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ADC12J4000EVM: Ripple in ADC measurements

Kyle Nathan
Prodigy 30 points
Part Number: ADC12J4000EVM
Other Parts Discussed in Thread: ADC12J4000, TRF3765

Hi, I am using an ADC12j4000 along with a tswj1456EVM to capture some RF measurements. I have a signal generator generating a 1GHz signal and when looking at the data I am seeing large amounts of ripple in the measurements (around 2.7dB). Is this a known issue or am I doing something incorrectly? Is 1GHz too high of a signal to put into the ADC12J4000 EVM? The measurements I have below are CW signals but I see the exact some behavior in pulsed measurements as well. One thing I found strange is 1GHz is  very rippley, but 900MHz is not. In fact, multiples of 300MHz look ok. Is there anything that I can do to mitigate this ripple? I have done this with a narrow bandpass filter as well but still see the same results.

Thanks for your time,

Kyle

                 1GHz CW signal                                         900MHz CW signal

        

  • 0
    TI__Guru* 91947 points

    Kyle,

    This is not to be expected. What mode and sample rate are you using for the ADC? What Rev is the EVM? Does this board have the TRF3765 on it for U4?

    Regards,

    Jim 

  • +1 in reply to jim s
    Prodigy 30 points

    Jim,

    We used the default mode and sample rate when the software booted up which is bypass mode;DDR and 4GSPS. I figured out late last night that when I changed the sampling rate to something lower, 2.7GSPS, the ripple went away. I'm not sure exactly what was wrong but the current idea is we were seeing some sort of phase drift between the ADC and the signal generator since it was sampling at an exact multiple of the signal generator. It's not we what expected, but the issue is fixed now.

    Thanks,

    Kyle