Subject: Voltage ranges

From: Arpad Muranyi <[email-masked]>
Date: Thu, 18 Aug 94 11:21:32 PST

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

---

From: [email-masked] ( Bob Ross)
Date: Sat, 20 Aug 94 13:51:16 PDT

Arpad and IBIS Committee:

Here are some comments to respond to your last note on the above subject.

1.  As we discussed, the 100 point limit still exists on some vendor's
controlled voltage and current sources.  What you are saying is that, if
necessary, tables with more than 100 points could be reduced to 100 points
or less.

2.  I think it is permissible and useful to extend the voltage ranges
beyond the IBIS limits on either direction to comply with real, practical
considerations, regardless of the interpretation or intent of the 
"Points for each curve must span the voltages listed below" statement.
Going beyond the span poses no technical problem with Spice based controlled
elements nor with data table based elements.  I also had a situation requiring
modeling a weak, internal non-linear pullup element for an Open device which
I resoved using an extended [Power clamp] table.  So I fully support releasing
any model that have tables going beyond the implied limits.

3.  I do not think it is necessary to require extending the IBIS ranges
for all tables to the same range because for most devices, it is of no
practical impact when the currents are equal or nearly equal to 0 ma.
Only when there is a need should an extension be considered.

4.  By providing tables referenced to various Voltage rails, you along
with others did provide an important architectural contribution for 
using IBIS to transfer model information for current and future needs.
The issue of range limits are not dictated by architectural limitations or 
acquisition of data, but by some practical considerations needed to 
directly map the data into certain simulator constructs.  In all cases,
care needs to be taken to decompose any sources of current into the
appropriate tables and to avoid double entries of the same current.
Even the "min" and "max" tables may have some minor, inconsequential
violation of this with a .5 V overlap when Vcc = 4.5V and a .5V gap when
Vcc = 5.5V for a -5V to 5V span of the [GND_clamp] table.

Bob Ross,
Interconnectix, Inc.

---

From: Will Hobbs <[email-masked]>
Date: Tue, 23 Aug 94 18:12:56 PST

Text item: Text_1

IBISers,

This is possibly a nit, but "span" indicates to met that it has to cover
_at least_ the stated range.  Going beyond it is not precluded.  Has anyone
checked out how the  parser handles greater ranges?

Will Hobbs
Intel Corp.

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:

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.

Sincerely

Arpad Muranyi
Intel Corporation

Text item: External Message Header

The following mail header is for administrative use
and may be ignored unless there are problems.

***IF THERE ARE PROBLEMS SAVE THESE HEADERS***.

Subject: Voltage ranges
To: [email-masked]
From: Arpad Muranyi <[email-masked]>
Date: Thu, 18 Aug 94 11:21:32 PST