| 摘要 |
PURPOSE:To suppress generation of a crosstalk current in a circuit that drives an image sensor to prevent crosstalk utilizing virtual grounding of an operational amplifier by providing a device that compensates an input offset voltage by applying a voltage reverse in polarity to the input offset voltage of the operational amplifier. CONSTITUTION:A circuit 3 that compensates an input offset voltage VOS of an operational amplifier OPA1 is provided, and a voltage of reverse polarity to the offset voltage VOS is applied to the inversion input side of the operational amplifier OPA1 to reduce the offset voltage VOS. As it is not clear whether the offset voltage VOS becomes +polarity or -polarity, the compensating circuit 3 is so structured that it can make a potential of a dividing point (a) of resistances R1 and R2 variable by a variable resistance VR to which bias voltages +Vcc and -Vcc are applied to both ends. As concrete method of compensating offset voltage VOS by the compensating circuit 3, it is enough to adjust the variable resistance VR to make the output voltage of the operational amplifier OPA1 to zero when the input end of a sensor resistance Rs is dropped to GND.
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