[SI-LIST] Re: Using W-element in HSPICE
- From: "Clewell, Craig" <cclewell@xxxxxxxxxxxxxx>
- To: 'john lipsius ' <johnlipsius@xxxxxxxxx>,"'si-list@xxxxxxxxxxxxx '" <si-list@xxxxxxxxxxxxx>
- Date: Thu, 30 May 2002 10:03:49 -0400
There is an alternative to calculating the impedance from the RLGC
parameters extracted by the W element... Since you have to run a simulation
to get the RLGC parameters why not set up a TDR while your at it and let
HSPICE do it for you. You can set up infinite pulses if you like (just
amplitudes and rise time), or add the fall time delay, etc...if you wish. By
adjusting the rise time you will be able to increase or decrease your
frequency content. Then, set up a TDR in your simulation by adding a small
delay (greater than your rise time)just before your DUT on both lines of the
differential pair. Probe these points and do the subraction within the
equation writer in AWAVES(V1-(-V2)). The result will be the reflection of
the lines. Calculate the reflection coefficient and then from there you can
calculate the impedance.
A trick that I use is make the voltage sources 100 Volts (passive device)
and assume that your NEXT has reached saturation. Then you can also probe
for the crosstalk and the value you get will already be in percent since the
100 Volts will cancel with the 100 multiplier.
This will allow you to get the Zo, NEXT and the RLGC parameters all in the
same run.
Craig
-----Original Message-----
From: john lipsius
To: si-list@xxxxxxxxxxxxx
Sent: 5/29/2002 11:22 PM
Subject: [SI-LIST] Re: Using W-element in HSPICE
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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