[IBIS] RE: [IBIS-Users] V-T different durations

Hi, Fabio,

I think 3 important things need to be kept in mind when you generate IBIS
buffer model V-T curves:

1. Starting time point: simulators do differently if you have
different time value at starting point for different V-T curves. To prevent
it, always use the same time Zero point for all V-T curves, at least for the
pair (rising/falling) using the same load conditions;

2. The end time point: As Tim pointed out, the most of simulators can
handle it correctly when the end points are different. The most important
thing for the end points is to have it stabled. The simulators will do the
different things if the simulators need to guess what it is after that.

3. Have the enough points among transition period. This will give a
lot of better simulation results compared with using the even-spacing points
in V-T curves. (it is what S2ibis produces.)

Hope this helps,

Lance Wang

SimDE™ IBIS Validator – Make sure it runs accurately. FREE!

www.iometh.com/Product/IBISValidator

From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org] On Behalf
Of Graham Kus
Sent: Friday, July 08, 2011 1:52 PM
To: 'Fabio BRINA'; 'ibis-users'
Subject: RE: [IBIS-Users] V-T different durations

Hi Fabio,

One thing to keep in mind is that S2IBIS defaults to a transient time of
10ns. So you will need to add the keyword to your s2ibis file to lengthen
this time to accommodate the longest transient time to prevent data
truncation.

Regards,

-Graham

Link:

http://www.ece.ncsu.edu/erl/abstracts/s2ibis2_doc.html

[Sim time] t

        t = Spice transient simulation time

        Optional.

        Default: t = 10ns.

       Describes the transient simulation time to be used by Spice.

From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org] On Behalf
Of Timothy Coyle
Sent: Friday, July 08, 2011 11:02 AM
To: 'Fabio BRINA'; 'ibis-users'
Subject: RE: [IBIS-Users] V-T different durations

Hi Fabio,

I asked this same question a few months ago and from what I recall the
responses were that most modern EDA tools can properly account for the
different VT length durations and it is not an IBIS spec violation. I was
concerned with potential over-clocking situations based upon the different
VT duration lengths. I have not done any follow up testing myself.

I have run into issues with some EDA tools that in certain situations do
have problems with these types of models. So you may want to do some testing
at least with one EDA tool to make sure it's not going to produce unexpected
results.

Best,

Tim

From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org] On Behalf
Of Fabio BRINA
Sent: Friday, July 08, 2011 10:24 AM
To: 'ibis-users'
Subject: [IBIS-Users] V-T different durations

Hello experts,

  a simply question (I suppose!) :

   Can I have different durations for the four V-T waveforms ?

   Till today I generated Rising0, Rising1, Falling0, Falling0 curves

    using the same durations, but Can I have the following situations:

    Rising0 à 12 ns duration

    Rising1 à 10ns duration

   Falling0 à 8ns duration

    Falling1 à 11ns duration

   Standard does not preclude it, but can cause problems to user?

 Thank you in advance.

Fabio

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