| 摘要 |
PURPOSE:To constantly obtain the same value in the quantity of change in the gain of all video frequency amplifiers when the gains of the plural video amplifiers are simultaneously changed by amplifying a superimposing signal by the video frequency amplifier, thereafter sampling it, comparing the levels of the sampled signals and controlling the gains of the respective video amplifiers so as to be equal according to the difference. CONSTITUTION:During a horizontal blanking period, the R.G.B signals on which the signal of a fixed level is superimposed are amplified by the video frequency amplifiers 2r, 2g, 2b and only the superimposing signal is sampled by superimposing signal sampling circuits 6r, 6g, 6b. By making the signal superimposed on, for instance, the R signal of the sampled signals a reference, the levels of the G signal and the B signal are compared in signal level comparison circuits 7g, 7b. If there is the difference in the level between the signal superimposed on the R signal and the signal superimposed on said signal, the output voltage of gain control voltage generating circuits 8g, 8b is impressed to gain control voltage terminals 4g, 4b and the gain of the video frequency amplifiers 2g, 2b is changed so as to make the difference in the level of the signal superimposed during the horizontal blanking period zero.
|
