A modified time-domain model for nonlinear analysis of an operational amplifier

A generalized two-pole time-domain model useful for op amp analysis in both linear and nonlinear regions is presented. It models slew enhancement and degradation effects for different types of input devices and voltage steps. This has been accomplished by taking a more limited two-pole model and modifying it to take into account the initial conditions in both the nonlinear and linear regions and the slope at the beginning of either the slewing or linearly settling time periods. Both the slewing period and settling period are accurately predicted by the model. A comparison of this model with SPICE analyses on a typical CMOS op amp circuit gives excellent agreement.