Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Reexamination Certificate
2000-09-15
2002-05-28
Hannaher, Constantine (Department: 2878)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
C313S382000, C313S414000, C313S449000
Reexamination Certificate
active
06396221
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a color cathode-ray tube and, more particularly, to a color cathode-ray tube including an electron gun which, in operation, emits three electron beams in line in a horizontal direction toward a fluorescent screen.
Owing to their fine picture-reproducing property, color cathode-ray tubes, such as color picture tubes or display tubes, have been extensively used for receiving TV broadcast programs and as monitors for data processing equipment.
The color cathode-ray tube of this type includes a panel portion having a face plate forming a fluorescent screen on the inner surface thereof, a neck portion containing an electron gun structure for emitting electron beams onto the fluorescent screen, and an evacuated envelope having at least a funnel portion for connecting said panel portion to said neck portion.
FIG. 39
is a diagram schematically illustrating, in cross section, the constitution of a shadow mask-type color cathode-ray tube to which the present invention is adapted, and wherein reference numeral
20
denotes a face plate portion,
21
denotes a neck portion,
22
denotes a funnel portion for connecting the panel portion to the neck portion,
23
denotes a fluorescent screen which constitutes an image display screen on the inner surface of the face plate,
24
denotes a shadow mask which operates as a color-selection electrode,
25
denotes a mask frame which constitutes a shadow mask structure to hold the shadow mask,
26
denotes an inner shield for shielding external magnetism,
27
denotes a suspension spring mechanism by which the shadow mask structure is suspended by studs that are located on the inner wall of the face plate,
28
denotes an electron gun accommodated in the neck portion for emitting three electron beams Bs (×2) and Bc in line,
29
denotes a deflection device for deflecting the electron beams in the horizontal and vertical directions, and reference numeral
30
denotes a magnetic device for correcting color purity or centering.
In the diagramed constitution, an evacuated envelope is constituted by the face plate
20
, neck portion
21
and funnel portion
22
. Three electron beams Bc and Bs (×2) emitted in line from the electron gun
28
are deflected in the horizontal and vertical directions by a deflecting magnetic field formed by the deflecting device
29
so as to two-dimensionally scan the fluorescent screen
23
. Here, symbol Bc denotes a center beam, and Bs denotes a side beam.
The three electron beams Bc and Bs (×2) are each modulated by color signals of red (side beam Bs), green (center beam Bc) and blue (side beam Bs), subjected to the color selection through beam passage holes of the shadow mask
24
arranged in front of the fluorescent screen
23
, and impinge upon fluorescent mosaics of red, green and blue colors that constitute the fluorescent screen
23
to reproduce a desired color image.
FIG. 40
is a horizontal sectional view of an in-line electron gun mounted in a conventional color cathode-ray tube, wherein reference numeral
1
denotes cathodes,
2
denotes a control electrode,
3
denotes an accelerating electrode,
4
denotes a focus electrode assembly,
5
denotes an anode, and reference numeral
6
denotes a shield cup. Reference numeral
41
denotes a first focus electrode,
42
denotes a second focus electrode, and the focus electrode assembly
4
is constituted by these focus electrodes. Reference numerals
411
and
421
denote plate electrodes constituting an electrostatic quadrupole lens.
Thermoelectrons emitted from the heated cathodes
1
are accelerated toward the control electrode
2
due to a potential applied to the accelerating electrode
3
, whereby three electron beams are formed. The three electron beams pass through apertures in the control electrode
2
and pass through apertures in the accelerating electrode
3
. Then, the three electron beams are focused to some extent by a prefocus lens formed between the accelerating electrode
3
and the first focus electrode
41
prior to entering into the main lens formed between the second focus electrode
42
and the anode
5
, the beams being fed to the main lens while being accelerated by the potential of the focus electrode
4
. The three electron beams are focused by the main lens formed between the second focus electrode
42
and the anode
5
on the fluorescent screen to form a projection spot.
The first focus electrode
41
is supplied with a predetermined voltage (Vf
1
)
7
, and the second focus electrode
42
is supplied with a dynamic voltage (Vf
2
+dVf)
8
that changes in synchronism with a change in the deflection angle for scanning the electron beams on the screen. Symbol Eb denotes an anode voltage.
The intensity of the main lens is changed depending upon the deflection angle of the electron beam, thereby to correct the curvature of the image field. Any astigmatism is corrected by the electrostatic quadrupole lens constituted by the vertical plate electrode
411
and the horizontal plate electrode
421
mounted on the first focus electrode
41
and on the second focus electrode
42
, in order to control the focusing distance of the electron beam and the shape of the beam spot, thereby obtaining a good focus on the screen at all times.
In the practical cathode-ray tube, however, a desired voltage is not obtained at the periphery of the screen due to a limitation on the drive circuit of the dynamic voltage
8
, and a favorable beam spot is not obtained.
Japanese Patent Laid-Open No. 43532/1992 (U.S. Pat. No. 5,212,423) discloses a method which suppresses the amount of change in the dynamic voltage that varies in synchronism with the deflection angle, in order not to increase the diameter of the electron beams.
FIG. 41
is a horizontal sectional view illustrating the constitution of a conventional in-line type electron gun disclosed in the above-mentioned publication, wherein a focus electrode assembly
4
is constituted by a first focus electrode
43
, a second focus electrode
44
, a third focus electrode
45
and a fourth focus electrode
46
. Reference numeral
442
denotes horizontal correction plate electrodes constituting the electrostatic quadrupole lens, and
454
denotes vertical correction plate electrodes for constituting an electrostatic quadrupole electrode. The same reference numerals as those of
FIG. 40
denote portions having the same functions.
As shown, the focus electrode assembly
4
is divided into a plurality of electrode groups
43
,
44
,
45
and
46
, and the electrostatic quadrupole lens is constituted by the horizontal plate electrodes
442
and vertical plate electrodes
454
among these focus electrode groups. Among these focus electrode groups there is further formed at least an electron lens which exhibits a strong focusing force in both the horizontal direction and the vertical direction. This electron lens (hereinafter referred to as a lens for correcting the field curvature) has a function for correcting the curvature of the image field, which corresponds to the inner surface of the panel.
Furthermore, a main lens formed between the opposing surfaces of the fourth focus electrode
46
and the anode
5
produces a strong astigmatism for vertically deforming the sectional shape of the electron beams. Here, in the conventional electron gun described above, a method of applying DC components (Vf
1
, Vf
2
) of two focus voltages must be changed in order to impart the action of the lens for correcting the field curvature to the electron lens that exhibits a strong focusing force in both the horizontal direction and the vertical direction. However, the method of applying a dynamic voltage is the same.
That is, so far, the two DC focus voltages have nearly equal values, and the dynamic voltage increases accompanying an increase in the amount of deflection of the electron beams. In the electron gun shown in
FIG. 41
, on the other hand, the one DC focus voltage (Vf
1
) is considerably greater than the other DC focus voltage (Vf
2
), and a dif
Kato Shin-ichi
Nagaoka Masafumi
Shirai Syoji
Uchida Go
Antonelli Terry Stout & Kraus LLP
Hannaher Constantine
Hitachi , Ltd.
Lee Shun
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