EMI Bites: Don't Let Your Signal Lose Its Reference Plane
Your signal trace may look clean on the layout, but if it crosses a gap in the return reference plane, the signal is in trouble.
Here’s why:
At that point, the signal loses its reference potential, and the return current has no defined path to follow.
Why this causes problems:
- The signal enters a cavity (a void between planes) where return current can’t flow directly.
- The electromagnetic fields spread out inside this cavity, searching for a way back to the source.
- As the fields spread, they couple into nearby traces, creating crosstalk.
- This degrades signal integrity and dramatically increases the risk of EMI issues.
Key Insight:
When the return path is broken, the fields spread—and they don’t ask for permission.
How to prevent this:
- Avoid routing signals across gaps or splits in the reference plane.
- Ensure every signal, not just high-speed, has a continuous return path directly beneath it.
- If transitions between layers are needed, use return & reference vias (RRV) to maintain return current continuity.
- Avoid creating cavities between planes, which can easily become antenna structures.
To electromagnetic enlightenment,
- Dario
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