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DAC38J84: VC707 is used as the sine wave transmitter and DAC38J84 as the sine wave receiver

user6440552
Prodigy 160 points
Part Number: DAC38J84

I configured the VC707 and DAC38J84, and the indicator light showed that they were properly configured. I followed the Quick Start Page of DAC38J84EVM without tuning the other control buttons in DAC38J84EVM.

I connected the SMA output port to the oscilloscope and spectrum analyzer, and the results were shown as follows:

In oscilloscope, the yellow sine wave is the expected output value and the blue sine wave is the actual output value.

I don't know what causes this result. Does DAC38J84 turn on the mixing function by default?

How do I find out why?

Thank you for your help.

  • 0
    TI__Guru 71789 points

    Hi,

    All the DACs will generate Nyquist images due to aliasing. You will need to filter out the images through anti-aliasing filter. See below app note for description.

    The DAC38J84 GUI does not turn on mixing function by default. You will need to enable the feature yourself manually.

    -Kang

  • 0 in reply to Kang Hsia
    Prodigy 160 points

    Thank you very much for your help. I wish you every success in your work and a happy life.

  • 0 in reply to Kang Hsia
    Prodigy 160 points

    orry, I have one more question.

    When I send a 2.88mhz sine wave to the spectrometer, the display is as follows:

    In the figure above, the first pulse is the fundamental pulse, and the remaining pulses are harmonic pulses whose frequency is an integer multiple of the fundamental frequency.

    Why is the amplitude of the harmonic so large?Is this normal?

    What could be the cause?

    I look forward to your reply. Thank you.

  • 0 in reply to Kang Hsia
    Prodigy 160 points

    In addition, I found that the 2.88 MHz sine wave would be accompanied by a lot of interference signals after passing through the DAC, so the sine wave could not be generated correctly.

    However, if I input sine waves of 10 MHz and 20 MHz, the DAC will be able to generate sine waves of the corresponding frequencies correctly.

    The following two pictures show the correct generation of sine waves.

    In the first question, a 2.88mhz sine wave generation image can be found.

    That's all.

    Thank you.

  • 0 in reply to user6440552
    TI__Guru 71789 points

    Hello,

    The DAC38j84 itself can be DC coupled. However, the default EVM setup has the DAC38J84 transformer coupled. The transformer has a bandpass response with range of 10MHz to 1GHz. Therefore, below 10MHz, the distortion is most likely introduced by the balun.

    You may make changes to the DAC output to have DC coupled response. 

    See below app note for detail:

    -Kang