| 摘要 |
PURPOSE:To improve the linearity of gain characteristic by fixing the sum of currents of differential amplifying circuits in the input side and the output side and controlling the current of the differential amplifying circuit in the input side in a Gilbert amplifying circuit. CONSTITUTION:Currents I7 and I8 of transistors TRs Q7 and Q8 are changed in accordance with an output voltage V8 of a variable resistance 26, and the sum of them is always a current I0. When the current I7 of the TR Q7 is denoted as K.I0 (0<=K<=1), a current I1 of the first differential amplifying circuit 6 is K.I0 and a current I2 of the second differential amplifying circuit 12 is (1-K).I0. A current I9 of a current source 30 is controlled to K.I0/2. As the result, proportional constant of an input voltage Vi to an AC component V02 of an output voltage V2 is -RL(1-K)/2KRE (RL and RE are resistance values of resistances 15 and 16 and resistances 7 and 8 respectively), and it is changed approximately linearly for the change of K.
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