Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Reexamination Certificate
2000-10-12
2003-03-18
Kim, Robert H. (Department: 2882)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
Reexamination Certificate
active
06534935
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a color CRT (cathode-ray tube) apparatus.
2. Related Background Art
A color CRT apparatus forms color images by superposing images with three colors of R (red), G (green), and B (Blue) on a screen. For an imaging device, it is necessary to perform this superposition, i.e. convergence with high precision.
In a conventional color CRT, generally, three electron sources corresponding to the three colors R, G, and B are arranged in parallel, and angles of respective paths of electron beams on both sides of a center beam (herein after referred to simply as “side electron beams”) with respect to a path of the center electron beam have been set so that the distance between becomes smaller gradually in the direction in which the electron beams travel, and imaging spots of the three electron beams emitted at an interval s between respective adjacent electron beams are superimposed on one point on the screen. In this case, since the distance from an electron gun to the periphery of the screen is longer than that from the electron gun to the center of the screen, when the angles are set so that the imaging spots of the three electron beams are superimposed on one point at the center of the screen, the conventional color CRT is designed so that the imaging spots of the three electron beams are superimposed on one point continually throughout the screen using means for easing the degrees (for reducing the angles) to which side electron beams are directed outward, according to the distance from the center of the screen (according to the deflection amount of the electron beams).
Such means are roughly divided into three specific means. The respective means are described briefly as follows.
A first specific means is called a “self-convergence system” and basically is a method of providing nonuniformity to magnetic deflection field distribution. In a general example, a horizontal magnetic deflection field is provided with pincushion magnetic field distribution and a vertical magnetic deflection field is provided with barrel magnetic field distribution. The magnetic field distributions are designed so that imaging spots of three electron beams are superimposed on one point continually throughout the screen by causing a difference in deflection amount of the respective electron beams in the trajectory where the electron beams pass through the magnetic deflection fields while the intervals between respective adjacent electron beams of the three electron beams are the same at the moment they are emitted from an electron gun (for example, NHK (Japan Broadcasting Association) Color Television Textbook, Vol. 1, pages 267 to 271).
A second specific means is referred to as “dynamic convergence”. In the dynamic convergence, a magnetic field (a magnetic dynamic convergence field) for dynamically changing the angles of side electron beams with respect to the center electron beam is provided in the vicinity of main lenses of an electron gun and the strength of the magnetic field is varied according to an intended deflection amount, thus making adjustment so that imaging spots of the three electron beams are superimposed on one point continually throughout the screen (for example, NHK Color Television Textbook, Vol. 1, pages 266 to 267).
A third specific means employs a picture signal circuit (for instance, U.S. Pat. No. 2,764,628) constructed as follows. Three electron beams are not necessarily superimposed on one point on the screen, and side electron beams are set to be directed slightly inward or approximately in parallel. Spatial differences among images with three colors R, G, and B on the screen are corrected by temporal differences in input timings of modulating signals input to electron sources for the respective electron beams, thus allowing images formed of imaging spots of the three electron beams to be superimposed to be matched apparently throughout the screen. For convenience, such a means is referred to as “signal phase convergence” in the present specification.
Among those means, the first specific means has been used most widely. However, since the display density of image information has increased rapidly in recent years, it has become difficult to superimpose imaging spots of three electron beams with sufficiently high precision merely using the design of the above-mentioned magnetic field distributions. On the other hand, there are demands for reducing the depth of a color CRT apparatus. When the depth is to be reduced, the deflection angle increases. Therefore, the difference between the distance from the electron gun to the center of the screen and that from the electron gun to the periphery of the screen is increased further. Consequently, it has become more difficult to superimpose the imaging spots of three electron beams with high precision.
Therefore, the second specific means or a specific means of the combination of the first and second specific means has come to be used. In such a means, however, the three imaging spots are not always aligned on a straight line and are displaced irregularly. Therefore, a complicated system is required for correcting the irregular displacement, resulting in cost increase, which has been a disadvantage.
The third specific means basically achieves the convergence using a picture signal circuit. This is not a general technique, but the possibility of achieving this has increased with the improvement in digital circuit (for instance, JP 2542592 B). In this technique, the time difference corresponding to the displacement amount of the three imaging spots, which is different depending on positions on the screen, is applied to picture signals using a circuit technique, thus achieving the convergence throughout the screen. However, when this is achieved using the circuit technique alone, loads on the circuit increase, which include, for example, storage of the amounts of correction in signal phase at each position on the screen in a memory. Consequently, costs of the circuit and for its adjustment increase, which has been a disadvantage.
Some specific means of the combination of the first and third specific means also have been studied (for example, JP 54-29227 B and JP 6-46812 B). Basically, however, their designs are complicated, and naturally, there has been a limitation in coping with the increased display density and the increased deflection angle.
Of course, a specific means of the combination of the second and third specific means also can be considered as one combination. In this case, however, such a specific means comes to have both the disadvantages of the second and third specific means. In other words, such a specific means comes to have both the complicated correction system in the dynamic convergence and the increased load on the circuit due to the signal phase convergence. Therefore, such a specific means does not have much point and thus has not been studied.
SUMMARY OF THE INVENTION
The present invention is intended to cope sufficiently with the increased display density of image information and the increased deflection angle due to the reduction in depth by improving one obtained basically by combining elements of the above-mentioned second and third specific means and adding specific conditions thereto, by which images formed of imaging spots of three electron beams are superimposed on a screen with a sufficiently high precision to be matched without causing a cost increase.
In order to solve the above-mentioned problems, a first color CRT apparatus of the present invention employs the following system. In the system, three electron beams emitted from three electron sources arranged in an in-line form in a horizontal direction corresponding to three colors R, G, and B are deflected by a horizontal magnetic deflection field and a vertical magnetic deflection field, imaging spots of the three electron beams that are not superimposed on one point on a screen at a time are formed, and according to a time difference in timings at which the th
Sakurai Hiroshi
Tagami Etsuji
Wakasono Hiromi
Kim Robert H.
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
Yun Jurie
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