Feras, I think the idea behind BIRD145 is similar to what Michael Mirmak proposed several years ago, and what Randy Wolf discussed at the DesignCon IBIS Summit. Both Randy and Michael wanted the ability to add a ladder RC circuit at the output pad of the buffer. This is a real requirement that SiSoft has implemented using an IBIS keyword Final_Stage, FinalStageDiff: Final_Stage <typ|min|max> <ISS file name> <ISS subckt name> and Final_Stage_Diff <typ|min|max> <ISS file name> <ISS subckt name> These are either a 2 port subckt (Final_Stage) or a 4 port subckt (Final_Stage_Diff), that is inserted between the pad(s) of the B element and the pad end(s) of the package). Would this satisfy your IC Vendor modeling requirements? What other ports would need to be included in this subckt? Walter Walter Katz <mailto:wkatz@xxxxxxxxxx> wkatz@xxxxxxxxxx Phone 303.449-2308 Mobile 720.333-1107