Hi Todd, the test loads you describe below are very similar to ones that I = typically use. There is no single test load that is appropriate for all = buffers; in general I use a test load that is the simplest possible = representation of the actual load the buffer will drive in service. For = a terminated bus this would be a transmission line at the nominal trace = impedance with the nominal termination at the endpoint(s) and a typical = receiver load capacitance, or in the simplest case a resistor equal to = the line impedance, connected to the termination voltage (useful for = measuring the drive strength and output waveforms only, no reflection = effects). For an unterminated or series terminated bus, a test load = with perfect termination to 1/2 VDD is not relevant, since this is a = case that does not occur on the bus in service. It may correlate fine, = but even if it doesn't, that isn't necessarily a mark against the model. = For these busses the best test load is the 2nd one you describe with no = termination on the line and a capacitance at the receiver. Jeremy -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Todd Westerhoff Sent: Tuesday, March 26, 2002 2:55 PM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: IBIS Model Quality (or lack thereof) Thanks everyone, for your contributions to this thread so far. By way = of summary, we've heard from the following semiconductor companies: - Intel - Fairchild - Serverworks (if I left anyone out, my apologies) ... and I'll vouch for both Intel and Micron myself, both in terms of = model quality and support. It is my strong suspicion that precious few IBIS models are validated in = any meaningful way before they are shipped to the customer. A few of your = have expressed hopes for the IBIS model quality committee that has just = gotten started, I share your hopes and enthusiasm for the effort. A number of you have outlined some of the testing processes you use, and = I'd like to suggest that we explore that subject a bit more. We've spent a = LOT of time here lately correlating IBIS models to their HSpice = counterparts. We're currently using two "standard" text fixtures to compare = IBIS/HSpice models: * I/O buffer connected to VDDQ/2 through 50 ohms * I/O buffer connected to 0.5ns, 50ohm tline, 5pf to GND at tline end The theory is that the first test fixture compares rising/falling edge characteristics and buffer strength, while the second test models the driver's response to a reflected wave (primarily the value of C_Comp). = If you get the HSpice/IBIS buffers to agree across these two tests, chances = are the rest of the puzzle falls into place, provided you agree on things = like pin parasitics and switching thresholds. So, I'm curious - for those of you who test IBIS models against any kind = of reference (HSpice or measurement) - what kinds of test loads are you = using, and what are you looking for? As always, all input (on and off the list) is greatly appreciated. Todd. Todd Westerhoff Signal Integrity Engineer Hammerhead Networks 5 Federal Street - Billerica, MA - 01821 email:twester@xxxxxxxxxxx - ph: 978-671-5084 =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 "I=92m starting With the man in the mirror I=92m asking him to change his ways And no message could have been any clearer If you wanna make the world a better place Take a look at yourself, and then make a change" - "Man in the Mirror", Michael Jackson ------------------------------------------------------------------ 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 archives are viewable at: =20 //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages=20 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 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