Minutes from the 21 November IBIS-ATM meeting are attached.
IBIS Macromodel Task Group
Meeting date: 21 November 2017
Members (asterisk for those attending):
ANSYS: Dan Dvorscak
Broadcom (Avago): Xingdong Dai
Cadence Design Systems: * Ambrish Varma
* Ken Willis
eASIC: David Banas
Ericsson: Anders Ekholm
GlobalFoundries: Steve Parker
IBM Luis Armenta
Intel: * Michael Mirmak
Keysight Technologies: Fangyi Rao
* Radek Biernacki
Maxim Integrated Products: Hassan Rafat
Mentor, A Siemens Business: John Angulo
* Arpad Muranyi
Micron Technology: * Randy Wolff
SiSoft: * Walter Katz
* Mike LaBonte
SPISim * Wei-hsing Huang
Synopsys: Rita Horner
Teraspeed Consulting Group: Scott McMorrow
Teraspeed Labs: * Bob Ross
TI: Alfred Chong
The meeting was led by Arpad Muranyi. Randy Wolff took the minutes.
- Arpad reviewed the schedule for upcoming ATM meetings.
- Walter asked if ATM should vote to recommend to the Open Forum that
BIRD165.1 be approved. Arpad noted he took the BIRD off the agenda, and he
did not think the ATM had to give approval. Bob confirmed that the BIRD will
be up for discussion at the December 5 Open Forum meeting.
Review of ARs:
- Arpad to submit BIRD165.1 to the Open Forum.
Call for patent disclosure:
- Ken Willis reported that Cadence had a patent granted, #9798848, relating to
channel simulations of parallel interfaces. Michael Mirmak asked if the
patent would be licensed under reasonable and non-discriminatory terms. Ken
noted he did not have any authority to speak for legal requirements. Bob
asked if there was anything in the IBIS specification impacted by the patent.
Ken said he needed to research that further. Bob noted we should report the
patent in the Open Forum meeting as well.
Review of Meeting Minutes:
Arpad asked if anyone had any comments or corrections. Walter moved to approve
the minutes. Bob seconded the motion. There were no objections.
BIRD189 - File_TS0 restrictions.
Arpad stated he would like a goal of finishing a proposal for what to put in
the BIRD. Radek noted he has not read the last minutes, but discussions
should be recorded there. We might bring up an email with options related to
the issue. Bob noted he and Radek may not agree entirely. One proposal is to
remove File_TS0 entirely. Bob thinks we've agreed to keep it in, although
some vendors may prefer not to have it. He had two possible wordings that are
actionable. One is if you use File_TS0, don't mix it with File_TS models.
Also, don't mix use of node 0 in IBIS-ISS. This might be a caution message.
He doesn't want to check looking for node 0 in IBIS-ISS subcircuits.
Arpad asked if anyone wanted a short summary of the issue. In BIRD189, there
are two subparameters, File_TS and File_TS0. For File_TS0, we don't
explicitly list the N+1 terminal for the reference for Touchstone files. This
reference is defined and connected for File_TS connections. Radek noted this
implicit connection to node 0 in File_TS0 could be dangerous. Walter added in
the common case where you have a component with pins connected to the databook
named ground, typically 0 volts, it isn't an issue because you use File_TS and
reference the ground pin on the component. The EDA tool can float that or tie
it to node 0. The big problem is our unusual case of ECL/PECL/RS232 where
there is no 0 volt pin on the buffer. In this case, there is no pin or signal
pin for the reference for the Touchstone file. File_TS0 was created to cover
this case. Bob noted it isn't limited to that, as buffers really do work
where a reference of ground is outside the buffer and the supplies to the
buffer exist relative to the reference outside the buffer.
Walter asked about components not having a pin for 0 volts. Bob said this
doesn't matter. Many EDA tools support those configurations where the
supplies are supplied relative to an outside ground and simulations are done
accurately relative to an external reference. Arpad noted this seems related
to discussions on C_comp too. We have the same disconnect there, where
capacitors are connected to node 0. Bob noted this has a fix to split C_comp
to explicit references.
Bob asked if there is a disconnect where any cascaded Touchstone files will
work with one having a node 0 reference and one an implicit node 0. There is
no current flow from the N port to the N+1 port.
Arpad asked about the suggestion to remove the File_TS0 parameter option.
Would we need a mechanism to define a connection to node 0 on the N+1
terminal? Bob noted this is the same thing as the shortcut. Radek noted you
still have to understand that the node connected to the N+1 terminal must be
within the node span. You can't connect to a node outside the span of the
Arpad asked if we allow the reference terminal to be connected to node 0 or
not. If we have no pin suitable for the connection, what do we do then?
Walter asked how it could be that you have an interconnect model that does not
have a reference of a pin of the package. If you have no node 0 on a pin,
then how could you have that package? If there is no current going through
that N+1 terminal, then it doesn't matter. Radek said it makes the
requirement that the model makers must understand. Walter said then we should
add a sentence that for File_TS0, there should be no current flowing through
the terminal N+1. Radek stated that this was a suggestion he had in his
Arpad said he agreed with what Walter said. The package model is pinned out
to the component pins. The ground pin could be 1000V away from a reference
node, and if there is still 5V across the ground pin to the power pin, why
does it matter? Radek noted his three options shared in an email to Bob and
1. Scrap File_TS0, or
2. Allow File_TS0 under the condition that node 0 (which, for example, can
named âGND!â following the IBIS-ISS specification, or some other name) is
(either following Bobâs text, or making an equivalent statement) throughout
for all interconnect paths, or
3. Allow File_TS0 and specify the restrictions on the Touchstone file
numerical data needed for unambiguous simulation setup (repeating my previous
If the same Touchstone file containing N-port data is used in an S-element
with N+1 nodes than for any loading conditions (the external circuitry outside
of that S-element) and at all frequencies present in the file the current
entering (or leaving) the (N+1)st node has to be zero.
Bob said whatever current flow rule for node 0 applies. Walter said we make a
choice if we have File_TS0 or not. If we get rid of it, every Touchstone file
must use a reference available as a pin of the component. Walter noted if you
ask anyone writing a package model, they do it to node 0 commonly. They may
also do it to VSS that is nominally 0V. Bob noted you can use an N+1
reference in these cases.
Arpad asked what you do with a 1 port model. Bob noted the second terminal
happens to connect to node 0. Arpad noted there would be current through node
0 in that case. Radek noted this is his second case, and the other node must
exist in the component pins. Bob described the ideal transmission line model
where the reference nodes at each end of the transmission line connect to node
Walter said we need to decide what to do, either keep File_TS0 or require
File_TS to have a reference N+1 node that is an existing pin. Bob doesn't
support the notion that there is a single reference for everything. Walter
noted you can have complex interconnect without single references for every
pin. In that case you can't use the shortcut, you have to use the Touchstone
file in an IBIS-ISS subcircuit.
Arpad moved to remove File_TS0. Walter seconded the motion. Bob said he saw
a case where the N+1 terminal is irrelevant. Walter said if you measure one
or create one from simulation of a layout, you know what the reference is, and
you can define the reference without the shortcut. Arpad noted the shortcut
states you can only have a single common reference for all ports. Mike
LaBonte asked if there was anything in the motion to allow the last terminal
to not be present with File_TS. Walter clarified that you must have an N+1
terminal that must be defined. Michael Mirmak moved to close the debate. Ken
Willis seconded the motion.
The vote tally was:
Cadence - abstain (Ken asked if there was another committee responsible for
Touchstone usage. Walter responded that there is no agreement in an IEEE
measurement committee on node 0 usage. Ken asked if this was supposed to be
voted on in another task group. Arpad responded that the discussion was moved
Intel - yes
Keysight - yes
Mentor - yes
Micron - yes
SiSoft - yes
Teraspeed Labs - yes (Bob noted he doesn't agree with a common reference for
The vote passed with 6 yes votes and one abstain vote. Arpad noted the BIRD
will need to be updated to remove the parameter. The syntax and rules will
need to be defined to handle the description of the reference.
Arpad thanked everyone for joining the call.
Next meeting: 28 November 2017 12:00pm PT
IBIS Interconnect SPICE Wish List:
1) Simulator directives