JPH05314922A - Electron gun for cathode ray tube - Google Patents

Abstract

PURPOSE:To extremely restrain expansion of an electron beam diameter due to increase of an electron beam current by constituting an electron gun for a cathode ray tube of three grids respectively having specific functions. CONSTITUTION:An electron gun is constituted of an electrode group comprising; a first grid Gw provided with plural small holes; a second grid G2 serving as an acceleration electrode for an electron beam; and a third grid electrode consisting of a cylinder having barriers at both ends thereof and small holes drilled in axial alignment at centers of the barriers. Another type electron gun can be formed by adding a main lens to this electron gun comprising the electrode group, adopted as a prefocus electrode. By fitting this electron gun to a cathode-ray tube, the cathode ray tube having an electron beam diameter depending little upon magnitude of electron beam quantity can be obtained. Accordingly, the cathode ray tube provided with this electron gun can display on a phosphor screen an image of high brightness having high resolution.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a cathode ray tube electron gun.

[0002]

2. Description of the Related Art A cathode ray tube is also called a cathode ray tube, and is widely used not only in industry but also in general households as a device for displaying an image on a fluorescent film, a display device for a TV receiver or a computer. In order to display an image on the surface of a fluorescent film with a cathode ray tube, energy of an electron beam is applied to the fluorescent film, and the fluorescent film can convert the energy into visible light. That is, the fluorescent film is scanned with a sharply focused electron beam, and a minute light emitting point synchronized with the scanning of the electron beam is moved on the fluorescent film surface to form an image. Therefore,
The size of the pixel of the image formed on the fluorescent film, that is, the resolution is mainly determined by the size of the electron beam diameter on the fluorescent film. In order to obtain a high-resolution image on the fluorescent film, it is necessary to obtain a small electron beam diameter, and many efforts have been attempted so far. The results did not improve the electron beam diameter over curve 1 in FIG.

[0003]

The problem to be solved is to develop an electron gun capable of extremely suppressing the spread of the electron beam diameter due to the increase of the electron beam current.

[0004]

It is known that in order to improve the brightness of the fluorescent film of the cathode ray tube, it is better to increase the magnitude of the electron beam current. However, when the electron beam current is increased, the electron beam diameter increases exponentially as shown by the curve 1 in FIG. As a result, the quality of the image on the phosphor film is extremely deteriorated. The exponential increase of the electron beam diameter deteriorates the image quality of a highlight scene in an image in which gradation is a problem, such as a TV image, and has been required to be improved. In general, it is believed that the spread of the electron beam diameter due to the increase of the electron beam current is the result of the increase in the number of electrons included in the electron beam diameter and the repulsive force between the electrons, which results in the spread of the electron beam diameter. It has been believed that it is not possible to change the characteristic curve shown in Curve 1 of. This hypothesis is
The next experiment loses its legitimacy.

In the method of measuring the electron beam diameter of the cathode ray tube, since the electrons are invisible, the electron beam diameter cannot be directly measured. Generally, an indirect measurement method of measuring a light emitting point on the fluorescent film is used. Therefore, a plurality of electron guns are installed in one cathode ray tube. After adjusting each electron gun to the optimum condition, each electron gun is adjusted so that the same electron beam flow has the same electron beam diameter. First, a fluorescent film is irradiated with an electron beam from the first electron gun to measure the electron beam diameter. After that, the electron beam from the second electron gun is overlapped and irradiated at the same place, and the electron beam diameter is measured. Then, the electron beam from the third electron gun is overlapped and irradiated at the same place, and the electron beam diameter is measured. It can be confirmed that the electron beam diameter does not expand even if the electron beams are superposed in this way. Then, with one electron gun, the electron beam flow is doubled and further tripled. The electron beam diameter certainly increases with the size of the electron beam flow. The following can be said from the above experimental results. Even if the electron density in the electron beam is tripled, no electron interaction occurs. It can be concluded that the spread of the electron beam diameter is not due to electron interaction, but is caused by other causes.

The electron beam flow in the cathode ray tube is controlled by the potential of the first grid G _{1 with} respect to the cathode. When the relationship between the electron beam flow rate and the potential of the first grating G ₁ is examined, the curve of FIG. 6 is obtained. The curve in FIG. 6 is the second lattice (electron acceleration electrode) G.
It is a curve obtained using the potential of ₂ as a parameter. This curve is well known as a basic characteristic of triodes. From this curve, therefore, no further information can be extracted. In order to extract a lot of new information necessary for designing the electron gun from this curve, it is preferable to add information on the line width that determines the characteristics of the electron gun. By inserting the electron beam diameter as a parameter into the curve of FIG. 6, the curves of line width 1 and line width 2 shown in the figure can be obtained. That is, it is understood that when the potential of the electron acceleration electrode G ₂ is increased, a sharp electron beam can be obtained even at a high electron beam flow rate. This means that the electron beam diameter is
First grating G for controlling extraction of electron beam from cathode
It can be seen that the potential depends more on the potential of the electron acceleration electrode G ₂ which is the second lattice than on the potential of ₁ .

According to the electron lens theory, the following experiments can be conducted. The state of the electron beam extracted from the first grid electrode can be changed by changing a plurality of electrode groups arranged below the second grid and potentials of the electrode groups. According to this method, the electron beam diameter on the fluorescent film surface can be changed to an arbitrary size. This change in the electron beam diameter is considered as a change in the pseudo focus formed on the cathode side, which gives an aberration to the main electron lens. The electrode group below the second grating that changes the pseudo focus of the electron beam incident on the main electron lens is considered as a prefocus lens system. Based on this idea, the development of electron guns is currently in progress. It has been found that controlling the diameter of the electron beam input to the main electron lens by such a method facilitates focusing by the main electron lens and obtains a small electron beam diameter even at a high electron flow rate. However, the electron beam diameter thus obtained does not change the characteristics of the curve 1 in FIG. 5 from the essence, and the electron beam diameter changes as the electron beam flow rate increases and decreases. That is, the problem of aberration is essentially unsolved.

Considering the problem of aberration, the following can be understood. When the angle of incidence of electrons on the lens is large, it occurs because the focal point of the electron incident near the center of the lens and the focal point of the electron incident on the peripheral portion of the lens are different. This is illustrated in FIG. From the figure, in order to eliminate the aberration, the electron beam should be focused as small as possible, and should be incident only on the central part of the lens, and not on the peripheral part of the lens. You can see that does not occur. The problem of electron beam aberration can be solved by finding a method for focusing the electron beam before it enters the main lens as sharply as possible.

The electron gun is operating under the constant potential of the second grid G ₂ . Considering the electron beam extracted from the first lattice electrode G ₁ under the constant potential of the second lattice G ₂ , it is as follows. In this case, of course, the potential between the cathode K and the second grid electrode G ₂ is kept constant. The first grid electrode G ₁ has one small hole, and the electron beam is extracted from this one small hole. When the electron beam amount is small,
That is, when the negative bias of the first lattice is deep, the negative bias electric field of the first lattice is deeply distributed in the peripheral portion of the small hole of the first lattice, and apparently, with respect to passage of electrons from the cathode,
The small hole is narrowed. Electrons from the cathode therefore cannot pass around the apparent eyelets open to the first lattice, but only through the center of the eyelets in the first lattice. FIG. 3 schematically shows this state. When the electron beam amount increased, that is, when the negative bias of the first lattice became shallow, the negative bias electric field became shallow at the periphery of the small hole of the first lattice, resulting in the formation of a larger hole. Then, the electrons from the cathode can pass through the larger surface of the eyelet of the first lattice. This state is shown in FIG. As is clear from the figure, the electron beam emitted from the substantially narrow hole contains more electrons having the kinetic energy on the electron gun axis. The electron beam emitted from the wide hole contains more electrons with kinetic energy discrete from the electron gun axis. Focusing of electrons with kinetic energy separated from the electron gun axis is difficult even with a focusing electrode. This can be understood from the fact that focusing is difficult and a clear image cannot be obtained unless a point electron source is obtained with an electron microscope. As is clear from the above description, it is understood that the characteristic of the electron beam diameter shown by the curve 1 in FIG. 5 is mainly caused by one small hole of the first lattice. In other words, the characteristic of the electron beam diameter shown by the curve 1 in FIG. 5 is that the apparent diameter through which the electrons can pass is
It depends on the magnitude of the negative potential of the first lattice.

The thermoelectrons distributed according to the Boltzmann distribution law on the cathode surface are taken out using the small holes of the first lattice, and water is taken out in one direction from a water tank at a constant water pressure using a thin pipe. Can be similar in case. With a thin pipe attached to the tank, if you want to take out water in one direction without being greatly affected by changes in water pressure, attach multiple small holes to the end of the thin pipe, and the water will not spread and it will be more efficient. Well taken out. Similarly, on the first grid of the electron gun,
If a plurality of small holes with a smaller diameter are attached instead of one small hole, as shown in the schematic diagrams in FIGS. The diameter can be obtained. 1 shows the case where the electron beam amount is small, and FIG. 2 shows the case where the electron beam amount is large.

The electron beam thus extracted does not completely solve the problem because the distribution of thermoelectrons on the cathode surface is the Boltzmann distribution law. The extracted electron beam contains a considerable amount of electrons having a motion component separated from the electron gun axis. In order to sharply focus the electron beam, it is necessary to perform an operation of aligning these dissociated electron components with the electron gun axis, and at the same time, an operation of removing electrons that cannot be aligned. At the same time aligning the direction of the undesired component, the best way to get rid of it still not aligned component electrons accelerated to the next grid G _2, a cylindrical electrode a voltage higher than the voltage applied to the acceleration grid G ₂ G ₃
Good to put. The first reason for using the cylindrical electrode G ₃ is to form an equipotential line along the electron gun axis at the center of a long cylinder and run the dissociative electron component along this equipotential line. It is to change the dissociated electron component into an electron having a motion along the electron gun axis. It is not easy to correct the trajectory of the separated electron component, and it requires a long distance. Therefore, long cylindrical electrodes are required. The effect of the cylindrical electrode is given by the ratio of the length to the diameter, and the effect is significantly exhibited when the (length / diameter) ratio is 2 or more. When the ratio is 10 or more, the length of the electrode of the electron gun becomes long, which is inconvenient for assembling and handling the electron gun. If the inconvenience is ignored, a ratio of 10 or more may be used. Practically less than 10 will be easier to handle. The second reason for using the cylindrical electrode is to provide a barrier at both ends of a long cylinder and to open a small hole of an arbitrary size at the center of the barrier with its central axes aligned. By doing so, the component of the electron separated from the electron gun axis is stopped by the barrier on the exit side of the cylindrical electrode. The removal of the electron component separated from the electron gun axis is effective when the length of the cylinder is long. As a result, the electron beam exiting the long cylindrical electrode contains more components along the electron gun axis. By attaching the barriers to both ends, the length of the cylindrical electrode can be slightly shortened. When the cylindrical electrode is sufficiently long, the electron beam emitted from the cylindrical electrode is sufficiently focused and can be used as it is. Further, it may be used after further focusing by the main electron lens. In any case, the size of the electron beam diameter depends on the size of the hole formed in the barrier of the cylindrical electrode. Therefore, the size of the hole formed in the barrier of the cylindrical electrode is determined by the amount of the electron beam to be extracted and the size of the electron beam diameter on the fluorescent film surface.

The combination of the cathode, the first grid, the second grid, and the cylindrical electrode can be combined into one set to be incorporated as an electron gun of a cathode ray tube. It is also possible to incorporate a plurality of combinations into an electron gun for a cathode ray tube. In this case, each electron gun is independent and can be operated individually.

[0013]

As described above, the first grating G ₁ having a plurality of small holes as described above, the second electrode G ₂ functioning as an accelerating electrode for the electron beam, and the barriers at both ends are provided at the center of the barrier. Third grid electrode G ₃ consisting of a cylinder with aligned small holes
It is possible to make an electron gun which is formed by adding the main lens as an electron gun or the above-mentioned electrode group as a pre-focusing electrode. When this electron gun is attached to a cathode ray tube, as shown by the curve 2 in FIG. 5, a cathode ray tube having an electron beam diameter less dependent on the size of the electron beam is obtained. The cathode ray tube equipped with this electron gun can display a high-luminance image having high resolution on the fluorescent film surface.

[Brief description of drawings]

FIG. 5 is a diagram showing the relationship between the electron beam diameter and the anode current. Curve 1 shows the characteristics of the conventional electron gun, and curve 2 shows the characteristics of the electron gun according to the present invention. FIG. 6 shows the relationship between the anode current and the first grid voltage, using the second grid voltages VG ₂ 1 and VG ₂ 2 as parameters. The line width 1 and the line width 2 shown in the figure have the electron beam diameter as a parameter. FIG. 7 is a diagram for explaining the reason why aberration occurs in the electron lens system. FIGS. 1 to 4 are conceptual diagrams showing the distribution of the electron beam extracted from the cathode, and FIGS. 3 and 4 show the electron beam of the conventional product. FIG. 1 and FIG. 2 show distributions of electron beams in the electron gun according to the present invention. 3 and 1 show a case where the electron beam amount is small, and FIGS. 4 and 2 show a case where the electron beam amount is large.

Claims (3)

[Claims] 1. A third lattice comprising a first lattice consisting of a plurality of small holes, a second lattice for accelerating electrons, a barrier at both ends, and a cylindrical hole with an axially aligned small hole in the center of the barrier. An electron gun for a cathode ray tube characterized in that 2. A third lattice comprising a first lattice consisting of a plurality of small holes, a second lattice for accelerating electrons, barriers at both ends, and a cylindrical hole with an axially aligned small hole at the center of the barrier. Electron gun for a cathode ray tube, characterized in that the formed electrode is prefocused. 3. An electron gun for a cathode ray tube according to claim 1, wherein a cylindrical electrode having a length-to-diameter ratio in the range of 2 to 10 is used as the third grid.