Abstract:
A demultiplexer disposed between a touch sensor circuit and electrodes of a touchpad electrode grid, wherein instead of using the touch sensor circuitry to directly drive each electrode, the touch sensor circuitry instead transmits control signals to the demultiplexer, wherein the control signals instruct the demultiplexer to select a subset of the plurality of electrodes to be driven, and thereby perform object detection and tracking, wherein by using the demultiplexer to drive electrodes, a much greater number of electrodes can be driven by the touch sensor circuit, thereby increasing the effective size of a touchpad that can be controlled by the touch sensor circuitry.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This document claims priority to and incorporates by reference all of the subject matter included in the provisional patent application docket number 3247.CIRQ.PR, having Ser. No. 60/651,890 and filed on Feb. 10, 2006. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates generally to capacitance sensitive touchpads. More specifically, the number of electrodes of a capacitance sensitive touchpad is significantly increased by sending signals through a demultiplexer, wherein the choice of which electrodes are activated by the demultiplexer are determined by signals sent by touch sensor circuitry to the demultiplexer, instead of sending the signals from the touch sensor circuit directly to the touchpad electrodes.  
       DESCRIPTION OF RELATED ART  
       [0003]     The state of the art in capacitance sensitive touchpads is characterized by the touchpad and touchpad sensor circuitry of Cirque® Corporation. Cirque® Corporation touchpad technology has evolved from its first implementation, but several features of the past and present hardware and testing methodology can be used to demonstrate the present invention.  
         [0004]     From a hardware perspective as shown in  FIG. 1 , a capacitance sensitive touchpad  10  as taught by Cirque® Corporation includes a grid of row  12  and column  14  (or X and Y) electrodes in a touchpad electrode grid. All measurements of touchpad parameters are taken from a single sense electrode  16  also disposed on the touchpad electrode grid, and not from the X or Y electrodes  12 ,  14 . No fixed reference point is used for measurements. A touchpad sensor circuit  20  generates signals from P,N generators  22 ,  24  that are sent directly to the X and Y electrodes  12 ,  14  in various patterns. Accordingly, there is a one-to-one correspondence between the number of electrodes on the touchpad electrode grid, and the number of drive pins on the touch sensor circuitry  20 .  
         [0005]     The touchpad  10  does not depend upon an absolute capacitive measurement to determine the location of a finger (or other capacitive object) on the touchpad surface. The touchpad  10  measures an imbalance in electrical charge to the sense line  16 . When no pointing object is on the touchpad  10 , the touch sensor circuitry  20  is in a balanced state, and there is no signal on the sense line  16 . There may or may not be a capacitive charge on the electrodes  12 ,  14 . In the methodology of Cirque® Corporation, that is irrelevant. When a pointing device creates imbalance because of capacitive coupling, a change in capacitance occurs on the plurality of electrodes  12 ,  14  that comprise the touchpad electrode grid. What is measured is the change in capacitance, and not the absolute capacitance value on the electrodes  12 ,  14 . The touchpad  10  determines the change in capacitance by measuring the amount of charge that must be injected onto the sense line  16  to reestablish or regain balance on the sense line.  
         [0006]     The touchpad  10  must make two complete measurement cycles for the X electrodes  12  and for the Y electrodes  14  (four complete measurements) in order to determine the position of a pointing object such as a finger. The steps are as follows for both the X  12  and the Y  14  electrodes:  
         [0007]     First, a group of electrodes (say a select group of the X electrodes  12 ) are driven with a first signal from P,N generator  22  and a first measurement using mutual capacitance measurement device  26  is taken to determine the location of the largest signal. However, it is not possible from this one measurement to know whether the finger is on one side or the other of the closest electrode to the largest signal.  
         [0008]     Next, shifting by one electrode to one side of the closest electrode, the group of electrodes is again driven with a signal. In other words, the electrode immediately to the one side of the group is added, while the electrode on the opposite side of the original group is no longer driven.  
         [0009]     Third, the new group of electrodes is driven and a second measurement is taken.  
         [0010]     Finally, using an equation that compares the magnitude of the two signals measured, the location of the finger is determined.  
         [0011]     Accordingly, the touchpad  10  measures a change in capacitance in order to determine the location of a finger. All of this hardware and the methodology described above assume that the touch sensor circuit  20  is directly driving the electrodes  12 ,  14  of the touchpad  10 . Thus, for a typical 12×16 electrode grid touchpad, there are a total of 28 pins (12+16=28) available from the touch sensor circuitry  20  that are used to drive the electrodes  12 ,  14  of the electrode grid.  
         [0012]     It would be an advantage over the state of the art to use existing touch sensor circuitry  20  that is capable of driving a typical electrode grid and instead drive a much larger number of electrodes than the number of available pins, and thereby increase the overall size, resolution and/or linearity of the capacitance sensitive touchpad  10  that can be controlled by standard touchpad circuitry  20 .  
       BRIEF SUMMARY OF THE INVENTION  
       [0013]     It is an object of the present invention to provide a demultiplexer between touch sensor circuitry and the electrodes of a capacitance sensitive touchpad.  
         [0014]     It is another object to use control signals from the touch sensor circuitry to thereby control the grouping of signals that are transmitted to the touchpad electrodes.  
         [0015]     It is another object to increase the total number of electrodes that are controllable by given touch sensor circuitry by not using the touch sensor circuit to directly drive touchpad electrodes.  
         [0016]     In a first embodiment, the present invention is a demultiplexer disposed between a touch sensor circuit and electrodes of a touchpad electrode grid, wherein instead of using the touch sensor circuitry to directly drive each electrode, the touch sensor circuitry instead transmits control signals to the demultiplexer, wherein the control signals instruct the demultiplexer to select a subset of the plurality of electrodes to be driven, and thereby perform object detection and tracking, wherein by using the demultiplexer to drive electrodes, a much greater number of electrodes can be driven by the touch sensor circuit, thereby increasing the effective size of a touchpad that can be controlled by the touch sensor circuitry.  
         [0017]     In a first aspect of the present invention, a single large touchpad can be operated using touch sensor circuitry that has much less drive pins than the total number of electrodes of the single large touchpad.  
         [0018]     In a second aspect of the present invention, a plurality of different touchpads can be operated using a single touch sensor circuit.  
         [0019]     These and other objects, features, advantages and alternative aspects of the present invention will become apparent to those skilled in the art from a consideration of the following detailed description taken in combination with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0020]      FIG. 1  is a schematic block diagram of a prior art touch sensor circuit and an electrode grid of a capacitance sensitive touchpad.  
         [0021]      FIG. 2  is a schematic block diagram that illustrates the elements of a preferred embodiment of the present invention that incorporates a demultiplexer to thereby effectively control an electrode grid that has a greater number of electrodes than the number of drive pins on the touchpad sensor circuitry.  
         [0022]      FIG. 3  is a schematic diagram that illustrates how the principles of the present invention can be applied to using a single touch sensor circuit to drive a plurality of touchpads. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]     Reference will now be made to the drawings in which the various elements of the present invention will be given numerical designations and in which the invention will be discussed so as to enable one skilled in the art to make and use the invention. It is to be understood that the following description is only exemplary of the principles of the present invention, and should not be viewed as narrowing the claims which follow.  
         [0024]     In a first embodiment of the present invention, a modified capacitance sensitive touchpad  30  is shown in  FIG. 2  that is capable of performing object detection and tracking on a surface thereof. Such a touchpad  30  is manufactured by Cirque® Corporation. The purpose of the first embodiment of the present invention is to make it possible to utilize a touchpad having a greater number of electrodes  32 ,  34  than the number of drive pins  42 ,  44  on the touchpad sensor circuitry  50 , without having to modify the touchpad sensor circuitry that transmits control signals to the electrodes  32 ,  34  of the touchpad  30 . Accordingly, the first embodiment overcomes the prior art limitation of having a one-to-one relationship between the drive pins  42 ,  44  on the touch sensor circuitry  50 , and the number of electrodes  32 ,  34  in the touchpad  30 . Another way of looking at the invention is to realize that an existing touchpad sensor circuit  50  can be used to drive a touchpad with many more electrodes than before because they are not being directly driven.  
         [0025]     The first embodiment uses indirection to increase the total number of touchpad electrodes  32 ,  34  that can be driven by a given set of drive pins  42 ,  44  of touchpad sensor circuitry  50 . Instead of directly driving electrodes  32 ,  34 , the touchpad sensor circuitry  50  sends control signals to a demultiplexer  60  as shown in  FIG. 2 .  
         [0026]     In one embodiment, the control signals take the form of a coded index using binary numbers that define a pattern of electrodes  32 ,  34  to be driven by the demultiplexer  60 . For example, if the touchpad sensor circuitry  50  has four drive pins, it would normally only be able to drive four electrodes. By generating binary numbers, the touchpad sensor circuit can generate a total of 24 or 16 unique binary numbers, and thus drive a much larger touchpad electrode grid.  
         [0027]     The control signals of the present invention can do more than just provide an index into which electrodes are to be driven by the demultiplexer. For example, the control signals can be used to provide at least one signal that controls transition timing which is used in driving the touchpad electrode grid.  
         [0028]     Another use of the control signals is to use them to enable the touchpad sensor circuitry to send a signal as to which axis of the touchpad electrode grid is to be driven. Thus, there may be a reason to drive the X axis of electrodes before the Y axis of electrodes, and vice versa.  
         [0029]     Another use of control signals may be to implement a wide/narrow scanning pattern. Detection of a pointing object on the touchpad surface is going to require broad scans across all electrodes of the touchpad, but not scans in great detail. Accordingly, a wide scan is implemented at first in order to simply detect a pointing object. Once the object is detected, the scanning method changes to a narrow scanning method in order to more precisely track movement of the pointing object on the touchpad surface. Accordingly, control signals may be used to implement wide scanning and narrow scanning modes of operation of the touchpad.  
         [0030]     A final use of control signals is the ability to shut down operation of the demultiplexer. This operation is desired in order to prevent unnecessary drive transitions.  
         [0031]     Cirque® Corporation presently manufactures two different touch sensor circuits for driving electrodes on a touchpad electrode grid. The two touchpad sensor circuits have 14 (6+8=14) and 28 (12+16=28) drive pins. Accordingly, the 14 pin touchpad sensor circuitry  50  can drive (2 6 −2) or 62 “X” electrodes  32 , and (2 8 −2) or 254 “Y” electrodes  34  using the 6×8 touchpad sensor circuitry  50 . The number of X and Y electrodes  32 ,  34  can be switched, as this selection was arbitrary. Likewise, the 12×16 touchpad sensor circuitry can drive (2 12 −2) or 4094 X electrodes, and (2 16 −2) or 1,048,574 Y electrodes.  
         [0032]     Further along this line of development, it should be apparent that the touchpad electrode grid  30  that can be driven using the demultiplexing of the present invention is not limited to the same grid patterns. In other words, the 6×8 touch sensor circuitry  50  that has  14  pins  42 ,  44  for driving electrodes  32 ,  34  can be divided up so as to be able to drive many different grid patterns. For example, the  14  pins can be divided up so that 3 pins are for X electrodes, and the remaining  11  pins are for the Y electrodes. This would result in a touchpad electrode grid having (2 3 −2) or 6 X electrodes  32 , and (2 11 −2) or 2046 Y electrodes  34 . Thus, even though the touch sensor circuitry  50  was originally designed to drive specific electrode grid patterns because of direct one-to-one pin assignments, the pins  42 ,  44  can now be reassigned for any desired electrode grid pattern.  
         [0033]      FIG. 2  is a block diagram of an embodiment of the present invention based on the principles described above. The touchpad is comprised of the touch sensor circuitry  50 , a demultiplexer  60 , and a single touchpad electrode grid  30 . The touch sensor circuitry  50  sends control signals to the demultiplexer  60  via the output pins  42 ,  44  to thereby select which electrodes  32 ,  34  of the touchpad electrode grid  30  are being driven to thereby perform object detection and tracking on the surface of the touchpad.  
         [0034]     The demultiplexer  60  receives the control signals and utilizes two lookup tables, on lookup table  62  for the X electrodes and one lookup table  64  for the Y electrodes, to thereby decode the control signals and determine which electrodes  32 ,  34  are to be driven on the touchpad electrode grid  30 . The number of electrodes  32 ,  34  that can be driven by the touch sensor circuitry  50  is now much greater than if the electrode grid  30  was being driven directly by the drive pins  42 ,  44 .  
         [0035]     In light of the increase in the number of electrodes that can be driven, the present invention makes possible another significant improvement over the state of the art. Specifically,  FIG. 3  is provided as a block diagram of another embodiment of the present invention. The same touch sensor circuitry  50  of  FIG. 2  can also be used to drive a plurality of touchpads  30 ,  70  instead of single large touchpad. Thus, a single demultiplexer  60  is now coupled to a plurality of touchpad electrode grids  30 ,  70 . In  FIG. 3 , only two touchpads  30 ,  70  are shown for illustration purposes only. It should be recognized that many more touchpads can be driven from the same demultiplexer  60 .  
         [0036]     By way of illustration, it is observed that other electronic circuitry can be used to replace the demultiplexer  60  of the present invention. Any equivalent circuitry can be used that is capable of receiving a control signal and then driving a selected set of electrodes of a touchpad electrode grid. What is important is that the function of the demultiplexer  60  be replicated in the equivalent circuitry.  
         [0037]     The control signals of the present invention should also be considered. Operation of a demultiplexer is well understood by those skilled in the art. Simple binary commands can be used to control the output. Similarly, the control signals that would be sent to equivalent circuitry may be identical binary coded control signals, or may be some equivalent. Thus, it is not important what form the controls signals should take, only that the control signals should be capable of being correctly formatted for the particular equivalent circuitry being used to replace the demultiplexer.  
         [0038]     It is to be understood that the above-described arrangements are only illustrative of the application of the principles of the present invention. Numerous modifications and alternative arrangements may be devised by those skilled in the art without departing from the spirit and scope of the present invention. The appended claims are intended to cover such modifications and arrangements.