On the effects of finite and nonlinear DC-gain of the amplifiers in switched-capacitor ΔΣ modulators

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 (ΔΣ) 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 ΔΣ 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.