Subject: Use of minimum and maximum Vcc reference

From: Mike LaBonte <[email-masked]>
Date: Thu, 21 Oct 1999 10:37:16 -0400

We have seen Pullup curves in IBIS files where current falls to zero at 0V for typical,
0.5V for minimum, and at -0.5V (approximately) in the maximum column. My guess is that
these measurements are all relative to the *typical* value of Vcc.

The IBIS spec and the cookbook have adequate explanation of the fact that voltages
for [Pullup] and [POWER Clamp] are "relative to Vcc". It is implicit that the minimum
current column in a [Pullup] should be relative to the minimum Vcc, and likewise for
maximum. For example, if one has "[Voltage Range] 5.0V 4.5V 5.5V", and the Pullup
curve has 0 current at 0V for typical, minimum, and maximum, then one would interpret
this to mean that current falls to zero at 5.0V, 4.5V, and 5.5V for typical, minimum
and maximum case, respectively. Putting it another way, "relative to Vcc" means
"relative to typical Vcc for the typical current column, relative to minimum Vcc
for the minimum current column", etc. For "normal" devices I would expect current
to fall to zero in all 3 current columns at 0V, or at least nearly in the same row.

First of all, is my assumption correct? Either way, the correct interpretation should
be explicitly stated in the IBIS spec. Is it in there somewhere?

Mike

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From: "Ross Pryor" <[email-masked]>
Date: Thu, 21 Oct 1999 11:38:49 -0400

Hi Mike,

My assumption is the same as yours - minimum current is relative to minimum VCC and maximum current is relative to maximum VCC.
Both SpecctraQuest and XTK operate under this assumption.  I too have seen many models from semiconductor suppliers where all pullup
and power clamp curves were adjusted relative to VCC typical, and consequently give incorrect VOH values  for min and max cases.  I
think this could be more explicitly covered in the spec so that there is no possibility of misinterpretation.

Ross
--------------
Ross Pryor
Nortel Networks
Billerica, MA
(978) 288-3811
ESN 248-3811
[email-masked]

-----Original Message-----
From: Mike LaBonte [mailto:[email-masked]]
Sent: Thursday, October 21, 1999 10:37 AM
To: [email-masked]
Subject: Use of minimum and maximum Vcc reference

Mike