PLL with integrated VCO

Question

We want to use ADF4360-8 as FM Modulator in frequency range 87.5 MHz to 108MHz with deviation 100KHz( max). Value of L1 & L2 will change from 226nH to 348nH . Can we use variable inductor to cover entire band? 
 For Audio signal input can we use a unity gain buffer (TL071) before VTune pin? 
 Please suggest

ADIApproved · Accepted Answer

Hi, 
 The inductor value that is calculated with the formula given in the datasheet gives the VCO center frequency. The center of your frequency band is 97.75 MHz. Equation gives ~285nH inductor value for 97.75 MHz center frequency. The only problem with using this inductor values is that VCO coverage ratio is specified as 1.2 (fmax/fmin). That being said min/max frequency that you can achieve with a single inductor value is 88.75Mz to 106.75 MHz. You can try to use variable inductor and change the value slightly to cover lower and upper ends. 
 For FM modulation you can check the below post and the ones given in that post. 
 fm modulator - Q&A - RF and Microwave - EngineerZone (analog.com) 
 Regards, 
 Kudret)

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PLL with integrated VCO