RF power supply filtering techniques

[utimgr]

Sometimes...you just accept a design...thats how its always been done, but I wonder...its a bit of black magik for a mostly digital guy.

3.3V board voltage being fed to a RF section (say..a 2.4GHz module). Do not take into account any filtering other than simple bypassing being done on the IC's of the RF section.

The prior engineer fed the board 3.3V thru a HUGE 330uH inductor with a 0.1uF cap on each side, and followed by a ferrite bead and .1uF, .01uF and 10pf cap. The reason for the bead is to suppress any noise from the RF section back onto the digital, but...whats the real reason for the 330uH choke? Is it really necessary?

 

[Skogsgurra]

If it is used to suppress 2.4 GHz, I would say no. The ferrite beads are probably all you need. Have had to add a small inductance to a PSU working close to an accelerator working around 3 GHz so that the sense circuitry wasn't disturbed by the high frequency. All I did then was to coil the leads around a lead pencil. Not more than six or seven turns.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...