[SI-LIST] Re: Using W-element in HSPICE
- From: "john lipsius" <johnlipsius@xxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Wed, 29 May 2002 20:22:38 -0700
Bob,
Also, see the si-list archives and gigatest.com
http://www.gigatest.com/pdfs/GTL48.pdf
and see avanti's HSpice Manual, chapter on "Using Transmission
Lines", section "Using the W Element". Ie: rtfm.
Disclaimer: I've done this with Apsim RLGC tool, which outputs a RLGCFILE
for use with W-element and calculates all the stuff you want. Also, as far as I
know, the built-in field solver option for W-element isn't accurate/reliable, so
the rlgc or Uelem input options must be used, instead.
to answer you...
The RLGC don't change. You calculate a differential impedance (using the RLGC)
if your signal is odd mode (+v on one, -v on the other). This is the Z that
the signal
will see, not a direct property of the traces. The Zdiff is a function of
Zodd which
*is* a function of the trace geometry:
Zdiff = 2 * Zodd = 2 * (Z11 - Z12) for coupled symmetric pair,
where Z12=Z21=Zmutual
and Zij = sqrt[ (R+jwL)/(G+jwC) ] i,j = 1,2 w=2*pi*freq ,
where the RLGC have subscripts "ij", too, and are what you input to the model.
Careful.... from what I can understand, the W-element G, C matrices' are what
avanti
calls "Maxwellian", so that the ii diagonal elements are actually the sum of
the ii and the
|ij elements| (abs value) for i=const. So, to get C11 in the above for Z11
you'd have to
take C11-|C12| from the model matrix. But, you better verify this.
If you use the U-model form with elev=2 you input RLGC matrices that have
'normal'
format, where for example C12 means C12 and C11 isn't the sum of elements in
its row.
Also note, PMC-Sierra has a good appnote on using W-element for high freq.
sim.
app note PMC-2010793 "High Freq. Simulation with HSpice" Issue 2 or
later
(Aug/01) See appendices B, E.
Ie: As with other models, the correct number of shorter length W-elem segments
must be
used in tandem to constitute the trace model, each segment being about 1/10 the
electrical
length traveled by one edge duration, to accurately model the system. App. E
offers important
HSpice parameters for accurate results in the face of short edge times.
----- Original Message -----
From: <Patrick_Carrier@xxxxxxxx>
To: <whizplayer@xxxxxxxxx>; <Patrick_Carrier@xxxxxxxx>;
<Michael_Greim@xxxxxxxx>;
<si-list@xxxxxxxxxxxxx>
Sent: Wednesday, May 29, 2002 4:33 PM
Subject: [SI-LIST] Re: Using W-element in HSPICE
>
> I do not know those formulas.
> I think odd-mode impedance is a function of twice the single-ended impedance
> minus twice Z12 or something like that. So you'd have to get your impedance
> numbers for the above formula from using your Rs, Ls, Gs, and Cs.
> Honestly I don't know. Perhaps someone on the SI-lIST could lend some
> knowledge.... ;-)
>
> --Pat
>
> -----Original Message-----
> From: Bob Patel [mailto:whizplayer@xxxxxxxxx]
> Sent: Wednesday, May 29, 2002 6:24 PM
> To: Patrick_Carrier@xxxxxxxxxxxxxxxxx; Michael_Greim@xxxxxxxxxxxxxxxxx;
> si-list@xxxxxxxxxxxxx
> Subject: RE: [SI-LIST] Re: Using W-element in HSPICE
>
>
> Hi! PAtrick, Thanks for the reply. Michael did correct
> the statements for the broadside & edge coupled
> structure.
> So, if I wanted the RLGC for differential from the
> extracted RLGC , you mentioned it would require some
> math. Are there some analyitical formulas that apply
> or is it something I have to write in say matlab.
> Thanks
> Bob
> --- Patrick_Carrier@xxxxxxxx wrote:
> > Bob--
> > Your RLGC information from the W-element will be
> > extracted regardless of
> > what stimulus you apply to it. In other words, the
> > RLGC information is
> > strictly a function of geometry and material
> > properties (with the exception
> > of your frequency-dependent losses, which have a
> > calculated value that is
> > multiplied by a frequency).
> >
> > So, to answer your question, the stimulus does NOT
> > matter for what goes into
> > your .RLGC file, if you have selected that option in
> > the field solver
> > definition to extract R,L,G, and C parameters.
> >
> > However, if you are using the W-element right in
> > your deck, you need to
> > apply a negative stimulus on one side and a positive
> > one on the other side.
> > This will give you the proper output waveform, but
> > will not effect the
> > numbers that go into the .RLGC file, if you are
> > creating one.
> >
> > I know APSIM RLGC puts out a differential impedance
> > for the pair, and you
> > can get that from the W-element as well but you need
> > to do quite a bit of
> > math with the outputted RLGCs...
> >
> > Hope this helps.
> > And since your traces are on the same layer
> > (coplanar), I believe they are
> > considered edge-coupled. Broadside-coupled traces
> > sit above one another on
> > different layers, with their broad sides facing one
> > another.
> >
> > --Pat
> >
> > -----Original Message-----
> > From: Bob Patel [mailto:whizplayer@xxxxxxxxx]
> > Sent: Wednesday, May 29, 2002 4:50 PM
> > To: Michael_Greim@xxxxxxxxxxxxxxxxx;
> > si-list@xxxxxxxxxxxxx
> > Subject: [SI-LIST] Re: Using W-element in HSPICE
> >
> >
> >
> > Hi! On item 3 I meant broadside coupled traces.
> > Thanks
> > Bob
> > --- Michael_Greim@xxxxxxxx wrote:
> > > On item three that sure looks edge coupled
> > > to me. Is that what you meant?
> > >
> > > MG
> > >
> > > -----Original Message-----
> > > From: Bob Patel [mailto:whizplayer@xxxxxxxxx]
> > > Sent: Wednesday, May 29, 2002 4:15 PM
> > > To: si_list
> > > Subject: [SI-LIST] Using W-element in HSPICE
> > >
> > >
> > >
> > > Hi!
> > > I had looked up the past archives on this subject
> > > pertaining to the definition of differential
> > pairs.
> > > I
> > > had additional questions as to
> > > 1)if I am extracting the RLGC for a diff pair do I
> > > apply the stimulus to one node only. And if YES
> > then
> > > shouldn't I excite both the nodes differentially
> > > i.e.
> > > positive going to one node and inverting to the
> > > other.
> > > 2)Also when defining the stimulus does the
> > stimulus
> > > have to represent the source of the frequency of
> > > interest i.e. the RLGC will be extracted based on
> > > the
> > > pulse source. e.g. at 2.5GHz the pulse source is
> > > (3.3
> > > 0 100ps 50p 50p 150p 400p)
> > > 3)When defining the model statement for the
> > > broadside
> > > coupled pair
> > > + CONDUCTOR = ( MATERIAL=copper, SHAPE=rect,
> > > ORIGIN=(0, 7.2mil) )
> > > + CONDUCTOR = ( MATERIAL=copper, SHAPE=rect,
> > > ORIGIN=(17mil, 7.2mil
> > > i.e. the traces are 6mil above the gnd plane and
> > are
> > > separated by 11mil & are 1.2mil thick. Is this
> > > correct?
> > > Thanks in advance.
> > > Bob
> > >
> > > __________________________________________________
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