IBIS Macromodel Task Group Meeting date: 05 January 2016 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 Cisco: Seungyong (Brian) Baek eASIC: David Banas Marc Kowalski Ericsson: Anders Ekholm GlobalFoundries: Steve Parker Intel: Michael Mirmak Keysight Technologies: Fangyi Rao * Radek Biernacki 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 The meeting was led by Arpad Muranyi. -------------------------------------------------------------------------------- Opens: - Arpad welcomed everyone back for 2016 and reminded them that there will be no ATM meeting on January 19th because DesignCon and the associated IBIS summit occur that week. - Arpad noted that he will attend DesignCon and deliver an ATM group status presentation. -------------------------- Call for patent disclosure: - None. ------------- Review of ARs: - None. ------------------------- Review of Meeting Minutes: - Arpad: Does anyone have any comments or corrections? [none] - Mike L.: Motion to approve the minutes. - Arpad: Second. - Arpad: Anyone opposed? [none] ------------- New Discussion: Discussion of language corrections regarding "ground": - Arpad: [Sharing Walter's recent document that listed all lines/paragraphs in which "GND" appeared] - Walter: In almost all examples in the spec, it is clear from context whether GND is a Model name or a signal_name. - In general, I think the new paragraph works with 3 considerations: - 1. We could change all signal_name uses from GND to VSS to eliminate confusion. I know Arpad and Bob R. object to that. - 2. We could just leave them and let the reader figure it out from context. - 3. We could insert additional comments in any place where it's not a Model name or signal_name. - In the figures and graphics, we have to look at each one where GND is used or the ground symbol is used. - In many cases we can replace the use of the ground symbol with “GND,” but not all. - I've highlighted in red the "GND" references in the text that I thought were not obvious. I have not yet done a similar exercise for "GROUND." - Discussion: Radek reiterated that he felt an important part of this exercise was clarifying the reference terminal for the signal pad. Walter agreed and said that if a receiver has threshold voltages (e.g., Vinl, Vinh) they have to be referenced to the same point the I/O (signal) pad is referenced to, and that it must be a local node on the buffer. It would have to be relative to some local ground. For every buffer, we need to know which one of the five voltages in [Pin Mapping] is the local reference. Bob R. objected to that and said that while Walter's description was physically reasonable, it was not the case for IBIS. He said that the various reference voltages in IBIS were all single valued entries with an implicit reference to absolute 0 (node 0). Radek said that implicit connection to node 0 was assumed in the past, but that our goal was to clarify the text and move beyond that assumption. Walter stated that Bob's interpretation was based on the discussions about test fixturing and measurements. The test fixture discussions assumed the pd or gc reference for a buffer is tied to the same reference as the fixture, which is absolute zero. But in terms of simulation for things like Vinl, they are typically going to be with respect to some local reference, most likely pd_ref or gc_ref terminals. Bob said we would have to be very careful in describing the new rules to avoid breaking existing Models. Bob and Mike L. pointed out a paragraph, on page 72 of the IBIS 6.1 spec, that described Composite Current extraction and used the term "absolute GND." Walter pointed out that this was with respect to test fixtures. Arpad and others objected to other elements of the paragraph including the term "absolute GND" itself, and the suggestion that it could serve as a reference for C_comp. Arpad noted that everyone had rejected the idea of connecting C_comp to node 0, and stated that it should be tied to some local ground. He suggested that there had been reluctance to specify that it be tied to the pd_ref or gc_ref terminals in case those were not the local ground pins, but we had not provided any way to specify the additional local reference we needed if the other two were non-zero. Radek agreed and said he would support adding a new reference terminal and did not support forcing pd_ref or gc_ref to be used as the reference. Bob worried that any of the discussed changes would involve substantial parser modifications, but Radek thought it might simply clarify things that had been implicit. - Discussion: Bob R. and Mike L. pointed out an example IBIS file that had been created for ibischk BUG 172. The example contained [Pin] and [Pin Mapping] sections that defined two "POWER" Pin associated buses providing positive voltage rails, a "GND" Pin associated bus providing a 0V rail, and two additional "POWER" Pin associated buses providing negative voltage rails. One I/O Pin used the VSS "GND" bus as its pd_ref and one of the positive voltage "POWER" buses as its pu_ref. Another I/O Pin used one of the negative voltage "POWER" buses as its pd_ref and the VSS "GND" bus as its pu_ref. This example illustrated problems we would have defining the "reference" terminal from amongst the five existing terminals defined by [Pin Mapping]. Mike L. pointed out that we might have simply called the buses "rails" instead of "POWER" and "GND". Bob said gc_ref was a misnomer and something like vss_ref might have been better. Arpad understood Bob's point, but said he had always objected to use of VSS because it was specific to transistor technology. Walter said the example pointed out the need to come up with constant rules for what was the reference terminal, perhaps pd_ref, or gc_ref, or whatever reference had Model name "GND." But Bob pointed out another Pin from the same example that had no reference using "GND" ("POWER" buses were used for all reference terminals). In this example the "POWER" buses used as references were at -2.5V and +2.5V. Everyone agreed that we have to clean up the overloaded use of the reference voltage terms ([Voltage Range], [POWER Clamp Reference], etc.), which are sometimes interpreted as ideal voltage values relative to ideal 0 (during extraction), and sometimes interpreted as terminals between which voltages are calculated for table lookup during simulation. - Arpad: I think we are starting to agree on the concepts that need work. - How many BIRDs might we be talking about? It seems like these 4 Voltage keywords themselves need work, as well as the ground cleanup. - Thank you all for joining. ------------- Next meeting: 12 January 2016 12:00pm PT ------------- IBIS Interconnect SPICE Wish List: 1) Simulator directives