Impedence matching

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khanna_gunjan

Joined Jan 29, 2006
8
i am designing a board for RF transicever and in one of the component specification ity says.. "line width should be designed to provide 50 Ω impedence matching characterstic".. and i am confused on hoe to do it.. kindly suggest
 

Papabravo

Joined Feb 24, 2006
12,767
Originally posted by khanna_gunjan@Mar 20 2006, 08:16 AM
i am designing a board for RF transicever and in one of the component specification ity says.. "line width should be designed to provide 50 Ω impedence matching characterstic".. and i am confused on hoe to do it.. kindly suggest
[post=15203]Quoted post[/post]​
You did not say what frequency range this transceiver is for. As a function of increasing frequency, a PC board trace starts to look like a trnasmission line. Each transmission line has a characteristic impeadance which is a function of its geometry, the frequency of operation, and other factors.

As you know impeadance is a complex quantity with both a real and an imaginary part. There are many values of real and imaginary parts that have a MAGNITUDE of 50 ohms.

The reason we do impeadance matching is to maximize the power transfered from one stage to another.

Check the Agilent website for a freeware program called AppCAD
AppCAD Webpage

It contains a program for computing characteristic impeadance from trace geometry and other factors such as frequency and the dielectric constant of the PC board material. A word of caution. In RF design it is extremely important to verify each and every theoretical result. Do not be surprised if the calculations that you make have unexpectedl errors.
 
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