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AD9516 reference spurs

Dear All,

I am using the AD9516-0 to clock the AD9122.

  • reference frequency = 122.88MHz
  • DAC sampling = 983.04MHz
  • PFD frequency = 61.44MHz

Around the 983.04MHz, I can observe a lot of spurs every 61.44MHz.

What is the maximum reference spurious level for the AD9516?

Thank you

Chris

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  • Hi Christophe,

    > What is the maximum reference spurious level for the AD9516?

    There is no maximum. You could have enormous spurs if you set the loop BW high enough and the PFD low enough.

    That said, one very easy way to get charge pump spurs is to have an extremely high loop BW. Therefore, reducing the charge pump current to drop the loop BW is one way to help fix the issue. By the way, what is the spur level?

    One way to get bad spurs is to solder new components down in the loop filter and not clean and wash the flux off the components.

    Another source of spurs is programming REFMON, LD, or STATUS to a dynamic signal like the R divider output.

    -Paul Kern

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  • Hi Christophe,

    > What is the maximum reference spurious level for the AD9516?

    There is no maximum. You could have enormous spurs if you set the loop BW high enough and the PFD low enough.

    That said, one very easy way to get charge pump spurs is to have an extremely high loop BW. Therefore, reducing the charge pump current to drop the loop BW is one way to help fix the issue. By the way, what is the spur level?

    One way to get bad spurs is to solder new components down in the loop filter and not clean and wash the flux off the components.

    Another source of spurs is programming REFMON, LD, or STATUS to a dynamic signal like the R divider output.

    -Paul Kern

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