Subject: BIRD27 [Diff Threshold] Comments

From: [email-masked] ( Bob Ross)
Date: Thu, 6 Apr 95 11:06 PDT

Bob Ward and IBIS Committee:

At this time I am undecided regarding BIRD27 for adding the [Diff Threshold]
keyword.  The choices are:

     (1) Do nothing - simplicity, but inconvenience
     (2) Accept the BIRD as is - convenience
     (3) Expand to allow for two [Diff Pin] columns - more convenience,       
         but with more rules to handle.

A fundamental consideration is that it is technically not necessary.  This
does not add any capablility that can be already handled by the existing
Spec.  Yet it would add to the growing list of keywords to process.

However, the real practical value of this keyword is to allow in one place
the setting of all of the [Diff Pin] thresholds.  Then we can use "NA"
(which is currently permitted) for each pin-pair.

Where do you intend to position the [Diff Threshold] keyword?  I
assume that it is another [Component] modifier similar to [Package].  

An attractive possibility is to include provisions in the BIRD for allowing
the [Diff Pin] table to contain just the first two columns with tdelay
subparameters assumed 0ns.  This could make the [Diff Pin] processing
rules more complicated, however.

For me the tradeoff is between complication and convenience.

Bob Ross,
Interconnectix, Inc.