PATENT DOCUMENT

Publication Number: US-9535544-B2
Application Number: US-201313907698-A
Country: US
Kind Code: B2

Title: Reducing touch pixel coupling

Abstract:
A touch screen to reduce touch pixel coupling. In some examples, the touch screen can include a first display pixel and a second display pixel in a row of display pixels, where the first display pixel can be configurable to be decoupled from the second display pixel during at least a touch sensing phase of the touch screen. In some examples, the touch screen can include a display pixel having a first and a second transistor, where the second transistor can be electrically connected to a gate terminal of the first transistor, and can be diode-connected. In some examples, the touch screen can include two display pixels, each display pixel having two transistors, where two of the transistors can be electrically connected to a first gate line, and the remaining two transistors can be individually electrically connected to a second and third gate line, respectively.

Claims:
The invention claimed is: 
     
       1. A touch screen comprising:
 a first drive region; 
 a first sense region; and 
 a first display pixel in the first drive region coupled to a first gate line, wherein the first display pixel includes a first transistor, and wherein the first transistor includes a first gate; and 
 a second display pixel in the first sense region coupled to a second gate line, different from the first gate line, wherein the second display pixel includes a second transistor, and wherein the second transistor includes a second gate; 
 wherein the first gate line is coupled to the first gate and the second gate line is coupled to the second gate, wherein the first gate line is decoupled from the second gate line during at least a touch sensing phase of the touch screen, and wherein the first gate line is coupled to the second gate line at least during a display phase of the touch screen. 
 
     
     
       2. The touch screen of  claim 1 , further comprising a third display pixel in a second drive region of the touch screen, wherein the first gate line is coupled to the third display pixel. 
     
     
       3. The touch screen of  claim 1 , further comprising a third display pixel in a second sense region of the touch screen, wherein the second gate line is coupled to the third display pixel. 
     
     
       4. The touch screen of  claim 1 , further comprising a decoupling portion between the first and second gate lines. 
     
     
       5. The touch screen of  claim 4 , wherein the decoupling portion comprises a capacitor electrically connected to a diode. 
     
     
       6. The touch screen of  claim 4 , wherein the decoupling portion comprises a diode electrically connected to a transistor. 
     
     
       7. The touch screen of  claim 4 , wherein the decoupling portion comprises a transistor controlled by a timing signal, the timing signal controlling a transition between the touch sensing phase and the display phase of the touch screen. 
     
     
       8. The touch screen of  claim 4 , wherein the decoupling portion comprises a first diode and a second diode electrically connected in a ring configuration. 
     
     
       9. The touch screen of  claim 4 , wherein the decoupling portion comprises:
 a switch controlled by a timing signal, the timing signal controlling a transition between the touch sensing phase and the display phase of the touch screen; and 
 a diode electrically connected to the switch. 
 
     
     
       10. The touch screen of  claim 1 , wherein the first gate line is configured to pass through the first sense region. 
     
     
       11. The touch screen of  claim 10 , wherein the second gate line is configured to pass through the first drive region. 
     
     
       12. The touch screen of  claim 10 , wherein the first sense region further comprises a first sense electrode, and the first gate line is configured to pass underneath the first sense electrode. 
     
     
       13. The touch screen of  claim 12 , wherein the first sense electrode is configured to operate as at least a portion of touch sensing circuitry during the touch sensing phase of the touch screen and is configured to further operate as at least a portion of a display sensing circuitry during the display phase of the touch screen. 
     
     
       14. The touch screen of  claim 1 , further comprising a third display pixel in the first sense region. 
     
     
       15. The touch screen of  claim 14 , wherein the third display pixel is coupled to the second gate line and is aligned with the first and second display pixels in the first direction. 
     
     
       16. The touch screen of  claim 14 , wherein the third display pixel is coupled to a third gate line, wherein the third gate line is decoupled from the first and second gate line and the third display pixel is aligned with the second display pixel in a second direction, perpendicular to the first direction. 
     
     
       17. The touch screen of  claim 14 , wherein the second display pixel and the third display pixel are immediately adjacent to one another. 
     
     
       18. The touch screen of  claim 1 , wherein the second gate line is parallel to the first gate line. 
     
     
       19. A method for operating a touch screen, the method comprising:
 providing a first drive region and a first sense region; 
 applying a first voltage to a first gate line coupled to a first display pixel in the first drive region, wherein the first display pixel includes a first transistor, and wherein the first transistor includes a first gate; and 
 applying a second voltage to a second gate line coupled to a second display pixel in the first sense region, wherein the second display pixel includes a second transistor, and wherein the second transistor includes a second gate; 
 wherein the first gate line is coupled to the first gate and the second gate line is coupled to the second gate, wherein the first gate line is decoupled from the second gate line during at least a touch sensing phase of the touch screen, and wherein the first gate line is coupled to the second gate line at least during a display phase of the touch screen. 
 
     
     
       20. The method of  claim 19 , wherein:
 a third display pixel in a second drive region of the touch screen is coupled to the first gate line; and 
 a fourth display pixel in a second sense region of the touch screen is coupled to the second gate line. 
 
     
     
       21. The method of  claim 19 , further comprising:
 electrically connecting the first gate line to the second gate line via a decoupling portion between the first and second gate lines. 
 
     
     
       22. The method of  claim 19 , wherein the first gate line passes through the first sense region. 
     
     
       23. The method of  claim 22 , wherein the second gate line passes through the first drive region. 
     
     
       24. The method of  claim 22 , wherein the first sense region further comprises a first sense electrode, and the first gate line is configured to pass underneath the first sense electrode. 
     
     
       25. The method of  claim 24 , wherein the first sense electrode is configured to operate as at least a portion of touch sensing circuitry during the touch sensing phase of the touch screen, and is configured to further operate as at least a portion of a display sensing circuitry during a display phase of the touch screen. 
     
     
       26. The method of  claim 19 , wherein the second gate line is parallel to the first gate line.

Description:
FIELD OF THE DISCLOSURE 
     This relates generally to touch sensing, and more particularly to reducing touch pixel coupling. 
     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 fields used to detect touch can extend beyond the surface of the display, and objects approaching the surface may be detected near the surface without actually touching the surface. 
     Capacitive touch sensor panels can be formed from a matrix of drive and sense lines of a substantially transparent conductive material, such as Indium Tin Oxide (ITO), often arranged in rows and columns in horizontal and vertical directions on a substantially transparent substrate. 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 integrating touch sensing circuitry into a display pixel stackup (i.e., the stacked material layers forming the display pixels). This integration of the touch hardware and display hardware can lead to parasitic capacitive pathways that can interfere with normal touch detection. 
     SUMMARY OF THE DISCLOSURE 
     The following description includes examples of reducing or eliminating touch pixel coupling in a touch screen that can interfere with normal touch detection during a touch sensing phase of the touch screen. Such touch pixel coupling can be caused by parasitic capacitive pathways that can exist over a shared gate line electrically connected to display pixels in both drive and sense regions of the touch screen. 
     In one example, display pixels in drive regions of the touch screen can be connected to different gate lines than display pixels in sense regions of the touch screen. In another example, the shared gate line between display pixels can include a decoupling portion that can temporarily decouple the shared gate. In another example, display pixels can include a diode-connected transistor electrically connected between the shared gate line and a gate terminal of another transistor in the display pixel. In another example, display pixels in drive regions can be electrically connected to the shared gate line and a second gate line, and display pixels in sense regions can be electrically connected to the shared gate line and a third gate line, different from the second gate line. The connections to the second and third gate lines can be such so as to reduce touch pixel coupling. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  illustrates an example mobile telephone that includes a touch screen. 
         FIG. 1B  illustrates an example digital media player that includes a touch screen. 
         FIG. 1C  illustrates an example personal computer that includes a touch screen. 
         FIG. 2  is a block diagram of an example computing system that illustrates one implementation of an example touch screen according to examples of the disclosure. 
         FIG. 3  is a more detailed view of a touch screen showing an example configuration of drive lines and sense lines according to examples of the disclosure. 
         FIG. 4  illustrates an example configuration in which common electrodes (Vcom) can form portions of the touch sensing circuitry of a touch sensing system. 
         FIG. 5  is a three-dimensional illustration of an exploded view (expanded in the z-direction) of example display pixel stackups showing some of the elements within the pixel stackups of an example integrated touch screen. 
         FIG. 6  illustrates an example touch sensing operation according to examples of the disclosure. 
         FIG. 7  illustrates an exemplary parasitic coupling pathway between a display pixel in a drive region segment and a display pixel in a sense region of an example touch screen according to examples of the disclosure. 
         FIG. 8  illustrates the variability of C ST  in a display pixel. 
         FIG. 9  illustrates an example equivalent touch sensing circuit with a variable parasitic capacitive coupling pathway according to examples of the disclosure. 
         FIG. 10A  illustrates an example configuration in which gate lines of display pixels in drive region segments can be different than gate lines of display pixels in sense regions. 
         FIG. 10B  illustrates an example equivalent touch sensing circuit with variable parasitic capacitive coupling between a display pixel in a drive region and a display pixel in a sense region when the two display pixels are connected to different gate lines. 
         FIG. 11A  illustrates an example configuration in which a gate line that connects display pixels in the drive and sense regions can be decoupled during a touch sensing phase of the touch screen according to examples of the disclosure. 
         FIG. 11B  illustrates another example configuration in which a gate line that connects display pixels in the drive and sense regions can be decoupled during a touch sensing phase of the touch screen according to examples of the disclosure. 
         FIG. 11C  illustrates another example configuration in which a gate line that connects display pixels in the drive and sense regions can be decoupled during a touch sensing phase of the touch screen according to examples of the disclosure. 
         FIG. 11D  illustrates another example configuration in which a gate line that connects display pixels in the drive and sense regions can be decoupled during a touch sensing phase of the touch screen according to examples of the disclosure. 
         FIG. 11E  illustrates another example configuration in which a gate line that connects display pixels in the drive and sense regions can be decoupled during a touch sensing phase of the touch screen according to examples of the disclosure. 
         FIG. 12  illustrates an example configuration in which a diode-connected transistor can be inserted between a gate line and a gate terminal of a pixel TFT of a display pixel. 
         FIG. 13A  illustrates an example configuration in which gate lines of two TFTs in a display pixel can be decoupled. 
         FIG. 13B  illustrates an example configuration in which the gate terminals of the second TFTs in display pixels in drive regions can be connected to each other, and the gate terminals of the second TFTs in display pixels in sense regions can be connected to each other. 
     
    
    
     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 touch screens can be formed by integrating touch sensing circuitry into a display pixel stackup (i.e., the stacked material layers forming the display pixels). This integration of the touch hardware and display hardware can lead to parasitic capacitive pathways that can interfere with normal touch detection. In one example, one or more display pixels in a drive region segment of the touch screen can be electrically connected to the same gate line as one or more display pixels in a sense region of the touch screen. This common connection can result in direct parasitic coupling between the one or more display pixels in the drive and sense regions. During a touch sensing phase of the touch screen, this parasitic coupling can cause unwanted perturbation of touch signals detected by the detection circuitry in the touch screen. However, the effect of the parasitic capacitive coupling pathway can be reduced by severing, to various degrees, the parasitic pathway from a drive common electrode to a sense common electrode. 
       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 personal computer  144  that includes a touch screen  128 . Although not shown in the figures, the personal computer  144  can also be a tablet computer or a desktop computer with a touch-sensitive display. Touch screens  124 ,  126 , and  128  may be based on, for example, self capacitance or mutual capacitance, or another touch sensing technology. For example, in a self capacitance based touch system, an individual electrode with a self-capacitance to ground can be used to form a touch pixel (touch node) for detecting touch. As an object approaches the touch pixel, an additional capacitance to ground can be formed between the object and the touch pixel. The additional capacitance to ground can result in a net increase in the self-capacitance seen by the touch pixel. This increase in self-capacitance can be detected and measured by a touch sensing system to determine the positions of multiple objects when they touch the touch screen. A mutual capacitance based touch system can include, for example, drive regions and sense regions, such as drive lines and sense lines. For example, drive lines can be formed in rows while sense lines can be formed in columns (i.e., orthogonal). Touch pixels (touch nodes) can be formed at the intersections or adjacencies (in single layer configurations) of the rows and columns. During operation, the rows can be stimulated with an AC waveform and a mutual capacitance can be formed between the row and the column of the touch pixel. As an object approaches the touch pixel, some of the charge being coupled between the row and column of the touch pixel can instead be coupled onto the object. This reduction in charge coupling across the touch pixel can result in a net decrease in the mutual capacitance between the row and the column and a reduction in the AC waveform being coupled across the touch pixel. This reduction in the charge-coupled AC waveform can be detected and measured by the touch sensing system to determine the positions of multiple objects when they touch the touch screen. In some examples, a touch screen can be multi-touch, single touch, projection scan, full-imaging multi-touch, or any capacitive touch. 
       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  could be included in, for example, mobile telephone  136 , digital media player  140 , personal computer  144 , or any mobile or non-mobile computing device that includes a touch screen. 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 , channel scan logic  210  and driver logic  214 . Channel scan logic  210  can access RAM  212 , autonomously read data from the sense channels and provide control for the sense channels. In addition, channel scan logic  210  can control driver logic  214  to generate stimulation signals  216  at various frequencies and/or phases that can be selectively applied to drive regions of the touch sensing circuitry 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). 
     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 a Liquid-Crystal Display (LCD) driver  234 . It is understood that although the examples of the disclosure are 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 Active-Matrix Organic LED (AMOLED) and Passive-Matrix Organic LED (PMOLED) displays. 
     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 , such as a touch input to the displayed UI. 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. 
     Touch screen  220  can include touch sensing circuitry that can include a capacitive sensing medium having a plurality of drive lines  222  and a plurality of sense lines  223 . 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  222  can be driven by stimulation signals  216  from driver logic  214  through a drive interface  224 , and resulting sense signals  217  generated in sense lines  223  can be transmitted through a sense interface  225  to sense channels  208  (also referred to as an event detection and demodulation circuit) in touch controller  206 . 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), such as touch pixels  226  and  227 . This way of understanding 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 whether a touch has been detected at each touch pixel in the touch screen, the pattern of touch pixels in the touch screen at which a touch occurred can be thought of as an “image” of touch (i.e., a pattern of fingers touching the touch screen). 
     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. An example integrated touch screen in which examples of the disclosure can be implemented will now be described with reference to  FIGS. 3-6 .  FIG. 3  is a more detailed view of touch screen  220  showing an example configuration of drive lines  222  and sense lines  223  according to examples of the disclosure. As shown in  FIG. 3 , each drive line  222  can be formed of one or more drive line segments  301  that can be electrically connected by drive line links  303  at connections  305 . Drive line links  303  are not electrically connected to sense lines  223 , rather, the drive line links can bypass the sense lines through bypasses  307 . Drive lines  222  and sense lines  223  can interact capacitively to form touch pixels such as touch pixels  226  and  227 . Drive lines  222  (i.e., drive line segments  301  and corresponding drive line links  303 ) and sense lines  223  can be formed of electrical circuit elements in touch screen  220 . In the example configuration of  FIG. 3 , each of touch pixels  226  and  227  can include a portion of one drive line segment  301 , a portion of a sense line  223 , and a portion of another drive line segment  301 . For example, touch pixel  226  can include a right-half portion  309  of a drive line segment on one side of a portion  311  of a sense line, and a left-half portion  313  of a drive line segment on the opposite side of portion  311  of the sense line. 
     In some examples, the configuration of drive lines  222  and sense lines  223  can be the reverse of that shown in  FIG. 3 . That is to say that each drive line  222  can be formed of a single drive line segment, whereas each sense line  223  can be formed of one or more sense line segments that can be electrically connected by sense line links. Further, in some examples, guard lines can exist between drive line segments  301  and sense lines  223 . Such guard lines can shield display pixel elements in sense lines from direct coupling to display pixel elements in adjacent drive line segments. For ease of description, the examples of the disclosure will be described with reference to the drive and sense line configuration of  FIG. 3 , although it is understood that the scope of the disclosure is not so limited. 
     The circuit elements in display pixel stackups can include, for example, elements that can exist in conventional LCD displays, as described above. It is noted that circuit elements are not limited to whole circuit components, such 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. 4  illustrates an example configuration in which common electrodes (Vcom) can form portions of the touch sensing circuitry of a touch sensing system. Each display pixel includes a common electrode  401 , which is 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 conventional LCD displays, e.g., fringe field switching (FFS) displays, that can operate as part of the display system to display an image. 
     In the example shown in  FIG. 4 , each common electrode (Vcom)  401  can serve as a multi-function circuit element that can operate as display circuitry of the display system of touch screen  220  and can also operate as touch sensing circuitry of the touch sensing system. In this example, each common electrode  401  can operate as a common electrode of the display circuitry of the touch screen, and can also operate together when grouped with other common electrodes as touch sensing circuitry of the touch screen. For example, a group of common electrodes  401  can operate together as a capacitive part of a drive line or a sense line of the touch sensing circuitry during the touch sensing phase. Other circuit elements of touch screen  220  can form part of the touch sensing circuitry by, for example, electrically connecting together common electrodes  401  of a region, switching electrical connections, etc. 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 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. 
     For example,  FIG. 4  shows common electrodes  401  grouped together to form drive region segments  403  and sense regions  405  that generally correspond to drive line segments  301  and sense lines  223 , respectively. Grouping multi-function circuit elements of display pixels into a region can mean operating the multi-function circuit elements of the display pixels together to perform a common function of the region. Grouping into functional regions may be accomplished through one or a combination of approaches, for example, the structural configuration of the system (e.g., physical breaks and bypasses, voltage line configurations), the operational configuration of the system (e.g., switching circuit elements on/off, changing voltage levels and/or signals on voltage lines), etc. 
     Multi-function circuit elements of display pixels of the touch screen can operate in both the display phase and the touch phase. For example, during a touch phase, common electrodes  401  can be grouped together to form touch signal lines, such as drive regions and sense regions. In some examples circuit elements can be grouped to form a continuous touch signal line of one type and a segmented touch signal line of another type. For example,  FIG. 4  shows one example in which drive region segments  403  and sense regions  405  correspond to drive line segments  301  and sense lines  223  of touch screen  220 . Other configurations are possible in other examples; for example, common electrodes  401  could be grouped together such that drive lines are each formed of a continuous drive region and sense lines are each formed of a plurality of sense region segments linked together through connections that bypass a drive region. 
     The drive regions in the example of  FIG. 3  are shown in  FIG. 4  as rectangular regions including a plurality of common electrodes of display pixels, and the sense regions of  FIG. 3  are shown in  FIG. 4  as rectangular regions including a plurality of common electrodes of display pixels extending the vertical length of the LCD. In some examples, a touch pixel of the configuration of  FIG. 4  can include, for example, a 64×64 area of display pixels. However, the drive and sense regions are not limited to the shapes, orientations, and positions shown, but can include any suitable configurations according to examples of the disclosure. It is to be understood that the display pixels used to form the touch pixels are not limited to those described above, but can be any suitable size or shape to permit touch capabilities according to examples of the disclosure. 
       FIG. 5  is a three-dimensional illustration of an exploded view (expanded in the z-direction) of example display pixel stackups  500  showing some of the elements within the pixel stackups of an example integrated touch screen  550 . Stackups  500  can include a configuration of conductive lines that can be used to group common electrodes, such as common electrodes  401 , into drive region segments and sense regions, such as shown in  FIG. 4 , and to link drive region segments to form drive lines. 
     Stackups  500  can include elements in a first metal (M1) layer  501 , a second metal (M2) layer  503 , a common electrode (Vcom) layer  505 , and a third metal (M3) layer  507 . Each display pixel can include a common electrode  509 , such as common electrodes  401  in  FIG. 4 , that is formed in Vcom layer  505 . M3 layer  507  can include connection element  511  that can electrically connect together common electrodes  509 . In some display pixels, breaks  513  can be included in connection element  511  to separate different groups of common electrodes  509  to form drive region segments  515  and a sense region  517 , such as drive region segments  403  and sense region  405 , respectively. Breaks  513  can include breaks in the x-direction that can separate drive region segments  515  from sense region  517 , and breaks in the y-direction that can separate one drive region segment  515  from another drive region segment. M1 layer  501  can include tunnel lines  519  that can electrically connect together drive region segments  515  through connections, such as conductive vias  521 , which can electrically connect tunnel line  519  to the grouped common electrodes in drive region segment display pixels. Tunnel line  519  can run through the display pixels in sense region  517  with no connections to the grouped common electrodes in the sense region, e.g., no vias  521  in the sense region. The M1 layer can also include gate lines  520 . M2 layer  503  can include data lines  523 . Only one gate line  520  and one data line  523  are shown for the sake of clarity; however, a touch screen can include a gate line running through each horizontal row of display pixels and multiple data lines running through each vertical row of display pixels, for example, one data line for each red, green, blue (RGB) color sub-pixel in each pixel in a vertical row of an RGB display integrated touch screen. 
     Structures such as connection elements  511 , tunnel lines  519 , and conductive vias  521  can operate as a touch sensing circuitry of a touch sensing system to detect touch during a touch sensing phase of the touch screen. Structures such as data lines  523 , along with other pixel stackup elements such as transistors, pixel electrodes, common voltage lines, data lines, etc. (not shown), can operate as display circuitry of a display system to display an image on the touch screen during a display phase. Structures such as common electrodes  509  can operate as multifunction circuit elements that can operate as part of both the touch sensing system and the display system. 
     For example, in operation during a touch sensing phase, gate lines  520  can be held to a fixed voltage while stimulation signals can be transmitted through a row of drive region segments  515  connected by tunnel lines  519  and conductive vias  521  to form electric fields between the stimulated drive region segments and sense region  517  to create touch pixels, such as touch pixel  226  in  FIG. 2 . In this way, the row of connected together drive region segments  515  can operate as a drive line, such as drive line  222 , and sense region  517  can operate as a sense line, such as sense line  223 . When an object such as a finger approaches or touches a touch pixel, the object can affect the electric fields extending between the drive region segments  515  and the sense region  517 , thereby reducing the amount of charge capacitively coupled to the sense region. This reduction in charge can be sensed by a sense channel of a touch sensing controller connected to the touch screen, such as touch controller  206  shown in  FIG. 2 , and stored in a memory along with similar information of other touch pixels to create an “image” of touch. 
     A touch sensing operation according to examples of the disclosure will be described with reference to  FIG. 6 .  FIG. 6  shows partial circuit diagrams of some of the touch sensing circuitry within display pixels in a drive region segment  601  and a sense region  603  of an example touch screen according to examples of the disclosure. For the sake of clarity, only one drive region segment is shown. Also for the sake of clarity,  FIG. 6  includes circuit elements illustrated with dashed lines to signify some circuit elements operate primarily as part of the display circuitry and not the touch sensing circuitry. In addition, a touch sensing operation is described primarily in terms of a single display pixel  601   a  of drive region segment  601  and a single display pixel  603   a  of sense region  603 . However, it is understood that other display pixels in drive region segment  601  can include the same touch sensing circuitry as described below for display pixel  601   a , and the other display pixels in sense region  603  can include the same touch sensing circuitry as described below for display pixel  603   a . Thus, the description of the operation of display pixel  601   a  and display pixel  603   a  can be considered as a description of the operation of drive region segment  601  and sense region  603 , respectively. 
     Referring to  FIG. 6 , drive region segment  601  includes a plurality of display pixels including display pixel  601   a . Display pixel  601   a  can include a TFT  607 , a gate line  611 , a data line  613 , a pixel electrode  615 , and a common electrode  617 .  FIG. 6  shows common electrode  617  connected to the common electrodes in other display pixels in drive region segment  601  through a connection element  619  within the display pixels of drive region segment  601  that is used for touch sensing as described in more detail below. Sense region  603  includes a plurality of display pixels including display pixel  603   a . Display pixel  603   a  includes a TFT  609 , a data line  614 , a pixel electrode  616 , and a common electrode  618 . TFT  609  can be connected to the same gate line  611  as TFT  607 .  FIG. 6  shows common electrode  618  connected to the common electrodes in other display pixels in sense region  603  through a connection element  620  that can be connected, for example, in a border region of the touch screen to form an element within the display pixels of sense region  603  that is used for touch sensing as described in more detail below. 
     Although display pixels  601   a  and  603   a  have been described as including a single TFT, in some examples the display pixels may include more than a single TFT. For example, display pixel  603   a  can include two TFTs connected in series, the gate terminals of which both being connected to gate line  611 . The same can be true of display pixel  601   a  and other display pixels in the touch screen. The operation of such display pixels can be substantially the same as the operation of the display pixels of  FIG. 6 . For ease of description, unless otherwise noted, the examples of the disclosure will be described with reference to the display pixel configuration of  FIG. 6 , although the scope of the disclosure is not so limited. 
     During a touch sensing phase, gate line  611  can be connected to a power supply, such as a charge pump, that can apply a voltage to maintain TFTs  609  in the “off” state. Drive signals can be applied to common electrodes  617  through a tunnel line  621  that is electrically connected to a portion of connection element  619  within a display pixel  601   b  of drive region segment  601 . The drive signals, which are transmitted to all common electrodes  617  of the display pixels in drive region segment  601  through connection element  619 , can generate an electrical field  623  between the common electrodes of the drive region segment and common electrodes  618  of sense region  603 , which can be connected to a sense amplifier, such as a charge amplifier  626 . Electrical charge can be injected into the structure of connected common electrodes of sense region  603 , and charge amplifier  626  converts the injected charge into a voltage that can be measured. The amount of charge injected, and consequently the measured voltage, can depend on the proximity of a touch object, such as a finger  627 , to the drive and sense regions. In this way, the measured voltage can provide an indication of touch on or near the touch screen. 
     Referring again to  FIG. 5 , it can be seen from  FIG. 5  that some display pixels of touch screen  550  include different elements than other display pixels. For example, a display pixel  551  can include a portion of connection element  511  that has breaks  513  in the x-direction and the y-direction, and display pixel  551  does not include tunnel line  519 . A display pixel  553  can include a portion of connection element  511  that has a break  513  in the x-direction, but not in the y-direction, and can include a portion of tunnel line  519  and a via  521 . Other display pixels can include other differences in the configuration of stackup elements including, for example, no breaks  513  in connection element  511 , a portion of tunnel line  519  without a via  521 , etc. 
     As described above, in some examples, one or more display pixels in a drive region segment of the touch screen can be electrically connected to the same gate line as one or more display pixels in a sense region of the touch screen. This common connection can result in direct parasitic coupling between the one or more display pixels in the drive and sense regions. During a touch sensing phase of the touch screen, this parasitic coupling can cause unwanted perturbation of touch signals detected by the detection circuitry in the touch screen. 
       FIG. 7  illustrates an exemplary parasitic coupling pathway between display pixel  701   a  in drive region segment  701  and display pixel  703   a  in sense region  703  of an example touch screen according to examples of the disclosure. Display pixels  701   a  and  703   a  can have the same structure as display pixels  601   a  and  603   a  as described above with reference to  FIG. 6 . Also as described above, display pixels  701   a  and  703   a  can share gate line  711 . Gate line  711  can provide a direct pathway through which signals, including noise, can be coupled from common electrode  717  in drive region segment  701  to common electrode  718  in sense region  703 . Because touch sensing during a touch sensing phase of the touch screen can be performed by detecting a signal at common electrode  718  in sense region  703 , unwanted noise that may be injected into common electrode  718  can result in inaccurate touch measurements. 
     In particular, the above-mentioned parasitic coupling pathway can originate at common electrode  717 . The pathway can continue to pixel electrode  715  through C ST    719 , the capacitance between common electrode  717  and the pixel electrode. C ST    719  can be a function of the materials used in the display pixel stackup, and the placement of pixel electrode  715  and common electrode  717  in display pixel  701   a . C ST    719  can include a variable component and a constant component. The variable component will be described later. The constant component can be a function of the materials used and the placement of pixel electrode  715  and common electrode  717 . 
     The pathway can proceed from pixel electrode  715  to gate line  711  through C Gate-Pixel    721 , the capacitance between the gate and drain terminals of TFT  707 . C Gate-Pixel    721  can include a variable component and a constant component. The variable component of C Gate-Pixel    721  will be described later. The constant component of C Gate-Pixel    721  can be a function of the materials used in the display pixel stackup, and the placement of circuit elements such as gate line  711  and pixel electrode  715 . The pathway can cross from drive region segment  701  into sense region  703  via gate line  711 . Next, the pathway can continue to pixel electrode  716  through C Gate-Pixel    722 , the capacitance between the gate and drain terminals of TFT  709 . Finally, the pathway can end at common electrode  718  by coupling from pixel electrode  716  to the common electrode through C ST    720 , the capacitance between the common electrode and the pixel electrode. A signal that travels through the above-described parasitic pathway and ends up on common electrode  718  can then be sensed during a touch sensing phase of the touch screen, as described above. If this signal does not represent the proximity of a touch object to drive region segment  701  and sense region  703  (i.e., the signal is noise), the signal could adversely affect the accurate measurement of touch on the touch screen. 
     The above-described parasitic coupling pathway can be especially problematic in some examples because C ST    719 , C ST    720 , C Gate-Pixel    721  and C Gate-Pixel    722  can be image grey level dependent. In other words, these capacitances through which the coupling pathway can exist can be variable, and can vary with the image displayed on the touch screen. Such variability can make it difficult to properly operate the touch screen. 
     It is noted that although the parasitic coupling pathway has been described as starting at common electrode  717 , noise or other unwanted signals from any point in display pixel  701   a  can be coupled to display pixel  703   a  via gate line  711 . Any such signals can prove problematic for proper touch screen operation. 
     The variability of C Gate-Pixel    721  will now be described with reference to display pixel  701   a  in  FIG. 7 . This description can similarly apply to display pixel  703   a  as well as any other display pixels in the touch screen according to examples of the disclosure. During a display phase of the touch screen, gate line  711  can be set to a voltage such that TFT  707  can be on. In some examples, this voltage can be a high voltage, and can be denoted by VGH. The following examples of the disclosure will be described as utilizing a high gate voltage to turn on the TFTs in display pixels. However, it is understood that the TFTs can be of the type such that a low gate voltage can turn them on. 
     As a result of TFT  707  being turned on, the voltage at data line  713  can be substantially transferred to pixel electrode  715 . The voltage difference between pixel electrode  715  and common electrode  717  can determine the grey level of display pixel  701   a . The voltage at data line  713  (and thus the voltage at pixel electrode  715 ) and the voltage at common electrode  717  can therefore be set to achieve the desired grey level for display pixel  701   a.    
     It is noted that it can be the magnitude, and not the sign, of the voltage difference between pixel electrode  715  and common electrode  717  that can determine the grey level of display pixel  701   a . For example, a voltage difference of +5V between pixel electrode  715  and common electrode  717  (i.e., the voltage at the pixel electrode being 5V higher than the voltage at the common electrode) can provide the same grey level for display pixel  701   a  as a voltage difference of −5V between those same electrodes (i.e., the voltage at the pixel electrode being 5V lower than the voltage at the common electrode). Therefore, in some examples of the disclosure, the voltage supplied to pixel electrode  715  with respect to the voltage at common electrode  717  may regularly alternate from negative to positive and back again during normal touch screen operation. 
     When the voltage from data line  713  has been transferred to pixel electrode  715 , the voltage at gate line  711  can be set such that TFT  707  can be turned off, and the voltage at the pixel electrode can be substantially maintained. As stated above, the gate voltage needed to turn off TFT  707  can be a low voltage, and can be denoted by VGL. However, this need not be the case in all examples, as noted above. Regardless, the following examples of the disclosure will be described as utilizing a low gate voltage to turn off the TFTs in display pixels. It is understood that the TFTs can be of the type such that a high gate voltage can turn them off. 
     During a touch sensing phase of the touch screen, the voltages of the touch circuitry can be shifted higher to facilitate proper touch sensing operation. In some examples, this shift can entail increasing the voltage at common electrode  717 . In order to keep the grey level of display pixel  701   a  constant during the above-mentioned shift, the voltage at pixel electrode  715  can also be shifted up by the same amount as common electrode  717  to maintain the voltage difference between the two electrodes during the transition. However, the voltage at gate line  711  can remain at VGL to ensure that TFT  707  can remain turned off. Therefore, during a touch sensing phase of the touch screen, the voltage difference between gate line  711  and pixel electrode  715  can change from the voltage difference that exists between the gate line and the pixel electrode during a display phase of the touch screen. 
     The above-described change in voltage difference can affect the value of C Gate-Pixel    721 . As described above, C Gate-Pixel    721  can include the gate-to-drain capacitance of TFT  707 . This gate-to-drain capacitance of TFT  707  can vary with the voltage difference between the gate and drain terminals of the TFT because of the characteristics and design of transistors such as TFT  707 . Therefore, because the voltage between pixel electrode  715  and gate line  711  can change when the touch screen transitions from a display phase to a touch sensing phase, as described above, C Gate-Pixel    721  can change during that same transition, thus making C Gate-Pixel  variable. 
     Further adding to the variability of C Gate-Pixel    721  can be the fact that the voltage at pixel electrode  715  can vary based on the desired grey level of display pixel  701   a , as described above. This can in turn result in the voltage difference between pixel electrode  715  and gate line  711  varying based on the grey level of display pixel  701   a , which can then cause further variance in C Gate-Pixel    721 . C Gate-Pixel    721  can therefore be image grey level dependent. 
     In addition to the variability of C Gate-Pixel    721 , C ST    719 , which can also be included in the parasitic capacitive coupling pathway between display pixels, can also be variable. The variability of C ST    719  in display pixel  701   a  will now be described with reference to  FIG. 8 . The following description can similarly apply to C ST    720  in display pixel  703   a  as well as other corresponding capacitances in other display pixels in the touch screen according to examples of the disclosure.  FIG. 8  illustrates an exemplary partial material stackup of a display pixel of the touch screen according to examples of the disclosure. Common electrode  817  and pixel electrode  815  can be separated by dielectric  825 . Common electrode  817  and pixel electrode  815  can, for example, correspond to common electrode  717  and pixel electrode  715 , respectively. Liquid crystal  827  can be formed over pixel electrode  815 . 
     As described above, a voltage difference can exist between pixel electrode  815  and common electrode  817  depending on the desired grey level of the display pixel in which they reside. This voltage difference can generate an electric field  823  between pixel electrode  815  and common electrode  817 . Electric field  823  can exist in both liquid crystal  827  and dielectric  825 . Therefore, the capacitance between pixel electrode  815  and common electrode  817 , which can be represented by C ST    719 , can be a function of the dielectric constants of both liquid crystal  827  and dielectric  825 . However, in some examples, the dielectric constant of liquid crystal  827  can change as a function of the electric fields  823  that penetrate it, and the electric fields can change as a function of the voltage difference between pixel electrode  815  and common electrode  817 . Therefore, the capacitance between pixel electrode  815  and common electrode  817 , which can be represented by C ST    719 , can change as a function of the voltage difference between the pixel electrode and the common electrode. Because this voltage difference can set the grey level of the corresponding display pixel, as described above, C ST    719  can be image grey level dependent. 
       FIG. 9  illustrates an example equivalent touch sensing circuit  900  with a variable parasitic capacitive coupling pathway according to examples of the disclosure. Touch sensing circuit  900  can include a drive common electrode  917  that can be stimulated by a stimulation voltage source  914 . Sense common electrode  918  can be located proximate to drive common electrode  917  such that charge on the drive common electrode provided by stimulation voltage source  914  can be partially coupled onto the sense common electrode via capacitive pathway C 0    901 . As discussed above, the amount of charge coupled onto sense common electrode  918  from drive common electrode  917  can vary depending on the proximity of a finger or a touch object to the drive and sense common electrodes. The charge coupled onto sense common electrode  918  can then be detected by detection circuitry  908 , which can detect the changes in the mutual capacitance C 0    901  between drive common electrode  917  and the sense common electrode. 
     As described above, a variable parasitic capacitive coupling pathway can exist between drive common electrode  917  and sense common electrode  918  via gate line  911 . This pathway can begin at drive common electrode  917  and can reach gate line  911  via C 1    903 . C 1    903  can include the series combination of C ST    719  and C Gate-Pixel    721 , both of which can be variable as described above. The pathway can continue to sense common electrode  918  via C 2    905 . C 2    905  can include the series combination of C ST    720  and C Gate-Pixel    722 , both of which can also be variable as described above. This parasitic capacitive coupling pathway can provide for additional coupling of charge onto sense common electrode  918 , which can then be detected by detection circuitry  908 , and can hamper touch sensing detection. 
     R G    907  can represent the effective resistance of gate line  911 , and can be a product of the metal used to create the gate line, for example. C G    909  can represent the effective capacitance of gate line  911 , and can be a combination of various capacitances created by elements in the touch screen such as data lines, pixel electrodes and common electrodes, as discussed above. 
     In the circuit  900  of  FIG. 9 , the signal coupling from drive common electrode  917  to sense common electrode  918  due to the parasitic pathway can be characterized by the following equation:
 
 R   G *( C   1   *ΔC   2   +C   2   *ΔC   1 )/(1+τ)  (1)
 
wherein τ can represent the RC time constant of the parasitic pathway. As described above, C 1    903  can include a constant component and a variable component, and can be represented by the equation:
 
C 1c +C 1v   (2)
 
wherein C 1c  can represent the constant component of C 1  and C 1v  can represent the variable component of C 1 . C 2    905  can also include a constant component and a variable component, and can be represented by the equation:
 
C 2c +C 2v   (3)
 
wherein C 2c  can represent the constant component of C 2  and C 2v  can represent the variable component of C 2 .
 
     The effect of the variable parasitic capacitive coupling pathway discussed above can be reduced by severing, to various degrees, the parasitic pathway from drive common electrode  917  to sense common electrode  918  through C 1    903 , gate line  911  and C 2    905 . 
     One way to sever the parasitic pathway can be to eliminate the common gate line connecting display pixels in drive and sense regions of the touch screen.  FIG. 10A  illustrates an example configuration in which gate lines of display pixels in drive region segments  1001  can be different than gate lines of display pixels in sense regions  1003 . G 1    1011  can be a gate line that is electrically connected to the gate terminals of TFTs in drive region display pixels  1001   a  in drive region segments  1001 . G 2    1012  can be a gate line that is electrically connected to the gate terminals of TFTs in sense region display pixels  1003   a  in sense region  1003 . G 1    1011  can pass through sense region  1003  without being electrically connected to display pixels in the sense region. Similarly, G 2    1012  can pass through drive region segments  1001  without being electrically connected to display pixels in the drive region segments. In this way, the direct coupling between display pixels in drive and sense regions via a gate line that connects them, as described with reference to  FIG. 7 , can be removed. In other words, in the configuration of  FIG. 10A , no direct electrical connection can exist between display pixels  1001   a  in drive region segments  1001  and display pixels  1003   a  in sense region  1003 . 
       FIG. 10B  illustrates an example equivalent touch sensing circuit  1000  with variable parasitic capacitive coupling between a display pixel in a drive region and a display pixel in a sense region when the two display pixels are connected to different gate lines. The configuration of touch sensing circuit  1000  can be similar to that of touch sensing circuit  900 , with some differences. Drive common electrode  1017  can be coupled to drive gate  1011  via C 1    1004 . Sense common electrode  1018  can be coupled to sense gate  1012  via C 2    1005 . C 1    1004  and C 2    1005  can be substantially similar to C 1    903  and C 2    905 . However, drive common electrode  1017  can also be coupled to sense gate  1012  via C 1C    1019 . C 1C    1019  can be a function of the positioning of sense gate  1012  passing underneath drive common electrode  1017 , as described in  FIG. 10A , and can be constant. Similarly, sense common electrode  1018  can also be coupled to drive gate  1011  via C 2C    1020 . C 2C    1020  can similarly be a function of the positioning of drive gate  1011  passing underneath sense common electrode  1018 , as described in  FIG. 10A , and can be constant. Two parasitic pathways can now exist between drive common electrode  1017  and sense common electrode  1018 : one through C 1    1004  and C 2C    1020  via drive gate  1011 , and one through C 1C    1019  and C 2    1005  via sense gate  1012 . 
     R GD    1007  can represent the effective resistance of drive gate  1011 , and can be a product of the metal used to create the gate line, for example. C GD    1013  can represent the effective capacitance of drive gate  1011 , and can be a combination of various capacitances created by elements in the touch screen such as data lines, pixel electrodes and common electrodes, as discussed above. Similarly, R GS    1009  can represent the effective resistance of sense gate  1012 , and can be a product of the metal used to create the gate line, for example. C GS    1015  can represent the effective capacitance of sense gate  1012 , and can be a combination of various capacitances created by elements in the touch screen such as data lines, pixel electrodes and common electrodes, as discussed above. 
     Although two parasitic pathways can exist between drive common electrode  1017  and sense common electrode  1018 , the effects from the variable components of C 1    1004  and C 2    1005  can be reduced. In particular, in the circuit  1000  of  FIG. 10B , the signal coupling from drive common electrode  1017  to sense common electrode  1018  due to the parasitic pathways can be characterized by the following equation:
 
 R *( C   1C   *ΔC   2   +C   2C   *ΔC   1 )/(1+τ)  (4)
 
wherein τ can represent the RC time constant of the parasitic pathways. If R GD    1007 ≈R GS    1009 ≈R G    907 , R can be approximately equal to R GD , R GS  and R G . C 1  and C 2  can be as described in equations (2) and (3). Comparing equation (4) to equation (1), it is apparent that the variable signal coupling between drive common electrode  1017  and sense common electrode  1018  in the configuration of  FIG. 10B  can be less than that of the configuration of  FIG. 9 . Specifically, ΔC 1  and ΔC 2  in equation (4) can be multiplied by C 2C  and C 1C , respectively, both of which can be constant. In contrast, in equation (1), ΔC 1  and ΔC 2  were multiplied by C 2  and C 1 , respectively, both of which can be variable. Accordingly, as long as R≈R GD ≈R GS ≈R G , the variable component of the parasitic coupling can be reduced as shown.
 
     In the examples described above, display pixels in drive regions have been decoupled from display pixels in sense regions by permanently eliminating gate lines that can be shared between the two sets of display pixels. As an alternative to permanently decoupling the shared gate lines, the shared gate lines can be decoupled only during a touch sensing phase of the touch screen of the disclosure. The touch sensing phase can be a time during which noise injection into the sense region can cause inaccurate detection of touch signals. 
       FIG. 11A  illustrates an example configuration in which a gate line  1111  that connects display pixels  1101   a  and  1103   a  in the drive  1101  and sense regions  1103  can be decoupled during a touch sensing phase of the touch screen according to examples of the disclosure. The general configuration of display pixels  1101   a  and  1103   a  can be that of  FIG. 7 . As in  FIG. 7 , display pixels  1101   a  and  1103   a  can be connected by gate line  1111 . However, in the configuration of  FIG. 11A , gate line  1111  can include capacitor C 3    1127  and diode D 1    1129  in region  1125 , connected as shown. Region  1125  can be a portion of gate line  1111  that can exist between display pixels at the boundaries of adjacent drive  1101  and sense regions  1103 . In other words, region  1125  need not exist in portions of gate line  1111  that connect display pixels within the same drive  1101  or sense region  1103 . Rather, region  1125  can exist only in portions of gate line  1111  that connect display pixels in different regions, e.g., a display pixel  1101   a  in drive region  1101  and a display pixel  1103   a  in sense region  1103 . In this way, as will be described below, the configuration of  FIG. 11A  can decouple gate line  1111  in drive region  1101  from the gate line in sense region  1103  during a touch sensing phase of the touch screen. 
     The operation of the components inside region  1125  will now be described. As stated above, region  1125  of gate line  1111  can include C 3    1127  and D 1    1129 , connected as shown. During a touch sensing phase of the touch screen, the voltage at gate line  1111  in drive region  1101  can be set to VGL, which can be a DC voltage. Because the voltage at gate line  1111  can be a DC voltage, C 3    1127  can act substantially like an open circuit. In that case, voltage signals from drive region  1101  can be blocked from being transmitted to sense region  1103  via gate line  1111  during a touch sensing phase of the touch screen. Further, the voltage at node Z  1130  can be set such that when the voltage at gate line  1111  is set to VGL, D 1    1129  can act as a sink to take signal noise on gate line  1111  in sense region  1103  to node Z  1130 . Further, the voltage at node Z  1130  can be set such that the voltage that transfers to node Y  1128  via D 1    1129  can be substantially VGL, which can maintain TFT  1109  in an off state. 
     During a transition of the touch screen from the touch sensing phase to a display phase, the voltage at gate line  1111  in drive region  1101  can transition from VGL, a low voltage, to VGH, a high voltage. Because the voltage at gate line  1111  during this transition is no longer a DC voltage, C 3    1127  can act substantially as a closed circuit and can couple the voltage at the gate line in drive region  1101  to the gate line in sense region  1103 , thus providing TFT  1109  a gate voltage sufficient to turn the TFT on. In some examples, the time during which the voltage at gate line  1111  can be high can be short enough such that the coupling of the voltage from drive region  1101  to sense region  1103  via C 3    1127  can be sufficient to maintain the high voltage at the gate line in the sense region. 
     Accordingly, as described above, during a touch sensing phase of the touch screen, gate line  1111  in drive region  1101  can be decoupled from the gate line in sense region  1103 , thus at least partially severing the parasitic coupling pathway between the drive region and the sense region. During a transition to a display phase of the touch screen, gate line  1111  in drive region  1101  and the gate line in sense region  1103  can remain substantially coupled to allow for proper touch screen operation. 
       FIG. 11B  illustrates another example configuration in which a gate line  1111  that connects display pixels  1101   a  and  1103   a  in the drive  1101  and sense regions  1103  can be decoupled during a touch sensing phase of the touch screen according to examples of the disclosure. The configuration of  FIG. 11B  can be substantially that of  FIG. 11A , except that region  1125  can instead include diode D 2    1131  and TFT T 1    1133  connected as shown. During a touch sensing phase of the touch screen, gate line  1111  in drive region  1101  can be set to VGL such that TFT  1107  can be off. T 1    1133  can be turned on to pull the voltage at node Y  1128  to the voltage at node Z  1130 . The voltage at node Z  1130  can be set such that the voltage at node Y  1128 , and thus the voltage at the gate of TFT  1109 , can be low enough to turn off TFT  1109 . For example, the voltage at node Z  1130  can be substantially VGL. Voltage noise signals at gate line  1111  in drive region  1101  can be blocked from traveling to the gate line in sense region  1103  by D 2    1131 , because D 2  can have a non-zero turn-on voltage. Additionally or alternatively, voltage noise signals that appear at node Y  1128  can be shunted to node Z  1130  via T 1    1133  instead of being allowed to travel to the gate of TFT  1109 . 
     During a display phase of the touch screen, T 1    1133  can be turned off. The voltage at the gate line  1111  in drive region  1101  can be substantially coupled by D 2    1131  to the gate line in sense region  1103 . The voltage at gate line  1111  can be VGH such that TFTs  1107  and  1109  can be turned on, which can allow for proper touch screen operation during the display phase. 
       FIG. 11C  illustrates another example configuration in which a gate line  1111  that connects display pixels  1101   a  and  1103   a  in the drive  1101  and sense regions  1103  can be decoupled during a touch sensing phase of the touch screen according to examples of the disclosure. The configuration of  FIG. 11C  can be substantially that of  FIG. 11A , except that region  1125  can include TFT T 2    1135  connected to gate line  1111  as shown. The gate terminal of T 2    1135  can be electrically connected to signal BSYNC  1137 . BSYNC  1137  can be a timing signal used synchronize operation of the touch screen, and can be low to signify a display phase and can be high to signify a touch sensing phase of the touch screen. 
     Therefore, during a touch sensing phase, BSYNC  1137  can be high, which can mean that T 2    1135  can be turned on. Turning T 2    1135  on can pull the voltage at node Y  1128  to the voltage at node Z  1130 . The voltage at node Z  1130  can be set such that the resulting voltage at node Y  1128 , and thus the voltage at the gate of TFT  1109 , can be low enough to turn off TFT  1109 . For example, the voltage at node Z  1130  can be substantially VGL. As a result of T 2    1135  being on, voltage noise signals at gate line  1111  in drive region  1101  can be shunted to node Z  1130  via T 2 , and can thus be prevented from travelling to the gate of TFT  1109 . 
     During a display phase of the touch screen, BSYNC  1137  can be low, which can mean that T 2    1135  can be turned off. When T 2    1135  is off, gate line  1111  can couple drive region  1101  and sense region  1103  in the manner described with reference to  FIG. 7 , and touch screen operation can proceed as usual. 
       FIG. 11D  illustrates another example configuration in which a gate line  1111  that connects display pixels  1101   a  and  1103   a  in the drive  1101  and sense regions  1103  can be decoupled during a touch sensing phase of the touch screen according to examples of the disclosure. The configuration of  FIG. 11D  can be substantially that of  FIG. 11A , except that region  1125  can include diodes D 2    1139  and D 3    1141  connected in a diode ring configuration as shown. The diode ring configuration in region  1125  can prevent small variations in voltage (i.e., voltage noise) from being transmitted from gate line  1111  in drive region  1101  to the gate line in sense region  1103 . However, the diode ring configuration in region  1125  can allow for larger variations in voltage to be transmitted through it. 
     For example, during a touch sensing phase of the touch screen, the voltage at gate line  1111  can be VGL and DC, as described above. Voltage noise signals in gate line  1111  in drive region  1101  whose magnitudes are less than the turn on voltage of D 2    1139  can be blocked from travelling to the gate line in sense region  1103 . Similarly, voltage noise signals in gate line  1111  in sense region  1103  whose magnitudes are less than the turn on voltage of D 3    1141  can be blocked from travelling to the gate line in drive region  1101 . 
     However, during a transition from the touch sensing phase to a display phase, the voltage at gate line  1111  in drive region  1101  can change from VGL to VGH. This change in voltage can be larger than the turn on voltage of D 2    1139 . Therefore, the voltage at gate line  1111  in drive region  1101  can be substantially transferred to the gate line in sense region  1103 , and can thus be mirrored at the gate of TFT  1109 . During a transition from the display phase back to the touch sensing phase, the voltage at gate line  1111  in drive region  1101  can change from VGH to VGL. This change in voltage can be larger than the turn on voltage of D 3    1141 . Therefore, the voltage at gate line  1111  in sense region  1103  can be substantially pulled down to VGL via D 3    1141 . 
       FIG. 11E  illustrates another example configuration in which a gate line  1111  that connects display pixels  1101   a  and  1103   a  in the drive  1101  and sense regions  1103  can be decoupled during a touch sensing phase of the touch screen according to examples of the disclosure. The configuration of  FIG. 11E  can be substantially that of  FIG. 11A , except that region  1125  can include switch S 1    1145  and diode D 4    1143  connected as shown. S 1    1145  can be any number of suitable electrical switches, such as a transmission gate. S 1    1145  can be controlled by signal BSYNC such that when BSYNC is low, S 1  can be closed, and when BSYNC is high, S 1  can be open. BSYNC can be a timing signal as described above. 
     During a touch sensing phase, BSYNC can be high, and S 1    1145  can be open. D 4    1143  can act as a sink to maintain the voltage at node Y  1128  at substantially the voltage at node Z  1130 . The voltage at node Z  1130  can be set such that the resulting voltage at node Y  1128  can be sufficient to maintain TFT  1109  in an off state. For example, the voltage at node Z  1130  can be substantially VGL. Further, voltage noise signals that appear at node Y  1128  can be shunted to node Z  1130  via D 4    1143 . 
     During a display phase, BSYNC can be low, and S 1    1145  can be closed. Further, the voltage at gate line  1111  can be VGH. Because S 1    1145  can be closed, the voltage at gate line  1111  in drive region  1101  can be substantially coupled to node Y  1128 . The voltage at node Y  1128  can be higher than the voltage at node Z  1130 , which can result in D 4    1143  being reverse-biased. Therefore, D 4    1143  can act as an open circuit. For example, the voltage at gate line  1111 , and thus the voltage at node Y  1128 , can be VGH, and the voltage at node Z  1130  can be substantially VGL. Accordingly, the voltage at node Y  1128  can be transmitted to the gate of TFT  1109 . 
     The configurations described above aim to decouple the display pixels in drive regions from display pixels in sense regions, whether permanently or during at least a touch sensing phase of the touch screen. In this way, the combination of C ST    719  and C Gate-Pixel    721 , and/or the combination of C ST    720  and C Gate-Pixel    722 , as described with reference to  FIG. 7 , can be at least partially removed from the parasitic coupling pathway between the drive and sense regions during a touch sensing phase of the touch screen. 
     In some examples, C Gate-Pixel    721  and  722  can be the dominant coupling mechanisms between the drive and sense regions of the touch screen. Therefore, it can be desirable to reduce the coupling effects of these capacitances. 
       FIG. 12  illustrates an example configuration in which a diode-connected transistor  1208  can be inserted between a gate line  1211  and a gate terminal of a pixel TFT  1207  of a display pixel  1201   a . The configuration of display pixel  1201   a  can be substantially that of display pixel  701   a  in  FIG. 7 , except that diode-connected TFT  1208  can be inserted between gate line  1211  and the gate terminal of TFT  1207 , as shown. TFT  1208  can be “diode-connected” because the gate terminal of the TFT can be connected to the drain terminal of the TFT. Although not shown in  FIG. 12 , the display pixel in sense region  1203  to which display pixel  1201   a  can be connected can have a similar configuration as display pixel  1201   a . Indeed, all display pixels in the touch screen can have a diode-connected TFT inserted between their respective gate lines and the gate terminals of their respective pixel TFTs. Because TFT  1208  can be diode-connected, it can always substantially transfer the voltage at its drain terminal to its source terminal. Therefore, diode-connected TFT  1208  can behave substantially transparently during the DC voltage operation of the touch screen. 
     However, diode-connected TFT  1208  can substantially alter the total capacitance seen between pixel electrode  1215  and gate line  1211  (C Gate-Pixel    721  in  FIG. 7 ). In particular, capacitance C gd    1221  can exist between pixel electrode  1215  and node X  1228 . As described above, C gd    1221  can include the gate-to-drain capacitance of TFT  1207 . Capacitance C gs    1222  can exist between node X  1228  and gate line  1211 . C gs    1222  can include the gate-to-source capacitance of TFT  1208 . In some examples, TFT  1208  can have the same or similar characteristics (size, shape, materials, etc.) as TFT  1207 , making C gd    1221  and C gs    1222  substantially equal. The capacitive pathway between pixel electrode  1215  and gate line  1211  can then be a series combination of C gd    1221  and C gs    1222 , which can be approximately one-half of C gd  (or one-half of C gs ) when C gd  and C gs  are substantially equal. 
     As a comparison, in the configuration of  FIG. 7 , the variable portion of C Gate-Pixel    721  can be substantially the gate-to-drain capacitance of TFT  707 . In contrast, in the configuration of  FIG. 12 , the variable portion of the total capacitance between pixel electrode  1215  and gate line  1211  can be substantially one-half of the gate-to-drain capacitance of TFT  1207 . This reduction in the variable capacitance can reduce the effect of the parasitic coupling pathway that may exist between drive region  1201  and sense region  1203  during a touch sensing phase of the touch screen. 
     As mentioned above, a display pixel in the touch screen of the disclosure can include two TFTs connected in series instead of a single TFT. In such examples, severing the coupling pathway between display pixels in the drive and sense regions can be accomplished by decoupling the gate lines of the two TFTs that can exist in every display pixel in the touch screen. 
       FIG. 13A  illustrates an example configuration in which gate lines of two TFTs in a display pixel can be decoupled. The configuration of  FIG. 13A  can be substantially that of  FIG. 7 , except that instead of having a single TFT  1307 , the display pixel in drive region  1301  can have a second TFT  1308  connected in series with TFT  1307 . In some examples, the gate terminals of TFTs  1307  and  1308  can both be connected to gate line  1311 . In the example of  FIG. 13A , however, the gate terminal of TFT  1308 , gate 1    1305 , can be isolated (or “decoupled”) from the gate terminal of TFT  1307 , and thus from gate line  1311 . The discussion above can similarly hold for the display pixel in sense region  1303 . Further, the gate terminal of TFT  1310 , gate 2    1307 , can be different and isolated from gate 1    1305 . 
     During a touch sensing phase, in addition to the operation described with reference to  FIG. 7 , the voltages at gate 1    1305  and gate 2    1307  can be set such that TFTs  1308  and  1310  can be turned off. During a display phase, the voltages at gate 1    1305  and gate 2    1307  can be set such that TFTs  1308  and  1310  can be turned on. In that state, the voltage at gate line  1311  can control the behavior of TFTs  1307  and  1309 , and the display pixels can operate substantially as described with reference to  FIG. 7 . In some examples, the voltages at gate 1    1305  and gate 2    1307  can be the same voltages as those at gate line  1311 ; namely, VGL during the touch sensing phase and VGH during the display phase. 
     By separating the gate lines of TFTs  1307 ,  1308 ,  1309  and  1310 , as shown, the parasitic pathway that can exist between drive region  701  and sense region  703  can be severed. In particular, during a touch sensing phase, most, if not all, of the voltage noise signals generated at common electrode  1317  can couple to pixel electrode  1315 , and then to gate 1    1305  via the gate-to-drain capacitance of TFT  1308 . Because gate 1    1305  can be separate and isolated from gate 2    1307 , no direct pathway can exist between the display pixels in drive region  1301  and sense region  1303  through which the noise can couple. In some examples, gate 1    1305  can be connected to and controlled by a light shield metal, such as ITO, that can exist underneath TFT  1308  in the display pixel material stackup. By using a preexisting light shield metal to control gate 1    1305 , the need for extra routing and traces can be minimized. Similarly, gate 2    1307  can be connected to and controlled by a light shield metal, such as ITO, that can exist underneath TFT  1310 . 
     In some examples, the light shields of display pixels in drive regions can be connected together, and the light shields of display pixels in sense regions can be connected together. That is to say that gate 1    1305  can be connected to other display pixels in drive regions  1301 , and gate 2    1307  can be connected to other display pixels in sense regions  1303 .  FIG. 13B  illustrates an example configuration in which the gate terminals of the second TFTs in display pixels in drive regions can be connected to each other, and the gate terminals of the second TFTs in display pixels in sense regions can be connected to each other. By using such a connection scheme, a direct coupling pathway between display pixels in drive region  1301  and display pixels in sense region  1303  can be avoided. 
     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. 
     Therefore, according to the above, some examples of the disclosure are directed to a touch screen comprising a first drive region, a first sense region, and a first display pixel in the first drive region, the first display pixel configurable to be decoupled from a second display pixel in the first sense region during at least a touch sensing phase of the touch screen, the first and second display pixels being in a row of display pixels. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the touch screen further comprises a first gate line electrically connected to the first display pixel, and a second gate line, different from the first gate line, electrically connected to the second display pixel. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the touch screen further comprises a third display pixel in a second drive region of the touch screen, wherein the first gate line is electrically connected to the third display pixel. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the touch screen further comprises a third display pixel in a second sense region of the touch screen, wherein the second gate line is electrically connected to the third display pixel. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the touch screen further comprises a gate line electrically connected to the first and second display pixels, the gate line including a decoupling portion between the first and second display pixels. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the decoupling portion comprises a capacitor electrically connected to a diode. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the decoupling portion comprises a diode electrically connected to a transistor. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the decoupling portion comprises a transistor controlled by a timing signal, the timing signal controlling a transition between the touch sensing phase and a display phase of the touch screen. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the decoupling portion comprises a first diode and a second diode electrically connected in a ring configuration. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the decoupling portion comprises a switch controlled by a timing signal, the timing signal controlling a transition between the touch sensing phase and a display phase of the touch screen, and a diode electrically connected to the switch. 
     Some examples of the disclosure are directed to a touch screen comprising a display pixel including a first transistor and a second transistor, the second transistor being electrically connected to a gate terminal of the first transistor and being diode-connected, and a gate line electrically connected to the second transistor. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first transistor has a first size, the second transistor has a second size, and the first and second sizes are substantially equal. Additionally or alternatively to one or more of the examples disclosed above, in some examples, a gate-to-drain capacitance of the first transistor is substantially equal to a gate-to-source capacitance of the second transistor. 
     Some examples of the disclosure are directed to a touch screen comprising a first display pixel in a first drive region of the touch screen, the first display pixel including a first transistor and a second transistor, a second display pixel in a first sense region of the touch screen, the second display pixel including a third transistor and a fourth transistor, a first gate line electrically connected the first and third transistors, a second gate line electrically connected to the second transistor, and a third gate line electrically connected to the fourth transistor. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the touch screen further comprises a third display pixel in a second drive region of the touch screen, the third display pixel including a fifth transistor and a sixth transistor, wherein the first gate line is electrically connected to the fifth transistor, and the second gate line is electrically connected to the sixth transistor. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the touch screen further comprises a third display pixel in a second sense region of the touch screen, the third display pixel including a fifth transistor and a sixth transistor, wherein the first gate line is electrically connected to the fifth transistor, and the third gate line is electrically connected to the sixth transistor. 
     Some examples of the disclosure are directed to a method for operating a touch screen, the method comprising providing a first drive region and a first sense region, and decoupling a first display pixel in the first drive region from a second display pixel in the first sense region during at least a touch sensing phase of the touch screen, the first and second display pixels being in a row of display pixels. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the method further comprises electrically connecting a first gate line to the first display pixel and to a third display pixel in a second drive region of the touch screen, and electrically connecting a second gate line, different from the first gate line, to the second display pixel and to a fourth display pixel in a second sense region of the touch screen. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the method further comprises electrically connecting a first gate line to the first and second display pixels, the first gate line including a decoupling portion between the first and second display pixels. 
     Some examples of the disclosure are directed to a method for operating a touch screen, the method comprising providing a display pixel including a first transistor and a second transistor, electrically connecting the second transistor to a gate terminal of the first transistor, the second transistor being diode-connected, and electrically connecting a gate line to the second transistor. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first transistor has a first size, the second transistor has a second size, and the first and second sizes are substantially equal. Additionally or alternatively to one or more of the examples disclosed above, in some examples, a gate-to-drain capacitance of the first transistor is substantially equal to a gate-to-source capacitance of the second transistor. 
     Some examples of the disclosure are directed to a method for operating a touch screen, the method comprising providing a first display pixel in a first drive region of the touch screen, the first display pixel including a first transistor and a second transistor, providing a second display pixel in a first sense region of the touch screen, the second display pixel including a third transistor and a fourth transistor, electrically connecting a first gate line to the first and third transistors, electrically connecting a second gate line to the second transistor, and electrically connecting a third gate line to the fourth transistor. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the method further comprises providing a third display pixel in a second drive region of the touch screen, the third display pixel including a fifth transistor and a sixth transistor, electrically connecting the first gate line to the fifth transistor, and electrically connecting the second gate line to the sixth transistor. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the method further comprises providing a third display pixel in a second sense region of the touch screen, the third display pixel including a fifth transistor and a sixth transistor, electrically connecting the first gate line to the fifth transistor, and electrically connecting the third gate line to the sixth transistor.

Metadata:
Filing Date: 20130531
Publication Date: 20170103
Grant Date: 20170103
Priority Date: 20130531
Inventors: YOUSEFPOR MARDUKE
SYED TAIF AHMED
AL-DAHLE AHMAD
WHITE KEVIN J.
JAMSHIDI-ROUDBARI ABBAS
POON STEPHEN S.
Assignee: APPLE INC
CPC Classifications: [{"code": "G06F3/0412", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/044", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F2203/04107", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/0412", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/0446", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0443", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0443", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F2203/04107", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F2203/04107", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/0412", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/0446", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 51984549