US3634626A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Noise-operated automatic stereo to monaural switch for fm receivers
Assignee: GTE Sylvania Inc
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Filing: 1970-04-06
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Granted: 1972-01-11
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Expires: 1990-04-06
Abstract
Abstract In an FM stereo receiver including an FM signal detector, a multiplex demodulating synchronous detector, and a circuit for coupling the output signal of the FM detector to one input of the synchronous detector and for separating a pilot signal from the FM detector output signal for application through a full-wave rectifier and transistor amplifier to provide a demodulating signal to a second input of the synchronous detector, a circuit for automatically switching from stereophonic to monaural operation in response to a predetermined noise level at the output of the FM signal detector. The switching circuit comprises a high-pass filter connected at the output of the FM signal detector, a transistor amplifier for processing the noise passed by the filter, a noise rectifier, and a voltage divider for applying the rectified noise signal as a base bias control voltage for the demodulating signal amplifier. The resistors comprising the voltage divider are selected to determine a noise level above which the demodulating signal amplifier is rendered nonconducting and below which that amplifier is biased to conduction. A manually operated switch in the base bias circuit of the noise amplifier provides means for inactivating the automatic switching circuit.
Inventors
- 👤 James Gordon Staley
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 03:50
CPC Classifications
H; H04; H04B; H04B1/00; H04B1/06; H04B1/16; H04B1/1646; H04B1/1653
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
264 words
In an FM Stereo receiver including an FM signal detector for detecting a signal including a first component at audiofrequencies and a second component amplitude modulated on a suppressed subcarrier wave, multiplex demodulating means having first and second inputs, means for processing an output signal from said detector and for coupling the processed output signal to the first input of said multiplex demodulating means, means for deriving a demodulating signal from said detector output signal and applying said demodulating signal to the second input of said multiplex demodulating means, said demodulating means being operative in response to signals applied to its first and second inputs to produce left and right audiofrequency signals, means for automatically switching said receiver from stereophonic to monaural operation in response to a predetermined noise level at the output of said signal detector comprising in combination: means for detecting the presence of noise at the output of said signal detector including a high-pass filter having a lowfrequency cutoff between the first and second components of the signal detected by said signal detector, means for converting the detected noise to a direct current signal representative of the magnitude of said noise, and means for applying said direct current signal as a control voltage for said means for deriving a demodulating signal, whereby said means for deriving a demodulating signal is enabled to provide said demodulating signal in response to a control voltage representative of noise below a predetermined level and is disabled to cut off the demodulating signal in response to a control voltage representative of noise above said predetermined level.
Claim 2
Dependent Claim
264 words
In an FM Stereo receiver including an FM signal detector for detecting a signal including a first component at audiofrequencies and a second component amplitude modulated on a suppressed subcarrier wave, multiplex demodulating means having first and second inputs, means for processing an output signal from said detector and for coupling the processed output signal to the first input of said multiplex demodulating means, means for deriving a demodulating signal from said detector output signal and applying said demodulating signal to the second input of said multiplex demodulating means, said demodulating means being operative in response to signals applied to its first and second inputs to produce left and right audiofrequency signals, means for automatically switching said receiver from stereophonic to monaural operation in response to a predetermined noise level at the output of said signal detector comprising in combination: means for detecting the presence of noise at the output of said signal detector including a high-pass filter having a lowfrequency cutoff between the first and second components of the signal detected by said signal detector, means for converting the detected noise to a direct current signal representative of the magnitude of said noise, and means for applying said direct current signal as a control voltage for said means for deriving a demodulating signal, whereby said means for deriving a demodulating signal is enabled to provide said demodulating signal in response to a control voltage representative of noise below a predetermined level and is disabled to cut off the demodulating signal in response to a control voltage representative of noise above said predetermined level.
Claim 3
Dependent Claim
26 words
The combination of claim 1 wherein said high-pass filter is connected to the output of said signal detector and said low-frequency cutoff is approximately 20 kHz.
Claim 4
Dependent Claim
53 words
The combination of claim 1 wherein said means for detecting the presence of noise further includes a first amplifier having an input terminal connected to the output of said high-pass filter, and an output terminal connected to a load across which the detected noise develops for subsequent conversion to a direct current signal.
Claim 5
Dependent Claim
29 words
The combination of claim 3 wherein said means for converting the detected noise to a direct current signal comprises a rectifier coupled to the output of said first amplifier.
Claim 6
Dependent Claim
40 words
The combination of claim 4 further including means for biasing said first amplifier including a switch for enabling selective reverse biasing of said first amplifier to thereby inactivate said means for automatically switching said receiver from stereophonic to monaural operation.
Claim 7
Dependent Claim
102 words
The combination of claim 5 wherein said first amplifier comprises a transistor having base, emitter and collector electrodes, said collector being connected to said load and coupled to said rectifier, said emitter being connected through first resistance means to a first source of potential, and said base being connected to the output of said high-pass filter, and wherein said means for biasing said first amplifier includes second resistance means connected between said first source of potential and said base electrode, and third resistance means and said switch serially connected between the base of said first amplifier and a second source of potential.
Claim 8
Dependent Claim
93 words
The combination of claim 4 wherein said means for deriving a demodulating signal includes a second amplifier for coupling said demodulating signal to the second input of said multiplex demodulating means, and said direct current noise signal is applied as a bias control voltage for said second amplifier, whereby said second amplifier is biased to the conducting state in response to a bias voltage representative of detected noise below a predetermined level and said second amplifier is rendered nonconducting in response to a bias voltage representatiVe of detected noise above said predetermined level.
Claim 9
Dependent Claim
98 words
The combination of claim 7 wherein said means for applying said direct current noise signal as a bias control voltage for said second amplifier comprises a voltage divider having an input terminal connected to the output of said rectifier, a reference terminal connected to a first source of potential and an output terminal connected to the input terminal of said second amplifier, said predetermined noise level above which said second amplifier is rendered nonconducting and below which said second amplifier is biased to conduction being substantially determined by the selected values of the elements comprising said voltage divider.
Claim 10
Dependent Claim
138 words
The combination of claim 8 wherein said second amplifier comprises a transistor having base, emitter and collector electrodes, said emitter being connected through first resistance means to a second source of potential, said collector being coupled to the second input of said multiplex demodulating means, and said derived demodulating signal being coupled to the base of said second amplifier, and wherein said voltage divider comprises second resistance means connected between the output of said rectifier and the base of said second amplifier, and third resistance means connected between the base of said second amplifier and said first source of potential, the junction of said second and said first source of potential, the junction of said second and third resistance means being the output of said voltage divider and said base electrode being the input of said second amplifier.
Claim 11
Dependent Claim
56 words
The combination of claim 8 wherein said first amplifier comprises a transistor having base, emitter and collector electrodes, said collector being connected to said load and coupled to said rectifier, said emitter being connected through first resistance means to a second source of potential, and said base being connected to the output of said high-pass filter.
Claim 12
Dependent Claim
29 words
The combination of claim 4 wherein said rectifier is a half-wave rectifier comprising a diode coupled between the output terminal of said first amplifier and a source of potential.
Claim 13
Dependent Claim
31 words
The combination of claim 3 wherein said load across which the detected noise develops comprises a choke connected between the output terminal of an amplifier and said first source of potential.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1975-01-10 | 1975-07-12 | 1976-01-11 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-01-10 | 1979-07-12 | 1980-01-11 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-01-10 | 1983-07-12 | 1984-01-11 | $7700.00 | Window Closed / Lapsed |