PATENT DOCUMENT

Publication Number: US-10936120-B2
Application Number: US-201415313549-A
Country: US
Kind Code: B2

Title: Panel bootstraping architectures for in-cell self-capacitance

Abstract:
A self-capacitance touch screen. In some examples, the touch screen comprises a plurality of display pixels, a first display pixel of the plurality of display pixels including a first touch electrode of a plurality of touch electrodes, and a gate line coupled to the first display pixel, wherein the gate line is configured such that a voltage at the gate line substantially follows a voltage at the first touch electrode. In some examples, the gate line is coupled to a resistor, the resistor being configured to decouple the gate line from ground. In some examples, the gate line is coupled to an AC voltage source.

Claims:
The invention claimed is: 
     
       1. A self-capacitance touch screen, the touch screen comprising:
 a plurality of display pixels, a first display pixel of the plurality of display pixels including a first touch electrode of a plurality of touch electrodes; and 
 a gate line coupled to the first display pixel, wherein the gate line is coupled to a resistor that:
 decouples the gate line from ground with respect to one or more AC signals such that a voltage difference between the gate line and the first touch electrode remains substantially unchanged while a self-capacitance of the first touch electrode is being sensed, which includes driving the first touch electrode at an AC voltage; and 
 allows one or more DC signals for operating the first display pixel to pass onto the gate line during a touch mode of the touch screen. 
 
 
     
     
       2. The touch screen of  claim 1 , wherein the touch screen is configured to enable an AC voltage to be present at both the gate line and the first touch electrode. 
     
     
       3. The touch screen of  claim 1 , wherein the resistor is in a border region of the touch screen. 
     
     
       4. The touch screen of  claim 1 , wherein the resistor is coupled to an AC voltage source. 
     
     
       5. The touch screen of  claim 4 , wherein:
 the AC voltage source is coupled to sense circuitry, and 
 the sense circuitry is coupled to the first touch electrode. 
 
     
     
       6. The touch screen of  claim 1 , wherein the gate line is coupled to an AC voltage source. 
     
     
       7. The touch screen of  claim 6 , further comprising sense circuitry coupled to: the first touch electrode, and the AC voltage source. 
     
     
       8. The touch screen of  claim 6 , wherein the gate line is further coupled to a DC voltage source. 
     
     
       9. The touch screen of  claim 1 , wherein the gate line is coupled to a transistor in the first display pixel. 
     
     
       10. The touch screen of  claim 1 , wherein the gate line is further coupled to a second display pixel of the plurality of display pixels. 
     
     
       11. A method for operating a self-capacitance touch screen, the method comprising:
 coupling a gate line to:
 a first display pixel of a plurality of display pixels, the first display pixel including a first touch electrode of a plurality of touch electrodes; and 
 a resistor that:
 decouples the gate line from ground with respect to one or more AC signals; 
 allows one or more DC signals for operating the first display pixel to pass onto the gate line during a touch mode of the touch screen; and 
 
 
 operating the gate line such that a voltage difference between the gate line and the first touch electrode remains substantially unchanged while a self-capacitance of the first touch electrode is being sensed, which includes driving the first touch electrode at an AC voltage. 
 
     
     
       12. The method of  claim 11 , wherein the voltage at the gate line and the voltage at the first touch electrode comprise an AC voltage. 
     
     
       13. The method of  claim 11 , wherein the resistor is in a border region of the touch screen. 
     
     
       14. The method of  claim 11 , further comprising coupling the resistor to an AC voltage source. 
     
     
       15. The method of  claim 14 , further comprising:
 coupling the AC voltage source to sense circuitry; and 
 coupling the sense circuitry to the first touch electrode. 
 
     
     
       16. The method of  claim 11 , wherein operating the gate line comprises coupling the gate line to an AC voltage source. 
     
     
       17. The method of  claim 16 , further comprising coupling the first touch electrode and the AC voltage source to sense circuitry. 
     
     
       18. The method of  claim 16 , further comprising coupling the gate line to a DC voltage source. 
     
     
       19. The method of  claim 11 , wherein coupling the gate line to the first display pixel comprises coupling the gate line to a transistor in the first display pixel. 
     
     
       20. The method of  claim 11 , further comprising coupling the gate line to a second display pixel of the plurality of display pixels.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a National Phase application under 35 U.S.C. § 371 of International Application No. PCT/US2014/039245, filed May 22, 2014, the contents of which is hereby incorporated by reference in its entirety for all intended purposes. 
     FIELD OF THE DISCLOSURE 
     This relates generally to touch sensor panels that are integrated with displays, and more particularly, to integrated touch screens in which a self-capacitance touch sensor is utilized to detect the presence of an object in contact with or in close proximity to a touch sensor panel. 
     BACKGROUND OF THE DISCLOSURE 
     Many types of input devices are presently available for performing operations in a computing system, such as buttons or keys, mice, trackballs, joysticks, touch sensor panels, touch screens and the like. Touch screens, in particular, are becoming increasingly popular because of their ease and versatility of operation as well as their declining price. Touch screens can include a touch sensor panel, which can be a clear panel with a touch-sensitive surface, and a display device such as a liquid crystal display (LCD) that can be positioned partially or fully behind the panel so that the touch-sensitive surface can cover at least a portion of the viewable area of the display device. Touch screens can allow a user to perform various functions by touching the touch sensor panel using a finger, stylus or other object at a location often dictated by a user interface (UI) being displayed by the display device. In general, touch screens can recognize a touch and the position of the touch on the touch sensor panel, and the computing system can then interpret the touch in accordance with the display appearing at the time of the touch, and thereafter can perform one or more actions based on the touch. In the case of some touch sensing systems, a physical touch on the display is not needed to detect a touch. For example, in some capacitive-type touch sensing systems, fringing electrical fields used to detect touch can extend beyond the surface of the display, and objects approaching near the surface may be detected near the surface without actually touching the surface. 
     Capacitive touch sensor panels can be formed by a matrix of substantially transparent conductive plates made of materials such as Indium Tin Oxide (ITO). It is due in part to their substantial transparency that 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 partially integrating touch sensing circuitry into a display pixel stackup (i.e., the stacked material layers forming the display pixels). 
     SUMMARY OF THE DISCLOSURE 
     Some capacitive touch sensor panels can be formed by a matrix of substantially transparent conductive plates made of materials such as Indium Tin Oxide (ITO), and some touch screens can be formed by partially integrating touch sensing circuitry into a display pixel stackup (i.e., the stacked material layers forming the display pixels). Touch events can be sensed on the above touch screens by detecting changes in the self-capacitance of the above conductive plates. However, in some examples, one or more capacitances resulting from the integration of touch sensing circuitry into display pixel stackups can cause offsets in the self-capacitance measurements that can reduce the dynamic range of corresponding sensing circuits, and can make touch detection difficult. The examples of the disclosure provide various techniques for reducing the offset effects of such capacitances. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1C  illustrate an example mobile telephone, an example media player, and an example portable computing device that each include an exemplary touch screen according to examples of the disclosure. 
         FIG. 2  is a block diagram of an exemplary computing system that illustrates one implementation of an example touch screen according to examples of the disclosure. 
         FIG. 3  illustrates an exemplary self-capacitance touch sensor panel having row and column electrodes, and sense channels, according to examples of the disclosure. 
         FIG. 4  illustrates an exemplary touch sensor circuit corresponding to a self-capacitance touch pixel electrode and sensing according to examples of the disclosure. 
         FIG. 5  illustrates an example configuration in which common electrodes can form portions of the touch sensing circuitry of a touch sensing system. 
         FIG. 6  shows a partial circuit diagram of some of the touch sensing circuitry within a display pixel of an example touch screen according to examples of the disclosure. 
         FIG. 7  illustrates an exemplary electrical circuit corresponding to a self-capacitance touch sensor electrode and sensing circuit according to examples of the disclosure. 
         FIG. 8  illustrates an exemplary electrical circuit corresponding to a self-capacitance touch sensor electrode and sensing circuit according to examples of the disclosure. 
         FIG. 9  illustrates an exemplary electrical circuit corresponding to a self-capacitance touch sensor electrode and sensing circuit according to examples of the disclosure. 
         FIG. 10  illustrates an exemplary electrical circuit corresponding to a self-capacitance touch sensor electrode and sensing circuit 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. 
     Some capacitive touch sensor panels can be formed by a matrix of substantially transparent conductive plates made of materials such as Indium Tin Oxide (ITO), and some touch screens can be formed by partially integrating touch sensing circuitry into a display pixel stackup (i.e., the stacked material layers forming the display pixels). Additionally, some capacitive touch sensor panels can be formed by rows and columns of substantially transparent conductive lines made of materials such as ITO, and can similarly form touch screens with touch sensing circuitry partially integrated into a display pixel stackup. Touch events can be sensed on the above touch screens by detecting changes in the self-capacitance of the above conductive plates and/or lines. However, in some examples, one or more capacitances resulting from the integration of touch sensing circuitry into display pixel stackups can cause offsets in the self-capacitance measurements that can reduce the dynamic range of corresponding sensing circuits, and can make touch detection difficult. The examples of the disclosure provide various techniques for reducing the offset effects of such capacitances. 
       FIGS. 1A-1C  show 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 portable computing device  144  that includes a touch screen  128 . Touch screens  124 ,  126 , and  128  can be based on self-capacitance. A self-capacitance based touch system can include small plates of conductive material that can be called a touch pixel or a touch pixel electrode. During operation, the touch pixel can be stimulated with an AC waveform and the self-capacitance of the touch pixel can be measured. As an object approaches the touch pixel, the self-capacitance of the touch pixel can change. This change in the self-capacitance of the touch pixel can be detected and measured by the touch sensing system to determine the positions of multiple objects when they touch, or come in proximity to, the touch screen. In some examples, the electrodes of a self-capacitance based touch system can be formed from rows and columns of conductive material, and changes in the self-capacitance 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. 
       FIG. 2  is a block diagram of an example computing system  200  that illustrates one implementation of an example touch screen  220  according to examples of the disclosure. Computing system  200  can be included in, for example, mobile telephone  136 , digital media player  140 , portable computing device  144 , 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 pixels 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. 
     Touch screen  220  can include touch sensing circuitry that can include a capacitive sensing medium having a plurality of touch pixels  222 . It is understood that while touch screen  220  is described here as including touch pixels  222 , the touch screen can similarly include rows and columns of conductive material (e.g., electrodes  302  in  FIG. 3 ); the operation and functions of such a touch screen would be similar to those described here. Touch pixels  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. Labeling the conductive plates used to detect touch (i.e., touch pixels  222 ) as “touch pixels” can be particularly useful when touch screen  220  is viewed as capturing an “image” of touch. In other words, after touch controller  206  has determined an amount of touch detected at each touch pixel  222  in touch screen  220 , the pattern of touch pixels 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). 
     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 . The LCD driver  234  can provide voltages on select (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 an image on touch screen  220 , such as an 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 above, 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. 3  illustrates an exemplary self-capacitance touch sensor panel  300  having row  302  and column  303  electrodes, and sense channels  308 , according to examples of the disclosure. Similar to touch pixels  222  described above, row  302  and column  303  electrodes can be coupled to sense channels  308 , which can be included in a touch controller such as touch controller  206 . In some examples, sense channels  308  can correspond to sense channels  208  in  FIG. 2 . Row  302  and column  303  electrodes can each have a self-capacitance to ground. The operation of touch sensor panel  300  can be similar to the operation of touch screen  220  described above—row  302  and column  303  electrodes can be driven by stimulation signals from sense channels  308 , and the self-capacitance of the row and column electrodes can be sensed by the sense channels. Specifically, when an object touches or is in close proximity to row  302  and/or column  303  electrodes, an additional capacitance can be formed between the respective electrodes and ground through the object, which can increase the self-capacitance of the respective electrodes. This change in the self-capacitance of the row  302  and/or column  303  electrodes can be detected by sense channels  308 . An “image” of touch can thus be captured. 
       FIG. 4  illustrates an exemplary touch sensor circuit  400  corresponding to a self-capacitance touch pixel electrode  402  and sensing circuit  414  according to examples of the disclosure. Touch pixel electrode  402  can correspond to touch pixel  222 . Touch pixel electrode  402  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  405 , is in proximity to or touching the electrode. The total self-capacitance to ground of touch pixel electrode  402  can be illustrated as capacitance  404 . Touch pixel electrode  402  can be coupled to sensing circuit  414 . Sensing circuit  414  can include an operational amplifier  408 , feedback resistor  412 , feedback capacitor  410  and an input voltage source  406 , although other configurations can be employed. For example, feedback resistor  412  can be replaced by a switched capacitor resistor in order to minimize any parasitic capacitance effect caused by a variable feedback resistor. Touch pixel electrode  402  can be coupled to the inverting input of operational amplifier  408 . An AC voltage source  406  (Vac) can be coupled to the non-inverting input of operational amplifier  408 . Touch sensor circuit  400  can be configured to sense changes in the total self-capacitance  404  of the touch pixel electrode  402  induced by a finger or object either touching or in proximity to the touch sensor panel. Output  420  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 touch or proximity event. It is understood that one or more of the operations described above with reference to touch pixel electrode  402  can similarly be performed with respect to a row/column electrode such as row  302  and column  303  electrodes in  FIG. 3 . 
     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, such as one or more pixel transistors (e.g., thin film transistors (TFTs)), gate lines, data lines, pixel electrodes and common electrodes. In any 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. 5  illustrates an example configuration in which common electrodes  502  can form portions of the touch sensing circuitry of a touch sensing system—in some examples of this disclosure, the common electrodes can form touch pixels used to detect an image of touch on touch screen  500 , as described above. Each common electrode  502  (i.e., touch pixel region) can include a plurality of display pixels  501 , and each display pixel  501  can include a portion of a common electrode  502 , which can be a circuit element of the display system circuitry in the pixel stackup (i.e., the stacked material layers forming the display pixels) of the display pixels of some types of LCD or other displays that can operate as part of the display system to display an image. 
     In the example shown in  FIG. 5 , each common electrode  502  can serve as a multi-function circuit element that can operate as display circuitry of the display system of touch screen  500  and can also operate as touch sensing circuitry of the touch sensing system. In this example, each common electrode  502  can operate as a common electrode of the display circuitry of the touch screen  500 , as described above, and can also operate as touch sensing circuitry of the touch screen. For example, a common electrode  502  can operate as a capacitive part of a touch pixel of the touch sensing circuitry during the touch sensing phase. Other circuit elements of touch screen  500  can form part of the touch sensing circuitry by, for example, switching electrical connections, etc. More specifically, in some examples, during the touch sensing phase, a gate line can be connected to a power supply, such as a charge pump, that can apply a voltage to maintain TFTs in display pixels included in a touch pixel in an “off” state. Stimulation signals can be applied to common electrode  502 . Changes in the total self-capacitance of common electrode  502  can be sensed through an operational amplifier, as previously discussed. The change in the total self-capacitance of common electrode  502  can depend on the proximity of a touch object, such as finger  405 , to the common electrode. In this way, the measured change in total self-capacitance of common electrode  502  can provide an indication of touch on or near the touch screen. 
     In general, each of the touch sensing circuit elements may be either a multi-function circuit element that can form part of the touch sensing circuitry and can perform one or more other functions, such as forming part of the display circuitry, or may be a single-function circuit element that can operate as touch sensing circuitry only. Similarly, each of the display circuit elements may be either a multi-function circuit element that can operate as display circuitry and perform one or more other functions, such as operating as touch sensing circuitry, or may be a single-function circuit element that can operate as display circuitry only. Therefore, in some examples, some of the circuit elements in the display pixel stackups can be multi-function circuit elements and other circuit elements may be single-function circuit elements. In other examples, all of the circuit elements of the display pixel stackups may be single-function circuit elements. 
     In addition, although examples herein may describe the display circuitry as operating during a display phase, and describe the touch sensing circuitry as operating during a touch sensing phase, it should be understood that a display phase and a touch sensing phase may be operated at the same time, e.g., partially or completely overlap, or the display phase and touch sensing phase may operate at different times. Also, although examples herein describe certain circuit elements as being multi-function and other circuit elements as being single-function, it should be understood that the circuit elements are not limited to the particular functionality in other examples. In other words, a circuit element that is described in one example herein as a single-function circuit element may be configured as a multi-function circuit element in other examples, and vice versa. 
     The common electrodes  502  (i.e., touch pixels) and display pixels  501  of  FIG. 5  are shown as rectangular or square regions on touch screen  500 . However, it is understood that the common electrodes  502  and display pixels  501  are not limited to the shapes, orientations, and positions shown, but can include any suitable configurations according to examples of the disclosure. 
       FIG. 6  shows a partial circuit diagram  600  of some of the touch sensing circuitry within a display pixel of an example touch screen according to examples of the disclosure. For the sake of clarity, only one display pixel structure is shown. However, it is understood that other display pixels of the touch screen can include the same or similar touch sensing circuitry as described below for display pixel  601 . Thus, the description of the operation of display pixel  601  can be considered a description of the operation of the touch panel, in general. 
     Display pixel  601  can include TFT  607 , gate line  611 , data line  613 , pixel electrode  615 , and common electrode  617 . Common electrode  617  can correspond to any one of touch pixels  222  in  FIG. 2 , row  302  or column  303  electrodes in  FIG. 3 , touch pixel electrodes  402  in  FIG. 4  and/or common electrodes  502  in  FIG. 5 . Gate line  611  can supply one or more voltages to the gate terminal of TFT  607  to control the operational state of the TFT (e.g., “on” or “off), and data line  613  can supply one or more voltages for setting the voltage on pixel electrode  615 . In some examples, gate line  611  can be shared by more than one display pixel (i.e., the gate line can be connected to the gate terminal of more than one display TFT), though a single display pixel is shown for simplicity. Storage capacitance  619  can exist between common electrode  617  and pixel electrode  615 , and can store a charge—set by the voltage difference between data line  613  and common electrode  617 —for controlling a luminance of display pixel  601 . In some examples, offset capacitance  621  (or “parasitic capacitance”) can exist between the drain terminal of TFT  607  and the gate terminal of the TFT. Offset capacitance  621  can vary based on the voltage difference between gate line  611  and pixel electrode  615 , and can include capacitances such as the gate-to-drain capacitance of TFT  607  and/or other capacitances due to the layout of various components of the touch screen. Operational amplifier  608  can be configured to sense changes in the total self-capacitance of common electrode  617 , as described above, to determine the presence of a proximity or touch event at the common electrode. Although display pixel  601  has been described as including a single TFT (i.e., TFT  607 ), in some examples, the display pixel may include more than a single TFT. For example, display pixel  601  can include two TFTs connected in series, the gate terminals of which both can be connected to gate line  611 . The operation of such display pixels can be substantially the same as the operation of the display pixel of  FIG. 6 . For ease of description, the examples of the disclosure will be described with reference to the display pixel configuration of  FIG. 6 , although it is understood that the scope of the disclosure is not so limited. 
     During a touch sensing phase of the touch screen, gate line  611  can supply a voltage to the gate of TFT  607  for turning “off” the TFT. Operational amplifier  608  can sense changes in the total self-capacitance of common electrode  617 . As described above, this total self-capacitance can include a touch capacitance  604  due to an object, such as finger  605 , being in proximity to or touching common electrode  617 , as well as any other capacitance that may be seen at the common electrode. In some examples, the total self-capacitance seen at common electrode  617  can include storage capacitance  619  in series with offset capacitance  621 . In some examples, storage capacitance  619  can be much larger than offset capacitance  621 , and can thus dominate the non-touch-related total capacitance seen at common electrode  617 . As such, the total self-capacitance seen at common electrode  617  can be approximately a combination of touch capacitance  604  and offset capacitance  621 . 
       FIG. 7  illustrates an exemplary electrical circuit  700  corresponding to a self-capacitance touch sensor electrode  717  and sensing circuit  714  according to examples of the disclosure. As discussed above, in some examples, storage capacitance  619  can be much larger than offset capacitance  621 . Thus, the total self-capacitance seen at common electrode  617  can be approximated as a combination of touch capacitance  604  and offset capacitance  621 . Ignoring touch capacitance  704 , the gain of operational amplifier in the configuration illustrated can be expressed as:
 
 A= 1+ C   gp   /C   fb   (1)
 
where A can represent the gain, C fb  can correspond to feedback capacitance  710 , and C gp  can correspond to offset capacitance  721 . In some examples, offset capacitance  721  can be on the order of nanofarads (˜1 nF, in some examples), and feedback capacitance  710  can be on the order of picofarads (˜10 pF, in some examples). In such cases, the gain of operational amplifier  708  due only to offset capacitance  721  can be approximately 101. In other words, an input voltage of 1V provided by AC voltage source  706  at the non-inverting input of operational amplifier  708  can result in an output voltage of 101V at the output of the operational amplifier. With such a large offset due simply to offset capacitance  721 , it can be difficult to detect changes in the output voltage of operational amplifier  708  resulting from changes in touch capacitance  704 , and thus it can be difficult to detect touch and/or proximity events. Additionally, the dynamic range of sensing circuit  714  can be significantly reduced due to the offset effect, and in some examples may render the sensing circuit inoperable.
 
     In some examples, in order to reduce the effect of offset capacitance  621  in  FIG. 6  on the output voltage of operational amplifier  608 , a resistor with a large AC impedance can be added to the end of gate line  611  so that the gate line can be effectively floating.  FIG. 8  illustrates an exemplary electrical circuit  800  corresponding to a self-capacitance touch sensor electrode  817  and sensing circuit  814  according to examples of the disclosure. Circuit  800  can be substantially that of  FIG. 7 ; however, resistor  823  can be added between offset capacitance  821  and ground. Resistor  823  in circuit  800  can correspond to a resistor added somewhere on gate line  611  in  FIG. 6 ; in some examples, the resistor can be added to the end of the gate line. The end of gate line  611  can be a portion of the gate line that can exist outside of a portion of the gate line that can include all connections between the gate line and the gate terminals of the display pixels to which the gate line is connected. In some examples, the end of gate line  611  can be in a border region (i.e., non-visible region) of the touch screen of the disclosure, and resistor  823  can be added to the gate line in the border region of the touch screen. Resistor  823  can have a sufficiently large AC impedance (or resistance) such that the terminal of offset capacitance  821  coupled to resistor  823  (i.e., node A) can be effectively floating with respect to AC signals (i.e., node A can be a high impedance node, an open circuit node, and/or decoupled from ground). However, the DC voltage at node A (i.e., the gate line) can still be controlled for proper display pixel operation, as described above. If node A is effectively floating, the voltage at node A can effectively follow (or shadow) the voltage at touch sensor electrode  817 . As such, current flow into offset capacitance  821  can be virtually eliminated, and the effect of offset capacitance  821  on the total self-capacitance seen at touch sensor electrode  817  can be substantially reduced. As a result, changes in touch capacitance  804 , and the effect of the touch capacitance on the output voltage of operational amplifier  808 , can be more readily detected, and thus touch and/or proximity events can be more easily sensed. 
     In some examples, the effect of offset capacitance  621  can be reduced as a result of circuitry—in or coupled to the touch screen—that is configured to apply substantially similar voltage signals at gate line  611  and common electrode  617 , as will be described with reference to  FIGS. 9-10 . In some examples, the effect of offset capacitance  621  can be reduced by driving gate line  611  in  FIG. 6  with the same AC voltage as is used to drive the non-inverting input of operational amplifier  608 .  FIG. 9  illustrates an exemplary electrical circuit  900  corresponding to a self-capacitance touch sensor electrode  917  and sensing circuit  914  according to examples of the disclosure. Circuit  900  can be substantially that of  FIG. 7 , except that node A of offset capacitance  921 , instead of being grounded, can be driven by the same AC signal as is driving the non-inverting input of operational amplifier  908 . Such a configuration can be the result of driving gate line  611  of  FIG. 6  with AC voltage source  606 , for example. In some examples, gate line  611  can be driven with AC voltage source  606  on top of any DC voltage that may be applied to the gate line to allow for proper touch screen operation, as described in this disclosure. In such an arrangement, the voltage at common electrode  917  can be virtually the same as the voltage provided by AC voltage source  906  (and the voltage at the non-inverting input of operational amplifier  908 ) due to the operational characteristics of operational amplifier  908 . The voltage at node A can also be virtually the same as the voltage provided by AC voltage source  906  because node A can be directly coupled to the AC voltage source. Thus, the voltage and/or changes in the voltage across offset capacitance  921  can be effectively zero, and current flow into the offset capacitance can be virtually eliminated. As a result, similar to the discussion above with respect to  FIG. 8 , the effect of offset capacitance  921  on the total self-capacitance seen at touch sensor electrode  917  can be substantially reduced. As such, changes in touch capacitance  904 , and the effect of the touch capacitance on the output voltage of operational amplifier  908 , can be more readily detected, and thus touch and/or proximity events can be more easily sensed. In some examples, node A can be driven by AC voltage source  906  at all times, and in other examples, node A can be driven by the AC voltage source only during certain times, such as during the touch sensing phase of the touch screen of the disclosure. 
     In some examples, a combination of adding a high AC impedance resistor to gate line  611  of  FIG. 6 , and driving the gate line with the same AC voltage source as is driving the non-inverting input of operational amplifier  608 , can be used to reduce the effect of offset capacitance  621  on the output voltage of the operational amplifier.  FIG. 10  illustrates an exemplary electrical circuit  1000  corresponding to a self-capacitance touch sensor electrode  1017  and sensing circuit  1014  according to examples of the disclosure. Circuit  1000  can be substantially that of  FIG. 7 , except that resistor  1023  can be coupled to node A of offset capacitance  1021 , and node B of the resistor can be driven by AC voltage source  1006 , which can also drive the non-inverting input of operational amplifier  1008 . The configuration of circuit  1000  can correspond to adding resistor  1023  to gate line  611  in  FIG. 6 , as described above, and driving the end of the gate line with AC voltage source  606 , also as described above. Such a configuration can reduce the effect of offset capacitance  1021  on the output voltage of operational amplifier  1008  in two ways, as discussed above: 1) resistor  1023  can have a sufficiently large AC impedance so as to contribute to the effect of making node A virtually floating with respect to AC signals, and 2) driving node B with AC voltage source  1006  can further contribute to the voltage at node A following the voltage at touch sensor electrode  1017 . Together, these effects can contribute to virtually eliminating the voltage and/or changes in the voltage across offset capacitance  1021 . Additionally, adding resistor  1023  can help increase the AC load that AC voltage source  1006  sees when driving offset capacitance  1021  and operational amplifier  1008 , and thus can make it easier for the AC voltage source to drive the various components to which it is connected. As a result of the above, the effect of offset capacitance  1021  on the total self-capacitance seen at touch sensor electrode  1017  can be substantially reduced. As such, changes in touch capacitance  1004 , and the effect of the touch capacitance on the output voltage of operational amplifier  1008 , can be more readily detected, and thus touch and/or proximity events can be more easily sensed. In some examples, node B can be driven by AC voltage source  1006  at all times, and in other examples, node B can be driven by the AC voltage source only during certain times, such as during the touch sensing phase of the touch screen of the disclosure. 
     Thus, the examples of the disclosure provide one or more configurations for reducing the effects of offset capacitances on the dynamic range of sensing circuitry in the touch screens of the disclosure, making it easier to detect touch and/or proximity events at the touch screen. 
     Therefore, according to the above, some examples of the disclosure are directed a self-capacitance touch screen, the touch screen comprising: a plurality of display pixels, a first display pixel of the plurality of display pixels including a first touch electrode of a plurality of touch electrodes; and a gate line coupled to the first display pixel, wherein the gate line is configured such that a voltage at the gate line substantially follows a voltage at the first touch electrode. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the touch screen is configured to enable an AC voltage to be present at both the gate line and the first touch electrode. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the gate line is coupled to a resistor, the resistor being configured to decouple the gate line from ground. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the resistor is in a border region of the touch screen. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the resistor is coupled to an AC voltage source. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the AC voltage source is coupled to sense circuitry, and the sense circuitry is coupled to the first touch electrode. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the gate line is coupled to an AC voltage source. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the touch screen further comprises sense circuitry coupled to the first touch electrode, and the AC voltage source. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the gate line is further coupled to a DC voltage source. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the gate line is coupled to a transistor in the display pixel. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the gate line is further coupled to a second display pixel of the plurality of display pixels. 
     Some examples of the disclosure are directed to a method for operating a self-capacitance touch screen, the method comprising: coupling a gate line to a first display pixel of a plurality of display pixels, the first display pixel including a first touch electrode of a plurality of touch electrodes; and operating the gate line such that a voltage at the gate line substantially follows a voltage at the first touch electrode. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the voltage at the gate line and the voltage at the first touch electrode comprise an AC voltage. Additionally or alternatively to one or more of the examples disclosed above, in some examples, operating the gate line comprises coupling the gate line to a resistor, the resistor being configured to decouple the gate line from ground. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the resistor is in a border region of the touch screen. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the method further comprises coupling the resistor to an AC voltage source. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the method further comprises coupling the AC voltage source to sense circuitry; and coupling the sense circuitry to the first touch electrode. Additionally or alternatively to one or more of the examples disclosed above, in some examples, operating the gate line comprises coupling the gate line to an AC voltage source. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the method further comprises coupling the first touch electrode and the AC voltage source to sense circuitry. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the method further comprises coupling the gate line to a DC voltage source. Additionally or alternatively to one or more of the examples disclosed above, in some examples, coupling the gate line to the first display pixel comprises coupling the gate line to a transistor in the first display pixel. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the method further comprises coupling the gate line to a second display pixel of the plurality of display pixels. 
     Some examples of the disclosure are directed to a self-capacitance touch screen, the touch screen comprising: a plurality of display pixels, a first display pixel of the plurality of display pixels including a first touch electrode of a plurality of touch electrodes; a gate line coupled to the first display pixel; and circuitry configured to apply substantially similar voltage signals at the gate line and the first touch electrode. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the gate line is further coupled to a second display pixel of the plurality of display pixels. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the circuitry comprises an AC voltage source coupled to the gate line and to sense circuitry, the sense circuitry being coupled to the first touch electrode. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the sense circuitry comprises an operational amplifier, the AC voltage source is coupled to a non-inverting input of the operational amplifier, and the first touch electrode is coupled to an inverting input of the operational amplifier. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the circuitry further comprises a resistor through which the AC voltage source is coupled to the gate line. 
     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: 20140522
Publication Date: 20210302
Grant Date: 20210302
Priority Date: 20140522
Inventors: YAO, WEIJUN
AL-DAHLE, AHMAD
NHO, HYUNWOO
SYED, TAIF A.
YAO, WEI HSIN
LI, YINGXUAN
Assignee: APPLE INC
CPC Classifications: [{"code": "H10D86/481", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10D86/441", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10D86/60", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0446", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/044", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F2203/04104", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/04166", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/04166", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F2203/04108", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/0446", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0412", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0418", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0416", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0418", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0412", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L27/1255", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L27/124", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/044", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0416", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F2203/04104", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/0418", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F2203/04108", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 54554442