Subject: Re: [IBIS-Users] Validation of IBIS model
From: Anshuli Goel (anshuli@india.ti.com)
Date: Mon Jan 06 2003 - 05:06:01 PST
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
[Image]
SPICE output
[Image]
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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