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DAC34sh84 output problem

pramod kumar1
Prodigy 10 points

Hi

I am using  DAC34SH84EVM  board to convert the digital signal (sine wave 375 k hz) generated from the FPGA in analog,and then am modulating this signal from IQ - modulator .

When we are taking differential (J6 and J7) output from DAC to IQ modulator then we are getting only carrier wave at the output of IQ modulator, on the other hand when we are taking only J6 or J7 then we are getting a wave modulated wave (base band that modulated wave is 96.4 M hz) that is  unexpected.

we have used 96.4M hz signal at in DAC (internally ) but it is not supposed to be there on the output port. 

PLease help , what could be the problem

Thanks

Pramod

  • 0
    TI__Guru 69994 points

    Pradmod,

    The connection of the DAC output to connector J6 or J7 is through the transformer path. The default ADT4-1T transformer allows the DAC's output to convert from differential to single-ended. The transformer response is a bandpass response from 2MHz to 775MHz. It is possible that the output of the transformer attenuates the signal at 375kHz. 

    The DAC is sampling at 96.4MSPS. There will be a second Nyquist image centered around 96.4MHz. These images are within the passband of the transformer, thus you are able to observe the image but not the fundamental.

    -Kang