Harmonic distortion in SC sigma-delta modulators

The maximum achievable resolution in noise-shaping modulators is a function of three principal parameters: oversampling ratio, M; noise-shaping order, L; and quantizer resolution, N. For practical implementations, thermal noise in MOS switches and amplifiers, bandwidth and slew-rate 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, which is a third design constraint in high-resolution SC noise-shaping modulators. Here we analyze harmonic distortion due to the nonideal DC-gain characteristic of operational amplifiers and derive a relationship for a standard SC integrator. Simulation results from a behavioral simulator we have developed validate the analysis.<
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