Patent ID: 7760125

Claim:
A serial and parallel A/D conversion circuit for use with low-potential and high-potential power supplies and for separating a high-order bit and a low-order bit and sequentially performing A/D conversion, the A/D conversion circuit comprising: a plurality of resistor elements connected in series between the low-potential power supply and the high-potential power supply; a plurality of comparators for comparing a reference voltage divided by each of the resistor elements with an analog input voltage, the comparators having a sample-and-hold function for holding a sampled analog input voltage, and the plurality of comparators including a high-order bit comparator and a low-order bit comparator having different sampling sources, wherein the high-order bit comparator is configured to compare the analog input voltage and one of the reference voltages to obtain a determination result; and selection circuitry configured to select one of the other reference voltages to be input to the low-order bit comparator for comparison with the analog input voltage according to the determination result of the high-order bit comparator.