FM modulator with PLL [hlp]

simply , if u have a frequency synthesizer the output is equal to the N*Fref , and u change the Fref , the output frequency changes as well , and u have frequency modulated signal and the modulating signal is the Fref

but if u need the most simple FM moduator is just a VCO

khouly

This patent describes how to do it:

pll frequency synthesizer,will works as a frequency modulator.
in place of tunning voltage,give information signal.according to the information signal strength the output frequency will vary.