EP0113113A1 - Cathode ray tube - Google Patents
Cathode ray tube Download PDFInfo
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- EP0113113A1 EP0113113A1 EP83113068A EP83113068A EP0113113A1 EP 0113113 A1 EP0113113 A1 EP 0113113A1 EP 83113068 A EP83113068 A EP 83113068A EP 83113068 A EP83113068 A EP 83113068A EP 0113113 A1 EP0113113 A1 EP 0113113A1
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- grid
- potential
- ray tube
- cathode ray
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
- H01J29/46—Arrangements of electrodes and associated parts for generating or controlling the ray or beam, e.g. electron-optical arrangement
- H01J29/48—Electron guns
- H01J29/488—Schematic arrangements of the electrodes for beam forming; Place and form of the elecrodes
Definitions
- the present invention generally relates to an improvement of a cathode ray tube and particularly to a cathode ray tube of high resolution.
- resolution of a cathode ray tube depends on the size of beam spot which forms picture element on a fluorescent screen. That is, as the diameter of the beam spot becomes smaller, the resolution of the reproduced picture becomes higher. On the other hand, since the diameter of the beam spot increases as beam current increases, when a relatively large beam current flows to produce a high luminance spot, a blooming is produced thereby lowering resolution.
- FIG. 1 shows sectional view along the axis showing configuration of a bipotential type electron gun of prior-art
- FIG. 2 is a graph showing potential distribution along the axis of the electron gun.
- Thermal electrons emitted from the cathode 1 is focused by means of an electrostatic lens 4 called cathode lens which is constituted with a first grid (G1) as a control grid 2 and a second grid (G2) as an acceleration electrode 3, to produce a crossover 5, which is then preliminarily focused by a pre-focus lens 7 produced between the second grid (G2) 3 and the a third grid (G3) 6 as a focusing grid.
- the pre-focused electron beam is finally focused by a main lens 9 constituted with the third grid (G3) 6 and a fourth grid (G4) 8 as a final acceleration grid, thereby to produce a beam spot 11 on a fluorescent screen 10 by impinging thereto. That is, the beam spot 11 is an image of the crossover 5 projected by the pre-focus lens 7 and the main lens 9.
- FIG. 1 and FIG. 2 which shows distribution of potential along axial position of the electron gun, the potential gradually rises from the cathode 1 to the rear end (inlet end) of the third grid (G3) 6, thereby forming the cathode lens 4 and the pre-forcus lens 7.
- the cathode lens 4 and the pre-focus lens 7 can not be clearly distinguished, hereinafter these two lenses together are comprehensively called a beam forming part.
- the axial distribution in the third grid (G3) 6 is substantially constant at a value of V foc , thereafter the axial potential distribution rapidly rises from the outlet end of the third grid (G3) 6 to the fourth grid (G4) 8 to a high potential V , thereby forming the main lens 9.
- the actual beam spot 11 projected on the fluorescent screen 10 by the main lens 9 is the image of virtual image of the crossover 5 having a diameter d.
- This virtual image of the crossover 5 can be obtained by extending the straight line part of the electron beam paths 12-17 towards the direction of the cathode 1. The crossing part of the straight lines gives the location of the virtual image.
- the diameter d of the beam spot 11 on the fluorescent screen 10 is represented by the following equation (1).
- the magnification M is represented by the following equation (2).
- the value of the bracketted part is determined by the size and operation conditions of the cathode ray tube and C s is determined by the diameter of lens used.
- the beam diameter D exists in .the form of D -1 in the leftest part. of the right side, and in the form of D 3 in the rightest part, accordingly there is a value that will make d s minimum, and usually such value is selected. Under such condition, when d s is intended to be small, it is necessary to decrease a ⁇ d o as small as possible.
- FIG. 4 is a graph showing relations between the gap between the second grid (G2) and the third grid (G3) versus the values a ⁇ d o , a and d as such.
- d o drastically decreases and a increases contrarily, but as a result, a ⁇ d o decreases.
- the reason that d o drastically decreases as shown in FIG. 4 is regarded as owing to peripheral aberration at the beam forming part decreases as the potential gradation increases.
- The'decrease of the beam diameter D of the electron beam can be prevented by decreasing length of the third grid (G3), but then it becomes necessary that the focal length of the main lens 9 must be shortened in order to satisfy the focusing condition. Accordingly, the potential of the third grid (G3) must be lowered. Such lowering of the third grid potential decreases potential gradient between the second grid (G2) and the third grid (G3), thereby wastly diminishing the effect of decrease of a ⁇ d o in spite of decreasing the gap between the second grid (G2) and the third grid (G3).
- the present invention intends to dissolve the above-mentioned problems and eliminates the above-mentioned shortcomings of the conventional cathode ray tube, to provide an improved cathode ray tube having uniform small diameter of beam spot even for a wide range of brightness from a low brightness range to a high brightness range of operation.
- the cathode ray apparatus in accordance with the present invention comprises an electron gun, a fluoresent screen and an evacuated enclosure enclosing the electron gun and the fluorescent screen therein,
- the cathode ray tube of the present invention by increasing potential gradation at the beam forming part, spherical aberration as well as diameter of virtual crossover can be decreased, and focal length of the main lens is shortened by adoption of a novel potential gradient profile in the main lens part formed by a third grid (G3), a fourth grid (G4) and a fifth grid (G5), thereby enabling to limit the diameter of the electron beam in the part of the main lens even under an increase of the beam divergence angle.
- This invention attains smallness of diameter of the beam spot on the fluorescent screen even when a large beam current flows for high brightness, thereby attaining high resolution characteristic.
- FIG. 5 shows a first embodiment wherein the electron gun comprises a first grid (Gl) 2, a second grid (G2) 3, a third grid (G3) 22, a fourth grid (G4) 23 and a fifth grid (G5) 21, in this order from the cathode side to the fluorescent screen side.
- the electron gun comprises a first grid (Gl) 2, a second grid (G2) 3, a third grid (G3) 22, a fourth grid (G4) 23 and a fifth grid (G5) 21, in this order from the cathode side to the fluorescent screen side.
- the first grid (Gl) 2 works as a known control grid
- the second grid (G2) 3 has the same configuration as a known acceleration grid
- a third grid (G3) 22 is shaped a bored disk and is disposed close to the second grid (G2) 3 in order to make a large potential gradient of 10 5 V/cm ⁇ 5 x 10 5 V/cm
- the fourth grid (G4) 23 and the fifth grid (G5) 21 are both in simple cylindrical shape, and the third grid (G3) 22 is impressed with a constant voltage Vg 3 of +10 KV, and the fourth grid (G4) 23 is impressed with a variable focus voltage V foc which is lower than the constant voltage V g3 , and the fifth grid (G5) 21 is impressed with a positive high voltage V of about 30 KV.
- the axial potential distribution in the fourth grid (G4) 23 is lower than the constant potential Vg 3 of the third grid (G3) 22, therefore the focal length of the main lens 25 is reduced in comparison with the conventional electron gun configuration. From the above-mentioned configuration, even with retaining the potential rise in the beam-forming-part very steep, mutual distance between the virtual image crossover and the main lens can be shortened, thereby enabling the diameter of diverged beam at the part of the main lens 25 to decrease even when the beam divergence angle a increases. In view of the equation (3), this means that the value a ⁇ d o can be decreased without increase of the diverged beam diameter, and therefore the beam spot diameter d can be decreased.
- FIG. 7 a second preferred embodiment is described with reference to FIG. 7 and FIG. 8.
- the mechanical configurations and their relative arrangements are substantially equal to the first embodiment of FIG. 5 and FIG. 6, but their potential distribution profile is modified. That is, the third grid (G3) 22 is electrically connected to the fifth grid (G5) 21, and the second grid (G2) 3 is impressed with a constant voltage so as to produce a potential gradient of 10 5 V/cm ⁇ 5x10 5 V/ cm.
- the substantially cylindrical fourth grid (G4) 23 is impressed with a variable potential V foc , variable from almost 0 V to several KV.
- the fifth grid (G5) 21 is impressed with a constant potential of about 30 KV.
- the third grid (G3) 22 and the fifth grid (G5) 21 are impressed with high potentials, and the fourth grid ( G 4) 23 is impressed with a lower potential of several K V or lower, so that the potential distribution profile as shown in FIG. 8 is produced.
- the fourth grid (G4) 23 and the fifth grid ( G 5) 21 are drawn to have substantially the same diameter, these may be of different diameters. Especially when the variable potential V foc is used at a voltage near 0 volt, the diameter of the fourth grid (G4) 23 should be preferably larger than the diameter of the fifth grid (G5) 21.
- axial potential distribution in the fourth grid (G4) 23 can be lower than the potential of the third grid (G3) 22 of the potential Vg3, accordingly the focal distance can be shortened. Furthermore, since the electron gun can be shortened/the overall cathode ray tube length can be shortened.
- FIG. 9 shows a third embodiment.
- the components corresponding to the first embodiment of FIG. 5 are designated by the corresponding numerals as marks, and their redundant superposed descriptions are omitted for simplicity.
- the principal difference of the third embodiment of FIG. 9 from the first embodiment of FIG. 5 is that between the fourth grid (G4) 23 and the fifth grid (G5) 21, an auxiliary grid (G4 ⁇ 5) 26 is added.
- the fourth grid (G4) 23, the auxiliary grid (G4.5) 26 and the fifth grid (G5) 21 are equally cylindrical-shaped, and the third grid (G3) 22 and the auxiliary grid (G4 ⁇ 5) 26 are each other electrically connected in the cathode ray tube, and they are to be impressed with a focusing potential V foc of about 6 KV-10 KV.
- the fourth grid (G4) 23 is impressed with a potential V 4 which is lower than the focusing potential V foc
- the fifth grid (G5) 21 is impressed with a high potential V a of about 30 KV.
- the axial potential distribution profile in the beam forming part steeply rises from the cathode 1 towards the fluorescent screen 10, thereby drastically decreasing the value a ⁇ d o when the beam current is large, and on the other hand the beam divergence angle a increases. That is, as shown in FIG. 10 which is a graph showing axial potential distribution profile drawn in relation to the electrode disposition of FIG. 9, the potential rises from the cathode 1 to the electron beam aperture 24 of the third grid (G3) 22 upto the focusing potential V foc , and thereafter gently decreases towards the central part of the fourth grid (G4) 23.
- the axial potential of the fourth grid (G4) 23 is lower than the focusing potential V foc , and therefore the main lens 27 has a shorter focal distance in comparison with the conventional electron gun configuration.
- the thick main lens 27 has electric field distribution which gently changes in a very broad range, the spherical aberration of the main lens . is small, thereby making the aberration coefficient C s of the rightest term of the equation (3) very small, accordingly minimizing the diameter d of the beam spot.
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- Electrodes For Cathode-Ray Tubes (AREA)
- Cathode-Ray Tubes And Fluorescent Screens For Display (AREA)
Abstract
Description
- The present invention generally relates to an improvement of a cathode ray tube and particularly to a cathode ray tube of high resolution.
- Generally speaking, resolution of a cathode ray tube depends on the size of beam spot which forms picture element on a fluorescent screen. That is, as the diameter of the beam spot becomes smaller, the resolution of the reproduced picture becomes higher. On the other hand, since the diameter of the beam spot increases as beam current increases, when a relatively large beam current flows to produce a high luminance spot, a blooming is produced thereby lowering resolution.
- The above-mentioned is elucidated with reference to attached FIGUREs 1, 2, 3 and 4. FIG. 1 shows sectional view along the axis showing configuration of a bipotential type electron gun of prior-art, and FIG. 2 is a graph showing potential distribution along the axis of the electron gun. Thermal electrons emitted from the
cathode 1 is focused by means of anelectrostatic lens 4 called cathode lens which is constituted with a first grid (G1) as acontrol grid 2 and a second grid (G2) as anacceleration electrode 3, to produce acrossover 5, which is then preliminarily focused by apre-focus lens 7 produced between the second grid (G2) 3 and the a third grid (G3) 6 as a focusing grid. Then, the pre-focused electron beam is finally focused by a main lens 9 constituted with the third grid (G3) 6 and a fourth grid (G4) 8 as a final acceleration grid, thereby to produce abeam spot 11 on afluorescent screen 10 by impinging thereto. That is, thebeam spot 11 is an image of thecrossover 5 projected by thepre-focus lens 7 and the main lens 9. - As shown in FIG. 1 and FIG. 2 which shows distribution of potential along axial position of the electron gun, the potential gradually rises from the
cathode 1 to the rear end (inlet end) of the third grid (G3) 6, thereby forming thecathode lens 4 and thepre-forcus lens 7. Thecathode lens 4 and thepre-focus lens 7 can not be clearly distinguished, hereinafter these two lenses together are comprehensively called a beam forming part. Though the axial distribution in the third grid (G3) 6 is substantially constant at a value of Vfoc, thereafter the axial potential distribution rapidly rises from the outlet end of the third grid (G3) 6 to the fourth grid (G4) 8 to a high potential V , thereby forming the main lens 9. - Though the behavior of thermal electrons in the aforementioned beam forming part is very much complicated when the beam current is larger the electron paths become as represented by
several curves electron beam paths 12 to 17 cross at one point, then an ideal crossover of a small diameter and a small beam spot are produced, but in actualcathode ray tubepaths cathode 1 cross at apoint 18 which is the farest crossing from thecathode 1, and on the contrarythermal electron paths nearer point 19. This is because the lens of the above-mentioned beam forming part has spherical aberration, and accordingly the effective crossover diameter and beam spot diameter are considerably larger than their theoretical limit values. - Since there is the
pre-focus lens 7,theactual beam spot 11 projected on thefluorescent screen 10 by the main lens 9 is the image of virtual image of thecrossover 5 having a diameter d. This virtual image of thecrossover 5 can be obtained by extending the straight line part of the electron beam paths 12-17 towards the direction of thecathode 1. The crossing part of the straight lines gives the location of the virtual image. Now, provided that the virtual image of the crossover has a diameter d., then the diameter d of thebeam spot 11 on thefluorescent screen 10 is represented by the following equation (1). - wherein M is a magnification of the main lens 9,
- Cs is spherical aberration coefficient of the main lens 9,
- D is diameter of the electron beam at the main lens 9..
-
- wherein a is a maximum divergence angle of electron beam emanated from the beam forming part,
- L is distance between the center of the main lens 9 and the
fluorescent screen 10, - Vg3 is potential of the third grid (G3) 6,
- Va is potential of the fourth grid (G4) 8.
-
- In the above-mentioned equation (3), the value of the bracketted part is determined by the size and operation conditions of the cathode ray tube and Cs is determined by the diameter of lens used. - The beam diameter D exists in .the form of D-1 in the leftest part. of the right side, and in the form of D3 in the rightest part, accordingly there is a value that will make ds minimum, and usually such value is selected. Under such condition, when ds is intended to be small, it is necessary to decrease a·do as small as possible.
- According to the study of the inventors, it has been found that when potential gradient in the part between the second grid (G2) and the third grid (G3) is made steep, a·do can be decreased. FIG. 4 is a graph showing relations between the gap between the second grid (G2) and the third grid (G3) versus the values a·do, a and d as such. When the gap between the second grid (G2), and third grid (G3) is decreased, do drastically decreases and a increases contrarily, but as a result, a·do decreases. The reason that do drastically decreases as shown in FIG. 4 is regarded as owing to peripheral aberration at the beam forming part decreases as the potential gradation increases.
- The effect of the decrease in product a·do becomes prominent for potential gradient above about 105 V/cm, and as the product a·do becomes smaller, the minimizing of beam spot diameter at a large current becomes easier. The diameter of beam spot, however, becomes.larger at a small beam current under such high potential gradient. Besides, when the potential gradient is excessively large, electron emission due to field emission is liable to take place from the surface of the second grid (G2),
- and the emitted electrons make undesirable light at impinging on the
fluorescent screen 10. - As has been described, practically admissible value of the potential gradient has an upper limit which is, according to the inventors' experiments, about 5 x 105 V/cm. Accordingly, when potential difference between the second grid (G2) and the third grid (G3) is selected 8 KV, taking account the above-mentioned admissible potential gradient, the gap between the second grid (G2) and the third grid (G3) becomes 0.8 mm to 0.16 mm.
- Even though the above-mentioned potential gradient is applied to the beam forming part of an electron gun of the conventional cathode ray tube, diameter of the beam spot on the fluorescent screen can not be decreased as desired. This is because that beam divergence angle a increases when the potential gradient between the second grid (G2) and the third grid (G3) is raised. When the beam divergence anglea increases, diameter D of the electron beam in the main lens 9 increases, thereby undesirably increasing such part of the rightest part of the equation (3) which is influenced by the aberration of the main lens 9. Since the leftest part is proportional to third power of D, even a small increase of the diameter D of the electron beam prominently increases the rightest part. Accordingly, even though the value a-do in the first term of the right side of the equation (3) decreases, the diameter d of
- the beam spot on the fluorescent screen increases, on the contrary.
- The'decrease of the beam diameter D of the electron beam can be prevented by decreasing length of the third grid (G3), but then it becomes necessary that the focal length of the main lens 9 must be shortened in order to satisfy the focusing condition. Accordingly, the potential of the third grid (G3) must be lowered. Such lowering of the third grid potential decreases potential gradient between the second grid (G2) and the third grid (G3), thereby wastly diminishing the effect of decrease of a·do in spite of decreasing the gap between the second grid (G2) and the third grid (G3).
- The present invention intends to dissolve the above-mentioned problems and eliminates the above-mentioned shortcomings of the conventional cathode ray tube, to provide an improved cathode ray tube having uniform small diameter of beam spot even for a wide range of brightness from a low brightness range to a high brightness range of operation.
- The cathode ray apparatus in accordance with the present invention comprises an electron gun, a fluoresent screen and an evacuated enclosure enclosing the electron gun and the fluorescent screen therein,
- the electron gun comprising
- a cathode,
- a first grid (Gl) as a control grid,
- a second grid (G2) on which an accelerating potential is to be applied,
- a third grid (G3),
- a fourth grid (G4) and
- a fifth grid (G5) as a final acceleration grid, which are disposed in this sequential order, wherein
- the third grid (G3) is impressed with a higher potential than a potential impressed on the second grid (G2) and
- the fourth grid (G4) is impressed with a lower potential than the potential impressed on the third grid (G3),
- thereby forming such an axial potential distribution of the cathode ray tube that
- a maximum potential is produced at an axial position of the third grid (G3), and thereafter the axial potential gradually decreases towards a minimum potential at an axial position of the fourth grid (G4) and further increases gradually towards an axial region of the fifth grid (G5), thereby forming substantially a single main lens at a region ranging from the third grid (G3) to the fifth grid (G5).
- According to the cathode ray tube of the present invention, by increasing potential gradation at the beam forming part, spherical aberration as well as diameter of virtual crossover can be decreased, and focal length of the main lens is shortened by adoption of a novel potential gradient profile in the main lens part formed by a third grid (G3), a fourth grid (G4) and a fifth grid (G5), thereby enabling to limit the diameter of the electron beam in the part of the main lens even under an increase of the beam divergence angle. This invention attains smallness of diameter of the beam spot on the fluorescent screen even when a large beam current flows for high brightness, thereby attaining high resolution characteristic.
-
- FIG. 1 is the sectional view along the axis of conventional electron gun, with schematically shown fluorescent screen.
- FIG. 2 is the graph showing the distribution of potential gradient along the axial position of the electron gun shown in relation to the positions..in FIG. 1.
- FIG. 3 is a schematical chart showing electron paths in the electron gun of the prior art of FIG. 1.
- FIG. 4 is a graph showing relations between the gap between the second grid (G2) and the third grid (G3) and value d , a and a·do.
- FIG. 5 is a sectional view along the axis of electron gun, with schematically shown fluorescent screen, as a first embodiment in accordance with the present invention.
- FIG. 6 is a graph showing the distribution of potential along the axial position of the electron gun shown in relation to the positions in FIG. 5.
- FIG. 7 is a sectional view along the axis of electron gun, with schematically shown fluorescent screenas a second embodiment in accordance with the present invention.
- FIG. 8 is a graph showing the distribution of potential along the axial position of the electron gun shown in relation to the positions in FIG. 7.
- FIG. 9 is a sectional view along the axis of electron gunwith schematically shown fluorescent screen, as a third embodiment in accordance with the present invention.
- FIG. 10 is a graph showing the distribution of potential along the axial position of the electron gun shown in relation to the positions in FIG. 9. Description of the Preferred Embodiments
- A cathode ray tube in accordance with the present invention is described on preferred embodiments shown hereinafter with reference to FIG. 5 and thereafter. FIG. 5 shows a first embodiment wherein the electron gun comprises a first grid (Gl) 2, a second grid (G2) 3, a third grid (G3) 22, a fourth grid (G4) 23 and a fifth grid (G5) 21, in this order from the cathode side to the fluorescent screen side. The first grid (Gl) 2 works as a known control grid, the second grid (G2) 3 has the same configuration as a known acceleration grid, and a third grid (G3) 22 is shaped a bored disk and is disposed close to the second grid (G2) 3 in order to make a large potential gradient of 105 V/cm― 5 x 105 V/cm. The fourth grid (G4) 23 and the fifth grid (G5) 21 are both in simple cylindrical shape, and the third grid (G3) 22 is impressed with a constant voltage Vg3 of +10 KV, and the fourth grid (G4) 23 is impressed with a variable focus voltage Vfoc which is lower than the constant voltage Vg3, and the fifth grid (G5) 21 is impressed with a positive high voltage V of about 30 KV.
- By such configuration, axial potential distribution at the beam forming part steeply rises from the cathode side towards the fluorescent screen, and accordingly the value a·do prominently decreases, but on the other hand, beam divergence angle a increases. That is, as shown in FIG. 6, the axial potential distribution rises in the
electron beam aperture 24 of the third grid (G3) 22 up to the potential Vg3, and gradually decreases towards the central part of the fourth grid (G4) 23. The potential again increases from the central part of the fourth grid (G4) 23 towards the central part of the fifth grid (G5) 21, and at the central part of the fifth grid (G5) 21 reaches the high potential V and remains almost constant thereafter. Accordingly, by the relative congigu- ration of the third grid (G3) 22, the fourth grid (G4) 23 and the fifth grid (G5) 21, and their potential distributions, a complex lens field is produced, thereby substantially forming a single thickmain lens 25. - The axial potential distribution in the fourth grid (G4) 23 is lower than the constant potential Vg3 of the third grid (G3) 22, therefore the focal length of the
main lens 25 is reduced in comparison with the conventional electron gun configuration. From the above-mentioned configuration, even with retaining the potential rise in the beam-forming-part very steep, mutual distance between the virtual image crossover and the main lens can be shortened, thereby enabling the diameter of diverged beam at the part of themain lens 25 to decrease even when the beam divergence angle a increases. In view of the equation (3), this means that the value a·do can be decreased without increase of the diverged beam diameter, and therefore the beam spot diameter d can be decreased. - Nextly, a second preferred embodiment is described with reference to FIG. 7 and FIG. 8. In the example of FIG. 7, the mechanical configurations and their relative arrangements are substantially equal to the first embodiment of FIG. 5 and FIG. 6, but their potential distribution profile is modified. That is, the third grid (G3) 22 is electrically connected to the fifth grid (G5) 21, and the second grid (G2) 3 is impressed with a constant voltage so as to produce a potential gradient of 105 V/cm―5x105 V/cm. The substantially cylindrical fourth grid (G4) 23 is impressed with a variable potential Vfoc, variable from almost 0 V to several KV. The fifth grid (G5) 21 is impressed with a constant potential of about 30 KV. That is, in this embodiment the third grid (G3) 22 and the fifth grid (G5) 21 are impressed with high potentials, and the fourth grid (G4) 23 is impressed with a lower potential of several KV or lower, so that the potential distribution profile as shown in FIG. 8 is produced.
- Though the fourth grid (G4) 23 and the fifth grid (G5) 21 are drawn to have substantially the same diameter, these may be of different diameters. Especially when the variable potential Vfoc is used at a voltage near 0 volt, the diameter of the fourth grid (G4) 23 should be preferably larger than the diameter of the fifth grid (G5) 21.
- As a result of the above-mentioned configuration and electric connection, axial potential distribution in the fourth grid (G4) 23 can be lower than the potential of the third grid (G3) 22 of the potential Vg3, accordingly the focal distance can be shortened. Furthermore, since the electron gun can be shortened/the overall cathode ray tube length can be shortened.
- FIG. 9 shows a third embodiment. In this embodiment, the components corresponding to the first embodiment of FIG. 5 are designated by the corresponding numerals as marks, and their redundant superposed descriptions are omitted for simplicity. The principal difference of the third embodiment of FIG. 9 from the first embodiment of FIG. 5 is that between the fourth grid (G4) 23 and the fifth grid (G5) 21, an auxiliary grid (G4·5) 26 is added. The fourth grid (G4) 23, the auxiliary grid (G4.5) 26 and the fifth grid (G5) 21 are equally cylindrical-shaped, and the third grid (G3) 22 and the auxiliary grid (G4·5) 26 are each other electrically connected in the cathode ray tube, and they are to be impressed with a focusing potential Vfoc of about 6 KV-10 KV. The fourth grid (G4) 23 is impressed with a potential V 4 which is lower than the focusing potential Vfoc, and the fifth grid (G5) 21 is impressed with a high potential Va of about 30 KV.
- As a result of the above-mentioned mechanical configuration and electric arrangement, the axial potential distribution profile in the beam forming part steeply rises from the
cathode 1 towards thefluorescent screen 10, thereby drastically decreasing the value a·do when the beam current is large, and on the other hand the beam divergence angle a increases. That is, as shown in FIG. 10 which is a graph showing axial potential distribution profile drawn in relation to the electrode disposition of FIG. 9, the potential rises from thecathode 1 to theelectron beam aperture 24 of the third grid (G3) 22 upto the focusing potential Vfoc, and thereafter gently decreases towards the central part of the fourth grid (G4) 23. Then the potential gently rises from the central part of the fourth grid (G4) 23 through the auxiliary grid (G4·5) 26 and to the central part of the fifth grid (G5) 21, as one continuous region, reaching up to the high potential of V. Accordingly, as a result of configurations, spatial dispositions and relative potential distributions of the third grid (G3) 22, the fourth grid (G4) 23, the auxiliary grid (G4.5) 26 and the fifth grid (G5) 21, an broad region electric field is produced, thereby forming a substantially single very thickmain lens 27 shown in FIG. 9. - In this embodiment, the axial potential of the fourth grid (G4) 23 is lower than the focusing potential Vfoc, and therefore the
main lens 27 has a shorter focal distance in comparison with the conventional electron gun configuration. - Furthermore, since the thick
main lens 27 has electric field distribution which gently changes in a very broad range, the spherical aberration of the main lens . is small, thereby making the aberration coefficient Cs of the rightest term of the equation (3) very small, accordingly minimizing the diameter d of the beam spot.
Claims (5)
electric field between said second grid (G2) and said third grid (G3) is selected to be 105 V/cm-5 x 105 V/cm.
potential of said third grid (G3) is 10 KV or lower.
said third electrode (G3) and said fifth grid (G5) are each other connected in said cathode ray tube.
an auxiliary grid (G4·5) between said fourth and fifth grid (G4, G5), which is connected to said third grid (G3) .
Applications Claiming Priority (6)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP23412982A JPS59123139A (en) | 1982-12-29 | 1982-12-29 | Picture tube device |
JP234130/82 | 1982-12-29 | ||
JP23413082A JPS59123140A (en) | 1982-12-29 | 1982-12-29 | Picture tube device |
JP234129/82 | 1982-12-29 | ||
JP122514/83 | 1983-07-05 | ||
JP12251483A JPS6014733A (en) | 1983-07-05 | 1983-07-05 | Picture tube device |
Publications (2)
Publication Number | Publication Date |
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EP0113113A1 true EP0113113A1 (en) | 1984-07-11 |
EP0113113B1 EP0113113B1 (en) | 1987-09-16 |
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Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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EP19830113068 Expired EP0113113B1 (en) | 1982-12-29 | 1983-12-23 | Cathode ray tube |
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EP (1) | EP0113113B1 (en) |
DE (1) | DE3373746D1 (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0319328A2 (en) * | 1987-12-04 | 1989-06-07 | Rank Brimar Limited | Electron guns for cathode ray tubes |
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-
1983
- 1983-12-23 DE DE8383113068T patent/DE3373746D1/en not_active Expired
- 1983-12-23 EP EP19830113068 patent/EP0113113B1/en not_active Expired
Patent Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US2902623A (en) * | 1956-08-17 | 1959-09-01 | Rca Corp | Electron gun structure |
US2971108A (en) * | 1958-09-26 | 1961-02-07 | Sylvania Electric Prod | Electron discharge device |
US3036238A (en) * | 1960-04-29 | 1962-05-22 | Sylvania Electric Prod | High resolution c.r. tube |
DE2850656A1 (en) * | 1977-11-22 | 1979-05-23 | Tokyo Shibaura Electric Co | Electron gun for in-line colour crt |
US4334170A (en) * | 1979-09-28 | 1982-06-08 | Zenith Radio Corporation | Means and method for providing optimum resolution of T.V. cathode ray tube electron guns |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0319328A2 (en) * | 1987-12-04 | 1989-06-07 | Rank Brimar Limited | Electron guns for cathode ray tubes |
EP0319328A3 (en) * | 1987-12-04 | 1990-05-30 | Rank Brimar Limited | Electron guns for cathode ray tubes |
US5034654A (en) * | 1987-12-04 | 1991-07-23 | Leyland John D | Beam focusing means for a CRT electron gun assembly |
Also Published As
Publication number | Publication date |
---|---|
DE3373746D1 (en) | 1987-10-22 |
EP0113113B1 (en) | 1987-09-16 |
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