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What classical circuit theory fails to teach you about designing Printed Circuit Boards (PCBs) is that it’s not about electrons moving through traces like water through pipes.
This is why not many PCB designs pass EMC tests on the first attempt, because many are designed with this incorrect concept in mind.
The circuit you see here has only two layers, both dedicated to signal traces.
Here is why the chances of passing EMC are extremely low:
- No consideration of how electromagnetic fields spread from the conductor traces.
- No consideration of how current loops are directly related to radiated emissions.
- No consideration of how common mode voltage drives antenna patterns once the cables are connected.
- No consideration of how signals do not see a characteristic impedance along their propagation, leading to signal integrity failures.
- No consideration of the impedance discontinuities signals encounter when crossing splits and other traces.
- No consideration of crosstalk and its impact on emissions and board performance.
- No considerations about return current and reference voltage during signal propagation.
The list goes on and on...
The same applies to immunity to external interferences, of course.
I mention this because I want to help you understand that these are the common failures when your board does not pass EMC tests.
95% of EMI issues can be addressed at the layout stage.
This means you can design the PCB correctly from the start.
You don't need to have four iterations of your board to finally pass the test.
EMC is all about prevention, not last-minute ferrite beads and copper tape SOS techniques.
I hope this helps you see that there are ways to take your designs to the next level.
But for that, you have to think in terms of Electromagnetic fields.
Dario