| 摘要 |
PURPOSE:To eliminate adverse effect exerted on an output amplitude by suppressing an input offset voltage from being generated to an output amplifier in a circuit regulating automatically an output level of a telephone set having an amplifier in response to the line current. CONSTITUTION:An emitter of a transistor (TR) 26 and a base of a TR27 are connected to a collector of a TR25, and an emitter of TRs 21, 22, 23 is connected to a collector of the TR26. Further, a collector of a TR23 is connected to an emitter of the TR27 and a collector of the TR27 and an emitter of the TRs 24, 25 are connected to a smoothing circuit being a power of a preamplifier 1. Then a base of the TR26 and a connecting point between the emitter of the TR27 and the collector of the TR23 are connected across a feedback resistor 101, 102 of the amplifier 11. In selecting properly values of resistors 101, 102, the amount of gain change depends on the resistance ratio only, the level is adjusted stably and no input offset voltage is generated to an output amplifier 2. |
