Voltage ranges

Text item: Text_1

Hi IBIS folks,

I had an AR to find out how SPICE people feel about the "100 point limit". From
the answers I received from three different SPICE simulation tool vendors I
concluded that there is no need to limit the data to 100 points. That's all I
want to say about this now, but we can discuss it in more detail on the next
Open Forum meeting.

Along the same lines, I would like to extend each I-V curve to cover the same
voltage span. Currently the GND clamp and POWER clamp curves are limited to a
smaller range than the pulldown and pullup curves. I see the need for this when
there is a weak pullup (or pulldown) "resistor" in a buffer or receiver. The
current understanding is that these kinds of "resistors" can be put into the 0
to 5V range of the GND clamp curve. However, putting a Vcc-relative pullup
resistor into a ground relative GND clamp curve creates a bunch of problems.

For this reason, it would be nice to be able to put the pullup "resistors" into
the POWER clamp curve, but it's voltage range - as defined in ver1.1 (and 2.0) -
does not provide room for it. The logical step would be to extend it's range to
be the same as the GND clamp's range is. But then why not just make all of the
ranges the same for simplicity sake?

When I wrote about this before, some people responded that they view the
specified ranges as minimum required ranges and it did not matter if I published
wider ranges in my models. However, I looked up in the ver1.1 spec, and it
says:

"Points for each curve must span the voltages listed below"

which means no more and no less. I am about to release a new set of models in
which I will most likely violate the spec. by using exdended voltage ranges in
some of the clamp curves. Since I do not want to get blamed for changing my
mind all the time, I would like to hear what you, IBIS people think about
releasing such models before I do so.

I must admit that I am not one of those Godly people who can see into the
future, so when I wrote ver1.1 I did not see this problem coming.

Sincerely

Arpad Muranyi
Intel Corporation
Received on Thu Aug 18 12:19:53 1994