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Original question:

IWR6843ISK: Re:AWR1642BOOST: Complex 1x and Complex 2x Modes

IWR6843ISK: Difference between real mode and complex1x

vincent fayet1
Intellectual 365 points
Part Number: IWR1843


Hello,

In a previous post, inside related discussion linked with this thread,  @ mentionned that : "Complex 1x mode, Only Real IF Spectrum is filtered and sent to ADC, so If Sampling rate is X, ADC data would include frequency spectrum from 0 to X."

But if that's true what's the difference between Complex1x mode en real one ?

thanks,

Vincent

  • 0
    TI__Mastermind 25835 points

    Vincent,

       Did you get a chance to look at the below white paper "Using a complex-baseband architecture in FMCW radar systems" on this topic?

    https://www.ti.com/lit/wp/spyy007/spyy007.pdf

    Thanks and regards,

    CHETHAN KUMAR Y.B.

  • 0 in reply to CHETHAN KUMAR Y.B.
    Intellectual 365 points

    Hello, yes i read a bunch of time this doc , but this pdf explqin the difference between real (I-only) ADC output and complex output. But doesn't explain the difference between complex1x and complex2x

    And when you try to understand this difference you find this post  but reading this post and especialy the answer of @

    the difference between complex1x and real become blurred

  • 0 in reply to vincent fayet1
    TI__Mastermind 25835 points

    Hello,

    ADC Digital front-end supports three output modes 1) Complex 1x 2)Complex 2x 3) Real output modes

    Complex 1x: The default mode being complex base-band output.

    In complex 1x, produce the optimal output sampling rate (i.e., output sampling rate fs = fb,max/0.9, fb is the baseband interest), which achieves the best noise figure and lowest (optimal) output sampling rate. In complex 1x case image band is not available, However image band is suppressed using anti aliasing filter and frequency is shifted such that 0 to fs frequency components are sent out.

    Complex 2x:

    An alternate mode being complex baseband output at 2X the optimal rate (i.e., fs = 2fb,max/0.9), which can be used if both inband and image band visibility is desired at the final output.  The in-band noise figure in this mode is identical to the default Complex 1X configuration.

    In this mode, In-band and the image band being visible at the final output, and since the image band is kept as alias-free as the in-band, image band monitoring can be used for purposes such as interference detection, etc. 

    Real output mode:

    In this configuration, the receiver is operated in real-only mode. Real output at fs = 2fb,max/0.9, which can be used if real-only analog chain is desired, for low power operation.Thus, the Q-channel IF, ADC and decimation chain are unused, and hence the noise figure is poorer compared to the complex baseband configurations.

    Thanks and regards,

    CHETHAN KUMAR Y.B.

  • 0 in reply to CHETHAN KUMAR Y.B.
    Intellectual 365 points

    Thank you very much,

    Vincent

  • 0 in reply to vincent fayet1
    TI__Mastermind 25835 points

    Dear Vincent,

        Thank you for the confirmation. I will close this thread. 

    Thanks and regards,

    CHETHAN KUMAR Y.B.