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Capacitive touch panel system with randomly modulated position measurement signal

  • US 4,922,061 A
  • Filed: 07/20/1989
  • Issued: 05/01/1990
  • Est. Priority Date: 06/13/1988
  • Status: Expired due to Term
First Claim
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1. In a display system including a display surface positioned adjacent an optically transparent, electrically conductive layer having a first resistivity and first and second opposed side margins of preselected lengths, a position address encoder for generating an address signal indicative of a location on the conductive layer in contact with a stylus that is electrically connected to a reference potential, comprising:

  • signal generating means for generating a time-varying position measurement signal of a preselected magnitude and a frequency that varies in a substantially random manner;

    first and second electrodes positioned along the lengths of the respective first and second opposed side margins and receiving the position measurement signal generated by the signal generating means, the resistivity of the conductive layer establishing an effective total resistance between the first and second electrodes; and

    current measuring means for measuring currents corresponding to the position measurement signal and drawn through the first and second electrodes whenever a stylus contacts the conductive layer, whereby the stylus contacting the conductive layer divides the total resistance into first and second resistances that cause currents to be drawn through the respective first and second electrodes in proportion to the separation between the electrodes and the location.

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