GENERATING CIRCUIT OF CLOCK FOR PICTURE SIGNAL CODING

摘要

PURPOSE:To code an optional picture signal, by securing an automatic switch between a synchronous sampling clock with a picture signal having the synchronous frequency accuracy set within the prescribed standard and a non-synchronous sampling clock with a picture signal having said frequency accuracy set outside the prescribed standard. CONSTITUTION:The picture signal supplied through a picture signal input terminal 1 is supplied to a synchronous separating circuit 2, and the horizontal synchronous signal is separated and supplied to a phase locked oscillating circuit 3. The circuit 3 produces the clock which is locked with the horizontal signal in terms of phase and delivers it to an out-of-phase detecting circuit 4 and a switching circuit 7. The circuit 4 delivers an out-of-phase signal in case the frequency of the output signal of the circuit 3 is out of the prescribed range. At the same time, a clock switch signal generating circuit 5 is reset by the signal which is supplied through an input terminal 6 for signal source switch timing signal and set by the output signal of the circuit 4 to deliver an output signal to the circuit 7.