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DAC39J84 and maximum bandwidth

Richard Funk
Prodigy 30 points

Hello,

  I have an application requiring 2 signals with 1GHz bandwidth and I would like to know if I am interpreting Table 11 correctly.  I am assuming that the complex BW specified requires 2 DACs so I would need 8 lanes and 4 DACs operating in High density mode for a max BW of 1250MHz (first line of the table).

  Would I be able to use the complex mixer to adjust the center frequency of both signals to 1.5GHz or would I need to perform such a task external to the chip?

thank you

  • 0
    TI__Genius 12965 points
    Richard,

    Yes you will need to use that mode to get 1GHz of spectrum into the device. Are you looking at trying to generate 2 different signals of 1GHz BW? This would require 4 DACs for 2 complex paths into the DAC as you indicated.

    If my understanding is correct, you can use the NCO independently on each complex signal to move it from basband to high IF, however having an IF of 1.5G is out of the range of the DAC. In this mode the output of the DAC will not toggle faster than 2.5Gsps, this will limit how much you can move your 1GHz signal to the left or right considering your available BW is from -1250M to +1250M. Any frequencies outside of these boundaries will suffer significant SINX attenuation.

    Ken
  • 0 in reply to Ken C
    Prodigy 30 points
    Thank you for your reply. I am indeed looking to generate 2 different signals of 1GHz bandwidth.

    Please correct me if I have a misunderstanding of complex bandwidth. If I modulate the I/Q signals with a 500MHz local oscillator can I get a real bandwidth of 1GHz centered around 500MHz? Could I get a single tone in this setup at 200MHz or at 700MHz (depending on I and Q data)?

    regards
  • 0 in reply to Richard Funk
    TI__Genius 12965 points

    Hi Richard,

    The IQ signal combined can have a signal BW of 1GHz centered at baseband 0Hz.  For 4 DACs that is 2 IQ signals.  If you take 1 set of IQ signals and put them into a complex IQ quadrature modulator then you can have an output that is 1GHz wide at the LO frequency.

    However most analog IQ modulators in general do not have perfect quadrature balance or gain balance across the +/-500MHz signal BW.  This will mean that there will be some IQ imaging due to imperfect sideband cancellation centered at  the LO frequency which will create an image of your signal in the same location as your signal BW.

    Ken