| 摘要 |
PURPOSE:To prevent channel skip mistake of an adjacent station due to consecutive depression of a switch by inputting a clock signal permission switch via a differentiation circuit extracting the front ridge of an input signal. CONSTITUTION:When the operator depresses a rising switch 1, an input signal is waveform-shaped via a chattering prevention circuit 3 and the result is inputted to a differentiation circuit 5. Then the circuit 5 extracts the front ridge of the input signal and it is fed to an input signal permission FF 7. The input signal is inputted to an up-down counter 8 via an AND gate 20 together with the clock signal and the output of an automatic channel selection FF 15. Thus, the counter 8 is incremented and the tuning point is detected via a D/A converter 9, an electronic tuner 10, an IF video detector 11 and a tuning point detection circuit 13 to reset the FF 15. In this case, the front ridge of the input signal is extracted via the circuit 5 to prevent the channel selection skip mistake of an adjacent station through the consecutive depression of the switch.
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