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Circuit arrangement for determining differences in capacitance

  • US 5,629,629 A
  • Filed: 04/04/1996
  • Issued: 05/13/1997
  • Est. Priority Date: 04/06/1995
  • Status: Expired due to Fees
First Claim
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1. A circuit arrangement for determining a difference between a capacitance of a first capacitor and a capacitance of a second capacitor, comprising:

  • a differential amplifier having an inverting input and a non-inverting input and having an output, a positive current source that delivers a current with a constant current intensity and a first flow direction, a negative current source that delivers a current with constant current intensity and a second flow direction opposite to the first flow direction, a ground terminal, a control device, a first switch device and a second switch device;

    said first switch device having first and second switch positions, in the first switch position the positive current source being connected to the inverting input of the differential amplifier and in the second switch position the negative current source being connected to the inverting input of the differential amplifier;

    the non-inverting input of said differential amplifier connected to the ground terminal;

    said second switch device configured such that in a first switch position a first terminal of the first capacitor is connected to the inverting input of the differential amplifier and a first terminal of the second capacitor is connected to the non-inverting input of the differential amplifier, and such that in a second switch position the first terminal of the first capacitor is connected to the non-inverting input of the differential amplifier and the first terminal of the second capacitor is connected to the inverting input of the differential amplifier;

    second terminals of said first and second capacitors connected to the output of said differential amplifier and to an input of said control device;

    said control device synchronously switching said first switch device and said second switch device;

    device for determining a time between two switching events and the voltage occurring at the first and second capacitors, for adding said times and for determining values required for defining a difference in capacitance between the first and second capacitances.

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