[SI-LIST] Re: Signal crossing Split plane
- From: "Lee Ritchey" <leeritchey@xxxxxxxxxxxxx>
- To: "Steve Weir" <weirsi@xxxxxxxxxx>
- Date: Wed, 21 Nov 2007 08:50:01 -0800
Iv've got the test PCBs, do you have the tools?
Lee
> [Original Message]
> From: steve weir <weirsi@xxxxxxxxxx>
> To: <leeritchey@xxxxxxxxxxxxx>
> Cc: Charles Harrington <ch_harrington@xxxxxxxxx>;
<shlepnev@xxxxxxxxxxxxx>; <scott@xxxxxxxxxxxxx>;
<sunil_bharadwaz@xxxxxxxxx>; SI LIST <si-list@xxxxxxxxxxxxx>
> Date: 11/20/2007 5:45:16 PM
> Subject: [SI-LIST] Re: Signal crossing Split plane
>
> Lee I don't think the original problem would have warranted
> measurements. But the thread has moved significantly since then. It
> might be a fun test of Simbeor to model your test vehicle and compare
> results. Rather than just drive with a TDR, it might be fun to drive
> with a pulse generator that can be set to the simulated resonant
> frequency and see if doing so impacts measured results in real life the
> way simulation predicts.
>
> Best Regards,
>
>
> Steve.
> Lee Ritchey wrote:
> > I've watched this thread for a while now and haven't seen anyone suggest
> > making measurements. I've done lots of that and have several test
boards
> > in my lab that represent the kind of plane splitting that is done to
> > accommodate two Vdds in the same plane. I've run traces over these
splits
> > and measured them with a TDR with a rise time of 40 pSEC. There is no
> > detectable disturbance of the signal when this is done. (Of course, the
> > Vdd PDS designs need to be done such that the frequencies in the signals
> > crossing the planes can be properly supported. If that has not been
done,
> > worrries about crossing plane splits will be the minor problem.)
> >
> > I've also measured hundreds of vias used to change layers from top to
> > bottom of a PCB and from adjacent layer to adjacent layer. Again,
> > measuring these vias with the same TDR they behave as though someone has
> > attached a very small parasitic capacitor, on the order of .5 pF for a
12
> > mil drill in a 100 mil thick PCB. There has been no detectable
coupling of
> > energy into the space between planes.
> >
> > Same thing for right angle bends. Not a detectable source of signal
> > degradation or EMI.
> >
> > Sometimes a little lab time saves a lot of agony and speculation.
> >
> > If there are those out there who have tests that prove otherwise,
perhaps
> > they should publish the results. I've published mine several times as
have
> > others.
> >
> > Hope this helps those who are confused by all of the complex
explanations
> > that have been offered without any supporting measurements.
> >
> > Lee Ritchey
> >
> >
> >
> >> [Original Message]
> >> From: Charles Harrington <ch_harrington@xxxxxxxxx>
> >> To: <shlepnev@xxxxxxxxxxxxx>; <scott@xxxxxxxxxxxxx>
> >> Cc: <sunil_bharadwaz@xxxxxxxxx>; SI LIST <si-list@xxxxxxxxxxxxx>
> >> Date: 11/20/2007 2:45:54 PM
> >> Subject: [SI-LIST] Re: Signal crossing Split plane
> >>
> >> Yuriy,
> >> I agree with some of your views. However, they contradict your via
> >>
> > models.
> >
> >> I couldn?t reply yesterday, because I was trying search for the
> >>
> > reference I mentioned, since you needed it. Many other people replied
> > off-line and so needed the reference. Got it from IEEE Xplore.
> >
> >>
> >>
> >> A Novel Methodology for Defining the Boundaries of Geometrical
> >>
> > Discontinuities in Electronic Packages
> >
> >> Ndip, I.; Reichl, H.; Guttowski, S.;
> >> Research in Microelectronics and Electronics 2006, Ph. D.
> >> 12- 15 June 2006 Page(s):193 - 196
> >>
> >>
> >> You mentioned in your mail that the near field zone as a result of
the
> >>
> > higher-order modes excited at the via expands with frequency and is very
> > small. I agree with you.
> >
> >> But the question is this. How small is it? How small or big is at 1
> >>
> > GHz, 10 GHz, 20 GHz? Have you ever studied it? You have to take this
zone
> > into consideration when studying vias or any other structures that
excite
> > higher order modes.
> >
> >> The method proposed in this paper is quite illustrative and
useful. I
> >>
> > understand it this way (Please correct me if I understand it wrongly):
> >
> >> These higher-order modes (e.g., TE, TM...) are characteristics of
the
> >>
> > trace or transmission line and they die exponentially away from the
point
> > of excitation, i.e., the via-trace interface. S-parameters, like other
> > network parameters, give us the relation between input and output
signals.
> > Now, to obtain S11, for example, you need to get the ratio of the
reflected
> > and input signals. Both signals must be of the same "type". We can not
> > directly compare cars and aeroplanes, though both are used for
> > transportation. You know your input signal (e.g., a transverse
> > electromagnetic wave), because you excited it at the port. At
> > discontinuities, an infinite order of given higher-order modes can be
> > excited. The orders or strength of the excited modes differ from one
> > discontinuity to another, although the modes can be the same. So, there
is
> > no way you can know all the orders of the higher-order modes excited and
> > how they interact. Now if you place your ports quite close to the point
> >
> >> of excitation of these modes, then your S-parameters must be wrong.
Why?
> >>
> > In this case, to obtain S11, you need to obtain the ratio of the unknown
> > higher-order modes and your known excited transverse electromagnetic
wave
> > at the port. That?s why in most 3D full-wave solvers, it is recommended
> > that ports should be placed far away from the discontinuities, so as to
> > enable these higher-order modes to die. When they die, then you can
easily
> > define your S-parameters which will then be the ratio of the input
signal
> > you know (transverse electromagnetic wave) and the reflected signal you
> > know (transverse electromagnetic wave). To define the points where these
> > modes die or have attenuated substantially, these authors argued that
near
> > the discontinuity, the imaginary part of the Poynting vector describes
the
> > reactive energy associated with these higher-order modes. So they
studied
> > this imaginary part and used it to define the point where the modes
die. I
> > think they mentioned that only
> >
> >> at a distance of about 1mm away from the via-trace interface, at 20
GHz
> >>
> > (or may be 30 GHz) may you place your ports, to get correct results.
> > Certainly, this depends on the via geometry and trace type. But I find
the
> > results very helpful and can be used as a base for further experiments.
You
> > can get the details from the paper.
> >
> >> Unfortunately in your case, you compare what you don?t know
(reflected
> >>
> > signal) and what you know (excited input signal). In your via models,
> > neither did you define the required distance away from the via-trace
> > interface needed for these modes to die nor did you follow the advice
given
> > in full-wave solvers to be far way from the via-trace interface. You
> > considered the via just as the barrel and the pads at 20 GHz and beyond.
> > That?s why I mentioned yesterday that your via models are not correct
and
> > your S-parameter results are misleading. If you wish to study only the
> > behaivor of the barrel alone at lower frequencies (for what ever reason
-
> > but not for realistic designs), then you don't even need a field solver.
> > You can get formulas from good SI texts like that of Horward Johnson or
> > from papers.
> >
> >> At first I was also making the same mistakes as you are making right
> >>
> > now. I had a lot of difficulties to correlate my simulation and
measurement
> > results. So I learnt a lot from this paper, from Professor C. Balanis
> > (Advanced engineering electromagnetics) and from Professor R. Collins
> > (Field theory of guided waves). I think these references will be good
for
> > you. You need all three of them.
> >
> >> There are also a lot of points that you need to modify in your
models.
> >> It?s ridiculous when you talk of -30 dB attenuation of higher-order
> >>
> > modes. Which higher-order mode? Which order of this mode? Basic
> > electromagnetic theory teaches us that an infinite order of a given
> > higher-order mode can be excited at any discontinuity. An interaction
> > between makes matters worst. So how do you separate the different
orders of
> > the modes and tell which one attenuates by -30 dB? Are the modes
> > propagating or evanescent? Never use rule of thumbs that have no base. I
> > supposed you meant attenuation of the fundamental mode which is
> > propagating.
> >
> >> I don?t know anything about the lumped ports you use. All I know is
> >>
> > that some lumped ports in some field solvers assume perfect H boundary
> > conditions on the sides. Consequently, depending you may not even
capture
> > stray fields. So you can even get the worst results with lumped ports.
> >
> >> You can only shift your reference S-parameters plane and get accurate
> >>
> > results if your model captured all the necessary field behavior. But you
> > can not simulate the via and traces differently and then do some
> > post-processing or circuit modeling afterwards and expect to get correct
> > results at higher frequencies. The traces too are part of the ?via
effect?
> > at least, at the frequencies you are interested in (20 GHz and beyond),
> > because the stored higher-order modes give rise to additional
inductances
> > and capacitances. These inductances and capacitances can not be
captured if
> > you analyze the vias separately from their traces.
> >
> >> Finally, the theory of multi-modal decomposition means different
things
> >>
> > to different electrical engineers. So I don?t know what you mean. If you
> > mean that different parts of a system can be analyzed separately and
then
> > put together, then it?s true that it has been done for decades now. But
the
> > question is this. How do you bring the different parts together in the
case
> > where there are discontinuities like vias? How do you define the via?
How
> > small or big is your near field zone? I bet you, we have not yet
understood
> > this type of decomposition and it has not been done, or at least
published
> > for decades. Whenever we have to deal with vias and other
discontinuities
> > at higher frequencies, straight-forward modeling can not be used.
> >
> >> Please Yuryi, don?t get me wrong. I?m not trying to highlight on
your
> >>
> > errors. I have mine too, like any body else. No one is perfect. I?m just
> > trying to raise the point that we need to be careful when modeling vias
at
> > your frequencies. I agree with most of the points you made, but
disagree on
> > the ones stated above. We learn from each other when we exchange ideas
> > about such fundamental issues that affect our modeling results. I think
> > that is one of the reasons why Ray and his team set up this forum.
> >
> >>
> >> Best regards.
> >> Charles
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >> Yuriy Shlepnev <shlepnev@xxxxxxxxxxxxx> wrote: Charles,
> >>
> >> I am sorry that the simulation examples were not helpful to you. I will
> >> appreciate if you send me the reference you mentioned - I am preparing
to
> >>
> > be
> >
> >> shocked:)
> >>
> >> You are absolutely right, the via-holes are not just pads and barrels
and
> >> there is no one solution that covers all possible cases. Analysis of
> >> different vias has to be done in different ways. Transition to the
traces
> >> have to be almost always included in the final model for analysis of
> >> multi-gigabit channels. Moreover sometime the via-hole problem cannot
be
> >> solved locally and require analysis of parallel plane structures with
all
> >> decoupling structures attached (see technical presentation #1 at
> >> http://www.simberian.com/Presentations.php for more details on
different
> >> structures).
> >>
> >> Considering the ports and excitation. Analysis of via-holes with lumped
> >> ports provides just rough idea about the via-hole behavior. It is
similar
> >>
> > to
> >
> >> what you would see from a differential probe attached to the pads of
the
> >> via-holes. Transition to traces and transmission line or wave-ports
have
> >>
> > to
> >
> >> be used for the final extraction of S-parameters for the system-level
> >> analysis (I am sorry that you missed this part in app notes). Note
that it
> >> is possible only for the localizable via-holes or via-holes not
coupled to
> >> parallel planes in general. Such t-line ports have to be positioned at
a
> >> distance from the via-hole that guaranties that the high-order modes
are
> >> attenuated substantially (for practical applications we usually use
-30 dB
> >> threshold at the highest frequency of interest). After such analysis,
the
> >> phase reference planes of S-parameters can be safely shifted closer to
the
> >> via-hole at the position where t-lines are still continuous to preserve
> >> causality (to the edges of anti-pads for instance). Such transformation
> >>
> > does
> >
> >> not affect the near field or high order modes around the via-holes and
the
> >> final model can be safely connected with the transmission line segments
> >>
> > in a
> >
> >> system-level solver. Though, the model have to be used with
transmission
> >> line segments with length not less than in the electromagnetic analysis
> >>
> > (to
> >
> >> avoid the near-field interaction between the vias and possible
> >> discontinuities). This technique called the multi-modal
de-compositional
> >> analysis and used in microwave engineering for decades at frequencies
even
> >> higher than 20 GHz.
> >> Note, that in typical PCB trace the cut-off frequencies for high-order
> >>
> > modes
> >
> >> are extremely high. 10 mil trace on 10 mil dielectric with dielectric
> >> constant 4.2 have cut-off frequency about 120 GHz, and the cross-over
with
> >> the surface TM mode may happen only at 200 GHz. Before 120 GHz the
> >> high-order modes are evanescent and essentially form the via-hole near
> >> field. This near-field zone is expanding with the frequency, but at 20
GHz
> >> the area is still relatively small. Thus S-parameters only for the
> >>
> > dominant
> >
> >> modes can be safely extracted and used as the via-hole model.
> >> Cases when via-hole excite the non-evanescent parallel-plane modes and
> >> planes are not stitched close to the via-hole cannot be solved locally
> >>
> > (non
> >
> >> localizable) and may require the system-level analysis with all
decoupling
> >> structures attached.
> >>
> >> Best regards,
> >> Yuriy
> >>
> >> Yuriy Shlepnev
> >> Simberian Inc.
> >> www.simberian.com
> >>
> >> -----Original Message-----
> >> From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]
> >>
> > On
> >
> >> Behalf Of Charles Harrington
> >> Sent: Monday, November 19, 2007 8:33 AM
> >> To: shlepnev@xxxxxxxxxxxxx; scott@xxxxxxxxxxxxx
> >> Cc: sunil_bharadwaz@xxxxxxxxx; 'SI LIST'
> >> Subject: [SI-LIST] Re: Signal crossing Split plane
> >>
> >> Yuriy,
> >> not only are your slot simulations on your page not so helpful, but
your
> >> via simulations are very misleading. I think you'll run into trouble
when
> >> you try to compare your simulation and measurement results, because
your
> >> simulation models are unrealistic.
> >>
> >> At such frequencies (20 GHz and beyond), the via can no longer be
> >>
> > considered
> >
> >> to be just the barrel and the pads, as you did. The modes excited at
the
> >> via-trace interface don't die abruptly, but extend along the traces to
the
> >> ports. So either you seperate these modes from the originally excited
> >>
> > modes
> >
> >> at the port (in order to obtain "clean" S-parameters') or you allow the
> >> modes to die before they reach the ports (as recommended in most 3D
> >> full-wave solvers).
> >> I just read a very interesting research paper the other day on defining
> >>
> > the
> >
> >> boundaries of discontinuties, in which these issues are properly
> >>
> > examined. I
> >
> >> can't really remember the exact title nor its authors at the moment,
but
> >>
> > the
> >
> >> paper was presented at a Ph.D. research conference on microelectronics
and
> >> electronics somewhere in Europe (Italy, I presume). You'll be shocked
at
> >>
> > the
> >
> >> error you are making when you read this work.
> >> You also connected the models of the via and transmission lines after
the
> >> simulations, correct? Here you go wrong again, because how do you know
> >>
> > where
> >
> >> the vias "actually" begin and end? And at what freqency? These are very
> >> complicated issues and I suggest you spend a little more time studying
> >>
> > them
> >
> >> well.
> >> Thanks.
> >> Charles
> >>
> >> Yuriy Shlepnev wrote: Scott,
> >>
> >> I agree with you. It was just an illustration of a slot-type
discontinuity
> >> in general for some stackup configurations. It shows how a slot-type
> >> discontinuity in a reference plane may reflect the signal even in the
case
> >> if slot does not cut across the board or around a patch (though, it
might
> >>
> > be
> >
> >> obvious for you). As soon as the coupling to a slot is strong, it has
to
> >>
> > be
> >
> >> simulated at the system level with a complete geometry of the slot or
> >>
> > split,
> >
> >> with all relevant traces crossing the slot and all de-caps (if any). I
> >> prefer to do it with the hybrid de-compositional approach on the base
of
> >> localized models built with an electromagnetic solver. The localized
strip
> >> to slot coupling effect can be captured with a 4-port S-parameter model
> >>
> > for
> >
> >> strip crossing the slot for instance (two ports for the strip and two
for
> >> the slot). Combined with the strip and slot line models, it produces a
> >> simple and computationally efficient system-level model that captures
> >> practically all coupling and resonance effects.
> >>
> >> Best regards,
> >> Yuriy
> >>
> >> Yuriy Shlepnev
> >> Simberian Inc.
> >> www.simberian.com
> >>
> >>
> >> -----Original Message-----
> >> From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]
> >>
> > On
> >
> >> Behalf Of Scott McMorrow
> >> Sent: Sunday, November 18, 2007 12:29 PM
> >> To: shlepnev@xxxxxxxxxxxxx
> >> Cc: sunil_bharadwaz@xxxxxxxxx; 'SI LIST'
> >> Subject: [SI-LIST] Re: Signal crossing Split plane
> >>
> >> Yuriy
> >>
> >> Actually, these sorts of slot simulations are pretty meaningless.
Slots
> >> normally occur due to plane splits. As a result, the either extend
from
> >> one edge of a board to another edge, or when the plane is a square
patch
> >> the slot is a closed loop around the periphery of the plane. When
this
> >> happens, it is quite interesting to simulate multiple signals crossing
> >> the slot. There is a very nice slot resonance mode that occurs that
is
> >> generally in the signal bandwidth (or at least 3rd harmonic) because
of
> >> the length of the slot. This induces a signficant amount of ringing
and
> >> crosstalk into neighboring traces.
> >>
> >> scott
> >>
> >> Scott McMorrow
> >> Teraspeed Consulting Group LLC
> >> 121 North River Drive
> >> Narragansett, RI 02882
> >> (401) 284-1827 Business
> >> (401) 284-1840 Fax
> >>
> >> http://www.teraspeed.com
> >>
> >> TeraspeedR is the registered service mark of
> >> Teraspeed Consulting Group LLC
> >>
> >>
> >>
> >> Yuriy Shlepnev wrote:
> >>
> >>> Sunil,
> >>>
> >>> A simple example of how an electromagnetic solver can be used to
> >>>
> >> investigate
> >>
> >>> the effect of a slot or split in a reference plane is provided at
> >>> http://www.simberian.com/AppNotes.php - see the topmost app note.
> >>>
> >>> Best regards,
> >>> Yuriy
> >>>
> >>> Yuriy Shlepnev
> >>> Simberian Inc.
> >>> www.simberian.com
> >>>
> >>> -----Original Message-----
> >>> From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]
> >>>
> >> On
> >>
> >>> Behalf Of sunil bharadwaz
> >>> Sent: Sunday, November 18, 2007 1:26 AM
> >>> To: SI LIST
> >>> Subject: [SI-LIST] Signal crossing Split plane
> >>>
> >>> Hi ,
> >>> I have few signals (@ 80 Mhz & 20 Mhz) crossing the split Power
> >>> plane in the adjacent layer.
> >>>
> >>> The 20 Mhz signal is diffrerential signal.The 80 Mhz is a single
> >>> ended signal.
> >>>
> >>> I want to analyse the affect on Signal Integrity of these two
> >>> signals due to split plane.
> >>>
> >>> I believe one need to define his stack up (Including the
> >>> split) & then extract the layout to simulate.
> >>>
> >>> I'am not too sure if the prevalent SI tools have an option
> >>> of creating split planes .
> >>>
> >>> Pls suggest me a right tool to carry out this.Also , i'am
> >>> looking for a free tool to start with (even if the accuracy
> >>> is slightly limited).
> >>>
> >>> Thanks in Advance!!
> >>>
> >>> Regards
> >>> Sunil.Bh
> >>>
> >>>
> >>> ---------------------------------
> >>> Be a better pen pal. Text or chat with friends inside Yahoo! Mail. See
> >>>
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> >>
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> > //www.freelists.org/webpage/si-list
> >
> > For help:
> > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
> >
> >
> > List technical documents are available at:
> > http://www.si-list.net
> >
> > List archives are viewable at:
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> > or at our remote archives:
> > http://groups.yahoo.com/group/si-list/messages
> > Old (prior to June 6, 2001) list archives are viewable at:
> > http://www.qsl.net/wb6tpu
> >
> >
> >
> >
> >
>
>
> --
> Steve Weir
> Teraspeed Consulting Group LLC
> 121 North River Drive
> Narragansett, RI 02882
>
> California office
> (408) 884-3985 Business
> (707) 780-1951 Fax
>
> Main office
> (401) 284-1827 Business
> (401) 284-1840 Fax
>
> Oregon office
> (503) 430-1065 Business
> (503) 430-1285 Fax
>
> http://www.teraspeed.com
> This e-mail contains proprietary and confidential intellectual property
of Teraspeed Consulting Group LLC
>
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> Teraspeed(R) is the registered service mark of Teraspeed Consulting Group
LLC
>
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> To unsubscribe from si-list:
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>
> 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 technical documents are available at:
> http://www.si-list.net
>
> List archives are viewable at:
> //www.freelists.org/archives/si-list
> or at our remote archives:
> http://groups.yahoo.com/group/si-list/messages
> 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 technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
