Patent ID: 6744444
Filing Date: 2004-06-01
Classification: G09G,H04N

Abstract:
A circuit for detecting a valid range of a video signal on the basis of a vertical sync signal which has a first period and has a first level only during a first range of time and a second level otherwise, a horizontal sync signal which has a second period and has a third level only during a second range of time and a fourth level otherwise, said valid range being a range of time of said video signal which is to be displayed on a display screen;said circuit comprising: a detection window signal generator for generating a detection region window signal which has a fifth level during at least one of a first detection disable range of time of a predetermined length and a second detection disable range of time of a predetermined length, and has a sixth level otherwise, said first detection disable range of time containing a point of time when said vertical sync signal changes from said first level to said second level so that said first detection disable range of time ends at a point of time when a predetermined time has passed since said vertical sync signal returns from said first level to said second level, said second detection disable range of time containing a point of time when said horizontal sync signal changes, from said third level to said fourth level so that said second detection disable range of time ends at a point of time when a predetermined time has passed since said horizontal sync signal returns from said third level to said fourth level, the first detection disable range of time and the second disable range of time each representing signals being generated in the detection window signal generator; and a valid range detector for detecting said valid range, during which said video signal has a level equal to or greater than a predetermined threshold and during which said detection region window signal has said sixth level.