Method and apparatus for minimizing system oscillations caused by

Abstract

An apparatus and method for canceling system oscillations caused by acoustical coupling is provided. The invention can be implemented in a low voltage environment and as an integrated circuit. Audio voltage signals generated by a microphone are provided as input to a data/fax/voice modem. The data/fax/voice modem processes the audio voltage signals and outputs differential transmit voltage signals to a hybrid/daa circuit for converting to a two-wire (tip and ring) circuit before connecting to a communication device such as a land based telephone or a cellular radio. Audio voltage signals generated by the communication device are provided via a two-wire (tip and ring) circuit to the hybrid/daa circuit for converting into a four-wire circuit and then provided as input to the data/fax/voice modem as differential receive voltage signals. The differential transmit voltage signals are amplified and phase shifted so that they are out of phase relative to the differential receive voltage signals which are also amplified. The differential transmit voltage signals and the differential receive voltage signals are then added together. The combined signals are then output to an audio speaker.