| Author |
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John Larkin
Guest
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 Posted:
Fri Feb 11, 2005 6:11 am Post subject:
Re: Transmission line-like resonances at ~30MHz |
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On Thu, 10 Feb 2005 17:11:21 -0800, Chris Carlen
<crcarle@BOGUS.sandia.gov> wrote:
| Quote: | John Larkin wrote:
Just be careful about any simple formula. Most work over a small range
of geometries. The classic "Motorola ecl" equation cruises clear
through zero ohms and goes negative as the trace gets wider. I like
Appcad and Txline, which are smarter. Both are free.
John
Thanks for the links. I could use some software to do this, as
Johnson's formulas (actually from I. J. Bahl and Ramesh Garg, "Simple
and accurate formulas for microstrip with finite strip thickness", Proc.
IEEE, 65, 1977, pp. 1611-1612.) are not very simple, with various
conditionals, functions of functions, and so forth. Once in a
spreadsheet they are a cinch, but I don't want to have to type in the
several foot long formulas for every geometry.
Good day!
|
The ultimate free tx line analyzer is ATLC, which will calculate the
impedance of a cowbell-shaped line inside a star-shaped tube with
mixed dielectrics. It's just an immense pain to use.
John
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Chris Carlen
Guest
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| Posted:
Fri Feb 11, 2005 6:11 am Post subject:
Re: Transmission line-like resonances at ~30MHz |
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John Larkin wrote:
| Quote: | Just be careful about any simple formula. Most work over a small range
of geometries. The classic "Motorola ecl" equation cruises clear
through zero ohms and goes negative as the trace gets wider. I like
Appcad and Txline, which are smarter. Both are free.
John
|
Thanks for the links. I could use some software to do this, as
Johnson's formulas (actually from I. J. Bahl and Ramesh Garg, "Simple
and accurate formulas for microstrip with finite strip thickness", Proc.
IEEE, 65, 1977, pp. 1611-1612.) are not very simple, with various
conditionals, functions of functions, and so forth. Once in a
spreadsheet they are a cinch, but I don't want to have to type in the
several foot long formulas for every geometry.
Good day!
--
_______________________________________________________________________
Christopher R. Carlen
Principal Laser/Optical Technologist
Sandia National Laboratories CA USA
crcarle@sandia.gov -- NOTE: Remove "BOGUS" from email address to reply. |
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Roy McCammon
Guest
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| Posted:
Sat Feb 12, 2005 2:19 am Post subject:
Re: Transmission line-like resonances at ~30MHz |
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Joel Kolstad wrote:
| Quote: | Looking at a Smith Chart, it's clear to me now that small lumped
capacitances along a transmission line will just make the line look
electrically longer than it physically is. Hmmmph. I have a few ideas
about how to fix the problem; namely by terminating the line and then adding
amplifiers.
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after doing several of these, I hit on the following strategy.
Calculate the minimum and maximum impedences over all the
loading conditions. Usually that means no loads and maximum loads.
Then series terminate the drivers with the minimum impedance,
and parallel terminate the end with the maximum impedance. Its
not perfect, but one end or the other is usually close enough
to damp out resonances.
--
local optimization seldom leads to global optimization
my e-mail address is: <my first name> <my last name> AT mmm DOT com
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Mark
Guest
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| Posted:
Tue Feb 15, 2005 2:07 am Post subject:
Re: Transmission line-like resonances at ~30MHz |
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Goggle
salphasic clock
for some interesting reading.
Mark |
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John Larkin
Guest
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| Posted:
Tue Feb 15, 2005 2:50 am Post subject:
Re: Transmission line-like resonances at ~30MHz |
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On 14 Feb 2005 12:07:53 -0800, "Mark" <makolber@yahoo.com> wrote:
| Quote: | Goggle
salphasic clock
for some interesting reading.
Mark
|
"It is estimated that the switching currents will peak at 1000 A
unless tightly controlled clock skews are utilized to avoid
simultaneous switching."
http://www.engalco.co.uk/new_page_16.htm
That's beyond interesting. That's terrifying.
John |
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Jeroen Belleman
Guest
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| Posted:
Tue Feb 15, 2005 2:27 pm Post subject:
Re: Transmission line-like resonances at ~30MHz |
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Mark wrote:
| Quote: | Goggle
salphasic clock
for some interesting reading.
|
That's precisely the thing that made Matthew Orman think
he had FTL propagation...
Jeroen Belleman |
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John Larkin
Guest
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| Posted:
Tue Feb 15, 2005 10:23 pm Post subject:
Re: Transmission line-like resonances at ~30MHz |
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On Tue, 15 Feb 2005 09:27:38 +0100, Jeroen Belleman
<jeroen@nospam.please> wrote:
| Quote: | Mark wrote:
Goggle
salphasic clock
for some interesting reading.
That's precisely the thing that made Matthew Orman think
he had FTL propagation...
|
The DLL clock buffers in the newer Xilinx FPGAs can be programmed for
negative propagation delay! Now if I just build a long shift register,
and run the stock ticker data through...
John |
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Keith Williams
Guest
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| Posted:
Tue Feb 15, 2005 10:55 pm Post subject:
Re: Transmission line-like resonances at ~30MHz |
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In article <1c84119sj82te4nq00l0h9gmaeqfsspslv@4ax.com>,
jjSNIPlarkin@highTHISlandPLEASEtechnology.XXX says...
| Quote: | On Tue, 15 Feb 2005 09:27:38 +0100, Jeroen Belleman
jeroen@nospam.please> wrote:
Mark wrote:
Goggle
salphasic clock
for some interesting reading.
That's precisely the thing that made Matthew Orman think
he had FTL propagation...
The DLL clock buffers in the newer Xilinx FPGAs can be programmed for
negative propagation delay!
|
Sure. The clock carries no information so it can go FTL. ;-)
| Quote: | Now if I just build a long shift register,
and run the stock ticker data through...
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....been done. There was an interesting insider attack on the horse
racing pari-mutual industry too. They only got caught because they
were a little too greedy and (un)lucky (several long-shots came in).
--
Keith |
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