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

Michael Mirmak,

 

Thanks for spending time in reviewing our issue and valuable
suggestions. Please see my responses in line with your suggestions.

 

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.

- Good point we will run for longer time.

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.

- We will work with simulator vendor to see if we get their opinion.

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?

- Interesting point, we will give a try.

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?

- Usually, we use transmission line and then capacitor as per typical
verification setup. However, for ATA buffer, we got the suggestion to do
verification without transmission line also.

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).

- Yes, as per the user guide, tool is using all 4 v-t waveforms. 

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.

- Yes. We need to update our methodology to support it. However, do you
have any idea how simulator will use these data?

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.

- We used transmission line and 30pf in the initial verification setup.
Hspice and IBIS did NOT match very well. Then we used transmission line
and 5pf in the verification setup. (did NOT match). After getting
suggestions, we did verification with only 5pf load. Hspice and IBIS
matched well. When we used 30pf alone, hspice and IBIS are not matching.
Now, we need to find what can be the reason.

 

Thanks in advance,

Nirav/Venu


 

 


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