US4224640A
Expired / Lapsed
US
⏱️ 0.0 years remaining
CRT Beam current control apparatus
Assignee: US Philips Corp
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Filing: 1978-12-22
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Granted: 1980-09-23
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Expires: 1998-12-22
Abstract
Abstract In a television picture display device wherein a cathode of a picture display tube is driven by an emitter-follower and a control signal for a beam current reference level control circuit is obtained from the collector circuit of this emitter-follower, measures are taken to compensate for leakage currents from and to the cathode. To this end a blacker-than-black current compensation circuit is provided while furthermore it is ensured that the blacker-than-black curent can be processed by the beam current reference level control circuit.
Inventors
- 👤 Paulus J. M. Hovens
- 👤 Miloslav Tryzna
- 👤 Wouter Smeulers
- 👤 Willem H. Amsen
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-28 22:51
CPC Classifications
H; H04; H04N; H04N9/00; H04N9/64; H04N9/72; H04N5/00; H04N5/14; H04N5/16; H04N5/165
Claims Analysis
Total Claims: 7
Claim 1
Independent Claim
117 words
A television picture display device for displaying pictures derived from video signals, said display device comprising a picture display tube having a cathode; an emitter-follower device coupled to said cathode for producing a beam current for driving said picture display tube; a beam current reference level control circuit coupled to said emitter-follower device for controlling the black level of the beam current; a blacker-than-black current compensation circuit incorporated in said beam current reference level control circuit for compensating for a leakage current in said cathode caused by a blacker-than-black level in the video signal; and a blacker-than-black current conduction circuit coupled to said cathode to enable compensation of said leakage current when said beam current is blanked.
Claim 2
Dependent Claim
117 words
A television picture display device for displaying pictures derived from video signals, said display device comprising a picture display tube having a cathode; an emitter-follower device coupled to said cathode for producing a beam current for driving said picture display tube; a beam current reference level control circuit coupled to said emitter-follower device for controlling the black level of the beam current; a blacker-than-black current compensation circuit incorporated in said beam current reference level control circuit for compensating for a leakage current in said cathode caused by a blacker-than-black level in the video signal; and a blacker-than-black current conduction circuit coupled to said cathode to enable compensation of said leakage current when said beam current is blanked.
Claim 3
Dependent Claim
61 words
A television picture display device as claimed in claim 1, wherein the blacker-than-black current conduction circuit comprises a direct current source coupled to the cathode of the picture display tube for keeping said emitter-follower device conductive at the occurrence of a blacker-than-black current in the cathode circuit of the picture display tube thereby allowing for the compensation of said blacker-than-black signal.
Claim 4
Dependent Claim
40 words
A television picture display device as claimed in claim 2, wherein the direct current source comprises a first and second resistor serially connected to a supply voltage said first resistor being a.c. coupled to the base of the emitter-follower device.
Claim 5
Dependent Claim
68 words
A television picture display device as claimed in claim 1, which further comprises a second emitter-follower device, of an opposite conduction type as said first-mentioned emitter-follower device, also coupled to said picture display tube cathode, and wherein said blacker-than-black current conduction circuit comprises a difference-forming circuit, coupled to the collector of the second emitter-follower device and coupled to an input of said beam current reference level control circuit.
Claim 6
Dependent Claim
50 words
A television picture display device as claimed in claim 4, wherein said difference-forming circuit comprises a current mirror circuit having an input and an output, the input of which is coupled to the collector of the second emitter-follower device and the output to the collector of the first-mentioned emitter-follower device.
Claim 7
Dependent Claim
59 words
A television picture display device as claimed in claims 2, 3, 4, 5 or 1, which further comprises a heater, a wehnelt electrode connection of the picture display tube and a leakage current conducting circuit, said heater and said wehnelt electrode connection being coupled to the collector of the first-mentioned emitter-follower device through a said leakage current conducting circuit.
References Cited (Backward Citations)
US3598913A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1983-09-23 | 1984-03-24 | 1984-09-23 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1987-09-23 | 1988-03-24 | 1988-09-23 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1991-09-23 | 1992-03-24 | 1992-09-23 | $7700.00 | Window Closed / Lapsed |