| 摘要 |
PURPOSE:To perform a gain control, by providing the negative feedback path at the push-pull amplifier provided at the output side of a modulator through the input side of the modulator and thus varying the quantity of the negative feedback. CONSTITUTION:The output of the double balanced modulator 60 is delivered through the push-pull amplifier 61. The modulated wave signal outputs of the output terminals 5 and 8 are applied to the band pass filter 64 through the transformer 63 to extract the pilot signal contained in the modulated wave signal. The extracted pilot signal is amplified by the amplifier 65 and then rectified by the rectifier 66 to be applied to the variable resistor 62 provided at the negative feedback path and in the form of the control voltage. Thus the quantity of negative feedback is controlled to the modulator 60, thus realizing an automatic gain control. |
