[SI-LIST] Re: stripline with unconnected reference planes
- From: "Yuriy Shlepnev" <shlepnev@xxxxxxxxxxxxx>
- To: "'Sexton, Brian M. \(US SSA\)'" <brian.m.sexton@xxxxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Wed, 7 Jan 2009 15:12:40 -0800
Brian,
Potentials of the planes do not have effect on the characteristic impedance
of a strip line mode. For the strip line mode both planes are the reference
planes. It means that the transition to the strip line mode may be
problematic especially at the multi-gigabit data rates. Such transitions are
not localizable with stitching vias due to the differences in the potentials
of the planes. A non-localized transition may behave as an impedance
transformer that may change the "visible" impedance of the strip line. A
hybrid analysis that includes a model of power delivery planes (transmission
line + transmission plane) may be used to simulate and validate such design
at lower data rates. At multi-gigabit data rates it is practically
impossible or extremely difficult to simulate such non-localized transitions
(via-holes) on real boards because of the problem cannot be solved correctly
in isolation from the rest of the power delivery structure.
Best regards,
Yuriy Shlepnev
www.simberian.com
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Sexton, Brian M. (US SSA)
Sent: Wednesday, January 07, 2009 1:41 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] stripline with unconnected reference planes
Does anyone understand the effect of having a stripline with two
reference planes at different potentials has on the characteristic
impedance? Some of the traces in a board I am working on are referenced
to GND on one plane, and 5V on the other reference plane. I'm curious
to know what effect, if any, this has on the characteristic impedance.
Thanks,
Brian
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