Lpc2000

Guillermo Prandi wrote:

>--- In lpc2000@yahoogroups.com, "Guillermo Prandi" 
><yahoo.messenger@...> wrote:
>  
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>>Hi. Sorry for the offtopic, guys. If anybody can point me out some 
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>good 
>  
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>>forum/group to post this question, I'll be glad.
>>
>>I need to calculate trace witdh and cleareance to achive an impedance 
>>of nearly 50 ohm for an RF trace surrounded by a GND polygon. My 
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>board 
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>>is SINGLE layered, so I have no power or GND planes. There's plenty 
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>>
Since RF is RF and not digital or analog, you may want to ask around 
some of the lists which deal with RF.  For example, Ham Radio (Amateur 
Radio).  I have an old copy of the: G.R. Jessop,G6JP "VHF UHF Manual", 
ISBN #0-900612-92-4

Jessop goes into a lot of detail about microwave and one section of the 
book deals with microstripline transmission circuits.  Both using double 
clad PCB as well as transmission line charactoristics of various types 
of materials: slab lines (PCB traces), parallel wires, wire parallel to 
infinite plane, wire in rectangular trough, etc.

For slablines:

=============== begin formula ======================


Where B is the overall length of the two parallel slabs, and, A == 
inside distance between the slabs:

Zo ~= 377 * (A / B)

(IOW Zout is approximately equal to 377 times A / B).

And, given that A << B then "edge effects are neglected"


================== snip =====================


That example is for two slablines in freespace.  However, depending on 
the cross-sectional area of the slabs, I would suspect that the effect 
of the PCB surface would be negligable.

If you present the line with a known impedance, design the slab line for 
that impedance and terminate in the same impredance, then you do not 
have to worry about 1/4 wavelength effects.  Radically change any of the 
three impedances and the wavelength of the line becomes a factor.

My copy is rather dated, 1991, but it is an excellent reference.

Regards,

TomW

-- 
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net, http://cyberiansoftware.com
"Windows? No thanks, I have work to do..."
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