US3719892A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Transistor radio receiver employing an improved squelch circuit
Assignee: Hitachi Ltd
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Filing: 1970-08-04
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Granted: 1973-03-06
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Expires: 1990-08-04
Abstract
Abstract In a transistor radio receiver, two time constant resistors, one of which is a variable resistor, are connected in series via a signal detection circuit to a power source and a time constant capacitor is connected to the junction point of the two resistors to form therewith an automatic gain control voltage generating circuit, and a squelch transistor whose base is connected to the movable terminal of a potentiometer, so that the squelch transistor which is normally biased to be conductive is quickly cut-off in response to even a weak signal input to the receiver.
Inventors
- 👤 S Yamazaki
- 👤 M Kaneda
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-04 04:15
CPC Classifications
H; H03; H03G; H03G3/00; H03G3/20; H03G3/30; H03G3/34; H03G3/341
Claims Analysis
Total Claims: 15
Claim 1
Independent Claim
395 words
In a radio receiver having a power source, a gain controllable intermediate frequency amplifying circuit for operatingly amplifying an intermediate frequency signal containing an audio frequency signal to be detected, a signal detection circuit connected to the output of said intermediate frequency amplifying circuit and including at least a detection diode, a resistor and a capacitor connected together in parallel, and an intermediate frequency transformer having a secondary winding connected in series with said diode across said parallel circuit of said resistor and said capacitor and a primary winding connected to the output of said intermediate frequency amplifying circuit, so that the audio frequency signal is separated from the intermediate frequency signal and appears across said parallel circuit, a time constant circuit including at least a potentiometer having an adjustable terminal and a time constant resistor connected in series with said signal detection circuit to said power source so that the audio frequency signal appearing across the parallel circuit inversely varies the potential at the junction between said potentiometer and said time constant resistor, and a time constant capacitor connected to said junction to provide a time constant, so that an automatic gain control voltage variable in response to the amplitude of the audio frequency signal thus separated is obtained across said time constant capacitor, said junction being connected to the input of said amplifying circuit, the amplification factor of which is inversely controlled by application thereto of the automatic gain control voltage, so that its output is successively transferred to said detection circuit, and an audio frequency amplifying circuit connected to said detection circuit for amplifying the audio frequency signal output of the detection circuit, an improved squelch circuit comprising: a squelch transistor; a biasing circuit including connecting means for connecting the adjustable terminal of said potentiometer to tHe base of said squelch transistor for providing between the base and emitter of said squelch transistor a bias voltage, which bias voltage is so determined by adjustment of said potentiometer that the conductivity state of the squelch transistor is provided only during a non-signal input condition of the receiver; and means for varying the bias voltage of the audio frequency amplifying circuit in response to change in the conductivity state of the squelch transistor so that the audio frequency amplifying circuit is conducting only when an audio frequency signal is detected by the detection circuit.
Claim 2
Dependent Claim
395 words
In a radio receiver having a power source, a gain controllable intermediate frequency amplifying circuit for operatingly amplifying an intermediate frequency signal containing an audio frequency signal to be detected, a signal detection circuit connected to the output of said intermediate frequency amplifying circuit and including at least a detection diode, a resistor and a capacitor connected together in parallel, and an intermediate frequency transformer having a secondary winding connected in series with said diode across said parallel circuit of said resistor and said capacitor and a primary winding connected to the output of said intermediate frequency amplifying circuit, so that the audio frequency signal is separated from the intermediate frequency signal and appears across said parallel circuit, a time constant circuit including at least a potentiometer having an adjustable terminal and a time constant resistor connected in series with said signal detection circuit to said power source so that the audio frequency signal appearing across the parallel circuit inversely varies the potential at the junction between said potentiometer and said time constant resistor, and a time constant capacitor connected to said junction to provide a time constant, so that an automatic gain control voltage variable in response to the amplitude of the audio frequency signal thus separated is obtained across said time constant capacitor, said junction being connected to the input of said amplifying circuit, the amplification factor of which is inversely controlled by application thereto of the automatic gain control voltage, so that its output is successively transferred to said detection circuit, and an audio frequency amplifying circuit connected to said detection circuit for amplifying the audio frequency signal output of the detection circuit, an improved squelch circuit comprising: a squelch transistor; a biasing circuit including connecting means for connecting the adjustable terminal of said potentiometer to tHe base of said squelch transistor for providing between the base and emitter of said squelch transistor a bias voltage, which bias voltage is so determined by adjustment of said potentiometer that the conductivity state of the squelch transistor is provided only during a non-signal input condition of the receiver; and means for varying the bias voltage of the audio frequency amplifying circuit in response to change in the conductivity state of the squelch transistor so that the audio frequency amplifying circuit is conducting only when an audio frequency signal is detected by the detection circuit.
Claim 3
Dependent Claim
395 words
In a radio receiver having a power source, a gain controllable intermediate frequency amplifying circuit for operatingly amplifying an intermediate frequency signal containing an audio frequency signal to be detected, a signal detection circuit connected to the output of said intermediate frequency amplifying circuit and including at least a detection diode, a resistor and a capacitor connected together in parallel, and an intermediate frequency transformer having a secondary winding connected in series with said diode across said parallel circuit of said resistor and said capacitor and a primary winding connected to the output of said intermediate frequency amplifying circuit, so that the audio frequency signal is separated from the intermediate frequency signal and appears across said parallel circuit, a time constant circuit including at least a potentiometer having an adjustable terminal and a time constant resistor connected in series with said signal detection circuit to said power source so that the audio frequency signal appearing across the parallel circuit inversely varies the potential at the junction between said potentiometer and said time constant resistor, and a time constant capacitor connected to said junction to provide a time constant, so that an automatic gain control voltage variable in response to the amplitude of the audio frequency signal thus separated is obtained across said time constant capacitor, said junction being connected to the input of said amplifying circuit, the amplification factor of which is inversely controlled by application thereto of the automatic gain control voltage, so that its output is successively transferred to said detection circuit, and an audio frequency amplifying circuit connected to said detection circuit for amplifying the audio frequency signal output of the detection circuit, an improved squelch circuit comprising: a squelch transistor; a biasing circuit including connecting means for connecting the adjustable terminal of said potentiometer to tHe base of said squelch transistor for providing between the base and emitter of said squelch transistor a bias voltage, which bias voltage is so determined by adjustment of said potentiometer that the conductivity state of the squelch transistor is provided only during a non-signal input condition of the receiver; and means for varying the bias voltage of the audio frequency amplifying circuit in response to change in the conductivity state of the squelch transistor so that the audio frequency amplifying circuit is conducting only when an audio frequency signal is detected by the detection circuit.
Claim 4
Dependent Claim
395 words
In a radio receiver having a power source, a gain controllable intermediate frequency amplifying circuit for operatingly amplifying an intermediate frequency signal containing an audio frequency signal to be detected, a signal detection circuit connected to the output of said intermediate frequency amplifying circuit and including at least a detection diode, a resistor and a capacitor connected together in parallel, and an intermediate frequency transformer having a secondary winding connected in series with said diode across said parallel circuit of said resistor and said capacitor and a primary winding connected to the output of said intermediate frequency amplifying circuit, so that the audio frequency signal is separated from the intermediate frequency signal and appears across said parallel circuit, a time constant circuit including at least a potentiometer having an adjustable terminal and a time constant resistor connected in series with said signal detection circuit to said power source so that the audio frequency signal appearing across the parallel circuit inversely varies the potential at the junction between said potentiometer and said time constant resistor, and a time constant capacitor connected to said junction to provide a time constant, so that an automatic gain control voltage variable in response to the amplitude of the audio frequency signal thus separated is obtained across said time constant capacitor, said junction being connected to the input of said amplifying circuit, the amplification factor of which is inversely controlled by application thereto of the automatic gain control voltage, so that its output is successively transferred to said detection circuit, and an audio frequency amplifying circuit connected to said detection circuit for amplifying the audio frequency signal output of the detection circuit, an improved squelch circuit comprising: a squelch transistor; a biasing circuit including connecting means for connecting the adjustable terminal of said potentiometer to tHe base of said squelch transistor for providing between the base and emitter of said squelch transistor a bias voltage, which bias voltage is so determined by adjustment of said potentiometer that the conductivity state of the squelch transistor is provided only during a non-signal input condition of the receiver; and means for varying the bias voltage of the audio frequency amplifying circuit in response to change in the conductivity state of the squelch transistor so that the audio frequency amplifying circuit is conducting only when an audio frequency signal is detected by the detection circuit.
Claim 5
Dependent Claim
46 words
The combination defined in claim 1, wherein the emitter of said squelch transistor is connected to said power source along with said parallel circuit so that the bias voltage on said squelch transistor is variable with changes in the audio frequency signal across said parallel circuit.
Claim 6
Dependent Claim
51 words
The combination defined in claim 2, wherein said means for varying the bias voltage of said audio frequency amplifying circuit includes a bias resistor in said audio frequency amplifying circuit connected to the collector of said squelch transistor for cutting-off said audio frequency amplifying circuit when said squelch transistor is conductive.
Claim 7
Dependent Claim
77 words
The combination defined in claim 3, wherein said audio frequency amplifying circuit includes an audio amplifying transistor having an emitter connected to said bias resistor and a base connected to a voltage divider circuit which is connected to said power source, said voltage divider circuit providing a bias to said base which is larger than said emitter bias when said squelch transistor is non-conductive and is smaller than said emitter bias when said squelch transistor is conductive.
Claim 8
Dependent Claim
302 words
In a radio receiver including a power source, a gain controllable intermediate frequency amplifying circuit for operatingly amplifying an intermediate frequency signal containing an audio frequency signal to be detected, a signal detection circuit including at least a diode, a resistor and a capacitor connected together in parallel, and an intermediate frequency transformer having a primary winding connected to the output of said intermediate frequency amplifying circuit and a secondary winding connected in series with said diode across the parallel circuit of said resistor and said capacitor, so that an output signal is obtained across said parallel circuit, an automatic gain control circuit including a time constant resistor, a time constant capacitor, and a potentiometer having an adjustable terminal, said time constant resistor and said potentiometer being connected in series with said parallel circuit across said power source, said time constant capacitor being connected at one end thereof to a junction between said time constant resistor and said potentiometer and at the other one end thereof to one polarity terminal of said power source, said power source being directed in such a manner that it normally biases said diode forwardly, and an audio frequency amplifying circuit for amplifying the output signal of said signal detection circuit, an improved squelch circuit comprising: a squelch transistor having emitter, base and collector, the emitter-collector circuit being connected across said power source; bias means for biasing said squelch transistor to the conductive or non-conductive side of its operating characteristic during a non-signal input or a signal input condition of the receiver, respectively, said biasing means including connecting means for connecting the adjustable terminal of said potentiometer to the base of said squelch transistor; and means for varying the conductivity of said audio frequency amplifying circuit inversely to the change in the conductivity of said squelch transistor.
Claim 9
Dependent Claim
302 words
In a radio receiver including a power source, a gain controllable intermediate frequency amplifying circuit for operatingly amplifying an intermediate frequency signal containing an audio frequency signal to be detected, a signal detection circuit including at least a diode, a resistor and a capacitor connected together in parallel, and an intermediate frequency transformer having a primary winding connected to the output of said intermediate frequency amplifying circuit and a secondary winding connected in series with said diode across the parallel circuit of said resistor and said capacitor, so that an output signal is obtained across said parallel circuit, an automatic gain control circuit including a time constant resistor, a time constant capacitor, and a potentiometer having an adjustable terminal, said time constant resistor and said potentiometer being connected in series with said parallel circuit across said power source, said time constant capacitor being connected at one end thereof to a junction between said time constant resistor and said potentiometer and at the other one end thereof to one polarity terminal of said power source, said power source being directed in such a manner that it normally biases said diode forwardly, and an audio frequency amplifying circuit for amplifying the output signal of said signal detection circuit, an improved squelch circuit comprising: a squelch transistor having emitter, base and collector, the emitter-collector circuit being connected across said power source; bias means for biasing said squelch transistor to the conductive or non-conductive side of its operating characteristic during a non-signal input or a signal input condition of the receiver, respectively, said biasing means including connecting means for connecting the adjustable terminal of said potentiometer to the base of said squelch transistor; and means for varying the conductivity of said audio frequency amplifying circuit inversely to the change in the conductivity of said squelch transistor.
Claim 10
Dependent Claim
51 words
The combination defined in claim 5, wherein said means for varying the conductivity of said audio frequency amplifying circuit includes a bias resistor in said audio frequency amplifying circuit connected to thE collector of said squelch transistor for cutting off said audio frequency amplifying circuit when said squelch transistor is conductive.
Claim 11
Dependent Claim
77 words
The combination defined in claim 6, wherein said audio frequency amplifying circuit includes an audio amplifying transistor having an emitter connected to said bias resistor and a base connected to a voltage divider circuit which is connected to said power source, said voltage divider circuit providing a bias to said base which is larger than said emitter bias when said squelch transistor is non-conductive and is smaller than said emitter bias when said squelch transistor is conductive.
Claim 12
Dependent Claim
388 words
In a radio receiver having a. a power source, b. a gain controllable intermediate frequency amplifier for operatingly amplifying an intermediate frequency signal applied thereto which contains an audio frequency signal to be detected, c. a signal detector including a diode, an intermediate frequency transformer having a primary coil coupled to an output terminal of said intermediate frequency amplifier and a secondary coil connected in series to said diode, a smoothing circuit coupled to said secondary coil through said diode, so that the audio frequency signal is separated from the intermediate frequency signal and appears across said smoothing circuit, d. an automatic gain control circuit including a potentiometer having a movable contact and connected in series with one electrode of said power source through said smoothing circuit as well as a series circuit formed by said secondary coil and said diode, and a time constant circuit connected between said potentiometer and the other one electrode of said power source so that said diode is normally biased forwardly by said power source and backwardly by an audio frequency signal appearing across said smoothing circuit, a junction point between said potentiometer and said time constant circuit at which an automatic gain control voltage is obtained being coupled to an input terminal of said intermediate frequency amplifier, so that the gain of said intermediate frequency amplifier is controlled by the automatic gain control voltage, and e. an audio frequency amplifier coupled to said signal detector for amplifying the audio frequency signal applied from said signal detector, an improved squelch circuit comprising: a squelch transistor which is operable in on and off states and operatingly drives said audio frequency amplifier to off and on states, respectively; first connecting means for connecting the movable contact of said potentiometer to a base of said squelch transistor; second connecting means for connecting an emitter of said squelch transistor to the other electrode of said power source, so that a bias voltage is provided between the emitter and the base of said squelch transistor, said bias voltage being so determined by adjustment of a position of the movable contact of said potentiometer that the bias voltage has a value larger than a threshold voltage of said squelch transistor unless the audio frequency signal of an intensity larger than a desired intensity appears across said smoothing circuit.
Claim 13
Dependent Claim
388 words
In a radio receiver having a. a power source, b. a gain controllable intermediate frequency amplifier for operatingly amplifying an intermediate frequency signal applied thereto which contains an audio frequency signal to be detected, c. a signal detector including a diode, an intermediate frequency transformer having a primary coil coupled to an output terminal of said intermediate frequency amplifier and a secondary coil connected in series to said diode, a smoothing circuit coupled to said secondary coil through said diode, so that the audio frequency signal is separated from the intermediate frequency signal and appears across said smoothing circuit, d. an automatic gain control circuit including a potentiometer having a movable contact and connected in series with one electrode of said power source through said smoothing circuit as well as a series circuit formed by said secondary coil and said diode, and a time constant circuit connected between said potentiometer and the other one electrode of said power source so that said diode is normally biased forwardly by said power source and backwardly by an audio frequency signal appearing across said smoothing circuit, a junction point between said potentiometer and said time constant circuit at which an automatic gain control voltage is obtained being coupled to an input terminal of said intermediate frequency amplifier, so that the gain of said intermediate frequency amplifier is controlled by the automatic gain control voltage, and e. an audio frequency amplifier coupled to said signal detector for amplifying the audio frequency signal applied from said signal detector, an improved squelch circuit comprising: a squelch transistor which is operable in on and off states and operatingly drives said audio frequency amplifier to off and on states, respectively; first connecting means for connecting the movable contact of said potentiometer to a base of said squelch transistor; second connecting means for connecting an emitter of said squelch transistor to the other electrode of said power source, so that a bias voltage is provided between the emitter and the base of said squelch transistor, said bias voltage being so determined by adjustment of a position of the movable contact of said potentiometer that the bias voltage has a value larger than a threshold voltage of said squelch transistor unless the audio frequency signal of an intensity larger than a desired intensity appears across said smoothing circuit.
Claim 14
Dependent Claim
51 words
The combination as defined in claim 8, which further includes a bias resistor for said audio frequency amplifier connected to a collector of said squelch transistor so as to allow collector current to flow therethrough to thereby operatingly cut off said audio frequency amplifying circuit when said squelch transistor is conductive.
Claim 15
Dependent Claim
29 words
The combination as defined in claim 9, which further includes a bypass capacitor connected in parallel with said bias resistor and connected to the collector of said squelch transistor.
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) | 1976-03-05 | 1976-09-04 | 1977-03-06 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-03-05 | 1980-09-04 | 1981-03-06 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-03-05 | 1984-09-04 | 1985-03-06 | $7700.00 | Window Closed / Lapsed |