| 摘要 |
PURPOSE:To improve temperature characteristics by applying a bias voltage applied to a compensating diode with the same characteristics and the reverse bias voltage of the diode bias voltage to the inverted input terminal of an operational amplifier which applies a DC bias to a diode for attenuation. CONSTITUTION:An input voltage EIN is applied to an amplifier 2 through a resistance R11 and the amplified voltage is outputted as an output voltage EOUT. The voltage EOUT appears at an AGC output terminal 6 through a detector 4 and an LPF5 and is also inputted to the inverted input terminal of the operational amplifier 7 through R16. The inverted input terminal of the amplifier 7 is grounded through R18 and compensating D20 with the same characteristics with the attenuating diode D12 and also applied with a positive voltage +EB through R19 and a negative voltage -EB through R21. The output of the amplifier 7 is applied to the D12 to vary the input voltage to an amplifier 2. The compensating voltage +ED of the D20 compensates the forward bias current of the D12 to compensate temperature variation in AGC voltage.
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