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METHODS AND SYSTEMS FOR GUARDING A CHARGE TRANSFER CAPACITANCE SENSOR FOR PROXIMITY DETECTION

  • US 20080042661A1
  • Filed: 10/29/2007
  • Published: 02/21/2008
  • Est. Priority Date: 06/03/2005
  • Status: Active Grant
First Claim
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1. A device for determining a measurable capacitance for proximity detection, the device comprising:

  • a plurality of sensing electrodes;

    a guarding electrode proximate the plurality of sensing electrodes;

    a passive network that includes a filter capacitance; and

    a controller coupled to the plurality of sensing electrodes, the guarding electrode, and the passive network, the controller configured to apply a pre-determined voltage to at least one of the plurality of sensing electrodes using a first switch, apply a first guard voltage to the at least one guarding electrode using a second switch, share charge between at least one of the plurality of sensing electrodes and the passive network such that shared charge is accumulated on the filter capacitance, apply a second guard voltage different from the first guard voltage to the guarding electrode; and

    measure a voltage on the filter capacitance for a number of measurements equal to at least one to produce at least one result to determine the measurable capacitance for proximity detection.

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