Misconceptions about electron flow cause EMC test failures.
Engineers often view signals as electrons moving through traces.
This overlooks the propagation of electromagnetic fields.
An ineffective stackup allows fields to radiate as EMI.
A well-designed stackup channels electromagnetic fields efficiently.
Some engineers delay electromagnetic interference (EMI) considerations until compliance testing, assuming issues can be resolved with quick fixes.
This approach often leads to costly redesigns and project delays.
EMI is best addressed early in the design phase through:
- Optimized PCB Layout: Minimize the area enclosed by current loops to reduce antenna-like structures that radiate or conduct high-energy harmonic content.
- Strategic Component Selection and Placement: Choose components and arrange them to limit EMI risks.
When you flip a light switch, the bulb lights up instantly.
You might think electrons flow through the wires, carrying energy from the battery to the bulb.
That’s a common idea, but it’s not quite right.
The Old Idea: Electrons Moving Inside Wires
Traditionally, electricity is like water in pipes: the battery pushes electrons inside wires to the bulb (the "load") and back.
One of the biggest game-changers for me in EMI control is visualizing the EM fields as signals propagate.
Too often, we focus only on the signal path and treat the return path as an afterthought, just to close the current loop at the end of the design.
In reality, the loop is closed as the signal travels (yes, displacement current in the dielectric magically closes it!), so any gaps or breaks in the return path—like splits in the reference plane—can mess with your signals, causing crosstalk or turning cables into antennas.
How bad? It depends on frequency (high-speed signals are pickier!), but it’s always better to know it’s coming.
I like to think of the PCB as a set of channels for guiding EM fields exactly where I want them.
PCB Hacker - Level 1
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