US2751516A - Polychrome cathode ray tube - Google Patents

Description

June 19, 1956 E. o. LAWRENCE 2,751,516

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June 19, 1956 E. o. LAWRENCE 2,751,516

POLYCHROME CATHODE RAY TUBE Filed April 25, 1950 3 Sheets-Sheet 3 a INVENTOR.

ERNEST LAWRENCE A T TORNE Y5.

.tion which follows, taken in connection with United States Patent POLYCHROME CATHODE RAY TUBE Ernest 0. Lawrence, Berkeley, Calif., assignor, by mesne assignments, to Chromatic Television Laboratories, Inc.',- New York, N. Y., a corporation of California Application April 25,1950, Serial No. 157,943

Claims. (Cl. 313-92) This invention relates to cathode ray display tubes wherein the color excited on a luminescent screen or target by the beam of cathode rays may be changed at will. Primarily the invention is intended for the direct display, on a cathode ray screen, of color television pictures transmitted by any of the sequential additive systems which have so far been proposed; i. e., the invention is intended for the display of television pictures of either field-sequential, line-sequential, or dot-sequential types.

The invention here considered is a development of and an improvement on the polychrome cathode ray tube described in this applicants prior application, Serial No. 150,732, filed March 20, 1950, now Patent No. 2,739,260.

.Among the objects of the invention are to provide a polyreasonably low power; and to provide a tube which is, as

has already .been mentioned, applicable to any type of sequential transmission which has thus far been proposed.

Other objects and advantages of the invention will be disclosed or will become apparentin the detailed descripthe accompanying drawings wherein:

Fig. 1 is-a diagrammatic view, largely in block form, .of the tubeof this invention with its accompanying control circuits;

Fig. 2 is an axial sectional view of the display end of the tube diagrammatically illustrated in Fig. 1, showing ,(not to scale the construction of one form of the viewing screen and the control or localizing electrodes for determining .thecolor displayed;

.Fig. 3 is a transverse sectional view of a portion of the tube,,the plane of section being indicated by the lines 3.,j3 in Fig. 2;

.Fig. 4 is a greatly enlarged view, in section, of a portion of the display screen as shown in Fig. 2 and the accompanying controlelectrodes;

Fig. 5 shows amodified type of screen with its control electrodes and a mask for determining the path of the .beamas it impinges upon the screen;

Fig. .6 is a fragmentary section illustrating a further modification of thegeneral type of screen shown in Fig. 5;

Fig. 7 shows a still further modification of screen, control electrodes and mask, the entire structure in this instance beingsupported upon the screen itself;

Fig. 8 is a diagram of ray paths indicating the mechanism of control; and

Fig. .9 is another ray path diagram, indicating the efiects that can be produced by'variation of the potentials upon the control electrodes.

Considered broadly the tube according to the invention comprises the usual evacuated envelope containing an electron gun comprising an electron emitting cathode, a grid or control electrode for modulating the beam of cathode rays developed by the cathode, and one or more anodes for accelerating the electrons. The essenceof the invention lies in the combination of a specific :type of luminescent target against which the beam of rays impinges, means for restricting the paths of the electrons constituting the beam to sub-areas on the target of less than picture element size, and an electrode structure ,for directing the electrons to sub-areas of the target which luminesce in diiferent colors. The target screen isformed of glass or other light transmitting material which will withstand the bombardment of the cathode rays without disintegration and may form the end wall of the tube but it also may be a separate structure mounted within the tube, both of these constructions being well known in the art. The screen is formed with a large number of indentations or recesses, preferably in the form of fine grooves extending linearly across it, the width of each groove being as small as or smaller than the dimension of the elementary areas to be reproduced by the system. Within these indentations there are deposited phosphors ,of a plurality of different kinds, each luminescing in one of the primary colors of an additive color system. In congreen and blue, one of the phosphors, say that fluorescing in green, will be deposited at the bottom of the recess, a second phosphor, which may be the red, occupies anintermediate position on both sides of the recess while the third phosphor, in this case the blue, is positioned adjacent the opening of the recess. Placed on the side of the target facing the electron gun is the means for restricting the electron flow to areas corresponding to the width of the various phosphors which may be a mask comprising alternate portions which are permeable and impermeable, respectively, to electrons. The mask may be integral with the target itself, being formed by the ends .of-the walls between the recesses, or it may be a separate structure; the requirement for its positioning is that the electron permeable portions, .which are preferably openings but which might be Lenard windows of thin foil, are positioned in alinement between the bottoms of the recesses and the virtual source of the cathode ray beam as it approaches the particular portion of the target under consideration, so that any electrons entering the recesses through these electron permeable portions will be so collimated as to fall upon the portions of the phosphor .deposited at the bottom of the recess when the beam is deflected across the screen in the course of normal television scanning. As an alternative to the mask, however, focusing electrodes may be used. There is also provided a series of color control or electron localizing electrodes which comprise thin conductive strips disposed in planes parallel to the paths of the rays between the electron gun and the screen, each of these strips being insu-lated from its next adjacent strip but connected to others of the series, alternate strips being preferably connected together, although other arrangements are possible. The separation of the strips is not critical, buttheir thickness should be small in comparison with the width of the apertures or electron permeable portions of the 1 3 mask-and their width should be equal to orgreater than their separation in order to achieve maximum ease of control of the electron beam. Control of the color displayedby the screen is achieved bylthe potentials applied between adjacent strips forming the localizing electrodes.

When such strips are at the same potential electrons en- -tering between them and passing through the collimating slits in the mask will impinge upon the phosphor at the bottom of the recesses. applied between adjacent control electrodes the beam will When a moderate potential is be deflected so that the electrons entering the slits enter the recesses at an angle and excite the phosphor deposited part way up its walls, while a higher potential w1ll cause 'the electrons to enter the recess at a greater angle and thus excite the phosphor lying adjacent the openings of the recesses.

1n the preferred form, with alternate control electrodes of opposite polarity, the electrons entering on opposite from anantenna 3. Associated with the receiver is a power supply 5, and a scanning oscillator 7 for exciting horizontal deflecting coils 9 and vertical deflecting coils .11, all of conventional type. These devices supply, in the usual manner, the cathode ray tube generally designated by the reference character 13, which includes an evacuated envelope and an electron gun having a cathode 17, a control electrode 19 for modulating the beam, and one or more anodes for focusing and accelerating the beam which are symbolized by the elements 21 and 23. None of this is shown in detail since all of the parts thus far referred to may be of purely conventional character.

At the distal end of the tube, opposite the electron gun, is target 25 which is indicated in purely conventional form in Fig. l, is shown in more detail in Fig. 2, and is best illustrated in the large scale figure of Fig. 4. As may be seen in the latter figure the target, preferably formed of glass, is provided with a large number of parallel grooves .27, which extend entirely across it. As shown in the figures which have been referred to, these recesses are separated by walls 29 having flat end surfaces 31, The sides .of these walls converge toward the virtual source of the .electron beam (Fig. 2) so that electrons passing directly from the gun to the screen, if deflected only by thecoils 9 and 11, will either strike directly upon the end faces .31.of the walls 29 or upon the bottom of the grooves,

practicallynone hitting the sides of the latter. Although here shown with rounded bottoms this is by no means an essential feature of the invention; the target will conveniently take this form if the recesses are rolled into the glass when it is in a plastic state, the target thus being a unitary structure. It may, however, be made of alternate wider and narrower strips, laid together. asindicated by the dotted lines 33 in the lower portion of Fig. 4, in which case the bottoms could be either rounded or flat.

Deposited in each recess is a phosphor coating 35. Th

granules or particles of phosphor forming such a coating are usually so fine as to form an almost impalpable dust. In. order to show the disposition of the coating, however, it 'is indicated by small circles, triangles, and squares which represent, symbolically, phosphors .luminescing respectively in green, red, and blue. It will be seen that in this case the green phosphor occupies the complete area of the bottom of the recess. Immediately adjacent the green'phosphor, and on each side of the recess is a strip of red phosphor while above it, adjacent the top of the recess the blue phosphor 35" is deposited;

In front of the target, i. e., between it and the cathode ray gun, there is disposed a grid of control or localizing electrodes 37. These electrodes may be mounted in a frame comprising insulating support members 38, which may be of glass into which the ends of control electrodes 37 are fused. The whole structure is preferably stiffened by combs 40 of thin mica between the teeth of which the electrodes 37 are fitted. The planes of the combs converge toward the virtual source of the beam. As is shown in Fig. 3 the control electrodes are connected alternately to supply and support leads 44 which extend out through the wall of the tube and connect to an oscillator 42 which, by applying suitable potentials to the localizing electrodes determines the color to be displayed by the tube.

The size of the entire structure as well as its details depends upon both the size of the tube as a whole, determining the size of the image which it is desired to produce, and upon the detail with which the image is to be depicted. The maximum separation of the recesses, center to center, should be as small as the elementary areas of the picture which the tube is to show, and they may, with advantage, be made smaller so that the electron beam as it strikes the target will always enter at least two recesses.

In the case of the target thus described collimation of the portion of the beam entering the recesses is achieved by the walls between them, the ends 31 of these walls serving as a mask and the openings between the two Walls of each recess forming the electron permeable portion of the mask. When the electrons enter the recesses under these conditions they will strike only the bottoms of the recesses and, in the case given, excite only the green phosphors. This is indicated by the dashed lines 39 in Fig. 4. Few if any of the electrons will strike either the red or the blue phosphors and the result will be the emission of green light only. If, now, a potential is imposed between the adjacent localizing electrodes 37, say a positive potential on the central one shown in Fig. 4 and a negative potential upon the two adjacent electrodes, the beam will be subjected to an additional deflection superimposed upon that imparted by the deflection coils 9 and 11. If a medium potential is imposed between the electrodes the beam will strike part way up the walls of the recesses and excite the red phosphor, while if a still greater potential is applied the electrons will pass in the direction indicated by the dotted lines 39' and impinge upon the blue phosphor.

It is known that the sensitivity of the eye to detail is largely concentrated in its response to green light. It is for this reason that the green phosphor is deposited at the bottom of the recesses, since the light from these portions passes in a' direct path through the glass with little scattering. The light from the red phosphor, part way up the side wall of the recesses,'is more difiused, some reach ing the eye in a direct path through the glass and. into the air while some reaches it after total reflections within the walls 29. The light from the blue phosphor in ,par ticular may be subjected to more than one total reflection within the walls 29. Total reflection of this character is a highly efiicient process, and little light is lost where it occurs. This is highly important and contributes materially to the efiiciency of the device. i j

It is not always possible to obtain phosphors which emit light of the most desirable primary colors, satisfactory reds being the mostditfi'cult to obtain. Where this is the case the color viewed from the screen side of the target can be corrected by interposing a filter 46, a ruby coating for example, between the phosphor and the glass.

A modification of the structure shown in Fig. 4 is illustrated in .Fig; 5. In this case the recesses and their intermediate walls are each of triangular cross-section as illustrated on thescreen 25a. In this case, however, the ends of the walls 290 between the recesses are not capable of serving as the electron impermeable portions of a mask, but a separate mask comprising parallel strips 41 is provided. The apertures or electron permeable portions 41 are disposed so that, in the absence of deflecting potentials on the control electrodes 37a, electrons entering them will, as before, fall only upon the green phosphor at the bottoms of the recesses. Selection by the potentials applied between the control electrodes has the same eflect as before, the color displayed by the screen depending not upon the direction of this control deflection but upon its magnitude. Total reflection, within the walls between the recesses also occurs here, and contributes to luminous efiiciency.

A further modification of the type of target shown in Fig. is indicated in Fig. 6, wherein the electron impermeable elements of the mask 41b are formed integrally with the walls 2% between the recesses. The target shown in Fig. 6 is diflicult to make and its use in practice is not at present contemplated for ordinary sized tubes, but for very large sizes it may have some advantages and it is shown for completeness.

Still another modification of the type of target shown in Fig. 5 is indicated by Fig. 7. In this case the localizing electrodes 37c are fused into the apices of the recess wails 29c, each carrying, at the end remote from the screen, an element 41c of the collimating mask, which also acts as a stiffener for the electrodes. In this. case the electrons are subjected to the color controlling fields after passing through the mask instead of before, but the ultimate effect is the same.

The use of a mask for localizing the electrons may be avoided and the efiiciency of the tube raised still further by substituting a form of electron lens for the collimating slits, as is shown by the structures illustrated in Figs. 8 and 9. Here the target and localizing electrodes are substantially as shown in Fig. 7, but interposed between each pair of localizing electrodes 37c are one or more focusing electrodes 45, which in operation are biased positively with respect to the localizing electrodes. The effect is to deflect the portions of the beam entering between the localizing and focusing electrodes toward the latter, while portions entering between two focusing electrodes are unaffected by the bias. The result is that nearly all of the electrons constituting the beam are concentrated on an area small enough to excite only one phosphor. Deflection due to the change of potential on the localizing electrodes is superposed on that due to the bias, swinging the concentrated beam electrons from one phosphor to the other as before. The focusing electrodes will intercept a portion of the beam, but the part intercepted is much smaller than that cut off by the mask. Construction is somewhat more difficult, but still quite practical, especially in tubes of the larger sizes. The method of supporting the focusing electrodes is the same as that of the localizing electrodes.

It should be apparent that with the tube of this invention the color controlling potentials may be applied at any desired frequency so as to give, at will, frame, line, or dot sequence, and the dot-sequence can be of the type described in the application Serial No. 150,731, filed March 20, 1950, now Patent No. 2,705,257, jointly by Mack, Aiken and this applicant, or by any other type of sequence desired.

The sequence used will determine both the frequency and the wave form supplied by oscillator 42 to control the color displayed by the tube as well as any permanent bias superposed on such wave form. If no bias is applied, the localizing electrodes swinging alternately positive and negative in equal amounts, the color cycle with the device as shown will be blue-red-green-red-blue in each half cycle of the oscillator, the electrons covering all portions of the groove walls. A bias equal to the peak oscillating voltage will center the beam on the bottom of the groove at one peak of the swing and on the blue at the other peak, resulting in a sequence green-redblue-rcd-green for a complete cycle, resulting in a much slower sampling rate relative to the rate of oscillation.

This latter would result in exactly thecycle described in the joint application mentioned above provided the normally used, and in this case the circuitry is simplified by the use of a bias.

The size of the deflecting electrodes, i. e., the absolute value of either their width or thickness, is not of primary importance to this invention. With a given relation between widths of the strips forming these electrodes and their separation a given voltage will result in a given angular deflection and hence the generation of a specified color irrespective of the absolute size of the parts, assuming, always, that the beams which the electrodes are called upon to deflect are of equal velocity. The strips of which the electrodes are formed should be as thin as possible, and this rather dictates that their width should be small and that they be placed fairly close together since under these circumstances misalinements with the paths of the beam will have minimum efiect in the proportion of the beam intercepted. Narrowing the electrodes with respect to their separation requires additional voltage to produce equal deflection.

As is the case with the tube described in above identified application Serial No. 150,732, the direction of the scanning deflections is not of particular importance. Scanning may be accomplished along the grooves constituting the recesses, transverse thereto, or diagonally. Scanning nearly but not quite along the grooves may result in the formation of undesired patterns, and hence transverse scanning is to be preferred, but in any case that the proper control potentials are applied the picture will appear in its proper colors, irrespective either of direction of deflection or of sequence, as the deflection may be transverse to the grooves with line sequence or along the grooves with dot sequence without ill effect on the picture.

It is known that other tubes have been proposed wherein masks having certain areas permeable to electrons have been used to locate the impinging cathode ray beam upon different phosphor areas. All of such tubes of which applicant is aware have relied on accurate alinement of collimating apertures with luminescent areas in all dimensions. They consequently require a degree of masking which absorbs a major portion of the electron beam. There is accordingly a resultant large loss of luminosity.

Other proposed tubes, because of the disposition of the phosphors, have resulted in loss of light for other reasons. The tube of this invention, even in its least efiicient embodiments from the luminosity point of view, would waste at a maximum only half of the potentially developed light because of masking of the beam. In its most efficient embodiments the tube of the present invention wastes considerably less light from this cause. The less eficient tube forms are the easier to construct, but even those of highest efiiciency do not require the accuracy of alinement that is necessary with prior devices.

After the light is produced in the instant invention it is used with high efliciency. Where the recesses are triangular in cross-section the light produced from the bottoms of the grooves is utilized directly, while most of that from adjacent the tops of the intervening walls strikes the opposite surface at such an angle as naturally to be totally reflected, and this occurs to a somewhat lesser extent with all types of recess.

In accordance with present tube manufacturing practice a thin coating of aluminum is frequently deposited over the phosphor coating of monochrome tubes. Such coating, by reflection, nearly doubles the light visible from the screen side of the target. In the tube here described such a coating will normally be used, and if it be applied to the end faces 31 of the recess walls of targets of the type shown in Fig. 4 will prevent the escape of light back 7 into the tube and reflect it through the screen, rendering this type practically as efficient as the others.

What is claimed is:

1. A target for receiving an electron beam comprising a recessed foundation having an electron-sensitive target surface, an electrode assembly having a plurality of oppositely located plate-like electrode elements mounted with one end adjacent to the target surface to define the outer boundary of an electron-beam path which terminates upon the said target surface, and electrode means disposed adjacent to the opposite ends of said plate-like electrode elements for limiting the diameter of any entering electron beam to a dimension smaller than that of the space between said outer boundary of said path.

2. The electrode arrangement claimed in claim 1 wherein the plate-like electrode and the electron beam limiting components are integral.

3. A target for receiving an electron beam comprising a recessed foundation having an electron-sensitive target surface, an electrode assembly having a plurality of substantially parallelly positioned plate-like electrode elements mounted with one end adjacent to the target surface to define the outer boundary of an electron-beam path which terminates upon the said target surface, and electrode means disposed adjacent to the opposite ends of said plate-like electrode elements for limiting the diameter of any entering electron beam to a dimension smaller than that of the space between said outer boundary of said path.

4. A target electrode for an electron-beam tube comprising a foundation member having an electron-sensitive target surface area and a plurality of elongated T-shaped electrodes mounted in register with said target area with the cross arms of the Ts extending substantially transverse to the path along which electrons are adapted to move to reach the target area to provide restricted openings by the spaces between their upstanding arms.

5. The invention set forth in claim 4 and wherein said foundation member is provided with a plurality of grooves in which the lower edges of said T-shaped electrodes are respectively seated.

References Cited in the file of this patent UNITED STATES PATENTS 2,307,188 Bedford Ian. 5, 1943 2,446,791 Schroeder Aug. 10, 1948 2,461,515 Bronwell Feb. 15, 1949 2,480,848 Geer Sept. 6, 1949 2,481,839 Goldsmith Sept. 13, 1949 2,498,705 Parker Feb. 28, 1950 2,518,200 Sziklai et a1. Aug. 8, 1950 2,529,485 Chew Nov. 14, 1950 2,532,511 Okolicsanyi Dec. 5, 1950 FOREIGN PATENTS 443,896 Great Britain Mar. 10, 1936 866,065 France Mar. 31, 1941

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