US4680792A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Demodulator comprising an indicator circuit for use in common to cancellation of a pilot signal and an indication of a reception state
Assignee: NEC Electronics Corp
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Filing: 1985-03-05
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Granted: 1987-07-14
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Expires: 2005-03-05
Abstract
Abstract In a demodulator comprising an indicator (31) for indicating either stereo reception or monaural reception, an indicator circuit (30) is used to cancel a pilot signal included in a stereophonic signal and to produce a drive signal for driving the indicator. The indicator circuit comprises a negative feedback loop formed by an adder circuit (41), a phase detector (43), and a cancellation circuit (45). The cancellation circuit supplies the indicator and the adder circuit with the drive signal and a cancelling signal synchronized with and approximate to the pilot signal, respectively. The adder circuit substracts the cancelling signal from the pilot signal to deliver an intermediate signal to a multiplex decoder and to the cancellation circuit through the phase detector. The cancellation circuit comprises a wave generator for generating a pair of currents proportional to an amplitude of the pilot signal and a level adjusting circuit for converting one of the currents into the cancelling signal. The other current is converted into the drive signal.
Inventors
- 👤 Kouichi Tanaka
- 👤 Takeshi Kuwajima
- 👤 Kiyoshi Amazawa
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 21:07
CPC Classifications
H; H04; H04H; H04H40/00; H04H40/18; H04H40/27; H04H40/36; H04H40/45; H03; H03D; H03D1/00; H03D1/22; H03D1/2209; H03D1/2236; H04B; H04B1/00; H04B1/06; H04B1/16; H04B1/1646; H04B1/1653; H04H40/81
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
254 words
A demodulator for use in producing a demodulated signal in response to a circuit input signal which is one of a stereophonic signal accompanied by a pilot signal of a predetermined frequency or a monophonic signal accompanied by no pilot signal, said demodulator comprising signal producing means responsive to said circuit input signal for producing a first local frequency signal having a frequency equal to said predetermined frequency and a second local frequency signal having a frequency equal to said predetermined frequency and a phase different from a phase of said local frequency signal, wherein the improvement comprises: intermediate signal producing means responsive to said circuit input signal and a local input signal to generate an intermediate signal; demodulating means coupled to said intermediate signal producing means for demodulating said intermediate signal into said demodulated signal; phase detecting means coupled to said intermediate signal producing means and responsive to said second local frequency signal for detecting a phase difference between said pilot signal and said second local frequency signal on reception of said stereophonic signal; first circuit means coupled to said phase detecting means and responsive to said first local frequency signal for producing first and second currents dependent on said phase difference; second circuit means for feeding said first current back to said intermediate signal producing means as said local input signal, said second circuit means forming a negative feedback loop together with said intermediate signal producing means; and indicating means responsive to said second current for indicating reception of said stereophonic signal.
Claim 2
Dependent Claim
254 words
A demodulator for use in producing a demodulated signal in response to a circuit input signal which is one of a stereophonic signal accompanied by a pilot signal of a predetermined frequency or a monophonic signal accompanied by no pilot signal, said demodulator comprising signal producing means responsive to said circuit input signal for producing a first local frequency signal having a frequency equal to said predetermined frequency and a second local frequency signal having a frequency equal to said predetermined frequency and a phase different from a phase of said local frequency signal, wherein the improvement comprises: intermediate signal producing means responsive to said circuit input signal and a local input signal to generate an intermediate signal; demodulating means coupled to said intermediate signal producing means for demodulating said intermediate signal into said demodulated signal; phase detecting means coupled to said intermediate signal producing means and responsive to said second local frequency signal for detecting a phase difference between said pilot signal and said second local frequency signal on reception of said stereophonic signal; first circuit means coupled to said phase detecting means and responsive to said first local frequency signal for producing first and second currents dependent on said phase difference; second circuit means for feeding said first current back to said intermediate signal producing means as said local input signal, said second circuit means forming a negative feedback loop together with said intermediate signal producing means; and indicating means responsive to said second current for indicating reception of said stereophonic signal.
Claim 3
Dependent Claim
71 words
A demodulator as claimed in claim 1, wherein said first circuit means comprises: means coupled to said phase detecting means for producing a reference signal dependent on said phase difference; first current producing means responsive to said reference signal for producing said first current in proportion to said reference signal; and second current producing means responsive to said reference signal for producing said second current in proportion to said reference signal.
Claim 4
Dependent Claim
72 words
A demodulator as claimed in claim 2, wherein said second circuit means comprises: a terminal; a resistor connected to said terminal, said first current producing means, and said intermediate signal producing means; and a capacitor connected between said terminal and ground and responsive to said first current for producing a capacitor voltage thereacross, said capacitor voltage being supplied through said resistor to said intermediate signal producing means as said local input signal.
Claim 5
Dependent Claim
34 words
A demodulator as claimed in claim 3, wherein said indicating means comprises: an indicator for optically indicating reception of said stereophonic signal; and driving means responsive to said second current for driving said indicator.
Claim 6
Dependent Claim
53 words
A demodulator as claimed in claim 4, wherein said driving means comprises: current-to-voltage converting means for converting said second current into a drive voltage; and a drive circuit having a threshold voltage and coupled to said drive voltage converting means for driving said indicator only when said drive voltage exceeds said threshold voltage.
Claim 7
Dependent Claim
343 words
A demodulator for use in producing a demodulated signal in response to a circuit input signal which is one of a stereophonic signal accompanied by a pilot signal of a predetermined frequency of a monophonic signal accompanied by no pilot signal, said demodulator comprising signal producing means responsive to said circuit input signal for producing a first local frequency signal having a frequency equal to said predetermined frequency and a second local frequency signal having a frequency equal to said predetermined frequency and a phase different from a phase of said first local frequency signal, the improvement comprising: an adder circuit responsive to said circuit input signal and a local input signal for producing an intermediate signal representative of a sum between said circuit input signal and said local input signal; demodulating means coupled to said adder circuit for demodulating said intermediate signal into said demodulated signal; phase detecting means coupled to said adder circuit and responsive to said second local frequency signal for detecting a phase difference between said pilot signal and said second local frequency signal on reception of said stereophonic signal; means coupled to said phase detecting means for producing a reference signal dependent on said phase difference; first current producing means responsive to said reference signal for producing a first current in proportion to said reference signal; second current producing means responsive to said reference signal for producing a second current in proportion to said reference signal; a resistor connected to said first current producing means, and to a negative input of said adder circuit so as to form a negative feedback loop together with said phase detecting means, said first current producing means, and said second current producing means; a capacitor connected between said resistor and ground and responsive to said first current for producing a capacitor voltage thereacross, said capacitor voltage being supplied through said resistor to said adder circuit as said local input signal; an indicator for optically indicating reception of said stereophonic signal; and driving means responsive to said second current for driving said indicator.
Claim 8
Dependent Claim
343 words
A demodulator for use in producing a demodulated signal in response to a circuit input signal which is one of a stereophonic signal accompanied by a pilot signal of a predetermined frequency of a monophonic signal accompanied by no pilot signal, said demodulator comprising signal producing means responsive to said circuit input signal for producing a first local frequency signal having a frequency equal to said predetermined frequency and a second local frequency signal having a frequency equal to said predetermined frequency and a phase different from a phase of said first local frequency signal, the improvement comprising: an adder circuit responsive to said circuit input signal and a local input signal for producing an intermediate signal representative of a sum between said circuit input signal and said local input signal; demodulating means coupled to said adder circuit for demodulating said intermediate signal into said demodulated signal; phase detecting means coupled to said adder circuit and responsive to said second local frequency signal for detecting a phase difference between said pilot signal and said second local frequency signal on reception of said stereophonic signal; means coupled to said phase detecting means for producing a reference signal dependent on said phase difference; first current producing means responsive to said reference signal for producing a first current in proportion to said reference signal; second current producing means responsive to said reference signal for producing a second current in proportion to said reference signal; a resistor connected to said first current producing means, and to a negative input of said adder circuit so as to form a negative feedback loop together with said phase detecting means, said first current producing means, and said second current producing means; a capacitor connected between said resistor and ground and responsive to said first current for producing a capacitor voltage thereacross, said capacitor voltage being supplied through said resistor to said adder circuit as said local input signal; an indicator for optically indicating reception of said stereophonic signal; and driving means responsive to said second current for driving said indicator.
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) | 1990-07-13 | 1991-01-12 | 1991-07-14 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1994-07-13 | 1995-01-12 | 1995-07-14 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1998-07-13 | 1999-01-12 | 1999-07-14 | $7700.00 | Window Closed / Lapsed |