Minutes from the 30 June 2015 ibis-atm meeting are attached.
IBIS Macromodel Task Group
Meeting date: 30 June 2015
Members (asterisk for those attending):
ANSYS: * Dan Dvorscak
* Curtis Clark
Avago (LSI) Xingdong Dai
* Bob Miller
Cadence Design Systems: * Ambrish Varma
Brad Brim
Kumar Keshavan
Ken Willis
eASIC * David Banas
Marc Kowalski
Ericsson: Anders Ekholm
IBM Steve Parker
Intel: Michael Mirmak
Keysight Technologies: * Fangyi Rao
Radek Biernacki
Nicholas Tzou
Maxim Integrated Products: Hassan Rafat
Mentor Graphics: * John Angulo
* Arpad Muranyi
Micron Technology: * Randy Wolff
Justin Butterfield
QLogic Corp. James Zhou
Andy Joy
SiSoft: * Walter Katz
Todd Westerhoff
* Mike LaBonte
Synopsys Rita Horner
Teraspeed Consulting Group: Scott McMorrow
Teraspeed Labs: Bob Ross
TI: Alfred Chong
(Note: Agilent has changed to Keysight)
The meeting was led by Arpad Muranyi.
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Opens:
- None
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Call for patent disclosure:
- None
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Review of ARs:
- Mike LaBonte to post Walter's draft GND document.
- Done.
- Mike LaBonte to send his BIRD spreadsheet to Arpad.
- Done.
- Arpad to add review of minutes to the weekly ATM agenda.
- Done.
- Arpad to add all BIRDs from the spreadsheet to the ATM agenda's tabled list.
- Done. [See first new discussion item below]
- Arpad to contact Romi Mayder regarding BIRD 157.
- Done. Received out of office bounce back.
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Review of Meeting Minutes:
- Arpad: This is the new agenda item we agreed upon last week.
- Curtis: I received no comments or corrections for last week's minutes.
- Arpad: Does anyone have any comments or corrections? [none]
- Mike L: Motion to approve.
- Arpad: Second. Anyone opposed? [none]
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New Discussion:
- Arpad: [showing the newly added BIRD list at the bottom of the agenda]
- Mike L.'s spreadsheet had more information for each BIRD.
- Columns for active, inactive, tabled, discussed, etc.
- Was I supposed to keep all that, or is this list enough?
- Walter: People can use the website to find additional info.
- Mike L.: I think the goal was just to make sure they're all listed somewhere.
- I'm okay with just having a list.
- Walter: I think we can leave it to the discretion of the chair.
- Arpad: We will leave it as is for now.
- Arpad: We were planning to talk about LTI analog models for AMI.
- Scott informed me that he couldn't make it today.
- We can discuss this in the future.
GND cleanup in IBIS:
- Arpad: Walter has a presentation.
- Walter: [sharing "GND BIRD" presentation]
- Expect an IBIS 6.2 that is dedicated to cleaning up "ground" issues in 6.1.
- Issues so endemic it's worth a separate task.
- We should agree on the charter for this task for the editorial committee.
- IBIS currently makes implicit assumptions about "Ground."
- References to GND, Ground, Reference Node, Node 0, A_gnd, absolute ground,
all need careful review and documentation.
- When IBIS was originally written, Ground was often interpreted as truly
global.
- Confusing. Is it node 0? How are things connected to Ground?
- In IBIS 1.0, C_comp is defined as "silicon die capacitance."
- IBIS 1.0 doesn't say anything about how C_comp is hooked up.
- My interpretation from 1.0 is that "Ground" was interpreted as node 0.
- GND needs to be reviewed:
- Under GENERAL SYNTAX RULES AND GUIDELINES, it says:
... following words are reserved and "must not be used"...
- This list includes "GND".
- This is not what we meant. We meant "GND" is a reserved [Model] name.
- GND is often used as a signal_name in [Pin] examples.
- In this case it is the data book name.
- IV Tables Reference Rail Voltages in Simulation.
- The voltage used is between the signal node and the appropriate power rail
buffer model terminals.
- This should not be confused with derivation methods.
- GND, Ground, Absolute Ground, or static voltages referenced to Test
Fixture Ground.
- GND, the ground symbol, and keywords such as [POWER_Clamp_Reference] are
voltages relative to the Test Fixture Ground.
- Simulator Netlists:
- The intent is to make sure IBIS models are only looking at voltage
differences between their terminals' nodes.
- Don't let node 0 enter into it.
- Simulator Reference Node:
- Simulators usually have an absolute reference node (node 0, etc.).
- I/O buffer or interconnect models should not use this node, and certainly
should not supply or draw current from it.
- This is the fundamental issue we've been discussing.
- What is C_comp connected to?
- IBIS 1.0 said nothing about it.
- In IBIS 6.0 we find many locations:
- GND, GND symbol, Text Fixture GND, GND_Clamp_Reference, etc.
- There has been an implication that simulators should connect C_comp
to the simulator reference node.
- This implication is incorrect. It's an interpretation based on the text
used to describe derivation of the IV curves.
- IBIS 6.2 should say C_comp should be connected to the local buffer ground
rail.
- I'd like to have everyone review it and understand it.
- Arpad: I'm in complete agreement with the final point.
- C_comp should be connected to the buffer's local ground rail.
- When I first saw simulators' implementations connecting C_comp to node 0, I
felt this was not what we intended.
- Walter: We have representatives of most of the simulator companies here.
- We could take the following interpretation:
- The original intent for C_comp in IBIS 1.0 was capacitance at the die, and
a reasonable interpretation is that it should be connected to a local
ground rail.
- There have been some strong statements to the contrary, but the simulator
companies should all come to agreement on this issue.
- There was no understanding of these requirements for IBIS 1.0 and it wasn't
made clear. Now is the time to make it clear.
- Randy and I discovered that you get excellent correlation with SPICE models
if C_comp is connected to the rail terminal. This is not true if C_comp is
connected to node 0.
- Compelling technical reasons that it's the right thing to do.
- We can justify that it was always the right thing to do.
- This is the only controversial part of the presentation document.
- Next step is further discussion here after conferring with our respective
companies.
- Arpad: I would like to suggest a clear AR for all the EDA companies.
- Check internally to see if we agree C_comp should not connect to node 0.
- Walter: Could someone make sure representatives of Synopsis and Zuken get the
question?
- Arpad: I'll take the AR to send an email to the reflector.
- Walter, would you forward it and respond to them privately?
- Walter: Yes.
- Arpad: Any other comments on this topic? [none]
- Arpad: Any motions to untable other topics to discuss? [none]
- Arpad: Let us close today's meeting.
- Thank you all for joining.
AR: Walter to send his "GND BIRD" presentation to the reflector.
AR: Mike LaBonte to post the "GND BIRD" presentation.
AR: Arpad to send an email to the reflector regarding EDA vendor input on C_comp
not being connected to node 0.
AR: Walter to forward/reply Arpad's email privately to Zuken and Synopsis to
ensure they get the request for input.
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Next meeting: 7 July 2015 12:00pm PT
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IBIS Interconnect SPICE Wish List:
1) Simulator directives
