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. ------------------------------------------------------------------------ Opens: - None -------------------------- Call for patent disclosure: - None ------------- 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. ------------------------- 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] ------------- 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. ------------- Next meeting: 7 July 2015 12:00pm PT ------------- IBIS Interconnect SPICE Wish List: 1) Simulator directives