Issue link: https://iconnect007.uberflip.com/i/1359517
24 DESIGN007 MAGAZINE I APRIL 2021 detail—the need is far more pedestrian. We're not servic- ing those needs when we focus primarily on the state of the art. SI tools have been around for 30 years now, and we still see the majority of people not simulating, so we need to con- sider doing something else. Shaughnessy: Maybe they don't need a tool that you have to be an experienced signal integrity engineer to operate. Can a regular system designer or layout designer use the sim- ulation tools we have today? Westerhoff: Depending on the tools you talk about, yes and no. Let's go back to our classes of users. Experts are looking for advanced tools with state-of-the-art performance and capac- ity. Ease of use is a consideration but not criti- cal, as experts can make pretty much anything work. ey have deep SI knowledge and can improvise analytical methods when the situ- ation calls for it. To your question, the tools used by full-time SI/PI engineers are typically not usable by mainstream designers, because the tools by themselves are not enough. You need an analytical methodology, or workflow, to apply the tools to a design and determine whether the design will work, and that process is typically complicated enough (and manual enough) to preclude use by someone who isn't performing analysis full-time. And that's the rub: if we're not designing a 112-gigabit serial link or a loaded DDR5 inter- face, most of the issues we face during design and layout don't require the kind of accuracy that an expert is looking for. ere are a lot of design issues you want to take off the table before you put a lot of effort into modeling and simulation. You can think of it this way: Experts typically simulate at the level of accu- racy needed to "sign-off " a design for fabrica- tion, but system designers are oen just trying to assess the impact of a tradeoff on design margin. In those cases, a good answer now is preferable to a great answer later. You can think of that as "trade-off " analysis. It's less accurate, but faster to run and accessible to a wider audience. at's the kind of analysis that needs to be accessible to regular system or layout designers. We have some of those tools in place today, but the world clearly needs more. Shaughnessy: Everyone agrees that it's rough going at first, trying to understand simulation without decades of experience. Where would a young EE start? Westerhoff: Signal integrity is one of those fields where there seems to be a lot of tribal knowl- edge and a relative scarcity of basic training material for new users. DesignCon papers are great for advancing the state of the art, but they are oen over the heads of people who don't do SI for a living (this stuff is complicated, aer all). What's the new engineer supposed to do? We seem to have basic material that's easy to understand but doesn't really help you make design decisions, and advanced material that gives you a mathematical formulation for how the physics work, but not enough in-between. ere are people who can look at Maxwell's equations and understand how EM waves propagate, but I'm not one of them. It took me a long time to understand why RF structures are characterized the way they are, and how that applies to time-domain circuit analysis. I don't see enough material that explains physi- cal phenomena at a practical, intuitive level and links to the types of design decisions that engineers need to make. Todd Westerhoff