Patent ID: 7564395

Claim:
A subranging analog-to-digital (AD) converter that converts, for output, an incoming analog signal into an N-bit digital signal, the converter comprising: a divided voltage generation circuit that equally divides a range of a predetermined voltage, and generates 2 m +1 divided voltages; a higher-order conversion circuit that generates, for output, a signal for higher-order m bits of the digital signal by comparing the analog signal with the 2 m −1 or less of the 2 m +1 divided voltages; a switch circuit that selects, for output, at least two of the 2 m +1 divided voltages based on information provided by the higher-order conversion circuit; a lower-order conversion circuit that generates, for output, a signal for lower-order n bits (n=N−m) of the digital signal by comparing the analog signal with the divided voltages being a selection result of the switch circuit; and an encoder that generates the digital signal based on the signal provided by the higher-order conversion circuit and the signal provided by the lower-order conversion circuit, wherein the switch circuit selects, from the 2 m +1 divided voltages, a first divided voltage being higher by a predetermined value compared with any two of the divided voltages closest to a voltage of the analog signal, and a second divided voltage being lower by the predetermined value compared therewith, when the first divided voltage is to exceed any of the 2 m +1 divided voltages being the highest, the switch circuit sets the highest divided voltage as the first divided voltage, and sets, as the second divided voltage, any of the 2 m +1 divided voltages being lower than the first divided voltage by a difference of r (r is an even number of 2 or more) of the divided voltages, and when the second divided voltage is to fall below any of the 2 m +1 divided voltages being the lowest, the switch circuit sets the lowest divided voltage as the second divided voltage, and sets, as the first divided voltage, any of the 2 m +1 divided voltages being higher than the second divided voltage by a difference of r (r is an even number of 2 or more) of the divided voltages.