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Coordinate input apparatus

  • US 5,684,277 A
  • Filed: 07/27/1995
  • Issued: 11/04/1997
  • Est. Priority Date: 07/29/1994
  • Status: Expired due to Fees
First Claim
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1. A coordinate input apparatus comprising:

  • a vibration transmission plate;

    input means for inputting a vibration onto said vibration transmission plate;

    vibration detection means for detecting at a plurality of detection positions an elastic wave vibration input to said vibration transmission plate;

    envelope output means for outputting an envelope signal of a detection signal from said vibration detection means;

    reference signal generation means for generating a reference signal by attenuating the envelope signal and adding a predetermined offset to the attenuated envelope signal;

    base signal generation means for generating a second-order differential signal of the detection signal from said vibration detection means as a base signal;

    gate signal generation means for comparing the reference signal and the base signal and generating a gate signal with a predetermined time width from a point where the base signal exceeds the reference signal;

    group delay detection means for detecting an inflection point of the envelope signal during a duration of the gate signal, and detecting a group delay time of the vibration with reference to the detected inflection point;

    phase delay detection means for detecting a zero cross point in a predetermined order of the envelope signal in the ON duration of the gate signal, and detecting a phase delay time of the vibration with reference to the detected zero cross point; and

    calculation means for calculating an input coordinate position of said input means on the basis of the group and phase delay times.

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