On Thu, Aug 10, 2017 at 9:14 AM, Hrvoje Lasic <las...@gmail.com> wrote:
> the case for GND around differential pairs cant hurt, maybe even can help. > But is it better to have GND in plane below that actually is doing same > things? If there is no clear path for signal to go back then I guess put > GND in parallel is good but if you have clean GND below than make it > somehow redundant. Or am I wrong? I am discussing these because most > probably there is tight space even without GND lines... the most amazing borad i saw was a 2-layer 5-port GbE router. man you should have seen the diff-pairs on that. it was... beautiful. every ethernet diffpair - bear in mind this is GbE with 5 ports - so that's TWENTY pairs - had GND vias equally spaced an absolute specific distance from them, absolutely regularly like clockwork every couple of mm. what that does is make *absolutely* certain that there's no cross-talk between the diff-pairs. with only a 5 mil GND trace between pairs i am really pushing it, but there really isn't any choice here. the first design (done by a superb senior engineer at wits-tech) didn't even have the GND separation between diff-pairs, and yet amazingly it worked. i don't feel comfortable leaving them out, but i can't get vias in at both ends on all pairs. l. _______________________________________________ arm-netbook mailing list arm-netbook@lists.phcomp.co.uk http://lists.phcomp.co.uk/mailman/listinfo/arm-netbook Send large attachments to arm-netb...@files.phcomp.co.uk
