Abstract:
A system and method for increasing a scanning rate, reducing the effects of noise and reducing power consumption when using a touch sensor having an electrode grid formed by co-planar but orthogonal XY electrodes, wherein the touch sensor may be used to determine the position of an object on a surface of the touch sensor in a single measurement cycle by using a single drive line that defines a touch sensor area and the XY electrodes as sense electrodes of the touch sensor.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates generally to touch sensors. More specifically, the present invention is a system and method for increasing a scanning rate using a traditional XY grid which can capture the full XY image in a single measurement when a single finger is present. 
         [0003]    2. Description of Related Art 
         [0004]    There are several designs for capacitance sensitive touch sensors. It is useful to examine the underlying technology to better understand how any capacitance sensitive touch sensor can be modified to work with the present invention. 
         [0005]    The CIRQUE® Corporation touchpad is a mutual capacitance-sensing device and an example is illustrated as a block diagram in  FIG. 1 . In this touchpad  10 , a grid of X ( 12 ) and Y ( 14 ) electrodes and a sense electrode  16  is used to define the touch-sensitive area  18  of the touchpad. Typically, the touchpad  10  is a rectangular grid of approximately 16 by 12 electrodes, or 8 by 6 electrodes when there are space constraints. Interlaced with these X ( 12 ) and Y ( 14 ) (or row and column) electrodes is a single sense electrode  16 . All position measurements are made through the sense electrode  16 . 
         [0006]    The CIRQUE® Corporation touchpad  10  measures an imbalance in electrical charge on the sense line  16 . When no pointing object is on or in proximity to the touchpad  10 , the touchpad circuitry  20  is in a balanced state, and there is no charge imbalance on the sense line  16 . When a pointing object creates imbalance because of capacitive coupling when the object approaches or touches a touch surface (the sensing area  18  of the touchpad  10 ), a change in capacitance occurs on the electrodes  12 ,  14 . What is measured is the change in capacitance, but 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 of charge on the sense line. 
         [0007]    The system above is utilized to determine the position of a finger on or in proximity to a touchpad  10  as follows. This example describes row electrodes  12 , and is repeated in the same manner for the column electrodes  14 . The values obtained from the row and column electrode measurements determine an intersection which is the centroid of the pointing object on or in proximity to the touchpad  10 . 
         [0008]    In the first step, a first set of row electrodes  12  are driven with a first signal from P, N generator  22 , and a different but adjacent second set of row electrodes are driven with a second signal from the P, N generator. The touchpad circuitry  20  obtains a value from the sense line  16  using a mutual capacitance measuring device  26  that indicates which row electrode is closest to the pointing object. However, the touchpad circuitry  20  under the control of some microcontroller  28  cannot yet determine on which side of the row electrode the pointing object is located, nor can the touchpad circuitry  20  determine just how far the pointing object is located away from the electrode. Thus, the system shifts by one electrode the group of electrodes  12  to be driven. In other words, the electrode on one side of the group is added, while the electrode on the opposite side of the group is no longer driven. The new group is then driven by the P, N generator  22  and a second measurement of the sense line  16  is taken. 
         [0009]    From these two measurements, it is possible to determine on which side of the row electrode the pointing object is located, and how far away. Pointing object position determination is then performed by using an equation that compares the magnitude of the two signals measured. 
         [0010]    The sensitivity or resolution of the CIRQUE® Corporation touchpad is much higher than the 16 by 12 grid of row and column electrodes implies. The resolution is typically on the order of  960  counts per inch, or greater. The exact resolution is determined by the sensitivity of the components, the spacing between the electrodes  12 ,  14  on the same rows and columns, and other factors that are not material to the present invention. 
         [0011]    The process above is repeated for the Y or column electrodes  14  using a P, N generator  24 . Although the CIRQUE® touchpad described above uses a grid of X and Y electrodes  12 ,  14  and a separate and single sense electrode  16 , the sense electrode can actually be the X or Y electrodes  12 ,  14  by using multiplexing. It should also be understood that the CIRQUE® touchpad technology described above can be modified in order to function as touch screen technology. 
       BRIEF SUMMARY OF THE INVENTION 
       [0012]    In a first embodiment, the present invention is a system and method for increasing a scanning rate, reducing the effects of noise and reducing power consumption when using a touch sensor having an electrode grid formed by co-planar but orthogonal XY electrodes, wherein the touch sensor may be used to determine the position of an object on a surface of the touch sensor in a single measurement cycle by using a single drive line that defines a touch sensor area and the XY electrodes as sense electrodes of the touch sensor. 
         [0013]    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 
         [0014]      FIG. 1  is a block diagram of the components of a capacitance-sensitive touchpad as made by CIRQUE® Corporation and which can be modified to operate in accordance with the principles of the present invention. 
           [0015]      FIG. 2  is a top view of an example of the first embodiment, where a single drive electrode travels a path through the entire sensing area of the touch sensor. 
           [0016]      FIG. 3  is a top view of a schematic diagram of an alternative embodiment of the invention where the drive and sense circuitry is combined into a single drive and sense controller. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    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. 
         [0018]    It should be understood that use of the term “touch sensor” throughout this document may be used interchangeably with “capacitive touch sensor device”, “touchpad”, “touch panel” and “touch screen”. 
         [0019]    In a first embodiment of the present invention, touch sensor technology having an XY grid of electrodes may be adapted for use with the present invention. Some touch sensor systems using an XY electrode grid have been modified to include a single sense electrode that is placed on the touch sensor so that it is intertwined with the XY electrodes. Drive signals are transmitted on the X electrode grid, and sensed on the single sense electrode. Then a signal is transmitted on the Y electrode and sensed on the sense electrode in order to obtain the location of an object or objects in both the X and Y dimensions. 
         [0020]    The first embodiment is essentially the opposite or the reverse of the process as described above. In this first embodiment, a drive electrode is placed throughout the touch sensor. In other words on a system that uses a single sense electrode, the sense electrode is now driven with a drive signal and functions as the drive electrode. The XY electrode grid is now modified so that instead of being configured to drive the different grids at different times, all of the X and Y electrodes are now configured to function as simultaneously operating sense electrodes. 
         [0021]      FIG. 2  is provided as an example of the first embodiment.  FIG. 2  is a top view of an XY electrode grid  30  that may be used in a touch sensor  44  of the first embodiment. The touch sensor  44  includes a plurality of X electrodes  32  and a plurality of Y electrodes  34 . The number of X and Y electrodes may be increased and decreased as desired. No limitation on the number of X or Y electrodes is being implied by  FIG. 2 . 
         [0022]    The single drive electrode  36  is shown intertwined among the X electrodes  32  and the Y electrodes  34 . It should be understood that the path of the drive electrode  36  is not limited to the path which is shown, and no limitations of a path are implied by  FIG. 2 . The path may cover an entire touch sensing area of the touch sensor or only a partial area. The single drive electrode  36  may have a branch, a plurality of branches or be a single wire. 
         [0023]    It should be understood that the shape of the path may change and not be a regular serpentine pattern as shown in  FIG. 2 . The path may not resemble any pattern at all. The path may or may not include random direction changes. What is important is that the single drive electrode  36  be near enough to the X electrodes  32  or the Y electrodes  34  such that the detectable object may alter the capacitive coupling between the electrodes. The path may result in a single drive electrode  36  that is substantially equal to the sum of the lengths of the X electrodes  32  and the Y electrodes  34 . 
         [0024]    What is important is that the single drive electrode  36  be adjacent to all areas of the electrode grid that contain any of the X electrodes  32  or the Y electrodes  34 . By virtue of trying to be adjacent to all of the X electrodes and Y electrodes  34 , the length of the single drive electrode  36  will be substantially or nearly the same as the sum of the lengths of the X electrodes  32  and the Y electrodes  34 . 
         [0025]    Another result of the relatively long path of the single drive electrode  36  is that the surface area defined by the path of the single drive electrode  36  will be substantially the same as the surface area of the touch sensor  44 . By stating the surface areas are similar is to suggest that the single drive electrode is adjacent so as to have a capacitive effect on all or substantially all of the X electrodes  32  and the Y electrodes  34 . 
         [0026]    The single drive electrode  36  may receive a signal from the drive circuitry  38  of the touch sensor  44 . The X electrodes  32  may send signals to sensing circuitry  40  and the Y electrodes  34  may send sense signals to sensing circuitry  42 . The sensing circuitry  40 ,  42  may generally be part of the touch sensor  44 . No limitations on the placement of the sensing circuitry  40 ,  42  should be implied by  FIG. 2 . 
         [0027]    On a surface of the touch sensor  44 , a finger or other detectable object may affect the capacitive coupling between the single drive electrode  36  and the X and Y sense electrodes  32 ,  34 . The change in capacitive coupling is detectable by the touch sensing circuitry of the first embodiment. 
         [0028]    The position of the finger may be calculated using standard prior art position determining techniques that require more than the two measurements of the present invention. No new position determining routines are necessary. 
         [0029]    This type of capacitance sensitive system is inherently ghosted (detects a false “ghost” image of a detectable object) when more than one finger is present on the touch sensor  30 . Ghosting refers to the inability of a touch sensor to determine the actual location of a finger because it may appear to be in two different locations at the same time due to the nature of the capacitive sensing technology being used. In other words, the first embodiment may provide single axis image information. 
         [0030]    Thus, N number of fingers may be detected in the X axis and N number of fingers may be detected in the Y axis. The X and Y positions may not be inherently correlated so anything more than one finger position will cause ghosted finger positions. The actual finger positions may then be determined by a process known as de-ghosting, by performing individual electrode traditional drive/sense measurements. In other words, the first embodiment operates very efficiently and quickly when there is a single finger present. However, for each finger that is added to the surface of the touch sensor  30 , more and more measurements must be performed in order to de-ghost the image and determine the actual positions of the multiple fingers. 
         [0031]    As the finger count increases, the improvements achieved by the first embodiment in time and power consumption may decrease. However, for single finger detection, this method and system of scanning may be the fastest that is theoretically possible, and consume the least amount of power. The first embodiment may also reduce noise or be less susceptible to noise than the prior art. 
         [0032]    As stated above, the scan rate may be substantially faster using the first embodiment as compared to prior art methods. In other conventional scan methods, individual electrodes need to be driven sequentially or in a spread/balanced approach. Using conventional methods, the numbers of measurements may match the electrode count. Thus, for a 16×16 array, at least 16 drive measurements per axis may be required for finger detection and position determination. In contrast, in the first embodiment, only two measurements capture an image of the entire X and Y axes, thus resulting in the large increase in speed. 
         [0033]    It was also stated that noise may be reduced in the first embodiment. Specifically, the signal on the touch sensor  30  is all received simultaneously. The advantage of receiving the sense signals on all of the sense electrodes at the same time is that any noise on the touch sensor  30  will affect all of the measurements of the sense signals by a same degree. Typically, the noise may be manifested as an offset in a signal on a sense line. Because the prior art may make measurements over a period of time, the noise signal may change, making the position determination less accurate. However, by making all of the measurements at the same time from all of the sense electrodes, the potential for noise to make the position determination less accurate may be reduced or eliminated. In other words, even if noise is present, it may be affecting all of the measurements simultaneously. Therefore it is likely that any noise being detected may be affecting all of the electrodes in substantially the same manner, but changing over time. By eliminating the variable of time, the present invention reduces vulnerability to noise. This means that position jitter should be significantly improved by this first embodiment because noise is affecting all of electrodes simultaneously. 
         [0034]    Another advantage of the first embodiment is that a faster scan rate results in lower power usage. Because only one measurement is required to capture the entire touch sensor in both the X and Y dimensions, the active mode current is reduced by 1/16th the power of a full axis receive system and 1/64th the power of a 4 ADC system. This type of scan may be the lowest power consumption possible because it is accomplished with one single measurement. 
         [0035]    Regarding the phenomenon of ghosting and the technique of de-ghosting, this process is well known to those skilled in the art and is taught in U.S. patent application Ser. No. 13/397,527, filed Feb. 15, 2012. 
         [0036]      FIG. 3  is provided as an alternative embodiment of the present invention. In this figure, the drive and sense circuitry is combined into a single drive and sense controller  50  that is able to transmit drive signals and receive sense signals. 
         [0037]    Another aspect of the invention is related to the concept of proximity sensing. It has been explained above that the single drive electrode  36  is intertwined among the X and Y electrodes  32 ,  34  of the electrode grid  30 , while the X and Y electrodes act as a single large sense electrode. 
         [0038]    The interesting and beneficial result is that when the single but very large drive electrode  36  is driven (toggled), the effect is to increase the projection of an electric field from the surface of the touch sensor  44 . An electric field that is projected farther from the surface of the touch sensor  44  results in the ability to detect a detectable object at a greater distance from the touch sensor than is possible when using prior art methods for toggling the drive electrodes. Thus, by simultaneously toggling the single drive electrode  36  which covers a large area of the electrode grid  30 , the touch sensor  44  is capable of improved proximity sensing because of the projected electric field. 
         [0039]    Accordingly, another aspect of the invention is that by performing the toggling of single drive electrode  36 , the touch sensor  44  enjoys improved electric field projection and therefore improved proximity sensing. 
         [0040]    It is to be understood that the above-described arrangements are only illustrative of the application of the principles of the embodiments of the 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.