| 摘要 |
PURPOSE:To obtain high performance with simple constitution by generating a video carrier and a sound carrier from a PLL circuit respectively and deciding a frequency dividing ratio of a frequency divider in a loop so that each PLL circuit is phase-locked to an output of a single reference oscillator having a frequency being a common measure of each carrier frequency. CONSTITUTION:A reference oscillator 11 and the 1st and 2nd PLL circuits (PLL1, PLL2) phase-locked to an output of the reference oscillation are provided. The 1st and 2nd PLL circuits include respectively VCO 12, 13 (voltage controlled oscillators), frequency dividers 14,15 and phase comparators 16, 17 and the frequency division ratio of the frequency dividers 14, 15 is decided so that the common measure of the frequencies of the video carrier fp and the sound carrier fs of the outputs of the VCOs is the output frequency of the reference oscillator. The VCO output of the 1st PLL circuit is modulated by the video signal to obtain the modulated video carrier and the modulated sound carrier is obtained from the VCO output by superimposing the sound signal onto the phase comparator output of the 2nd PLL circuit so as to lead out each VCO output in mixture. Thus, the constitution of the oscillator is simplified and the oscillator is operated highly stably with no adjustment.
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