An ISI Scrambling Technique for Dynamic Element Matching Current-Steering DACs

The linearity of high-resolution current-steering digital-to-analog converters (DACs) is often limited by inter-symbol interference (ISI). While dynamic element matching (DEM) can be applied to convert a portion of the ISI to uncorrelated noise instead of nonlinear distortion, DEM alone fails to prevent ISI from at least introducing strong second-order nonlinear distortion. This paper addresses this problem by proposing, analyzing, and experimentally demonstrating a low-cost add-on technique, called ISI scrambling, that, in conjunction with DEM, causes a DAC's ISI to be free of nonlinear distortion. The ISI scrambling technique is demonstrated in a 1-GS/s, 14-bit DEM DAC implemented in 90 nm CMOS technology. The DAC's measured linearity is in line with the state-of-the-art and its measured output power spectra closely match those predicted by this paper's theoretical results.