IWR6843ISK-ODS: Change the start frequency

Part Number: IWR6843ISK-ODS
Other Parts Discussed in Thread: IWR6843

Hi experts,

I'm using the demo code of "overhead_mount_occupancy" but I would like to change the start frequency.

Test scenario: If other settings are the same as default but the start frequency changes to 60.50 GHz.

Here is the debug message:

From the comment of "startFreqConst", my setting is within the valid range.

May I know what's the reason for this and how to solve this issue?

Thanks,

Best Regard,

Jack

  • Hello Jack,

    Please see the following document on defining chirp parameters: https://www.ti.com/lit/an/swra553a/swra553a.pdf

    There is also information on decoding error codes in the following training: https://training.ti.com/easy-evaluation-and-development-mmwave-systems-software-development-kit

    That error code is saying that the ramp end freq is not within the limits, so you may have to modify other parameters of the chirp.

    Regards,

    Jackson

  • Hi Jackson,

     

    Thanks for your reply.

    After I checked the setting based on your reference, I still could not find why this setting failed.

    By the way, the comment says the valid range is between 76 ~ 81 GHz but I’m using the IWR6843 which operates between 60 ~ 64 GHz. Is it make sense (I'm using mmWave SDK version 03_05_00_04)?

     

     

    Here were my detailed settings:

    • Start frequency: 60.5 GHz <profileCfg.startFreqConst = 1503735656, which is between the valid range 1491308088 ~ 1590728628>
    • Tx start time: 1 us <profileCfg.txStartTime = 100, which is between the valid range -4096 ~ 4095>
    • ADC start time: 10 us <profileCfg.adcStartTimeConst = 1000, which is between the valid range 0 ~ 4095>
    • Ramp end time: 40 us <profileCfg.rampEndTime = 4000, which is between the valid range 0 ~ 500000>
    • Idle time: 205us <profileCfg.idleTimeConst = 20500, which is between the valid range 0 ~ 524287>
    • Slope: 97.984 MHz/us < profileCfg.freqSlopeConst = 2706, which is between the valid range -6905 ~ 6905>

     

    • Bandwidth = Slope / sampling rate * N_sample = 2.8504 GHz. The end frequency should be 60.5 GHz + 2.8504 GHz = 63.3504 GHz, which is less than 64 GHz.
    • Sampling time = N_sample / sampling rate = 64 / 2.2e6 = 29.191 us. The total time is ADC start time + sampling time = 10 + 29.191 = 39.191 us, which is less than the ramp end time (40 us).

     

    Do you have any idea that the error code said the end frequency exceeds the limit?

    Or can you give me an example to set the profile with the start freq = 60.50 GHz with the BW = 2.85 GHz and N_sample = 64?

     

    Thanks,

     

    Best Regards,

    Jack

  • Hello Jack,

    The comment in the error is old and should only apply to the 76GHz sensors. Please disregard that.

    Can you please confirm that your profileCfg line in your cfg file is the following?

    profileCfg 0 60.5 205 10 40 328965 0 97.984 1 64 2200 2 1 40

    Please allow me another day to check the parameters and get back to you.

    Regards,

    Jackson

  • Hi Jackson,

    The profileCfg that I'm using is "profileCfg 0 60.50 205 10 40 1513239 0 97.984 1 64 2200 0 0 36".

    (I have tried your profileCfg, the error code was the same.)

    Except for the start Freq and Tx power, other settings are the same as the default.

    Best Regards,

    Jack

  • Hi Jack,

    The settings you have for ADC start time and ramp end time push the max frequency over the 64GHz limit. While your BW is lower, there is ramp time before and after the ADC samples that exceeds the frequency limit. Please try lowering these parameters, or using the Ramp Timing Calculator in the mmWave studio package as detailed in the following app note.

    https://www.ti.com/lit/an/swra553a/swra553a.pdf

    Regards,

    Jackson

  • Hi Jackson,

    After measured the BW with the default setting, I found the end frequency was 63.895 GHz (please ignore the frequencies which less than 60 GHz, it is the image), which was totally wrong (from my setting, the end frequency should be 62.850 GHz). If my measurement was correct, of course, the start frequency cannot shift to 60.5 GHz (the end frequency will exceed 64 GHz).

    Or, maybe my understanding is wrong. If the Tx start is triggered, then, the Tx starts ramping?

    Based on the below figure, the start frequency which we set in the "profileCfg" for the "Tx Start" time slot or "F0"? If the start frequency that we set is for the "Tx start", the BW which I measured might correct.  As you mentioned, shorten the time between "Tx start" and "F0" may solve my question.

    Thanks,

    Best Regards,

    Jack

  • Hello Jack,

    Your measurement should show the correct measured full BW.  Please see the below image from the ramp timing calculator. Besides the ADC sample time, there is ADC start time and ramp end time. With your high chirp slope, this extra time will increase beyond the 64GHz limit if you shift the start frequency up by 500MHz.

    You can try reducing the chirp slope to reduce the total bandwidth and shift the start frequency. A slope below 83MHz/us should fit.

    Regards,

    Jackson

  • Hi Jackson,

     I really appreciate your help in resolving my problem.

    After shortened the ADC start time, the sensor could normally operate with my expected setting.

    Best Regards,

    Jack