Question about Re: Serious s2ibis problem?

Hello Alan Glaser :

I am now developing a IBIS model by s2ibis program in Japan.

I would like to have a question concerning your answer
and make sure IBIS V2.1 spec.

Could you please give your response to me ?

My question is,
Is the following my assumption right ?
Is that the algorithm of IBIS simulators ?

The following shows my assumption for IBIS simulator's algorithm.

IBIS Version 2.1 (8/22/95) spec. say below.
---------------------------------------------------------
  It is assumed that the simulator sums the clamp curves
  together with the appropriate pull-up or pull-down curve
  when a buffer is driving high or low,respectively.
  From this assumption and the nature of 3-statable buffers,
  it follows that the data in the clamping curve sections
                  ======================================(A)
  are handled as constantly present curves and the pull-up
  and pull-down curves are used only when needed in the simulation.
---------------------------------------------------------

IBIS model have 4 tables for 3-state buffer.

  Pullup table = Pullup(enable High out) - (Disable output)
                                        at the range -Vcc~2*Vcc
  Pulldown table = Pulldown(enable Low out) - (Disable output)
                                        at the range -Vcc~2*Vcc
  GND-clamp table = Disable output at the range -Vcc~Vcc

  POWER-clamp table = Disable output at the range Vcc~2*Vcc

If the ranges are right,IBIS simulator must add GND-clamp table(-Vcc~Vcc)
and POWER-clamp table(Vcc~2*Vcc) to constract the full range clamp datas
(the data in the clamping curve sections) and handle it as constantly present
=====================================(A)(see above IBIS spec.)
current, when OUTPUT is disable state , High-Z state or OFF.

And IBIS simulator must add the full range clamp datas to Pullup table
to construct the full range pull-up curve,when a pullup transistor is ON.

Similarly,simulator must add the full range clamp datas to Pulldown table
to construct the full range pull-down curve,when a pulldown transistor is ON.

Here,my 3-state buffer has n-channel pullup transistor.
(Note)
My 3-state buffer is not a inverter which consist of P-ch. and N-ch.
transistors,but a output buffer which consist of N-ch. pullup transistor
and N-ch. pulldown transistor and is able to out High,Low and High-Z.
My 3-state buffer have Hogh-out and Low-out I/V curves which exit a big
current at the range -VCC~0V.
But POWER-clamp table which s2ibis program generated for my 3-state buffer
is only at VCC~2*VCC range and "all zero" of course.
Is the POWER-clamp table for my buffer right ?

If IBIS simulator add pullup table to only POWER-clamp table which
expand to the full range,I think it is wrong either s2ibis or simulator.

Best Regards,
Nakamae.

At 10:46 AM 96.11.8 -0500, awglaser@eos.ncsu.edu wrote:
><snip>
>> Why does s2ibis not subtract the ***Tri-state (un-enabled)*** data
>> from the entire range of both pull-down and pull-up data to derive the
>> corresponding [Pulldown] and [Pullup] tables? Instead, it appears that it
>> takes EXTRA steps to produce seemingly innacurate tables... Is this a
>> serious mistake with s2ibis, or are am I missunderstanding something.
>> Thanks ahead for all feedback.
><snip>
>
>Scott:
>
>While I didn't write the version of s2ibis that you refer to, I think I
>can answer your question.
>
>The answer lies in the voltage ranges of the pullup (or pulldown) and
>power clamp (or ground clamp) curves, and the assumption that a tool
>will add the pullup and power clamp curves of a tristate device together
>to get the correct total behavior.
>
>If you look at the voltage points in the pullup curve, you'll see that
>they vary from -Vcc to 2*Vcc, while those in the power clamp curve only
>vary from Vcc to 2*Vcc. When the simulator adds these two curves
>together, then, it only adds values to the pullup curve in the range Vcc
>to 2*Vcc, not the whole range of the curve.
>
>If one were to subtract the tristated pullup curve from the active
>pullup curve over the entire -Vcc to 2*Vcc range, the IBIS tool would be
>unable to reconstruct the correct behavior of the model, as the required
>data (i.e. the tristated data from -Vcc to Vcc) would not be present in
>the IBIS file.
>
>Hope that clears things up.
>
>Regards,
>
>--
>Alan Glaser "It's not a competition,
>ECE Dept. it's just a mint..." - K
>North Carolina State University
Received on Mon Nov 11 04:21:47 1996