| 摘要 |
PURPOSE:To set the correction value of an echo cancel signal to depend only on a phase shift direction so as to reduce the storage capacity of a memory by simultaneously controlling a phase shift compensation table and a variable frequency divider and controlling a phase. CONSTITUTION:A digital transmission equipment consists of two units of a line termination(LT) 23 and a network termination(NT) 24. An adder 13-3 adding the outputs of the phase shift compensation table 19, a phase shift control circuit 18 and an adaptive filter 8-2 is provided in an echo cancel part on the side of NT24. A phase control signal 48 which the circuit 18 outputs and a phase shift direction signal 40 which a phase detector 17 outputs change the frequency- dividing ratio of the variable frequency divider. The frequency-dividing ratio shows -1 at the time of control in the direction of travel and it shows +1 in a delay direction. On the other hand, the table 19 outputs the correction value of the echo cancel signal, adds the outputs of the filter 8-2 and corrects the echo cancel signal. Thus, the number of storage elements for correction can be reduced to about nine or eighteen. |
