| 摘要 |
PURPOSE:To obtain an automatic gain controller having excellent leading characteristic by using a transistor (TR) connected to a smoothing error amplifier means so as to clamp the smoothing error amplifier means to a prescribed value when no input signal is fed to a gain means. CONSTITUTION:When the automatic gain controller is operated stably at a point of time t12 while an input signal Vi is impressed and some time is elapsed, an error signal Ve is fluctuated in a range around a prescribed value and a resistance value of a CdS22a of a photocoupler 22 changes accordingly. As a result, the gain of the input signal Vi is set by a voltage dividing ratio of an attenuator 21 and the CdS22a and an output signal Vo is controlled to a prescribed value. In this case, a base-emitter voltage of a TR 30d is operated at nearly 0.6V and an output voltage V1 of an operational amplifier 30a at stable operation is nearly -0.6V. Thus, the time when the input signal Vi is applied until an output of the operational amplifier 30d reaches a value the same as that at a stable state is very short as shown in T11 and the time until the device is operated stably is decreased to nearly the hunting time of the CdS22a as shown in T12.
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