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IWR1443: How to Ensure the Phase Coherence of the Sampling Time Gate?

fang_h_y
Intellectual 290 points
Part Number: IWR1443

Hello,

During the sampling every chirp, how to ensure the start time of the ADC Sampling is strictly identical in the follow picture use the blue rectangle and the blue arrow? Because the phase coherence is needed. 

  • 0
    TI__Guru*** 140994 points
    Hi,

    Can you please provide more details about your application?

    Thank you
    Cesar
  • 0 in reply to Cesar
    Intellectual 290 points
    Many times, we need to do the 2D-FFT to get the velocity. We need the phase to compute the velocity. In the sampling process, we must guarantee the ADC start time is strictly identical. If the ADC start time is not identical, the velocity is not accurate. So can you tell me what is the way to ensure that the ADC start time is strictly identical?
  • 0 in reply to fang_h_y
    TI__Expert 5235 points
    it is already guaranteed by the hardware, otherwise, as you said, we would not be able to do velocity estimation (we do 2D FFT velocity estimation in many of our demos).
  • 0 in reply to Piyush_
    Intellectual 290 points
    Hello, Piyush_,
    Can you tell me how the hardware guaranteed?
    fang_h_y
  • 0 in reply to fang_h_y
    TI__Expert 5235 points
    Perhaps your question arises from your assumption that you cannot specify the adc start time. The times indicated in the picture -idle time, ramp end time and adc start time are specified by the user in profile configuration. This completely and uniquely determines all the chirp timing and these are faithfully reproduced on every chirp that points to the same chirp configuration (which is a delta spec over the profile configuration). At the lower interface layer of mmwavelink, you can see from its documentation (also known as ICD) that these timings are specified in chunks of 10 ns i.e 1 LBS = 10 ns. We cannot give you all internal details of the hardware here but you can imagine the timings are based on counting in this chunks of 10 ns and counter limits determined by the user configuration are not randomly changing from chirp to chirp that belong to the same chirp configuration. Note also that the timing is relative to Tx and the tx phase is also therefore important, the hardware does not vary the tx start phase on different chirps corresponding to same tx antenna transmission, unless user wants to do this which on some devices is allowed for the purpose of say tx beamforming (tx phase shifter in profile configuration for example).
  • 0 in reply to Piyush_
    Intellectual 260 points
    Hi,
    i want to change the ADC start time for each chirp, I'm setting it with RadarSudio, but the properties of each chirp seem exactly the same.
    just like e2e.ti.com/.../705793
  • 0 in reply to user5223549
    TI__Guru 50240 points
    Hello,

    This question is outside the scope of this thread. If you'd like to ask a TI Expert then feel free to open up a new thread!


    Cheers,
    Akash