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AWR1642BOOST: Where is the digital frequency shifter mentioned in the TI white paper?

Peter010
Genius 4165 points
Part Number: AWR1642BOOST
Other Parts Discussed in Thread: AWR1243

Hello everyone

In this white paper. it said that "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)." Can you tell me where can I find this digital frequency shifter on the chip?

Another question, as mentioned in the document "The band-pass IF chain has configurable lower cutoff frequencies above 350 kHz and can support bandwidths up to 15 MHz. ", which means any frequencies below 350KHz would be filtered out. This does not make sense, because the low beat frequencies in the close range detection will be filtered. Can you tell me why?

Thanks

Peter

  • 0
    TI__Guru 58035 points
    Hello Peter,
    The digital frequency shifter is part of the image rejection block shown in the figure above.

    Regarding the 350Khz HPF, you are right that the signals less than 350 Khz would be filtered. This is intentionally done to avoid saturation due to bumper of the car (for example) or antenna -antenna coupling (since the TX and RX antennas would be close to each other).

    Regards,
    Vivek
  • 0 in reply to Vivek Dham
    Genius 4165 points

    Thanks for your reply.

    Don't  you think 350KHz cutoff frequency is too high for the close range detection? For example, in TI mmw demo, the maximum beat frequency is 4.4MHz (10 meter range), and the size of FFT is 256. So, each bin in frequency domain equals to 4.4e6/256=17KHz. As the cutoff frequency is 350KHz, the beat frequency for the first 350kHz/17Khz =20 bins will be filtered out. Don't you think it will be a problem?

    Regards
    Peter

  • 0 in reply to Peter010
    Prodigy 195 points

    I think it depends on the FM slope you chose.

    If you chose a 100MHz/us slope(maxim for TI mm-wave device), the filtered range information is less than 1 meters.

  • 0 in reply to juan cai
    Genius 4165 points
    Yes, you are correct. However, for some cases, we cannot choose to use the maximum slope rate. For example, when we want to use high PRT for the long range detection, as the limitation of the ADC sampling rate, the frequency slope cannot be too high.

    -Peter
  • 0 in reply to Peter010
    Prodigy 195 points
    Yes, I guess that why TI offer us three chips to chose. Maybe XWR1243 is a good choice for long range radar.
  • 0 in reply to Peter010
    TI__Guru 58035 points
    Hello Peter,
    You should look at it in terms of the distance your application is intended for. If you are looking for a long range application then the HPF would not be a problem since it would only filter out close by objects.

    Another point to keep in mind is its a HPF with a finite attenuation (intended to avoid saturation) , not a complete removal of the signal in the 0- 350Khz range. So a very close by object might still be detected since the reflected power would also be much stronger because its so close. For example you can try our EVM and keep a metallic object at 20cms distance, you will be able to detect it using the demo application even though the IF might be within the 350Khz HPF.

    Regards,
    Vivek
  • 0 in reply to Vivek Dham
    Genius 4165 points

    Hi Vivek

    Thanks for your reply.

    Vivek Dham said:
    Another point to keep in mind is its a HPF with a finite attenuation (intended to avoid saturation) , not a complete removal of the signal in the 0- 350Khz range. So a very close by object might still be detected since the reflected power would also be much stronger because its so close.

    Yes, I had noticed this on the evaluation board. Thanks for your explanation.

    Can you tell me how much attenuation is in the HPF?

    Thanks

    Peter

  • 0 in reply to juan cai
    Genius 4165 points
    AWR1243 chip contains the same high-pass filter as AWR OR IWR series chips.

    -Peter
  • 0 in reply to Peter010
    TI__Guru 58035 points

    Hello Peter,

    You are right, AWR1243 also has the same HPF.

    The devices have two HPF's one can be set to min cutoff freq 350Khz and other one at 175khz. Each of these have a 20dB/ decade roll off.

    Regards,

    Vivek

  • 0 in reply to Peter010
    Prodigy 195 points

    XWR1243 offers a higher sampling rate than the other two chips, that why I mentioned it above.

    And Thanks  Vivek for answering the question.

  • 0 in reply to juan cai
    TI__Guru 58035 points
    Hello Juan,
    You are right, 1243 offers higher sampling rate and hence higher IF bandwidth. This makes it suitable for long range application , as you mentioned.

    Regards,
    Vivek