JPS618833A - Beam focusing device - Google Patents

Abstract

PURPOSE:To reduce the spot diameter of a corner spot and increase the read threshold by providing a magnetic field generation device that generates a quadpole magnetic field correction magnetic field in front of a deflection means. CONSTITUTION:A focusing lens system 2 for focusing an electron beam, deflection means 4 that applies horizontal and vertical scanning to the electron beam focused by this focusing lens system 2, and a target surface 3 that reproduces a deflected beam picture are provided. In addition, a magnetic field generation device 5 that generates a control magnetic field in which the direction of magnetic flux density B on a flat surface made at right angles to the beam axis differs on both sides of the beam axis and the magnetic flux density B is reduced to zero at the center is provided in front of the deflection means 2. Furthermore, a spot picture around a screen is controlled by modulating the magnetic flux density B of the magnetic field generation device 5 by means of vertical and horizontal cycles. For example, the reverse distortion correction generated in the deflection distortion is applied previously before the beam spot is incident on the focusing lens 2 by applying force F to the beam spot using the quadpole magnetic field generation device shown in the diagram.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a beam focusing device for a cathode ray tube.

Conventional configuration and its problems In recent years, large displays using cathode ray tubes (hereinafter abbreviated as CRT) have been put into practical use, but in order to achieve high brightness,
There is a trend to further increase the beam current. Particularly in projection displays where the phosphor is operated at a high current density, the performance of the focusing characteristics influences the image quality. Furthermore, for high-definition applications such as character displays and high-definition television displays, the focusing characteristics around the screen are becoming most important.

A conventional beam focusing device will be explained below.

FIG. 1 shows a configuration diagram of a conventional beam focusing device, where 1 is an electron gun from which an electron beam is emitted. A focusing lens 2 focuses the emitted electron beam onto the target surface 3.

Reference numeral 4 denotes a deflection means for deflecting and scanning the electron beam on the target surface 3, which is generally a deflection means for deflecting and scanning, and generally a deflection yoke is used.

The operation of the conventional beam focusing device configured as described above will be described below. The electron beam emitted from the electron gun 1 is focused by a focusing lens 2. Generally, an electrostatic focusing lens is used, but a high-definition CR
In T, a magnetic field lens using an electromagnetic focusing coil is often used. In the picture tube, the deflection means 4 uses an electromagnetic deflection method as described above, and forms a raster by horizontally scanning and vertically scanning a target surface coated with a phosphor.

However, with the above configuration, due to problems with the uniformity of the magnetic field distribution of the deflection coil, at the periphery of the screen where deflection scanning is applied, the beam spot shape becomes larger than the center, and the spot diameter becomes larger as shown in Figure 5. This often results in spots that are distorted diagonally. In particular, from the viewpoint of saving deflection power, it is desirable to make the neck diameter of the CRT and the deflection yoke as small as possible, which has the problem of increasing peripheral distortion. When displaying images and videos, there is no problem even if the peripheral image quality deteriorates a little, but the combination?
= In cases such as sunset or graphic information, on the contrary, the image quality of the surrounding areas becomes more important. therefore,
The limit of deciphering peripheral characters will determine the upper limit of the beam current, making it impossible to raise the brightness to the same level as when shooting images.

Purpose of the Invention The present invention solves the above-mentioned conventional problems.It is an object of the present invention to provide means for correcting the shape of the beam spot in front of the focusing lens without lowering the deflection sensitivity, thereby reducing the spot diameter of the corner spot and reducing the decoding limit. The purpose of the present invention is to provide a beam focusing device capable of elevating the beam.

Structure of the Invention The present invention is a beam focusing device that includes a focusing lens system 2, deflection means 4, and a magnetic field generator 6. A modulation current corresponding to the periphery of the screen is passed through the magnetic field generator to shape the beam spot. It is possible to dynamically control the beam current so that the image quality of one periphery does not deteriorate even if the beam current is increased.

DESCRIPTION OF EMBODIMENTS FIG. 2 shows a configuration diagram of an embodiment of the present invention.
It is a good thing. Components having the same role as in FIG. 1 are given the same reference numerals. Reference numeral 5 in FIG. 2 is a magnetic field generating device which controls the beam spot, the structure of which is shown in FIG. 3 as a specific example.

The operation of the beam focusing device of this embodiment constructed as described above will be explained below.

As can be seen from the electron beam trajectory in FIG. 1, at the position of the deflection means 4, the beam is not completely focused but is distributed in a certain size. Therefore, since the deflection magnetic field is not uniform around the tube axis, the deflected beam spot is distorted. Therefore, in the present invention, as shown in 5 in FIG. 2, the opposite distortion correction that occurs in the deflection distortion is given in advance at a location before the beam enters the focusing lens 2, and the quadrupole magnetic field shown in FIG. This is a generator that applies force to the beam spot. The beam axis is the two axes, and the horizontal is the X axis.

If the vertical direction is the y-axis, and the magnetic poles are arranged in the x and y directions, magnetic flux B is generated in the angular direction of the x' and y' axes. Moreover, the magnetic fluxes B cancel each other out and become zero on the z-axis.

Moreover, since the direction of the magnetic flux B is reversed with the center being symmetrical, the force applied to the beam spot is in the vector direction shown by the arrow F, and the beam shape can be controlled in an oblique direction.

FIG. 4 shows the magnetic flux B along the X-axis, and shows the control current 11 of the quadrupole magnetic field. If I2 is reversed, the force F will be in the opposite direction. Therefore, in order to correct the distortion in a part of the corner as shown in Fig. 5, it is sufficient to add a waveform that is a balanced modulation of the horizontal period waveform with the vertical period to the current of I1, as shown in Fig. 6. I understand. That is, the center of the screen is not modulated in any way by the magnetic field generator 5, and only the periphery can be corrected.

As described above, according to this embodiment, the magnetic field generating device 6 is placed in front of the focusing lens system 2, and the peripheral spot can be improved by temporally modulating the magnetic field generating device 6. The so-called astigmatism correction can be dynamically corrected, and the aberration of the beam spot that remains due to the deflection aberration after the dynamic focus correction is improved.

In the embodiment, the magnetic field generator 4 has been described as being provided in front of the focusing lens system, but the same operation is possible if it is in front of the deflection means, so it may be placed behind the focusing lens system. You may. Generally, the deflection means is often a deflection coil, so it is easier to arrange it in front of the focusing lens system.

As mentioned above, whether the focusing lens system is an electrostatic type or an electromagnetic type has no effect on the operation of the present invention. As long as the deflection means uses a horizontal/vertical scanning method, corner deflection aberration will similarly occur, and both electromagnetic deflection and electrostatic deflection methods are possible. In particular, since the magnetic field generator generates an alternating magnetic field, it goes without saying that when placed behind the focusing lens, the electrostatic deflection method can reduce magnetic field coupling.

Effects of the Invention As described above, the beam focusing device of the present invention can improve the peripheral beam spot diameter by providing a magnetic field generating device that generates a correction magnetic field for the quadrupole magnetic field in front of the deflection means. As a result, it becomes possible to increase the beam current by φ compared to the marginal resolution before correction, and it also has the effect of increasing the brightness. Therefore, it has a beneficial effect on high current density projection tubes and high definition projection tubes.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional beam focusing device;
3 is a structural diagram of a magnetic field generator of the same device, FIG. 4 is a distribution diagram of the same magnetic field, and FIG. 5 is a beam focusing device in an embodiment of the present invention. The spot shape diagram and FIG. 6 are modulation waveform diagrams in the embodiment. 1... Electron gun, 2... Focused/Z system,
3...Target surface, 4...Deflection means, 6...Magnetic field generator. Name of agent: Patent attorney Toshio Nakao

Claims (1)

[Claims] A focusing lens system for focusing an electron beam, a deflection means for giving horizontal and vertical scanning to the electron beam focused by the focusing lens system, and a target surface for reproducing a deflected beam image, A magnetic field generator that generates a control magnetic field in which the direction of magnetic flux density in a perpendicular plane is different on both sides of the beam axis and the magnetic flux density is zero at the center is provided in front of the deflection means, and the magnetic flux density of the magnetic field generator is A beam focusing device that modulates the beam spot image around the screen by modulating it in horizontal and vertical cycles.