[SI-LIST] Re: Ground vias and the land of ID ("It Depends")
- From: "Loyer, Jeff" <jeff.loyer@xxxxxxxxx>
- To: "si-list (si-list@xxxxxxxxxxxxx)" <si-list@xxxxxxxxxxxxx>
- Date: Wed, 22 Oct 2014 12:55:46 +0000
Oops - bad link. Please try this one.
https://www.filesanywhere.com/fs/v.aspx?v=8b6e6587616373beac6b
Jeff Loyer
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Loyer, Jeff
Sent: Wednesday, October 22, 2014 5:45 AM
To: si-list (si-list@xxxxxxxxxxxxx)
Subject: [SI-LIST] Ground vias and the land of ID ("It Depends")
At the risk of finding myself embroiled in a furball, I thought I'd see if I
could clear up (in my own mind anyway) some of the effects of ground vias. I
ran 3-D simulations on a pair of single-ended signal vias with various
configurations of ground vias around them and compared impedance, NEXT, and
FEXT. The results strongly suggest that nearby ground vias are a good
investment to reduce via crosstalk. Of course, if you can absorb the extra
crosstalk, it's a moot point. And ground vias are often hard to put where we
want them, since they impede routing on every layer, so we seldom have the
luxury of all the vias we might like (the "no xtalk" configuration in the
study).
Here's a link to the study.
https://www.filesanywhere.com/fs/v.aspx?v<6e658761616dab72a2
Note: I'm leaving the presentation a bit vague (leaving out any conclusions,
many exact dimensions, and not stipulating simulation assumptions) on purpose -
this should not be regarded as any formal "report-out". It's only a
"quick-and-dirty" peek at the issue. Others may duplicate the simulation with
different results, though that seems improbable - I don't see anything leading
me to believe they are fundamentally flawed. They are not overly complex
topologies, so I invite others to replicate the simulations if the results seem
questionable.
And, of course, exact results will depend on design specifics (stackups, via
dimensions, etc.). Your mileage may vary...
Cheers,
Jeff Loyer
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