Frequency domain analysis for operational amplifier macromodels

Under large signal conditions, active circuits containing operational amplifiers as elements can exhibit discontinuous response in the frequency domain. A computational procedure is described in this paper for the prediction of large signal frequency response characteristics of active circuits based upon an operational amplifier macromodel containing nonlinear circuit components to represent slew-rate limiting. The interconnection circuitry, exclusive of the operational amplifiers, is mathematically represented in the hybrid matrix form and a mininal set of nonlinear equations for the active circuit is given. A Newton-Raphson iteration, based on a describing function representation for the nonlinear circuit components, is used to numerically solve the circuit equations. Two active circuit configurations that have been observed to exhibit discontinuous large signal frequency response characteristics are described. Data obtained by application of the algorithm to these two circuits is given. Correlation between experimental data and computational results has been excellent.