JPH0118536B2 - - 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 of an electron gun 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 former, and an electron beam focusing device that focuses the electron beam on the fluorescent surface of the cathode ray tube. It consists of a main lens system, and the former is usually called a triode part and the latter a focusing lens (main lens) system. Most of the focusing lens (main lens) systems of electron guns for cathode ray tubes currently on the market are of the electrostatic focusing type, in which separate conductive tubular elements (electrodes) are arranged coaxially, and a predetermined pattern is formed to obtain the desired focused electric field. voltage is applied.

Generally, electron guns are of bipotential type, unipotential type, and tripotential type as described in US Pat. No. 3,995,194.

Next, the electrode arrangement and axial potential distribution of each main lens (focusing lens) system of these three electron guns will be explained with reference to FIG. That is, the bipotential type shown in FIG. Electrode 2 has a relatively high potential, and the potential between these two electrodes has a monotonically increasing distribution as shown by curve 3, and this potential distribution forms the main lens system. The axial potential distribution of the main lens system of this type of bipotential electron gun is said to be "monotonic" because its first derivative does not change sign. However, some types of bipotential main lens systems with such a structure have poor spherical aberration characteristics, and in a fairly small space such as the neck of a cathode ray tube containing such an electron gun, it is difficult to achieve a focused beam spot. It is not possible to make it sufficiently small, especially at high current beam levels, and therefore resolution cannot be improved.

Next, the main lens system of the unipotential type (single potential type) shown in Fig. 1b has three focusing electrodes 4, 5, 6.
The axial potential distribution is approximately saddle-shaped as shown by curve 7, and the starting and ending ends of the main lens system are at approximately the same potential.

However, although the monopotential main lens system having such a structure can reduce the size of the focused beam spot, it has the disadvantage that it is susceptible to internal discharge in the cathode ray tube incorporating the electron gun.

Finally, the tripotential main lens system shown in FIG. The potential monotonically changes from a relatively intermediate potential to a relatively low potential, and then monotonically and continuously changes to a relatively high potential.

An electron gun with such a lens system is the above-mentioned 2
Unlike other types of electron guns, it has a good concentrated beam spot, but it requires a relatively intermediate potential, so it requires a separate power supply, the length of the electron gun is longer, and it is difficult to assemble the triode part. It has drawbacks such as requiring more precision than necessary.

Next, considering the characteristics required of an electron gun, the performance of an electron gun is primarily determined by the focusing lens (main lens) system of the electron gun, which focuses the electron beam onto the fluorescent surface of the cathode ray tube. It is said that the smaller the diameter of the 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 It consists of the broadening component (D _SC ) of the electron beam diameter due to the mutual repulsion effect, and is expressed by the following formula.

_{D T} = √ _{( X + SA )} ² + ² _SC where D _X = M_・ ^d ( _It is _the product _{of d} (Focusing lens) is the magnification (M), the size of _the virtual object point seen from the main lens system ( _d It is desirable that the divergence angle (α _O ) of each is small.

However, when the geometric dimensions of a color picture tube, which is a type of cathode ray tube, are constant, especially when the distance from the geometric center of the main lens of the electron gun to the phosphor surface (approximate image point distance) is constant, the electron optical magnification _The electron _{beam diameter} ( _D , the optimum solution for obtaining the minimum electron beam diameter is obtained for each of the unipotential type and bipotential type as shown in FIGS. 2a and 2b, 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 electrode distances for each of the three poles, that is, the first, second, and third electrodes. The divergence angle and virtual object point position are determined, and therefore the design of the triode and main lens system must be comprehensively considered, especially the electrode closest to the cathode side of the main lens system (1, The prefocus characteristics are determined by the applied voltage and the electrode distance from the triode portion (4, 8), 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 aforementioned 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 second electrode is approximately 400V to 800V, the third electrode (first focusing electrode) is several KV (4.4KV to 5.0KV), and the fourth electrode (second focusing electrode) is approximately 400V to 800V.
20KV to 30KV is applied to the focusing electrode) at the same potential as the fluorescent surface.

Therefore, the length of the third electrode (first focusing electrode) is approximately 3.5 degrees based on the diameter of the main lens, and the divergence angle of the electron beam as seen from the main lens system is approximately 4 degrees to
It is approximately 5.5°, which is relatively large, and the third electrode (first focusing electrode) has a power of several KV at most (4.4 to 50 KV).
Therefore, the so-called crossover position formed in the triode section varies with respect to the video signal applied to the first electrode or cathode, and tends to cause blooming (modulation defocusing), especially at high currents. 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 third electrode (first focusing electrode) and fifth electrode (third focusing electrode). is applied, and substantially zero volts or several KV is applied to the fourth electrode (second focusing electrode), so the divergence angle is as small as approximately 2 degrees, but on the other hand, the electro-optical magnification is bipotential. Although it is slightly larger than the main lens and its resolution at low brightness is slightly inferior, its uniformity, blooming characteristics, etc. are relatively good.

In the case of the unipotential type, between the second electrode and the third electrode (first focusing electrode) of the triode part, the third electrode (first focusing electrode)
Since a high voltage is applied between the focusing electrode (focusing electrode) and the fourth electrode (second focusing electrode), the withstand voltage characteristics between the electrodes are poor, and the discharge may damage the video circuit of the color receiver, and the cathode of the electron gun. It is not used much these days because it can destroy itself.

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 V ₀
In the region where the electron beam diameter is small or 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. That is, Fig. 1c As shown in FIG. A focusing lens is constructed from two electrodes, and a relatively intermediate potential (10 to 12 KV) is applied to the third and fifth electrodes (first and third focusing electrodes), and a relatively intermediate potential (10 to 12 KV) is applied to the fourth electrode (second focusing electrode). Relatively low (5~7KV)
A fluorescent surface potential is applied to the sixth electrode (fourth focusing electrode), and the axial potential distribution changes smoothly and monotonically from a relatively intermediate potential to a relatively low potential, Furthermore, the electrode configuration and voltage must be such that the voltage changes smoothly and monotonically to a relatively high potential, and the axial potential distribution acts as an extended lens.

Therefore, the length of each focusing electrode normalized by the diameter of the main lens system is 0.5 to
2.2, the fifth electrode (third focusing electrode) 10 is 0.75 or less,
The third electrode (first focusing electrode) 8 is uniquely determined by the geometric dimensions of the color picture tube and the applied voltage. The feature of the tripotential electron gun is that it gains electron-optical magnification by applying two types of focusing potentials (6 to 7 KV and 10 to 12 KV) that are relatively higher than conventional bipotential electron guns. As mentioned above, the design minimizes the increase in spherical aberration by using an extended single lens, so low-luminance resolution (relatively low current range where aberrations are negligible) is significantly improved. Ru.

Also, the third electrode (first focusing electrode) 8 has a voltage of 10 to 12 KV.
Since a relatively high voltage is applied, the blooming characteristics are 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, the lens is susceptible to deflection aberration, resulting in poor focus uniformity, and the fact is that the spherical surface difference is affected by the deflection aberration and generates astigmatism, which further deteriorates the uniformity. It is. The cathode ray tube electron gun of the present invention has been developed in view of the above drawbacks,
This system provides a new main lens system as the basis for electro-optical analysis using electronic computers, and is particularly suitable for use in electron guns for cathode ray tube devices, such as self-concentrating color picture tube devices, where the deflection yoke magnetic field has an extremely high degree of asymmetry. It is ideal as a lens system.

A specific embodiment will be described in detail below with reference to the drawings. FIG. 3 shows the structure of an electron gun equipped with a main lens (focusing lens) system adapted to the electron gun of the present invention. In the figure, 21 is a cathode, 22 is a first electrode, 23
is a second electrode, and these three electrodes form a so-called triode part, and the main lens system includes a third electrode (first focusing electrode) 24, a fourth electrode (second focusing electrode) 25,
Fifth electrode (third focusing electrode) 26, sixth electrode (fourth focusing electrode)
It is formed by four electrodes (focusing electrode) 27. A DC voltage of 100 to 150 V and a video signal are usually applied to the cathode 21, a roughly ground potential is applied to the first electrode 22, a potential of about 400 to 1000 V is applied to the second electrode 23, and a third electrode The first focusing electrode) 24 and the fifth electrode (third focusing electrode) 26 are kept at the same potential inside or outside the cathode ray tube, and approximately
A voltage of 4.4KV to 10KV is applied and constitutes a desired focus electrode. The fourth electrode (second focusing electrode) 25 is connected to the third electrode (first focusing electrode) 24 and the fifth electrode (third focusing electrode) by a power source inside or outside the tube.
Further, a high voltage (approximately 20 KV to 30 KV), which is the same as the potential of the fluorescent surface, is applied to the sixth electrode (fourth focusing electrode) 27. In such an electrode configuration, each electrode length normalized by the diameter of the main lens system is one of the preferred embodiments, and the fourth electrode (second focusing electrode) is as described below.
The length of 25 is approximately 0.2 to 0.5 and the length of the other third electrode 24,
It is designed to be very thin compared to the fifth electrode 26.

The potential distribution on the axis of the main lens system adapted to the electron gun of the invention described above changes slightly from a relatively intermediate potential to a relatively low potential monotonically, and then to a relatively high potential, as shown in FIG. The potential changes monotonically, and instead of forming a smooth extended single lens like the axial potential distribution of a tripotential type lens, it has an axial potential distribution that is macroscopically similar to that of a bipotential type main lens. It is located in

In other words, the greatest feature of the present invention is that, as mentioned above, the third electrode (first focusing electrode) of the bipotential main lens system is divided into two parts, and the space between the divided parts is relatively very thin. Apply a relatively low voltage, for example, approximately the same as the second electrode, and locally insert a unipotential lens 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. are doing. Figure 5 explains this point, where OB represents the object point, IM represents the image point, angle α ₁ represents the case of the bipotential type, angle α ₀ represents the case according to the present invention, and angle α ₁ =
It is characterized by a slightly reduced divergence angle α of 4 to 5 degrees, angle α ₀ =3 to 4 degrees, and α ₁ >α ₀ . To explain in more detail, the definition of "slightly" is as follows.

That is, suppose that in a cathode ray tube using an arbitrary bipotential electron gun, the length of the third electrode (first focusing electrode) is determined so that the focusing voltage is Vf ₀ . If the length of the third electrode (first focusing electrode) of this bipotential type is constant, for example, 1.27, and the electrode spacing g ₁ , g ₂ =0.027, as shown in FIG. 5,
The length of the main lens system adapted to the electron gun of the present invention (G _1L +G _2L +G _3L +g ₁ +g ₂ ) is made equal to the length of the third electrode (first focusing electrode) 1 of the bipotential type, and The third, fourth, and
Fifth electrode (first, second, third focusing electrode) 24, 2
If Vf ₀ is applied to 5 and 26, it becomes completely equivalent to the bipotential type mentioned above (here,
G _1L , G _3L ≫g ₁ , g ₂ ) Next, by keeping the inter-electrode distances g ₁ and g ₂ constant and changing G _2L slightly, as shown in Figure 6,
Third and fifth electrodes (first and third focusing electrodes) 24, 2
The focus voltage Vf of No. 6 rises sharply from a certain point and eventually becomes unfocused.

In the present invention, "slightly" means that the focus voltage changes by at most about 0.5 to 2.5 KV compared to a bipotential electron gun of the same size. It is necessary to select the focusing electrode) 25 length and the inter-electrode distances g ₁ and g ₂ . In other words, as described in Japanese Patent Publication No. 29-2216, it "exhibits a focusing effect on the electron flow and sufficiently prevents the electron flow from diffusing into the anode _A1 and being collected by the anode." In order to prevent the electron beam from concentrating in the small hole of the blocking electrode S, it is necessary to configure the main lens system so as to slightly reduce the divergence angle of the electron beam rather than having a large focusing effect. Judging from this, 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, for example, the spherical aberration component 1/2・M・_CS・α ₀ ³
When comparing an embodiment of the present invention with an example of a conventional general electron gun, it is found that the conventional value of 0.64 becomes 0.14 according to the present invention, which reduces the spherical aberration by approximately 1/1.
It can be reduced to 5. (Because spherical aberration is proportional to the cube of the divergence angle.) Second, because the spherical aberration has been greatly reduced, it can be used especially around the screen in systems with large deflection aberrations, such as self-focusing color picture tube devices. Comparing the diameter of the electron beam spot at the periphery of the screen between an embodiment of the present invention and an example of a conventional general electron gun, it is found that in the past, the vertical length was Approximately 8.0
According to the present invention, the width was approximately 7.0 mm.
The length is 5.2 mm and the width is 4.55 mm, which can improve focus uniformity by 30 to 40%. (Because uniformity and astigmatism are proportional to the convergence angle of the electron beam.) Third, unlike conventional unipotential electron guns, the electro-optical magnification is not large, but rather is even smaller than that of bipotential electron guns. For example, when comparing the resolution at low brightness between an embodiment of the present invention and an example of a conventional general electron gun, it is found that since this resolution is proportional to the magnification M, the magnification of the conventional electron gun is 18.7. , the magnification of the electron gun of the present invention is
14.0, so the resolution can be improved by about 25%.

Fourth, like the conventional bipotential type, the first to second
It is not necessary to make a compromise design that increases the distance between the electrodes and between the second and third electrodes and relatively degrades the resolution in the center of the screen, and uniformity can be arbitrarily improved.

Fifth, and more importantly, when the improvements described in item 4 above are made as in the conventional bipotential type, the cathode- It is necessary to narrow the distance between the first electrodes, and there are problems such as a short circuit between the cathode and the first electrode due to conductive impurities in the color picture tube, but the present invention eliminates such concerns at all.

Sixthly, unlike the unipotential type, there is no concern about withstand voltage characteristics.

Seventh, unlike the tripotential type, it does not require two types of relatively high focus power sources (5-7 KV and 10-12 KV) (in the case of the present invention, the fourth electrode (second focusing electrode) 25 is (can be internally connected to the second electrode 23, etc.).

Next, a second embodiment of the electron gun for a cathode ray tube according to the present invention will be described with reference to FIGS. 7 and 8. 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, and these three electrodes form a so-called triode part. It is formed of four electrodes (second focusing electrode) 35, a fifth electrode (third focusing electrode) 36, and a sixth electrode (fourth focusing electrode) 37, and the third electrode 34 is formed by an opposing shallow cap electrode element 34 ₁ , 34 ₃ , flat plate electrode elements 34 ₂ are inserted at a predetermined interval,
The fourth electrode 35 consists of two flat plate electrode elements, and the fifth electrode 36 consists of shallow cap electrode elements 36 ₁ ,
Two flat plate elements 36 ₂ are inserted between the electrodes 36 ₃ at a predetermined interval, and a sixth electrode 37 is formed by opposing shallow cap electrode elements 37 ₁ and 37 ₂ .

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.

Electrode elements for applying the same potential, such as 36 ₁ , 36 ₂ , 36 ₃ of the electron gun having the above structure, are connected by one conductive wire 41 and further connected to a pin 43 of a stem 42, and each of the electrodes is connected to an insulating support rod 44. The in-line unitizing gun is completed by disposing the guns at predetermined intervals.

In the cathode ray tube having the above-described structure, the length G _2L of the fourth electrode (second focusing electrode) 35 and this electrode as explained in FIGS. 3 to 6 in the first embodiment are By making the distances (g ₁ ) and (g ₂ ) between the opposing electrodes satisfy the value specified by the diameter (l) of the main lens system, the characteristics shown in Figure 6 can be achieved. However, in this case, the focusing state of the main lens system may differ depending on the deflection state of the central electron beam and the electron beams on both sides. Of course, it is sufficient to select the diameter.

In the above two embodiments, it has been explained that the fourth electrode (second focusing electrode) 25, 35 is kept at the same potential as the second electrode 23, 33 inside or outside the cathode ray tube, but this is not necessarily a necessary condition. For example, the potentials may be maintained at the first electrodes 22, 32 or the cathodes 21, 31, or different potentials may be applied individually.

Macroscopically, the main lens system of the electron gun of the present invention is close to a bipotential type, with a slight valley in the axial potential distribution; in other words, it is locally configured as a unipotential lens. to the fourth electrode (second focusing electrode) 25, 35.
A voltage relatively lower than that applied to the electrodes (first 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 bipotential 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. An explanatory diagram for calculating the beam diameter, FIG. 3 is a simplified sectional view showing the structure of an embodiment of the electron gun for cathode ray tube of the present invention, and FIG. 4 is a simplified structure of the main lens system of FIG. 3 and the potential on the axis. An explanatory diagram showing the distribution,
FIG. 5 is an explanatory diagram of the main lens system in FIG. 4, and FIG. 6 is a curve diagram showing the relationship between the focus voltage of the first and third focusing electrodes and the length of the second focusing electrode in FIG. FIG. 7 is a simplified explanatory diagram of another embodiment of the electron gun for a cathode ray tube according to the present invention, and FIG. 8 is an assembled perspective view of the electron gun of FIG. 7. 24, 34...Third electrode (first focusing electrode), 2
5, 35...4th electrode (second focusing electrode), 26,
36...Fifth electrode (third focusing electrode), 27, 37
...Sixth electrode (fourth focusing electrode).

Claims (1)

[Scope of Claims] 1. An electron gun for a cathode ray tube having an electron beam generation source, a triode part constituting an object point forming part, and a main lens system that focuses the electron beam emitted from the electron beam generation source. 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 generation source, and The potential of the electrode and the third focusing electrode is about 4KV to
10 KV, the second focusing electrode has approximately the same potential as any one of the electrodes forming the triode, the potential of the fourth focusing electrode is about 20 KV to 30 KV, and the second focusing electrode By setting the axial length of 0.5 to 0.2 with respect to the diameter of the main lens system and making it shorter than the first and third focusing electrodes, the axial potential distribution is changed so that the change in each potential is 2. An electron gun for a cathode ray tube, characterized in that the electron gun is slightly lower near the focusing electrode and changes monotonically as a whole. 2. The cathode ray tube electron gun according to claim 1, wherein the fourth focusing electrode is composed of a plurality of electrodes.