AD9361 - DC Leakag(LO) Present at TX

Dear Fellow Engineers

   i am new to the engineering community and currently working with AD9361. Through out my research so far, i have seen the Presence of DC Offset (DC Leakage from Mixer inside ad9361) on the TX side as shown below in attachment. This is the something that i would like to remove or minimize even more so that it is negligible.  Any helpful feed back or suggestions will be greatly appreciated.  Thanks

DC is at MR (Unwanted)  and M1 is just a single tone.

  • Are you using Evaluation board and Evaluation GUI (IIO oscilloscope) ?

    What is the output power of the tone.?

    With 0 dB attenuation and max digital power , you should get around +6 dBm at 2.4GHz. DC leakege is relative and at max output power it will be ~ -50 dBc.

    Test with 0 dB attenuation.

  • Yes dear, i am using ZedBoard with AD9361(FMCOMMS3-EBZ) for testing Purpose. i am also using Signal view to observe the spectrum on the TX1. Through ssh, i am able to access OSC and put on a single tone as shown below. Now when you say relative, does that mean it has some sort of relation to the power of signal? Also do you think that there is any other way(For example using Notch filter or Modifying Registers via SPI bust) to minimize DC even further if so, how?

  • -23dBc DC spur is very high.  if you can spool your I and Q out of the final xN interpolator filter before the DACs, compute the mean or histogram it, and see how far from DC is the center value of the histogram.  You must have large I/Q imbalance!, perhaps miscalling of the interpolator filters, or initialization errors in the I/Q compensator. 

  • DC offset is specified for max output power. The dBc level will not be linearly decreasing when you decrease the Tx power.

    Can you try measuring same again with 0 dB attenuation and Tone power at -3 dBFS.  In this measurement if you are not getting LO leakage  better than -50 dBc , you need to check on the calibrations.

    If your requirement is to operate at a lower power and the LO leakage is higher than requirement , recommend to use an external attenuator for this application.