| 摘要 |
PURPOSE:To prevent wrong discrimination, intermittent selective switching of filter circuits, and noise produced as a result of the selective switching, by changing the deciding time of a residue deciding circuit in accordance with the signal detecting level of a near-end talker detecting circuit. CONSTITUTION:A near-end talker signal is outputted from a terminal 1 to a four-wire transmission terminal 2 through a two-wire signal line 4, two-wire/ four-wire changeover circuit 5, and adder 6. On the other hand, a four-wire received signal is outputted from a terminal 3 to the two-wire signal line 4 through the changeover circuit 5. Moreover, a received signal from the terminal 3 is added to the adder 6 through filters 8 and 9 and change-over switch 10 and offsets an echo signal produced by the impedance mismatching of the signal line. Switching of the filters 8 and 9 is performed by a residue discriminating circuit 12 and selection controlling circuit 13 and the deciding time of the discriminating circuit 12 is changed in accordance with the detecting level of a near-end talker detecting circuit 14.
|
