Solution: Mixer output noise with ADL5802 Demo Board - varying Supply Current

Discussion created by Jan_V on Jan 1, 2016

We found a problem with our ADL5802 Demo Board,  showing high levels of output noise on Mixer output. This board was purchased direct from AD.  We also noticed fluctuating Bias Current from 130mA to 150mA with Vset=2V  and raised Case #: 2E15LU04568. 


Subsequently we found that flexing the board and pressing down the ADL5802 chip seems to indicate a hardware problem with the board with poor connection or soldering joint suspected. 

Solution:  As the demo board was no longer in warranty, we resoldered all components on the board.

We then found there was no connection between the VPOS board pin and chip pins that should see supply voltage.

As the supply lines run on inner layers which are not documented by AD, we soldered a wire from the board pin to one of the points where we knew the supply voltage should go. Now, the mixer current is back and rock stable at 160mA for Vset=2V. Also the mixer output level is now constant. No more flexing or pressure sensitivity.
We believe the issue was caused by an poor connection in one of the inner layer tracks on the ADL5802 Demo board.
This information is posted for the benefit of other users of this board.

a)  Mixer Output noise as found on first use at 100 MHz Mixer Output.  Note Y scale is 0.01 dB/Div is correct. 
Ref1  indication is with attenuation applied.

The RF source at 100MHz delivers a ‐13dBm sinewave signal to the mixer RF1 input port.

The LO source at 110.7MHz delivers a 2dBm rectangle signal to the mixer LO port.

Mixer output is at 10.7 MHz.
Screenshots taken with DG8SAQ Vector Network Analyzer.

Mixer output noise of new unused ADL5802 Demo board.jpg

b) Mixer output noise as found after repair of the ADL5802 Demo board.

Mixer output is clean  and Current consumption is rock steady at 160mA

Again note Y scale resolution 0.01 dB

ADL5802 mixer noise after hardware repair.jpg

This information is posted for the benefit of other users of this board.