Subject: IBISCHK Warnings

From: [email-masked] (Bob Ross)
Date: Mon, 9 Nov 98 08:10:44 PST

Shaggy:

Then non-monotonic inforation is valuable as a Warning.
Many models contain some non-monotonic behavior in the
clamping regions, but the summation of clamping tables
with the corresponding [Pulldown] or [Pullup] table
produces a monotonic response which many simulators
can handle.  However, there could be regions which
cause problems.  So the tables should be examined with
a graphical viewer.

The Typical AC points not within 2% ... Warning needs
to be taking very seriously.

It usually reveals one of several things which can cause
serious distortion of IBIS model simulations:

(1) The [Rising Waveform] or [Falling Waveform] is not
constructed in a consistent manner with the various IV
tables.

(2) The time range for the [Rising Waveform] or [Falling
Waveform] table did not extend long enough for the voltage
entry to converge to the final value.  This usually occurs
for the minimum entry under loading conditions which cause
the response to be the slowest.

(3) Some malformed clamping tables (usually the [Power Clamp]
table] which ends as 0 V) would linearly extrolate in a
manner that causes it to appear as a resistor in the normal
operating region.  For example the last two entries may
appear as:
|  V   typ min max
 ...
   0.1 1m  1m  1m
   0   0   0   0

This would extrapolate as a 10 ma per volt (100 ohm) pullup
resistor into the operating region - enough to cause the
calculated response to be different than the captured
response.  ibischk3 test for extropolated values when
predicting the DC starting and ending points of waveforms.

These are serious problems.  The technical reason that this
is treated only as a Warning is that the 2% tolerance limit is
arbitrary.  In some cases if you are within a slightly higher
error limit, you may still get good simulations.

Bob Ross
Interconnectix/Mentor Graphics

> From: "Shaggy Gonzalez" <[email-masked]>
> To: [email-masked]

> Hi,
> Could you tell as to why are the warnings like :
> Typical/Max/Min Data Non-Monotonic Pullup/PullDown.
>  What are these and how can they be removed..
> Also. some warnings are: Typical AC points not within 2% etc
> How are they taken care of..
> shaggy 
> ASD Design Solutions:

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