Decoupling a baseband VDD

[analog_chip]

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?

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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.

 

[malli_1729]

Decoupling 20Mhz is easier option. Select capacitor with 20Mhz Resonant frequency. Decoupling 2.4Ghz is difficult.....2.4Ghz decoupling requires capacitance in pF range may be 2-10pf range. check with RF capacitor manufacturers. decoupling 2.4Ghz requires very good layout..so, that mounting inductance is very low.....Try to simulate the system.....

 

[analog_chip]

Hi malli_1729,

What about the anti-resonance peak created between 20MHz and 2.4GHz? How to deal with it?

 

[malli_1729]

have you measured this peak....These 2 frequencies are well separated.......first select the corresponding capacitors for both frequencies....then approximate inductance's(mounting+actual) of both capacitors.....finding out resonant frequencies of CAP20Mhz and INDofCAP2.4Ghz and CAP2.4Ghz and INDofCAP20Mhz....I am not sure about the recommended techniques.......