Hello, I am trying to derive the equations for Mixed mode S-parameters for more than one diff pair. This is my setting: p1 <---> p2 p3 <---> p4 p5 <---> p6 p7 <---> p8 For a single diff pair (p1,2,3,4) the equations are readily available. Smixed = [M]*[S]*[Mt] M = 1/(sqrt(2)) * Matrix-bellow [1 0 -1 0] [0 1 0 -1] [1 0 1 0] [0 1 0 1] and Mt is the Transpose of M I have all the single ended S-parameters [8x8]matrix. Now what I need to know is: 1. If I give a differential mode stimulus to p5,7, how much differential and common mode coupling will I have on p1,3 and p2,4 ?. 2. If I give a common mode stimulus to p5,7, how much differential and common mode coupling will I have on p1,3 and p2,4 ?. 3. How can I extend the equations to more than two differential lines, for example five. (Note that I am not necessarily interested on the stimulus/response for the following ports p3,5 : p4,6 : p1,7 : p2,8 although this may come for free on the equations) Any papers, info will be appreciated. Thanks. -----Original Message----- From: Ingraham, Andrew [mailto:Andrew.Ingraham@xxxxxx] Sent: Thursday, February 13, 2003 10:29 AM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: IBIS I/O model in HSPICE question I believe this is not a model issue. As far as IBIS is concerned, how to stimulate a buffer is implementation dependent. IBIS doesn't really define HOW a simulator should make the driver do its stuff. HSPICE happens to implement IBIS models using a node voltage as a "binary" control signal to tell the buffer when to switch. Once it starts to switch, its behavior should be independent of that control signal. I think this would be true regardless of whether you are using an IBIS 1.x model or an IBIS 2.x model. Either way, HSPICE should tell the model to "go do thy stuff, switch to the other state according to your characteristics," and the control input should not affect it from that point on. The main exception to this, is if the control input is strongly non-monotonic or toggles back before the IBIS buffer model has completed switching. Behavior is unpredictable if you try to switch an IBIS model faster than it needs to get all the way from [Pullup] to [Pulldown] or vice-versa; and people have observed bizarre output waveforms when trying to do this (which are likely to be very simulator-dependent). The HSPICE 2000.2 manual does say you can optionally use (for example) a 0-3.3V signal as the "digital" input; but it will be interpreted like a 0-1V signal that happens to go past 1.0V up to 3.3V. That is, the IBIS model starts switching at 0.8V on rising edges and 0.2V on falling edges. (I think the reason the thresholds aren't both 0.500V, is for hysteresis in case of noise, mathematical or otherwise.) I can think of a few things that might cause the behavior you describe. How did you connect the 0-1V or 0-3.3V control voltage source? Is it between appropriate nodes ... do both nodes directly connect to the IBIS B-element? Be careful around package parasitics, which might introduce an undesired feedback loop. I think the B-element monitors the nd_in node (V_in) relative to global GND. Are you sure the input voltage waveform at the B-element node nd_in is what you think it is? Monitor it. Is it precisely trapezoidal, or is there any ringing, especially in the 0.2-0.8V range? Try faster or slower edges. The edge rate at nd_in should have zero effect on the output, except to shift the time when it starts switching (when the input waveform crosses 0.2V or 0.8V). Finally, we like to think that there's no interaction between nodes that are electrically unconnected. But SPICE is not perfect, and something happening in one part of the circuit can sometimes mathematically affect nodes elsewhere even if they aren't connected. Remember, they are all part of the same matrix operations within SPICE. It is remotely possible that the 0-3.3V waveform is doing this. Keeping the timestep lower, among other things, may help reduce this effect. Regards, Andy ------------------------------------------------------------------ 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