SYNCHRONIZATION DETECTION CIRCUIT

摘要

PROBLEM TO BE SOLVED: To provide a synchronization detection circuit which stably outputs a vertical synchronizing output signal at a proper timing even in such a state that noise is increased in a vertical synchronizing input signal. SOLUTION: The synchronization detection circuit is provided with; an edge detection part 101 which detects an effective edge of a vertical synchronizing input signal VDin to output a vertical detection signal Se; a video non-display period detection part 106 which detects a video non-display period from the level of an input video signal Sv to output a video non-display period detection signal Sd; a gate part 102 which outputs the vertical detection signal Se as a gate output signal Sg in the case that the on-display period detection signal Sd and a blanking signal Sb are effective; a counter 103 which is reset by the gate output signal Sg to start counting a horizontal synchronous input signal HDin; a blanking period discrimination part 104 which outputs the blanking signal Sb to the gate part in the case that a counted value Sc is within a prescribed range; and a vertical synchronizing signal generation part 105 which outputs a vertical synchronizing output signal VDout in response to reaching a prescribed value of the counted value. COPYRIGHT: (C)2004,JPO&NCIPI