Analog Circuit Design, an Updated View

My previous post was based on a book written late in the previous millenium, so you would be right to expect that the attitudes and process of designing analog circuits has changed dramatically. Certainly, the knowledge base and the tools have changed in the past 30-odd years.

I was fortunate to find an article about analog design tools in Electronic Design from 2011. After a round-up of the tools, Don Tuite interviewed a design engineer at Linear Technology to see how the tools are used in circuit design today. Don asked Leonard Shtargot about his personal experience with analog design tools. He eventually answered the question, but first gave us some insight into the whole process of analog circuit design:

“LTC (Linear) is a really interesting place because a lot of the folks that work here were either part of the original wave of innovation that created the first analog ICs or the next generation. So seeing how their minds work about designing integrated circuits and solving problems is really valuable,” he said. 

“As an undergraduate engineering student, I learned analysis techniques, and how existing circuits work, but there wasn’t an emphasis on creating new circuits. Working at Linear, I learned the missing 70% or 80% about creating something new,” he said. 

“Analysis is certainly important, but doing something new requires the human mind to build abstractions in terms of the various building blocks, abstractions that are simple enough so you can synthesize them to do what you want. That’s a tool that you can only learn from people who’ve been doing this for decades. The people who did these things originally looked at circuits from their physical embodiment.”

Shtargot didn’t hold much hope for a future generation of analog EDA tools.

“Another thing you can actually learn from more experienced designers is what I’d call intuition. Current EDA tools don’t contain enough ‘intelligence’ to make an analog circuit work right the first time, regardless of the number of simulations you run,” he said. 

“Spice works well if your models are good, but characteristics change with how the device is drawn, or with relative temperatures. That’s hard to model. Essentially, the problem is that if you tried to build a generalized CAD system that could capture any variant of an analog circuit that you’d want to design, it would take much longer than to go and talk to experienced people who can pass their knowledge along and then just build the circuits. Maybe one day programming techniques will get better.” 

“With analog design, a big part of the challenge is defining the problem, defining what you really want,” Shtargot said. 

“One of the things that we learn from folks here who have a long history is that, when you visit a customer, you have to ignore what the customer said he wants, and listen to his problem. It’s often better to apply the fundamentals to solve the problem, rather than try to force an existing part into a role it wasn’t intended for.”  

While not quoting Gilder, he seemed to echo the ideas that they cannot rely on some prefabricated system of knowledge and that electrical engineering will not teach them everything. But Shtargot stopped short of saying that intuition is something that must be learned mostly by themselves. Instead he emphasized the continuity of learning from those who came before, following in their footsteps (figuratively, and possibly literally too).

NOTES:

1. "Contrasts Mark Analog Design Tool Use", Don Tuite, Electronic Design, Oct. 24, 2011