AD9164 - This DAC handles complex signal processing. In figure 120 of the datasheet what drives the actual DAC, OUT_I or OUT_Q? Could it be one or the other, or the sum? If it is OUT_I, why bother developing OUT_Q?

Figure 120 shows NCO Modulator Block Diagram.

This has the expected structure, and indicates 2 outputs, OUT_I and OUT_Q.

However there is only one DAC output port.

Should I assume OUT_I is converted to analog?

It seems OUT_Q is a no connect. But why is OUT_Q developed?

I'll note that OUT_I and OUT_Q are quadrature modulated on the same carrier, so they could be combined before conversion to analog.

The datasheet needs some additional details in this output area.

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    •  Analog Employees 
    on May 3, 2017 10:35 PM

    The NCO is a complex modulator to enable image (or sideband) rejection of digital mixing images of the signal coming into the modulator. The combination of complex input plus the full complex NCO/modulator serves to create a single sideband (SSB) upconverter.  Because there is only one DAC core on the device, there is no need for the complex output and thus the real portion is routed to the DAC core and the quadrature portion is discarded.

  • Hi,

    attached you will find two measurements performed in the following ways:

    Figure 1: JESD mode, FDAC=5 GHz, MIX-Mode, Fout=2.7 GHz and FIR85 on;





    Figure 2 NCO, FDAC=5 GHz, MIX-Mode,
    Fout=2.7 GHz and FIR85 on.



    With NCO, the image frequency at 2.3 GHz (in first Nyquist zone) is more reduced than
    that obtained with JESD mode.

    Does this difference depend on the fact that NCO being a complex SSB modulator that rejects 
    the image frequency?

    Thank you in advance.
    Matteo Ricci
Reply
  • Hi,

    attached you will find two measurements performed in the following ways:

    Figure 1: JESD mode, FDAC=5 GHz, MIX-Mode, Fout=2.7 GHz and FIR85 on;





    Figure 2 NCO, FDAC=5 GHz, MIX-Mode,
    Fout=2.7 GHz and FIR85 on.



    With NCO, the image frequency at 2.3 GHz (in first Nyquist zone) is more reduced than
    that obtained with JESD mode.

    Does this difference depend on the fact that NCO being a complex SSB modulator that rejects 
    the image frequency?

    Thank you in advance.
    Matteo Ricci
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