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Echo cancelling device

  • US 4,007,341 A
  • Filed: 05/12/1975
  • Issued: 02/08/1977
  • Est. Priority Date: 05/24/1974
  • Status: Expired due to Term
First Claim
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1. Echo canceller comprising a transversal filter, to form a synthetic echo signal y (t) effecting a convolution of N samples X (t) each coded on n bits of a received signal x (t), recorded in a first memory and of N filtration weighting samples C obtained by correlation of the residual echo signal ε

  • (t) and of the samples X(t) and recorded in a second memory, a digital subtractor forming the residual echo signal ε

    (t) coded on n bits based on the true echo signal y (t) and on the synthetic echo signal y (t), means for determining the absolute value of the residual echo signal, means for determining the sign of the variations of the weighting coefficients, and means including an adaptive control loop for adjusting the filtration weighting coefficients C from the absolute value of the said residual echo signal and from the correlation of the signs of N samples X (t) of the received signal and of the residual echo signal determining the sign of each of the variations of the filtration weighting coefficients C, said filtration weighting coefficients C in said first memory being less than 2n, and being recorded in the said second memory each on n + m bits, said adaptive control loop including a first adder having (n + m) first inputs receiving the successive filtration weighting coefficients and having (n + m) second inputs receiving the residual echo signal ε

    (t) multiplied by a coefficient α

    close to zero and accompanied by the sign of the correlation of the signs effected, m being the minimum number of bits necessary for representing the reverse of the coefficient α

    , said second adder sending out the filtration weighting coefficients to the said second memory to which it is looped.

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