[SI-LIST] Re: Signal crossing Split plane

  • From: "Lee Ritchey" <leeritchey@xxxxxxxxxxxxx>
  • To: "Istvan Novak" <istvan.novak@xxxxxxxxxxx>
  • Date: Thu, 29 Nov 2007 09:38:01 -0800

Istvan,

That would be great.  It always helps to see meaured results.

Lee


> [Original Message]
> From: Istvan Novak <istvan.novak@xxxxxxxxxxx>
> To: <leeritchey@xxxxxxxxxxxxx>
> Cc: Istvan Novak <Istvan.Novak@xxxxxxx>; Steve Weir <weirsi@xxxxxxxxxx>;
Charles Harrington <ch_harrington@xxxxxxxxx>; <shlepnev@xxxxxxxxxxxxx>;
<scott@xxxxxxxxxxxxx>; <sunil_bharadwaz@xxxxxxxxx>; SI LIST
<si-list@xxxxxxxxxxxxx>
> Date: 11/24/2007 7:33:50 AM
> Subject: [SI-LIST] Re: Signal crossing Split plane
>
> 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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