[SI-LIST] Re: IBIS model.


Abe and SignalDude,

Those are good points but I would like to add to the discussion regarding
non-monotonicity and discontinuities in the I-V curves.  Non-
monotonicities can and do exist in I-V curves. These non-monotonicities can
be valid and accurate representations of the device being modeled
especially since they range over a broad voltage domain that goes beyond
the recommended operating limits of the device i.e. -Vcc to 2Vcc.
Simulators have difficulty processing the non-monotonicities, but this does
not make the curves invalid.

Best Regards,
Adam Tambone






"abe riazi" <ariazi@xxxxxxxxxxxxxxx>@freelists.org on 08/21/2001 09:16:13
PM

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Subject:  [SI-LIST] Re: IBIS model.




 Signalguy Wrote:


Also how can I make sure the values under the pullup and pull down =
curves are correct.=20

regards,
Signalguy.


Hi:

Some of the steps related to verification of the Pullup and Pulldown =
curves consist of:

1. Evaluation of the I-V curves for monotonic behavior and lack of =
discontinuities.
2. Examination of the Pullup and Pulldown tables for origin (e.g. both V =
and I approximately  0 ) crossing.
3. Inspection of the voltage range, and polarity sign of the current.

Let us briefly explore the meaning of these tasks.

Existence of monotonicity (or lack thereof) for the I-V curves (as well =
as for V-T waveforms) can be checked using a program such as the =
HyperLynx Visual IBIS Editor.  Executing the IBIS golden parser can also =
produce valuable information about accuracy of the model.

Each I-V table contains four columns namely Voltage, I(typ), I(min), and =
I(max). Nonetheless, a model may lack I(min) and I(max) data, since the =
IBIS specs require data only for the typical column.

Regarding the voltage values; the I-V tables for many buffer models are =
generated based on sweep voltage range of -Vdd to  2 * Vdd; however, the =
Pullup and POWER Clamp data are Vdd or Vcc relative (e.g. voltage =
entries in the table represent Vcc - V output.).  The current polarity =
also deserves attention as positive sign implies current flowing into =
the part (sink), and vice versa.

Furthermore, the Pullup and Pulldown data can be readily exported to an =
Excel Spreadsheet for additional analyses.

Certain model problems prove simple to fix, whereas complicated =
deficiencies usually necessitate contacting the model creator.

I hope you find this information helpful.

Best Regards,

Abe Riazi
ServerWorks

=20
=00

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