[SI-LIST] Re: Assessing insertion loss profiles
- From: "Yuriy Shlepnev" <shlepnev@xxxxxxxxxxxxx>
- To: <buenos@xxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Sun, 14 Jul 2013 09:51:18 -0700
Istvan,
Just a couple of thoughts on a link analysis in case if a signal is not
perfectly differential or link is not balanced.
The case of un-coupled or loosely coupled pairs is trivial (though if
requires the localization). Both single-ended and mixed-mode S-parameters
can be used to estimate the imbalance and its impact on the link
performance.
In the case of tightly coupled pairs, I think only the mixed-mode
S-parameters may be useful to estimate the signal degradation and link
quality especially in cases if the link is not balanced and signal is not
perfectly differential. Differential block of the mixed-mode S-parameters
naturally describes degradation of the useful signal. If generated signal is
a mixture of differential and common mode, then the common mode transmission
and reflection naturally describe the problem and allows properly solve it
(terminate common mode for instance). If link is not balanced (weave effect
or imbalanced discontinuities), then transformation from the differential to
common mode block of the mixed-mode S-parameters is useful to pinpoint and
address the problems. Something similar to app notes #2009_01 and 2009_02 at
http://www.simberian.com/AppNotes.php. Description of the bends in tightly
coupled microstrip link with the single-ended S-parameters cannot be used to
do such analysis. Though, as you can see, the mixed-mode S-parameters
provide useful information and actually define the link optimization goals.
Instead of length compensation, the goal becomes minimization of both
differential reflection and transformation to common mode.
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; Fax +1-702-482-7903
Cell +1-206-409-2368
Skype: Shlepnev
www.simberian.com
Simbeor - Accurate, Fast, Easy and Affordable Electromagnetic Signal
Integrity Software
2010 and 2011 DesignVision Award Winner
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Istvan Nagy
Sent: Saturday, July 13, 2013 10:56 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Assessing insertion loss profiles
Assessing insertion loss profiles
Hi,
Sometimes I have to look at insertion loss profiles (before running a full
channel simulation with IBIS AMI models) to assess the quality of a channel
on a PCB.
Someone says we have to look at the mixed mode Sdd21 for this purpose, but I
think we should look at the S21 single-ended curve. The PCB-EM simulations
are done with single ended ports.
The Sdd21 looks a lot better than the S21, resonances look smaller.
I think Sdd21 would only be indicative if the channel and the return path
was perfect without discontinuities.
I have doubts about the signals being perfectly differential at both TX and
RX buffers. (for example 10GBASE-KR from an FPGA) So, what is the correct
approach?
Regards,
Istvan Nagy
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts: