| 摘要 |
PURPOSE:To obtain normal AFC operation by using a voltage comparator so as to compare an outut signal of an FM demodulation circuit and a signal being the result of its DC recovery in terms of voltage and using its difference voltage so as to control a voltage controlled oscillator even if a carrier frequency is set to a level of a video signal being sent. CONSTITUTION:Part of a video signal from a discriminator 5 is fed to a DC recovery circuit 8, its pedestal level or a synchronizing signal tip is arranged to a reference potential and the result is fed to one input of a voltage comparator 7. On the other hand, the said video signal is fed as it is to other input of the voltage comparator 7. A voltage proportional to a difference voltage of the video signals fed to the comparator 7 is extracted from the comparator 7 and fed to a VCO 3 to control its oscillated frequency as the AFC. Thus, even if the content of the video signal is changed, a prescribed control difference voltage is supplied to the VCO 3.
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