| 摘要 |
PURPOSE:To perform excellently auto-phase control in a video tape recorder or the like by converting the phase difference between a burst signal and the output of a voltage control oscillator to the absolute value and the sign of a digital signal and controlling the control voltage of this oscillator in accordance with this sign. CONSTITUTION:The video signal including a chrominance signal from an input terminal 10 is subjected to A/D conversion by an A/D converter 11 and is not only outputted to an output terminal 12 but also sent to an operating circuit 14 through a phase comparator 13. The sign of an output terminal 15 of the circuit 14 switches a switch circuit 17 and switches a switch circuit 21 through an inverter 20. As the result, the potential of a capacitor 23 is raised when the phase of the burst signal leads the phase of the output of a voltage control oscillator 24, and the switch 21 is closed and the potential of the capacitor 23 is reduced when the phase of the burst signal is behind the phase of the output. The potential of the capacitor 23 controls the oscillator 24 through a resistance 22 to form a negative feedback loop, and the phase difference between the burst signal and the output signal of the oscillator 24 is made of zero.
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