Andrey,
IBIS as a rule describes model data, and generally does not tell the user
or EDA tool how to use the data. More explicitly is describes how to
measure the physical device, and the conditions on how the measurements
are made. "Measurement" can be a physical measurement (e.g. TDR, TDT, .),
or can be done using simulation techniques. The user/EDA tool is
responsible on how to hook up the model of the physical device to the rest
of a channel or system.
Any time we have in the standard rules on how to use models, we get into
conflicts between EDA tool vendors. One rule does not fit all cases. It is
the responsibility of the user/EDA tool to understand how the model was
"Measured" and how to use it. There are well defined rules on test
conditions for generating S-Parameters for interconnect. EDA vendors (at
least some of us), understand the correct way to use models based on
understanding how the physical device was measured.
So you need to understand that all IBIS package modeling is simply an
ASCII format of how a device was measure, how it is used requires
engineering thought (neural processing).
I suggest you check out the Dorothy parker quote "You can lead a
horticulture ."
Walter
Walter Katz
<mailto:wkatz@xxxxxxxxxx> wkatz@xxxxxxxxxx
Phone 303.449-2308
Mobile 303.335-6156
From: Matvienko, Andrey [mailto:andrey_matvienko@xxxxxxxxxx] ;
Sent: Wednesday, July 19, 2017 4:42 PM
To: Walter Katz <wkatz@xxxxxxxxxx>; IBIS-ATM <ibis-macro@xxxxxxxxxxxxx>;
IBIS-Interconnect <ibis-interconn@xxxxxxxxxxxxx>
Subject: RE: [ibis-interconn] Re: Question about references in BIRD189
Walter,
As Arpad answered about what spec says - it enforces to use open-circuit
approximation by default, which may sometimes happen, but is far from a
typical condition in analysis considerations (and should not be used as
default then).
* What would you suggest adding to the standard do deal with this?
First I would suggest removing this "open-circuit approximation" from
BIRD.
I also suggest adding explicit rule on termination of unused ports of
Touchstone models with resistance of reference value(s) specified in
touchstone model.
Thanks,
Andrey
From: Walter Katz [mailto:wkatz@xxxxxxxxxx] ;
Sent: Wednesday, July 19, 2017 3:43 PM
To: Matvienko, Andrey; IBIS-ATM; IBIS-Interconnect
Subject: RE: [ibis-interconn] Re: Question about references in BIRD189
Andrey,
I said what the spec says. The SiSoft EDA tools terminate everything with
the Reference resistance of the S parameter port. There is a subtlety that
the EDA tool knows that cannot be captured in the package model itself.
Suppose one had a subcircuit of a section or all of the pins of a package.
On the board that the package is mounted, a there may or may not be a
connection, or it may in fact be unused on the board. If unused we would
at a 1Meg termination, if used then a 50 Ohm termination. We can be
directed to do other things, but all signal connections tend to be ~ 50
Ohm.
We discussed this often and decided specific rules cannot cover all cases,
so we allow the EDA tool to make situational decisions.
What would you suggest adding to the standard do deal with this?
Walter
Walter Katz
<mailto:wkatz@xxxxxxxxxx> wkatz@xxxxxxxxxx
Phone 303.449-2308
Mobile 303.335-6156
From: Matvienko, Andrey [mailto:andrey_matvienko@xxxxxxxxxx] ;
Sent: Wednesday, July 19, 2017 3:31 PM
To: Walter Katz <wkatz@xxxxxxxxxx <mailto:wkatz@xxxxxxxxxx> >; IBIS-ATM
<ibis-macro@xxxxxxxxxxxxx <mailto:ibis-macro@xxxxxxxxxxxxx> >;
IBIS-Interconnect <ibis-interconn@xxxxxxxxxxxxx
<mailto:ibis-interconn@xxxxxxxxxxxxx> >
Subject: RE: [ibis-interconn] Re: Question about references in BIRD189
Hi Walter,
* If Unused_port_termination is not specified for S-Parameters, then
the EDA tool would (could, should?) terminate the unused Touchstone ports
(terminals) with a resistor to GND with the resistance specified by the
Touchstone port reference resistance which can be per port (terminal).
Unfortunately this is not what BIRD currently says. It currently
prescribes to use open-circuit conditions (thus it will be reflections,
which can be very strong):
"If this parameter is not defined, the EDA tool may connect terminals to
terminations as needed to prevent numerical instability in simulation (EDA
tools are recommended to alert users when this occurs and document the
termination value used). Note that the terminals remain technically open,
and terminations connected by the EDA tool are intended to approximate
open-circuit conditions."
* One can always wrap a Touchstone file or subckt in a subckt and do
any terminations you desire for that specific use of the model.
We also should cover cases where EDA tool need automatically terminate
ports of large package models, say for the cases where package uses a big
s176p S-parameter, but only one net is selected for simulation on the
board.
Thanks,
Andrey
From: ibis-interconn-bounce@xxxxxxxxxxxxx
<mailto:ibis-interconn-bounce@xxxxxxxxxxxxx>
[mailto:ibis-interconn-bounce@xxxxxxxxxxxxx] On Behalf Of Walter Katz
Sent: Wednesday, July 19, 2017 3:13 PM
To: IBIS-ATM; IBIS-Interconnect
Subject: [ibis-interconn] Re: Question about references in BIRD189
Andrey,
If Unused_port_termination is not specified for S-Parameters, then the EDA
tool would (could, should?) terminate the unused Touchstone ports
(terminals) with a resistor to GND with the resistance specified by the
Touchstone port reference resistance which can be per port (terminal).
One can always wrap a Touchstone file or subckt in a subckt and do any
terminations you desire for that specific use of the model.
Walter
Walter Katz
<mailto:wkatz@xxxxxxxxxx> 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: Wednesday, July 19, 2017 2:49 PM
To: 'IBIS-ATM' <ibis-macro@xxxxxxxxxxxxx <mailto:ibis-macro@xxxxxxxxxxxxx>
; IBIS-Interconnect <ibis-interconn@xxxxxxxxxxxxx<mailto:ibis-interconn@xxxxxxxxxxxxx> >