FAST-20 Question

Lohmeyer, John JLOHMEYE at cosmpdaero.ftcollinsco.ncr.com
Mon Jan 23 14:35:00 PST 1995



Ron DeRemer wrote:
> I have a question about section 6.1.2 e. of the FAST-20 working draft.
>
> From the words below e) it appears that the intent is to insure that
> the driver will drive 22 mA at ALL voltages below 2,0 V.  I believe
> that the way e) is written it is only necessary for the driver to
> drive 22 mA at ANY voltage below 2,0 V.  For example, I believe that
> driving 22 mA at 0,0 V would meet section e) , but I'm not sure that
> was the intent.
>
> Perhaps a better wording would be:
>
>  e) Ioh (high-level output current > 22 mA (signal negated) @
>     Voh = 2,0 V. d.c.
>
>     Note the = rather than < on the voltage.
>
> If I'm misunderstand the intent of e) please clarify the intent.
>
> Ronald DeRemer, Advisory Engineer, VLSI Circuit Development

You may or may not be right about the words.  I recall the committee 
struggling with this topic and finally leaving the choice of words to the 
silicon designers. But we did have a foil that captured our intentions 
(better than words, I think).  I've converted the foil (crudely, of course) 
to ASCII (view this with a monospaced font):

                                                     3.0V
      |                                              |xxxxxxxxxxxxxxxxxx
      |                                              |xxxxxxxxxxxxxxxxxx
30 mA |                                              |xxxxxxxxxxxxxxxxxx
      |                                              |xxxxxxxxxxxxxxxxxx
      |                                              |xxxxxxxxxxxxxxxxxx
      |                                              |xxxxxxxxxxxxxxxxxx
22 mA +-------------------------------+              |xxxxxxxxxxxxxxxxxx
20 mA |xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx|              +---+xxxxxxxxxxxxxx 20 
mA
      |xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx|                  |xxxxxxxxxxxxxx
      |xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx|                  |xxxxxxxxxxxxxx
      |xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx|                  |xxxxxxxxxxxxxx
      |xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx|                  |xxxxxxxxxxxxxx
10 mA |xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx|                  |xxxxxxxxxxxxxx
      |xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx|                  |xxxxxxxxxxxxxx
 7 mA |xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx|                  +--------+xxxxx  7 
mA
      |xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx|                           |xxxxx
      |xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx|                           |xxxxx
 0 mA +---------------+---------------+---------------+---+-------+-----
      0V              1V              2V              3V  3.24V   3.7V

                   Active Negation Current vs. Voltage

Fast-20 drivers are supposed to operate in the areas not blocked out.  If we 
get another opportunity to make technical improvements to Fast-20, I'd like 
to include a prettier version of this V-I curve in the document.

The status of the Fast-20 draft standard is that we (X3T10) have voted to 
forward Fast-20 to X3 for first public review.  We have resolved the 
negative comments received and are just waiting until everyone has had an 
opportunity to review the corrected draft standard before we send it on.  If 
we receive public review comment(s) and if we agree to make substantive 
changes as a result of such comments (if any), then we can make technical 
changes to Fast-20.  We, of course, have some pressure to avoid making 
changes unless there are serious defects.

John

 --
John Lohmeyer             E-Mail:  john.lohmeyer at hmpd.com
NCR Microelectronics       Voice:  719-573-3362
1635 Aeroplaza Dr.           Fax:  719-573-3037
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