Cathode ray tube having a corrector for a deflection yoke

A cathode ray tube includes an electron gun for emitting an electronic beam, a deflection yoke which deflects the emitted electronic beam, and a corrector including electromagnets installed in the up-and-down and right-and-left sides of a separator of the deflection yoke for correcting the shape of the section of the emitted electronic beam. Resolution of the picture can be improved by correcting the distortion of the section of the electronic beam which is landed at the edge of a fluorescent film.

BACKGROUND OF THE INVENTION 
The present invention relates to a cathode ray tube, and, more 
particularly, to a cathode ray tube having a corrector for preventing the 
cross-section of an electron beam which is emitted from an electron gun, 
deflected by a deflection yoke, and lands on a fluorescent film, from 
being distorted. 
Generally, a cathode ray tube forms pixels by directing the electron beam 
emitted from the electron gun sealingly coupled in the neck portion 
thereof to a fluorescent film on the inside of a pannel. The electron beam 
is selectively deflected by the deflection yoke and forms a picture from 
the collective pixels. The electron beam should and correctly on the 
fluorescent point of the fluorescent film to produced a fine picture. 
However, the spot of the electron beam which lands on the fluorescent film 
may be distorted since the deflection coil of the deflection yoke forms 
nonuniform deflection magnetic fields and the geometric curvature of the 
inside of the panel is distorted. 
The deflection magnetic field of the deflection yoke which deflects the 
electron beam, as shown in FIG. 1, consists of a pin-cushion magnetic 
field 11 formed by a horizontal deflection coil and a barrel magnetic 
field 12 formed by a vertical deflection coil. As shown, the magnetic 
fields respectively applied to the red (R), green (G), and blue (B) 
electron beams emitted from an electron gun (not shown) are all 
nonuniform. Therefore, when the electron beam which receives a deflection 
force, passing through the nonuniform pin-cushion magnetic field 11 and 
the barrel magnetic field 12 lands on a fluorescent film 200 of a panel 
(not shown), the spot of the electron beam is distorted by the Lorentz 
effect and is lengthened in the diagonal direction of the picture at the 
edge of the fluorescent film 200, as shown in FIG. 2. 
To solve this problem, a conventional method distorts the section of the 
electron beam emitted from the electron gun in the reverse direction of 
the nonuniform magnetic direction of the deflection yoke and 
differentiates the length of the focus of the electron beam scanning the 
center of the fluorescent film 200 from the focus of the electron beam 
scanning the edge of the fluorescent film 200. 
This method distorts the cross-section of the electron beam which passes 
through the electronic lens (not shown) located between the electrodes of 
the electron gun in the reverse direction of the distortion by the 
deflection yoke, by making particular electronic lens have focusing and 
the emitting powers which respectively operate in vertical and horizontal 
directions. However, the electronic lens for thus distoring the electron 
beam complicates the manufacture of the electron gun since the the form of 
the passing hole of the electron beam in the electrodes of the electron 
gun must be changed. Therefore, there are limitations in changing the 
cross-section of the electron beam using the difference between the 
focusing power and the emitting power of the electronic lens. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a cathode ray tube 
designed to prevent the distortion of the spot of the electron beam 
scanned at the edge of a fluorescent film, by correcting the distortion of 
the section of the electron beam emitted from an electron gun. 
It is another object of the present invention to provide a cathode ray tube 
designed to improve resolution by preventing the lengthening of shape of 
the section of the electron beam which is lands at the edge of the 
fluorescent film. 
To achieve the objects, there is provided a cathode ray tube comprising an 
electron gun for emitting an electron beam, a deflection yoke which 
deflects the emitted electron beam, and correcting means including 
electromagnets disposed about a separator of the deflection yoke for 
correcting the shape of the cross-section of the emitted electron beam. 
According to another aspect of the present invention, there is provided a 
cathode ray tube comprising an electron gun for emitting an electron beam, 
a cone portion on which is installed a deflection yoke which deflects the 
emitted electron beam, and correcting means including electromagnets 
disposed about the cone portion for correcting the cross-section of the 
emitted electron beam.

DETAILED DESCRIPTION OF THE INVENTION 
An embodiment of a cathode ray tube according to the present invention is 
shown in FIGS. 3A and 3B. 
The cathode ray tube includes of a panel 20 inside which a fluoresent film 
21 is located, a neck portion 31 which is coupled with the panel 20 and 
contains an electron gun 33 and on which is mounted a deflection yoke 34. 
A funnel 30 having a cone portion 32 is also provided. The deflection yoke 
34 has a corrector 50. The corrector 50 is bonded with the deflection yoke 
34 and compensates the cross-section of the electron beam emitted from the 
electron gun 33. The corrector 50 may be fixed to the neck portion 31 of 
the cathode ray tube by bonding or a separate fixing member (not shown). 
A corrector according to the present invention is shown in FIG. 4. 
Referring to the drawing, the corrector includes electromagnets 51, 52, 53 
and 54 respectively installed positioned about the circumference of the 
separator 34a of the deflection yoke. More particularly, the respective 
electromagnets 51, 52, 53 and 54 include iron members 51a, 52a, 53a and 
54a, respectively and a coil 55 continuously wound on the pieces of iron. 
In a preferred embodiment, iron members 51a, 52a, 53a, and 54a are 
positioned about the neck portion at 90.degree., 0.degree., -90.degree., 
and 180.degree., respectively. Also, as shown in FIG. 5, electromagnets 
61, 62, 63 and 64 can include pieces of iron 61a, 62a, 63a and 64a and 
coils 65a, 65b, 65c and 65d independently wound on the respective pieces 
of iron. The electromagnets 51, 52, 53 and 54 of FIG. 4 can be installed 
spaced from each other by a predetermined angle around the circumference 
of the separator 34a, the cone portion 32 of FIG. 3 or the neck portion 31 
of FIG. 3 as necessary. 
The voltage applied to the coil 55 is preferably applied synchronously with 
the deflection signal of the deflection yoke. 
In the operation of the cathode ray tube according to the present 
invention, if the electron beam emitted from the electron gun 33 of FIG. 3 
is deflected by the deflection yoke 34 and is scanning the edge of the 
fluorescent film 200 of FIG. 2, a voltage which is synchronized with the 
deflection signal is applied to the coil 55 (FIG. 4) of the corrector 50 
(FIG. 3). With voltage thus-applied to the coil 55, a magnetic field is 
formed around the respective iron members 51a, 52a, 53a and 54a. The 
cross-section 100 of the electron beam emitted from the electron gun 33 is 
lengthened vertically and horizontally by the effect of the magnetic field 
as shown in FIG. 6, since an outward force is imposed on the electron beam 
at locations corresponding to the position of iron members 51a, 52a, 53a, 
and 54a. Therefore, as shown in FIG. 7, the cross-section of the electron 
beam is not lengthened diagonally by correction of the distortion of the 
cross-section of the electron beam scanning the edge of the fluorescent 
film 200 in the diagonal directions. 
The respective electromagnets 51, 52, 53 and 54 of the corrector 50 can 
independently correct the distortion of the cross-section of the 
electronic beam. 
As described above, the cathode ray tube according to the present invention 
improves the resolution of the picture at the edge of the fluorescent 
film. Also, distortion of the cross-section of the electron beam that 
lands on the fluorescent film, which is due to the nonuniform magnetic 
field and which occurs when the electron beam emitted from the electron 
gun is deflected by the deflection yoke and scans the fluorescent film, is 
prevented, 
The present invention is not restricted to the above embodiment, and it is 
clearly understood that many variations within the scope and spirit of the 
present invention can be made by anyone skilled in the art.