| 摘要 |
PURPOSE:To reduce the error of an output current due to input offset, by a method wherein the output current of an operational amplifier is negatively fed back by a current mirror circuit and controlled in accordance with negative feedback quantity by the operation of the operational amplifier. CONSTITUTION:Transistors Q1, Q2 constitute a first current mirror circuit and transistors Q11, Q12 constitute a second current mirror circuit. Now, when it is supposed that an input signal Vin has a level higher than that of reference voltage Vref, a current Ia flows through an input resistor Ra, while a current Ia/2 flows to the transistor Q1 as a reference current and sucked in the output side of an operational amplifier 1 through a resistor R2. The current Ia/2 corresponding to the above mentioned reference current also flows to the transistor Q2 as an output signal and output voltage Va is obtained as the voltage drop of an output resistor R11. Vb is obtained in the same way as such as case that voltage Vin has a level lower than that of voltage Vref and rectifying output is alternately obtained from the resistors R11, R12.
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