US2884558A - Cathode-ray tube for presenting stored and non-stored displays - Google Patents

Description

2 Sheets-Sheet 1 April 28, 1959 G. F. SMITH CATHODE-RAY TUBE FOR PRESENTING STORED AND NON-STORED DISPLAYS Filed Dec. 19. 1955 April 28, 1959 G. F. SMITH 2,884,558

CATHODE-RAY TUBE FOR PRESENTING STORED AND NON-STORED DISPLAYS Filed Deo. 19, 1955 2 Shasta-Sheet 2 1 `4 .zzz 11, 1 l a 2 Iy, A

L l1 h United States Patent O CATHODE-RAY TUBE FOR PRESENTING STORED AND NON-STORED DISPLAYS George F. Smith, Los Angeles, Calif., asslgnor to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Application December 19, 1955, Serial No. 553,880

4 Claims. (CL 315-12) This invention relates to direct-viewing storage tubes and more particularly to a cathode-ray tube incorporating apparatus for simultaneously presenting stored and non-stored infomation in an integrated display.

There are numerous applications for a cathode-ray tube capable of simultaneously presenting both stored and non-stored information in an integrated display wherein the stored information is retained for periods of the order of from several milliseconds to several minutes, or longer, if desired. One example of such an application is to provide a display for a moving-target-indication radar system wherein the non-stored portion of the display is used to present moving targets and the stored portions t provide a low intensity background corresponding to the position of the aircraft.

In accordance with the present invention, a storage electron gun and a non-storage electron gun, together with associated electron beam deflection apparatus, are spaced a predetermined distance apart and generate writing" and direct-reading" electron beams, respectively, which are directed towards a target assembly. A conductive mask, interposed between the target assembly and the electron guns, has openings disposed so that the writing and direct-reading electron beams are incident on mutually exclusive integrated areas of the target assembly. A layer of dielectric material having secondary electron emission characteristics is disposed within the areas on which the writing beam is incident to provide a storage surface within these areas. In addition, the device includes apparatus for directing a broad beam of electrons, that is, a beam of flood electrons uniformly through the conductive mask towards the target assembly and a viewing screen disposed adjacent to and coextensive with the target screen on the side thereof farthest from the electron guns.

In operation, a portion of the current of the directreading electron beam penetrates through the conductive mask and the interstices of the target assembly to the viewing screen to function in a manner similar to a conventional cathode-ray tube. The portion of the current of the writing electron beam which penetrates through the conductive mask, on the other hand, produces a charge pattern on the storage surface of the target assembly which in turn controls the dow of ood electrons to the viewing screen to produce a visual presentation of the stored information. If desired, the storage portion of the target assembly may be operated to reproduce halftones in the manner described, for example, in a copending application for patent Serial No. 459,403 entitled, Direct-Viewing Half-Tone Storage Device" liled by Elvin E. Herman and George F. Smith on September 30. 1954, now U.S. Patent 2,790,929, and assigned to the assignee of the present application.

It is therefore an object of the present invention to provide a cathode-ray tube capable of simultaneously presenting stored and non-stored displays in an integrated presentation.

Another object of this invention is to provide a cathode-ray tube incorporating a target electrode having first and second integrated portions for storage and non-storage purposes, respectively.

The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawings in which several embodiments of the invention are illustrated by way of example. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only, and are not intended as a definition of the limits of the invention.

Fig. l is a diagrammatic sectional view of an embodiment of the cathode-ray tube of the invention;

Fig. 2 is an enlarged perspective view showing the relationship of the mask with respect to the target assembly; and

Fig. 3 is an enlarged perspective view of an alternative embodiment of the target assembly.

Referring to Fig. 1, there is shown a diagrammatic view of the cathode-ray tube of the present invention. The tube comprises an evacuated bulbous envelope 10 having a neck portion 11 and a tlat end portion 12 disposed at opposite extremities thereof, as shown in the drawing. The neck portion l1 of the envelope 10 houses storage and non-storage electron guns 14, 16 for producing writing and direct-reading electron beams, respectively; deecting means 18, 20 for the writing and directreading electron beams; and a flood gun 22 for producing a beam of flood electrons. Deflecting means 18, 20 are disposed about the paths of the writing and directreading electron beams, respectively, and have a predetermined distance between their respective centers of deflection 23, 24, as will be hereinafter explained. In addition, the deflecting means 18, 20 are energized with appropriate beam deflection control signals to cause the electron beams to trace desired rasters on a target assembly 26 disposed adjacent to a viewing screen 28 disposed on the inner surface of the at end portion 12 of the envelope 10. A mask electrode 30 is interposed between the target assembly 26 and the electron guns 14, 16 and 22 at a distance from the target assembly 26 necessary to intercept the appropriate portions of the current of the writing and direct-reading electron beams so that the remaining portions of the current thereof are incident on mutually exclusive integrated elemental areas of the target assembly 26. Conductive coatings 32, 34 are disposed concentrically about the inner surface of envelope 10 in the intervening space between the flood gun 22 and the target assembly 26.

More particularly, storage electron gun 14 for producing the electron writing beam includes a cathode 40 and a control grid 42. The cathode 40 is maintained at a potential of the order of 2500 volts negative with respect to ground. This is accomplished by means of a connection therefrom to the negative terminal of a battery 44, the positive terminal of which is referenced to ground. The control grid 42 is maintained at a quiescent potential in the order of 50 volts negative with respect to the potential of cathode 40. To this end, control grid 42 is connected through a resistor 46 to the negative terminal of a battery 48, the positive terminal of which is referenced to the cathode 40. Means for intensity modulating the current of the writing beam is provided by a connection from the control grid 42 through a capacitor 50 to stored input terminals 52.

Similarly, non-storage electron gun 16 includes a cathode 60 and a control yid 62. The cathode 60 is maintained at a potential of the order of -4000 volts negative with respect to ground by means of a connection therefrom to the negative terminal of a battery 64, the positive terminal of which is referenced to ground. Also, in a manner similar to the electron gun 14, the control grid 62 is maintained at avnegative quiescent potential of the order of 50 volts negative with respect to the cathode 60. This is elected by means of a connection therefrom through a resistor 64 to the negative terminal of a battery 66, the positive terminal of which is referenced to the potential of cathode 60. In addition to the above, the control grid 62 is coupled through a capacitor 68 to non-stored input terminals 70 to provide a means for intensity modulating the current constituting the direct-reading electron beam.

The flood gun 22, for producing the broad beam of electrons, includes a cathode 72 and intensity grid 74 having a circular opening 75 in alignment with the electron emitting surface of cathode 72, and an annular anode 76 disposed concentrically about the opening 75, as shown in the drawing. In operation the cathode 72 is maintained at ground potential, the intensity grid 74 at a potential of the order of 50 volts negative with respect to ground and the anode 76 at a potential of the order of 200 volts positive with respect to ground. The foregoing may be accomplished, for example, by referencing an intermediate terminal on a battery 78 to ground along with the cathode 72, and connecting an appropriate negative terminal of the battery 78 to the intensity grid 74 and an appropriate positive terminal to the anode 76. Flood gun 22, in conjunction with conductive coatings 32, 34, produces a broad beam of flood electrons which are directed uniformly over the mask electrode 30. For this purpose the conductive coatings 32, 34 may be maintained at potentials of the order of +200 volts and of from +50 to +100 volts with respect to ground, respectively.

The target assembly 26, which together with mask electrode 30 is shown in perspective in Fig. 2, is disposed at the opposite extremity of the envelope l adjacent the viewing screen 28. The target assembly 26 comprises a metallic sheet 80 which has on the order of from 250 to 400 parallel longitudinal slots per lineal inch which are disposed normal to a line joining the centers of deflection 23 and 24 of the deflecting means 18, 20. The metallic sheet 80 is of a thickness of the order of 0.001 inch, and composed of a metal such as, for example, nickel, and has cross-members 81 periodically disposed across the slots for reinforcing purposes. A thin layer 82 of dielectric material having secondary electron emission characteristics such as, for example, magnesium fluoride is disposed along alternate rows of longitudinal slots across the entire width of the target assembly 26 and extends from the edge of each of the alternate slots to a point approximately half-way towards the next adjacent slot. In the event that magnesium uoride is used, the thickness of the thin layer 82 of dielectric material need only be of the order of two microns thick. Slots having the thin layer 82 of dielectric material disposed therealong are referred to as storage slots and the remaining slots as direct-reading slots. The direct-reading slots may, of course, be made wider to increase the efliciency of the non-storage phase of operation. In the operation of the device the metallic sheet 80 of the target assembly 26 is maintained at a potential of the order of l0 volts negative with respect to ground.

Disposed in front of and adjacent to target assembly 26 is the mask electrode 30. The mask electrode 30 has one longitudinal opening 84 with reinforcing members 85 for each pair of storage and non-storage slots of the target assembly 26. These openings 84 have a width somewhat less than the distance between centers of adjacent slots in the target assembly 26 and may, for example, be tapered so that only the surface facing the electron guns 14, 16, 22, intercepts the beam electrons. At

the center of the mask electrode 30 the openings 84 are disposed midway between the center lines of the corresponding storage and non-storage slots in the target assembly 26. As the outer periphery of the mask elec trode 30 is approached, however, suitable allowances must be made for parallax of the electron beam. In addition, the actual distance between the mask electrode 30 and the target assembly 26 is made proportional to the distance of the target assembly 26 from the centers of detection 23, 24 and the center-to-center distance between slots in target 26 and inversely proportional to the distance between the centers of deection 23, 24. In operation the mask electrode 30 also functions as a collector electrode and it is accordingly maintained at a potential of the order of +150 volts positive with respect to ground.

The viewing screen 28 comprises a transparent conductive coating 86 and a uorescent screen 88 disposed in the order named on the inner surface of the at end portion l2 of the envelope 10. A suitable potential to impress on the transparent conductive coating 86 is of the order of +5000 volts positive with respect to ground.

In the operation of the device, the signal for producing the non-stored portion of the display is applied to the non-stored input terminals 70 to intensity modulate the direct-reading electron beam produced by the non-storage electron gun 16. The direct-reading electron beam is scanned over the target assembly 26 in synchronism with the non-stored signal by means of appropriate deflection signals applied to the detiecting means 20. Upon being scanned over the target assembly 26, the portion of the beam current not intercepted by the mask electrode 30 is incident only over the non-storage slots in target assembly 26 and hence does not effect a charging of the storage surface along the adjacent storage slots of the target assembly 26. Because of the high velocity of the directreading electron beam, the electrons constituting the beam are not affected by the small bias applied to the metallic sheet of the target electrode 26 and hence proceed therethrough to the viewing screen 28 to produce the non-stored portion of the visual presentation.

The signal for producing the stored portion of the display, on the other hand, is applied to the stored input terminals 52 to intensity modulate the writing beam produced by the electron storage gun 14. The writing electron beam is scanned over the target assembly 26 in synchronism with the signal to be stored by means of appropriate deflection signals applied to detiecting means 18. In this instance, however, the portion of the current of the writing beam not intercepted by the mask electrode 30 is incident on the storage slots of the target assembly 26 to produce a charge pattern thereon corresponding to the signal to be stored. A portion of the writing beam current also passes through the storage slots of the target assembly 26 to the viewing screen 28 to produce an initial visual indication of the charge pattern.

Simultaneously with the above, the flood gun 22, in conjunction with electrodes 32, 34, directs a ood beam of electrons uniformly over the mask electrode 30 which is maintained at volts positive with respect to ground. The electrons penetrating through the openings in the mask electrode 30 are decclerated by the bias potential applied to the metallic sheet 80 whereby they are diffused uniformly over the target assembly 26. In that the cathode 72 of the Hood gun 22 is maintained at ground potential, the -10 volt biasing potential applied to the metallic sheet 80 will prevent the ood electrons from penetrating through the non-storgae slots of the target assembly 26 to the viewing screen 28. In the case of the storage slots, however, the etect of this biasing potential is neutralized by the potentials constituting the charge pattern to the extent that ood electrons are allowed to pass through the storage slots in proportion to the charge on the immediately adjacent storage surface whence they are accelerated to the viewing s screen 28 to produce the stored portion of the visual diaplay. This portion ol the device may, ol' course, be operated in accordance with the teachings ol' the aforementioned application by Herman and Smith to reproduce half-tones in the stored portion of the display.

Under certain circumstances it may happen that the biasing potential applied to metallic sheet 80 will not provide optimum contrast in the stored portion of the display and simultaneously prevent ood electrons from penetrating through the non-storage slots to the viewing screen 28 where they illuminate the screen without conveying any infomation. This condition may exist, for example, if the width of'tlie non-storage slots is in creased to improve the etiiciency of the direct-reading beam. In view of the above, an alternative target assembly 26a is shown in Fig. 3.- Referring to this gure, target assembly 26a comprises the metallic sheet 80 shown in Figs. 1 and 2 in connection with the description of target assembly 26. Unlike the target assembly 26, however, target assembly 26a has a uniform layer 90 of dielectric material having secondary electron emission characteristics such as, for example, magnesium tluoride, evaporated over the meshes on one side of sheet 80 facing the electron guns 14, 16 and 22. Thin layers 92 of metal such as, -for example, aluminum, are evaporated along both sides of the non-storage slots, each of which have widths that extend approximately half-way towards the next adjacent slot. ln operation the metallic sheet 80 may now be maintained at a potential to produce optimum contrast in the stored portion of the presentation such as, for example, volts negative with respect to ground. The thin layers 92 of metal, on the other hand,

` are maintained at a suliciently negative potential to prevent any tlood electrons from penetrating through the non-storage slots of the target assembly 26a and yet not produce a negative electric licld across the storage slots. A suitable potential for this purpose is of the order of 15 volts negative with respect to ground.

What is claimed is:

-1. A cathode-ray tube comprising a target assembly having manually exclusive integrated elemental areas of storage surface and conductive surface on one side there- `of with at least one intersticethrough each of said elemental areas; a view screen disposed adjacent the other side of and coextensive with said target assembly; means for producing trst and second high energy electron beams of elemental cross-sectional area and so disposed with respect to said target assembly so as to permit said beams to be directed toward said one side thereof; means for individually controlling the intensity of said first and `second electron beams with rst and second signals;

rst and second deilecting means disposed about the paths of said lrst and second electron beams, respectively, the centers of dellection of said deilecting means being spaced a predetermined distance apart in a plane parallel to said target assembly; a mask electrode disposed coextensive with and at a predetermined distance from said one side of said target assembly, said maalt electrode having openings to allow said first electron beam to impinge only on said elemental areas of conductive surface and said second electron beam to impinge only on said elemental areas of storage surface of said target assembly; means for energizing said tlrat deiiecting means to scan said lrst electron beam over said elemental areas of conductive surface on said one side of said target assembly in synchronism with said tiret signal, whereby a portion of the current of said first electron beam proceedsthrough the interstices of said target assembly to said viewing screen to produce a nonstored display representative of said ilrst signal; means for energing said second dedecting means to scan said second electron beam over said elemental areas of storage surface on said one side of said target assembly in synchronism withsaid second signal .to produce a charge pattern on said storage surface;

directing a broad beam of flood electrons uniformly over said target assembly, whereby the ood electrons penetrate through the interstiees of said target assembly within the elemental areas of storage surface in proportion to the charge thereon and proceed to said viewing screen to produce a stored display representative of said second signal that is integrated with said non-stored display.

2. A cathode-ray type tube comprising a target assembly including a metallic sheet having a plurality of uniformly spaced parallel slots which extend throughout its eective area, a layer of dielectric material having secondary electron emission characteristics disposed on one side of said metallic sheet, and a thin layer of conductive material disposed over portions of said dielectric layer along both sides of alternate slots to provide nonstorage slots, said thin layer of conductive material extending to a point approximately midway between centers of the adjacent slots whereby the exposed portions of 4said dielectric material cooperate with said adjacent slots to provide storage slots and the electrically conductive coated portions cooperate with said remaining slots to provide non-storage slots; a viewing screen disposed adjacent the other side of said metallic sheet and coextensive with said target assembly; means for producing irst and second high energy electron beams of elemental cross-sectional area; means for individually controlling the intensity of said lrst and second electron beams with first and second signals; first and second dellecting means disposed about the paths of said first and second electron beams, respectively, the centers of deflection of said deecting means being equidistant from said target assembly and spaced a predetermined distance apart in a plane normal to the slots in said metallic sheet; a mask electrode disposed coextensive with and at a predetermined distance from said target assembly on said one side of said metallic sheet, said mask electrode having one opening for each adjacent pair of storage and nonstorage slots disposed so as to allow said first electron beam to impinge only on said non-storage slots and said second electron beam to impinge only on said storage slots; means for energizing said rst deflecting means to scan said irst electron beam over said non-storage slots in synchronism with said first signal, whereby a portion 'of the current of said first electron beam proceeds through said non-storage slots to said viewing screen to produce a non-stored display representative of said signal; means for energizing said second dellecting means to scan said second electron beam over said storage slots in synchronism with said second signal to produce a charge pattern thereon; and means for directing a broad beam of ilood electrons uniformly over said target assembly whereby the flood electrons penetrate through the storage slots in proportion to the charge therealong and proceed to said viewing screen to produce a stored display representative of said second signal that is integrated with said non-stored display.

3. The cathode-ray tube as defined in claim 2 wherein said thin layer of conductive material is electrically insulated from said metallic sheet, thereby enabling said thin layer of conductive material to be maintained at :h potential different from that applied to said metallic oet.

4. In a plural beam cathode ray tube having means to store infomation and to display said stored information 'as well as non-stored information, the improvement comprising, in combination, a target assembly including an electrically conductive base member having a plurality of apertures therein, storage means cooperatively associated with alternate rows of said apertures to store electrical charges established by a tirst electron beam corresponding to information to be displayed, the other rows of said apertures permitting a second electron beam to pass therethrough without storage of elecandmeansforzstricalchargeaandamaskelectrodehavingaplurality ,ssuss A 1 8 y l of apertures therein and disposed with respect lo said Mereneuclhdinthelile'ofthis patent larga assembly t0 mit Bald lt QIWU'OD beim (0 im- UNITED gr Av1-BS P pings substantially only on said alternate rows ot aper- 2,761,089 Hae Aug. 28, 1956 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,884,558 April 28, 1959 George F. Smith e in the printed specification It is hereby certified that error appear tion and that the said Letters of the above numbered patent requiring correo Patent should read as corrected below.

Column 4, line 68, for "non-etorgae" read non-storage column 5 line 4l, for "maually" read mutually Signed and sealed this 25th day of August 1959.

(SEAL) Attest:

KARL H MINE ROBERT C. WATSON Attesting Ocer Commissioner of Patente

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