Abstract:
A system for controlling a touch screen. A touch screen element having a plurality of contacts, such as one contact electrode at each of four corners. A multiplexer coupled to the touch screen element for forming a plurality of connections, such as various combinations of the contact electrodes to allow measurements to be made of the impedance of the touch screen element from the left side to the right side, from the top to the bottom, and do forth. A touch screen processor coupled to the touch screen element for determining an oscillation frequency of the touch screen element as a function of the electrode connections.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to touch screen controllers, and more particularly to a method and system for an adaptive high dynamic range surface capacitive touch screen controller with DC offset control. 
       BACKGROUND OF THE INVENTION 
       [0002]    Surface capacitive touch screen controllers determine the location where a screen has been touched between the left and right sides and top and bottom of a touch screen element. Time-varying signals are fed into the corners of the touch screen element, and digital analysis of the waveforms and signals is used to determine the location at which the screen has been touched. These prior art methods are complex and result in incorrect data. 
       SUMMARY OF THE INVENTION 
       [0003]    A system for controlling a touch screen is provided. The system includes a touch screen element having a plurality of contacts, such as one contact electrode at each of four corners. A multiplexer is coupled to the touch screen element for forming a plurality of connections, such as various combinations of the contact electrodes to allow measurements to be made of the impedance of the touch screen element from the left side to the right side, from the top to the bottom, and so forth. A touch screen processor is coupled to the touch screen element for determining an oscillation frequency of the touch screen element as a function of the electrode connections and the point at which the touch screen has been touched. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0004]      FIG. 1  is a diagram of a system for determining a location where a surface capacitive touch screen has been touched in accordance with an exemplary embodiment of the present invention; 
           [0005]      FIG. 2  is a diagram of a system for a surface capacitive touch screen controller in accordance with an exemplary embodiment of the present invention; 
           [0006]      FIG. 3  is a diagram of a system utilizing a difference amplifier in accordance with an exemplary embodiment of the present invention; 
           [0007]      FIG. 4  is a diagram of a system of an integrator in accordance with an exemplary embodiment of the present invention; 
           [0008]      FIG. 5  is a diagram of a system for a hysteresis comparator including start-up and integrator reset functions in accordance with an exemplary embodiment of the present invention; 
           [0009]      FIG. 6  is a diagram of a system for providing an integrator hold function in accordance with an exemplary embodiment of the present invention; 
           [0010]      FIG. 7  is a diagram of a system for a hysteresis or inverse hysteresis comparator in accordance with an exemplary embodiment of the present invention; 
           [0011]      FIG. 8  is a diagram of a system for reducing the number of difference amplifiers required in a surface capacitive touch screen controller in accordance with an exemplary embodiment of the present invention; 
           [0012]      FIG. 9  is a diagram of a waveform showing attributes of a system for use in accordance with an exemplary embodiment of the present invention; and 
           [0013]      FIG. 10  is a diagram of an algorithm for calibrating a touch screen element and determining a location at which a touch screen element has been touched in accordance with an exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0014]    In the description that follows, like parts are marked throughout the specification and drawings with the same reference numerals, respectively. The drawing figures might not be to scale and certain components can be shown in generalized or schematic form and identified by commercial designations in the interest of clarity and conciseness. 
         [0015]      FIG. 1  is a diagram of a system  100  for determining a location where a surface capacitive touch screen has been touched in accordance with an exemplary embodiment of the present invention. System  100  utilizes a novel method for determining the location at which a surface capacitive touch screen element has been touched by using frequency measurement. 
         [0016]    System  100  includes touch screen element  102 , which can be a surface capacitive touch screen element that includes display elements and other conventional features of surface capacitive touch screen elements, or other suitable touch screen elements. Touch screen element  102  includes lower left (LL) terminal, lower right (LR) terminal, upper left (UL) terminal, and upper right (UR) terminal, which are coupled to multiplexer  104 . Multiplexer  104  can couple suitable combinations of touch screen element  102  terminals to allow an oscillation frequency of a signal applied to the terminals to be determined. In one exemplary embodiment, multiplexer  104  can couple the upper left (UL) and upper right (UR) terminals of touch screen element  102  to input A of multiplexer  104 , and can couple the lower left (LL) and lower right (LR) terminals of touch screen element  102  to output B of multiplexer  104 , so as to allow the oscillation frequency of a signal applied to the upper terminals through the lower terminals of touch screen element  102  from input A to output B to be determined. In another exemplary embodiment, multiplexer  104  can couple the upper left (UL) and upper right (UR) terminals of touch screen element  102  to output B of multiplexer  104 , and can couple the lower left (LL) and lower right (LR) terminals of touch screen element  102  to input A of multiplexer  104 , so as to allow the oscillation frequency of a signal applied to the lower terminals through the upper terminals of touch screen element  102  from input A to output B to be determined. 
         [0017]    In another exemplary embodiment, multiplexer  104  can couple the lower right (LR) and upper right (UR) terminals of touch screen element  102  to input A of multiplexer  104 , and can couple the lower left (LL) and upper left (UL) terminals of touch screen element  102  to output B of multiplexer  104 , so as to allow the oscillation frequency of a signal applied from the right terminals to the left terminals of touch screen element  102  from input A to output B to be determined. In another exemplary embodiment, multiplexer  104  can couple the upper left (UL) and upper right (UR) terminals of touch screen element  102  to input A of multiplexer  104 , and can couple the lower left (LL) and lower right (LR) terminals of touch screen element  102  to output B of multiplexer  104 , so as to allow the oscillation frequency of a signal applied to the upper terminals through the lower terminals of touch screen element  102  from input A through output B to be determined. Other suitable combinations of input out output terminals and other suitable frequencies or circuit component values can also or alternatively be used. 
         [0018]    Touch screen processor  106  is coupled to multiplexer  104  to allow it to process signals using touch screen element  102  to determine the resistive-capacitive oscillation frequency of touch screen element  102  as a function of where touch screen element  102  has been touched by a user. Touch screen processor  106  can be implemented in hardware or a suitable combination of hardware and software, and can be one or more software systems operating on a processing platform. As used herein and by way of example and not by limitation, “hardware” can include a combination of discrete components, an integrated circuit, an application-specific integrated circuit, a field programmable gate array, a digital signal processor, or other suitable hardware. As used herein and by way of example and not by limitation, “software” can include one or more objects, agents, threads, lines of code, subroutines, separate software applications, one or more lines of code or other suitable software structures operating in one or more software applications or on one or more processors, or other suitable software structures. In one exemplary embodiment, software can include one or more lines of code or other suitable software structures operating in a general purpose software application, such as an operating system, and one or more lines of code or other suitable software structures operating in a specific purpose software application. 
         [0019]    Touch screen processor  106  allows the oscillation frequency of a signal applied to input A of multiplexer  104  and measured at output B of multiplexer  104  to be determined. In one exemplary embodiment, surface capacitive touch screen element  102  will form a series/parallel resistive-capacitive element depending on where the touch screen element  102  is touched by a user, and other characteristics such as the resistance and capacitance to ground of the user, the relative humidity, the temperature, and other variables. The value of the series/parallel resistive-capacitive element will also depend on which terminals of touch screen element  102  are coupled together and how the signal is driven through touch screen element  102 . In general, when touch screen element  102  is not being touched and the signal is applied from the left terminals to the right terminals, the oscillation frequency of touch screen element  102  will be at a minimum. When a user touches the left-most side of touch screen element  102 , the oscillation frequency will increase by a relatively small amount, but as the user moves the point of contact from the left-most side towards the right-most side, the oscillation frequency will increase in a generally linearly manner to a maximum when the point of contact reaches the right-most side. 
         [0020]    In a similar manner, the oscillation frequency of a signal measured from right to left, top to bottom, and bottom to top will also start at a minimum and increase as the point of contact moves from the near side of the circuit to the far side of the circuit. Using this phenomenon, it is possible to determine a point of contact or possibly multiple points of contact on a touch screen element  102  by making several measurements between top, bottom, left and right terminals of touch screen element  102 . 
         [0021]    Touch screen processor  106  includes left-right frequency processor  108  (for measuring a frequency associated with a signal applied to the left side and measured at the right side), right-left frequency processor  110  (for measuring a frequency associated with a signal applied to the right side and measured at the left side), top-bottom frequency processor  112  (for measuring a frequency associated with a signal applied to the top side and measured at the bottom side) and bottom-top frequency processor  114  (for measuring a frequency associated with a signal applied to the bottom side and measured at the top side), all of which are used to determine the location at which touch screen element  102  has been touched based on the frequency measured by the associated multiplexed combination of touch screen element  102  contacts as described above. Calibration system  116  is used to generate an indication for a user to touch to allow the circuit-specific variations in the capacitance and resistance of touch screen element  102  to be determined and compensated for, and also calibrates for circuit variations within the controller/processor. Controller  118  is described in further detail below, and is used to determine the frequency variation as a function of multiplexer configurations and point of contact with touch screen element  102 . 
         [0022]    In operation, system  100  allows a capacitive touch screen element to be operated in a manner to allow the location at which the touch screen element has been touched to be determined without complex signal processing and by using simple frequency measurements. 
         [0023]      FIG. 2  is a diagram of a system  200  for a surface capacitive touch screen controller in accordance with an exemplary embodiment of the present invention. System  200  can be implemented in hardware or a suitable combination of hardware and software. 
         [0024]    System  200  includes contacts LL (lower left), LR (lower right), UL (upper left) and UR (upper right) from the touch screen panel, and contacts LL, LR, UL and UR to the touch screen panel. These switches are configured so as to measure left-right or top-bottom touch locations, such as using a multiplexer as previously described. For example, shorting the LL and LR contacts from the touch screen panel and the UL and UR contacts to the touch screen panel allows the location between the top and bottom at which the touch screen panel is being touched to be determined from the series-parallel resistive/capacitive characteristics of the touch screen element, such as by measuring the frequency variation of a signal driven by the controller from the top to the bottom and from the bottom to the top. Likewise, shorting the LL and UL contacts from the touch screen panel and the LR and UR contacts to the touch screen panel allows the location between the left and right sides of the touch screen panel at which the touch screen panel is being touched to be determined, such as by using the controller to drive a signal from the left to the right and from the right to the left, as previously described. As previously described, the frequency differences between the different paths provide the basis for determining the location at which the touch screen panel has been touched. 
         [0025]    Driver  216  provides a drive signal to the surface capacitive touch screen panel contact multiplexer, which connects the terminals of the surface capacitive touch screen element in a manner to provide a series/parallel resistive-capacitive load that causes system  200  to oscillate at a frequency that is a function of the location at which the surface capacitive touch screen has been touched. Driver  214  provides a feedback voltage (VF) that is used to compare with the voltage measured at the panel output multiplexer terminals (VT), and frequency counter  220  counts the oscillation frequency, which is provided as an input to touch screen processor  106  (not explicitly shown). 
         [0026]    Difference amplifier  202  receives a voltage signal from the output terminals of the touch screen (VT) and a feedback voltage (VF) representing the input voltage applied to the input of the touch screen and generates a difference signal. The difference signal is integrated using integrator  204 , which generally outputs a square wave signal that is integrated using integrator  206 , which generally outputs a saw tooth signal. The output of integrator  206  drives hysteresis comparator  210 , which controls reset pulse generator  208  based on the setting at which hysteresis occurs. The output of hysteresis comparator  210  resets integrators  204  and  206  through reset pulse generator  208 . 
         [0027]    In addition, integrator hold  218  can be provided to switch integrator  204  off during the period where no effective difference signal is being generated between the input and output signals, to remove a DC offset component that may be present due to mismatch between VF and VT that would be present during all times, namely, when the difference signal is present and when the difference signal is not present because VF and VT have essentially reached equilibrium. A loss of dynamic range may occur due to integration of the DC offset present during the signal response period (i.e. when VF is different from VT), but that loss would be less compared to the loss of accuracy from integrating a DC signal component during the period which there is essentially no signal response or difference between VF and VT, because the signal response period is approximately 300 nanoseconds in length, whereas the period during which there is no signal response is about 6 microseconds in length, a difference of greater than one order of magnitude. This alternative solution is targeted to cancel the DC offset during the time when there is no signal response. Another exemplary alternative to the integrator hold process is to run the panel driver at a higher frequency, although a high frequency could increase electromagnetic interference. 
         [0028]    To implement this alternative configuration, an inverse hysteresis comparator can be used in integrator hold  218  as a low power solution to determine when the difference between VT and VF settles close to a predetermined amount, such as between 5 mV to 10 mV, and the inverse hysteresis comparator changes the output state at the time when the response from the surface capacitor element ends for a positive and negative edge input. At this time, the input to integrator  204  is disconnected from the output of difference amplifier  202 , to prevent voltage droop during idle time. The inverse hysteresis comparator is described in further detail below. 
         [0029]    When an inverse hysteresis buffer mechanism is not utilized, then a single XOR gate between hysteresis comparator  210  and delay element  212  can be used. If an inverse hysteresis buffer is used, then an additional XOR gate can be utilized between the inverse hysteresis buffer and a switch that is located between difference amplifier  202  and integrator  204  (not explicitly shown). An XOR gate in series with hysteresis comparator  210  and delay element  212  can also be used as a startup circuit for the surface capacitor element frequency measuring solution to ensure that an initial pulse is propagated into the filter chain at the time the closed loop condition is established. This startup process is achieved by applying a high logic pulse to the XOR gate, which acts as an inverter to cause the oscillator loop to become positive, such that system  200  does not oscillate. When the input to the XOR gate goes from logic high to low, a positive edge is fed to the surface capacitive touch screen panel after a predetermined delay. The delay element and XOR 2  gate in  208  create an integrator reset pulse at each point in time where the output driven to the panel changes state (high to low or low to high), but the integrator reset pulse is not a contributing factor in the startup mechanism but rather is used every time the panel driver switches state, even after startup, and by the time the output response from the surface capacitive touch screen panel reaches difference amplifier  202 , oscillation is setup in negative feedback mode as the “startup” signal is low, and system  200  starts to oscillate. 
         [0030]    In operation, system  200  provides a driver circuit for driving a surface capacitive touch screen panel from left to right, right to left, top to bottom and bottom to top, so as to generate an oscillation frequency as a function of the series/parallel resistive-capacitive circuit characteristics of the surface capacitive touch screen panel. In this manner, the touch location can be determined based on a simple frequency measurement instead of using more complex prior art methods. 
         [0031]      FIG. 3  is a diagram of a system  300  utilizing an operational amplifier D 1  in accordance with an exemplary embodiment of the present invention. Operational amplifier D 1  receives power from sources AVDD and AVSS, and receives an input of VT at a positive input across resistance R 2 , with an additional resistance R 3  to ground. Likewise, input VF is received through resistance R 1 . A coupling resistance R 4  can be provided where suitable. Switches S 1  and S 2  can be used in some exemplary embodiments to disconnect the output of D 1  from the following stage, such as integrator  204 . 
         [0032]    In operation, system  300  provides an exemplary difference amplifier for use in a surface capacitive touch screen driver in accordance with novel features of the present invention. 
         [0033]      FIG. 4  is a diagram of a system  400  of an integrator in accordance with an exemplary embodiment of the present invention. System  400  can be used as integrator  204 , and includes operational amplifier D 1 ; which receives power from sources AVDD and AVSS, a positive input tied to ground AGND, and a negative input from a prior stage such as difference amplifier  202  across resistor R 1 . Integrating capacitor C 1  is used to allow operational amplifier D 1  to act as a first order integrator, and switch Si is used to reset the integration mode of system  400 . 
         [0034]    System  400  can also or alternatively be used as a second integrating stage such as integrator  206 , where the input received at the negative input from a prior stage is received from integrator  204 . 
         [0035]      FIG. 5  is a diagram of a system  500  for a hysteresis comparator including start-up and integrator reset functions in accordance with an exemplary embodiment of the present invention. System  500  is shown with an exemplary XOR 1  gate that can be used to provide a startup function, rather than the integrator hold function. While XOR 1  might not be optional, it might not be absolutely needed. The output of XOR 1  can be used as an input to the integrator hold function of system  600 , but where XOR 1  is not implemented, such as where there is no startup function, then the output of the hysteresis comparator or other suitable functionality can be used instead. 
         [0036]    The hysteresis comparator operational amplifier D 1  receives an input from a previous stage, such as integrator  206 , which can output a ramp signal based on the input from integrator  204  or other suitable signals. The output of operational amplifier D 1  is cascaded through delay element DEL whose input and output are fed to XOR 2  to generate a reset pulse for the integrators. The output of delay element DEL is also provided to inverting buffers, one of which drives the panel through output multiplexer, another of which drives the feedback input of difference amplifier  202 , and another of which is used to drive frequency counter  220 . When system  500  is configured as an inverse hysteresis comparator with XOR 1 , a startup signal is also provided as described above. 
         [0037]      FIG. 6  is a diagram of a system  600  for providing integrator hold function control signals in accordance with an exemplary embodiment of the present invention. System  600  includes inverse hysteresis circuit IH 1 , which receives ground signal AGND and the output from XOR 1  of hysteresis comparator  210  where a hysteresis function is provided. The output of inverse hysteresis circuit IH 1  drives XOR to generate switch control signal  1  and inverter INV to generate switch control signal  2 , such as for use with an integrator hold function, a DC offset correction, or other suitable functionality as further described herein. 
         [0038]    In another exemplary embodiment, a time delay circuit can be used in place of inverse hysteresis circuit IH 1 , where the delay time is based on the approximate time that the differential signal is active, and where the integrator function is cut off once the differential signal goes to zero or essentially to zero. In this exemplary embodiment, the required time delay can be independent of the oscillation frequency. In this exemplary embodiment, the connection from system  500  would be from the output of the delay element in that system, rather than from the output of the XOR 1  gate. The delay is approximately equal to the signal delay time through the driver  214  plus the panel plus the difference amplifier. 
         [0039]      FIG. 7  is a diagram of a system  700  for a hysteresis or inverse hysteresis comparator in accordance with an exemplary embodiment of the present invention. System  700  includes a conventional implementation of a hysteresis comparator where hysteresis is achieved by sizing the two load transistors differently in the positive feedback decision circuit. To achieve inverse hysteresis operation, an offset current source is applied to the decision circuit load depending on the edge that has been applied to the surface capacitive touch screen panel (hystout and hystoutb). In this exemplary embodiment, the load transistors have the same size. The same current source can also be used, and can be switched through switches to keep the trip voltage symmetrical with respect to the reference voltage. 
         [0040]      FIG. 8  is a diagram of a system  800  for reducing the number of operational amplifiers required in a surface capacitive touch screen controller in accordance with an exemplary embodiment of the present invention. System  800  receives the hysteresis output Hystout from system  500  into the LATCH circuit, and the state of switch  1  and switch  2  from system  600  controls whether op amp D 1  is used to drive the difference amplifier or the hysteresis comparator, which have duty cycles that allow a single op amp to be utilized. Nodes  1  and  2  control corresponding switches that reconfigure the resistive structure around op amp D 1  to allow it to be utilized alternatively as a difference amplifier and hysteresis comparator. Nodes  1  and  2  also control the hold function at the input of the first integrator, and node  2  also controls the open/closed state of the LATCH circuit. Because the surface capacitive touch screen controller oscillates at frequencies close to 200 Khz, the refresh times are long enough to allow a single op amp to be used for the difference amplifier and the hysteresis comparator. 
         [0041]      FIG. 9  is a diagram of a waveform  900  showing attributes of a system for use in accordance with an exemplary embodiment of the present invention. Waveform  900  includes times T 1  and T 2 , which are the times at which the difference between 1) the signal applied to the input of the surface capacitive touch screen that is driven as described, and 2) the corresponding signal that is measured at the output of the driven surface capacitive touch screen, reach a maximum value and a first break point. In a surface capacitive touch screen element, applying a driver signal to the shorted left-right or top-bottom nodes can create an output that differs from the driver signal, where the difference signal characteristically includes the T 1  and T 2  breakpoint times, where T 1  represents the time the signal is applied or removed, and T 2  is a function of the location where the surface capacitive touch screen element has been touched. 
         [0042]    As shown in waveform  900 , DC offset values may exist due to variations in circuitry values. Integrating the waveforms over the periods where the differential output is essentially zero can create inaccurate position measurements. By using the disclosed embodiment of an inverse hysteresis comparator, or alternatively a time delay circuit, to dynamically determine the point at which the differential signal has essentially reached zero thereby compensating for any DC offset, a more accurate determination of the location at which the surface capacitive touch screen element has been touched can be obtained. 
         [0043]      FIG. 10  is a diagram of an algorithm  1000  for calibrating a touch screen element and determining a location at which a touch screen element has been touched in accordance with an exemplary embodiment of the present invention. Algorithm  1000  can be used with a surface capacitive touch screen element having four corner electrodes at locations arbitrarily referred to as “top left,” “top right,” “bottom left” and “bottom right,” or other suitable touch screen elements. Algorithm  1000  can be implemented in conjunction with a general purpose processor to create a special purpose processor, or can be implemented using hardware elements such as application-specific integrated circuits, field-programmable gate arrays, digital signal processors or other suitable hardware. 
         [0044]    Algorithm  1000  begins at  1002 , where a touch indicator is generated. In one exemplary embodiment, a touch indicator can be generated using a visual display that is oriented with the touch screen element, so as to allow the location of the visual display to be correlated with the location at which the touch screen element is touched. Likewise, multiple touch indicators can be generated, such as where the touch screen element is capable of generating signals that allow multiple touch locations to be discriminated. The algorithm then proceeds to  1004 . 
         [0045]    At  1004 , a left-right multiplexer control is generated. In one exemplary embodiment, a multiplexer is used to couple the top left and bottom left electrodes of the touch screen element as a first connection and the top right and bottom right electrodes of the touch screen element as a second connection so as to form a circuit element from the touch screen element to which a signal can be input at the left side and measured as an output at the right side. Other suitable processes can also or alternatively be used. The algorithm them proceeds to  1006 , where a frequency is measured. As previously discussed, a baseline oscillation frequency may exist when there is no contact with the touch screen element, and as contact is made at the left side and moved towards the right side, the frequency can change, such as by increasing or decreasing, based on the design of the touch screen element. The change can be linear or otherwise variable as a function of location. After the frequency has been measured, the algorithm proceeds to  1008 . 
         [0046]    At  1008 , a right-left multiplexer control is generated. In one exemplary embodiment, a multiplexer is used to couple the top right and bottom right electrodes of the touch screen element as a first connection and the top left and bottom left electrodes of the touch screen element as a second connection so as to form a circuit element from the touch screen element to which a signal can be input at the right side and measured as an output at the left side. Other suitable processes can also or alternatively be used. The algorithm them proceeds to  1010 , where a frequency is measured. As previously discussed, a baseline oscillation frequency may exist when there is no contact with the touch screen element, and as contact is made at the right side and moved towards the left side, the frequency can change, such as by increasing or decreasing, based on the design of the touch screen element. The change can be linear or otherwise variable as a function of location. After the frequency has been measured, the algorithm proceeds to  1012 . 
         [0047]    At  1012 , a top-bottom multiplexer control is generated. In one exemplary embodiment, a multiplexer is used to couple the top left and top right electrodes of the touch screen element as a first connection and the bottom left and bottom right electrodes of the touch screen element as a second connection so as to form a circuit element from the touch screen element to which a signal can be input at the top side and measured as an output at the bottom side. Other suitable processes can also or alternatively be used. The algorithm them proceeds to  1014 , where a frequency is measured. As previously discussed, a baseline oscillation frequency may exist when there is no contact with the touch screen element, and as contact is made at the top side and moved towards the bottom side, the frequency can change, such as by increasing or decreasing, based on the design of the touch screen element. The change can be linear or otherwise variable as a function of location. After the frequency has been measured, the algorithm proceeds to  1016 . 
         [0048]    At  1016 , a bottom-top multiplexer control is generated. In one exemplary embodiment, a multiplexer is used to couple the bottom left and bottom right electrodes of the touch screen element as a first connection and the top left and top right electrodes of the touch screen element as a second connection so as to form a circuit element from the touch screen element to which a signal can be input at the bottom side and measured as an output at the top side. Other suitable processes can also or alternatively be used. The algorithm them proceeds to  1018 , where a frequency is measured. As previously discussed, a baseline oscillation frequency may exist when there is no contact with the touch screen element, and as contact is made at the bottom side and moved towards the top side, the frequency can change, such as by increasing or decreasing, based on the design of the touch screen element. The change can be linear or otherwise variable as a function of location. After the frequency has been measured, the algorithm proceeds to  1020 . 
         [0049]    At  1020 , the calibration frequencies are stored. In one exemplary embodiment, an error signal can be generated if calibration failed, such as if the measured frequencies did not correlate with the expected location, and the calibration process can be repeated. Likewise, the frequencies measured at the different algorithm steps can be compared with predetermined frequency variation models for the touch screen element, such as to verify that the location associated with the frequency measured at  1006  correlates with the location associated with the frequency measured at  1010 , to verify that the location associated with the frequency measured at  1014  correlates with the location associated with the frequency measured at  1018 , or for other suitable purposes, such as where multiple touch screen locations can be measured. The algorithm then proceeds to  1022 . 
         [0050]    At  1022 , a touch indication is received. In one exemplary embodiment,  1022  can be separate in time from the calibration procedure, and can be performed after the touch screen element has been turned off, relocated, or otherwise separated from the calibration procedure. The touch indication can be received in response to a touch input detection control, such as after a display has been generated to which a user touch response is expected. Alternatively, the touch indication can be based on a change in frequency, impedance, or other electrical circuit changes. The algorithm then proceeds to  1024 . 
         [0051]    At  1024 , the multiplexer and touch screen controller are cycled to measure the frequencies corresponding to the different combinations of touch screen element electrodes. The algorithm then proceeds to  1026 , where it is determined whether a touch location has been determined. If a touch location has not been determined, such as if conflicting frequency measurements have been recorded, the algorithm returns to  1024 , otherwise the algorithm proceeds to  1028  where location data is generated identifying where the touch screen element has been touched. 
         [0052]    In operation, method  1000  allows a touch screen element to be operated in a novel manner so as to allow the touch screen element to be used to identify a location at which a user has touched the touch screen element in a simpler and more accurate manner that only requires measurement of frequencies, instead of the more complicated prior art processes. 
         [0053]    While certain exemplary embodiments have been described in detail and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention. It will thus be recognized to those skilled in the art that various modifications may be made to the illustrated and other embodiments of the invention described above, without departing from the broad inventive scope thereof. It will be understood, therefore, that the invention is not limited to the particular embodiments or arrangements disclosed, but is rather intended to cover any changes, adaptations or modifications which are within the scope and the spirit of the invention defined by the appended claims.