| 摘要 |
PURPOSE:To obtain an amplifying circuit having a good working with no effect caused by a change of the input impedance, by giving a voltage-current conversion to the DC component which is obtained from an output signal of an operational amplifier and through an LPF and supplying this current to the transistor of a differential amplifier in the form of a base current. CONSTITUTION:The output terminal of an operational amplifier 6 is earthed via a series circuit of a resistance 11a forming an LPF11 and a capacitor 11b. The output terminal of the LPF11 is connected to the positive input terminal of an operational amplifier 12a forming an integral network 12, and the output terminal of the amplifier 12a is connected to the negative input terminal (-) of the amplifier 12a via a capacitor 12b forming a feedback circuit. The terminal (-) is earthed via a resistor 12c. The DC component obtained from the network 12 is supplied to a voltage-current converting circuit 13, and the current obtained at the output side of the circuit 13 is supplied to the base of a transistor 4a of a differential amplifier 4 in the form of a base current. |
