JPH03203147A - Focusing device of crt - Google Patents

Abstract

PURPOSE:To reduce the projection magnification without increasing the neck length of a CRT and make a display image highly minute by disposing lenses functioning as concave lens and convex lens in determined positions to form an electronic lens. CONSTITUTION:Electron beams 5 emitted from an electron gun 7 are focused on a phosphor screen 6 through an electrostatic concave lens 4 and an electromagnetic convex lens 11 to form a display image. The main point positions H, H' of lens systems formed by each electron lens are present on the image side (side P') from the electromagnetic convex lens 11. Therefore, the projection magnification is reduced, compared with the case having no electrostatic concave lens 4 and only the electromagnetic convex lens 11. Thus, the projected spot image can be minimized to make the display image highly minute.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a CRT focusing device that focuses an electron beam on a fluorescent screen of a CRT to form a spot image.

[Conventional technology]

There are two types of CRT focusing devices: an electrostatic type using an electrostatic lens and an electromagnetic type using an electromagnetic lens.

Regarding electrostatic lens arrangement, BPF type, UPF type, H
I-BPF type, HI-UPF type, B-UPF type, U-B
There are various types such as PF type and U-UPF type, and they are used depending on the purpose. There are two types of electromagnetic lens arrangements: internal magnetic type and external magnetic type, and the external magnetic type is often used in CRTs for projection televisions.

FIG. 4(a) is a diagram showing the structure of an electrostatic HI-BPF type.

The electron gun 47 is composed of a cathode 41 and a grid 42. The electron beam 45 emitted from the electron gun 47 is focused on the phosphor screen 46 by electrostatic convex lenses 441 and 442 formed by applying a voltage to the electrode 43, and is focused on the phosphor screen 46. The light is deflected by the provided polarization yoke 48 and emitted onto the fluorescent screen 46 .

FIG. 4(b) is a diagram showing the configuration of an electromagnetic external magnet type.

In this conventional example, the electron beam 45 is focused by an electromagnetic convex lens 50 formed by an electromagnetic focusing coil 50.

Both the electrostatic lens and the electromagnetic lens described above are used by forming a convex lens that focuses an electron beam. In electrostatic types, multiple lenses are often formed, and in electromagnetic types, a single lens is often formed.

[Problems to be Solved by the Invention] In order to increase the definition of display images on CRTs, it is effective to reduce the spot image projected by the electron beam onto the fluorescent screen, that is, to reduce the projection magnification. be.

One possible method for lowering the projection magnification is to position an electron lens (a general term for electrostatic lenses and electromagnetic lenses) closer to the phosphor screen. However, as in the conventional examples shown in FIGS. 4(a) and 4(b), since the deflection yoke 8 is provided behind the CRT funnel section 9,
When bringing the electron lens close to the phosphor screen, the limit is at a position where no contact or interference with the polarizing yoke 8 occurs, and the projection magnification cannot be lowered sufficiently.

Another way to reduce the projection magnification is to position the electron gun at the rear (away from the phosphor screen), but this method would increase the neck length of the CRT. If a TV device is constructed using the CRT, there is a drawback that the device becomes large in size.

SUMMARY OF THE INVENTION An object of the present invention is to realize a CRT focusing device that can reduce projection magnification without increasing the neck length of the CRT.

[Means to solve the problem]

A CRT focusing device according to the present invention is a CRT focusing device in which a plurality of electron lenses are formed between an electron gun and a phosphor screen in order to focus an electron beam emitted from an electron gun onto a phosphor screen. At least one of the electron lenses is formed to have a concave lens function, and the electron lens located closest to the phosphor screen is formed to have a convex lens function.

[For production]

Since the present invention is configured as described above, the position of the principal point of the lens system formed by each electron lens moves toward the phosphor screen, and the lens system substantially approaches the phosphor screen. Magnification becomes smaller.

[Embodiment] FIG. 1 is a diagram showing the main part configuration of a first embodiment of the present invention.

In this embodiment, an electrostatic lens and an electromagnetic lens are combined to reduce the projection magnification.
It consists of

3a, 3b, and 3c are three sets of electrodes for forming a tJPF type electrostatic lens, and the voltage EO applied to the two sets of electrodes 3a and 3c is applied to one set of electrodes 3b provided between them. The applied voltage E1 is set to be lower than the applied voltage E1, and is set to form an electrostatic concave lens 4 having a predetermined power. 10 is an electromagnetic focus coil, which forms an electromagnetic convex lens 11. Reference numeral 5 indicates an electron beam, which is emitted from the cathode 1 and is transmitted to the first grid 2a and the second grid.
After being crossed over when passing through grid 2b,
After passing through the electrostatic concave lens 4 and the electromagnetic convex lens 11, the phosphor screen 6
A beam spot image is formed on the top.

In this way, in this embodiment, an electron beam lens system is constructed by a concave electron lens and a convex electron lens.

FIG. 2 is a diagram showing the optical configuration of this embodiment.

The lens system of this embodiment constitutes a retrofocus lens system in the optical field. Electrostatic concave lens 4 that spreads the incident light beam is an electromagnetic convex lens 11 that serves as an output lens.
Because it is provided at the front stage of ,
It is smaller than the case of only the electromagnetic convex lens 11 without the electrostatic concave lens 4.

In this way, in this embodiment, even if the actual lens position cannot be brought closer to the phosphor screen by a predetermined position or more due to constraints caused by the deflection yoke, the principal point position can be brought closer to the phosphor screen. Therefore, the projection magnification of the beam spot image becomes smaller, and a smaller beam spot can be obtained.

Further, in this embodiment, the electron beam spread by the electrostatic concave lens 4 is focused using the external magnetic type electromagnetic convex lens 11. In the external magnetic type electromagnetic lens, it is possible to reduce aberrations by increasing the inner diameter of the electromagnetic focusing coil 10, so that an even better beam spot can be obtained.

Furthermore, in this embodiment, since the electron beam is once expanded and then focused, the angle of concentration at which the beam spot is formed is large.

Therefore, electrostatic repulsion (
It also has the advantage of reducing the number of revisions (revisions) and the negative effects of this.

FIG. 3 is a diagram showing the main structure of a second embodiment of the present invention.

In this embodiment, the electron lens formed inside the CRT is composed only of electrostatic lenses. For this reason, in this embodiment, instead of the electromagnetic focusing coil, four sets of electrodes 33a to 33d are provided in order from the electron gun side to the phosphor screen side. Since the other configurations are the same as those shown in FIG. 1, the same reference numerals are given and explanations are omitted.

Reference numeral 14 denotes an electrostatic convex lens for prefocusing, which is formed by an electric field generated by the electrode 33.a and the second grid 2b. The three sets of electrodes 33a, 33b33c are each electrode 33a.
, 33b is lower than the voltage E2 applied to the electrode 33b, a UPF type electrostatic concave lens 35 is formed. Also, 12 is
Applied voltage E2E3 to each of electrodes 33c and 33d
This is a BPF type electrostatic convex lens formed by (E3 > E2).

In this embodiment, the electron beam 5 emitted from the cathode 1 is crossed over when passing through the first grid 2a and the second grid 2b, and then reaches the electrostatic convex lens 14 for prefocusing. After being slightly focused here, the light passes through an electrostatic concave lens 35 and an electrostatic convex lens 36, which are the main lens system, and is emitted onto the phosphor screen 6.

In this embodiment, an electrostatic convex lens 36 is used as the convex lens of the main lens, but the function of this lens system is exactly the same as that of the electromagnetic convex lens 11 (see FIG. 1) in the first embodiment.

Therefore, in this embodiment as well, due to the effect of the combination of the electrostatic concave lens 35 and the electrostatic convex lens 36, the projection magnification of the beam spot image is reduced, and a smaller beam spot can be obtained. Furthermore, in this embodiment, since the lens system is entirely electrostatic, it is possible to reduce the cost compared to that of the first embodiment.

Note that the present invention is not limited to the embodiments described above, and may be configured as follows.

(1) Based on the combination of an electron lens that acts as a concave lens and an electron lens that acts as a convex lens, various electronic lenses are added for aberration correction and the like.

(2) Application to multi-electron gun type CRTs such as CRTs for color TVs.

(3) Employing various types of electrostatic lenses.

(4) The neck length of the CRT is shortened by moving the electron gun closer to the phosphor screen by an amount that offsets the reduction in projection magnification achieved by the lens system of the present invention. This does not improve the beam spot diameter, but this CR
Various devices using T can be made more compact.

〔Effect of the invention〕

Since the present invention is configured as described above, it produces the effects described below.

By moving the principal point position toward the phosphor screen, it is possible to lower the projection magnification, which increases the angle of concentration when incident on the phosphor screen, which reduces electrostatic repulsion between electrons and reduces the negative effects caused by this. Become. As a result, CRT for color TV,
CRT for OA display, CRT for projection
This has the effect of increasing the definition and resolution of various types of CRTs.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the main part configuration of the first embodiment of the present invention, FIG. 2 is a diagram showing the optical configuration of the first embodiment, and FIG. 3 is a diagram of the second embodiment of the present invention. Diagram showing the main part configuration, Fig. 4(a)
, (b) are diagrams each showing the configuration of a conventional example. DESCRIPTION OF SYMBOLS 1... Cathode, 2a... 1st grid, 2b... 2nd grid, 3a-3c, 33a-33d-electrode, 4
．． 35... Electrostatic concave lens, 5... Electron beam, 6.
... Fluorescent screen, 7... Electron gun, 10...
Electromagnetic focus coil, 1 11... Electromagnetic convex lens, 34.36... Electrostatic convex lens.

Claims (1)

[Scope of Claims] 1. A CRT focusing device in which a plurality of electron lenses are formed between the electron gun and the phosphor screen in order to focus the electron beam emitted from the electron gun onto the phosphor screen, comprising: A focusing device for a CRT, characterized in that at least one of the electron lenses has a concave lens function, and further, the electron lens located closest to the phosphor screen has a convex lens function.