Computer graphics processing and selective visual display system – Data responsive crt display control – Data responsive deflection control
Reexamination Certificate
1997-11-10
2002-04-23
Nguyen, Chanh (Department: 2675)
Computer graphics processing and selective visual display system
Data responsive crt display control
Data responsive deflection control
C345S075200
Reexamination Certificate
active
06377231
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image-casting control method of a cathode ray tube image display device such as for a television picture tube or data terminal device, and particularly to an image-casting control method of a cathode ray tube image display device having a cold cathode.
2. Description of the Related Art
The fundamental operation of a cathode ray tube involves the use of electron emission from electron sources, focusing, acceleration, and deflection to cause excitation of fluorescent material on a screen by electron beams and, finally, emission of light. Cathode ray tubes of the prior art use an thermionic source in the electron source that takes advantage of development through thermionic emission.
The thermionic source generally employed in a cathode ray tube obtains thermions by using a heater to heat a cathode pellet made up of oxide mixtures such as barium, calcium, and strontium. An electron gun is constructed by combining these thermionic sources and a plurality of electrodes, and various functions such as the control of the amount of electron emission as well as focusing and acceleration of the electron beam can be achieved by applying a prescribed voltage to each of the electrodes.
When a power source is turned on to operate the thermionic sources when in a halted state, about
5
seconds is necessary for the temperature of the thermionic source to increase from room temperature to a prescribed temperature (for example, about 750° C.) that allows electron emission.
Conversely, when the thermionic sources are stopped while in operation, several seconds are necessary before the temperature drops to the point at which electron emission ends (about 500° C.) even when power to the heater is cut, and thermionic are therefore emitted from the cathode during this interval, and an electron beam may be irradiated toward the screen.
In a display device using a cathode ray tube, when the power source is turned off, a high-capacity smoothing capacitor is used in the high-voltage power source that supplies a positive high voltage to the screen to stabilize the high, direct-current voltage. As a result, even though the power source is cut off, the high-voltage output is not immediately interrupted but rather, drops gradually. In comparison, horizontal and vertical deflection circuits that do not use thermions fall rapidly, and this results in a state in which the electron beam undergoes no deflection and continues to irradiate for a period of time concentrated at only the central portion of the fluorescent screen, and this state results in the problem of a remaining spot that can cause “sticking” or burning of this portion of the fluorescent screen. Several image output circuit control methods, generally referred to as “spot killers,” have been disclosed as a means of avoiding this type of phenomenon after electron beam emission has reached a normal state.
As shown in
FIG. 1
, Japanese Patent Laid-open No. 231567/91 discloses a method of preventing a remaining spot by which capacitor
24
is charged after the power source is turned on and a steady state is achieved, and when the power source is turned off, the fall of voltage at the +B terminal is sensed, whereby spot-killer circuit
22
is activated, the voltage of charged capacitor
24
is used to change the bias of image output circuit
23
to the direction of flow of the beam current, and the high voltage charged in cathode ray tube
21
is discharged before the horizontal and vertical deflection circuits are stopped.
Japanese Patent Laid-open No. 245178/88 discloses a method for a case in which a circuit system as shown in
FIG. 2
is digitized. In a case in which synchronizing deflection circuit
39
is digitized, when the power source is turned off, the fall in voltage is sensed, and system reset circuit
32
is caused to operate, whereby synchronizing deflection circuit
39
is halted instantaneously and horizontal and vertical deflection are no longer performed. To prevent this from happening, a system reset signal causes on-screen blanking transistor
33
to turn on, and this in turn causes image output transistors
35
,
36
, and
37
of image output circuit
34
to turn off instantaneously, whereby the cathode ray tube (not-shown) enters a blanking state in which the bias of the cathode is cut off and electron emission is halted. The electron beam can therefore be prevented from entering a static spot state. The on-screen blanking used in this case is a function used for blanking the background portion of letters displayed on the screen.
A cathode ray tube that employs a cold cathode such as a field emission cold cathode, which is a quick-acting electron source, as the electron source can dispense with the heating of the cathode by a heater, which is required in a hot cathode. The principle of electron emission in a field emission cold cathode is the emission of electrons from a solid to a vacuum brought about by a quantum-mechanical tunnel effect when a strong field of
10
7
V/cm or more is impressed to a solid surface.
FIG. 3
shows one example of the structure of a field emission cold cathode. A high field can be obtained by applied voltage between a sharp needle-like emitter cathode
15
having a tip radius on the order of 100 nm and gate electrode
14
arranged approximately 0.5 to 1 &mgr;m away from the emitter, thereby creating field concentration at the tip of emitter electrode
15
. A multiplicity of emitter-gate constructions of this type formed on a substrate
12
and connected in parallel can be used to lower the applied voltage so as to obtain a prescribed current.
The degree of sharpness of the tip of emitter electrode
15
and the isolation characteristic between emitter electrode
15
and gate electrode
14
are key conditions for maintaining the electron emission characteristic of a field emission cold cathode.
As described hereinabove, the size of each emitter and gate is extremely small, and a large number of structures can be integrated in a small area. As shown in
FIG. 4
, one example of the electron emission characteristic with respect to the applied voltage shows that electron emission starts from approximately 30 V and rises sharply.
However, the above-described prior art has the following problems. First, when power is turned on to a display device using a cathode ray tube that employs a quick-acting electron source such as a field emission cold cathode, the electron beam irradiates only the center of the screen, thereby causing burning of the fluorescent screen. The reason for this is that electron emission in a field emission cold cathode begins immediately upon applying voltage that meets prescribed electron emission conditions. When the power source of the device is turned on, electron emission thus begins before the horizontal and vertical deflection circuits have risen sufficiently, whereby the electron beam irradiates the center of the screen without undergoing deflection.
The second problem is the destruction of element structures caused by sputtering resulting from the bombardment of positive ions and the degrading of isolation characteristics caused by re-adhesion of sputtered particles. The electron beam ionizes residual gas molecules or gas molecules generated by irradiation of the screen within the cathode ray tube, and positive ions thereby generated are accelerated in the direction opposite that of the electron beam. When the electron beam is being deflected in a stationary state, the paths of electrons and positive ions differ due to their difference in mass, and the positive ions therefore do not reach the electron source, but when the electron beam is directed straight ahead without being deflected, the positive ions bombard the electron source. As shown in
FIG. 3
, a field emission cold cathode involves-the input of voltage to a minute structure, and a field emission cold cathode is therefore extremely sensitive to bombardment by positive ions.
SUMMARY OF THE INVENTION
It is an object of the presen
Seko Nobuya
Tomihari Yoshinori
NEC Corporation
Nguyen Chanh
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