BIRD14 Comment

To John Keifer, Arpad Muranyi, and IBIS Committee:

There are two proposals in BIRD14. The first concerns a new keyword [Specs]
to override parameters of a particular [Model]. There is merit in this
idea, but I am currently opposed to doing this now for some contradictory
reasons - it overrides some parameters that I feel should not touched, and
it does not include some parameters which would really be useful for
efficiency. Furthermore, it provides an unneccessary level of indirection
which can add to confusion to IBIS at this time and perhaps create a real
problem for implementors using IBIS. Before we introduce [Specs] we really
need a lot more consideration as to what is to be included (e.g, should
Model_type also be included as a practical override, is Cref needed in IBIS,
etc.). Your point is well taken, however, that such a keyword can help
reduce much redundant [Model] data.

The second proposal is about adding two more Sub Parameters to [Model]. The
one parameter I really like is Vt for "test voltage". This is different
than the V_fixture of BIRD12.1 and is more like the Output counterpart
of Vinh and Vinl. I think it should be available as a timing sub-parameter,
particularly for 3-state and Output models where Vinh and Vinl may not
be available to help provide an estimate of Vt. As you show in the example,
Vt will give the intended voltage on which timing at the output is based
such as 1.5V or 2.5V. However, I think Cref should NOT be included because
it is really a timing specification test capacitance (the specification
resistance typically 500 Ohm would then also have to be included), and IBIS
at this time does not cover actual absolute internal delay characterization.
Other databases cover this area, and IBIS could incorrectly specify a
load condition that is not used in the other databases.

Bob Ross
Interconnectix, Inc.
Received on Sat May 7 20:57:39 1994