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Below are all of the forum threads, including all
the responses to the original posts.
Post subject: input impedance of RF trace on PCB Posted: Fri May 11, 2007 3:22 pm
Joined: Tue Apr 24, 2007 1:10 pm
From PA2460 datasheet, we got
FR4,1.2mm; trace line: MLIN: W=12mil; L=616mil.
What can we expect to know?
what is the input
impedance Zin of this line?
thickness between trace and ground?
1.2mm = what? 4-layer board thickness? or
dlelectric constant = 4.3?
I mean, we should either know Zin or exactly dimension / dielectric constant
to calculate Zin. but we don't know any thing.
May someone help us?
Thank you very much.
Post subject: Posted: Sat May 12, 2007 7:53 am
Joined: Mon Jun 27, 2005
You can get the following from this information:
The data sheet of this PA IC shows that the board is a 2-layers board therefore the 1.2mm is the width of the
substrate itself. (From the metal to the GND layer).
The lines that you mention are micrstrip transmission
lines. You can easily calculate the impedance of the line under the following link:
At frequency of 500MHz the impedance of this line (With the parameters you provided) is almost 125 ohm.
There is a freeware transmission line calculator available from Microwave Office call TXLine which you can
download and use for calculating the impedance of the line based on physical parameters.
Hope this helps.
Post subject: Posted: Wed May 16, 2007 4:36 pm
Joined: Wed May 16, 2007 4:16 pm
One thing to keep in mind is that the impedence of a
microstrip trace is usually not an issue if the length is relative small in terms of wavelengths. I use an
emperically derived rule of thumb where I don't really care about the strip impedence until the length is >1/16th
What you really want to be careful with when designing source and load traces is to make sure
that you are minimizing parasitic capacitance to ground. Having ground plane or grounded vias too close to the
trace can cause shorts at RF.