RE: [IBIS-Users] Strange implications of ISSO_P* keywords

Michael:

 

The [ISSO_PU] and [ISSO_PD] keywords describe simulation implementation

in terms of Ksso_pd and Ksso_pu multipliers to the K-tables used with
[Pullup]

and [Pulldown] tables.     Therefore there is a strong implication that the
keywords

should be used only with I/O* and Output type buffers.

 

The parser could be enhanced to prohibit Model_types Input*, Terminator, and
Series

for the [ISSO P*] keywords.

 

Bob

 

From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org] On Behalf
Of Mirmak, Michael
Sent: Friday, April 18, 2014 6:01 PM
To: 'ibis-users' (ibis-users@eda.org)
Subject: [IBIS-Users] Strange implications of ISSO_P* keywords

 

I was recently asked about IBIS and power-aware buffer modeling, but for
*inputs*.  

 

At present, IBIS supports two sets of keywords for power-aware modeling:
[Composite Current] and [ISSO_PU]/[ISSO_PD].  [Composite Current] requires
the presence of [Rising Waveform] and/or [Falling Waveform], which in turn
require output Model_types, such as Output, Open_sink, etc.

 

However, there is no obvious requirement that [ISSO_PU]/[ISSO_PD] must be
used with any particular Model_type at all.  While there are notes about
using the keywords with ECL buffers, and recommendations about the
Open_drain, etc. types, no other mention of Model_type is made for these
keywords in the specification.

 

There are implications, though, in other language: the phrase "output
transistors" is used, and there is no mention of Input or any I/O Model_type
in the specification language for these keywords.

 

Realistically, we should be concerned about SSO effects on input buffers
connected to supplies shared with multiple transitioning outputs.  Further,
there's nothing in the time-dependent equations for the keywords that
prevents the current distribution in the pullup and pulldown at an input
from being calculated based on the V(t) of an incoming waveform at the pad.
Finally, the parser has no problem with Model_type Input being used with
[ISSO_PU] and [ISSO_PD].

 

Is there any reason why ISSO_P* cannot be used for input buffers?

 

-          MM

 

 

 


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