Patent ID: 7978114

Claim:
An A/D conversion apparatus comprising: an A/D converter that converts a potential difference between a reference voltage input and a voltage input to be measured to a digital signal and outputs the digital signal; a first switch connected between a voltage source to be measured and the voltage input to be measured; a first sampling capacitor having a first end connected to the voltage input to be measured and to a first end of said first switch, and having a second end connected to a reference power source; a second switch connected between a reference voltage source and the reference voltage input; a second sampling capacitor having a first end connected to the reference voltage input and to a first end of said second switch, and having a second end connected to the reference power source; and an impedance adjusting circuit which is connected between the reference voltage source and a second end of said second switch and changes, in stepwise fashion, impedance between the reference voltage source and the second end of said second switch.