[SI-LIST] Re: (no subject)

  • From: "Loyer, Jeff" <jeff.loyer@xxxxxxxxx>
  • To: <lifehappiest@xxxxxxxxxxx>, <steven.corey@xxxxxxxxxxxxxx>,<si-list@xxxxxxxxxxxxx>
  • Date: Tue, 10 Dec 2002 09:54:37 -0800

I've been trying to better understand dispersion and its effects on =
signal integrity.  Allow me to state what I believe, and feel free to =
correct any falacies I've developed (or clarify what I've stated).

1) The key factor "creating" dispersion is the fact that, for a given =
medium, different frequencies will travel at different velocities.  =
I.E., the Er for a material varies, depending on frequency.  This same =
effect is responsible for prisms' breaking light into its constituent =
components and, interestingly enough, causes distortion of earthquake =
waves as they travel through the earth.

2) I've heard the term associated with microstrip, but don't know why it =
couldn't be present in stripline.

3) The net effect on our (digital S.I. types) signals of interest would =
be that a pulse would appear rounded after passing through a dispersive =
medium.

3) I don't think Hspice can simulate this phenomena, and I don't know if =
ADS can, either.

4) The way I would expect to measure the effect would be with a VNA - I =
would expect my S21 phase rate-of-change to vary with frequency.  I.E., =
for a non-dispersive medium, S21 phase appears as a regular sawtooth.  =
For a dispersive medium, I would expect the period of that sawtooth to =
vary with frequency (probably very linearly).  I haven't measured the =
effect this way (that I know of, it might have been too subtle for me to =
notice), nor have I seen data demonstrating the effect.

I would love clarification on the terms "medium dispersion" vs. "wave =
dispersion" vs "phase dispersion".  I thought there was only a single =
dispersion effect of phase velocities being different for different =
frequencies.

Thanks for your insights...

Jeff Loyer


-----Original Message-----
From: Xin Wu [mailto:lifehappiest@xxxxxxxxxxx]
Sent: Tuesday, December 10, 2002 6:54 AM
To: steven.corey@xxxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: (no subject)



Steve, it is not a good idea to mix things together. Wave dispersion=20
definitely has nothing to do with loss, conceptually. Dispersion is =
related=20
to phase velocity, but the loss is related to energy. Of cause, because=20
signal pulse consists of a bunch of frequency components, different=20
components propagate at different speed, this makes the pulse shape =
change=20
at the reception. However, the total energy of the pulse won't be=20
dissipated. Dispersion of medium is another concept. If we talking about =
a=20
dispersive medium, this means that the dielectric constant of the medium =
is=20
frequency dependent, the medium is dispersive. Kramer Kronig =
relationship is=20
to explain the medium dispersion rather than wave dispersion.
Of cause, when the medium is frequency dependent, both wave dispersion =
and=20
signal loss will be happening.





Xin Wu
Ph.D student,
University of Maryland, College Park
Http://www.wam.umd.edu/~xwu






>From: Steve Corey <steven.corey@xxxxxxxxxxxxxx>
>Reply-To: steven.corey@xxxxxxxxxxxxxx
>To: si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] Re: (no subject)
>Date: Mon, 09 Dec 2002 16:44:28 -0800
>
>
>This illustrates an interesting point, which is that if you have
>dispersion, then you have to have frequency-dependent losses as well.
>The Kramers-Kronig relationship (a.k.a. causality) states that the real
>part and the imaginary parts of the dielectric constant are tightly
>related to each other.  As a result, frequency-dependent phase velocity
>is always accompanied by frequency-dependent attenuation, and vice
>versa.  So you can easily make the argument that describing something =
as
>"dispersive" is the same as describing it as "lossy".
>
>Yu Liu wrote:
>
> > Jeff,
> >
> > By definition, I think dispersive effect is the frequency-related =
effect
> >   (phase velocities at different spectrums). However, since the =
losses
> > are also frequency-dependent, sometimes people just use the term
> > interchangbly, which causes confusions. Distinguish the two terms
> > (dispersive and loss) would make things clearer.
> >
> > Yu
> > =3D=3D=3D
> >
> > Loyer, Jeff wrote:
> >
> >
> >>Yu,
> >>When you use the term "dispersive", are you talking about losses=20
>(resistive, skin effect, dielectric), or about differences in phase=20
>velocities (page 170 of Pozar's book)?  I've heard others refer to loss =

>effects as dispersive and have had confusion as a result.  Are both =
uses of=20
>the term "dispersive" correct?
> >>
> >>Jeff Loyer
> >>
> >>
> >>-----Original Message-----
> >>From: Yu Liu [mailto:yu_liu@xxxxxxxxxxxxx]
> >>Sent: Friday, December 06, 2002 9:32 PM
> >>To: xlzhou@xxxxxxxxx
> >>Cc: 'Xin Wu'; si-list@xxxxxxxxxxxxx
> >>Subject: [SI-LIST] Re: (no subject)
> >>
> >>
> >>
> >>Mick,
> >>
> >>To answer your question: In theory, Yes. In practice, No.
> >>
> >>The fundamental principle for SPICE model approach is using lumped
> >>elements (RLC) to model distributed effect (S-parameter). For lower
> >>frequency and small size, it is possible. But for broad-band =
frequency
> >>and large size (say, 20' FR-4), it is very hard to model the =
dispersive
> >>effects accurately. That's why people start to use =
frequency-dependent
> >>elements, or better yet, import S-parameter directly into Spice =
engine.
> >>
> >>
> >>Regards,
> >>
> >>Yu
> >>=3D=3D=3D
> >>
> >>Apache Design Solutions
> >>web: www.apache-da.com
> >>
> >>
> >>
> >>Zhou, Xingling (Mick) wrote:
> >>
> >>
> >>
> >>>Xin Wu
> >>>
> >>>Thanks for your information. It will be valuable.
> >>>However, it still contains something like (from the example on the =
web=20
>you
> >>>referred)
> >>>
> >>>E11 11 12 FREQ {V(10,5)}=3D
> >>>
> >>>which will not be accepted by some circuit simulators such as ADS. =
It=20
>is
> >>>similar to Ansoft fullwave SPICE. I know HSPICE and PSPICE can =
handle=20
>it.
> >>>
> >>>Although it is still a research topic in terms of efficiency, =
stability=20
>and
> >>>accuracy etc., I know the problem [S] ---> SPICE model (reduced =
models)=20
>is
> >>>solvable without the following limitations in several ways. But, =
can we
> >>>generate broadband SPICE models without frequency dependent lookup=20
>tables
> >>>such as " FREQ " ?  Or is it still solvable without components =
"FREQ"=20
>etc. ?
> >>>
> >>>Regards,
> >>>
> >>>Mick
> >>>
> >>>-----Original Message-----
> >>>From: Xin Wu [mailto:lifehappiest@xxxxxxxxxxx]
> >>>Sent: Friday, December 06, 2002 8:38 PM
> >>>To: scott@xxxxxxxxxxxxx; xlzhou@xxxxxxxxx
> >>>Cc: si-list@xxxxxxxxxxxxx
> >>>Subject: Re: [SI-LIST] Re: (no subject)
> >>>
> >>>
> >>>Hi, XL,
> >>>  If you want to convert S-matrix into a spice simulator, a lot of
> >>>commercial software can do that--that's the simplest way. However, =
it=20
>is
> >>>possible for yourself to make a equivalent subcircuit which can =
include=20
>the
> >>>timing and frequency info and then import to a spice like =
simulator.=20
>Here
> >>>are some application notes:
> >>>http://wwwinfo.cern.ch/ce/ae/Maxwell/apps/2stripem/2stripem.html
> >>>If you want to get involved in more details, I remembered that =
somebody=20
>did
> >>>his Ph.D work on this in UIUC around early 1990s'.
> >>>
> >>>
> >>>
> >>>Xin Wu
> >>>Ph.D student,
> >>>University of Maryland, College Park
> >>>Http://www.wam.umd.edu/~xwu
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>>From: "Scott McMorrow" <scott@xxxxxxxxxxxxx>
> >>>>Reply-To: scott@xxxxxxxxxxxxx
> >>>>To: xlzhou@xxxxxxxxx
> >>>>CC: "'si-list@xxxxxxxxxxxxx'" <si-list@xxxxxxxxxxxxx>
> >>>>Subject: [SI-LIST] Re: (no subject)
> >>>>Date: Fri, 06 Dec 2002 13:45:41 -0800
> >>>>
> >>>>
> >>>>Mick,
> >>>>
> >>>>There are two solutions which I use:
> >>>>
> >>>>1) Apache Nspice is an Hspice compatabible simulator that can
> >>>>co-simulate with Touchstone S-parameter files.
> >>>>http://www.apache-da.com/
> >>>>
> >>>>2) Sigrity BroadBand Spice can convert Touchstone s-parameter =
files=20
>into
> >>>>spice black boxes.
> >>>>http://www.sigrity.com/
> >>>>
> >>>>Both are scary accurate in both the frequency and time domain.
> >>>>
> >>>>regards,
> >>>>
> >>>>scott
> >>>>
> >>>>--
> >>>>Scott McMorrow
> >>>>Teraspeed Consulting Group LLC
> >>>>2926 SE Yamhill St.
> >>>>Portland, OR 97214
> >>>>(503) 239-5536
> >>>>http://www.teraspeed.com
> >>>>
> >>>>
> >>>>Zhou, Xingling (Mick) wrote:
> >>>>
> >>>>
> >>>>
> >>>>
> >>>>>Hello,
> >>>>>
> >>>>>Did anybody successfully generate broadband (DC-20GHz) SPICE =
model=20
>from S
> >>>>>matrix for complex structures using the SPICE generator in ADS ? =
Or=20
>any
> >>>>>other alternatives. I know Ansoft fullwave SPICE does the work.
> >>>>>Unfortunately, some circuit simulators do not support the =
frequency
> >>>>>dependent lookup table sources. We can definitely use [S] =
directly,=20
>but
> >>>>>
> >>>>>
> >>>>>
> >>>>some
> >>>>
> >>>>
> >>>>
> >>>>>users still prefer SPICE models. Any experience to share ?
> >>>>>
> >>>>>Thanks,
> >>>>>
> >>>>>Xingling(Mick) Zhou, PhD
> >>>>>Signal Integrity Technologist
> >>>>>Agere Systems
> >>>>>
> >>>>>Tel: 610-712-7462
> >>>>>Fax: 610-712-4081
> >>>>>
> =
>>>>>------------------------------------------------------------------
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> >>.
> >>
> >>
> >>
> >
> >
> >
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>
>--
>-------------------------------------------
>Steven D. Corey, Ph.D.
>Time Domain Analysis Systems, Inc.
>"The Interconnect Modeling Company."
>http://www.tdasystems.com
>
>email: steven.corey@xxxxxxxxxxxxxx
>phone: (503) 246-2272
>fax:   (503) 246-2282
>-------------------------------------------
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