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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From: ibis-interconn-bounce@xxxxxxxxxxxxx
[mailto:ibis-interconn-bounce@xxxxxxxxxxxxx] On Behalf Of Walter Katz
Sent: Friday, July 21, 2017 9:01 AM
To: Scott@xxxxxxxxxxxxx; Muranyi, Arpad <Arpad_Muranyi@xxxxxxxxxx>; 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
Scott,
Thanks for the clarifications. Assuming most pins of a component are in fact
connected to something on the board, we need to be concerned about used
connections in the package that are adjacent (near) interconnect on the
package that are not connected to anything on the Board. What is the EDA tool
to do? What is the package model maker to do?
If a pin is marked NC in a component, and in fact, that pin has routing in the
package, then the most accurate thing to do is to include all these NC pins
along with the pins of interest in the terminals of the interconnect mode, and
then set the termination of all of the unused terminals to ~50 Ohms. An
alternative is to make the interconnect model for a specific pin include all of
the significant aggressor pins. The EDA tool could chose to terminate those
aggressor pins that have connections on the board with ~50 Ohms, and those pins
that do not have connections on the board (whether NC or not) with 1Meg Ohm.
Without this help from the interconnect model maker, the EDA tool can either
run with all 1 MegOhm terminations (pessimistic), or all ~50 Ohm terminations
(optimistic), and compare the results.
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: Thursday, July 20, 2017 4:04 PM
To: IBIS-ATM <ibis-macro@xxxxxxxxxxxxx<mailto:ibis-macro@xxxxxxxxxxxxx>>;
IBIS-Interconnect
<ibis-interconn@xxxxxxxxxxxxx<mailto:ibis-interconn@xxxxxxxxxxxxx>>
Subject: [ibis-interconn] Re: Question about references in BIRD189, and related
comments about AMI Flows
Walter,
Let's keep the AMI related topics out of this subject line, and discuss them in
a separate
thread...
So, regarding this discussion about BIRD189, I am sensing a slight
miscommunication or a
different perspective here. Let me try to explain what I mean.
Using the reference impedance in Touchstone files we can terminate the unused
ports
of a Touchstone file in such a way that there will be no reflections at those
unused ports.
This is usually done to generate waveforms with the used ports of the
Touchstone file
as if the adjacent unused ports did not exist. I understand there are
numerical techniques
which can be applied to Touchstone files to reduce them to a smaller number of
ports
using this concept.
Now, the other perspective that you seemed to describe in your earlier email is
different.
In this interpretation, an "unused port", for example a pin of a package, is
actually connected
to the printed circuit board, and perhaps there are no further traces on the
board attached
to that pin. This is often called a "No Connect" (NC). When a user runs their
simulations,
they may be interested in seeing the effects of this dangling pin, i.e. they
WANT to see
the reflections at that pin, and they WANT to see how these reflections
influence the
adjacent lines through crosstalk, etc... But I would not call this scenario
"unused ports",
because the ports are indeed in use for a good reason.
So I would suggest that we come to an agreement first on what we mean by
"unused ports",
and perhaps put that in BIRD189 to eliminate any confusions or
misinterpretations.
Thanks,
Arpad
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