FM Stereo Demodulator (Using a Phase Locked Loop) U.S. Patent 3,714,595
An FM stereo demodulator uses a phase locked loop to synchronize a 76 kHz oscillator with a received 19 kHz pilot. A two stage binary frequency divider is coupled in cascade with the oscillator to provide a symmetrical 38 kHz waveform for carrier reinsertion and a 19 kHz waveform for phase comparison. The received pilot is coupled to a phase detector in the phase locked loop through a high pass filter formed of passive components. A pilot detector uses EXCLUSIVE OR gates coupled to the frequency divider to develop a 19 kHz waveform in phase with the pilot for phase comparison with the received composite signal to determine the presence of the received pilot.
Denenberg, Jeffrey N. and Padgett, William J., "FM Stereo Demodulator (Using a Phase Locked Loop) U.S. Patent 3,714,595" (1973). Engineering Faculty Publications. 91.
Denenberg; Jeffrey N. , Padgett; William J., FM Stereo Demodulator (Using a Phase Locked Loop) U.S. Patent 3,714,595 issued January, 1973