Current-steering digital-to-analog converter for providing bi-directional currents through a load

A digital-to-analog converter capable of bi-directional output currents which is especially useful for direct conversion of digitally encoded audio signals. The converter is made up of a plurality of bit-cell circuits, one per bit in the digital number to be decoded, each fed by a pair of current sources of identical magnitude and opposite direction. Each bit-cell is a bridge circuit of four controllable devices, controlled by a data bit and its complement so that the current flow through the current output of the cell reverses based upon the value of the data bit. The outputs of the bit-cells are paralleled, and the current source pairs are scaled in a binary fashion, so that each bit-cell steers a current which is one-half that of the next-higher cell. In a preferred embodiment, the current sources are made up of two binary scaled current generators using R-2R resistor networks to scale currents from two reference sources. The two references are preferably linked to each other through a feedback circuit. One reference may be varied (the other tracking automatically) to act as a volume control.