I think a bit more explanation would help. Looking at the ECL_0V model,
the key data are:
Vinh = -1.13V | 3.87V
Vinl = -1.48V | 3.52V
.
[Voltage Range] 0.0V 0.0V 0.0V
| [Pullup Reference] 0.0V 0.0V 0.0V
| [Pulldown Reference] 0.0V 0.0V 0.0V
| [POWER Clamp Reference 0.0V 0.0V 0.0V
[GND Clamp Reference] -5.2V -5.2V -5.2V
My interpretation is that the four supply voltages in this case are
exactly what they would be if the other 3 references were uncommented and
the [Voltage Range] were deleted. IBISCHK6s find no problem. This is
Walter's case 3, for which he points out there is a choice between GC and
PD as the reference rail for Vinh/Vinl. Those values appear to be relative
to PD, which I think is always the correct answer, although IBIS is silent
on that. Is this an example of an OK case or a problem case?
Mike
From: ibis-editorial-bounce@xxxxxxxxxxxxx
[mailto:ibis-editorial-bounce@xxxxxxxxxxxxx] On Behalf Of Bob Ross
Sent: Friday, April 15, 2016 1:54 PM
To: wkatz@xxxxxxxxxx; ibis-editorial@xxxxxxxxxxxxx
Subject: [ibis-editorial] Re: Comparing simulated Vpad with VinL
All,
I did not follow all the rules, but IBIS must address all cases,
whether or not any vendor chooses to support them for
business reasons.
The attached file, which issues Warnings and Error, shows
the impact of making a revised interpretation than currently
checked by ibischk6.
I have attached a test case that fails if we follow literally some
of the statements. The issue of voltage references apply
not only to [Voltage Range], [* References], and also
Vmeas, V_fixture, and the [Rising Waveform] and [Falling Waveform]
entries and for Vinl and Vinh and all the [Model Spec]
voltage entries.
We need to be careful not to break many existing models
that are issued by IC vendors and supported by many tools.
Bob
From: ibis-editorial-bounce@xxxxxxxxxxxxx
[mailto:ibis-editorial-bounce@xxxxxxxxxxxxx] On Behalf Of Walter Katz
Sent: Friday, April 15, 2016 10:26 AM
To: ibis-editorial@xxxxxxxxxxxxx
Subject: [ibis-editorial] Comparing simulated Vpad with VinL
All,
When determining Vpad to an IBIS threshold value (e.g. VinL) we do the
following:
1. When only [Voltage Range] is specified or [Pulldown
Reference]=[GND Clamp Reference]=0. (assumes Pdref=Gcref)
a. Compare (Vpad-gcref) to the value of VinL
b. One might argue that this is really a function of (Vpad-gcref) and
(Pcref-Gcref) and (Puref- Gcref), but IBIS does not tell you that either.
2. When [Pulldown Reference]=[GND Clamp Reference]=DUT_Reference !=
0. (assumes Pdref=Gcref)
a. Compare (Vpad-(gcref- DUT_Reference)) to the value of VinL
3. When [Pulldown Reference] != [GND Clamp Reference] (Pdref !=
Gcref)
a. Can do one of two things
i.
Compare (Vpad-(gcref- [GND Clamp Reference] )) to the value of VinL
ii.
Compare (Vpad-(pdref- [Pulldown Reference] )) to the value of VinL
All SiSoft cares about is 1. Bob's answer to 2 and 3 is to generate
multiple models with different values of [Pulldown Reference] and [GND
Clamp Reference] for each condition that he plans to simulate with these
models.
IBIS is silent on the answer to 3. I point out that since there does not
seem to exist a case in nature (other than IBIS allows it), I think it
will be impossible to find out which is correct 3.a.i or 3.a.ii, since
nobody has ever made (or plans to make) such an I/O buffer.
I feel I am wasting my time in these meetings by trying to resolve what to
do for item 3, and I suggest that we simply state that although IBIS
allows this impossible construct, we leave it up to the User/EDA tool on
how do handle measurement thresholds. We do this already for VinL and VinH
(are they fixed voltage (relative to the local Pdref and Gcref) or are
they really meant to represent percentage of the voltage swing.
I hope that MM's introductory paragraph on this will let us move on.
Walter
Walter Katz
<mailto:wkatz@xxxxxxxxxx> wkatz@xxxxxxxxxx
Phone 303.449-2308
Mobile 303.335-6156
