Serial-parallel type a/d converter having reference resistor chain and

Abstract

A serial-parallel type a/d converter comprises first comparators whose one input is supplied with an input signal, for producing upper-digit signals; a circuit for supplying first different potentials determined according to arithmetic progression with respect to a reference potential to respective another input of the first comparators when the control signal is of first state, and for producing N-1 second different potentials with difference 1/N of voltage difference of first potentials over potential P (N, P: natural numbers) given by the upper-digit signals when the control signal is of second state; and N-1 second comparators whose one input is supplied with the input signal and another input is supplied with the respective second different potentials for producing lower-digit signals. A second a/d converter further comprises a circuit for additional reference potentials and additional comparators to make the lower-digit conversion range larger than one unit of the upper-digit conversion to improve conversion speed limited by settling time. Also, the upper-digit can be corrected by output from additional comparators. The number of comparators is reduced by switches for switching over from upper-digit to lower-digit potentials sent to the comparators.