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IWR1443: Question about inter-chip time/chirp time in sensing estimator

Chris Meng
Mastermind 37786 points
Part Number: IWR1443

Hi,

What does the inter-chirp time mean? Does it mean the time between two chirps? Does it means idle time+adc start time?  Why the inter-chirp time is so long and the chirp time is so short in the output and chip design?

Below is the default value in sensing estimator. You can see the inter-chip time is 20.20us.  The Idle time is 7us and ADC start time is 6us. So inter-chip time > idle time + ADC start time.  Why?  The chirp time is 45.48us.  I think the chirp time is the total time of one chirp. The ramp end time is 58.85us and it only covers the slop in one chirp. In below table, the chirp time is less than ramp end time, which is not reasonable.

Would you pls kindly advise what I missed?

 

 

  • 0
    Genius 4165 points

    Hi Meng
    I am not TI employee. But i can tell you what I learnt, the inter-chirp time is minimum time between continuous chirps, which is limited by chirp set up time in between chirps. The ramp time should include ADC start time(6us), chirp time(45.48us), and unsampled time, which means ADC only sample portion of the entire slope. In this case, the ADC only sample 45.48 us in 58.85us.

    If i am incorrect, pls correct me.
    Regards
    Peter

  • 0 in reply to Peter010
    TI__Mastermind 21295 points

    Peter, Thanks for your reply.  You are correct.

    Chris,

    Please find a diagram below which shows an example chirp with the various chirp parameters labeled.  The inter-chirp time is labeled "Total inter-chirp gap" in the figure.  It is the time from the end of the “ADC Sampling Time” for the previous chirp to the start of the “ADC Sampling Time” for the next chirp (in the same frame).

    Please tell me if you have more questions about it or mark the thread as answered if your question is answered.

    Regards,

    John

  • 0 in reply to JohnH
    TI__Mastermind 37786 points

    Peter and John,

    Thanks for your help!

    John，

    Does the chirp time in sensing estimator is same as the adc sample time in the diagram you shared?

    Thanks,

  • 0 in reply to Chris Meng
    TI__Mastermind 21295 points
    Chris,

    Yes, the "Chirp time, Tc (us)" parameter in the Sensing Estimator is the time length (in us) of the “ADC Sampling Time” in the diagram.

    Regards,
    John
  • 0 in reply to JohnH
    TI__Mastermind 37786 points
    John,

    Thanks for your help! It is better to add these explanation info in sensing estimator guide.

    My customer feedback that the inter-chirp time in sensing estimator is quite long compared with the idle time/adc start time calculated by RampTiingCalculator in Radar studio.

    I think the sensing estimator gave a relaxed timing, and radar studio gives a tight timing which need customer to test and fine tune. That it, customer can refer to sensing estimator and they can also fine tune the parameter based on radar studio and own test to get best performance. Would you pls kindly check if my understanding is correct? If not, would you pls kindly correct me?

    Thanks,
  • 0 in reply to Chris Meng
    TI__Mastermind 21295 points

    Chris,

    Thanks for the feedback regarding the tool and user guide.  We will look at incorporating it.

    Currently the Sensing Estimator does use more relaxed values for the Idle Time and ADC Start Time that work for all of the possible inputs.  So, yes, customers can then fine tune and test smaller values for their application/use-case.

    Regards,
    John