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ADC12DJ3200: sample harmonics is high

Kailyn Chen
Genius 9560 points
Part Number: ADC12DJ3200

Hello，

Our customer used his own ADC12DJ3200 board, 2.4Gbps sampling rate, MODE3，16lane，dual-channel mode, input 264Mhz, -1dBFS single frequency signal, signal source output added low pass filter inhibit harmonics, sample analysis harmonics less than - 50dBFS, and  is  different with the datasheet, Below is a sample signal, what is the cause of this? Data Sheet 347MHz, - 1dBFS, HD2=-73dBFS 

Best regards

kailyn

  • 0
    TI__Genius 9560 points

    Hello，

    Is there any updates about this question?

    Best regards

    Kailyn

  • +1 in reply to Kailyn Chen
    TI__Mastermind 19875 points

    Hi Kailyn,

    Sorry about the delay, our primary support for this device has been out of office. I will try to provide some assistance in the meantime.

    If I am understanding correctly, the fullscale input in the plot is at ~146.3 on the y-scale, meaning the fundamental at 264.1MHz is at -1dBFS. This would indicate HD2 and HD3 being roughly 48dBc which is not datasheet performance.

    Currently, I am guessing the customer is not windowing the sampled data prior to calculation of the FFT, I would like to suggest the customer use a coherent frequency input if a rectangular window is used as this will accurately place energy into unique bins. I suspect upon application of a coherent input signal or integration of some kind of FFT window (such as Blackman or Hamming) that the energy levels will be properly located into unique bins and the levels of the harmonics will be reduced.

    Thanks, Chase