Patent ID: 7557864

Claim:
A video signal judgment circuit arranged to detect the condition of a video signal compounding a picture signal and a synchronization signal comprising: a synchronization separation unit adapted to: filter an inputted video signal with a low-pass filter having a cutoff frequency adjustable by a first control signal; and separate a synchronization signal from the filtered video signal to output a pulsed synchronization detection signal; and a video signal judgment unit adapted to compare a detection signal formed on the basis of said synchronization detection signal with a judgment reference value that is adjustable by a second control signal and output a judgment signal based on the comparison; wherein said video signal judgment unit includes: a mono-multi circuit that undergoes mono-stable operation in response to said synchronization detection signal to output a mono-multi output signal having a pulse width regulated according to the period of cycle of said synchronization detection signal but stop said mono-multi output signal when no synchronization detection signal is fed in a predetermined period of time; a smoothing circuit arranged to smooth said mono-multi output signal and to output the smoothed signal as said detection signal; and a detection judgment comparison circuit including a first comparator arranged to compare said detection signal with a first judgment reference value adjusted by said second control signal, said detection judgment comparison circuit adapted to output a judgment signal based on the comparison made.