JPH0419660B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to cathode ray tubes, particularly color picture tubes used in home television receivers and their electron guns. As schematically illustrated in FIG. 1, an electron gun commonly used in color picture tubes comprises a cathode 2, a control grid 3, a shielding grid 4 and a plurality of alignment electrodes, including two or more focusing electrodes 5, 6. . The portion of the electron gun up to the shielding grid constitutes a beam forming section 7, and the portion beyond the shielding grid constitutes a focusing section 8. In the operation of such an electron gun, electrons 9 emitted from the cathode are concentrated at a gathering point 10 near the shielding grid, and the electrons 9 at the focusing part of the electron gun are concentrated at a gathering point 10.
By means of the main focusing lens formed between 6 and 6, this gathering point 10 is imaged as a small light spot on the imaging plane on the display surface 11. Here, the gathering angle α at which electrons approach this gathering point is called the approach angle, and the divergence angle β at which electrons leave the gathering point is called the withdrawal angle. These angles α and β are substantially equal if no deflection field exists at this assemblage point, but in reality, the electric field that exists in this region causes electrons to undergo a certain deflection when entering and exiting this assemblage point. As a result, a set complication occurs, resulting in a difference between the angles α and β. Most people skilled in the art generally understand that the beam forming section 7 of an electron gun
It was believed that there was no interaction between the electron gun and the convergence section 8, and when improving an electron gun, it was common to pay attention to one of these parts without paying much attention to the other. However, the inventor of this application discovered that the first gathering point, which is imaged on the display surface by the focusing system of the electron gun, is located much further forward in the electron gun than previously thought, and based on this, the We now know the interdependence between the gun's beam-forming function and its subsequent focusing function. As a result, it was found that by correctly selecting and combining various design values of the electron gun, an unexpected improvement in the beam spot performance could be obtained. The main characteristics of the novel electron gun according to the present invention compared to similar electron guns of the prior art are that the shielding grid is thick, the electric field between the shielding grid and the first lens electrode is strong, and/or the object distance of the main focusing system is It is a long thing. To obtain optimal results from this design concept, it is desirable to eliminate or minimize prefocusing of the electron beam after the collection point. Embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. FIG. 2 shows a prismatic color picture tube 10 having a glass envelope including a prismatic faceplate panel 12, a cylindrical neck portion 14, and a prismatic funnel portion 16 joining them. The panel 12 consists of a display face plate 18 and a side wall 20 surrounding it, and this side wall is joined to the funnel portion 16 by a frit sealing portion 21. Face plate 1
8 has a mosaic three-color phosphor display surface 22 on its inner surface.
The display surface is preferably a linear display surface having phosphor stripes perpendicular to the desired high frequency scanning direction. A porous color selective shadow mask electrode 24 is detachably attached to the display surface 22 at a predetermined distance using a conventional method. This mask 2
4 along a concentrated path on a common plane.
A novel in-line electron gun 26, which generates three electron beams 28 that travel to two directions, is mounted in the center of the network 14. The picture tube in Figure 2 has a network part 14 and a funnel part 1.
The three electron beams 28 are scanned horizontally and vertically using an external magnetic deflection yoke 30 that surrounds the vicinity of the junction with the display surface 22 to form a rectangular raster on the display surface 22. Except for the new modifications described below, this electron gun 2
6 may be of the three-beam in-line type as described in US Pat. No. 3,772,554. FIG. 3 is a side view of the 3-beam 2-potential gun 26.
A portion thereof is shown in a central longitudinal section along a plane perpendicular to the common plane of the beams 28. Therefore, only one of the three beams is shown in this figure. The electron gun 26 has two glass columns 32 with various electrodes attached to them, and these electrodes include three cathodes 34 (one for each of the three beams) arranged at equal intervals on the same plane. (Only one of them is shown)
, a control grid electrode 36 , a shielding grid electrode 38 , and a first lens or focusing electrode 40 .
and a second lens electrode or focusing electrode 42. The second lens electrode is provided with an electrically shielding cup 44. All of these electrodes are arranged in a straight line along the central beam axis A.times.A, and are mounted at intervals along the glass column 32 in the order described above. Focusing electrodes 40, 42 also serve as accelerating electrodes in two-potential electron gun 26. The electron gun 26 also includes a plurality of magnetic members 46 at the bottom of the shield cup 44, as shown, to correct for coma in the raster produced by the electron beam scanning the display surface 22. This magnetic member 46 can be, for example, the one described in the above-mentioned US Pat. No. 3,772,554. The cylindrical cathode 34 of the electron gun 26 has a planar electron emitting surface 48 at one end thereof. The control grid electrode 36 and the shield grid electrode 38 each have a plate-shaped portion 50, 52 perpendicular to the axis, each having a central hole 54, 56, respectively, aligned with each other.
The first focusing electrode 40 is proximate to the shielding grid 38 and includes an elongated cylindrical member having a central hole 60 and a bottom surface 58 perpendicular to the axis. Similarly, the second
The focusing electrode 42 also includes a cylindrical member, each of which has an inwardly curved lip 62, 64 at its opposite end, between which the main focusing lens of the electron gun is formed. . The above-described two-potential type electron gun 26 of the present invention has the following features. (1) A strong operating electric field to extract the smallest diameter beam from the collection point, i.e. approximately 3937-15748 V/mm (100-
400V/mil) preferably about 5906-9843V/mm
(150−250V/mil). (2) The thickness of the flat plate portion 52 of the shielding grid is 0.4 to 1.0 times the diameter of the aperture 56 in order to reduce the convergence angle of the electron beam. (3) In order to maximize the object distance and reduce the magnification of the electron gun, the length of the first focusing electrode 40 is abnormally long, 2.5 to 5.0 times the diameter of the focusing lens of the electrode.
In most cases this will be about 40− of the thickness of the shielding grid.
It is 60 times more. (4) In order to avoid pre-focusing of the electron beam, the diameter of the flat part surrounding the center hole of the shielding grid is approximately twice or more the distance between the shielding grid and the first focusing electrode. FIG. 4 is an enlarged sectional view of the beam forming section of the electron gun 26, showing the nature of the equipotential lines formed between the cathode, the control grid, the shielding grid, and the first focusing lens during operation of the electron gun, and the nature of the equipotential lines formed between the cathode, the control grid, the shielding grid, and the first focusing lens during operation of the electron gun. This shows the nature of the electron path that leaves the center, gathers at the convergence point, and then diverges toward the main focusing lens. A characteristic feature of an electron gun that operates by convergence of beams is a strong focused electric field formed in the vicinity of the cathode 34 and the control grid 36, as shown by equipotential lines 66, so that the electron beam 68 is directed toward the cathode 34. After leaving the center, the light is strongly focused and converges at a convergence point 70, and from there it advances to the main focusing lens while diverging. The electron gun 26 is operated with a relatively narrow spacing between the shield grid 38 and the first focusing electrode 40 such that a strong electric field is created between the shield grid 38 and the first focusing electrode 40 and/or with a relatively high voltage on the first focusing electrode. This high voltage field due to the first focusing electrode 40 enters the aperture in the shielding grid 38, as shown by equipotential lines 72, but the thickness of the shielding grid 38 is substantially the same as that of the control grid 36 and the first focusing electrode Unlike conventional electron guns in which the high voltage from 40 passes completely through the aperture in the shield grid, the thick shield grid in the electron gun of the present invention is sufficiently thick compared to the diameter of the aperture 56 to penetrate the aperture. Only part of it can fit in. This allows the electric field created by the control grid voltage to enter the aperture 56 in the shield grid from the control grid side of the shield grid and exert a diverging force on the electron beam 68, as shown by the equipotential lines 74.
Therefore, the assemblage point approach angle α (FIG. 1) is reduced compared to other cases, and the assemblage point 70 is closer to the display surface than in other cases. As a result, the withdrawal angle β decreases, and the electron beam 76 diverges from the convergence point, increasing the density of the electron beam that advances to the main focusing lens, and as shown in the figure, the electron beam 76 becomes relatively narrow at any distance from the cathode 34. A dense beam 78 is formed. Also a feature of the electron gun 26 of the present invention is a relatively flat, axis-perpendicular plate 52 of the shielding grid 38. Such a flat electrode structure thus forms a relatively flat equipotential line 82 between the shielding grid and the first focusing electrode, which is substantially free of prefocusing effects. Avoiding prefocusing in this part of the electron gun leads to a reduction in magnification, as detailed below. FIG. 5 is an enlarged sectional view similar to FIG. 4, but
A conventional electron gun 84 is shown having a conventional thin shield grid in place of the thick shield grid of the electron gun 26 of the present invention. In FIG. 5, electron gun 84 has a cathode 86, a control grid 88, a shield grid 90, and a focusing electrode 92. This conventional electron gun 8
4 has the same electrode spacing and dimensions as electron gun 26, except that its shield grid 90 is of the conventional type and is thinner than thick plate shield grid 38 of electron gun 26. This electron gun 84, like the electron gun 26 of FIG. 4, exhibits a strong focused electric field represented by equipotential lines 94 in the aperture of the control grid adjacent the cathode. In the case of the electron gun 26 of the present invention, the electron beam 98 emitted from the cathode is focused at the collection point 96 by this electric field,
In the case of the electron gun 84, the shielding grid electrode 90 is thin, so that the equipotential lines due to the high voltage of the focusing electrode 92 completely pass through the apertures in the shielding grid, and as shown by the equipotential lines 100, the equipotential lines are separated between the control grid and the shielding grid. A focusing effect is produced between the two. This is in contrast to the electric field 74 created by the electron gun 26 of the present invention.
As a result of this addition of the focusing effect, the angle of approach α (FIG. 1) becomes larger than in the case of the electron gun 26 of the present invention, and the collection point 96 approaches the cathode, so that the electron beam 102 emitted from the collection point 96 The withdrawal angle β increases, and a beam 104 with a lower density than the beam 78 produced by the electron gun 26 is formed at the same distance from the cathode. The equipotential lines 106 between the shielding grid and the focusing electrode in the electron gun 84 are essentially equivalent to the equipotential lines 82 in the electron gun 26 of the present invention, but the field strength is significantly lower than in the electron gun 26. Become. FIG. 6 shows a conventional electron gun 108 that is similar to conventional electron gun 84 except for the shield grid electrode.
This electron gun 108 has a cathode 110, a control grid 1
11, shielding grid 112 and focusing electrode 113
However, the shielding grid electrode is in the shape of a tip with an upright peripheral wall 114. The peripheral wall 114 has the effect of shaping the equipotential lines 115 between the shielding grid and the focusing electrode to produce a prefocusing effect of the electron beam 116 leaving the collection point 118. As a result, when the electron beam 116 leaves the gathering point, it is bent (in a focused manner) to approach the central axis, and the electron beam 116 of the present invention
A high density beam 120 having dimensions somewhat similar to beam 78 of No. 6 is produced. However, as will be explained in more detail below, the fact that the high density beam 120 is obtained with the electron gun 108 does not mean that a reduction in magnification equivalent to that obtained with the electron gun 26 is obtained. What the electron gun 26 of the present invention seeks to avoid is the prefocusing effect produced by the focusing equipotential lines 115 in the region between the shielding grid 112 and the focusing electrode 113; This is achieved by not using any structures, such as the upright peripheral walls 114 of the shielding grid, that would curve the essentially relatively flat equipotential lines 115 in the vicinity of the electron beam line 116. FIG. 7 shows the relationship between the electric field strength between the shielding grid and the focusing electrode and the beam spot size of the general-grade electron gun described here. In FIG. 7, the electric field strength is plotted as a function of the ratio of the actual beam spot size S _cr to the theoretical beam spot size S th at the gathering point. The theoretical minimum beam spot size Sth is determined by the effect of thermionic radiation on the light spot at the convergence point. As shown in the figure, this light spot size ratio has an electric field strength of approximately 5906-9843V/mm.
(150-250V/mil), it falls sharply, but approaches a horizontal line on both sides of this range. A typical prior art two-potential electron gun with a simple single main focusing lens, such as that described in U.S. Pat. The focusing electrode voltage can be approximately 6000 V and the shielding grid voltage can be approximately 600 V, and this structure and operating conditions provide electron gun operation with an electric field strength of approximately 3858 V/mm (98 V/mil) between the electrodes. On the other hand, in the electron gun 26 of the typical recommended embodiment of the present invention, the distance between the two electrodes is approximately
0.838−1.219mm (33~48mil), focusing electrode voltage approximately
8500V, with a shielding grid voltage of about 625V, which gives a voltage of about 9409-6457V/mm (239-6457V/mm).
This results in an electric field of 164V/mil) between both electrodes. The light spot size ratio (1 is the optimal value in the quality scale of the light spot size) plotted as shown in Figure 7 is:
Compared to about 1.6 for the electron gun 26 of the present invention, which operates with an electric field strength of about 9409 V/mm (239 V/mil) between both electrodes,
For conventional electron guns, it is approximately 2.5. This improvement in the spot size ratio from 2.5 to 1.6 suggests that the higher the electric field strength between the shielding grid and the focusing electrode, the better, but without some compensatory modifications to the electron gun, the If only the electric field between the electron beams is strengthened is increased, the electron beam will be The withdrawal angle β increases. One standard conventional method to compensate for this increase in withdrawal angle is to provide a prefocusing lens between the shielding electrode and the focusing electrode. However, it is believed that this pre-focusing field may not provide optimal compensation for the increase in withdrawal angle, as detailed below. Another conventional method for dealing with this increase in the assemblage point withdrawal angle is suggested in U.S. Pat. is used. However, such a composite focusing system is uneconomical in terms of the structure of the electron gun and the additional means of operating potential. FIG. 8 shows a focusing electrode 40 with a shielding grid aperture diameter of about 0.635 mm (25 mil) in an electron gun 26 of the present invention.
2 is a chart showing the assembly point withdrawal angle β and the optimum focusing electrode 40 lens length as a function of shielding grid thickness for an example lens diameter of about 5.436 mm (214 mils). This curve has a shielding grid thickness of approximately 0.254mm.
(10mil) or 0.4 times the opening to approximately 0.635mm
(25 mil), that is, when changing to 1.00 times the aperture, the assemblage point withdrawal angle β decreases from 0.0675 radian to 0.042 radian. Since the beam diameter decreases as the withdrawal angle β decreases, the length of the focusing electrode 40 can be increased without overfilling the lens with the beam, thus increasing the object distance of the focusing system and reducing the magnification. can be done. This curve also covers the shielding grid thickness approximately
The required optimal focusing electrode 40 length for 0.254 mm (10 mil) and approximately 0.635 mm (25 mil) is approximately 13.970 mm, respectively.
mm (550mil) and approximately 26.924mm (1060mil). Thus, the thickness of the shielding grid can be expressed as the ratio of the length of the focusing electrode 40/the lens diameter of the focusing electrode 40. This ratio varies from approximately 0.254 mm (10 mil) to approximately 0.635 shielding grid thickness.
It can be seen that when changing to mm (25 mil), it changes from 2.57 to 4.95. Therefore, as the shield grid thickness varies from 0.4 to 1.0 times its aperture diameter, the range of optimal focusing electrode 40 length varies from about 2.5 to 5.0. From these numbers it can be seen that for this embodiment of the electron gun 26 of the present invention, the optimum focusing electrode 40 length varies from approximately 40 times to 60 times the shielding grid thickness over the range of preferred dimensional variations noted above. 9a-9d schematically illustrate a comparison of the present and conventional electron gun designs with respect to magnification reduction effects. As is well known, the magnification of an electron gun is expressed by the following equation. Here, M is the magnification of the beam spot, Q is the imaging distance, that is, the distance between the imaging plane on which the beam spot is formed and the main focusing lens, and P is the object distance, that is, the distance between the main focusing lens and the beam gathering point. , V _c is the voltage at the gathering point,
V _a is the voltage at the anode or image plane. FIG. 9a shows the electron beam formation of the electron gun 26 of the present invention in which electrons from the cathode 34 are concentrated at a first collection point 70 located relatively far from the cathode at a relatively small angle of approach α. . The electrons diverge from this convergence point to the main focusing lens MF, where they are focused onto the anode A to form an image of the convergence point. Since the gathering point withdrawal angle β is relatively small, the spread of the beam that reaches the main focusing lens is also relatively small, and it works in the low spherical aberration part at the center of the lens, creating a beam spot image with relatively little aberration on the display surface. can be formed.
Also, since the beam gathering point withdrawal angle β is relatively small,
The object distance P ₁ is relatively large, so Q ₁ /P ₁
The small ratio of 0 to 1 provides a more favorable or lower magnification than conventional electron guns. Figure 9b shows P ₂ using a conventional electron gun 84.
By making P equal to ₁ , we show the effect of trying to obtain the same magnification. Since the electron gun 84 operates with a large convergence point withdrawal angle β, the electron beam rapidly diverges from the convergence point 96 and enters the main focusing lens.
By the time it reaches MF, it has expanded so much that it suffers severe spherical aberration when passing through the lens aperture. FIG. 9c shows one attempt at solving the problem described with respect to FIG. 9b for electron gun 84.
Here, the cathode 86 of the electron gun is moved close to the lens MF so that the object distance P ₃ is shortened, so that the beam does not spread too much before reaching the main focusing lens MF. This naturally avoids severe spherical aberrations, but the magnification increases due to the shortening of the object distance P ₃ and the corresponding increase in the Q ₃ /P ₃ ratio. FIG. 9d shows an attempt at a conventional method to solve the problems of FIGS. 9b and 9c by using a pre-focusing lens in the electron gun 108. Since the electrons leave the collection point 118 with a relatively large withdrawal angle β,
As mentioned for Figure 6, the pre-focusing lens
The PF prefocuses the electrons between the shielding grid and the focusing electrode. The electrons then leave the lens PF with a smaller divergence than before and when they reach the main focusing lens MF, in the case of the electron gun 26 of this invention (No. 9a
The result is a relatively dense beam with a similar size to that shown in Figure).
In this case, since Q ₄ /P ₄ and Q ₁ /P ₁ are equal, it seems that equal magnifications can be obtained, but in the electron gun shown in Figure 9d, focusing is performed by a pair of lenses, namely the pre-focusing lens PF and the main focusing lens. That doesn't happen because it relies on lens MF. That is, an equivalent focusing lens EF is formed between these two lenses, and an effective object distance P ₅ and an effective image distance Q ₅ are created. The magnification is therefore proportional to Q ₅ /P ₅ , which is greater than that of the electron gun 26 shown in FIG. 9a, which has a magnification proportional to Q ₁ /P ₁ of the present invention. The comparison made with Figures 9a to 9d shows that the resulting advantage of a high density beam is provided in the area of the control grid and the shielding grid, rather than as a focusing function provided by a pre-focusing lens next to the shielding grid. Shown as a beam forming function. This advantage is obtained by increasing the electric field between the shielding grid and the focusing electrode and by increasing the thickness of the shielding grid relative to its aperture diameter. Preferable 2 used in the electron gun 26 of this invention
One embodiment of the potential type uses the following dimensions, spacing, and operating potentials.

[Table] The above description has been made on the assumption that the thick shielding grid of the electron gun 26 of the present invention consists of a single thick perforated plate 52, but this is made by stacking a plurality of thin perforated plates with their perforations aligned. It may be something you have. For example, in FIG. 10, 1
A thick shielding grid 130 is shown consisting of a pair of relatively thin perforated plates 132. This shielding grid 130
The effective thickness of is the distance between the outer surface of one plate 132 and the outer surface of the other plate 132. Figure 11 shows another embodiment of a thick shielding grid 140
shows. The shielding grid 140 consists of a pair of medium-thickness perforated plates 142 closely stacked with aligned apertures. This grid 14
The effective thickness of 0 is the distance between the outer surfaces of each plate 142. Generally speaking, the smaller the spacing between the shielding grid and the focusing electrode for a given G3 voltage, the better the electro-optical properties of the electron gun. The electric field between the shielding grid and the focusing electrode is approximately 15748V/mm.
(400V/mil), the light spot formed on the display surface becomes progressively smaller, all other factors being constant. For example, in the electron gun 26 of the present invention, the distance between the shielding grid and the focusing electrode is approximately 0.838 mm.
(33mil), the electric field strength between them is approximately 9409V/mm
(239V/mil), at a certain beam current
While we created a light spot of 2.75mm, the above distance was changed to approx.
At 1.219 mm (48 mil) and working with the same field strength and beam current, the light spot became 2.95 mm. If the above-mentioned spacing is reduced so that the electric field strength exceeds 15748 V/mm (400 V/mil), the voltage becomes extremely unstable, and furthermore, a problem arises in that discharge occurs between the two electrodes. The recommended range of the electric field strength between the electrodes above is approximately 5906−
9843 V/mm (150-250 V/mil), and this range includes the steepest portion of the curve that allows the most significant adjustment of beam characteristics for a given change in field strength. At the lower end of this recommended range, significant improvements are made over conventional electron guns operating at electric fields of approximately 3940 V/mm (100 V/mil), while at the upper end, high voltage breakdown problems are well avoided. The diameters of the control grid and shield grid apertures are selected according to conventional electron gun design standards. After considering the required maximum beam current, spot size and drive sensitivity, the shielding grid thickness is determined according to the design criteria according to the present invention. It has been found that increasing the thickness of the shielding grid from 0.4 to 1.0 times the diameter of its apertures produces the required divergence at the entrance to the grid. Its thickness is 0.4 of its aperture diameter
If the thickness is less than that, little or no divergence effect will be obtained, and if the thickness begins to exceed the diameter of the aperture, aberration effects will become significant, causing premature focusing of the electron beam on the outside of the beam inward. Forms an out-of-focus beam spot with a dark core with a blurred periphery. Also, the ratio of the thickness of the shielding grid to the aperture diameter is 1.
As it begins to exceed this point, an unnecessary drift region is created through the grid, and it becomes increasingly difficult for conventional punching methods to form the required apertures in the material. Therefore, the range of the above ratio from 0.4 to 1.0 is realistic not only from the viewpoint of electronic engineering but also from the viewpoint of mechanical engineering technology. The length of the first focusing electrode was arbitrarily chosen to be 3.5 m.
When the electron gun is operated with the reference highlight drive current of A, the diameter of the electron beam in the main focusing lens at the forward end of this electrode is about 1/2 or more than the diameter of the lens-forming aperture of this electrode. Choose one that is slightly smaller. In an electron gun having the preferred structural dimensions and operating voltage as described above,
When this is driven with a beam current of 3.5mA, the diameter of the electron beam inside the main focusing lens is approximately 2.229mm.
(87.74 mil), or 0.41 times the diameter of the first focusing electrode aperture of the lens. Further lengthening of the focusing lens electrode increases object distance and further reduces magnification, but this increases the beam diameter within the lens and increases the problem of spherical aberration of the lens. Further, if this electrode is made even shorter, the spherical aberration decreases, but the magnification increases. Designing the electron gun for the maximum allowable beam diameter in the main focusing lens also provides the advantage of a low density beam that is less susceptible to space charge effects. When the thickness of the shielding grid varies from about 0.4 to 1.0 times its aperture diameter,
The gathering point withdrawal angle β of the beam is approximately 0.0675 radian.
0.042 radians, resulting in an optimal focusing electrode length of about 2.5 to 5.0 times the lens aperture diameter. This 2.5-5.0 times relationship between the length of the first focusing lens electrode and the lens diameter applies not only when the shielding grid aperture diameter is approximately 0.635 mm (25 mil) (Figure 7), but also for other suitable It has been experimentally shown that the same holds true when the opening size is changed. Spherical aberration is a limiting factor in the allowable beam diameter, but if the beam diameter can become extremely large within the yoke field, so too can the distortion of the beam cross section due to the yoke field. This is particularly true for recently developed self-focusing precision in-line picture tube and yoke combinations. As mentioned above, in order to reduce the convergence point angle and form the convergence point image on the display surface, it is necessary to weaken the main focusing lens. The main focusing lens is formed between the first focusing electrode and the second focusing electrode and the second focusing lens is formed between the first focusing electrode and the second focusing electrode.
Since the ultor-shielding potential is applied to the focusing electrode, the first focusing electrode voltage must be higher than that of a conventional electron gun in order to obtain the required weak lens. This has the effect of forcing the first focusing electrode voltage to penetrate further into the shielding grid aperture, contradicting the theoretical desire to avoid complete penetration in order to generate the desired diverging field effect at the entrance of the aperture. do. However, this apparent discrepancy can be compensated for simply by increasing the shielding grid thickness/aperture diameter ratio beyond what would otherwise be necessary. The advantage of a weak main lens is basically that it has less spherical aberration. The distance between the control grid and the shielding grid is approx.
Experiments have shown that a range of 0.229-0.381 mm (9-15 mils) is the optimal operable range. If this spacing is greater than about 15 mils, the divergent electric field at the entrance of the shielding grid will move into or beyond the constellation point, and the desired reduction in the convergence point approach angle α will not be achieved. Also, if the spacing is less than about 9 mils, mechanical tolerance problems will prevent shorting between the control grid and the shield grid. Furthermore, if this spacing is significantly smaller than approximately 0.229 mm (9 mils), the divergent electric field at the entrance to the shielding grid will be enhanced, compressing the electron beam too much and creating space charge effects that will negate the advantage of a small collection point angle. There is. Also, if the voltage difference between the control grid and the shield grid is too large, a similar result will occur because the divergent electric field at the entrance of the shield grid will be too strong. Fluctuations in the divergent electric field strength at the entrance of the shielding grid aperture not only affect the magnitude of the gathering point approach angle α, but also have the effect of moving the gathering point back and forth. However, this movement of the gathering point is relatively small and is not an important design factor. The curve in Figure 8 shows that the diameter of the shielding grid aperture is approximately
When the length is 0.889 mm (25 mil), the required length of the first focusing electrode is slightly shorter than approximately 22.86 mm (900 mil). It was approximately 23.495mm (925mil). The reason for this length is the voltage of the first focusing electrode.
This is to obtain an integrated structure that can operate properly at 8,500V and the second focusing electrode voltage at 30,000V. Considering the advantages and disadvantages of spherical aberration versus magnification, departure from the optimum length is not an important issue. Although the electron gun assembly of the present invention has been described as forming part of a three-beam in-line electron gun, the present invention can also be implemented in a three-beam delta electron gun or a single-beam electron gun. Similarly, although the present invention has been described as being implemented in a two-potential type electron gun, it can also be implemented in other types of electron guns, such as those using a three-potential or one-potential focusing system. Although the above-mentioned focusing electrode length may not be applicable for systems other than two-potential focusing systems, the appropriate length of the focusing electrode used is simply a matter of adjusting the length of the focusing lens so that the optimum filling density of the lens with the electron beam is obtained. is determined by determining the position of .

[Brief explanation of drawings]

FIG. 1 is a diagram schematically showing a typical electron gun and its electron beam forming and focusing functions, FIG. 2 is a cross-sectional view of a cathode ray tube implementing the electron gun of the present invention, and FIG. 4 is an enlarged partial cross-sectional view of one embodiment of the electron gun of the present invention shown in FIG. An enlarged view similar to FIG. 4 showing the beam forming part of the gun for comparison, FIG. 6 a similar view to FIG. 5 showing another conventional electron gun, and FIG. 7 showing beam dimensions at the gathering point. and the shielding grid and the first
A diagram showing the relationship between the electric field strength and the focusing electrode,
FIG. 8 is a diagram showing the relationship between the shielding grid thickness and the focusing electrode length in the electron gun of the present invention;
Figures 9 to 9d are schematic diagrams for comparing beam forming and focusing effects between the electron gun of the present invention and a conventional electron gun, and Figures 10 and 11 can be used for the electron gun of the present invention. FIG. 7 is a cross-sectional view of another embodiment of a thick shield grid electrode. 10...Aggregation point, 11, 22...Display surface, 9,
28...Electron beam, 2,34...Cathode, 3,3
6... Control grid, 4, 38... Shielding grid, 5, 40... First focusing lens electrode, 6, 42
...Second focusing lens electrode.

Claims (1)

[Scope of Claims] 1. A cathode, a perforated plate-like control grid, a perforated plate-like shielding grid, a cylindrical first lens electrode and a second lens electrode, which are spaced apart from each other and arranged in this order; An electron gun characterized in that the shielding grid has a thickness of 0.4 to 1.0 times the diameter of the aperture, and the first lens electrode has a length of 2.5 to 5.0 times the diameter of the lens. 2. The gap between the shielding grid and the first lens electrode is 3937 mm between them during operation of the electron gun.
The electron gun according to claim 1, wherein an electric field having a strength of 15748 V/mm (100 to 400 V/mil) is generated.