PATENT DOCUMENT

Publication Number: US-12056321-B2
Application Number: US-202318446835-A
Country: US
Kind Code: B2

Title: Apparatus to reduce negative pixel from capacitive touch

Abstract:
Touch electrode architectures for reducing the occurrence of negative pixels in mutual capacitance touch sensor panels that are caused by poorly grounded objects are disclosed. A touch electrode architecture can utilize mutual capacitance unit cells, each of which include a drive electrode, a sense electrode, and one or more ground bars. The one or more ground bars can provide an increased capacitive path to ground for a poorly grounded finger, which can result in a larger reduction in mutual capacitance between the drive and sense electrodes, improving touch detection. In addition, the increased capacitive coupling between the object and ground reduces the amount of charge that couples back onto nearby sense electrodes, which can reduce the negative pixel that can occur at those electrodes and reduce the number of touch detection errors. The one or more ground bars can be formed in the same layer as the drive electrode.

Claims:
The invention claimed is: 
     
       1. A mutual capacitance touch pixel, comprising:
 a first drive electrode formed in a first layer, the first drive electrode including a plurality of first drive spines arranged in a first direction, a plurality of first drive ribs coupled to the plurality of first drive spines in a second direction, and at least one first drive connector coupled to the plurality of first drive spines and arranged in the second direction; 
 a first sense electrode formed in a second layer different from the first layer, the first sense electrode including a first sense spine arranged in the first direction; 
 a plurality of first sense fingers coupled to the first sense spine in the second direction and interleaved between the plurality of first drive ribs and the at least one first drive connector to form an active mutual capacitance sensing area; and 
 one or more first ground bars formed in the first layer in the second direction along a portion of a perimeter of the active mutual capacitance sensing area. 
 
     
     
       2. The mutual capacitance touch pixel of  claim 1 , wherein the plurality of first drive spines are routed along the perimeter of the active mutual capacitance sensing area and positioned to be electrically couplable to a drive spine of an adjacent mutual capacitance touch pixel. 
     
     
       3. The mutual capacitance touch pixel of  claim 1 , wherein the first sense spine extends to the perimeter of the active mutual capacitance sensing area and is positioned to be electrically couplable to a sense spine of an adjacent mutual capacitance touch pixel. 
     
     
       4. The mutual capacitance touch pixel of  claim 1 , wherein the one or more first ground bars are routed along a top and bottom side of the active mutual capacitance sensing area, each first ground bar positioned to be electrically couplable to a ground bar of an adjacent mutual capacitance touch pixel. 
     
     
       5. A touch sensor panel including the mutual capacitance touch pixel of  claim 4 , the touch sensor panel comprising an array of mutual capacitance touch pixels having their first ground bars electrically coupled together to form a continuous ground bar extending along a width of the touch sensor panel. 
     
     
       6. The mutual capacitance touch pixel of  claim 1 , further comprising one or more second ground bars formed in the first layer in the first direction and coupled to the one or more first ground bars. 
     
     
       7. The mutual capacitance touch pixel of  claim 6 , wherein the one or more second ground bars are routed along a left and right side of the active mutual capacitance sensing area, each second ground bar positioned to be electrically couplable to a ground bar of an adjacent mutual capacitance touch pixel. 
     
     
       8. A touch sensor panel including the mutual capacitance touch pixel of  claim 7 , the touch sensor panel comprising an array of mutual capacitance touch pixels having their first and second ground bars electrically coupled to the ground bars of the other mutual capacitance touch pixels to form a ground lattice around the mutual capacitance touch pixels. 
     
     
       9. The mutual capacitance touch pixel of  claim 6 , wherein the one or more first ground bars and the one or more second ground bars form a ring around the active mutual capacitance sensing area. 
     
     
       10. The mutual capacitance touch pixel of  claim 1 , wherein the first layer is arranged to be closer to a touch surface of the touch pixel than the second layer. 
     
     
       11. A unit cell mutual capacitance touch electrode, comprising:
 a drive electrode formed on a first layer and having a plurality of drive ribs; 
 a sense electrode formed on a second layer and having a plurality of fingers interleaved with the plurality of drive ribs to form a mutual capacitance sensing area; and 
 a first ground bar formed on the first layer outside the mutual capacitance sensing area; 
 wherein the drive electrode, the sense electrode, and the first ground bar in the unit cell are arranged within the unit cell to be electrically couplable with the drive electrode, the sense electrode, and the first ground bar of a plurality of other unit cells to form a mutual capacitance sensing array. 
 
     
     
       12. The unit cell mutual capacitance touch electrode of  claim 11 , further comprising:
 a second ground bar coupled to the first ground bar and formed on the first layer outside the mutual capacitance sensing area. 
 
     
     
       13. The unit cell mutual capacitance touch electrode of  claim 11 , wherein the first layer is arranged to be closer to a touch surface of the touch electrode than the second layer. 
     
     
       14. A mutual capacitance touch sensor panel, comprising:
 a plurality of mutual capacitance touch pixels, each mutual capacitance touch pixel including
 a first drive electrode formed in a first layer, the first drive electrode including a plurality of first drive spines arranged in a first direction, a plurality of first drive ribs coupled to the plurality of first drive spines in a second direction, and at least one first drive connector coupled to the plurality of first drive spines and arranged in the second direction, 
 a first sense electrode formed in a second layer different from the first layer, the first sense electrode including a first sense spine arranged in the first direction, 
 a plurality of first sense fingers coupled to the first sense spine in the second direction and interleaved between the plurality of first drive ribs and the at least one first drive connector to form an active mutual capacitance sensing area, and 
 one or more first ground bars formed in the first layer in the second direction along a portion of a perimeter of the active mutual capacitance sensing area. 
 
 
     
     
       15. The mutual capacitance touch sensor panel of  claim 14 , wherein the plurality of first drive spines within each mutual capacitance touch pixel are routed along the perimeter of the active mutual capacitance sensing area and electrically coupled to a drive spine of an adjacent mutual capacitance touch pixel. 
     
     
       16. The mutual capacitance touch sensor panel of  claim 14 , wherein the first sense spine of each mutual capacitance touch pixel extends to the perimeter of the active mutual capacitance sensing area and electrically coupled to a sense spine of an adjacent mutual capacitance touch pixel. 
     
     
       17. The mutual capacitance touch sensor panel of  claim 14 , wherein the one or more first ground bars of each mutual capacitance touch pixel are routed along a top and bottom side of the active mutual capacitance sensing area and electrically coupled to a first ground bar of an adjacent mutual capacitance touch pixel. 
     
     
       18. The mutual capacitance touch sensor panel of  claim 17 , wherein the electrically coupled first ground bars of adjacent mutual capacitance touch pixels form a continuous ground bar extending along a width of the touch sensor panel. 
     
     
       19. The mutual capacitance touch sensor panel of  claim 14 , each mutual capacitance touch pixel further including one or more second ground bars formed in the first layer in the first direction and coupled to the one or more first ground bars. 
     
     
       20. The mutual capacitance touch sensor panel of  claim 19 , wherein the one or more second ground bars within each mutual capacitance touch pixel are routed along a left and right side of the active mutual capacitance sensing area and electrically coupled to a second ground bar of an adjacent mutual capacitance touch pixel.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application No. 63/376,421, filed Sep. 20, 2022, the entire disclosure of which is hereby incorporated by reference in its entirety for all purposes. 
    
    
     FIELD OF THE DISCLOSURE 
     This relates generally to touch sensor panels, and more particularly to touch electrode architectures for reducing the occurrence of so-called “negative pixels” in mutual capacitance touch sensor panels that are caused by poorly grounded or ungrounded objects in proximity to the touch surface. 
     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 sensor panels and touch screens, in particular, are popular because of their ease and versatility of operation as well as their declining price. Capacitive touch sensor panels can be formed from a matrix of conductive plates (e.g., touch electrodes) made of materials such as copper, silver, conductive polymers, metal mesh, graphene, nanowires (e.g., silver nanowires) or nanotubes (e.g., carbon nanotubes). Capacitive touch sensor panels can also be formed from a substantially transparent material such as Indium Tin Oxide (ITO). 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. The display can be 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 touch sensor panel so that a touch-sensitive surface of the touch screen can cover at least a portion of the viewable area of the display device. Some touch screens can be formed by at least partially integrating touch sensing circuitry into a display pixel stack-up (i.e., the stacked material layers forming the display pixels). 
     Touch panels and touch screens can allow a user to perform various functions by touching the touch sensor panel or touch screen using a finger, stylus or other object at a location. In the case of touch screens, those locations are often dictated by a user interface (UI) being displayed by the display device. In general, touch panels and 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 position of the touch (and in the case of a touch screen in accordance with the display appearing at the time of the touch), and thereafter perform one or more actions based on the touch. In the case of some touch sensing systems, a physical touch on the display is not needed to detect a touch. For example, in some capacitive-type touch sensing systems, fringing electrical fields used to detect touch can extend beyond the surface of the display, and objects approaching near the surface may be detected near the surface without actually touching the surface. 
     Capacitive touch sensor panels detect a touch, or a near-touch, of a proximate object by detecting the effect of capacitive coupling between the object and the touch electrodes. When the object is well-grounded, the capacitive coupling can couple charge to ground through the object. In the case of mutual capacitance touch sensing, this coupling of charge to ground reduces the mutual capacitance between the drive electrode and the sense electrode of a touch pixel, and this reduction in mutual capacitance can be detected and recognized as a touch by sensing circuitry. However, when the object is poorly grounded or ungrounded, there can be less of a capacitive path to ground through the object. As a result, there is less shunting of charge to ground through the object, and a smaller reduction in mutual capacitance between the drive and sense electrode than with a well-grounded object. Because there is a smaller reduction in mutual capacitance, it can be more difficult to detect the presence of the object. In addition, when a poorly grounded or ungrounded object is located over multiple mutual capacitance touch pixels, such as when two fingers are touching the touch panel, charge that would have been coupled to ground (in the case of a well-grounded object) can instead couple back onto a nearby sense electrode, creating a so-called “negative pixel” at that location due to the unexpected increase in charge at that nearby sense electrode. The decreased touch detection capability and the negative pixels that can result from a poorly grounded or ungrounded object can lead to touch detection errors. 
     BRIEF SUMMARY OF THE DISCLOSURE 
     This relates generally to touch sensor panels, and more particularly to touch electrode architectures for reducing the occurrence of so-called “negative pixels” in mutual capacitance touch sensor panels that are caused by poorly grounded or ungrounded objects in proximity to the touch surface. In some examples, a touch electrode architecture can utilize mutual capacitance unit cells or touch pixels, each of which include a drive electrode, a sense electrode, and one or more ground bars. The one or more ground bars can provide an increased capacitive path to ground for a poorly grounded or ungrounded object such as a finger, which can result in a larger reduction in mutual capacitance between the drive and sense electrodes when the object is proximate a touch electrode, improving touch detection. In addition, the increased capacitive coupling between the object and ground reduces the amount of charge that couples back onto nearby sense electrodes, which can reduce the negative pixel that can occur at those electrodes and reduce the number of touch detection errors. In some examples, the one or more ground bars can be formed in the same layer as the drive electrode. The unit cell touch electrodes can be designed such that when multiple unit cells are employed in an array, they can abut each other, and continuous rows of drive electrodes, continuous columns of sense electrodes, and continuous row and/or column ground bars can be formed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS.  1 A- 1 E  illustrate example systems that can include a touch electrode architecture for reducing negative pixels according to examples of the disclosure. 
         FIG.  2    illustrates an example computing system including a touch electrode architecture for reducing negative pixels according to examples of the disclosure. 
         FIG.  3 A  illustrates an example touch sensor circuit corresponding to a self-capacitance measurement of a touch node electrode and sensing circuit according to examples of the disclosure. 
         FIG.  3 B  illustrates an example touch sensor circuit corresponding to a mutual-capacitance drive line and sense line and sensing circuit according to examples of the disclosure. 
         FIG.  4 A  illustrates a touch screen with touch node electrodes arranged in a pixelated touch node electrode configuration according to examples of the disclosure. 
         FIG.  4 B  illustrates a touch screen with touch electrodes arranged in rows and columns according to examples of the disclosure. 
         FIG.  5    is a symbolic circuit diagram of negative pixels being created at two mutual capacitance touch electrodes due to the touching of two fingers of a poorly grounded hand according to some examples of this disclosure. 
         FIG.  6 A  illustrates a unit cell of a touch pixel architecture that can be replicated to form a mutual capacitance touch sensor panel according to some embodiments of the disclosure. 
         FIG.  6 B  illustrates a reduced circuit model of a poorly grounded finger in proximity to mutual capacitance touch pixels as shown in  FIG.  5   , where the touch pixels are unit cells of the example architecture shown in  FIG.  6 A  according to some embodiments of the disclosure. 
         FIG.  6 C  illustrates a plot of negative pixel % and C SIGSense  versus sense line width according to some embodiments of the disclosure. 
         FIG.  6 D  illustrates a plot of negative pixel % and C FS /C SIGSense  versus sense line width according to some embodiments of the disclosure. 
         FIG.  6 E  illustrates a plot of negative pixel % and the drive-to-ground capacitance C DG  versus drive line width according to some embodiments of the disclosure. 
         FIG.  6 F  illustrates a plot of negative pixel % and C FS /C SIGSense  versus drive line width according to some embodiments of the disclosure. 
         FIG.  6 G  illustrates four clustered unit cells of the example architecture shown in  FIG.  6 A  that have been replicated and arranged to form a portion of a mutual capacitance touch sensor panel according to some embodiments of the disclosure. 
         FIG.  6 H  illustrates a unit cell of an alternative touch pixel architecture that can be replicated to form a mutual capacitance touch sensor panel according to some embodiments of the disclosure. 
         FIG.  6 I  illustrates four clustered unit cells of the example architecture shown in  FIG.  6 H  that have been replicated and arranged to form a portion of a mutual capacitance touch sensor panel according to some embodiments of the disclosure. 
         FIG.  7    illustrates a unit cell of an alternative touch pixel architecture that can be replicated to form a mutual capacitance touch sensor panel according to some embodiments of the disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     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 touch sensor panels, and more particularly to touch electrode architectures for reducing the occurrence of so-called “negative pixels” in mutual capacitance touch sensor panels that are caused by poorly grounded or ungrounded objects in proximity to the touch surface. In some examples, a touch electrode architecture can utilize mutual capacitance unit cells or touch pixels, each of which include a drive electrode, a sense electrode, and one or more ground bars. The one or more ground bars can provide an increased capacitive path to ground for a poorly grounded or ungrounded object such as a finger, which can result in a larger reduction in mutual capacitance between the drive and sense electrodes when the object is proximate a touch electrode, improving touch detection. In addition, the increased capacitive coupling between the object and ground reduces the amount of charge that couples back onto nearby sense electrodes, which can reduce the negative pixel that can occur at those electrodes and reduce the number of touch detection errors. In some examples, the one or more ground bars can be formed in the same layer as the drive electrode. The unit cell touch electrodes can be designed such that when multiple unit cells are employed in an array, they can abut each other, and continuous rows of drive electrodes, continuous columns of sense electrodes, and continuous row and/or column ground bars can be formed. 
       FIGS.  1 A- 1 E  illustrate example systems that can include a touch electrode architecture for reducing negative pixels according to examples of the disclosure.  FIG.  1 A  illustrates example mobile telephone  100  that includes touch screen  102  (which includes a touch electrode architecture for reducing negative pixels) according to examples of the disclosure.  FIG.  1 B  illustrates an example digital media player  104  that includes touch screen  102  (which includes a touch electrode architecture for reducing negative pixels) according to examples of the disclosure.  FIG.  1 C  illustrates an example personal computer  106  that includes a touch screen  102  (which includes a touch electrode architecture for reducing negative pixels) and a trackpad  108  (which also includes a touch electrode architecture for reducing negative pixels) according to examples of the disclosure.  FIG.  1 D  illustrates an example tablet computing device  110  that includes a touch screen  102  (which includes a touch electrode architecture for reducing negative pixels) according to examples of the disclosure.  FIG.  1 E  illustrates an example wearable device  112  that includes a touch screen  102  (which includes a touch electrode architecture for reducing negative pixels) according to examples of the disclosure. It is understood that touch screen  102  (which includes the touch electrode architecture for reducing negative pixels) and/or trackpad  108  (which includes the touch electrode architecture for reducing negative pixels, but not a display) can be implemented in other devices as well. 
     In some examples, trackpad  108 , along with the touch sensor panels within touch screens  102 , can be based on self-capacitance. A self-capacitance-based touch system can include a matrix of small, individual plates of conductive material or groups of individual plates of conductive material forming larger conductive regions that can be referred to as touch electrodes or as touch node electrodes (as described below with reference to  FIG.  4 B ). For example, a touch sensor panel can include a plurality of individual touch electrodes, each touch electrode identifying or representing a unique location (e.g., a touch node) on the touch sensor panel at which touch or proximity is to be sensed, and each touch node electrode being electrically isolated from the other touch node electrodes in the touch sensor panel. Such a touch sensor panel can be referred to as a pixelated self-capacitance touch sensor panel, though it is understood that in some examples, the touch node electrodes on the touch sensor panel can be used to perform scans other than self-capacitance scans on the touch sensor panel (e.g., mutual capacitance scans). During operation, a touch node electrode can be stimulated with an alternating current (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 sensor panel. In some examples, the touch node electrodes of a self-capacitance-based touch system can be formed from rows and columns of conductive material, and changes in the self-capacitance to ground of the rows and columns can be detected, similar to above. In some examples, a touch sensor panel can be multi-touch, single touch, projection scan, full-imaging multi-touch, capacitive touch, etc. 
     In some examples, trackpad  108 , along with the touch sensor panels within touch screens  102 , 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 (in a double-sided configuration), or may be adjacent to each other on the same layer (e.g., as described below with reference to  FIG.  4 A ). 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. As described herein, in some examples, a mutual capacitance-based touch system can form touch nodes from a matrix of small, individual plates of conductive material. 
     In some examples, trackpad  108 , along with touch sensor panels within touch screens  102 , can be based on mutual capacitance and/or self-capacitance. The electrodes can be arranged as a matrix of small, individual plates of conductive material (e.g., as in touch node electrodes  448  in touch screen  402  in  FIG.  4 A ) or as drive lines and sense lines (e.g., as in row touch electrodes  438  and column touch electrodes  440  in touch screen  402  in  FIG.  4 B ), 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    illustrates an example computing system including a touch electrode architecture for reducing negative pixels according to examples of the disclosure. Computing system  214  can be included in, for example, a mobile phone, tablet, touchpad, portable or desktop computer, portable media player, wearable device or any mobile or non-mobile computing device that includes a touch screen or touch sensor panel. Computing system  214  can include a touch sensing system including one or more touch processors  216 , peripherals  218 , a touch controller  220 , and touch sensing circuitry (described in more detail below). Peripherals  218  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  220  can include, but is not limited to, one or more sense channels  222 , channel scan logic  224  and driver logic  226 . Channel scan logic  224  can access RAM  228 , autonomously read data from the sense channels and provide control for the sense channels. In addition, channel scan logic  224  can control driver logic  226  to generate stimulation signals  230  at various frequencies and/or phases that can be selectively applied to drive regions of the touch sensing circuitry of touch screen  202 , as described in more detail below. In some examples, touch controller  220 , touch processor  216  and peripherals  218  can be integrated into a single application specific integrated circuit (ASIC), and in some examples can be integrated with touch screen  202  itself. 
     It should be apparent that the architecture shown in  FIG.  2    is only one example architecture of computing system  214 , and that the system could have more or fewer components than shown, or a different configuration of components. In some examples, computing system  214  can include an energy storage device (e.g., a battery) to provide a power supply and/or communication circuitry to provide for wired or wireless communication (e.g., cellular, Bluetooth, Wi-Fi, etc.). The various components shown in  FIG.  2    can be implemented in hardware, software, firmware, or any combination thereof, including one or more signal processing and/or application specific integrated circuits. 
     Computing system  214  can include a host processor  232  for receiving outputs from touch processor  216  and performing actions based on the outputs. For example, host processor  232  can be connected to program storage  234  and a display controller/driver  236  (e.g., a Liquid-Crystal Display (LCD) driver). It is understood that although some examples of the disclosure may be described with reference to LCD displays, the scope of the disclosure is not so limited and can extend to other types of displays, such as Light-Emitting Diode (LED) displays, including Organic LED (OLED), Active-Matrix Organic LED (AMOLED) and Passive-Matrix Organic LED (PMOLED) displays. Display driver  236  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. 
     Host processor  232  can use display driver  236  to generate a display image on touch screen  202 , such as a display image of a user interface (UI), and can use touch processor  216  and touch controller  220  to detect a touch on or near touch screen  202 , such as a touch input to the displayed UI. The touch input can be used by computer programs stored in program storage  234  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  232  can also perform additional functions that may not be related to touch processing. 
     Note that one or more of the functions described herein can be performed by firmware stored in memory (e.g., one of the peripherals  218  in  FIG.  2   ) and executed by touch processor  216 , or stored in program storage  234  and executed by host processor  232 . 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. In some examples, RAM  228  or program storage  234  (or both) can be a non-transitory computer readable storage medium. One or both of RAM  228  and program storage  234  can have stored therein instructions, which when executed by touch processor  216  or host processor  232  or both, can cause the device including computing system  214  to perform one or more functions and methods of one or more examples of this disclosure. 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. 
     Touch screen  202 , which can include a touch electrode architecture for reducing negative pixels, can be used to derive touch information at multiple discrete locations of the touch screen, referred to herein as touch nodes. Touch screen  202  can include touch sensing circuitry that can include a capacitive sensing medium having a plurality of drive lines  238  and a plurality of sense lines  240 . It should be noted that the term “lines” is sometimes used herein to mean simply conductive pathways, as one skilled in the art will readily understand, and is not limited to elements that are strictly linear, but includes pathways that change direction, and includes pathways of different size, shape, materials, etc. Drive lines  238  can be driven by stimulation signals  230  from driver logic  226  through a drive interface  242 , and resulting sense signals  244  generated in sense lines  240  can be transmitted through a sense interface  246  to sense channels  222  in touch controller  220 . In this way, drive lines and sense lines can be part of the touch sensing circuitry that can interact to form capacitive sensing nodes, which can be thought of as touch picture elements (touch pixels) and referred to herein as touch nodes, such as touch nodes  248  and  250 . This way of understanding can be particularly useful when touch screen  202  is viewed as capturing an “image” of touch (“touch image”). In other words, after touch controller  220  has determined whether a touch has been detected at each touch nodes in the touch screen, the pattern of touch nodes in the touch screen at which a touch occurred can be thought of as an “image” of touch (e.g., a pattern of fingers touching the touch screen). 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, drive lines  238  may be directly connected to driver logic  226  or indirectly connected to drive logic  226  via drive interface  242  and sense lines  240  may be directly connected to sense channels  222  or indirectly connected to sense channels  222  via sense interface  246 . In either case an electrical path for driving and/or sensing the touch nodes can be provided. 
     In some examples, computing system  214  can also include one or more optical devices  252 , which may also be referred to herein as optical components. In some examples, the one or more optical devices  252  can include components for light emitting and/or light sensing. In some examples, the one or more optical devices  252  can include light-emitting diodes (e.g., LEDs, OLED s, etc.), cameras, lasers (e.g., vertical-cavity surface-emitting lasers, etc.), light detectors, photodiodes, and the like. In some examples, the operation of the optical devices can be controlled by host processor  232  or an optical controller (not shown) to perform functionality using the optical devices. The functionality can include, without limitation, projecting light, imaging, proximity sensing and ranging, ambient light sensing, photography, etc., among other possibilities. In some examples, the one or more optical devices  252  can be implemented in proximity to touch screen  202  (e.g., on a periphery of or in a notch region along a perimeter of touch screen  202 ). As described in more detail herein, in some examples, the one or more optical devices  252  can be integrated with touch screen  202  such that light passes through one or more layers of the touch screen. 
     In some examples, computing system  214  can also include one or more input and/or output devices, such as speaker  254 . It is understood that speaker  254  is an example input and/or output device, but other input and/or output devices are possible. In some examples, the operation of the input and/or output devices, including speaker  254 , can be controlled by host processor  232  or an input/output controller (not shown) to perform functionality using the input and/or output devices. The functionality can include audio functionality for speaker  254 . In some examples, the one or more input and/or output devices can be implemented in proximity to touch screen  202  (e.g., on a periphery of or in a notch region along a perimeter of touch screen  202 ). As described in more detail herein, in some examples, the one or more input and/or output devices can be integrated with touch screen  202 . For example, integrated speaker  254  with touch screen  202 , and having touch screen  202  can include an opening or one or more hole(s), can enable audio to pass through the touch screen. In some such examples, the opening(s) in the touch screen results in one or more touch electrode-free regions. 
       FIG.  3 A  illustrates an example touch sensor circuit  356  corresponding to a self-capacitance measurement of a touch node electrode  348  and sensing circuit  358  according to examples of the disclosure. Touch node electrode  348  can have an inherent self-capacitance  382  to ground associated with it, and also an additional self-capacitance to ground that is formed when an object, such as finger  360 , is in proximity to or touching the electrode, and is itself capacitively coupled to ground via capacitance  384 . As  FIG.  3 A  illustrates, the presence of finger  360  creates an additional capacitive path to ground (through capacitances  362  and  384 ) in parallel with the inherent self-capacitance  382 , resulting in an increase in self-capacitance seen at touch node electrode  348 . Touch node electrode  348  can be coupled to sensing circuit  358 . Sensing circuit  358  can include an operational amplifier  364 , feedback resistor  366  and feedback capacitor  368 , although other configurations can be employed. For example, feedback resistor  366  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  348  can be coupled to the inverting input (−) of operational amplifier  364 . An AC voltage source  370  (V ac) can be coupled to the non-inverting input (+) of operational amplifier  364 . Touch sensor circuit  356  can be configured to sense changes (e.g., increases) in the total self-capacitance  362  of the touch node electrode  348  induced by a finger or object either touching or in proximity to the touch sensor panel. The output of touch sensor circuit  356  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.  3 B  illustrates an example touch sensor circuit  372  corresponding to a mutual-capacitance drive line  338  and sense line  340  and sensing circuit  358  according to examples of the disclosure. Drive line  338  can be stimulated by a stimulation signal output from AC voltage source  370  (e.g., an AC voltage signal). The stimulation signal can be capacitively coupled to sense line  340  through mutual capacitance  378  between drive line  338  and the sense line. When an object, such as finger  360 , approaches the touch node created by the intersection of drive line  338  and sense line  340 , a finger-to-drive line capacitance C FD    386 , and a finger-to-ground capacitance  384 , and a finger-to-sense line capacitance C FS    388  is also formed. As a result, charge is coupled to ground through finger  360  rather than onto sense line  340  through C FS    388 , and mutual capacitance  378  can change (e.g., decrease). This change in mutual capacitance  378  can be detected to indicate a touch or proximity event at the touch node, as described herein. The sense signal coupled onto sense line  340  can be received by sensing circuit  358 . Sensing circuit  358  can include operational amplifier  364  and at least one of a feedback resistor  366  and a feedback capacitor  368 .  FIG.  3 B  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  364 , and the non-inverting input of the operational amplifier can be coupled to a reference voltage V ref . Operational amplifier  364  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  358  can be mostly a function of the ratio of mutual capacitance  378  and the feedback impedance, comprised of resistor  366  and/or capacitor  368 . The output of sensing circuit  358  Vo can be filtered and heterodyned or homodyned by being fed into multiplier  380 , where Vo can be multiplied with local oscillator  374  to produce V detect . V detect  can be inputted into filter  376 . One skilled in the art will recognize that the placement of filter  376  can be varied; thus, the filter can be placed after multiplier  380 , 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. Note that while  FIGS.  3 A- 3 B  indicate the demodulation at multiplier  380  occurs in the analog domain, output Vo may be digitized by an analog-to-digital converter (ADC), and multiplier  380 , filter  376  and oscillator  374  may be implemented in a digital fashion (e.g., multiplier  380  can be a digital demodulator, filter  376  can be a digital filter, and oscillator  374  can be a digital NCO (Numerical Controlled Oscillator). 
     Referring back to  FIG.  2   , in some examples, touch screen  202  can be an integrated touch screen in which touch sensing circuit elements of the touch sensing system can be integrated into the display pixel stack-ups of a display. The circuit elements in touch screen  202  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. Additionally, as described herein, in some examples, the integrated touch screen can include optical devices and one or more high-transmittance regions corresponding to the optical devices. Additionally, as described herein, in some examples, the integrated touch screen can include one or more input and/or output devices and one or more touch-electrode free regions corresponding to the input and/or output devices (e.g., speaker hole, high-transmittance region without touch electrodes, etc.). 
       FIG.  4 A  illustrates touch screen  402  with touch node electrodes  448  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  448 , 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  448  can be on the same or different material layers on touch screen  402 . In some examples, touch screen  402  can sense the self-capacitance of touch node electrodes  448  to detect touch and/or proximity activity on touch screen  402 , and in some examples, touch screen  402  can sense the mutual capacitance between touch node electrodes  448  to detect touch and/or proximity activity on touch screen  402 . 
       FIG.  4 B  illustrates touch screen  402  with touch electrodes  438  and  440  arranged in rows and columns according to examples of the disclosure. Specifically, touch screen  402  can include a plurality of touch electrodes  438  disposed as rows, and a plurality of touch electrodes  440  disposed as columns. Touch electrodes  438  and touch electrodes  440  can be on the same or different material layers on touch screen  402 , and can intersect with each other, as illustrated in  FIG.  4 A . In some examples, the electrodes can be formed on opposite sides of a transparent (partially or fully) substrate and from a transparent (partially or fully) semiconductor material, such as ITO, though other materials are possible. Electrodes displayed on layers on different sides of the substrate can be referred to herein as a double-sided sensor. In some examples, the touch electrodes can be formed on the same layer, and may be referred to herein as a single-sided sensor. In some examples, touch screen  402  can sense the self-capacitance of touch electrodes  438  and  440  to detect touch and/or proximity activity on touch screen  402 , and in some examples, touch screen  402  can sense the mutual capacitance between touch electrodes  438  and  440  to detect touch and/or proximity activity on touch screen  402 . 
     When the architecture of  FIG.  4 B  is configured for mutual capacitance sensing (as shown in  FIG.  3 B ), but an object is poorly grounded or ungrounded, there can be less of a capacitive path to ground through the object. As a result, there is less shunting of charge to ground through the object, and a smaller reduction in mutual capacitance between the drive and sense electrode than with a well-grounded object. Because of this smaller reduction in mutual capacitance, it can be more difficult to detect the presence of the object. In addition, when a poorly grounded or ungrounded object is located over multiple mutual capacitance touch pixels, such as when two fingers are touching the touch panel, charge that would have been coupled to ground (in the case of a well-grounded object) can instead couple back onto a nearby sense electrode, creating a so-called “negative pixel” at that location due to the unexpected increase in charge at that nearby sense electrode. The decreased touch detection capability and the negative pixels that can result from a poorly grounded or ungrounded object can lead to touch detection errors. 
       FIG.  5    is a symbolic circuit diagram of negative pixels being created at two mutual capacitance touch electrodes due to the touching of two fingers of a poorly grounded hand according to some examples of this disclosure. In the example of  FIG.  5   , two drive lines D 1  and D 2  ( 538 - 1  and  538 - 2 ) and two sense lines S 1  and S 2  ( 540 - 1  and  540 - 2 ) intersect (without making direct electrical contact) to form four mutual capacitance touch pixels, D 1 S 1 , D 1 S 2 , D 2 S 1  and D 2 S 2 . A mutual capacitance C SIG_SENSE  ( 578 - 1 ) is formed at D 1 S 1  when drive line D 1  is stimulated, and a mutual capacitance C SIG_SENSE  ( 578 - 2 ) is formed at D 2 S 2  when drive line D 2  is stimulated. Note that C SIG_SENSE  is the reduced capacitance between the drive line and sense line due to the finger. Finger  560 - 1  is proximate to D 1 S 1  and finger  560 - 2  is proximate to D 2 S 2 . A finger-to-drive capacitance C FD  ( 586 - 1 ) forms between drive line  538 - 1  and finger  560 - 1 , and a finger-to-sense capacitance C FS  ( 588 - 1 ) forms between finger  560 - 1  and sense line  540 - 1 . In addition, a finger-to-drive capacitance C FD  ( 586 - 2 ) forms between drive line  538 - 2  and finger  560 - 2 , and a finger-to-sense capacitance C FS  ( 588 - 2 ) forms between finger  560 - 2  and sense line  540 - 2 . 
     In the example of  FIG.  5   , both fingers  560 - 1  and  560 - 2  are from the same hand of a user. If the user is well-grounded, when drive line D 1  ( 538 - 1 ) is stimulated, charge from D 1  is shunted to ground through finger  560 - 1  via C FD  ( 586 - 1 ), and sense line S 1  ( 540 - 1 ) sees a decrease in coupled charge and a decrease in mutual capacitance  578 - 1  at mutual capacitance touch pixel D 1 S 1 . Similarly, when drive line D 2  ( 538 - 2 ) is stimulated, charge from D 2  is shunted to ground through finger  560 - 2  via C FD  ( 586 - 2 ), and sense line S 2  ( 540 - 2 ) sees a decrease in coupled charge and a decrease in mutual capacitance  578 - 2  at mutual capacitance touch pixel D 2 S 2 . No negative pixels are generated. 
     However, if the user is poorly grounded, a small capacitance C FG  between the finger of the user and ground is nevertheless still present, a capacitance C BODY  between the body of the user and earth ground (symbolically shown as “E” in  FIG.  5   ) is present. A capacitance C CHASSIS  between the chassis of the device and earth ground completes the loop of charge flow. When drive line D 1  ( 538 - 1 ) is stimulated, rather than charge from D 1  being shunted to ground through finger  560 - 1  via C FD  ( 586 - 1 ), charge is coupled back onto sense line S 1  ( 540 - 1 ) via C FS  ( 588 - 1 ), and onto sense line S 2  ( 540 - 2 ) via C FS  ( 588 - 2 ). Sense line S 1  therefore sees less of a decrease in the mutual capacitance C SIG_SENSE  ( 578 - 1 ) than when a well-grounded touch is present, which can falsely indicate a lesser amount of touch, or no touch at all. Sense line S 2  ( 540 - 2 ) sees an increase in charge and an increase in mutual capacitance (e.g., a so-called “negative pixel”) at mutual capacitance touch pixel D 1 S 2 , even though no finger is present at that touch pixel. Similarly, when drive line D 2  ( 538 - 2 ) is stimulated, rather than charge from D 2  being shunted to ground through finger  560 - 2  via C FD  ( 586 - 2 ), charge is coupled back onto sense line S 1  ( 540 - 1 ) via C FS  ( 588 - 1 ). Sense line S 2  ( 540 - 2 ) therefore sees less of a decrease in the mutual capacitance C SIG_SENSE  ( 578 - 2 ) than when a well-grounded touch is present, which can falsely indicate a lesser amount of touch, or no touch at all. Sense line S 1  ( 540 - 1 ) sees an increase in charge and an increase in mutual capacitance (a negative pixel) at mutual capacitance touch pixel D 2 S 1 , even though no finger is present at mutual capacitance touch pixel D 2 S 1 . 
     In some examples, negative pixels can lead to errors in palm rejection. For example, when a user inadvertently places a palm on a trackpad, a palm rejection algorithm can disregard those palm touches as being inadvertent touches. However, because of negative pixels, a palm splitting effect can occur, wherein instead of being recognized as a single palm, the palm touches can be interpreted as multiple fingers or objects. Because the touches are not recognized as a palm touch and disregarded, the touches can be recognized as valid separate touches, and errors such as false tracking can occur. Conversely, because of negative pixels, two separate (but closely spaced) finger touches can be incorrectly recognized as a palm, and can be improperly disregarded. 
       FIG.  6 A  illustrates a unit cell of a touch pixel architecture that can be replicated to form a mutual capacitance touch sensor panel according to some embodiments of the disclosure. In the example of  FIG.  6 A , drive electrode  638  includes left drive spine  638 -L, two left top drive ribs  638 -LT, two left bottom drive ribs  638 -LB, right drive spine  638 -R, two right top drive ribs  638 -RT, two right bottom drive ribs  638 -RB, and one horizontal drive connector  638 -H, all continuously formed on a single drive layer of conductive material. Sense electrode  640  includes one vertical sense spine  640 -V and eight sense fingers  640 -F continuously formed on a single sense layer of conductive material that is located at lower (or different) level of the touch sensor panel stackup. The sense fingers  640 -F extend horizontally from vertical sense spine  640 -V and are interleaved between horizontal drive connector  638 -H, the left top drive ribs  638 -LT, the left bottom drive ribs  638 -LB, the right top drive ribs  638 -RT, and the right bottom drive ribs  638 -RB. The area in the center with the interleaved ribs, connectors and fingers can be referred to herein as the active mutual capacitive sensing area due to the fringing electric fields that form between the drive electrode and the sense electrode. In addition, top ground bar  690 -T and bottom ground bar  690 -B are formed above the topmost left top drive rib  638 -LT and the topmost right top drive rib  638 -RT, and below the bottommost left bottom drive rib  638 -LB and the bottommost right bottom drive rib  638 -RB, respectively, along a perimeter of the active mutual capacitance sensing area. Note that the electric fields between drive electrode  638  and sense electrode  640 , which form C SIG_SENSE , are important for mutual capacitance sensing. Therefore, top ground bar  690 -T and bottom ground bar  690 -B are formed at the outmost top and bottom edges of the unit cell, outside of the center area, so as not to disrupt C SIG_SENSE , and yet are adjacent to the top and bottom drive ribs to increase the capacitive coupling between the drive line and the ground bars. 
     In some examples, top ground bar  690 -T and bottom ground bar  690 -B are formed on the same drive layer as drive electrode  638  but are not directly electrically coupled to drive electrode  638 . However, in other examples, top ground bar  690 -T and bottom ground bar  690 -B could also be formed on the sense layer. In some examples, drive layer  638 , top ground bar  690 -T and bottom ground bar  690 -B are formed on the layer closer to the touch surface than the sense layer, so that the ground bars can more easily capacitively couple to a proximate object. In addition, placing top ground bar  690 -T and bottom ground bar  690 -B on the layer closer to the touch surface can advantageously decrease the inherent drive-to-ground capacitance C DG , particularly when a system ground is located on a lower layer of the touch sensor panel stackup. 
     In one example, the width w 1  of the drive ribs and horizontal drive connector  638 -H can be 300 microns (although in other examples the widths of the drive ribs and horizontal drive connector can be different), the gap w 2  between the fingers  640 -F and the drive ribs or horizontal drive connector  638 -C can be 295.5 microns, the gap w 3  between two drive ribs can be 622.5 microns, the gap w 4  between a ground bar  690  and an adjacent drive rib can be 160 microns, and the ground width w 5  can be 500 microns (note that this is the width of a ground bar in a unit cell; when the unit cell of  FIG.  6 A  is clustered into an array of unit cells, the total width of the ground bar can be 1000 microns due to two ground bars from adjacent cells being merged together). In addition, the width w 6  of the drive spine can be 75 microns (note that this is the width of a drive spine in a unit cell; when the unit cell of  FIG.  6 A  is clustered into an array of unit cells, the total width of the drive spine can be 150 microns due to two drive spines from adjacent cells being merged together), the width w 7  of a sense finger  640 -F or vertical sense spine  640 -V can be 105 microns, and the distance w 8  between the end of a finger  640 -F and a drive spine can be 225 microns. However, it should be understood that other dimensions fall within the scope of the disclosure. In general, the widths of the drive ribs, the sense fingers, the ground bars, and the gaps between all of these structures can be adjusted to optimize touch detection while minimizing negative pixels. 
       FIG.  6 B  illustrates a reduced circuit model of a poorly grounded finger in proximity to mutual capacitance touch pixels D 1 S 2  and D 2 S 2  as shown in  FIG.  5   , where the touch pixels are unit cells of the example architecture shown in  FIG.  6 A  according to some embodiments of the disclosure. In the example of  FIG.  6 B , a finger-to-drive capacitance C FD  ( 586 - 1 ) forms between drive line D 1  ( 538 - 1 ) and finger F ( 560 - 1 ), and a finger-to-sense capacitance C FS  ( 588 - 2 ) forms between finger F ( 560 - 2 ) and sense line S 2  ( 540 - 2 ). Because the fingers are poorly grounded, a small capacitance C FG  between the finger of the user and ground is present, a capacitance C BODY  between the body of the user and earth ground is present, and a capacitance C CHASSIS  between the chassis of the device and earth ground completes the loop. C CHASSIS  depends on system dimensions, as is fixed for a given system. 
     However, the addition of top and bottom ground bars  690 -T and  690 -B as shown in  FIG.  6 A  provides several benefits. First, some of the electric field lines emanating from drive line D 1  ( 538 - 1 ) are intercepted by top and bottom ground bars  690 -T and  690 -B, resulting in some charge coupling directly to ground and a reduction in the capacitive coupling from drive to finger, C FD . Second, an additional capacitive path to ground C FG * is created due to the capacitive coupling of the fingers to the ground bars. The additional capacitive path from the finger to ground through the ground bars can be dependent on the size and location of the ground bars. The increased finger-to-ground capacitance C FG * provided by the capacitive path allows for charge to be shunted through the finger to ground, which can create a greater decrease in the mutual capacitance between drive line D 1  ( 538 - 1 ) and sense line S 1  ( 540 - 1 ), making touch detection easier and more accurate. Third, the shunting of charge to ground through C FG * decreases the amount of charge coupled back onto sense line S 1  ( 540 - 1  and sense line S 2  ( 540 - 2 ), and decreases the negative pixel formed at touch pixel D 1 S 2 . In summary, top and bottom ground bars  690 -T and  690 -B allow for the reduction in C FD , an increase in C FG *, and a decrease in C FS , all of which can contribute to improved touch detection and a reduction in negative pixels. With improved touch detection and decreased negative pixels, palm rejection and other functions can performed more accurately. 
     An example negative pixel percentage for the touch pixel D 1 S 2  can be computed as: 
                     Negativepixel   ⁡   (   %   )     =         -   100     ⁢     C     D   ⁢   1   ⁢   S   ⁢   2             C   SIGSense     -     C     D   ⁢   1   ⁢   S   ⁢   2                   (   1   )                     where   :                           C     D   ⁢   1   ⁢   S   ⁢   2       =         C   FD     ⁢     C   FS           C   FD     +     C   FS     +     C   FG           ,               (   2   )                 
and C D1S2  is the total capacitive coupling between drive line D 1  and sense line S 2  through the finger (that takes into account the new capacitive path to ground created by ground bars  690 -T and  690 -B), C SIGSense  is the mutual capacitance between drive line D 1  and sense line S 1 , C FD  is the finger-to-drive (D 1 ) capacitance, C FS  is the finger-to-sense (S 2 ) capacitance, and C FG * is the additional capacitive path from the finger to ground created by ground bars  690 -T and  690 -B. As can be seen from Equation (1), C DIS2  should be small to minimize the negative pixel percentage. As Equation (2) illustrates, in order to minimize C D1S2 , either C FD  and C FS  can be minimized, or C FG * (the new capacitive path to ground) can be maximized. However, because C FD  and C FS  are small values, C FG * will dominate.
 
     With reference to the example dimensions provided in  FIG.  6 A , various adjustments to some of these dimensions can have a beneficial effect on certain key parameters, as will be demonstrated in the examples presented below. 
       FIG.  6 C  illustrates a plot of negative pixel % and C SIGSense  versus sense line width (w 7  in  FIG.  6 A ) according to some embodiments of the disclosure. The example plot of  FIG.  6 C  generally illustrates that for approximately a 20 micron increase in sense line width w 7 , about a 10% increase in C SIGSense  can be achieved (which can beneficially increase the SNR of the sense signal), with a corresponding decrease in negative pixel % of about 0.2%. With reference to Equation (1), the addition of ground bars  690 -T and  690 -B can decrease the negative pixel %, but if any regression in C SIGSense  is observed, the sense width w 7  can be increased to counteract the regression in C SIGSense . 
       FIG.  6 D  illustrates a plot of negative pixel % and C FS /C SIGSense  versus sense line width (w 7  in  FIG.  6 A ) according to some embodiments of the disclosure. The example plot of  FIG.  6 D  generally illustrates that for approximately a 20 micron increase in sense line width w 7 , about a 1% increase in C FS /C SIGSense  can be achieved, with a corresponding decrease in negative pixel % of about 1%. In some examples, a general rule can be employed to limit the ratio C FS /C SIGSense  to be below five. Thus, if C FS /C SIGSense  is trending towards five, the sense line width w 7  can be decreased to counteract the increase in C FS /C SIGSense  and keep it below five. 
       FIG.  6 E  illustrates a plot of negative pixel % and the drive-to-ground capacitance C DG  versus drive line width (w 1  in  FIG.  6 A ) according to some embodiments of the disclosure. The example plot of  FIG.  6 E  generally illustrates that for approximately a 50 micron decrement in drive line width, about a 5% reduction in C DG  can be achieved, with a corresponding decrease in negative pixel % of about 0.1%. In some examples, a general rule can be employed to limit C DG  to not more than 100 pF. Thus, if C DG  is trending towards 100 pF, the drive line width w 1  can be decreased to counteract the increase in C DG  and keep it below 100 pF. 
       FIG.  6 F  illustrates a plot of negative pixel % and C FS /C SIGSense  versus drive line width (w 1  in  FIG.  6 A ) according to some embodiments of the disclosure. The example plot of  FIG.  6 F  generally illustrates that for approximately a 50 micron increase in drive line width w 1 , about a 10% increase in C FS /C SIGSense  can be achieved, with a corresponding decrease in negative pixel % of about 1%. In some examples, a general rule can be employed to limit the ratio C FS /C SIGSense  to be below five. Thus, if C FS /C SIGSense  is trending towards five, the drive line width w 1  can be decreased to counteract the increase in C FS /C SIGSense  and keep it below five. 
       FIG.  6 G  illustrates four clustered unit cells of the example architecture shown in  FIG.  6 A  that have been replicated and arranged to form a portion of a mutual capacitance touch sensor panel according to some embodiments of the disclosure. In the example of  FIG.  6 G , the right drive spine  638 -R and left drive spine  638 -L of the drive electrodes  638  of two different unit cells are merged together when two unit cells are arranged side-by-side during fabrication, creating a continuous drive electrode that is connected horizontally across the mutual capacitance touch sensor panel. In addition, the bottom ground bar  690 -B and top ground bar  690 -T of two different unit cells are merged together when two unit cells are stacked vertically during fabrication. It can be envisioned from  FIG.  6 G  that when an two-dimensional array of until cells are formed to create a touch sensor panel, a plurality of continuous ground bars are formed horizontally across the panel. The vertical sense spines  640 -V of two vertically stacked unit calls can also be merged together, creating a continuous sense electrode that is connected vertically across the mutual capacitance touch sensor panel. 
       FIG.  6 H  illustrates a unit cell of an alternative touch pixel architecture that can be replicated to form a mutual capacitance touch sensor panel according to some embodiments of the disclosure.  FIG.  6 H  is similar to  FIG.  6 A , except that left ground bar  690 -L and right ground bar  690 -R have been added to the left and right sides of the unit cell. In some examples, left ground bar  690 -L and right ground bar  690 -R are formed on drive layer  638  (along with top ground bar  690 -T and bottom ground bar  690 -B) but are not directly electrically coupled to drive electrode  638 . However, in other examples, left ground bar  690 -L and right ground bar  690 -R could also be formed on the sense layer. In some examples, drive layer  638 , left ground bar  690 -L and right ground bar  690 -R are formed on the layer closer to the touch surface than the sense layer, so that the ground bars can more easily capacitively couple to a proximate object. In addition, placing left ground bar  690 -L and right ground bar  690 -R on the layer closer to the touch surface can advantageously decrease the inherent drive-to-ground capacitance C DG , particularly when a system ground is located on a lower layer of the touch sensor panel stackup. 
       FIG.  6 I  illustrates four clustered unit cells of the example architecture shown in  FIG.  6 H  that have been replicated and arranged to form a portion of a mutual capacitance touch sensor panel according to some embodiments of the disclosure. In the example of  FIG.  6 I , the right ground bar  690 -R, left ground bar  690 -L, top ground bar  690 -T and bottom ground bar  690 -B of the clustered unit cells are merged together, creating a ground ring around each mutual capacitance sensor (drive electrode and sense electrode) that is connected horizontally and vertically across the mutual capacitance touch sensor panel as a lattice. The vertical sense spines  640 -V of two vertically stacked unit calls can also be merged together, creating a continuous sense electrode that is connected vertically across the mutual capacitance touch sensor panel. Note, however, that in the embodiment of  FIG.  6 I , the left and right ground bars  690 -L and  690 -R block the drive electrodes  638  of adjacent unit cells from being merged together (as shown in  FIG.  6 C , for example). Thus, in some examples of the disclosure, the drive electrodes  638  include vias  692  to provide a conductive pathway to a different layer, so that connections between the drive electrodes  638  in two unit cells arranged side-by-side can be made while bypassing left and right ground bars  690 -L and  690 -R. 
       FIG.  7    illustrates a unit cell of an alternative touch pixel architecture that can be replicated to form a mutual capacitance touch sensor panel according to some embodiments of the disclosure. In the example of  FIG.  7   , drive electrode  738  includes left drive sense spine  738 -L, left top drive rib  738 -LT, left bottom drive rib  738 -LB, right drive sense spine  738 -R, right top drive rib  738 -RT, right bottom drive rib  738 -RB, and two horizontal drive connectors  738 -H, all continuously formed on a single drive layer of conductive material. Sense electrode  740  includes one vertical spine  740 -V and six sense fingers  740 -F continuously formed on a single sense layer of conductive material that is located at a lower (or different) level of the touch sensor panel stackup. The sense fingers  740 -F extend horizontally from vertical spine  740 -V and are interleaved between the two horizontal drive connectors  738 -H, the left top drive rib  738 -LT, the left bottom drive rib  738 -LB, the right top drive rib  738 -RT, and the right bottom drive rib  738 -RB. In addition, top ground bar  790 -T and bottom ground bar  790 -B are formed above left top drive rib  738 -LT and right top drive rib  738 -RT, and below left bottom drive rib  738 -LB and right bottom drive rib  738 -RB, respectively. Note that the electric fields between drive electrode  738  and sense electrode  740 , which form C SIGSENSE , are important for mutual capacitance sensing. Therefore, top ground bar  790 -T and bottom ground bar  790 -B are formed at the outmost top and bottom edges of the unit cell, outside of the center area, so as not to disrupt C SIGSense , and yet are adjacent to the top and bottom drive ribs to increase the capacitive coupling between the drive line and the ground bars. 
     In some examples, top ground bar  790 -T and bottom ground bar  790 -B are formed on the same drive layer as drive electrode  738  but are not directly electrically coupled to drive electrode  738 . However, in other examples, top ground bar  790 -T and bottom ground bar  790 -B could also be formed on the sense layer. In some examples, drive layer  738 , top ground bar  790 -T and bottom ground bar  790 -B are formed on the layer closer to the touch surface than the sense layer, so that the ground bars can more easily capacitively couple to a proximate object. In addition, placing top ground bar  790 -T and bottom ground bar  790 -B on the layer closer to the touch surface can advantageously decrease the inherent drive-to-ground capacitance C DG , particularly when a system ground is located on a lower layer of the touch sensor panel stackup. Although not shown in  FIG.  7   , in some examples of the disclosure left and right ground bars can be added to the architecture in a manner similar to that shown in  FIG.  6 H . Also, the unit cell of  FIG.  7    can be arranged in an array of unit cells, such that the ground bars, the drive electrodes, and the sense electrodes of the unit cells can be electrically coupled together. 
     Therefore, according to the above, some examples of the disclosure are directed to a mutual capacitance touch pixel, comprising a first drive electrode formed in a first layer, the first drive electrode including a plurality of first drive spines arranged in a first direction, a plurality of first drive ribs coupled to the plurality of first drive spines in a second direction, and at least one first drive connector coupled to the plurality of first drive spines and arranged in the second direction, a first sense electrode formed in a second layer different from the first layer, the first sense electrode including a first sense spine arranged in the first direction, a plurality of first sense fingers coupled to the first sense spine in the second direction and interleaved between the plurality of first drive ribs and the at least one first drive connector to form an active mutual capacitance sensing area, and one or more first ground bars formed in the first layer in the second direction along a portion of a perimeter of the active mutual capacitance sensing area. Additionally or alternatively to one of more of the examples disclosed above, in some examples the plurality of first drive spines are routed along the perimeter of the active mutual capacitance sensing area and positioned to be electrically couplable to a drive spine of an adjacent mutual capacitance touch pixel. Additionally or alternatively to one of more of the examples disclosed above, in some examples the first sense spine extends to the perimeter of the active mutual capacitance sensing area and is positioned to be electrically couplable to a sense spine of an adjacent mutual capacitance touch pixel. Additionally or alternatively to one of more of the examples disclosed above, in some examples the one or more first ground bars are routed along a top and bottom side of the active mutual capacitance sensing area, each first ground bar positioned to be electrically couplable to a ground bar of an adjacent mutual capacitance touch pixel. Some examples of the disclosure are directed to a touch sensor panel comprising an array of mutual capacitance touch pixels according to one or more of the examples disclosed above, the array of mutual capacitance touch pixels having their first ground bars electrically coupled together to form a continuous ground bar extending along a width of the touch sensor panel. Additionally or alternatively to one of more of the examples disclosed above, in some examples the mutual capacitance touch pixel further comprises one or more second ground bars formed in the first layer in the first direction and coupled to the one or more first ground bars. Additionally or alternatively to one of more of the examples disclosed above, in some examples the one or more second ground bars are routed along a left and right side of the active mutual capacitance sensing area, each second ground bar positioned to be electrically couplable to a ground bar of an adjacent mutual capacitance touch pixel. Additionally or alternatively to one of more of the examples disclosed above, in some examples the one or more first ground bars and the one or more second ground bars form a ring around the active mutual capacitance sensing area. Some examples of the disclosure are directed to a touch sensor panel comprising an array of mutual capacitance touch pixels according to one or more of the examples disclosed above, the array of mutual capacitance touch pixels having their first and second ground bars electrically coupled to the ground bars of the other mutual capacitance touch pixels to form a ground lattice around the mutual capacitance touch pixels. Additionally or alternatively to one of more of the examples disclosed above, in some examples the first layer is arranged to be closer to a touch surface of the touch pixel than the second layer. 
     Some examples of the disclosure are directed to a unit cell mutual capacitance touch electrode, comprising a drive electrode formed on a first layer and having a plurality of drive ribs, a sense electrode formed on a second layer and having a plurality of fingers interleaved with the plurality of drive ribs to form a mutual capacitance sensing area, and a first ground bar formed on the first layer outside the mutual capacitance sensing area, wherein the drive electrode, the sense electrode, and the first ground bar in the unit cell are arranged within the unit cell to be electrically couplable with the drive electrode, the sense electrode, and the first ground bar of a plurality of other unit cells to form a mutual capacitance sensing array. Additionally or alternatively to one of more of the examples disclosed above, in some examples the unit cell mutual capacitance touch electrode further comprises a second ground bar coupled to the first ground bar and formed on the first layer outside the mutual capacitance sensing area. Additionally or alternatively to one of more of the examples disclosed above, in some examples the first layer is arranged to be closer to a touch surface of the touch electrode than the second layer. 
     Some examples of the disclosure are directed to a mutual capacitance touch sensor panel, comprising, a plurality of mutual capacitance touch pixels, each mutual capacitance touch pixel including a first drive electrode formed in a first layer, the first drive electrode including a plurality of first drive spines arranged in a first direction, a plurality of first drive ribs coupled to the plurality of first drive spines in a second direction, and at least one first drive connector coupled to the plurality of first drive spines and arranged in the second direction, a first sense electrode formed in a second layer different from the first layer, the first sense electrode including a first sense spine arranged in the first direction, a plurality of first sense fingers coupled to the first sense spine in the second direction and interleaved between the plurality of first drive ribs and the at least one first drive connector to form an active mutual capacitance sensing area, and one or more first ground bars formed in the first layer in the second direction along a portion of a perimeter of the active mutual capacitance sensing area. Additionally or alternatively to one of more of the examples disclosed above, in some examples the plurality of first drive spines within each mutual capacitance touch pixel are routed along the perimeter of the active mutual capacitance sensing area and electrically coupled to a drive spine of an adjacent mutual capacitance touch pixel. Additionally or alternatively to one of more of the examples disclosed above, in some examples the first sense spine of each mutual capacitance touch pixel extends to the perimeter of the active mutual capacitance sensing area and electrically coupled to a sense spine of an adjacent mutual capacitance touch pixel. Additionally or alternatively to one of more of the examples disclosed above, in some examples the one or more first ground bars of each mutual capacitance touch pixel are routed along a top and bottom side of the active mutual capacitance sensing area and electrically coupled to a first ground bar of an adjacent mutual capacitance touch pixel. Additionally or alternatively to one of more of the examples disclosed above, in some examples the electrically coupled first ground bars of adjacent mutual capacitance touch pixels form a continuous ground bar extending along a width of the touch sensor panel. Additionally or alternatively to one of more of the examples disclosed above, in some examples each mutual capacitance touch pixel further includes one or more second ground bars formed in the first layer in the first direction and coupled to the one or more first ground bars. Additionally or alternatively to one of more of the examples disclosed above, in some examples the one or more second ground bars within each mutual capacitance touch pixel are routed along a left and right side of the active mutual capacitance sensing area and electrically coupled to a second ground bar of an adjacent mutual capacitance touch pixel. Additionally or alternatively to one of more of the examples disclosed above, in some examples the one or more first ground bars and the one or more second ground bars form a lattice around the active mutual capacitance sensing area of the plurality of mutual capacitance touch pixels. Additionally or alternatively to one of more of the examples disclosed above, in some examples the first layer is arranged to be closer to a touch surface of the touch sensor panel than the second layer. 
     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: 20230809
Publication Date: 20240806
Grant Date: 20240806
Priority Date: 20220920
Inventors: JAIN, KARAN S.
POKHREL, SANTOSH
Assignee: APPLE INC
CPC Classifications: [{"code": "G06F3/0445", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0448", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0446", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0445", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0443", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/0443", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/0445", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0443", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 90245034