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AWR2243: complex 1x vs complex 2x

camidz
Prodigy 70 points
Part Number: AWR2243

Hello, 

I collected data both with complex 1x mode and complex 2x mode and I want to plot the range FFT in both cases. With the same chirp configuration and general setup the range FFTs show the peak corresponding to the strongest reflector in different positions (2~3 meters of difference).

It's not clear to me the reason of it. Should I use different formulas to compute the range axis? Or is there any other configuration parameter that should be changed apart from the adcFormat? 

Thank you for the help

  • 0
    TI__Expert 3171 points

    Hello Camidz, 

    Thanks for your question.  

    For complex 1x mode, DFE applies IQ imbalance correction and then downsample the signal. So it allows 80%-90% of the signal bandwidth compare to the sampling rate.
    For complex 2x mode, only half of the bandwidth (0~fs/2) is occupied by the signal, and the other half (the image band) can be occupied by other noise source like interference. So complex 2x mode is mainly designed for applications that needs interference cancellation.

    Could you give us some understanding of your test setup?  By chance are you seeing any interference in your setup?

    Regards,

    James

  • 0 in reply to James Murdock65
    Prodigy 70 points

    Hello, 

    thanks for the answer. I found out that the shift was caused by the programmable filter. 

    I found on the Radar Interface Control document the meaning of the parameters and how to select the frequency shift one but it is still not clear to me how to choose the best number of taps for the filter. Can you give some insights on that?

    Thank you

  • +1 in reply to camidz
    TI__Expert 3171 points

    Hello Camidz,

    You can find the default filter response here:

    https://e2e.ti.com/support/sensors-group/sensors/f/sensors-forum/611381/awr1243-parameters-about-adc-and-if-chain 

    May I ask why you are wanting to program the filter?  In most cases its ok to use the default filtering chain.  

    In general a higher number of taps can be used to achieve a tighter filter response (e.g. faster roll-off per decade going from the pass band to the stop band), so if you are having trouble with interference from the stop band frequencies or interference at frequencies near the transition frequency of the filter, a higher order can be helpful.  However, higher orders also increase latency and computational load.  

  • 0 in reply to James Murdock65
    Prodigy 70 points

    Hello,

    I was making some experiments to remove noise from subsequent frames. Indeed, when I collect more than one frame starting from the second one I see a lot of noise in some receivers.

    Thank you for the support

  • 0 in reply to camidz
    TI__Expert 3171 points

    Thanks Camidz, good luck with your development!