Analysis of op-amp phase margin impact on SC ΣΔ modulator performance

The impact of operational amplifier (op-amp) phase margin on switched-capacitor (SC) sigma-delta modulator (ΣΔΜ) performance is investigated in this paper. An ad-hoc integrator settling model is developed and verified by circuit simulations performed in a commercial 0.35 μm CMOS technology. The model allows the effect of op-amp phase margin to be taken into account in ΣΔΜ behavioural analysis. Behavioural simulations of a typical single-bit second-order modulator are presented, as an example. As shown, the proposed analysis allows well-found specifications for the op-amp unity-gain frequency, slew rate and phase margin to be defined since the preliminary behavioural simulation phase.