Abstract:
The present invention is directed to a method of driving an in-cell touch screen. In one embodiment, adjacent common voltage (VCOM) electrodes, a source line and/or a gate line is set high-impedance, such that an equivalent capacitor is not possessed by the current VCOM electrode. In another embodiment, a gate line is set high-impedance in the touch sensing mode. A voltage waveform of the current VCOM electrode is applied to adjacent VCOM electrodes abutting the current VCOM electrode and/or to a source line, such that an equivalent capacitor has no effect on the current VCOM electrode.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 62/160,948, filed on May 13, 2015, and U.S. Provisional Application No. 62/189,033, filed on Jul. 6, 2015, the entire contents of which are hereby expressly incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention generally relates to a touch screen, and more particularly to an in-cell touch screen. 
         [0004]    2. Description of Related Art 
         [0005]    A touch screen is an input/output device that combines touch technology and display technology to enable users to directly interact with what is displayed. A capacitor-based touch panel is a commonly used touch panel that utilizes capacitive coupling effect to detect touch position. Specifically, capacitance corresponding to the touch position changes and is thus detected, when a finger touches a surface of the touch panel. 
         [0006]    In order to produce thinner touch screens, in-cell technology has been adopted that eliminates one or more layers by building capacitors inside the display. Conventional in-cell touch screens, however, possesses substantive parasitic capacitors that form a large load, thereby affecting sensitivity of the touch screen. Accordingly, a need has arisen to propose a novel scheme for driving an in-cell touch screen with enhanced touch sensitivity. 
       SUMMARY OF THE INVENTION 
       [0007]    In view of the foregoing, it is an object of the embodiment of the present invention to provide a method of driving an in-cell touch screen in order to reduce capacitance of the parasitic capacitors, or to reduce power consumption. 
         [0008]    According to one embodiment, a touch screen has a common voltage (VCOM) layer divided into VCOM electrodes which act as sensing points in a touch sensing mode. In one embodiment, adjacent VCOM electrodes abutting a current VCOM electrode, a source line underlying the current VCOM electrode, and/or a gate line underlying the current VCOM electrode is set high-impedance in the touch sensing mode, such that an equivalent capacitor is not possessed by the current VCOM electrode, thereby substantially reducing a load at the sensing point. In another embodiment, a gate line underlying a current VCOM electrode is set high-impedance in the touch sensing mode. A voltage waveform of the current VCOM electrode is applied to adjacent VCOM electrodes abutting the current VCOM electrode and/or to a source line underlying the current VCOM electrode, such that an equivalent capacitor has no effect on the current VCOM electrode, thereby substantially reducing a load at the sensing point. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  schematically shows a perspective view of a capacitive in-cell touch screen according to an embodiment of the present invention; 
           [0010]      FIG. 2  shows the VCOM layer of  FIG. 1 ; 
           [0011]      FIG. 3  shows a circuit diagram illustrating equivalent capacitors among the VCOM electrodes, the source lines and the gate lines of  FIG. 1 ; 
           [0012]      FIG. 4  shows a circuit diagram illustrating equivalent capacitors among the VCOM electrodes, the source lines and the gate lines according to a first embodiment of the present invention; 
           [0013]      FIG. 5  shows a circuit diagram illustrating equivalent capacitors among the VCOM electrodes, the source lines and the gate lines according to a second embodiment of the present invention; 
           [0014]      FIG. 6  shows voltage waveforms of a current VCOM electrode and the underlying source line according to a third embodiment of the present invention; 
           [0015]      FIG. 7  shows voltage waveforms of a current VCOM electrode and the underlying source line according to a fourth embodiment of the present invention; 
           [0016]      FIG. 8  shows voltage waveforms of a current VCOM electrode and the underlying source line according to a fifth embodiment of the present invention; 
           [0017]      FIG. 9  shows voltage waveforms of a current VCOM electrode and the underlying source line according to a sixth embodiment of the present invention; 
           [0018]      FIG. 10  shows a circuit diagram illustrating equivalent capacitors among the VCOM electrodes, the source lines and the gate lines of  FIG. 1 ; 
           [0019]      FIG. 11  shows a circuit diagram illustrating equivalent capacitors among the VCOM electrodes, the source lines and the gate lines according to a seventh embodiment of the present invention; and 
           [0020]      FIG. 12A ,  FIG. 12B  and  FIG. 12C  show voltage waveforms of VCOM electrodes, the underlying source line and the underlying gate line. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]      FIG. 1  schematically shows a perspective view of a capacitive in-cell touch screen  100  according to an embodiment of the present invention. The self-capacitance in-cell touch screen (hereinafter touch screen)  100  primarily includes, from bottom up, gate (G) lines  11 , source (S) lines  13  and a common voltage (VCOM) layer  15 , which are isolated from each other. For brevity, some components of the touch screen  100  are not shown. For example, a liquid crystal layer may be disposed above the VCOM layer  15 . 
         [0022]    Specifically, gate lines  11  are disposed latitudinally or in rows, and source lines  13  are disposed longitudinally or in columns. The VCOM layer  15  is divided into VCOM electrodes  151  as exemplified in  FIG. 2 , which act as sensing points (or receiving (RX) electrodes) in a touch sensing mode, and the VCOM electrodes  151  are connected to a common voltage, e.g., a direct-current (DC) voltage, in a display mode. 
         [0023]    As the VCOM electrodes  151 , the source lines  13  and the gate lines  11  are close to each other for a compact touch screen  100 , parasitic capacitors are possessed by the touch screen  100 .  FIG. 3  shows a circuit diagram illustrating equivalent capacitors among the VCOM electrodes  151 , the source lines  13  and the gate lines  11 . VCOM 1 , VCOM 2  and VCOM 3  represent three adjacent VCOM electrodes  151 . C C1  and C C2  represent equivalent capacitors between the VCOM electrodes  151 . C S1 , C S2  and C S3  represent equivalent capacitors between the VCOM electrodes  151  (i.e., VCOM 1 , VCOM 2  and VCOM 3 ) and underlying source lines  13 , respectively. C G1 , C G2  and C G3  represent equivalent capacitors between the VCOM electrodes  151  (i.e., VCOM 1 , VCOM 2  and VCOM 3 ) and underlying gate lines  11 , respectively. Each sensing point (or VCOM electrodes  151 ) possesses a total capacitance of (C CX +C SX +C GX ) (where X is 1, 2, or 3), which results in a load that affects sensitivity of the touch screen  100 . In order to reduce capacitance of the parasitic capacitors, some embodiments are thus proposed. 
         [0024]      FIG. 4  shows a circuit diagram illustrating equivalent capacitors among the VCOM electrodes  151 , the source lines  13  and the gate lines  11  according to a first embodiment of the present invention. In the embodiment, VCOM 1 , VCOM 2  and VCOM 3  are under touch sensing in turn. When a current VCOM electrode  151  (e.g., VCOM 2 ) is currently under touch sensing, adjacent VCOM electrodes  151  (e.g., VCOM 1  and VCOM 3 ) are set high-impedance (Hi-Z) or floating, for example, by a high-impedance unit  21  shown in  FIG. 2 . Further, the source line  13  (e.g., S 2 ) underlying the current VCOM electrode  151  and the gate line  11  (e.g., G 2 ) underlying the current VCOM electrode  151  are set high-impedance (Hi-Z) or floating. Accordingly, the equivalent capacitors C C1 , C C2 , C S2  and C G2  are no longer possessed by the current VCOM electrode  151  (or the sensing point), thereby substantially reducing the load at the sensing point. 
         [0025]      FIG. 5  shows a circuit diagram illustrating equivalent capacitors among the VCOM electrodes  151 , the source lines  13  and the gate lines  11  according to a second embodiment of the present invention. In the embodiment, VCOM 1 , VCOM 2  and VCOM 3  are under touch sensing in turn. When a current VCOM electrode  151  (e.g., VCOM 2 ) is currently under touch sensing, a voltage waveform at the current VCOM electrode  151  is applied to adjacent VCOM electrodes  151  (e.g., VCOM 1  and VCOM 3 ), for example, by a VCOM unit  22  shown in  FIG. 2 . Accordingly, the adjacent VCOM electrodes  151  and the current VCOM electrode  151  operate simultaneously. The voltage waveform at the current VCOM electrode  151  is also applied to the source line  13  (e.g., S 2 ) underlying the current VCOM electrode  151 . Accordingly, the current VCOM electrode  151  and the underlying source line  13  operate simultaneously. As two ends of an equivalent capacitor (e.g., C C1 , C C2  or C S2 ) have the same voltage waveform or operates simultaneously, the equivalent capacitor therefore has no effect on the current VCOM electrode  151  (or the sensing point). Further, the gate line  11  (e.g., G 2 ) underlying the current VCOM electrode  151  is set high-impedance (Hi-Z) or floating. Accordingly, the equivalent capacitor C G2  is no longer possessed by the current VCOM electrode  151  (or the sensing point), thereby substantially reducing the load at the sensing point. 
         [0026]      FIG. 6  shows voltage waveforms of a current VCOM electrode  151  and the underlying source line  13  according to a third embodiment of the present invention. In this embodiment, the voltage waveform of the current VCOM electrode  151  is applied to the underlying source line  13  during a conversion phase and a pre-charge phase, which compose a sensing period. 
         [0027]    In practice, the equivalent capacitor due to the source line  13  has effect on touch sensing result only in the conversion, but has no effect on the touch sensing result in the pre-charge phase. Accordingly, as shown in  FIG. 7 , a fourth embodiment of the present invention, the voltage waveform of the current VCOM electrode  151  is applied to the underlying source line  13  only during a conversion phase. 
         [0028]      FIG. 8  shows voltage waveforms of a current VCOM electrode  151  and the underlying source line  13  according to a fifth embodiment of the present invention. In the embodiment, the voltage waveform of the current VCOM electrode  151  is applied to the underlying source line  13  only when the voltage waveform becomes stable in the conversion phase and the pre-charge phase. During sub-periods when the voltage waveform is not stable or sub-periods of transition (from high level to low level or from low level to high level), the source line  13  (e.g., S 2 ) underlying the current VCOM electrode  151  is set high-impedance (Hi-Z) or floating, thereby reducing power consumption. It is noted that, during the sub-periods of transition, the voltage at the source line  13  may be pulled up or down via the equivalent capacitor (e.g., C S2 ). 
         [0029]    As described above that the equivalent capacitor due to the source line  13  has effect on touch sensing result only in the conversion, the voltage waveform of the current VCOM electrode  151  is applied to the underlying source line  13  only when the voltage waveform becomes stable in the conversion phase, as shown in  FIG. 9 , a sixth embodiment of the present invention. During sub-periods when the voltage waveform is not stable or sub-periods of transition, the source line  13  (e.g., S 2 ) underlying the current VCOM electrode  151  is set high-impedance (Hi-Z) or floating, thereby reducing power consumption. Similar to the fifth embodiment ( FIG. 8 ), during the sub-periods of transition, the voltage at the source line  13  may be pulled up via the equivalent capacitor (e.g., C S2 ). 
         [0030]      FIG. 10  shows a circuit diagram illustrating equivalent capacitors among the VCOM electrodes  151 , the source lines  13  and the gate lines  11 . VCOM 1 , VCOM 2  and VCOM 3  represent three adjacent VCOM electrodes  151 . C C1  and C C2  represent equivalent capacitors between the VCOM electrodes  151 . C S1 , C S2  and C S3  represent equivalent capacitors between the VCOM electrodes  151  (i.e., VCOM 1 , VCOM 2  and VCOM 3 ) and underlying source lines  13 , respectively. C G1 , C G2  and C G3  represent equivalent capacitors between the VCOM electrodes  151  (i.e., VCOM 1 , VCOM 2  and VCOM 3 ) and underlying gate lines  11 , respectively. C P1 , C P2  and C P3  represent equivalent capacitors pertaining to the VCOM electrodes  151  (i.e., VCOM 1 , VCOM 2  and VCOM 3 ) caused by other than the source lines  13  and the gate lines  11 . Each sensing point (or VCOM electrodes  151 ) possesses a total capacitance of (C CX +C SX +C GX +C PX ) (where X is 1, 2, or 3), which results in a load that affects sensitivity of the touch screen  100 . In order to reduce capacitance of the parasitic capacitors, further embodiments are thus proposed. 
         [0031]      FIG. 11  shows a circuit diagram illustrating equivalent capacitors among the VCOM electrodes  151 , the source lines  13  and the gate lines  11  according to a seventh embodiment of the present invention. In the embodiment, VCOM 1 , VCOM 2  and VCOM 3  are under touch sensing in turn. When a current VCOM electrode  151  (e.g., VCOM 2 ) is currently under touch sensing having a voltage waveform with a first amplitude VB, the same voltage waveform with a second amplitude VA is applied to adjacent VCOM electrodes  151  (e.g., VCOM 1  and VCOM 3 ), for example, by a VCOM unit  22  shown in  FIG. 2 . The same voltage waveform with the second amplitude VA is also applied to the source line  13  (e.g., S 2 ) and the gate line  11  (e.g., G 2 ) underlying the current VCOM electrode  151 . 
         [0032]    Let Q C1  represents the charge contributed to the VCOM electrode  151  by the equivalent capacitor C C1 , Q C2  represents the charge contributed to the VCOM electrode  151  by the equivalent capacitor C C2 , Q S2  represents the charge contributed to the VCOM electrode  151  by the equivalent capacitor C S2 , Q G2  represents the charge contributed to the VCOM electrode  151  by the equivalent capacitor C G2 , Q P2  represents the charge contributed to the VCOM electrode  151  by the equivalent capacitor C P2 , and Q total  total represents the charge contributed to the VCOM electrode  151  by the total capacitance (C C1 +C C2 +C S2 +C G2 +C P2 ): 
         [0000]        Q   C1 =( VB−VA )* C   C1    
         [0000]        Q   C2 =( VB−VA )* C   C2    
         [0000]        Q   S2 =( VB−VA )* C   S2    
         [0000]      Q G2 =( VB−VA )* C   G2    
         [0000]      Q P2   =VB*C   P2    
         [0000]    
       
      
       Q 
       total 
       =Q 
       C1 
       +Q 
       C2 
       +Q 
       S2 
       +Q 
       G2 
       +Q 
       P2  
      
     
         [0033]    It is noted that, if the second amplitude VA is greater than the first amplitude VB (i.e., VA&gt;VB), the charges Q C1 , Q C2 , Q S2  and Q G2  are inverse to the charge Q P2 , thereby compensating for the effects caused by Q P2 . 
         [0034]    The present embodiment is more useable when multiple channels are sensed concurrently, in that case the equivalent capacitor C P2  (that is, the equivalent capacitors pertaining to the VCOM electrodes  151  caused other than the source lines  13  and the gate lines  11 ) predominates with greater effects on the touch sensitivity. 
         [0035]      FIG. 12A ,  FIG. 12B  and  FIG. 12C  show voltage waveforms of VCOM electrodes  151 , the underlying source line  13  (e.g., S 2 ) and the underlying gate line  11  (e.g., G 2 ). It is observed in  FIG. 12A  that the voltage waveform applied to the underlying source line  13  (e.g., S 2 ), the underlying gate line  11  (e.g., G 2 ) and the adjacent 
         [0036]    VCOM electrodes  151  (e.g., VCOM 1  and VCOM 3 ) has a fixed amplitude (i.e., the second amplitude VA) during a conversion phase. However, in  FIG. 12B , the applied voltage waveform overdrives before settling on the second amplitude VA in the conversion phase and the pre-charge phase. Alternatively, in FIG. 
         [0037]      12 C, the applied voltage waveform underdrives before settling on the second amplitude VA in the conversion phase and the pre-charge phase. 
         [0038]    Although specific embodiments have been illustrated and described, it will be appreciated by those skilled in the art that various modifications may be made without departing from the scope of the present invention, which is intended to be limited solely by the appended claims.