On the Effects of Finite and Nonlinear DC-Gain of the Amplifiers in Switched-Capacitor ΔΣ Modulators

Abstract

This paper presents a study of the effects of the op-amps' finite DC-gain (FDCG) and nonlinear DC-gain (NLDCG) on switched-capacitor (SC) delta-sigma (/spl Delta//spl Sigma/) modulators. Starting with the theoretical point of view, these two nonidealities are analytically studied, modeled and their effects on the overall signal to noise plus distortion ratio (SNDR) of a modulator are discussed. Several simulations are performed to clarify the various effects of FDCG and NLDCG on a typical single loop modulator. It is shown that although FDCG of the first stage of the modulators has always attracted the most concerns on /spl Delta//spl Sigma/ literature, NLDCG of the first stage could have a worse effect in the output SNDR due to its nonlinear nature which directly manifests itself as a distortion error and increases the in-band noise of the modulator.