who to use phase detector as a GFSK demodulator

hi , everyone
Is there any method to make phase detector output as a FSK demodulated signal?
thx advance

Lots. With analog phase detector, you basically split the signal into two paths. One path goes to one port of the phase detector. the other path goes thru some frequency dependent structure (LC resonator, coaxial delay line, etc) to impart a phase shift that changes with frequency. You send that phase shifted 2nd signal to the other port of the phase detector. Then Vout is proporitional to Frequency in. There are often criteria that have to be met, such as 90 degree quadrature.

Digital phase detectors employ the same idea, one path has a frequency dependent time delay, and you look to see if port 1 rising edge is in front of or behind port 2 rising edge.