SFDR Improvement Algorithms for Current-Steering DACs

Abstract

This paper presents algorithms for improving spurious-free dynamic range (SFDR) of current-steering digital-to-analog converters (DACs) — targeted at communication applications — by minimizing both current-source mismatches and glitches. Conventional segmented current-steering DACs suffer from static mismatches among current sources which cause nonlinearity and degrade SFDR, though glitch energy is relatively small. The data-weighted averaging (DWA) algorithm can reduce static current source mismatch effects, but it increases the effects of glitch energy. Here we investigate the use of both conventional Switching-Sequence Post-Adjustment (SSPA) calibration and One–Element-Shifting (OES) methods in order to reduce the effects of both nonlinearity and glitch energy. For further improvement, we propose and investigate a fully-digital combined algorithm to reduce static current source mismatch effects with minimal increase in the glitch energy. We also did simulations of the effect of combining these two compensation methods. Our MATLAB simulations show that the combined algorithm can improve SFDR performance by 24 dB, 22dB and 2dB compared to conventional thermometer-coded, one-element-shifting and SSPA methods respectively in some conditions. When we take current mismatch into account, the combined algorithm causes glitch energy to increase by only 0.02 to 0.2 % compared to the other three methods alone.