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Capacitive pressure sensor having circuitry for eliminating stray capacitance

  • US 5,424,650 A
  • Filed: 09/24/1993
  • Issued: 06/13/1995
  • Est. Priority Date: 09/24/1993
  • Status: Expired due to Term
First Claim
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1. A sensing circuit, comprising:

  • a variable sensing capacitor having first and second capacitor plates with a capacitance between the plates which varies as a function of a sensed parameter, each of the capacitor plates having stray capacitance relative to guard plates arranged around the first and second capacitor plates;

    a reference potential;

    a drive circuit providing an alternating drive potential to the first capacitor plate;

    a differential amplifier having a non inverting input connected to the reference potential and generating a virtual reference potential at a negative input which is substantially equal to the reference potential and having an output related to the sensed parameter; and

    switching circuitry connected to the second capacitor plate and connecting the second capacitor plate alternately to the reference potential and the virtual reference potential at the negative input of the differential amplifier such that there is substantially no potential difference between the second capacitor plate and the guard plates.

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