or more touch node electrodes  912  and one or more guard planes  914 . In some examples, chassis or earth ground referenced touch sensing chip  920  can include voltage driver  922 , differential amplifiers  928 , and ADC  926 . Guard referenced touch sensing chip  930  can include one or more sense amplifiers  932  configured to be coupled to touch node electrodes  912  of touch sensor panel  910  (e.g., by switching circuitry such as multiplexers  938 ). In some examples, chassis or earth ground referenced touch sensing chip  920  can be referenced to earth or chassis ground  924  and guard referenced touch sensing chip  930  can be referenced to guard ground  922 . 
     Chassis or earth ground referenced touch sensing chip  920  can include voltage driver  922  configured to generate a guard voltage. In some examples, voltage driver  922  can be coupled to one or more guard planes  914  of touch sensor panel  910  and ground pin  934  of guard referenced touch sensing chip  930 . In this way, guard referenced touch sensing chip  930  can “float” relative to earth or chassis ground  924 , which can shield one or more components of touch circuitry from noise. For example, earth or chassis ground  924  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  920  can further include one or more touch sensing components for touch sensing, such as differential amplifiers  928  and ADCs  926 . 
     In some examples, one or more guard planes  914  can be located between touch node electrode  912  and display circuitry (not shown) included in an electronic device having touch and/or proximity detection system  900 . 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  912  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  914  can be coupled to voltage driver  922  of chassis or earth ground referenced touch sensing chip  920  to receive a guard voltage (e.g., guard ground). Touch node electrode  912  can become capacitively coupled to an object proximate to or touching the touch sensor panel  910 , for example. 
     Touch node electrode  912  can be coupled to the inverting input of sense amplifier  932 , allowing sense amplifier  932  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  912  of touch sensor panel  910  can be coupled to sense amplifiers  932  through multiplexer  938  (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) 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  932  can be coupled to virtual ground pin  936  referenced to the guard voltage generated by voltage driver  922 . Although multiplexers  938  are illustrated in guard referenced touch sensing chip  930 , in some examples, they may be implemented separately from guard referenced touch sensing chip  930  (e.g., in a different chip). 
     The block diagram of  FIG. 9A  includes in the guarded domain only a portion of the touch sensing circuitry illustrated in the guarded domain in  FIG. 7A  (e.g., the single ended to differential conversion and analog to digital converter implemented in the guarded domain in  FIG. 7A  can be implemented in the earth or chassis ground domain as illustrated in  FIG. 9A ). The remaining touch sensing circuitry can be implemented in the earth or chassis ground domain. This arrangement 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). 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. Specifically, the level shifting can be performed on the single-channel analog output of sense amplifiers  932 , rather than on the multi-channel output of ADC  740  (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  928 . In some examples, the non-inverting inputs of differential amplifiers  928  can be coupled to the guard voltage output by voltage driver  922  and the inverting input can receive the analog output from sense amplifier  932 . In this way, the touch signals from sense amplifiers  932  can be level shifted from the virtual ground domain to the earth or chassis ground domain (e.g., by subtracting the guarded voltage contribution to the touch signal from the touch signal). The differential amplifiers  928  can be referenced to earth or chassis ground  924 . Additionally, the ADC can be referenced to earth or chassis ground  924 . The differential ADC  926  can convert the differential output of differential amplifier  928  to a digital signal. Although analog circuitry is shown in  FIG. 9A , additional digital signal processing can be included on the chassis or earth ground referenced touch sensing chip  920  (e.g., touch processor  202 , touch controller  206 ). It should be understood that touch and/or proximity detection system  900  can divide touch signal processing between guard referenced touch sensing chip  930  and chassis or earth ground referenced touch sensing chip  920  in other ways than illustrated in  FIG. 9A . 
     Implementing the sense amplifier  932  in a guard domain chip separate from other analog and/or digital circuitry can improve scalability for touch sensor panels of different sizes.  FIG. 9B  illustrates an exemplary block diagram of a touch and/or proximity detection system  901  according to examples of the disclosure. In some examples, proximity detection system  901  can include a touch sensor panel  950 , chassis or earth ground referenced touch sensing chip  960 , and multiple touch sensing chips  970 . Touch sensor panel can include one or more touch node electrodes  952  (and one or more guard planes). In some examples, chassis or earth ground referenced touch sensing chip  960  can include voltage driver  962 , differential amplifiers  968 , and ADCs  966  for a first number of sense channels. The chassis or earth ground referenced touch sensing chip  960  can act as a master chip for multiple guard referenced touch sensing chips  970 . Guard referenced touch sensing chips  970  can each include sense amplifiers  972 . Although one sense amplifier is illustrated in each guard referenced touch sensing chip  970 , it should be understood that each can include multiple sense amplifiers. 
     Although not shown in  FIG. 9B , in some examples, each guard referenced touch sensing chip  970  can further include one or more multiplexers (e.g., multiplexer  938 ) or other switching circuitry, which can enable each sense amplifier  972  of the touch circuitry  972  to be coupled to some or all of the touch node electrodes of the touch sensor panel. In some examples, the multiplexers can be implemented separately from guard referenced touch sensing chips  970  to enable sharing. For example, one multiplexer chip can be shared by two (or more) guard referenced touch sensing chips  970 . In such examples, the multiplexer can also be a guard referenced multiplexer chip. Additionally or alternatively, chassis or earth ground referenced touch sensing chip  960  can include a plurality of multiplexers (e.g., between the sense amplifiers  972  and the inverting inputs of the differential amplifiers  968 ), for example. 
     The number of guard referenced touch sensing chips  970  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  970 . For example, when using a guard referenced touch sensing chip  970  including 20 sense channels (e.g., 20 sense amplifiers), two guard referenced touch sensing chips  970  can be used for a touch sensor panel including 40 touch node electrodes and ten guard referenced touch sensing chips  970  can be used for a touch sensor panel including 200 touch node electrodes. In some examples, chassis or earth ground referenced touch sensing chip  960  can include the same number of differential amplifiers and ADCs as each of the guard referenced touch sensing chips  970 . For example, a chassis or earth ground referenced touch sensing chip  960  with a fixed number m of differential amplifiers  968  and ADCs  966  can be used for scalability for use with a flexible number of guard referenced touch sensing chips (e.g., each including m sense amplifiers). Although proximity detection system  901  is illustrated as including m sense amplifiers  972 , m differential amplifiers  968 , and m ADCs  966 , in some examples, the number of sense amplifiers can be different from the number of differential amplifiers and ADCs included in a touch and/or proximity detection system according to examples of the disclosure. For example, chassis or earth ground referenced touch sensing chip  960  can include switching circuitry (e.g., analog MUXs) which can be operated to couple the sense amplifiers  972  of respective guard referenced touch sensing chips  970  to differential amplifiers  968 . Such a configuration can reduce the number of differential amplifiers and ADCs in chassis or earth ground referenced touch sensing chip  960  while maintaining the ability to interface with a larger number of sense channels distributed in multiple guard referenced touch sensing chips  970 . 
     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. 9A , the guard voltage generated in chassis or earth ground referenced touch sensing chip  920  can be supplied to differential amplifier  928  by a trace within chassis or earth ground referenced touch sensing chip  920 . In some examples, as illustrated in  FIG. 9B , the guard voltage generated in chassis or earth ground referenced touch sensing chip  960  can be supplied to differential amplifier  968  by a routing trace from the guard referenced touch sensing chip  970  to the chassis or earth ground referenced touch sensing chip  960 . 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 differential amplifiers  968  can be directly connected to guard source  962  within earth or chassis ground referenced touch sensing chip  960 . For example, one or more conductive traces carrying the guard signal can have a wide cross-sectional area, thereby reducing electrical resistance of the conductive trace and reducing phase drift of the guard signal. 
     Additionally or alternatively, the routing traces carrying the touch signals from the guard referenced touch sensing chip  970  to the chassis or earth ground referenced touch sensing chip  960  can be proximate to one or more guard planes. 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). Additionally or alternatively, one or more routing traces conducting a signal from a touch node electrode  952  can be shielded using a coaxial cable structure, for example. 
     In some examples, the guard referenced touch sensing chips  970  can be physically located close to touch sensor panel  950 . For example, a first guard referenced touch sensing chip  970  sensing touch node electrodes in a first portion of the touch sensor panel can be placed proximate to the first portion. Likewise a second guard referenced touch sensing chip  970  sensing touch node electrodes in a second portion of the touch sensor panel can be placed proximate to the second portion. This proximity can reduce the routing complexity near the touch sensor panel and improve the sensing of changes in capacitances at touch node electrodes of the touch sensor panel. 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. 9C  illustrates an exemplary process  980  of operating touch and/or proximity detection systems  900  or  901  according to examples of the disclosure. Some of process  980  can be executed in the earth or chassis ground domain and some of process  980  can be executed in the guard domain. 
     At  982  of process  980 , a virtual ground signal can be provided (e.g., by voltage driver  922  or  962 ). At  984 , a proximate object can capacitively couple to a touch node electrode (e.g., touch node electrode  912  or  952 ). In some examples,  982  and  984  can occur in the earth or chassis ground domain. 
     At  982 , a guard voltage can be generated (e.g., by voltage driver  922  or  926  of guard chip  920  or  970 ). As described herein, the guard voltage can be used as the ground reference for the touch and/or proximity sensing. At  984 , touch node electrodes of the touch sensor panel (such as touch node electrode  912  or  952 ) can be stimulated using the guard voltage. At  986  one or more guard planes  914  of the touch sensor panel can be stimulated using the guard voltage. The stimulation of the touch node electrodes and the guard planes can occur simultaneously in some examples. In such examples, the guard voltage can be generated and applied to guard planes when necessary for shielding during touch and/or proximity sensing operations, and not be generated or applied when touch and/or proximity sensing does not occur. At  988 , the touch node electrodes can be sensed by touch sensing circuitry (e.g., by sense amplifier  932  or  972 ) referenced to the guard voltage. Sensing the touch node electrodes can generate touch signals for each touch node (where the magnitude of the touch signal can indicate the presence or a touching or proximate object). A proximate or touching object, which is grounded to the chassis/earth ground, can capacitively couple to one or more touch node electrodes causing changes in capacitance that can be measured through the touch signals.  982 - 988  can be performed by the touch sensing chip  930  or chips  970  operating in the guarded domain. At  990 , the analog touch signals can be level shifted from the guard domain to the earth or chassis ground domain. At  992 , the touch signals sensed by the touch sensing circuitry can be converted into a digital touch signal for further processing (e.g., by ADC  926  or  966 ). In some examples, the digital touch signal can be generated by single-ended circuitry. In some examples, the digital touch signal can be generated by differential circuitry. In such examples, the touch signal can be inverted (e.g., by an inverter) and supplied to the second input of the differential circuitry along with the touch signal supplied to the first input of the differential circuitry. At  994 , the touch processor can process the digital touch signals to identify the presence of and/or locate one or more objects in contact with or proximate to the touch sensor panel  910  or  950 . The processing by the touch processor can be performed in the earth or chassis ground domain. 
     Although process  980  has been described with reference to  FIG. 9C , in some examples, additional or alternative steps are possible. Further, some or all of process  980  can be repeated, omitted, or modified without departing from the scope of the disclosure. 
     Therefore, according to the above, some examples of the disclosure are directed to an electronic device. The electronic device can comprise a first chip operating in a first power domain referenced to a first voltage and a second chip operating in a second power domain referenced to the second voltage. The first chip can comprise an analog-to-digital converter (ADC) having a first input and a voltage source configured to output a second voltage. The second chip can comprise a sense amplifier having a first input configured to be coupled to a touch node electrode, having a second input configured to be coupled to the second voltage, and having an output configured to be coupled to the first input of the ADC. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first voltage can be a chassis ground of the electronic device. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first chip can further comprise a differential amplifier having a first input configured to be coupled to the output of the sense amplifier, having a second input configured to be coupled to the second voltage, and having an output coupled to the first input of the ADC. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the electronic device can further comprise one or more guard electrodes between the first chip and the second chip. The one or more guard electrodes can be configured to be coupled to the second voltage. The second input of the differential amplifier can be configured to be coupled to the one or more guard electrodes between the first chip and the second chip to supply the second voltage. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the electronic device can further comprise a first conductive trace carrying the output of the sense amplifier to the first input of the differential amplifier and a second conductive trace carrying the second voltage to the second input of the differential amplifier. The first conductive trace and the second conductive trace can have the same length. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the electronic device can further comprise a third conductive trace carrying the second voltage. The second conductive trace and the third conductive trace can be routed on opposite sides of the first conductive trace to shield the output of the sense amplifier. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first chip can further comprise a plurality of sense amplifiers and the second chip can further comprise a plurality of ADCs and a plurality of differential amplifiers. Each sense amplifier can be coupled to one of the plurality of differential amplifier and each differential amplifier is coupled to one of the ADCs. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the electronic device can further comprise one or more guard electrodes coupled to the second voltage. The one or more guard electrodes can be configured to shield the output of the sense amplifier. 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. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the electronic device can further comprise a touch screen including the touch node electrode, display circuitry and a guard electrode. The guard electrode can be disposed between the display circuitry and the touch node. The guard electrode and touch node electrode can be configured to be coupled to the second voltage during touch sensing. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the second voltage can be a guard voltage. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first chip can further comprise a power supply with a third voltage referenced to the first voltage and the second chip can further comprise a voltage regulator referenced to the second voltage. The voltage regulator can have an input configured to be coupled to the third voltage and an output configured to generate a fourth voltage referenced to the second voltage to power the sense amplifier. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the second chip can further comprise a capacitor referenced to the second voltage and coupled to the input of the voltage regulator. The capacitor can be configured to maintain the input to the voltage regulator within a threshold amount of the third voltage during a first state of the second voltage. 
     Some examples of the disclosure are directed to a method of touch sensing with an electronic device including a first chip operating in a first power domain referenced to a first voltage and a second chip operating in a second power domain referenced to a second voltage. The method can comprise generating, at the first chip, the second voltage; sensing, at the second chip, an analog touch signal of a touch node electrode; transmitting the analog touch signal from the second chip to the first chip; and converting, at the first chip, the analog touch signal to a digital touch signal. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first voltage can be a chassis ground. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the method can further comprise shifting, at the first chip, the analog touch signal transmitted from the second chip to the first chip from the second power domain to the first power domain. Shifting the analog touch signal can comprise subtracting, in the first chip, the second voltage from the analog touch signal transmitted from the second chip to generate to an analog touch signal relative to the first voltage. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the method can further comprise driving one or more guard electrodes with the second voltage. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the second voltage can be a virtual ground voltage. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the method can further comprise supplying a third voltage from the first chip to the second chip; and generating, at the second chip, a fourth voltage to power touch sensing circuitry of the second chip. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the third voltage can be supplied during a first time interval corresponding to a first state of the second voltage and maintained by circuitry in the second chip during a second time interval corresponding to a second state of the second voltage. 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, can cause the one or more processors to perform any of the above methods. 
     Some examples of the disclosure are directed to an electronic device. The electronic device can comprise a first chip operating in a first power domain referenced to a first voltage and a plurality of second chips operating in a second power domain referenced to the second voltage. The first chip can comprise one or more analog-to-digital converters (ADCs) having a first input and a voltage source configured to output a second voltage. Each second chip can comprise a sense amplifier having a first input configured to be coupled to a touch node electrode, having a second input configured to be coupled to the second voltage, and having an output configured to be coupled to the first input of one of the one or more ADCs. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first chip can further comprise one or more differential amplifiers. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first chip can further comprise analog switching circuitry coupled to the one or more differential amplifiers. The switching circuitry can be configured to couple outputs from one or more of the second chips to the one or more differential amplifiers in the first chip. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the switching circuitry can comprise one or more analog multiplexers. 
     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: 20210427
Grant Date: 20210427
Priority Date: 20170929
Inventors: KRAH, CHRISTOPH H.
Assignee: APPLE INC
CPC Classifications: [{"code": "G06F3/04166", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F2203/04101", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F2203/04107", "inventive": false, "first": false, "tree": "[]"}, {"code": "G05F1/46", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/0418", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/0446", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F2203/04107", "inventive": false, "first": false, "tree": "[]"}, {"code": "G05F1/46", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/04166", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0446", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/0418", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F2203/04108", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/0418", "inventive": true, "first": true, "tree": "[]"}, {"code": "G05F1/46", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/04166", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0446", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F2203/04108", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F2203/04101", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F2203/04107", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 63794662