ADRF5547 LNA : Measuring spur at LNA output on 4.4GHz frequency

Question

Hi 
 We used ADRF5547 on our design. ADRF5547 integrated dual channel LNA. When we only turn on single LNA, the behavior is normally. But when we turn on dual channel LNA, we would measure a spur at LNA output on 4.4GHz frequency without any signal input LNA. And this spur power ~ -67dBm. Is ADRF5547 have this spur when turn on dual channel LNA? If yes, how to resolved it? 
 Thanks 
 
 BR 
 
 Leo Kuo

salemdar · Accepted Answer

Hi Leo, 
 There shouldn't be a spur at the output of ADRF5547 and this is not expected. 
 LNAs inside ADRF5547's two channel are identical. Thus, if you don't observe spurs when LNAs are individually turned on, but observe spur when both turns this suggests us to look couple of things: 
 1) Are you supplying the part from and ideal supply or a switching supply? If the total current consumption increases, switching supplies, regulators may start to generate unexpected components 
 
 2)Do you have enough vias on the exposed paddle or dense vias like shown in our example EVB? Not enough vias on the exposed paddle may introduce ground inductance and may lead to oscillation. Not enough via placement for RFs may cause leakages. We could review your layout if you like 
 
 3)What are the supply currents, can you measure? How does the spur changes with receive high gain, receive low gain, receive PD or TX modes?)

Partner Forums

Partner Libraries

Products Mentioned

ADRF5547 LNA : Measuring spur at LNA output on 4.4GHz frequency