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DAC38J82 / JESD204B SerDes line

Toshiyuki
Mastermind 7075 points

HI,

I would like to comfirm about SerDes line.

Customer is considering whether real data could be used for QAM signal created by FPGA.

Could they use real data, not  complex IQ ?

Best Regards,

Kato

  • 0
    TI__Genius 17310 points

    Hi Kato,

    Yes, they can send real data. The NCO and complex mixer cannot be used in this case, so they will need to send the data at their desired IF.

    Regards,
    Matt Guibord

  • 0 in reply to Matt Guibord
    Mastermind 7075 points

    Hi Matt - san,

    Thank you for the reply. I understood customer should use IQ data in their system.

    *customer system

    input->Zero IF(bandwidth=56MHz,QAM)

    output->844MHz,bandwidth=56MHz

    Would you give us the reason frequency by using real data couldn't be shifted ?

    Best Regards,

    Kato

  • 0 in reply to Toshiyuki
    TI__Genius 17310 points

    Hi Kato,

    Real data cannot make use of negative frequencies so you cannot have a ZIF system. However, QAM by definition is complex data... so I'm confused about what's being asked here. They can generate a QAM signal at ZIF and mix it up to some IF (real IF) in their FPGA and then send this new signal to the DAC. In this case they are sending real data (which is fine) but the complex mixer cannot be used because it will generate an image sitting at a frequency of NCO - IF. Or they can send the ZIF data (I/Q data) to the DAC and they can use the NCO to mix the signal from ZIF to 844 MHz. This is the usual use case.

    Regards,
    Matt Guibord

  • 0 in reply to Matt Guibord
    Mastermind 7075 points

    Hi Matt - san,

    Thank you for the reply. Would you give us more detail about an image sitting at a frequency of NCO - IF ?

    Customer would like to know why real data couldn't be used for the complex mixer.

    Best Regards,

    Kato