US2719241A - Three color kinescope for sequential color systems - Google Patents

Description

United States Patent Ofiice Patented Sept. 27, 1955 THREE COLOR KINESCOPE FOR SEQUENTIAL COLOR SYSTEMS John W. Coltman, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application April 18, 1952, Serial No. 283,069

8 Claims. (Cl. 313-65) My invention relates to cathode-ray tubes and, more particularly, to cathode-ray tubes used in color television.

In accordance with the prior art of which I am aware, color television tubes have been built employing phosphor screens in which the colored phosphors are applied in strips across the screen. In such an apparatus, it is very difficult to insure that the electron scanning beam will impinge only on phosphors of the proper color at any given time. If the scanning beam should move slightly off its prescribed course, it would produce information on the screen of the wrong color which would obviously produce an undesirable efiect. One method of overcoming this effect which has been suggested in the prior art is the employment of a plurality of electrodes extending across the tube parallel to the phosphor strips and located in a plane a substantial distance from the plane of the phosphor strips. By applying proper potentials to these electrodes, the direction of the electron beam scanning the phosphor strips could be so controlled that only phosphor strips of the desired composition would be activated at any given time. However, there are many disadvantages to this system. The support of such electrodes would be extremely difficult due to their small cross-sectional dimensions and the great distance over which they extend. The large capacity of such electrodes, together with the high potentials necessary to give the electron scanning beam which is composed of high velocity electrons sufficient vertical acceleration to have any substantial eflect, requires relatively high switching currents if rapid switching is desired.

It is accordingly an object of my invention to provide a color television tube wherein a high degree of control is maintained over the colors produced.

Another object of my invention is to provide a color television tube employing a screen of strip phosphors whereby electrons are allowed to impinge only on phosphors of a given color at any particular time.

Still another object of my invention is to provide a color television tube employing electrons which are carefully controlled for activating the color phosphors.

Still another object of my invention is to provide a color television tube having two screens, a first of said screens emitting low velocity electrons in response to electrons of an electron scanning beam impinging thereon.

An ancillary object of my invention is to provide an improved color television tube.

Still another ancillary object of my invention is to provide a new and novel electronic apparatus.

The invention with respect to both the organization and the operation thereof, together with other objects and advantages may be best understood from the following description of specific embodiments when read in connection with the accompanying drawing, in which:

Figure 1 is a schematic showing of a television tube built in accordance with my invention;

Fig. 2 is a cross-sectional showing of a small portion of the two screens of the tube shown in Fig. 1 when no potentials are being applied between successive conducting strips;

Fig. 3 is a cross-sectional showing of the apparatus shown in Fig. 2 when potentials are being applied between successive conducting strips;

Fig. 4 is a large scale cross-sectional showing of a portion of the first of the two screens of the tube shown in Fig. 1;

Fig. 5 is a schematic showing of the electrical connections to the conducting strips of the first screen;

Fig. 6 is a graph showing the potentials applied to the conducting strips of the first screen; and

Fig. 7 is a large scale cross-sectional view showing of a portion of the second of the two screens of the tube shown in Fig. 1.

In accordance with my invention, I provide an envelope 8 comprising glass or other dielectric material. Near one end of the envelope 8, I provide an electron gun 10 for producing a beam of relatively high velocity electrons in accordance with the principles well known in the art.

Near the opposite end of the envelope 8 from the electron gun 10, I provide a viewing or picture screen 12 lying generally perpendicular to a line between the screen 12 and the gun 10. The picture screen 12 comprises a supporting element 14 of transparent material having coated thereon, on the side thereof toward the electron gun, a plurality of strips 16, 18 and 20 of phosphor material. These strips are so organized that successive strips emit different colors of light when electrons impinge thereon. For example, the phosphor strips may be organized in accordance with my invention in the following order: Blue, green, red, green, blue, green, red. In this organization there is a green strip 18 between each of the blue and red phosphor strips 16, 20. There are, therefore, more green strips 18 than either blue strips 16 or red strips 20 and it is desirable that the green strips 18 be slightly narrower than either the red strips 20 or the blue strips 16. Though the picture screen 12 is shown as a separate structure, it may be desirable to use the end of the envelope 8 as an underlying support for the phosphors.

On top of the layer of phosphor strips is a thin aluminum layer 33, penetrable by electrons, which serves the dual purpose of preventing light from screen 12 from reaching screen 22, and providing a conducting electrode by which the potential of screen 12 may be maintained at the desired value.

A short distance from the picture screen 12 and parallel thereto, there is a primary or photoelectric screen 22. The photoelectric screen 22 lies between the picture screen 12 and the electron gun it). The photoelectric screen 22 comprises a supporting element 23 of transparent material. On the side of the supporting element 23 of the photoelectric screen 22 toward the electron gun 10, there is a layer 24 of electron responsive phosphor material capable of emitting light when electrons from the electron beam of the electron gun It) impinge thereon. In accordance with one embodiment of my invention there is coated on the phosphor layer 24 an electron transparent semiconducting metallic light reflecting layer 25 preferably of aluminum.

On the side of the photoelectric screen 22 toward the picture screen 12, there is a layer 34 of transparent semiconducting material such as properly deposited tin oxide and coated on top of this layer there are a plurality of strips of electrically conducting material 26. These strips of electrically conducting material are parallel to the phosphor strips 16, 18 and 20 and lie substantially opposite to the blue and red phosphor strips 16, 20. The electrically conducting strips 26 are separated by a gap 28 of a width substantially equal to the width of the green phosphor strips 18. Coated over the electrically conducting strips 26 and the region 28 where the semi-conductor is exposed between them is a thin layer 30 of photoelectric material such as cesium antimony. Means are provided including an electric circuit 32 for impressing variable potentials between successive strips of electrically conducting material 26. The potentials between the successive strips of electrically conducting material 26 are relatively small since electrons emitted by the photoelectric layer 30 in the region of the electrically conducting strips 26 will have relatively low initial velocities and may, there fore, be deflected with relative small energies. Between the layer 34 on screen 22 and the aluminum coating on screen 12, connections are made for applying a constant direct-current potential of relative large magnitude. An electric field is thus established for accelerating the electrons emitted by the photoelectric screen 22 toward the picture screen 12.

In the operation of my invention, electrons are emitted in a beam from the gun with relatively high velocity. The electron beam is caused to scan the primary screen 22, in the usual manner of a television picture, causing the emission of light from the phosphor material 24 coated on the primary screen 22. Light traveling from the first phosphor layer 24 toward the photoelectric layer and impinging on the conducting strips 26 is absorbed or reflected by those strips and will not activate the photoelectric layer 30. However, the light which passes through between successive conducting strips 26 will activate the photoelectric layer 30 between the successive strips so as to cause the emission of electrons.

When no potentials are applied between successive phosphor strips, electrons, emitted by the photoelectric layer in the regions between successive conducting strips, travel across the region between the photoelectric screen 22 and the picture screen 12 in a line substantially normal to the plane of the picture screen 12. These electrons, therefore, impinge only on the green phosphor strips 18 as is shown in Fig. 2.

When a potential is placed between successive conducting strips so that alternate strips are positive with respect to the intermediate strips, the electrons coming from alternate gaps will be given a deflection in one direction and the electrons coming from the remaining gaps will be given a deflection in the opposite direction. For example, as shown in Fig. 3, part of the electrons will be deflected upward and part of the electrons will be deflected downward so that all of the electrons will impinge on red phosphor strips. Thus, under this condition, only red light can be emitted by the picture screen.

If the signals applied to the conducting strips 26 are reversed, the beams will be moved in the opposite direction and all of the secondary electrons will impinge on the blue phosphor strips 16 thereby causing the emission of blue light from the picture screen 12.

By making the transparent material 23 which separates the conducting strips 26 and the first phosphor layer 24 very thin, it is possible to maintain a high degree of resolution during the transformation from the high speed electrons emitted by the electron gun 10 to the low speed electrons emitted by the photoelectric layer 30. Moreover, by the proper choice of materials, it may even be possible to obtain a net gain in the number of electrons available, thus producing a brighter final picture.

When the electrons are emitted from the photoelectric layer 30, they have very small velocities and, therefore, only a very small potential between successive conducting strips is necessary to produce the desired deflection in the electron beams extending from the photoelectric layer 30 to the picture screen 12.

By employing the construction shown herein, there is no problem of supporting the conducting strips and maintaining their separation at a uniform distance, as was the case in devices of the prior art. The apparatus disclosed herein is, therefore, believed to be relatively simple in construction and it is believed to be a highly dependable apparatus. In addition, the form of the conducting strips is such as to reduce substantially the capacity between the two sets of electrodes.

Although I have shown and described specific embodiments of my invention, I am aware that other modifications thereof are possible. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and the spirit of the invention.

I claim as my invention:

1. A color television tube having therein a viewing screen and a photoelectric screen, said viewing screen being located near the end of said tube and having thereon a plurality of strips of phosphor emitting a plurality of different colors of light, said phosphor strips lying parallel to each other, said photoelectric screen being parallel to said phosphor screen and comprising a layer of supporting material which is transparent to light, a layer of electron responsive phosphor on one side of said supporting material remote to said viewing screen, a layer of electron-emissive material on the other side of said supporting material facing said viewing screen, a plurality of strips of electrically conducting material extending across said electron-emissive material in a direction parallel to said phosphor strips.

2. A color television tube having therein a viewing screen and a photoelectric screen, said viewing screen being located near the end of said tube and having thereon a plurality of strips of phosphor emitting a plurality of different colors of light, said phosphor strips lying parallel to each other, said photoelectric screen being parallel to said phosphor screen and comprising a layer of supporting material which is transparent to light, a layer of electron responsive phosphor on one side of said supporting material remote to said viewing screen, a layer of electron-emissive material on the other side of said supporting material facing said viewing screen, a plurality of strips of electrically conducting material extending across said electron-emissive material in a direction parallel to said phosphor strips, electrodes for accelerating the electrons emitted by said electron-emissive material toward said viewing screen, each of said conducting strips having a width substantially equal to the phosphor strip opposite it.

3. A cathode-ray tube comprising an envelope having therein a primary screen and a picture screen, said primary screen lying in a plane parallel to the plane of said picture screen, said primary screen having thereon on the side near said picture screen a plurality of strips of electrically conducting material separated from each other, said picture screen having a plurality of strips of phosphor material, said phosphor strips lying alternately opposite said conducting strips and opposite the gaps between said conducting strips, each of said phosphor strips being of substantially the same width as the conducting strips or the gap which is opposite it, means for producing electrons in the region of the gaps between successive conducting strips, and electrodes for accelerating said electrons from the region of said conducting strips toward said phosphor strips.

4. In combination, a primary screen and a secondary screen, said primary screen lying parallel to said secondary screen, a plurality of conducting strips on said primary screen on the side of that screen nearest said secondary screen, said conducting strips being separated from each other by a substantial distance, a plurality of phosphor strips on said secondary screen on the side nearest said primary screen, said phosphor strips lying parallel to said conducting strips, said phosphor strips comprising a first phosphor representative of a first selected color, a second phosphor representative of a second selected color, and a third phosphor material representative of a third selected color, said phosphor strips being arranged in the following order: first phosphor, second phosphor, third phosphor, second phosphor, first phosphor, second phosphor, third phosphor; the said second phosphor strips lying opposite the region between successive conducting strips, means for emitting electrons from the region between the conducting strips so that the electrons pass through the region between successive conducting strips, electrodes for accelerating said electrons toward said secondary screen.

5. In combination, a primary screen and a secondary screen, said primary screen lying parallel to said secondary screen, a plurality of conducting strips on said primary screen on the side of that screen nearest said secondary screen, said conducting strips being separated from each other by a substantial distance, a plurality of phosphor strips on said secondary screen on the side nearest said primary screen, said phosphor strips lying parallel to said conducting strips, said phosphor strips comprising a first phosphor representative of a first selected color, a second phosphor representative of a second selected color, and a third phosphor material representative of a third selected color, means for emitting electrons from the region between the conducting strips so that the electrons pass through the region between successive conducting strips, electrodes for accelerating said electrons toward said secondary screen.

6. In combination an envelope having therein a primary screen and a picture screen substantially parallel to each other and separated by a short distance, said picture screen having thereon over difierent areas of said screen a plurality of phosphors capable of producing light of a plurality of colors, said primary screen comprising a layer of photoelectric material facing said picture screen, electrodes for producing an electric field in a first direction parallel to said primary screen in the region of a first small portion of said layer, electrodes for producing an electric field in a second direction parallel to said primary screen in the region of a second small portion of said layer, and electrodes for producing an electric field across the region between said primary screen and said picture screen.

7. A television tube comprising an envelope having therein a primary screen and a picture screen substantially parallel to each other, said primary screen comprising a rigid sheet of light transparent material, a plurality of strips of electrically conducting material deposited on said sheet on the side of said sheet toward said picture screen, and a photoelectric material in the regions between successive strips, and electrodes for producing an electric field between said primary screen and said picture screen so as to accelerate electrons emitted by said photoelectric layer toward said picture screen.

8. A television tube comprising a primary screen and a picture screen separated by a short distance from each other and substantially parallel to each other, said primary screen comprising a solid rigid sheet of transparent material, a plurality of deflecting electrodes deposited on said rigid sheet facing said picture screen, and means for emitting electrons in the region of said electrodes.

References Cited in the file of this patent UNITED STATES PATENTS 2,307,188 Bedford Jan. 5, 1943 2,446,791 Schroeder Aug. 10, 1948 2,568,448 Hansen Sept. 18, 1951 2,573,777 Sziklai Nov. 6, 1951 2,577,038 Rose Dec. 4, 1951

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