Noop, BTDT. Any TEM approximation will be way off. Especially when you calculate crosstalk, impedance and prop delay (if the mesh is uniformly defined). I am talking about 50%-200% error. If you don't believe me, try it yourself. BTW, this is a well known problem. IBM engineers realise this way back when they design the TCM modules for their mainframe. Albert Ruehli's PEEC method works great on these problems. -----Original Message----- From: Steve Corey [mailto:steven.corey@xxxxxxxxxxxxxx] Sent: Thursday, September 18, 2003 11:32 PM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: TEM approximation This is a good example of one of the basic assumptions underlying TEM transmission line theory -- that the lines have to be uniform in the direction of propagation. In other words, a 2D problem. A more interesting question from my perspective as a tool developer is what is the "right answer" to which you refer. From an analytical perspective, no tool will give the exact answer due to imprecision and inherent model inaccuracies. From an engineering perspective, there are many "right answers", since any answer that falls within an acceptable error range of the exact answer is a right answer. So I can see where in some applications a TEM approximation for the example below will be fine and give a right answer, whereas in others it will not. It depends how much accuracy you need to get a reliable design. Since our tools have both TEM and non-TEM capabilities, we recommend that our customers use measurement validation to determine which approach is necessary to get them the accuracy they need. -- Steve ------------------------------------------- Steven D. Corey, Ph.D. Time Domain Analysis Systems, Inc. "The Interconnect Analysis Company." http://www.tdasystems.com email: steven.corey@xxxxxxxxxxxxxx phone: (503) 246-2272 fax: (503) 246-2282 ------------------------------------------- Chris Cheng wrote: > I can easily give you an example where TEM assumption will break down even > with relatively slow edge rate. > > Take a simple uniform stripline. Start meshing the reference planes directly > below and above the trace. The size of the hole is dimensionally large > compared with the trace itself but electrically small compared with the edge > rate so that quasi-static mode still holds. e.g. drill 50-100 mil holes > uniformly spaced along a 5 mil stripline trace. No TEM mode tools or > approximation will give you the right answer. The imagine current on the > reference plane is forced to run with orthogonal components to the signal > current, thus breaking the TEM mode. This is a very real life problem as it > exist in many signal traces in organic substrate packages. > > -----Original Message----- > From: Dima Smolyansky [mailto:Dima.Smolyansky@xxxxxxxxxxxxxx] > Sent: Wednesday, September 17, 2003 4:01 PM > To: swamydp@xxxxxxxxx; si-list@xxxxxxxxxxxxx > Subject: [SI-LIST] Re: TEM approximation > > > Hello, Swami, > > Interestingly, we at TDA Systems determined that the TEM assumptions can be > used to surprisingly high risetimes if the parameters are accurately > extracted and verified. Our lossy line examples verify this. > > I hope this helps. > > Thanks, > > -Dima > > ----- Original Message ----- > From: "Swamy Dhoss" <swamydp@xxxxxxxxx> > To: <si-list@xxxxxxxxxxxxx> > Sent: Sunday, September 07, 2003 4:28 PM > Subject: [SI-LIST] TEM approximation > > > >>Hi >> >>Could anyone tell me about the concept of TEM >>approximation for the propagation of an electrical >>signal through a transmission line ? >>Over what range of frequencies TEM approximation is >>valid ? and what model can be used above this >>frequency limit ? >> >>Regards >>swamy >> >> >>__________________________________ >>Do you Yahoo!? >>Yahoo! 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