Abstract: The effects of the op-amps' Nonlinear DC-gain on Delta-Sigma (ΣΔ) modulators is studied in this paper.A system-level model consists of a hyperbolic tangent model for the input/output characteristic of op amps and a recursive solution of nonlinear integrators.The proposed model can simply be used to evaluate the effect of amplifier's DC-gain nonlinearity.Simulations at different levels of abstraction indicate the accurateness of this model.