| 摘要 |
PURPOSE:To prevent the fluctuation in a DC voltage component from giving effect on an output signal by connecting an AGC control circuit to an output terminal of a differential amplifier and controlling the 1st and the 2nd variable impedance circuits by the AGC control circuit. CONSTITUTION:The 1st variable impedance circuit 13 changes the impedance of a transistor (TR) Q1 so as to bring its output level to a set value, then the base potential of the TRQ1 is increased to a ground potential, a fluctuation is generated in the DC voltage component and this DC voltage is applied to a differential amplifier 11. However, the same DC voltage fluctuation is produced in the 2nd variable impedance circuit 16 and this DC voltage is applied to minus input of the differential amplifier 11, then the fluctuation of the said DC voltage is cancelled and does not appear as the output signal of the amplifier 11. |
