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Touch panel with automatic nulling

  • US 4,707,845 A
  • Filed: 08/26/1986
  • Issued: 11/17/1987
  • Est. Priority Date: 08/26/1986
  • Status: Expired due to Term
First Claim
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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 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;

    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 touch sensing surface;

    panel output signal processing means having a first input coupled to the touch signal output for receiving the touch current 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 nulling circuit means for automatically nulling the touch current signals when the touch sensing surface is untouched.

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