| 摘要 |
PURPOSE:To prevent sudden generation of an interchannel noise on the completion of a broadcast without providing a muting ON/OFF switch, by outputting the interchannel noise during channel selection, and stopping the output of the noise on the completion of the broadcast. CONSTITUTION:A muting signal outputted from a PLL controller 10 goes up to a level H on channel selection, and is tuned to a desired frequency and then goes down to a level L a specified time later. This signal resets a D type flip- flop 12 on every channel selection without fail. When a broadcast is received after the channel selection, a clock input goes down to the level L and after the broadcast ends, it goes up to the level H. If the broadcast ends abruptly, the level H of the input D is read at the leading edge of the clock input, and the Q output goes up to the level H to perform muting through a diode D1. When no broadcast is received during channel selection, the Q output does not go up to the level H and muting is not performed. |
