Cathode Ray Tube

The present invention relates to a cathode ray tube, and more particularly to a cathode ray tube which prevents the mislanding of the electron beam emitted from an electron gun and intended for the corner areas of a fluorescent layer, which occurs after colliding with the inner surface of the funnel.

Generally, a cathode ray tube as shown in FIG. 1, comprises a panel 10 on whose inner surface is formed a fluorescent layer 11, and a funnel 20 connected to panel 10 and including an electron gun 22 mounted inside a neck portion 21 and a deflection yoke 23 installed around the cone portion near the neck portion 21. In the cathode ray tube of FIG. 1, an electron beam emitted from the outlet G of the final accelerating electrode of electron gun 22 is deflected by deflection yoke 23 according to the scanning position on fluorescent layer 11, to land on fluorescent layer 11 and thus form a pixel; many such pixels are gathered to form a picture. However, since the screen is highly minute and elongated in the horizontal direction, the deflection angle is enlarged, so that the electron beam emitted from electron gun 22 collides with the inner surface of funnel 20 and cannot be precisely landed on the corner areas of fluorescent layer 11. The collision against the inner surface of funnel 20 by the electron beam emitted from electron gun 22 and intended for the corner areas of fluorescent layer 11, is due to the shape of funnel 20, installation conditions of deflection yoke 23, positioning of electron gun 22 and deflection yoke 23, etc. If, to solve the above problems, the cone portion near the neck of funnel 20 is formed such that it is large enough for the electron beam to avoid the above-described collision, the cathode ray tube must be enlarged accordingly, which necessitates that each part thereof be designed differently. Particularly, a cathode ray tube so enlarged significantly increases the process time required to adequately vacuumize its interior.

It is an object of the present invention to provide a cathode ray tube which prevents the electron beam emitted from an electron gun from colliding with the inner surface of cone portion of a funnel to subsequently misland, when intended for the corner areas of a fluorescent layer.

To achieve the above object of the present invention, there is provided a cathode ray tube comprising a panel formed with a fluorescent layer therein, and a funnel connected to the panel and provided with an electron gun and a deflection yoke mounted inside and near the neck portion thereof, respectively, which satisfies the following equation: ##EQU1## where .theta. denotes a deflection angle of an electron beam emitted from the electron gun, G denotes the outlet of the final accelerating electrode of the electron gun mounted in the neck portion, and R denotes the reference line which is the boundary between the deflection region where the electron beam emitted from the electron gun is deflected and curved by the deflection yoke and the linear region where the electron beam moves linearly.

Further features and advantages will become more apparent from the following and more particular description of the preferred embodiment of the invention as illustrated in the accompanying drawings in which the same reference characters generally refer to like parts throughout the views, and in which:

FIG. 1 is a cut-away side view of a conventional cathode ray tube; and

FIG. 2 is a cut-away side view of a cathode ray tube according to the present invention.

As shown in FIG. 2, a cathode ray tube generally comprises a panel 100 on whose interior surface is formed a fluorescent layer 101, and a funnel 200 connected to panel 100 and provided with an electron gun 202 mounted inside a neck portion 201 and a deflection yoke 203 installed around the cone portion near the neck portion which deflects the electron beam emitted from electron gun 202 according to the scanning position of fluorescent layer 101. In the cathode ray tube constructed as above, as the CRT size is enlarged and the screen becomes elongated in the horizontal direction, the deflection angle of the electron beam emitted from the outlet of the final accelerating electrode of electron gun 202 becomes large. At this time, the electron beam emitted from electron gun 202 collides with the inner surface of cone portion of funnel 200 and cannot be precisely landed on the corner areas of fluorescent layer 101, so that the picture of the corner areas is not clear. The inventor has studied the causes of the above problems (i.e., why the electron beam emitted from the electron gun cannot be precisely landed on the corner areas of the fluorescent layer), and found the following contributing factors to such a phenomenon: (1) the installation conditions of the deflection yoke and the magnitude of the deflection angle; (2) the eccentric distance between the centers of the electron beam passing holes of three electron guns emitting electron beams of red, blue and green, respectively; and (3) the distance between the outlet of the last accelerating electrode and a reference line R which is the boundary between the deflection region (where the electron beam emitted from the electron gun is deflected and curved by the deflection yoke) and the linear region (where the electron beam moves linearly).

Accordingly, in order to prevent the electron beam emitted from the electron gun from colliding with the inner surface of the cone portion and mislanding on the corner areas of the fluorescent layer, the inventor formulated the below equation in respect to the above reasons, and experimented to extract the results shown in Tables 1 and 2.

where FL denotes the distance in millimeters from the edge of the funnel to the reference line R, RL denotes the distance in millimeters between the outlet of the last accelerating electrode and the reference line R, .theta. denotes the deflection angle in degrees of the electron beam emitted from the electron beam, and S denotes the eccentric distance in millimeters between centers of electron beam passing holes of electrodes constituting the electron gun.

As shown in Tables 1 and 2, this phenomenon, wherein the electron beam emitted from electron gun 202 collides with the inner neck portion, is closely related to a distance RL between the outlet of the last accelerating electrode of electron gun 202 and reference line R which is the boundary between the deflection region and the linear region of the electron beam, while having less correlation with an eccentric distance S and a distance FL between the reference line R and the edge of panel 101.

Accordingly, the applicant formulated the below equation, with reference to the above tables, and experimented to extract the results shown in Table 3.

where .theta. denotes the deflection angle in degrees of an electron beam, and RL denotes the distance in millimeters between the outlet of the last accelerating electrode and reference line R.

As shown in Table 3, when the value of .beta. (satisfying the above equation) is between 1 and 1.3, an enlarged deflection angle of the electron beam emitted from the electron gun is optimized so that the electron beam does not collide with the inner surface of the funnel, and the image is clearly formed in the corner areas of fluorescent layer. This is accomplished without enlarging the interior volume of the funnel.

Therefore, in the cathode ray tube of the present invention, as the deflection angle of the electron beam emitted from the electron gun may be enlarged as the screen becomes elongated in the horizontal direction, which may result in the electron beam emitted from the electron gun colliding with the inner surface of the funnel and thus not being precisely landed on the corner areas of the fluorescent layer, the funnel can be optimally designed without increasing its interior volume.