Signal modulation across capacitors

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, 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.

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.

A circuit for communicating a signal across an isolation barrier, said circuit comprising:

• 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.