| 摘要 |
PURPOSE:To prevent the mixing of harmonics to a signal after demodulation by shifting a signal subjected to frequency modulation by a prescribed quantity to a high frequency side and demodulating its output. CONSTITUTION:A HPF 36 outputs a luminance signal (carrier frequency fc) subjected to FM modulation and the output is balanced and modulation by a carrier (frequency fs) at a balanced modulator 40. In this case, the time base fluctuation of the FM modulated signal is absorbed. A fc+fs component and a fc-fs component exist in the output of the balanced modulator 40 by balanced modulation, and the HPF 42 extracts only the component of fc+fs and applies it to a FM demodulation circuit 44. On the other hand, a horizontal synchronizing signal separated by a synchronizing signal separation circuit 38 is fed to one input of a phase comparator circuit 46, an output voltage of the phase comparator circuit 46 is applied to a voltage-controlled oscillator (VCO)48 to control the oscillated frequency. The output fs of the VCO 48 synchronously with the horizontal synchronizing signal is supplied to the balanced modulator 40 and applied also to the 1/n frequency divider 50, where the signal has the same frequency as that of the horizontal synchronizing signal and the result is applied to the other input of the phase comparator circuit 46.
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