There are still a lot non busses that people need to simulate, not all of them will be terminated. In addition some people simulate open connectors which may have non terminated lines by definition. So, yes there are places where it does not make sense to do the -Vcc to 2*Vcc range but there are cases still where it makes sense. Tom Dagostino Teraspeed(R) Labs 13610 SW Harness Lane Beaverton, OR 97008 503-430-1065 tom@xxxxxxxxxxxxx www.teraspeed.com Teraspeed Consulting Group LLC 121 North River Drive Narragansett, RI 02882 401-284-1827 -----Original Message----- From: ibis-quality-bounce@xxxxxxxxxxxxx [mailto:ibis-quality-bounce@xxxxxxxxxxxxx]On Behalf Of Mirmak, Michael Sent: Tuesday, July 12, 2005 12:00 PM To: ibis-quality@xxxxxxxxxxxxx Subject: [ibis-quality] IV curve sweep range Forwarded from Arpad Muranyi... - MM -----Original Message----- From: Muranyi, Arpad Sent: Tuesday, July 12, 2005 11:20 AM To: ibis-quality-bounce@xxxxxxxxxxxxx Cc: Mirmak, Michael Subject: IV curve sweep range Hello everyone, I am not monitoring this email reflector, and I don't plan on subscribing, but Mike Mirmak forwarded me a message regarding the IV curve sweep range discussion, to which I would like to add a few comments. I don't know what exactly is being proposed, I am just going to mention my views here. The problem I see is that IBIS requires a sweep range of -Vcc to 2*Vcc. This comes from the days when most buffers switched rail to rail and most buses were unterminated. The reason for this range stems from the T-line reflection theory, that the signal can double at the end of the line. If we had a strong driver, which could drive close to the rail, then the doubling of this signal could span a range close to -Vcc or +2*Vcc assuming no clamping effects at the end of the line. The problem is that most modern buses and drivers are not operating like this any more. For one, the signal swing doesn't go rail-to-rail any more, and second, most buses are terminated. Even if we ignore the termination question, the reduced-swing signaling alone warrants a reconsideration of the IBIS rule. One of my favorite examples is GTL. The signal goes from a low level between 0-0.5V to a high level of 1.5V. If I took 0-1.5, even if I doubled the signal swing on the top and bottom, I would get a range of -1.5V to 3.0V. Aside from the fact that the bus is terminated and we will never see a doubling at the end of the T-line, compare this range with what IBIS would require if this buffer was powered by 3.3V: it would be -3.6V to 6.6V, almost double! This clearly doesn't make sense. I would propose that we should write a BIRD on this, and change the IBIS specification so that it would not REQUIRE the range of -Vcc to 2*Vcc. I am not sure what it should say yet, but I would definitely NOT favor that the parser should be changed to check the ranges in the IBIS files against the IBIS rules. I would much prefer to have a rule that is based on signaling, though I have to admit that this may be somewhat more complicated to spell out. Please comment, Arpad =========================================================== --------------------------------------------------------------------- IBIS Quality website: http://www.eda.org/pub/ibis/quality_wip/ IBIS Quality archives: //www.freelists.org/archives/ibis-quality To unsubscribe send an email: To: ibis-quality-request@xxxxxxxxxxxxx Subject: unsubscribe --------------------------------------------------------------------- IBIS Quality website: http://www.eda.org/pub/ibis/quality_wip/ IBIS Quality archives: //www.freelists.org/archives/ibis-quality To unsubscribe send an email: To: ibis-quality-request@xxxxxxxxxxxxx Subject: unsubscribe