| 摘要 |
PURPOSE:To decrease the required number of bits of a D/A converter by providing two adaptive digital filters and canceling roughly echo by one filter and then canceling the remaining echo by the other. CONSTITUTION:An output of the D/A converter 9 is inputted to the adaptive digital filter (ADF1)51 via switches 141, 142 by a signal from a timing generating circuit 15. An output of the ADF151 is supplied to an adder 131 via D/A converters 61, 62 and an echo replica depending on the transmission data supplied to an input terminal 1 appears at an output of the adder 131. In the 2nd step next, the switches 141, 142 are switched, an output of the converter 9 is given to the adaptive digital filter (ADF2)52, which starts an operation properly. This is operated so as to decrease the residual echo appearing at the output of a subtractor 71. |
