All major competitors in the operational amplifier markets are providing their customers Spice-based macromodels. These models give the designer a tool to do initial characterization and a limited amount of system troubleshooting. In the interest of faster simulation times and lower CPU memory requirements, macro topologies have been developed to simulate a majority of the op amp’s performance characteristics. Several different approaches to creating macromodels have been used, each producing a macro with its own set of strengths and weaknesses. Circuit simulations have become increasingly important to the systems level designer.