LO Feed-through improvement

Hi Jan,

I'm better understanding now the time domain and frequency domain plots. I would have expected both to be equal. Shouldn't   the marker in the frequency plot (-63 dBm) be equal to the time domain level (-47dBm). But, leaving that aside, yes, if you have the inputs ac-coupled, your dominant output power should come from LO Leakage. 

I think that you should be able to get more out of the I and Q offset adjustment. The datasheet says that it can be reduced from -43 dBm to -64 dBm. There is a section in the datasheet that discusses the approach to tweaking the I and Q offset. I'm also attaching a link to an old ap-note on the topic. In this we suggest sweeping the I offset until you find an initial minimum. Then with I value held, you sweep Q and look for a deeper trough. Finally, you can do a third sweep of I to fine tune things. It can be done in any order, that is, I first or Q first. But when the temperature changes, much of this good work goes out the window (unless you are willing to re-cal over temperature). 

The noise floor does look a bit messy in the frequency domain plot. But it's well below the fundamental tone (the LO Leakage) at -63 dBm. It may be from your signal generator or it may be pick-up. 

Hi Jan,

I'm better understanding now the time domain and frequency domain plots. I would have expected both to be equal. Shouldn't   the marker in the frequency plot (-63 dBm) be equal to the time domain level (-47dBm). But, leaving that aside, yes, if you have the inputs ac-coupled, your dominant output power should come from LO Leakage. 

I think that you should be able to get more out of the I and Q offset adjustment. The datasheet says that it can be reduced from -43 dBm to -64 dBm. There is a section in the datasheet that discusses the approach to tweaking the I and Q offset. I'm also attaching a link to an old ap-note on the topic. In this we suggest sweeping the I offset until you find an initial minimum. Then with I value held, you sweep Q and look for a deeper trough. Finally, you can do a third sweep of I to fine tune things. It can be done in any order, that is, I first or Q first. But when the temperature changes, much of this good work goes out the window (unless you are willing to re-cal over temperature). 

The noise floor does look a bit messy in the frequency domain plot. But it's well below the fundamental tone (the LO Leakage) at -63 dBm. It may be from your signal generator or it may be pick-up.