[SI-LIST] Re: 10G Return Path
- From: "Yuriy Shlepnev" <shlepnev@xxxxxxxxxxxxx>
- To: "'Cotton, Chris'" <Chris.Cotton@xxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Thu, 15 Dec 2011 11:28:44 -0800
Chris,
I think that a 3D field solver will not be helpful in your case. If you
simulate the via in isolation from the rest of the board or with just the
nearest stitching via, the model will not correlate well with your
measurements above about 3 GHz (see examples in app notes #2009_05 and
#2009_05i at http://www.simberian.com/AppNotes.php). The whole board must be
simulated with models for all components attached to get a good correlation
up to 20-25 GHz as may be required in your case - it may be either not
possible, not accurate enough or not practical. An alternative is to use
only localizable vias that can be reliably simulated in isolation from the
rest of the board - either differential or single with sufficient number of
stitching vias. In both cases distance between vias should less than
1/10-1/8 of wavelength in dielectric at the highest frequency of interest.
The impact of such via can be reliably estimated with a full-wave
electromagnetic analysis.
Best regards,
Yuriy
Yuriy Shlepnev, Ph.D.
President, Simberian Inc.
3030 S Torrey Pines Dr. Las Vegas, NV 89146, USA
Office +1-702-876-2882
Cell +1-206-409-2368
Skype: shlepnev
www.simberian.com
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Cotton, Chris
Sent: Wednesday, December 14, 2011 2:34 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] 10G Return Path
I have a 10G MDI signal that uses microstrip routing. It starts out on the
Top layer and then transitions to the Bottom layer. Both Top and Bottom
layers are referenced to Chassis GND however there is no GND transition via
nearby for the return current to follow. The nearest Chassis GND via
connection is ~0.5" away
I don't (yet) have a 3D field solver. Is there another good way to quantify
the impact of the via discontinuity?
Thanks,
Chris
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