Fast-20 active negation current

Lohmeyer, John JLOHMEYE at cosmpdaero.ftcollinsco.ncr.com
Tue Jan 24 13:48:00 PST 1995


I have received more email from silicon people who are not happy with how 
we've specified the minimum active negation current in Fast-20.  Apparently, 
several of the driver/receiver silicon people were not present at the June 
2, 1994 meeting.

The common thread seems to be agreement that the active negation drivers 
must smoothly swing the signal through the transition region, but not 
agressively source current above the transition region.  Our 22 mA @ 2.0 
volt requirement is difficult to meet at best and appears unnecessary.

I am looking for suggestions on how to best state the actual requirements so 
that we do not over-design the interface.  Should this be some sort of 
series of stepped requirements?  For example, at least 22 mA @ 1.3 V and 
below, at least 10 mA @ 1.9 V and below, etc.:

                                                     3.0V
      |                                              |xxxxxxxxxxxxxxxxxx
      |                                              |xxxxxxxxxxxxxxxxxx
30 mA |                                              |xxxxxxxxxxxxxxxxxx
      |                                              |xxxxxxxxxxxxxxxxxx
      |                                              |xxxxxxxxxxxxxxxxxx
      |                                              |xxxxxxxxxxxxxxxxxx
22 mA +--------------------+                         |xxxxxxxxxxxxxxxxxx
20 mA |xxxxxxxxxxxxxxxxxxxx|                         +---+xxxxxxxxxxxxxx
      |xxxxxxxxxxxxxxxxxxxx|                             |xxxxxxxxxxxxxx
      |xxxxxxxxxxxxxxxxxxxx|                             |xxxxxxxxxxxxxx
      |xxxxxxxxxxxxxxxxxxxx|                             |xxxxxxxxxxxxxx
      |xxxxxxxxxxxxxxxxxxxx|                             |xxxxxxxxxxxxxx
10 mA |xxxxxxxxxxxxxxxxxxxx+--------+                    |xxxxxxxxxxxxxx
      |xxxxxxxxxxxxxxxxxxxxxxxxxxxxx|                    |xxxxxxxxxxxxxx
 7 mA |xxxxxxxxxxxxxxxxxxxxxxxxxxxxx|                    +--------+xxxxx
      |xxxxxxxxxxxxxxxxxxxxxxxxxxxxx|                             |xxxxx
      |xxxxxxxxxxxxxxxxxxxxxxxxxxxxx|                             |xxxxx
 0 mA +---------------+----+--------+-+---------------+---+-------+-----
      0V              1V   1.3V   1.9V2V              3V  3.24V   3.7V

                   Active Negation Current vs. Voltage

Or perhaps we really need a formula.  Or as Tak suggests, perhaps we need an 
AC specification...

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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