| 摘要 |
PURPOSE:To reduce noises by shortening a previous-value holding time, by changing a switching circuit over to a side where neither an LPF nor a previous-value holding circuit resides in a period except when the previous value of a dropout period including a transient period due to the LPF is held. CONSTITUTION:An audio FM signal passed through a BPF2 is detected by a dropout detecting circuit 7 and at the ending of the dropout detection signal, a monostable multivibrator 16 is triggered, thereby outputting a pulse with pulse width equivalent to the transient periof of a signal delay circuit 14. Then, a previous-value holding circuit 6 is put in operation by operating an OR circuit 9, and a switching circuit 15 is changed over to a circuit 6 side. Consequently, the switching circuit is connected to the side of the previous-value holding dircuit 6 where an LPF6 is connected only during the dropout period of the audio FM signal and the short transient period of the output of the circuit 14 due to the BPF2, so a previous-value holding time is shortened to reduce noises of the audio FM signal due to dropouts. |
