VIDEO SIGNAL DETECTION CIRCUIT AND AV SIGNAL SELECTOR USING THE SAME

摘要

PURPOSE: To surely discriminate the presence of a video signal to be reproduced by detecting an average voltage level of a signal part on which a luminance signal and a carrier chrominance signal of an input video signal are superimposed and comparing the average voltage level with a prescribed reference voltage level. CONSTITUTION: A low pass filter 20 of a video detection circuit 14 passes through a low frequency component of a detection object video signal VDT. A clamp circuit 21 clamps the low frequency component so that an average voltage level of the detection object video signal VDT based on an output signal of the low pass filter 20. Succeedingly a chroma trap circuit 22 eliminates a chrominance carrier signal from the clamped detection object video signal VDT. Then a comparator 23 compares a voltage VCMP of the clamped detection object video signal VDT with a reference voltage VREF to provide an output of a comparison result signal. As a result, a motion image signal is distinguished from a video signal such as a blue back signal or a black back signal.