| 摘要 |
PURPOSE:To assure the stable characteristics of an automatic gain controller even to the shrinkage of a noise and a synchronizing signal, by limiting the width of a horizontal synchronizing signal within a prescribed period from the front edge of said signal in case the width of the signal is extraordinarily increased so that the rear edge of the reference pulse lags by a prescribed time from the rear edge of the horizontal synchronizing signal in a normal state. CONSTITUTION:The composite video signals of the Fig. A are supplied, and the signals of the Fig. B are obtained at an output of a synchronizing signal separating circuit 5. In this case, signals (c) and (d) are generated by the malfunction of the circuit 5 which are due to a noise pulse (a) and the shrinkage (b) of a synchronizing signal. When such signals (c) and (d) are applied to a pulse delaying circuit 9, a pulse (c) of a narrow width is eliminated and the signals of the Fig. C are obtained. When the signals of the Fig. B are applied to a monostable multivibrator 10, an output of the Fig. D is obtained regardless of the pulse width. Therefore signals of the Figures C and D are applied to a multiplier 11, and the signals of the Fig. E are obtained at the output of the multiplier 11. Then the signal of the Fig. F emerge to the output of a mixing circuit 4, i.e., the input of a peak value detecting circuit 7. Thus the normal signal level V0 is detected to keep the stable gain of a gain control circuit 2. |
