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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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  • I'm bothered that the level changes every time you reprogram the chip.

    I don't know which loop filter you're using, but if I use the default for the AD9516-3, and set the charge pump current to its minimum value (0.6mA), I get a closed loop BW of 140 kHz, 50 deg of phase margin, and CP spur that's -159 dBc,

    This filter is: (from the CP pin to the LF pin:

    1st shunt C:     1.2 nF

    Series R-C in parallel with the first shunt C: 750 ohms and 0.01uF

    Final shunt C: 150 pF.

    Are you sure you don't have any dynamic signals activated on the status pins?

    Also, which input reference mode are you using? Could it be that you have a CMOS ref input that's coupling through to the outputs?

    -Paul Kern

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  • I'm bothered that the level changes every time you reprogram the chip.

    I don't know which loop filter you're using, but if I use the default for the AD9516-3, and set the charge pump current to its minimum value (0.6mA), I get a closed loop BW of 140 kHz, 50 deg of phase margin, and CP spur that's -159 dBc,

    This filter is: (from the CP pin to the LF pin:

    1st shunt C:     1.2 nF

    Series R-C in parallel with the first shunt C: 750 ohms and 0.01uF

    Final shunt C: 150 pF.

    Are you sure you don't have any dynamic signals activated on the status pins?

    Also, which input reference mode are you using? Could it be that you have a CMOS ref input that's coupling through to the outputs?

    -Paul Kern

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