============================================================================== IBIS INTERCONNECT TASK GROUP Mailing list: ibis-interconnect@freelists.org ================================================================================ Attendees from March 26, 2025 Meeting (* means attended at least using audio) ANSYS Curtis Clark, Wei-hsing Huang, Juliano Mologni Arista Networks Jim Antonellis Broadcom James Church Intel Corp. Michael Mirmak*, Xiaoning Ye Keysight Technologies Ming Yan Marvell Steve Parker MathWorks Walter Katz* Micron Technology Justin Butterfield Siemens EDA Weston Beal, Arpad Muranyi*, Randy Wolff* Simberian Yuriy Shlepnev ST Microelectronics Aurora Sanna Synopsys Ted Mido, Edna Moreno University of Illinois Jose Schutt-Aine Zuken USA Lance Wang Michael Mirmak convened the meeting. No patents were declared. Michael reviewed the March 19, 2025 meeting minutes, noting a typographical error: "Michael noted that he still had an open AR to update the IBIS-ISS text with am ISSIRD to correct the character set definitions used for the files." The word "am" should be "an". Randy Wolff moved to approve the minutes with this corrected; Walter Katz seconded. The minutes were approved without objection. During Opens, Arpad Muranyi noted that he may not be able to attend next week's meeting due to travel. Michael shared a presentation regarding connecting different circuits, particularly Touchstone and SPICE, suggesting that perhaps IBIS-ISS changes are needed to ensure correct intent for the whole system (for example, ensuring loop currents are maintained across connected circuits from different sources). Arpad stated that it would indeed help a lot to know how the entire circuit is built when assembling individual component models. However, any IBIS-ISS change may not be followed by other SPICEs. This introduces some potential dangers and challenges related to ompatibility. Michael mentioned that he believed a ".iss" structure may exist already in some SPICE variants. Arpad raised two suggestions: 1) adding dot statements to describe content of subcircuits to be used for external connectivity 2) adding support for by-name connectivity (a different issue, related to SPIM, in contrast to SPICE assumptions of by-position connectivity) Michael added a suggestion that IBIS-ISS set rules prohibiting node 0 inside subcircuit definitions. Arpad stated that, in IBIS-ISS, be believed that there is a rule that node 0 inside a subcircuit t is a different node 0 than one for the entire netlist. Walter Katz suggested that SPIM is academic in this discussion; you cannot mix IBIS-ISS and Touchstone. Arpad agreed, noting that he was thinking more of EMD and IBIS Interconnect. Walter suggested that, for signal integrity analysis, one wouldn't connect a Touchstone S-parameter file with a SPICE circuit that uses non-ideal VSS rail information. Michael asked whether co-simulation of signal and power integrity was therefore impossible. Walter replied that co-simulation was effectively off-the-table for IBIS at present, as it is really difficult; Kinger Cai agreed in other meetings that one cannot do it. What is the effect of PI on SI? Walter suggested performing PI first, getting spectral density, creating a power waveform, but not simulating power and signal together. Walter added that his company's tool uses intelligent node names in the subcircuit definition. Arpad suggested separating the subcircuit naming and referencing topics. He asked for clarification as to the intent for the SPIM approach - was this for efficiency, just to avoid repeating name lists? One thought from Arpad was to generate a two-column mapping table, consisting of position and name. The table would apply everywhere, so no duplication would be needed. Walter replied that this table is just what the IBIS Interconnect model already does; if you constrain the connectivity, and allow Touchstone, then everything allows ideal node zero. Walter added that there was no way to check the SPICE netlists for consistency; everyone across the industry uses ideal node 0 for Touchstone referencing. Arpad added that using SPICE with non-short VSS paths is problematic. Walter replied that one should use a universal node for return currents. Michael suggested making a distinction between how Touchstone is generated and how Touchstone is used (elsewhere, this has been discussed as the "wrapper problem"). Randy noted that one circuit being shown uses 2N referencing, and 2N is extremely difficult to get to work. Arpad added that some of his examples use N+1 referencing. He added that the problem with this is that N+1 referencing forces connections only to other N+1-referenced circuits. The 2N approach doesn't cause this problem. He identified himself as a fan of the 2N or per-interface referencing approach. Michael asked whether the Touchstone 3.0 draft is fine as-is. If so, does this mean that EMD and IBIS Interconnect need to be revised? Arpad suggested that some example circuits shown use common nodes which should share the same physical location. Michael asked about different sources, suggesting a problem may emerge if the sources use different x/y/z reference locations. Walter replied that the EDA vendor can check this. Michael asked where the specification changes should go from here. Arpad suggested that one can have 3-terminal SPICE circuits connected easily with Touchstone files. The team agreed that the parser cannot police connectivity at the EMD or IBIS Interconnect level. Michael suggested that the team could just put in language in the specifications to advise against some connection combinations. Walter replied that, for SPIM, given the package model, you are driven to create the board model in a certain way. Using N+1 versus 2N referencing does not change how you generate the S-parameter. Arpad agreed, but noted that how one uses it will be different. Walter replied that the N-port referencing approach is the same as N+A_gnd. The team agreed to cancel next week's meeting. Michael accepted the AR to send out proposed IBIS and IBIS-ISS language regarding connections, as well as the Touchstone 3.0 latest draft. [AR] Arpad moved to adjourn; Randy seconded. The meeting adjourned. The next meeting will be held April 9, 2025. ================================================================================ Bin List: 1) Complete port naming proposal (Katz et al) 2) Complete/revise Touchstone 3.0 draft outline (Mirmak) 3) Complete ISS-IRD 1 Draft - enable cascading of S-parameters through W-element (Mirmak) - TABLED 4) ISS-IRD ISO/IEC Tabled ARs: - Arpad to give an example of the physical connectivity needed for EMD automation.