Echo canceller using impulse response estimating method

Claim 1

An echo canceller using an FIR filter for removing an echo from at transmission input signal, the echo resulting from a reflection of a received signal through an echo path, comprising: a first memory for storing N latest samples of the received signal; a second memory for storing an N-th order impulse response of the echo path; a first delay circuit for delaying the received signal by M samples; a third memory for storing N samples of an output of said first delay circuit; a second delay circuit for delaying the transmission input signal by M samples; a first convolution circuit for multiplying and adding the outputs of said first and second memories; a second convolution circuit for multiplying and adding the outputs of said second and third memories; a first subtractor for subtracting the output of said first convolution circuit from the transmission input signal to produce a transmission output signal; a second subtractor for subtracting the output of said second convolution circuit from the output of said second delay circuit; a first correction amount calculating circuit for determining a first correction amount on the basis of the transmission output signal from said first subtractor and said received signal; a first multiplier for multiplying said first correction amount by the output of said first memory; `a first adder for adding the output of said first multiplier to the impulse response from said second memory; a second correction amount calculating circuit for determining a second correction amount on the basis of the output of said second subtractor and the output of said first delay circuit; a second multiplier for multiplying said second correction amount by the output of said third memory; and a second adder for adding the output of said second multiplier to the output of said first adder and feeding back the resulting sum to said second memory.