[SI-LIST] Re: AFR
- From: "Yuriy Shlepnev" <shlepnev@xxxxxxxxxxxxx>
- To: <jim.nadolny@xxxxxxxxxx>, "'Jeremy Buan'" <jeremybuan10@xxxxxxxxx>
- Date: Thu, 1 Jan 2015 14:57:12 -0800
Hi Jim,
Just wanted to mentioned that we have recently extended the GMS-parameters
algorithm (already mentioned by Scott and Al) from just material identification
to complete de-embedding of test fixtures. The algorithm is deterministic (no
optimization) and produces causal S-parameters if some conditions are
satisfied. It is a hybrid of the S-parameters bifurcation and the
measurement-based modeling (aka jitter decomposition). As in the case of the
material identification, it requires S-parameters measured for two t-line
segments with different lengths and nearly identical launches and
cross-sections (t-line type and impedance does not matter). It extracts
S-parameters of the launch + t-line segment with adjustable length that can be
then subtracted from a multiport with DUT and test fixtures with nearly
identical connectors, launches and t-lines. So far we have tested the GMS
algorithm on the Channel Modeling Platform CMP-28 from Wild River Technology.
The results are promising - the useful bandwidth of the de-embedded models was
40-45 GHz (causality quality estimated with the rational approximation was over
98%). This is mostly due to good identity of the connectors and launches on
CMP-28 platform, high quality of the measured S-parameters, and special way to
handle the t-line segments.
I will demonstrate some examples at the DesignCon session VS32: J. Mallon, Y.
Shlepnev, "S-parameter Quality Metrics and Analysis to Measurement Correlation"
on January 29 at 11 AM - here is schedule
http://www.designcon.com/santaclara/scheduler/list - everyone with the Exhibit
Pass can attend. I will also demonstrate the de-embedding with GMS-parameters
at Simberian's booth #423.
Happy New Year to All!
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; Virtual +1-408-627-7706
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 Jim Nadolny
Sent: Tuesday, December 30, 2014 11:48 AM
To: Jeremy Buan
Cc: han.guobing@xxxxxxxxx; si-list
Subject: [SI-LIST] Re: AFR
Resending - 1st transmission was garbled...
Hey Jeremy –
Excellent point on causality. Al Neves points to it as well – you need
“perfect” cal standards and test fixtures to get “acceptable” causality. And
causality correction is sort of a misnomer IMO. You can create more problems
correcting for causality than you fix. My colleague Stefaan is going to cover
causality correction at DesignCon this year (Paper 14-TH1, “Causality
Demystified”).
ISD and iTRL are what I refer to as custom Matlab code. As I understand it,
these methods synthesize the exact test fixture response from measurement and
that leads to significant improvements in the resultant S-parameter quality.
TRL/LRM/AFR rely on cal structures to mimic the test fixture response. Given
the tolerances of PCB fabrication (+/-5% or so) the cal structure is never
going to be a perfect match to the test fixture and therein lies 90% of the
problem.
ISD and iTRL are one way to get better data. Al Neves/WRT has a second way
that he is going to cover at his DesignCon tutorial and alludes to other
methods that are forthcoming at the conference. Should be interesting as
always.
From: Jeremy Buan [mailto:jeremybuan10@xxxxxxxxx]
Sent: Tuesday, December 30, 2014 11:29 AM
To: Jim Nadolny
Cc: han.guobing@xxxxxxxxx; si-list
Subject: Re: [SI-LIST] Re: AFR
Hi Jim,
I've never used AFR before, since I use ISD from Ataitec. You mentioned that
AFR has been validated compared to TRL calibration. In my experience, TRL
calibration results in non-causal s-parameters, which can be seen clearly when
converted to time-domain. I'm curious, does AFR also yield this kind of
causality error?
Regards,
Jeremy
On Tue, Dec 30, 2014 at 6:10 AM, Jim Nadolny <jim.nadolny@xxxxxxxxxx> wrote:
Greetings Robin -
Jim Nadolny here and our team at Samtec uses AFR on a regular basis. We use
custom designed test boards with the required cal structures for AFR
de-embedding. We typically test connectors, cable assemblies and PCB
structures (via fields, coupled traces, etc.) in a controlled lab environment.
The power of AFR is in its simplicity. You don't need to be an expert in
microwave network theory to get reliable data. That said, it is easy to fall
into the trap of simply trusting the results without checking a few simple
parameters of the cal structure. I would argue that using a 3rd party tool
has advantages over custom matlab code, particularly when supporting customers.
No one can reproduce your results if you are using home brew code and this can
be problematic as it requires peers/clients/customers to trust you, your code,
your test methodology, etc. In contrast, numerous papers/studies have been
written validating AFR compared to TRL/LRM de-embedding methods.
The weakness of AFR is that it does not de-embed crosstalk in the test fixture.
Most de-embedding algorithms do not, so this is not unique to AFR. This
crosstalk limitation that I refer to applies to inter-pair coupling, intra-pair
coupling effects are accounted for in AFR. So if you are testing a high port
count coupled structure (like a high density connector) you need to design the
test vehicle accordingly.
We don't have a lot of experience using AFR on prototype/production electronic
hardware and I would welcome comments from users who do. I understand that you
can use AFR in a "1 port mode" to probe a populated PCB for S-parameters, but I
have not done this myself.
Regards,
jn
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Han, Guobing
Sent: Tuesday, December 30, 2014 3:06 AM
To: si-list
Subject: [SI-LIST] AFR
Hello Experts,
Does anyone have the experience of agilent AFR?
Who can tell me what's the weakness of AFR?
--
Thanks,
- Robin (Han, Guobing)
TEL: 86-21-61094805
MSN: han_guobing@xxxxxxxxxxx
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