Nec Home Electronics, Inc.

Koichi Sunada

Hiroshi Sato

A keyed type synchronization wave detecting circuit comprises a phase wave detector for synchronizing and wave detecting a composite video signal responsive to a signal for wave detection. A synchronizing signal generator provides a horizontal synchronizing signal controlled by the frequency of a horizontal synchronizing signal of the composite video signal. A keying pulse generator provides a keying pulse signal from the synchronizing signal of the synchronizing signal generator. A phase controller outputs a phase difference signal in accordance with the difference in phase between the signal for wave detection and a carrier of the composite video signal such that the phase difference approaches a predetermined level, the phase controller having a comparator for performing a keying outputting operation of the phase difference signal by the input of the keying pulse signal, and a filter for removing the high frequency component of the phase difference signal and forming a control signal. A lock detector controls the output of at least the keying pulse signal to the phase controller when it is detected that the signal for wave detection is phase-locked to the carrier. Means are provided for generating the signal for wave detection synchronized with the carrier based on the control signal.

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Osaka, Japan

Koichi Sunada