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One terminal capacitor interface circuit

  • US 7,235,983 B2
  • Filed: 03/08/2006
  • Issued: 06/26/2007
  • Est. Priority Date: 03/09/2005
  • Status: Active Grant
First Claim
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1. A one terminal capacitor interface circuit for sensing the capacitance of a capacitor comprising:

  • a differential integrating amplifier having an input common mode voltage and two summing nodes whose voltage is substantially equal to said input common mode voltage;

    a switching circuit for charging said capacitor to a first voltage level in a first phase, connecting, in a second phase, said capacitor to one of said summing nodes of said differential amplifier to provide a first output change substantially representative of the difference between said first voltage level and said input common mode voltage, and also representative of said capacitor;

    charging said capacitor to a second voltage level in a third phase, and connecting, in a fourth phase, said capacitor to the other summing node of said differential amplifier to provide a second output change substantially representative of the difference between said second voltage level and said input common mode voltage, and also representative of said capacitor;

    the combined first and second output changes representing the capacitance of said capacitor substantially independent of said input common mode voltage.

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