[SI-LIST] Re: AC Coupling Cap Voids Questions
- From: "Yuriy Shlepnev" <shlepnev@xxxxxxxxxxxxx>
- To: <signal.integrity2@xxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Thu, 5 Jul 2012 11:10:12 -0700
Dan,
In addition to Steve's reply I would like to note that you can answer your
own questions by simply doing some additional electromagnetic analyses.
Q1: Analyze structure without another reference plane under the cutout -
the current will go around the cut out in this case. Compare the results
with and without plane.
Q2: Analyze structure with the vias to the reference plane under the cutout
and compare the results again.
Q3: Analyze cut-outs for single-ended line and use it as completely
un-coupled case. Compare the results.
Q4: Analyze structure with "floating" reference plane under the cutout.
The results may be S-parameters. In cases if the results for the modified
structures are close to the results for the original structure, the
modification is not important and the physics is captured by the original
model. Large differences may point out at things that are important to
account for.
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 Dan
Sent: Thursday, July 05, 2012 10:17 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] AC Coupling Cap Voids Questions
HI ALL
I have a few question in AC coupling capacitors void in high speed routing.
It would be helpful if you can answer the questions I have.
I am providing cutout under AC coupling capacitor in a high speed channel
(PCIE gen3). The length of the cutout is around 50 mil and then referenced
to ground layer. I performed simulation in HFSS and came up with this cutout
height in order to minimize impedance discontinuity.
Question1 : how the return current travel in the region of discontinuity.
Is it around the void in the next ground layer or in the ground layer after
50 mil cutout?
Question 2: Do I need to provide a ground via for the return current to pass
through at AC cap area?
Question 3: this is a tightly coupled diff pair. Will this be changed in a
loosely coupled configuration?
Question 4: can I give power as reference under void area?
Thank you
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