Method and a circuit for deriving a synchronisation signal from a video signal

Abstract

A method for deriving a synchronisation signal () from a video signal comprises tracking the blanking level () of the video signal with first and second slice level signals () and tracking the sync tip level () of the horizontal sync signal () of the video signal with third and fourth slice level signals () for determining the blanking level () and the sync tip level (). A value for an intermediate slice level signal () is computed from the first, second, third and fourth slice level signals () so that the value of the intermediate slice level signal () lies approximately halfway between the blanking level () and the sync tip level (). The video signal is compared with the intermediate slice level signal (), and the synchronisation signal () is prepared from a logic signal by transitioning the logic signal from one of the logic high and logic low levels to the other of the logic high and logic low levels, each time the video signal transitions across the intermediate slice level signal ().