A 20-Bit Digital-to-Analog Converter (DAC) Using a Magnetic Modulator

The instabilities of weighting circuits (e. g., R-2R ladder or current summer) limit the resolution, the linearity, and the accuracy in a DAC. In order to improve the instability of a weighting circuit, a low-noise ampere-turn comparator using a second-harmonic type of magnetic modulator is used. A 20-bit DAC, using an ampere-turn comparator which has an input winding and a MOSFET switch for each bit (instead of an R-2R ladder network), is described. The linearity error in the ampere-turn comparator due to the magnetic leakage flux around the input and the feedback winding in the weighting circuit, and the output noise of the DAC due to the input noise of the ampere-turn comparator, are discussed. The output noise of the DAC obtained is less than 1/107 of the full scale output range.