[ibis-quality] Re: I/V voltage sweep requirements

Mike a few comments

I've seen buffers that were capable of sinking over an amp of current in the
active region.  The one amp limit seems low to me.

Won't zero slope areas on curves cause problems?  I know some simulators
will add some slope to IV curves if required and it is unlikely that any
simulation would get to that current level.

Define Vcc, is it Vcctyp?  Vccmin or Vccmax?  I ask this because I'm
occasionally asked to model a buffer over a very wide voltage range: min =
2.5, typ = 3.3 and max = 3.6V.  Even for normal 3.0/3.3/3.6 Volt modeling
what is Vcc?

Tom Dagostino
Teraspeed(R) Labs
13610 SW Harness Lane
Beaverton, OR 97008
503-430-1065
tom@xxxxxxxxxxxxx
www.teraspeed.com

Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
401-284-1827

-----Original Message-----
From: ibis-quality-bounce@xxxxxxxxxxxxx
[mailto:ibis-quality-bounce@xxxxxxxxxxxxx]On Behalf Of Mike LaBonte
(milabont)
Sent: Tuesday, July 12, 2005 8:09 AM
To: ibis-quality@xxxxxxxxxxxxx
Subject: [ibis-quality] I/V voltage sweep requirements


I have an action item to revise I/V voltage sweep requirement checks.
There is a little controversy, so I'd like to propose it by showing
fragments with commentary here. There are 4 separate checks for I/V
sweep range. The [Pullup] check looks like this:

4.3.4  {LEVEL 1}  [Pullup] voltage sweep range is correct

  The sweep for [Pullup] should be made between -vcc to  2*vcc.
  Pullup tables are relative to Pullup reference.  The Pullup table
  combined with the power and ground clamp tables should be monotonic.
  Non-monotonic combined I-V tables must be documented.

  +++ IBISCHK NOTES
+++++++++++++++++++++++++++++++++++++++++++++++++++++
  Proposal: ibischk caution message if the lower endpoint of the
    [Pullup] voltage column is greater than -vcc, or if the upper
endpoint
    is less than 2vcc.

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++


My suggested change to that one is:

4.3.4  {LEVEL 1}  [Pullup] voltage sweep range is correct

  The sweep for [Pullup] should be at least from -vcc to  2*vcc.
  Pullup tables are relative to Pullup reference.  The Pullup table
  combined with the power and ground clamp tables should be monotonic.
  Non-monotonic combined I-V tables must be documented.

  For ECL devices [Pullup] data must cover the range of vcc to vcc -
2.2.
  An exception is that any [Pullup] table may be truncated at points
  where current reaches the limit specified in 4.3.3. In this case there
  must be two points with the same current at the end of the table, so
  that the final slope of the curve is flat.

  +++ IBISCHK NOTES
+++++++++++++++++++++++++++++++++++++++++++++++++++++
  Proposal: ibischk caution message if the lower endpoint of the
    [Pullup] voltage column is greater than -vcc, or if the upper
endpoint
    is less than 2vcc.

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++


The above:

a) Allows voltage ranges greater than required.
b) Handles ECL differently
c) Allows narrower sweep ranges as long as table reaches 1A and is flat.

We never discussed c), are there any objections?

Also, I discovered that we did cover ECL in a separate check:

4.3.15 {LEVEL 1}  ECL models I-V tables swept from -Vdd  to +2 Vdd.

  I-V tables in ECL models should be swept from -Vdd  to +2 Vdd, even
  though the operating range is narrower.


Obviously this is easy to miss, written into a separate check a page or
two away from the others. I think we should change 4.3.4 through 4.3.7
to cover ECL and eliminate 4.3.15.

Lastly, I would like to propose that [GND Clamp] and [Power Clamp]
tables would be allowed to end at the point where current cross the zero
point in the case of buffers with on-die termination. The final slope of
these would have to be zero to avoid double counting.

Mike
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