| 摘要 |
PURPOSE:To stabilize an envelope detection output by providing a reproduced chroma low-frequency conversion signal eliminating circuit, a synchronizing signal extraction circuit and an envelope detection circuit, eliminating a reproduced chroma low-frequency conversion signal from a reproduced video FM signal and applying the envelope detection of a reproduced video FM signal passing through an extraction circuit of a synchronizing signal. CONSTITUTION:A reproduced video FM signal is inputted from an input terminal 1 to a reproduced chroma low-frequency conversion signal eliminating circuit 3, where the reproduced chroma low-frequency conversion signal is eliminated. The reproduced video FM signal with the reproduced chroma low-frequency conversion signal eliminated thereof in this way is inputted to a synchronizing signal extraction circuit 4. The resonance point or the band width is located at the portion of the synchronizing signal and the effect of the APL change in the video signal is decreased. Then the reproduced video FM signal passing through the synchronizing signal extraction circuit is given to an envelope detection circuit 5, and only the extracted synchronizing signal is subjected to envelope detection. Thus, a stable detection output is obtained without giving fluctuation to the change in the chroma signal and the APL change in the signal content.
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