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Post subject: BROAD BAND RF PCB DESIGN Posted: Thu Nov 20, 2008 8:41 am
Joined: Wed Aug 16, 2006 8:20 am
I am designing PCB which should work
from DC to 8 GHz. I am connecting 3 amplifiers in cascade. Each of these broadband (DC to 8 GHz) amplifiers are 50
Ohm matched internally. Only a DC blocking capacitor is needed at the input and output. Here are some questions
that are troubling me.
1. What should be the minimum distance between the components (i mean the amplifier
stages). I am using lambada/4 as the minimum distance corresponding to 8 GHz.
2. Should I use 2 capacitors
(for DC blocking) between any two amplifiers or a single Capacitor would be sufficient.
3. Will my design
require some off chip impedance matching.
I am using Rogers Board material with 20 mil height, Er of 3.5
and aCPWG traces.
Please share your valuable comments
Design Engineer- RF
Post subject: Posted: Thu Nov 20, 2008
Joined: Thu Sep 25, 2003 1:19 am
1. What should be the minimum distance between the components (i mean the amplifier stages). I
am using lambada/4 as the minimum distance corresponding to 8 GHz.
When I consider distance between
components I keep the distance as short as possible while keeping it big enought for my soldering iron. Assuming
the network is matched there should not really be a max or min. The longer the trace, the more resistive loss and
possibilities for radiation, transmitted and received.
2. Should I use 2 capacitors (for DC
blocking) between any two amplifiers or a single Capacitor would be sufficient.
As long as the Voltage
rating and SRF work for your design, you only need to use one cap.
3. Will my design require some
off chip impedance matching.
If the gain blocks are in fact 50ohms and you a the impedance of your line
is 50ohms up to 8GHz then you should not need any matching. I would leave place holders for some shunt elements
just in case.