Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Reexamination Certificate
2001-07-23
2002-12-17
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
C315S388000, C315S030000, C348S712000, C348S806000
Reexamination Certificate
active
06495978
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to CRT display devices and, more particularly, to a CRT display device having a Hi-Gm tube which is capable of obtaining an ordinary intensity of current under a low drive voltage.
2. Description of the Background Art
FIG. 6
is a block diagram showing a constitution of a conventional CRT display device. In
FIG. 6
, reference characters
17
,
2
,
3
,
4
,
6
,
7
,
9
,
10
,
11
,
13
,
18
and
19
denote a CRT, a cathode, a G
1
electrode, a G
2
electrode, a G
3
electrode, an anode, a video cathode amplifier, a cathode bias voltage source, a video input, an adjustment input, a flyback transformer and a resistor, respectively. An electron gun which irradiates an electron beam on a phosphor screen comprises the cathode
2
, the G
1
electrode
3
, the G
2
electrode
4
and the G
3
electrode
6
. The cathode
2
is provided with cathodes for red, green and blue each of which emits the beam for hitting the phosphor screen of red, green and blue.
Next,
FIG. 6
is explained below. The video signal input
11
is inversely amplified by a video cathode amplifier
9
and then capacitor-coupled. The thus capacitor-coupled input is applied with the cathode bias voltage in accordance with the adjustment input
13
by the cathode bias voltage source
10
and then inputted to the cathode
2
. On the other hand, the anode
7
is applied with a high voltage of about 25 kV which has been boosted by the flyback transformer
18
. This high voltage of the anode
7
of the CRT
17
(hereinafter referred to as CRT anode high voltage) is created by boosting and then rectifying a horizontal retrace pulse generated by a horizontal deflection output circuit. The G
2
electrode
4
is applied with a voltage of about 700 V to about 1000 V generated by dividing the voltage of about 25 kV, which has been boosted by the flyback transformer
18
, by the resistor
19
. In the conventional CRT display device, since it is characteristic that a current does not flow in the G
2
electrode
4
, the resistor
19
for dividing the high voltage is about 100 M&OHgr;.
Under a condition that the voltage to be applied to the cathode
2
(hereinafter also referred to as cathode voltage) is changed while respective voltages to be applied to the G
1
electrode
3
, the G
2
electrode
4
, the G
3
electrode
6
and the anode
7
are held to be constant, when the cathode voltage becomes lower than a specified level, the electron beams emitted from the cathode
2
start flowing in a direction of a screen. The resultant flow of the electron beams from the cathode
2
in the direction of the screen is called as a beam current. The state in which the beam current is flowing shows that the beam hits the phosphor screen comprising phosphors of red, green and blue thereby allowing the screen to light. When the beam current flows in volume, the electron beam which reaches the phosphor screen is increased in number so that luminance of the screen is enhanced. In contrast, when the beam current is scarcely flowing, the luminance of the screen is decreased whereupon a video to be displayed on the screen turns to be dark. A display level of the image in which a dark screen starts lighting is called a black level. A voltage which is applied to the cathode
2
so as to display the black level is called as a black level bias voltage or a cutoff voltage.
In the conventional CRT display device, processing of adjusting the black level bias voltage called as a cutoff adjustment is performed by adjusting the cathode bias voltage to be applied to the cathode
2
. A black level bias voltage value of the cathode has a variance ,for example, between 80 VDC and 110 VDC in each of the electron guns (cathodes) for R (red), G (green) and B (blue) depending on production process of the CRT. Unless such variance is corrected, a specified black color can not be displayed on the screen. The cutoff adjustment is an adjustment which allows a point in which the beam starts lighting and the black level of the video signal to agree with each other and also a processing operation which is performed for allowing the cutoff voltage of each of electron guns for R, G and B to agree with the black level of each signal so as to correctly represent a black portion and a dark portion of an image. Specifically, a coarse adjustment is first performed by adjusting a G
2
electrode voltage such that a point in which the beam starts lighting to some extent is adjusted (or the G
2
electrode voltage is fixed). The black level bias voltage value to be applied to each of cathodes for R, G and B is next adjusted thereby allowing the video on the screen of the CRT (hereinafter also referred to as CRT screen) and the luminance of the black color to agree with each other.
On the other hand, Japanese Patent Laid-Open No. 224618/1999 discloses a high-luminance CRT (hereinafter also referred to as Hi-Gm tube) in which a modulation electrode (hereinafter referred to as Gm electrode) is further provided between the G
2
electrode and the G
3
electrode.
FIG. 7
is a block diagram showing a constitution of the Hi-Gm tube. In
FIG. 7
, reference characters
20
,
21
,
22
,
23
,
24
and
25
denotes a G
1
electrode, a G
2
electrode, a G
3
electrode, a cathode, an electron emissive material provided on a surface of the cathode and the newly provided Gm electrode, respectively. Electrodes after the G
3
electrode and the constitution as a whole are the same as those of a conventional electron gun.
FIG. 8
illustrates a potential distribution on a rotation symmetry axis in the proximity of the cathode of the Hi-Gm tube. In
FIG. 8
, the abscissa axis and the ordinate axis show a position (distance) (mm) from the cathode
23
and potential (V), respectively. Reference characters
26
,
27
and
28
shown in
FIG. 8
denote potential (electric field), a region in which the Gm electrode exists and an area in which the potential is low, respectively. Further, a dashed line shown in
FIG. 8
shows potential of the cathode
23
, that is, the cathode bias voltage. In the Hi-Gm tube, the Gm electrode
25
is disposed in the region shown by the reference character
27
which lies in about 0.5 mm inclusive of its vicinity far from the cathode
23
. The potential
26
of the region
27
in which the Gm electrode
25
is disposed is determined by setting a direct-current voltage (DC potential) of the Gm electrode
25
at a specified voltage value, for example, 80 V. When the cathode voltage (dashed-lined portion) is changed while the Gm electrode voltage is fixed at 80 V, a quantity of the electrons which proceeds in the direction of the screen can be controlled. That is, when the potential of the cathode shown by the dashed line becomes smaller than the potential (electric field), the electrons flow whereas, when the potential of the cathode becomes larger, the electrons do not flow. It should be noted that the potential (electric field) is changed as the voltage to be applied to the Gm electrode
25
is changed.
As shown in
FIG. 8
, in a side of the Gm electrode
25
facing the cathode
23
, electrons always exist in volume in an operating area of the cathode. Moreover, potential gradient after passing through the Gm electrode
25
is about one digit larger than that between the cathode and the G
1
electrode of a conventional type. That is, the electrons which have passed in the proximity of the Gm electrode
25
do not suffer from an influence of a space charge effect whereupon many of them can proceed in the direction of the screen. Therefore, the current flowing in the direction of the screen depends on a quantity of electrons which can pass through a position where the Gm electrode
25
exists and whose potential is the lowest. By the reason described above, the same beam current as a conventional one is allowed to flow by half or less the conventional potential difference of the cathode
23
. In other words, when the potential difference is the same as conventional, twice or more the convention
Heishi Akinori
Yasui Hironobu
Birch & Stewart Kolasch & Birch, LLP
Mitsubishi Denki & Kabushiki Kaisha
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