| 摘要 |
PURPOSE:To freely set a voltage gain, by feeding back the output of a negative feedback opposite-phase amplifier to an input terminal after dividing the outputs by means of a resistor and variable resistance element. CONSTITUTION:A gain variable amplifier is composed of an amplifier AMP 1, resistance 2 which gives an input voltage VIN to an input terminal 10 to the ingot of the AMP 1, resistance R4 which divides the output of the AMP 1 and output voltage VOT of an output terminal 11, variable resistance element VR 5, and feedback resistance R3. When the base current Ib1 of the element VR 5 is made smaller, the output voltage VOT can be made lower. When the base current Ib1 is made larger, the output voltage VOT can be made higher and the thermal agitation noise produced by the element VR 5 becomes smaller, and thus, the S/N is improved.
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