Electronic-design-automation (EDA) tools are used for a variety of simulation and modeling tasks—from developing matching circuits for amplifiers through complete system simulation. Some RF/microwave engineers may work with EDA software every day, but how much do they trust these tools? Among their biggest concerns is model accuracy. The good news is that the EDA houses are involved in a constant feedback loop with their customers. They are striving to provide the most accurate models possible, as well as the necessary support and tools to verify them. In addition, EDA vendors have an eye on the entire system design, allowing engineers to create components and then combine their functions for a full system-level simulation. The myriad of complementary tools include statistical analysis to help translate simulated results into reproducible products.

Martin Timm, CST’s Marketing Director, sums up the challenge facing EDA vendors and their customers: “The accurate modeling of input geometry, materials, and physics—as well as the accuracy and efficiency of the simulation process—represent the software vendors’ challenge. There is, of course, the basic worry of most design engineers: Have they chosen the right tool for the job, or would another tool deliver another, probably more accurate answer?”

This demand for the best possible accuracy is what forces EDA vendors to remain in such close contact with their customers. “We’re really in a unique situation in that, for many years, we have had hundreds of design engineers [who] use our EDA tools to design Agilent’s RF/microwave instruments,” notes Charles Plott, Agilent EEsof EDA Product Planning & Marketing Manager - Core Products. “Along with our customers, these internal designers provide regular feedback on what their challenges are and how we can improve their productivity (Fig. 1).”

Plott also cites model accuracy as the number-one design worry. “This is true for both passive circuit design and nonlinear circuits. For example, for passive circuit design (filters, matching circuits, connectors, antennas, etc.), accuracy has been the main driver for the existence of electromagnetic (EM) simulation. Of equal or greater importance is the accuracy of the device model for nonlinear designs with active components. That accuracy is mission critical. This is something in which foundries, design engineers, and EDA companies all invest.”

Timm points out that simulation accuracy depends on various factors, including whether a simulation model truly represents its real-life counterpart and whether structural and material effects have been considered. These concerns are generally outside of the software vendor’s control. Yet he believes that it is important to deal with these complex structures in order to develop accurate, realistic models.

Shawn Carpenter, Vice President, Sales and Marketing, Sonnet Software, agrees that RF/microwave designers are most concerned with accuracy. He adds, “A second concern, but closely related, is whether they can come to terms with whatever complexity the tool presents in order to get the necessary level of accuracy out of that tool.” Designers are clamoring for tools that are more intuitive and easier for them to master in order to feel confident that they are extracting the most accurate designs and simulations.

Sherry Hess, Vice President of Marketing, AWR Corp., echoes the call for ease of use: “First and foremost, designers want to make sure their circuits are functionally sound (that they work) rather than spending undue time on understanding the nuances of the software used to first design them.”

Of course, all of these concerns must be weighed against how long it takes to achieve a solution. Tradeoffs must be made in terms of simulation time, points out Markus Kopp, Corporate Product Manager, Electronics, ANSYS, Inc. One way that ANSYS addresses this tradeoff is by combining its core technology—adaptive meshing— with a new technology called Solver on Demand. “Combining these technologies ensures that the simulation is extremely easy to create,” explains Kopp. “But it will always have a fine, accurate mesh where it is most important to provide accuracy and a coarse mesh elsewhere for efficiency.”

DESIGN CONFIDENCE
Achieving a sound design can be challenging. In today’s increasingly complex designs, how do designers know that their signal chains will not be influenced by nearby components? “Today, it’s rare that an RF design is standalone,” observes Per Viklund, Product Marketing Director, Mentor Graphics. “RF always shares limited board space with non-RF circuits. Implementing an RF circuit in sync with other circuitry—while making sure there are no harmful interactions—is a serious challenge.”

CST’s Timm concurs: “What we have learned from interacting with our customers is that there is an increasing need to deal with the high levels of complexity found in real-world examples in a simple and straightforward way. Here, ‘real world’ means not just a single component—for example, an antenna—but also the influence of the placement and feed and potentially the effect of thermal stress or general EMC considerations.”

To boost their customers’ confidence in the accuracy and usability of their designs, analysis, and simulations, EDA companies are making strides both to allay designers’ fears and build design confidence. CST, for example, addresses the accuracy question on different levels. Within the different CST STUDIO SUITE simulators, methods such as the Perfect Boundary Approximation (PBA)®, True Geometry Approximation, and arbitrary order curved finite elements are designed to increase simulation accuracy and performance. The firm also offers a System Assembly and Modeling (SAM) feature, which allows designers to set up an EM system in schematic diagram form. The user can assign simulation tasks to a single component, sections of the schematic diagram, or the entire design as a three-dimensional (3D) structure. As a result, he or she can study or optimize it in part or as a whole.

Designers want to run complex simulations for accuracy, but this has to occur within a reasonable amount of time to be useful. By adding Solver on Demand technology to its HFSS software, ANSYS enables engineers to access the HFSS solver from an enhanced-computer-aided-design (ECAD) interface (Fig. 2). This aspect—combined with the adaptive meshing technique in HFSS—allows engineers with very little experience in 3D modeling to create, set up, and solve extremely complex EM simulations.