| 摘要 |
PURPOSE:To avoid deterioration of the talking quality by fixing the gain of an AGC circuit when the control AC signal is cut off and therefore suppressing the overload of a reception circuit part to suppress the crosstalks to other channes as well as the increase of the device noises. CONSTITUTION:A resistance R5 and a variable resistance RV1 are provided between a power supply 7 and a ground, and an intermediate output terminal of the RV1 is connected to an input terminal 2 of a resistance R2. Then a DC is superposed on the control AC signal supplied from the terminal 2. Thus a signal of a fixed level is supplied to a rectifier 3 although the control AC signal is lost. Then a rectifying signal of a proper fixed level is supplied to a multiplier 4. Thus the gain of an AGC circuit is fixed at a fixed level. While the maximum level of the gain of an amplifier can be decided by varying the DC bias by the resistance RV1.
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