Patent ID: 6847409

Claim:
A video switchover detection circuit comprising a phase-locked loop circuit for comparing the phase of an input signal with that of an oscillating signal that is based on the input signal to perform phase synchronization, said video switchover detection circuit detecting switchover of input video signals by using a synchronization signal for a video signal used as said input signal and a reference signal that is based on said oscillating signal, said video switchover detection circuit comprising: phase comparison means for comparing the phase of a horizontal synchronization signal for said video signal with that of said reference signal; phase difference count means for starting to count time when a phase difference has occurred between both signals based on said phase comparison results and counting the period in which the phase difference persists; horizontal synchronization decision means for determining out of synchronization of said video signal in the horizontal direction in case the count value has exceeded a predetermined decision value based on the count value of said phase difference count means; and detection output means for outputting a video switchover detection signal indicating switchover of video signals based on the output of said horizontal synchronization decision means.