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Design >> RF Design >> Decoupling cap for RF PCB
https://designers-guide.org/forum/YaBB.pl?num=1406909267

Message started by mixed_signal on Aug 1^st, 2014, 9:07am

Title: Decoupling cap for RF PCB
Post by mixed_signal on Aug 1^st, 2014, 9:07am

Hi,

I have designed a receiver with 2.4GHz LO, 2.42GHz RF and 20MHz baseband. The baseband has a seperate VDD and I want to decouple the 20MHZ in VDD. What kind of capacitors shall I use to decouple 20MHz ? Shall I use electrolytic cap with srf=20MHz? Can anyone suggest a good decoupling strategy?

The baseband has both 20MHz and 2.4GHz component. I can use 20nF for 20MHz and 20F for 2.4 GHz but since they are widely spaced I am concerned about antiresonance issues.

Title: Re: Decoupling cap for RF PCB
Post by loose-electron on Aug 1^st, 2014, 5:37pm

you want a parallel combination of electrolytic for low frequency and ceramic for high frequency.

Research self resonance of capacitors a bit.

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&cad=rja&uact=8&ved=0CEcQFjAE&url=http%3A%2F%2Fwww.intersil.com%2Fdata%2Fan%2Fan1325.pdf&ei=PTLcU5-bHZGJogSahIBw&usg=AFQjCNFBVO69ozXzfzdsSegWzdzwZ91u9Q&sig2=xLvBwZcqgtYjHQ9Bn5hjfg&bvm=bv.72197243,d.cGU

Above is a good basics document

Title: Re: Decoupling cap for RF PCB
Post by Ken Kundert on Aug 3^rd, 2014, 5:24pm

Here is a description of how to design a bypassing network: http://www.designers-guide.org/Design/bypassing.pdf

-Ken

Title: Re: Decoupling cap for RF PCB
Post by loose-electron on Aug 4^th, 2014, 2:00pm

Understanding the subtle aspects of the different capacitor types, strengths and weaknesses, thermal varinace issues, dielectric issues, ESR, self resonance frequencies of a capacitor, etc, are all useful items to be familiar with.