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The key to understanding EMI starts with understanding Signal Integrity.
To me, thinking about signal integrity means reasoning from first principles.
How can I ensure that the integrity of the signal remains constant throughout its entire propagation, from where I send it to where I want it to reach?
How can I ensure that, by controlling the way I design the layout, I don’t alter the signal I intend to transmit within my board?
How can I ensure that the signal—or, more precisely, the electromagnetic fields that constitute what I call a signal—remains confined within the structures I create (e.g., the stackup and layout), rather than allowing it to expand beyond my PC board?
Most of the issues we encounter during EMC testing arise because these fundamentals are overlooked.
Think about it: when you measure radiated (or conducted) emissions, you’re simply measuring how much electromagnetic energy is escaping outside your board, rather than being directed where it’s supposed to go.
Control the fields and their energy, and you’ll pass EMC tests.
Simple, right?
EMI is simple. Not easy.
-Dario
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