[IBIS] RE: [IBIS-Users] IBIS model correlation...

Venu,
 
Thanks for your interest in IBIS.  After looking at the waveforms and
parser output, I have a few comments:
 
1) I strongly agree with Itzik that the min corner V-t tables should be
allowed to settle to their final DC level to remove I-V/V-t mismatches.
2) The ground clamp table is highly discontinuous.  While this shouldn't
cause problems in the operating region, I cannot vouch for what tools
will do to or with the summed data when the pulldown and ground clamp
tables are added together to drive.  You may wish to add some data
points (the table contains fewer than 50) or recheck your extraction
procedure for that device state.
3) I note that the voltage ordering for the pulldown and ground clamp
tables is positive-to-negative.  This is perfectly legal in IBIS, but I
recall this has caused simulators some trouble in the distant past.
Have you tried reordering these negative-to-positive and checking the
results?
4) To clarify, are you using a test load with a capacitor *before* the
transmission line?  Is there a reason your test load includes this
unusual structure?
5) Please ensure that your SPICE tool is using all the V-t tables
available (some tools feature a setting for a number of rising and/or
falling tables -- ensure this is set to use all 4 present in your
model).
6) (minor point) You may wish to make use of the [Test Load] and [Test
Data] keywords to include your loading and correlation waveform
information from your SPICE tool, to ease comparison.
7) One last question: how does the correlation look into a capacitor
alone (both values) and a transmission line alone?  If these match well,
I would inquire with your vendor about checking the algorithm used for a
mixed load like this one.
 
Good luck!
 
- Michael Mirmak
  Intel Corp.
  

 
 

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