[SI-LIST] Re: Signal crossing Split plane
- From: Istvan Novak <istvan.novak@xxxxxxxxxxx>
- To: leeritchey@xxxxxxxxxxxxx
- Date: Sat, 24 Nov 2007 16:02:39 +0100
Lee,
Agree, it is better to speak about data than verbal arguments. Will
write it up and publish.
Hope you have a great Thanksgiving weekend.
Istvan
Lee Ritchey wrote:
> Istvan,
>
> If your data is public, why not share it with us. It would make your case
> solidly.
>
> Lee
>
>
>
>> [Original Message]
>> From: istvan novak <Istvan.Novak@xxxxxxx>
>> To: <leeritchey@xxxxxxxxxxxxx>
>> Cc: Steve Weir <weirsi@xxxxxxxxxx>; Charles Harrington
>>
> <ch_harrington@xxxxxxxxx>; <shlepnev@xxxxxxxxxxxxx>; <scott@xxxxxxxxxxxxx>;
> <sunil_bharadwaz@xxxxxxxxx>; SI LIST <si-list@xxxxxxxxxxxxx>
>
>> Date: 11/21/2007 1:08:00 PM
>> Subject: [SI-LIST] Re: Signal crossing Split plane
>>
>> Lee,
>>
>> You are correct in saying that how much problem we have from plane
>> splits strongly depends on how the split is done and how the PDNs
>> are designed on those planes. If, for instance, we have a solid ground
>> plane behind the split planes, the return loop size just temporarily
>> expands, signal degradation may be minimal, crosstalk may go up
>> proportionally to how much the normalized spacing of traces over the
>> split decreases. If the split is narrow, the extra crosstalk pulse will
>> be similarly narrow. With today's sub 100-ps edges it still may come
>> close to the saturated crosstalk value over the gap.
>>
>> I dont claim that I have analyzed all possible practical parameter
>> combinations, but those that I have looked at, it WAS NOT the
>> signal integrity of a particular signal that suffered first when traces
>> crossed plane splits. First suffers crosstalk and EMI radiation.
>> I have 12-year-old measured data to show this, though it has not
>> been published. The data is not confidential, it just happens to be
>> part of the SI courses I do.
>>
>> Regards,
>> Istvan
>>
>>
>>
>>
>> Lee Ritchey wrote:
>>
>>
>>> 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
>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>> how.
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>
>>>
>>>
>>>
>>>
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