ADF4360-9 spurs -55 dbc

I use ADF4360-9 as a heterodyne at freqs 125...140 MHz (step and PFD freq = 25 kHz).

Ref = 55700 kHz  (R = 2228),shematic as recommended in ADIsimPLL, both inductors on pins 9,10 = 136 nH (100 nH + 36 nH LQW18A), Loop filter CPP_2C.

Spurs at freqs 139125...139450 kHz (N = 5565...5578) are about -55 dbc.

At 139125 spurs are on 250 kHz from carrier (both sides),

At 139450 spurs are on 425 kHz from carrier (both sides).

All frequencies outside the band 139125...139450 are OK, spurs < 70 dbc.

Can anybody test this situation on EvBoard?

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  • 0
    •  Analog Employees 
    on Jul 28, 2015 6:38 PM

    Hello Vladimir,

    Reference spectral purity requirement will depend on the application as the noise of the reference inside the loop is not attenuated, but is well attenuated outside the loop bandwidth. We dont spec it.

    Check the spectral purity of your reference?( DIVOUT from the other ADF4360-9).

    It would help if you sent me your .pll file that you used for both ADF4360-9 as well as your register writes, also a spectral plot of your ADF4360-9 reference, as well as your ADF4360-9 heterodyne

    Regards,

    Brigid.

Reply
  • 0
    •  Analog Employees 
    on Jul 28, 2015 6:38 PM

    Hello Vladimir,

    Reference spectral purity requirement will depend on the application as the noise of the reference inside the loop is not attenuated, but is well attenuated outside the loop bandwidth. We dont spec it.

    Check the spectral purity of your reference?( DIVOUT from the other ADF4360-9).

    It would help if you sent me your .pll file that you used for both ADF4360-9 as well as your register writes, also a spectral plot of your ADF4360-9 reference, as well as your ADF4360-9 heterodyne

    Regards,

    Brigid.

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