Patent Publication Number: US-2016246411-A1

Title: In-cell touch screen and a concurrent sensing circuit

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. application Ser. No. 14/626,777, filed on Feb. 19, 2015 and entitled TOUCH SENSING DEVICE AND CONCURRENT SENSING CIRCUIT, and claims the benefit of U.S. Provisional Application No. 62/160,884, filed on May 13, 2015, and entitled LOW POWER CONCURRENT SENSING ADAPTABLE TO TOUCH SENSING. The entire contents of both applications are expressly incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to an in-cell touch screen, and more particularly to a concurrent sensing circuit adaptable to an in-cell touch screen. 
     2. Description of Related Art 
     A touch sensing device may, for example, accompany a display to form a touch screen, which combines touch technology and display technology to enable users to directly interact with what is displayed. Capacitive touch sensing is one of a variety of touch sensing technologies with different methods of sensing touch. 
     A capacitive touch sensing device is comprised of a conductor (e.g., indium tin oxide) and an insulator (e.g., glass). When a human body, as an electrical conductor, touches a surface of the capacitive touch sensing device, electrostatic field is distorted and measurable as a change in capacitance, according to which the location of touch may be determined. 
     A mutual-capacitive touch sensing device is one type of capacitive touch sensing device.  FIG. 1A  shows a schematic diagram illustrated of a mutual-capacitance touch sensing device  100 , which may be made up of row electrodes and column electrodes, for example, in 3-by-5 array as exemplified in  FIG. 1A . Driving signals are applied to transmitting ends TX 1 -TX 3 , and sensing signals are collected at receiving ends RX 1 -RX 5 . 
     A self-capacitive touch sensing device is another type of capacitive touch sensing device.  FIG. 1B  shows a schematic diagram illustrated of a self-capacitance touch sensing device  102 , which may be made up of row electrodes and column electrodes, for example, in 3-by-5 array as exemplified in  FIG. 1B . Unlike the mutual-capacitance touch sensing device  100 , the self-capacitance touch sensing device  102  has only receiving ends RX 11 -RX 15  and RX 21 -RX 23 , at which sensing signals are collected. 
     In either the mutual-capacitance touch sensing device  100  or the self-capacitance touch sensing device  102 , each receiving end (RX) is associatively coupled with one receiving circuit (or receiving unit)  11  such as an analog-to-digital converter (ADC). For the architecture shown in  FIG. 1A  or  FIG. 1B , the number of the receiving circuits  11  should be equal to the number of the receiving ends. Therefore, the architecture suffers large circuit area and cost, particularly for a large size touch sensing device. The architecture shown in  FIG. 1A  or  FIG. 1B  may still be at a disadvantage for a small size touch sensing device that has limited space to accommodate the receiving circuits  11  and/or limited power available to the receiving circuits  11 . 
     In order to resolve the problem mentioned above, a modified architecture is proposed as schematically illustrated in  FIGS. 2A and 2B , in which less receiving circuits  11  (than the receiving ends (RX)) are used in a touch sensing device  200 . Specifically, in the first phase as illustrated in  FIG. 2A , sensing signals associated with a portion of the receiving ends (e.g., RX 1 -RX 3 ) are received (and processed) by the receiving circuits  11 . Subsequently, in the second phase as illustrated in  FIG. 2B , sensing signals associated with the other portion of the receiving ends (e.g., RX 4 -RX 6 ) are then received (and processed) by the same receiving circuits  11 . As the receiving circuits  11  in  FIG. 2A  and  FIG. 2B  are used in a time-sharing manner, the architecture shown in  FIG. 2A  and  FIG. 2B  suffers long latency for processing all the sensing signals. This disadvantage becomes severer for an in-cell touch screen that performs display and touch sensing in turn, such that less time is available for touch sensing than a typical touch sensing device (e.g.,  FIG. 1A  or  FIG. 1B ). 
     A need has thus arisen to propose a novel in-cell touch screen to reduce circuit area without incurring long latency. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, it is an object of the embodiment of the present invention to provide a concurrent sensing circuit adaptable to an in-cell touch screen to save circuit area and cost without incurring latency. 
     According to one embodiment, an in-cell touch screen includes a display panel, a plurality of summing circuits and a plurality of receiving circuits. The display panel has a common voltage (VCOM) layer divided into VCOM electrodes that act as sensing points in a touch sensing mode. Each summing circuit has a plurality of input ends for receiving a plurality of sensing signals provided at associated sensing points of the display panel, the input ends of each summing circuit either adding the sensing signals or performing no operation, thereby generating a summing signal at an associated output end of the summing circuit. The receiving circuits are associatively coupled to receive output ends of the summing circuits, respectively. The receiving circuits process summing signals, thereby generating summing values, respectively, according to which a touch position or positions are determined. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  shows a schematic diagram illustrated of a mutual-capacitance touch sensing device; 
         FIG. 1B  shows a schematic diagram illustrated of a self-capacitance touch sensing device; 
         FIG. 2A  and  FIG. 2B  show schematic diagrams illustrated of a time-sharing touch sensing device; 
         FIG. 3  shows a schematic diagram illustrated of a touch sensing device according to one embodiment of the present invention; 
         FIG. 4  shows an exemplary timing sequence of the summing circuits of  FIG. 3 ; 
         FIG. 5  shows a circuit diagram illustrated of the summing circuit of  FIG. 3 ; 
         FIG. 6  shows a timing diagram of the sensing signals according to the operation of  FIG. 4 ; 
         FIG. 7  shows a circuit diagram illustrating equivalent capacitors among the VCOM electrodes, the source lines and the gate lines; 
         FIG. 8  shows an exemplary timing sequence of the summing circuits of  FIG. 3  adaptable to an in-cell touch sensing device according to another embodiment of the present invention; and 
         FIG. 9  shows a timing diagram of the sensing signals according to the operation of  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 3  shows a schematic diagram illustrated of a touch sensing device  300  according to one embodiment of the present invention. The touch sensing device  300  of the embodiment may, but not necessarily, accompany a display to form a touch screen. 
     The touch sensing device  300  of the embodiment includes a touch panel  31  and a concurrent sensing circuit  32  adaptable to the touch panel  31 . The touch panel  31  may, for example, a resistive touch panel, a capacitive touch panel or an optical touch panel. The touch panel  31  may be made up of row electrodes and column electrodes, for example, in 3-by-6 array as exemplified in  FIG. 3 . In the embodiment, receiving ends RX 1 -RX 6  are, for example, associated with column electrodes, and sensing signals may be provided (or generated) at the receiving ends RX 1 -RX 6 . 
     The concurrent sensing circuit  32  of the embodiment includes a plurality of summing circuits  321 . Each summing circuit  321  has a plurality of input ends for receiving a plurality of sensing signals provided at associated receiving ends. For example, the right-hand summing circuit  321  in  FIG. 3  has three input ends for receiving three sensing signals provided at associated receiving ends RX 1 -RX 3 . Similarly, left-hand summing circuit  321  in  FIG. 3  has three input ends for receiving three sensing signals provided at associated receiving ends RX 4 -RX 6 . It is noted that each receiving end is associated with one and only one summing circuit  321 . According to one aspect of the embodiment, the summing circuit  321  is adopted to add or subtract the sensing signals, thereby generating a summing signal at an associated output end. 
     The concurrent sensing circuit  32  of the embodiment further includes a plurality of receiving circuits (or receiving units)  322  such as analog-to-digital converters (ADCs). The receiving circuits  322  are associatively coupled to output ends of the summing circuits  321 , respectively. In the embodiment, the number of the summing circuits  321  is equal to the number of the receiving circuits  322 . The receiving circuit  322  is adopted to process the summing signal, thereby generating a summing value, according to which a touch position or positions may then be determined. 
       FIG. 4  shows an exemplary timing sequence of the summing circuits  321  of  FIG. 3 . Although the timing sequence for time t 0  to t 3  is depicted, it is appreciated that the following timing sequences would repeat the shown timing sequence. In the figure, RX 1 -RX 6  denote associated sensing signals, respectively, “+” denotes that the summing circuit  321  performs addition on the associated sensing signal, and “−” denotes that the summing circuit  321  performs subtraction on the associated sensing signal. It is observed that, in the embodiment, the combinations of addition and subtraction operations associated with the input ends of the summing circuit  321  during three continuous time periods are distinct from each other. For example, the summing circuit  321  has a combination of “+,+,−” operations at time to, has a combination of “+,−,+” operations at time t 1 , and has a combination of “−,+,+” operations at time t 2 . Generally speaking, the combinations of addition and subtraction operations associated with n input ends of a summing circuit  321  during n continuous time periods are distinct from each other, where n is a positive integer larger than two. 
     Assume the right-hand summing circuit  321  has the summing values a, b and c (from the receiving circuit  322 ) in the three time periods shown in  FIG. 4 , the summing values a, b and c may be expressed as follows: 
     
       
         
           
             { 
             
               
                 
                   
                     
                       
                         
                           
                             RX 
                              
                             
                                 
                             
                              
                             1 
                           
                           + 
                           
                             RX 
                              
                             
                                 
                             
                              
                             2 
                           
                           - 
                           
                             RX 
                              
                             
                                 
                             
                              
                             3 
                           
                         
                         = 
                         a 
                       
                     
                   
                   
                     
                       
                         
                           
                             RX 
                              
                             
                                 
                             
                              
                             1 
                           
                           - 
                           
                             RX 
                              
                             
                                 
                             
                              
                             2 
                           
                           + 
                           
                             RX 
                              
                             
                                 
                             
                              
                             3 
                           
                         
                         = 
                         b 
                       
                     
                   
                   
                     
                       
                         
                           
                             
                               - 
                               RX 
                             
                              
                             
                                 
                             
                              
                             1 
                           
                           + 
                           
                             RX 
                              
                             
                                 
                             
                              
                             2 
                           
                           + 
                           
                             RX 
                              
                             
                                 
                             
                              
                             3 
                           
                         
                         = 
                         c 
                       
                     
                   
                 
                  
                 
                   
 
                 
                  
                 
                   
                     or 
                      
                     
                         
                     
                     [ 
                     
                       
                         
                           
                             + 
                             1 
                           
                         
                         
                           
                             + 
                             1 
                           
                         
                         
                           
                             - 
                             1 
                           
                         
                       
                       
                         
                           
                             + 
                             1 
                           
                         
                         
                           
                             - 
                             1 
                           
                         
                         
                           
                             + 
                             1 
                           
                         
                       
                       
                         
                           
                             - 
                             1 
                           
                         
                         
                           
                             + 
                             1 
                           
                         
                         
                           
                             + 
                             1 
                           
                         
                       
                     
                     ] 
                   
                    
                   
                     [ 
                     
                       
                         
                           
                             RX 
                              
                             
                                 
                             
                              
                             1 
                           
                         
                       
                       
                         
                           
                             RX 
                              
                             
                                 
                             
                              
                             2 
                           
                         
                       
                       
                         
                           
                             RX 
                              
                             
                                 
                             
                              
                             3 
                           
                         
                       
                     
                     ] 
                   
                 
               
               = 
               
                 [ 
                 
                   
                     
                       a 
                     
                   
                   
                     
                       b 
                     
                   
                   
                     
                       c 
                     
                   
                 
                 ] 
               
             
           
         
       
     
     After receiving the summing values a, b and c from the receiving circuit  322 , the sensing signals RX 1 -RX 3  may then be obtained accordingly. 
       FIG. 5  shows a circuit diagram illustrated of the summing circuit  321  of  FIG. 3 . In the figure, C RX1 , C RX2  and C RX3  denote equivalent capacitances associated with the receiving ends RX 1 -RX 3  of the touch panel  31 . Regarding the input end associated with the receiving end RX 1 , a (first) switch SW RX1  is closed to receive a predetermined positive voltage (e.g., 3V) when an addition operation is performed, otherwise a (second) switch ˜SW RX1  is closed to receive the ground when a subtraction operation is performed. Similarly, regarding the input end associated with the receiving end RX 2 , a (first) switch SW RX2  is closed to receive a predetermined positive voltage (e.g., 3V) when an addition operation is performed, otherwise a (second) switch ˜SW RX2  is closed to receive the ground when a subtraction operation is performed. Further, regarding the input end associated with the receiving end RX 3 , a (first) switch SW RX3  is closed to receive a predetermined positive voltage (e.g., 3V) when an addition operation is performed, otherwise a (second) switch ˜SW RX3  is closed to receive the ground when a subtraction operation is performed. 
     The equivalent capacitances C RX1 , C RX2  and C RX3  associated with the receiving ends RX 1 -RX 3  of the touch panel  31  are coupled at a point S, followed by an amplifier  51  (e.g., an operational amplifier). A capacitor C is coupled between an output end and an input end of the amplifier  51 . The capacitor C is charged when an addition operation is performed, and is discharged when a subtraction operation is performed. 
     According to the embodiment disclosed above, as less receiving circuits  32  are used than the receiving ends, circuit area and cost may thus be saved, and the embodiment may thus be more adaptable for a large size touch sensing device compared to the architecture of  FIG. 1A  or  FIG. 1B . Moreover, as all the sensing signals are processed by the receiving circuits  32  at the same time or concurrently, in stead of operating in a time-sharing manner as in  FIG. 2A / 2 B, the embodiment therefore does not suffer latency. 
       FIG. 6  shows a timing diagram of the sensing signals RX 1 -RX 6  according to the operation of  FIG. 4 . Specifically, each input end of the summing circuit  321  is associated with either an addition operation or a subtraction operation. Therefore, charging and discharging are performed in all time periods (e.g., t 0  to t 3 ). 
     For a self-capacitance in-cell touch screen (hereinafter touch screen), a common voltage (VCOM) layer of a display panel is divided into VCOM electrodes, which act as sensing points (or receiving (RX) electrodes) in a touch sensing mode, and the VCOM electrodes are connected to common voltage, e.g., a direct-current (DC) voltage, in a display mode. 
     As the VCOM electrodes, the source lines and the gate lines are close to each other for a compact touch screen, parasitic capacitors are possessed by the touch screen.  FIG. 7  shows a circuit diagram illustrating equivalent capacitors among the VCOM electrodes, the source lines and the gate lines. VCOM 1 , VCOM 2  and VCOM 3  represent three adjacent VCOM electrodes. C C1  and C C2  represent equivalent capacitors between the VCOM electrodes. C S1 , C S2  and C S3  represent equivalent capacitors between the VCOM electrodes (i.e., VCOM 1 , VCOM 2  and VCOM 3 ) and underlying source lines, respectively. C G1 , C G2  and C G3  represent equivalent capacitors between the VCOM electrodes (i.e., VCOM 1 , VCOM 2  and VCOM 3 ) and underlying gate lines, respectively. 
     According to the operation depicted in  FIG. 4  and  FIG. 6 , the equivalent capacitors (e.g., C S  and C G ) associated with each VCOM electrode are subjected to charging and discharging in all time periods (e.g., t 0  to t 3 ). 
       FIG. 8  shows an exemplary timing sequence of the summing circuits  321  of  FIG. 3  adaptable to an in-cell touch sensing device according to another embodiment of the present invention. Although the timing sequence for time t 0  to t 3  is depicted, it is appreciated that the following timing sequences would repeat the shown timing sequence. In the figure, RX 1 -RX 6  denote associated sensing signals, respectively, “+” denotes that the summing circuit  321  performs addition on the associated sensing signal, and “0” denotes that the summing circuit  321  performs no operation (i.e., inactive operation) on the associated sensing signal. It is observed that, in the embodiment, the combinations of addition and inactive operations associated with the input ends of the summing circuit  321  during three continuous time periods are distinct from each other. For example, the summing circuit  321  has a combination of “+,+,0” operations at time to, has a combination of “+,0,+” operations at time t 1 , and has a combination of “0,+,+” operations at time t 2 . Generally speaking, the combinations of addition and inactive operations associated with n input ends of a summing circuit  321  during n continuous time periods are distinct from each other, where n is a positive integer larger than two. 
     Assume the right-hand summing circuit  321  has the summing values a, b and c (from the receiving circuit  322 ) in the three time periods shown in  FIG. 8 , the summing values a, b and c may be expressed as follows: 
     
       
         
           
             { 
             
               
                 
                   
                     
                       
                         RX 
                          
                         
                             
                         
                          
                         1 
                       
                     
                     
                       + 
                     
                     
                       
                         RX 
                          
                         
                             
                         
                          
                         2 
                       
                     
                     
                       
                           
                       
                     
                     
                       
                           
                       
                     
                     
                       = 
                     
                     
                       a 
                     
                   
                   
                     
                       
                         RX 
                          
                         
                             
                         
                          
                         1 
                       
                     
                     
                       
                           
                       
                     
                     
                       
                           
                       
                     
                     
                       + 
                     
                     
                       
                         RX 
                          
                         
                             
                         
                          
                         3 
                       
                     
                     
                       = 
                     
                     
                       b 
                     
                   
                   
                     
                       
                           
                       
                     
                     
                       
                           
                       
                     
                     
                       
                         RX 
                          
                         
                             
                         
                          
                         2 
                       
                     
                     
                       + 
                     
                     
                       
                         RX 
                          
                         
                             
                         
                          
                         3 
                       
                     
                     
                       = 
                     
                     
                       c 
                     
                   
                 
                  
                 
                   
 
                 
                  
                 
                   
                     or 
                      
                     
                         
                     
                     [ 
                     
                       
                         
                           
                             + 
                             1 
                           
                         
                         
                           
                             + 
                             1 
                           
                         
                         
                           0 
                         
                       
                       
                         
                           
                             + 
                             1 
                           
                         
                         
                           0 
                         
                         
                           
                             + 
                             1 
                           
                         
                       
                       
                         
                           0 
                         
                         
                           
                             + 
                             1 
                           
                         
                         
                           
                             + 
                             1 
                           
                         
                       
                     
                     ] 
                   
                    
                   
                     [ 
                     
                       
                         
                           
                             RX 
                              
                             
                                 
                             
                              
                             1 
                           
                         
                       
                       
                         
                           
                             RX 
                              
                             
                                 
                             
                              
                             2 
                           
                         
                       
                       
                         
                           
                             RX 
                              
                             
                                 
                             
                              
                             3 
                           
                         
                       
                     
                     ] 
                   
                 
               
               = 
               
                 [ 
                 
                   
                     
                       a 
                     
                   
                   
                     
                       b 
                     
                   
                   
                     
                       c 
                     
                   
                 
                 ] 
               
             
           
         
       
     
     After receiving the summing values a, b and c from the receiving circuit  322 , the sensing signals RX 1 -RX 3  may then be obtained accordingly. 
       FIG. 9  shows a timing diagram of the sensing signals RX 1 -RX 6  according to the operation of  FIG. 8 . Specifically, each input end of the summing circuit  321  is associated with either an addition operation or an inactive operation. It is noted that no charging/discharging is performed when no operation (i.e., inactive operation) is performed on the associated sensing signal. Compared with  FIG. 6 , one third of power consumption may be saved according to  FIG. 9 . 
     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.