FAQ:  How should I terminate the RFoutA and RFoutB pins on the ADF4350?

Document created by JKent on Jul 30, 2009Last modified by AndyR on Jan 31, 2012
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Q.

How should I terminate the RFoutA and RFoutB pins on the ADF4350?

 

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A.

Well...  50 Ohm resistors directly to GND on the unused RFoutB pins are definitely not recommended!

 

These unused RFout pins can be left floating, or AC coupled to GND with a 50 Ohm resistor, or connected with an RF choke to VDD and then AC coupled to GND with a 50 Ohm resistor.

 

ADI has not seen any appreciable difference in performance between either setup.

 

Regarding the used RF outputs RFoutA+/-:  If a wide range of frequencies is covered, then 50 Ohm resistors to Vdd is preferable to the 390 nH/3.9 nH arrangement. The inductor network is good for a narrow range of frequencies, but parasitics/SRF etc can sometimes cause problems.

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