Full duplex modem having two echo cancellers for a near end echo and a far end echo

摘要

The modem comprises a first echo canceller (100) for cancelling a near end echo and a second echo canceller (200) for a far end echo. The second echo canceller (200) has a variable delay circuit (201) responsive to the round-trip delay of the far end echo for setting the cancellation start timing of the far end echo. A comparator compares the round-trip delay and the echo cancellation time of the first echo canceller (100). A control circuit is responsive to the output of the comparator to control the echo cancellation time of the first echo canceller. This modem comprises echo cancellers whose time of convergence in echo cancellation does not decrease even where the round-trip delay is short.