ABSTRACT
Computer-Aided Design (CAD) tools were proprietary, in-house efforts running on text-only terminals. The 1980s brought the development of the microprocessor and UNIX workstations. The UNIX workstation played a large role in the development of more sophisticated CAD tools. The greatest innovation in the 1990s was the emergence of CAD tools based on the direct solution of Maxwell’s equations. CAD of low frequency circuits is at least 30 years old and microwave circuits have been analyzed by computer for at least 20 years. Optimization is a key component of modern linear and nonlinear circuit design. In the simpler examples, most circuitry and components are mounted on the top layer while inner layers are used for routing of radio frequency signals and DC bias. However, more complex examples can be found where printed passive components and discontinuities are located in one or more buried layers.
