DISPLAY DEVICE COMPRISING A FLAT CATHODE RAY TUBE

Abstract: In a flat type cathode ray tube, electron beams (27) are vertically emitted from electron beam emitting sources (10) along vertical scanning electrodes (13) which have strip-shaped long configuration in horizontal direction and are each other insulatedly lined-up in vertical direction, and turn at predetermined position toward a phosphor screen (21) for vertically scanning and are horizontally focussed and deflected onto the phosphor screen (21) by horizontal focussing and deflection electrodes (17, 18 and 19).

Description: The present invention relates to a display device comprising a flat cathode ray tube as described in the first part of claim 1 which is to be used in a color television set or as a computer terminal display. FIG. 1 is a perspective view showing a conventional flat type cathode ray tube disclosed in the Japanese unexamined published Patent Application Sho 61-203545 assigned to the assignee of the present invention. Although a glass enclosure actually encloses whole the parts shown in FIG. 1 therein, an illustration of the glass enclosure is omitted in order to show an internal configuration of the flat type cathode ray tube clear. In the figure, horizontal and vertical directions are shown by arrow marks H and V on a face plate 128, respectively. FIG. 1 is illustrated extended in rectangular direction to the H and V-directions for easier illustration. A line cathode 110 has an electron emitting oxide layer on a tungsten wire and is long in the V-direction, and plural such line cathodes 110 are parallelly disposed with regular (i.e. equal) intervals in the H-direction making a parallel row. Behind (opposite side to the face plate 128) the row of the line cathode 110, vertical scanning electrodes 112, which are long strips in the H-direction and are separated to insulate each other, are vertically lined up with regular intervals on an insulator panel 111. In ordinary TV set, number of the vertical scanning electrodes 112, which respectively form independent electrode, is selected a half number of horizontal scanning lines (in case of NTSC system, the number is 480). Between the line cathode 110 and the face plate 128, there exist a first grid 113, a second grid 114, a third grid 115 and a fourth grid 116, from the line cathode 110 toward the face plate 128 in the above-mentioned order. The first grid 113 is formed with plural portions which are divided in H-direction in a manner to be disposed in front of the respective individual line cathodes 110, and the respective portions has apertures corresponding to positions of the vertical scanning electrodes 112. Video signals are applied to the respective portions of the first grid 113 so as to make beam current modulation. The second grid 114 is formed as single plate and has apertures similar to that of the first grid 113 and is disposed for extracting electron beam from the line cathode 110. The third grid 115 has the similar configuration to the second grid 114 and is disposed for shielding between electric field for extracting electron beam and the following electric field. The fourth grid 116 is also formed as single plate and has apertures which are longer in horizontal direction than in vertical direction. FIG. 2(A) is a horizontal sectional view of FIG. 1, and FIG. 2(B) is a vertical sectional view of FIG. 1. In front of the fourth grid 116 (in a direction toward the face plate 128), vertical deflection electrodes 117 and 118, which have similar apertures to the fourth grid 116, are disposed so that each center of the apertures are shifted each other in vertical direction in staggered manner as shown in FIG. 2(B). In front of the vertical deflection electrodes 117 and 118, plural sets of horizontal deflection electrodes which are long in vertical direction are disposed horizontally between adjacent line cathodes 110. In FIG. 1, three sets of horizontal deflection electrodes are shown as an example. That is, a first horizontal deflection electrode 119, a second horizontal deflection electrode 120 and a third horizontal deflection electrode 121 are provided, and are connected to common bus lines 122, 123 and 124 as shown in FIG. 2(A), respectively. The same voltage is applied to the third horizontal deflection electrode 121 as d.c. voltage applied to a metal back electrode 126 of the face plate 128. Voltage for focussing electron beam is applied to the first horizontal deflection electrode 119 and the second horizontal deflection electrode 120. Light emitting layer comprising a phosphor screen 127 and the metal back electrode 126 is formed on an inner surface of the face plate 128. In case of color displaying, the phosphor screen 127 comprises stripes of red phosphor (R), green phosphor (G) and blue phosphor (B) and black guard bands 127a which are inserted between stripes of adjacent phosphors of different colors one by one. Next, operation of the above-mentioned conventional flat type cathode ray tube is described with reference to FIGs. 2(A) and 2(B). By flowing current in the line cathodes 110, the line cathodes 110 are heated, and substantially the same voltage as potential applied to the line cathodes 110 are applied also to the first grid 113 and the vertical scanning electrode 112. At that time, electron beams from the line cathodes 110 travel toward the first grid 113 and the second grid 114 by applying higher voltage (for instance 100-300 V) than the potential of the line cathode 110 to the second grid 114 so that the electron beams pass through respective apertures of the first and second grid 113 and 114. Hereupon, the amount of the electron beams passing through the apertures of the first grid 113 and the second grid 114 is controlled by changing voltage applied to the first grid 113. The electron beams which pass through the aperture of the second grid 114 travel through the third grid 115, the fourth grid 116, the vertical deflection electrodes 117 and 118 and further through spaces formed by parallel disposition of horizontal deflection electrodes 119, 120 and 121. Predetermined voltages are applied to these grids and electrodes so that the electron beams are focused into small beam spots onto the phosphor screen 127. Beam focussing in the vertical direction is made by a static lens which is formed among the third grid 115, the fourth grid 116 and the vertical deflection electrodes 117 and 118, while beam focussing in horizontal direction is made by a static lens which is formed among the horizontal deflection electrodes 119, 120 and 121. The above-mentioned two static lenses are formed only in vertical or horizontal directions, and therefore focussing area of the beam spots can be adjusted individually. Deflection voltage signal of saw-tooth wave triangle wave or step like wave having period of horizontal scanning with same voltage is applied to the bus lines 122, 123 and 124 which are connected with the horizontal deflection electrodes 119, 120 and 121, respectively, and thereby the electron beams are deflected within predetermined width in horizontal direction. The phosphor screen 127 is scanned by these electron beams thereby to display light image. Vertical scanning of the conventional apparatus is described with reference to FIG. 3(A) and FIG. 3(B). As aforementioned, by controlling voltages of the vertical scanning electrodes 112 thereby to make the potential of the spaces surrounding the line cathodes 110 positive or negative against the potential of the line cathodes 110, generation or ceasing of the electron beams from the line cathodes 110 (hereinafter is referred as ON and OFF, respectively) is controlled, respectively. At this time, when the distance between the line cathode 110 and the vertical scanning electrode 112 is small, voltage required for controlling the generation and ceasing of the electron beams can be made small. In such current TV set that interlaced scanning system is adopted therein, in the first field period, the vertical deflection electrodes 117 and 118 are impressed with a predetermined deflection voltage for one field period, and one of the vertical scanning electrodes 112A is impressed with beam-ON voltage for one horizontal scanning period (IH), and the other vertical scanning electrodes 112B-112Z are impressed with beam-OFF voltage. In the next 1H period, only the next one of the vertical scanning electrodes 112B is impressed with the beam-ON voltage, and thereafter, in the similar manner, one verical scanning electrodes in consecutive order is impressed with the beam-ON voltage one after another until the lowest one 112Z is impressed with that voltage; and thereby a first one field period of the vertical scanning is completed. In subsequent second field, an inverted deflection voltage is applied to the vertical deflection electrodes 117 and 118 for one field period. The vertical scanning electrodes 112 are impressed with beam-ON voltage signals each for 1H period in the same way as the first one field. At that time, amplitude of the deflection voltages which are applied to the vertical deflection electrodes 117 and 118 are adjusted so that horizontal scanning lines of the second field are positioned respectively between with those of the first field. As mentioned above, the vertical scanning electrodes 112 are impressed with the same voltage signals both for vertical scannings in the first and the second fields, while the deflection voltages applied to the vertical deflection electrodes 117 and 118 are inverted each other in the first and second field, and thus one frame of vertical scanning is completed. Next, signal processing system, wherein video signals are applied to electron beam deflection electrodes of the cathode ray tube having horizontally plural electron beam generating sources as the above-mentioned flat type cathode ray tube, is described with reference to FIG. 4. A timing pulse generator 144 receives TV synchronous signal 142 and generates timing pulses which drives line memory circuit 145, 146 and a D/A converter 147. Primary color signals, which is demodulated by one of the above timing pulses and comprises three color signals E R , E G and E B corresponding to R(red), G(green) and B(blue), are converted into digital signals by an A/D converter 143, and thereby signals for 1H period are inputted to the first line memory circuit 145. When all signals for 1H period are inputted to the line memory circuit 145, those signals are transferred simultaneously to the second line memory circuit 146, and next signals for 1H period are also inputted to the first line memory circuit 145. The second line memory circuit 146 stores the transferred signals for 1H period, and transfers those signals to the D/A converter (or pulse width converter) 147, and therein those signals are converted into original analogue signals (or pulse width modulation signals). And those analogue signals are amplified by the D/A converter 147 for application to a modulation electrode (namely the first grid) of the cathode ray tube. These line memory circuits are provided for time delaying for a predetermined period. In the above-mentioned flat type cathode ray tube, since plural electrodes having at least the same plate-shaped electrodes as the phosphor screen are required, the price becomes high. Further, very high technique is required to provide correct intervals of the apertures for passing electron beams and uniform size of apertures and to assemble a lot of electrodes with centers of these apertures on the same line. The object of the present invention is to provide a display device comprising a flat cathode ray tube with improved accuracy of deflection of a tube type having a small number of electrodes and a simple construction and being manufacturable at low costs and being easy to be assembled. In order to achieve the above-mentioned object, a display device comprising a flat cathode ray tube with the features of the preamble of claim 1 is considered further. A display device with such features is known from the EP-A-0 079 108. This prior art discloses three types of electrodes, i.e. accelerating, focusing and deflecting electrodes. Only one pair of deflecting electrodes is provided. The US-A-4 451 758 discloses horizontal and vertical deflection electrodes and further acceleration electrodes. According to the invention a different concept is provided by making use of the characterizing features of claim 1. Thus, in the special type of a display device considered each of the plural electrodes of the horizontal focusing and deflection electrode units work as deflection electrodes and contribute to improved accuracy of deflection. In spite of this improvement, the concept is maintained that the necessary number of plate-shaped electrodes which have at least the same configuration as the phosphor screen, is at most one, and thereby the inner construction of electrodes is simple. Therefore, a display device as concerned which is of very low costs and easy to assembly can be offered. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is the partial perspective view showing the conventional flat type cathode ray tube. FIG. 2(A) is the horizontal sectional view of the flat type cathode ray tube of FIG. 1. FIG. 2(B) is the vertical sectional view of the flat type cathode ray tube of FIG. 1. FIG. 3(A) is the partial vertical sectional view of the flat type cathode ray tube of FIG. 1. FIG. 3(B) is the time chart showing waveforms of the signals which are applied to the electrodes shown in FIG. 3(A). FIG. 4 is the block diagram showing the video signal processing system of the conventional flat type cathode ray tube. FIG. 5 is a partial perspective view showing an embodiment of a flat type cathode ray tube in accordance with the present invention. FIG. 6(A) is a partial vertical sectional view of a flat type cathode ray tube of FIG. 5. FIG. 6(B) is a partial horizontal sectional view of a flat type cathode ray tube of FIG. 5. FIG. 7 is a partial vertical sectional view showing vertical deflection and focussing of a flat type cathode ray tube of FIG. 5. FIG. 8(A) is a partial vertical side view showing vertical scanning operation of a flat type cathode ray tube of FIG. 5. FIG. 8(B) is a time chart showing waveforms of signals which are applied to electrodes shown in FIG. 8(A). FIG. 9 is a partial horizontal sectional view showing horizontal focussing operation of a flat type cathode ray tube of FIG. 5. FIG. 10 is a partial perspective view showing control of electron beams of a flat type cathode ray tube of FIG. 5. FIG. 11 is a partial perspective view showing another embodiment of a flat type cathode ray tube in accordance with the present invention. Hereafter, preferred embodiment of the present invention is described with reference to the accompanying drawings. FIG. 5 is a perspective view showing a partial construction of inner electrodes of a cathode ray tube. FIG. 6(A) and FIG. 6(B) are a partial vertical (Y-direction) sectional view and a partial horizontal (X-direction) sectional view of FIG. 5, respectively. In FIG. 5, the flat type cathode ray tube has a vacuum enclosure (shown only partly) which comprises an optically transparent face plate 22, a rear plate 14, an upper plate (not shown), a bottom plate (not shown) and both side plates (not shown). Inner space of the vacuum enclosure is separated into plural uniform size unit spaces by means of supporters 20 and 25 made of insulating material (for example a glass) and metal pins 26, and the rear end of the supporter 25 is in contact with the rear plate 14, and the front end of the supporter 25 and the rear end of the supporter 20 are in contact with a shield electrode 15 from opposite directions. The metal pins 26 are sticked in the front end of the supporter 20 and lined up vertically with regular intervals, and tips of the metal pins 26 are in contact with the face plate 22 thereby to support the face plate 22 against the force caused by atmospheric pressure on the vacuum enclosure to prevent implosion between the face plate 22 and the rear plate 14. In each unit space, there exists an electron beam source 10, and therefrom an electron beam 27 is emitted upward (Y-direction of FIG. 5). Intensities of each electron beam 27 is modulated by video signals which are applied to the electron beam source 10. The shield electrode 15 is parallelly disposed nearer to the rear plate 14 than the face plate 22, and has vertically (in Y-direction of FIG. 6) long slit apertures 16 in each compartment of unit. Vertical scanning electrodes 13, which are long strips in horizontal direction (X-direction of FIG. 5) and are separated to insulate each other, are vertically lined up (or integrally formed) on the rear plate 14. Number of the vertical scanning electrodes 13 is selected at least the number of effective horizontal scanning lines (about 240) for one field in case of standard NTSC TV system. By making the vertical scanning electrodes 13, the shield electrode 15 and charge-up-prevention electrode 24 each other equipotential, the electron beam 27 travels straight upwardly through field-free space. In order to deflect the electron beam 27 to the aperture 16 of the shield electrode 15 as shown in FIGs. 6(A) and 6(B), potential of the vertical scanning electrode 13, which is in parallel with the electron beam 27, is made equal to potential of a cathode (not shown) of the electron beam source 10, as shown in FIG. 7. When normal state potentials of the shield electrode 15 and the vertical scanning electrodes 13 are made 400 V, and potentials of the vertical scanning electrodes 13A and 13B are made potential of the cathode of the electron beam source 10, namely 0 V, and potential of the vertical scanning electrode 13C is made an intermediate voltage, namely 200 V, the electron beam 27 is deflected toward the shield electrode 15 by electric field shown by broken lines in FIG. 7. Based on the above, vertical scanning operation is described with reference to FIG. 8(A) and FIG. 8(B). Width of the uppermost one 13Ao of the vertical scanning electrodes 13 and the lowermost one 13Zo are made larger than other vertical scanning electrodes from 13Bo to 13Yo as shown in FIG. 6(A). The uppermost electrode 13Ao and the lowermost electrode 13Zo are always impressed with fixed voltages of 0 V and 400 V, respectively. In FIG. 8(B), a time chart 41 shows an effective scanning period in one field period (1V). The subsequent waveforms shows voltages which are applied to the vertical scanning electrodes 13A-13Z are designated by attaching suffixes S, as 13AS-13ZS, respectively. When potential of the vertical scanning electrode 13A is made 200 V, incident position of the electron beam 27 is made on a position "a" of the shield electrode 15. After one horizontal scanning period (1H), by making potentials of the vertical scanning electrodes 13A and 13B, 0 V and 200 V, respectively, incident position of the electron beam 27 is made on a position "b" of the shield electrrode 15. Thus, by changing voltages which are applied to the vertical scanning electrodes 13C-13Z in a predetermined order, incident positions of the electron beams 27 are shifted from "a" to "z", and thereby one field scanning is completed. At that time, vertical intervals of incident positions are corresponded with the intervals of the vertical scanning electrodes 13. In ordinary TV set of interlaced scanning, in the subsequent second field, appplied voltages to the vertical scanning electrodes 13A-13Z should be lowered less than 200 V so that incident positions of the electron beams are positioned alternating with those of the first field. As shown in FIG. 5, the electron beams 27 which are passed through the aperture 16 of the shield electrode 15 and scanned horizontally within a width of one unit (shown by an arrow 28) by horizontal focussing and deflection electrodes 17, 18 and 19 which are attached on the supporter 20. These electrodes 17, 18 and 19 can be made on the supporter 20 by known process of vacuum evaporation, screen printing or sputtering. The supporter 20 is made of insulating materials, for example glass or ceramic etc.. As shown in FIG. 9, the horizontal focussing and deflection electrodes 17, 18 and 19 are impressed with predetermined voltages, respectively. And thereby, the electron beam 27, which is passed through the aperture 16 of the shield electrode 15, is focused into small spot on a phosphor screen 21. And simultaneously, voltage of saw-tooth wave, step like wave for 1H period or triangle wave for 2H period are superimposed on the horizontal focussing and deflection electrodes 17, 18 and 19 (inverted voltage is applied to opposite horizontal focussing and deflection electrode 17′, 18′ and 19′). And thereby, the electron beam 27 is deflected horizontally. At that time, the horizontal focussing and deflection electrodes 19 and 19′ are impressed with a d.c. voltage which is substantially the same voltage as that applied to a metal back electrode (not shown) of the phosphor screen 21; and the horizontal focussing and deflection electrodes 18 and 18′ are impressed with substantially a half potential of that of the metal back electrode; and the horizontal focussing and deflection electrodes 17 and 17′ are impressed with a voltage whereby electron beams are focused into the minimum spot on the phosphor screen 21. In FIG. 10, electron beam position detecting electrodes 23a and 23b having projections 23d and 23e, respectively, or slit like apertures (not shown) are symmetrically disposed each other across a center line 61 of each electron beam source 10. This is in order that the electron beam 27 (FIG. 5) is guided upward in parallel with the vertical scanning electrodes 13, and vertical focussing positions of each electron beam 27 on the phosphor screen 21 (FIG. 9) becomes coincident each other at any vertical scanning position, and the electron beam 27 is guided to a center of the aperture 16 (FIG. 5) of the shield electrode 15 (FIG. 5). When electron beam current is kept constant, the electron beam 27 (FIG. 6(A)) can travel in parallel with the vertical scanning electrode 13 (FIG. 6(A)) by adjusting voltages applied to auxiliary deflection electrodes 12a and 12b in a manner to make the electron beam currents which flow into the electron beam position detecting electrodes 23a and 23b each other equal. Further, the projections 23d and 23e are provided only at a position near the centerline 61 of the electron beam source 10 on the electron beam position detecting electrodes 23a and 23b, respectively, and control voltages are applied to auxiliary deflection electrodes 11a and 11b so that the electron beam currents which flow into the electron beam position detecting electrodes 23a and 23b are made maximum and equal. Thereby, the electron beam 27 (FIG. 5) can be passed through the horizontal center of the aperture 16 (FIG. 5) in the shield electrode 15 (FIG. 5). The above-mentioned control is carried out by individual electron beam source 10. An electron beam catching electrode 23c is provided for catching electron beam 27 (FIG. 5) which are passed through a gap between the electron beam position detecting electrodes 23a and 23b; but it is not always necessary. FIG. 11 is a partial perspective view showing another embodiment of a flat type cathode ray tube of the present invention. In this embodiment, the shield electrode 15 (FIG. 5) is removed from the first embodiment shown in FIG. 5. In FIG. 11, width of an charge-up-prevention electrode is made wide, and voltages which are applied to the horizontal focussing and deflection electrode 17 are adjusted so as not to affect potentials of the electron beam 27 which travel upward. Since other parts of this embodiment are identical with those of the first embodiment, description for them are omitted. While specific embodiments of the invention have been illustrated and described herein, it is realized that other modifications and changes will occur to those skilled in the art. It is therefore to be understood that the appended claims are intended to cover all modifications and changes as fall within the scope of these claims.

Claims: Display device comprising a flat cathode ray tube with: a phosphor screen (21); a plurality of vertical scanning electrodes (13) which each have an oblong configuration in the horizontal direction and are separated from each other in the vertical direction, the plurality of vertically separated scanning electrodes (13) forming a plane which is substantially parallel to said phosphor screen (21), said vertical scanning electrodes (13) being provided for vertically scanning electron beams (27) onto said phosphor screen (21) by changing potentials which are to be applied to said respective vertical scanning electrodes (13); a plurality of horizontal focusing and deflection electrode units (17,17',18,18',19,19') which are disposed between said phosphor screen (21) and said vertical scanning electrodes (13) and are aligned in parallel with each other in the horizontal direction, for horizontally scanning and focusing electron beams (27) within respective predetermined ranges onto said phosphor screen (21); a plurality of electron beam emitting means (10) which are disposed between said vertical scanning electrodes (13) and said horizontal focusing and deflection electrode units (17,17',18,18',19,19') in each space partitioned by adjacent two horizontal focusing and deflection electrodes (17,17',18,18',19,19'), for emitting electron beams (27) in a substantially vertical direction in substantially parallel with said plane formed by said vertical scanning electrodes (13); and a vacuum enclosure (14,22 and others) for enclosing the above-mentioned parts; characterized in that: each of said horizontal focusing and deflection electrode units is separated into plural opposing pairs of electrodes (17,17',18,18',19,19') in a travelling direction of electron beams (27), said plural opposing pairs of electrodes being insulated from each other and the display device comprises means to impress d.c. voltages different from each other to each of these pairs of electrodes for focusing and to superimpose the same deflection voltage to each of the pairs of opposing electrodes. Display device in accordance with claim 1, further comprising a plate-shaped shield electrode (15), disposed between said vertical scanning electrodes (13) and said phosphor screen (21), and having inner surfaces that define a plurality of slit apertures for passing electron beams (27). Display device in accordance with claim 1 or 2, wherein said electron beam emitting means (10) includes auxiliary deflection electrodes (11a,11b,12a,12b) for adjusting each course of each of said electron beams (27). Display device in accordance with one of claims 1 to 3, wherein said vacuum enclosure (14,22 and others) comprises a face plate (22) on which said phosphor screen (21) is provided and a rear plate (14) on which said vertical scanning electrodes (13) are provided, and each of said horizontal focusing and deflection electrode units (17,18,19) has supporting means (26) on an end thereof for supporting said face plate (22) and said rear plate (14) against atmospheric pressure impressed thereto. Display device in accordance with one of claims 1 to 4, further comprising applying means for sequentially impressing deflection voltages to said vertical scanning electrodes (13), for deflecting electron beams (27) to said phosphor screen (21). Display device in accordance with one of claims 1 to 5, further comprising an electron beam position detecting electrode (23) which is disposed to face said electron beam emitting means (10) for detecting positions of electron beams (27) which travel along said vertical scanning electrodes (13). Display device in accordance with claim 6, wherein said electron beam position detecting electrode (23) comprises two electron beam position detecting electrode strips (23a,23b) which have projections or slits like apertures nearly to centerlines of said electron beam emitting means (10) and are oppositely disposed each other, and said electron beam emitting means (10) has an auxiliary deflection electrode (11a,11b,12a,12b) to which control voltages are applied for making beam currents which flow into said two electron beam position detecting electrodes (23a,23b) maximum and equal. Display device in accordance with claim 6 or 7, further comprising an electron beam catching electrode (23c), which is disposed above said electron beam position detecting electrode (23) for detecting electron beams (27) which passes through an aperture of said electron beam position detecting electrode (23) to thereby adjust control voltages of said electron beam emitting means (10). Display device in accordance with claims 3 and 6 and possibly any other of the above claims, wherein said electron beam position detecting electrode (23) is disposed along an extended surface of said vertical scanning electrodes (13), and control means are provided for controlling voltages which are applied to said auxiliary deflection electrodes (11a,11b,12a,12b) to adjust electron beam currents which flow into said electron beam position detecting electrode (23) maxmimum and equal.

Inventors: KAWAUCHI, YOSHIKAZU, MIYAMA, HIROSHI, NISHIDA, JUN, TOMII, KAORU
Applicants: MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1987
Main classification: H01J31
IPC codes: H01J31, H01J29