| 摘要 |
PURPOSE:To obtain a video modulation signal improved distortion in a carrier signal over a wide band without changing a modulation factor by providing the titled device with a signal generator with a prescribed frequency, a limiter amplifier, a balance modulator, and a level control part. CONSTITUTION:The amplitude level of the signal generator 1 is fixed by the limiter amplifier 9, a video signal wave is superposed to a signal outputted from the amplifier 9 by the balance modulator 10, the superposed signal is AM-modulated and supplied to a level control circuit 11. The level of the supplied signal is adjusted to a prescribed level by a level adjuster 4 based on a feedback signal obtained from a comparator 12, a harmonic distortion is suppressed by a filter 5 and the suppressed signal is supplied to a variable resistor attenuator 8 through an amplifier 6. One side of an output from the amplifier 6 is detected by an envelope detector 7a, the detected result is converted into a low frequency component (video signal component), a video modulation signal in a high band is accurately detected as a peak by a peak detector 7b, the detected peak is compared with a reference voltage by a comparator 12, the peak-to- peak value level of the video modulation signal is controlled and stabilized at a fixed value by a feedback signal based on the compared result and the stabilized signal is outputted. Since the level control part 11 forms an APC loop, a required level can be stably outputted independently of a modulation factor once calibrating the output level.
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