SIGNAL SELECTING CIRCUIT

PURPOSE:To enable automatic switching of the synchronizing signal separated from a composite video signal and a separate horizontal synchronizing signal by providing a logical circuit which outputs the synchronizing signal inverted by a polarization inverting circuit at the time of detecting the separate horizontal synchronizing signal and outputs the synchronizing signal separated in a synchronizing sepn. circuit at the time of non-detection. CONSTITUTION:A horizontal synchronizing signal input terminal Bb is connected to the base of a transistor 7 via a resistor R6, a capacitor 4, a diode 6, and a resistor R7, and the TR 8 forms a detection circuit of the separate horizontal synchronizing signal. The detection circuit turns off the TR 8 at the time of detecting the separate horizontal synchronizing signal. The output of the TR 8 and the polarity-inverted separate horizontal synchronizing signal are ANDed by the logical circuit 10 and the polarity-inverted separate horizontal synchronizing signal is outputted to the next stage. The TR 8 turns on to output the synchronizing signal separated from the composite video signal in the synchronizing sepn. circuit 2 at the time of the non-detection of the separate horizontal synchronizing signal. Two kinds of the synchronizing signals which are different in specifications are thereby automatically switched.