[SI-LIST] Re: TEM approximation
- From: Steve Corey <steven.corey@xxxxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Sat, 20 Sep 2003 08:04:59 -0700
Chris -- I see we're talking different languages. I'm talking about
extracting parameters based on measurement, you're talking about
extracting parameters based on field solution. While measurement-based
extraction isn't always an option, in many cases it is. So, to make my
assumptions more explicit:
IF you are doing a measurement-based extraction (or an extraction based
on 3-D results, such as PEEC, if you prefer), then in a number of
applications (depending on edge rate and noise margins), using a TEM
element (such as SPICE lossless TLines or HSPICE lossy W-Element) to
model a trace propagating over munched-up package reference planes will
be sufficiently accurate. Comparison of extracted model response vs.
measurement will verify whether the accuracy is sufficient, or whether a
more involved model is necessary.
Our customers deal with these problems as well, so I agree it's a
real-life problem and not a contrived one. And no, I wouldn't quibble
about the results you have seen from field solver runs with various
tools, particularly since I have no intention of replicating your
effort... 8^)
-- 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:
> 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
>>>
>>>
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>>>
>>
>>
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>
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>
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