AD9957 modulation questions

I'm a microwave guy trying to figure out if I it makes more sense to use the AD9957 instead of a traditional Direct I/Q modulator.  I already plan a dual conversion solution so your app not AN-0996 makes sense to me.  The critical parameters that I must satisfy are dynamic range, modulation speed, low phase noise and spurious and channet to channel synchronization.  The applicatoin involves amplitude and phase modulating a mircowave signal essentially providing specific and varied envelope shapes and phases of a microwave carrier in the time domain. These shapes could be gaussian pulses, multilevel steps, etc.  The application is to excite Qbits used by researchers studying quantum computing.  My questions follow:

  1. Is the I/Q modulation bandwidth 250MHz?  I ask this because I have a requirement to create 4nsec amplitude modulated pulse widths as a minimum.  If not, what is the minimum time resolution for amplitude changes?
  2. I see the SFDR is -54dBc @400MHz.  I need the absolute best possible SFDR.  Is there a way to improve this number?
  3. As I understand this the app note I can get an IF output of up to about 400-450MHz (limited by DAC) and then upconvert to my desired final output frequency from there.  Is that correct?

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  • 0
    •  Analog Employees 
    on Oct 1, 2010 10:14 PM

    The maximum data rate of the AD9957 parallel port is 250Msps, which equates to an I/Q pair at a 125Msps rate. Hence, the maximum modulated bandwidth is 125MHz.

    The SFDR is limited primarily by harmonic distortion associated with the DAC. For narrow modulation bandwidths, frequency planning and subsequent bandpass filtering can result in improved spurious performance, but wideband modulation constrains frequency planning options.

    With a system clock of 1GHz, the AD9957 output can provide up to 125MHz modulation bandwidth. This puts the upper band edge 62.5MHz above the programmed carrier frequency. Assuming a 400MHz carrier, the upper band edge appears at 462.5MHz. This is only 37.5MHz shy of the 500MHz Nyquist frequency (1/2 the system clock frequency), which places a severe burden on the DAC reconstruction filter (37.5MHz to transition from passband to stopband). In any case, the modulated (and filtered) output can serve as the IF input signal to an RF upconverter, thereby translating the original baseband signal up to the final RF carrier frequency.

  • Hi SIR

    I want to use a QDUC & DAC up to maximum modulated bandwidth  150MHz.could you please give some suggestions (part number)?

    Regards

  • 0
    •  Analog Employees 
    on Aug 2, 2018 4:12 PM
    This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

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    EZ Admin