| 摘要 |
PURPOSE:To execute the retraining without making each training signal overlap even if a variation of a circuit is detected automatically except when connecting the circuit, in an echo cancelling system for estimating an echo characteristic by transmitting a training signal. CONSTITUTION:When a circuit is connected, control signals C7, C3 operate a controlling circuit 16 in accordance with an outgoing call or an incoming call, and in case of the outgoing side, a control signal C1 is made to ''01'' preferentially, a training signal is selected from a selecting circuit 12, is sent out to an echo canceller 13 and a hybrid circuit 14, subsequently for a prescribed time of T1+T1, the signal C1 is made to ''00'', and after that, it is made to ''10'', and a transmission signal from a telephone set 15 is selected, by which a call can be executed. In case of the incoming side, the signal C1 is made to ''00'' for a prescribed time, and after that, it is made to ''01'' for a time of T1, is made to ''10'' by sending out the training signal, by which a call of the telephone set can be executed, and at first, the outgoing side estimates an echo, and subsequently the incoming side executes the estimation. If a characteristic is varied in the course of a call, training is restarted by a signal C5 of a detecting circuit 18 and a signal C4 for detecting nonsignal on the circuit. |
