2017-08-01 16:11 GMT+02:00 Luke Kenneth Casson Leighton lkcl@lkcl.net:
On Tue, Aug 1, 2017 at 2:51 PM, mike.valk@gmail.com mike.valk@gmail.com wrote:
[trimming a huge amount of unnecessary context on your behalf, mike... hint, hint....]
My apologies to all.
there's a lot of other stuff in here which is really good, such as making sure that lengths on each *layer* are matched, and that even when turning corners the lengths are matched. and matching just after VIAs *not* before... damn
Between via's the length should be matched right? Length mismatch should be solved as soon as possible to accommodate eddy-currents right?
yes. the toradex article explains it very well, also mentions the importance of symmetry (as does the TI post).
Found a nice post from TI https://e2e.ti.com/blogs_/b/analogwire/archive/2015/06/10/differential-pairs...
nice! dang, above 10ghz the thickness of the via starts to matter and needs to be drilled out, post-production. dang.
*sigh* unfortunately symmetry is not completely achievable with the drastically-reduced amount of space available. the HDMI signals come out right at the bottom of the board.
That might not be to problematic. I've search to the net for talk about running tracks on top of each other. It keeps hunting me. And found a knowledable awnser.
http://www.sigcon.com/Pubs/news/2_30.htm
On of the things mentioned is that the differential signals might not be quite aligned to begin with. So achieving symmetry might look nice on but can only give limited help in minimizing emission and pickup.
l.