Abstract:
A capacitive touch system uses at least two integrated circuits to simultaneously scan a touch panel, each of the integrated circuits scanning only a portion of the touch panel. If any one of the integrated circuits has not detected any objects on its scanning zone for a long time, it will enter a suspend mode to lower the scanning frequency thereof for power saving.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is related generally to a capacitive touch system and, more particularly, to power reduction of a capacitive touch system. 
       BACKGROUND OF THE INVENTION 
       [0002]    In conventional applications, all the large scale capacitive touch panels use a surface capacitance sensing technique to scan thereto for determining a touch information, which uses a set of sensing currents, each directed to an endpoint of the large scale touch panel to produce sensed values, and therefore, even multiple fingers simultaneously touch the large scale touch panel, this sensing technique still retrieves only one set of sensed currents in response to this multi-finger touch. For this reason, the surface capacitance sensing technique can identify only one set of absolute coordinates. In a two dimensional matrix for instance, only one set of parameters (X,Y) will be determined, and thereby it can&#39;t implement a multi-finger touch detection. 
         [0003]    An all points addressable (APA) projected capacitance sensing technique is capable of implementing a multi-finger touch detection, but not applicable to large scale touch panels because, to implement this sensing technique, it is necessary to charge and discharge each point sensor on the large scale touch panel. Taking a matrix-type touch panel for example, when the X and Y traces increase, the pixel number of an APA projected capacitance touch panel dramatically increases and thereby significantly degrades the frame rate of the touch panel due to the very long time period for scanning the large scale touch panel in a frame. 
         [0004]    An axis intersect (AI) projected capacitance sensing technique is also capable of implementing a multi-finger touch detection, but not applicable to large scale touch panels, too.  FIG. 1  is a schematic diagram of a conventional AI projected capacitance sensing technique applied to a small scale touch panel  10 , in which an AI projected capacitance touch IC  12  is used to scan the small scale touch panel  10 . Assuming that the AI projected capacitance touch IC  12  can support up to 22 traces, a good frame rate can be attained for a small scale touch panel  10  having ten X traces TRX 1 -TRX 10  and ten Y traces TRY 1 -TRY 10 . However, if a this type touch IC  12  is applied to a large scale touch panel  14  having forty X traces TRX 1 -TRX 40  and forty Y traces TRY 1 -TRY 40 , as shown in  FIG. 2 , the total number of traces that the touch IC  12  needs to scan dramatically increases. Unfortunately, the frame rate of the overall touch panel application is dependent to a very large extent on the time it takes the touch IC  12  to charge and discharge capacitors each time. In other words, the frame rate is determined mainly by the time in a frame that the touch IC  12  charges and discharges the capacitors. Hence, if an AI projected capacitance touch IC capable of scanning a greater number of traces is applied to a large scale touch panel  14 , a major drawback would be a significantly decreased frame rate in the overall application, which leads to compromised performance at the application end. 
       SUMMARY OF THE INVENTION 
       [0005]    An object of the present invention is to provide a power saving capacitive touch system and a power saving method for a capacitive touch system. 
         [0006]    According to the present invention, a capacitive touch system includes at least two first integrated circuits to simultaneously scan a touch panel, each of the first integrated circuits scanning only a portion of the touch panel, and a second integrated circuit to receive sensed data from the first integrated circuits and calculate therewith. If any one of the integrated circuits has not detected any objects on its scanning zone for a long time, it will enter a suspend mode to lower the scanning frequency thereof for power saving. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    These and other objects, features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings, in which: 
           [0008]      FIG. 1  is a schematic diagram of a conventional AI projected capacitance sensing technique applied to a small scale touch panel; 
           [0009]      FIG. 2  is a schematic diagram of a conventional AI projected capacitance sensing technique applied to a large scale touch panel; 
           [0010]      FIG. 3  is a schematic diagram of a capacitive touch system using at least two AI projected capacitance touch ICs to scan a touch panel; 
           [0011]      FIG. 4  is a schematic diagram of an embodiment according to the present invention, which adds a suspend mode into a capacitive touch system to reduce the overall power consumption of the capacitive touch system; and 
           [0012]      FIG. 5  is a timing diagram of the sensed data sent by a slave touch IC to a master touch IC under normal mode. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    According to the present invention, as shown in  FIG. 3 , a capacitive touch system  20  uses four AI projected capacitance touch ICs  24 ,  26 ,  28  and  30  to simultaneously scan a large scale touch panel  22  to increase the frame rate of the capacitive touch system  20 . Assuming that the large scale touch panel  22  has eighty traces, for example, given the order numbers of 1-80, each of the touch ICs  24 - 30  is responsible for scanning respective twenty traces. Each of the touch ICs  24 - 30  is a slave touch IC, scans the traces in one or more directions, and transmits its sensed values to a master touch IC  32  where the received sensed values are used for final and overall calculation, and subsequent actions may be determined for intended applications. The master touch IC  32  is also responsible for coordinating the overall operation of the capacitive touch system  20  and external communications. If needed, the master touch IC  32  may also take part in scanning, as indicated by the dashed line in  FIG. 3 . Alternatively, the slave touch ICs  24 - 30  may share some calculation to reduce the loading of the master touch IC  32 . 
         [0014]    The touched area of a user&#39;s finger is very small in comparison with the entire area of the large scale touch panel  22 , and in most applications, the user&#39;s finger usually operates on only some local portions of the large scale touch panel  22 . Therefore, most of the slave touch ICs  24 - 30  can enter a suspend mode for most of the time for power saving. For example, if some of the scanning zones of the slave touch ICs  24 - 30  have not been touched for a long time, the responsible slave touch ICs for those scanning zones may enter the suspend mode and thereafter scans their responsible scanning zones at a longer interval. For example, each of the slave touch ICs  24 - 30  scans its responsible scanning zone at an interval of about 4 ms in a normal mode, but at an interval of about 40 ms in the suspend mode. 
         [0015]      FIG. 4  is a schematic diagram of an embodiment according to the present invention, which adds a suspend mode into a capacitive touch system  40  to reduce the overall power consumption of the capacitive touch system  40 . This capacitive touch system  40  uses 2N AI projected capacitance touch ICs  42 ,  44 ,  46 ,  48 ,  50  and  52 , where N is a natural number, as slave touch ICs to simultaneously scan a touch panel (not shown). If some of the scanning zone of the slave touch ICs  42 - 52  are not touched for a long time, their responsible slave touch ICs will enter the suspend mode and thereafter scan at a longer interval to reduce power consumption of the capacitive touch system  40 . A master touch IC  54  sends a clock CLK to each of the slave touch ICs  42 - 52  and receives the sensed data therefrom for computation. In this embodiment, each of the slave touch ICs  42 - 52  has a pin PN[M-1:0] to send a signal SDA[M-1:0] carrying its sensed data to the master touch IC  54 , and the pins PN[M-1:0] of all the slave touch ICs  42 - 52  are connected together to the master touch IC  54 . To prevent collision between the sensed data from the slave touch ICs  42 - 52 , the master touch IC  54  sends an address signal Addr[N-1:0] to each of the slave touch ICs  42 - 52  to select therefrom to transmit its sensed data. For example, the address signal Addr[N-1:0] of “0” signifies that the slave touch IC  42  is requested to send its sensed data to the master touch IC  54 , and in this case the pins PN[M-1:0] of all the other slave touch ICs  44 - 52  are set in a high impedance or floating. In addition, the master touch IC  54  sends a selection signal Typesel[K-1:0] to each of the slave touch ICs  42 - 52  to select the data format for the data transmission of the sensed data it desires to receive. A pull-down resistor RPL is connected between the pin PN[M-1:0] of each of the slave touch ICs  42 - 52  and a ground terminal GND. 
         [0016]    For the master touch IC  54  to read the sensed data from any one of the slave touch ICs  42 - 52 , the slave touch ICs will send out a password of several timing cycles as a packet start acknowledgement code. Taking an example that the sensed data is transmitted with one bit width, i.e., M=1,  FIG. 5  is a timing diagram of the signal SDA[M-1:0] sent by one of the slave touch ICs  42 - 52  to the master touch IC  54  under normal mode. The waveform  60  represents the signal SDA[M-1:0] and the waveform  62  represents the clock CLK. In this embodiment, the signal SDA[M-1:0] has one bit and the password has two timing cycles. Upon the detection of an address signal Addr[N-1:0] directing to itself, a particular one of the slave touch ICs  42 - 52  pulls up the signal SDA[M-1:0] and waits for the master touch IC  54  to send out the clock CLK to alter the data. The master touch IC  54  reads data at the rising edge of the clock CLK, and therefore, in a normal transmission mode, the master touch IC  54  will not start reading data until it detects a signal SDA[M-1:0] having a start acknowledgement code of “1” followed by “0”. If some of the scanning zones of the slave touch ICs  42 - 52  have not been touched for a long time, their responsible slave touch ICs will enter the suspend mode and thereafter scan their responsible scanning zone at a longer interval. Even a slave touch IC is in the suspend mode, the master touch IC  54  still keeps requesting sensed data therefrom for each frame. Besides, as mentioned above, only when a slave touch IC detects the address signal Addr[N-1:0] sent by the master touch IC  54  directing to it, it will set the signal SDA[M-1:0] as “1” or “0” while all the other slave touch ICs are set in a high impedance or floating. Thus, if the master touch IC  54  requests sensed data from, say, the slave touch IC  42 , which happens to be in the suspend mode and cannot respond, the pull-down resistor R PL  will pull down the level of the pin PN[M-1:0] of the slave touch IC  42  to “0”, so that the master touch IC  54  detects no such start acknowledgement codes as “10” in the signal SDA[M-1:0], skips the slave touch IC  42  and moves on to request sensed data from the next slave touch IC  44 . 
         [0017]    While the present invention has been described in conjunction with preferred embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and scope thereof as set forth in the appended claims.