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US4404431A
Expired / Lapsed
US
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AM Stereo receiver
Assignee: Hitachi Ltd
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Filing: 1981-11-18
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Granted: 1983-09-13
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Expires: 2001-11-18
Abstract
Abstract In an AM stereo receiver, a sum signal L+R is generated by subjecting an IF signal to AM detection while a difference signal L-R is generated by subjecting the IF signal to PM detection. The sum signal is applied to one of input terminals of a matrix circuit while the difference signal is applied to the other input terminal via a variable gain circuit. An AM detector for obtaining the sum signal L+R includes a detecting transistor formed in a monolithic integrated circuit and an AGC voltage can be obtained by smoothing the sum signal obtained from the emitter of this detecting transistor. A level shift transistor is formed in the same monolithic integrated circuit, and a voltage virtually equal to a base input d.c. voltage of the detecting transistor of the AM detector is applied to the base of the level shift transistor so that a level shift voltage is obtained from the emitter of the level shift transistor. The variable gain of the variable gain circuit is controlled by a difference voltage between the AGC voltage and the level shift voltage, whereby change in stereo separation due to the temperature dependency of the base-emitter voltage of the detecting transistor can be prevented.
Inventors
- 👤 Kazuo Watanabe
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-08 10:48
CPC Classifications
H; H04; H04H; H04H20/00; H04H20/44; H04H20/46; H04H20/47; H04H20/49
Claims Analysis
Total Claims: 6
Claim 1
Independent Claim
267 words
In an AM stereo receiver, comprising: a signal source circuit for producing a signal containing an amplitude modulation sum signal component and a phase modulation difference signal component; an AM detector circuit connected to receive said signal from said signal source circuit for generating a signal proportional to said amplitude modulation sum signal component, including a detecting transistor formed in an integrated circuit; a PM detector circuit connected to receive said signal from said signal source circuit for generating a signal proportional to said phase modulation difference signal component; a variable gain circuit connected to receive said signal proportional to said phase modulation difference signal from said PM detector circuit; a matrix circuit connected to receive the outputs of said AM detector circuit and said variable gain circuit for generating stereo reproduction signals by composing said signal proportional to said sum signal component and said signal proportional to said difference signal component received via said variable gain circuit; means for producing an AGC voltage in response to said sum signal component obtained from said detecting transistor of said AM detector circuit; a level shift transistor formed in said integrated circuit in which said detecting transistor is formed; means for applying a voltage virtually equal to the base input d.c. voltage at the base of said detecting transistor to the base of said level shift transistor, thereby providing a level shift voltage from the emitter of said level shift transistor; and means for controlling the gain of said variable gain control circuit by a signal equal to the difference between said AGC voltage and said level shift voltage.
Claim 2
Dependent Claim
267 words
In an AM stereo receiver, comprising: a signal source circuit for producing a signal containing an amplitude modulation sum signal component and a phase modulation difference signal component; an AM detector circuit connected to receive said signal from said signal source circuit for generating a signal proportional to said amplitude modulation sum signal component, including a detecting transistor formed in an integrated circuit; a PM detector circuit connected to receive said signal from said signal source circuit for generating a signal proportional to said phase modulation difference signal component; a variable gain circuit connected to receive said signal proportional to said phase modulation difference signal from said PM detector circuit; a matrix circuit connected to receive the outputs of said AM detector circuit and said variable gain circuit for generating stereo reproduction signals by composing said signal proportional to said sum signal component and said signal proportional to said difference signal component received via said variable gain circuit; means for producing an AGC voltage in response to said sum signal component obtained from said detecting transistor of said AM detector circuit; a level shift transistor formed in said integrated circuit in which said detecting transistor is formed; means for applying a voltage virtually equal to the base input d.c. voltage at the base of said detecting transistor to the base of said level shift transistor, thereby providing a level shift voltage from the emitter of said level shift transistor; and means for controlling the gain of said variable gain control circuit by a signal equal to the difference between said AGC voltage and said level shift voltage.
Claim 3
Dependent Claim
109 words
The AM stereo receiver as defined in claim 1, which further includes: a limiter amplifier having a signal input terminal connected to the base of said detecting transistor, a negative feedback input terminal connected to the base of said level shift transistor and an output terminal connected to the input terminal of said PM detector; and a d.c. negative feedback circuit interposed between said output terminal and said negative feedback input terminal of said limiter amplifier in such a manner as to cause the voltage at said negative feedback input terminal of said limiter amplifier to be virtually equal to the base input d.c. voltage of said detecting transistor.
Claim 4
Dependent Claim
134 words
The AM stereo receiver as defined in claim 1 or 2, wherein said signal source circuit includes an RF amplifier stage, a frequency converter stage connected to said RF amplifier stage, an IF amplifier stage connected to said frequency converter stage, another AM detector connected to said IF amplifier stage, an AGC filter for controlling the gains of said RF amplifier stage and said IF amplifier stage in response to the detection output signal of said another AM detector, and voltage comparator means for comparing the signal amplitude value of the output of said RF amplifier stage with a reference value, and when the signal amplitude value of said RF amplifier stage exceeds the reference voltage, for applying an output signal to said AGC filter to lower the gain of said RF amplifier stage.
Claim 5
Dependent Claim
34 words
An AM stereo receiver as defined in claim 1, wherein said means for producing said AGC voltage includes a filter circuit connected between the emitter of said detecting transistor and said gain controlling means.
Claim 6
Dependent Claim
55 words
An AM stereo receiver as defined in claims 1 or 4, wherein said gain controlling means includes a comparator having one input connected to receive said AGC voltage and a second input connected to receive said level shift voltage, the output of said comparator being connected to control the gain of said variable gain circuit.
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) | 1986-09-12 | 1987-03-14 | 1987-09-13 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1990-09-12 | 1991-03-14 | 1991-09-13 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1994-09-12 | 1995-03-14 | 1995-09-13 | $7700.00 | Window Closed / Lapsed |