Sprague Electric Company

Allegro Microsystems, LLC

Thomas L Field

Oliver L Richards, Jr

An FM stereo decoding and separating circuit has an (AM) demodulator multiplier to which is connected the FM stereo composite signal and a signal of dominant frequency equal to and in phase (0.degree.) with respect to the pilot signal for retrieving the L-R signal from the composite signal. This demodulator also has a blend control circuit for diminishing the magnitude of the L-R signal as a function of a blend control voltage that may be applied to the input of the blend control circuit. The decoding circuit also includes a special multiplier to which is connected the FM stereo composite signal and a signal of dominant frequency equal to that of the 38 KHz subcarrier but shifted 90.degree. with respect to the phase of the pilot, for AM demodulating the composite signal with respect to the subcarrier, and a low pass filter connected to the special mixer output for producing an output containing only demodulated noise originally appearing about the pilot in the composite signal, and a rectifier connected to the filter output and to the blend-control input for effecting blending to a degree directly related to the amount of noise in a narrow band about the pilot in the composite signal.

Blend-on-noise stereo decoder

A stereo FM radio transmission system with FMX transmission and reception capability includes a transmitter that transmits a pilot-coherent FMX-tone indicator signal at a frequency of an exact integer submultiple of the pilot frequency. The system also includes a receiver for dividing the frequency of the received pilot signal by various submultiples, nearly equal to the exact submultiple, toward quickly finding a match in phase of the received tone and the received pilot and finally dividing the pilot by the exact submultiple to establish an operational lock mode of the receiver tone detector to keep-on an FMX-indicator lamp, to change the receiver decoder to an FMX-reception operating mode and to stand by to quickly recapture the pilot and FMX-tone in the event of multipath or other interfering signals.

FM stereo tone detector

An integrated circuit relaxation oscillator having all NPN transistors includes three interconnected differential transistor pairs with an externally connected parallel R-C timing circuit. Each of the transistor pairs has a separate current source that compensates for temperature changes in the components of the corresponding transistor-pair circuits.

Growing community of inventors

Rutland, MA, United States of America

Thomas L Field