RE: [IBIS-Users] V-t curves discussion

Ramiro,

Don't mess with the rwf_scal and fwf_scal parameters to compensate
the delay. Those will scale the entire time axis of the Vt curves,
i.e. they will not only change the delay, but also effect the "edge
rate" or "slope" of the waveform. You probably do not want that to
happen.

Regarding the duty cycle, it is important to make sure that the SPICE
model is also stimulated with fast edges, so that the waveforms you
generate are correlated to the same time point for all waveforms.
If you make an IBIS model this way, and stimulate the IBIS model
with a fast edge also, then you should get the same behavior and
duty cycle with the SPICE and IBIS models.

Arpad
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-----Original Message-----
From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org] On Behalf Of RODRIGUEZ_LECONA_RAMIRO
Sent: Friday, October 15, 2004 9:01 AM
To: ibis-info@eda.org; ibis-users@eda.org
Subject: [IBIS-Users] V-t curves discussion

Arpad, Bob, Tom, Lynne, Aubrey, Giovanni, Nitin:

    Thanks for your feedback. I agree the delay differences are generated by
the difference of switching thresholds of IBIS model buffer simulated in
HSPICE and transistor model, because to a output buffer implemented with
IBIS in HSPICE its input signal is a digital signal with values 0 and 1,
and its Vinl and Vinh values are 0.2 and 0.8 respectively. This is the
cause!!
    But, there is an additional problem, those threshold differences modify
the duty cycle.
    HSPICE has two keywords that can help to compensate the delay: rwf_scal
and fwf_scal. I have been playing with those keywords and the delay is
compensated but occurs some mismatchs between wave shapes, in the edges of
course; when I shift the V-t tables to compensate de delay this mismatch
doesn't occurs!!
    To the IBIS users the delay doesn't represent a problem because they
don't have a reference to comparate the delay. However the duty cycle is now
the problem because it will be modified if the input stimulus transistion
time is changed.
    Here my questions: Is a IBIS's goal to simulate correctly the duty
cycle?
                       Does PCB engineers need to simulate the correct duty
cycle?
                       Or Is their job more directed to a electrical
phenomenoms (electrical or electromagnetic behavior)?
    If it is necessary to simulate correctly the duty cycle using IBIS then
I have a new problem because I can correct it to use it in HSPICE (in
addition I will have to write notes about valid rise/fall times) but if the
IBIS model is simulated in other tool maybe this correction is not going to
work.

    Thanks.

    Regards,

    Ramiro Rodriguez
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Received on Mon Oct 18 08:48:44 2004