| 摘要 |
PURPOSE:To prevent the malfunction due to the pseudo signal, by detecting the change of the AFT signal via the ascent of the tuning voltage which is caused by the delay of response of the LPF. CONSTITUTION:With operation of the channel selection start key 2, the channel searching is started by the clock of the clock oscillator 3'. And the operation of the channel searching is discontinued in case the output is caused in the AND circuit 11 and by the fall of the output. During this discontinuation, the tuning voltage of the LPF6 ascends by the delay of response of the LPF6. The change of the AFT signal voltage thus caused is detected by the comparator 10b. Then the clock frequency is switched by the output of the comparator 10b, and at the same time the up-down counter 4 performs a down-counting for the clock to start the channel searching. And when the output is caused again in the circuit 11, the channel searching is stopped completely by the rise of the output of the circuit 11. In such way, the malfunction due to the pseudo signal can be prevented. |
