| 摘要 |
PURPOSE:To obtain an AGC circuit with excellent attenuation efficiency by using a push-pull amplifier circuit from which an output signal with less distortion and a large amplitude is obtained. CONSTITUTION:A bias voltage is applied to each base of a couple of transistors (TRs) 6a, 6b, a primary coil 8a of an induction coupling circuit 8 is connected between the emitters, the midpoint is grounded via an impedance circuit 11 and an AGC voltage is applied to the emitter of the said TRs in such a way that the collector current is decreased as an input signal increases so as to output a signal to the induction coupling circuit 8. Since the operation is conducted between the TRs 6a and 6b at each half cycle of the input signal in this way, the attenuation of the input produced in the primary coil 8a of a high frequency amplifier stage is increased depending on the amplitude of the input signal thereby attaining the self-attenuating operation. Then the base potential of the TRs 6a, 6b is varied by applying the said AGC voltage to the midpoint (A) of the coil 2b. Thus, a large attenuation is obtained through the synergistic effect between the attenuation attended with the application of the said voltage and the said self-attenuation. |
