[SI-LIST] Re: Best Signal integrity Schools in the USA
- From: "Chris Cheng" <Chris.Cheng@xxxxxxxx>
- To: "Roy Leventhal" <Roy.Leventhal@xxxxxxxx>
- Date: Mon, 24 Mar 2008 15:29:31 -0700
No need. I just yap, really.
If you look at your own questions, they are so fundamental that you =
either knew the answer already or you really need an education in SI. =
All four tasks I mentioned have been well documented and done plenty of =
times by companies I worked for and people who even hang out in the =
SI-list. There is no books or discussion boards to talk about them =
because they are called core competencies.=20
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Roy Leventhal
Sent: Monday, March 24, 2008 2:46 PM
To: Chris Cheng
Cc: Charlotte and/or Roy Leventhal; olaney@xxxxxxxx;
avtaarenator@xxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Best Signal integrity Schools in the USA
=A0
Thank you Chris and tank you for your "yapping." You are a valuable
contributor to SI-LIST.
Roy
Chris Cheng wrote:
> There is an old Chinese saying along the line of "frogs view of the
> world underneath the well".
> I am sitting underneath my well and yapping. I think I have said
> enough in my last mail and I have nothing else to add.
> Those who get what I am saying already got it, there is no point of
> repeating. But the topic is sure appropriate, getting some SI
> education in the USA. More than a few of us need it.
>
> =
------------------------------------------------------------------------
> *From:* Roy Leventhal [mailto:Roy.Leventhal@xxxxxxxx]
> *Sent:* Mon 3/24/2008 1:39 PM
> *To:* Chris Cheng
> *Cc:* Charlotte and/or Roy Leventhal; olaney@xxxxxxxx;
> avtaarenator@xxxxxxxxx; si-list@xxxxxxxxxxxxx
> *Subject:* Re: [SI-LIST] Re: Best Signal integrity Schools in the USA
>
>
> Chris,
>
> For the past six years I have been advocating the use of more =
simulation
> tools among my EMI engineering colleagues (at work and in the IEEE EMC
> Society), so I am not unsympathetic to some of your points.
>
> I find many EMI engineers reluctant to use EDA tools and relatively =
few
> simultaneously cognizant of theory, estimating (yellow pad), =
simulation,
> and measurement in both SI and EMI. Meanwhile, I find continual =
progress
> being made by EDA tool vendors that should be continually evaluated by
> the EMI engineering discipline. I also find a growing level of
> acceptance of, an interest in, modeling and simulation tools.
>
> Historically, those EMI EDA tools have not been ready for prime time =
as
> far as EMI engineers are concerned. So they do what they have to do to
> get a product to pass regulatory: Test, measure, find and fix, and
> iterate until they get a product to pass.
>
> What I see is that when an EMI engineer is in a test cell measuring
> conducted and radiated emissions and susceptibility they are working
> with frequency spectrum scans. Those frequency spectrum scans are the
> data they have to present, not diagrams of eye opening and other SI
> plots. Simulating partial planes an IC package is part of the detailed
> design but usually too much detail for them to simulate at the system
> level.
>
> My first question is, can you provide me some insight into your model
> abstraction and simplification process? I usually can=92t afford
> simulating a system down to the gate level when seeking EMI answers.
> Some modern CMOS models incorporate around 250 factors for around 50
> elements per gate and I/Os have multiple gates.
>
> Also, what models are you using for the IC? Are you using Berkeley
> SPICE, EKV, PSPICE, S-Parameter, large or small signal, or IBIS, or
> what? I=92m seeing evidence that factors we can control at the system
> level are sometimes interactive AND non-linear and would like to know
> the best models to use and their valid frequency, voltage, and
> temperature limitations. I suspect that some of the non-linearities =
are
> due to power system noise modulation of my IC I/Os. I also would like =
to
> investigate if there is core-switching noise getting to my I/Os.
>
> Since I=92m trying to correlate with hardware I would also need to =
know
> the distributions of the IC model parameters for the various parts on
> the board, as well as the passive components, and the variables for =
your
> dielectric uniformity, trace parameters, etc. I suspect that I=92ll =
have
> to do a statistical simulation since in my prototypes I=92m not quite =
sure
> which part of the distribution my parts came from. I would like to
> repeat the =9650 dB you achieved especially since I would expect to =
verify
> the results against hardware. What particular statistical method did =
you
> use in achieving your results? And when you verified those results did
> you do it against at least 25 working prototypes to remove the element
> of chance?
>
> How about your measurement repeatability, I assume its good. I know =
for
> myself that when cables are moved just a bit on my test bench my
> repeatability is a problem. The movement of objects in my anechoic
> chamber and the use of different measurement antennas seem to cause
> similar problems. Of course you have modeled all this in verifying =
your
> results, so I seek your guidance since as you state you have many =
years
> of both SI and EMI experience. Since I=92m dealing with the safety of =
an
> airplane I can=92t be too careful.
>
> Also, I=92m seeing changes in my EMI results with changes in the data
> patterns on my boards and changes in the strengths of emitters in
> various positions on my boards. So I=92m sure that your 50 dB EMI
> correlation must account for magnitude and phase at any place in your
> measurement chamber.
>
> One thing that upsets me is a 500 KHz switching power supply in my
> system that is producing significant harmonics out to 50 MHz and =
beyond.
> I know that if I simulate its effects that I=92ll have to use a SPICE =
EDA
> tool that can model layout structure and converge with resonant
> circuits. I haven=92t found one readily available that I can import my
> layout from Allegro into. Unfortunately, I have to contend with such
> beasties operating alongside my moderately fast digital stuff and I
> can=92t quite do everything I want with the board stackup because =
I=92m
> dealing with 10s to 100s of amps in my system, not milliamps to
microamps.
>
> One of my EMI colleagues in another company has become more interested
> in simulation (I think I inspired him a little) and who is working =
with
> some first class EMI EDA companies. A real breakthrough was achieved
> when his technical contact said =93Aha, you want a virtual test bench =
so
> you can directly compare simulation to measurement.=94 They=92re =
working on
> it and achieving some good, if varied results. They=92ll need such a =
tool
> when they need to do a quick turn-around on a design iteration. But, =
he
> didn=92t indicate 50 dB correlations real soon. They had to simplify =
the
> problem to get it to run in a reasonable time. One thing they didn=92t =
do
> is model the antenna.
>
> Do I believe that EMI modeling and simulation is an absolute =
necessity?
> You bet I do. But, I see a different world with different emphasizes =
and
> needs that will have to be addressed by EDA vendors before the much
> criticized and much harried =93average=94 EMI engineer can be =
successfully
> engaged in making greater use of those tools.
>
> I have many more questions about the issues I raised above and some
> others I have. I=92m sure that we=92ll get into them after you have
> instructed me further in my deficiencies as you have already kindly
> done. I know that I don=92t know near enough in my business and I=92m =
open
> to your instruction.
>
> Best Regards,
>
> Roy
>
>
> Chris Cheng wrote:
> > I walked many miles in EMI and still do.
> > My company had never and will never have EMI only design engineers. =
I
> > am responsible for anything that is not 1 and 0 in our system. I =
don't
> > care if it is call SI or EMI. Analog is analog. Any engineer who =
work
> > for me is capable of doing both.
> > > As things stand today any EMI engineer can tell you that they can
> > > make an entire
> > > career on fixing prototype SI/EMI problems based on the same
> > > half-dozen principles
> > I am still waiting for you to tell me how your EMI engineer can make
> > their career out of my examples below.
> >
This email and any attachments thereto may contain private, =
confidential, and privileged material for the sole use of the intended =
recipient. Any review, copying, or distribution of this email (or any =
attachments) by others is strictly prohibited. If you are not the =
intended recipient, please contact the sender immediately and =
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