| 摘要 |
PURPOSE:To simplify an FM modulation circuit by switching a frequency of an oscillation signal of a PLL means in phase-locking with a horizontal synchronizing signal included in a luminance signal into a frequency division ratio of 1/N and 1/N+1 so as to obtain two conversion carrier signals at a luminance signal processing system. CONSTITUTION:An FM modulation signal including a luminance signal is fed to a variable frequency oscillator 11 to control the oscillating frequency, which is inputted to a frequency converter 12. Further, a conversion carrier signal from a 1/2 frequency divider 13 is fed to the converter 12 to apply heterodyne conversion and a heterodyne FM signal is outputted via a filter 14. An input signal is fed to the frequency divider 13 from a PLL circuit 15 and a horizontal synchronizing signal of the luminance signal from a synchronizing separator circuit 16 is inputted to a phase comparator 152 of the circuit 15. Further, the output frequency from a VCO 151 is subjected to frequency division by 1/N and 1/N+1 frequency dividers 171, 172 of the frequency division section 17, selected by a switch 173, fed to the comparator 152 and the FM carrier is shifted by 1/2 by a simple circuit.
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