Patent Publication Number: US-8988388-B2

Title: Electronic device and method for scanning a touch panel thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefits of U.S. provisional application Ser. No. 61/535,377, filed on Sep. 16, 2011. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electronic device and a method for scanning a touch panel thereof. More particularly, the present invention relates to charging the touch sensors of the touch panel in the aforementioned scanning. 
     2. Description of the Related Art 
       FIG. 1  is a schematic diagram showing a conventional electronic device  100  including a touch controller  120  and a touch panel  140 , which is a capacitive touch panel. The touch panel  140  includes a set of driving lines (the vertical lines) and a set of sensing lines (the horizontal lines). Each location where a driving line crosses a sensing line is a touch sensor of the touch panel  140 . For example, three touch sensors of the touch panel  140  are marked as  142 ,  144  and  146 , respectively. 
     When a user performs some operations on the touch panel  140 , the touch controller  120  can detect resultant touch events by scanning the touch panel  140 . For scanning of the touch panel  140 , the touch controller  120  sends driving signals to the driving lines of the touch panel  140 . The driving signals charges the touch sensors of the touch panel  140  and the touch sensors generate sensing signals in response. Next, the touch controller  120  receives the sensing signals from the sensing lines of the touch panel  140 . The touch controller  120  analyzes the sensing signals to determine the locations of the touch events. The electronic device  100  may perform predetermined functions according to the touch events. 
     In the scanning of a touch panel, noises often affect the sensing signals and cause erroneous results of the detection of touch events. The noise is always a problem. For example, many electronic devices, such as smart phones and tablet computers, are equipped with touch displays that consist of touch panels and liquid crystal modules (LCMs). An LCM generates a lot of noises when the polarities of its pixels are inverted. 
     Another conventional problem is the different charge times of the touch sensors of a touch panel. The equivalent resistances and equivalent capacitances of the touch sensors of a touch panel are not uniform, which means the charge characteristics of the touch sensors are not uniform, either.  FIG. 2  is a schematic diagram showing the curves  202 ,  204  and  206  of the voltage-time characteristics of the charging of the touch sensors  142 ,  144  and  146  of the conventional touch panel  140 , respectively. As shown in  FIG. 2 , a far-end touch sensor such as the touch sensor  146  charges slower than a near-end touch sensor such as the touch sensor  142  charges because the far-end touch sensor has a larger time constant. Here the time constant of a touch sensor is the product of the equivalent resistance and the equivalent capacitance of the touch sensor. Ideally, in the scanning of the touch panel  140 , all touch sensors are required to charge to the voltage level V R . The near-end touch sensor  142  takes a period T N  to charge to the voltage level V R , while the far-end touch sensor  146  takes a much longer period T F  to charge to the voltage level V R . 
     However, the touch sensors of a conventional touch panel are all charged according to the same charge period, which might cause undercharge or overcharge of the touch sensors. For example, the touch sensors  144  and  146  are undercharged when all the touch sensors are charged according to the charge period T N , while the touch sensors  142  and  144  are overcharged when all the touch sensors are charged according to the charge period T F . 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to an electronic device and a method for scanning a touch panel of the electronic device. The electronic device and the method can solve or alleviate the aforementioned noise problem and charge problem. 
     According to an embodiment of the present invention, an electronic device is provided. The electronic device includes a touch panel and a control circuitry. The touch panel includes a plurality of touch sensors. The control circuitry is coupled to the touch panel. The control circuitry charges each of the touch sensors according to a preset charge period of the touch sensor and detects the maximum difference in charge characteristics of the touch sensors. The control circuitry adjusts the preset charge periods of the touch sensors according to the charge characteristics of the touch sensors and a preset limit of the preset charge periods of the touch sensors when the maximum difference is higher than a preset threshold. 
     According to another embodiment of the present invention, an electronic device is provided. The electronic device includes a display and a control circuitry. The display is integrated with a plurality of touch sensors. The display may be liquid crystal display, OLED (organic light emitting) display, in-cell, on-cell display or transparent OLED display. The control circuitry is coupled to the touch panel. The control circuitry charges each of the touch sensors according to a preset charge period of the touch sensor and detects the maximum difference in charge characteristics of the touch sensors. The control circuitry adjusts the preset charge periods of the touch sensors according to the charge characteristics of the touch sensors and a preset limit of the preset charge periods of the touch sensors when the maximum difference is higher than a preset threshold. 
     According to another embodiment of the present invention, a method for scanning a touch panel of the aforementioned electronic device is provided. The method includes the following steps. Charge each touch sensor of the touch panel according to the preset charge period of each touch sensor. Detect the maximum difference in charge characteristics of the touch sensors of the touch panel. Adjust the preset charge periods of the touch sensors according to the charge characteristics of the touch sensors and a preset limit of the preset charge periods of the touch sensors when the maximum difference is higher than a preset threshold. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a schematic diagram showing a conventional electronic device with a touch panel. 
         FIG. 2  is a schematic diagram showing the charging of the touch sensors of a conventional touch panel. 
         FIG. 3  is a schematic diagram showing an electronic device according to an embodiment of the present invention. 
         FIG. 4  is a flow chart showing a method for charging a touch panel of an electronic device according to an embodiment of the present invention. 
         FIG. 5  is a schematic diagram showing the charging of the touch sensors of a touch panel according to an embodiment of the present invention. 
         FIG. 6  is a schematic diagram showing the preset charge periods of the touch sensors of a touch panel according to an embodiment of the present invention. 
         FIG. 7  is a schematic diagram showing the preset charge delay of a touch sensor of a touch panel according to an embodiment of the present invention. 
         FIG. 8  is a schematic diagram showing the preset charge periods and the preset charge delays of the touch sensors of a touch panel according to an embodiment of the present invention. 
         FIGS. 9-12  are schematic diagrams showing electronic devices according to some embodiments of the present invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to the present embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
       FIG. 3  is a schematic diagram showing an electronic device  300  according to an embodiment of the present invention. The electronic device  300  may be a smart phone, a personal digital assistant, a tablet computer or a notebook computer. The electronic device  300  includes a touch panel  340  and a control circuitry  320  coupled to the touch panel  340 . The touch panel  340  may be a capacitive touch panel that includes a plurality of touch sensors for sensing touch events, such as the touch sensors  342 ,  344  and  346 . The control circuitry  320  may detect touch events by scanning the touch panel  340 . The control circuitry  320  scans the touch panel  340  by sending driving signals to the touch panel  340  to charge the touch sensors and then receiving and analyzing the sensing signals from the touch panel  340 . The electronic device  300  may execute predetermined functions according to the touch events. 
       FIG. 4  is a flow chart showing a method for charging a touch panel of an electronic device according to an embodiment of the present invention. The method may be executed by the control circuitry  320  on the touch panel  340 . The method may also be executed by another similar control circuitry on another similar touch panel. 
     The flow shown in  FIG. 4  is discussed below. In step  410 , charge some or all of the touch sensors of the touch panel. Each touch sensor is charged according to a preset charge period of the touch sensor. Here the preset charge period is the length of time for which a touch sensor is charged. When step  410  is executed for the first time, the preset charge period of each touch sensor is the same default value. When step  410  is executed later, the preset charge period of each touch sensor may be a value which was determined when the method in  FIG. 4  was executed previously and the preset charge periods of the touch sensors may be the same or different. 
     In step  420 , detect charge characteristics of the touch sensors and detect the maximum difference in charge characteristics of the touch sensors. In this embodiment, the charge characteristic of each touch sensor may be the voltage level to which the touch sensor is charged in the preset charge period of the touch sensor. Alternatively, the charge characteristic of each touch sensor may be the time constant of the touch sensor. In step  430 , compare the maximum difference in the charge characteristics of the touch sensors with a preset threshold. 
     When the maximum difference is lower than the preset threshold, the flow proceeds to step  450 . The control circuitry keeps the preset charge periods of the touch sensors unchanged and the control circuitry charge each touch sensor according to the preset charge period of the touch sensor. Since the maximum difference in the charge characteristics of the touch sensors is lower than the preset threshold, the conventional problem of non-uniform charge does not exist in this case. 
     When the maximum difference in the charge characteristics of the touch sensors is higher than or equal to the preset threshold, the flow proceeds to step  440  to adjust the preset charge periods of the touch sensors according to the charge characteristics of the touch sensors and a preset limit T L  of the preset charge periods of the touch sensors. A purpose of the adjustment in step  440  is determining the preset charge period of each touch sensor to unify the voltage level to which each touch sensor is charged in order to avoid the conventional problem of non-uniform charge. Another purpose of the adjustment in step  440  is limiting the lengths of the preset charge periods of the touch sensors in order to avoid the interference of noises. The preset charge periods determined in step  440  may be stored in a table to be used later. Next, in step  450 , the control circuitry charges each touch sensor according to the preset charge period of the touch sensor determined in step  440 . 
     The longer the charge period of a touch sensor, the more noises might appear during the charge period. Therefore, there is a preset limit T L  of the preset charge periods of the touch sensors in this embodiment. The preset charge period of each touch sensor must be shorter than or equal to the preset limit T L . In step  440 , the control circuitry first determines the length of the preset charge period of the slowest touch sensor with the largest time constant among the touch sensors according to the preset limit T L . The control circuitry sets the length of the preset charge period of the slowest touch sensor to be the time the slowest touch sensor takes to be fully charged to the ideal voltage level V I  when the slowest touch sensor can be fully charged to V I  in the preset limit T L . Alternatively, the control circuitry sets the length of the preset charge period of the slowest touch sensor to be the preset limit T L  when the slowest touch sensor cannot be fully charged in the preset limit T L . The ideal voltage level V I  is the voltage level to which each touch sensor should be charged for the scanning of the touch panel. A partially charged touch sensor can still detect touch events as long as the voltage level to which the touch sensor is charged is not too much lower than the ideal voltage level V I . 
     Next, the control circuitry determines the lengths of the preset charge periods of the other touch sensors according to the length of the preset charge period of the slowest touch sensor and the charge characteristics of the other touch sensors. For example, please refer to  FIG. 5 .  FIG. 5  is a schematic diagram showing the charging of three touch sensors of a touch panel according to an embodiment of the present invention. The curves  501 - 503  show the voltage-time characteristics of the charging of the three touch sensors, respectively. The slowest touch sensor with the largest time constant is corresponding to the curve  503 . 
     Assume the slowest touch sensor is charged to the voltage level V L  in its preset charge period determined according to the preset limit T L  in the aforementioned manner V L  may be lower than or equal to the ideal voltage level V I . The control circuitry may set the length of the preset charge period of each of the other touch sensors to be the time the touch sensor takes to be charged to the same voltage level V L . As shown in  FIG. 5 , the slowest touch sensor takes a period of time T S  to charge to the voltage level V L . The other two touch sensors take the periods of time T 1  and T 2  to charge to the voltage level V L , respectively. Therefore, the control circuitry sets the lengths of the preset charge periods of the other two touch sensors to be T 1  and T 2 , respectively. The control circuitry may detect the voltage level V L  by charging the slowest touch sensor or calculate the voltage level V L  according to the charge characteristic of the slowest touch sensor. The control circuitry may detect the lengths of T 1  and T 2  by charging the other two touch sensors or calculate the lengths of T 1  and T 2  according to the voltage level V L  and the charge characteristics of the other two touch sensors. 
       FIG. 6  is a schematic diagram showing the preset charge periods of four touch sensors of a touch panel according to an embodiment of the present invention. In  FIG. 6 , T L  is the preset limit of the preset charge periods of the touch sensors. T P1 , T P2 , T P3  and T P4  are the preset charge periods of the four touch sensors determined by the control circuitry in step  440  in the aforementioned manner, respectively. As shown in  FIG. 6 , the touch sensors begin charging at the same moment and end charging at different moments. The charging of the fastest touch sensor with the smallest time constant ends first. The preset charge periods T P1 , T P2 , T P3  and T P4  of the touch sensors span no longer than the preset limit T L . 
     In some other embodiments of the present invention, the control circuitry may determine not only the preset charge periods of the touch sensors but also the preset charge delays of the touch sensors.  FIG. 7  is a schematic diagram showing the preset charge delay of a touch sensor of a touch panel according to an embodiment of the present invention. T D  is the preset charge delay of the touch sensor. As shown in  FIG. 7 , the touch sensor does not charge until its preset charge delay T D  expires. 
     When the preset charge delays are involved, the method shown in  FIG. 4  needs the following modification. In steps  410  and  450 , the control circuitry charges each of the touch sensors according to the preset charge period and the preset charge delay of the touch sensor. When the maximum difference is lower than the preset threshold in step  430 , the control circuitry keeps the preset charge periods and the preset charge delays of the touch sensors unchanged. When the maximum difference is higher than or equal to the preset threshold in step  430 , the control circuitry adjusts the preset charge periods and the preset charge delays of the touch sensors according to the charge characteristics of the touch sensors and the preset limit T L  in step  440 . 
     For example,  FIG. 8  is a schematic diagram showing the preset charge periods and the preset charge delays of four touch sensors of a touch panel according to an embodiment of the present invention. In  FIG. 8 , T L  is the preset limit of the preset charge periods of the touch sensors. T P1 , T P2 , T P3  and T P4  are the preset charge periods of the four touch sensors determined by the control circuitry in step  440  in the aforementioned manner, respectively. T D1 , T D2  and T D3  are the preset charge delays of three of the four touch sensors determined by the control circuitry in step  440 , respectively. The preset charge delay of the slowest touch sensor with the largest time constant is zero. As shown in  FIG. 8 , the touch sensors begin charging at different moments and end charging at the same moment. The charging of the fastest touch sensor with the smallest time constant begins last. The preset charge periods T P1 , T P2 , T P3  and T P4  of the touch sensors span no longer than the preset limit T L . The example in  FIG. 6  may be considered as a special case of the example in  FIG. 8  in which the preset charge delays are all zero. The control circuitry may arrange the preset charge delays of the touch sensors arbitrarily as long as the preset charge periods of the touch sensors span no longer than the preset limit T L . 
       FIG. 9  is a schematic diagram showing an electronic device  900  according to an embodiment of the present invention. The electronic device  900  includes a touch panel  940  and a control circuitry  920 . The control circuitry  920  includes a touch driver  925 . The touch driver  925  may execute the method for scanning a touch panel discussed above on the touch panel  940 . 
       FIG. 10  is a schematic diagram showing an electronic device  1000  according to another embodiment of the present invention. The electronic device  1000  includes a touch panel  1040 , an display  1060  and a control circuitry  1020 . The touch panel  1040  includes a plurality of touch sensors. The touch panel  1040  is integrated as a part of the display  1060 . For example, the conductive layers of the touch panel  1040  may be fabricated among the layers of the display  1060 . The control circuitry  1020  includes a touch driver  1025  and a display driver  1027 . The display driver  1027  drives the pixels of the display  1060  to display images, such as the graphical user interfaces of the electronic device  1000 . 
     The touch driver  1025  and the display driver  1027  cooperate to execute the method for scanning a touch panel discussed above on the touch panel  1040 . The display driver  1027  executes steps  410  and  450 . The display driver  1027  sends driving signals to the touch panel  1040  to charge the touch sensors and the touch driver  1025  receives the resultant sensing signals from the touch panel  1040 . The touch driver  1025  may decide when to charge the touch sensors and send a control signal to inform the display driver  1027  to begin sending the driving signals to the touch sensors. Alternatively, the display driver  1027  may decide when to charge the touch sensors and send a control signal to inform the touch driver  1025  to receive the sensing signals from the touch sensors. 
     The touch driver  1025  executes step  420 . The touch driver  1025  or the display driver  1027  may execute step  430 . The touch driver  1025  or the display driver  1027  may execute step  440  to determine the preset charge periods (or both the preset charge periods and the preset charge delays) of the touch sensors of the touch panel  1040 . When the preset charge periods (or both the preset charge periods and the preset charge delays) of the touch sensors are determined by the touch driver  1025 , the touch driver  1025  sends a control signal to inform the display driver  1027  of the preset charge periods (or both the preset charge periods and the preset charge delays) of the touch sensors. When the preset charge periods (or both the preset charge periods and the preset charge delays) of the touch sensors are determined by the display driver  1027 , the touch driver  1025  sends a control signal to inform the display driver  1027  of the necessary data, such as the charge characteristics of the touch sensors. 
       FIG. 11  is a schematic diagram showing an electronic device  1100  according to another embodiment of the present invention. The electronic device  1100  includes a touch panel  1140  and a control circuitry  1120 . The control circuitry  1120  includes a process unit  1123  and a touch driver  1125 . The process unit  1123  is the main system of the electronic device  1100 . The process unit  1123  and the touch driver  1125  cooperate to execute the method for scanning a touch panel discussed above on the touch panel  1140 . The process unit  1123  executes predetermined functions of the electronic device  1100  according to the detected touch events. The touch driver  1125  executes steps  410 ,  420  and  450 . The process unit  1123  executes step  440  to determine the preset charge periods (or both the preset charge periods and the preset charge delays) of the touch sensors of the touch panel  1140 . The process unit  1123  or the touch driver  1125  executes step  430 . 
       FIG. 12  is a schematic diagram showing an electronic device  1200  according to another embodiment of the present invention. The electronic device  1200  includes a touch panel  1240 , an display  1260  and a control circuitry  1220 . The touch panel  1240  is integrated as a part of the display  1260 . The control circuitry  1220  includes a system  1223 , a touch driver  1225  and a display driver  1227 . The system  1223  is the main system of the electronic device  1200 . The display driver  1227  drives the pixels of the display  1260  to display images, such as the graphical user interfaces of the electronic device  1200 . 
     The system  1223 , the touch driver  1225  and the display driver  1227  cooperate to execute the method for scanning a touch panel discussed above on the touch panel  1240 . The system  1223  executes predetermined functions of the electronic device  1200  according to the detected touch events. The display driver  1227  executes steps  410  and  450 . The display driver  1227  sends driving signals to the touch panel  1240  to charge the touch sensors and the touch driver  1225  receives the resultant sensing signals from the touch panel  1240 . The touch driver  1225  or the display driver  1227  may decide when to charge the touch sensors. 
     The touch driver  1225  executes step  420 . The system  1223 , the touch driver  1225  or the display driver  1227  may execute step  430 . The system  1223  executes step  440  to determine the preset charge periods (or both the preset charge periods and the preset charge delays) of the touch sensors of the touch panel  1240 . 
     All of the systems, the touch drivers and the display drivers in  FIGS. 9-12  are hardware circuits. 
     In summary, the present invention sets difference charge periods (or different charge periods and different charge delays) for the touch sensors of a touch panel in order to prevent the conventional problem of non-uniform charge of the touch sensors. In addition, the present invention imposes a preset limit on the preset charge periods of the touch sensors in order to avoid or alleviate the interference of noises during the scanning of a touch panel. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.