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Original question:

CCS/IWR6843: Minimal distance from sensor due to high pass filters HPF1 and HPF2

IWR6843: Distance for calibration of radar due to HPF

Johanwww
Intellectual 500 points
Part Number: IWR6843

Due to the high pass filters in the signal chain, HPF1 at a minimal cut of frequency of 175kHz and HPF2 with a minimal cut of frequency of 350kHz, frequencies from objects close to the radar will be dampened.
As we understand it, these filters can not be turned off.
This is a problem when we are going to do the antenna calibration, since we want to make the calibration setup as small as possible, since we pay for the space we are using in the production facility.
 
How does TI handle this when doing calibration? Which distance do you recommend as the minimal distance for a reflector, and which size do you recommend for the reflector?
 
What are the HPF meant for except for removing the DC component?
Are they for preventing "negative distances" due to phase noise in the signal? Or are they there for attenuating the signal at short distances to prevent overload/saturation/compression effects in the signal chain?
Just to be sure, are there any way to disable the HPF (without getting DC troubles of course)?

  • 0
    TI__Guru 50240 points

    I've asked an expert to look into this and we should have an answer for you sometime next week.

     

    Cheers,

    Akash

  • 0 in reply to Akash Gondalia
    TI__Mastermind 25835 points

    Hello,

         Typically for calibration antenna need to be in far field radiation. 

    Below expression gives the absolute minimum far field distance needed as the function of Antenna aperture. 

    You may want to add sufficient margin for this number.

     

    For the calibration, controlled environment (with the mmWave absorbers ) would be better. 

    There is no recommendation for the corner reflector as long as reflected signal strength is higher than the noise-floor or clutter it should see around within it's field of view.

    HPF filter provides isolation for the Tx to Rx coupling which will results lower IF frequency signal, Without this it would reduce the dynamic range of the weaker signal by compressing the receiver. Depending upon the Antenna position (and also slope of FWCW signal ) Tx to Rx coupled signals could vary at lower frequency.  Also it would also offer attenuation for the close reflections coming in from Radome/Housing. Hence it's not just serves DC component removal, it also helping in improving dynamic range of receivers as well. 

    Currently, there is no way to disable these HPF filters. 

    Thanks and regards,

    CHETHAN KUMAR Y.B.

     

     

  • 0 in reply to CHETHAN KUMAR Y.B.
    Intellectual 500 points

    Thank you for your answer.

    One question that remains:

    We have got information from TI through mail that it should be possible to disable the HPF somehow, this does not necessarily contradict the answer here, if you mean support to disable the HPF in the SDK and the mail means support to disable the HPF in the firmware of the chirp.

    There was a forum post showing measurements of some sort, with one of the HPF turned off, I am trying to find it again, so I can link to it. But it indicates also that there is support for turning the HPF off somehow.

    Is there any documentation for how to disable the HPF on our own, bypassing the SDK? I will start by looking into the OOB demo documentation in the SDK.

  • 0 in reply to Johanwww
    TI__Mastermind 25835 points

    Hello,

        Unfortunately, In the current implementation for the functional mode, HPF filters cannot be disabled. 

    Thanks and regards,

    CHETHAN KUMAR Y.B.

  • 0 in reply to CHETHAN KUMAR Y.B.
    Intellectual 500 points

    Ok, thank you for your help.

  • 0 in reply to CHETHAN KUMAR Y.B.
    Intellectual 500 points

    How much would you say is sufficient margin?

    Which distance does TI use?

  • 0 in reply to Johanwww
    TI__Mastermind 25835 points

    Hello,

        1~1.5m would be sufficient. 

    Thanks and regards,

    CHETHAN KUMAR Y.B.