What if I told you there is a way to pass EMC tests and control EMI without adding extra filters to your designs?
What if I told you there is a way to pass EMC tests and control EMI without adding extra filters to your designs?
Yes, not all EMI control tips involve the classical answers of shielding, filtering, and ‘earth grounding’ (whatever that even means).
The reason most electronic designs fail to pass EMC tests is that signals are not properly channeled in the circuit structures.
What does this mean?
Unlike air or other media where conductors are not used, electrical circuits use conductors to control and channel electromagnetic fields from one point to another for power or information.
The channel for these fields in a circuit is typically formed by at least two conductors, the Signal Conductor and the Return and Reference Conductor, commonly (and wrongly) called ‘ground.’
The signal then propagates in this channeled space between (and in cases around) the conductors.
In a PCB, the channel is formed between one layer and an adjacent layer, where signals are typically routed on one layer, and the adjacent layer is dedicated to the Return and Reference Plane (RRP).
The problem in terms of EMI is created when we break this controlled channel.
What we are essentially doing is, in fact, creating a gap, allowing fields to leak out.
This causes EMC lab equipment to detect these leaked fields, which, if above limits, results in a test failure.
This is also why the first thing I check during a PCB EMI review is the stackup.
If the stackup is not chosen to create this channel for signals, a multitude of problems can arise.
Hence the simple rule:
When choosing the stackup, place the Return and Reference Plane (RRP) adjacent to the signal (or power) layer to channel fields effectively and avoid EMI.
-Dario
P.S. Want to learn how to pass EMC by preventing EMI?