Signal modulation across capacitors
First Claim
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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Accused Products
Abstract
A method and apparatus for communicating a modulated signal across an isolation barrier using capacitors is provided. The present invention allows low distortion communication of an audio signal across an isolation barrier without the need for a large and bulky isolation transformer. The present invention may be used to provide telephone line isolation for modem applications compliant with governmental regulations. A line interface integrated circuit (IC) may be connected directly to a telephone line and powered by the telephone line. The line interface IC may include a sigma delta modulator to communicate the receive signal across a capacitor over an isolation barrier and a digital-to-analog (D/A) converter to provide an analog transmit signal from a sigma delta bit stream communicated across a capacitor over an isolation barrier. Circuitry on the opposite side of the isolation barrier includes similar components to process the transmit and receive signals.
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Citations
14 Claims
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1. A circuit for communicating a signal across an isolation barrier, said circuit comprising:
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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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2. A circuit for communicating a signal across an isolation barrier, said circuit comprising:
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a modulator for receiving an analog input signal and for providing a modulated signal; a capacitor coupling said modulated signal across an isolation barrier, said isolation barrier not including a transformer element; 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. - View Dependent Claims (3, 4, 5, 6, 7, 8, 9, 10)
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11. A circuit for communicating a signal across an isolation barrier, said circuit comprising:
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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.
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12. A circuit for communicating a signal across an isolation barrier, said circuit comprising:
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a sigma delta modulator for receiving an analog input signal and for providing a modulated signal; a capacitor coupling said modulated signal across an isolation barrier; a sigma delta demodulator coupled to said isolation barrier for receiving said modulated signal and for providing a digital output signal; and 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. - View Dependent Claims (13, 14)
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Specification