Knowing the difference between differential-mode and common-mode currents is key to mastering radiated emissions and passing EMC certification quickly.
Why? They propagate differently and require distinct handling methods.
The critical point is understanding their root causes.
What drives these phenomena?
Can I control them during PCB and system design?
Traces get routed to redirect electrons, not EM fields.
Stackups follow the “cheapest, fewest layers” rule.
The result? Uncontrolled fields radiating chaos.
Look at the left: fields spreading everywhere, untamed.
EMC instruments spot that mess and fail you instantly.
I’m mainly addressing those who think skipping "GND" layers or swapping them for segmented power layers will save big money in production.
This is a misconception.
A lie often spread by project managers without a proper electrical or electronic background.
Yes, fewer layers mean a cheaper PCB, but that doesn’t guarantee your project will cost less overall.
The issue here is typically not a problem of cost increase, but a problem of wrong cost assessments to begin with.
It could save your design now, or in the next round of testing, particularly for radiated and conducted emission or immunity.
The reason your device failed the test is that its emissions exceeded the allowed limits.
Emissions are generated by time-varying currents, not voltage.
This means that wherever you have currents, you have emissions.
The question is: how much, and from which source?
PCB Hacker - Level 3
PCB Hacker Level 2
PCB Hacker - Level 1
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