Patent US4481678A successfully refreshed from Google Patents.
US4481678A
Expired / Lapsed
US
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Signal receiving circuit for optical communication
Assignee: Sumitomo Electric Industries Ltd
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Filing: 1982-08-04
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Granted: 1984-11-06
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Expires: 2002-08-04
Abstract
Abstract A signal receiving circuit for optical communication, which receives light modulated with frequencies corresponding to two values, to receive data, comprises an addition circuit provided in the front stage of a demodulator, the addition circuit adapted to superpose on an electrical signal provided by converting light received a signal having a frequency which is smaller in amplitude than the electrical signal.
Inventors
- 👤 Fukuma Sakamoto
- 👤 Shizuo Izumida
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 18:44
CPC Classifications
H; H04; H04L; H04L27/00; H04L27/10; H04L27/14
Claims Analysis
Total Claims: 6
Claim 1
Independent Claim
126 words
A signal receiving circuit for optical data communication for preventing false signals during periods when no data is being transmitted comprising a light receiving element adapted to receive a data signal, an amplifier, a demodulator connected to an output of said amplifier, a signal source of a specific frequency, an attenuator having an input connected to said signal source for attenuating the amplitude of the specific frequency signal from said signal source to a value less than that of said data signal, and an addition circuit having one input from said light receiving element and a second input from said attenuator and connected to an input of said amplifier, said addition circuit superposing on a data signal received by said light receiving element said attenuated signal.
Claim 2
Dependent Claim
126 words
A signal receiving circuit for optical data communication for preventing false signals during periods when no data is being transmitted comprising a light receiving element adapted to receive a data signal, an amplifier, a demodulator connected to an output of said amplifier, a signal source of a specific frequency, an attenuator having an input connected to said signal source for attenuating the amplitude of the specific frequency signal from said signal source to a value less than that of said data signal, and an addition circuit having one input from said light receiving element and a second input from said attenuator and connected to an input of said amplifier, said addition circuit superposing on a data signal received by said light receiving element said attenuated signal.
Claim 3
Dependent Claim
40 words
A signal receiving circuit as claimed in claim 1, further including a transmitting circuit for transmitting a signal represented by at least two different frequencies and said specific frequency is derived from one of the frequencies of said transmitting circuit.
Claim 4
Dependent Claim
28 words
A signal receiving circuit as claimed in claims 1 and 2, further comprising an identification circuit connected to said output of said amplifier for identifying said data signals.
Claim 5
Dependent Claim
26 words
A signal receiving circuit as claimed in claim 3, wherein said identification circuit consists of a band-pass filter, a rectifying and smoothing circuit and a comparator.
Claim 6
Dependent Claim
22 words
A signal receiving circuit as claimed in claim 3, wherein said identification circuit consists of an FM detection circuit and a comparator.
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) | 1987-11-06 | 1988-05-07 | 1988-11-06 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1991-11-06 | 1992-05-07 | 1992-11-06 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1995-11-06 | 1996-05-07 | 1996-11-06 | $7700.00 | Window Closed / Lapsed |