CATHODE-RAY TUBE

Abstract: A cathode-ray tube comprises an electron gun (5) for emitting an electron beam (6), and a reflecting electrode (8) for forming in front thereof a substantially planar reflecting potential surface (9) which reflects the electron beam from the electron gun toward an anode target (2) formed on the inner surface of the tube.

Description: BACKGROUND OF THE INVENTION This invention relates to a cathode-ray tube having a reflecting potential surface for reflecting toward a phosphor screen an electron beam which is emitted from an electron gun and deflected by a deflector, and more particularly to an electrode structure for formation of the reflecting potential surface. A cathode-ray tube of this type has hitherto been proposed wherein an electron gun is disposed sidewise of a phosphor screen and a reflecting potential surface for reflecting toward the phosphor screen an electron beam emitted from the electron gun and deflected by a deflector is configured into a form of convexly curved surface, in order that the deflection angle can be increased and the overall length of a bulb can be reduced. Since the cathode-ray tube constructed as above has the convexly curved reflecting potential surface for reflecting the deflected electron beam toward the phosphor screen, the deflection, on one hand, can advantageously be amplified to a great extent but the size or diameter of a beam spot, on the other hand, is concurrently increased to disadvantageously degrade a focus character­ istic. SUMMARY OF THE INVENTION An object of this invention is to provide a cathode-ray tube which can exhibit an excellent focus characteristic while attaining the reduction in the over­ all length of a bulb and the high deflection sensitivity. To accomplish the above object, according to the invention, the reflecting potential surface is made substantially planar. BRIEF DESCRIPTION OF THE DRAWINGS Fig. l is a sectional view showing a cathode-ray tube according to an embodiment of the invention; Fig. 2 is an enlarged plan view showing a reflecting electrode of Fig. l; Fig. 3 is a diagram for explaining the operation of the reflecting electrode; Fig. 4 is a graph showing a potential gradient applied to the reflecting electrode; and Figs. 5 to 7 are plan views showing other embodi­ ments of the reflecting electrode. DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention will now be described by way of example with reference to the accompanying drawings. Fig. l is a sectional view showing the essential part of a cathode-ray tube according to an embodiment of the invention. Referring to Fig. l, the cathode-ray tube comprises a glass bulb l including a glass faceplate la, an anode target 2 comprised of a phosphor film 3 coated on the inner surface of the glass faceplate la and an aluminum film 4 vapor-deposited on the back surface of the film 3, an electron gun 5 fixedly supported within the glass bulb l at the bottom thereof, a planar reflect­ ing electrode 8 for forming a frontal zero potential reflecting surface 9 which reflects an electron beam 6 toward the anode target 2, and a shielding plate l0 maintained at the same potential as that of the anode target 2 to guard against disturbance of electric field due to the electron gun 5. With this construction, the electron beam 6 emitted from the electron gun 5 is reflected at the zero potential reflecting surface 9 formed in front of the planar reflecting electrode 8 so as to be deflected toward the anode target 2. As shown in Fig. l, a deflector 7 to deflect the electron beam may be provided in order to direct or introduce the electron beam from the electron gun 5 to the planar reflecting electrode 8. The planar reflecting electrode 8 has, as shown in plan view in Fig. 2, a plurality of, for example, eight dot-like elemental electrodes 8a, 8b, 8c, 8d, 8e, 8f, 8g and 8h which are formed on a disc-like insulating substrate 8' circumferentially along the periphery thereof at predetermined angular spacings. When the respective dot-like elemental electrodes 8a to 8h of the reflecting electrode 8 are applied with identical potential which is negative relative to the cathode potential, the zero potential reflecting surface 9 as best illustrated from Fig. 3 showing a side view of the Fig. 2 electrode is formed which contains a equipotential line 9a or 9b substantially parallel to a surface defined by an array of the dot-like elemental electrodes 8a to 8h. The electron beam 6 incident to the zero potential reflecting surface 9 is reflected or deflected at a reflection angle substantially equal to an angle of incidence to the surface 9. When the dot-like elemental electrodes 8a to 8h are applied with different levels of voltage in the order of arraying at a potential gradient as exemplified in Fig. 4, a zero potential reflecting surface ll now formed is inclined as shown at dotted line in Fig. 3 with respect to the array surface of the dot-­ like elemental electrodes 8a to 8h and an electron beam 6 incident to this zero potential reflecting surface ll is reflected or deflected at a reflection angle substantially equal to an angle of incidence to the surface ll, as indicated by a beam 6'. Assuming that the zero potential reflecting surface ll inclines by an angle of α from the zero potential reflecting surface 9, the deflection angle of the reflected electron beam 6' is increased by 2α. Accordingly, by differently varying the levels of voltages applied to the individual dot-like elemental electrodes 8a to 8h to provide a desired potential gradient, the orientation of the zero potential reflecting surface per se can be varied to deflect the electron beam 6 corre­ spondingly. For example, in order to deflect the incoming electron beam by 90°, the inclination angle α of the zero potential reflecting surface is set to be ±22.5°. In addi­ tion, by modulating the potential gradient with the vertical and horizontal deflection frequencies, the electron beam reflected and deflected at the zero potential reflecting surface can scan the entire screen. In this case, the application of voltage levels merely required for establishment of a requisite potential gradient to the respective dot-like elemental electrodes 8a to 8h suffices, and hence there is no need of supplying a considerably large amount of power which is otherwise required for deflection per se of the electron beam. Since the zero potential reflecting surface 9 or ll formed by the reflecting electrode 8 in accordance with this invention is substantially planar, the spot diameter of the electron beam 6 deflected by the zero potential reflecting surface is not enlarged so that a beam spot of high quality can be obtained. In the embodiment described hereinbefore, the reflecting electrode 8 has a plurality of dot-like elemental electrodes 8a to 8h which are arranged circumferentially on the insulating substrate 8'. But, the invention is not limited to this configuration. In another embodiment of the reflecting electrode, rod-like elemental electrodes 8i to 8p are used as shown in Fig. 5. Further, in addition to the circular arrangement of the elemental electrodes described previously, the elemental electrodes of the reflecting electrode may be arranged in other various ways to take, for example, a square, rectangular or polygonal contour, thereby attaining the same effects as those by the previous embodiments. In further embodiments, the reflecting electrode 8 is constituted by a number of resistors l2 interconnected in mesh configuration as shown in Fig. 6 and by a circular resistor-coated layer (resistor sheet) l3 as shown in Fig. 7. In the embodiment shown in Fig. 6, a horizontal deflection voltage V H modulated with the horizontal deflection frequency is applied across diametrically opposite portions of the reflecting electrode 8, and a vertical deflection voltage V V modulated with the vertical deflection frequency is applied across other diametrically opposite portions. In the embodiment shown in Fig. 7, too, similar horizontal and vertical deflection voltages V H and V V are applied to the reflecting electrode 8 in a similar manner. In these embodiments of Figs. 6 and 7, the zero potential reflecting surface is smoothed and its geometrical shape can be controlled freely, as compared to the zero potential reflecting surface obtained with the reflecting electrode 8 having the dot-like elemental electrodes 8a to 8h. In the foregoing embodiments, the reflecting electrode as applied to a monochromatic cathode-ray tube has been described for illustration purpose only, but obviously, the invention may also be applied to various types of cathode-ray tubes such as shadow mask type, beam index type and penetration type cathode-ray tubes to attain the same effects as those described hereinbefore. As described above, according to the invention, by constructing the reflecting electrode such that the electron beam emitted from the electron gun and deflected by the deflector can be reflected toward the anode target by the substantially planar zero potential reflecting surface following the deflector, the high-quality beam spot size can be obtained. Advantageously, the present invention can therefore provide the cathode-ray tube which can exhibit an excellent focus characteristic while attaining the reduction in the overall length of a bulb and the high deflection sensitivity.

Claims: 1. A cathode-ray tube comprising in a bulb (6): an anode target (2) formed on the inner surface of said bulb (l); an electron gun (5) for emitting an electron beam (6); and a reflecting electrode (8) for forming a planar reflecting potential surface (9) which reflects the electron beam from said electron gun toward said anode target. 2. A cathode-ray tube according to Claim l, wherein said reflecting electrode has a plurality of elemental electrodes (8a to 8h; 8i to 8p), potential levels of said elemental electrodes being controlled to vary the orientation of said planar reflecting potential surface. 3. A cathode-ray tube according to Claim l, wherein said reflecting electrode has a number of resistors (l2) interconnected in mesh configuration, potential levels across a plurality of pairs of diametrically opposite portions of said mesh configuration being controlled to vary the orientation of said planar reflecting potential surface. 4. A cathode-ray tube according to Claim l, wherein said reflecting electrode has a sheet resistor (l3), potential levels across a plurality of pairs of diametri­ cally opposite portions of said sheet resistor being controlled to vary the orientation of said planar reflect­ ing potential surface.

Inventors: YAMAZAKI, ELICHI
Applicants: HITACHI, LTD.
Application year: 1986
Main classification: H01J29
IPC codes: H01J29, H01J31