In one embodiment of the present invention, an operational amplifier circuit, a switching element is closed and a switching element is opened. A latch circuit DL latches an output voltage of an operational amplifier and supplies a Q output corresponding to the output voltage. A control circuit supplies an offset adjustment signal to an offset adjustment input terminal OR of the operational amplifier, thereby adjusting an offset of the output voltage. The latch circuit DL latches again the output voltage thus adjusted and minutely adjusts the offset adjustment signal so as to adjust the remaining offset. Weighting is carried out in accordance with how many times latching has been carried out, and the offset of the output voltage of the operational amplifier is quantized, thereby obtaining a binary logical signal and storing the signal in the control circuit.
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