| 摘要 |
PURPOSE:To eliminate noise at switching, by mitigating the change in muting signals at switching from monaural to stereo mode and making the change of switching from the stereo to monaural mode steep, in a demodulator of an AM stereo system. CONSTITUTION:A muting circuit 2 consists of a differential DC amplifier in which a control signal is applied to the base of a transistor (TR)Q207, and a circuit comprising a TRQ213 to which a difference signal (R-L) is applied, a TRQ214 having a constant bias, and TRs Q209-Q212. At switching from the monaural to stereo mode, an output of a gate 6 goes to L, and a base voltage of the TRQ207 slowly rises depending on the time constant comprising resistors R72, R73 and a capacitor C01. At the switching to the monaural mode, the output of the gate 6 goes to H, the TRQ74 turns on, and the base voltage of the TRQ207 is rapidly decreased. |
