[SI-LIST] Re: IBIS Model Quality (or lack thereof)
- From: "Dunbar, Tony" <tony_dunbar@xxxxxxxxxxx>
- To: 'SI-List' <si-list@xxxxxxxxxxxxx>
- Date: Tue, 26 Mar 2002 11:22:16 -0600
All,
As with other threads on the SI List, we are teetering on the brink of
getting away from the original question or topic. I apologize to Todd
up-front for pitching in and contributing further to the distractions with
my own comments. I also applaud Adam for his contribution and those he has
made in the past because, as far as I'm aware, he's the only Si vendor IBIS
model-maker that I ever see on the List. I'm ready to be flamed for that,
but I suspect I won't feel much heat because, somewhat indicative of the
problem, there are so few other IBIS model-makers on the List and/or have
any affinity for the end-user situation, as Todd indicated in his opening
post.
As regards the matter of IBIS model "cleansing service" and using that term
as a eupemism for "sanitization", I'm afraid the latter is often the more
appropriate one to use. The fact that this should even be necessary for a
simulation model is quite appalling to me. I, along with my customers, have
fought this for over 7 years. I know there are many on the list who have
fought it for longer. Please note that I am not saying that a model should
not be checked when it is received and prior to being used; that's only good
engineering practice.
But let me ask the following question, which, though stated in hypothetical
terms, it is not too wide of the mark:
If your ASIC or FPGA or any other Si vendor supplied digital simulation
models (e.g. VHDL or Verilog) to the same quality that many IBIS models are
supplied, would the industry tolerate it to the same extent poor quality
IBIS models are tolerated?
Sorry, but poor quality IBIS models is a pet subject of mine, since it
consumes so much of my time and that of my customers.
Regards,
Tony
-----Original Message-----
From: Joe Socha [mailto:Joe.Socha@xxxxxxxxxx]
Sent: Tuesday, March 26, 2002 9:45 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: IBIS Model Quality (or lack thereof)- Cleansing
service
Hello All,
It is matter of Knowledge and Time. And, as we all know time is money.
Yes the Vendors need to be IBIS savvy, and they have to want to put in the
time to check their models. I believe Todd is asking the semiconductor
community to let us know which of them takes the time to check / test/
verify/ correlate their models before releasing them to the public. ( I just
saw the response from Adam at Fairchild.)
Plexus provides engineering and SI services, and as such we cleanse all the
model we use. (I prefer to describe it as cleansing rather than Sanitize
because sanitize sounds too drastic.) This includes reviewing all the data
testing, modifying the model as needed, working with the vendor as
necessary, testing the model on some standard loads and other activities
such as that. Unfortunately or fortunately depending on your point of view,
the cleansed model is owned by the customer paying for the work we do. This
becomes a competitive advantage for our customer, but unfortunately does not
benefit the overall user community
I like to use the free " Visual IBIS editor" from Innoveda ( formerly
Hyperlynx) There is a new version ( V 3.0) on the web site, and it has some
significant improvements over V2.0. As with all tools it is not perfect, but
it is a time saver for me.
http://www.innoveda.com/products/datasheets_HTML/ibis.asp When dealing the
semiconductor supplier I always ask them to download it so we can talk"
apples to apples" for comparisons and understandings. We have also produced
some models for semiconductor companies and we run the models in several of
the simulators and overlay the results to show that under some typical
topologies the models/simulators all produce similar results.
So it comes down to time. Somebody has to put in the time. The semiconductor
company, the user, or outsourcing.
Thanks,
Joe Socha
----------------------------------------------------------------------------
-------
Joe Socha: Technical Lead, Signal Integrity Analysis
Plexus Technology Group
Snail Mail: 400 Amherst Street Nashua, NH 03063
Email: joe.socha@xxxxxxxxxx
Direct: 603.864.1334, Fax: 603.864.1301, Main: 603.864.1300
----------------------------------------------------------------------------
-------
-----Original Message-----
From: pwelling@xxxxxxxxxxxxxx [mailto:pwelling@xxxxxxxxxxxxxx]
Sent: Monday, March 25, 2002 6:56 PM
To: twester@xxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: IBIS Model Quality (or lack thereof)
Todd,
Many IBIS Models will indicate in the comments section that they are a =
SPICE
to IBIS conversion or a Benched model. Even though they say they are =
bench
models, sometimes they don't correlate very well because test =
conditions
versus real world loading are two different things sometimes. Sometimes =
the
power supply / ground isn't as clean as desired, load impedance varies =
with
trace topology, etc.
I have had reasonable correlation on some models and some not.=20
The first thing (in my oppinion) that needs to done is to at least =
parse the
models - before they are published. So many times I have opened models =
just
to find stupid little syntax problems and things like 1/0 Buffer =
(instead of
I/O Buffer) for the I/O type. They could not have parsed it before
publishing it, so how did it run when they tested the model - and on =
what
simulation tool? Do vendors test the model on more than 1 tool, it's
supposed to be universal, but I think they would be surprised how the =
model
might behave.
I opened one today (a new device) that had several errors in it - =
stupid and
complex.
Then there is the problem of what revision IBIS models the Simulator =
will
support. On older simulators, I have had to strip out 3.x model =
information
to get them compile or to even run without hanging up the system.
IBIS can work, as long as you know the models, where they came from, =
have
"sanitized" them, and your simulator will support them. Generally, you =
can't
just use them off of the web without some work. Some model houses will
create them for you, but be sure you understand what you are getting. =
Some
just SPICE to IBIS, some create minimal point models, dV/dT's are =
typical
(whatever that is), etc.
Yes, SPICE will give more accurate results, take longer to run, and are
generally not applicable for routed board level trace simulation within
budget and schedule constraints.
I agree with you that we need help with IBIS models and it has to =
originate
with both the device vendor and simulator vendor.
Philip Ross Wellington
Mgr. Signal Integrity & EMI
L-3 Communications CSW
-----Original Message-----
From: Todd Westerhoff [mailto:twester@xxxxxxxxxxx]
Sent: Monday, March 25, 2002 4:28 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: IBIS Model Quality (or lack thereof)
Oh no, here we go ...
For the record, we've had *VERY* good luck getting HSpice to correlate =
with
IBIS simulations - the problem is, we've had to create most of the IBIS
models ourselves ir order to get things to match.
Please, let's save the "ultimate HSpice accuracy" arguments for another
thread (preferably one that gets redirected to /dev/null). I'm well =
aware
of IBIS' limitations, and we've done lots of real-world comparisons for =
our
current applications. IBIS will work just fine if we have decent =
models ...
AND, I'll be able to do all the post-route analysis I want.
The question remains, folks ... what semiconductor vendors are willing =
to
"step up the plate" and tell us how they test their IBIS models to =
ensure
correlation to a known source (measurement or HSpice)?
Inquiring minds want to know!
Todd ;-)
Todd Westerhoff
Signal Integrity Engineer
Hammerhead Networks
5 Federal Street - Billerica, MA - 01821
email:twester@xxxxxxxxxxx - ph: 978-671-5084
"starting With the man in the mirror
asking him to change his ways
And no message could have been any clearer
If you wanna make the world a better place
Take a look at yourself, and then make a change"
- "Man in the Mirror", Michael Jackson
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Chris Cheng
Sent: Monday, March 25, 2002 5:18 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: IBIS Model Quality (or lack thereof)
Why use IBIS at all ?
If you are convinced that IBIS is not good enough (which I am), don't
simulate and just follow whatever the vendors design rules say. After =
all,
if you deviate from the rules based on your incorrect IBIS models, do =
you
think the vendor will really take responsibility if it doesn't work ? =
If you
follow the design rules, what value does the simulation add to you
design ?
If you are serious enough to simulate, you must be working on something =
that
is unique about your own system that needs to be custom optimized
beyond
what the component guideline can tell you. Get the SPICE model and do a =
good
job of modeling your own system. If a small little start up like mine =
can
get SPICE model from vendors, anyone can. Its just a matter of a few =
NDA and
extra effort.
-----Original Message-----
From: Todd Westerhoff [mailto:twester@xxxxxxxxxxx]
Sent: Monday, March 25, 2002 12:59 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] IBIS Model Quality (or lack thereof)
Hi all,
We have been doing a lot of comparisons between IBIS and HSpice models
lately, with a lot of less-than-satisfactory results.
I have an open question for the semiconductor suppliers among us:
What testing is performed after an IBIS model is created, to ensure
that the
completed model behaves as expected? I'm interested in responses from
vendors that actually SIMULATE the IBIS model before distributing it =
for
customer use. It looks to me as though many of the models I've
received
were never used in a simulation before being released ... and, as a
potential customer, I find that quite disheartening.
So the question is - what processes are being used to test IBIS models =
and
ensure they function properly before their release to customers?
As always, replies both on and off the list are greatly appreciated.
Todd.
Todd Westerhoff
Signal Integrity Engineer
Hammerhead Networks
5 Federal Street - Billerica, MA - 01821
email:twester@xxxxxxxxxxx - ph: 978-671-5084
"starting With the man in the mirror
asking him to change his ways
And no message could have been any clearer
If you wanna make the world a better place
Take a look at yourself, and then make a change"
- "Man in the Mirror", Michael Jackson
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