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Capacitive touch entry apparatus using drive pulse signals of different phases

  • US 5,526,294 A
  • Filed: 04/27/1990
  • Issued: 06/11/1996
  • Est. Priority Date: 04/28/1989
  • Status: Expired due to Fees
First Claim
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1. A key input device comprising:

  • a dielectric base;

    a plurality of spaced key input electrodes formed on a first surface of the base;

    spaced signal input electrodes formed on an opposite surface of the base and respectively positioned in opposing relation to the key input electrodes, the signal input electrodes being separated into first and second groups;

    signal output electrodes formed on the opposite surface of the base and respectively positioned in opposing relation to the key input electrodes, the signal output electrodes being separated into first and second groups spaced from corresponding groups of the signal input electrodes;

    oscillation means for delivering a constant frequency signal to the signal input electrodes of the first group;

    phase shifting means connected between the oscillation means and the second group of signal input electrodes for providing them with a phase shifted constant frequency signal; and

    a plurality of level detecting means connected to respective signal output electrodes for detecting any voltage change thereat, which exceeds a threshold reference level--indicative of capacitive coupling contact with a key input electrode in excess of stray capacitance between key input electrodes.

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