JPS6051775B2 - cathode ray tube - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of an electron gun for a cathode ray tube, particularly an electron gun for a color cathode ray tube.

A cathode ray tube electron gun normally focuses an electron beam emitted from a hot cathode using a lens electric field formed by a plurality of cylindrical or plate-shaped electrodes with small holes arranged on the same axis. A beam spot is generated, which stimulates the fluorescent surface to produce a minute light-emitting spot on the fluorescent surface.

Since this light spot becomes the picture element of the image reproduced on the fluorescent surface, its size is an important factor governing the sharpness of the image. Generally, the spot of an electron beam becomes larger as the beam current increases, and the optical spot also becomes larger accordingly, so in order to obtain a clear image, it is necessary to limit the beam current to as small a range as possible. However, in the case of color cathode ray tubes, a considerable portion of the beam current is absorbed by the shadow mask, resulting in poor current utilization on the phosphor surface, and in order to obtain a screen with the necessary brightness, the beam current must be increased. Must be.
This has the disadvantage that the light spot generated on the fluorescent surface becomes too large and the clarity tends to deteriorate, and improving this problem is one of the major challenges in current cathode ray tube manufacturing technology. The purpose of the present invention is to provide an electron gun structure in which the spot size does not become excessive even when the beam current is increased, and to realize a cathode ray tube that can obtain extremely clear images even on a high-brightness screen. '
shall be. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained in detail below with reference to the drawings, while comparing it with a conventional example.

FIG. 1 shows the schematic structure of the most commonly used electron gun in the past.

The electron beam 2 emitted from the hot cathode 1 (hereinafter referred to as cathode or cathode surface) passes through a first grating 3, a second grating 4,
Once focused by a so-called triode lens electric field 5 formed by the beam, a beam crossover 6 occurs. At this crossover point, the electron beam diameter becomes minimum, but after that it diverges, and when it enters and passes through the main lens 9 formed by the third grating 7 and the fourth grating 8, it receives a strong focusing effect. A cross-over image is again formed on the fluorescent surface 10 to produce a beam spot 11. At this time, if the beam diameter 12 incident on the main lens 9 becomes too large relative to the lens diameter, lens aberration will become noticeable and the beam spot 11 will become large. A brief focus lens 13 formed by the third grating 7 is provided to perform preliminary focusing and to control the beam diameter 12 entering the main lens 9 to an appropriate size. On the other hand, if the beam current is increased by changing the potential of the first grating 3, the beam spot 11 will generally become larger, but in the case of a color cathode ray tube, the beam current value at the peak is very large, about 3 mA, so the spot The increase in size is also remarkable, from about 1Tmmφ at low current to 3 to 4Trmm at peak current! There may be cases where it reaches nφ.

Many factors are intricately intertwined and related to such an increase in the beam spot at the time of large current, and cannot be explained by a simple single event.

However, one of the factors with the greatest influence is due to the behavior of the crossover 6. That is, when the current is small, the first grid 3 has a large negative potential, so electrons are emitted only from a small part at the center of the cathode. Since a strong focusing lens electric field 5 is created in front of the cathode by the lattice 4, the electrons emitted from the cathode clearly form a lossover immediately in front of the cathode. At this time, the current density distribution on the crossover cross section is a sharp distribution close to a Gaussian distribution, so the beam spot on the fluorescent surface that is created when the crossover is imaged by the focusing lens system also has a sharp current density distribution. , and its effective diameter is small. However, the crossover behavior at high currents is significantly different from that at low currents. FIG. 2 shows the state of the beam near the crossover and the on-axis potential distribution VO(Z) 14 at the time of large current. At the time of large current, the negative potential of the first grating 3 is maintained at a small value, so the triode lens 5 formed by the cathode surface 1, the first grating 3, and the second grating 4 becomes weaker, and the electron beam 2
will now be emitted from a wider surface of the cathode. Moreover, as the current density of the beam increases, the repulsion effect due to space charges within the beam becomes significantly stronger and prevents the beam from converging closely. Due to these factors, the current density of the crossover 6 does not increase as the beam current value increases, and as a result, the density distribution in the crossover cross section expands significantly in the radial direction and becomes flat at the prod. . The axial point of the crossover also becomes axially widened and undefined, moving in the opposite direction to its positional force. and in severe cases the holes 16 of the second grid 4
It moves out of the way and moves closer to the third grid 7. On the fluorescent surface, the increase in current causes the crossover to expand spatially and take on an indistinct shape, that is, the quality of the crossover as an object point in the electron optical system deteriorates. This is a major factor in the beam spot becoming excessively large. By the way, as mentioned above, several factors are related to the deterioration of the quality of the crossover, but among them, the repulsion effect due to space charge has an extremely large influence. Therefore, in order to improve the quality of the crossover at the time of large current, that is, to form a crossover with a sharp current density distribution, it is necessary to suppress the repulsion effect of the space charge in the crossover as much as possible. As is well known, the beam spread due to the repulsion effect of space charges is suppressed as the space potential becomes higher. Therefore, one way to improve the quality of the crossover at high currents is to make the spatial electric position 7 of the crossover point as high as possible. In order to increase the space potential at the crossover point in an electron gun as shown in FIG. 1, the following three methods can be considered.

The first is to increase the potential of the second grid 4, the second is to increase the potential of the third grid 7, and the third is to increase the potential of the third grid 7.
The third grid 7 is moved closer to the second grid 4 while the potential of the third grid 7 remains the same. By the way, considering the first method, the second lattice 4 originally has the role of an accelerating electrode for emitting electrons from the cathode 1, and the value of its potential is controlled by the dimensions of the triode part of the electron beam. Usually, the cutoff voltage is set to a required value.

Therefore, in reality, the limit is about 1 KV at most, and it is difficult in reality to increase it further, and even if it is increased to this level, it cannot be expected to have as great an effect in improving the quality of the crossover. Considering the second method, it is theoretically possible to increase the third grid potential by 10KV.
If it is made higher than this, the spatial electric position 7 of the crossover point can be increased considerably, which has a remarkable effect on improving the quality of the crossover.

However, at 10 KV or less, no significant effect can be expected.
In the case of the electron gun structure shown in FIG. 1, applying a potential to the third grating 7 from the outside is usually done through a stem pin of the neck tube glass. In this case, if the applied voltage is 10K or less, there will not be any serious problem with the withstand voltage, but 10K
(2) If a higher voltage is to be applied, special consideration must be taken to maintain the withstand voltage, and extremely expensive glass stems, sockets, etc. must be used. Considering the third method, the third grid potential is set to 10 KV or less, which is a potential that does not cause problems in terms of withstand voltage, and the third grid potential is
If it is located close to the second grating 4, the crossover potential can be raised, and this has a significant effect in suppressing the space charge effect in the crossover.

However, although this method can improve the quality of the crossover, it is difficult to ultimately improve the quality of the beam spot on the fluorescent surface due to the following drawbacks.
That is, a prefocus lens 13 is formed between the second grating 4 and the third grating 7, which has the role of controlling the spread of the beam diverging from the crossover to an appropriate size. If the grating 7 is brought close to the second grating 4, the position of the prefocus lens 13 will be narrowly limited to the vicinity of the hole 16 in the second grating. On the other hand, as described in detail in the example of Fig. 2, the crossover at the time of large current is located in the space that exits the hole 16 of the second grid, so
In such a case, the pre-focusing effect will not work at all after the crossover, and the beam will enter the main lens 9 while remaining divergent. As a result, the diameter 12 of the beam at the main lens becomes too large and spherical aberration appears significantly, making it impossible to keep the beam spot 11 on the fluorescent surface small. The present invention increases the space potential at the crossover point without requiring special considerations for withstand voltage, etc., and controls the spread of the beam after the crossover to an appropriate amount. The present invention provides an electron gun structure that can greatly improve spot quality.

FIG. 3 shows the state of the beam near the crossover and the axial potential distribution VO(Z)18 in the electron gun structure according to the present invention.
This diagram corresponds to the case of the conventional device shown in FIG. 2. The structure of the triode section consisting of the cathode surface 1, the first grating 3, and the second grating 4 is basically the same as the conventional one. The present invention is characterized in that the third grating 7 in the conventional device is divided into three parts to form a unique arrangement.

From the second grid 4 side, these are respectively 3-1 grid 19,
They are named the 3-2nd lattice 20 and the 3-3rd lattice 21. Of these, the 3rd-3rd lattice 21 is the 4th lattice placed to the right of it.
In forming a main lens between the grating 8 (not shown in FIG. 3, see FIG. 1), it functions similarly to the third grating of the conventional structure. The conventional third grating 7 and second grating 4 require 2w! because it is necessary to form a prefocus lens of appropriate strength between them. In contrast, in the present invention, the interval between the 3-1st grating 19 and the second grating 4 is 0.5 m! n~1T1rm, and the 3-2nd grating 20 is connected to the 3rd-3rd grating 21 and the above-mentioned 3rd
Position it at the center of S with the -1 grid. The hole diameter of the 3-2 lattice 20 and the 3-3L lattice 21 is about 2 to 3 mm diameter, and the hole diameter of the 3-1 lattice is the hole diameter of the 3-2 lattice 20 and the 3-3 lattice 21. It is desirable to set the value between the hole diameter of the second grid 4 and the hole diameter of the second lattice 4. Then, the 3-1 grid 19 is given a potential that is the same as or close to the potential of the 3-3 grid 21, and the 3-2 grid 20 is given a potential lower than that. By doing this, the on-axis potential 22 at the crossover point 6 during large currents can be maintained about 3 to 4 times higher than in the conventional structure, and as a result, the current density distribution at the crossover point 6 can be maintained. It becomes possible to achieve a sharp distribution and to significantly reduce the effective diameter.
Furthermore, the 3-1st lattice 19 and the 3rd 3-2nd lattice 20 are
By applying a potential lower than that of the -3 grating 21, an effective focusing lens 23 can be formed in the space after the crossover. Therefore, the divergence angle of the electron beam diverging from the crossover 6 is controlled by the action of the electric field of this focusing lens, and it can enter the main lens with an optimal beam diameter, thereby reducing the spherical aberration experienced by the main lens. It becomes possible to form a small beam spot on the fluorescent surface. In addition, the 3rd-2nd lattice 20
3-1 grating 19 to form a focusing lens 23.
Since a lower potential is applied than that of the 3-3rd grid 21, the axial potential 24 of this part decreases, which seems to be disadvantageous in terms of suppressing the repulsion effect due to space charges, but unlike the crossover point, At this position, the beam has already expanded to some extent and the current density has become small, so even if the potential is somewhat low, the adverse effects of the space charge effect are minor.

Further, in the electron gun structure according to the present invention, the potential applied to the 3-1st grid 19 and the 3-3rd grid 21 is 10K.
Even if the voltage is maintained below V, it is sufficiently effective in increasing the space potential at the crossover point, so there is no need to apply a potential of 10 K or more to the glass stem at the end of the neck tube, and this reduces the need for tube design and manufacturing. Various restrictions regarding withstand voltage in manufacturing the drive circuit are not particularly severe, and there is no need to use special expensive materials.

FIG. 4 schematically shows the configuration of an embodiment of the present invention.

The dimensions of the main parts and the applied potential are shown below. Here, the shape and dimensions of the triode section consisting of the cathode, the first grating, and the second grating, and the fourth grating to which high voltage is applied are the same as in the prior art.
Cathode first lattice spacing 0.1? 1st lattice - 2nd lattice 0.1Tn! 1t 1st grating thickness 0.05wt 2nd grating
0.1wm first grid hole diameter
0.6? ! 2nd grid
0.6 hawk 2nd grid - 3rd - 1st grid spacing
0.5Tfun 3rd-1st lattice - 3rd-2nd lattice interval
0.8WIfL 3rd-2nd lattice - 3rd-3rd lattice interval 0
．． 8w0n 3rd-3rd lattice - 4th lattice interval 1.2
TWE・3rd-1 grid plate thickness 0.27
wt 3rd-2nd lattice 0.2Wf&
3-3 grid 0.20 3-3
Lattice cylinder length 257m 3rd-1st lattice hole diameter 1.0mφ 3rd-2nd lattice
2. ``φ3-3rd lattice〃
2.0Wr! nφ 3rd-3rd lattice cylindrical part diameter
10mmφ cathode potential 0V
1st grid -120~-20V 2nd
Lattice 500-1000V 3-1
Lattice 〃 5~10KV 3rd-2nd lattice〃
1~5KV 3rd-3rd grid
5-10KV 4th grid 2
0-30KV Comparing the diameter of the light spot on the fluorescent surface obtained with this structure with the conventional one, it is 100μA to 500μA.
At a small current of pA, the value is about the same as before, but 2000
Approximately 70% of conventional power at large currents of μA to 3000 pA
, and a significant improvement effect was observed.

Based on the basic configuration shown in FIG. 4, several modified structures can be obtained to obtain greater effects. In FIG. 5, new grid electrodes 25 and 26 are added between the 3-1 grid 19 and the 3-2 grid 20, and between the 3-2 grid 20 and the 3-3 grid 21, respectively. By making these two grid electrodes common and giving an intermediate potential between the 3-1st grid potential and the 3-2nd grid potential, a focusing lens is formed between the 3-1st grid 19 and the 3-3rd grid 20. It is possible to modify the electric field to a more favorable distribution. Further, FIG. 6 shows a method for facilitating the assembly of the electrode configuration shown in FIG. 4.
The gratings 19, 20, and 21 are integrated in advance using an appropriate adhesive substance with an insulating ring 27 made of ceramic or crystallized glass interposed therebetween, and the 3-1 lattice 19 and the 3-3
-3 grid 21 is electrically common, 3-2 grid 20
This shows a structure in which a separate lead line is provided to enable application of a separate potential. This method can also be applied to the configuration shown in FIG. As described above, the present invention increases the space potential at the crossover point without requiring any special consideration in manufacturing, controls the beam spread to an appropriate amount, and increases the The quality of the beam spot can be greatly improved, and this will greatly contribute to improving the performance of cathode ray tubes.

[Brief explanation of drawings]

Fig. 1 is a schematic cross-sectional view of the main parts of a conventional cathode ray tube, Fig. 2 is an enlarged view showing the electron beam near the crossover of the conventional cathode ray tube and a diagram showing the axial potential distribution, and Fig. 3 is a diagram according to the present invention. FIG. 4 is a schematic cross-sectional view showing the entire structure of the electron gun according to the present invention, and FIG. 5 is a diagram showing the axial potential distribution in the vicinity of the crossover of the electron gun. Schematic sectional view showing another example of the electron gun structure, No. 6
The figure is a schematic cross-sectional view showing another example of the electron gun structure according to the present invention. 1... Hot cathode, 2... Electron beam, 3
...First grid, 4...Second grid, 18
...Axis potential distribution, 19...3-1st lattice, 20...3-2nd lattice, 21...3-3rd lattice, 22. ...Crossover axial potential, 24...Prefocus lens spatial potential,
27... Insulation ring.

Claims (1)

[Claims] 1 A focusing lens electric field forming electrode disposed adjacent to the triode consisting of the hot cathode, the first grating for controlling electron flow, and the second grating for extracting electron flow is arranged at least at the 3-1st grating and the 3rd grating.
-2 lattice and 3-3 lattice, the 3-1 lattice located on the second lattice side and held at a potential higher than the second lattice potential is made of a plate-like body, The 3-3rd grating, which is located at and forms a main lens together with the 4th grating, is a cylindrical body held at approximately the same potential as the 3-1st lattice potential. 3-
The third lattice potential is held at a potential lower than any of the three lattice potentials.
A cathode ray tube, wherein the 3-2nd grating forming a preliminary focusing lens electric field between the 3-1st grating and the 3-3rd grating is made of a plate-shaped body.