Patent ID: 8358361

Claim:
An A/D converter unit for an image sensor, comprising: a plurality of column A/D converters for converting a plurality of analog image signals being output from the image sensor on a column-by-column basis into digital data simultaneously in parallel, and a reference voltage group supplier for supplying a reference voltage group having a plurality of reference voltages, wherein each column A/D converter includes a first D/A converter for selecting and outputting two reference voltages from among the reference voltage group, a second D/A converter for outputting a voltage ranging between an upper limit and a lower limit each determined by each of the two reference voltages output from the first D/A converter, a comparator for comparing each analog image signal voltage being output from the image sensor with the output voltage of the second D/A converter, and based on the output of the comparator, a controller for controlling the first and the second D/A converters so as to produce the output voltage of the second D/A converter substantially equal to each analog image signal voltage.