We have interfaced the HMC869 output (single ended) to the AD605 with a 69.8E shunt resistor and 0.1uF series capacitor.
We are not getting the IF (20MHz) from the output of the HMC869 at the desired level, infact it is much lower (60dB lower).
Please advise if the interface between the HMC869 and the AD605 is ok?
Thank you for your time in advance,
We removed the shunt resistor and there is a signal. There is a different issue now however.
Following is an image of the RF chain: It has 2 HMC903 amplifiers in cascade followed by a HMC869.
The problem is as follows: There is no output on one of the IF outputs (I and Q if we name them) i.e., There is an output on I but only the I that is leaking onto the Q output (can be seen by the oscilloscope capture of the outputs).
I say it is the I that is leaking into Q because of the phase relationship.
However, if we touch the input trace of the mixer or touch any of the amplifiers, we get the following output which seems correct as the signals have an ~90degree phase shift between them.
Please advise. Thank you for your time in advance for looking into this,
1) Both the output pins (I and Q have been tested and show almost the same resistance with a multimeter). So contact or soldering issue might not be the problem.
2) Both the amplifiers are behaving normally (giving the proper gain and drawing normal current).
I read your notes, and I still believe you have a layout or solder issue. If you are touching the board and the problem goes a way maybe you have a GND problem.
Please try to probe the output when you touch the board and not and see if you see any difference.
another thing to try is the power supplies, check the voltage and current and see if you have any different between touching the board and not.
Hope it helps