Patent US3582545A successfully refreshed from Google Patents.
US3582545A
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Automatic black level video signal clipping and clamping system
Assignee: RCA Corp
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Filing: 1969-03-21
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Granted: 1971-06-01
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Expires: 1989-03-21
Abstract
Abstract A transistor amplifier converts a video signal voltage at its input circuit into a corresponding video signal current at its output circuit which is applied to the input of a black level clipper transistor. A high impedance constant reference current source is coupled to both the input of the clipper transistor and to the output circuit of the amplifier. The clipper transistor linearly transfers the video signal at its input to its output circuit until the input video signal current equals the constant current, whereupon the clipper transistor is cut off preventing further video signal current conduction in its output circuit. The excess of the video signal current beyond the reference clipping level is detected by a sensor transistor, the output current from which is sampled by a transistor pulsed during the synchronizing interval. The current samples are integrated and, after direct current amplification, are converted to a corresponding voltage which is applied as a feedback clamping control signal to clamp the video signal voltage at a reference black level.
Inventors
- 👤 Laurence Joseph Thorpe
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 23:09
CPC Classifications
H; H04; H04N; H04N5/00; H04N5/14; H04N5/16; H04N5/165; H04N5/18; H04N5/185; H04N5/66
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
173 words
An automatic black level video signal clipping system, comprising: a source of a video signal-representing light values of a subject varying from black to white; a black level clipper for transferring to its output circuit those portions of a video signal impressed upon its input circuit which represent light values above a predetermined black level and for clipping said video signal by preventing those video signal portions at and below said predetermined black level from being transferred to its output circuit; coupling means for impressing said video signal derived from said source upon the input circuit of said black level clipper; detecting means coupled to the junction of said coupling means and said clipper for producing a difference signal corresponding to the difference between the video signal level and the clipping level; and feedback-clamping means coupled between said detecting means and said video signal source and responsive to said difference signal, for applying a control signal to said video signal source to automatically clamp said video signal at substantially said predetermined black level.
Claim 2
Dependent Claim
173 words
An automatic black level video signal clipping system, comprising: a source of a video signal-representing light values of a subject varying from black to white; a black level clipper for transferring to its output circuit those portions of a video signal impressed upon its input circuit which represent light values above a predetermined black level and for clipping said video signal by preventing those video signal portions at and below said predetermined black level from being transferred to its output circuit; coupling means for impressing said video signal derived from said source upon the input circuit of said black level clipper; detecting means coupled to the junction of said coupling means and said clipper for producing a difference signal corresponding to the difference between the video signal level and the clipping level; and feedback-clamping means coupled between said detecting means and said video signal source and responsive to said difference signal, for applying a control signal to said video signal source to automatically clamp said video signal at substantially said predetermined black level.
Claim 3
Dependent Claim
43 words
An automatic black level video signal-clipping system as defined in claim 1, wherein: said video signal source produces a video signal voltage; and said coupling means includes a signal conversion amplifier to convert said video signal voltage into a corresponding video signal current.
Claim 4
Dependent Claim
55 words
An automatic black level video signal clipping system as defined in claim 2, wherein: said black level clipper includes a source of substantially constant unidirectional current connected to its input circuit and means for combining said constant current with current representative of said video signal for establishing the video signal transfer capability of said clipper.
Claim 5
Dependent Claim
83 words
An automatic black level video signal clipping system as defined in claim 3, wherein: said feedback-clamping means includes a sampler coupled to said sensing means for response to said indicating signal; means for operating said sampler during horizontal line blanking intervals to produce a series of pulses corresponding to the amplitude of said indicating signal; and conversion means coupled to said sampler and responsive to said series of pulses to produce a continuous unidirectional control signal for application to said video signal source.
Claim 6
Dependent Claim
67 words
An automatic black level video signal clipping system as defined in claim 4, wherein: said conversion means includes an integrating circuit coupled to said sampler and responsive to said series of pulses to produce a continuous unidirectional voltage; and unidirectional signal-amplifying means coupled to said integrating circuit and responsive to said continuous unidirectional voltage for producing said control signal and applying it to said video signal source.
Claim 7
Dependent Claim
40 words
An automatic black level video signal-clipping clipping system as defined in claim 5, wherein: said black level clipper comprises a grounded base singal-amplifying transistor havIng an input circuit including its emitter electrode and an output circuit including its collector electrode.
Claim 8
Dependent Claim
59 words
An automatic black level video signal clipping system as defined in claim 6, wherein: said substantially constant unidirectional current source comprises a transistor having its collector electrode connected to the emitter electrode of said black level clipper transistor, its emitter electrode connected to a source of electrical energy, and its base electrode coupled to said source of electrical energy.
Claim 9
Dependent Claim
159 words
An automatic black level video signal-clipping system as defined in claim 7, wherein: said signal conversion amplifier comprises an operational amplifier having input and output terminals and a pair of input and output transistors of opposite conductivity; said input transistor having its base electrode coupled to said operational amplifier output terminal and being operated in a common emitter electrode mode with its collector electrode connected to the emitter electrode of said output transistor, and said output transistor being operated in a grounded base electrode mode; means for impressing said video signal derived from said source of video signal upon the input terminal of said operational amplifier; and means including a diode coupled between the collector electrode of said conversion amplifier output transistor and the common connection of the emitter electrode of said black level clipper transistor and the collector electrode of said constant current transistor, said diode being poled to conduct current in the direction of said common connection.
Claim 10
Dependent Claim
101 words
An automatic black level video signal-clipping system as defined in claim 9, wherein: said detecting means comprises a grounded base transistor having its emitter electrode connected to the collector electrode of said signal conversion amplifier output transistor and its collector electrode coupled to said sampler; said sampler including a transistor having its collector-to-emitter electrode circuit coupled between said sensing transistor collector electrode and said integrating circuit; and means for applying an operating pulse during each horizontal line blanking interval to the base electrode of said sampler transistor to produce said series of pulses corresponding to the amplitude of said indicating signal.
Claim 11
Dependent Claim
48 words
An automatic black level video signal-clipping system as defined in claim 9, wherein: said unidirectional signal-amplifying means comprises a transistor operated in a common emitter mode having its base electrode coupled to said integrating circuit and its collector electrode coupled to the input of said video signal source.
Claim 12
Dependent Claim
61 words
An automatic black level video signal-clipping system as defined in claim 10, wherein: said input transistor of said signal conversion amplifier, said black level clipper transistor, said substantially constant undirectional current transistor, said sampler transistor, and said unidirectional signal-amplifying means transistor are NPN devices; and said output transistor of said signal conversion amplifier and said sensing means transistor are PNP devices.
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) | 1974-05-31 | 1974-11-30 | 1975-06-01 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1978-05-31 | 1978-11-30 | 1979-06-01 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1982-05-31 | 1982-11-30 | 1983-06-01 | $7700.00 | Window Closed / Lapsed |