Electrical audio signal processing systems and devices – Binaural and stereophonic – Broadcast or multiplex stereo
Patent
1984-02-09
1985-10-29
Isen, Forester W.
Electrical audio signal processing systems and devices
Binaural and stereophonic
Broadcast or multiplex stereo
329103, 329110, 329137, H04H 500
Patent
active
045504245
ABSTRACT:
An AM stereo receiver decoder is shown. An AM detector produces the stereo L+R signal and a PM detector produces the L-R signal. The PM detector is created from a conventional FM detector that employs an input limiter driving a balanced multiplier. The limiter also drives a tuned circuit which provides quadrature drive to the multiplier. An integrator connected to the FM detector converts the response to a PM decoder. A large value inductor is simulated to appear across the integrator so as to create a low modulation frequency resonance at a subaudible frequency thereby providing a controlled pilot tone response. The inductor is simulated by the action of a first G.sub.m amplifier driving a capacitor which drives a second G.sub.m amplifier having an output coupled back to the input of the first G.sub.m amplifier. The capacitor is switched by means of a series connected switch that disconnects the capacitor when the AM exceeds a predetermined value. This means that when the L+R negative modulation peaks exceed some predetermined value the simulated inductor acts to short out the L-R signal channel. Since the switch is in series with the capacitor, the charge cannot vary when the switch is open, thereby creating a sample and hold action.
REFERENCES:
patent: 4362999 (1982-12-01), Sauer
patent: 4379208 (1983-04-01), Isbell et al.
patent: 4430747 (1984-02-01), Streeter
patent: 4479234 (1984-10-01), Yokoya et al.
Cheng Fred T. J.
Sauer Don R.
Isen Forester W.
National Semiconductor Corporation
Pollock Michael J.
Winters Paul J.
Woodward Gail W.
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