Conference telephone using dynamic modeled line hybrid

Abstract

A speaker telephone for use with a two wire telephone system and incorporating an audio input circuit for receiving an audio signal to be transmitted over a conventional two-wire telephone system is disclosed. A transmitted signal processing circuit for receiving the audio signal and altering the audio characteristics provides the altered audio signal at the output of the signal processing circuit to the input of the two wire telephone system. A first line hybrid echo canceler is coupled to receive the output of the transmitted signal processing circuit and produce a plurality of first echo outputs in response to the transmitted signal processing circuit output and has a first error signal input. A first difference circuit has an input of first polarity and is coupled to the output of the input coupling circuit, and inputs of opposite polarity coupled to the echo outputs of the first line hybrid echo canceler. The difference circuit has a difference output producing the difference between signals present at the first polarity input and a pair of opposite polarity inputs. The output of the first difference circuit is coupled to the first error signal input. An audio output circuit is coupled to the output of the difference circuit and has an electrical output coupled to a loudspeaker.