PURPOSE: To maintain image safety and S/N ratio satisfactory and prevent the generation of color flicker by varying the characteristics of a detection filter during the period of the presence of a burst signal in vertical retrace line eliminating period of a chrominance signal and accelerating the response velocity of a correction loop.
CONSTITUTION: A change-over switch circuit 19 is normally closed at a contact B and is connected to a voltage source 22 of a reference voltage V0. The burst existence period in the vertical retrace line eliminating period of a chrominance signal is detected by a head output change-over signal from an input terminal 20 and a horizontal synchronizing signal from an input terminal 12, and a change- over signal denoting this existence period is generated. This change-over signal switches said circuit 19 to contact A and the reference voltage V0 is not applied to a detection filter 8, thereby changing the characteristics of said filter 8 so that response of an APC loop will be speed up. As a result, smoothing characteristics of a phase error signal from a phase detector 6 are changed and the stable image with high quality can be obtained.
MIURA KUNIAKI
FUKUSHIMA ISAO
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