Walter,
My confusion was that the "Other Notes" in Slides 2 appear under the
[Pullup]/.. keywords.
However, in refining the terminology, we should clarify that Vcc is just a
generic name for a reference. It does not need to be a "pin", and I can
show some data sheets that use internal charge pump voltage rails where the
Vcc "pin" is not exposed externally. (We cannot use [Pin Mapping] for those
devices.) We are sloppy here and need to understand that "Vcc" for [Pullup
Reference] can have a different value than a "Vcc" for the [Power Clamp
Reference]. Separate terms may be needed.
For slide 3, we may be overloading the word "GND" when we really might mean
the [Pulldown Reference] Vee voltage. The [Gnd Clamp Reference] can be
different from the [Pulldown Reference].
We might also state that Vcc/Vee is generic in this document - they could
mean Vdd/Vss or other reference names used by a component.
Regarding Slide 4, we may not spell this out. But the real rules for
entering values in table based on DUT extraction is:
[Pullup]: Vtable = [Pullup Reference] - Voutput
[Power Clamp]: Vtable = [Power Clamp Reference] - Voutput
[Pulldown]: Vtable = Voutput - [Pulldown Reference]
[Gnd Clamp]: Vtable = Voutput - [Gnd Clamp Reference]
ECL:
[Pulldown]: Vtable = [Pulldown Reference] - Voutput
where [Pulldown Reference] = [Pullup Reference]
All Reference voltages entries are values with respect to an assumed
internal 0 V local reference, whether or not such a local reference is
exposed externally for the [Model].
Slide 5:
The notion is mostly correct for Vinl and VInh. They are adjusted for the
voltages of the clamp references for most cases
However, while not common, it would be legal to change the references
differently - Vdd+9 V, Vee + 10 V, or they could be compressed.
Then the Vinh and Vinh rules should follow the technology and data sheet
intent. Here are 3 common rules for Vinl and Vinh:
TTL: Always an offset from Vee (0.8, 2.0 V)
CMOS: 30% and 70% of Vdd (with Vss = gnd) meaning that threshold difference
could get rescaled
PECL: Always an offset from Vcc.
----
So, part of fixing all references in IBIS is to be precise about our
terminology and application.
Bob
From: ibis-interconn-bounce@xxxxxxxxxxxxx
[mailto:ibis-interconn-bounce@xxxxxxxxxxxxx] On Behalf Of Walter Katz
Sent: Friday, March 04, 2016 7:33 AM
To: ibis-interconn@xxxxxxxxxxxxx
Subject: [ibis-interconn] What does a Voltage mean in IBIS
All,
Voltages in IBIS model data, and IBIS model simulations are different. In
IBIS data they are reference to a test fixture "Ground", and in simulation
they are referenced to a reference terminal of the model instance (adjusted
for the value of that reference terminal used to generate the IBIS data. The
enclosed presentation should clarify this. We need to keep this in mind when
"cleaning up" IBIS.
Walter
Walter Katz
<mailto:wkatz@xxxxxxxxxx> wkatz@xxxxxxxxxx
Phone 303.449-2308
Mobile 303.335-6156
