| 摘要 |
PURPOSE:To improve the S/N at a part where the color saturation degree of a carrier color signal is low and also to suppress the secondary distortion or a white-black inversion phenomenon caused at a part where said color saturation degress is high, by providing an amplitude control circuit that makes the amplitude of a color video part of a low band conversion color signal constant in level at the preceding stage of a mixing amplifier. CONSTITUTION:The carrier color signal of the color video signal supplied from an input terminal 1 is separated through a BPF2, and the amplitude of the video signal is limited by an amplitude control circuit 3. Then the video signal undergoes the low band conversion through a frequency converter 4. Thus a low band conversion carrier color signal is produced. The burst signal obtained by a burst signal sampling circuit 9 performs the switching control so that a changeover switch 13 is closed toward a contact (a) in a period of a color video part via an amplitude detection circuit 11 and then toward a contact (b) in a period of the burst signal. Then the circuit 3 controls the amplitude of the burst signal of the carrier color signal with the voltage of a fixed level given from a constant power supply 12 used as the control voltage. While the color video part is controlled by the control voltage produced by a color video part sampling part 8 and an amplitude detection circuit 10. Then the color video part is controlled so that its amplification factor is increased and decreased with small and large amplitudes respectively.
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