| 摘要 |
PURPOSE:To cancel an echo with a high precision by driving a first echo canceller at the timing of a transmission clock and driving a second echo canceller at the timing of a reception clock. CONSTITUTION:A transmission signal is sent to a subscriber's line through a buffer 1 operated with the transmission clock from the transmitter 2, a transmission filter 3, and a hybrid 4. The echo passing a hybrid 4 and the signal from the subscriber's line are applied to an adder 8 through a reception filter 5. The first echo canceller 6 is operated by the transmission clock to generate a signal resembling the echo component from the transmission signal, and this generated signal passes a D/A converter 7 and is subtracted by the adder 8 to eliminate the echo. The remaining echo from the adder 8 is applied to an adder 12, and a signal obtained by the second echo canceller 11 which is operated by the reception clock to generate a signal simulating the remaining echo is subtracted from the remaining echo from the adder 8 to generate a reception signal from which the echo is eliminated. A PLL 13 generates a reception timing signal.
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