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IWR6843: 64.8MHz signal is generated by IWR6843

Chris Meng
Mastermind 37736 points
Part Number: IWR6843

Hi,

My customer found if they uses 2Mbps sample rate, IWR6843 will generated a noise signal around 64.8MHz. If they changes the sample rate, the frequency of the noise signal will change.

Customer doesn't wants the noise signal around 64.8Mhz. So they want to know how the 64.8Mhz signal is generated by IWR6843 and why the sample rate will effect the frequency of the noise signal. Would you pls kindly help?

Any suggest to remove the noise signal excluding adding a shield?

  • 0
    TI__Mastermind 25835 points

    Chris,

       Could you please provide more details on this? Is this on TI EVM or customer hardware? If it's custom hardware we need to review the system block diagram.

    Where is this frequency found? How it is measured? 

    Thanks and regards,

    CHETHAN KUMAR Y.B.

  • 0 in reply to CHETHAN KUMAR Y.B.
    TI__Mastermind 37736 points

    CHETHAN KUMAR Y.B. said:
    Could you please provide more details on this? Is this on TI EVM or customer hardware?

    Customer found the noise signal on both TI EVM and customer's own board.

    CHETHAN KUMAR Y.B. said:
    Where is this frequency found? How it is measured? 

    Customer uses spectrum analyzer to find the noise signal.

  • 0 in reply to Chris Meng
    TI__Mastermind 25835 points

    Chris,

        It's difficult to understand the situation and problem just from the above statement.

    mmWave radar is an intentional radiator and it radiates between 60-64GHz frequency.

    Other frequency components are below the emission limits of the regulatory body. How is the 64.8Mhz is measured? is it radiated measurement coming from the Transmitter port? or Is it conducted measurement on the board at certain location? Where is spectrum analyzer connected? Block diagram of the setup and measurement condition would help to understand the problem. 

    Thanks and regards,

    CHETHAN KUMAR Y.B.

  • 0 in reply to CHETHAN KUMAR Y.B.
    TI__Mastermind 37736 points

    Chethan，

    Pls find test setup below.


    Customer found 64.8Mhz noise signal at below 1~5 regions on the IWR6843 chip. And the noise signal at region 1/2 is stronger than other regions.

  • 0 in reply to Chris Meng
    TI__Mastermind 25835 points

    Chris,

    Thanks for providing detailed with a diagram. 

        There could radiation possible, but we need to check what level it would be. And we need to check if it's violates any regulatory standards. 

    Below is the Radiation emission test report as per ETSI European standard. 

     

     

    Below is the Test which includes 64.8Mhz band and it's sufficiently below the regulatory standard.  

    For more details you could refer to below ETSI test report and refer to section 7.6 Radiated spurious emissions for the test reports. http://dev.ti.com/tirex/explore/node?node=AK24mFy5ZZqRg5mtMe9tBw__VLyFKFf__LATEST

    Thanks and regards,

    CHETHAN KUMAR Y.B.

  • 0 in reply to CHETHAN KUMAR Y.B.
    TI__Mastermind 37736 points

    Chethan,

    Thanks for your reply. Though the ISK radiation emission passes ETSI European standard, but it affects customer's application.

    As customer found this noise signal frequency is related to sample rate, they want to know how the sample rate affects the noise signal frequency. Customer wants to change the sample rate to move the noise signal frequency out of their interested frequency band. Would you pls help again?

  • 0 in reply to Chris Meng
    TI__Mastermind 25835 points

    Chris,

    Sampling rate is derived through the sigma delta modulator's Digital Front End chain. In the digital front end chain there are lots Analog/Digital blocks works on various divided version of root clock for Decimation, interpolation filters stages. Customers could choose their desired frequency anywhere between 2MSPS to 25MSPS in real mode or 12.5MSPS  in complex rates depending upon the applications interest.  

    We have not seen this to be a problem, in our tests, Also from the most of the customers we have interacted. If this is a problem to the customers application then following options could be explored

    1) Metallic Shield on top of the  device could be explored. The shield should be well grounded, covering the components of interest which would act as a Farady's cage.

    2) High frequency absorber material could be looked at for suppressing emissions.  

    For more informaiton you could refer to the below TI mmWave Radar Device Regulatory Compliance Guide app-note.

    https://www.ti.com/lit/an/spracp3a/spracp3a.pdf 

    Thanks and regards,

    CHETHAN KUMAR Y.B.

  • 0 in reply to CHETHAN KUMAR Y.B.
    TI__Mastermind 37736 points

    Chethan,

    Thanks for your help!

    CHETHAN KUMAR Y.B. said:
    Customers could choose their desired frequency anywhere between 2MSPS to 25MSPS in real mode or 12.5MSPS  in complex rates depending upon the applications interest.

    Do you mean the minimum sample rate customer can use on IWR6843 is 2Msps? Is it a hardware limitation?

  • 0 in reply to Chris Meng
    TI__Mastermind 25835 points

    Chris,

       Yes, Digital front end in the ADC limits the max and min frequency

    Thanks and regards,

    CHETHAN KUMAR Y.B.