Subject: Re: [IBIS-Users] Validation of IBIS model
From: hazem@qualim.com
Date: Mon Jan 06 2003 - 09:45:17 PST
Hi,
Sorry for my late response.
Actually it’s hard to tell why you have overlay with
spice in short and open circuit condition. I also agree
with Andrew as the problem might be somewhere else.
This why I’ve suggested the former model regeneration
and corrections in order to be sure from the model
quality before we provide more effort on it.
By the way, I still see IBIS steady state =2.4V while
SPICE steady state = 2.7V. This might be the entrance
of why this is happening.
I hope it helps
On Mon, 06 Jan 2003, Anshuli Goel wrote:
Hello Hazem
Sorry for bombarding you with so many mails.
I picked up the data for rising and falling waveform
from directly
the files made by s2ibis2 script and now I don't see
and ringing. So I
guess the problem that I had was due to bigger
timestep. Now I am
closely matching with the results of spice and IBIS
model but except one
trouble.
IBIS output
SPICE output
If you see at the waveforms the edges of IBIS output is
sharper as compared
to spice output. Otherwise the rise time and voltage
level is closely matching
. Why I am getting these sharp edges. I still have only
1 Rising and 1
falling waveform . So does it have to do something
with this ? ???
Thanx for the help .
Regards
Anshuli
Anshuli Goel wrote:
Hello Hazem
Thanx for pointing out these problems with the model .
I have a few
questions though ?
1. Why the response at short and open load matching ?
(Is it because
there I don't have any load resistance )
2. How do I change the step size of rising and falling
waveforms in
s2ibis2 scripts ? (By default it is 0.2ns)
3. How do I take into account of the load which is
capacitive in nature
( I had posted this question earlier on this reflector
and I got the
answer from ("Mike LaBonte" <milabont@cisco.com>) that
for this
purpose
I should use the
R_f V_f V_f_min V_f_max L_f C_f
R_d C_d L_d etc parameters for
that purpose)
4. I don't understand about the four waveforms that
you have
referred. Can you point me out to some doc or some
thing on that
. How
does s2ibis2 generates these 4 waveforms or do I need
to do smiulations
in spice and put the waveforms in IBIS. if I do that
what is the syntax
in IBIS model for that ?
Regards
Anshuli
Hazem Hegazy wrote:
I'm not sure of the model quality because of the
followings:
-
The number of point in the rising and falling edges is
quit a few before it
reach steady state.
-
There are Rising to gnd and Falling to VDD only V-T
data,
I strongly recommend
to have the other two (Rising to VDD and Falling
to ground).
-
There is C_Fixture = 30p in the V-T data!! This is not
recommended while you
generate the IBIS model wave forms, Please
regenerate the V-T
tables without these
capacitance.
-
The C_comp value must be calculated and optimized in
order
to get complete
overlay with SPICE.
I think that all of these might be the cause.
One more thing, I noticed also from the validation you
sent in this
mail
the SPICE
simulation reaches 2.7 as a steady state, while the
IBIS simulation
reached 2.4 !!
BR,
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Hazem Hegazy
IBIS Modeling Team
www.qualim.com
Tel: +20(2)4043350
Mobile: +20(10) 6052154
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