[SI-LIST] Re: TDR Resolution
- From: "Moeller, Merrick" <mmoeller@xxxxxxxxxxxxxxx>
- To: "Scott McMorrow" <scott@xxxxxxxxxxxxx>
- Date: Tue, 18 Jan 2005 09:17:51 -0600
Scott,
In this case lets assume that the retention feature is surrounded on
either side
by uniform impedance section. Although these sections have more length
than the
retention feature itself they are less than 1mm, and the retention
feature itself
is less than .3mm. Would it be feasible to run the simulation to a
bandwidth that
would allow for that kind of resolution? 150GHz? More? Also assume
meshing
is sufficient. Would Max frequency of the structure permit such a high
frequency limit?
Would frequency cutoff limit simulation?
Merrick
________________________________
From: Scott McMorrow [mailto:scott@xxxxxxxxxxxxx]
Sent: Monday, January 17, 2005 4:50 PM
To: Moeller, Merrick
Cc: si-list@xxxxxxxxxxxxx
Subject: Re: [SI-LIST] Re: TDR Resolution
Merrick
That's what I suspected. In that case, you need to reduce your problem
size to that of retention structure surrounded by uniform impedance
crosssections. Otherwise, you will obscure resolution of the retention
structure with other reflections. If you want to TDR the assembly
without any spurious high frequencies then you will need to create a
custom TDR waveform that is created from a low pass filtered trapizoidal
edge. You will also need to be sure that there sufficient mesh cells to
correctly discretize the structure you are simulating. Depending upon
the geometry, this might be as few as two cells in each direction, but
quite posibly it could be more. You can increase the mesh density
across the retention structure locally by selecting the component,
selecting its mesh properties and changing them. Finally, you will need
to adjust your simulation frequency for meshing and your minimum mesh
step size to guarantee that the simulation will be performed at a high
enough bandwidth to resolve your TDR rising edge.
If you don't want to reduce your problem size by slicing the model, then
you can create the necessary waveforms in CST and then pass them back
through software the performs the reverse scattering algorihm and
provides a true impedance profile. With a bit of data manipulation you
should be able to pass your data back through TDA iConnect.
In either case, your key to good results is to create a well filtered
TDR waveform at the appropriate edge rates, to control the mesh density
to gain the resolution you desire across your structure, and to set the
frequency and smallest mesh step size so that you have enought
simulation bandwidth.
scott
Moeller, Merrick wrote:
Scott,
3D solver. CST Microwave Studio...
TDR impedance profile at various rise times.
M
________________________________
From: Scott McMorrow [mailto:scott@xxxxxxxxxxxxx]
Sent: Monday, January 17, 2005 2:02 PM
To: Moeller, Merrick
Cc: si-list@xxxxxxxxxxxxx
Subject: Re: [SI-LIST] Re: TDR Resolution
Merrick,
It depends on the type of simulation you are performing. Is
this a spice simulation based on extracted cascaded model sections, or
is it a 3D time domain field solver/simulation environment?
Also, it depends on what you are trying to resolve: final
impedance of the retention feature, electrical length of the retention
feature, signal distortion due to retention feature at various
risetimes?
scott
Moeller, Merrick wrote:
Thanks for all the help everyone. I found
Kipp's solution suitable for my needs..
To continue the discussion:
This scenario is taking place in a simulation. It is
Possible to create increased frequency bandwidth
simulations
That may handle faster rise times... What are some=20
Of the limiting factors when considering a MAXIMUM
FREQUENCY
BANDWIDTH for a simulation? For example, I wanted to=20
Resolve some retention feature in a coaxial type
structure.
Is there a Max frequency.... Strictly speaking of TDR
and
Square wave reproduction. I realize that the structure
will
Have cutoff frequencies for particular modes.
M
-----Original Message-----
From: Ed Sayre III [mailto:esayre3@xxxxxxxx]=20
Sent: Monday, January 17, 2005 12:17 PM
To: Moeller, Merrick
Cc: si-list@xxxxxxxxxxxxx
Subject: Re: [SI-LIST] TDR Resolution
Merrick,
As you can see from the responses the "Rule-of-Thumb
depends on your
signaling needs. The risetime of the TDR really depends
on the the data
rate of the signals. R. K Poon's book has an excellent
section on
sampling and risetime effects. I believe it is in an
appendix in
chapter 5.
Also a word to the warning, don't use a ramp
function, it tends to
give you unrealistic results and lots of ringing and
convergence
problems.
Regards
-Ed
At 10:21 AM 1/17/2005 -0600, Moeller, Merrick wrote:
Experts,
I am in the process of running a
simulation In order to=20
resolve signal path discontinuities. Is there a
Rule of thumb that=20
would give the minimum rise time signal To
resolve a min length=20
discontinuity?
Regards,
Merrick
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Scott McMorrow
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
(401) 284-1827 Business
(401) 284-1840 Fax
http://www.teraspeed.com
Teraspeed is the registered service mark of
Teraspeed Consulting Group LLC
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