Abstract:
A method and system for enabling a near field communication antenna to be disposed adjacent to electrodes of a touch sensing device, the near field communication antenna being operated, and the magnetic field inductance and electric field coupling between the electrodes and the near field communication antenna being minimized in order to substantially reduce or eliminate induced currents on the electrodes.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This document claims priority to and incorporates by reference all of the subject matter included in the provisional patent application, having Ser. No. 61/505,350, filed Jul. 7, 2011. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to the use of a near field communication antenna and a touch sensing device, wherein the antenna and the touch sensing device are used in close proximity to each other such that the near field communication antenna can interfere with operation of the touch sensing device. 
     2. Description of Related Art 
     The present invention describes the use of a touch sensing device in combination with a near field communication (NFC) antenna. The use of the term “touch sensing device” should be considered as interchangeable with the terms “touchpad”, “touch screen” and “touch sensitive device”. Likewise, the term near field communication antenna should be considered as interchangeable with the terms “contactless card reader”, “RFID reader” and “blue tooth antenna”. Furthermore, the “systems” referred to will include a combination of a touch sensing device and a near field communication antenna, using all of the interchangeable terms. 
     There are several designs for capacitance sensitive touchpads. It is useful to examine the underlying technology to better understand how any capacitance sensitive touchpad can be modified to work with the present invention. 
     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 . 
     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. 
     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 . 
     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. 
     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. Using an equation that compares the magnitude of the two signals measured then performs pointing object position determination. 
     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. 
     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. 
     One problem with integrating a near field communication antenna and a touch sensing device is interference. For example, the strong magnetic field necessary to power a near field communication antenna that is used as a contactless card reader may create strong eddy currents within electrodes of the touch sensing device, thereby causing operation outside of specifications, and malfunctions or inoperability is the result. Similarly, a near field communication antenna can electrically couple to the electrodes of the touch sensing device. Thus, a near field communication antenna may cause magnetic field inductance and electric field coupling with the touch sensing device. 
     In a related interference problem, the touchpad creates strong electrostatic fields that are necessary to detect a finger. These strong fields often cause the near field communication antenna to have insufficient signal integrity. 
     The adverse effects of the both electrostatic field coupling and magnetic field inductance may be a result of 1) the near field communication antenna signal causing non-linear effects due to noise/interference signal levels being large enough to trigger ESD diodes in touch sensing device circuitry, 2) difficulty for the touch sensing device front-end electronics or analog-to-digital converters (ADCs) in tracking the interference also causing non-linear effects and error in measurement, and 3) the amplitude modulation frequency of near field communications is often very close to the touch sensing stimulus frequency, thereby creating in-band ground bounce. 
     It would be a further advantage to dispose the circuitry of the near field communication antenna and the touch sensing device near enough to each other to prevent eavesdropping or tapping into the signals between them to thereby provide an integrated system that is more secure than existing integrated systems. Furthermore, it would be an advantage to remove the electrical and magnetic interaction between them. Finally, it would also be of benefit to integrate the electronics into a single package to address the very limited space of the touch sensing device and the NEAR FIELD COMMUNICATION antenna and associated routing space typical of today&#39;s electronic appliances. 
     BRIEF SUMMARY OF THE INVENTION 
     In a first embodiment, the present invention is a method and system for enabling a near field communication antenna to be disposed adjacent to electrodes of a touch sensing device, the near field communication antenna being operated, and the magnetic field inductance and electric field coupling between the electrodes and the near field communication antenna being minimized in order to substantially reduce or eliminate induced currents on the electrodes. 
     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 
         FIG. 1  is a block diagram of the components of a capacitance-sensitive touchpad as made by CIRQUE® Corporation and which can be successfully operated in conjunction with a near field communication antenna. 
         FIG. 2  is a diagram that illustrates a layout for a near field communication antenna and electrodes of a touch sensing device. 
         FIG. 3  is a diagram that illustrates a different layout for electrodes of the touch sensing device. 
         FIG. 4  is a diagram of a near field communication antenna and a signal source that will couple currents to electrodes of a touch sensing device. 
         FIG. 5  is a diagram showing an alternative embodiment of a near field communication antenna. 
         FIG. 6  is a diagram showing additional detail of the electrode grid that is combined with the alternative near field communication antenna. 
         FIG. 7  is a diagram showing additional detail of the electrode grid that is combined with the alternative near field communication antenna. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     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. 
       FIG. 2  is a diagram of electrodes of a near field communication antenna and electrodes of a touch sensing device. The present invention may be implemented in electrodes  40  of a touch sensing device  42  that are adjacent to a near field communication antenna  50 . For the purposes of this document, the term adjacent implies that operation of the near field communication antenna  50  may influence operation of the electrodes  40  by inducing current flow in the electrodes. 
     In this first embodiment, the near field communication antenna  50  is disposed in a same plane as the electrodes  40 . However, the near field communication antenna  50  may be in a different plane but substantially parallel plane as the electrodes  40 , either above or below. Furthermore, the electrodes  40  may be part of a touchpad, a touch screen, or any other touch sensing device as is known to those skilled in the art. 
     The near field communication antenna  50  is shown as being a loop of wire that is wound twice around the electrodes  40 . This specific layout or configuration for the near field communication antenna  50  is for illustration purposes only and should not be considered as limiting. The near field communication antenna  50  may be formed as a partial loop, a single loop or multiple loops around the electrodes  40 . 
     The first embodiment is directed to minimizing, reducing or substantially eliminating interference between the near field communication antenna and the electrodes  40  of the touch sensing device  42  when the near field communication antenna is operated. Reduced, minimized or substantially eliminated interference is defined as interference that is too small to prevent operation of the near field communication antenna  50  or the electrodes  40  of the touch sensing device  42 . 
     In the first embodiment, functions of the near field communication antenna  50  include, but should not be considered limited to, wireless communication functions such as using a contactless card reader for communication with a smart card, reading a smart card at keyless entry systems, or any other functions that require near field communication. The near field communication antenna  50  may or may not use relatively high voltages when compared to the voltages on the electrodes  40  of a touch sensing device  42 . Near field communication antennas are known to use voltages at least as high as 60 volts, while touch sensing devices may operate nearer to 5 volts. These voltages are only examples, and the systems are capable of operating at other voltages. 
       FIG. 2  is a first embodiment that may reduce or substantially eliminate interference by a near field communication antenna  50  on the electrodes  40 . The near field communication antenna  50  is connected to near field communication circuitry  52 . The electrodes  40  are connected to touch sensing device circuitry  42 . 
     For this example, current is flowing through the near field communication antenna  50  as shown by arrows  60 . A magnetic field is generated around the near field communication antenna  50  in the direction as shown by curved arrow  62 . Electrodes  40  that are nearest to the near field communication antenna  50  may have induced currents caused by the magnetic field generated by the near field communication antenna  50 . 
     The electrodes  40  are arranged to form a sensing area that may be a series of parallel rows of electrodes extending from a top edge  30  to a bottom edge  32  of the sensing area, each of the plurality of electrodes being electrically separate from each other. Each of the plurality of electrodes  40  follows a path that is beginning at a first edge  34  and ends at an opposite second edge  36  of the sensing area. 
     To reduce or substantially eliminate the tendency of the magnetic field to induce currents on the electrode  46 , the electrode is made to pass through the magnetic field twice. This is accomplished by extending the length of the electrode  46  at location  48  so that it is now twice as long as other electrodes  40  in the sensing area that is used for detecting objects. Because the electrode  46  may be essentially folded back on itself so that it spans the distance between opposites sides of the near field communication antenna  50  two times, the sum of current at location  66  may be reduced or substantially eliminated. 
     The electrode  54  that is shown near the bottom of the electrodes  40  is also shown as spanning the distance twice between opposite sides of the near field communication antenna  50 . Thus, the sum of current at location  68  may be reduced or substantially eliminated. 
     The electrodes  40  that are not immediately adjacent to the top or bottom edges of the near field communication antenna  50  are not shown as being doubled in length. This is because the effect of the magnetic field around the near filed communication antenna  50  may diminish rapidly. However, any electrode  40  that experiences magnetically induced currents can be made to travel back and forth between sides of the near field communication antenna  50  so as to eliminate the effect of induced currents. Therefore, this example should not be considered as limiting, but only as an illustration of principles of the present invention that demonstrate how to reduce or eliminate induced currents in the electrodes  40 . 
     While  FIG. 2  illustrates the ability to reduce induced currents because of magnetic fields generated by the near field communication antenna  50 , it may not address the problems of electrostatic fields that couple to the electrodes  40 . Current flow through the near field communication antenna  50  also creates an electrostatic field around the near field communication antenna  50  that can couple to the electrodes  40  and also induce current flow. 
       FIG. 3  is provided as a top view of a near field communication antenna  50  connected to near field communication antenna circuitry  52 , wherein the antenna is disposed around electrodes  40  that are connected to touch sensing circuitry  42 . 
     In  FIG. 3 , a sensing area is now formed from a series of concentrically aligned partial electrode loops  38 , the partial loops all being electrically open at a first location  78 , and having a connection to touch sensing circuitry  42  at an opposite second location  88 . Each of the partial electrode loops  38  may have two arms of substantially equal length. The induced current in a first arm of each of the plurality of concentrically aligned partial electrode loops  38  may be equal and opposite to the induced current in a second arm. 
     There may also be an electrode  90  of the electrodes  38  that is not formed as a partial loop but is instead formed as a “T” shape. This electrode  90  will be affected by the coupling of current from the near field communication antenna  50  in the same manner as all of the partial electrode loops  38  because it also has two arms of substantially equal length. 
     In  FIG. 3 , arrows  70  show the direction of current flow in the near field communication antenna  50  in a moment of time. The direction of current flow may change because the signal source is an AC current, but for this moment in time, current flow  70  is in the indicated direction. Electrode  44  is shown as being split into two arms of approximately equal length. The magnetic field induces current in electrode  44  as indicated by arrows  72  and  74 . The sum of the current at point  76  is thus reduced or substantially eliminated. 
     It should be understood that the scale and spacing of the electrodes  38  and the near field communication antenna  50  is for illustration purposes only and should not be considered as limiting. 
     With the magnetic field accounted for, it may be possible to also affect current that is coupled from electrostatic fields. The electrostatic fields generated by the near field communication antenna  50  can also be coupled into the electrodes  38  because the current on the near field communication antenna is an AC current. 
       FIG. 4  is an illustration of the application of a stimulus signal on the near field communication antenna  50 . One side of the near field communication antenna  50  may be grounded  80 , while the other side  82  has a stimulus signal applied. Disadvantageously, the result may be a coupling of a net change in voltage of approximately half of the maximum applied voltage on the electrodes  40  shown in  FIG. 3 . 
     To overcome this problem of coupling voltage onto the electrodes  38 , a stimulus signal source is used as shown in  FIG. 3 .  FIG. 3  shows that there are stimulus signals  84 ,  86  on each end of the near field communication antenna  50 . The stimulus signals  84 ,  86  may be 180 degrees out of phase with respect to each other. The effect of the stimulus signals  84 ,  86  may be a coupling of a net change in voltage of approximately zero volts on the electrodes  38  shown in  FIG. 3 . 
     Another way to characterize the stimulus signals  84 ,  86  is to say that they form a differential signal source. The same amount of current may still be applied to the near field communication antenna  50 , but by using the differential signals  84 ,  86 , the near field communication antenna may no longer be radiating a signal that is being coupled to the electrodes  38 . Thus, the configuration of the near field communication antenna  50  still radiates a magnetic field, but the differential signals  84 ,  86  may eliminate or substantially reduce the electrostatic field. 
     It is an aspect of the present invention that the design of the electrodes that will reduce or substantially eliminate induced currents caused by operation of the near field antenna may be changed from the examples illustrated herein. However, any such changes are considered to be within the scope of the principles of the present invention and should be considered to be within the scope of the claims herein. 
     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.