[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
=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

"I=92m starting With the man in the mirror
 I=92m 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 =
=3D
all,
if you deviate from the rules based on your incorrect IBIS models, do =
=3D
you
think the vendor will really take responsibility if it doesn't work ? =
=3D
If you
follow the design rules, what value does the simulation add to you =3D
design ?
If you are serious enough to simulate, you must be working on something =
=3D
that
is unique about your own system that needs to be custom optimized =3D
beyond
what the component guideline can tell you. Get the SPICE model and do a =
=3D
good
job of modeling your own system. If a small little start up like mine =
=3D
can
get SPICE model from vendors, anyone can. Its just a matter of a few =
=3D
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 =3D
that the
completed model behaves as expected?  I'm interested in responses from
vendors that actually SIMULATE the IBIS model before distributing it =
=3D
for
customer use.  It looks to me as though many of the models I've =3D
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 =
=3D
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
=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D=
3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D
=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D=
3D=3D3D=3D3D=3D3D=3D3D=3D3D

"I=3D92m starting With the man in the mirror
 I=3D92m 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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