I believe the 2 requirements that must be met are: 1) For passivity - the total energy in the S-parameter model's impulse response must be less than 1: Int.{h(t) * CC[h(t)]} <=3D 1 where "Int." means integral over infinite limits, and "CC" means complex conjugate. For a discrete S-parameter model, the integration becomes a sum, and using Parseval's theorem: Sum.{H(n) * CC[H(n)]} <=3D 1 where "Sum." means the summation over all discrete entries in the model, and "H(n)" is the nth, possibly complex, entry. 2) For causality - the group delay through the S-parameter model must be greater than zero: -d{Arg.[H(w)]}/dw > 0 where "Arg." means "the phase of", and "H(w)" is the transfer function of the model as a function of angular frequency, "w". Again converting to discrete algebra: -{[Arg.(H(n+1)) - Arg.(H(n))]/W} > 0 Where "W" is the angular frequency step between adjacent entries in the model. -db > -----Original Message----- > From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] > On Behalf Of Gregory R Edlund > Sent: Friday, December 07, 2007 6:12 AM > To: ria_rr_84@xxxxxxxxx; si-list@xxxxxxxxxxxxx > Subject: [SI-LIST] Fw: si-list Digest V7 #410 >=20 > Ria, > I'll take a stab it this. >=20 > Passivity - a passive network that has no external power cannot add energy > to a signal. If you look at amplitude vs. frequency for a passive network > (e.g. s21 parameter), it should never go above one. I believe the math is > more complicated than that, but this is the general idea. Anybody care to > elaborate? >=20 > Causality - a signal cannot traverse any transmission medium faster than > the speed of light in that medium. This term comes from relativity where > event A cannot cause event B unless it happens before event B. >=20 > Besides nonphysical simulation results, models that have these problems > can also give simulators numerical trouble. >=20 > Has anyone on the list seen a set of publicly available canned routines > for evaluating causality and passivity of s-parameters? >=20 > Greg >=20 > Greg Edlund > Senior Engineer > Signal Integrity > IBM Global Engineering Solutions > 3605 Hwy. 52 N, Dept. HDC > Rochester, MN 55901 > gedlund@xxxxxxxxxx >=20 > ----- Forwarded by Gregory R Edlund/Rochester/IBM on 12/07/2007 08:00 AM > ----- >=20 > FreeLists Mailing List Manager <ecartis@xxxxxxxxxxxxx> > 12/07/2007 01:19 AM > Please respond to > si-list@xxxxxxxxxxxxx >=20 >=20 > To > si-list digest users <ecartis@xxxxxxxxxxxxx> > cc >=20 > Subject > si-list Digest V7 #410 >=20 >=20 >=20 >=20 >=20 >=20 > si-list Digest Fri, 07 Dec 2007 Volume: 07 Issue: > 410 >=20 > In This Issue: > #1: From: Ria R <ria_rr_84@xxxxxxxxx> > Subject: [SI-LIST] Passivity/Causality >=20 > ---------------------------------------------------------------------- >=20 > Msg: #1 in digest > Date: Thu, 6 Dec 2007 21:58:24 -0800 (PST) > From: Ria R <ria_rr_84@xxxxxxxxx> > Subject: [SI-LIST] Passivity/Causality >=20 > Gurus, > I have heard these 2 terms alot in the world of SI: Passivity and > Causality. > I tried googling it and I dont seem to get what I am lookimg for. > Can someone please throw some light on the definitions of these 2 terms > and what significance they have in Signal Integrity? > Thanks in advance, > Best Regards, >=20 > Ria. >=20 >=20 >=20 > ________________________________________________________________________ __ > __________ > Looking for last minute shopping deals? > Find them fast with Yahoo! Search. > = http://tools.search.yahoo.com/newsearch/category.php?category=3Dshopping >=20 >=20 > ------------------------------ >=20 > End of si-list Digest V7 #410 > ***************************** >=20 >=20 >=20 > ------------------------------------------------------------------ > To unsubscribe from si-list: > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field >=20 > or to administer your membership from a web page, go to: > //www.freelists.org/webpage/si-list >=20 > For help: > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field >=20 >=20 > List technical documents are available at: > http://www.si-list.net >=20 > 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 >=20 >=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 technical documents are available at: http://www.si-list.net 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