I will be presenting In-Situ De-embedding (ISD) and Material Property
Extraction (MPX) at DesignCon 2017. See:
http://ataitec.com/about-us/events/ We can discuss in more details at that
time. All comments are welcome.
Ching-Chao Huang
On Mon, Dec 12, 2016 at 1:34 PM, Alfred P. Neves <al@xxxxxxxxxxxxxxxxx>
wrote:
C.C. Hwang,
What method do you use to confirm your claim regarding causal de-embedded
results?
I just processed your published S-parameters results, as measured by the
IEEE Plug and Play fixtures, and your de-embedded data failed our WRT
S-parameter internal quality flow for causality quite badly.
In some cases there was, at most 20-some GHz of usable bandwidth out of
60GHz of raw measured. Secondly, the group delay noise was very high
suggesting T-matrix ill conditioning. It also looks like some of the THRU
lines had 100% causality suggesting you actually force causality which we
think creates problems, unless youâre doing a polynomial rational model
fit.
This isnât meant as any attack, please donât misunderstand, but you claim
it - you have to back it up with data! The industry is having issues
with S-parameter testing(at this time), so it would be interesting how you
approach that problem since I know you have a background in the area of
S-parameter quality.
All the de-embedding schemes have, what we call, a de-embedding bandwidth
efficiency. Your algorithm, based on my analysis, is comparable to other
bifurcating de-embedding schemes and offers no advantage as you claim -
sorry!
The WRT Measure Based Modeling (MBM) scheme has the highest efficiency
since it does not use measurements (that are inherently noisy) for the
de-embedding S-parameters, they are synthesized from time/frequency domain
measure based modeling methods. The tradeoff is you have to create the
model which takes some engineering time, versus simply measuring and using
a canned algorithm. Our method is outlined in DesignCon tutorial on our
website. The S-parameter quality flow for our MBM de-embedding scheme
demonstrates almost 100% causality, as demonstrated in the report.
Another method that works extremely well for us is the Simbeor GMS. We
also has been successful in using Keysightâs AFR as well for a host of
projects in the past.
I am working up a basic and rough powerpoint for anyone interested.
- Al
*Products for the Signal Integrity Practitioner*
*Alfred P. Neves*
Chief Technologist
Office: 503-679-2429 <(503)%20679-2429>
*www.wildrivertech.com* <http://www.wildrivertech.com/>
*2015 Best In Design&Test Finalist*
On Dec 12, 2016, at 8:12 AM, C.C. Hwang <cchwang2013@xxxxxxxxx> wrote:
To see the trace-only return loss, you need to de-embed the launches.
For causal de-embedding, see http://ataitec.com/products/isd/
Ching-Chao Huang
On Mon, Dec 12, 2016 at 1:42 AM, Havermann, Gert
<Gert.Havermann@xxxxxxxxxxx> wrote:
Hi Sunil,
Return Loss is not only a function of Impedance. The Return Loss is just
showing you the reflections over the complete signal path, and reflections
can be caused by impedance mismatch and even stronger by impedance
discontinuities. Bad launch into the test cupon, signal vias in the test
cupon, missing return vias, Return vias at bad positions, Plane voids,
via-antipads, etching roughness and copper roughness can and will all
impact your Return loss way more then the trace impedance itself.
Look at Insertion Loss and Return loss in one diagram to find out whats
going on. If you see opposing peaks in both curves at the same frequency,
then there is a resonance, and those are always caused by at least two
discuntinuities. The frequency of appearance indicates the distance between
the discuntinuities.
In Time Domain (TDR) those discuntinuities are easier to find and to
quantify.
BR
Gert
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx
<si-list-bounce@xxxxxxxxxxxxx>] On Behalf Of sunil bharadwaz
Sent: Sunday, December 11, 2016 5:18 PM
To: si-list <si-list@xxxxxxxxxxxxx>
Subject: [SI-LIST] 50 ohm - RF Impedance Traces
Hello Group ,
We seem to be running into issues while getting PCB's fabricated with 50
ohm lines.Our Freq band of interest is 2 Ghz to 6 Ghz.Tried checking these
traces on a VNA.The return loss looks decent @ 2 Ghz , but seldom looks
good at 5Ghz & above .
The fabricator does send test coupons & impedance reports @ TDR .This does
notcover the freq response .
This is not issue with any single fab . This seems to be a general problem
, where return loss isnot flat across freq band .
Wanted to check if there are ways to tackle this issue .
Thanks much.
RegardsSunil.B
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