Digital-to-analog converter circuit

Abstract

A digital-to-analog converter circuit mainly comprises a D/A conversion part, an operational amplifier and a reference-voltage producing circuit. The D/A conversion part is configured by a resistance string, consisting of a string of resistors connected in series, and a plurality of switches which are each turned on or off response to a digital input. The reference-voltage producing circuit produces a reference voltage, the level of which is stabilized and is not affected by power-supply voltage. The operational amplifier has two inputs, wherein a noninverting input receives the reference voltage, while an inverting input is connected to a center-tap terminal of the resistance string. An output terminal of the operational amplifier is connected to a positive-power-supply terminal of the D/A conversion part. Because of the characteristic of the operational amplifier, the reference voltage is applied to the center-tap terminal of the resistance string, so that an analog output of the D/A conversion part varies up and down with respect to the reference voltage. The output of the D/A conversion part can be supplied to an amplifier circuit, which operates based on the reference voltage, through a voltage follower.

Dependencies are inferred from the claim text.