| 摘要 |
PURPOSE:To prevent the malfunctions of a superposed call detecting means which are caused when an echo path is opened by controlling the attenuation value based on the outputs of a transmission input level measuring means, an erasion residual signal level measuring means, a reception input level measuring means and a superposed call detecting means. CONSTITUTION:A control circuit 13 measures the input receiving side signal via a receiving side signal level measuring circuit 8 to decide the presence or absence of a receiving side signal. At the same time, the receiving side signal level is measured by a sending side signal level measuring circuit 12. Then the difference of both signal levels is decided. Then the sending signal level is measured by an erasion residual signal level measuring circuit 9 and the difference of levels is decided between the sending signal and the erasion residual signal. Furthermore, a superposed call detecting circuit 11 compares the levels between the receiving signal and the erasion residual signal. A deciding circuit of the circuit 13 detects the open state of an echo path based on the outputs of those circuits and then decreases the measurement value an attenuation value measuring circuit. Thus the malfunctions of the circuit 11 can be avoided.
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