RE: [IBIS-Users] input stimulus for extracting IBIS VT curves

Yuangcheng,
 
When you put a load on the IBIS model which was used to
extract the V-t curves from the transistor model (i.e.
the same V_fixture and R_fixture combination), you should
get the same waveforms at the output of the IBIS buffer
as the V-t curve inside the IBIS model.
 
The stimulus to the IBIS model is usually not accessible
in most tools. However, in some tools, like the HSPICE
B-element case you can still define your own stimulus.
This should be as fast as possible, since in theory this
should be a perfect digital transition.
 
When you extract the V-t curves from the transistor models
it is important to set the fastest possible edge rate for
the stimulus, because a relatively slow edge can have an
effect on the apparent delay since the stimulus will take
a certain time to reach the threshold levels of the input
causing some unwanted delays.
 
If you set fast stimulus edge rates, you will usually not
have to massage anything in the waveforms you get from the
transistor model when you make your IBIS model.
 
I hope this helps.
 
Arpad
===========================================================

________________________________

From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org] On
Behalf Of ji xiao
Sent: Wednesday, August 25, 2010 4:53 AM
To: ibis-users@eda.org
Subject: [IBIS-Users] input stimulus for extracting IBIS VT curves

Dear all,
I am trying to validate the IBIS VT data from SPICE simulation. Many
technical papers described the setup as 'apply an appropriate input
stimulus', can anyone tell me in detail how to set the 'appropriate'
one, such as any standards for setting the delay, rise and falling time?
As the original IBIS file does not describe the input stimulus
condition, how can I set it to make me get a totally same rising and
falling waveform?
Thanks and regards,
 
Yuancheng

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