US3411029A - Color television picture tube - Google Patents

Description

Nov. 12, 1968 R. D. KARR 3,411,029

COLOR TELEVISION PICTURE TUBE Filed April 4, 1966 2 Sheets-Sheet 1 lfl llllllifllllllllll!!!"|llll|!!!l.l|l|ll!!l|llllllllllllllllllllllllllillllul 5 8 INVENTOR- w 5 CHARD HARP) a2 W F1 g 8 W AT TOR/\IEYS 2 Sheets$heet 2 Filed April 4, 1966 TELEVISION SIGNAL j w W i O 1 mm mm WLWLWLW m mm Mm T TO m mm l m m m of m w E g g w WM Ms? 7 W F Q M 9 m m I film 8 g 1 w .m I a m 8 3w m mm L a F I a E 3 u am m R z a 1 MW 4 j j fl W; W a 5 L w INVENTOR. RICHARD D. KARI? BY AT TORN E Y5 United States Patent 3,411,029 COLOR TELEVISION PICTURE TUBE Richard D. Karr, 1720 Dean York Lane, St. Helena, Calif. 94574 Filed Apr. 4, 1966, Ser. No. 540,009 7 Claims. (Cl. 315-13) ABSTRACT OF THE DISCLOSURE A three-gun color television picture tube and an electron focusing system therefor is described. The tube includes a display screen having three different color radiating materials disposed on the display surface in separate horizontal rows in a repeating color sequence with adjacent rows of material radiating a different color upon electron bombardment. Three electron guns, one for each of the color radiating materials are positioned at different elevations for directing electron beams unto the dis play screen. The electron accelerating system of each electron gun assembly includes a dynamic focusing electrode which is disposed between two segments of the initial accelerating electrode. A varying voltage generator is coupled to the dynamic focusing electrode to impress upon it a voltage which varies during the scanning of the electron beam over the display screen substantially in accordance with the variation in distance between the gun assembly and the screen.

The present invention relates generally to three-gun color television picture tubes. More particularly, it pertains to an improved color television picture tube having a new electroluminescent display system including a unique electroluminescent display screen, a new orientation of the electron guns of a three-gun array, and a new electron focusing system.

In general, there are presently in use, two types of electro-luminescent display system; to wit the three-gun shadow-mask system and the chromatron system. Both of these display systems are considered to leave much to be desired in the way of color reproduction. For example, standard three-gun shadow-mask systems include three electron guns which generate three modulated electron beams, each gun being modulated by separate color signals; a three-color phosphor-dot display screen; and a shadow-mask having an orderly arrangement of up to 3x10 apertures interposed between the guns and display screen. The shadow-mask has imposed certain limitations on the electro-luminescent display systems. For example, about 85% of the electrons comprising the electron beams impinge upon and are collected by the shadow-mask, leaving only 15% of the electrons of the beams to pass through the shadow-mask and excite the phosphor dots. Hence, such systems are characterized by inefiicient use of the electron beams and comparatively loW image brightness. Furthermore, the shadow-mask is easily magnetized by surrounding external fieldseven fields as weak as the earths magnetic field or those created by home appliances. Since this magnetization distorts the focusing of the beams, the shadow masks must be degaussed to neutralize such magnetization. In addition, the three electron beams must be converged into a precise cluster before passing through the holes in the shadowmask en route to the phosphor dot target. Because of the criticality of this convergence, the apertures of the shadow-mask must be precisely aligned with the phosphor-dot patterns defining the individual picture elements. The slightest misalignment results in the shadow-mask partially shrouding or blanking the phosphor-dot patterns defining the picture elements. Concomitant with this partial shrouding is a distortion in the reproduction of colors Patented Nov. 12, 1968 due to reduction in the intensity of one or more of the beam reaching the display screen.

In an attempt to eliminate the above limitations and disadvantages characteristic of three-color phosphor-dot shadow mask electro-luminescent display systems, chromatron systems were developed. Standard chromatron systems include a single electron beam generator which is modulated sequentially by the three color signals; a display screen. Since all chromatron systems use a single eluding red, green and blue radiating phosphors arranged in a repeating color sequence; and focusing grid wires extending parallel with the phosphor strips adjacent the display screen. Since all chromatron systems use a single electron beam and do not require a shadow-mask, they do not have any beam convergence or magnetization problems. However, defocusing problems still exist due to charge accumulation on the grid wires. Because of the elimination of the shadow-mask though, a considerably greater portion of the electron beam reaches the display screen of the chromatron systems in comparison to the shadow-mask type systems, hence enabling the chromatron systems to produce much brighter images.

However, in spite of the apparent advantages that chromatron systems have over the three-gun shadow-mask systems, they have not gained wide acceptance. The extremely large power requirement, overall circuit complexities, and two deflection systems required of the chromatron systems have discouraged its wide acceptance.

Considerable improvement is therefore to be gained by the rovision as in the present invention, of an electroluminescent display system which overcomes those limitations and disadvantages characteristic of prior art systems. More specifically, by eliminating the necessity of a shadow-mask and beam switching which consumes large quantities of power, a simple and low power electroluminescent display system can be realized which faithfully reproduces exceedingly, bright, high resolution images and which does not require the annoying periodic degaussing. Other advantages will be realized where the electroluminescent display system of the present invention is provided wtih a dynamic particle focusing system capable of converging the electrons of a beam to a point which remains coincident with the display screen for the entire scan of a frame.

The present invention is an electroluminescent display system which overcomes those disadvantages and limitations of the prior art systems. More particularly the electroluminescent display system of the present invention includes three electron guns arranged at the vertexes of a triangle, preferably equilateral, the vertexes being at different elevations. Each gun generates an electron beam which is intensity modulated by a color signal and which is deflected by suitable force fields to scan over the area of an electroluminescent display screen for reproducing images thereat. The electroluminescent display screen is a three-color phosphor type display screen with each raster line including phosphors which emit color radiation corresponding to the primary colors, i.e., red, green and blue, when excited by an impinging electron beam. The different color radiating phosphors are arranged at different, fixed elevations within the same raster line.

In the most preferred embodiment of the present invention, the different color radiating phosphors of each raster line are arranged in individual spaced apart horizontally parallel rows, each row including a multiplicity of spaced apart segments of one particular color-radiating phosphor. The rows of phosphor segments are arranged so that segments of each row are aligned vertical ly with those of the other two rows. The color sequence, vertical alignment of the segments and horizontal alignment of the rows are repeated in each raster line. To insure the accurate reproduction of images, the electron guns are arranged with one gun at the intermediate elevation point equidistant from the other two guns, and the force fields operated so that each of the rows of phosphor radiating one color are excited by the modulated electron beam generated by an associated gun.

Because of the arrangement of the different colorradiating phosphor dots at different elevations, each horizontal row of color radiating phosphor can be arranged to include a phosphor which radiates only one color when excited by an electron beam. Hence, by directing each electron beam to impinge only the phosphors in one horizontal row during each scan of a raster line, the shadow-mask, characteristic of conventional three-gun, three-beam systems can be eliminated. Such a shadowmask-free system is capable of accurately reproducing exceedingly bright, high resolution images. Furthermore, since three electron beams are used simultaneously in scanning each raster line, comprised of three separate color rows, the focusing grid wires, large switching power and complex switching circuits required by the chromatron systems are eliminated.

Accordingly, it is an object of this invention to provide a simple electro-luminescent display system capable of faithfully reproducing high resolution images.

More particularly, it is an object of this invention to provide a simple electro-luminescent display system characterized by efficiently using the scanning electron beams to generate exceedingly bright images.

Another object of this invention is to provide an electroluminescent display system which will not distort the colors of the original scene in producing the image.

A further object of this invention is to provide a dynamic particle focusing system particularly suited for use in the electro-luminescent display system of the present invention which is capable of converging the electrons of each beam to a point which remains coincident with the target surface of the display screen for the entire scan of a frame.

The invention possesses other objects and features of advantage, some of which, with the foregoing, will be set forth in the following description of the preferred form of the invention which is illustrated in the drawings accompanying and forming part of the specification. It is to be understood, however, that variations in the showing made by the said drawings and description may be adopted within the scope of the invention as set forth in the claims.

FIGURE 1 is a diagrammatic cross sectional view of a color television picture tube employing the electroluminescent display system of the present invention.

FIGURE 2 is a sectional view of the picture tube of FIGURE 1 taken along lines 22.

FIGURE 3 is a diagrammatic view of an electron gun assembly.

FIGURE 4 is an enlarged pictorial representation of the phosphor-dot pattern of prior art electroluminescent display screens.

FIGURE 5 is an enlarged pictorial representation of the orientation of phosphor-dot pattern of the electroluminescent display screen of the present invention.

FIGURE 6 is an enlarged pictorial representation of a circular phosphor dot pattern embodiment of the display screen of the present invention.

FIGURE 7 is an enlarged pictorial representation of a rectangular phosphor dot pattern embodiment of the display screen of the present invention.

FIGURE 8 is an enlarged pictorial representation of a horizontal strip phosphor pattern suitable for use in the electroluminescent display system of the present invention.

FIGURE 9 illustrates the dynamic particle focusing system of the present invention, partly in schematic and partly in diagrammatic form.

FIGURE 10 is an enlarged pictorial representation of the rectangular phosphor dot pattern employed in a reversing color sequence embodiment of the present invention.

FIGURE 11 is a block diagram of control circuits employed with the display screen embodiment of FIG- URE 10*.

With reference to FIGURES 1-3, a three-gun color television picture tube 11 including the electroluminescent display system of the present invention comprises three electron gun assemblies 12, 13 and 14 mounted within the neck portion 16 of a conventional picture tube envelope 17. Each gun assembly generates a particular color-related electron beam which is guided by suitable force fields to scan the novel electroluminescent display screen 18 of the present invention. The novel display screen will be described in detail infra.

As portrayed in FIGURE 3, each electron gun assem bly includes an electron emissive cathode 19 indirectly heated by a filament 21. The cathode 19 and filament 21 are surrounded by a control grid 22 for modulating the stream of electrons emitted in accordance with a particular color signal. Initial and final accelerations of the modulated stream of electrons emerging from grid 22 are provided by suitably charged circular cylindrical electrodes 23 and 24 respectively disposed in succession along the path of the electron stream. The second, or final, accelerating electrode 24 is generally charged to a voltage which is an order of magnitude greater than that to which the first, or initial, accelerating electrode 23 is charged. The resultant electric field established therebetween serves to focus the electrons of the stream at a point distal the gun assembly. By proper adjustments of the static voltages impressed on electrodes 23 and 24, the focal point of the electrons forming each beam can be made to coincide at the centric of the display screen 18.

Standard television picture tubes used in reproducing images employ a display screen 18 having a target surface 26 which is preferably substantially flat. That is with respect to the position of the gun assemblies, the target surface 26 can be considered to have no curvature since standard tubes generally have a low curvature relative to the location of the gun assemblies. Since each picture element of an image frame covers a very small area of the target surface 26, generally on the order of 10 to 10- square inches, and since the axes of the gun assemblies occupy an area of one square inch, the three beams generated by the gun assemblies 12, 13 and 14 must be converged. T o maintain the convergence point of the three beams fixed relative to the target surface 26 during the entire scan of the flat display screen 18, the angle of convergence of the beams must be changed as they are swept horizontally and vertically. To carry out standard dynamic convergence, each gun assembly is provided with soft iron pole pieces 27 and 28 disposed at each side of the electron stream. The pole pieces communicate respectively with iron core converging solenoids (not shown) which are energized in the conventional manner by parabolically varying horizontal and vertical correcting currents derived by standard techniques from the vertical and horizontal sweep circuits. In order to converge all three beams generated, one of the gun assemblies must be provided with a second set 29 of pole pieces for establishing a magnetic field in quadrature with that established by pole pieces 27 and 28. The quadrature magnetic field is adjusted so that the three beams converge toward a single point, so that they will impinge upon three color phosphors on the target surface.

In accordance with the present invention, the electron gun assemblies 12, 13 and 14 are disposed at different elevations within neck portions 16 of envelope 17. To facilitate initial convergence of the beams, the gun assemblies are tilted 'a finite amount, generally about 1", towards the central axis of the envelope. In one preferred embodiment, the gun assemblies are disposed at the vertexes of an equilateral triangle, the vertexes being at the different elevations. Gun assemblies 13 and 14 define the base line of the equilateral triangle, the base line being oriented perpendicular to the raster lines with gun assembly 12 disposed at an elevation intermediate the elevations of gun assemblies 13 and 14 and horizontally displaced therefrom (see FIGURE 2). With the gun assemblies 12, 13 and 14 arranged in the preferred equilateral triangular array, the possibility of each beam generated by the respective gun assemblies impinging on color radiating phosphors adjacent to that which is intended to be impinged, hence color overlap and smear, is minimized. Furthermore, by arranging the electron gun assemblies, 12, 13 and 14 at different elevations, and by arranging the different color radiating phosphors of each raster line 33 in separate horizontal rows 34, 36 and 37 (FIG. 1) in registry with the three beams issuing from the gun assemblies, each beam generated by each gun assembly can be caused to scan each horizontal raster line 33 without interruption. Hence, in contrast to prior art three-gun systems, the undesirable shadow-mask can be eliminated. As noted hereinbefore the elimination of the shadow-mask enables construction of an electroluminescent display system which efficiently utilizes its electron beams to reproduce faithfully highly resolved and brighter images.

Images are reproduced at display screen 18 by modulating the intensity of the electron beam generated by each of the electron gun assemblies 12, 13 and 14 in accordance with a particular primary color signal. For example, as shown in Figure 3, the blue color signal is separated from composite television signal by a conventional television receiver 38 and coupled from output terminal 40 to grid 22 of the blue gun assembly 12. The green and red color signals also are separated from the television signal and coupled from terminals 39 and 41 of receiver 38 to modulate the electron beams generated by gun assemblies 13 and 14 respectively. For sake of convenience, the gun assemblies 12, 13 and 14 will hereinafter be referred to respectively as blue, green and red guns.

The electron beams generated by the blue. green and red guns are directed simultaneously by suitable force fields to scan sequentially the plurality of raster lines 33 of the picture tube 11. As in standard practice, each frame is reproduced by interlaced scanning, i.e., scanning the display screen 18 from left to right and top to bottom, with the image frame being reproduced by scanning the target surface two times once along the odd numbered rasters only and once along the even numbered rasters only. The particular number of raster lines 33 may vary as desired. For example, in the United States and Japan, 525 raster lines are employed, in most of Europe 625 raster lines, in England 405 raster lines and in France 819 raster lines. In any case, the particular number of raster lines employed will merely require a particular vertical spacing of the color radiating phosphors comprising the target surface 26.

The scanning is accomplished by controlling the force fields in accordance with the horizontal and vertical sweep signals separated from the television signal by receiver 38. Although in the embodiment illustrated in FIGURES l-3. magnetic type beam deflection force fields are shown as being used, electrostatic beam deflection force fields could be used equally as well. Where magnetic force fields are used to deflect the three beams from the blue, green and red guns, a yoke 42 is mounted about the neck portion 16 of envelope 17 to deflect the beams emerging from the three color guns. The coils of the yoke 42 are energized in the conventional manner by suitable vertical and horizontal sweep signals present at the output terminals 43 and 44 of the television reecivers sweep circuits. Referring to FIGURE 2, the manner in which the magnetic deflection is accomplished is portrayed by poles 42 and poles 42", each pair representing respectively the establishment of the horizontal and vertical field components of the resultant magnetic beam deflecting field established by yoke 42. The deflected electron beams are subsequently accelerated to impinge target surface 26 by a post accelerating voltage applied thereto at terminal 45 (see FIGURE 1).

Considering now the novel display screen of the present invention, attention is directed to FIGURES 4-7. In the figures, horizontal cross hatching represents blue radiating phosphor dots 51; vertical cross hatching, red radiating phosphor dots 52; and inclined cross hatching, green radiating phosphor dots 53. Referring to FIGURE 4, standard phosphor-dot type display screens of conventional color television picture tubes employ triangle three-color phosphor-dot pattern 54 arranged to have two different color radiating phosphor dots in a horizontal line. Furthermore, the phosphor-dot patterns 54 are nested so that the phosphor-dot patterns 54 of one raster line are separated by portions of the phosphor-dot patterns 54a and 54b of vertically adjacent raster lines. Hence, it is seen that each horizontal row 56 of phosphor dots presently include in repeating sequence the three different color radiating phosphor dots 51, 52 and 53. Consequently, during each scan of the raster line, the electron beams must be blanked, for example, by a shadow-mask for approximately twothirds of the scan. As noted herein before, the necessity of blanking has led to many limitations, inconveniences and, in general, a less than desirable reproduction of the images. Furthermore, because of the large horizontal spacing of successive phosphor-dot patterns 54, much color information is lost, thereby degrading the resolution of the image reproduced.

With reference to FIGURE 5, the display screen 18 of the present invention employs a unique and superior phosphor-dot pattern 54'. As shown, the three different color phosphor dots 51, 52 and 53 defining the patterns 54' are positioned so that their centric points are at different elevations. In the preferred pattern 54', the centric points of the phosphor dots 51, 52 and 53 of each pattern 54' are positioned at the vertexes of an equilateral triangle with two of the phosphor dots, for example, red and green radiating phosphor dots 52 and 53, vertically aligned. Although, in this configuration there still remains some overlap of different color radiating phosphor dots in each horizontal row 56 of phosphor dots, it is seen that the phosphor-dot patterns 54' of each raster line are separated by only two-thirds of the distance of separation of the phosphor-dot patterns 54 of the prior art display screens as represented by FIGURE 4. Hence, since more picture elements can be produced during each horizontal scan, the resolution of the images reproduced by a display screen having a phosphor-dot pattern constructed in accordance with FIGURE 5 will be far superior to those reproduced by the prior art three-color phosphor-dot display screens as represented by FIGURE 4. Furthermore, although blanking would be required, it is seen that it would be necessary to blank the electron beams only onehalf the time during each horizontal scan. Hence, brighter images Will be obtained by using the phosphor-dot pattern of FIGURE 5. It is noted, however, that to maintain vertical resolution, hence superior overall resolution, the size of each phosphor-dot should be reduced. It is preferred to reduce their size so that vertical distance covered by three vertically aligned phosphor dots of the pattern 54' of the present invention equals that covered by two vertically aligned phosphor dots of the prior art pattern 54 as represented by FIGURE 4.

In FIGURE 6 another phosphor-dot pattern embodiment employed in the display screen 18 of the present invention is shown which eliminates the necessity of blanking the electron beams with, for example, a shadow-mask. As illustrated therein, as one possible phosphor dot color array, the different color radiating phosphor dots 51, 52 and 53 are arranged in individual rows with the blue color radiating phosphor dots 51 substantially interposed between the red and green color radiating phosphor dots 52 and 53 respectively. The immediately vertically aligned blue, red and green radiating phosphor dots do not form a triangle which is similar to that formed by the blue, green and red guns 12, 13 and 14. Hence, the position of the blue radiating dots 51 is adjusted so that the blue phosphor dots of one generally vertical row of phosphor dots forms with the red and green dots of laterally adjacent generally vertical row of phosphor dots the requisite equilaterally triangular three-color phosphor-dot pattern 54". If the size of the phosphor dots of pattern 54" is reduced to approximately one-third that of the phosphor-dot pat tern 54 of the prior art as represented by FIGURE 4, the resolution of the image reproduced will be greatly enhanced since each frame reproduced will include considerably more picture elements.

Referring now to FIGURE 7, a most preferred embodiment of the three-color phosphor-dot pattern used to form the target surface 26 of the display screen 18 of the present invention is illustrated. In this embodiment, the phosphor dots are rectangular and are arranged in horizontal rows 57 of single color radiating phosphor dots, the phosphor dots being vertically aligned. Preferably, the horizontal rows 57 of different color radiating phosphors are arranged in a vertically repeating color sequence, i.e., red, blue, green, red, blue, etc. radiating phosphors. In accordance with the particular arrangement of the gun assemblies 12, 13 and 14 of FIGURES 1 and 2, the row of blue radiating phosphor rectangular dots 51 are interposed between an upper row of red radiating phosphor rectangular dots 52 and a lower row of green radiating phosphor rectangular dots 53'.

Each rectangular dot of the color radiating phosphors are preferably adjusted to a height-to-width ratio of 1:1.73, for example, 0.014:0.024 inch. By constructing the rectangular dots in accordance with this preferred ratio, the centrics of the red and green radiating phosphor dots in one vertical row defines the requisite equilateral triangle with the centric of the blue radiating phosphor dot of an immediately laterally adjacent vertical row.

A display screen 18 having a target surface 26 constructed in accordance with the phosphor-dot arrangement of FIGURE 7 will be characterized by being capable of faithfully reproducing, with high resolution, an extremely bright image. The high resolution is gained as a result of the target surface 26 having two times the number of picture elements (each picture element defined by a phosphor dot pattern 54) as compared to the prior art display screens constructed in accordance with FIGURE 4.

With the gun assemblies arranged as shown in FIG- URE 2, continuous horizontal strips 58, 59 and 61 of red, blue and green radiating phosphors arranged in the color sequence of FIGURE 7 can be employed in a threegun electroluminescent display system. Such a pattern is shown in FIGURE 8. To prevent loss in color fidelity due to interactions between adjacently excited points on a phosphor strip, straight conductive wires 62 are mounted at regular horizontal intervals, for example, 0.024 inch apart, to extend vertically in front of the phospher strips 58, 59 and 61. The wires 62 intercept the electron beams as they are deflected to scan the display screen 18 thereby interrupting the excitation of the continuous phosphor strips at regular intervals. The electrons intercepted by the wires 62 are collected by imposing a suitable positive voltage on the conductive wires 62. While the wires 62 interrupt the excitation, there is some migration of excitation through the areas which are shielded by the wires. Thus, the resolution obtained with this embodiment is not quite as good as that obtained with the configuration of FIGURE 7. It is to be noted, however, that the conductive wires 62 do not consume power to the extent that the beam focusing grid wires of the chromation systems do. This is because the conductive wires 62 are not employed to deflect the electron beams.

To enhance the ability of the display screens of the present invention to faithfully reproduce images as well as to reproduce images of good contrast, it is contemplated that the color radiating phosphor elements will be separated by finite zones, e.g., 0.005 inch Wide, of light absorbing and preferably also non-luminescent, black area 63. (See FIGURES 7 and 8.) For example, black manganese oxide or silver particles could be employed.

In constructing target surface 26 of the three-color radiating phosphor display screen 18, any of the known color radiating materials such as the following can be deposited in the desired pattern on, for example, clear glass; for the red radiating zones, manganese activated zinc phosphate; for the green radiating zones, manganese activated silicate; and for the blue-radiating zones, silver activated zinc sulfide. To render the entire target surface 26 capable of being maintained at a uniform potential, the target surface 26 defined by the color radiating phosphors is covered by a sheet layer 64 of electron permeable highly reflective conductive material such as silver or aluminum.

Since in the preferred three-color phosphor-dot pattern embodiments of the display screen of the present invention, the size of at least one dimension of the radiating phosphors is reduced in comparison to the dimensions of prior art three-color phosphor-dot patterns, it is desirable to focus the electrons of each beam to a point at the target surface 26 for the entire scan of surface 26.

Referring now to FIGURES 3 and 9, in one preferred embodiment of the electroluminescent display system of the present invention which employs the substantially flat target surface display screen 18, the focal point of the electrons forming each of the beams is maintained at the target surface 18 by providing each gun assembly with a dynamic cylindrical focusing electrode 31 interposed be tween segments of electrodes 23 and in register with the electrodes 23 and 24. A suitably varying voltage relative to electrode 23 is impressed simultaneously on the dynamic focusing electrodes 31 of the gun assemblies at terminal 32 thereof. In a manner to be described infra, the varying voltage is selected to automatically adjust the focus of the electrons forming the respective streams so that the focal point of each stream coincides with target surface 26 for the entire scan of the display screen. Where the target surface 26 has a discernable curvature relative to the location of the gun assemblies, the instantaneous voltage V is varied in direct proportion to the variation in the distance between a spherically curved surface having its center of curvature at the gun assemblies and the generally flat target surface 26 tangent at the centric of such curved surface.

If the curvature of surface 26 is considered flat relative to the position of the electron gun assemblies, the required voltage is defined by the equation:

V is the instantaneous voltage in volts applied to the dynamic focusing electrode 31 relative to electrode 23;

D is the distance in inches to the furthest point on the target surface 26 measured from the centric of surface 26;

d is the instantaneous position in inches of the beam at target surface 26 measured from the centric of surface 26; and

V is the voltage in volts required to be impressed on dynamic focusing electrode 31 relative to electrode 23 to focus the electrons of the beam at point D. Although V will vary depending on the size of the target surface 26, the particular potentials applied to electrodes 23, 24, and 3 1, the geometry of the electrodes, and the distance between display screen 18 and final accelerating electrode 24 as well as other factors, the particular V for any particular color television picture tube assembly can be empirically determined easily by directing the electron beam to impinge the target surface 26 at point D and then varying V until the required V is reached that will focus the electrons at that point. Since the centric of target surface 26 is the closest point to the electron gun assemblies, the voltage applied to electrode 31 required to focus the electrons of a beam at other points on the target surface 26 will be more negative than that voltage required to focus them at the centric point.

As can be seen from Equation 1, the voltage impressed at dynamic focusing electrode 31 varies as a parabolic function of the instantaneous position of the beam. Hence, the horizontal and vertical converging currents applied to the converging coils can be used to derive the required varying voltage, V. However, it is to be noted that separate suitable function generator or generators could be employed to generate the requisite varying voltage V. In the former case, a resistor 64 is placed in series with the horizontal converging coil associated with any one of the beams to derive a voltage which varies as the scanning current through the coil. Similarly, a resistor 66 is placed in series with the vertical con-verging coil associated with the beam to derive a voltage which varies as the current through the coil. The voltages are summed in a voltage summing circuit 67, e.g., a high gain summing amplifier, which issues a resultant voltage function which varies, for example, from zero volts relative to the voltage level at electrode 23 to some more negative value relative to the voltage level at electrode 23. The output of summing circuit 67 is applied between electrodes 23 and 31 by leads 68 and 69.

As an illustrative example, for a 25 inch rectangular television picture tube having an aspect ratio of 4:3, having 600 volts direct current (VDC) applied to electrode 23, having 5 kilovolts direct current (KVDC) applied to electrode 24, having parabolically varying currents applied to the beam converging coils, and the distance from the final accelerating electrode 24 to display screen 18 measuring twelve inches, a V equal to 60 volts will focus the electrons of the beams at the target surface 26 at the four corners of the rectangular thereof. The four corners measure 12.5 inches from the centric of target surface 26. Hence, Equation 1 reduces to Such a varying voltage can be generated by combining a voltage issuing from summer 67 and derived from the parabolically varying current applied to the horizontal convergence coil which varies from 38 v. to 0 v. to 38 v. with a voltage issuing from summer 67 and derived from the parabolically varying current applied to the vertical convergence coil which varies from 22 v. to 0 v. to 22 v. Since these varying voltages are derived from the horizontal and vertical sweep circuits, their addition in the proper manner will be automatically synchronized with the sweep of the beams over the target surface 26 of display screen 18. It is to be noted that dynamic focusing electrodes 31 of each gun assembly 12, 13 and 14 can be controlled by the same voltage function V.

Referring to FIGS. and 11, another embodiment of the electroluminescent display system employs an electroluminescent display screen including horizontal rows of red, blue and green color radiating phosphor dots 71, 72 and 73 respectively, arranged vertically in a reversing color sequence, i.e., a red row 71, a blue row 72, a green row 73, a blue row 72, a red row 71, a blue row 72", a green row 73, etc. In the embodiment illustrated in FIG. 10, the rows of red and green radiating phosphors are employed in two vertically adjacent rasters, for example, green row 73 is used in both vertically adjacent rasters 76 and 74. Hence, when the electron beams are deflected to scan vertically adjacent rasters, the red color information must be delivered to the normally considered red gun 14 during the scan of one raster and the normally considered green gun 13 during the scan of the vertically adjacent raster. Similarly, the green color information must be delivered to the different guns 13 and 14 during the scan of vertically adjacent rasters.

Referring to FIG. 10, it is noted that the vertical color sequence of the horizontal rows of color radiating phosphors is the same in alternate raster lines. Hence, since in interlaced scanning, alternate raster lines are scanned during a particular scanning of the target surface, it is necessary to switch the delivery of the red and green color signals only after each complete scan of each raster of the target surface. One electronic circuit for accomplishing the above noted switching of the delivery of the color signals is shown in FIG. 11. The switching means is electrically coupled between terminals 39 and 41 of television receiver 38 (see FIG. 3) and the electron guns 13 and 14. The switching is accomplished by coupling first and second electronic gates 78 and 79 to receive the red color signal information from terminal 39 of television receiver 38 via input terminal 39'. Third and fourth electronic gates 81 and 82 are coupled to receive the green color signal information from terminal 41 via 41'. Gates 78 and 79 are maintained in opposite conducting states with the output of gate 78 connected via terminal 83 to the control grid 22 of red gun 14 and the output of gate 79 connected via terminal 84 to the control grid 22 of the green gun 13. Similarly, gates 81 and 82 are maintained in opposite conducting states, with gate 82 in the same conducting state as gate 7 8. The outputs of the gates 81 and 82 are connected respectively to terminals 83 and 84.

To control the conducting states of the gates, the output of the first half of a triggered bistable multivibrator 86 is coupled via terminal 87 to the control electrode of gates 78 and 82, for example the control grid of a pentode tube coincidence amplifier. The output of the second half of bistable multivibrator 86 is coupled via terminal 88 to, for example, the control grid of coincidence amplifier gates 79 and 81. Where vacuum tubes are employed in constructing the bistable multivibrator 86, a negative pulse is derived from the vertical retrace signal generated in the vertical synchronizing circuit of the television receiver 38 and coupled simultaneously via terminal 89 to the plate circuits of the multivibrator 86. As in conventional practice, each time a negative pulse appears at the plates of the tubes comprising the multivibrator 86, the conduction state of each tube changes. Hence, the voltage level at the output terminals 87 and 88 will change as will the conduction state of the gates. In this manner the color signal information will be delivered to the proper electron gun assembly during the reproduction of images at the target surface.

While the invention has been described with respect to several specific embodiments thereof, may variations are possible. For example, it should be realized that the vertical sequence of each three rows of the primary color phosphors is unimportant and that any other sequence other than the red, blue and green sequence shown in the figures may be used. The invention is only to be considered limited by the claims.

What is claimed is:

1. An electroluminescent display system for reproducing color images comprising three electron guns for generating three electron beams, each of said electron guns positioned at a different elevation, a display screen disposed to receive said electron beams on a surface thereof comprising three different color radiating materials responsive to electron impingement, each of said different color radiating materials disposed on said surface in separate horizontal rows in a repeating color sequence with adjacent rows of material radiating a different color upon electron bombardment, means for generating a force field for deflecting simultaneously said electron beams horizontally across said surface sequentially at selected different successive vertical elevations, said horizontal rows of color radiating material arranged so that said electron beams coincide individually with three adjacent horizontal rows of color radiating material during each horizontal deflection across said surface, said electron guns being positioned at the vertexes of an equilateral triangle with two of said guns vertically aligned, each horizontal row being defined by a plurality of segments of color radiating material, said segments arranged so that the segments of three adjacent horizontal rows define an equilateral triangle, said segments being rectangular, and vertically aligned, each segment having a height-to-width ratio of 1:1.73, said display screen being substantially flat, and said rectangular segments being separated from their adjacent rectangular segments by zones of light absorbing material.

2. An electroluminescent display system for reproducing color images comprising three electron guns for generating three electron beams, each of said electron guns positioned at a different elevation, a display screen disposed to receive said electron beams on a surface thereof comprising three diiferent color radiating materials responsive to electron impingement, each of said different color radiating materials disposed on said surface in separate horizontal rows in a repeating color sequence with adjacent rows of material radiating a different color upon electron bombardment, means for generating a force field for deflecting simultaneously said electron beams horizontally across said surface sequentially at selected different successive vertical elevations, said horizontal rows of color radiating material arranged so that said electron beams coincide individually with three adjacent horizontal rows of color radiating material during each horizontal deflection across said surface, said electron guns being positioned at the vertexes of an equilateral triangle with two of said guns vertically aligned, said horizontal rows of different color radiating material being arranged in a reversing repeating color sequence, and switching means electrically connected to said vertically aligned electron guns for alternately coupling a first color signal information to the lower and uppermost electron gun and a second color signal information to the upper and lowermost electron gun in synchronism with the each scan of the entire target surface.

3. An electroluminescent display screen for use in a color television picture tube comprising a light pervious sheet defining a regular surface, a plurality of horizontal rows of segments of electron responsive red radiating material, a plurality of horizontal rows of segments of electron responsive blue radiating material and a plurality of horizontal rows of segments of electron responsive green radiating material, said horizontal rows of red, blue and green radiating material disposed vertically on said surface in a repeated color sequence, said segments of material being rectangular and said color sequence being defined by three adjacent horizontal rows, said segments in said horizontal rows being vertically aligned, each segment having a height-to-width ratio of 1:1.73, and said regular surface being substantially flat.

4. The apparatus according to claim 3 further comprising a layer of electron permeable highly reflective conductive material disposed to cover said horizontal rows of material, and wherein said rectangular segments are separated from their adjacent rectangular segments by zones of light absorbing material.

5. In an electron gun assembly including an initial accelerating electrode maintained at a given first voltage and an adjacent final accelerating electrode maintained at a given second voltage higher than said first voltage for accelerating and directing electrons of a beam to impinge a target surface of a given size and being positioned at a given distance from said gun assembly and said beam being scanned over said target surface by a force field, the combination therewith comprising; a dynamic focusing electrode insulatingly interposed between segments of said initial accelerating electrode; a varying voltage generator providing a voltage output which varies, during the scanning of the beam, substantially according to the variation in distance between said gun assembly and said target surface; and means for coupling said varying voltage from said generator to impress same on said dynamic focusing electrode relative to said initial accelerating electrode to focus said electrons of said beam at the target surface.

6. The apparatus according to claim 5 wherein said varying voltage generator provides a voltage output which varies substantially according to the equation where V is the instantaneous voltage in volts provided by said generator, D is the distance in inches to the furthest point on the target surface measured from the centric of said target surface, d is the instantaneous position in inches of the beam at said target surface measured relative to its centric point during the scanning of said beam, and V is the voltage in volts required to be impressed on said dynamic focusing electrode relative to said initial accelerating electrode to focus said electrons of said beam at point D.

7. A color television system comprising a picture tube employing three electron gun assemblies positioned at different vertical elevations and each of which includes an initial accelerating electrode maintained at a given first voltage and an adjacent final accelerating electrode maintained at a given second voltage higher than said first voltage for accelerating and directing electrons of a beam to impinge a target surface of a given size positioned at a given distance from said gun assemblies; means for pro viding a force field for scanning-together the beams from said guns over said target surface; said means deflecting said beams over said target surface in sequence at selected different successive vertical elevations; a dynamic focusing electrode insulatingly interposed between segments of said accelerating electrode of each of said gun assemblies; a varying voltage generator providing a voltage output which varies, during the scanning of the beam, substantially according to the variation in distance between said gun assembly and said target surface; means for coupling said varying voltage from said generator to impress same on the dynamic focusing electrode relative to their respective associated initial accelerating electrodes to focus electrons of said beam at the target surface; said target surface comprising three different color radiating materials responsive to electron impingement, each of said different color radiating materials disposed on said surface in separate horizontal rows in a repeating color sequence with adjacent rows of material radiating a different color upon electron bombardment, said horizontal rows of color radiating material arranged so that said electron beams coincide individually with three adjacent horizontal rows of color radiating material during each horizontal deflection across said surface.

References Cited UNITED STATES PATENTS 2,792,521 5/1957 Sziklai et a1. 3l5l3 X 3,018,405 1/1962 Oxenham 31392 X 3,028,521 4/1962 Szegho 31513 RICHARD A. FARLEY, Primary Examiner.

M. F. HUBLER, Assistant Examiner.

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