JPH0261091B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electron gun for a cathode ray tube, and more particularly to a main lens system for focusing an electron beam suitable for use in an in-line three-electron gun type shadow mask type color picture tube.

As is well known, the electron gun of a cathode ray tube (not shown) generally has two basic parts: an electron beam source including an object point forming part and a main electron beam focusing lens that focuses the electron beam on the fluorescent surface of the cathode ray tube. The former is usually called the triode part and the latter the main lens system.

Generally, most of the main lens systems mentioned above are of the electrostatic focusing type,
Separate conductive tubular elements (electrodes) are arranged coaxially,
A predetermined pattern of voltages is applied to obtain a desired focused electric field.

Generally, the types of electron guns are bipotential type (double potential), unipotential type (single potential),
There is also a tripotential type described in US Pat. No. 3,995,194.

Next, the electrode arrangement and axial potential distribution of each main lens system of these three electron guns will be explained with reference to FIGS. 1a, b, and c.

That is, the bipotential type shown in FIG. The lens system is such that one electrode 2 has a relatively high potential, and the axial potential distribution between these two electrodes 1 and 2 increases monotonically as shown by a curve 3. The axial potential distribution of this type of bipotential lens is said to be "monotonic" because its first derivative does not change sign.

However, some types of bipotential lenses have poor spherical aberration characteristics, and in a fairly small space such as the neck of a cathode ray tube containing an electron gun, it is necessary to make the focused beam spot sufficiently small, especially for high currents. Resolution cannot be improved at beam level.

Next, in the unipotential type (single potential type) shown in Figure 1b, the main lens system has three focusing electrodes 4, 5, 6.
The axial potential distribution is approximately saddle-shaped, and the starting end electrode 4 and the ending end electrode 6 of the lens system are at substantially the same potential.

However, although a single-potential main lens system with a lever-like structure can reduce the focused beam spot, a cathode ray tube with an internal electron gun having such a structure has the disadvantage that it is susceptible to internal discharge. be.

Finally, the main lens system of the tripotential type shown in FIG. The potential decreases monotonically from a medium potential to a relatively low potential, and then increases monotonically and continuously to a relatively high potential.

An electron gun with such a tripotential main lens system is different from the two types of electron guns mentioned above.
A concentrated beam spot is also good, but because it requires a relatively intermediate potential, a separate power source is required, the overall length of the electron gun becomes longer, and it is difficult to assemble the triode. It has drawbacks such as requiring more precision than necessary.

Furthermore, when we calculate the second derivative of the axial potential distribution of the various lens systems mentioned above, we find that as shown in Figure 2,
The bipotential type has a simple curve 3 in Figure 2a, the unipotential type has a simple curve 7'' in Figure 2b, and the tripotential type has a single positive maximum value, as shown in curve 12'' in Figure 2c. Since it is a curve,
These are said to be single lenses.

Next, considering the characteristics required of an electron gun, the performance of an electron gun is primarily expressed by the diameter of the electron beam focused on the fluorescent surface of the cathode ray tube by the main lens system of the electron gun. It is said that the smaller the diameter of this focused electron beam, the better the performance of the main lens system and the better the focus quality.

An electro-optical explanation is as follows. That is, in general, the electron beam diameter (D _T ) focused by the focusing lens of an electron gun is determined by _the electron beam diameter ( _D The expansion component of the electron beam diameter due to the mutual repulsion effect (D _SC ) is expressed by the following formula: D _T = √ ( _X + _SA ) ² + ² _SC where D _X = M・d _X D _SA = 1/2 MC _S α _O ³ or D _X is the product of _the electron optical magnification (M) and the size of the virtual _object point ( _d It is proportional to the cube of the divergence angle (α _O ). Therefore, the desired size of the virtual object point ( _dX ) as seen from the main lens system of the electron gun is
Spherical aberration coefficient (C _S ) and divergence angle of the electron beam (α _O ) as seen from the main lens system (focusing lens) of the electron beam
It is desirable that each of them be small.

However, in a color picture tube, which is a type of cathode ray tube, its geometric dimensions, especially the distance from the geometric center of the main lens system of the electron gun to the phosphor surface (approximate image point distance), are constant. In the _case of , _the electron beam diameter _{( D}
are in a contradictory relationship with each other, and the optimal solutions for obtaining the minimum electron beam diameter are determined for each of the unipotential type and bipotential type as shown in FIGS. 3a and 3b, respectively. More specifically, if the combination of the electron gun's triode (object point forming area) and main lens (focusing lens) system is not optimal, for example, the resolution at the center of the screen, the uniformity between the periphery and the center of the screen,
The balance of each characteristic such as blooming (modulation defocusing) at high current becomes worse.

Therefore, it is necessary to pay sufficient attention to the selection of the distance between the three electrodes, that is, the first, second, and third electrodes. The divergence angle and virtual object point position are determined. Therefore, it is necessary to comprehensively consider the design of the triode part and the main lens system, especially the electrodes closest to the cathode side of the main lens system (1, 4, 8 in Figure 1).
The brief focus characteristics are determined by the applied voltage and the distance between the electrodes and the triode, and therefore the divergence angle of the electron beam and the virtual object point position are determined by these.

Taking as an example a color receiver using a three-electron gun type shadow mask type color picture tube, the above-mentioned bipotential type electron gun is generally used, the cathode is approximately 100 to 150V, the first electrode is approximately ground voltage, and the second electrode is approximately 100 to 150V. The voltage of the electrode is approximately 400-800V, and the voltage of the first focusing electrode 1 is several KV.
(4.4 KV to 5.5 KV), and 20 KV to 30 KV is applied to the second focusing electrode 2 at the same potential as the fluorescent surface.

Here, the length of the first focusing electrode 1 is approximately 3.5 degrees based on the diameter of the main lens, and the divergence angle of the electron beam seen from the main lens system is relatively large, approximately 4° to 5.5°. Furthermore, since the first focusing electrode 1 has a voltage of only a few KV (4.4 to 5.0 KV), the so-called crossover position formed in the three-pole section varies with respect to the video signal applied to the first electrode or the cathode, especially when the current is high. Sometimes blooming (modulation defocusing) tends to occur. On the other hand, the electro-optical magnification is smaller than that of a unipotential electron gun, so the so-called low brightness (at low current) resolution is relatively good, but the large divergence angle results in poor focus uniformity and the aforementioned blooming. It has the disadvantage of poor characteristics.

In the case of a unipotential type electron gun, the three-pole part is almost the same as the bipotential type, but a high voltage (fluorescent surface potential) is applied to the first focusing electrode 4 and the third focusing electrode 6, and the second focusing electrode 5 Since substantially zero volts or several KV is applied to the lens, the divergence angle is as small as approximately 2 degrees, but on the other hand, the electro-optical magnification is slightly larger than that of a bipotential main lens.
Although the resolution at low brightness is slightly inferior, uniformity, blooming characteristics, etc. are relatively good.

Note that the characteristics of the above-mentioned unipotential lens are similarly exhibited by a unipotential lens in which the potential of the middle electrode is higher than the potential of the electrodes on both sides.

In the case of the unipotential type, a high voltage is applied between the second electrode and the first focusing electrode 4 of the triode part, between the first focusing electrode 4 and the second focusing electrode 5, etc., so the withstand voltage characteristics between the electrodes are Unfortunately, the discharge can damage the video circuits of color receivers and destroy the cathode of the electron gun, so it is not used much these days.

As a result of computer analysis, it was found that the spherical aberration of the tripotential type focusing lens largely depends on the line integral of the following quantity, as described in U.S. Pat. No. 3,995,194, and the region where V ₀ is small. Or in a region where the electron beam diameter is large.
It has been discovered that keeping V ₀ ″ as small as possible provides the necessary focusing power and suppresses the resulting spherical aberration.

[(V ₀ ″) ² / (V ₀ ) ^3/2 ] r ³ where V ₀ is the axial potential distribution of the lens system and r is the radial coordinate of the electrons in the beam, i.e.
As shown in FIG. 1c, a first focusing electrode 8, a second focusing electrode 9, a third focusing electrode 10, a fourth focusing electrode 11
A focusing lens is constructed from four electrodes;
The third focusing electrode 8, 10 has a relatively intermediate potential (10-12 KV), the second focusing electrode 9 has a relatively low potential (5-7 KV), and the fourth focusing electrode 11 has a fluorescent potential. A surface potential is applied, the axial potential distribution changes smoothly and monotonically from a relatively intermediate potential to a relatively low potential, and then smoothly and monotonically changes to a relatively high potential, and The electrode configuration and voltage must be such that the axial potential distribution acts as an extended lens. This can be understood from the fact that, as is clear from FIGS. 2b and 2c, the axial potential distributions of the unipotential type and the tripotential type are completely the same.

Therefore, the length of each focusing electrode normalized by the diameter of the main lens system is 0.5 to 2.2 for the second focusing electrode 9, 0.75 or less for the third focusing electrode 10, and the length of the first focusing electrode 8 is the geometric dimension of the color picture tube. , and the applied voltage. Hereinafter, all electrode lengths will be explained using standard values.

The characteristics of the tripotential type electron gun are that it is relatively higher than the conventional general bipotential type electron gun2.
Electro-optical magnification is achieved by applying a specific focusing potential (6 to 7 KV and 10 to 12 KV), and the inevitable increase in spherical aberration is minimized by using an extended single lens as described above. Therefore, low-luminance resolution (in a relatively low current region where aberrations are negligible) is significantly improved.

Furthermore, since a relatively high voltage of 10 to 12 KV is applied to the first focusing electrode 8, the blooming characteristic is also good.

On the other hand, although the electrode length of the main lens system becomes longer and a relatively high voltage is applied to the third electrode (first focusing electrode) 8, the divergence angle of the electron beam as seen from the main lens system does not become very small. Therefore, the convergence angle of the electron beam becomes large, and as a result, the focus at the center of the screen is very good. In this case, it is easy to receive deflection aberration, resulting in poor focus uniformity, and the fact is that the spherical aberration is affected by the deflection aberration and causes astigmatism, which further deteriorates the uniformity. However, there are additional problems that will be discussed later.

That is, the trend in color picture tubes is to improve focus quality. In other words, improving the focus quality means forming a very small electron beam spot on the phosphor surface, but in the case of a conventional main lens system, a high precision electron gun assembly is required as a trade-off.

As is well known, a color purity correction magnet and a convergence correction magnet are arranged in the neck portion of the picture tube in order to correct various assembly errors of the color picture tube, and these magnets correct assembly errors of the picture tube (including the electron gun). is being corrected.

As mentioned above, when aiming to improve the performance of an electron gun, the electron beam diameter broadening component (D _SA ), which depends on the spherical aberration of the main lens system, increases. Even in the center of the tube screen, so-called bleeding tends to occur due to spherical aberration and partial astigmatism, resulting in deterioration of focus quality. Therefore, in order to improve the performance of an electron gun, it is necessary to improve the assembly precision of the electron gun.

As mentioned above, spherical aberration and astigmatism depend on the divergence angle of the electron beam emitted from the electron beam generation source, so there is relatively no problem in the case of the unipotential type, but it is relatively difficult for electron optics such as the bipotential type and tripotential type. In the case of the main lens system of an electron gun, which has a small target magnification and a slightly large spherical aberration component,
It has become a very big problem. In other words, the ideal design is to keep the electrode length as short as possible, maintain the uniformity of the unipotential type, and maintain the low magnification of the bipotential type.

The present invention was invented in view of the various drawbacks of the various types of electron guns for cathode ray tubes, and was developed through repeated experimental trials based on electron optical analysis using an electronic computer. The purpose is to provide a tube electron gun, and although it is very similar to the well-known tripotential type, its structure and effect are completely different, and it is a type of cathode ray tube, especially a self-concentrating color picture tube. The present invention relates to an electron gun that is most suitable for use with cathode ray tubes, which generate a large amount of deflection aberration, such as other devices.

Next, one embodiment of the present invention will be described with reference to the drawings.

FIG. 4 is a simplified cross-sectional view of essential parts for explaining one embodiment of the electron gun of the present invention, in which 21 is a cathode;
22 is a first electrode, 23 is a second electrode, and these 3
The two electrodes form a so-called triode, and the main lens system includes a first focusing electrode 24, a second focusing electrode 25,
It is formed by four electrodes: a third focusing electrode 26 and a fourth focusing electrode 27. Usually 100 for cathode 21
~150V DC voltage and video signal are applied,
The first electrode 22 is applied with approximately ground potential, the second electrode 23 is applied with a potential of about 400 to 1000 V, and the first focusing electrode 24 and the third focusing electrode 26 are at the same potential inside or outside the cathode ray tube. Maintained, approximately 4.4KV~
10 KV is applied, the second focusing electrode 25 is connected to the fourth focusing electrode 27, and a high voltage (approximately 20 to 30 KV) which is substantially the same as the fluorescent surface potential of the cathode ray tube is applied. In such an electrode configuration, the length of each electrode normalized by the diameter of the main lens system is one of the preferred embodiments, and the length of the second focusing electrode 25 is approximately 0.1 to 0.5 of the major axis D, that is, 0.1D≦ _G2L ≦
It is designed to be 0.5D and very thin compared to the other third electrode 24 and fifth electrode 26.

The axial potential distribution of the main lens system adapted to the electron gun of the present invention described above is slightly monotonous from a relatively low potential to a relatively medium potential, as shown by curve 28 in FIG. The voltage potential changes, then decreases substantially to the relatively lower potential, and then monotonically changes to the relatively higher potential. 2 of the above-mentioned on-axis potential distribution
The second derivative constitutes a complex lens having two positive maximum values and two negative maximum values, as shown by curve 28'' in FIG. 6a.

The form of this second derivative depends on the length of the third focusing electrode 26, the diameter of the aperture of the main lens system, etc., and in some cases, it may have three positive maximum values as shown in the curve 28 ₁ '' in Figure 6b. In some cases, a compound lens having three negative maximum values is constructed.

In other words, the greatest feature of the present invention is that, as mentioned above, the first focusing electrode 1 of the bipotential main lens system is divided into two parts, and the space between the two parts is relatively very thin, that is, 0.1D≦G. ₂ Apply a voltage that is very thin so that L≦0.5D and relatively high voltage, for example, approximately the same as that of the fluorescent surface of a cathode ray tube,
A unipotential lens, in which the potential of the intermediate electrode is higher than that of the electrodes on both sides, is locally inserted as an auxiliary lens to slightly reduce the divergence angle of the electron beam as seen from the main lens system of the electron gun. That is, as shown in FIG. 7, in the case of a bipotential lens, the electron beam divergence angle α ₁ (=4 to 5 degrees) is changed to the electron beam divergence angle α ₀ (=3 to 5 degrees) by inserting a unipotential lens. It is characterized by a slight change in focusing to 4°). Furthermore, in order to obtain a "slight" change in the focusing effect, the focus voltage is "slightly" changed, and the extent of the "slight" is as follows.

That is, suppose that in a cathode ray tube using an arbitrary bipotential electron gun, the length of the first focusing electrode is determined so that the focusing voltage Vf ₀ is obtained. The length of this bipotential type first focusing electrode 1 is, for example, 1.27
When the electrode spacing g ₁ , g ₂ =0.072, the length of the main lens system suitable for the electron gun of the present invention is as shown in FIG. 7 (G _1L +G _2L +G _3L +g ₁ +g ₂ ) be equal to the length of the bipotential first focusing electrode 1, and further to (first, second, third focusing electrodes) 24, 25, 26 of the main lens system of the present invention.
Naturally, if Vf ₀ is applied, it becomes completely equivalent to the bipotential type (here, G _1L , G _3L ,
≫g ₁ , g ₂ ) Next, keep the lengths of G ₁ L and G ₃ L constant,
If the distances g ₁ and g ₂ between the electrodes are also kept constant and the length G ₂ L of the second focusing electrode to which a high voltage of 20 to 30 KV is applied is slightly changed, the first and third focusing electrodes are changed as shown in Fig. 8. The focus voltage Vf of the electrodes 24 and 25 increases sharply from a certain point and eventually becomes unfocused.

In the present invention, "slightly" means that in order to obtain a focused state, the focus voltage must change by at most 0.5 to 2.5 KV compared to a bipotential electron gun of the same size. means, so that the second focusing electrode 25 length
G ₂ L and inter-electrode distances g ₁ and g ₂ need to be selected.
Therefore, the second focusing electrode length G ₂ L needs to be set to 0.5 to 0.1. Further, as the position of the second focusing electrode 25 approaches the fluorescent surface side, its action as an auxiliary focusing electrode becomes stronger, and as a result, the feature of low magnification of the bipotential type is lost. Therefore, it is desirable that the third focusing electrode be close to the cathode 21 to some extent, and therefore the length G ₃ L of the third focusing electrode is made long. That is, it is desirable that each focusing electrode length satisfies the following formula.

G ₃ L≧G ₁ L>G ₂ L where G ₁ L: first focusing electrode length G ₂ L: second G ₃ L: third In other words, as described in Japanese Patent Publication No. 29-2216, "Exhibits a focusing effect on the electron flow and concentrates it in the small hole of the blocking electrode S so as to sufficiently prevent the electron flow from diffusing into the anode _A1 and being collected by the anode." It is necessary to configure the main lens system so that the divergence angle of the electron beam is slightly reduced, rather than having a large focusing effect.
Judging from the electrode arrangement, they are very similar, but their effects are completely different.

Forming the main lens system of the electron gun as described above has the following advantages.

First, since the divergence angle of the electron beam can be easily reduced, spherical aberration at the center of the screen can be significantly reduced, and as a result, astigmatism caused by assembly errors of the electron gun can be reduced. (This is because spherical aberration is proportional to the cube of the divergence angle of the electron beam, and astigmatism is less likely to occur if spherical aberration is reduced.) Second, since the spherical aberration is reduced, self-focusing color image reception is possible. In systems with large deflection aberrations, such as tube devices, astigmatism at the periphery of the screen can be reduced and focus uniformity can be improved. (Uniformity and astigmatism are proportional to the convergence angle of the electron beam.) Thirdly, basically, the virtual object point is slightly retreated in the far direction within the range of the bipotential type, so as a result, the shape is smaller than the bipotential type. Electro-optical magnification can be achieved.

Fourthly, in order to improve focus uniformity as in the conventional bipotential type, the first/second electrodes,
It is not necessary to make a compromise design that increases the distance between the second and third electrodes and relatively degrades the resolution in the center of the screen, and more importantly, it is possible to improve uniformity. The distance between the cathode and the first electrode, which occurs when the tube is bent, becomes smaller in order to obtain the desired return point elimination voltage, and as a result, it is possible to prevent problems such as cathode/first electrode conduction due to floating objects within the tube.

Fifth, astigmatism caused by unnecessary magnetic fields such as a pieurity magnetic field is less likely to occur. (Basically, the electrode length is shorter than the tripotential type).

Next, a second embodiment of the electron gun for a cathode ray tube according to the present invention will be described with reference to FIG. In the drawings, the same reference numerals as in the above embodiment indicate the same parts.

In the figure, 31 is a cathode, 32 is a first electrode, and 33 is a second electrode. These three electrodes form a so-called triode part, and the main lens system includes a first focusing electrode 34 and a second focusing electrode 35. , a third focusing electrode 36, and a fourth focusing electrode 37, and the first focusing electrode 34 has a flat plate electrode element ₃₄₂ inserted at a predetermined interval between the shallow cap electrode elements ₃₄₁ and ₃₄₃ arranged oppositely. There is,
The second focusing electrode 35 consists of three flat plate electrode elements, and the third focusing electrode 36 has one shallow cap electrode element 36 2 between the opposed shallow cap electrode elements 36 ₁ and 36 ₄ and one flat plate electrode element 36 ₂ . Electrode elements 36 ₃ are inserted at a predetermined interval, and a fourth focusing electrode 37 is formed by opposed shallow cap electrode elements 37 ₁ , 37 ₁ .

As mentioned above, by using each electrode as a flat plate electrode element or a shallow cap electrode element, processing accuracy can be improved.
This helps prevent thermal distortion from changing over time and simplifies assembly.

The electrode elements for applying the same potential of the electron gun having the above structure, for example, 36 ₁ , 36 ₂ , 36 ₃ are connected by a single conductive wire (not shown) and further connected to a stem pin (not shown), and each of the electrodes is connected to a pair (not shown) or a stem pin (not shown). Two pairs of insulated support rods are arranged at a predetermined interval to complete an in-line unitizing gun.

In the cathode ray tube having the above-mentioned structure, the length G _2L of the second focusing electrode 35 and each electrode opposite to this electrode as explained in FIGS. 4 to 7 in the first embodiment. By adjusting the distance (g ₁ ) (g ₂ ) to satisfy the value specified by the diameter (l) of the main lens system, the characteristics shown in Figure 7 can be obtained. However, in this case, the focusing state of the main lens system may differ between the center electron beam and the electron beams on both sides depending on their deflection state, so in this case, the shape or diameter of the electron beam aperture should be selected. Of course.

It goes without saying that the present invention can also be applied to an electron gun in which an auxiliary electrode is arranged in a three-pole portion including an electron beam source.

The main lens system of the electron gun of the present invention is macroscopically close to a bipotential type, with a slight peak in the axial potential distribution; in other words, it is locally configured as a unipotential lens. from 1st
A relatively higher voltage than the focusing electrodes 24 and 34 may be applied.

Further, as other embodiments, the fifth electrode (third focusing electrode) 26, 36 and the sixth electrode (fourth focusing electrode) 2
By dividing parts 7 and 37 and applying a desired voltage to each, it is possible to make the whole into a unipotential or tripotential type electron gun.

In the present invention, for example, acceleration such as the third electrode,
The focusing electrode is also expressed as a focusing electrode to simplify the explanation.

As described above, the main lens system of the cathode ray tube electron gun of the present invention is completely different from the conventional bipotential type, unipotential type, and tripotential type, and its effects are as described above, and its industrial value is extremely large. .

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing the simplified structure and axial potential distribution of the main lens system of conventional bipotential, unipotential, and tripotential electron guns, and Figure 2 is the axis of each electron gun shown in Figure 1. A curve diagram showing the second derivative of the upper potential distribution, FIG. 3 is an explanatory diagram for calculating the electron beam diameter of each bipotential and unipotential electron gun, and FIG. 4 is an embodiment of the electron gun for a cathode ray tube of the present invention. 5 is an explanatory diagram showing the simplified structure of the main lens system in FIG. 3 and the axial potential distribution. FIG. 6 is a diagram showing the second derivative of the axial potential distribution in FIG. Figure 7 is an explanatory diagram of the main lens system in Figure 5, and Figure 8 shows the relationship between the focus voltage of the first and third focusing electrodes and the length of the second focusing electrode in Figure 5. Curve diagram shown, No. 9
The figure is a simplified explanatory diagram of another embodiment of the electron gun for a cathode ray tube according to the present invention. 24, 34...first focusing electrode, 25, 35...
Second focusing electrode, 26, 36...Third focusing electrode, 2
7, 37... Fourth focusing electrode.

Claims (1)

[Scope of Claims] 1. An electron gun for a cathode ray tube, comprising an electron beam source generating section comprising at least a cathode, a first electrode, and a second electrode, and a main lens system for focusing the electron beam emitted from the electron beam source generating section. The electrodes forming the main lens system form a coaxial electrode group consisting of at least a first focusing electrode, a second focusing electrode, a third focusing electrode, and a fourth focusing electrode from the vicinity of the electron beam source generating part, And substantially the same potential is applied to the first focusing electrode and the third focusing electrode, and the first focusing electrode and the third focusing electrode are applied to the second focusing electrode and the fourth focusing electrode.
A high potential is applied from the focusing electrode, and the second focusing electrode slightly changes the focusing action of the main lens system, so that the axial potential distribution formed by the main lens system changes from a relatively low position. a monotonically slight change to a relatively intermediate potential, then a substantial decrease to said relatively low potential, and then a monotonous increase to said relatively high potential; , a compound lens in which the second derivative of the axial potential distribution has at least two positive maximum values and two negative maximum values, and the length of the second focusing electrode in the axial direction is the same as that of the main lens system. An electron gun for a cathode ray tube, characterized in that the diameter is 0.5 to 0.1, and the axial lengths of the first focusing electrode, the second focusing electrode, and the third focusing electrode satisfy the following formula. G ₃ L≧G ₁ L>G ₂ L where G ₁ L: First focusing electrode length G ₂ L: Second focusing electrode length G ₃ L: Third focusing electrode length 2 First focusing electrode and third focusing electrode The potential of is approximately
2. The cathode ray tube electron gun according to claim 1, wherein the potential of the second focusing electrode and the fourth focusing electrode is about 20 KV to 30 KV. 3. The cathode ray tube electron gun according to claim 1, wherein the fourth focusing electrode comprises a plurality of electrodes.