| 摘要 |
The invention provides a subscriber circuit for a public telephone set which eliminates the necessity to make a voice signal to be introduced to a channel filter a small signal. A voltage holding circuit is controlled with a polarity reversal indication signal which is supplied also to a loop current supply circuit so that a voltage detected by a line voltage detection circuit is held by the voltage holding circuit. A reversal circuit is controlled with the polarity reversal indication signal so that the polarity of the voltage held by the voltage holding circuit is reversed. The voltage of the reversed polarity is buffered by a low-pass filter having a characteristic same as that of a low-pass filter which buffers polarity reversal in the loop current supply circuit, and is then subtracted from the output of the line voltage detection circuit by a subtraction circuit.
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