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Noiseproof digitizing apparatus with low power cordless pen

  • US 5,528,002 A
  • Filed: 07/12/1994
  • Issued: 06/18/1996
  • Est. Priority Date: 07/15/1993
  • Status: Expired due to Fees
First Claim
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1. A noiseproof digitizing apparatus, comprising:

  • a tablet having a plurality of grid conductors disposed along X and Y coordinate axes;

    a cordless pen for transmitting an electric signal to the grid conductors by electrostatic capacity coupling;

    an AC signal generator disposed within the cordless pen for generating an AC signal and applying an output of the AC signal to the cordless pen;

    power supplying means for supplying power to the AC signal generator;

    two conductors disposed at the extreme end of the cordless pen and driven in balance or driven in pseudo balance by the AC signal generator such that electrostatic capacitive coupling between the cordless pen and the grid conductors causes a major balanced AC signal component and two minor unbalanced AC signal components to be produced in the grid conductors in response to the AC signal on the cordless pen;

    signal level measuring means for measuring the level of a signal current resulting from a sum of the major balanced AC signal and a difference of the two minor unbalanced AC signal components produced in the grid conductors;

    means for measuring a frequency of the AC signal; and

    means for processing signal values measured by the signal level measuring means to digitally output a coordinate of the extreme end of the cordless pen.

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