| 摘要 |
PURPOSE:To prevent not only the erroneous operation is a FM detecting and muting circuit but also the output of noise at the time of the change-over of muting, by making it possible to respectively arbitrarily setting charge time constant and discharge time constant. CONSTITUTION:When a signal is inputted to the input terminal 10 of a peak level detection circuit 9, the input terminal 3 of a comparing circuit 2 is held to constant potential by the time constant set by an integrator circuit 21. At this time, a comparing circuit 23 compares the output signal level of the circuit 9 with a reference bias 26 to perform control so as to bring a discharge circuit 22 to a cut-off state. Next, when the input signal level inputted to the terminal 10 is lowered, the circuit 23 detects the lowering in the input signal level to perform control so as to set the circuit 22 to an active state. As a result, the holding potential of the terminal 3 of the circuit 2 starts discharge on the basis of the time constant set by the circuit 22. Therefore, charge time constant and discharge time constant can be respectively arbitrarily set.
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