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REFIN clock effect on Phase noise in ADF4159 PLL

Hi team,

Using ADF4159 PLL, I'm implementing a FMCW Radar application. Instead of onboard 100MHz clock source, I connected an external clock source of 100MHz whose part number is as follows "LNO 100 SG 58 C 12100M". I designed a loop filter that meets my RF out and waveform requirements in ADIsimPLL. I'll attach the settings screenshot at the end. So coming to point, I ran a simulation in ADIsimPLL to observe the phase noise produced in PLL at 10KHz offset. As you can notice in the right column, under reference menu, I selected phase noise as 'Point/Floor' because I selected custom reference clock option while designing.

So my questions are as follows,

  1. Could using external clock source as ref. signal affect the phase noise in PLL significantly? 
  2. I'm trying to achieve phase noise value as -106 dBm/Hz at 10KHz offset. Is is possible to achieve it with the settings I mentioned?
  3. ADIsimPLL is getting terminated whenever I'm selecting the external Ref. oscillator from Library menu. What could be the reason?
  4. Is there any way to edit or add the external Ref. frequency oscillator libraries in ADIsimPLL such as 'LNO 100'? 

  • 1) Yes, especially at the lower frequency offsets. If you go to the freq domain tab in ADIsimPLL you can see each of the noise components and the reference signal 's PN component will be shown as part of this.

    2) This will depend on operating frequency, PFD frequency and the quality of your reference but overall I do not think it will be possible to meet this with ADF4159. Especially since this is a ramping application where wide LBW/fast settle times are required. ADIsimPLL will help simulate all of this.

    3) Not sure about that one, are you getting an error message or is the software crashing? The ADisimPLL dev is active in this forum so perhaps he can help out

    4) At the top bar use Libraries>Reference Library editor. It also may be easier to create a new library/model for your chose reference

  • Thank you for the response. I it was helpful.