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Capacitive circuit for measuring a parameter having a linear output voltage

  • US 4,743,836 A
  • Filed: 12/06/1985
  • Issued: 05/10/1988
  • Est. Priority Date: 12/06/1985
  • Status: Expired due to Term
First Claim
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1. A capacitive electrical circuit for measuring a parameter, comprising:

  • timing circuitry for providing first, second and third clock signals, and for providing a periodic square wave signal;

    a capacitive integrating circuit having an integrator, discharge circuitry, a reference capacitor and a sensing capacitor responsive to the external parameter, one of said capacitors responsive to said square wave signal and the other to its inverse, said square wave signal providing alternative charging and discharging of said reference capacitor and said sensing capacitor, said reference and sensing capacitors providing a charge difference signal indicative of the difference in magnitude of the charge stored therein, said integrator responsive to a reference signal and to said charge difference signal for integrating said charge difference signal and providing an integrated output signal indicative of the magnitude of said charge difference, said discharge circuitry discharging said integrator each half cycle of said square wave signal in response to said first clock signal;

    sampling circuit means including first and second sampling means for alternatively sampling, in alternate half cycles of said square wave signal, said integrated output signal from said capacitive integrating circuit in response to said second and third clock signals, respectively, and providing first and second sampled signals; and

    a differential amplifier, responsive to said reference signal, and responsive to said first and second sampled signals, for providing from the difference in magnitudes therebetween, a linear signal having a magnitude proportional to the magnitude of the capacitance of said parameter responsive sensing capacitor.

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