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AWR1642: Question about the HPF in Analog IF

Chris Meng
Mastermind 36665 points
Part Number: AWR1642

Hi,

Per datasheet there are two HPF in analog IF module.

Available HPF Corner Frequencies (kHz)
HPF1                            HPF2
175, 235, 350, 700    350, 700, 1400, 2800

But customer found based on their chirp configuration, the radar should not be able to detect the object in 0.3~0.7m range. But in IF signal data, they still find the info below 175KHz. The same result on xWR1443.

Customer confused about this. Would you pls kindly advise if customer miss anything?

Thanks,

  • 0
    Prodigy 195 points
    Hi Meng
    The attenuation of HPF in stop band is limited to tens of dB.
    The reflection of near target is very strong so you can observe its attenuated reflecting wave in frequency domain.
    Wish this can help you.
  • 0 in reply to juan cai
    TI__Mastermind 37500 points

    Hello Chris,

    The analog High Pass filters provide low frequency attenuation.   Here is an approximate analog attenuation

    Setting, frequency, attenuation

    Freq, attn 175k, attn 350k, attn 500k, 750k, 900k

    2e4, 30, 36, 38, >40, >40

    1e5, 18, 22, 28, 28, 33

    1e6, 13, 13, 13, 14, 14

    So if the customer has the Rx LNA gain set high enough, and they have a closer object or lower Freq Slope, they can still detect close in objects.

    Regards,

    Joe Quintal

  • 0 in reply to Radio-Joe
    TI__Mastermind 36665 points
    Joe,

    The HPF Corner Frequencies can be set as 175, 235, 350, 700, 1400, 2800. How to match them with the setting you shared (attn 175k, attn 350k, attn 500k, 750k, 900k)?

    Can you share the table clearly? Current format is hard to read.

    Thanks,
  • 0 in reply to Chris Meng
    TI__Guru 58035 points
    Hello Chris,
    The two HPF filters will have a 20dB per decade attenuation roll off from their corner frequency. For example if the HPF1 corner frequency is set to 175Khz , it would have 3dB attenuation at 175Khz and ~23dB attenuation at 17.5Khz and so on. You need to add the attenuation provided by both the HPFs to get to the final attenuation at a particular frequency.

    As Juan mentioned, even within the HPF region the objects can be detected if they are strong enough.

    Regards,
    Vivek