JPH0419661B2 - - 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. Then, the main lens 9 generated between the _G3 electrode 6 and the _G4 electrode 8, which is the final accelerating electrode, receives the final focusing action and hits the phosphor screen surface 10 to generate a beam spot 11. The beam spot 11 is a projected image of the clockover 5.

The axial potential distribution from cathode 1 to _G3 electrode 6 is
The cathode lens 4
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 in _G3 electrode 6 is Vfoc
is approximately constant, but the axial potential between the G ₃ electrode 6 and the G ₄ electrode 8 rapidly rises to a high potential Va,
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 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, the crossover is actually projected as shown in FIG. What is shown is a virtual image of the crossover (diameter d), and this virtual image crossover is obtained as the intersection point when electron trajectories 12 to 17 are extended in opposite directions, as shown by broken lines in the figure.

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

ds=do×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, Vfoc is the _G3 electrode potential, and Va is the _G4 electrode potential. .

Substituting equation (2) into equation (1), we get 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 and do smaller.

According to the research results of the present inventors, G ₂ electrode and G ₃
If the potential between the electrodes rises steeply, a・do
can be made smaller. Figure 4 shows G ₂ electrode and
This figure shows how a and do decrease when the distance from the _G3 electrode is reduced, and it can be seen how a and do change independently. When the distance between the G ₂ and G ₃ electrodes is reduced, do decreases significantly,
On the contrary, a increases, but since the degree of decrease in do is more remarkable, the product a·do decreases. The reason that do 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. Furthermore, 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 and causes unwanted light emission.

In this way, there is an upper limit to the practical potential gradient, and according to experimental results, the value is approximately 5 × 10 ⁵ V/cm.
It is. If the potential difference between the G ₂ electrode and the G ₃ electrode is 8KV, the G ₂ electrode and the G ₃ electrode can give a potential gradient of the above value.
The distance between the electrodes is 0.8 mm to 0.2 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. Since the second term is proportional to the cube of D, the electron beam diameter D
Even a slight increase in ds has a large effect, and even if a·do in the first term of equation (3) is diligently reduced, the beam spot diameter ds will instead increase.

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 can 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 a/do reduction effect 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 is equipped with a G ₂ electrode, a G ₃ electrode, a G ₄ electrode, and a G ₅ electrode arranged sequentially from the electrode side to the G ₆ electrode side as the final accelerating electrode, and the G ₃ electrode is a flat _plate . The aperture diameter of the electrode is D ₂ G The aperture diameter of the ₃ electrode is D ₃ G The aperture diameter of the ₄ electrode is D ₄ G The distance between _{the 2} electrode and G ₃ electrode is g ₂₃ G The distance between the ₃ electrode and G ₄ electrode is g ₃₄ , the relational expression D ₂ ≦D ₃ ≦2D ₂ , D ₃ ≦D ₄ ≦2D ₃ 0.5D ₂ ≦g ₂₃ ≦1.5D ₂ , 0.2D ₃ ≦g ₃₄ ≦1.5D ₃ holds, and G ₄ electrodes include G ₃ electrodes and G ₅
A potential lower than the focus potential is applied to the electrode, and the axial potential distribution reaches a maximum value in the G ₃ electrode area, then gradually decreases to a minimum value in the G ₄ electrode area, and reaches from the G ₄ electrode to the G ₆ electrode. The structure is such that the G ₂ and G ₃ electrodes generate a strong converging lens, and the G ₃ and G ₄ electrodes generate a strong diverging lens. This is shown in the drawing below. This will be described in detail along with the illustrated embodiments.

DESCRIPTION OF EMBODIMENTS The electron gun shown in FIG. 5 has G ₁ as a control electrode.
_G6 electrode 21 as the final accelerating electrode from the electrode 2 side
G ₂ electrode 3, G ₃ electrode 22 arranged sequentially toward the side;
A G ₄ electrode 23 and a G ₅ electrode 24 are provided. G ₂
The electrode 3 has a structure similar to the accelerating electrode in a conventional electron gun, and has a plate-like structure adjacent to the G ₂ electrode 3.
The G ₃ electrode 22 is 10 ⁵ V/cm to 5× with respect to the G ₂ electrode 3.
They are placed close together so that the potential gradient is 10 ⁵ V/cm.

The _G4 electrode 23 is formed into a cup shape,
The G ₅ electrode 24 and the G ₆ electrode 21 are cylindrical, and the G ₃ electrode 22 and the G ₅ electrode 24 are connected to each other inside the tube and have a focus potential Vfoc of about 6KV to 10KV.
is given. Furthermore, a potential lower than the focus potential Vfoc is applied to the G ₄ electrode 23, and a high potential Va of about 30 KV is applied to the G ₆ electrode 21, so that
The axial potential distribution is as shown in FIG.

That is, the axial potential distribution rises to the focus potential Vfoc within the aperture 25 of the G ₃ electrode 22, then gradually decreases toward the G ₄ electrode 23, and then decreases to the G ₄ electrode 23.
3. It rises continuously in a region spanning three electrodes, G ₅ electrode 24 and G ₆ electrode 21, and reaches a high potential Va within G ₆ electrode 21.

On the other hand, as shown in FIG. 7, the aperture diameter of the G ₂ electrode 3 is D ₂ , the aperture diameter of the G ₃ electrode 22 is D ₃ ,
The aperture diameter of G ₄ electrode 23 is D ₄ , G ₂ electrode 3 and G ₃
The distance between the electrode 22 is g ₂₃ , and the G ₃ electrode 22 and G ₄ electrode 2
3, _the relationship between D ₂ ≦D ₃ ≦2D ₂ , D ₃ ≦D ₄ ≦2D ₃ 0.5D ₂ ≦g ₂₃ ≦1.5D ₂ , 0.2D ₃ ≦g ₃₄ ≦1.5D ₃ The dimensions are set so that the formula holds true.
Further, the plate thickness t ₃ of the G ₃ electrode 22 is relatively large, t ₃ ≈D ₃ .

According to such a configuration, a strong focusing lens 26 is generated between the G ₂ electrode 3 and the G ₃ electrode 22,
Since a strong diverging lens 27 is generated between the G ₃ electrode 22 and the G ₄ electrode 23, a.
do decreases and the beam divergence angle a increases.

Since the potential of the G ₄ electrode 23 is lower than the focus potential Vfoc, the focal length is shorter than in the conventional electron gun configuration. This means that the distance between the virtual image crossover and the main lens can be shortened while sharply increasing the axial potential distribution in the beam forming section, and even if the beam divergence angle a increases, the main lens 28 It becomes possible to maintain the beam diameter D at an appropriate value. If we compare this with equation (3), we can see that a・do can be decreased without increasing the beam diameter D, so the beam spot diameter ds
It turns out that it is possible to downsize the .

Furthermore, since the lens electric field of the main lens 28 is distributed gently over a wide range, the spherical aberration of the main lens is small, which means that the aberration coefficient Cs in the second term of equation (3) becomes small. ,
This effect also reduces the beam spot diameter ds.

Effects of the Invention As described above, according to the picture tube device of the present invention, the effects of reducing lens spherical aberration in the beam forming section, reducing the diameter of the virtual image crossover, and reducing the main lens spherical aberration are combined, and when a large beam current is used, Also, a beam spot with a small diameter can be obtained, and good resolution characteristics can be obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the electron gun electrode configuration of a conventional picture tube device, FIG. 2 is an axial potential distribution diagram of the electron gun, and FIG. 3 is an explanatory diagram of the operation mode in the beam forming section of the electron gun. Figure 4 is a characteristic diagram showing the relationship between the beam divergence angle and the virtual image cronover diameter with respect to the mutual distance between the G ₂ electrode and the G ₃ electrode, and Figure 5 shows the electrode configuration of the electron gun of the picture tube device implementing the present invention. Figure, 6th
The figure is an axial potential distribution diagram of the electron gun, and FIG. 7 is an electrode cross-sectional view for explaining the electrode dimensions of the electron gun. 3...G ₂ electrodes, 21...G ₆ electrodes, 22...G ₃
Electrode, 23...G ₄ electrode, 24...G ₅ electrode.

Claims (1)

[Scope of Claims] 1. Includes a G ₂ electrode, a G ₃ electrode, a G ₄ electrode, and a G ₅ electrode arranged sequentially from the G ₁ electrode side as a control electrode to the G ₆ electrode side as a final acceleration electrode. , the G ₃ electrode is a flat plate, and the aperture diameter of the G ₂ electrode is D ₂ The aperture diameter of the G ₃ electrode is D ₃ The aperture diameter of the G ₄ electrode is D ₄ The distance between the G ₂ electrode and the G ₃ electrode is g ₂₃ When the distance between the G ₃ electrode and the G ₄ electrode is g ₃₄ , D ₂ ≦D ₃ ≦2D ₂ , D ₃ ≦D ₄ ≦2D ₃ 0.5D ₂ ≦g ₂₃ ≦1.5D ₂ , 0.2D ₃ ≦g The relational expression ₃₄ ≦1.5D ₃ is established, and the G ₄ electrode is connected to the G ₃ electrode and the G ₅
A potential lower than the focus potential is applied to the electrode, and the axial potential distribution reaches a maximum value in the G ₃ electrode area, then gradually decreases to a minimum value in the G ₄ electrode area, and reaches from the G ₄ electrode to the G ₆ electrode. A picture tube device characterized in that the _G2 electrode and the _G3 produce a strong converging lens, and the _G3 and _G4 electrodes produce a strong diverging lens.