Walter,
My comment was based on what I quoted from the BIRD (highlighted text). If the
purpose for this termination is defined in the BIRD that way, doesn't that
reduce
or eliminate the "it depends" factor in all this discussion?
Thanks,
Arpad
===============================================================
From: ibis-interconn-bounce@xxxxxxxxxxxxx
[mailto:ibis-interconn-bounce@xxxxxxxxxxxxx] On Behalf Of Walter Katz
Sent: Friday, July 21, 2017 11:08 AM
To: IBIS-ATM <ibis-macro@xxxxxxxxxxxxx>; IBIS-Interconnect
<ibis-interconn@xxxxxxxxxxxxx>
Subject: [ibis-interconn] Re: [ibis-macro] Re: Re: Question about references in
BIRD189, and related comments about AMI Flows
Arpad,
Exactly so. Based on your comment, onw would want to terminate all of the not
used ports with the Touchstone file reference impedance of the port, not the
high impedance as suggested in the BIRD. This is not so obvious if the
interconnect was an IBIS-ISS subckt.
In a crossing e-mail I asked Scott if interconnect sNp are measured with all of
the non-measured pins (and die pads) left unterminated, then is this
self-induce crosstalk already included in the s12. I just got Scott's response
which is repeated here:
Correct. Which is why for correlation to measurements this is the way to go.
Measurement are artificial, and we need to replicate the same artificial
environment in modeling as we do in measurements. In this case, we'll see the
traveling crosstalk wave from excitation of the open circuit nets superimposed
on the measurement.
This is one of the reasons I hate microprobes for measurement. Since it is not
easy to terminate unused lines, the measurements do not match terminated
modeling 1-to-1, unless you correct for the open circuit conditions.
Connectorized measurements are more faithful to the transmission line
environment, since we can terminate unused connectors. But then we have the
issue of removing the connector from the measurement.
Either way, we are dealing with the law of Conservation of Misery. - Misery is
neither created nor destroyed. It is merely transferred from one place (or
person) to another.
I do not think we can solve this problem because the answer will always be "It
Depends". I think the following statement:
Note that the terminals remain technically open, and terminations connected by
the EDA tool are intended to approximate open-circuit conditions."
With something like:
Note that the terminals remain technically open, and the User/EDA tool may
choose an appropriate termination."
Walter
Walter Katz
wkatz@xxxxxxxxxx<mailto:wkatz@xxxxxxxxxx>
Phone 303.449-2308
Mobile 303.335-6156
From:
ibis-interconn-bounce@xxxxxxxxxxxxx<mailto:ibis-interconn-bounce@xxxxxxxxxxxxx>
[mailto:ibis-interconn-bounce@xxxxxxxxxxxxx] On Behalf Of Muranyi, Arpad
Sent: Friday, July 21, 2017 11:22 AM
To: IBIS-ATM <ibis-macro@xxxxxxxxxxxxx<mailto:ibis-macro@xxxxxxxxxxxxx>>;
IBIS-Interconnect
<ibis-interconn@xxxxxxxxxxxxx<mailto:ibis-interconn@xxxxxxxxxxxxx>>
Subject: [ibis-interconn] Re: [ibis-macro] Re: Re: Question about references in
BIRD189, and related comments about AMI Flows
Walter,
Regarding "...those pins that do not have connections on the board...", I read
the following
statement in the latest draft of BIRD189:
This optional subparameter defines the termination that is to be applied by the
EDA tool during simulation to the terminals of any IBIS-ISS subcircuit or
Touchstone network that is not being used in the [Interconnect Model]/[End
Interconnect Model] group.
Note that the highlighted text basically says that the purpose of this
parameter is to terminate
those terminals/ports which are not mentioned on any of the "terminal lines" in
the
[Interconnect Model] keyword. I believe that terminating ports for this reason
is a little
different from terminating ports in situations you are talking about (when the
pin of a device
is not connected to any traces on the board).
If the purpose of this termination is to make the interconnect model look like
as if that
terminal/port didn't exist, wouldn't you want to terminate it with the
"correct" termination
value to eliminate any reflections on that port, and/or potentially allow to
EDA tool to
numerically reduce the Touchstone file to a lower number of ports?
Thanks,
Arpad
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