IBIS-USERS - EIA IBIS Open Forum Users Activity: RE: [IBIS-Users

From: Tess Trethewey <tnt@cypress.com>
Date: Wed Jul 14 2004 - 08:47:49 PDT

Lee

Although we check vs. Spice, one additional check we require is that the
clamps be verified against silicon. Many (most) device models (used in
Spice) are checked/guaranteed accurate only in the range [0, Vcc]. What
you'll see in the clamping regions is [-Vcc, 0], [Vcc, 2Vcc] is that one of
two things usually happens:
1. Clamp currents are excessive - more than an amp or so. This is most
common and in simulation can be avoided by adding a small series resistor
(eg. 0.2 ohm)
2. Clamp Min/Typ/Max curves invert so the Min becomes the strongest
clamping. This is usually due to temperature sensitivity in the device
model; to overcome this the device model parameters need to be revisited.
Unfortunately the same problem happens in SPICE, so verifying against the
spice model does not guarantee accuracy.

We haven't found a way to accurately model clamps without either spending
weeks revisiting device model parameters, or (easier) just using a curve
tracer to check the clamps in the lab.

While the pullup and pulldowns silicon measurements are nice to have,
experience shows that the simulated pu/down are fairly accurate; however
the simulated clamps are almost always different and we require that this
check be done.

Hope this helps.

Regards,
Tess Trethewey
Sr Apps Eng, Cypress Seminconductor

-----Original Message-----
From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org]On
Behalf Of Lynne Green
Sent: Friday, July 02, 2004 10:32 AM
To: 'lee yang'
Cc: ibis-users@eda.org
Subject: RE: [IBIS-Users] IBIS Model Verification

This is so new, that there is no established "accepted percentage".
This will probably be defined by individual "end user" companies.

- Lynne

-----Original Message-----
From: lee yang [mailto:changly_80@hotmail.com]
Sent: Thursday, July 01, 2004 10:52 PM
To: lgreen22@mindspring.com; ibis-users@eda.org
Subject: RE: [IBIS-Users] IBIS Model Verification

Hi Lynne,

Thanks a lot for your information and prompt responce.
Regarding to item 3, let say I am comparing the waveforms between IBIS and
Spice simulations,
besides considering the rise/fall time, should I also compare the waveforms
in terms of the overshoot,undershoot,amplitude? For the rise/fall time, what

is the acceped percentage of
accuracy? (90%???)
Thanks!

Best regards,
L.Y. Chang

>From: "Lynne Green" <lgreen22@mindspring.com>
>Reply-To: <lgreen22@mindspring.com>
>To: "'lee yang'" <changly_80@hotmail.com>, <ibis-users@eda.org>
>Subject: RE: [IBIS-Users] IBIS Model Verification
>Date: Thu, 1 Jul 2004 16:18:24 -0700
>
>Hello, Lee,
>
>1) For checking IBIS against SPICE, there is a method and a FOM (figure of
>merit) documented on the IBIS Quality checklist and document.
>The link is http://www.sisoft.com/ibis-quality/
>
>2) IBIS files should pass the IBIS parser and be tested in at least one SI
>simulator; it sounds like you are already at this point. Additionally, one
>could check the file against the IBIS Quality checklist.
>
>3) Most users expect the models to predict SI performance into a range of
>loads (transmission lines with and without termination). Also important is
>the use of V-t tables to describe internal buffer delays and any asymmetry
>in rise/fall driver characteristics.
>
>As a semiconductor model maker, you might be interested in submitting a
>file
>to the IBIS Review Committee. This committee represents a number of EDA
>tool makers.
>The link is http://www.eigroup.org/ibis/support.htm
>
>Best regards,
>Lynne
>
>
>"IBIS training when you need it, where you need it."
>
>Dr. Lynne Green
>Green Streak Programs
>http://www.greenstreakprograms.com
>425-788-0412
>lgreen22@mindspring.com
>
>
>
>
>-----Original Message-----
>From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org] On Behalf
>Of lee yang
>Sent: Wednesday, June 30, 2004 8:11 PM
>To: ibis-users@eda.org
>Subject: [IBIS-Users] IBIS Model Verification
>
>Hi IBIS experts,
>
>I have generated a list of IBIS models and my next task to check whether
>the
>
>generated IBIS models are correlated to the Spice model.I have no idea at
>all how am I going to verify whether the generated IBIS models are
>accurate.
>
>My questions here are:
>1) Does IBIS committee define a standard procedure of verifying the IBIS
>models to see if they are correlated to Spice models? If yes, then where
>can
>
>I get this document?
>2) Normally, how do IBIS providers assure that the IBIS models provided to
>customers are accurate or correlated to Spice model?
>3) What are the criteria to be considered in order to determine the
>accuracy
>
>of an IBIS model compared to Spice model?
>Could anyone please give some help? Detailed explainations are desired as I
>am just a beginner to IBIS world.
>Many thanks.
>
>-L.Y. Chang
>
>_________________________________________________________________
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