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 Sent from my iPhone iPhone: 408-858-4528 Office: 702-570-6108 Email: doug@xxxxxxxxxx Website: http://dsmith.org > 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 > > > ------------------------------------------------------------------ > To unsubscribe from si-list: > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > > or to administer your membership from a web page, go to: > //www.freelists.org/webpage/si-list > > For help: > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > > List forum is accessible at: > http://tech.groups.yahoo.com/group/si-list > > List archives are viewable at: > //www.freelists.org/archives/si-list > > Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > > ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List forum is accessible at: http://tech.groups.yahoo.com/group/si-list List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu