Color cathode ray tube having an improved electron gun

Information

  • Patent Grant
  • 6624562
  • Patent Number
    6,624,562
  • Date Filed
    Thursday, August 8, 2002
    22 years ago
  • Date Issued
    Tuesday, September 23, 2003
    21 years ago
Abstract
Each of an anode and one of the sub-electrodes of a main lens of a shadow mask color cathode ray tube includes a first member having a single opening in their facing ends, and a second member having three beam apertures, wherein(A+566)/106>H−2×Sis satisfied, where A is V1×V2×T, V1 is a vertical diameter of the opening, V2 is a vertical diameter of the center beam aperture, T is a distance between the opening and the second electrode member, H is a horizontal diameter of the opening, S is P×L/Q, where P is a horizontal center-to-center spacing between adjacent phosphor elements, Q is a spacing between the phosphor screen and the shadow mask, and L is a distance between the shadow mask and the opening in the first member.
Description




BACKGROUND OF THE INVENTION




The present invention relates to a color cathode ray tube and particularly to a shadow mask type color cathode ray tube having an improved resolution capability. Color cathode ray tube such as color picture tubes and display tubes have been widely used as receivers of TV broadcasting or monitors in information processing equipment because of their high-resolution capability.




Generally, such color cathode ray tubes comprise a phosphor screen formed on an inner surface of a faceplate of a panel portion of an evacuated envelope, a shadow mask having a multiplicity of electron beam apertures and spaced from the phosphor screen within the panel portion, an electron gun of the in-line type for projecting electron beams toward the phosphor screen and housed in a neck portion of the evacuated envelope, and a deflection yoke mounted around a funnel portion of the evacuated envelope.





FIG. 6

is a schematic cross sectional view for explaining a construction of a shadow mask type color cathode ray tube as an example of a color cathode ray tube to which the present invention is applicable. In

FIG. 6

, reference numeral


20


is a faceplate,


21


is a neck,


22


is a funnel for connecting the faceplate


20


and the neck


21


,


23


is a phosphor screen serving as an image display screen formed on an inner surface of the faceplate


20


,


24


is a shadow mask serving as a color selection electrode,


25


is a mask frame for supporting the shadow mask


24


and for forming a shadow mask assembly,


26


is an inner shield for shielding extraneous ambient magnetic fields,


27


is a suspension spring mechanism for suspending the shadow mask assembly on studs embedded in the inner sidewall of the faceplate


20


,


28


is an electron gun housed in the neck


21


for projecting three electron beams Bs (X2) and Bc,


29


is a deflection device for deflecting the electron beams horizontally and vertically,


30


is a magnetic device for adjusting color purity and centering the electron beams,


31


is a getter,


32


is an internal conductive coating,


33


is an implosion protection band, and


34


are stem pins for supplying voltages on the electron gun


28


.




The evacuated envelope is formed of a faceplate


20


, a neck


21


and a funnel


22


. The magnetic deflection fields generated by the deflection device


29


deflect the three in-line electron beams emitted from the electron gun


28


horizontally and vertically to scan the phosphor screen


23


in two dimensions. The three electron beams Bc, Bs X2 are modulated by the green signal (center beam Bc), the blue signal (side beam Bs) and the blue signal (side beam Bs), respectively, and after being subjected to color selection by beam apertures in the shadow mask


24


disposed immediately in front of the phosphor screen


23


, impinge on respective phosphor elements of red, green and blue colors of the tricolor mosaic phosphor screen


23


to reproduce the intended color image.





FIGS. 7A

to


7


C are illustrations of a construction example of the in-line type electron gun applicable to the color cathode ray tube shown in

FIG. 6

,

FIG. 7A

is a horizontal sectional view thereof, and

FIG. 7B

is a schematic sectional view of the major portion of

FIG. 7A

, taken along the VIIB—VIIB, and

FIG. 7C

is a schematic sectional view of the major portion of

FIG. 7A

, taken along the VIIC—VIIC. In

FIG. 7A

, reference numerals Ia to Ic are cathode structures,


2


is a control grid electrode,


3


is an accelerating electrode,


4


is a focus electrode,


5


is an anode,


6


is a shield cup,


41


is a first focus sub-electrode,


42


is a second focus sub-electrode, and the first and second sub-electrodes


41


,


42


form a focus electrode


4


. Vertical plates


411


are attached to the first focus sub-electrode


41


on the second focus sub-electrode


42


side thereof such that they sandwich each of three electron beams horizontally and they extend toward the second focus sub-electrode


42


, a pair of horizontal plates


421


are attached to the second focus sub-electrode


42


on the first focus sub-electrode


41


side thereof such that they sandwich three electron beams vertically and they extend toward the first focus sub-electrode


41


, and the vertical plates


411


and the horizontal plates


421


form a so-called electrostatic quadrupole lens. The correction plate electrode


422


with a beam aperture for each of the three electron beams is disposed within the second focus sub-electrode


42


and the correction plate electrode


51


with a beam aperture for each of the three electron beams is disposed within the anode


5


.




The vertical plates


411


and the horizontal plates


421


of the electrostatic quadrupole lens, as respectively shown in

FIGS. 7B and 7C

, are such that the vertical plates


411


are comprised of four plates


411




a


,


411




b


,


411




c


and


411




d


arranged in such a manner as to sandwich side beam apertures


41




s


and a center beam aperture


41




c


in the first focus sub-electrode


41


individually and horizontally and the horizontal plates


421


are comprised of a pair of plates


421




a


and


421




b


arranged in such a manner as to sandwich side beam apertures


42




s


and a center beam aperture


42




c


in the second focus sub-electrode


42


in common and vertically.




The cathode structures


1




a


to


1




c


, the control grid electrode


2


and the accelerating electrode


3


form an electron beam generating section. Thermoelectrons emitted from the heated cathode structure


1


are accelerated toward the control grid electrode


2


by an electric potential of the accelerating grid electrode


3


and form three electron beams. The three electron beam pass through the apertures in the control grid electrode


2


, and the apertures in the accelerating electrode


3


, and after having astigmatism corrected by the electrostatic quadrupole lens disposed between the first and second focus sub-electrodes


41


and


42


, and enter the main lens formed between the second focus sub-electrode


42


and the anode


5


. The three electron beams are focused by the main lens, and after being subjected to color selection by the shadow mask, and impinge upon the intended respective phosphor elements of the phosphor screen and produce the bright spots of the intended colors.




The first focus sub-electrode


41


is supplied with a fixed voltage Vf


1


and the second focus sub-electrode


42


is supplied with a dynamic voltage Vf


2


+dVf which is a fixed voltage Vf


2


superposed with a voltage dVf varying in synchronism with deflection angles of the electron beams. The anode


5


is supplied with the highest voltage Eb via the internal conductive coating


32


(see

FIG. 6

) coated on the inner surface of the funnel


22


.




With this construction, the curvature of the image field is corrected by varying the lens strength with the deflection angle of the electron beams and astigmatism is corrected by the electrostatic quadrupole lens such that the focus length of the electron beams and the shape of the beam spots are controlled to provide good focus over the entire phosphor screen.




To obtain a normal round beam spot at the center of the phosphor screen, the horizontal and vertical effective lens diameters are approximately equalized with each other for each of the three electron beams by optimization in terms of the dimensions of the single openings common for the three electron beams in the second focus sub-electrode


42


and the anode


5


for forming the main lens portion, the dimensions of the beam apertures in the correction plate electrodes


422


,


51


disposed within the second focus sub-electrode


42


and the anode


5


, and the axial distances between the correction plate electrodes


422


,


51


and the single openings in the second focus sub-electrode


42


and the anode


5


incorporating the correction plate electrodes


422


,


51


.




With such a lens, the resolution capability of the electron beams scanning the phosphor screen was improved and reproduced the high quality image.




The prior art as described above is disclosed in Japanese Patent Application Laid-open Publication No. Hei 2-189842, for example.




SUMMARY OF THE INVENTION




Focus characteristics of cathode ray tubes are greatly influenced by the width of horizontal scan lines. In the prior art electron guns, the horizontal and vertical effective lens diameters of the main lens are equalized with each other and the problem arises in that the maximum lens diameter of the main lens is limited by the smaller one of the maximum allowable horizontal and vertical lens diameters of the main lens which are limited by the horizontal or vertical dimension of the structure of the electron gun housed in the neck portion of the cathode ray tube.




Generally, the lens dimension is limited more rigidly in the horizontal direction in which the three in-line electron beams are arranged, and the vertical lens dimension is made so smaller as to be equal to the horizontal lens dimensional though the vertical lens dimension can be increased. Therefore the vertical diameter of an electron beam spot on the phosphor screen cannot be decreased compared with its horizontal diameter and this causes a problem in that it is difficult to reduce the width of the horizontal scan lines.




Also there is a problem in that, if eccentricity of the electrodes is caused in the manufacturing process such as the assembling of the electron gun and the electron beams do not pass through the center of the main lens, the vertical diameter of the beam spot at the phosphor screen increases as much due to vertical eccentricity as its horizontal diameter increases due to horizontal eccentricity, although the increase in the vertical diameter of the beam spot due to the vertical eccentricity can be suppressed to a smaller value.




An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a color cathode ray tube capable of a high resolution image display by reducing the vertical diameter of the electron beam spots on the phosphor screen.




To accomplish the above object, in accordance with the present invention, there is provided a color cathode ray tube comprising an evacuated envelope comprising a panel portion, a neck portion and a funnel portion for connecting the panel portion and the neck portion, a three-color phosphor screen formed on an inner surface of the panel portion, a shadow mask having a multiplicity of apertures therein and spaced from the phosphor screen, a three-beam in-line type electron gun housed in the neck portion, the three-beam in-line type electron gun including an electron beam generating section for generating three electron beams and a main lens section for focusing the three electron beams on the three-color phosphor screen, and a deflecting device mounted in a vicinity of a transition region between the funnel portion and the neck portion for scanning the three electron beams on the three-color phosphor screen, wherein the main lens section comprises a focus electrode and an anode facing the focus electrode, the focus electrode being composed of plural focus sub-electrodes, each of the anode and a first one of the focus sub-electrodes facing the anode comprises a first electrode member having a single opening common for the three electron beams in an end thereof facing another of the anode and the first one of the focus sub-electrodes, and a second electrode member set back from the end of the first electrode member for forming three beam apertures for passing the three electron beams, respectively, and a following inequality is satisfied:






(


A+


566)/106


>H−


2


×S,








where A is V


1


×V


2


×T, V


1


is a vertical diameter of the single opening, V


2


is a vertical diameter of a center one of the three beam apertures and T is an axial distance between the single opening and the second electrode member, H is a horizontal diameter of the single opening, and S is P×L/Q, where P is a horizontal center-to-center spacing between adjacent phosphor elements at a center of the three-color phosphor screen, Q is an axial spacing between the three-color phosphor screen and the shadow mask at the center of the three-color phosphor screen, and L is an axial distance between the shadow mask and the single opening in the first electrode member of the first one of the focus sub-electrodes.




In accordance with an embodiment of the present invention, there is provided a color cathode ray tube comprising an evacuated envelope comprising a panel portion, a neck portion and a funnel portion for connecting the panel portion and the neck portion, a three-color phosphor screen formed on an inner surface of the panel portion, a shadow mask having a multiplicity of apertures therein and spaced from the phosphor screen, a three-beam in-line type electron gun housed in the neck portion, the three-beam in-line type electron gun including an electron beam generating section for generating three electron beams arid a main lens Section for focusing the three electron beams on the three-color phosphor screen, and a deflecting device mounted in a vicinity of a transition region between the funnel portion and the neck portion for scanning the three electron beams on the three-color phosphor screen, wherein the main lens section comprises a focus electrode and an anode facing the focus electrode, the focus electrode being composed of plural focus sub-electrodes, each of the anode and a first one of the focus sub-electrodes facing the anode comprises a first electrode member having a single opening common for the three electron beams in an end thereof facing another of the anode and the first one of the focus sub-.electrodes, and a second electrode member set back from the end of the first electrode member for forming three beam apertures for passing the three electron beams, respectively, the focus sub-electrodes include at least one sub-electrode of a first group adapted to be supplied with a first focus voltage and at least one sub-electrode of a second group adapted to be supplied with a second focus voltage, the second focus voltage being a fixed voltage superposed with a dynamic voltage varying with deflection of the three electron beams, an electrostatic quadrupole lens is formed between facing ends of one of the at least one sub-electrode of the first group and one of the at least one sub-electrode of the second group facing the one of the at least one sub-electrode of the first group, and a following inequality is satisfied:








V




1


>


H−


2


×S,








where V


1


is a vertical diameter of the single opening, H is a horizontal diameter of the single opening, and S is P×L/Q, where P is a horizontal center-to-center spacing between adjacent phosphor elements at a center of the three-color phosphor screen, Q is an axial spacing between the three-color phosphor screen and the shadow mask at the center of the three-color phosphor screen, and L is an axial distance between the shadow mask and the single opening in the first electrode member of the first one of the focus sub-electrodes.











BRIEF DESCRIPTION OF THE DRAWINGS




In the accompanying drawings, in which like reference numerals designate similar components throughout the figures, and in which:





FIG. 1

is a horizontal cross sectional view of an electron gun used in a first embodiment of a color cathode ray tube of the present invention;





FIGS. 2A and 2B

are enlarged view of electrodes which can be used as a second focus sub-electrode and an anode in the electron gun of

FIG. 1

,

FIG. 2A

being a front view of the second focus sub-electrode


42


viewed along the line IIA—IIA of

FIG. 1

in the direction of the arrows, and

FIG. 2B

being a cross sectional view of the second focus sub-electrode


42


viewed along the line IIB—IIB of

FIG. 2A

;





FIG. 3

is a schematic horizontal cross sectional view of a color cathode ray tube of the present invention;





FIG. 4

is a horizontal cross sectional view of an electron gun used in a second embodiment of the color cathode ray tube of the present invention;





FIG. 5

is a graph showing the relationship between the product A in the electron guns employed in the color cathode ray tubes of the present invention, where the product A is defined as the product V


1


×V


2


×T and V


1


is a vertical diameter of a single opening common for three electron beams and formed in the focus electrode for forming the main lens, V


2


is a vertical diameter of the center beam aperture in the plate electrode disposed in the focus electrode and T is an axial distance between the single opening and the plate electrode, and a lens diameter D (mm) of a circular lens equivalent having a substantially same amount of aberration as a lens of the present invention;





FIG. 6

is a schematic cross sectional view of a shadow mask type color cathode ray tube as an example of the color cathode ray tube to which the present invention is applicable; and





FIGS. 7A

to


7


C are illustrations of a construction example of the in-line type electron gun applicable to the color cathode ray tube shown in

FIG. 6

,





FIG. 7A

is a horizontal sectional view thereof, and





FIG. 7B

is a schematic sectional view of the major portion of

FIG. 7A

, taken along the VIIB—VIIB, and





FIG. 7C

is a schematic sectional view of the major portion of

FIG. 7A

, taken along the VIIC—VIIC.











DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS




The embodiments of the present invention will be explained in detail hereunder with reference to the accompanying drawings.





FIG. 1

is a horizontal cross sectional view of an electron gun used in an embodiment of a color cathode ray tube of the present invention.

FIGS. 2A and 2B

are enlarged view of electrodes which can be used as a second focus sub-electrode and an anode in the electron gun of

FIG. 1

,

FIG. 2A

being a front view of the second focus sub-electrode


42


viewed along the line IIA—IIA of

FIG. 1

in the direction of the arrows, and

FIG. 2B

being a cross sectional view of the second focus sub-electrode


42


viewed along the line IIB—IIB of FIG.


2


A.




The following explain the case in which the electrodes of

FIGS. 2A and 2B

are used for the second focus sub-electrode


42


. The following explanation applies to the anode


5


as well as to the second sub-electrode


42


, and reference numerals in the parentheses refer to corresponding parts of or associated with the anode


5


.





FIGS. 2A and 2B

define the vertical diameter V


1


(mm) of the single openings


42




a


,


5




a


common for the three electron beams, the vertical diameter V


2


(mm) of the beam apertures


422




c


,


422




s


,


51




c


,


51




s


, in the plate electrodes


422


,


51


disposed within the electrodes


42


,


5


having the single openings


42




a


,


5




a


, and the axial distances T between the plate electrodes


422


,


51


and the single openings


42




a


,


5




a


in the electrodes


42


,


5


incorporating the plate electrodes


422


,


51


.




The effective vertical lens diameter of the main lens is determined by the vertical diameter V


1


(mm) of the single openings


42




a


,


5




a


common for the three electron beams, the vertical diameter V


2


(mm) of the beam apertures


422




c


,


422




s


,


51




c


,


51




s


in the plate electrodes


422


,


51


disposed within the electrodes


42


,


5


having the single openings


42




a


,


5




a


, and the axial distance T (mm) between the plate electrodes


422


,


51


and the single openings


42




a


,


5




a


in the electrodes


42


,


5


incorporating the plate electrodes


422


,


51


. The product A is defined as the product V


1


×V


2


×T.




The amount of penetration of electric fields into the electrode is approximately proportionate to each of V


1


, V


2


and T, and the vertical lens diameter Dv (mm) increases with an increasing amount of the penetration. The lens diameter Dv increases approximately linearly with the product A. The inventors have found the following relationship by analyzing various lens structures.








A=


106


Dv−


566  (1)






In the electron gun of the color cathode ray tube of the present invention, a distance Dh/2 between the center of the path of the undeflected side electron beam and the closest vertical edge of the single opening is the minimum distance between the center of the path of the undeflected side electron beam and the edge of the single opening and is the minimum effective horizontal radius of the main lens.




Generally, in the main lens of the electron gun, the position of the plate electrodes and the shape of the elliptical apertures in the plate electrodes are adjusted to equalize the horizontal and vertical lens radii for the center electron beam with those for the side electron beams. If a difference in the effective main lens diameters between the center electron beam and the side electron beams is present, the difference in the optimum focusing conditions at the phosphor screen is produced between the center and side electron beams, increases the beam spot diameter of one of the center and side electron beams and degrades resolution.




With the structure of the electron gun in the color cathode ray tube of the present invention, the effective horizontal diameters of the main lens are approximately the above-described Dh for both the center and side beams. The horizontal diameter Dh of the main lens is represented by the horizontal diameter H of the single opening and the beam spacing S between the center and side electron beams in the main lens as follows:








Dh=H


−(2


×S


)  (2)






In ordinary shadow mask type color cathode ray tubes, as described subsequently with reference to

FIG. 3

, the beam spacing S between the center and side electron beams in the main lens is represented by the horizontal center-to-center spacing P between adjacent phosphor dots or phosphor lines at the center of the phosphor screen, the axial spacing Q between the inner surface of the panel portion and the shadow mask at the center of the panel portion, and the axial distance L between the shadow mask and the single opening common for three electron beams formed in the focus electrode as follows:








S=P×L/Q








where reference character ML indicates the position of the main lens.




This is because the center and side electron beams are spaced a distance S from each other when they pass through the main lens, pass through the same aperture in the shadow mask and impinge upon the respective phosphor elements of the corresponding colors coated on the inner surface of the panel portion. The above equation is obtained because the triangle FGU is similar to the triangle RTU in FIG.


3


and the relationship of S/P≈L/Q exists.




To accomplish the object of the present invention which is to make the vertical diameter Dv of the main lens larger than its horizontal diameter Dh, it is necessary that the following inequality is satisfied:






Dv>Dh  (3)






The substitution of Dv from the equation (1) and Dh from the equation (2) into the inequality (3) gives the following:






(


A


+566)/106


>H


−(2


×S


)  (4)






The structure of the electron gun designed to satisfy the inequality (4) can reduce the vertical diameter of the beam spot on the phosphor screen and improve the resolution.




Next, the specific embodiments of the present invention will be explained in detail hereunder with reference to the accompanying drawings.





FIG. 1

is a horizontal cross sectional view of an electron gun used in a first embodiment of a color cathode ray tube of the present invention. Reference numeral


1


is a cathode structure,


2


is a control grid electrode,


3


is an accelerating electrode,


4


is a focus electrode,


5


is an anode, and


6


is a shield cup. Reference numeral


41


is a first focus sub-electrode,


42


is a second focus sub-electrode, these two electrodes form a focus electrode. Reference numerals


411


and


421


are plate electrode segments for forming the electrostatic quadrupole lens, and


422


and


51


are plate electrodes having three beam apertures therein disposed in the second focus sub-electrode


42


and the anode


5


, respectively.




Thermoelectrons emitted from the heated cathode structure


1


are accelerated toward the control grid electrode


2


by an electric potential applied to the accelerating electrode


3


and form three electron beams. These three electron beams pass through the respective apertures in the control grid electrode


2


and then through the respective apertures in the accelerating electrode


3


, are slightly focused by a prefocus lens formed between the accelerating electrode


3


and the first focus sub-electrode


41


before they enter the main lens formed between the second focus sub-electrode


42


and the anode


5


, and enter the main lens accelerated by an electric potential of the first focus sub-electrode


41


. Then the electron beams are focused by the main lens onto the phosphor screen to produce beam spots on the screen.




The plate electrodes


422


and


51


, respectively, disposed in the second focus sub-electrode


42


and the anode


5


control the shape and focus of the beam spots on the phosphor screen by adjusting the size and shape of the beam apertures


422




c


,


422




s


,


51




c


,


51




s


in the plate electrodes


422


and


51


, and the amount of the setback of the plate electrodes


422


and


51


from the single opening in the second focus sub-electrode


42


and the anode


5


into the second focus sub-electrode


42


and the anode


5


, respectively, as described later.




The first focus sub-electrode


41


is supplied with a fixed voltage (Vf


1


)


7


and the second focus sub-electrode


42


is supplied with a dynamic voltage (Vf


2


+dVf)


8


varying in synchronism with deflection angles of the electron beams scanning the phosphor screen. Reference character Eb denotes the anode voltage.




With this constitution, the curvature of the image field is corrected by varying the strength of the main lens with the deflection angle of the electron beams and astigmatism is corrected by the electrostatic quadrupole lens formed by the vertical electrode segments


411


and the horizontal electrode segments


421


respectively attached to the first focus sub-electrode


41


and the second focus sub-electrode


42


so that the focus length of the lens and the shape of the beam spot are controlled to produce finely focused beam spots over the entire phosphor screen.





FIGS. 2A and 2B

are enlarged view of electrodes which can be used as a second focus sub-electrode


42


and an anode


5


in the electron gun of FIG.


1


. The following explain the case in which the electrodes of

FIGS. 2A and 2B

are used for the second focus sub-electrode


42


. The following explanation applies to the anode


5


as well as to the second sub-electrode


42


, and reference numerals in the parentheses refer to corresponding parts of or associated with the anode


5


.

FIG. 2A

is a front view of the second focus sub-electrode


42


viewed along the line IIA—IIA of

FIG. 1

in the direction of the arrows.

FIG. 2B

is a cross sectional view of the second focus sub-electrode


42


electrode


42


taken along the line IIB—IIB of FIG.


2


A.




In

FIGS. 2A and 2B

, V


1


and H are respectively vertical and horizontal diameters of a single opening


42




a


common for three electron beams and formed in the second focus sub-electrode


42


for forming the main lens. V


2


is a vertical diameter of the center beam aperture


422




c


in the plate electrode


422


having three beam apertures


422




s


and


422




c


and disposed in the second focus sub-electrode


42


and T is an axial distance between the single opening


42




a


and the plate electrode


422


.




As explained above, the first focus sub-electrode


41


is supplied with a first focus voltage of a fixed value and the second focus sub-electrode


42


is supplied with a second focus voltage which is a fixed voltage superposed with a dynamic voltage varying in synchronism with the deflection angle of the electron beams.




When V


1


is 10 mm, V


2


is 10 mm and T is 5 mm, the product A which is








V




1


×


V




2


×


T


is 10×10×5=500.







FIG. 3

is a schematic horizontal cross sectional view of a color cathode ray tube of the present invention, and reference character ML denotes the position of the main lens. The same reference numerals as utilized in

FIG. 6

designate corresponding portions in FIG.


3


. In

FIG. 3

, suppose the horizontal center-to-center spacing P between adjacent phosphor dots or phosphor lines at the center of the phosphor screen is 0.15 mm, the axial spacing Q between the inner surface (phosphor screen) of the panel portion


20


and the shadow mask


24


at the center of the panel portion is 10.5 mm, and the axial distance L between the shadow mask


24


and the position ML of the main lens is 360 mm. The above-described beam spacing S becomes






0.15×360/10.5=5.14.






In

FIG. 2A

, suppose the horizontal diameter H of the single opening


42




a


formed in the second focus sub-electrode


42


on the anode


5


side thereof for forming the main lens is 19 mm. Substitution of these values into the inequality (4) gives 10.6>8.72.




This indicates the inequality (4) is satisfied and the vertical diameter of the electron beam spot can be reduced on the phosphor screen.




In this embodiment, the electron gun satisfying the inequality (4) includes the electrostatic quadrupole lens the lens strength of which varies with a focus voltage varying with the deflection angle of the electron beams and supplied to the second focus sub-electrode


42


. This construction enables correction for a difference in focusing conditions of the electron beams between the horizontal and vertical directions, and focusing of the electron beams is easily optimized in the horizontal and vertical diameters of the electron beam spots, and the resolution can be effectively improved even though the horizontal and vertical diameters of the main lens differ from each other.




The above explanation is given in connection with the center beam aperture


422




c


in the plate electrode


422


because the center electron beam is usually used to display green signals, green color provides a larger contribution to the brightness of white than red and blue colors for displaying a white scene, and consequently the green electron gun is required to provide a high resolution image. Therefore it is essential for the main lens for the center electron beam to satisfy the inequality (4), and when the high resolution display. By the side electron beams are required, it is preferable for the side beam apertures


422




s


in the plate electrode


422


and the structure associated with it to satisfy the inequality (4).




In the above embodiment, the single opening


42




a


in the second focus sub-electrode


42


, the beam aperture


422




c


in the plate electrode


422


, and the setback distance T in the first focus sub-electrode


42


are identical to the single opening


5




a


, the plate electrode


51


, the beam aperture


51




c


, and the setback distance T in the anode


5


, respectively, but it is not always necessary, it is sufficient that each of the anode electrode geometry and the focus electrode geometry satisfies the inequality (4) independently to provide the advantages in the above embodiment even if they are different in electrode geometry.




Next, a second embodiment of the present invention will be explained.





FIG. 4

is a horizontal cross sectional view of an electron gun used in a second embodiment of the color cathode ray tube of the present invention. The same reference numerals as utilized in

FIG. 1

designate corresponding portions in FIG.


4


. The focus electrode


4


is comprised of first, second, third and fourth sub-electrodes


43


,


44


,


45


,


46


.




The first group of focus sub-electrodes is comprised of the first focus sub-electrode


43


and the third focus sub-electrode


45


both of which are supplied with a first focus voltage Vf


1


,


7


of a fixed value. The second group of focus sub-electrodes is comprised of the second focus sub-electrode


44


and the fourth focus sub-electrode


46


both of which are supplied with a second focus voltage Vf


2


+dVf,


8


which is a fixed voltage Vf


2


superposed with a voltage dVf varying in synchronism with the deflection angle of the electron beams.




The electrostatic quadrupole lens is formed between the second focus sub-electrode


44


and the third focus sub-electrode


45


and functions as in the previous embodiment. The electrostatic quadrupole lens is comprised of horizontal plates


442


and vertical plates


454


attached to the second focus sub-electrode


44


and the third focus sub-electrode


45


, respectively.




In this embodiment, the electrostatic quadrupole lens is formed between the second focus sub-electrode


44


and the third focus sub-electrode


45


, but the present invention is not limited to this arrangement, the electrostatic quadrupole lens can be formed between the first focus sub-electrode


43


and the second focus sub-electrode


44


,




or between the third focus sub-electrode


45


and the fourth focus sub-electrode


46


, for example.




The order of the arrangement of the vertical and horizontal plates of the electrostatic quadrupole lens is not limited to the order shown in

FIG. 4

, the vertical plates can be attached to one on the cathode side of the two opposing electrodes and the horizontal plates can be attached to the other on the phosphor screen side of the two opposing electrodes.




The focus electrode


4


comprised of the first, second, third and fourth focus sub-electrodes


43


,


44


,


45


and


46


is configured such that a curvature of the image field correction lens is formed to vary the lens strength for focusing the three electron beams in both the horizontal and vertical directions with the magnitude of the applied voltage, and the electrostatic quadrupole lens is formed to vary the lens strength for focusing the three electron beams in one of the horizontal and vertical directions and diverging them in the other of the two directions with the magnitude of the applied voltage.




When the fourth focus sub-electrode


46


and the anode


5


for forming the main lens adopt the same dimensions as in the previous embodiment in which the horizontal and vertical diameters of the main lens differ from each other, focusing of the electron beams is easily optimized in the horizontal and vertical diameters of the electron beam spots and the resolution can be effectively improved.




The electron gun of this structure includes, within the focus electrode, the lens for correcting the curvature of the image field which weakens its lens strength with beam deflection angle so as to control its focus length and provides the best focused beam spot shape even at the periphery of the phosphor screen, for the purpose of lowering the dynamic focus voltage by improving the sensitivity of correction of the curvature of the image field compared with the electron gun of the first embodiment shown in

FIG. 1

, as disclosed in Japanese Patent Application Laid-Open Publication No. Hei 4-43532, for example. When the electron gun of this structure is as indicated in

FIG. 4

, the electrode voltages are such that the first focus voltage Vf


1


of a fixed value applied to the first group of focus sub-electrodes is made higher than the second focus voltage Vf


2


of a fixed value applied to the second group of focus sub-electrodes and the dynamic voltage dVf superposed on the fixed voltage Vf


2


increases with the increasing beam deflection angle, and the undeflected electron beams are vertically focused and horizontally diverged by the electrostatic quadrupole lens formed between the opposing portions of the second focus sub-electrode


44


and the third focus sub-electrode


45


and produce horizontally elongated beam spots. Therefore the electron gun of

FIG. 4

requires the main lens portion to exert an astigmatic lens action on the electron beams to produce the vertically elongated cross section of the electron beams. The main lens which satisfies the above requirement of the present invention has a vertical main lens diameter larger than its horizontal main lens diameter and facilitates production of the astigmatic lens action to provide the vertically elongated cross section of the electron beams.





FIG. 5

is a graph showing the relationship between the product A in the electron guns employed in the color cathode ray tubes of the present invention, where the product A is defined as the product V


1


×V


2


×T, V


1


is a vertical diameter of a single opening common for three electron beams and formed in the focus electrode for forming the main lens, V


2


is a vertical diameter of the center beam aperture in the plate electrode disposed in the focus electrode and T is an axial distance between the single opening and the plate electrode, and a lens diameter D (mm) of a circular lens equivalent having a substantially same amount of aberration as a lens of the present invention.





FIG. 5

indicates the effective vertical main lens diameter Dv becomes approximately 10 mm when A=500 as in the first embodiment. The product A is linearly related to the diameter of the main lens limited by the inside diameter of the neck portion of a color cathode ray tube as indicated in FIG.


5


.




By designing the dimensions of the electrodes of the main lens so as to satisfy the above relationship, focusing of the electron beams is easily optimized in the horizontal and vertical diameters of the electron beam spots and the resolution can be effectively improved.




As explained above, by solving the problem in that the maximum lens diameter of the main lens is limited by the smaller one of the maximum allowable horizontal and vertical lens diameters of the main lens which are limited by the horizontal or vertical dimension of the structure of the electron gun housed in the neck portion of the cathode ray tube, and consequently making possible reduction of the vertical diameter of the beam spot and facilitation of the optimization of both horizontal and vertical focusing of the electron beam, the present invention can provide the color cathode ray tube having a high resolution improved more effectively.



Claims
  • 1. A color cathode ray tube comprising:an evacuated envelope comprising a panel portion, a neck portion and a funnel portion for connecting said panel portion and said neck portion; a three-color phosphor screen formed on an inner surface of said panel portion; a shadow mask having a multiplicity of apertures therein and spaced from said phosphor screen; a three-beam in-line type electron gun housed in said neck portion; said three-beam in-line type electron gun including an electron beam generating section for generating three electron beams and a main lens section for focusing said three electron beams on said three-color phosphor screen; and a deflecting device mounted in a vicinity of a transition region between said funnel portion and said neck portion for scanning said three electron beams on said three-color phosphor screen; said main lens section comprising a focus electrode and an anode facing said focus electrode; wherein said main lens section comprises a focus electrode and an anode facing said focus electrode, said focus electrode being composed of plural focus electrodes; each of said anode and a first one of said focus sub-electrodes facing said anode comprises a first electrode member having a single opening common for said three electron beams in an end thereof facing another of said anode and said first one of said focus sub-electrodes, and a second electrode member set back from said end of said first electrode member for forming three beam apertures for passing said three electron beams, respectively; and a following inequality being satisfied: (A+566)/106>H−2×S;  where A is V1×V2×T, V1 is a vertical diameter of said single opening, V2 is a vertical diameter of a center one of said three beam apertures, T is an axial distance between said single opening and said second electrode member, H is a horizontal diameter of said single opening, and S is P×L/Q, where P is a horizontal center-to-center spacing between adjacent phosphor elements at a center of said three-color phosphor screen, Q is an axial spacing between said three-color phosphor screen and said shadow mask at the center of said three-color phosphor screen, and L is an axial distance between said shadow mask and said single opening in said focus electrode member of said first one of said focus sub-electrodes.
  • 2. A color cathode ray tube according to claim 1, wherein said focus sub-electrodes includes a first group of said focus sub-electrodes adapted to be supplied with a first focus voltage and a second group of said focus sub-electrodes adapted to be supplied with a second focus voltage,one of said second group of said focus sub-electrodes faces said anode, said second focus voltage is a fixed voltage superposed with a dynamic voltage varying with deflection of said three electron beams; and at least one electrostatic quadrupole lens is formed between facing ends of one of said first group of said focus sub-electrodes and one of said second group of said focus sub-electrodes facing said one of said first group of said focus sub-electrodes.
  • 3. A color cathode ray tube according to claim 2, wherein at least one electrostatic lens is formed between facing ends of one of said first group of said focus sub-electrodes and one of said second group of said focus sub-electrodes,a focusing strength of said at least one electrostatic lens increasing in horizontal and vertical directions with an increasing difference between said first focus voltage and said second focus voltage for correcting a curvature of an image field.
  • 4. A color cathode ray tube comprising:an evacuated envelope comprising a panel portion, a neck portion and a funnel portion for connecting said panel portion and said neck portion; a three-color phosphor screen formed on an inner surface of said panel portion; a shadow mask having a multiplicity of apertures therein and spaced from said phosphor screen; a three-beam in-line type electron gun housed in said neck portion; said three-beam in-line type electron gun including an electron beam generating section for generating three electron beams and a main lens section for focusing said three electron beams on said three-color phosphor screen; and a deflecting device mounted in a vicinity of a transition region between said funnel portion and said neck portion for scanning said three electron beams on said three-color phosphor screen; wherein said main lens section comprises a focus electrode and an anode facing said focus electrode, said focus electrode being composed of plural focus sub-electrodes each of said anode and a first one of said focus sub-electrodes facing said anode comprises a first electrode member having a single opening common for said three electron beams in an end thereof facing another of said anode and said first one of said focus sub-electrodes, and a second electrode member set back from said end of said first electrode member for forming three beam apertures for passing said three electron beams, respectively; said focus sub-electrodes include at least one sub-electrode of a first group adapted to be supplied with a first focus voltage and at least one sub-electrode of a second group adapted to be supplied with a second focus voltage; said second focus voltage being a fixed voltage superposed with a dynamic voltage varying with deflection of said three electron beams; an electrostatic quadrupole lens is formed between facing ends of one of said at least one sub-electrode of said first group and one of said at least one sub-electrode of said second group facing said one of said at least one sub-electrode of said first group; and a following inequality is satisfied: V1>H−2×S;  where V1 is a vertical diameter of said single opening, H is a horizontal diameter of said single opening, and S is P×L/Q, where P is a horizontal center-to-center spacing between adjacent phosphor elements at a center of said three-color phosphor screen, Q is an axial spacing between said three-color phosphor screen and said shadow mask at the center of said three-color phosphor screen, and L is an axial distance between said shadow mask and said single opening in said first electrode member of said first one of said focus sub-electrodes.
  • 5. A color cathode ray tube according to claim 4, wherein said electrostatic quadrupole lens is configured such that said three electron beams are vertically focused and horizontally diverged when said three electron beams are not deflected.
  • 6. A color cathode ray tube according to claim 4, wherein said at least one sub-electrode of at least one of said first and second groups is plural in number.
  • 7. A color cathode ray tube according to claim 6, wherein an electrostatic lens is formed between facing ends of one of said at least one sub-electrode of said first group and one of said at least one sub-electrode of said second group, and a focusing strength of said electrostatic lens decreases with an increasing deflection angle of said three electron beams for correcting a curvature of an image field.
Priority Claims (1)
Number Date Country Kind
9-241290 Sep 1997 JP
CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 09/645,606, filed Aug. 25, 2000, now U.S. Pat. No. 6,445,116, which is a continuation of U.S. application Ser. No. 09/145,884, filed Sep. 2, 1998, now U.S. Pat. No. 6,111,350, the subject matter of which is incorporated by reference herein.

US Referenced Citations (5)
Number Name Date Kind
5909080 Uchida et al. Jun 1999 A
5942844 Nakamura et al. Aug 1999 A
6031346 Shirai et al. Feb 2000 A
6111350 Uchida et al. Aug 2000 A
6445116 Uchida et al. Sep 2002 B1
Foreign Referenced Citations (14)
Number Date Country
63-86224 Apr 1988 JP
63-12147 May 1988 JP
5-225930 Sep 1993 JP
6-223739 Aug 1994 JP
6-236737 Aug 1994 JP
6-283112 Oct 1994 JP
7-29509 Jan 1995 JP
7-50138 Feb 1995 JP
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Continuations (2)
Number Date Country
Parent 09/645606 Aug 2000 US
Child 10/214368 US
Parent 09/145884 Sep 1998 US
Child 09/645606 US