This is a pretty difficult thing to simulate without a 3D field solver unless
you have a prototype that you can measure the portion of the line that goes
through the connector and vias, and represent that as an S parameter block or a
coupled line model. You will need to either measure the 4 port S parameters of
the block and deembed them to the part of the circuit you need to represent, or
TDR/TDT the signal and build a coupled transmission line model from it. You
will need to account for both the even and odd mode propagation through the
discontinuity to account for the ground return current, which gets pretty
darned ugly when the vias are that far away. Honestly, even simulation is
difficult in this case unless you build in good material properties and account
for the manufacturing variations in both the etching and the via dimensions.
Best Wishes,
Josiah Bartlett
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On ;
Behalf Of Dennis Han
Sent: Monday, February 22, 2016 3:58 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] 28 Gb/s Ground Vias
I have some differential data channels running at 28 Gb/s that are laid out
correctly in every way except perhaps one: The ground vias at a connector are
about a half wavelength from the signal vias. The signal vias are in front of
the connector pads, and the ground vias are the other side of the connector
pads, so the return currents have a longer path. I don't have a 3D field
solver, so what is the best way to model this discontinuity with a circuit
simulator?
Thanks for any advice.
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