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

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? 

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? 

Attached layout for you reference. Please help to check. We will measure current consumption with receive high gain, receive low gain, receive PD or TX modes and update for you later.

Thanks

BR

Leo Kuo

Hi Leo,

Do you have the 10uF capacitors for LNA supplies? Also 100pF caps are recommended to filter noise/interference at PD,BP,SWCTRL pins.

Also, do you have ar harmonic/subharmonic of 4.4GHz signal which may be leaking to the part through the pcb or do you see 4.4GHz when ONLY ADRF5515 is turned-on. Also, do you have 50ohms loads at input and outputs?

Hi Leo,

Do you have a metal enclosure/lid so that you might have an environment prone to crosstalks and leakages?