ABSTRACT:   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.

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17 patents reference this one

Patent No. Inventor Issued Title 3401353 * Hughes 9 /1968   3163823 * Kellis et al. 12 /1964   3283079 * Dixon 11 /1966   3466399 * Dias 9 /1969     * some details unavailable FIRST CLAIM: Show all 11 claims 1. In a system including a source of composite signal having a reference component and an information modulated component, a demodulator for recovering the modulated information, comprising: phase detector means having reference input means and oscillator input means for generating at an output a control signal having a value dependent on the phase difference between signals at said input means; coupling means connected to said source for coupling said reference component to said reference input means of said phase detector; controlled oscillator means for generating an oscillatory signal having a frequency a multiple of the frequency of said reference component, the value of the control signal output of said phase detector means controlling the phase of said oscillatory signal; divider means for frequency dividing said oscillatory signal to produce a divided signal and an insertion signal; loop means connected to said divider means for coupling said divided signal to the oscillator input means of said phase detector means to produce a phase locked loop including said phase detector means, said controlled oscillator means, and said divider means; and detector means having inputs coupled to said source and said divider means for demodulation of said information modulated component by use of said RELATED U.S. APPLICATIONS: none FOREIGN APPLICATION PRIORITY DATA: none FOREIGN REFERENCES: none OTHER REFERENCES: none PRIMARY/ASSISTANT EXAMINERS: Brody; Alfred L.; ADDED TO DATABASE: Aug. 21, 1996