Abstract:
An IC architecture improving the sensing latency time in Projected Capacitance Touch comprises a sensor, a touch control integrated circuit, a sensing bus, a driving bus, the sensor comprising a plurality of sensing electrodes, and a plurality of driving electrodes. The driving electrodes comprise a selected driving electrode. The sensing electrodes are scanned and the capacitance change in each is recorded while a driving electrode is selected as said selected driving electrode. The touch control integrated circuit comprises a sensing IC, a driving IC, and a micro-programmed control unit (MCU), wherein the sensing IC comprises a module on receiving sensing electrode signal. The module on receiving sensing electrode signal comprises two sets analog latches and two sets analog multiplexers. The two sets analog latches comprising first stage analog latches and second stage analog latches and the two sets analog multiplexers comprising first stage analog multiplexers and second stage analog multiplexers.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a capacitive touch system. More specifically, it is an IC architecture design, which reduces the sensing latency time. 
       BACKGROUND OF THE INVENTION 
       [0002]    The touch screen technology has been widely used recent years in computing devices, such as mobile phones, notebook computers, and variety of portable electronic devices (such as game console, multimedia players, and the like). With this technology used in the user-interface, interaction between user and the computing device become more convenient and efficiency. Instead of using a mouse, keyboard, or any other intermediate devices, users can interact with what is displayed directly. Some touch screen can not only controlled through single or multi-touch gestures but also detect specially coated gloves and stylus. 
         [0003]    Among a variety of different touch screen technologies, capacitive touch panels became more popular after the releases of new portable electronic devices. Unlike the surface capacitive touch panels can only detect single touch, the projected capacitive touch (PCT) panels are capable of implementing multi-finger touch detection. The PCT technology makes multi-gesture control possible like enlarge, narrow, rotate, or drag a pattern on a projected capacitive touch panel simultaneously. 
         [0004]    Projected capacitive touch screens are made up of a matrix of rows and columns of resistive transparent conductive material such as indium tin oxide (ITO) layered on sheet of glass. The two axes of conductive material are driving electrodes and sensing electrodes. Capacitance exists among them. 
         [0005]    As the human body is also an electrical conductor, touching the surface of the display results in a distortion of the screen&#39;s electrostatic field. There is a change in the level of capacitance. The chips measures cross capacitive in the X-axis and Y-axis of a projected capacitive touch screen structure and for every intersection of the drive/sense lines the capacity change is interpreted and converted to XY coordinates that correspond to the actual touch position. 
         [0006]    Projected touch screen panel contains driving electrodes lay on X-axis direction and sensing electrode lay on Y-axis direction. In the common model of the operation, only one of the driving electrodes will connected to a periodic driving signal, the sensing electrodes can sense the capacitance change of the cross capacitive between driving electrodes and sensing electrodes. By scanning every sensing electrode, the capacitance change in each can be recorded. In order to finish a touch panel scanning, the total time of scanning of sensing electrodes is the number of driving electrodes times the number of sensing electrodes. In the implement of receiving sensing signals, one, or a plurality of ICs are needed to receive signals from sensing electrodes simultaneously for the sake of increasing the frame rate per second also called refresh rate. 
         [0007]    The minimum frame rate is 50 frames per second. The higher frame rate the smoother the line drawing. It is easily understood that when drawing a line on screen, the start point is the first frame and the last point is the last frame. Filling more points between the start point and the last point can make the drawing line looking smoother. There is no standard for frame rate per second in specification, but the target frame rate in the current invention is 100 frames per second independent from touch panel size. 
         [0008]    In the prior art, parallel processing is using to manipulate the data from sensing electrodes, which means one or several IC process signals from all sensing electrodes as the same time. Suppose there are M sensing electrodes, in this case, M analog circuit modules will needed to manipulate the data from each sensing electrode so that the demand of frame rate per second can be satisfied. This kind of IC architecture design has bigger die size and higher power consumption. It is not suitable for the large size touch application and driving electrodes with high resistance because of the high power consumption and the explosion of cost in order to satisfy the frame rate per second by adding more IC. 
         [0009]    In the current invention, analog latches and multiplexers are added in the IC. The analog latches can cut the sensing signals received from sensing electrodes into a few pipes and the multiplexers can multi-tasking the sensing signals. The total sensing signal processing time can be shorten significantly. By multi-tasking the sensing signals, some circuits with typical function can be shared during non-critical pipe. The die area and power consumption can be saved in this case. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic illustration of the architecture of projected capacitive touch system. 
           [0011]      FIG. 2  is a schematic illustration of the module on receiving sensing electrode signals. 
           [0012]      FIG. 3  is a schematic illustration of the module on receiving sensing electrode signals added two analog latches. 
           [0013]      FIG. 4  is a schematic illustration of the module on receiving sensing electrode signals added two analog latches and two multiplexers. 
           [0014]      FIG. 5  is a schematic illustration of the timing diagram of some key elements in the module on receiving sensing electrode signals during the first two critical path periods. 
           [0015]      FIG. 6  is a schematic illustration of the operation process of the current module on receiving sensing electrode signals. 
           [0016]      FIG. 7  is a schematic illustration of the detailed operation of multiplexers in the module on receiving sensing electrode signals. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    All illustrations of the drawings and description of embodiments are for the purpose of describing selected versions of the present invention and are not intended to limit the scope of the present invention. 
         [0018]    The present invention comes up with a novel IC algorithm on projected capacitive touch panel. As shown in  FIG. 1 , there are three main sections in projected capacitive touch panel touch control IC  101 ; they are driving, sensing, and MCU. Wherein sensing IC and driving IC are connected to sensor  100  through sensing bus  102  and driving bus  103  respectively. The MCU will execute the firmware program based on touch algorithm to provide driving signal and select driving electrode. The MCU then connect to system through system bus  104  and the touch coordinates will be calculated according to typical algorithm based on the sensing signals scanned from sensing electrodes. In order to achieve the main objective of the present invention, the IC sensing architecture has been improved. 
         [0019]    In the common module on receiving sensing electrode signal of the projected capacitive touch panel operation as shown in  FIG. 2 , module on receiving sensing electrode signals  200  contains several sub-modules with typical functions. While a driving electrode is selected to connect to a periodic driving signal, sensing charge collection circuits  201  will detect and collect charge change from every sensing electrode, which is caused by capacitance change between driving electrodes and this sensing electrode. Charge change is a continuous analog signal that sent from the sensing charge collection circuits  201  to noise filters  202 , which can filter out noise signal. Analog signal processing circuits  203  then make the filtered analog signal subtracted from the untouched signal and get the signal change rate. The analog signal processing circuits  203  can also process signal amplifying. The processed analog signals are then converted into digital signals by the analog to digital converters (ADC)  204 . The digital signals are manipulated by a MCU  206  and touch coordinates are calculated based on typical algorithm. Digital decoders  205  are used to control storing the digital signals into the memory of the MCU  206  set by set and they are connected to the analog to digital converters  204 . Y stands for the minimum decoders&#39; output of total analog to digital converters (ADC) data transfer from the sensing charge collection circuits  201  to MCU memory. Y can calculated by formula Y=(R*M)/B. Wherein R is analog to digital converters (ADC) resolution, normally is 10 bits, 12 bits or 16 bits; B is bus width of the MCU  206 , normally is 8 bits, 16 bits or 32 bits; and M is the number of the analog to digital converters (ADC). In this case, the number of module on receiving sensing electrode signals is the same as the number of sensing electrodes. 
         [0020]    In order to achieve the main objective of the present invention, two key parts of the PCT technology have been improved. One is to add analog latches into the module on receiving sensing electrode signals. By adding a plurality of latches, the module do not need to process sensing data after sampling sensing signals scanning from every driving electrode, which can reduce latency time significantly. Further, the IC architecture can be continuously improved by adding multiplexers after the analog latches. The sensing signals can be processed in multiple task way. According to different time required in every stage of the processing, multi-tasking allows some circuits with typical functions like analog signal processing circuits and analog to digital converters (ADC) being shared during non-critical pipe. The two improvements can significantly saving IC die area and reduce power consumption. 
         [0021]    As illustrated in  FIG. 3 , two analog latches are added in the module on receiving sensing electrode signals. First stage analog latches  301  are added between the noise filters  202  and the analog signal processing circuits  203 . A digital signal is connected with the first stage analog latches  301  as a control signal  302 . This signal controls the sampling and holding status of the first stage analog latches  301 . Similarly, second stage analog latches  303  are added between the analog signal processing circuits  203  and the analog to digital converters  204 . A control signal  304  is connected with the second stage analog latches  303 . The control signal  304  is a digital signal as well and controls the sampling and holding status of the second stage analog latches  303 . The function of sampling and holding of the added two analog latches are controlled by two independent digital signals respectively. The waveform of the control signals are single pulse square wave and the low pulse is holding state the high pulse is sampling state. The high pulse width depends on the response time of the analog latches and the pulse is controlled by the MCU  206 . 
         [0022]    In the module on receiving sensing electrode signals, signals processing on the sensing charge collection circuits  201  and the noise filters  202  require the longest time. Analog signals are continuous signals. In most design, sensing charge and noise filtering circuits are bounded. Analog filters are used for filtering out unwanted frequency noise, (most of the analog filters are low pass filter or band pass filter), and the signals in output node of analog latches is DC voltage. In this case, noise filters will be useless. In the present invention, the process from input of the sensing charge collection circuits  201  to output of the noise filters  202  will be critical path. The latency time during this process can be used to manipulate data in other processes. In order to share some circuits with typical functions during the latency time of critical path, analog multiplexers and digital decoders are added in the module on receiving sensing electrode signals as illustrated in  FIG. 4 . 
         [0023]    Multiplexers are mainly used to increase the amount of data that can be sent over the network within a certain amount of time and bandwidth. Multiplexer requires parallel input and serial output. An electronic multiplexer makes it possible for several signals to share one device or resource, for example using one analog to digital converter or one communication line, instead of having one device per input signal. As shown in  FIG. 4 , input end of first stage analog multiplexers  401  are connected to the output end of the first stage analog latches  301  and output end of the first stage analog multiplexers  401  are connected to the input end of the analog signal processing circuits  203 . Digital decoders  402  are connected to the first stage analog multiplexers  401 . Input end of second stage analog multiplexers  403  are connected to the output end of the second stage analog latches  303  and output end of the second stage analog multiplexers  403  are connected to the input end of the analog to the digital converters  204 . Digital decoders  404  are connected to the second stage analog multiplexers  403 . In the current invention, suppose the number of driving electrodes is N and the number of sensing electrodes is M. In design stage, number of first analog latches data can be operated X is fixed. The first stage analog multiplexers  401  totally need A=M/X times to handle the M lines of first analog latches data. A is the number of output of the digital decoders  402 . A digital decoder of n inputs has 2 n  outputs, so input of the digital decoders  402  is log 2  A. There are X second analog latches  303  needed. Number of the analog to digital converters (ADC)  204  Z that can parallel process second stage latches data is fixed. The second stage analog multiplexers totally need B=X/Z times to handle the X lines of second analog latches data. B is the number of output of the digital decoders  404 . Input of the digital decoders  404  is log 2  C. In this case, only X analog signal processing circuits and Z analog to digital converters are needed instead of M of them. Latches change form set state to hold state after they get M sensing signals from selected driving electrodes. N driving electrodes need N times latches change. By connecting with the digital decoders, all M lines input can be decoded. 
         [0024]      FIG. 5  illustrates timing diagram of some key elements in the module on receiving sensing electrode signals. As an example, only the first two critical path periods are shown in  FIG. 5 . The first two critical path periods are the time T of the first driving electrode being selected and the time T of the second driving electrode being selected. After a low pulse  501  enables the chip, the module begins to work. During the first critical path period, pulse  502  changed into high level, the first driving electrode is selected, and the module on receiving sensing electrode signals  200  corresponding to M sensing electrodes begins to receive sensing signals sensed from the first selected driving electrode. The first stage analog latches are sampling until the control signal  302  sending a low-level pulse that changing it into hold state. Sensing signals sensed from the first selected driving electrode are holding on the first stage analog latches  301  before the control signal  302  change back to high level. During the second critical path period, pulse  503  changed into high level, the second driving electrode is selected, and module on receiving sensing electrode signals corresponding to M sensing electrodes begins to receive sensing signals sensed from the second driving electrode. According to the first stage analog multiplexer&#39;s latency time  504 , the first stage analog multiplexers  401  output X lines of signal to the analog signal processing circuits  203 . Analog signal processing circuits&#39; latency time  505  reflects signal-processing time of the signals output from the first stage analog multiplexers  401 . The second stage analog latches  303  hold the X lines of data after the second critical path period controlled by the control signal  304 . Then the second stage analog multiplexers  403  output Z lines of signal to the analog to the digital converters  204 . The analog to digital converter latency time  506  shows the latency time before signal outputted into the MCU  206 . Keep changing the selected driving electrode until the last one. For each selected driving electrode, repeat the same steps as that in the second critical period. When the last driving electrode is selected, the signals sensed from the second last one are processing in the module on receiving sensing electrode signals  200 . When restart from the first driving electrode, the signals sensed from the last one are processing in the module on receiving sensing electrode signals  200 . 
         [0025]    The operation process is illustrated in  FIG. 6 , wherein consider the structure in  FIG. 4 . When chip enable, a selected driving electrode will driving an AC signal, meanwhile the M modules on receiving sensing electrode signals corresponding to the M sensing electrodes will begin receiving signals. The first and second stage analog latches  301  and  303  are keeping sampling state. The sensing charge collection circuits  201  and the noise filters  202  are bounded in the current invention. Signals send from the sensing charge collection circuits  201  input ends to the noise filters  202  output ends will be critical path and latency time of the first driving electrode selected processes  601  will be T. After the latency time is longer than the latency time T of the critical path, the first stage analog latches  301  changed to holding state. The selected driving electrode switches to next driving electrode. All other elements in module on receiving sensing electrode are enabled. More specifically, the sensing charge collection circuits  201  and the noise filters  202  receive signals from new selected driving electrode. The first stage analog multiplexers  401  and the analog signal processing circuits  203  are enabled. The second stage analog latches  303  changed to holding state. The analog to digital converters (ADC)  204  are enabled and send data into the memory of the MCU  206 . The second stage analog latches  303  changed to sampling state. 
         [0026]    During second period T, the first stage analog multiplexers  401  output X lines of signals to the analog signal processing circuits  203 . Detail of operation of multiplexers is illustrated in  FIG. 6 . M first stage analog latches are needed to store M sensing electrode voltage in the prior art, by using analog multiplexers, only X analog signal processing circuits  203  need to be built, and after A=M/X times operation, all M lines of signals from the first analog latches  301  can be executed by the analog signal processing circuits  203 . After the second period T, the second stage analog latches  303  control signal will hold X lines of data. The analog to digital converters (ADC)  204  will convert the analog signals output of the second stage analog latches  303  to digital signals. After the second stage multiplexers  403 , only Z analog to digital converters  204  need to be built, and after B=X/Z times operation, all X lines of analog signals from the second stage analog latches  303  can be converted to digital signals by the analog to digital converters (ADC)  204 . 
         [0027]    By adding the two analog latches and the two multiplexers, number of analog signal processing circuits and analog to digital converters (ADC) used in the IC is reduced and as mentioned above, the current invention can achieve a high frame rate per second with fewer die area and power consumption and particularly suitable for the large size touch applications. While using driving electrodes with high resistance, it needs a longer signal transmission time leading to a low frame rate per second. The current invention can also get rid of this problem. Besides, when the M and N tracks increase, the pixel number of a projected capacitance touch panel dramatically increases and thereby the frame rate of the touch panel degrades significantly due to the long time period for scanning the large scale touch panel in a frame. The capacitive touch system can maintain a good frame rate; even the touch panel is a large scale touch panel. 
         [0028]    Although the invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as herein described.