All,
This is the text we arrived at in the IBIS-ATM meeting today:
"Note: Using the IBIS-ISS ground node (0, GND, !GND, GND!, or GROUND) in
IBIS-ISS subcircuits or A_gnd on [Interconnect Model] terminal lines may not
account for all currents going through pins, and therefore potentially cause
incorrect simulation results."
Hoping to see this in the next BIRD189 draft.
Thanks,
Arpad
=========================================================
From: ibis-macro-bounce@xxxxxxxxxxxxx [mailto:ibis-macro-bounce@xxxxxxxxxxxxx] ;
On Behalf Of Walter Katz
Sent: Tuesday, April 17, 2018 2:41 PM
To: IBIS-ATM <ibis-macro@xxxxxxxxxxxxx>
Subject: [ibis-macro] FW: [ibis-interconn] Re: BIRD 189 [Interconnect Model
Set] [Description] and [Manufacturer]
Walter Katz
wkatz@xxxxxxxxxx<mailto:wkatz@xxxxxxxxxx>
978.461-0449 x 133
Mobile 303.335-6156
From: Walter Katz <wkatz@xxxxxxxxxx<mailto:wkatz@xxxxxxxxxx>>
Sent: Wednesday, April 11, 2018 11:31 AM
To: Mike LaBonte <mlabonte@xxxxxxxxxx<mailto:mlabonte@xxxxxxxxxx>>
Cc: IBIS-Interconnect
(ibis-interconn@xxxxxxxxxxxxx<mailto:ibis-interconn@xxxxxxxxxxxxx>)
<ibis-interconn@xxxxxxxxxxxxx<mailto:ibis-interconn@xxxxxxxxxxxxx>>
Subject: RE: [ibis-interconn] Re: BIRD 189 [Interconnect Model Set]
[Description] and [Manufacturer]
All,
I think the following IBIScheck informational message would be useful:
The following interconnect models use Node 0 (aka GND, !GND, GROUND and GND!)
in their IBIS-ISS subckts (and A_gnd on terminals). Using Node 0 in IBIS-ISS
subckts may not account for all currents going to "ground" pins, and therefore
potentially cause incorrect simulation results when doing power aware
simulations where ground and power loops are fully modeled.
<Interconnect model name> <Interconnect model name> <Interconnect model name>
<Interconnect model name> <Interconnect model name> <Interconnect model name>
We can discuss in tomorrows meeting the following I propose adding to BIRD 189.
The historical usage of "Ground" is implemented as Node 0 (GND, !GND, GROUND
and GND!) in IBIS-ISS and A_gnd in IBIS and this BIRD):
* All voltage measurements were made relative to the global simulator
reference Node 0.
The modern usage of "Ground" is "Ground is for potatoes and carrots).
Some power aware simulations need to account correctly for return path
currents. Also the reference node for any voltage measurement should be close
to the measurement point. (Note that in order to compare measurement/simulation
to Data Book Thresholds). "Close" is generally excepted as 1/10 of a UI
wavelength. Twenty years ago "Close" was measured in feet, today "Close" is ~20
mils. Many existing tools historically and continue to generate package,
connector and board level interconnect models using Node 0 in w-line, t-line,
s-parameter, capacitor and resistor elements. These are valid models if the
power rail interconnect is adjusted for this:
* Circuit theory says that we can go from a partial element system where
ground and power loops are fully modeled to a ground referenced system where
node 0 ground is applied to every element in the path. But, ground bounce
inductance and resistance is then lumped into power circuit and signal path
circuits, and the discrimination between the these is lost. From a
differential node voltage perspective at the receiver, the result is the same.
The voltage between the signal and ground will remain the same. If there is a
difference, then somewhere in the circuit, the ground partial inductance has
not been reduced into the loop inductance for the signal path and power paths.
* This is a pretty standard transformation from partial
inductance/resistance matrices to loop inductance/resistance matrices, and is
covered quite extensively in Brian Young's book, which is still the best on the
subject.
*
http://www.amazon.com/Digital-Signal-Integrity-Simulation-Interconnects/dp/0130289043
BIRD 189 also supports package models "where ground and power loops are fully
modeled". This requires that Interconnect Models to not contain Node 0 (unless
there is no net current flowing to Node 0). If some of the return path currents
flow to Node 0, then this would take away currents from ground paths and
thereby change the voltage at the close reference node. Note that even if all
of the package models fully support models ground and power loops, the other
models in the channel (e.g. board, connector, SPICE buffer models, and package
models on other components in the channel) should fully support models ground
and power loops. This is only important for Power Aware simulation. For
non-power aware simulations, the EDA tool can supply DC voltage sources to all
"Power" rails, and a 0.0 voltage source (relative to Node 0) to all "Ground"
rails.
Walter
Walter Katz
wkatz@xxxxxxxxxx<mailto:wkatz@xxxxxxxxxx>
978.461-0449 x 133
Mobile 303.335-6156
From:
ibis-interconn-bounce@xxxxxxxxxxxxx<mailto:ibis-interconn-bounce@xxxxxxxxxxxxx>
<ibis-interconn-bounce@xxxxxxxxxxxxx<mailto:ibis-interconn-bounce@xxxxxxxxxxxxx>>
On Behalf Of Bradley Brim
Sent: Tuesday, April 10, 2018 4:40 PM
To: Mike LaBonte <mlabonte@xxxxxxxxxx<mailto:mlabonte@xxxxxxxxxx>>
Cc: IBIS-Interconnect
(ibis-interconn@xxxxxxxxxxxxx<mailto:ibis-interconn@xxxxxxxxxxxxx>)
<ibis-interconn@xxxxxxxxxxxxx<mailto:ibis-interconn@xxxxxxxxxxxxx>>
Subject: [ibis-interconn] Re: BIRD 189 [Interconnect Model Set] [Description]
and [Manufacturer]
Hi Mike,
If this condition is worth a warning, then it is worth end users relying on it
and therefore worth implementing in other than an optional keyword in an
arbitrary string format.
Any text in the spec saying model makers could/should include arbitrarily
formatted text in the [Description] string concerning explicit or implicit
application of global node 0 (or its equivalent A_gnd) is a redundant statement
(because by definition they could address this or any other condition with such
string) and serves absolutely no reliable purpose for the end user. One could
argue such ambiguity does not belong in a formal specification, even if only a
comment.
I am in favor of such warning but believe it must be in a clearly specified
location/format and must be reliable and include all explicit and implicit
applications of the global node 0 (or its surrogates). If it is part of the
model, then there may need to be a parser and/or runtime validation of the
condition?
Best regards,
-Brad
From:
ibis-interconn-bounce@xxxxxxxxxxxxx<mailto:ibis-interconn-bounce@xxxxxxxxxxxxx>
<ibis-interconn-bounce@xxxxxxxxxxxxx<mailto:ibis-interconn-bounce@xxxxxxxxxxxxx>>
On Behalf Of Mike LaBonte
Sent: Tuesday, April 10, 2018 1:19 PM
To: ibis-interconn@xxxxxxxxxxxxx<mailto:ibis-interconn@xxxxxxxxxxxxx>
Subject: [ibis-interconn] BIRD 189 [Interconnect Model Set] [Description] and
[Manufacturer]
EXTERNAL MAIL
After the discussion in IBIS ATM about whether to warn tools/users when a BIRD
189 interconnect model makes use of node 0, I looked into how we would do that,
if we wanted to. One possibility would be yet another new keyword or
subparameter. But if it's OK to have something that is not machine parseable, a
simple approach would be simply to suggest that [Interconnect Model Set]
[Description] contain a note about the use of global node 0. We could even
include an example to show that.
But I noticed that [Description] is limited to one line, so such a note might
need to be short. For example (addition highlighted):
Keyword: [Manufacturer]
Required: No
Description: Specifies the name of the [Interconnect Model Set]
manufacturer.
Usage Rules: The length of the manufacturer's name shall not exceed 40
characters (blank characters are allowed, e.g., Oklahoma Instruments).
Example:
[Manufacturer] NoName Corp.
Keyword: [Description]
Required: No
Description: Provides a concise yet easily human-readable description of
what kind of interconnect the [Interconnect Model Set] represents.
Usage Rules: The description shall fit on a single line, and may contain
spaces.
Example:
[Description] 220-Pin Quad Ceramic Flat Pack (uses node 0)
On another note, are the usage rules for [Manufacturer] sufficient to exclude
multiple lines? I would say yes, as long as "blank characters" means spaces and
not line ending characters. For that matter, why do we say "blank characters"
for [Manufacturer] and "spaces" for [Description]?
Mike
