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Henry Ott is one of the gurus of EMC and noise control. After retiring from a distinguished thirty year career at Bell Labs, Whippany, he started a new company to focus on EMC education and consulting. For years, he has shared his practical expertise in electronic circuit design with the rest of us.

I first learned about correct cable shield termination for low noise design from his classic book, Noise Reduction Techniques in Electronic Systems, which he wrote in 1976. If you missed this classic of EMC design, it’s not too late.

His latest book, Electromagnetic Compatibility Engineering was just published by Wiley in 2009. While it includes much of the content of his first book, it’s been updated and more than half the book is brand new information.

I recently had a chance to chat with Henry about his book and about splitting planes and stack up design. The interview is part of the Shaughnessy Report on PCBDesign007.

“When is it appropriate to split ground planes?” I asked him.

“Never split ground planes unless you absolutely have to,” Henry said. “You have to have some external reason, not because you’re just laying out a board; for example, like a low leakage application in medical applications.”

“If you split ground planes and there is no compelling reason, the performance could be worse. I often fix problems my clients have by making the ground planes solid. 98% of the time, tie all the grounds together with a solid ground plane.”

An entire chapter of his new book is devoted to recommendations for circuit board stack ups. He evaluates 1, 2, 4, 6, 8, 10 and even 12 layer stack-ups to analyze the tradeoffs. There is sometimes more than one stack up that will work, but some might have higher performance margins than others. To select the best stack up for your application, you have to know the criteria for what is “better”. He offers six considerations:

  1. a signal layer should always be adjacent to a plane
  2. signal layers should be tightly coupled to their adjacent planes
  3. power and ground planes should be closely coupled together
  4. high speed signals should be routed on buried layers and located between planes
  5. multiple-ground planes are very advantageous
  6. when critical signals are routed on more than one layer they should be confined to two layers adjacent to the same plane.

If you work in signal integrity or EMC design this is a must have book. It has something for everybody.
 
One of the features that distinguishes this book from many others on the same subject is the inclusion of questions at the end of each chapter. While this of itself is nice, even better is that the answers are in the back of the book, in appendix F.

For example, question 12.8 is, “If a small circular and a small rectangular loop both have the same area and carry the same current at the same frequency, which will produce the greater radiated emissions?”

For the answer, you’ll have to check Henry’s book.