Resistor string dac with current source lsbs

Abstract

The present invention provides for a method and apparatus for converting an N-bit digital word to an analog voltage signal in which a first circuit (410) provides for conversion of the most significant bits of the N-bit digital word and a second circuit (430) provides for the conversion of the least significant bits. The first circuit (410) includes an array of resistors coupled in series between reference nodes and a switch matrix for providing a node voltage to a first input of a buffer (420) responsive to an indication of the most significant bits of the N-bit digital word in which the buffer output provides the analog voltage signal. The second circuit (430) includes a current device electrically isolated from the resistors of the first circuit (410) and coupled to a second input of the buffer (420) in which the second input is further coupled in a feedback arrangement with the buffer output. The current device is operable to provide a select current such that the resistance of the feedback loop and the select current are cooperable to modify the analog voltage signal by an incremental voltage corresponding to the least significant bits of the N-bit digital word.

Dependencies are inferred from the claim text.