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AD9959 Output analysis with Spectrum Analyzer

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Product Number: AD9959

Hi, 

I passed the output from the DDS AD9959 through a spectrum analyzer. Even though the frequency is less than 0.5 of the clock frequency (Nyquist frequency), why am I observing multiple frequencies in the spectrum analyzer? The input clock frequency is 25 MHz, the PLL multiplier varies from 16 to 20

Regards

Prerna Baranwal



added multiplier for better clarity
[edited by: pbar at 7:54 AM (GMT -4) on 19 Aug 2022]
Parents
  • HI Prerna,

    The multiple frequencies that are present in your spectrum analyzer are spurious signals. Any non harmonically related is a spurious signal. Any nonlinear connections in the RF field can cause mixing of signals and/or harmonics, corrosion, dissimilar metals and such can cause spurious signals.

    This simulation tool will help you give the optimal performance expectation for the AD9959. 

    Here's an example simulation of AD9959 setting which DDS component with their corresponding multiplier, clock input, system clock, and target output frequency. 

    You can also hover the cursor to determine the expected spur in each frequency range. For example as shown in the picture below, you are expected to get a spur of -96dB at 400MHz. 

    All the best,

    Jules

Reply
  • HI Prerna,

    The multiple frequencies that are present in your spectrum analyzer are spurious signals. Any non harmonically related is a spurious signal. Any nonlinear connections in the RF field can cause mixing of signals and/or harmonics, corrosion, dissimilar metals and such can cause spurious signals.

    This simulation tool will help you give the optimal performance expectation for the AD9959. 

    Here's an example simulation of AD9959 setting which DDS component with their corresponding multiplier, clock input, system clock, and target output frequency. 

    You can also hover the cursor to determine the expected spur in each frequency range. For example as shown in the picture below, you are expected to get a spur of -96dB at 400MHz. 

    All the best,

    Jules

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