But I always thought SPICE models are perfect, aren't they? So if I can match the SPICE model with my IBIS model, I should be able to go home happily, shouldn't I? When I worked for the world's largest semiconductor company, I often started by making an IBIS model from SPICE models, and when it turned out that they were garbage, because the SPICE models were garbage, we started to tweak the I-V and V-t curves by all kinds of methods. So we often had IBIS models which were more accurate to measured behavior than the SPICE models the designer used. Go figure... I know this may raise a burst of flame and mud slinging (as it has in the past), but I think there are times when behavioral modeling can have advantages over full transistor modeling. This example is just one of those cases... Arpad =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] = On Behalf Of Alfred P. Neves Sent: Monday, March 31, 2008 3:47 PM To: 'Tom Dagostino'; 'Schumacher, Richard (HSTD Signal Integrity)'; = si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Do you ever measure any of the things you model? Adding to what Tom already said... My personal experience working at numerous semiconductor companies marketing high speed products (both =3D digital and analog oriented, including PHY's, SERDES, etc.,) is that they =3D typically select a design engineer that generates the IV and VT curves, along with dynamic characteristics with only simulations, no measurements. =3D20 Unfortunately, since design engineering time is expensive and the good = =3D ones are VERY busy designing new products, to my experience (not a rule, and = =3D not meant to insult any engineers who pride themselves in this effort) it = =3D was not always the most experienced or talented engineer that was designated = =3D for this activity. =3D20 This all of course assumes the design represents the process variations, = =3D the package model was included in the full simulation suite and the =3D simulation was set up and performed correctly. Anyhow, I recall a significant number of customers complaining that the models either would not work at all (a test parser was not run) or they poorly matched measurements. =3D20 Maybe it is the geek in me, but it sends tingles up my spine when my simulations match almost perfectly to measure-based results. Alfred P. Neves=3DA0=3DA0=3DA0=3DA0=3DA0 <*)))))><{=3D20 Hillsboro Office:=3D20 735 SE 16th Ave.=3D20 Hillsboro, OR, 97123=3D20 (503)=3DA0718 7172=3DA0 Business=3D20 (503)=3DA0679 2429=3DA0=3DA0 Mobile=3DA0 =3DA0=3D20 Main Corporate office:=3D20 Teraspeed Consulting Group LLC=3D20 121 North River Drive=3D20 Narragansett, RI 02882=3D20 (401) 284-1827 Business=3D20 (401) 284-1840 Fax=3D20 http://www.teraspeed.com=3D20 =3DA0=3D20 Teraspeed is the registered service mark=3D20 of Teraspeed Consulting Group LLC=3D20 -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] = =3D On Behalf Of Tom Dagostino Sent: Monday, March 31, 2008 2:54 PM To: 'Schumacher, Richard (HSTD Signal Integrity)'; si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Do you ever measure any of the things you model? Richard We measured one Quellan device for the model and used a different device = =3D for the system test. When we measure a device we vary it's temperature and supply voltage over the datasheet's operating limits. We usually do not = =3D get process corner sample but if we did we would have used the strong fast corner at the cold high voltage operating point and the slow weak corner = =3D at the hot low voltage point for a CMOS device. This would have given a complete process/temperature/voltage model. =3D20 But what we have seen from much experience is the IV and VT curves of = =3D the random devices we get are very consistent from part to part of the same manufacturing process. When I say part to part we are including both the different die of the same part number and different part numbers from = =3D the same process. We see stronger effects from temperature and voltage than = =3D we see from process variation. Regards Tom Dagostino Teraspeed(R) Labs 13610 SW Harness Lane Beaverton, OR 97008 503-430-1065 503-430-1285 FAX tom@xxxxxxxxxxxxx www.teraspeed.com Teraspeed Consulting Group LLC 121 North River Drive Narragansett, RI 02882 401-284-1827=3D20 -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] = =3D On Behalf Of Schumacher, Richard (HSTD Signal Integrity) Sent: Monday, March 31, 2008 2:19 PM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Do you ever measure any of the things you model? Drifting the topic a little: "[...] developed a measure-based IBIS model of the Quallan equalizer [...] We were able to achieve excellent correspondence between system =3D simulation =3D3D and measurements (a few psec correspondence for a 10Meter length signal = =3D pat=3D3D h, see page 36) made with our DSO. The correspondence was very much =3D =3D3D3D du=3D3D e to the quality of the model in that it was generated with very =3D carefully =3D3D acquired measure-base data using a high signal integrity fixture, fast = =3D TDR =3D3D head, etc. I checked the IBIS model separately and it looked exactly like measured = =3D dat=3D3D a in terms of not just rise/fall time in an eye diagram but also the =3D pedest=3D3D al and features of the eye were captured extremely well. I have found = =3D IBIS=3D3D model accuracy to be critical, and unfortunately most of the vendor =3D based =3D3D models are a bit disappointing in their representation. Check it out: http://www.home.agilent.com/upload/cmc_upload/All/SI3_Teraspeed_Equalizat= =3D io=3D3D n06.pdf " To be precise, this uses an IBIS model of a specific instance of the =3D Qualla=3D3D n RX, true? In other words parameters such as silicon characteristics, = =3D ope=3D3D rating temperature, supply voltages, channel impedances etc. were =3D identical=3D3D in both the system and in the measurement-based model of that system. = =3D How=3D3D good is the agreement when that same IBIS model is used to simulate =3D anothe=3D3D r instance of the same device type, or when that same device instance is = =3D op=3D3D erated at different but within-spec values for temperature or voltage? Could an IBIS model of the TX be used? ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: =3D20 //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu =3D20 ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: =3D20 //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu =3D20 ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: =20 //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu =20 ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu