All,
To clarify what the standard says:
Note that the terminals remain technically open, and terminations
connected by the EDA tool are intended to approximate open-circuit
conditions.
However, if the terminals are connected to traces that go off with known
transmission line impedances, the EDA tool should terminate with an
resistance ~impedance off the traces. True, these transmission lines can
be terminated at other than a nice termination there can be reflections,
but if the user felt these affects were importance then the user (or EDA
tool), then a more complex termination circuit should be inserted by the
user or EDA tool.
We cannot anticipate everything here. Thus users using any model should
apply neural processing to decide what needs to be done.
Walter
Walter Katz
<mailto:wkatz@xxxxxxxxxx> wkatz@xxxxxxxxxx
Phone 303.449-2308
Mobile 303.335-6156
From: Muranyi, Arpad [mailto:Arpad_Muranyi@xxxxxxxxxx] ;
Sent: Wednesday, July 19, 2017 4:12 PM
To: Walter Katz <wkatz@xxxxxxxxxx>; Matvienko, Andrey
<andrey_matvienko@xxxxxxxxxx>; IBIS-ATM <ibis-macro@xxxxxxxxxxxxx>;
IBIS-Interconnect <ibis-interconn@xxxxxxxxxxxxx>
Subject: RE: [ibis-interconn] Re: Question about references in BIRD189
Walter,
Here is what BIRD189.5_draft3 says:
Unused_port_termination rules:
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. The subparameter
name shall be followed by a single numeric argument greater than zero on
the same line. The argument shall be separated from the subparameter name
by the "=" character. The subparameter name, "=" character, and argument
may optionally be separated by whitespace.
If this subparameter is present, the EDA tool should connect the unused
terminals to a reference terminal through a resistor with the value of
resistance in ohms provided in the argument.
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.
Only one Unused_port_termination subparameter may appear for a given
[Interconnect Model] keyword.
I believe Andrey was asking for a mechanism to make use of the reference
impedance defined
in Touchstone v2.0 files. I don't see that mentioned in the BIRD. Where
did you get these words
from in your email below:
* "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)."
Thanks,
Arpad
==========================================================================
====
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 2:43 PM
To: Matvienko, Andrey <andrey_matvienko@xxxxxxxxxx
<mailto:andrey_matvienko@xxxxxxxxxx> >; 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
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> >