Patent ID: 7012558

Claim:
An A/D converter comprising: an amplifying circuit amplifying a voltage difference between a first external input voltage and a voltage corresponding to a second external input voltage, and outputting the amplified voltage; an A/D converting circuit converting the output voltage of said amplifying circuit into a digital value by making a comparison with a reference voltage, and outputting the resultant digital value; a bias circuit selecting either the second external input voltage or a voltage obtained by adding a bias voltage to the second external input voltage, according to the output voltage of said amplifying circuit, in order to prevent the output voltage of said amplifying circuit from falling outside an A/D convertible range of said A/D converting circuit, and outputting the selected voltage as the voltage corresponding to the second external input voltage; and a first storing circuit storing a measured value of the bias voltage in advance, and outputting the stored measured value as a digital value whose bit number is greater than that of the digital value from said A/D converting circuit, when the voltage corresponding to the second external input voltage is the voltage obtained by adding the bias voltage to the second external input voltage.