Unlike the gate of a transistor, the control input of an IBIS 2.x buffer is intended to be pure digital. I would be surprised if any simulator has ordinary elements reading the control voltage, as opposed to a software function checking the control voltage state to initiate IBIS actions. In fact, the moment the control voltage is not zero an IBIS 2.x buffer should initiate the rising waveform sequence and ignore the control voltage value until the rising waveform completes or the control voltage again reaches exactly 0V. The significance of 1V is to give a corresponding voltage to test against for initiating the falling wave sequence. I think simulators should sample the control voltage at the end of the rise sequence and use that voltage as the reference for detecting when to trigger a fall sequence, so that any voltage can be used as the control input for the high state. Now, if an IBIS 1.x model with no waveforms is used, it wouldn't surprise me to find simulators using the control input in analog mode, proportionally scaling the pullup and pulldown resistors. In this case the 1V level would be a given, and higher control voltages might cause any kind of unexpected math to work it's way through the model. When I want to make an IBIS buffer behave more like a silicon transistor model so that core level control voltages can be used, I wrap the IBIS buffer in a subckt that contains a voltage controlled voltage source to scale the core level control signal down to 1V to make the IBIS buffer happy. Mike -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Ed Sayre III Sent: Wednesday, February 12, 2003 6:16 PM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] IBIS I/O model in HSPICE question Hi All, I am running an IBIS I/O model in HSPICE and have see some very strange results dependant on the input voltage swing. I am using the Ibis I/O in the driver mode, driving a simple resistor load and another sim driving a match terminated 25 Ohm tline and resistor load. According to Page 18-43 of the 2000.2 manual either a 0-1V swing can be used for the input or a typical 0-3.3V input swing can be used. When I compare the outputs of the I/O the two input level I find they are significantly different in wave shape and peak overshoot. The 3.3V swing gives significant overshoot spikes on the output node of the I/O model. When I look at the output current (very clean and controlled, it would seem that ohms law is not observed, this doesn't make sense. Does anyone have an idea of why this is occurring, and is it typical of Ibis model outputs run in HSPICE to behave differently dependant on what voltage swing is applied to the input node of the driver??? BTW, I am in direct contact with the vendor so I am interested in seeing if people have seen this and if it is a model or an IBIS/HSPICE issue. Thanks in advance, -Ed ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ NORTH EAST SYSTEMS ASSOCIATES, INC ------------------------------------- "High Performance Engineering & Design" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Dr. Edward Sayre 3rd e-mail: esayre3@xxxxxxxx NESA, Inc. http://www.nesa.com/ 5 Lan Drive, Suite 200 Tel +1.978.392-8787 x 218 Westford, MA 01886 USA Fax +1.978.392-8686 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ------------------------------------------------------------------ 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