| 摘要 |
PURPOSE:To reduce noises by shortening a previous-value holding time when the previous value of the output signal of an LPF is held, by changing an input to a previous-value holding circuit over to a signal, which neither passes through the LPF nor has a transient period, during the transient periood of the LPF. CONSTITUTION:An audio FM signal passed through a BPF2 is detected by a dropout detecting circuit 7 and the trailing edge of its dropout detection signal is used as a trigger to operate a monostable multivibrator 16, so that a pulse having pulse width equivalent to the short transient period of a signal delay circuit 14 is outputted. Then, an OR circuit 9 is operated to operate a previous-value holding circuit, and the trailing edge of the output signal of an OR circuit 12 is used as a trigger to operate a monostable multivibrator 18, thereby generating and outputting a pulse reading the trailing edge of the long transient period of an LPF5 to an OR circuit 19. Consequently, the input side of the circuit 6 is changed over to the side of a signal delay circuit 14 in the very short transient period of the BPF2 only during the period when the transient phenomenon of the LPF5 attenuates, so the previous- value holding period is shortened to reduce noises due to dropouts. |
