[SI-LIST] Re: Ground vias and the land of ID ("It Depends")
- From: emceed <doug@xxxxxxxxxx>
- To: "jeff.loyer@xxxxxxxxx" <jeff.loyer@xxxxxxxxx>
- Date: Wed, 22 Oct 2014 08:07:16 -0700
One problem to remember, the amount of energy extracted from a signal to cause
an EMC emissions problem is often so low that the effect on SI is
insignificant. So EMC simulations and measurements are in order. I present live
experiments in my seminars to illustrate this effect, very easy to set up an
experiment to show this right on a table top, no chamber needed!
Doug Smith
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> On Oct 22, 2014, at 05:44, Loyer, Jeff <jeff.loyer@xxxxxxxxx> wrote:
>
> 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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