Re: [IBIS] Validation of composite current

When you write "IBIS I-T curves are getting truncated at the rise and fall
transitions" do you mean EDA tools are doing the truncating? There are
several behaviors among the tools, and the tendency is to reduce the length
of the V-T curves to the minimum needed to represent an edge, to avoid
overclocking issues. But the fact that current changes often appear before
the voltage changes at the output does raise does raise some questions:

1) Is it necessary to capture pre-driver current? The intention of
[Composite Current] was to improve k-factor determination for
Pullup/Pulldown turnon/turnoff. Currents before the start of the output
transition should be irrelevant.

2) Should IBIS add features to model transition intervals that are shorter
than the waveforms needed to fully characterize each transition, without
discarding data? This was discussed recently, and I believe it was seen as
a significant challenge.

Mike


On Fri, Mar 8, 2013 at 11:01 AM, Rinsha Reghunath <
Rinsha.Raghunath@synopsys.com> wrote:

>  Hi,****
>
> ** **
>
> I am trying to validate an IBIS 5.1 model generated for DDR3 with
> ISSO_PU/PD and Composite Current data. The V-T and I-T data is not clipped
> in order to capture pre-driver current better and the I-T table has 1000
> points. When I tried to do a transient analysis for validation, SPICE and
> IBIS V-T waveforms are matching at the DDR3 frequency, but IBIS I-T curves
> are getting truncated at the rise and fall transitions and doesnot
> correlate well with SPICE. The pre-driver current is being lost. When the
> frequency is reduced, there is good SPICE – IBIS matching for I-T. ** **
>
>
> ****
>
> Is this issue known or is it an issue in the IBIS model?****
>
> ** **
>
> I have read in http://www.eda.org/ibis/summits/may11/m051111.pdf that
> “adding [Composite Current] data to the model reduced the valid switching
> rate of the model.” Is the above issue related to this?****
>
> ** **
>
> Thanks.****
>
> ** **
>
> Regards,****
>
> Rinsha****
>
> ** **
>
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