If the planes are not continuous, EMI may result whether the traces are
straight or serpentine.Â
Lee RitcheySpeeding Edge
P.O. Box 817Bodega Bay, CA94923408-781-0253lritchey49@xxxxxxx
Worry is like a rocking chairIt keeps you busy, but it doesn't get you
anywhere.
I just took the energy it takes to get madand wrote some blues.Count Basie
-----Original Message-----
From: Chuck Corley <corley@xxxxxxxxx>
To: zmp@xxxxxxxxxxxxxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx; si-list-bounce@xxxxxxxxxxxxx
Sent: Fri, Jun 4, 2021 8:49 pm
Subject: [SI-LIST] Re: Serpentine length tuning þMI problem?
Short answer:Â If you have a good plane (âreference planeâ) as you
should have under those traces to set the proper trace impedance then
they will couple to that plane and not significantly radiate.
If you didnât have a solid reference plane close under your traces then
youâve built an antenna and they will radiate. Some people do this
accidentally, by having big gaps or other bad features in their
reference plane.
Chuck
---
Chuck Corley
On 2021-06-04 20:16, Zachariah Peterson, NWES wrote:
Hi everyone,------------------------------------------------------------------
While I was conducting a design review today, my client expressed some
concern over serpentine routing that was used to enforce length
matching
between an SDRAM chip running at 166 MHz (1 ns rise time) and an MCU.
The concern was that the serpentine routing structure would create an
EMI problem. The traces are routed according to specs in the datasheet
with a reference plane on the adjacent layer.
I have never heard of serpentine routing creating a new EMI problem or
making some existing EMI problem worse. I started looking into it and I
find mixed recommendations. This is one instance where I won't trust
application notes, they all give inconsistent guidance, and they show
poor images of the exact way serpentine routing should be implemented.
I looked into the literature and there are some studies on EMI, effects
on eye diagrams, and reflections from serpentine routing structures.
Here's one example:
https://www.researchgate.net/publication/321143234_Differential_Lines_Paired_with_Serpentine_as_Potential_EMI_Aggressors_in_Mobile_Electronic_Devices
If anyone can provide some perspective, or if someone can confirm this
is just another signal integrity myth, I'd appreciate it. Thanks in
advance.
--
Zachariah Peterson
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