| 摘要 |
PROBLEM TO BE SOLVED: To provide a video detection circuit in which, when an over-modulation state is detected, a video signal is prevented from being returned, and drifting in the VCO oscillation frequency of a PLL circuit is reduced. SOLUTION: The video detection circuit includes: a PLL circuit for producing a reproduction carrier wave based on a video modulation signal (PIF signal) obtained by amplitude-modulating a carrier wave in accordance with a video signal; a VDET 23 which synchronizing-detects the video signal from the video modulation signal while using the reproduction carrier wave; a comparator 33 for detecting an over-modulation state where a video modulation degree of the video modulation signal exceeds a predetermined modulation degree threshold; and an inversion and switch circuit 34 for inverting the video modulation signal and outputting it to an APC 24 of a PLL circuit when the over-modulation state is detected by the comparator 33. COPYRIGHT: (C)2011,JPO&INPIT
|
