Calibration algorithm for current-output R-2R ladders

The paper presents a new calibration algorithm for current-output R-2R ladders. The widely used R-2R ladders are easy to realize as an integrated circuit, but the resistance tolerances limit their linearity properties. However, it is possible to achieve higher linearity with self-calibration techniques. A formerly published calibration algorithm by Cutkosky is available for the so-called Cutkosky R-2R ladders. A similar algorithm can be derived for the current-output ladders, which are widely used as multiplying digital-to-analog converters (NMACs) or digital-to-analog converters (DACs). In this paper, the Cutkosky divider is briefly discussed, and then a new description of the inverse ladder is presented as a basis of the calibration algorithm. The calibration algorithm is discussed in detail, and the error budget is analyzed. A simulator was also written to verify the theory.