(attaching a text version of the minutes for ease of archiving)
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IBIS INTERCONNECT TASK GROUP
http://www.ibis.org/interconnect_wip/
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Attendees from March 2 Meeting (* means attended at least using audio)
ANSYS Curtis
Clark*
Cadence Design Systems Bradley Brim*
Cisco David
Siadat
Intel Corp. Michael
Mirmak*
Keysight Technologies Radek Biernacki*
Mentor Graphics Arpad Muranyi*
Micron Technology Justin Butterfield*,
Randy Wolff*
SAE ITC Maureen
Lemankiewicz, Logen Johnson
Signal Integrity Software Walter Katz*, Mike
LaBonte*
Teraspeed Labs Bob Ross*
University of Aveiro in Portugal Wael Dghais
Michael Mirmak convened the meeting. No patents were declared. No minutes
were available from the previous meeting for approval.
Walter Katz presented "Currants in S-Parameters" examples, including a two-port
network shown in Keysight Technologies on-line material. The "-" terminal is
the return terminal, which is usually ignored in schematics. Each port has two
terminals. The return terminal is on the "ground" pad. Currents are equal and
opposite.
Bob Ross noted that the reference can be on the power rail. Walter replied
that "reference" as a term is deliberately not being used in his discussion.
Bob suggested that the term "return terminals" is appropriate.
Brad Brim asked whether every terminal has a voltage. Voltage is measured
between the terminals. This is a subtle point, but a necessary one. Walter
agreed, adding that a voltage can always be measured with respect to the core
of the earth, but that is not what is used in lab measurements.
The total current in and out of a terminal block is zero. Brad clarified that
the "universe" here is simply one signal node and one Vss (etc.) node.
Arpad Muranyi responded that he agreed with everything discussed so far except
the last slide. This assumes that the terminals on the die side are using the
same terminal (due to N ports + 1) for a reference as the pin side. Walter
disagreed, stating that this is a convenience for linking the return terminals
to the reference node of the simulator. N+1 convention does NOT mean that the
N+1th terminal is the reference; the simulator is responsible for figuring out
how to connect the node to the reference.
Brad and Radek Biernacki disagreed with this directly. Brad summarized three
ways of connecting this kind of network:
1) terminal 1, terminal 2 - reference is zero
2) terminal 1, terminal 2, another node - no node zero usage, and the
other node is used as reference
3) terminal 1, reference 1, terminal 2, reference 2 - no node zero usage
Walter agreed. Using an S-element with node zero at the end of the node list
means that you had better be sure that everything in that path uses reference
node zero.
Arpad stated that there is an implication about an ideal short between
references at the pin side, and another at the pad side. You cannot simulate
ground bounce in that situation. Walter replied that he will correct the title
of the slide to, "So What Does the S-parameter Shortcut Mean?"
Radek commented about the distinction between terminals and ports. Walter
emphasized the 2N vs. N+1 distinction. Radek replied that one cannot infer the
reference if you are not told what it is. Walter responded that the near
terminal is used as reference.
Radek repeated an example case described in the last meeting: imagine a
traditional IBIS package RLC with only R and L. This is two terminals, or
1-port data in Touchstone. Reference would be a shunt element that does not
exist. Brad replied that this situation could not be handled through the
shortcut approach. Radek disagrees, stating that he wanted to have 100%
equivalent treatments for all circuit topologies.
Arpad added that the shortcut is based on an assumption. Radek noted that the
original solution had a certain number of terminals available for connection,
with N+1 terminals for TS data with N port. Brad suggested that 99% of models
that Walter was concerned about would be covered by the shortcut. If the
shortcut is not desirable, then perhaps requiring a wrapper in all cases was
appropriate.
Brad presented one slide, due to time constraints. The objective is to provide
a shortcut so that you don't have to provide an IBIS-ISS wrapper for many
cases. A key requirement is that all simulator tools would use a common format
for netlisting the shortcut in a universal, identical fashion.
Brad and Walter agreed that "node" and "terminal" are not synonymous. Next
time, Brad will complete his presentation and the team will resolve the
shortcut approach.
Arpad moved to adjourn. Brad seconded the motion. The meeting adjourned.
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