FAST CONVERGENCE METHOD AND SYSTEM FOR ECHO CANCELLER

An echo canceller for cancelling echoes which result from impedance mismatching in a two-wire/four-wire conversion circuit. The prior art employed an input terminal, an output terminal, a transmitter section, a receiver section, a digital-to-analog converter, an adaptive digital filter, a subtractor, a sample hold circuit, an analog-to-digital converter, a multiplier, a low pass filter, a hybrid circuit, and a two-wire communication path, for the purpose of generating a replica of the echo signal to cancel such echos. A method has also been proposed which employs a polarity discriminator circuit instead of an analog-to-digital converter, and utilizes approximation algorithms to correct an adaptive digital filter tap coefficient using the signs of an error signal. In order to carry out this alternative method, the invention employs a fast convergence system comprising a circuit for generating an echo replica in response to a transmit signal, a circuit for producing a difference signal by subtracting the echo replica from a signal which contains a receiver signal and echo, a circuit for multiplying and averaging the difference signal and a polarity of the echo replica, a circuit for absorbing a fluctuation in an absolute value of the averaged output, and a circuit for adaptively varying a tap correction amount of a filter of the echo canceller in response to an output of the fluctuation absorbing circuit.