Echo canceller for two-wire full duplex digital data transmission

Claim 1

An echo canceller for a two-wire full duplex digital data transmission system comprising: an adaptive digital filter containing a transversal filter with a plurality of taps for generating an echo replica signal by estimating adaptively time-varying transfer characteristics of an echo path in order to suppress an echo signal from said echo path; means for producing a residual echo signal by obtaining the difference between said echo signal and said echo replica signal at a tail portion of an impulse response of said adaptive digital filter; low frequency component supressor means for suppressing low frequency components contained in said residual echo signal, said suppressor means being installed in parallel with the final stage of said adaptive digital filter to effectively increase the number of taps of said transversal filter, said suppressor means including: first order recursive filter means responsive to said residual echo signal and an output from said final stage of said adaptive digital filter for producing a waveform of said low frequency components, tap coefficient updating means responsive to said waveform of said low frequency components and said residual echo signal for updating a tap coefficient to produce an updated tap coefficient, and first multiplier means for multiplying said waveform of said low frequency components by said updated tap coefficient to produce a low frequency component replica which is used to cancel said low frequency components.