External synchronous system and camera chain using the same system

When using a counter to determine the field, many gates are needed in manufacturing the counter, so that the circuit scale increases, costs increase. In the present invention, comprising a circuit for separating the sync separator in the composite sync signal CSYNC horizontal synchronizing signal and a vertical synchronizing signal and the internal vertical synchronizing signal and a horizontal synchronizing signal based on a vertical synchronizing signal and the separation level is formed inside synchronization signal timing control circuit, the pulses P2 and P3 are formed in the sync separation circuit for determining the presence of the field is determined, when the external synchronization signal CSYNC as input, determining the field is an odd field or an even field.