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Charge balance network with floating ground capacitive sensing

  • US 6,316,948 B1
  • Filed: 07/01/1998
  • Issued: 11/13/2001
  • Est. Priority Date: 07/01/1998
  • Status: Expired due to Fees
First Claim
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1. A system for generating a signal which is a predetermined function of the capacitance of a sensor capacitor, comprising:

  • A. a sensor network including a reference capacitor and said sensor capacitor coupled in series, said reference capacitor being coupled between an input terminal and a junction terminal, and said sensor capacitor being coupled between said junction terminal and a system ground;

    B. a switching network including a switch element having a first state and a second state, and a switch control having means for cyclically alternating said switch network between said first state and said second state;

    C. a feedback network including an amplifier coupled by way of a demodulator to an integrator, said amplifier and integrator being coupled between an upper voltage supply terminal and a lower voltage supply terminal, said upper supply terminal being coupled to a first reference potential and said lower voltage supply terminal coupled to a second reference potential, said first reference potential being a fixed, predetermined voltage above said second reference potential and independent of said system ground, said feedback network being coupled to said sensor network and said switching network, and including means for generating a feedback signal at a feedback terminal, said feedback signal being representative of the difference in charge stored on said series capacitors from a predetermined value;

    D. a voltage driving element for providing said first reference potential voltage, said driving means being responsive to at least one of a plurality of signals from said switching network;

    wherein said switching network is operative to (i) electrically couple, while in said first state, an input of said voltage driving element with said feedback signal and said sensor input terminal with said second reference potential, and (ii) electrically couple, while in said second state, said input of said voltage driving element with said second reference potential, and said sensor input with a third reference potential, whereby an average change in charge stored on said series capacitors over each cycle is substantially equal to said predetermined value, said feedback signal being said predetermined function of the capacitance of said sensor capacitor.

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