Demodulation circuits of FM stereophonic receivers

Details Demodulation circuits of FM stereophonic receivers Demodulation circuits of FM stereophonic receivers

1977-12-19

1979-08-14

Claffy, Kathleen H.

Demodulators

Amplitude modulation demodulator

Having specific distortion, noise or other interference...

329124, H04H 500

Patent

active

041646240

ABSTRACT:
A demodulation circuit for an FM stereo receiver is constructed to invert the FM stereo composite signal by an inverting amplifier and then to supply the inverted signal to a switching circuit for producing demodulated left and right signals. The composite signal is applied to a phase-locked loop circuit for applying a 38 kHz switching signal to the switching circuit. A 19 kHz signal produced by the phase-locked loop circuit is converted into a sine wave signal by a waveform converting circuit. The sine wave signal is converted into a direct current signal which is applied to one input of a level comparator having the other input connected to receive the 19 kHz pilot signal extracted from the composite signal. The output of the comparator is sent to a level control circuit which controls the level of the signal supplied to the input of the inverting amplifier. Accordingly, the pilot signal is canceled in the signal sent to the switching circuit. The left and right output terminals of the switching circuit are connected to the input of the inverting amplifier through negative feedback circuits.

REFERENCES:
patent: 3949314 (1976-04-01), Machida
patent: 4047116 (1977-09-01), Ogita
patent: 4069398 (1978-01-01), Fujie
patent: 4076963 (1978-02-01), Fujie et al.

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