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Signal modulation across capacitors

  • US 5,654,984 A
  • Filed: 12/03/1993
  • Issued: 08/05/1997
  • Est. Priority Date: 12/03/1993
  • Status: Expired due to Term
First Claim
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1. A circuit for communicating a signal across an isolation barrier, said circuit comprising:

  • a modulator for receiving an analog input signal and for providing a modulated signal;

    a capacitor coupling said modulated signal across an isolation barrier;

    a demodulator for receiving said modulated signal and for providing an output signal;

    a filter circuit coupled to a telephone line and to said modulator for providing an analog input signal to said modulator, said filter circuit and said modulator powered from said telephone line;

    a lowpass filter coupled to said demodulator for filtering said output signal, said modulator comprising a sigma delta modulator circuit and said filter circuit comprising an anti-alias and highpass filter;

    a second filter circuit for filtering a second signal, said second filter circuit comprising a second anti-alias and highpass filter;

    a second modulator coupled to said second filter circuit for receiving said second signal from said second filter circuit and for producing a second modulated signal, said second modulator comprising a second sigma delta modulator circuit;

    a second capacitor coupled to said second modulator for coupling said second modulated signal across said isolation barrier;

    a second demodulator coupled to said second capacitor for receiving said second modulated signal from said second capacitor and for producing a second output signal;

    a second lowpass filter coupled to said second demodulator for filtering said second output signal;

    said signal being communicated in a first direction across said isolation barrier and said second signal being communicated in an opposite direction across said isolation barrier;

    a dock oscillator for producing a dock signal;

    a third capacitor coupled to said dock oscillator for coupling said dock signal across said isolation barrier;

    a dock receiver for receiving said dock signal from said third capacitor.

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