Hi Scott,
We matched all single-ended, common and differential S parameters
(magnitude and phase of IL, RL, NEXT and FEXT) PLUS all single-ended,
common and differential TDR/TDT. It is "self-consistent" because of
built-in self verification.
Matching only idealized insertion loss (i.e., attenuation and phase
delay) from eigenvalue solution is a necessary but not sufficient
condition. Return loss, for example, is affected by DK and
cross-sectional geometry. The cross-sectional geometry in turn
affects the surface roughness and DF extraction. It's hard to imagine
that matching only idealized insertion loss to extract DK/DF will give
the same original IL, RL, NEXT, FEXT and TDR/TDT.
Regards,
Ching-Chao Huang
On Wed, May 24, 2017 at 1:39 PM, Scott McMorrow <Scott@xxxxxxxxxxxxx> wrote:
C.C.------------------------------------------------------------------
I agree with the need for FEXT and NEXT to dial in the characteristics of the
resin-rich layer between differential pair conductors. I published this in
my training years ago. Another simple way to perform the separation of
dielectric properties is to use the separation of differential and common
mode phase delay.
I'm surprised by your omission of phase delay. Everything you need is
contained in amplitude and phase. TDR/TDT is an integration and obscures the
primary information. Good for a final check but not the best way to identify
the primary material parameters. Of all the measurements you can make, phase
delay is also the one most free of noise.
Just sayin'.
Scott
Scott McMorrow, CTO Signal Integrity Group
Samtec
Office 401-284-1827 | +1-800-726-8329
www.samtec.com
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On ;
Behalf Of C.C. Hwang
Sent: Wednesday, May 24, 2017 11:54 AM
To: dmarc-noreply@xxxxxxxxxxxxx
Cc: shlepnev@xxxxxxxxxxxxx; John Lin <johnlinc@xxxxxxxxx>;
jose.moreira@xxxxxxxxxxxxx; si-list <si-list@xxxxxxxxxxxxx>
Subject: [SI-LIST] Re: Differential vs. SE for PCB Dk/Df extraction
For accurate DK/DF extraction, we should measure differential traces and
match all IL, RL, NEXT, FEXT and TDR/TDT after causal de-embedding. Because
the glass/resin composite makes PCB stripline structures inhomogeneous, the
extracted DK/DF will depend on the cross-sectional model being used. The
extracted DK/DF can be considered "effective" values and they are self
consistent with the model being used when all IL, RL, NEXT, FEXT and TDR/TDT
are matched.
We showed that FEXT and its polarity, among others, can have profound
implication in DK/DF extraction in a DesignCon paper:
http://www.ataitec.com/PDF/Paper_AfullyautomatedSIPlatform.pdf and ;
http://www.ataitec.com/PDF/MPX.pdf
Regards,
Ching-Chao Huang
www.ataitec.com
On Wed, May 24, 2017 at 8:28 AM, Bert Simonovich
<dmarc-noreply@xxxxxxxxxxxxx> wrote:
John,------------------------------------------------------------------
To add to the discussion, the roughness of the copper used in the
fabrication of the core laminate and etching before final lamination
will affect total phase delay which translates into and effective Dk
(Dkeff). So the Dkeff you extract is only good for the particular
geometry measured. It is not the intrinsic Dk of the dielectric material.
See my DesignCon2017 paper, "A Practical Method to Model Effective
Permittivity and Phase Delay Due to Conductor Surface Roughness".
http://bit.ly/2qWcHPm
Furthermore, since the dielectric is non-homogeneous, the glass style,
resin content, number of dielectric layers used and where the traces
are positioned relative to the glass weave pattern will affect results.
Best regards,
Bert Simonovich
Signal/Power Integrity Practitioner | Backplane Specialist | Founder
LAMSIM Enterprises Inc.
Email:Lsimonovich @lamsimenterprises.com Web Site:
http://lamsimenterprises.com
Blog: http://blog.lamsimenterprises.com/
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Yuriy Shlepnev
Sent: 24-May-17 10:37 AM
To: johnlinc@xxxxxxxxx
Cc: jose.moreira@xxxxxxxxxxxxx; 'si-list'
Subject: [SI-LIST] Re: Differential vs. SE for PCB Dk/Df extraction
Hi John,
Let's take a practical case and analyze possible outcomes - such as
FR408HR in the "Lessons Learned" project - paper #2014_01 at
http://www.simberian.com/AppNotes.php
The dielectric around the strips is mostly resin.
If we use single ended strip and identify one effective model for
dielectric, the result is usable for either single-ended strips or for
loosely coupled differential. Nothing else is needed to cover those cases.
If we use tightly coupled differential traces, the complex propagation
constants for differential and common modes will be different due to
the resin around the strips (result of the spatial "averaging" of
E-field). To identify one dielectric model, we can use either
differential or common mode for the model identification. The model
identified with the common model will be close to the single-ended
case, but not accurate for the differential mode analysis - does not
matter what solver is used. The dielectric model identified with the
differential propagation will be different, but usable only for the
analysis of differential modes in the line with similar geometry. It
will give wrong result for the common mode propagation. Simply put,
isotropic one dielectric model will not be sufficient for such case.
Two dielectric models are needed - one for layer around the strips
(resin) and one for the rest of the cross-section (three-layer model for
strips, anisotropic dielectric is an alternative).
Such model will be more accurately for all cases - single-ended,
loosely and tightly coupled differential for both differential and common
modes.
Dielectric models for such layered model of the cross-section can be
identified with the two modes in the tightly coupled differential traces.
Best regards,
Yuriy
Yuriy Shlepnev, Ph.D.
President, Simberian Inc.
2629 Townsgate Rd., Suite #235, Westlake Village, CA 91361, 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, Productive and Cost-Effective Electromagnetic
Signal Integrity Software 2010 and 2011 DesignVision Award Winner,
2015 Best In Design&Test Finalist
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of John Lin
Sent: Tuesday, May 23, 2017 9:27 PM
To: shlepnev@xxxxxxxxxxxxx
Cc: jose.moreira@xxxxxxxxxxxxx; si-list
Subject: [SI-LIST] Re: Differential vs. SE for PCB Dk/Df extraction
Thank all to shed light on my questions. I appreciate.
Hi Dr. Yuriy,
Thank you for your insightful explanation.
Based on it, can I conclude that the Dk/Df extraction for
Single Ended shall be close to the that of loosely coupling
differential but different from tightly coupling due to the E field in
between the tightly coupling traces and common mode convention?
If the extracted dk/df are used for simulator to model any structures,
ie SE, tightly/ loosely coupling differential pair ...etc., does Dk/Df
extracted from SE makes more sense and more accurate assuming the tool
automatically calculate the E field in between two tightly coupling
differential traces?
Thanks again for helps.
John Lin
2017Е││5Ф°T24Ф?г 04:04О+-"Yuriy Shlepnev"
<shlepnev@xxxxxxxxxxxxx>Е│LИ│?О+
Hi Jose,
Technically, any structure on PCB with measurable parameters can be
used to "tune" the material parameters if we can build a model of the
structure. I agree with your statement that "A simple trace is not a good
structure".
However, use of Beatty standard with de-embedding may be not the best
approach either. First of all because of the de-embedding (as I can
see in your paper) - that is difficult and error-prone for PCB
materials with inhomogeneous dielectrics and large manufacturing
variations. Also, the number of parameters to match simulations with
measurements is also excessive - reflection and transmission
parameters of the de-embedded structure should be matched
simultaneously. This problem is common for all material identification
techniques based on de-embedding - too complicated and error-prone for
PCBs. So, what is better than a simple trace? - it is two simple
traces :-) S-parameters of two trace segments can be used to extract
either reflection-less generalized modal S-parameters - the simplest
form of S-parameters of a t-line segment for any line with any number
of traces (not an approximation). It is just one complex transmission
for single ended case and two transmissions for differential case
(reflections and mode transformations are zero by definition, not by
approximation). It is easy to fit same reflection-less model for a
t-line segment, to find the material properties - the technique is in
practical use since 2009 - see
#2010_01 and all papers after that at http://www.simberian.com/AppNotes.php.
The logarithm of the generalized modal transmission parameter divided
by the length difference is the modal complex propagation constant or
Gamma - that can be also used for the material identification in the
same way (sometime called eigenvalue technique). Though, the
techniques with Gamma, such as SPP light with S-parameters (see
#2016_02 at http://www.simberian.com/AppNotes.php), requires one
additional step - taking the logarithms. Usually it is easy step and
produces the same result as the technique with GMS-parameters. And, as
Scott mentioned, both GMS or Gamma techniques allow easy dielectric and
conductor loss separation.
Considering the single-ended vs. differential, as Gert already
mentioned, the identification results can be very different. This is
because of the layered type of inhomogeneity of the PCB materials. We
always identify some effective permittivity averaged by the applied
electric field. Techniques based on a wide strip line resonator have
preliminary out of plane component of electric field - the identified
value of Dk are good for structures with primarily out of plane
electric field. The other extreme is techniques with E parallel to
dielectric surface - they identify in plane value of Dk. It is
consequence of the layered structure. A strip line with regular width
(close to target impedance) has both out of plane and in plane
electric fields - Dk identified with it will be between the out or plane
(min value) and in plane (max value). See more on that and references in
the "Material World..."
tutorial #2016_01 at
http://www.simberian.com/TechnicalPresentations.php The bottom line is
that the end result of the identification should be usable for the modeling
of traces within the actual interconnects width range.
Which value would be better for that? - the answer is obvious, the
values identified with the traces used as the actual interconnects.
Values identified with single-ended can be safely used for loosely
coupled differential, simply because of almost the same structure of
the electric field. However, tightly coupled differential traces have
more energy in the out of plane electric field. The space between the
tightly coupled traces with mostly in plane electric field can be
filled mostly with the resin and property of the resin may be
different from the rest of the resin-fiber mixture. That changes the
identified Dk. The effect shows up as difference in the phase or group
delay of the differential and common modes or as NEXT on single-ended
S-parameters. Layered dielectric model should be used in such cases to
improve accuracy for both differential and common mode modeling. Use
of differential traces is essential for such cases - see examples is
at the "Lessons learned..." paper #2014_01 at
http://www.simberian.com/AppNotes.php
Best regards,
Yuriy
Yuriy Shlepnev, Ph.D.
President, Simberian Inc.
2629 Townsgate Rd., Suite #235, Westlake Village, CA 91361, 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, Productive and Cost-Effective Electromagnetic
Signal Integrity Software
2010 and 2011 DesignVision Award Winner, 2015 Best In Design&Test
Finalist
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Moreira, Jose
Sent: Tuesday, May 23, 2017 1:36 AM
To: johnlinc@xxxxxxxxx; si-list
Subject: [SI-LIST] Re: Differential vs. SE for PCB Dk/Df extraction
In my opinion differential or single-ended makes no difference for
Dk/Df extraction. Important is the kind of structure you use. A simple
trace is not a good structure. I suggest a resonant standard like a Beatty
Standard.
Check the Designcon 2018 paper "Non-Destructive Analysis and EM Model
Tuning of PCB Signal Traces using the Beatty Standard"
Jose
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of John Lin
Sent: Dienstag, 23. Mai 2017 05:53
To: si-list <si-list@xxxxxxxxxxxxx>
Subject: [SI-LIST] Differential vs. SE for PCB Dk/Df extraction
Hi SI gurus,
While using VNA to measurement traces on PCB for loss and Dk/Df
extraction, my colleagues say the differential handhold probe head can
have wider bandwidth than single ended handhold probe head. Is it true?
Can someone help to explain the reasons?
Also, for Dk/Df extraction, which is better structure, using single
ended or differential traces? Why?
Thank you for helps in advance.
Thanks,
John Lin
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