PATENT DOCUMENT

Publication Number: US-9582114-B2
Application Number: US-201615040928-A
Country: US
Kind Code: B2

Title: Display to touch crosstalk compensation

Abstract:
A touch sensitive display capable of compensating for crosstalk in the display is disclosed. Crosstalk in display components can be reduced, eliminated, or otherwise compensated for by reducing or eliminating parasitic capacitances that cause the crosstalk. To do so, gate voltages to the display components, such as thin film transistors (TFTs), that introduce the parasitic capacitances can be reduced or otherwise adjusted. In one approach, the gate voltage can be set at multiple different low levels to generate respective sets of touch signals having different amounts of crosstalk. The different crosstalk amounts can then be used to determine and compensate for the crosstalk in the touch signals. In another approach, gate voltage can be modulated between multiple different low levels to push crosstalk out of band with the generated touch signals. The out-of-band crosstalk can then be used to compensate for the crosstalk in the touch signals.

Claims:
What is claimed is: 
     
       1. A method of compensating for crosstalk in a touch sensitive display, the touch sensitive display having display pixels for displaying data and touch components for sensing a touch or hover event, the method comprising:
 during a touch sensing mode of operation, driving the touch components with a stimulation voltage, the touch components generating an output within a frequency band, the output indicative of the touch or hover event; 
 during the touch sensing mode of operation, driving the display pixels with the varying voltage at a modulation frequency, the display pixels causing the crosstalk; 
 wherein the modulation frequency is such as to push at least a portion of the crosstalk out of the frequency band of the output; 
 demodulating the output to isolate the crosstalk therefrom; 
 determining a crosstalk compensation factor based on the isolated crosstalk; and 
 applying the determined crosstalk compensation factor to the output to provide a crosstalk compensated output. 
 
     
     
       2. The method of  claim 1 , wherein demodulating the output comprises:
 demodulating the output at a first demodulation frequency to isolate touch components indicative of a touching or hovering object at the display; and 
 demodulating the output at a second demodulation frequency to isolate crosstalk components indicative of the crosstalk. 
 
     
     
       3. The method of  claim 1 , wherein determining the crosstalk compensation factor comprises:
 retrieving from a lookup table the crosstalk compensation factor corresponding to the isolated crosstalk, the lookup table including correlations between crosstalk amounts and crosstalk compensation factors. 
 
     
     
       4. The method of  claim 1 , wherein applying the crosstalk compensation factor comprises:
 subtracting the compensation factor from the output to provide the crosstalk compensated output. 
 
     
     
       5. The method of  claim 1 , comprising generating a crosstalk lookup table including:
 setting at least one display component of the display pixel to display a predetermined value, the display component causing the crosstalk; 
 setting an input of the display component to a predetermined level; 
 driving the display pixel at the modulation frequency to generate a display output signal; 
 demodulating the display output signal at a first demodulation frequency to isolate signals indicative of a touch or hover at the display; 
 demodulating the display output signal at a second demodulation frequency to isolate the crosstalk; 
 repeating setting the display component, setting the input, driving, demodulating at the first demodulation frequency, and demodulating at the second demodulation frequency at multiple displayed predetermined values to acquire multiple isolated signals and isolated crosstalks; 
 for each displayed predetermined value, calculating a crosstalk compensation factor based on the corresponding isolated signals and isolated crosstalk; and 
 providing in the lookup table correlations between the isolated crosstalks and the calculated crosstalk compensation factors. 
 
     
     
       6. A touch sensitive display having a display mode of operation and a touch sensing mode of operation comprising:
 a stimulation voltage source configured to drive touch components with a stimulation voltage to generate a sensed signal output within a frequency band, the sensed signal output indicative of a touch or hover event; and 
 a voltage source configured to drive display components during the touch sensing mode of operation with a voltage at a modulation frequency, the display components introducing crosstalk into the sensed signal output; 
 the modulation frequency such as to push at least a portion of the crosstalk out of band with respect to the frequency band of the sensed signal output; and 
 a demodulator configured to reject the crosstalk within the sensed signal output and provide a crosstalk a compensated output. 
 
     
     
       7. The display of  claim 6 , wherein the voltage is amplitude modulated. 
     
     
       8. An apparatus for compensating for crosstalk in a touch sensitive display comprising:
 a plurality of display pixels; 
 a plurality of touch components; 
 a modulator providing a modulating voltage; 
 a demodulator; 
 a control circuitry configured for: 
 during a touch sensing mode of operation, driving the touch components with a stimulation voltage, the touch components generating an output within a frequency band, the output indicative of the touch or hover event; 
 during the touch sensing mode of operation, driving the plurality of display pixels with the modulating voltage at a modulation frequency, the display pixels causing the crosstalk; 
 wherein the modulation frequency is such as to push at least a portion of the crosstalk out of the frequency band of the output; 
 demodulating the output using the demodulator to isolate the crosstalk therefrom; 
 determining a crosstalk compensation factor based on the isolated crosstalk; and 
 applying the determined crosstalk compensation factor to the output to provide a crosstalk compensated output. 
 
     
     
       9. The apparatus of  claim 8 , wherein control circuitry is further configured for:
 demodulating the output at a first demodulation frequency to isolate touch components indicative of a touching or hovering object at the display; and 
 demodulating the output at a second demodulation frequency to isolate crosstalk components indicative of the crosstalk. 
 
     
     
       10. The apparatus of  claim 8 , wherein control circuitry is further configured for:
 retrieving from a lookup table the crosstalk compensation factor corresponding to the isolated crosstalk, the lookup table including correlations between crosstalk amounts and crosstalk compensation factors. 
 
     
     
       11. The apparatus of  claim 8 , wherein the control circuitry is further configured for:
 subtracting the compensation factor from the output to provide the crosstalk compensated output. 
 
     
     
       12. The apparatus of  claim 8 , wherein the control circuitry is further configured for generating a crosstalk lookup table by:
 setting at least one display component of the plurality of display pixel to display a predetermined value, the display component causing the crosstalk; 
 setting an input of the display component to a predetermined level; 
 driving the plurality of display pixel at the modulation frequency to generate a display output signal; 
 demodulating the display output signal at a first demodulation frequency to isolate signals indicative of a touch or hover at the display; 
 demodulating the display output signal at a second demodulation frequency to isolate the crosstalk; 
 repeating setting the display component, setting the input, driving, demodulating at the first demodulation frequency, and demodulating at the second demodulation frequency at multiple displayed predetermined values to acquire multiple isolated signals and isolated crosstalks; 
 for each displayed predetermined value, calculating a crosstalk compensation factor based on the corresponding isolated signals and isolated crosstalk; and 
 providing in the lookup table correlations between the isolated crosstalks and the calculated crosstalk compensation factors.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 13/007,459, filed Jan. 14, 2011, and published on Jul. 19, 2012 as U.S. Patent Publication No. 2012-0182251, the contents of which are incorporated by reference herein in their entirety for all purposes. 
    
    
     FIELD 
     This relates generally to touch sensitive devices and more particularly, to compensating for crosstalk between display and touch components in touch sensitive devices. 
     BACKGROUND 
     Many types of input devices are available for performing operations in a computing system, such as buttons or keys, mice, trackballs, touch sensor panels, joysticks, touch pads, touch screens, and the like. Touch sensitive devices, and touch screens, in particular, are becoming increasingly popular because of their ease and versatility of operation as well as their declining price. Touch sensitive devices 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, or integrated with the panel, so that the touch sensitive surface can substantially cover the viewable area of the display device. Touch sensitive devices can generally allow a user to perform various functions by touching or hovering over the touch sensor panel using one or more fingers, a stylus or other object at a location often dictated by a user interface (UI) including virtual buttons, keys, bars, displays, and other elements, being displayed by the display device. In general, touch screens can recognize a touch event and the position of the touch event on the touch sensor panel or a hover event and the position of the hover event on the touch sensor panel, and the computing system can then interpret the touch or hover event in accordance with the display appearing at the time of the event, and thereafter can perform one or more operations based on the event. 
     The ability to recognize and interpret the touch or hover event can be compromised by crosstalk between the display device and the touch sensor panel. However, it can be challenging to substantially reduce or eliminate the crosstalk so that the touch sensitive device can perform touch and hover operations effectively and efficiently. 
     SUMMARY 
     This relates to a touch sensitive display that can compensate for crosstalk between touch and display components. The touch sensitive display can include an active area of pixels having display components for displaying graphics and/or text data during a display mode of the display, and touch components for sensing a touch or hover event during a touch mode of the display. During the touch mode, some display components, such as thin film transistors (TFTs), can introduce crosstalk that can interfere with touch signals. To reduce the crosstalk, gate voltages that drive the TFTs can be reduced or otherwise adjusted so as to reduce parasitic capacitances causing the crosstalk. In one example, during the touch mode, the gate voltage can be at multiple different low levels during different scans of the active area (to sense the touch or hover event), resulting in different crosstalk components for each scan. These different crosstalk components can then be used to determine and compensate for the crosstalk in the display. In another example, during the touch mode, the gate voltage can be modulated during a scan of the active area to push at least a portion of the crosstalk component out-of-band. The out-of-band crosstalk component can then be used to compensate for crosstalk in the display. Crosstalk compensation can advantageously improve touch and hover sensing in the touch sensitive display by providing clearer, more accurate touch and hover events for processing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an exemplary touch sensitive display having crosstalk compensation capabilities according to various embodiments. 
         FIG. 2  illustrates a partial circuit diagram of a touch sensitive display having crosstalk compensation capabilities according to various embodiments. 
         FIG. 3  illustrates a partial circuit diagram of an exemplary pixel in an active area of a touch sensitive display having crosstalk compensation capabilities according to various embodiments. 
         FIG. 4  illustrates exemplary touch circuitry of a touch sensitive display having crosstalk compensation capabilities according to various embodiments. 
         FIG. 5  illustrates an exemplary timing diagram of signals used for crosstalk compensation in a touch sensitive display according to various embodiments. 
         FIG. 6  illustrates an exemplary method for determining crosstalk compensation amounts using gate voltage adjustments in a touch sensitive display according to various embodiments. 
         FIG. 7  illustrates a graph of gate driver voltage versus crosstalk amounts that can be used to compensate for crosstalk in a touch sensitive display according to various embodiments. 
         FIG. 8  illustrates a graph of change in crosstalk amounts per gate voltage from  FIG. 7  that can be used to compensate for crosstalk in a touch sensitive display according to various embodiments. 
         FIG. 9  illustrates an exemplary method using gate voltage adjustment to compensate for crosstalk in a touch sensitive display according to various embodiments. 
         FIG. 10  illustrates another exemplary touch circuitry of a touch sensitive display having crosstalk compensation capabilities according to various embodiments. 
         FIG. 11  illustrates another exemplary timing diagram of signals used for crosstalk compensation in a touch sensitive display according to various embodiments. 
         FIG. 12  illustrates another graph of gate driver voltage versus crosstalk amounts that can be used to compensate for crosstalk in a touch sensitive display according to various embodiments. 
         FIG. 13  illustrates an exemplary method for determining crosstalk compensation amounts using gate voltage modulation in a touch sensitive display according to various embodiments. 
         FIG. 14  illustrates an exemplary method using gate voltage modulation to compensate for crosstalk in a touch sensitive display according to various embodiments. 
         FIG. 15  illustrates an exemplary computing system having crosstalk compensation capabilities according to various embodiments. 
         FIG. 16  illustrates an exemplary mobile telephone having crosstalk compensation capabilities according to various embodiments. 
         FIG. 17  illustrates an exemplary digital media player having crosstalk compensation capabilities according to various embodiments. 
         FIG. 18  illustrates an exemplary personal computer having crosstalk compensation capabilities according to various embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description of example embodiments, reference is made to the accompanying drawings in which it is shown by way of illustration specific embodiments that can be practiced. It is to be understood that other embodiments can be used and structural changes can be made without departing from the scope of the various embodiments. 
     This relates to a touch sensitive display that can compensate for crosstalk between touch and display components. The touch sensitive display can include an active area of pixels having display components for displaying graphics and/or text data during a display mode of the display, and touch components for sensing a touch or hover event during a touch mode of the display. During the touch mode, some display components, such as thin film transistors (TFTs), can introduce crosstalk that can interfere with touch signals, where the amount of crosstalk can be dependent on a displayed image of the graphics and/or text data. To reduce the image dependent crosstalk, gate voltages that drive the TFTs can be reduced or otherwise adjusted so as to reduce parasitic capacitances causing the crosstalk. To so do, in some embodiments, during the touch mode, the gate voltage can be at a low level during a first scan of the active area (to sense the touch or hover event), at a lower level during a second scan, and at different lower levels at subsequent scans, resulting in different crosstalk components for each scan. These different crosstalk components can then be used to determine and compensate for the crosstalk in the display. In other embodiments, during the touch mode, the gate voltage can be modulated during a scan of the active area to push at least a portion of the crosstalk component out-of-band. The out-of-band crosstalk component can then be used to compensate for crosstalk in the display. Crosstalk compensation can advantageously improve touch and hover sensing in the touch sensitive display by providing clearer, more accurate touch and hover events for processing. 
     Although some embodiments are described herein in terms of touch sensitive displays, it should be understood that the various embodiments are not so limited, but can be generally applicable to devices utilizing display capabilities during display mode and touch capabilities during touch mode. It should be further understood that although the touch sensitive displays described herein are integrated, where touch sensors and display components are together in a pixel (“in cell” configuration), other touch sensitive displays can also be used, such as a touch sensitive display in which the touch sensors and the display are separate components (“out cell” configuration) and a touch sensitive display in which the touch sensors forms a layer of the display (“on cell” configuration). 
       FIG. 1  illustrates an exemplary touch sensitive display having crosstalk compensation capabilities according to various embodiments. In the example of  FIG. 1 , touch sensitive display  10  can include display controller  11  to drive displaying, touch controller  12  to drive touch and hover sensing, active area  14  to display data and to sense a touching or hovering object, and gate driver  13  to drive gate lines in the active area with voltages to facilitate the displaying and sensing. Note that although the touch controller  12 , display controller  11 , and gate driver  13  are shown as separate components in  FIG. 1 , in some embodiments one or more of these components can be combined in a single ASIC. The display  10  can operate in two modes—a display mode and a touch mode. The display mode can include displaying image and/or graphics data on circuitry, e.g., pixels, in the active area  14  of the display  10 . The touch mode can include sensing a touch or hover by circuitry, e.g., pixels, in the active area  14  of the display  10 . The pixels will be described in more detail in  FIGS. 2 and 3 . 
     The active area  14  can integrate display and touch capabilities in circuitry, e.g., pixels, which can be used to display images and/or graphics during the display mode of the display and which can be used to sense a touch or hover on the display during the touch mode. The active area  14  can receive image and/or graphics display signals  11   a  from the display controller  11  and gate signals  13   a  from the gate driver  13  for displaying the data on the pixels during the display mode. The active area  14  can receive stimulation signals  12   a  from the touch controller  12  to stimulate the pixels to sense a touch or hover during the touch mode. The active area  14  can receive the gate signals  13   a  from the gate driver  13  to help reduce or eliminate interference, e.g., crosstalk, in the display  10  during the touch mode. How the crosstalk can be reduced, eliminated, or otherwise compensated for will be described herein according to various embodiments. The active area  14  can also transmit sense (or touch) signals  12   b  indicating a touch or hover to the touch controller  12  for processing during the touch mode. 
     The display controller  11  can drive data lines of the active area  14  and can cause the gate driver  13  to drive gate lines of the active area for displaying image and/or graphics data transmitted on the data lines during the display mode. The display controller  11  can transmit the image and/or graphics display signals  11   a  to the active area  24  and can transmit voltage signals  11   b  and control signals  11   c  to the gate driver  13  during the display mode. The display controller  11  can also transmit the voltage signals  11   b  and control signals  11   c  to the gate driver  13  during the touch mode. 
     The touch controller  12  can drive the active area  14  to sense touch or hover on the display  10 . The touch controller  12  can transmit the stimulation signals  12   a  to the active area  14  to stimulate the pixels to sense touch or hover during the touch mode. The touch controller  12  can receive the sense signals  12   b  from the active area  14  during the touch mode. In some embodiments, the touch controller  12  can be based on capacitance. By detecting changes in capacitance at each of the active area pixels and noting the position of the pixels, the touch controller  12  can recognize multiple objects and determine one or more of the location, pressure, direction, speed, and acceleration of the objects as they are moved across the display  10 . By way of example, some embodiments can be based on self capacitance and some embodiments can be based on mutual capacitance. In some embodiments, the display  10  can be multi-touch, single touch, projection scan, full-imaging multi-touch, or any capacitive touch. 
     The gate driver  13  can drive gate lines of the active area  14 . The gate driver  13  can receive the voltage signals  11   b  and the control signals  11   c  from the display controller  11 . During the display mode, the gate driver  13  can transmit the voltage signals  11   b  as the gate signals  13   a  to the gate lines of the active area  14  to activate the pixels to display images and/or graphics on the display  10 . During the touch mode, the gate driver  13  can also transmit the voltage signals  11   b  as the gate signals  13   a  to the gate lines of the active area  14  to help reduce or eliminate crosstalk in the display  10 . In some embodiments, the magnitudes of the voltage signals  11   b  can be different between the display and touch modes. The gate signals will be described in more detail in  FIG. 2 . 
     Each stimulation signal  12   a  can stimulate a corresponding drive line or multiple drive lines. Each gate signal  13   a  can drive a corresponding gate line. Each display signal  11   a  can drive a corresponding data line. Each sense signal  12   b  can transmit information of a sensed touch or hover on a corresponding sense line. 
     Crosstalk can be introduced in a touch sensitive display in a number of ways. One such way can be through undesirable coupling in the active area that can produce image dependent parasitic capacitances to interfere with touch capacitances during the touch mode. Therefore, by reducing the image dependent parasitic capacitances in the active area, crosstalk in the display can be reduced, eliminated, or otherwise compensated for.  FIG. 2  illustrates a partial circuit diagram of a touch sensitive display that can be used to reduce or eliminate crosstalk by reducing parasitic capacitances in the active area of the display. In the example of  FIG. 2 , parasitic capacitances causing crosstalk can result from undesirable capacitive couplings in thin film transistors (TFTs)  24  in the active area pixels of touch sensitive display  20 , where a TFT&#39;s gate line can capacitively couple with its source line to form capacitance Cgs, the gate line with its drain line to form capacitance Cgd, and the source line with the drain line to form capacitance Cds. To reduce the parasitic capacitances and hence the crosstalk, the gate voltage transmitted along gate line  23   a  can be appropriately reduced or otherwise adjusted during the touch mode. 
     In the example of  FIG. 2 , multiple TFTs  24  can drive multiple pixel electrodes  25  to a voltage level provided by source driver  27  along source line  27   a  when the TFTs are enabled via gate drivers  23 . The pixel electrodes  25  can be arranged above a Vcom layer divided into drive segments  22 - 1 , sense segments  22 - 2 , and guard segments  22 - 3 , with transparent insulator  28 - 1  between the electrodes and the segments. During display mode, the drive, sense, and guard segments  22 - 1  through  22 - 3  can be shorted together and driven by a dynamic or static signal dependent on the display controller&#39;s drive scheme. The orientation of liquid crystals in liquid crystal layer  21  can be controlled by the magnitude of an electric fringe field between the Vcom segments  22 - 1  through  22 - 3  and the pixel electrodes  25 . 
     During touch mode, the sense segments  22 - 2  can be connected to charge amplifier  29  of a touch controller, the drive segments  22 - 1  to touch stimulus  26  of the touch controller, and the guard segments  22 - 3  to a bias voltage (e.g. 2.5V). When the display  20  senses a touch or hover event, the electric field in the display can be coupled from the drive segment  22 - 1  to the sense segment  22 - 2  through transparent insulator layers  28 - 1  and  28 - 2 , the pixel electrodes  25 , and the liquid crystal layer  21 . Note that the TFTs  24  can be disabled in touch mode by connecting the TFT gates to gate voltage Vgl from gate lines  23   a , causing the TFT drains and therefore the pixel electrodes  25  to be floating. As a result, the pixel electrodes  25  and thus the TFT drains can be held at a certain image dependent voltage level. The TFTs  24  can have parasitic capacitances that can cause crosstalk in the proximate drive, guard, and sense segments  22 - 1  through  22 - 3 . For example, as illustrated in  FIG. 2 , TFT  24   c  proximate to a drive segment  22 - 1  can have parasitic capacitances Cgs_drv between the TFT gate and source lines, Cdg_drv between the TFT gate and drain lines, and Cds_drv between the TFT drain and source lines, causing crosstalk between the TFT and the drive segment. Similarly, TFT  24   b  proximate to a guard segment  22 - 3  can have parasitic capacitances Cgs_go between the TFT gate and source lines, Cdg_go between the TFT gate and drain lines, and Cds_go between the TFT drain and source lines, causing crosstalk between the TFT and the guard segment. Also similarly, TFT  24   a  and a sense segment  22 - 2  can have parasitic capacitances Cgs_sns between the TFT gate and source lines, Cdg_sns between the TFT gate and drain lines, and Cds_sns between the TFT drain and source lines, causing crosstalk between the TFT and the sense segment. 
     The TFT parasitic capacitances Cdg, Cds and Cgs can be a function of TFT depletion and therefore dependent on the image dependent drain voltage level Vtft_d, which is equivalent to the pixel voltage level at which the associated pixel electrode is held. Similarly, Cdg, Cds and Cgs can also be dependent on the Vgl voltage level applied to the TFT gate during touch mode. 
     In a touch sensitive display, drive segment  22 - 1  can cover multiple pixels and hence multiple TFTs depicted as TFT  24   c . For example, a drive segment can cover an array of 18×64 RGB (red, green, blue) pixels, each pixel having as many as 3 TFTs, one per RGB color. Similarly, guard segment  22 - 3  can cover multiple pixels and hence multiple TFTs depicted as TFT  24   b  and sense segment  22 - 2  can cover multiple pixels and multiple TFTs depicted as TFT  24   a . However, for simplicity, in  FIG. 2 , the drive, guard, and sense segments  22 - 1  through  22 - 3  are depicted as each covering a single pixel and respective TFT  24   c ,  24   b , and  24   a.    
     During touch mode, a capacitance Cdtx can form between the drive and sense segments  22 - 1  and  22 - 2 , where the capacitance Cdtx can represent the image dependent crosstalk between the segments. A portion of the crosstalk Cdtx can be caused by the coupling path (depicted by the broken line (1) in  FIG. 2 ) from the drain of the TFT proximate to the drive segment  22 - 1  to the drain of the TFT proximate to the sense segment  22 - 2 , e.g., from the parasitic capacitance Cdg_drv in the drive segment through the parasitic resistance of the gate line  23   a  to the parasitic capacitance Cdg_sns in the sense segment. Another portion of the crosstalk Cdtx can be caused by the coupling path (depicted by the broken line (2) in  FIG. 2 ) from the drain of the TFT proximate to the drive segment  22 - 1  to the drain of the TFT proximate to the sense segment  22 - 2 , e.g., from the parasitic capacitance Cds_drv in the drive segment through the parasitic resistance of the source line  27   a  to the parasitic capacitance Cds_sns in the sense segment. Since the coupling path has a high-pass response, the crosstalk Cdtx can be frequency dependent and crosstalk compensation can be performed based on the touch stimulus frequency used. 
     As described previously, the display controller can transmit voltage signals, e.g., a negative high voltage signal Vgl and a positive high voltage signal Vgh, and control signals to the gate drivers  23 . The control signals can be used to switch the gate driver  23  between voltage signals Vgl, Vgh according to the display or touch modes. For example, the control signals can activate the gate driver  23  during the display mode to transmit a high voltage signal Vgh to the TFTs  24  for displaying image data. Similarly, the control signals can activate the gate driver  23  during the touch mode to transmit a negative high voltage signal Vgl to the TFTs  24  for reducing crosstalk and for facilitating touch and hover sensing. Accordingly, during touch mode, to reduce crosstalk, the display  20  can reduce or otherwise adjust the negative high voltage signal Vgl to the TFTs  24 , thereby reducing the parasitic capacitances in the TFTs. 
     It is to be understood that a touch sensitive display according to various embodiments is not limited to the components and configurations illustrated in  FIGS. 1 and 2 , but can include additional or other components in the same or different configurations capable of performing touch and hover sensing according to the various embodiments. 
       FIG. 3  illustrates a partial circuit diagram of an exemplary pixel of an active area of a touch sensitive display having crosstalk compensation capabilities according to various embodiments. In the example of  FIG. 3 , active area  30  can include pixels that can be configured for dual-functionality as both display pixels and touch sensor elements. That is, the pixels can include circuit elements, such as capacitive elements, electrodes, etc., that can operate as part of the display circuitry of the pixels and that can also operate as elements of touch and hover sensing circuitry. In this way, active area  30  can operate as a display with integrated touch and hover sensing capability.  FIG. 3  shows details of pixels  37 ,  38 , and  39  of the active area  30 . Note that each of the pixels can represent red (R), green (G) or blue (B), with the combination of all three R, G and B pixels forming a single color pixel. 
     Pixel  38  can include a TFT with gate  38   a , source  38   b , and drain  38   c . As described previously, this TFT can introduce parasitic capacitances into the active area  30  by undesirable capacitive couplings between the gate, source, and drain lines, thereby causing crosstalk. Pixel  38  can also include storage capacitor, Cst  38   h , with upper electrode  38   i  and lower electrode  38   j , liquid crystal capacitor, Clc  38   d , with pixel electrode  38   e  and common electrode  38   f , and color filter voltage source, Vcf  38   g . Pixel  38  can further include a portion of a data line for green (G) color data, Gdata line  33   a , and a portion of gate line  35   a . As described previously, display signals from a display controller (not shown) can be transmitted along the Gdata line  33   a  for displaying data during the display mode and gate signals from a gate driver (not shown) can be transmitted along the gate line  35   a  for helping reduce crosstalk during the touch mode. Gate  38   a  can be connected to gate line portion  35   a , and source  38   c  can be connected to Gdata line portion  33   a . Upper electrode  38   i  of Cst  38   h  can be connected to drain  38   c , and lower electrode  38   j  of Cst  38   h  can be connected to a portion of a common voltage line that runs in the x-direction, xVcom  36   a . Pixel electrode  38   e  of Clc  38   d  can be connected to drain  38   c , and common electrode  38   f  of Clc  38   d  can connected to Vcf  38   g.    
     The circuit diagram of pixel  39  can be identical to that of pixel  38 . However, as shown in  FIG. 3 , color data line  34   a  running through pixel  39  can carry blue (B) color data. 
     Similar to pixels  38  and  39 , pixel  37  can include a TFT with gate  37   a , source  37   b , and drain  37   c , which can introduce parasitic capacitances into the active area  30  thereby causing crosstalk. Pixel  37  can also include storage capacitor, Cst  37   h , with upper electrode  37   i  and lower electrode  37   j , liquid crystal capacitor, Clc  37   d , with pixel electrode  37   e  and common electrode  37   f , and color filter voltage source, Vcf  37   g . Pixel  37  can further include a portion of a data line for red (R) color data, Rdata line  32   a , and a portion of gate line  35   a . As described previously, display signals from a display controller (not shown) can be transmitted along the Rdata line  32   a  for displaying data during the display mode and gate signals from a gate driver (not shown) can be transmitted along the gate line  35   a  for helping reduce crosstalk during the touch mode. Gate  37   a  can be connected to gate line portion  35   a , and source  37   b  can be connected to Rdata line portion  32   a . Upper electrode  37   i  of Cst  37   h  can be connected to drain  37   c , and lower electrode  37   j  of Cst  37   h  can be connected to a portion of xVcom  36   a . Pixel electrode  37   e  of Clc  37   d  can be connected to drain  37   c , and common electrode  37   f  of Clc  37   d  can be connected to Vcf  37   g.    
     Unlike pixels  38  and  39 , pixel  37  can also include a portion of a common voltage line running in the y-direction, yVcom  31   a . In addition, pixel  37  can include a connection  30   a  that connects portion of yVcom  31   a  to portion of xVcom  36   a . Thus, connection  30   a  can connect xVcom  36   a  and yVcom  31   a . As described previously, stimulation signals from a touch controller (not shown) can be transmitted along xVcom  36   a  and sense signals from the active area  30  can be transmitted along yVcom  31   a  to the touch controller during the touch mode to sense a touch or hover at the pixel  37 . 
     A pixel (only partially shown at the right in  FIG. 3 ) can be similar to pixel  37 , except that a portion of yVcom  31   b  can have a break (open)  30   c , and a portion of xVcom  36   a  can have a break  30   d.    
     Multiple pixels can be grouped together to form separate regions in the active area  30 . For example, touch regions in the active area  30  can be formed by groups of pixels (each pixel including a red, green, and blue pixel as in  FIG. 3 ) electrically connected together to form drive regions for driving stimulation signals, sense regions for sensing a touch or hover of an object, such as a finger, on the display, during touch mode, and guard regions between the drive and sense regions for reducing undesirable coupling between the drive and sense regions. The regions can be separated by forming breaks (opens) in the horizontal and/or vertical common lines. For example, yVcom  31   b  of active area  30  can have break  30   c , which can allow pixels above the break to be isolated from pixels below the break. Likewise, xVcom  36   a  can have break  30   d , which can allow pixels to the right of the break to be isolated from pixels to the left of the break. 
     It is to be understood that pixel configurations according to various embodiments are not limited to that illustrated in  FIG. 3 , but can include other configurations capable of crosstalk compensation. 
       FIG. 4  illustrates exemplary touch circuitry of a touch sensitive display having crosstalk compensation capabilities according to various embodiments. In the example of  FIG. 4 , touch components of touch sensitive display  40  can be used to capture multiple touch images at different gate voltages, determine how much to compensate for crosstalk based on the captured images, and output a crosstalk compensated touch image as a result. Touch stimulus of amplitude Vstim and frequency Fstim can drive a touch pixel in active area  44  of a display during the touch mode to form a capacitance Csig indicative of a touch or hover at the pixel. Gate stimulus of amplitude Vgl and frequency Fvgl can drive a TFT in the pixel and can be reduced or otherwise adjusted in a manner, as described below, so as to help reduce, eliminate, or otherwise compensate for the crosstalk. 
     The touch pixel capacitance, including Csig and Cdtx, can be inputted to analog front end  47  to generate a count Nresult representative of the touch pixel capacitance Csig+Cdtx, where Cdtx represents the TFT induced crosstalk capacitance which can be dependent on the gate driver voltage Vgl and the average display pixel voltage Vtp level in a given touch pixel region. The display voltage Vtp can vary due to image modulation at the frame frequency Fframe (e.g., 60 Hz). Nresult can then be digitally demodulated at Fstim in vector demodulation engine  49  and posted to a first touch image memory  41 - 1  during a first scan at a first gate voltage and to a second touch image memory  41 - 2  during a second scan at a second gate voltage. Subtractor  43 - 1  can process the first and second touch images from their respective memories  41 - 1  and  41 - 2  and send an output indicative of the amount of crosstalk in the touch sensitive display to crosstalk compensation lookup table (LUT)  45 . The LUT  45  can lookup the crosstalk compensation value based on the subtractor output and transmit the compensation value to summer  43 - 2 . The summer  43 - 2  can average the first and second touch images from memories  41 - 1  and  42 - 2 , subtract the compensation value and post a crosstalk compensated image to output touch image memory  41 - 3  for further processing. 
     It is to be understood that additional or other touch components to those of  FIG. 4  can be used according to various embodiments. 
       FIG. 5  illustrates an exemplary timing diagram of signals in touch circuitry, as in  FIG. 4 , of a touch sensitive display to compensate for crosstalk according to various embodiments. During the touch mode, the touch sensitive display can perform multiple scans of the active area pixels at different gate voltage levels. As previously described, the gate voltage level can affect the strengths of the parasitic capacitances in the pixel TFTs and hence the crosstalk amounts. Therefore, by performing multiple scans at different gate voltage levels, the resulting sense signals can have different amounts of crosstalk. These different amounts can be used to determine how much to compensate the sense signals so as to reduce or eliminate crosstalk therefrom. The timing diagram in  FIG. 5  illustrates select signal outputs during the display and touch modes of the touch sensitive display to demonstrate this approach. The signals include a Bsync signal indicative of touch mode when high, a stimulation signal Vstim to stimulate a pixel for sensing a touch or hover during the touch mode, and a gate signal to help facilitate reducing or eliminating crosstalk during the touch mode. 
     During the display mode, Bsync can be low indicating display mode, Vstim can be at or around zero because the active area is displaying rather than sensing, and Vgl can be at Vgl_lcm (and/or modulating). Note that, during display mode, Vgl can be any suitable value because it can be ignored until the touch mode, while Vgh can be used to provide the gate signals during the display mode, as described previously. In some embodiments, during the display mode, Vstim=−1 to +1 V, Vgl=−9V, and Vgh=10V. 
     During the touch mode, Bsync can be high indicating touch mode, Vstim can be an AC signal which is modulated relative to positive voltage bias to stimulate the pixels for sensing during the multiple sub-frame scans, e.g., 2 sub-frame scans, and Vgl can have different negative values during the different scans, e.g., a the first negative voltage Vgl_touch 1  during the first sub-frame scan and a lower negative value Vgl_touch 2  during the second sub-frame scan. In this example, Vgl_touch 1  during the first sub-frame scan can result in a first crosstalk amount and Vgl_touch 2  during the second sub-frame scan can result in a second crosstalk amount. In some embodiments, during the touch mode, Vstim can have a DC component of +2.5V and an AC component of 4 Vpp and Vgl_touch 1 =−9 V during the first sub-frame scan and Vgl_touch 2 =−12 V during the second sub-frame scan. Each sub-frame scan can be comprised of multiple touch scan steps, e.g. 16 touch scan steps in some embodiments. 
     Although only two sub-frame scans at two gate voltages are illustrated in  FIG. 5 , it is to be understood that multiple sub-frame scans at multiple gate voltages can be performed during the touch mode, in which a first sub-frame scan can be performed at a first low gate voltage, a second sub-frame scan at a second low gate voltage, a third sub-frame scan at a third low gate voltage, and so on. 
       FIG. 6  illustrates an exemplary method for determining crosstalk compensation amounts using gate voltage adjustments according to various embodiments. This method can be applied to the touch sensitive display of  FIG. 4 , for example. In some embodiments, this method can be applied during factory calibration of the display. In some embodiments, this method can be applied during startup or other operations of the display by a user. In the example of  FIG. 6 , a color code gc can be set to zero, where the color code represents the color of the image outputted by the pixels ( 61 ). An image of uniform color having the red, green and blue pixel components set to the color code gc of zero can be outputted from the display controller ( 62 ). In some instances, a white image can have a color code gc=255 (i.e. RGB(255,255,255)), while a black image can have a color code gc=0 (i.e. RGB(0,0,0)), etc. The display controller can assert a Bsync signal to indicate that the display is transitioning to touch mode ( 63 ). Upon a rising edge of Bsync, data lines connecting to TFT sources in the active area can be set at a fixed voltage level ( 64 ). This can be done to ensure that the source biases of the connected TFTs are constant and independent of the voltage level output prior to entering touch mode. After entering touch mode upon the rising edge of Bsync, a first touch pixel can be captured at a first Vgl voltage level Vgl_touch 1  and recorded as NPIX 1 ( gc ) ( 65 ). After adjusting the Vgl voltage level to Vgl_touch 2 , a second touch pixel can be captured and recorded at NPIX 2 ( gc ) ( 66 ). Note that NPIX can be a count that is representative of touch capacitance Csig and crosstalk capacitance Cdtx. The above actions ( 62 )-( 66 ) can be repeated for one or more color codes gc from 1 to 255 ( 68 ). 
     After the touch pixels have been captured at the desired color code levels ( 67 ), a crosstalk LUT can be derived as follows. The captured touch pixels at the various color codes gc and Vgl voltage levels can be plotted as shown in  FIG. 7 . The slope NPIX_SLOPE(gc) of each graph can be determined by subtracting the touch pixel values NPIX 1  and NPIX 2  at the different Vgl voltage levels and dividing the result by the difference between the voltage levels, where (NPIX 1 −NPIX 2 )/(Vgl_touch 1 −Vgl_touch 2 ) ( 69 ). A crosstalk correlation factor NDTX_CORR(gc) can then be calculated as the average of the touch pixel values NPIX 1  and NPIX 2  at the different Vgl voltage levels minus the touch pixel value at gc=0, where (NPIX 1 +NPIX 2 )/2−NPIX 2 (0) ( 70 ). NPIX_SLOPE can be representative of the average pixel voltage Vtp, and NDTX_CORR can represent the average touch pixel value count between Vgl_touch 1  and Vgl_touch 2  for a given grey level relative to the touch pixel value NPIX 2 (0) associated with the lowest cross-coupling capacitance. The cross-coupling capacitance Cdtx can be the lowest at the highest level of depletion, which is the case for a black uniform image and minimum Vgl voltage level. 
     In  FIG. 7 , the transfer function of crosstalk capacitance Cdtx can be a function of Vgl and the average pixel voltage Vtp across a given touch pixel region. Functions  70  through  73  show the depletion capacitance Cdtx as a function of Vgl for different average pixel voltage levels Vtp(Min) to Vtp(Max). As Vgl increases, the depletion in the TFT decreases and Cdtx increases. Note that because Vgl is negative, an increase of Vgl can result in a decrease of the absolute level of Vgl. For a white image, the average pixel voltage Vtp can be at a minimum, i.e. Cdtx can be highest such that the absolute slope ΔCdtx/ΔVgl=(Cdtx 1 −Cdtx 2 )/(Vgl_touch 1 −Vgl_touch 2 ). Therefore, the slope of the function Cdtx vs. Vgl can be directly mapped to the average pixel voltage of a given touch region. In order to perform crosstalk compensation, the slope of the function Cdtx vs. Vgl can be mapped to a correction factor Cdtx_corr=(Cdtx 1 +Cdtx 2 )/2−Cdtx_min, whereas Cdtx_min can be the minimum allowable crosstalk capacitance in a given application.  FIG. 8  illustrates an exemplary transfer function that relates slope ΔCdtx/ΔVgl to a crosstalk correction factor Cdtx_corr. 
     The crosstalk LUT can be generated for color codes gc=0 to 255, where each color code has a slope value NPIX_SLOPE and a corresponding crosstalk correction factor NDTX_CORR ( 71 ). The LUT can then be used during operation to compensate for crosstalk in a touch sensitive display. 
     It is to be understood that various crosstalk LUTs can be derived to account for crosstalk capacitance Cdtx dependencies for different parameters such as stimulus frequency, temperature, etc. In order to keep the memory requirements to a minimum, the crosstalk LUT transfer function can be represented by an nth order polynomial or a piecewise linear function, which can be sub-interpolated. 
       FIG. 9  illustrates an exemplary method using gate voltage adjustment to compensate for crosstalk in a touch sensitive display according to various embodiments. In the example of  FIG. 9 , a Bsync signal can be asserted to transition from display mode to touch mode in a touch sensitive display ( 91 ). Upon a rising edge of Bsync, data lines connecting to TFT sources in an active area of the display can be set to a fixed voltage level ( 92 ). A first touch image can be acquired at a first Vgl voltage level Vgl_touch 1  ( 93 ). A second touch image can be acquired at a second Vgl voltage level Vgl_touch 2  ( 94 ). A differential touch image can be derived by subtracting the first and second touch images ( 95 ). Subtracting the first and second touch images can remove the touch component but preserve a residual crosstalk component representing ΔCdtx/ΔVgl. For each touch pixel in the differential touch image, a crosstalk correction factor can be found by applying the differential touch pixel to a crosstalk LUT, previously derived as in  FIG. 6 , resulting in a crosstalk compensation image ( 96 ). The first and second touch images can be averaged and the crosstalk compensation image subtracted from the averaged image ( 97 ). The resulting output can be a touch image compensated for crosstalk in the display. 
     In an alternate embodiment, during the touch mode, the touch sensitive display can scan its active area multiple times, rather than just twice, where the first scan can be done with a gate signal at a first voltage Vgl_touch 1 , the second scan at a second voltage Vgl_touch 2 , and so on to the nth scan at an nth voltage Vgl_touchn. Touch images from the multiple scans can be captured, where the touch images indicate different crosstalk amounts at the different gate voltages Vgl_touch 1 , Vgl_touch 2 , . . . Vgl_touchn. A crosstalk compensation image can be determined as described previously based on the captured images, the captured images can then be averaged, the determined crosstalk component can be subtracted from the averaged image, and the crosstalk compensated image can be outputted. 
     In another alternate embodiment, rather than averaging the captured images, a single one of the captured images can be selected and the determined crosstalk compensation image subtracted from that selected image. That selected image can be outputted as the crosstalk compensated image. Alternatively, a subset of the captured images can be selected and averaged, and the determined crosstalk compensation image subtracted from the averaged image of that selected subset. That averaged image can be outputted as the crosstalk compensated image. 
     It is to be understood that methods for crosstalk compensation are not limited to those illustrated in  FIGS. 6 and 9 , but can include additional or other actions for performing crosstalk compensation according to various embodiments. 
       FIG. 10  illustrates another exemplary touch circuitry of a touch sensitive display having crosstalk compensation capabilities according to various embodiments. In the example of  FIG. 10 , touch components of touch sensitive display  100  can be used to capture a touch image at a modulating gate voltage, determine how much to compensate for crosstalk based on the captured image, and output a crosstalk compensated touch image as a result. Touch stimulus of amplitude Vstim and frequency Fstim can drive a touch pixel in active area  104  of the display during the touch mode to form a capacitance Csig indicative of a touch or hover at the pixel. Gate stimulus of amplitude Vgl and frequency Fvgl can drive a TFT in the pixel and can be modulated in a manner, as described below, so as to help reduce, eliminate, or otherwise compensate for the crosstalk. The touch pixel capacitance, including Csig and Cdtx, can be inputted to analog front end  107  to generate a digital sense reading Nresult, which can be inputted to first vector demodulation engine  109 - 1  and second vector demodulation engine  109 - 2 . The first vector demodulation engine  109 - 1  can include mixer  106 - 1  to multiply the sense reading Nresult with a digital demodulation signal of frequency Fstim. The demodulated touch results can be posted to first touch image memory  101 - 1  for subsequent processing. The second vector demodulation engine  109 - 2  can include mixer  106 - 2  to multiply the sense reading Nresult with a digital demodulation signal of frequency Fstim+Fvgl to pass the crosstalk components and reject the touch components. The demodulated touch results can be posted to crosstalk image memory  101 - 3  for subsequent processing. Crosstalk compensation LUT  105  can include crosstalk compensation values based on amounts of crosstalk in images. The appropriate crosstalk compensation values can be retrieved from the LUT  105  based on the crosstalk image from the crosstalk image memory  101 - 3 . The retrieved crosstalk compensation values and the touch image data in the first touch image memory  101 - 1  can be inputted to subtractor  108 , which can then subtract the compensation values from the touch image data and post the resulting crosstalk compensated image to second touch image memory  101 - 2  for further processing. 
       FIG. 11  illustrates an exemplary timing diagram of signals in touch circuitry, as in  FIG. 10 , of a touch sensitive display to compensate for crosstalk according to various embodiments. During the touch mode, the touch sensitive display can perform a scan of the active area pixels with a modulating gate voltage. As previously described, the gate voltage level can affect the strengths of the parasitic capacitances in the pixel TFTs and hence the crosstalk amounts. By modulating the gate voltage at an appropriate frequency and hence the TFTs, at least a portion of the crosstalk introduced by the gate voltage level can be pushed out of band, i.e., isolated and away from the frequency band of the sense signals. In some embodiments, the gate voltage can be modulated coincident with the steps of the scan. Accordingly, when the sense signals are demodulated, the residual crosstalk component can be compensated for based on the out-of-band crosstalk component. The timing diagram in  FIG. 11  illustrates select signal outputs during the display and touch modes of the touch sensitive display to demonstrate this approach. The signals include a Bsync signal to cause transition to the touch mode, a stimulation signal Vstim to stimulate a pixel for sensing a touch or hover during the touch mode, and a gate signal to help facilitate reducing or eliminating crosstalk during the touch mode. 
     During the display mode, Bsync can be low indicating display mode, Vstim can be at or around zero because the active area is displaying rather than sensing, and Vgl can be low (and/or modulating). Note that, during display mode, Vgl can be any suitable value because it can be ignored until the touch mode, while Vgh can be used to provide the gate signals during the display mode, as described previously. 
     During the touch mode, Bsync can be high indicating touch mode, Vstim can have a positive or negative non-zero value to stimulate the pixels for sensing during a scan, and Vgl can modulate between a low value and a lower value during the scan. In some embodiments, during the touch mode, Vstim can have a DC component of 2.5V and an AC component of 4 Vpp and Vgl modulates between −9 V and −12 V at a frequency of 20 kHz, thereby pushing the crosstalk component to ±20 kHz from the sense signals frequency of Fstim. 
     Although only two voltage levels in the modulating gate voltages are illustrated in  FIG. 11 , it is to be understood that multiple voltage levels can be used during the touch mode for the modulating gate voltages. 
       FIG. 12  shows the effects of gate voltage modulation with a dynamic Vgl voltage in a touch sensitive display according to various embodiments. The dynamic Vgl voltage can be defined as follows.
 
 Vgl _mod= Vgl _ ac/ 2*sin(2* pi*Fvgl*t )+ Vgl _ dc,  
 
where Vgl_ac=the dynamic Vgl component (e.g. 3 Vpp), Vgl_dc=the static Vgl component (e.g. −10.5V), and Fvgl=the Vgl modulation frequency. For simplicity, Vgl_mod can be applied to the approximately linear portion of the Cdtx vs. Vgl transfer function between points A and B. The resultant modulated Cdtx_mod can therefore be as follows.
 
 Cdtx _mod( Fvgl )=α VGL   *Vgl _mod=α VGL *( Vgl _ ac/ 2*sin(2* pi*Fvgl*t )+ Vgl _ dc ),
 
where Cdtx_mod=the modulated Cdtx, and α VGL =the image dependent slope of the Cdtx vs. Vgl transfer function between points A and B. Note that Cdtx_mod(Fvgl) can also have non-linear terms, which have been omitted here for simplicity. The slope α VGL  can also be a function of the stimulus amplitude Vstim during touch mode. Note that the drain of the TFT can be modulated with the dynamic stimulus during touch mode and therefore, the slope of the Cdtx vs. Vgl transfer function between points A and B can vary with the stimulus voltage level. Therefore, α VGL  can be defined as follows.
 
α VGL =α VGL   _   AC   *Vstim/ 2*sin(2* pi*Fstim*t )+α VGL   _   DC .
 
where α VGL   _   AC =the touch stimulus dependent slope of the Cdtx vs. Vgl transfer function and α VGL   _   DC =the slope offset of the Cdtx vs. Vgl transfer function. Note that α VGL  can also have non-linear terms, which have been omitted here for simplicity.
 
     By substitution, 
                 Cdtx_mod   ⁢     (   Fvgl   )       =         α     VGL   ⁢   _   ⁢   AC       *     Vstim   /   2     *     Vgl_ac   /   2     *     sin   ⁡     (     2   *   pi   *   Fvgl   *   t     )       *     sin   ⁡     (     2   *   pi   *   Fstim   *   t     )         +       α     VGL   ⁢   _   ⁢   AC       *   Vgl_dc   *     Vstim   /   2     *     sin   ⁡     (     2   *   pi   *   Fstim   *   t     )         +       α     VGL   ⁢   _   ⁢   DC       *     Vgl_ac   /   2     *     sin   ⁡     (     2   *   pi   *   Fvgl   *   t     )         +       α     VGL   ⁢   _   ⁢   DC       *   Vgl_dc         ,         
where the first term in above equation is the relevant dynamic term representative of the crosstalk image component and can be rewritten as follows.
 
 Cdtx _ dyn=α   VGL   _   AC   *Vstim/ 2* Vgl _ ac/ 2*½*(cos(2* pi *( Fstim−Fvgl )* t )−cos(2* pi *( Fstim+Fvgl )* t )).
 
The first cosine term can represent the left sideband and be proportional to the slope α VGL   _   AC . Similarly, the second cosine term can represent the right sideband and be proportional to the slope α VGL   _   AC . In order to recover Cdtx_dyn, vector demodulation can be performed at Fstim−Fvgl or Fstim+Fvgl. The second term in above equation is Cdtx_stat term representative of the uncompensated touch image component
 
 Cdtx _stat=α VGL   _   AC   *Vgl _ dc*Vstim/ 2*sin(2* pi*Fstim*t ).
 
The last two terms of above equation can be rejected during vector demodulation.
 
       FIG. 13  illustrates an exemplary method for determining crosstalk compensation using gate voltage modulation in a touch sensitive display according to various embodiments. This method can be applied to the touch sensitive display of  FIG. 10 , for example. In some embodiments, this method can be applied during factory calibration of the display. In some embodiments, this method can be applied during startup or other operations of the display by a user. In the example of  FIG. 13 , a color code gc can be set to zero ( 131 ). A uniform color image having the red, green and blue components set to the color code gc of zero can be outputted from the display controller ( 132 ). In some instances, a white image can have a color code gc=255 (i.e. RGB(255,255,255)), while a black image can have a color code gc=0 (i.e. RGB(0,0,0)), etc. The display controller can assert a Bsync signal ( 133 ). Upon a rising edge of Bsync, data lines connecting to the TFT sources in the display active area can be set at a fixed voltage level ( 134 ). This can ensure that the source biases of the connected TFTs are constant and independent of the voltage level output prior to entering touch mode. While modulating the gate driver line with a dynamic Vgl stimulus of Vgl_ac (e.g. 3 Vpp) relative to a DC voltage level Vgl_dc (e.g. −10.5V) at a frequency Fvgl (e.g. 20 KHz), a touch scan can be performed and touch image data captured ( 135 ). The captured touch image data can be vector demodulated at Fstim to isolate touch and residual crosstalk components in the data and recorded as NPIX(gc) ( 136 ) and also vector demodulated at Fstim+Fvgl to isolate crosstalk components needed to compensate for residual crosstalk components in the touch image data and recorded as NDTX(gc) ( 137 ). The above actions ( 132 )-( 137 ) can be repeated for one or more color codes gc from 1 to 255 ( 139 ). 
     After the touch image data has been captured at the desired color code levels ( 138 ), a crosstalk LUT can be derived as follows. The captured touch pixels at the various color codes gc and modulating voltage Vgl can be plotted as shown in  FIG. 12 . A crosstalk correction factor NDTX_CORR(gc) can be calculated as NPIX(255)−NPIX(0) at each color code gc, where NPIX(255) is proportional to Cdtx_stat for Vtp(Min) and NPIX(0) is proportional to Cdtx_stat at Vtp(Max) ( 140 ). The crosstalk LUT can be generated for color codes gc=0 to 255, where each color code has a slope value NDTX representative of Cdtx_dyn and a corresponding crosstalk correction factor NDTX_CORR ( 141 ). 
     It is to be understood that multiple crosstalk LUTs can be derived to account for crosstalk capacitance Cdtx dependencies for different parameters such as stimulus frequency, temperature, etc. In order to keep the memory requirements to a minimum, the crosstalk LUT transfer function can be represented by an nth order polynomial or a piecewise linear function, which can be sub-interpolated. 
       FIG. 14  illustrates an exemplary method using gate voltage modulation to compensate for crosstalk in a touch sensitive display according to various embodiments. In the example of  FIG. 14 , a Bsync signal can be asserted to transition into touch mode of a display ( 151 ). After a rising edge on Bsync, data lines connecting to TFT sources can be set at a fixed voltage level ( 152 ). While modulating a gate driver line with a dynamic Vgl stimulus of Vgl_ac (e.g. 3 Vpp) relative to a DC voltage level Vgl_dc (e.g. −10.5V) at a frequency Fvgl (e.g. 20 KHz), a touch scan can be performed and touch image data captured ( 153 ). While performing the touch scan, the touch image data can be vector demodulated at Fstim to derive touch and residual crosstalk components and posted to a first touch image memory ( 154 ). While performing the touch scan, the touch image data can also be vector demodulated at Fstim+Fvgl to isolate crosstalk components needed to compensate for residual touch components and posted to a second touch image memory ( 155 ). The isolated crosstalk components from the second touch image memory can be applied to a crosstalk compensation LUT to derive a crosstalk compensation image ( 156 ). The crosstalk compensation LUT can be previously derived as described in  FIG. 13 , for example. The crosstalk compensation image can be subtracted from the touch image posted to the first touch image memory to obtain a crosstalk compensated image ( 157 ). 
     It is to be understood that methods for crosstalk compensation are not limited to those illustrated in  FIGS. 13 and 14 , but can include additional or other actions for performing crosstalk compensation according to various embodiments. 
       FIG. 15  illustrates an exemplary computing system that can have crosstalk compensation capabilities according to various embodiments. In the example of  FIG. 15 , computing system  1500  can include touch controller  1506 . The touch controller  1506  can be a single application specific integrated circuit (ASIC) that can include one or more processor subsystems  1502 , which can include one or more main processors, such as ARM968 processors or other processors with similar functionality and capabilities. However, in other embodiments, the processor functionality can be implemented instead by dedicated logic, such as a state machine. The processor subsystems  1502  can also include peripherals (not shown) such as random access memory (RAM) or other types of memory or storage, watchdog timers and the like. The touch controller  1506  can also include receive section  1507  for receiving signals, such as touch (or sense) signals  1503  of one or more sense channels (not shown), other signals from other sensors such as sensor  1511 , etc. The touch controller  1506  can also include demodulation section  1509  such as a multistage vector demodulation engine, display scan logic  1510 , and transmit section  1514  for transmitting stimulation signals  1516  to touch display  1524  to drive the display. The scan logic  1510  can access RAM  1512 , autonomously read data from the sense channels, and provide control for the sense channels. In addition, the scan logic  1510  can control the transmit section  1514  to generate the stimulation signals  1516  at various frequencies and phases that can be selectively applied to rows of the touch display  1524 . 
     The touch controller  1506  can also include charge pump  1515 , which can be used to generate the supply voltage for the transmit section  1514 . The stimulation signals  1516  can have amplitudes higher than the maximum voltage by cascading two charge store devices, e.g., capacitors, together to form the charge pump  1515 . Therefore, the stimulus voltage can be higher (e.g., 6V) than the voltage level a single capacitor can handle (e.g., 3.6 V). Although  FIG. 15  shows the charge pump  1515  separate from the transmit section  1514 , the charge pump can be part of the transmit section. 
     Computing system  1500  can include display controller  1542 . The display controller  1542  can be a single application specific integrated circuit (ASIC) that can include one or more processor subsystems (not shown), which can include one or more main processors, such as ARM968 processors or other processors with similar functionality and capabilities. However, in other embodiments, the processor functionality can be implemented instead by dedicated logic, such as a state machine. The processor subsystems can also include peripherals such as random access memory (RAM) or other types of memory or storage, watchdog timers and the like. The display controller  1542  can control the touch display  1524  during the display mode. The display controller  142  can supply voltage signals  1533  and timing signals  1535  to the gate driver  1538  to cause the gate driver to drive the touch display  1524  via the gate signals  1536  during the display mode and the touch mode. The display controller  1542  can also transmit pixel control signals  1541  via source drivers (not shown) to the active area  1534  to facilitate the displaying of data at the touch display  1524 . 
     Computing system  1500  can include host processor  1528  for receiving outputs from the processor subsystems  1502  and performing actions based on the outputs 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 coupled 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. The host processor  1528  can also perform additional functions that may not be related to touch processing. 
     Touch display  1524  can include active area  1534  having touch and hover sensing circuitry that can include a capacitive sensing medium having drive lines and sense lines. It should be noted that the term “lines” can sometimes be used herein to mean simply conductive pathways, as one skilled in the art can readily understand, and is not limited to structures that can be strictly linear, but can include pathways that change direction, and can include pathways of different size, shape, materials, etc. Drive lines can be driven by stimulation signals  1516  and resulting touch signals  1503  generated in sense lines can be transmitted to receive section  1507  in touch controller  1506 . In this way, drive lines and sense lines can be part of the touch and hover 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  1526 . This way of understanding can be particularly useful when touch display  1524  can be viewed as capturing an “image” of touch. In other words, after touch controller  1506  has determined whether a touch or hover has been detected at each touch pixel in the touch display, the pattern of touch pixels in the touch display at which a touch or hover occurred can be thought of as an “image” of touch (e.g. a pattern of fingers touching or hovering over the touch display). 
     The touch display  1524  can also include gate driver  1538 , which can receive the voltage signals  1533  and the timing signals  1535  and generate gate signals  1536  for driving the active area  1534  of the touch display  1524  to display data during the display mode and to help reduce crosstalk and to sense a touch or hover during the touch mode. 
     Note that one or more of the functions described above, can be performed, for example, by firmware stored in memory (e.g., one of the peripherals) and executed by the processor subsystem  1502 , or stored in the program storage  1532  and executed by the host processor  1528 . The firmware can also be stored and/or transported within any computer readable storage medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this document, a “computer readable storage medium” can be any medium that can contain or store the program for use by or in connection with the instruction execution system, apparatus, or device. The computer readable storage medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus or device, a portable computer diskette (magnetic), a random access memory (RAM) (magnetic), a read-only memory (ROM) (magnetic), an erasable programmable read-only memory (EPROM) (magnetic), a portable optical disc such a CD, CD-R, CD-RW, DVD, DVD-R, or DVD-RW, or flash memory such as compact flash cards, secured digital cards, USB memory devices, memory sticks, and the like. 
     The firmware can also be propagated within any transport medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this document, a “transport medium” can be any medium that can communicate, propagate or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The transport readable medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic or infrared wired or wireless propagation medium. 
     It is to be understood that the touch display, as described in  FIG. 15 , can sense touch and hover according to various embodiments. In addition, the touch display described herein can be either single- or multi-touch. 
       FIG. 16  illustrates an exemplary mobile telephone  1640  that can include touch sensitive display  1644  and other computing system blocks for crosstalk compensation according to various embodiments. 
       FIG. 17  illustrates an exemplary digital media player  1750  that can include touch sensitive display  1754  and other computing system blocks for crosstalk compensation according to various embodiments. 
       FIG. 18  illustrates an exemplary personal computer  1860  that can include touch sensitive display  1864  and other computing system blocks for crosstalk compensation according to various embodiments. 
     The mobile telephone, media player, and personal computer of  FIGS. 16 through 18  can have improved touch and hover sensing as a result of compensating for crosstalk in the devices according to various embodiments. 
     Although embodiments 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 the various embodiments as defined by the appended claims.

Metadata:
Filing Date: 20160210
Publication Date: 20170228
Grant Date: 20170228
Priority Date: 20110114
Inventors: KRAH CHRISTOPH H.
Assignee: APPLE INC
CPC Classifications: [{"code": "G06F2203/04101", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/0418", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/0412", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/04182", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0443", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0412", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/04182", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0443", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0412", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F2203/04101", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 45562709