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AWR1243: Sampling speed selection

Peter010
Genius 4165 points
Part Number: AWR1243

 Hello everyone

In this white paper, it mentions the frequency shift and Image reject filtering. Does it mean if I use TI mmwave chirp and the maximum beat frequency is 10Mhz, a 10Mhz sampling frequency would be enough and there is no negative frequency after FFT?

Thanks

Xining

  • 0
    TI__Mastermind 37500 points

    Hello,

    In the DFE processing of the ADC output data, the first 2 DFE digital stages provide for CIC, FIR filtering / decimate by 2, IQ imbalance correction, and a resampler.

    The first two DFE stages reduce the ADC output rate to 2x DFE output rate (real, complex 2x), or 4x DFE output rate (complex 1x).

    The third DFE stage provides for filtering and decimate by 2 processing for real, complex 2x mode.

    The third DFE stage works differently for complex 1x mode, it acts as a shifted complex spectrum,  The 4x DFE out data, is input to a complex mixer(centering), to shift by Fs/4.   The complex spectrum can be (-Fs/4 to 3Fs/4, or (-3Fs/4 to Fs/4).  The next stage is an 80% passband decimate by 2 filter.  The next stage provides the final digital filtering (same filter as real and complex 2x).   Another digital NCO is used to shift (decentering)    (0 to Fs) or (-Fs to 0).   After the digital mixing a donwsample by 2 is performed.  

    The final filter bandwidth is 90%.   Throughout the other digital filters we have 80% bandwidth.  So in Complex 1x mode, if your desire is to have a 10Mhz tone, in band, with a 1.1x oversampling, you need 11Msps DFE output rate to transport a 10Mhz tone.

    Regards,

    Joe Quintal