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Engineering design and analysis (EDA) software has evolved into an essential tool for wireless circuit and system design. High-frequency engineers are now using RF/microwave EDA software tools to achieve effective and efficient design flows for a wide range of circuits and systems, in commercial, industrial, and military markets. In addition, engineers now rely on EDA software tools to shorten the product design cycles significantly for many different circuits and systems.

Although EDA software tools have been in use for many years, early EDA tools have not always been central to the process of creating circuits. EDA software has been available, in one form or another, almost since the early days of computers. Even when available, however, the software was often cumbersome to use. Most early circuit designs were performed with a pencil and a slide rule.

In the early days of simulation software, computer programs such as SPICE and ECAP were the only available EDA tools. SPICE was developed at the University of California at Berkeley and made available to the public in the mid-1970s. SPICE included nonlinear analysis in the time domain, but not transmission lines or scattering (S) parameters. It was not very useful for RF or microwave work. The latest version of SPICE, Spice3, is still supported and available along with user manuals from the University of California at Berkeley website. The ECAP software contained no transistor models (the user had to generate their own models and create a netlist for them), and it could not handle noise or nonlinearity.

By the 1970s, computers had evolved sufficiently to allow for improved EDA software capabilities. One catalyst was the PDP series of VAX computers from Digital Equipment Corp. (DEC). These “mini-computers” as they were known, occupied the space of a large office and provided more sophisticated functionality, eventually including integrated-circuit (IC) layout capabilities. These computers and their processing power levels were a huge step in the direction of improved EDA capabilities.

Evaluate EDA Software For A Wireless World, Fig. 1Changes in high-frequency technologies were a second factor in the development of EDA software. Before 1960, virtually all microwave components were realized in waveguide or machined transmission-line structures. In the 1970s and 80s, microwave hybrids on both hard and soft substrates became much more common, but the development process involved an approximate design and lots of manual “tweaking.” Software tools appropriate to this kind of design were developed; one of the most important was COMPACT. It ran originally on mainframe computers with a timesharing system, and later on DEC VAX machines. Figure 1 shows a hybrid circuit developed with aid from software of this era: a 1980s-era, 30-GHz mixer hybrid realized on a fused-silica substrate. Individual pieces of the circuit were designed using the EDA software of the day, but the circuit as a whole was not simulated. Layout was performed by a technician who received a dimensioned drawing (which, fortunately in this case, was error-free).

As hybrid technology evolved into increased use of ICs, it became evident that the “build-and-tweak” approach would not be adequate. It was obviously impossible for ICs, but even for hybrids, the cost in development time was increasingly becoming a burden. The problem was not so much the circuit analysis as the circuit-element modeling. Such elements as microstrip step and tee discontinuities were not well characterized, and these structures had profound effects on high-frequency circuits. Precise design was usually impossible.

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