| 摘要 |
PURPOSE:To detect the dropout of a frequency modulated wave, by providing a phase comparator in addition to the phase comparator that demodulates the frequency modulated wave of a video disk and adding the output of a voltage control oscillator to the phase comparator via a phase shifter to perform synchronizing wave detection. CONSTITUTION:The frequency modulated wave of a video disk is amplified by an intermediate frequency amplifier 1. A voltage controlling oscillator 2 oscillates the frequency approximate to a signal wave. The output of the oscillator 2 is applied to a phase comparator 3 to be compared with the output of the oscillator 2. The output of comparison is turned into the control signal for the oscillator 2 as well as into the demodulated signal after the high frequency is eliminated through an LPF4. The output of the amplifier 1 and the output of the oscillator 2 obtained via the phase shifters 6 and 7 are applied to a phase comparator 5. Thus the comparator 5 works as a synchronizing wave detector. The input signal of the comparator 5 is set at zero for a period during which the dropout is caused for the frequency modulated wave. As a result, no voltage is caused at the output terminals 8 and 9. The voltage is produced when the normal input signal exists. Therefore the dropout of the modulated wave can be detected by the presence or absence of the difference voltage between the terminals 8 and 9. |
