U.S. patent application number 09/885014 was filed with the patent office on 2002-06-13 for color crt and driving method of the same.
Invention is credited to Bae, Min-Cheol, Kwon, Yong-Geol.
Application Number | 20020070690 09/885014 |
Document ID | / |
Family ID | 19684373 |
Filed Date | 2002-06-13 |
United States Patent
Application |
20020070690 |
Kind Code |
A1 |
Bae, Min-Cheol ; et
al. |
June 13, 2002 |
Color CRT and driving method of the same
Abstract
A color CRT is driven by focusing and accelerating an electron
beam emitted from a cathode by forming a plurality of electron lens
including a quadrupole lens by applying a predetermined voltage to
the cathode of an electron gun installed at a neck portion of a
funnel and each of electrodes, focusing the electron beam on a
fluorescent film by applying a voltage having a horizontal dynamic
waveform having a ratio of slopes of 6.85 or more between a
unilateral area of 90% and a unilateral area of 50% of a raster
area to which a video signal of an image is applied, to at least
one of the electrodes forming the quadrupole lens, synchronized
with a horizontal deflection signal of a deflection yoke installed
at a cone portion of the funnel, in order to deflect an electron
beam emitted from the electron gun and scan the deflected electron
beam onto the fluorescent film of a panel sealed to the funnel, and
forming an image by having the deflected electron beam land on the
fluorescent film to excite fluorescent substance. Thus, resolution
of the overall screen is increased.
Inventors: |
Bae, Min-Cheol; (Suwon-city,
KR) ; Kwon, Yong-Geol; (Suwon-city, KR) |
Correspondence
Address: |
LEYDIG VOIT & MAYER, LTD
700 THIRTEENTH ST. NW
SUITE 300
WASHINGTON
DC
20005-3960
US
|
Family ID: |
19684373 |
Appl. No.: |
09/885014 |
Filed: |
June 21, 2001 |
Current U.S.
Class: |
315/368.28 ;
315/1; 315/366; 348/E3.048 |
Current CPC
Class: |
H04N 3/26 20130101; H01J
31/203 20130101 |
Class at
Publication: |
315/368.28 ;
315/1; 315/366 |
International
Class: |
H01J 029/98 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 22, 2000 |
KR |
2000-48542 |
Claims
What is claimed is:
1. A color CRT comprising: a panel having a screen surface on which
a fluorescent film is formed in a predetermined pattern; a funnel
sealed to the panel; an electron gun installed at a neck portion of
the funnel and having electrodes for forming at least one
quadrupole lens; and a deflection yoke installed throughout the
neck portion and a cone portion of the CRT, and a dynamic voltage
waveform having a ratio of slopes of 6.85 or more between a
unilateral area of 90% and a unilateral area of 50% of a raster
area to which a video signal of an image is applied, is applied to
at least one electrode forming the quadrupole lens.
2. The color CRT as claimed in claim 1, wherein the inclination of
a voltage relatively decreases in a unilateral area of 90% or more
of the raster area to which a video signal of an image is
applied.
3. A driving method of a color CRT comprising the steps of:
focusing and accelerating an electron beam emitted from a cathode
by forming a plurality of electron lens including a quadrupole lens
by applying a predetermined voltage to the cathode of an electron
gun installed at a neck portion of a funnel and each of electrodes;
focusing the electron beam on a fluorescent film by applying a
voltage having a horizontal dynamic waveform having a ratio of
slopes of 6.85 or more between a unilateral area of 90% and a
unilateral area of 50% of a raster area to which a video signal of
an image is applied, to at least one of the electrodes forming the
quadrupole lens, synchronized with a horizontal deflection signal
of a deflection yoke installed at a cone portion of the funnel, in
order to deflect an electron beam emitted from the electron gun and
scan the deflected electron beam onto the fluorescent film of a
panel sealed to the funnel; and forming an image by having the
deflected electron beam land on the fluorescent film to excite
fluorescent substance.
4. The method as claimed in claim 3, wherein a voltage in which the
inclination of a horizontal dynamic waveform relatively decreases
in a unilateral area of 90% or more of the raster area to which a
video signal of an image is applied, is applied.
5. A driving method of a color CRT comprising the steps of:
focusing and accelerating an electron beam emitted from a cathode
by forming a plurality of electron lens including a quadrupole lens
by applying a predetermined voltage to the cathode of an electron
gun installed at a neck portion of a funnel and each of electrodes;
focusing the electron beam on a fluorescent film by applying a
voltage having a horizontal dynamic waveform having a ratio of
voltage amounts of 7.14 or more between a unilateral area of 90%
and a unilateral area of 50% of a raster area to which a video
signal of an image is applied, to at least one of the electrodes
forming the quadrupole lens, synchronized with a horizontal
deflection signal of a deflection yoke installed at a cone portion
of the funnel, in order to deflect an electron beam emitted from
the electron gun and scan the deflected electron beam onto the
fluorescent film of a panel sealed to the funnel; and forming an
image by having the deflected electron beam land on the fluorescent
film to excite fluorescent substance.
6. The method as claimed in claim 5, wherein a voltage in which the
inclination of a horizontal dynamic waveform relatively decreases
in a unilateral area of 90% or more of the raster area to which a
video signal of an image is applied, is applied.
7. A driving method of a color CRT comprising the steps of:
focusing and accelerating an electron beam emitted from a cathode
by forming a plurality of electron lens including a quadrupole lens
by applying a predetermined voltage to the cathode of an electron
gun installed at a neck portion of a funnel and each of electrodes;
focusing the electron beam on a fluorescent film by applying a
voltage having a horizontal dynamic waveform having a ratio of
voltage amounts of 33.4 or more between a unilateral area of 90%
and a unilateral area of 25% of a raster area to which a video
signal of an image is applied, to at least one of the electrodes
forming the quadrupole lens, synchronized with a horizontal
deflection signal of a deflection yoke installed at a cone portion
of the funnel, in order to deflect an electron beam emitted from
the electron gun and scan the deflected electron beam onto the
fluorescent film of a panel sealed to the funnel; and forming an
image by having the deflected electron beam land on the fluorescent
film to excite fluorescent substance.
8. The method as claimed in claim 7, wherein a voltage in which the
inclination of a horizontal dynamic waveform relatively decreases
in a unilateral area of 90% or more of the raster area to which a
video signal of an image is applied, is applied.
9. A driving method of a color CRT comprising the steps of:
focusing and accelerating an electron beam emitted from a cathode
by forming a plurality of electron lens including a quadrupole lens
by applying a predetermined voltage to the cathode of an electron
gun installed at a neck portion of a funnel and each of electrodes;
focusing the electron beam on a fluorescent film by applying a
voltage having a horizontal dynamic waveform having a ratio of
voltage amounts of 4.78 or more between a unilateral area of 50%
and a unilateral area of 25% of a raster area to which a video
signal of an image is applied, to at least one of the electrodes
forming the quadrupole lens, synchronized with a horizontal
deflection signal of a deflection yoke installed at a cone portion
of the funnel, in order to deflect an electron beam emitted from
the electron gun and scan the deflected electron beam onto the
fluorescent film of a panel sealed to the funnel; and forming an
image by having the deflected electron beam land on the fluorescent
film to excite fluorescent substance.
10. The method as claimed in claim 9, wherein a voltage in which
the inclination of a horizontal dynamic waveform relatively
decreases in a unilateral area of 90% or more of the raster area to
which a video signal of an image is applied, is applied.
11. A driving method of a color CRT comprising the steps of:
focusing and accelerating an electron beam emitted from a cathode
by forming a plurality of electron lens including a quadrupole lens
by applying a predetermined voltage to the cathode of an electron
gun installed at a neck portion of a funnel and each of electrodes;
focusing the electron beam on a fluorescent film by applying a
voltage having a horizontal dynamic waveform having a ratio of
slopes of 19.5 or more between a unilateral area of 90% and a
unilateral area of 25% of a raster area to which a video signal of
an image is applied, to at least one of the electrodes forming the
quadrupole lens, synchronized with a horizontal deflection signal
of a deflection yoke installed at a cone portion of the funnel, in
order to deflect an electron beam emitted from the electron gun and
scan the deflected electron beam onto the fluorescent film of a
panel sealed to the funnel; and forming an image by having the
deflected electron beam land on the fluorescent film to excite
fluorescent substance.
12. The method as claimed in claim 11, wherein a voltage in which
the inclination of a horizontal dynamic waveform relatively
decreases in a unilateral area of 90% or more of the raster area to
which a video signal of an image is applied, is applied.
13. A driving method of a color CRT comprising the steps of:
focusing and accelerating an electron beam emitted from a cathode
by forming a plurality of electron lens including a quadrupole lens
by applying a predetermined voltage to the cathode of an electron
gun installed at a neck portion of a funnel and each of electrodes;
focusing the electron beam on a fluorescent film by applying a
voltage having a horizontal dynamic waveform having a ratio of
slopes of 2.87 or more between a unilateral area of 90% and a
unilateral area of 25% of a raster area to which a video signal of
an image is applied, to at least one of the electrodes forming the
quadrupole lens, synchronized with a horizontal deflection signal
of a deflection yoke installed at a cone portion of the funnel, in
order to deflect an electron beam emitted from the electron gun and
scan the deflected electron beam onto the fluorescent film of a
panel sealed to the funnel; and forming an image by having the
deflected electron beam land on the fluorescent film to excite
fluorescent substance.
14. The method as claimed in claim 13, wherein a voltage in which
the inclination of a horizontal dynamic waveform relatively
decreases in a unilateral area of 90% or more of the raster area to
which a video signal of an image is applied, is applied.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a color cathode ray tube
(CRT), and more particularly, to a color CRT for correcting
distortion of a profile of an electron beam according to an
increase of a deflection angle of the electron beam emitted from an
electron gun, and to a driving method of the same.
[0003] 2. Description of the Related Art
[0004] A typical color CRT is shown in FIG. 1. As shown in the
drawing, a color CRT includes a panel 12 having a fluorescent film
11 formed an inner surface thereof, a shadow mask frame assembly 13
installed inside the panel 12 and including a shadow mask 13a
having a color selection function of an electron beam with respect
to fluorescent substances of three colors and a frame 13b
supporting the shadow mask 13a, a funnel 14 sealed to the panel 12,
an electron gun 20 for installed inside a neck portion 14a of the
funnel 14 forming a seal, and a deflection yoke 15 installed at a
cone portion of the funnel 14 for deflecting an electron beam
emitted from the electron gun 20.
[0005] In the color CRT having the above structure, as a
predetermined electric potential is applied to the electron gun 20,
an electron beam emitted from the electron gun 20 is selectively
deflected according to the position of scanning and excites
fluorescent substances so that an image is formed.
[0006] In the above color CRT, an electron beam does not accurately
land on a fluorescent point of a fluorescent film at the peripheral
portion of a screen surface due to lowering of a focus property
caused by making a screen surface flat and a wide deflection angle.
That is, as shown in FIG. 2, when a deflection angle of an electron
beam increases (from 102.degree. to 120.degree.) and a screen has a
predetermined curvature, distortion of a spot S1 of an electron
beam B1 is not severe at the peripheral portion of the screen.
However, in the case of a flat screen, an incident angle of an
electron beam B2 scanned onto the peripheral portion of the screen
decreases so that the electron beam is distorted and a spot S2
increases. Also, when the deflection angle increases as described
above, since densities of a pincushion magnetic field (MP) and a
barrel magnetic field (MB) increase at the peripheral portion of an
area where an irregular magnetic field is formed by a deflection
yoke, as shown FIG. 3, an electron beam is severely distorted. As
shown in FIG. 4, since the overall length of a CRT 10b having a
relatively small deflection angle is shorter than that of a CRT 10a
having a relatively large deflection angle, a difference in length
of focusing at the central portion of a screen and the peripheral
portion thereof increases. The difference in the length of focus
makes the profile of an electron beam landing at the central
portion and peripheral portion of the screen large.
[0007] According to a conventional technology to solve the above
problem, at least one quadrupole lens is adopted in an electron gun
in the CRT and a dynamic focus voltage synchronized with a
deflection signal is applied to one of electrodes forming the
quadrupole lens. Thus, the magnification of the quadrupole lens and
the shape of the profile of an electron beam are changed, and
simultaneously, a difference in voltage between an electrode
forming the quadrupole lens and another electrode forming an
electron lens installed adjacent to the electrode is reduced, so
that the length of focus is changed.
[0008] However, the above methods of correcting the profile of an
electron beam by using the quadrupole lens and adjusting the length
of focus by changing the magnification of the electron lenses are
not able to sufficiently correct distortion due to the distortion
of the profile according to an increase of the deflection angle and
the irregular magnetic field of the deflection yoke.
[0009] In particular, in the case of an electron gun forming at
least one quadrupole lens, the shape of a waveform of a dynamic
voltage fitting into a qudratic equation is substantially not
useful because application of the dynamic voltage applied to the
electrode forming the quadrupole lens of the electron gun in an
area other than a raster area where a video signal of an image is
applied does not affect at all a surface of the image. Thus, since
a dynamic parabola voltage is effective only in the raster area to
which the video signal of an image is applied, the shape of a
dynamic waveform of a screen should be considered by assuming that
the raster area makes 100%.
[0010] When the shape P1 of the dynamic horizontal voltage is
fitting into a quadratic equation in he raster area as shown in
FIG. 5, since a voltage lower than a necessary voltage is applied
at the central portion of a screen, a halo phenomenon that the
profile of an electron beam landing at the central portion of the
screen is vertically crushed is generated. If the voltage is raised
by moving the center of the horizontal voltage waveform upward as
shown in FIG. 13, to remove the halo phenomenon, a parabola voltage
in a horizontal direction which is very higher than a necessary
voltage is applied at the central portion of the screen. Thus, the
profile of the electron beam is vertically elongated as much as the
difference between the necessary voltage and the actually applied
voltage. When the elongated electron beam is deflected by an
irregular magnetic field of the deflection yoke toward the
peripheral portion of the screen, the electron beam receives a
divergent force in a horizontal direction, considerably lowering
resolution of a screen. As shown in FIGS. 5 and 13, a rapid
increase in the applied voltage in the outer area of a screen
results in a rapid increase in the voltage in an area other than
the screen, so that reliability of a high voltage circuit is
lowered.
[0011] When the waveform is formed by a quadratic equation, the
horizontal dynamic parabola voltage has a ratio of 1.8 between a
slope in a unilateral area of 90% of the raster signal and a slope
in a unilateral area of 50% thereof. Thus, since the difference
from a fitting trace of an electron beam having a sharp slope at
the peripheral portion of a screen surface according to an increase
in a deflection angle increases, the electron beam does not
accurately land on a fluorescent point of the fluorescent film.
SUMMARY OF THE INVENTION
[0012] To solve the above problems, it is an object of the present
invention to provide a color CRT which can prevent lowering of a
focusing property of an electron beam due to distortion in the
profile of the electron beam and a change in the length of focus
according to an increase of a deflection angle of the electron beam
by the deflection yoke, and a driving method of the same.
[0013] Accordingly, to achieve the above object, there is provided
a color CRT comprising a panel having a screen surface on which a
fluorescent film is formed in a predetermined pattern, a funnel
sealed to the panel, an electron gun installed at a neck portion of
the funnel and having electrodes for forming at least one
quadrupole lens, and a deflection yoke installed throughout the
neck portion and a cone portion of the CRT, and a dynamic voltage
waveform having a ratio of slopes of 6.85 or more between a
unilateral area of 90% and a unilateral area of 50% of a raster
area to which a video signal of an image is applied, is applied to
at least one electrode forming the quadrupole lens.
[0014] It is preferred in the present invention that the horizontal
dynamic parabola voltage waveform is applied to at least one of
electrodes forming the quadrupole lens of the electron gun.
[0015] It is preferred in the present invention that the
inclination of a voltage relatively decreases in a unilateral area
of 90% or more of the raster area to which a video signal of an
image is applied.
[0016] Alternatively, to achieve the above object, there is
provided a driving method of a color CRT comprising the steps of
focusing and accelerating an electron beam emitted from a cathode
by forming a plurality of electron lens including a quadrupole lens
by applying a predetermined voltage to the cathode of an electron
gun installed at a neck portion of a funnel and each of electrodes,
focusing the electron beam on a fluorescent film by applying a
voltage having a horizontal dynamic waveform having a ratio of
slopes of 6.85 or more between a unilateral area of 90% and a
unilateral area of 50% of a raster area to which a video signal of
an image is applied, to at least one of the electrodes forming the
quadrupole lens, synchronized with a horizontal deflection signal
of a deflection yoke installed at a cone portion of the funnel, in
order to deflect an electron beam emitted from the electron gun and
scan the deflected electron beam onto the fluorescent film of a
panel sealed to the funnel, and forming an image by having the
deflected electron beam land on the fluorescent film to excite
fluorescent substance.
[0017] It is preferred in the present invention that a voltage in
which the inclination of a horizontal dynamic waveform relatively
decreases in a unilateral area of 90% or more of the raster area to
which a video signal of an image is applied, is applied.
[0018] Alternatively, to achieve the above object, there is
provided a driving method of a color CRT comprising the steps of
focusing and accelerating an electron beam emitted from a cathode
by forming a plurality of electron lens including a quadrupole lens
by applying a predetermined voltage to the cathode of an electron
gun installed at a neck portion of a funnel and each of electrodes,
focusing the electron beam on a fluorescent film by applying a
voltage having a horizontal dynamic waveform having a ratio of
voltage amounts of 7.14 or more between a unilateral area of 90%
and a unilateral area of 50% of a raster area to which a video
signal of an image is applied, to at least one of the electrodes
forming the quadrupole lens, synchronized with a horizontal
deflection signal of a deflection yoke installed at a cone portion
of the funnel, in order to deflect an electron beam emitted from
the electron gun and scan the deflected electron beam onto the
fluorescent film of a panel sealed to the funnel, and forming an
image by having the deflected electron beam land on the fluorescent
film to excite fluorescent substance.
[0019] Alternatively, to achieve the above object, there is
provided a driving method of a color CRT comprising the steps of
focusing and accelerating an electron beam emitted from a cathode
by forming a plurality of electron lens including a quadrupole lens
by applying a predetermined voltage to the cathode of an electron
gun installed at a neck portion of a funnel and each of electrodes,
focusing the electron beam on a fluorescent film by applying a
voltage having a horizontal dynamic waveform having a ratio of
voltage amounts of 33.4 or more between a unilateral area of 90%
and a unilateral area of 25% of a raster area to which a video
signal of an image is applied, to at least one of the electrodes
forming the quadrupole lens, synchronized with a horizontal
deflection signal of a deflection yoke installed at a cone portion
of the funnel, in order to deflect an electron beam emitted from
the electron gun and scan the deflected electron beam onto the
fluorescent film of a panel sealed to the funnel, and forming an
image by having the deflected electron beam land on the fluorescent
film to excite fluorescent substance.
[0020] Alternatively, to achieve the above object, there is
provided a driving method of a color CRT comprising the steps of
focusing and accelerating an electron beam emitted from a cathode
by forming a plurality of electron lens including a quadrupole lens
by applying a predetermined voltage to the cathode of an electron
gun installed at a neck portion of a funnel and each of electrodes,
focusing the electron beam on a fluorescent film by applying a
voltage having a horizontal dynamic waveform having a ratio of
voltage amounts of 4.78 or more between a unilateral area of 50%
and a unilateral area of 25% of a raster area to which a video
signal of an image is applied, to at least one of the electrodes
forming the quadrupole lens, synchronized with a horizontal
deflection signal of a deflection yoke installed at a cone portion
of the funnel, in order to deflect an electron beam emitted from
the electron gun and scan the deflected electron beam onto the
fluorescent film of a panel sealed to the funnel, and forming an
image by having the deflected electron beam land on the fluorescent
film to excite fluorescent substance.
[0021] Alternatively, to achieve the above object, there is
provided a driving method of a color CRT comprising the steps of
focusing and accelerating an electron beam emitted from a cathode
by forming a plurality of electron lens including a quadrupole lens
by applying a predetermined voltage to the cathode of an electron
gun installed at a neck portion of a funnel and each of electrodes,
focusing the electron beam on a fluorescent film by applying a
voltage having a horizontal dynamic waveform having a ratio of
slopes of 19.5 or more between a unilateral area of 90% and a
unilateral area of 25% of a raster area to which a video signal of
an image is applied, to at least one of the electrodes forming the
quadrupole lens, synchronized with a horizontal deflection signal
of a deflection yoke installed at a cone portion of the funnel, in
order to deflect an electron beam emitted from the electron gun and
scan the deflected electron beam onto the fluorescent film of a
panel sealed to the funnel, and forming an image by having the
deflected electron beam land on the fluorescent film to excite
fluorescent substance.
[0022] Alternatively, to achieve the above object, there is
provided a driving method of a color CRT comprising the steps of
focusing and accelerating an electron beam emitted from a cathode
by forming a plurality of electron lens including a quadrupole lens
by applying a predetermined voltage to the cathode of an electron
gun installed at a neck portion of a funnel and each of electrodes,
focusing the electron beam on a fluorescent film by applying a
voltage having a horizontal dynamic waveform having a ratio of
slopes of 2.87 or more between a unilateral area of 90% and a
unilateral area of 25% of a raster area to which a video signal of
an image is applied, to at least one of the electrodes forming the
quadrupole lens, synchronized with a horizontal deflection signal
of a deflection yoke installed at a cone portion of the funnel, in
order to deflect an electron beam emitted from the electron gun and
scan the deflected electron beam onto the fluorescent film of a
panel sealed to the funnel, and forming an image by having the
deflected electron beam land on the fluorescent film to excite
fluorescent substance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The above object and advantages of the present invention
will become more apparent by describing in detail preferred
embodiments thereof with reference to the attached drawings in
which:
[0024] FIG. 1 is a sectional view of a conventional color CRT;
[0025] FIG. 2 is a view showing the state in which electron beams
having different defection angles land on a screen having a
curvature and a flat screen;
[0026] FIG. 3 is a view showing the state of distortion of an
electron beam due to an irregular magnetic field of the deflection
yoke;
[0027] FIG. 4 is a view showing the relationship between the
deflection angle of the deflection yoke and the overall length of
the CRT;
[0028] FIG. 5 is a graph showing a waveform of a horizontal dynamic
parabola voltage applied to a quadrupole lens of the electron beam
and a video signal;
[0029] FIG. 6 is a perspective view of a color CRT according to the
present invention;
[0030] FIG. 7 is a graph showing the horizontal dynamic parabola
voltage synchronized with a horizontal defection signal is fitted
into various polynomials;
[0031] FIG. 8 is a graph showing the shape of a conventional
dynamic parabola voltage;
[0032] FIGS. 9 and 10 are views showing the horizontal dynamic
parabola voltage of the present invention which is synchronized
with the horizontal deflection signal;
[0033] FIGS. 11A through 1D and 12A through 12D are photographs
showing the state in which an electron beam lands on a fluorescent
film according to the waveform of the deflection signal;
[0034] FIG. 13 is a graph showing the relationship of the dynamic
focus voltage and the position of the electron beam landing on a
screen;
[0035] FIG. 14 is a graph showing the relationship of the diameter
of an electron beam and the position of the electron beam landing
on the screen surface;
[0036] FIGS. 15A through 15C are photographs and a view showing an
electron beam shown in a screen when the conventional dynamic
parabola voltage is applied;
[0037] FIGS. 16A and 16B are photographs showing the electron beam
focused on the screen according to the present invention; and
[0038] FIG. 17 is a graph showing another relationship between the
position of a horizontal screen and a dynamic voltage.
DETAILED DESCRIPTION OF THE INVENTION
[0039] FIG. 6 shows a color CRT according to a preferred embodiment
of the present invention. As shown in the drawing, a color CRT 30
according to a preferred embodiment of the present invention
includes a panel 32 where red, green and blue fluorescent
substances 31 are formed on an inner surface of the panel 32 in a
predetermined pattern, that is, a stripe or dot type patten, a
shadow mask frame assembly 33 formed of a shadow mask 33a installed
in the panel 32 and having a color selection function and a frame
33b supporting the shadow mask 33a, and a funnel 34 sealed to the
panel 32 and having a neck portion 34a. An electron gun 35 for
emitting an electron beam is installed in the neck portion 34 of
the funnel 34. The electron gun 35 includes a plurality of
electrodes for forming a cathode, focusing lenses, and a quadrupole
lens. A deflection yoke 36 for deflecting an electron beam emitted
from the electron gun 35 and having a deflection angle of the
electron beam of 110.degree. or more, is installed throughout the
neck portion 34a and a cone portion of the funnel 34.
[0040] In the color CRT 30 having the above structure, the electron
beam emitted from the cathode is focused and accelerated by the
focusing lenses and the quadrupole lens and deflected by the
deflection yoke 36 and land on a fluorescent film.
[0041] In the above process, since the deflection angle of the
deflection yoke 36 in the color CRT is 110.degree. or more, the
deflection angle increases rapidly after passing a unilateral area
of 50% of a raster area of a screen to which a video signal is
applied. In particular, when a screen has a 16:9 size, such a
phenomenon is severe. In this case, although the profile of the
electron beam distorted by a deflection magnetic field is corrected
while it passes through the quadrupole lens formed by the
electrodes, distortion is generated to an electron beam landing on
the peripheral portion of a screen by the shape of the waveform of
the voltage so that a sufficient resolution cannot be obtained on
the overall screen.
[0042] To correct the distortion of the electron beam, as shown in
FIG. 7, in the state in which the period of a waveform of a
horizontal deflection voltage in a raster area applied to a video
signal of an image, a horizontal dynamic voltage waveform P2 having
a ratio of 6.85 or more between slopes in a unilateral area of 90%
and a unilateral area of 50% is applied to at least one of the
electrodes forming the quadrupole lens of the electron gun 35 by
synchronizing a deflection signal and a horizontal deflection
voltage and the vertical deflection voltage with the deflection
yoke 36. As shown in FIG. 17, to prevent an increase in the voltage
at the outer portion of the raster area of the CRT, it is preferred
to apply a voltage having a waveform (C in FIG. 17) in which the
inclination of the applied voltage in an area over the unilateral
area of 90% of the waveform period decreases or a waveform (D in
FIG. 17) in which the peak point portion is truncated at the end of
the screen in which the voltage is the highest.
[0043] In the above CRT having a wide deflection angle, the density
of a pincushion magnetic field increases rapidly when an electron
beam is deflected in a horizontal direction. Thus, when the
electron beam is deflected toward the peripheral portion of the
screen surface, the electron beam received a sharp deflection
distortion. As a result, when the electron beam is deflected toward
the peripheral portion of a fluorescent film, the profile of the
electron beam is vertically elongated. Since the waveform of the
dynamic voltage applied to the quadrupole lens and a main lens to
increase the length of focusing can make the deflection distortion
of the profile of an electron beam at the peripheral portion of a
screen due to the wide deflection angle corrected by a rapid
increase of the dynamic voltage at the peripheral portion.
[0044] In detail, since a dynamic focus voltage synchronized with a
deflection signal is applied to at least one electrode forming the
quadrupole lens in the electron gun 35, the dynamic focus voltage
applied is high as the electron beam goes toward the peripheral
portion of the screen. When the electron beam is deflected toward
the peripheral portion, deflection astigmatism by the deflection
yoke for focusing the electron beam in a vertical direction and
diverging the same in a horizontal direction by an effect by the
pincushion magnetic field by the deflection yoke, is generated to
the electron beam. As the wide deflection angle of a CRT increases
and the CRT is made to have a flatter surface, the amount of the
deflection astigmatism sharply increases so that the electron beam
is severely distorted. A focus deterioration phenomenon is
generated to the electron beam defected by the deflection yoke. A
dynamic electron gun is used to compensate for the deterioration
phenomenon in the electron gun. An improved design of the
quadrupole lens is needed to prevent an excess increase of a
voltage. The lens for horizontal focusing and vertical divergence
of the quadrupole lens is intensified to vertically elongate the
electron beam and lengthen the length of focus. Thus, an optimal
focusing is made at the peripheral portion of a screen with respect
to a change of a lower voltage.
[0045] However, although at a low voltage, a distortion phenomenon
of an electron beam generated as the electron beam is deflected by
the deflection yoke causes a rapid distortion of the beam. Thus, by
applying an appropriate dynamic parabola voltage to the electrode
forming the quadrupole lens of an electron gun, a uniform
resolution can be obtained over the entire screen.
[0046] In a CRT having a wide deflection angle of 110.degree. or
more, since the deflection angle is not relatively great in a
screen area between a point 0% of the raster pattern (the central
portion of the screen) and a unilateral area of 50%, a rate of
increase of a vertical deflection dynamic voltage makes a smooth
voltage waveform (please refer to P2 of FIG. 7). In the case of
being out of the unilateral area of 50% at the peripheral portion
of a screen, deformation of the profile of the electron beam is
generated by the deflection magnetic field to make the ratio
between slopes in the unilateral area of 90% and the unilateral
area of 50% to be 6.85. Thus, by applying a dynamic parabola
voltage waveform corresponding to the above deformation to the
quadrupole lens of the electron gun, a high resolution can be
obtained over the entire screen. Also, like a waveform C of FIG.
17, application of a voltage waveform in which the inclination of a
voltage decreases over 90% of the screen may prevent deterioration
of reliability in the high pressure circuit due to a rapid increase
of voltage in an area other then the screen.
[0047] The above-described function and effect will be clarified by
the following experiments performed by the present inventor.
EXPERIMENT EXAMPLE 1
[0048] In this experiment, the waveform shape of a horizontal
deflection voltage of each of color CRTs having deflection angles
of 102.degree., 110.degree. and 116.degree. is obtained through
simulation (waveform of a voltage obtained by fitting in a quartic
equation and a sextic equation), the results of which are shown in
graphs of FIGS. 8 through 10 and the following Table 1.
1TABLE 1 Voltage value (V) Slope Screen Screen (%) 116.degree.
110.degree. 102.degree. (%) 116.degree. 110.degree. 102.degree. 0 0
0 0 0 0.0 0.0 0.0 25 42.4 27 26 25 3.3 2.3 2.1 50 180.9 129 113 50
9.2 6.6 5.0 90 1711 919 455 90 98.7 44.3 13.0 100 3011 1480 600 100
166.2 69.6 16.0 90/50 9.46 7.14 4.05 1.80 10.68 6.73 2.61 90/50
40.3 33.4 17.7 3.6 30.0 19.5 6.1
[0049] in Table 1,116.degree., 110.degree.and 102.degree. denote
deflection angles and the percentage (%) of a screen is determined
by setting the period of a horizontal dynamic parabola waveform in
a raster area to which a video signal of an image is applied as
100% with respect to the center of the screen.
[0050] As can be seen from the above table and graphs, a difference
is not much in a dynamic parabola voltage applied to the electrode
forming a quadrupole lens of an electron gun because a difference
in slope applied to the central portion and the peripheral portion
of a visual screen is not much in the case of a deflection angle of
102.degree. having a ratio of slopes of 2.61 in the unilateral area
of 90% of the raster signal and a unilateral area of 50% of the
screen.
[0051] However, when the deflection angle is over 110.degree., the
value of the slope increases gradually until the unilateral area of
50% from the central portion of the screen and steeply after the
unilateral area of 50%. Thus, the voltage waveform has a horizontal
dynamic waveform having a gradual slope as shown in FIG. 8, the
state of distortion of an electron beam at the corner portions of a
raster pattern, that is, at corner portions and both lateral sides
of a screen, is severe as shown in FIGS. 11A through 11D so that
focusing of the electron beam is not performed accurately.
[0052] When the horizontal defection voltage waveform has a slope
of at least 6.73 or more and the deflection angle of the electron
beam is made great as shown in FIGS. 8 and 9, it can be seen that
the distortion of the electron beam at the central portion and the
peripheral portion of the electron beam is corrected and a focusing
property is improved as shown in FIG. 12A through 12D.
[0053] As shown in FIGS. 13 through 14, by making the dynamic
parabola voltage applied to the electrode forming the quadrupole
lens of the electron gun increase steeply in an unilateral area
between 50% through 90% of the raster signal area, compared to the
conventional dynamic focus voltage (please refer to a curve A of
FIG. 13), the amount of the electron beam at each of positions
between the central portion and the peripheral portion on a screen
according to the present invention (please refer to a curve D of
FIG. 14, FIG. 16A and FIG. 16B) is drastically reduces compared to
the amount of the electron beam at each position when the
conventional dynamic focus voltage is applied (please refer to a
curve D of FIG. 14, FIG. 15A, FIG. 15B, and FIG. 15C). As a result,
it can be seen that resolution of the overall screen can be
increased.
[0054] As described above, according to the color CRT and the
driving method of the same according to the present invention, the
distortion of an electron beam due to the deflection magnetic field
and the overall length of the CRT which becomes severe as the
deflection angle of the electron beam increases can be basically
prevented. Further, resolution of a screen can be improved.
[0055] It is noted that the present invention is not limited to the
preferred embodiment described above, and it is apparent that
variations and modifications by those skilled in the art can be
effected within the spirit and scope of the present invention
defined in the appended claims.
* * * * *