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BIRD ID#:        141
ISSUE TITLE:     [Composite Current] Clarifications
REQUESTER:       Randy Wolff, Micron Technology and Lance Wang, IO Methodology
DATE SUBMITTED:  July 1, 2011
DATE ACCEPTED BY IBIS OPEN FORUM: September 16, 2011

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STATEMENT OF THE ISSUE:

The [Composite Current] section currently states that "the currents documented 
in the I-T table correspond to the voltages in the V-T table at the identical
time points and for the given *_fixture load."  This language limits the 
ability of IBIS data extraction tools to apply 'best point fit' algorithms to 
the original I-T waveform data.  The best data points for a specific I-T 
waveform will not be the same best points for the corresponding V-T waveform.

The [Composite Current] section also states that "It can be omitted, or it can
be positioned under a few, but not all of the rising and falling waveform 
tables."  This language implies that I-T waveforms can not be included under 
all V-T waveforms.  [Composite Current] waveform data should be allowed under
all V-T waveforms.

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STATEMENT OF THE RESOLVED SPECIFICATIONS:

All changes, with the exception of spacing and line break adjustments, are 
shown with |*.

Under [Composite Current], replace:

|   The [Composite Current] keyword is optional. It can be
|   omitted, or it can be positioned under a few, but not all of
|   the rising and falling waveform tables.

with:

|    The [Composite Current] keyword is optional. It can be
|*   omitted, or it can be positioned under some or all of
|    the rising and falling waveform tables.

Under [Composite Current], replace:

|    The I-T table data must be time-correlated with the V-T data
|    above it. That is, the currents documented in the I-T table
|    correspond to the voltages in the V-T table at the identical
|    time points and for the given *_fixture load.

with:

|    The I-T table data must be time-correlated with the V-T data
|*   above it. That is, the I-T data should be entered with respect
|*   to the same point in time that the V-T table above it references
|*   and for the given *_fixture load.  See the [Rising Waveform] and 
|*   [Falling Waveform] section for more information about the common 
|*   input stimulus time.  Note that additional "lead-in" time may 
|*   need to be added to all V-T waveforms, as a portion of the I-T 
|*   waveform data describes pre-driver current that may occur earlier
|*   in time than the V-T rising or falling edge transitions.


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ANALYSIS PATH/DATA THAT LED TO SPECIFICATION

An IBIS 5.0 model was created that included [Composite Current] data tables.
As part of the Spice-to-IBIS process, a 'best points fit' algorithm was 
applied separately to the V-T waveforms tables and the I-T waveform tables.
IBISCHK5 V5.0.6 generated the message "ERROR - Model Model1: Rising Waveform 
[1] and its Composite Current don't have identical time points."  EDA 
simulation tool vendors were consulted and indicated that they did not see a
need for the V-T waveforms and the I-T waveforms to have identical time 
points.  This change will allow a 'best points fit' algorithm to be applied 
separately to I-T and V-T data.

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ANY OTHER BACKGROUND INFORMATION:


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