Measurement of nonlinearity in high-resolution sigma-delta converters

Sigma-delta conversion techniques are now common in high-resolution analog-to-digital (AD) and digital-to-analog (DA) converter design, and are capable of achieving high dynamic range with low distortion. One of the biggest problems in evaluating the performance of such converters is in measuring nonlinear errors at either the design stage (by simulation) or in physical realisations. This paper reviews techniques commonly used to evaluate performance, such as sinewave testing and dc-level sweeps, and presents a new technique for measuring nonlinearity using maximum-length sequence (pseudo-random noise) stimuli. Maximum-length-sequence (MLS)-based distortion measurements are possible because of the separation of linear and nonlinear signal components that occurs under MLS cross correlation, and possess some unique and desirable properties