Adaptive echo canceller using differential pulse code modulation encoding

Claim 1

In an echo canceller of the type having, a transversal filter means for performing convolution of an input signal on a received line and a replica of the impulse response of an echo path to generate an approximation of an echo signal for subtraction from a real echo signal on a send line, and an adaptive control loop responsive to the residual echo resulting from said subtraction and to stored samples of said input signal for incrementally varying said replica to reduce said residual echo, said transversal filter comprising means for sampling said input signal and converting each sample to an (n+1)-bit digital word, means to store a plurality of n-bit digital words corresponding to samples of said input signal and means for replacing the n-bit digital word corresponding to the oldest sample with an n-bit digital word corresponding to each new sample, said adaptive control loop comprising means for varying elements of said replica only in response to said residual echo and said individual stored samples being greater than threshold levels, the improvement comprising, differential pulse code modulation encoding means connected between said sampling means and said means for storing digital words corresponding to samples of said input signals for encoding said (n+1)-bit digital words as n-bit digital words as a function of the difference between said (n+1)-bit digital words and computed estimates of said (n+1)-bit digital words based on the redundancy present in said input signal.