| 摘要 |
PURPOSE:To realize a fast response and to set an arbitrary limit voltage by providing a variable gain amplifier circuit, a transistor for gain control, and a constant voltage generating part. CONSTITUTION:A current flows on the base of the transistor 14 for gain control at a time when an amplified signal is increased than the voltage of the constant voltage generating part 15 by the Vbe of the transistor 14 for gain control, and continuity between the collector and the emitter is obtained, and the gain of the variable gain amplifier circuit 11 is lowered. Since no limit operation is started until the base current of the transistors 14 for gain control flows, the signal can be amplified to a preset limit voltage. Therefore, the gain itself of the variable amplifier circuit 11 is lowered by the transistor 14 for gain control when an invalid large signal is inputted. Thereby, no saturation occurs in output, and the fast response can be expected, and also, the limit current can be set at an arbitrary level. |
