FLUORESCENT DISPLAY APPARATUS

Abstract: Fluorescent display apparatus for use in a large-screen display comprising a display portion having fluorescent display portions arranged in a matrix and coated with fluorescent material for emitting light upon being bombarded by thermoelectrons, cathodes of the type consuming small power shaped in a linear form oriented in the direction of the row or column and disposed to oppose the display portion arranged that one cathode corresponds to two or four of the fluorescent display portions, a first control electrode in a planar form having openings made therein corresponding to the fluorescent display portions of the display portion and disposed between the display portion and the cathodes, second control electrodes disposed on the side of the cathodes opposite to the display portion, and arranged corresponding to each cathode along the length of the cathode, and third control electrodes disposed on both sides of the second control electrodes in the direction of the column, and arranged so as to correspond to each cathode.

Description: The invention relates to a fluorescent display apparatus consisting of a plurality of display elements arranged in a common vacuum chamber, each display element containing a cathode for emitting thermoelectrons, an arrangement of control electrodes for controlling the flow of the emitted thermoelectrons, and a fluorescent display portion coated with fluorescent material and emitting light upon being bombarded by the thermoelectrons. Large-screen displays are in use for displaying progress and result of sports events in such places as an outdoor stadium. A fluorescent display apparatus utilized in such a large-screen display is constructed of a large number of monochromatic illuminating tubes arranged in a matrix. FIG. 1 is a schematic diagram showing an internal arrangement of a prior art monochromatic illuminating tube. The interior of the glass tube 1 is in a vacuum with air inside the tube evacuated through an exhaust hole 2. As a heater 3 heats up a cathode 4 surrounding the heater 3, thermoelectrons are emitted from the cathode 4. The thermoelectrons emitted from the cathode 4 is controlled in their flow by three types of grids 5, 6, 7 and allowed to bombard a fluorescent display screen 1a coated with fluorescent material. The fluorescent display screen 1a is applied with a high voltage and the part of the fluorescent display screen 1a bombarded by the thermoelectrons emits light. The grid 5 controls the quantity of the thermoelectrons emitted from the cathode 4, the grid 6 controls the diameter of the beam of the emitted thermoelectrons, and the grid 7 accelerates the emitted thermoelectrons. While potential for the grids 6, 7 is fixed, potential for the grid 5 is controlled, and thereby the quantity of the emitted thermoelectrons is controlled and the brightness of the fluorescent display screen 1a is regulated. FIGS. 2 and 3 show a fluorescent display apparatus integrating a number of such monochromatic illuminating tubes therewith. On the apparatus, there are disposed the fluorescent display portions 8 of three primary colors, i.e., red (R), green (G), and blue (B) colors, suitably spaced apart in vertical and horizontal directions so as to be regularly distributed. Thus, with the potential of the grid 5 of each of the monochromatic illuminating tubes controlled, each of the fluorescent display portions 8 are controlled in their brightness and thereby a display is given with a desired color tone. As a means to improve the resolution of such an apparatus provided with a number of monochromatic illuminating tubes, it is known from JP-A-64/995 to use an illuminating tube which is provided with a plurality of fluorescent display portions. However, since such an apparatus is of the structure that the cathode and grids must be provided for each of the fluorescent display portions, there are problems with it that the number of the component parts of the fluorescent display apparatus becomes larger, the internal structure becomes complex, and the power consumption becomes larger. From EP-B1-217 003 a fluorescent display tube is known which is similar to the tube as shown in Fig. 3, but which is additionally provided with column selection back electrodes below the discrete cathodes, and row selection control grids provided with apertures and being placed between the cathodes and fluorescent display portions. With these column selection back electrodes and row selection control grids it is possible to control the matrix of fluorescent display elements, but each of these fluorescent display elements contains a separate cathode which has to be separately heated. It is an object of the present invention to provide a fluorescent display apparatus having a simpler internal structure and consuming less heating power for the cathodes. According to the present invention, a fluorescent display apparatus as defined above is characterized in that said fluorescent display portions are arranged in a matrix of rows and columns to form a display screen; that said cathodes are of elongated form oriented in the direction of the row or column and supported on a substrate to oppose said display screen, the cathodes being arranged in an array of rows and columns, in which each cathode is provided for two of said fluorescent display portions; and that said arrangement of electrodes for controlling the flow of the emitted thermoelectrons are made up of a first control electrode in a planar form disposed between said display screen and said cathodes and having openings made therein corresponding to said fluorescent display portions of said display screen, second control electrodes disposed on the substrate near said cathodes and arranged in an array of rows and columns, in which each thereof corresponds to one of said cathodes and third control electrodes disposed on the substrate on two sides of said second control electrodes in the direction of the column, in which two thereof correspond to one of said cathodes. Preferable embodiments are defined in the dependent claims. The invention will now be described in connection with the drawings. FIG. 1 is a schematic diagram showing internal structure of a prior art monochromatic illuminating tube; FIG. 2 is a top view of a prior art fluorescent display apparatus; FIG. 3 is a side view in section of the same; FIG. 4 is an exploded view in perspective showing component parts of an embodiment of the present invention; FIG. 5 is a plan view showing electrode structure; FIG. 6 is a timing chart schematically showing timing of signals; FIG. 7 is a schematic plan view showing a display portion; FIGS. 8 and 9 are schematic diagrams showing state of potential in the vicinity of cathodes; FIG. 10 is a plan view showing electrode structure of another embodiment of the present invention; FIG. 11 is an exploded view in perspective showing component parts of still other embodiment of the present invention; and FIG. 12 is a plan view showing electrode structure of the embodiment of FIG. 11. FIG. 4 is an exploded view in perspective showing component parts of an embodiment of a fluorescent display apparatus according to the present invention. Referring to the figure, 1a denotes a display portion in a planar form having 16 fluorescent display portions 8, 1b denotes a frame member constituting the side walls of the fluorescent display apparatus, 14 denotes a planar electrode as a first control electrode having 16 openings 15 made therein, and 1c denotes a substrate with cathodes 4, second and third control electrodes 10, 12, wiring conductors as signal lines 11, 13 therefor formed thereon. The fluorescent display apparatus is assembled by having the planar electrode 14 disposed in the space surrounded by the frame member 1b, attaching the display portion 1a to one side of the frame member 1b, and attaching the substrate 1c to the other side of the frame member 1b. The display portion 1a has 16 fluorescent display portions 8 arranged in a matrix (four rows by four columns) and coated with fluorescent material. Each fluorescent display portion 8 is applied with a high voltage and emits light when bombarded by thermoelectrons. The planar electrode 14 is provided with 16 openings 15 made therein, arranged in a matrix (four rows by four columns), at the positions corresponding to their respective fluorescent display portions 8. FIG. 5 is a plan view showing the electrode arrangement on the substrate 1c, in which the horizontal direction corresponds to the direction of the row and the vertical direction corresponds to the direction of the column. In the center of the substrate 1c, there is formed an exhaust hole 2 as the passage for evacuating air from the interior of the fluorescent display apparatus. There are provided eight directly heated, elongated cathodes 4 disposed slightly separated from the surface of the substrate 1c. As each cathode 4 is heated by electric current passed therethrough, thermoelectrons are emitted from the cathode 4. At the portions on the surface of the substrate 1c below each of the cathodes 4, there are formed eight data electrodes 10 in an array of two rows by four columns as second control electrodes for controlling the emission of the thermoelectrons from the cathodes 4. Each data electrode 10 controls the emission of the thermoelectrons from each of the corresponding cathodes 4 by being applied with a positive or negative potential relative to the potential of the cathode 4. On the surface of the substrate 1c and at both sides of each of the data electrodes 10 in the direction of the column, there are formed 16 scanning electrodes 12 as third control electrodes arranged in a matrix of four rows by four columns for controlling the progression of the thermoelectrons emitted from the cathode 4. The data electrode 10 has a smaller surface area than the scanning electrode 12. The eight data electrodes 10 are grouped in four columns, each column being connected to a respective wiring conductor 11 as column signal line. The 16 scanning electrodes 12 are grouped in four rows, each row being connected to a respective wiring conductor 13 as row signal line crossing the wiring conductors 11 at right angles. The wiring conductors 11 and the wiring conductors 13 are electrically isolated from another by means of an insulating layer so as not to contact each other through. And, these data electrodes 10, scanning electrodes 12, wiring conductors 11, and wiring conductors 13 are printed on the surface of the subtrate 1c. Below will be described the operation of the apparatus. Referring to FIG. 5, S₁, S₂, S₃, and S₄ denote scanning signals to be applied, respectively, to four scanning electrodes 12 each in the direction of the row, while D₁, D₂, D₃ and D₄ denote data signals to be applied, respectively, to four data electrodes 10 each in the direction of the column. FIG. 6 is for showing time of application of these signals S₁ - S₄ and D₁ - D₄. And, FIG. 7 is for showing the arrangement of the fluorescent display portions 8 formed in a matrix on the display portion 1a, wherein the fluorescent display portions 8 are controlled in their emission of light by the control of the signals S₁ - S₄ and D₁ - D₄. The operation for controlling the emission of light will be described below. ON (positive) or OFF (negative) state of each of the data electrodes 10 and ON (positive) or OFF (negative) state of each of the scanning electrodes 12 are controlled by the timing of application of the data signals and the scanning signals. With regard to the ON or OFF state of the scanning electrode 12 and the ON or OFF state of the data electrode 10, there are four cases: the case where both the scanning electrode 12 and the data electrode 10 are in the ON state, where the scanning electrode 12 is in the ON state and the data electrode 10 is in the OFF state, where the scanning electrode 12 is in the OFF state and the data electrode 10 is in the ON state, and where both the scanning electrode 12 and the data electrode 10 are in the OFF state. The condition of emission of light by the fluorescent display portion 8 in each case will be described below. FIGS. 8 and 9 are schematic diagrams showing states of potential in these four cases. 1 ○ Where both the scanning electrode 12 and the data electrode 10 are in the ON state: The electric field in the vicinity of the heated cathode 4 becomes positive on account of the electric field of the data electrode 10 and the scanning electrode 12 and hence thermoelectrons are emitted. The emitted thermoelectrons are deflected by the electric field of the scanning electrode 12 and accelerated by the planar electrode 14 to advance to the corresponding fluorescent display portion 8 and bombard it. Then, the thermoelectrons coming into contact with the fluorescent material causes the fluorescent display portion 8 to emit light (FIG. 8 1 ○). 2 ○ where the scanning electrode 12 is in the ON state and the data electrode 10 is in the OFF state: Since the data electrode 10 is formed closer to the cathode 4, the electric field of the data electrode 10 affects the cathode 4 more strongly. Hence, in this case, the electric field in the vicinity of the cathode 4 becomes negative so that the emission of the thermoelectrons from the cathode 4 is restrained and the fluorescent display portion 8 does not emit light (FIG. 9 2 ○). 3 ○ where the scanning electrode 12 is in the OFF state and the data electrode 10 is in the ON state: Although the data electrode 10 is positive, both the scanning electrodes 12 formed on both sides of the data electrode 10 are negative, and moreover, the scanning electrode 12 is larger in surface area than the data electrode 10, and hence the electric field in the vicinity of the cathode 4 becomes negative so that the emission of the thermoelectrons from the cathode 4 is restrained and the fluorescent display portion 8 does not emit light (FIG. 8 3 ○). 4 ○ where both the scanning electrode 12 and the data electrode 10 are in the OFF state: The electric field in the vicinity of the cathode 4 becomes negative so that the emission of the thermoelectrons from the cathode 4 is restrained and the fluorescent display portion 8 does not emit light (FIG. 9 4 ○). In the described manner, the emission of light by each of the fluorescent display portions 8 is controlled at will by combination of the potential of the data electrode 10 and the scanning electrode 12. Since, here, the potential of the data electrode 10 and the scanning electrode 12 is controlled by the data signals D₁ - D₄ and the scanning signals S₁ - S₄, it is enabled to have each of the fluorescent display portions 8 emitting light or not at will by the control of these signals. The relationship in concrete terms between the control of signals and the control of light emission in each of the fluorescent display portions 8 will now be described according to Fig. 7. First, when the scanning signal S₁ is ON, fluorescent display portions P₁₁ - P₁₄ are selected, and according to ON/OFF states of the data signals D₁ - D₄, the corresponding fluorescent display portions 8 are chosen whether or not to emit light. Then, upon turning ON of the signal S₂, the fluorescent display portions P₂₁ - P₂₄ are selected and, according to ON/OFF states of the data signals D₁ - D₄, similarly to the above, the corresponding fluorescent display portions 8 are chosen whether or not to emit light. Upon turning ON of the signals S₃, S₄, similarly to the above, corresponding fluorescent display portions 8 according to ON/OFF states of the data signals D₁ - D₄ are chosen whether or not to emit light. Thus, by the application of the timing signals as shown in FIG. 6, the conditions of the fluorescent display portions 8 whether or not to emit light can be controlled at will. By the construction and the control of the fluorescent display apparatus described above, the number of the cathodes can decrease by half and the power consumption can also be made smaller as compared with the prior art fluorescent display apparatus. FIG. 10 is another embodiment of the present invention wherein the cathodes are arranged in the column direction. Thus arrangement, as the cathode length is longer than that in Fig. 4 wherein the cathodes are arranged in the row direction, the emission efficiency of the thermoelectrons is better and the power consumption can furthermore decrease. FIGS. 11 and 12 show another embodiment of the fluorescent display apparatus of the present invention having display portions which are arranged in four rows by four columns. FIG. 11 is an exploded view showing the electrode arrangement on the substrate 1c, in which the horizontal direction corresponds to the direction of the row and the vertical direction corresponds to the direction of the column. In the center of the substrate 1c, there is formed an exhaust hole 2 as the passage for evacuating air from the interior of the fluorescent display apparatus. There are provided four directly heated, elongated cathodes 4 disposed slightly separated from the surface of the substrate 1c. As each cathode 4 is heated by electric current passed therethrough, thermoelectrons are emitted from the cathode 4. At the portions on the surface of the substrate 1c below each of the cathodes 4, there are formed eight data electrodes 10 as second control electrodes for controlling the emission of the thermoelectrons from the cathodes 4 in an array of two rows by four columns. Each data electrode 10 controls the emission of the thermoelectrons from each of the corresponding cathodes 4 by being applied with a positive or negative potential relative to the potential of the cathode 4. On the surface of the substrate 1c and at both sides of each of the data electrodes 10 in the direction of the column, there are formed eight double scanning electrodes 12 as third control electrodes for controlling the progression of the thermoelectrons emitted from the cathode 4 arranged in a matrix of four rows by two double columns. The data electrode 10 has smaller surface area than the scanning electrode 12. The eight data electrodes 10 are grouped in four columns, each being connected to a respective wiring conductor 11. The eight scanning electrodes 12 are grouped in four rows, each row being connected to a respective wiring conductor 13 crossing the wiring conductors 11 at right angles. The wiring conductors 11 and the wiring conductors 13 are electrically isolated from another by means of an insulating layer so as not to contact each other. And, these data electrodes 10, scanning electrodes 12, wiring conductors 11, and wiring conductors 13 are printed on the surface of the substrate 1c. The operation of the fluorescent display apparatus thus constructed is the same as that of FIG. 4. By the above construction of the fluorescent display apparatus, the number of cathodes can decrease to a quarter and the power consumption can also be made smaller as compared with the prior art fluorescent display apparatus. According to the present invention, the control electrodes are arranged in a matrix, light emitting conditions of the fluorescent display portions 8 are controlled for each row by the scanning signal, and the light emitting conditions of the fluorescent display portions 8 for each column are controlled by the data signal, and therefore, the peripheral circuits for the control electrodes can be made smaller in number as compared with the prior art fluorescent display apparatus wherein the fluorescent display portions 8 are individually controlled for emitting light. Further, the data electrodes, scanning electrodes, and wiring conductors for these electrodes are formed on the same surface by printing, and hence the internal structure can be made simpler. Although the present embodiment was described above as to its case where four rows by four columns, but these are not limitative. Even if more numbers of row and column are used, similar arrangements as above can of course be realized. According to the present invention as described above in detail, cathodes in a elongated form are used, and besides, a single cathode is arranged to be commonly used for two or four, or further more fluorescent display portions, and hence the power consumption can be kept lower. Further, since the number of peripheral circuits of the control electrodes is reduced on account of the arrangement that emission of light by the fluorescent display portions arranged in a matrix is controlled for each row and each column, the effect is obtained that the internal structure of the fluorescent display apparatus can be made simpler.

Claims: A fluorescent display apparatus consisting of a plurality of display elements arranged in a common vacuum chamber, each display element containing a cathode (4) for emitting thermoelectrons, an arrangement of control electrodes (14, 10, 12) for controlling the flow of the emitted thermoelectrons, and a fluorescent display portion (8) coated with fluorescent material and emitting light upon being bombarded by the thermoelectrons; characterized in that said fluorescent display portions (8) are arranged in a matrix of rows and columns to form a display screen (1a); that said cathodes (4) are of elongated form oriented in the direction of the row or column and supported on a substrate (1c) to oppose said display screen (1a), the cathodes (4) being arranged in an array of rows and columns, in which each cathode (4) is provided for two of said fluorescent display portions (8); and that said arrangement of electrodes (14, 10, 12) for controlling the flow of the emitted thermoelectrons is made up of a first control electrode (14) in planar form disposed between said display screen (1a) and said cathodes (4) and having openings (15) made therein corresponding to said fluorescent display portions (8) of said display screen (1a), second control electrodes (10) disposed on the substrate (1c) near said cathodes (4) and arranged in an array of rows and columns, in which each thereof corresponds to one of said cathodes (4), and third control electrodes (12) disposed on the substrate (1c) on two sides of said second control electrodes (10) in the direction of the column, in which two thereof correspond to one of said cathodes (4). Display apparatus according to claim 1, wherein at least two of the third control electrodes (12) of the same row are combined with another in each row. Display apparatus according to claim 1 or 2, wherein said second and third control electrodes (10, 12) and wiring conductors (11, 13) are all formed on the same surface of the substrate (1c) by printing. Display apparatus according to any of claims 1 to 3, wherein the second control electrodes (10) of each column are connected to column signal lines (11), while the third control electrodes (12) of each row are connected to row signal lines (13) crossing said column signal lines (11) at right angles. Display apparatus according to any of claims 1 to 4, wherein the cathodes (4) are supported on the substrate (1c) between the second control electrodes (10) and the first control electrode (14).

Inventors: HARA, ZENICHIRO, IWATA, SHUJI MITSUBISHI DENKI KABUSHIKI KAISHA, KOBAYASHI, MASAAKI, TATSUDA, KAZUNORI, TERAZAKI, NOBUO
Applicants: ISE ELECTRONICS CORPORATION, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1988
Main classification: H01J31
IPC codes: H01J63, G09G3, H01J31