HARMONIC DISTORTION IN SC SIGMA-DELTA MODULATORS

The maximum achievable resolution in noise-shaping modulators is a fun ction of three principal parameters: oversampling ratio, M; noise-shap ing order, L; and quantizer resolution, N. For practical implementatio ns, thermal noise in MOS switches and amplifiers, bandwidth and slew-r ate in integrator circuits in switched-capacitor (SC) implementations, and jitter noise in continuous-time (CT) and mixed CT-SC realizations have to be considered. This paper deals with harmonic distortion, whi ch is a third design constraint in high-resolution SC noise-shaping mo dulators. Here we analyze harmonic distortion due to the nonideal dc-g ain characteristic of operational amplifiers and derive a relationship for a standard SC integrator. Simulation results from a behavioral si mulator we developed validate the analysis.