JPS62264541A - Electron gun - Google Patents

Abstract

PURPOSE:To reduce a spot diameter of electron beams to minimize spherical aberration, by impressing respectively given voltages on the third to sixth grids and then specifying the length of the fifth grid electrode and that of a main lens-syetem main part. CONSTITUTION:The fourth grid 5 and sixth grid 7 are electrically connected, with phosphor-screen voltage VB being impressed on them. The third grid 4 and fifth grid 6 are electrically connected, with focusing voltage VF being impressed on them. Because electrical gradient between the second grid 3 and the third grid 4 is emall, spherical aberration of a focusing lens formed there is remarkably reduced. Length l5 of the fifth grid electrode 6 is larger than a half of its inner diameter D, and length lL from a cathode-side terminal plane of the third grid 4 to the sixth grid 7-side terminal plane of the fifth grid 6 is made to be within the range of 3.5D-6D. Hence, a spot diameter of electron beams can be reduced to minimize the spherical aberration.

Description

[Detailed description of the invention] The present invention relates to an electron gun, particularly an electron gun for a cathode ray tube.

Conventionally, the two types most commonly used as converging lenses for electron guns for cathode ray tubes are the unipotential type and the pipotential type.

In order to minimize the spherical aberration of a conventional unipotential lens system, the present inventors have proposed constructing a lens system with electrodes as shown in FIG. That is,
The electron beam current emitted from the cathode 1 is transferred to the first grid 2.
and the second grid 3 to form a crossover, and the third grid 4. 4th grid 5. The main lens system ζ, which is composed of three cylindrical electrodes of the fifth grid 6, photographs a crossover image on the fluorescent surface to obtain an electron beam spot.

In the unipotential type of AM, the third grid 4 and the fifth grid 6 apply the voltage VB of the fluorescent surface, and the fourth grid is often selected as the focus voltage V, which is around zero voltage. In order to do this, the length of the fourth grid 5 must be set to 1/1 of the inner diameter of the electrode due to the lens strength.
It is difficult to make it longer than 2.

In this type of lens system, when the length of the fourth grid 5 serving as the focus electrode relative to the inner diameter is increased, the focus voltage increases rapidly, and at the same time, the spherical aberration decreases significantly.

An electron gun using such a lens system has a feature that the spot diameter of the electron beam is smaller than that of an electron gun having a conventional pi-potential type lens system.

The present invention aims to provide an electron gun that improves such a unipotential type electron gun and further reduces the spot diameter of the electron beam, thereby minimizing spherical aberration.

In order to achieve this object, the present invention consists of a lens system consisting of four cylindrical electrodes, J3, X4 in order from the cathode side.
, fifth, and sixth grid electrodes, a focus voltage is applied to the third and fifth grid electrodes, and a voltage that is equal to the fluorescent surface voltage of the cathode ray tube is applied to the fourth and sixth grid electrodes. is applied, and the length of the fifth grid electrode is made longer than 1/2 of its inner diameter, and the length from the cathode side end face of the third grid to the sixth grid side end face of the fifth grid is the inner diameter of the fifth grid electrode. Further, the focus voltage is set to 174 to 1/2 of the fluorescent plane voltage.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 2 is a diagram showing an embodiment of the configuration of an electron gun using the lens system of the present invention. Cathode 1. 1st gris, d 2. a second grid 3 and a third grid 4 forming a lens system. Fourth
Grid 5. Consisting of a fifth grid 6 and a sixth grid 7, the fourth grid 5 and the sixth grid 7 are electrically connected and have a phosphor surface voltage (voltage applied to the phosphor surface) v.

is applied, and the third grid 4 and the fifth grid 6 are electrically connected and a focus voltage V is applied.

Here, the fourth grid 5. The lens system formed by the fifth grid 6 and the sixth grid 7 is of a unipotential type, and the third grid 4. The lens system formed by the fourth grid 5 is a pi-potential type lens system.

Voltage V applied to the third grid 4 of this embodiment.

is several times lower than the third grid voltage v8 of the unipotential type, so the potential gradient between the second grid 3 and the third grid 4 becomes small, and the focus formed here The spherical aberration of the lens is significantly reduced.

On the other hand, the fifth grid electrode 6 that constitutes the main part of the lens system
has the same effect as the unipotential type fourth grid electrode 5, and the longer it is, the longer it is.

Spherical aberration of the main lens system can be reduced. Figure 3 (al is the change in the amount of spherical aberration when the length 15 of the fifth grid electrode 6 of the main lens system is changed in the electron gun of the present invention, and Figure 3 (bl is the change in focus voltage) This is the result of analyzing the electron gun of the present invention.
It can be seen that as the length of the grid electrode increases, the spherical aberration in the main lens system decreases and the focus voltage becomes worse.

FIG. 4 shows an electron gun configuration according to the present invention in which the length of the electrode of the fifth grid 6 is 1.0 while keeping the length JL of the lens system constant. This is the result of actually measuring the change in spot diameter in the large current region obtained when changing .

From Figure 4, in order to obtain a small spot diameter in a large current range, the length of 15 is 1/2 of the inner diameter of the fifth grid electrode.
It needs to be longer.

Figure 5 shows the conventional pi-potential type 15-element gun G1
The unipotential electron gun G2 shown in the figure. The electron beam spot diameter with respect to the cathode current was actually measured and compared for the electron gun G3 of the present invention.

Compared to the conventional pi-potential type G1, in the electron gun G3 of the present invention, the spot diameter is reduced by about 30% at high current,
Furthermore, even in a small current range, there is no deterioration as seen in the unipotential type G2, and on the contrary, the spot diameter can be reduced.

FIG. 6 shows the change in the spot diameter obtained on the fluorescent surface when the thickness of the electron beam in the main lens system is changed during high current operation in the electron gun of the present invention. The characteristics can be explained by the superposition of two contradictory effects. That is, the component of the spot diameter determined by the silent velocity dispersion of the electrons in the electron beam and the space charge effect (indicated by curve C2 in the figure) is the component of the spot diameter in the main lens. The wider the electron beam, the smaller the circle of least confusion caused by the spherical aberration of the main lens system (as shown by curve C3 in the figure). increases in proportion to the cube of the thickness. Therefore, the actual electron beam spot diameter where these effects overlap is the 6th
As shown by curve C1 in the figure, it reaches a minimum at a certain point. In the electron gun of the present invention, when the electron beam in the lens is thicker than 1/2 of the inner diameter of the electrode during high current operation, the spot diameter on the phosphor surface becomes minimum.

A change in the beam spot diameter of an electron gun using a conventional pi-potential type lens is shown as a curve C4 in FIG. According to this curve C4, the spot diameter becomes minimum when the thickness of the electron beam in the lens is 1/3 of the inner diameter of the electrode. According to the invention, therefore, curve C1.

As is clear from C4, by selecting the maximum value of the electron beam diameter to be larger than 1/3 of the inner diameter of the lens, it is possible to make the spot diameter smaller than that of the conventional electron gun.

Figure 7 shows the fifth grid electrode length in the electron gun of the present invention! , 1
．． The length of the main part of the main lens system selected as 7D! .

The changes in the spot diameter of the electron beam and the focus voltage V in the large current region and the small current region are investigated.

The spot diameter of the large current area process □ shown in Figure 7 (al) is
Since jL is minimum near 4D, up to 3.5D in approximately jL is acceptable in the practical range. Note that Is indicates a small current region. On the other hand, under the condition that the value for large current and the value for small current match around 5.3D in Fig. 7 (the focus voltage v2 shown in bl is !), and there is no need to adjust the focus voltage depending on the electron beam current. Therefore, in the practical range, up to 6.0D in about 4L is acceptable.

In addition, in the figure, V1. V2 indicates the focus voltage of large current and small current, respectively, and S indicates the practical area when j = 1.7D. Therefore, by changing the length of j5, the practical area S becomes 3.5D≦1. ≦6. It changes slightly between OD.

It is extremely difficult to dynamically adjust the focus voltage using an electronic circuit to match the operating beam current of a cathode ray tube, and it is economically impractical. The characteristics of a voltage operated electron gun are highly desirable.

The reason why this focus voltage is constant is as follows. When the electron beam current is increased, the crossover moves toward the fluorescent surface and the space charge effect in the beam increases, so the beam spot that is intended to be created on the fluorescent surface extends beyond the fluorescent surface. . To correct this, the focusing power of the lens system must be strengthened, that is, the voltage of the fifth grid must be lowered in the electron gun of the present invention. On the other hand, when the beam current is increased, the divergence angle of the electron beam from the crossover increases with the current, the thickness of the dome in the lens increases, the spherical aberration of the lens system increases, and the circle of least confusion increases. Moves from the light surface to the cathode side. Therefore, if the amount of spherical aberration of the lens system and the thickness of the beam are selected so that these two effects cancel each other out, there is a condition where the focus voltage remains constant regardless of the current as shown in Figure 7 (bl). .

In the electron gun of the present invention, the fifth grid electrode length 15 is kept constant, so it is shown in FIG. In the range of , the change in the amount of spherical aberration of the main lens system is relatively small, while the thickness of the electron beam in the main lens increases in proportion to the aperture jL. It can be assumed that the characteristics of the lens system are determined by 0. From this point of view, it is appropriate to select the range of lL to be in the range of 3.5D<6D.

As mentioned above, the electron gun of the present invention does not depend on the beam current;
The spot diameter is about 30% smaller than that of the conventional method, and it has an extremely excellent effect in that it operates with a constant focus voltage regardless of the beam current.

Although the same vF is applied to the third and fifth grid electrodes in Figure 2, it is acceptable to apply different voltages, and the inner diameters of the electrodes that make up the main lens system must all be equal. Not at all.

The characteristics shown in FIGS. 3 to 7 in the above description were measured with an electron gun, 20 inches, 110° deflection, and a light surface voltage of 18 kV.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a unipotential electron gun proposed by the present inventor. FIG. 2 is a diagram showing the configuration of an embodiment of the present invention. FIG. 3 (al shows the change in the amount of spherical aberration when the length of the fifth grid electrode of the lens system of the present invention is changed, and FIG. 3 (bl is a characteristic diagram showing the change in focus voltage). Figure 4 shows an electron gun using a conventional pi-potential type lens, while the length of the lens system of the present invention is kept constant t.
FIG. 2 is a characteristic diagram showing the relationship between cathode current and beam spot diameter of an electron gun using a unipotential lens shown in the Mx diagram and an electron gun using a lens system according to the present invention. Figure 6 shows the components of the spot diameter due to silent velocity dispersion and space charge effect, and the spherical yield of the lens system with respect to the beam thickness in the lens of the electron gun of the present invention and the conventional lens system. FIG. 6 is a diagram illustrating changes in spot diameter components and . FIG. 7(a) is a diagram showing the change in spot diameter with respect to the length of the lens portion of the electron gun of the present invention, and FIG. 7(b) is a diagram showing the change in focus voltage. Fig. 1 Fig. 2 Unfinished surface roughening large y2 Kishi J Fig. 4 Oθ, 5 7. OiK, ), θ, it/l:) No.! ;''' times and r ne yo, t li E (yuA) ring 6 times 7 yen (n) L10 It/D

Claims (1)

[Claims] 1. In an electron gun equipped with a lens system that focuses an electron beam emitted from an anode, the lens system uses four cylindrical electrodes as third, fourth, fifth, and sixth grid electrodes in order from the cathode side. Consisting of arranged electrodes, a focus voltage is applied to the third and fifth grids, and a fluorescent surface voltage is applied to the fourth and sixth grids to form a bipotential lens system and a unipotential lens system. In addition, the length of the fifth grid electrode is set to 1 of its inner diameter.
/2, and the length from the cathode side end surface of the third grid to the sixth grid side end surface of the fifth grid is in the range of 3.5 to 6 times the inner diameter of the electrode of the fifth grid, and The above focus voltage is set to 1 of the above fluorescent surface voltage.
An electron gun characterized by having a size of 1/4 to 1/2.