Apparatus and method for increasing the output impedance of a current-type digital-to-analog converter

摘要

A current-output CMOS DAC with a compensation circuit to increase output impedance. The circuit includes an auxiliary MOS current source matched to at least one of the DAC bit-current sources. A comparator compares the drain voltage of the main MOS current source (which is connected to an external reference current source Iref) with the drain voltage of the auxiliary current source. The output of the comparator controls the magnitude and sign of a correction current which is directed to the main current source transistor and thereby alters the bit-current output to reduce the ouput sensitivity to changed conditions.