Abstract: Full duplex circuits provide a bi-directional signal path at one port for transmit and receive signals and also provide separation between the transmit and receive signals at their respective ports. To accomplish this, the circuits employ amplifiers arranged in either a bilateral T hybrid or balanced impedance configuration. One application is in a transducer interface, where a single transducer is used as both a speaker/ear phone and a microphone. Another application is in a telephone line interconnect, where the telephone line interface simultaneously transmits and receives electrical signals representing audio data, e.g., voice data. The transducer interface drives a receive signal onto a transducer to create audio output while simultaneously generating a transmit signal from audio input. The telephone line interconnect drives a transmit signal through a transformer to send the transmit signal to a telephone line while simultaneously transferring a receive signal from the telephone line.