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Original question:

AWR1642: AWR1642 A2D sampling rate and ADC sampling rates

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

Lukas Liao
Prodigy 250 points
Part Number: IWR6843ISK
Other Parts Discussed in Thread: IWR6843

Hi TI supports,

I read the following page http://e2e.ti.com/support/sensors/f/1023/t/719503?tisearch=e2e-quicksearch&keymatch=complex%201x#pi320995filter=answers&pi320995scroll=false

I got the conclusion from that. 

1x=only real part spectrum data filtered

2x = real part+imaginary part spectrum data filtered

But I see the A2D sampling rate(real) in IWR6843 datasheet.

Q1: What is the difference between A2D sampling rate(real) and  A2D sampling rate(1x)? 

Q2: If I use complex 1x mode, I cannot do angle estimation because of no data of the imaginary part. Is it true? Why did TI design the function for different mode? Is there any concern?

BR,

Lukas

  • 0
    TI__Mastermind 25825 points
    Hello,

    In a complex-1x baseband implementation, it is not necessary to double the ADC output interface rate. In fact, it is possible to frequency-shift the spectrum, perform image-reject filtering and send out decimated I and Q ADC samples to the DSP at max possible beat frequency.

    Thus, the interface rate of the ADC samples going to the DSP does not really increase due to the use of the complex baseband. The "real output" at twice the max supported beat frequency changes to a "complex 1x output" at just a max supported beat frequency.

    The frequency shift to center the spectrum around DC helps simplify the implementation of image-reject filtering (Thus improving the noise figure without increasing the interface bandwidth). TI’s radar chip includes a built-in digital frequency shifter to frequency-shift the samples, perform image-reject filtering and send out the complex baseband output at the reduced interface rate (similar to a real-only implementation).

    For further details please refer to below application note:
    "Using a complex-baseband architecture in FMCW radar systems"
    www.ti.com/.../spyy007.pdf

    For the second question, Angle estimation is done using multiple receivers with IQ samples.
    Please refer to below training material.

    training.ti.com/intro-mmwave-sensing-fmcw-radars-module-5-angle-estimation

    Thanks and regards,
    CHETHAN KUMAR Y.B.