Touch panel system

• US 4,698,460 A
• Filed: 08/26/1986
• Issued: 10/06/1987
• Est. Priority Date: 08/26/1986
• Status: Expired due to Term

• Current Assignee: Tektronix Incorporated (Fortive Corp.)
• Original Assignee: Tektronix Incorporated (Fortive Corp.)
• Inventors: Krein, Philip T., Murdock, Bruce, Teichmer, Daniel G., Meadows, Robert D.
• Primary Examiner(s): SCHREYER, STAFFORD
• Application Number:
  US06/900,646
• Time in Patent Office: 406 Days
• Field of Search: 178/19, 178/18, 178/20, 340/712, 340/706, 364/520, 364/518
• US Class Current: 345/173
• CPC Class Codes: G06F 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment
• CPC Class Codes: G06F 3/045 using resistive elements, e.g. a single continuous surface or two parallel surfaces put in contact

Abstract

A touch panel has panel scanning signals selectively applied to the four sides of a touch sensing surface of the panel so as to establish alternating current voltage gradients in desired directions across the touch sensing surface. When the panel is touched, touch signals or currents result and are utilized by a touch location circuit in determining the location of touch. The impedance touch current resulting from a user'"'"'s touch may also be determined and used. The touch panel circuit automatically compensates for changes in impedance touch current, such as result when users touch the panel with ungloved and gloved fingers. An analog multiplier is included in the touch location circuit to improve noise rejection. Auto nulling and automatic frequency adjustment is included in the touch panel device, together with overcurrent protection circuitry.

Claims

1. A touch panel device for determining the touch location at which a touch sensing surface of the device is touched comprising:

signal generator means for producing an alternating-current voltage output;

panel scanning signal applying means for applying panel scanning signals to the touch sensing surface, the panel scanning signal applying means having an input coupled to the first signal generator output, the panel scanning signal applying means having first and second panel scanning outputs comprising respective first and second alternating-current voltage panel scanning signals which are driven by the signal generator output and which are one hundred and eighty degrees out of phase from one another;

touch signal detection means having inputs coupled to the first and second panel scanning outputs and a touch signal output, the touch signal detection means comprising means for producing touch current signals at the touch signal output corresponding to the difference between the first and second panel scanning signals at the touch sensing output;

switching means for selectively coupling the first and second panel scanning outputs to the touch sensing surface so as to selectively apply the first and second panel scanning signals to the touch sensing surface and generate touch current signals at the touch sensing output upon touching the panel;

panel output signal processing means including an analog multiplier means with a first input coupled to the touch signal output for receiving the touch current signals, the analog multiplier means having a second input coupled to the second signal generator output for receiving reference signals derived therefrom and a multiplier output, the analog multiplier means comprising means for multiplying the received touch current signals and received reference signals to provide multiplier output signals corresponding to the received touch current signals, integrator circuit means having an integrator input coupled to the multiplier output for receiving the multiplier output signals, the integrator circuit means also having an integrator output, the integrator circuit means comprising means for integrating the multiplier output signals over integration time periods to provide an analog output of integrated multiplier output signals corresponding to the touch current signals during such integration time periods, analog to digital converter means having a converter input coupled to the integrator output for receiving the integrated multiplier output signals and for converting the integrated multiplier output signals to corresponding digital touch current signals, the analog to digital converter means having a converter output at which the digital touch current signals are provided; and

the panel output signal processing means also including processor circuit means having an input coupled to the converter output for receiving the digital touch current signals and comprising means for determining the touch location from the digital touch current signals, the processor circuit means having a synchronization input coupled to the second signal generator output and including means coupled to the integrator circuit means for synchronizing the integration time periods to the signal generator reference signal.

2. A touch panel device according to claim 1 in which the panel output signal processing means includes means for interrupting the application of panel scanning signals to the touch sensing surface when at least one of the touch current signals exceed a predetermined magnitude.

3. A touch panel device according to claim 1 in which the panel output signal processing means includes means for adjusting the duration of integration time periods so as to adjust the magnitude of the integrated touch current signals to a magnitude which is greater than a predetermined minimum magnitude and less than a predetermined maximum magnitude.

4. A touch panel device according to claim 1 in which the panel output signal processing means includes means for adjusting the duration of the integration time periods between minimum and maximum time periods so as to adjust the magnitude of the integrated touch current signals, the panel output signal processing means including means for interrupting the application of panel scanning signals to the touch sensing when at least one of the touch current signals are greater than a predetermined magnitude and the integration time period is of the minimum duration.

5. A touch panel device according to claim 1 which has a first positive voltage supply and a second negative voltage supply, the touch sensing surface has four sides and a respective set of voltage clamping diodes coupled to each of the sides of the touch sensing surface, each set of clamping diodes comprising a first diode with its cathode coupled to the touch sensing surface and its anode coupled to the negative voltage supply and a second diode with its cathode coupled to the positive voltage supply and its anode coupled to the touch sensing surface, the touch panel device also including a first zener diode with its anode coupled to ground and its cathode coupled to the positive voltage supply and a second zener diode with its cathode coupled to ground and its anode coupled to the negative voltage supply, whereby voltages across the touch sensing surface are limited to thereby protect the touch sensing surface.

6. A touch panel device according to claim 1 in which the switching means comprises means for selectively coupling one of the first and second panel scanning outputs to a first side of the touch sensing surface and the other of the first and second panel scanning outputs to a second side of the touch sensing surface, the second side being located across the touch sensing surface in a first direction from the first side, so as to establish a voltage gradient across the touch sensing surface in the first direction from the first to the second sides and so as to provide a first touch current signal at the touch signal output when the touch sensing surface is touched, the switching means also comprises means for selectively and simultaneously coupling one of the first and second panel scanning outputs to the first and second sides of the touch sensing surface to provide an impedance touch current signal at the touch signal output when the touch sensing surface is touched, and the panel output signal processing means comprises means for determining the touch location along the first direction from the first and impedance touch current signals.

7. A touch panel device according to claim 1 in which the switching means comprises means for selectively coupling one of the first and second panel scanning outputs to a first side of the touch sensing surface and the other of the first and second panel scanning outputs to a second side of the touch sensing surface, the second side being located across the touch sensing surface in a first direction from the first side, so as to establish a voltage gradient across the touch sensing surface in the first direction from the first to the second sides and so as to provide a first touch current signal at the touch signal output when the touch sensing surface is touched, the switching means also comprising means for selectively coupling one of the first and second panel scanning outputs to a third side of the touch sensing surface and the other of the first and second panel scanning outputs to a fourth side of the touch sensing surface, the fourth side being located across the touch sensing surface in a second direction from the first side, so as to establish a voltage gradient across the touch sensing surface in the second direction from the third to the fourth sides and so as to provide a second touch current signal at the touch signal output when the touch sensing surface is touched, the switching means comprising means for selectively and simultaneously coupling one of the first and second panel scanning outputs to at least one of the first, second, third and fourth sides of the touch sensing surface to provide an impedance touch signal at the touch signal output when the touch sensing surface is touched, and the panel output signal processing means comprises means for determining the touch location along the first and second directions from the first, second and impedance touch current signals.

8. A touch panel device according to claim 7 in which the panel signal applying means comprises transformer means having a primary winding means coupled to the first signal generator output so as to be driven by the signal generator means, the transformer means also having a secondary winding means with first and second secondary winding outputs comprising the first and second panel scanning signal outputs, and a center tap comprising the touch signal output, the secondary winding means providing the panel scanning signals as the primary winding means is driven by the signal generator output, and the first, second and impedance touch current signals being generated at the center tap.

9. A touch panel device according to claim 1 including a parallel output and a telecommunications serial output, the processor means comprising means for controlling the delivery of touch location signals to the parallel output and to the telecommunications output.

10. A touch panel device according to claim 1 including means responsive to the processor means for automatically nulling the touch current signals when the touch sensing surface is untouched.

11. A touch panel device according to claim 10 in which the signal generator means has a frequency control input and comprises means for producing an alternating current voltage output of a frequency which is variable and controllable in response to frequency control signals at the frequency control input;

and

the panel output signal processing means including signal generator frequency control circuit means coupled to the frequency control input for automatically generating frequency control signals and applying such frequency control signals to the frequency control input, the frequency control means comprising means for automatically generating frequency control signals so as to shift the frequency of the signal generator means output away from fixed interference frequency spectra, such as due to cathode-ray-tube flyback signals, in the environment in which the touch panel is used.

12. A touch panel device for determining the touch location at which a touch sensing surface of the device is touched comprising:

signal generator means for producing an alternating-current voltage output;

panel scanning signal applying means for applying panel scanning signals to the touch sensing surface, the panel scanning signal applying means having an input coupled to the signal generator output, the panel scanning signal applying means having first and second panel scanning outputs of respective first and second alternating-current voltage panel scanning signals which are driven by the signal generator output and which are one hundred and eighty degrees out of phase from one another;

touch signal detection means having inputs coupled to the first and second panel scanning outputs and a touch signal output, the touch signal detection means comprising means for producing touch signals corresponding to the difference between the first and second panel scanning signals at the touch signal output;

switching means for selectively coupling the first and second panel scanning outputs to the touch sensing surface so as to selectively apply the first and second panel scanning signals to the touch sensing surface and generate touch signals at the touch signal output upon touching of the panel;

panel output signal processing means having a first input coupled to the touch signal output for receiving the touch signals, the panel output signal processing means comprising means for determining the touch location from the touch signals; and

the panel output signal processing means including means for automatically stopping the application of the panel scanning signals to the touch sensing surface when the touch signal output exceeds a predetermined level.

13. A touch panel device for determining the touch location at which a touch sensing surface of the device is touched comprising:

signal generator means for producing first and second alternating-current voltage outputs, the signal generator means having a frequency control input and comprising means for producing alternating current voltage outputs of a frequency which is variable and controllable in response to frequency control signals at the frequency control input;

panel scanning signal applying means for applying panel scanning signals to the touch sensing surface, the panel scanning signal applying means having an input coupled to the first signal generator output, the panel scanning signal applying means having first and second panel scanning outputs comprising respective first and second alternating-current voltage panel scanning signals which are driven by the signal generator output and which are one hundred and eighty degrees out of phase from one another;

touch signal detection means having inputs coupled to the first and second panel scanning outputs and a touch signal output, the touch signal detection means comprising means for producing touch current signals at the touch signal output corresponding to the difference between the first and second panel scanning signals at the touch signal output;

switching means for selectively coupling the first and second panel scanning outputs to the touch sensing surface so as to selectively apply the first and second panel scanning signals to the touch sensing surface and generate touch current signals at the touch signal output upon touching the panel;

panel output signal processing means including an analog multiplier means with a first input coupled to the touch signal output for receiving the touch current signals, the analog multiplier means having a second input coupled to the second signal generator output and a multiplier output, the analog multiplier means comprising means for multiplying the signals received at the analog multiplier inputs to provide multiplier output signals corresponding to the received touch current signals, integrator circuit means having an integrator input coupled to the multiplier output for receiving the multiplier output signals, the integrator circuit means also having an integrator output, the integrator circuit means comprising means for integrating the multiplier output signals over integration time periods to provide an analog output of integratd multiplier output signals corresponding to the touch signals during such integration time periods, analog to digital converter means having a converter input coupled to the integrator output for receiving the integrated multiplier output signals and for converting the integrated multiplier output signals to corresponding digital touch current signals, the analog to digital converter means having a converter output at which the digital touch current signals are provided;

the panel output signal processing means also including processor circuit means having an input coupled to the converter output for receiving the digital touch current signals and comprising means for determing the touch location from the digital touch current signals, the processor circuit means having a synchronization input coupled to the second signal generator output and including means coupled to the integrator circuit means for synchronizing the integration time periods to the second signal generator output signals;

the panel output signal processing means including means for adjusting the duration of integration time periods so as to adjust the magnitude of the integrated touch current signals to a magnitude which is greater than a predetermined minimum magnitude and less than a predetermined maximum magnitude;

the switching means comprising means for selectively coupling one of the first and second panel scanning outputs to a first side of the touch sensing surface and the other of the first and second panel scanning outputs to a second side of the touch sensing surface, the second side being located across the touch sensing surface in a first direction from the first side, so as to establish a voltage gradient across the touch sensing surface in the first direction from the first to the second sides and so as to provide a first touch current signal at the touch signal output when the touch sensing surface is touched, the switching means also comprising means for selectively coupling one of the first and second panel scanning outputs to a third side of the touch sensing surface and the other of the first and second panel scanning outputs to a fourth side of the touch sensing surface, the fourth side being located across the touch sensing surface in a second direction from the first side, so as to establish a voltage gradient across the touch sensing surface in the second direction from the third to the fourth sides and so as to provide a second touch current signal at the touch signal output when the touch sensing surface is touched, the switching means comprising means for selectively and simultaneously coupling one of the first and second panel scanning outputs to at least one of the first, second, third and fourth sides of the touch sensing surface to provide an impedance touch current signal at the touch.signal output when the touch sensing surface is touched, and the panel output signal processing means comprises means for determining the touch location along the first and second directions from the first, second and impedance touch current signals;

nulling means controlled by the processor means for automatically nulling the touch current signals when the touch sensing surface is untouched; and

the panel output signal processing means including signal generator frequency control circuit means coupled to the frequency control input for automatically generating frequency control signals and applying such frequency control signals to the frequency control input, the frequency control means comprising means for automatically generating frequency control signals to shift the frequency of the signal generator means output away from fixed frequency interference spectra, such as due to cathode-ray-tube flyback signals, in the environment in which the touch panel is used.

14. A touch panel device according to claim 13 in which the panel signal applying means comprises transformer means having a primary winding means coupled to the first signal generator output so as to be driven by the signal generator means, the transformer means also having a secondary winding means with first and second secondary winding outputs comprising the first and second panel scanning signal outputs and a center tap comprising the touch signal output, the secondary winding means providing the panel scanning signals as the primary winding means is driven by the signal generator output, and the first, second and impedance touch current signals being generated at the center tap.

15. A touch panel device according to claim 14 including a parallel output and a serial telecommunications output, the processor means comprising means for controlling the delivery of touch location signals to the parallel output and to the telecommunications output.