JPH0158823B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a picture tube device configured to provide high resolution even at high brightness.

Conventional Structure and Problems Therein Generally, the resolution of a picture tube depends on the size of a beam spot (bright spot) serving as a picture element, and the smaller the diameter of the beam spot, the higher the resolution can be obtained. on the other hand,
Since the diameter of the beam spot increases as the beam current increases, blooming occurs at high brightness times when a relatively large beam current flows, resulting in a decrease in resolution.

To explain this with the drawings, FIG. 1 shows the electrode configuration of a bipotential electron gun, and FIG. 2 shows the axial potential distribution of the electron gun. Thermionic electrons emitted from the cathode 1 are passed through a crossover 5 by a so-called cathode lens 4 generated in a triode consisting of the cathode 1, the _G1 electrode 2 as a control electrode, and the _G2 electrode 3 as an accelerating electrode.
A prefocusing lens 7 is formed between the _G2 electrode 3 and the _G3 electrode 6, which is a focusing electrode, to perform a prefocusing action. The main lens 9 formed between the _G3 electrode 6 and the _G4 electrode 8, which is the final accelerating electrode, receives the final focusing action and impinges on the phosphor screen surface 10 to generate a beam spot 11. The beam spot 11 is a projected image of the crossover 5.

The axial potential distribution from the cathode 1 to the _G3 electrode 6 rises gradually, and this causes the cathode lens 4 to
and prefocus lens 7 is generated,
Since both lenses 4 and 7 are difficult to clearly distinguish, in the following description, these two lens regions will be referred to as a beam forming section. The axial potential distribution within the G ₃ electrode 6 is approximately constant at V _fpc , but the axial potential between the G ₃ electrode 6 and the G ₄ electrode 8 rapidly increases to a high potential V _a .
The main lens 9 is generated here.

The behavior of the thermoelectrons in the beam forming section is very complicated, but when the beam current is large, the electrons pass through electron trajectories 12 to 17, which are representatively shown by several lines in FIG. If the electron trajectories 12 to 17 all intersect at one point, an ideal small-diameter crossover and beam spot will be generated, but in reality, thermionic trajectories 12 and 13 emitted from the center of the cathode 1 are intersect at the farthest position 18 from the cathode 1, and the trajectory 16, 1 of the thermionic electrons emitted from the periphery of the cathode 1
7 intersect at a position 19 close to the cathode 1. This is because the lens in the beam forming section is accompanied by spherical aberration, and the actual diameter of the crossover is significantly larger than the theoretical limit value.

Then, this crossover is projected onto the phosphor screen surface 10 by the main lens 9, but precisely because of the presence of the prefocus lens 7, it is actually projected as shown in FIG. What is projected is a virtual image of crossover (diameter d),
This virtual image crossover is obtained as the intersection point when the electron trajectories 12 to 17 are extended in opposite directions, as shown by broken lines in FIG.

Now, if the diameter of the virtual image crossover is d ₀ ,
The diameter ds of the beam spot 11 generated on the phosphor screen surface 10 can be expressed by the following relational expression.

ds=d ₀ ×M+1/4CsD ³ ...(1) Here, M is the magnification of the main lens, Cs is the spherical aberration coefficient of the main lens, D is the spread diameter of the electron beam at the main lens, and M is the following formula. It is expressed as

Here, a is the maximum divergence angle of the electron beam emitted from the beam forming section, L is the distance between the center of the main lens 9 and the phosphor screen surface 10, V _g3 is the _G3 electrode potential, and V _a is the _G4 electrode potential. Indicates potential.

Substituting equation (2) into equation (1) gives us becomes.

The value in parentheses in this equation is determined by the size of the picture tube and operating conditions, and Cs is determined by the aperture of the lens used.

The spread diameter D of the electron beam is D ^-1 in the first term,
Since the second term is entered in the form of D ³ , there is a value of D that minimizes ds, and that value is usually selected. And under such constraints ds
If you try to make it smaller, you will have to make the first term a・d ₀ smaller.

According to the research results of the present inventors, G ₂ electrode and G ₃
By making the potential rise between the electrodes steeper, a·d ₀ can be reduced. Figure 4 shows G ₂ electrode and G ₃
This shows how a·d ₀ decreases when the distance between the electrodes is reduced, and it can be seen how a and d ₀ change independently. When the distance between the G ₂ electrode and the G ₃ electrode is reduced, d ₀ decreases significantly and a increases, but since the degree of decrease in d ₀ is more significant, the product a·d ₀ of the two decreases. The reason why d ₀ decreases in this way is that the spherical aberration of the lens in the beam forming section decreases when the potential rises steeply.

Such an effect clearly appears at a potential gradient of about 10 ⁵ V/cm, and the larger this value is, the more advantageous it is to reducing the diameter of the beam spot at high currents. However, when the current is small, the beam spot diameter becomes larger. Also, if the potential gradient becomes too large,
Electron emission occurs from the surface of the G ₂ electrode due to field emission, which impinges on the phosphor screen surface to produce unwanted light emission.

As described above, there is an upper limit to the practical potential gradient, and the value is approximately 5×10 ⁵ V/cm according to experimental results. If the potential difference between the G ₂ electrode and the G ₃ electrode is 8 KV, the distance between the G ₂ electrode and the G ₃ electrode that can provide the potential gradient of the above value is 0.8 mm to 0.16 mm.

However, even if such a potential gradient is directly applied to the beam forming section of a conventional picture tube electron gun, the beam spot diameter on the phosphor screen surface cannot be reduced. This is because increasing the potential gradient between G ₂ and _{G 3} increases the beam divergence angle a. When the beam divergence angle a increases, the electron beam diameter D at the main lens 9 increases, and the contribution of the main lens aberration in the second term on the right side of equation (3) increases. And the second
Since the term is proportional to the cube of D, even a slight increase in the electron beam diameter D has a large effect, and even if a・d ₀ in the first term of equation (3) is reduced, the beam spot diameter ds will change. This results in an increase in

An increase in the electron beam diameter D can be avoided by reducing the length of the _G3 electrode, but in order to satisfy the focus condition, the main lens focal length must be shortened by the length of the _G3 electrode. is required, and for this purpose the G ₃ electrode potential must be lowered. In this case, the potential gradient between G ₂ and G ₃ decreases, and the effect of reducing a·d ₀ is lost even though the electrode spacing is diligently narrowed.

Purpose of the Invention The present invention was made to eliminate the above-mentioned conventional disadvantages, and provides a picture tube device that can obtain a beam spot with a substantially constant diameter from a low brightness region to a high brightness region. .

Structure of the Invention The picture tube device of the present invention has G ₁ as a control electrode.
It includes a G ₂ electrode, a flat G ₃ electrode, and a cylindrical G ₄ electrode, which are arranged in sequence from the electrode side to the G ₅ electrode side as the final accelerating electrode. G ₃ electrode is G ₅ in the tube
connected to the electrode and given a high potential, G ₂ electrode and
The distance between the _G3 electrode and the potential gradient between the two electrodes is 10 ⁵
V/cm ~ 5×10 ⁵ V/cm, G ₄
A potential of several kilovolts or less, which is lower than the high potential, is applied to the electrode. The axial potential distribution reaches a maximum value in the G ₃ electrode region, then gradually decreases to a minimum value in the G ₄ electrode region, and increases continuously in the region from the G ₄ electrode to the G ₅ electrode. Through the involvement of the potentials of the ₃ electrodes to the _G5 electrodes, a substantially single thick main lens is produced, which will be described in detail below in conjunction with the embodiments shown in the drawings.

DESCRIPTION OF EMBODIMENTS The electron gun shown in FIG. 5 has G ₁ as a control electrode.
_G5 electrode 21 as the final accelerating electrode from the electrode 2 side
G ₂ electrode 3 and G ₃ electrode 22 arranged sequentially to the side
and a G ₄ electrode 23. The G ₂ electrode 3 has a structure similar to the accelerating electrode in a conventional electron gun, and the flat G ₃ electrode 2 adjacent to the G ₂ electrode 3
2 is connected to the G ₅ electrode 21 and placed close to the G ₂ electrode 3 so as to have a potential gradient of 10 ⁵ V/cm to 5×10 ⁵ V/cm. G ₄ electrode 23 and G ₅
All electrodes 21 are cylindrical, and G ₄ electrodes 2
3 is given a relatively low variable focus potential V _fpc from near 0 V to several KV, and the G ₅ electrode 21 is given a
A high potential V _a of 30KV is applied. Although the G ₄ electrode 23 and the G ₅ electrode 21 are shown as having the same diameter in FIG. 5, they may have mutually different diameters.
In particular, when using V _fpc near 0 V, it is desirable that the G ₄ electrode diameter is larger than the G ₅ electrode diameter.

With such a configuration, the axial potential distribution in the beam forming section rises steeply, and a·d ₀ at the time of large beam current decreases significantly, while the beam divergence angle a
increases. That is, as shown in FIG. 6, the _axial potential distribution is
It increases to the maximum value within the G ₄ electrode 23 and gradually decreases. And G ₄ electrode 23 and G ₅ electrode 24
It rises continuously in the region of , reaches the high potential V _a within the G ₅ electrode 21, and becomes constant. On the other hand, since the G ₃ electrode is flat, the diverging lens electric field generated immediately after that is extremely weak, and the G ₃ electrode 22,
The lens electric field generated by the G ₄ electrode 23 and the G ₅ electrode 21 creates a substantially single, short focal length main lens 25 . The generation of a main lens with a short focal length means that the distance between the virtual image crossover and the main lens can be shortened while keeping the potential rise in the beam forming part steep, and the beam divergence angle a increases. However, it is possible to maintain the beam diameter D at the main lens 25 at an appropriate value. When this is compared with equation (3), it can be seen that since a·d ₀ can be decreased without increasing the beam diameter D, the beam spot diameter ds can be reduced.

Effects of the Invention As described above, according to the picture tube device of the present invention, since the potential gradient in the beam forming section is increased,
The effect of reducing the spherical aberration and the virtual image crossover diameter in the same area can be obtained, and the main lens electric field has a short focus due to the involvement of the three electrodes, G ₃ electrode, G ₄ electrode, and G ₅ electrode. Despite the increased beam divergence angle, the electron beam diameter at the main lens can be maintained at an appropriate value, and a beam spot with a small diameter is generated even at high brightness when a large beam current flows, resulting in good resolution characteristics. Obtainable. Furthermore, since the electron gun is short and small, there is an advantage that the total length of the tube can be shortened.

[Brief explanation of drawings]

Fig. 1 is an electrode configuration diagram of an electron gun of a conventional picture tube device, Fig. 2 is an axial potential distribution diagram of the electron gun, Fig. 3 is an explanatory diagram of the operation mode in the beam forming section of the electron gun, and Fig. 4 The figure is a characteristic diagram showing the relationship between the beam divergence angle and the virtual image crossover diameter with respect to the mutual distance between the G ₂ electrode and the G ₃ electrode. FIG. 6 is an axial potential distribution diagram of the electron gun. 1... cathode, 2... G ₁ electrode, 3... G ₂ electrode,
21...G ₅ electrode, 22...G ₃ electrode, 23...G ₄
electrode.

Claims (1)

[Claims] 1 _G2 electrode, G3 electrode, and _G4 electrode are arranged sequentially from the _G1 electrode side as a control electrode to the _G5 electrode side as a final acceleration electrode, and _{the G3 electrode} is a flat plate. It is connected inside the tube to the _G5 electrode, which is given a high potential, and the distance between the _G2 and _G3 electrodes is such that the potential gradient between the two electrodes is 10 ⁵ V/cm to 5 × 10 ⁵ V/cm. The cylindrical _G4 electrode is given a potential of several KV or less, which is lower than the above-mentioned high potential, and the axial potential distribution reaches its maximum value in the _G3 electrode area.
It gradually decreases to the minimum value in the G ₄ electrode region, and rises continuously in the region from the G ₄ electrode to the G ₅ electrode.
A picture tube device characterized in that a substantially single thick main lens is generated by the involvement of the potential of the _G3 electrode or the _G5 electrode.