[SI-LIST] Re: Is there any relationship between IBIS simulation accuracy and frequency?
- From: "Moran, Brian P" <brian.p.moran@xxxxxxxxx>
- To: "Andrew Ingraham" <a.ingraham@xxxxxxxx>, "SI LIST" <si-list@xxxxxxxxxxxxx>
- Date: Tue, 26 Feb 2008 12:36:58 -0800
I'll defer to the IBIS experts out there for a more definitive answer,
but there are a
couple things that come to mind regarding IBIS models and switching
frequency.
=20
Traditional V-I and V-T curve based IBIS models are created with the V-T
curves clipped
to less than one half the period of the maximum switching rate. If you
run an IBIS model
beyond this intended frequency, your V-T curves will be clipped,
resulting in the phenomenon
of 'switching into an unfinished edge', potentially resulting in
discontinuities in the
output waveform. This can be easily checked for by examining the model
V-T tables.=20
Conversely, when you create an IBIS model, if you clip the V-T curves
too short, and
do not allow the buffers to settle, you will get distortion in the
model.=20
Also, traditional table based IBIS models are limited in how well they
can model buffers
with data dependent predriver levels. So as your frequency increases,
if the actual buffer
starts to exhibit data pattern dependency, then IBIS miscorrelation will
increase.
=20
Brian Moran
MPG/MPHD/EDE/PEA Group=20
Intel Corp.
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Andrew Ingraham
Sent: Tuesday, February 26, 2008 10:44 AM
To: SI LIST
Subject: [SI-LIST] Re: Is there any relationship between IBIS simulation
accuracy and frequency?
> I think the higher the frequency is ,the lower accuracy the IBIS
models
> are.Is my opinion right?
It is probably true that the earliest generation IBIS models, with a
lumped
R-L-C package model and no coupling, may deviate from reality more as
one
goes higher in frequency. But IBIS has come a long way since then.
A well prepared IBIS model, created with attention paid to the actual
frequencies at which the device will be used, and then used in a
simulator
that is aware of all the features in that model, could be very accurate
at
those higher frequencies. The accuracy of any model increases the
closer it
is used to the frequencies at which the model (or IBIS data sheet, in
this
case) was created.
Models created by people who don't really know modeling, who do it just
because their bosses told them they had to get an IBIS model on their
website, might be inaccurate at DC as well as higher frequencies.
Andy
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=20
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