| 摘要 |
PROBLEM TO BE SOLVED: To stabilize operation by detecting the gain fluctuation of the auxiliary differential amplifier of the same constitution as a differential amplifier thereby controlling the gain of the differential amplifier to suppress gain fluctuation in spite of the variation of elements, temperature variation and power source variation. SOLUTION: A differential amplifier 7 and an auxiliary differential amplifier 10 have completely equally constituted elements and connections, and an auxiliary circuit 8 operates DC. The voltage across a resistor generated by making a fixed current flow through a gain detecting part 9 is applied to the differential input of the amplifier 10, and the output voltage of the amplifier 10 is returned to the part 9. In addition, the part 9 controls the amplifier 7 to make the same gain as the auxiliary differential amplifier with the gain control of the amplifier 10 so as to match the above voltage to the pseudo output voltage of another resistor generated by making a fixed current flow through. Since this circuit gain does not depend on the variation of current but on the ratio of the element of the same kind, influence of temperature variation and element variation is reduced to stabilize a gain.
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