Hi Tom,
The 100 ohm trace pulls up the 85 ohm DUT, so the embedded 85 ohm DUT
appears as flat 87 ohm. If we cascade multiple 85 ohm DUT, we will see
more clearly the impedance rise that is caused by attenuation. This
example just shows that TDR or improper de-embedding will give you 87 ohm
in this case when the actual DUT is 85 ohm.
See Pages 10-13 of http://ataitec.com/test/In-Situ_De-embedding.pdf for
some examples of how well In-Situ De-embedding (ISD) tunes out bad
launches. If you send me data offline, we can go through them, too.
Ching-Chao Huang
On Wed, May 6, 2015 at 11:29 AM, Tom Dagostino <tom@xxxxxxxxxxxxxxxxx>
wrote:
C.C.
This data looks like it was derived from simulations. The transitions
from the start of the data and at the junctions of the different impedances
have no aberrations at all. And I see differences in the 85 Ohm section.
When it is imbedded between the two 100 Ohm segments its impedance is
essentially flat over its length. When it is pulled out it has a change of
1 Ohm over its length. Whereas both 100 Ohm sections have a 1 Ohm change.
Why the difference? If it has enough losses to show a 1 Ohm change of
impedance in one plot I would expect to see it in the other.
Do you have any data that shows results where the ringing of the launch
continues to the DUT section? As you said, tune out bad launches?
Tom Dagostino
Teraspeed Labs
9999 SW Wilshire Street
Suite 102
Portland, OR 97225
tom@xxxxxxxxxxxxxxxxx
www.teraspeedlabs.com
971-279-5325 office
503-430-1065 cell
*From:* C.C. Hwang [mailto:cchwang2013@xxxxxxxxx]
*Sent:* Tuesday, May 05, 2015 4:48 PM
*To:* Alfred P. Neves
*Cc:* Tom Dagostino; jun zhang; si-list; istvan.novak@xxxxxxxxxxx
*Subject:* Re: [SI-LIST] Re: some questions about a PCB test coupon to
measure the impedance curve and crosstalk curve
Hi Al,
I put one test case under http://ataitec.com/test/impedance_test_case.zip
The DUT (85 ohm differential) sees 2 ohm difference with or without 1.5"
100 ohm differential trace before it.
Ching-Chao Huang
On Tue, May 5, 2015 at 1:50 PM, Alfred P. Neves <al@xxxxxxxxxxxxxxxxx>
wrote:
With .07dB/inch/GHZ typical loss you have approximately 2dB of loss at
20GHz for a 1.5inch and this loss impacts a peeled impedance profile by
2ohms, really? I doubt it.
As for âtuningâ out the launch do you have any organized data using
carefully based standards or channels to prove that claim? Again, most
launch designs will resonate past the .6inch electrical distance, so it
will be very difficult to de-embed.
We check de-embedding on our Channel Modeling platforms using THRU
structures with intentional excess capacitive and inductive pathology, then
compare it to pristine launch design. Most of the de-embedding schemes
except measured-modeled (see Keysight/WRT 32G Test fixture Tutorial on our
website) and the new Simbeor THz approach simply has major issues with
crappy or even mediocre launch designs (Yuriy has data and reports to
support that and has done an incredible amount of work validating his EDA
tool). A good launch is roughly defined to have better than -10dB of
return loss at Fstop.
All de-embedding schemes are compromises and have an effective bandwidth
efficiency, it would be helpful to outline the limitations and assertions
with hard data and reports.
- Al
Products for the Signal Integrity Practitioner
Alfred P. Neves
Chief Technologist
Office: 503-679-2429
www.wildrivertech.com
On May 5, 2015, at 1:21 PM, C.C. Hwang <cchwang2013@xxxxxxxxx> wrote:
Hi Tom,
If the launch and lead-in trace have little discontinuity and loss (i.e.,
ideal 50 ohm lossless transmssion line), then indeed TDR will give true
impedance reading at DUT. The ~2 ohm increase for ~1.5" microstrip
attenuation is from many typical designs we saw. One of ISD's main
advantages is that it can "tune out" bad launches.
Ching-Chao Huang
On Tue, May 5, 2015 at 11:15 AM, Tom Dagostino <tom@xxxxxxxxxxxxxxxxx
wrote:Ching-Chao
As Al Neves pointed out if the DUT is swamped out by ringing from poorly
designed launches or the transitions from the co-planar to DUT you will not
be able to de-embed the fixture from the DUT.
I'm not sure why you predict the DUT impedance will be higher for TDR
based measurements, especially after a short 1.5" lead-in. If there are
low discontinuities and losses there should be no issue. If the
discontinuities are bad then some well-known techniques can be employed
such as the peeling algorithms in IConnect from Tektronix.
Tom Dagostino
Teraspeed Labs
9999 SW Wilshire Street
Suite 102
Portland, OR 97225
tom@xxxxxxxxxxxxxxxxx
www.teraspeedlabs.com
971-279-5325 office
503-430-1065 cell
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of C.C. Hwang
Sent: Tuesday, May 05, 2015 10:40 AM
To: al@xxxxxxxxxxxxxxxxx
Cc: zhangjun5960@xxxxxxxxx; si-list; istvan.novak@xxxxxxxxxxx
Subject: [SI-LIST] Re: some questions abou a PCB test coupon to measure
the impedance curve and crosstalk curve
Hi Jun,
Your DUT is 0.6" and the rest of fixture is 2", so ISD should give you
very good de-embedded results. (If your DUT is 0.01", then you'll need to
be
careful.) We have routinely used ISD to extract a 0.5" to 1" connector
from a 12" board. On the other hand, your DUT is a short trace (0.6"), so
it will be affected more by local fiber weave effect. If you are looking
for good average impedance, you can consider increasing the length of your
DUT.
Due to fixture's trace attenuation, TDR will give you higher impedance at
DUT than it actually is. We saw ~2 ohm higher impedance at DUT due to
~1.5" lead-in trace attenuation. This can be easily verified
through simulation. Good de-embedding is the only way to get correct
impedance of DUT.
Ching-Chao Huang
On Tue, May 5, 2015 at 9:01 AM, Alfred P. Neves <al@xxxxxxxxxxxxxxxxx>
wrote:
A typical poorly designed SMA resonates for >100psec, and since 1ââ¬trouble.
of microstrip prop delay is around 150psec your going to run into
Since your fixture probably goes single ended then coplanar coupledwas a
my guess is you have a significant impedance bump on the coupling region
also. Our platform SE to coupled DIFF is not trivial to design and
challenge.
We do not de-embed when doing crosstalk analysis like ICR, ICN, PEXT,
etc., for compliance.
- Al
Products for the Signal Integrity Practitioner
Alfred P. Neves
Chief Technologist
Office: 503-679-2429
www.wildrivertech.com
On May 5, 2015, at 3:55 AM, Istvan Novak <istvan.novak@xxxxxxxxxxx>wrote:
co-planar
An 0.6-inch long trace is very challenging to measure...
Regards,
Istvan Novak
Oracle
On 5/5/2015 3:11 AM, jun zhang wrote:
Hi experts,
I have designed a PCB test coupon to measure the impedance curve
and crosstalk curve from 0-10GHz.
My test trace is about 0.6". At each end of the trace, there is a
thetrace about 1" connected to SMA connector. Therefore the total
length of the coupon is about 2.6".
I have some question below:
1. When testing TDR, do you think 0.6" is too short to be
displayed? If
tocharacteristic can be displayed, I think I need not to de-embed the
influences of the co-planar traces at both ends. Am I right?
2. When testing TDR, I have two ways. The first is using TDR
instrument
VNA tomeasure it directly; the second way is tranforming SDD11 obtained
by
moretime domain.The second way is more convinient for me. Which method
is
ISDsuitable for displaying the impedance for the 0.6" test trace? .
3.When testing crosstalk, I will de-embed the co-planar trace to
reveal only the characteristic of the test trace. I plan to do
de-embedding by
onlyoffered by AtaiTec Co. My concern is still that whether this
method can give me accrate de-embedding result in the case that my
test trace is
of0.6" long. I think if the trace is longer, maybe the influence of
multi-reflection from co-planar trace will be minor because of the
loss
the trace. Under this consideration, I think the longer the test
trace length is, the better accurate de-embedding results we can
obtain. Am I right?
Hope to your reply
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