I sat down with Brad Brim recently. He was retiring from Cadence literally the following day. He has worked on signal integrity his entire career, which spans the period from signal integrity not really being anything at all in the digital world, to where we are today, with digital signal frequencies in the range that we used to call microwave or even millimeter wave. So I asked him to use his own career to give me the history of signal integrity analysis.

Brad did his undergrad and masters at Washington State University in Pullman, WA (about 60 miles south of Spokane). Then he did a Ph.D. at the University of Colorado at Boulder. At grad school, he had focused on microwave design, PCBs and antennas. When he finished, he'd basically studied numerical computations and how to calculate the way these things work. He had the choice of being a professor since he loved teaching, but he decided that as a junior professor he'd have too much grunt work. Instead, he knew someone at HP who had been tasked with putting together and EDA group. They already had circuit simulation. In fact, Ken Kundert was already there. Ken would later go on to be the creator of the original Spectre simulator and worked for me when I ran what was then the Custom IC group at Cadence in the early 2000s. Brad joined HP before the group shipped their first product, MDS (for Microwave Design System). He worked on algorithms and software development for EM computation, the "method of moments", which was really good for PCBs and forms the basis of the product “Momentum” for which Brad was HP’s lead engineer.

HP also worked with Ansoft, which was an odd relationship since HP had tens of thousands of employees and Ansoft was only a few hundred. To add to the confusion, that part of HP would go on to become named Agilent when HP was first split, and then Keysight when Agilent was itself split. In the meantime, Ansoft was acquired by ANSYS.

But back in 1988, when Brad joined, and the early 1990’s it was still HP working with Ansoft. Ansoft would develop the code, and HP would provide the specs, manufacturing, and distribution. In about 1995, Ansoft and HP went their separate ways and both companies independently developed their own version HFSS (high-frequency structure solver). Brad was at HP in that era, but he left HP in 2000 and went to Ansoft where he was an application engineer for electromagnetic (EM) simulation software and produce marketing manager for HFSS. As Kleenex is to facial tissue, HFSS (now trademarked by Ansys) is a trade name for a product like Clarity that Cadence recently announced (see my post Bringing Clarity to System Analysis for details). HFSS is based on making finite element approaches work for RF and microwave. In discussing the diversity of applications to which 3D EM simulation software applies Brad joked that in the span of a single day he helped customers simulate the electrical behavior of on-die spiral inductors and nuclear bombs.

During his time at HP, there was an explosion of RF and microwave simulation. There were many commercial microwave applications, including government agencies, measurement companies, aerospace and small manufacturing machining metal for the broadcast industry making things like waveguides, resonators, filters, and connectors. It used to be done by hand and would literally take months or even years to get right.

The first thing we simulated took two years to design, and we could simulate it in a week of computer time in 1989. By the time I left Agilent in 2000, I could do the same design optimized for manufacturing tolerances in 15 minutes. Analysis went from weeks to minutes due to algorithm improvements and computer speeds.

Later, in 2006, Brad left Ansoft and joined Sigrity. Sigrity had been created in the late 1990s (SPEED97 was its first product). It had been a university spinout created when IBM encouraged Dr. Jiayuan Fang to commercialize the technology for analyzing complex packages. Brad joined as the marketing guy, although in his interviews apparently nobody asked him anything about marketing, they only wanted to quiz him about numerical EM algorithms.

Over the years, digital frequencies went up and up. As Brad put it to me:

After we shipped MDS, people doing digital would just look at “how much capacitative load, rise time, slew rates.” Then it became “ringing, overshoot etc”. But at that time microwave/RF was low single digit GHz up to about 40GHz. But now we have 112Gbps SerDes, which with PAM4 signaling is 56GHZ baseband. So what we used to think of as the highest microwave frequencies is now a digital serial interconnect frequency.

Brad described the early high-speed digital market segment. They didn't need to do anything unique from the ground up, they could just apply the same microwave design techniques to digital and include more of the parasitics that the digital people ignored and never included. So HP/Agilent and Ansoft were coming from the high-frequency down. Even as late as 2005, there was a dichotomy between that approach and others who were going from the low frequency up. Sigrity truly focused on signal integrity and whole-board/package characterization. They would start with the whole board design database from tools such as Allegro® from Cadence, bring it in, and characterize it. This approach became the mainstream in the early 2000s and started to take off about the time Brad joined Sigrity. Cadence had some signal and power integrity (PI) technology working up from schematic or layout, but it was the low-frequency up and low-fidelity approach, still really circuit simulation. In 2012, Cadence acquired Sigrity (and Brad). The full potential of tightly integrating PBC/package physical design (layout) and SI/PI analysis continues to develop with these two previously independent pursuits now part of a single business unit in Cadence.

Digital frequencies are so high that they are really "RF with a digital focus". The tools that used to work on things like rectangular tube waveguides are now simulating on-die spiral inductors, wire bonds and multi-gigabit serial interconnects. It is no longer enough to use lumped inductors and capacitors as parasitics, everything is a distributed circuit described by transmission lines and S-parameters (frequency domain data).

Brad told me that the big thing that the combination of Allegro (PCB design) and Sigrity (signal and power integrity analysis) brings is that companies need solutions that work in the context of the design. A big company might have hundreds of PCB layout people but only a dozen signal integrity analysis experts. The end goal is not just to make the SI simulator run ten times faster, but it is to get a design "done" and signed off by the analysis gurus much faster. A lot of that is “screening” type design assessment, identifying which signals the experts need to simulate in detail so that the layout guy and the integrity guy can work together quickly to make the final few adjustments.

We have accurate enough simulations and design flows and it is a question of making them work faster, and better.

As Brad likes to remind his algorithm-focused software development colleagues, “Put the ‘A’ back in EDA.”

Brad told me that through his career he never wanted to be a manager, always an individual contributor. That way, he reckoned, you could do your job and simultaneously create your own next job. He managed to do that working for just three companies: HP, Ansys, and Sigrity (and, obviously, Cadence after the acquisition, which you can count as a fourth company if you want). He now plans to spend more time with his family, remodeling various properties that he owns, gardening and brewing beer. He is also volunteering with a non-profit focused on sustainable community gardens, and healthy organic food production, up near Olympia in Washington, where he lives.

More Information

See the Clarity product page or what's new in Sigrity.

Video

Here's a video I made with Brad recently talking about DesignCon, which increasingly is a signal integrity conference (see my post DesignCon: The Integrity Show).

Sign up for Sunday Brunch, the weekly Breakfast Bytes email.