Different offset between IQ signals

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kkao
Posts: 6
Joined: Wed Jun 25, 2014 11:42 pm

Different offset between IQ signals

Post by kkao »

Hello,
I'm trying to run a simple loopback model on a bladeRF with a XB-200 transverter.
Loopback mode is set to "RF_LNA3".

My environment is below.
Windows 10
MATLAB/Simulink: R2016a
bladeRF-cli version: 1.4.0
libbladeRF version: 1.7.2
Firmware version: 2.0.0
FPGA version: 0.6.0

The graph displays transmitting sine waves (upper graph) and receiving sine waves (lower graph).
Two waves (yellow line and blue line) in each graph show I signals and Q signals.
Received IQ signals seem to have each offset at a different level.
That wasn't improved even if I executed "cal lms" "cal dc tx" "cal dc rx".

How should I improve this offset?
Thank you.
jynik
Posts: 455
Joined: Thu Jun 06, 2013 8:15 pm

Re: Different offset between IQ signals

Post by jynik »

The "cal dc [rx|tx]" operations only perform DC offset calibration. There is not automatic IQ imbalance correction currently, but you can manually adjust these.

Check the help text for the bladeRF-cli's "calibrate" command -- you can run the following to adjust the gain and phase.
- RX and TX I/Q balance correction parameter calibration

- calibrate iq <rx|tx> <gain|phase> <value>

Set the specified IQ gain or phase balance parameters.
This libbladeRF documentation page provides more information about the range of <value> parameters and what they mean.

In MATLAB, the bladeRF_IQCorr object provides access to these same manual IQ balance parameters. See the help text for bladeRF_IQCorr for more info.
kkao
Posts: 6
Joined: Wed Jun 25, 2014 11:42 pm

Re: Different offset between IQ signals

Post by kkao »

I really thank you for the information. I ran the cal command with some options and understood that gains and phases of IQ signals can be corrected finely, and each DC offset of IQ signals can be set separately. MATLAB functions will be also useful.
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