[SI-LIST] Re: FR4 non-linear
- From: Jim G Roberts <jgroberts@xxxxxxxxxx>
- To: scott@xxxxxxxxxxxxx
- Date: Mon, 13 Jan 2003 18:04:11 +0100
Hi,
Another factor often forgotten and giving much bandwidth reduction of
FR4 is the Temperature effeect of Tand and Er. This will give rise closed "eye"
and errors. A good reason why many highspeed vendors are trying to move away
from its use.
--
Regards, __________ James G Roberts
/___ ____ | jrobert@xxxxxxxxxxxxxxxxxxxxx
Jim __ / /___/ / jgroberts@xxxxxxxxxx
/ /_/ /---| | Room: BE436, Hilversum
\____/ /_/ Tel: +31 35 687 4308 Fax: 5976
Scott McMorrow wrote:
> Jeff,
>
> I used the term "non-linear" in a very imprecise fashion. A was
> replying to someone who believed that Er for Fr4 could be considered as
> a constant. I should have said that Fr4 has a non-constant and
> non-intuitive Er that is a function of frequency.
>
> regards,
>
> scott
>
> oyer, Jeff wrote:
>
> >Thanks for doing posting your summary, Matt! A brief synopsis like this =
> >is very valuable. It summarizes what we think we heard, and gives folks =
> >a chance to clarify misunderstandings.
> >
> >It was interesting that you wondered about the statement that FR4 is =
> >non-linear. I also would like to hear some clarification there =
> >(especially about it being extremely non-linear, which the original =
> >posting said). Folks have already clarified that T-lines on FR4 must be =
> >reciprocal (I.E., S21 equal to S12); it seems that it would also be =
> >linear. If not, for TDR and VNA measurements, wouldn't we have to apply =
> >the same voltage that was actually being driven into the system to =
> >properly characterize it? I.E., a non-linear system would have =
> >different S-parameters for a 1V pulse or sine wave than it would a 0.5V =
> >pulse or sine wave.
> >
> >Or am I missing something?
> >
> >Jeff Loyer
> >
> >
> >-----Original Message-----
> >From: Matthew Herndon [mailto:mherndon@xxxxxxxxx]
> >Sent: Friday, January 10, 2003 2:26 PM
> >To: 'si-list@xxxxxxxxxxxxx'
> >Subject: [SI-LIST] Re: (no subject)
> >
> >
> >
> >Hi, everyone -
> >
> >I really enjoyed the recent thread with subject "(no subject)" (it was=20
> >about using s-parameters in SPICE-like simulators and about dispersion=20
> >and loss). So I wrote a summary for my own notes. It occurred to me=20
> >that others on the list might find the summary useful, so I've included=20
> >a shortened version of it below. If anyone wants the full version,=20
> >contact me offline. If more than, say, 10 people request it, I'll post=20
> >it to the list.
> >
> >Thanks to everyone who participated in this very interesting and=20
> >informative discussion!
> >
> >Happy reading!
> >
> >-matt
> >Matthew K Herndon, PhD
> >ECAD Group
> >Apple Computer, Inc.
> >Cupertino, CA.
> >
> >
> >The original question was submitted by Mick Zhou of Agere on Dec 6,2002=20
> >[1]:
> >
> > Has "anybody successfully generate broadband (DC-20GHz) SPICE model
> > from S matrix for complex structures using the SPICE generator in
> > ADS?"
> >
> >Responses indicated that the following additional simulators have this
> >capability; there was various discussion of accuracy, speed, ease of
> >use, bugs, etc:
> >
> > Fullwave SPICE (Ansoft)
> > IConnect (TDA Systems)
> > Nspice (Apache)
> > Broadband Spice (Sigrity)
> >=09
> >At this point, we split into two sub-threads: generating SPICE models
> >without frequency-dependent lookup tables, and the relationship between
> >dispersion and loss.
> >
> >Spice models without frequency-dependent sources:
> >=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
> >=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> >
> >In theory, one can create such models. In practice, one needs to
> >overcome a few difficulties, especially for broadband simulation and for
> >long lines: it is hard to model dispersion accurately [6].
> >
> >There are two approaches to simulating S-parameters in SPICE-like
> >simulators (the following quotes and summarizes [26]):
> >(1) Convert S-parameters to certain forms, either equivalent circuit
> >representations or certain table lookup format, from which SPICE engines
> >can read and run.
> >(2) Enable a SPICE solver to read S parameters directly. The SPICE
> >solver will then internally do the things in (1), or do convolution
> >directly which can be quite demanding for computer resources for large
> >number of such circuit components. Often the original S-parameters or
> >the circuit model representing them may not be stable, causal, and
> >passive. Also, extrapolation of the S-parameter data to DC is often a
> >problem and separate DC values may be needed.
> >
> >The equivalent circuit (using lumped elements, usually RLC)
> >approach does work well in some situations; and converges for the same
> >reason that the Fourier transform converges [8] (Note: I would like to
> >know more about this analogy). We don't have to know anything about
> >the dielectric properties other than what is implicitly contained in the
> >measurements. The only assumption is a linear, time-invariant system
> >
> >It takes a lot of lumped elements to (perfectly) match the measured
> >s-parameters. One calculation came up with 400K elements. So "curve
> >fitting" approximations are used. Questions then arise about how many
> >elements are needed. Apparently, 40 is a "typcial" number in some=20
> >cases. Clearly it
> >depends on the complexity of the shape of the S-parameters curve. And if
> >you happen to drive the circuit at frequencies where the curve-fit is
> >poor, you can get erroneous results (imagine a single sinusoid at a
> >point where the curves are far apart).
> >
> >Dispersion and loss
> >=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> >
> >Dispersion means that the velocity of spectral components of a signal
> >depend on frequency, effectively scattering or "dispersing" the arrival
> >times of the signal wavefront. This effect is not the same as loss,
> >either skin effect or dielectric loss. Dispersion happens when Er varies
> >with frequency (so therefore velocity varies with frequency), as in a
> >prism.
> >
> >However, if dispersion is caused by the dielectric material (the most
> >common situation in SI), there must also be loss; the Kramers-Kronig
> >relationship (aka causality) states that the real and imaginary parts of
> >the dielectric constant are related to each other [15]. So in this
> >sense, you can say that if a MEDIUM is "dispersive" it must also be
> >"lossy".
> >
> >[40] FR4 is non-linear (?), non-uniform and has significant changes in
> >Er across frequency (e.g., 4.2 to 4.0 over the range 0.5 to 5 GHz). Real
> >air exhibits some change in Er with frequency due to humidity; pure
> >(dry?) air does have a flat response and extremely low losses. Likewise
> >some other materials, e.g., Rogers and some PTFE (teflon) and ceramic
> >materials.
> >
> >Dispersion will (always?) occur if the medium non-homogeneous, e.g.,
> >microstrip.
> >
> >
> >SI-list postings quoted directly:
> >
> >[6] From: Yu Liu <yu_liu@xxxxxxxxxxxxx>
> > Date: Fri Dec 6, 2002 9:31:32 PM US/Pacific=09
> >[8] From: Steve Corey <steven.corey@xxxxxxxxxxxxxx>
> > Date: Mon Dec 9, 2002 11:05:10 AM US/Pacific
> >[15] From: Steve Corey <steven.corey@xxxxxxxxxxxxxx>
> > Date: Mon Dec 9, 2002 4:44:28 PM US/Pacific
> >[26] From: Raj Raghuram <raghu@xxxxxxxxxxx>
> > Date: Tue Dec 10, 2002 3:20:06 PM US/Pacific=09
> >[40] From: Scott McMorrow <scott@xxxxxxxxxxxxx>
> > Date: Wed Dec 11, 2002 10:45:28 AM US/Pacific
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >On Friday, December 6, 2002, at 11:42 AM, 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 =
> >>
> >>
> >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
> >>
> >>------------------------------------------------------------------
> >>To unsubscribe from si-list:
> >>si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
> >>
> >>or to administer your membership from a web page, go to:
> >>//www.freelists.org/webpage/si-list
> >>
> >>For help:
> >>si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
> >>
> >>List archives are viewable at:
> >> //www.freelists.org/archives/si-list
> >>or at our remote archives:
> >> http://groups.yahoo.com/group/si-list/messages
> >>Old (prior to June 6, 2001) list archives are viewable at:
> >> http://www.qsl.net/wb6tpu
> >>
> >>
> >>
> >>
> >
> >------------------------------------------------------------------
> >To unsubscribe from si-list:
> >si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
> >
> >or to administer your membership from a web page, go to:
> >//www.freelists.org/webpage/si-list
> >
> >For help:
> >si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
> >
> >List archives are viewable at: =20
> > //www.freelists.org/archives/si-list
> >or at our remote archives:
> > http://groups.yahoo.com/group/si-list/messages=20
> >Old (prior to June 6, 2001) list archives are viewable at:
> > http://www.qsl.net/wb6tpu
> > =20
> >------------------------------------------------------------------
> >To unsubscribe from si-list:
> >si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
> >
> >or to administer your membership from a web page, go to:
> >//www.freelists.org/webpage/si-list
> >
> >For help:
> >si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
> >
> >List archives are viewable at:
> > //www.freelists.org/archives/si-list
> >or at our remote archives:
> > http://groups.yahoo.com/group/si-list/messages
> >Old (prior to June 6, 2001) list archives are viewable at:
> > http://www.qsl.net/wb6tpu
> >
> >
> >
> >
>
> --
> Scott McMorrow
> Teraspeed Consulting Group LLC
> 2926 SE Yamhill St.
> Portland, OR 97214
> (503) 239-5536
> http://www.teraspeed.com
>
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
> or to administer your membership from a web page, go to:
> //www.freelists.org/webpage/si-list
>
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
> List archives are viewable at:
> //www.freelists.org/archives/si-list
> or at our remote archives:
> http://groups.yahoo.com/group/si-list/messages
> Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
>
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
