| 摘要 |
PURPOSE:To prevent the title circuit from signal distortion and to improve its SN ratio by converting an input signal voltage to a current, multiplying the signal current by a specified value in accordance with a control current, negatively feeding back the multiplied current to then input side, and the subtracting the feedback current from the input signal current. CONSTITUTION:An input sinal VIN applied to an input terminal 32 is applied to a voltage/current converting circuit 36 through a subtracting means 34 and converted into a signal current IS on the basis of a specific reference operation point voltage Vref set up on a terminal 37. The current IS is applied to a current control amplifier 38, multiplied by a specific magnification (k) in accordance with a control current IC applied to a control input terminal 40, negatively fed back through a feedback circuit 41, and then applied to the subtracting means 34. In this case, an input signal current IIN based upon the signal VIN is led into the amplifier 38 side in accordance with the output current of the amplifier 38 and equivalently regarded as a resistor. Consequently, level adjustment free from signal distortion can be attained.
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