Bridging the Simulation Tool Divide


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Todd Westerhoff of Siemens EDA recently spoke with the I-Connect007 Editorial Team about the divide between users of high-powered enterprise simulation tools and those who need a more practical tool for everyday use, and how Siemens is working to bridge the gap. Todd also shared his views on why so many engineers do not use simulation, as well as advice for engineers just getting started with simulation tools.

Andy Shaughnessy: Hi, Todd. This is our simulation issue, and we want to get your thoughts on some of the challenges in this area. What do you see right now? What’s the biggest problem in simulation?

Todd Westerhoff: I think the biggest challenge is that there just aren’t enough people simulating. There are a lot of people who are designing to rules of thumb, manufacturer guidelines, or getting somebody else to run analysis for them—but there aren’t that many simulating themselves. I usually break simulation users into two broad groups: SI experts, who run simulations full time; and everyone else, who run simulations intermittently, if at all. The SI experts have the most advanced requirements and are also the smaller of the two groups.

The general assumption about simulation seems to be that it starts at the top—if we meet the analysis needs of the experts, knowledge and technology will trickle down over time to the broader audience. The problem is that, as an industry, we have too many designs in progress with too few experts to support all that activity. Simulation has two main purposes:

1. Providing a basis for making informed decisions about design trade-offs.

2. Validating a design before manufacture to reduce the risk of prototype spins.

How do we expect the majority of system designers to make decisions and reduce risk if they don’t have data to back up those decisions? Most of the simulation that we need to make design decisions and detect issues during layout doesn’t require expert-level attention to detail—the need is far more pedestrian. We’re not servicing 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 consider 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 simulation 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 capacity. Ease of use is a consideration but not critical, as experts can make pretty much anything work. They have deep SI knowledge and can improvise analytical methods when the situation 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 interface, most of the issues we face during design and layout don’t require the kind of accuracy that an expert is looking for. There 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 accuracy needed to “sign-off” a design for fabrication, but system designers are often 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. That’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.

To read this entire interview, which appeared in the April 2021 issue of Design007 Magazine, click here.

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