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DAC38RF82EVM: TSW14J56 and DAC38RFxx EVM GUI v2p0 support using CMODE3 with a Dac Clock Frequency of 2400 MHz

Kainalu Matthews
Prodigy 30 points
Part Number: DAC38RF82EVM

 I am using the DAC38RF82EVM with the TSW14J56 and am trying to use the onboard clock CMODE3. My issue is that I cannot seem to figure out why the DAC Clock Frequency of 2400 MHz is producing an error (the box where you enter the frequency just keeps flashing red), and I have changed the settings under the DAC MODE in the DAC38RFxx EVM GUI v2p0 multiple times with no fixes yet. 

Will you please assist me with this? My end goal is to have the following:

Test 1 using CMODE1:

DAC Clock Frequency of 2400 MHz, 2x Interpolation, other settings TBD (any input on this is appreciated)

Test 1 using CMODE3:

DAC Clock Frequency of 2400 MHz, 2x Interpolation, other settings TBD (any input on this is appreciated)

End goal:

At the output of J6 SMA Connector on DAC38RF82EVM board I have a spectrum analyzer (SA) connected. I would like to see a single tone on the SA at 2.95 GHz that I can sweep to 3.5 GHz by altering the NCO values.

Thanks!

  • 0
    TI__Genius 9695 points
    Hi Matthews,

    CMODE3 uses the DACs internal PLL which does not support 2.4GHz so you will have to provide an external clock (CMODE1). You can refer to the datasheet for the frequency range supported by the on-chip PLL.

    If your end goal is to generate a single tone from DAC, then you can use the DDS feature. If you are flexible with the sampling rate,you can also change it to a valid range for the on-chip PLL.
    Refer to section 7 of this document for more details about the DDS in DAC:
    www.ti.com/.../tidubo0.pdf

    Thanks,
    Eben.
  • 0 in reply to Ebenezer Dwobeng
    Prodigy 30 points

    Hi Dwobeng,

    Thank you for your response. I have another question regarding some additional tones seen on the spectrum analyzer when running the DAC38RF82EVM with the TSW14J56 using one of the examples given in the user guide. In the DAC38RF8xEVM user's guide they have you run through two different examples (one using external clock and another using the on-board PLL). At the very end, at around page 12, the guide explains that there should be two tones seen on the spectrum analyzer, which in fact I do see. However, I also see some other tones at sometimes higher and lower frequency bands than what was mentioned in the guide. Are these additional tones to be expected and in ideal cases filtered out with bandpass filters and what not?

    Thanks!

  • 0 in reply to Kainalu Matthews
    TI__Genius 9695 points
    Hi Matthews,

    You are probably referring to the DAC images in the higher Nyquist zones? This is expected as the output spectrum is only unique from DC to Fs/2 (or first Nyquist zone) and will repeat itself in higher Nyquist zones.

    Thanks,
    Eben.