摘要 |
PURPOSE:To stabilize the oscillation frequency of a local oscillator to perform the frequency conversion of a reception television FM signal even when a power source is applied or a signal is interrupted transiently. CONSTITUTION:A signal processing circuit 6, when detecting the specific period of a demodulated video signal (a), outputs a pulse voltage signal (b) synchronized with the period. When the pulse voltage signal (b) is obtained based on the acquisition of the pulse voltage signal (b), a mode that a switch 13 makes a hold circuit 14 hold the specific period of the video signal (a) by sampling the video signal (a) by the pulse voltage signal (b), and a switch 16 makes a hold circuit 17 hold a comparison voltage from a comparison voltage generation circuit 15 similarly is set. When no pulse voltage signal (b) is obtained, the switches 13, 16 are always turned on by a fixed voltage, and a mode to hold the mean voltage of the video signal (a) by an integration circuit 9 and the comparison voltage by the hold circuits 14, 17, respectively can be set. A differential amplifier 18 controls the local oscillator 3 by the differential voltage of the hold circuits 14 and 17.
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