Modeling Op Amp Nonlinearity in Switched-Capacitor Sigma-Delta Modulators

A system-level methodology for the inclusion of op amp nonlinearity in discrete-time integrators and SigmaDelta modulators is proposed that consists of a hyperbolic tangent model for the input/output characteristic of op amps and a recursive solution of nonlinear integrators. Simulations at different levels of abstraction indicate that the methodology incurs an error of no more than 1.1 dB in the magnitude of harmonics while providing a 50times advantage in the simulation speed with respect to transistor-level implementations