Bob, Thanks for your reply. I am glad you understand my situation. However I did not quite understand the last part of your email. Are you suggesting that one should interpolate the curve and approximate it as a linear ramp beyond the inital diode "Knee" ? If yes, are there any established methods for doing so? Thanks again! Abhijit. Robert Haller wrote: > > Abhijit, > The IBIS spec requires you to model a curve from -Vcc to +2Vcc. > This is well beyond the rail voltages (and can often Melt silicon :-) . > Many people do not correctly model clamp curves. One of the reasons > is often CMOS I/O cells contain a lateral PNP structure that has > spreading resistance. This manifests itself by modifying the actual > behavior of the ESD clamp structures. I spent a significant amount of > time working with a semiconductor vendor to get this right. Even if they > extract their ESD clamp diode structures accurately, they may miss the > vertical PNP's. > Practically The important parts of the clamp model is the turn on > behavior and resulting Slope. Theoretically you need to get enough > points on the "turn on" and to establish a slope. If you don't want the > a tool to interpolate do the sweep from -VCC to +2 Vcc. > Regards, > Bob > -- > Robert J. Haller (rhaller@xxxxxxxxxx) > Principal Consultant > Signal Integrity Software Inc. > 6 Clock Tower Place, Suite 250 > Maynard, MA 01754 > Phone: (978) 461-0449, ext 15 > > Volk, Andrew M wrote: > > It is important if your signal goes any significant amount beyond the rail. > > Series terminated buses like PCI depend on the clamping diodes for signal > > integrity, to stop excessive reflections that can also impact timing. Some > > interfaces depend on them to limit the voltage swing at the receiver to safe > > limits on newer processes. If you need to check for these kind of effects, > > the clamps are essential. > > > > Andrew Volk > > Intel Corp. > > > > -----Original Message----- > > From: Abhijit Mahajan [mailto:amahajan@xxxxxxxxxxxx] > > Sent: Thursday, October 17, 2002 11:15 AM > > To: si-list@xxxxxxxxxxxxx > > Subject: [SI-LIST] Beyond Rail Operation in IBIS > > > > > > > > It is often difficult to get accurate curves for beyond rail > > operation of IO Buffers. The problem is mainly in diode models that > > are not accurate and results in 100s of Amps of current. > > > > I am sure this question has been asked before, > > > > "How important is it to have accurate beyond rail curves? Does the IBIS > > spec. allow models to not have IV curves beyond rail voltages?" > > > > Thanks for your help. > > > > Abhijit. > > > > > > ------------------------------------------------------------------ > 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 > ------------------------------------------------------------------ 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