Electric lamp and discharge devices – Cathode ray tube – Beam deflecting means
Patent
1995-01-25
1997-01-28
Oberley, Alvin E.
Electric lamp and discharge devices
Cathode ray tube
Beam deflecting means
H01J 3112
Patent
active
055980546
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a display device having a vacuum envelope, said display device comprising an electroluminescent screen and a row of transport ducts for transporting electrons, means for generating electrons and injecting electrons into the transport ducts, means for applying potential differences across the transport ducts to transport electrons through said transport ducts by means of secondary emission, means for extracting electrons from the transport ducts and means for directing electrons towards the electroluminescent screen.
A display device of the type mentioned in the opening paragraph is described in EP-A 0 436 997 corresponding to U.S. Pat. No. 5,347,199. In EP-A 0 436 997 a description is given of a display device in which the means for generating and injecting electrons comprise a line cathode which generates electrons which are injected into the transport ducts by means of electrodes. In general, the aim is to obtain display devices which are constructed so that, in operation, the electron flows in the transport duets do not deviate from a desired value or deviate so little that it is not disturbing or only to a very small degree. Variations in electron flows, both in one transport duct and between transport ducts, cause a deterioration of the picture quality.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a display device of the type described in the opening paragraph, in which variations in the electron flows are precluded or reduced. Within the scope of the invention, it has been recognized that the cooperation between and mutual influencing of the means for generating electrons and injecting electrons into the transport ducts are of essential importance in this respect.
This recognition is elaborated in various aspects of the invention.
According to a first aspect of the invention, the display device is characterized in that the means for generating electrons comprise juxtaposed line cathodes.
If one line cathode is used as the source for all transport ducts in the display device, problems with the homogeneity of the image displayed are, for example, caused by a relatively great voltage drop across the line cathode (of the order of magnitude of, for example 100 volts). As a result thereof, the effectiveness with which electrons are generated by the line cathode and injected into the transport ducts varies along the line cathode. Due to this, differences between electron flows in different transport ducts occur. The homogeneity of the image displayed is adversely affected thereby. A long line cathode is also sensitive to vibrations. Vibrations cause changes in the position of the line cathode relative to the transport ducts, which may result in variations in the electron flows and hence a reduction of the homogeneity of the image displayed. By using a number of line cathodes, the voltage difference across each line cathode and the vibration sensitivity of each of the line cathode can be separately reduced. This results in an improved homogeneity of the image displayed and hence an improved picture display.
In an embodiment of the display device in accordance with the first aspect of the invention, the display device comprises a mixing means which is located between the line cathodes and the transport ducts and which serves to mix electron flows generated by the line cathodes before the electrons are injected into the transport ducts.
This results in an improved homogeneity of the image displayed. Said mixing means causes the electrons generated by various line cathodes to be mixed before the electrons are injected into the transport ducts. When the electrons are mixed, a number of transport ducts receive electrons originating from more than one line cathode. By virtue thereof, electron-emission differences between line cathodes are less visible. In addition, adverse effects caused by differences in the positions of the line cathodes relative to the transport ducts are reduced.
Intensity differences caused by the fact that the l
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Baller Theunis S.
Cosman Edward C.
De Zwart Siebe T.
Lambert Nicolaas
Montie Edwin A.
Kraus Robert J.
Oberley Alvin E.
Richardson Lawrence O.
U.S. Philips Corporation
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