ITT IDEAL COLOR 3331 OSCAR CHASSIS PIL ST CHASSIS 456813/8B CRT TUBE ITT(SEL) A51-210X.

In-line gun system for a color picture tube:
Super Precision In-Line ITT SEL.

In a color picture tube with an in-line gun system elliptic beam-spot distortion caused by the deflection field is compensated for by pairs of plates in at least one focus electrode. The plates project into the apertures for the electron beams and are located at a distance from the bottom of the focus electrode.

What is claimed is: 1. A color picture tube, comprising:
a screen;
a funnel;
a neck;
a deflection system mounted on said neck at the transition of said neck to said funnel and which contains an inline gun system comprising cathodes and grid and focus electrodes, said focus electrodes having separate apertures each with a continuous edge for guiding electron beams to said screen, at least one of said focus electrodes having plates attached thereto which are located on both sides of the electron beams and are disposed on the screen side of said at least one said focus electrodes; said plates having curved portions which project into said apertures and are arranged in a spaced relationship from the screen side of the aperture of the respective focus electrode; and
one of the grid electrodes contains a slit diaphragm.
2. A color picture tube as claimed in claim 1, wherein:
vertices of said curved portions of said plates for the outer electron beams are located beside the center lines of said apertures for these electron beams in the focus electrode.
3. A color picture tube as claimed in claim 1, wherein:
the distances (w) between opposite ones of said plates
are different for the different electron beams.
4. A color picture tube as claimed in claim 1, wherein:
the distances between said plates and the bottom of the respective focus electrode differ for the individual electron beams.

Description:

BACKGROUND OF THE INVENTION

The present invention relates to a color picture tube.

U.S. Pat. No. 4,086,513 discloses a color picture tube with an in-line gun system in which parallel plates are attached to a focus electrode on both sides of the beam plane. This parallel pair of plates is directed towards the screen and serves to compensate the elliptic distortion of the beam spots by the deflection field, such distorted beam spots reducing the sharpness of the image reproduced. The pair of plates is attached to the focus electrode nearest to the screen. Alternatively, plates can be attached to a focus electrode near the first-mentioned focus electrode on both sides of the beams directed towards the last focus electrode. These plates are mounted at an angular distance of 90 degrees from the first-mentioned parallel pair of plates.

SUMMARY OF THE INVENTION

It is one object of the invention to provide a color picture tube with an in-line gun system causing an improvement in the compensation of the distortion of beam spots.

BRIEF DESCRIPTION OF THE DRAWING

The embodiments of the invention will now be explained with reference to the accompanying drawings, in which:

FIG. 1 is a side view of a color picture tube;

FIG. 2 is a side view of an in-line gun system;

FIG. 3 is a top view of a focus electrode;

FIG. 4 is a section through the focus electrode of FIG. 3 along line IV--IV.

DETAILED DESCRIPTION

FIG. 1 shows a color picture 10 tube comprising a screen 11, a funnel 12, and a neck 13. In the funnel 13, an in-line gun system 14 (drawn in broken lines) is located producing three electron beams 1, 2, 3, which are swept across the screen 11 (1', 2', 3'). A magnetic deflection system 15 is located at the transition from the neck 13 to the funnel 12.

FIG. 2 is a side view of the in-line gun system 14. It has a molded glass disk 20 with sealed in contact pins 21. The contact pins 21 are conductively connected (not shown) to the electrodes of the in-line gun system 14. The contact pins are followed by grid electrodes 23, 24, focus electrodes 25, 26 and a convergence cup 27. Inside the grid electrode 23, cathodes 22 are arranged which are shown only schematically in broken lines. The first grid electrode 23 is also called control grid, and the second grid electrode 24 is also called screen grid. The cathode together with the control grid and the screen grid is called triode lens. The focus electrodes 25, 26 form a focusing lens. The individual parts of the in-line electrode gun 14 are held together by two glass beads 28.

The focus electrode 25 consists of 4 cup-shaped electrodes 25.1 to 25.4, of which two each are joined together at their free edges and thus form a cup-shaped electrode. In all electrodes of the in-line gun system 14, there are three coplanar aperatures through which the electron beams 1, 2, 3 produced by the three cathodes 22 can pass. Three beams 1, 2, 3 are thus produced in the in-line gun system which strike the Luminescent Layer of the screen 11. In order to change the shape of the beam spot to obtain improved sharpness of the reproduced image, a suitable astigmatism is imparted to the in-line gun system. This effect is obtained by a slit diaphragm in the grid electrode 24 of the triode lens and by plates on both sides of the beam plane or on both sides of the beams in the focus electrode(s).

It is necessary to divide the astigmatism of the beam system between the triode lens and the focusing lens. The triode lens forms a smallest beam section which--in analogy to optics--is imaged on the screen with the following lenses. The astigmatic construction of this triode lens also leads to an astigmatism of the aperture angle of the bundle of rays emerging from the triode lens. A larger aperture angle facilitates defocusing of the image of the smallest beam section and the viewer of the color picture tube focuses on the plane with the larger aperture angle, i.e., the vertical and not the horizontal focal line of the astigmatic beam section of the triode lens is imaged on the screen. On the other hand, the aperture angle must not become too large, because then the bundle of rays moves to the bordering region of the imaging lenses. The large spherical aberration of these rather small electrostatic lenses does not permit a sharp image. Therefore, a sufficient astigmatic deformation of the bundle of rays is possible only if it is partly effected in the last focusing lens of the beam system where the aperture angle of the bundle of rays is no longer influenced.

FIG. 3 is a top view of the cup-shaped focus electrode 26. In the bottom of the focus electrode 26, there are three coplanar apertures 30 for the passage of the electron beams 1, 2, and 3, respectively. At the walls 32 of the focus electrode 26 two plates 31 are attached opposite each other, each of which has three curved portions 33. These curved portions 33 project into the apertures 30. The plates 31 can also consist of three individual curved portions 33. In the embodiment shown in FIG. 3, the curved shape of the portions 33 corresponds to an arc of a circle. The shape of the portions 33 can also be elliptic or parabolic or have a similarly curved shape. The distance w ₁ between the opposite vertices of the portions 33 projecting into the central aperture is smaller than the distance w ₂ between the opposite vertices of the portions 33 for the outer apertures 30. Furthermore, the vertices of the portions 33 for the outer apertures are not on the center line of the outer apertures 30. In order to make this clear, the distance of the central points of the apertures 30 from each other is designated by the letter S in FIG. 3. The distance of the vertices of the outer portions 33 from the central vertex in the plate 31 is designated by s ₁ . It is clear that the value s ₁ is smaller than the value S. This makes it possible to influence the angle the outer electron beams 1, 3 make with the central electron beam 2 to achieve static convergence.

FIG. 4 is a section of the focus electrode 26 along line IV--IV of FIG. 3. The apertures 30 in the bottom of the focus electrode 26 have burred holes whose height for the individual apertures can be different. The plates 31, which may be attached to the wall 32 of the focus electrode 26 by weld spots 34, are arranged in a defined spaced-apart relation with respect to the inner edge of the burred holes. The distance from the bottom of the focus electrode 26 to the lower edge of the portions 33 of the plates 31 projecting into the apertures 30 is designated by the letter d. The distance d ₁ for the portion 33 projecting into the central aperture 30 is larger than the corresponding distances d ₂ of the outer portions 33 from the bottom of the focus electrode 26. By varying the distance d, the astigmatism of the focus electrode can be influenced. It is thus possible to choose the distances d of the various portions 33 from the bottom of the focus electrode individually in order to optimize the adjustment of the astigmatism individually for each electron beam. The height of the portions 33 of the plates 31 is designated by the letter b. By varying this height b, the astigmatism of the focus electrode can also be changed. Here, too, it is possible to determine the height b individually for each portion 33 in order to optimize the adjustment of the astigmatism for each electron beam. In the embodiment shown in FIG. 4, the height b ₂ of the outer portions 33 is larger than the height b1 of the inside portion 33.

The plates 31 described above do not only influence the astigmatism of the focusing lens, but also the other lens aberrations, i.e., the spherical aberration and the further higher-order aberrations. This influence is different for each of the embodiments described above. The higher-order aberrations can be seen mainly at the edge of the picture. They can be minimized by a suitable combination of the plates at the electrodes of the focusing length. It is possible, for example, to distribute the correction to the two focus electrodes or to impress too strong an astigmatism on one of the two focus electrodes, with partial compensation at the other focus electrode. By the use of the plates 31 described above, it is possible to adjust the astigmatism very finely, thus producing an improved sharpness across the entire screen. By the fine adjustment of the static convergence, which is possible as well, the sharpness can also be improved. Furthermore, the dynamic convergence is improved, too.

Electron-gun system NOKIA GRAETZ ITT CRT

In a cathode-ray tube with a thick grid No. 2 (24) in the electron-gun system, current transfer into grid No. 2 (24) may result in a lack of picture sharpness. To avoid this error, the aperture (4) in grid No. 2 (24) has a widening (6) of conical shape or stepped diameter.

1. Electron-gun system for cathode-ray tubes comprising at least one cathode and at least three electrodes, the second of which is a screen grid, which are arranged one behind the other and have apertures through each of which an electron beam can pass, characterized in that the aperture (4) in the screen grid (24) has an unwidened part and a conical widening (6) on its side facing the third electrode (25), whereby current transfer into the screen grid and the third electrode is greatly reduced. 2. An electron gun system for cathode ray tubes, comprising:

at least one cathode;

at least three electrodes, said electrodes and said cathode being arranged one behind the other and having apertures through each of which an electron beam can pass, the aperture of the second electrode having a widening on its side facing the third electrode, said widening being conical in shape and extending over part of the depth of the aperture, and that the other part of the depth satisfies the relationship a divided by d is less than or equal to 0.5, where d is the diameter of the unwidened part of the aperture and a is the depth of the unwidened part of the aperture.

3. An electron-gun system as claimed in claim 2, characterized in that on its side facing the third electrode (25), in the area of the opening (4), the second electrode (24) bears a plate (8) containing the conical widening (6). 4. An electron gun system for cathode ray tubes, comprising:

at least one cathode;.

5. An electron gun system for cathode ray tubes, comprising:

at least one cathode;

at least three electrodes, said electrodes and said cathode being arranged one behind the other and having apertures through each of which an electron beam can pass, the apertures of the second electrode having widenings on sides facing the third electrode, each of said widenings being formed by a step wherein the diameter (d1) of the widened part satisfies the relation d1=d0+2ctanα, where d0 is the diameter of the unwidened part of the aperture (4), c is the depth of the widened part, and α≥10°.

6. Electron-gun system for cathode-ray tubes comprising at least one cathode and at least three electrodes, the second of which is a screen grid, which are arranged one behind the other and have apertures defined by cylindrical surfaces through each of which an electron beam can pass, characterized in that the aperture (4) in the screen grid (24) has a conical widening defined by a conical surface contiguous with the cylindrical surface on its side facing the third electrode (25), whereby current transfer into the screen grid and the third electrode is greatly reduced.

Description:

The present invention relates to an electron-gun system for cathode-ray tubes and more particularly, an electron gun system having at least one cathode and at least three electrodes which are arranged one behind the other and have apertures through each of which an electron beam can pass.

Electron-gun systems for cathode-ray tubes comprising a cathode as well as grid and focusing electrodes are known from (DE-OS 32 12 248) corresponding to U.S. Pat. No. 4,682,073. To achieve a thin electron beam and, thus, a small electron spot on the screen of the cathode-ray tube, it is necessary to make grid No. 2 relatively thick. This means that the aperture in grid No. 2 must have a great depth, it being quite possible that the depth of the aperture is equal to the diameter of the aperture.

With such a design of grid No. 2, it may happen that during the period from the turning on of the cathode-ray tube to the creation of stable space-charge conditions around the cathode, the electron beam expands, touching the wall of the aperture in grid No. 2. The electrons touching the wall of the aperture in grid No. 2 cause the emission of secondary electrons which reach grid No. 3, also called "focusing electrode". Such leakage currents are first unmeasurably small, but with increasing service life, measurable currents in the pA range occur at grid Nos. 2 and 3 for short times because due to deposition of evaporated cathode materials into the aperture of grid No. 2, the secondary-electron yield of initially about 1 multiplies. These leakage currents cause a change in the voltage across grid No. 2 - it becomes more positive - and in the voltage across the focusing electrode, which becomes more negative. Due to these changes in potential, the electron beam is not optimally focused for short periods of time, which leads to a lack of picture sharpness. In unfavorable cases, even self-blocking may be caused by total current transfer into grid Nos. 2 and 3.

It is the object of the present invention to provide an electron-gun system for cathode-ray tubes having a thick grid No. 2 in which no lack of picture sharpness is caused by current transfer into grid Nos. 2 and 3.

This object is attained by making the aperture in grid No. 2 so that it becomes wider at its side facing grid No. 3. Further advantageous features of the invention are achieved by making the aperture widening conical in shape, and in particular, that the conical widening extends over part of the depth of the aperture, and that the other part of the depth satisfies the relation a divided by d is less than or equal to 0.5, where d is the diameter of the aperture and a is the depth of the unwidened part of the aperture. Other features of the invention include the widening of the aperture has an angle of at least 10°, and preferably 15°. In another embodiment, the side of grid No. 2 facing grid No. 3 bears a plate containing the conical widening. The widening may also be in the form of a step, wherein the diameter of the widened part between the step and the side of the grid facing grid No. 3 satisfies the relationship d1=d0+2c tanα, where d0 is the diameter of the unwidened part of the aperture, c is the depth of the widened part, and α is greater than or equal to 10°.

Embodiments of the invention will now be explained with reference to the accompanying drawings, in which:

FIG. 1 is a side view of a cathode-ray tube;

FIG. 2 is a side view of an electron-gun system;

FIG. 3 is a cross-sectional view of a first embodiment of a grid No. 2;

FIG. 4 shows the detail Z of FIG. 3;

FIG. 5 is a cross-sectional view of a second embodiment of a grid No. 2;

FIG. 6 is a cross-sectional view of a third embodiment of a grid No 2;

FIGS. 7a and 7b show the details X and Y of FIG. 6;

FIG. 8 is a cross-sectional view of a further embodiment, and

FIG. 9 shows the detail X of FIG. 8.

FIG. 1 shows a cathode-ray tube 10 comprising a screen 11, a funnel section 12, and a neck 13. There are singlegun and multigun tubes. In multigun tubes, the electron guns are either separate from each other or combined into one mechanical assembly The present invention relates to all these forms of electron-gun systems even though it will be explained as applied to a multibeam electron-gun system of integrated construction.

The neck 13 of the cathode-ray tube 10 houses an electrongun system 14 (indicated by broken lines) which generates three electron beams 1, 2, 3 These beams are scanned (1', 2', 3') across the screen 11 by a magnetic deflection system 15 located in the junction region of the funnel section 12 with the neck 13.

FIG. 2 shows the electron-gun system 14 in a side view. Seen in the beam direction, the system 14 comprises a grid No 1, designated 23, a grid No. 2, 24, first and second focusing electrodes 25 and 26, and a convergence cup 27. Grid No. 1, 23, contains cathodes 22, which are indicated by dashed lines This grid is also called the "control grid", and grid No. 2, 24, the "screen grid". The cathode, the control grid, and the screen grid are referred to as a "triode lens"The focusing electrodes 25, 26 constitute a focusing lens. The individual parts of the system are held together by two glass rods 28 The electrical connections of the system 14 are not shown for the sake of clarity.

All electrodes of the system 14 contain three apertures which are arranged in a horizontal line and through which can pass the electron beams generated by the three cathodes 22, which later land on the phosphor screen 11.

FIG. 3 shows grid No. 2, 24, in a sectional view. Indicated above this grid is the first focusing electrode 25. In this embodiment, grid No. 2 has the shape of a cup whose bottom 5 contains the aperture 4 for the electron beam. The other apertures for the other electron beams are not visible in this sectional view. The aperture 4 has a great depth, i.e., its diameter d is approximately equal to the thickness of the bottom 5 of the grid. On the side of the grid facing the first focusing electrode 25, the aperture 4 has a widening 6 which is conical in shape.

FIG. 4 shows the detail Z of FIG. 3. The conical widening 6 need not extend over the entire depth of the aperture 4. In the example shown, the aperture 4 has a depth a over which its sidewalls are parallel to the central axis of the aperture 4. This portion is followed by the conical widening 6. The conical widening has an angle α of at least 10°, preferably 15°. For the relation of the depth a of the aperture 4 to the diameter d, the condition a/b≤0.5 should be satisfied.

FIG. 5 shows a second embodiment of grid No. 2. In this embodiment, grid No. 2 is made from thin metal sheet. Here, too, the conical widening 6 includes an angle α of at least 1O°, and the relation a/d≤0.5 is satisfied.

FIG. 6 shows a third embodiment of grid No. 2. It has the shape of a cup, and the bottom 7 of the cup contains the rectangular aperture 4. A plate 8 resting on the bottom 7 contains an aperture aligned with the aperture 4 and having a conical widening 6. This structure of grid No. 2 permits an astigmatic beamforming element in the grid to be combined in a simple manner with the plate 8 containing the conical widening 6.

FIGS. 7a and 7b show the details X and Y, respectively, of FIG. 6. The details X and Y represent two sections through the grid 24 which are displaced relative to each other by 9O°. The plate 8 contains a rotationally symmetric aperture consisting of a cylindrical portion of depth a and the conical widening 6. The widening again has an angle α of at least 1O°. It does not extend over the entire depth of the aperture but passes into the portion whose depth is designated a and whose sidewalls are parallel to the central axis of the aperture 4. Here, too, the condition a/d≤=0.5 should be satisfied. The depth of the aperture 4 in the bottom 7 is designated by b, the width by e, and the length by f, and this portion of the aperture acts as an astigmatic beam hole.

FIG. 8 shows a further embodiment of grid No. 2. Here, the widening 6 is formed by a step, and its depth is designated c. In this embodiment, too, the grid can have the shape of a cup whose bottom 7 contains the aperture 4. The bottom 7 then bears the plate S, whose aperture is aligned with the aperture 4 and has the diameter d1 (FIG. 9). This diameter is greater than the diameter dO of the aperture in the bottom 7, so that the step is obtained Here, the condition d1=d0+2ctanα should be satisfied, where α≥10°. FIG. 9 shows the detail X of FIG. 8. In this embodiment, too, the bottom 7 may contain a rectangular aperture which acts as an astigmatic beam hole.