The aim of this paper is to present a new analog behavioral SPICE macromodeling technique of the operational amplifiers, based on a direct implementation of their time and frequency domain internal equations with nonlinear controlled voltage and current sources. It greatly increases the simulation accuracy by considering the high order poles and zeros of the differential and common mode gains, as well as of the input and output impedances. Also the macromodel includes the temperature dependencies of the main OpAmp electrical parameters and it considers their tolerances for the Monte Carlo simulation. The proposed behavioral macromodel is a unified one, valid for all the existing OpAmp technologies and it is portable easily in all the modem SPICE simulators that support the Analog Behavioral Macromodeling facilities. It is made only of passive elements and controlled sources, and thus it leads to a very low computation time, with no convergence problems. It uses directly the common data-sheets specifications as model parameters and thus eliminates the time consuming model calibration step.
A SURVEY OF EXISTING OPAMP SPICE MODELSAlthough the detailed transistor level OpAmp modeling offers the highest possible simulation accuracy, it is rarely used in the large designs analysis, due to the prohibitive large computation time. Actually there exist two methods of OpAmp SPICE modeling for efficient simulation of large designs: the simplified transistor level modeling, and the structural macromodeling. The simplified transistor level modeling consists in developing a simplified equivalent circuit in which all the signal path transistors are modeled with the high accuracy SPICE transistor model, and all the auxiliary circuitry (biasing, protection, etc) are described with equivalent voltage or current sources [ I , 2].The advantage of this method is the nearly full transistor level accuracy, with a lower simulation time. However, it has some drawbacks that limits drastically its wide use: the models are specific for each structure of OpAmp, the model parameters extraction algorithm is complicated and needs additional physical and geometrical knowledge about the internal transistors, and the simulation time is still high. Actually the most used method of OpAmp SPICE modeling is the structural macromodeling, that consists in modeling the input stage with a simplified transistor level unity gain circuit, and all the other stages are modeled with controlled sources. The advantages of this method are the simplicity, and thus the computational efficiency, the portability in all the existing SPICE simulators, and the easy algorithm of model parameters extraction from data-sheets characteristics. The macromodel is no more part dependent, but is still specific for a given type of input stage (bipolar, JFET, MOS). The most popular OpAmp structural macromodel is the one developed by Boyle [3], with its derivatives 14-71, However, it do not include many of the second order effects: higher order poles and zeros, the input equivalent n...