| 摘要 |
PURPOSE:To attain an optimum gain control by applying automatic control to the gain of a telephone circuit corresponding to a counting signal so as to detect the condition of signal transmission such as the distance of signal transmission in advance. CONSTITUTION:A detection circuit 4 detecting the connection between a telephone set 1 and the telephone circuit, a counter circuit 8 whose operation is started by a detection signal obtained from the detection circuit 4 and counting the initial pulse signal number generated from the dialing and obtaining a count signal V1 when the number of pulses such as 10 pulses corresponding to the dial 0 representing the toll talking are counted, and a gain control circuit controlling the gain of the telephone circuit attended with the count signal supply are provided. Thus, the condition in the case of signal transmission, that is, whether or not the call is a toll call is detected and the gain of the telephone circuit being the signal transmission path is subjected to an optimum automatic control.
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