Cathode ray tube with efficiently driven electron gun

Details Cathode ray tube with efficiently driven electron gun Cathode ray tube with efficiently driven electron gun

2002-09-25

2004-07-27

Vo, Tuyet T. (Department: 2821)

Electric lamp and discharge devices: systems

Cathode ray tube circuits

Combined cathode ray tube and circuit element structure

C315S500000, C315S382000, C313S414000

Reexamination Certificate

active

06768267

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cathode ray tube (CRT), and, more particularly, to a CRT having an electron gun in which a cathode for emitting electron beams, a control electrode for controlling emission of the electron beams from the cathode, and a screen electrode for accelerating the flow of the electron beams passing the control electrode are arranged in series.
2. Description of the Related Art
Referring to
FIG. 1
, a conventional CRT includes a panel
12
, a funnel
13
, an electron gun
11
, and a deflection yoke
15
. A fluorescent film
14
in which fluorescent substances for producing red (R), green (G), and blue (B) light are aligned in a dot or strip pattern is installed on the inner surface of the panel
12
. The funnel
13
having a neck portion
13
a
and a cone portion
13
b
is sealed to the panel
12
. The electron gun
11
is installed in the neck portion
13
a
of the funnel
13
. The deflection yoke
15
is installed on and surrounding the cone portion
13
b
of the funnel
13
for deflecting the electron beams emitted from the electron gun
11
.
The performance of the CRT
1
is determined according to a state of the electron beams emitted from the electron gun
11
and landing on the fluorescent film
14
. To make the electron beams emitted from the electron gun
11
accurately land on the fluorescent film
14
, a number of technologies improving focus characteristics and reducing aberration of electron lenses have been developed.
In particular, the shapes of the electron beams landing on the fluorescent film
14
are horizontally elongated when the electron beams emitted from the electron gun
11
are deflected by the deflection yoke
15
, due to a difference between barrel and pincushion magnetic fields. To prevent the elongation, a dynamic focus electron gun is used. The dynamic focus electron gun synchronizes the electron beams emitted from the electron gun
11
with horizontal and vertical deflection periods so that the shapes of the electron beams are vertically elongated.
However, in the dynamic focus electron gun, as the size of the screen of the CRT increases, horizontal line deformation at the peripheral portion of the screen becomes severe. To solve that problem, a double focus CRT is used.
FIG. 2
shows a conventional double dynamic focus CRT. Referring to the drawing, a video signal processing portion
21
processes a composite video signal Sc and outputs a horizontal synchronizing signal, a vertical synchronizing signal, a data signal, and a horizontal/vertical blanking signal. The data signal including red (R), green (G), and blue (B) brightness signals, is amplified by a data signal amplifier
27
. The amplified data signal Sd is biased by a voltage supplied by a first bias supplier
31
and applied to a cathode K of the electron gun
11
.
A vertical deflecting signal generator
22
generates a vertical deflecting signal corresponding to the vertical synchronizing signal output from the video signal processor
21
and supplies the vertical deflecting signal to a vertical deflecting signal amplifier
24
. A horizontal deflecting signal generator
23
generates a horizontal deflecting signal corresponding to the horizontal synchronizing signal output from the video signal processor
21
and supplies the generated horizontal deflecting signal to a horizontal deflecting signal amplifier
25
. The vertical and horizontal deflecting signals amplified by the vertical and horizontal deflecting signal amplifiers
24
and
25
are respectively applied to vertical and horizontal deflecting yokes
15
on the CRT
1
.
The horizontal/vertical blanking signal output from the video signal processor
21
is amplified by a blanking signal amplifier
26
. A horizontal/vertical blanking signal Sb output from the blanking signal amplifier
26
is applied to the cathode K of the electron gun
11
. A control signal Vc from a fifth bias supplier
37
is supplied to a control electrode C of the electron gun
11
. A heater power supplier
36
supplies electric power to a heater (not shown) of the cathode K of the electron gun
11
. A second bias supplier
32
applies a screen voltage Vec to a screen electrode S and a second focus electrode F
2
of the electron gun
11
. A third bias supplier
33
applies a static focus voltage Vfs having a positive polarity to first, third, and fifth focus electrodes F
1
, F
3
, and F
5
of the electron gun
11
. The static focus voltage Vfs has a positive polarity and a magnitude higher than the screen voltage Vec, which also has a positive polarity, to enhance acceleration and focus of the electron beams. A dynamic focus driver
35
applies a dynamic focus voltage Vfd, which changes periodically within a range above and below the static focus voltage Vfs, to fourth and sixth focus electrodes F
4
and F
6
so that the electron beams emitted from the electron gun
11
are made relatively oval. A fourth bias driver
34
applies an anode voltage Veb having the highest positive polarity to a final acceleration electrode A of the electron gun
11
.
FIG. 3
shows the structure of the electron gun in the CRT of FIG.
2
. In
FIG. 3
, the same reference numerals denote the same elements shown FIG.
2
. In
FIG. 3
, reference characters K
R
, K
G
, and K
B
denote respective cathodes for producing electron beams that generate red, green, and blue light when the electron beams land on the fluorescent screen. Reference character Sd
R
/Sb
R
denotes data and blanking signals for red light, reference character Sd
G
/Sb
G
denotes data and blanking signals for green light, and reference character Sd
B
/Sb
B
denotes data and blanking signals for blue light respectively applied to cathodes K
R
, K
G
, and K
B
.
FIG. 4
shows the relationship between driving voltages in a conventional double dynamic focus method. In
FIG. 4
, reference character T
HS
denotes horizontal scanning period, reference character V
pl
denotes the minimum voltage of the dynamic focus voltage Vfd, and reference character V
ph
denotes the maximum voltage of the dynamic focus voltage Vfd.
FIG. 5A
shows electron lenses formed in the electron gun of
FIG. 3
during the period t
1
-t
3
, when the static focus voltage Vfs is higher than the dynamic focus voltage Vfd.
FIG. 5B
shows electron lenses formed in the electron gun of
FIG. 3
during the periods
0
-t
1
and t
3
-t
4
, when the static focus voltage Vfs is lower than the dynamic focus voltage Vfd. In
FIGS. 5A and 5B
, reference character A
V
denotes the vertical direction in the electron gun, reference character A
H
denotes the horizontal direction in the electron gun, reference character P
B
denotes direction of movement of the electron beams, reference character F
V
denotes the vector force in the vertical direction A
V
applied to the electron beams, and F
H
denotes the vector force in the horizontal direction A
H
applied to the electron beams.
Referring to
FIGS. 3
,
4
,
5
A, and
5
B, electron beams are generated according to the data signals S
dR
, S
dG
, and S
dB
corresponding to the respective cathodes K
R
, K
G
, and K
B
. The electron beams are emitted in response to the control voltage Vc applied to the control electrode C. The electron beams emitted through openings of the control electrode C are accelerated by the screen voltage Vec applied to the screen electrode S.
The static focus voltage Vfs applied to the first focus electrode F
1
is higher than the screen voltage Vec applied to the screen electrode S. The shapes of an outlet of the screen electrode S and an inlet of the first focus F
1
are circular, but the outlet of the screen electrode S is smaller than the inlet of the first focus F
1
. Thus, a focus lens is formed between the screen electrode S and the first focus electrode F
1
. The shapes of the inlets of the first focus electrode F
1
to which the static focus voltage Vfs is applied, the inlets and outlets of the second focus electrode F
2
to which the screen voltage Vec is applied, and the inlets of the third focus e

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