To solve the problem that an offset of several mV to several tens of mV due to working precision, manufacturing irregularity, etc., is generated in an operational amplifier, when an operational amplifier circuit of a switched capacitor amplifier or the like is realized by using a CMOS semiconductor process.
In the switched capacitor amplifier having an operational amplifier 121 in which a feedback capacitor 122 is connected to a part between an output terminal and an opposite phase input terminal, an offset canceling circuit 13 is installed, thereby canceling the offset of the operational amplifier 121. The circuit 13 comprises a switch 131 connected to a part between a positive side terminal of a reference voltage source 16 for supplying a reference voltage Vref and a positive phase (+) input terminal of the amplifier 121, switches 132, 133 which are connected in series to a part between the positive side terminal of the voltage source 16 and an opposite phase input terminal of the amplifier 121, and a canceling capacitor 134 connected to a part between the respective output terminals of the switches 131, 132.
YANO MOTOYASU
SHINOZAKI KEIICHI
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