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DAC38RF82: Use of MultiDUC with two I/Q streams

ILIAS ALEXOPOULOS
Prodigy 60 points
Part Number: DAC38RF82

Tool/software:

Hello,

We want to confirm a potential configuration for DAC38RF82 for our application.

We would like to output two I/Q streams from an FPGA, and they need to avoid overlap at the RF frequency.

Let's say we have two I/Q streams with a bandwidth of 100MHz, we need to space them at the output accordingly (side-by-side for example).

Paramaters:

  • DAC Clock Frequency: 3300 MHz
  • DAC Mode: Single DAC A
  • IQ Pairs: 2
  • JESD204 Lanes: 4
  • Interpolation: 24x
  • SERDES Rate: 2750MHz

RF Outputs:

  • Output1: 1900 MHz [bandwidth: 1850-1950]
  • Output2: 2100 MHz [bandwidth: 2050-2150]

Would the following setup work?

I am also concerned about the 3300MHz DAC clock which is too close to the 2GHz center frequency. Would this be a problem (by Nyquist terms or distortions)?

I cannot use 6600 MHz as the SERDES lane rate gets to 5500 MHz which is above the DAC limits?

Thanks in advance,

Ilias

  • 0
    TI__Expert 3410 points

    Hey Ilias, 

    Running the DAC at 3300MHz would indeed be problematic if you want to have center frequencies at ~2GHz. Nyquist boundaries are defined at every multiple of FS/2 so your first Nyquist zone ends at 3300MHz/2 = 1650MHz. If you wanted to put spectral energy at 2.2GHz you would actually put it at 1,100MHz and high pass filter it to remove the 1st Nyquist component. You would have reduced power in the second Nyquist zone as well due to the SINC response of a sample and hold DAC. The 1,900MHz tone would be even harder as it would have a 1st Nyquist image at 1,400MHz. 

    Ideally you would want to run the DAC at a faster update rate. As you are already running at the highest interpolation this would also imply running the SERDES at a faster rate. Something else to consider, the DAC does have a built in PLL which would allow you to run the DAC at ~6Ghz or ~9GHz with a lower frequency reference as well. 

    Regards, 

    Matt

  • 0 in reply to Matthew Kramer
    Prodigy 60 points

    Thank you Matt,
    you are correct, just wanted to be sure. Is there any limit of the SERDES frequency? Can we go up to 7500MHz as per the tool settings for 9GHz?
    Also are the settings on the MultiDUC correct for this case (dual output bands)?

  • +1 in reply to ILIAS ALEXOPOULOS
    TI__Expert 3410 points

    Hey Ilias, 

    Yes you can run the SERDES at 7.5GSPS no issue in this mode. I just verified this in the GUI just to be sure. 

    LMFS = 442 7.5GSPS SERDES rate. 

    Regards, 

    Matt