A Current-Comparator-Based 20-Bit Digital-to-Analog Converter

A current-comparator technique for obtaining a 20-bit digital-to-analog converter (DAC) is described. A self-balancing dc comparator is used to establish currents proportional to a reference quantity. The code weight of each input bit is established through turns on a magnetic core rather than by a resistor ladder network. The converter has a full-scale voltage output of 10 V, a linearity error of less than 1 ppm of full scale, and a settling time of approximately 6 ms.