US3828216A

US3828216A - Color display tube with elongated phosphor dots and shadow mask apertures

Info

Publication number: US3828216A
Application number: US00324133A
Authority: US
Inventors: Y Fuse
Original assignee: Sony Corp
Current assignee: Sony Corp
Priority date: 1970-02-14
Filing date: 1973-01-16
Publication date: 1974-08-06
Anticipated expiration: 1991-08-06

Abstract

A shadow mask tube having elongated apertures arranged in rows with the ends of apertures in each row extending between apertures in the next row to improve light emission and eliminate moire patterns caused by scanning non-emissive areas.

Description

I United States Patent 1191 1111 3,828,216

Fuse 1 Aug. 6, 1974 COLOR DISPLAY TUBE WITH 3,448,316 6/1969 Yoshida et a1. 313/70 ELONGATED PHOSPHOR DOTS AND 3,663,854 /1972 Tsuneta et a1 313/92 B X SHADOW MASK APER Es FOREIGN PATENTS OR APPLICATIONS [75] Inventor: Yum Fuse Japan 393 417 10/1965 Switzerland 313/85 s [73] Assignee: Sony Corporation, Tokyo, Japan 807Zl29 1/1959 Great Britain. led Ja 16 1973 1,023,334 3/1966 Great Britain 313/85 S [2]] App! 324,133 Primary ExaminerRobert Segal Related Application Data Attorney, Agent, or Firm--Lewis H. Eslinger, Esq.; [63] Continuation of Ser. No. 114,981, Feb. 12, 1971, Alvin Sinderbrand, Esq.

abandoned.

[] Foreign Application Priority Data Feb. 14, 1970 Japan -12886 [57] ABSTRACT A shadow mask tube having elongated apertures arg% 5 ranged in rows with the ends of apertures in each row d 313/85 92 B extending between apertures in the next row to im- 1 0 prove light emission and eliminate moire patterns References Cited caused by scanning non-emissive areas.

UNITED STATES PATENTS 6 Claims 5 Drawing Figures 2,922,073 1/1960 Oestreicher 313/ S 2 7 a9 7-Lv L i g L X 3: Mr .L

PAIENIEB 5W4 SHEEI 1 0f 2 INVENTOR.

Yuzo E15 BY ATTORNEY 2 COLOR DISPLAY TUBE WITH ELONGATED PHOSPI'IOR DOTS AND SHADOW MASK APERTURES This is a continuation of application Ser. No. 114,981, filed Feb. 12, 1971, and now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the field of shadow mask cathode ray tubes for color display and particularly to an improved shadow mask arrangement for such tubes.

2. Description of the Prior Art Apertured shadow mask cathode ray tubes for color television have been made in the past so that each aperture was circular and was equally spaced from six surrounding apertures. Each aperture controlled the access path to three circular phosphor elements substantially equidistant from that aperture. While it was thought that all of the elements should be of the same diameter and contiguous with six other elements, experience has shown that the phosphor elements should be smaller in diameter and should have some space around them. Preferably this surrounding area is made black to improve the contrast ratio of the color television picture. The apertures are also made smaller than they theoretically could be, which makes the mask more opaque to electron beams than it might be and reduces the maximum possible brightness of the picture. Another adverse effect is that the scanning electron beam (or beams) may follow a path that strikes mostly opaque sections of the shadow mask rather than sections having apertures. For example, one scanning line may pass through the centers of a row of apertures and may therefore cause the maximum amount of light to be emitted. The next line may strike only metal portions of the mask and may pass between two rows of apertures. This latter beam would cause little or no light to be emitted from the phosphor screen. Depending on the relative spacing of the scanning lines and the apertures, and depending also upon the amount and location of those sections of the screen not coated with light-emitting phosphor, a moire pattern of alternate light and dark strips may be produced in the television picture.

It is one of the primary objects of the present invention to provide a shadow mask arrangement that minimizes or eliminates moire patterns in the television picture and increases the amount of screen area capable of emitting light.

It is another object of the invention to provide a shadow mask having apertures of more nearly optimum arrangement and spacing than in previous shadow mask tubes.

Other object will become apparent from the following specification and drawings.

BRIEF DESCRIPTION OF THE INVENTION In accordance with the invention, a shadow mask with non-circular apertures is provided. The apertures are preferrably arranged so that their longer dimensions are perpendicular to the scanning lines of the color television picture. Furthermore, the spacing between the most closely adjacent apertures in the direction perpendicular to the scanning lines is approximately equal to the spacing between the most closely adjacent apertures in the direction of the scanning lines, thereby equalizing the resolution of the color television picture in the horizontal and vertical directions. Also in accordance with the invention, the elongated apertures in one horizontal row are displaced from the next adjacent horizontal row by a distance less than the vertical dimension of the apertures, thus producing some interleaving of elongated apertures in adjacent rows. Ideally, the apertures may have a rhombic shape, but they can also be more or less in the shape of elongated hexagons or even ellipses. The operation of the tube may be further improved by making the apertures larger in size than the phosphor elements behind them.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 shows an arrangement of round phosphor elements on a color television cathode ray tube constructed in accordance with the prior art;

FIG. 2 is an array of square phosphor elements arranged for use with a modified shadow mask;

FIG. 3 is an array of rectangular phosphor elements arranged in a more efficient pattern than the phosphor elements of FIGS. 1 and 2;

FIG. 4 shows an array of rhombic phosphor elements and shadow mask apertures according to the present invention; and

FIG. 5 is a cross-sectional view of a color television tube constructed to incorporate the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS Basically, FIG. 1 shows a screen 10 with an array of circular phosphor elements of maximum permissible size so that each element is contiguous with six others surrounding it. The elements are arranged in horizontal rows in a repetitive pattern and are identified as R, B, and G to correspond to the fact that all elements bearing the letter R emit red light, all those bearing the letter B emit blue light, and all those bearing the letter G emit green light. The space 11 between the round phosphor elements is supposed to be incapable of emitting light and therefore has been shown shaded.

FIG. 1 also shows the perpendicular projection of holes in the aperture mask that controls the access of electrons to the individual phosphor elements. For example, the hole 12 is centered between three phosphor elements 13-15, which emit, respectively, green, red, and blue light. Also shown is a perpendicular projection of the paths of the electrons that pass through the aperture 12 on the way to the three phosphor elements 13-15. The size of the aperture 12 is such that only the central area of the phosphor elements 13-15 is struck by electrons and the annular region surrounding this central area is shielded from all of the electron beams. As a result, this surrounding area may be a material other than the phosphor and in particular it may be carbon or manganese dioxide so that it absorbs light, thereby improving the contrast ratio of the color television picture.

The arrangement of phosphor elements 13-15 in triangular groups produces the closest spacing of the three primary color elemental light sources and would appear to produce the highest resolution of a color television picture. However, due to the fact that the apertures l2 and the phosphor elements 13-15 are arranged in triangular arrays of densely packed equilateral triangles, the pitch spacing P between apertures horizontally displaced on the same line is different from the pitch spacing P between apertures spaced vertically in the same column. As a matter of fact, the pitch spacing P is 3 times the pitch spacing P Another defeet in the color screen in FIG. 1 is the relatively large area of the screen that produces no light due to the limited size of the apertures 12 and the excited phosphor areas. As shown in the drawing, there are horizontal bands having a width W from which no light can be emitted. If these bands are spaced apart by a distance that differs from the distance between scanning lines of the color television picture, or is in a different direction, a moire pattern will be produced which will adversely affect the quality of the television picture.

FIG. 2 shows a screen 16 in which an attempt has been made to achieve greater light output by arranging the phosphor elements 17-19 as squares instead of circles. This eliminates the area that is not coated with any phosphor, but the screen 16 in FIG. 2 still has apertures 21 smaller in size than the size of the phosphor elements. Therefore, there are horizontal lines of width W from which no light will be emitted and these can produce the same type of undesirable moire effect as the corresponding bands of width W in the screen 10 of FIG. 1.

FIG. 3 shows a modified screen 22 having rectangular phosphor elements 23-25. The ratioof width to height of these rectangular phosphor elements is such that the spacing between the most closely adjacent phosphor elements of the same color, for example, the phosphor elements 23 that emit green light, is reduced to a minimum. Lines through the center ofthe most closely adjacent phosphor elements make angles of approximately 45 with respect to the horizontal and vertical. In addition, the vertical pitch spacing P is approximately equal to the horizontal pitch spacing P which results in uniform resolution in the horizontal and vertical directions. However, there is still the possibility of producing a moire pattern due'to'bandsof width W from which no light is emitted.

FIG. 4 shows a fluorescent screen 27 with an array of phosphor elements according to the present invention. Each phosphor element is in the shape of a rhombus, and, as before, the elements are divided into groups capable of emitting light in the three primary colors. The elements 28 emit green light, the elements 29 emit blue light, and the elements 30 emit red light.

The rhombic phosphor elements have their major dimension in the vertical direction and their minor dimension in the horizontal direction. As a result, the

phosphor elements may be considered to be arrangedin horizontal rows L and elements of the same color characteristic are arranged in vertical columns Ly.

The apertures and the shadow mask to be used with the screen 27 are indicated by reference numeral 31 and are also rhombic. Unlike the apertures in the embodiments shown in FIGS. 1-3, the apertures 31 of one row overlap the apertures 31 in the adjoining row. The width of each row, for example as indicated by X, and X is determined by the maximum dimension of the apertures and the spacing between a line through the centers of the apertures in each of two adjoining rows is less than the width of those rows. As shown, the apertures 31 in each row are partly interleaved with the apertures 31in the next adjoining row so that every horizontal line or nearly horizontal line can be traced out by the electron beam that passes through apertures in either one row or the next adjoining row. Consequently, there is no significant moire pattern produced by this screen of FIG. 4 even if the apertures 31 are somewhat smaller than the phosphor elements 28-30.

The rhombic shape of the apertures 31 and of the phosphor elements for each of the individual colors, for example the elements 28, is such that the vertical spacing P is approximately equal to the horizontal spacing P thereby equalizing the resolution between the horizontal and vertical directions. In addition, the spacing of the nearest adjacent apertures 31 is such that these apertures lie along lines that make 45 angles with respect to the horizontal and vertical direction.

In order to make the aperture mask 27 sufficiently rigid, the vertically adjoining apertures must not run into each other. As may be seen, making the apertures 31 even slightly smaller than the phosphor elements permits the closest bands of vertically adjacent apertures to be spaced by a substantial distance d. As a result, the mask 27 is strong enough to stand up under commercial usage.

Although the preferred shape of the apertures 31 is rhombic, they may be slightly flattened off at the top and bottom or on the sides to form elongated hexagons, or they may be rounded off to form ellipses.

FIG. 5 shows a complete cathode ray tube 32 constructed according to the invention. This tube is basically of the same type shown in U.S. Pat. No. 3,448,316 and comprises three cathodes 33-35 that emit, respectively, beams of electrons to energize phosphor elements that produce green, blue, and red light. The cathodes 33-35 are supported in properly spaced relationship to a common first grid, or control electrode, 36 which has three apertures 37-39 aligned with the cathodes 33-35, respectively. The tube has a second grid electrode 41 with apertures 42-44 aligned with the apertures 37-39. Beyond the electrode 41 is an anode 46 which, together with the electrode 41, produces a common lens field 47 that causes all of the electron beams from the cathodes 33-35 to converge to the center of an electron lens 48 so as to minimize deleterious effects due primarily to spherical aberration and coma. The central rays of the three electron beams are indicated by reference numerals 49-51 and they are modulated with information corresponding, respectively, to green, red, and blue portions of a television picture.

The main electron lens 48 is formed by electrostatic fields of the anode 46, a focusing electrode 52, and another anode section 53 directly electrically connected to the anode 46. The lens thus formed may also be referred to as an einzel lens. Beyond the lens field is a set of converging deflection'electrodes 54-57 of which the

electrodes

55 and 56 are at one potential, preferably the potential of the

anodes

46 and 53 and the

electrodes

54 and 57 are at a negative potential with respect to the

electrodes

55 and 56. As a result, the electron beam 49 is not subjected to any deflecting forces and continues directly along the axis, and the electron beams 50 and 51 are deflected back toward the axis. The inner wall of the tube 32 has a conductive coating 58 that is electrically connected to the

anodes

46 and 53.

The electron beams converge at a shadow mask 59 in which the apertures 31 of FIG. 4 are located. The shadow mask is a thin sheet of metal supported by a rim 61 held in place by springs 62 on ceramic studs 63 that determine the exact location of the mask. The mask is curved in accordance with the curvature of the face plate 64 of the tuve 32, and the inner surface of this face plate is the screen 27 on which the phosphor elements 28-30 of FIG. 4 are deposited. The orientation of the apertures 31 in the mask 59 is such that the long dimension of these apertures is perpendicular to the plane of the drawing and the short dimension is in the plane of the drawing. A deflection yoke 66 is located on the neck of the tube to deflect the electron beams 49-51 across the surface of the mask 59, and the mask is so oriented that the line deflection of the beams in forming a television picture is perpendicular to the long dimension of the apertures 31 and parallel to the short dimension of these apertures.

The arrangement of the beam-forming electrodes in the tube in FIG. 5 is such that all three of the beams 49-51 are in the same plane, which should be oriented so that it is perpendicular to the major dimension of the apertures 31. As the beams pass through the apertures, they do so along paths that lead to specific sets of the phosphor elements on the screen. The beam 49, for example, passes through the apertures 31 along paths that lead only to phosphor elements that emit green light, which are the phosphor elements 38 in FIG. 4. The beam 50 passes through the apertures 31 along paths that lead only to the elements 30 that emit red light, and the beam 51 passes through-the apertures 31 along paths that lead only to the elements 29 that emit blue light.

As an alternative to arranging the beam-forming electrodes so that the beams 49-51 are in line with each other, they may be arranged in what has come to be known as a delta configuration corresponding to the triangular array of phosphor elements. If the beams are so arranged in the present case for use with a screen of the type of screen 27 in FIG. 4, two of the beams should strike the screen along a line parallel to the direction of the scanning lines and parallel to the smaller dimension of the apertures 31 and the third beam should lie along a perpendicular bisector of the line joining the other two beams. This perpendicular bisector is parallel to the major dimension of the apertures 31. As a further alternative a three-gun structure could be used instead of the single-gun structure shown to direct beams toward the shadow mask 59.

What is claimed is:

l. A cathode ray tube comprising:

A. Means for generating a plurality of electron beams and for converging said beams from originating points spaced apart in a flat plane;

B. A viewing screen;

C. An array of phosphor elements arranged in a repetitive pattern of groups thereof at predetermined locations on said screen, with each of said groups including phosphor elements each relating to a respective one of said electron beams and emitting light of a characteristic color when impinged upon by the respective beam; and

D. A shadow mask positioned adjacent said screen and having an array of apertures each located in correspondence to a respective one of said groups of phosphor elements, said apertures and said phosphor elements being longer in one direction than in a direction substantially perpendicular to said one direction and arranged in rows in said perpendicular direction which is generally parallel to said flat plane, the width of each of said rows being defined by the lengths of said apertures in that row, the centers of adjoining rows being spaced apart by a distance less than the width of each of said adjoining rows, said apertures of each of said rows being interleaved with said apertures of each of the adjoining rows, each of said apertures in each of said rows being substantially aligned in the direction of the aperture length with one of said apertures two rows therefrom, and the center-to-center spacing between the aligned apertures two rows apart being substantially equal to the center-tocenter spacing between adjacent ones of said apertures in the same row.

2. The cathode ray tube of claim 1 in which said apertures are rhombic.

3. The cathode ray tube of claim 1 in which lines joining the centers of the nearest adjacent apertures not in the same row make an angle of approximately 45 with respect to said rows.

4. A cathode ray tube according to claim 1; in which said phosphor elements are of rhombic shape and substantially cover the entire area of said screen.

5. A cathode ray tube according to claim 1; in which said apertures and phosphor elements have substantially similar shapes.

6. A cathode ray tube according to claim 5; in which said similar shapes of the apertures and phosphor elements are substantially rhombic.

* III

Claims

1. A cathode ray tube comprising: A. Means for generating a plurality of electron beams and for converging said beams from originating points spaced apart in a flat plane; B. A viewing screen; C. An array of phosphor elements arranged in a repetitive pattern of groups thereof at predetermined locations on said screen, with each of said groups including phosphor elements each relating to a respective one of said electron beams and emitting light of a characteristic color when impinged upon by the respective beam; and D. A shadow mask positioned adjacent said screen and having an array of apertures each located in correspondence to a respective one of said groups of phosphor elements, said apertures and said phosphor elements being longer in one direction than in a direction substantially perpendicular to said one direction and arranged in rows in said perpendicular direction which is generally parallel to said flat plane, the width of each of said rows being defined by the lengths of said apertures in that row, the centers of adjoining rows being spaced apart by a distance less than the width of each of said adjoining rows, said apertures of each of said rows being interleaved with said apertures of each of the adjoining rows, each of said apertures in each of said rows being substantially aligned in the direction of the aperture length with one of said apertures two rows therefrom, and the center-to-center spacing between the aligned apertures two rows apart being substantially equal to the center-to-center spacing between adjacent ones of said apertures in the same row.

2. The cathode ray tube of claim 1 in which said apertures are rhombic.

3. The cathode ray tube of claim 1 in which lines joining the centers of the nearest adjacent apertures not in the same row make an angle of approximately 45* with respect to said rows.