Mitigating skin effect’s impact on high-speed signals. 

I’ve spent much of the past seven years dealing with insertion loss as it relates to PCB dielectrics, as well as losses due to copper roughness. During that period, there’s been comparatively little discussion regarding “skin effect,” a significant contributor to signal attenuation that in my view gets less attention than it should. While discussing the phenomenon in-depth, we’ll also discuss what, if anything, can be done to mitigate its impact on high-speed signals.

While writing this article, I’ve been thinking of places that skin appears in nature and pop culture. When I started writing, I flipped on Skinwalker Ranch on the History Channel for the first time as background noise, and they were talking about magnetic fields, current flow, and Tesla coils.

Skin is said to be the largest organ in the human body. It has multiple layers and some amazing properties. Galvanic skin response, used in lie detectors, measures changes in skin conductance caused by sweat-gland activity. I suppose you could call that a “skin effect” too.

It's perfectly reasonable for engineers and PCB designers to ask, “Where should I focus my attention?” insofar as loss is concerned. In Signal and Power Integrity – Simplified,1 Dr. Eric Bogatin points out five ways energy can be lost to the receiver while the signal is propagating down a transmission line:

1. Radiative loss
2. Coupling to adjacent traces
3. Impedance mismatches and glass-weave skew (the latter being my addition)
4. Conductor loss
5. Dielectric loss.

Each of these mechanisms reduces or affects the received signal, but they have significantly different causes and remedies. Plenty of articles over the years have discussed managing impedance and crosstalk, including ones I’ve written. I’ve also written about managing loss through dielectric-material selection and copper roughness, one of the two components of conductor loss. The other contributor to conductor loss is commonly known as skin effect.

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