PLL is a good way to do FM demodulation in analogue domain ,A PLL system can be used to implement an FM demodulator. When a PLL is locked on an FM signal, the VCO tracks the instantaneous frequency of that signal. Since the VCO output tracks the FM signal, and the VCO input voltage is proportional to the VCO output frequency, then the VCO input will be equal to the demodulated signal.

see more http://freecircuitdiagram2009/09/17/pll-fm-demodulator/ (circuit diagram and more)

A disadvantage of the PLL technique is that it trickier to get it right compared to a discriminator. An advantage is that the threshold (knee in the SNRout vs SNRin curve) can be lower than for a discriminator


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http://digitalsignallabsDigradio.pdf