Predicting nonlinear distortion in multistage amplifiers and gm-C filters

Abstract

Closed-form expressions to predict nonlinear distortion in analog integrated circuits are derived by calculating the solution through a perturbation method up to the second-order of approximation, in both cases of a single and of a two-tone input signal. The expressions of the harmonics and of the intermodulation products are derived by approximating the circuit nonlinearities by cubic polynomials, which are widely used in the analysis of the distortion in multistage amplifiers and continuous-time transconductor---capacitor (gm-C) filters. The application to two typical circuits, belonging to these two classes of circuits, shows the simplicity and versatility of the presented formulas, whose accuracy is checked by numerical simulations performed using the method of harmonic balance.