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AWR2944: Regarding the issue of phase calibration

L mx
Prodigy 90 points
Part Number: AWR2944

Tool/software:

Hi TI teams:

I have the following questions. I would appreciate it if you could answer them. Thank you.

Question 1.Using only one transmitting antenna, the phase of each Chirp is increased by 5.625°.The figure below shows the results of both without and with RFINIT calibration. The values in the figure represent the phase difference between each Chirp.

   

It seems that the result phase after enabling RFINIT calibration has become much more stable. Does this prove that the API call was correct and the phase calibration has taken effect?

Question 2.However, the phase deviation of the first Chirp in each frame is quite large, and the phase values of the same Chirp in different frames are unstable. Is this normal?

     

The above figure shows the result when the phase shift is set to 45°. The actual phases of each Chirp are shown in the left and right figures. The four marked Chirps have quite different actual phase values, but the Delta is approximately the same. Moreover, the differences of the 2nd, 3rd, and 4th Chirps are around 45°, which is in line with the design value. However, the difference between the 1st and 2nd Chirps is quite large.

Question 3,For 2944, if one wants to perform automatic calibration and temperature compensation, is it sufficient to just configure and call "rlRfRunTimeCalibConfig" to achieve automatic calibration? Are there any other steps required?

Best Regards

Minxi

  • 0
    TI__Expert 4130 points

    Hello Minxi,

    It appears to me that the RFINIT calibrations are running fine. You may look at the status of the calibration as per the AWR_CAL_DATA_SAVE_SB API, refer to section 5.3 of the ICD.

    On second question, please confirm that the x-axis is chirp number and that you have configured a Delta Dither of 45°. It is not expected behaviour to have that phase instability between first chirp and second chirp. Is this behavior visible if you set Delta Dither = 0?

    On third question, your understanding is correct.

    Regards,
    Shailesh

  • 0 in reply to Shailesh Joshi
    Prodigy 90 points

    Hi Shailesh

    Thank you for your answers to Question 1 and Question 3. I understand now.

    And regarding Question 2,The X-axis indeed represents Chirp number and configured a Delta Dither of 45°.Therefore, the X-axis range in the picture is from 1 to 256, because one frame of the configuration sends 256 Chirps.

    I have an idea regarding this issue. Since the slope and step frequency we have configured are negative, the ICD indicates that if the value is negative, then a very small negative LUT needs to be added to the first Chirp.so,we add -1 to LUT for 1st Chirp,And the slope we have configured is greater than +/-3MHz/us（We used ADV_Chirp_ADV_frame）.

    I gave it a try and disabled the LUT for this starting frequency. As a result, the differences for all the Chirps were normal again.

    I wonder if the above information can help us analyze the problem.

    If the above viewpoint is correct, then there is only one remaining question.

    The phase difference values of different Chirp in one frame are fixed, but the phase of the same Chirp in different frames is different. Is this normal?

    This phase increment is set to 5.625°.

      

    The X-axis represents different frames, and the Y-axis represents the angle (in degrees).

    The left figure shows the average phase difference of Chirp in different frames.

    The right figure shows the actual phase values of the same Chirp in different frames.

    Best Regards

    Minxi

  • 0 in reply to L mx
    TI__Expert 4130 points

    Hi Minxi, 

    Thanks a lot for finding that note, it definitely appears to be related to the issue.

    As it says in the last point, there is no other workaround if your slope dither is more than 3MHz/us, you have to discard the first chirp. 

    We do expect some phase instability when seen across frames, which can also arise due to small temperature or calibration changes that happen between frames. I will need to check and get back on how much instability is expected. 

    Regards,
    Shailesh

  • 0 in reply to Shailesh Joshi
    Prodigy 90 points

    Hi Shailesh

    Then we only have one question left. If you find the allowable phase difference for different frames, please let me know. Thank you. 

    In addition, your solution has solved my problem.

    Best Regards

    Minxi

  • 0 in reply to L mx
    TI__Expert 4130 points

    Hello Minxi, 

    The jumps during the first section are as expected. These are due to calibration based updates and temperature deviation.

     

    Not quite sure why we are seeing the fast variations in the second part of your plot. Could this be due to some instability in the setup itself?

    Regardless, please note that over a long period of time there can be large variation in phase due to temperature and calibrations itself. 

    Regards,

    Shailesh

  • 0 in reply to Shailesh Joshi
    Prodigy 90 points

    Hi Shailesh

    Thank you for your answer.

    Then I understand that we don't need to pay attention to the phase difference of the same Chirp between frames. We only need to ensure that the phase difference between different Chirps is a fixed shift.

    Best Regards

    Minxi

  • 0 in reply to L mx
    TI__Expert 4130 points

    Hi Minxi,

    Thats correct. We ensure that phase remains stable within a frame and that is usually what is required for most algorithms.

    As all the questions are answered, I will close this e2e. Thanks.

    Regards,
    Shailesh