Real Time with… AltiumLive: Eric Bogatin on Unlearning What You’ve Learned

The second day of the virtual AltiumLive 2020 event started off with Dr. Eric Bogatin's course. Its official name is "You must not learn what you have learned", but it can also be easily referred to as "Design to reduce the burden of interconnection."

Eric is a lecturer in signal integrity, a professor at the University of Colorado Boulder, and is a "

.

But Eric is indeed an inner teacher. He may teach kindergarten or fifth grade, but he still achieves good results. In the signal integrity course, he likes to tell some stories about how college students gradually teach him something.

He started the AltiumLive course from the story in the UC Boulder classroom. He recently explained to his students that many downstream problems stem from interconnection problems.

Eric said to his class: "Once interconnectivity is established, interconnection will mess things up."

A student replied: "You mean our job is to design interconnections to reduce interconnection consumption?" Eric agreed, and this sentiment described their work to T. This reminds me of the Hippocratic Oath in the medical world: First, don't hurt.

Then he shifted gears and switched to the business at hand-showing the designer how to learn the bad habits he had learned over the years. Eric started with switching noise and pointed out that many anti-noise technologies that were effective 50 years ago do not work now, and even if they do, they can be very inefficient and/or expensive.

For example, Eric explained that the traditional view once required: "You must use 0.1, 1, and 10uF capacitors on the PCB to combat noise." The capacitance of 0.1uF capacitors is small, but the loop inductance is also very high. Low, so it will not have much impact on switching noise.

Now, for today's modern capacitors, you may not need to use 0.1uF capacitors, because 10uF capacitors can have the same low loop inductance as the old 0.1uF capacitors. However, many design engineers still follow the 0.1, 1, and 10uF capacitor rules learned decades ago.

As Eric said: "The interaction of capacitance and loop inductance is where you find ways to reduce switching noise and parallel resonance." He also pointed out that you should never do something just because you see other people doing the same thing. , Such as adding copper to the signal layer. Eric said: "Unless you have a good reason, don't pour copper into the signal plane."

As Eric concluded, what worked decades ago usually doesn't work today, so you'd better not learn those old "old-style" habits.

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