[SI-LIST] Re: Do you ever measure any of the things you model?

But I always thought SPICE models are perfect, aren't they?
So if I can match the SPICE model with my IBIS model, I
should be able to go home happily, shouldn't I?

When I worked for the world's largest semiconductor company,
I often started by making an IBIS model from SPICE models, and
when it turned out that they were garbage, because the SPICE
models were garbage, we started to tweak the I-V and V-t curves
by all kinds of methods.  So we often had IBIS models which were
more accurate to measured behavior than the SPICE models the
designer used.  Go figure...

I know this may raise a burst of flame and mud slinging (as it
has in the past), but I think there are times when behavioral
modeling can have advantages over full transistor modeling.
This example is just one of those cases...

Arpad
=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=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D


-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
On Behalf Of Alfred P. Neves
Sent: Monday, March 31, 2008 3:47 PM
To: 'Tom Dagostino'; 'Schumacher, Richard (HSTD Signal Integrity)'; =
si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Do you ever measure any of the things you model?

Adding to what Tom already said...   My personal experience working at
numerous semiconductor companies marketing high speed products (both =3D
digital
and analog oriented, including PHY's, SERDES, etc.,) is that they =3D
typically
select a design engineer that generates the IV and VT curves, along with
dynamic characteristics with only simulations, no measurements.  =3D20

Unfortunately, since design engineering time is expensive and the good =
=3D
ones
are VERY busy designing new products, to my experience (not a rule, and =
=3D
not
meant to insult any engineers who pride themselves in this effort) it =
=3D
was
not always the most experienced or talented engineer that was designated =
=3D
for
this activity.  =3D20

This all of course assumes the design represents the process variations, =
=3D
the
package model was included in the full simulation suite and the =3D
simulation
was set up and performed correctly.

Anyhow, I recall a significant number of customers complaining that the
models either would not work at all (a test parser was not run) or they
poorly matched measurements. =3D20

Maybe it is the geek in me, but it sends tingles up my spine when my
simulations match almost perfectly to measure-based results.




Alfred P. Neves=3DA0=3DA0=3DA0=3DA0=3DA0 <*)))))><{=3D20

Hillsboro Office:=3D20
735 SE 16th Ave.=3D20
Hillsboro, OR, 97123=3D20
(503)=3DA0718 7172=3DA0  Business=3D20
(503)=3DA0679 2429=3DA0=3DA0 Mobile=3DA0
=3DA0=3D20
Main Corporate office:=3D20
Teraspeed Consulting Group LLC=3D20
121 North River Drive=3D20
Narragansett, RI 02882=3D20
(401) 284-1827 Business=3D20
(401) 284-1840 Fax=3D20
http://www.teraspeed.com=3D20
=3DA0=3D20
Teraspeed is the registered service mark=3D20
of Teraspeed Consulting Group LLC=3D20

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
=3D
On
Behalf Of Tom Dagostino
Sent: Monday, March 31, 2008 2:54 PM
To: 'Schumacher, Richard (HSTD Signal Integrity)'; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Do you ever measure any of the things you model?

Richard

We measured one Quellan device for the model and used a different device =
=3D
for
the system test.  When we measure a device we vary it's temperature and
supply voltage over the datasheet's operating limits.  We usually do not =
=3D
get
process corner sample but if we did we would have used the strong fast
corner at the cold high voltage operating point and the slow weak corner =
=3D
at
the hot low voltage point for a CMOS device.  This would have given a
complete process/temperature/voltage model. =3D20

But what we have seen from much experience is the IV and VT curves of =
=3D
the
random devices we get are very consistent from part to part of the same
manufacturing process. When I say part to part we are including both the
different die of the same part number and different part numbers from =
=3D
the
same process. We see stronger effects from temperature and voltage than =
=3D
we
see from process variation.

Regards

Tom Dagostino
Teraspeed(R) Labs
13610 SW Harness Lane
Beaverton, OR 97008
503-430-1065
503-430-1285 FAX
tom@xxxxxxxxxxxxx
www.teraspeed.com

Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
401-284-1827=3D20


-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
=3D
On
Behalf Of Schumacher, Richard (HSTD Signal Integrity)
Sent: Monday, March 31, 2008 2:19 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Do you ever measure any of the things you model?


Drifting the topic a little:

"[...] developed a measure-based IBIS model of the Quallan equalizer
[...]
We were able to achieve excellent correspondence between system =3D
simulation =3D3D
and measurements (a few psec correspondence for a 10Meter length signal =
=3D
pat=3D3D
h, see page 36) made with our DSO.  The correspondence was very much =3D
=3D3D3D du=3D3D
e to the quality of the model in that it was generated with very =3D
carefully =3D3D
acquired measure-base data using a high signal integrity fixture, fast =
=3D
TDR =3D3D
head, etc.

I checked the IBIS model separately and it looked exactly like measured =
=3D
dat=3D3D
a in terms of not just rise/fall time in an eye diagram but also the =3D
pedest=3D3D
al and features of the eye were captured extremely well.  I have found =
=3D
IBIS=3D3D
 model accuracy to be critical, and unfortunately most of the vendor =3D
based =3D3D
models are a bit disappointing in their representation.

Check it out:

http://www.home.agilent.com/upload/cmc_upload/All/SI3_Teraspeed_Equalizat=
=3D
io=3D3D
n06.pdf "


To be precise, this uses an IBIS model of a specific instance of the =3D
Qualla=3D3D
n RX, true?  In other words parameters such as silicon characteristics, =
=3D
ope=3D3D
rating temperature, supply voltages, channel impedances etc. were =3D
identical=3D3D
 in both the system and in the measurement-based model of that system.  =
=3D
How=3D3D
 good is the agreement when that same IBIS model is used to simulate =3D
anothe=3D3D
r instance of the same device type, or when that same device instance is =
=3D
op=3D3D
erated at different but within-spec values for temperature or voltage?

Could an IBIS model of the TX be used?


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