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Signal extraction apparatus and method

  • US 5,115,128 A
  • Filed: 12/29/1989
  • Issued: 05/19/1992
  • Est. Priority Date: 01/06/1989
  • Status: Expired due to Fees
First Claim
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1. A signal extraction apparatus comprising:

  • a modulating signal generator;

    light generating means for generating a drive signal comprising a carrier signal amplitude modulated by a modulating signal from said modulating signal generator;

    coupling means for coupling the drive signal to a resonant sensor having a resonant frequency substantially equal to a frequency of the modulating signal;

    a demodulator comprising a photodetector for demodulating a portion of the drive signal reflected by the sensor; and

    frequency determining means for determining changes in the resonant frequency of the sensor, said modulating signal generator comprisinga voltage controlled oscillator having an output and a control voltage input,a low pass filter having an output connected to said control voltage input of said voltage controlled oscillator and an input,a phase sensitive detector having an output connected to said input of said low pass filter, a first input connected to said output of said voltage controlled oscillator and a second input connected to said demodulator, anddivide-by-two frequency divider having an input connected to said output of said voltage controlled oscillator and an output connected to said generating means.

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