US2825845A - Cathode ray tube for reproducing color television images - Google Patents

Description

March 4, 1958 JONKER ET AL 2,825,845

CATHODE RAY TUBE FOR REPRODUCING COLOR TELEVISION IMAGES Filed April 1, 1955 2 Shets-Sheet 1 SOURCE OF sleuAL SOURCE OF SIGNALS OF BANDWIDTH A S N RR I wm TKO 6 NNN H 9 mm A m A H w & T J v m w W D N A B Y F B o A w AA H T W F w N M. WF 80 3 6 March 1958 J. L. H. JONKER ET AL 2,825,345

CATHODE RAY TUBE FOR REPRODUCING COLOR TELEVISION IMAGES Filed April 1, 1955 2 SheetsSheet 2 INVENTOR JOHAN LODEWIJK HENDRIX JONKER 55.5 JAN CAREL FRANCKEN BY fl fiW AGENT luminesce in diflerent colors. stances or phosphors are arranged in a predetermined 2,825,845 CATHODE RAY TUBE FOR REPRODUCING COLOR TELEVISION IMAGES Johan Lodewijk Hendrik .lonker and Jan Carel Francken,

Eindhoven, Netherlands, assignors, by mesne assignments, to North American Philips Company, Inc., New

York, N. Y., a corporation of Delaware Application April 1, 1955, Serial No. 498,676

Claims priority, application Netherlands April 3, 1954 16 Claims. (Cl. 315-13) The invention relates to cathode-ray tubes and systems for reproducing color television images and, in particular, to cathode-ray tubes of the multi-gun type.

One popular cathode-ray tube of the foregoing type comprises three electron guns by means of which three concentrated electron beams can be directed to an image screen containing three luminescent substances which The luminescent submanner, and during operation of the tube are each excited by a beam of only one electron gun. An input signal is supplied to the control grid of each electron gun, .which comprises at least a cathode, a control grid, and

an anode constituting a first lens, and a second concentrating or focussing electron lens. It has been found that it is not necessary for the three guns to have applied thereto input signals of the same bandwidth, since in order to obtain a satisfactory image it is sufiicient for a signal having larger bandwidth to be supplied to only one of the guns, which gun then determines the definition of the image.

In most systems in present use, three primary colorsred, green and blueare used, and

for visual observation it has been found to be preferable for the definition to be determined by means of the green image. This is easy to understand since the human eye has the highest resolving power in the green part of the spectrum. However, if desired, the definition might just as conveniently be determined by one of the other colors. Although not described, it is obvious that what has been mentioned hereinbefore with respect to the bandwidth also applies if use is made of only two or of more than three electron guns and of a corresponding number of primary colors.

The use of ditierent bandwidths was discovered in an efifort to produce a composite color television signal which would not occupy an excessive total bandwidth, and which, preferably, would not be larger than the signal used for black-and-white television. However, the insight gained as a result of these efforts has so far not influenced the construction of cathode-ray tubes for use in color television. Normal tubes containing three identical guns are still used, each gun of which consequently produces picture elements of identical size on the image screen.

In accordance with the invention, a new construction of the electrode system of such cathode-ray tubes is provided to utilize the color television signal and its special bandwidth properties. Thus, the cathode-ray tube according to the invention, comprising an image screen and at least two electron guns, each of which comprises at least a cathode, a control-grid, an anode and a second concentrating electron lens, is characterized by a gun structure in which the gun to which the signal having the largest bandwidth is supplied exhibits a ratio between the relative spacing of the second electron lens and the image screen and the relative spacing of the second lens and the cross-over point which is less than the same ratio in the other electron guns. In its simplest embodiment,

the second electron lens of the gun to which the largest bandwidth signal is applied is closer to the image screen than are the second electron lenses of the other-guns.

2,825,845 Patented Mar. 4, 1958 ice The term relative spacing of the electron lens and theimage screen and the term relative spacing of the electron lens and the cross-over as used herein are to be understood to means the distance between the image screen or the cross-over, respectively, and the infinitely thin lens which would have the same effect as the said second electron lens. As is well-known, the cross-over" is the constriction of the beam produced in the proximity of the control grid, which usually is a diaphragm having a small aperture.

The invention is based upon the fact that the size of the picture elements on the image screen decreases with a decrease in the ratio between the relative spacing of the second electron lens and the image screen and the relative spacing of the lens and the beam node or cross-over. Consequently, the gun to which the signal having the largest bandwidth is supplied in a tube in accordance with the invention and thus having the smallest ratio, will produce the smallest picture elements on the image screen. As indicated hereinbefore, the colorproducing-component of the screen excited by this gun preferably produces a green image. The size of these picture elements and consequently the absolute values of the two spacings are made such that the image has the required definition. With respect to the other guns, one distance or both distances are made difierent with the result that certain structural advantages are obtained, as will be set out more fully hereinafter.

In one embodiment, the distances by which the second electron lenses and the image screen are spaced apart can be made equal ,for all the guns, so that the distance by which the electron lens and the cross-over are spaced apart is smaller for the guns to which the signals having the smaller bandwidth are supplied than for the gun having the signal of larger bandwidth supplied to it. Thus, the length of these guns will be reduced with a resultant considerable saving in material, while more space will become available in the cathode-ray tube.

As an alternative, the second electron lenses of the various guns may be arranged so as to be spaced away from the image screen by various distances. This results in a particular structural advantage. Whether the electron lenses operate electrostatically or electromagnetically, they substantially always comprise components the diameter of which exceeds that of their anodes. Since the distance by which they are spaced away from the image screen is different, the axes of the electron guns can, it the differences are properly chosen, be arranged in closer proximity to each other than if the electron lenses were equidistant from the image screen and the broad parts of the lenses were arranged side by side. Consequently, in this embodiment of a cathode-ray tube in accordance with the invention, the projections of the components of the electron lenses of the various guns onto a plane at right angles to the tube axis will partially overlap. It will be obvious that due to this arrangement, a considerable saving in space is obtained, and the neck of the tube in which the guns are arranged can be made narrower.

In the last-mentioned construction comprising staggered electron lenses, the object distance and consequently the length of the gun can be varied subject to the condition that in the gun to which the signal having the largest bandwidth is supplied, the ratio between the image distance and the object distance is less than the corresponding ratio of the other guns.

A very simple construction of a tube containing three guns is obtained if the axes of the guns are parallel and the second electron lens of the central gun is nearer the image screen. Thus, the lengths of the two outer guns may be made equal, and the central gun maybe made such that the cathodes of they three guns are equidistant from the image screen. However, as an alternative, the lengths of the three guns might be made equal, since in {this case due to the smaller image distance of the lens ,of the central gun, :the requirement is fulfilled that this gun has the. smallest-magnification. For mass production, it may be advantageous to manufacture only one type of :edges of aright equilateraluprism. In certain cases, the axes of the guns will preferably be arranged at an angle toeach other such that the electron beams meet in-a point at the image screen. In .this event, no additional fields are required to converge the initially-parallel electron .heams.

The invention will now be described more fully with reference to the accompanying drawing, in which:

Fig. 1 shows diagrammatically the construction of one form of cathode-raytube according to the inventioncomprising threeelectron guns, the axes of which are parallel .and lie in .one plane;

Fig. 2. shows the neck of another form of cathode-ray tube in accordance with the invention comprising three electron guns arranged at an angle to each other such ,that their axes meet in a point at the image screen;

Fig. v3 shows the neck ofstill another form of cathoderay tube in accordance with the invention comprising ethreeelectron guns, theaxes of which form the edges of a right equilateral prism;

.Fig. 4 is a side view .of a tube shown in Fig. "3;

'Fig. 5 shows the neck of another form of cathoderay tube in accordance with the invention comprising three electron guns the axes of which are parallel andlie ,in one plane, the lengths of the electron guns varying from one gun ,to another.

Referring to Fig. 31, the cathode-ray tube shown consists of ;a cylindrical neck' portion 1 and a mating conical part 2 closed off by a transparent window 3. This window supports an electron-receiving, luminescent or fluorescent screen 4, ,In the-neckl of .theatube, three electron guns are arranged, in which .the two outer electron guns are identical. Therefore only one of these guns will be provided with reference numerals. These two guns comprise a cathode 5,.a diaphragm 6 acting as a control-grid, an'accelerating orfirstanode 7, another-anode 8, .an additional electrode 59 and a final electrode '10. Due to the cooperation .of .the electrodes 5, .6 and .7, which serve as an immersion .or first lens, a cross-over is produced approximately in the aperture of passage of the electrode 6. This crossover, which constitutes an optical object, is projected to form an image .on the luminescent screen 4 by means of the second electron lens consisting of the electrodes 8, 9 and :10. The electrodes 8, 9 and 10 constitute a so-called unipotential lens, since the electrodes Sand 10 are directly interconnected electrically and are thus at the same potential. The electrode 9 has a potential applied to it which is lower than thepotentia-l applied to the electrodes 3 and It). The central electron gun comprises a cathode 14,2. control electrode 15, an accelerating or first anode 16, which constitute the immersion lens, .and another anode 17, an additional electrode 18 and a final electrode 19. As may be seen from the drawing, the unipotential lens constituted by the electrodes 17, 18 and 1 9 is arranged nearer the image screen 5%. Consequently, for this lens, the ratio between the distan in h chis s a e qm h ho c h ima scr en 4 a d th istance b wh it i a d t ots th crossover produced approximately in the aperture of the di ph m .1 s e than he r ondin ti f t lenses of the two remaining electron guns. Thus, the cenneck of the kind 4 tral gun is the gun to which during operation the signals having the largest bandwidth are supplied. This is illustrated in Fig. 1 by showing three signal sources 61, 62 and 63 coupled each to the control electrode of one of the three guns. The sources 61 and 62, which are coupled to the outer two guns, produce color signals of smaller bandwidth A for driving the outer two guns. The third source 63, which produces a color signal of larger bandwidth A-l-AA, is coupled to the center gun whose ratio of second lens to screen distance and second lens to crossover distance is smaller than the corresponding ratio for the outer'two guns. The three electron beams are deflected with theaid of deflector coils 20 and 21 and of two additional coils ensuring the deflection in the plane of thedr-awing (not shown). Between the electron guns and the ,deflector .coils a field is produced such that-the electron beams meet in a point 12 .of the image screen 4. 'For'the sakeof clearness, this field which is not important for an'u'nderstanding of the invention is not shown. "However, many constructions of electrode systems which operate electromagnetically and/or electrostaticallyhave been described for bringing together the three electron beams. As will be seen from the drawing,

the two outer guns are considerably'shorter than the central electron gun. Compared with a tube of known construction, it should .be noted that the length of the centralelectron gun is the same as the guns proposed for 'these known tubes. However, the outer guns are considerably shorter than the corresponding guns of these known .tubes.

In Fig. 2 la modification is shown in which a neck 22 of a tube contains three electron guns arranged at an angle to each other such that their axes meet in a point of the image screen (not shown). Only the anodes and the ,unipotential second lenses of these guns are shown. As will be seen from the drawing, the three lenses of the guns comprise the additional electrodes 23, 24 and 25, the widths of which considerably exceed that of the anodes 26, 27 and 28. Since the lens of the central gun is arranged nearer the image screen, the outer electron guns may be arranged such that the projections of the electrodes 23, 24 and 25 on to a plane at right angles to the tubes axis 2929 overlap each other. This results in a considerable saving in space, since otherwise the width of the neck should be equal to the sum of the diameters of the electrodes 23, 24 and 25. In this construction, the electron lenses of the two outer guns are equidistant from the image screen. However, this is not necessary and may even be impossible, as will be set out with reference to Fig. 3.

Fig. 3 shows a further modification comprising three electron guns the axes of which constitute the edges of a right equilateral prism. In this case also, the electron .beams are deflected, similarly to those in the embodiment shown in Fig. 1, 'bymeans of a special field so that they meet ina point of the collecting screen. In this embodiment, the electron guns shown diagrammatically by rectangles 30, 31 and 32 are accommodated in separate tubes 33, 34 and 35. The second electron lenses operate electromagneticallyand consist of'coils 36, 37 and 38. The electron gun 3t) and the coil 36 constitute the system to which the signal having the largest bandwidth is supplied. As may be seen more clearly from the side elevation shown in Fig. 4, the axes of the electron guns form the edges of a right equilateral prism and are arranged in closer proximity to each other than the sum of the radii of the circumferences of the coils, which is possible .by means of the fact that the coils are staggered in the direction of their length. In Fig. 4, which is a projection on to :a plane at right angles to the tube axis, the coils therefore partially overlap. Such an arrangement can also be used if use is made of electrostatic focussing by means of widened cylinders, as is shown in Fig. 2. In Fig. 3, the image screen 4 (not shown) is to the left of the figure.

Fig. 5 shows the neck of a further cathode-ray tube in accordance with the invention comprising three electron guns the lenses of which are of different construction. The axes of the guns are parallel and lie in one plane and the lengths of the guns are difierent similarly to the embodiment shown in Fig. 1. The second electron lenses of the outer guns consist of electrodes 39, 40 and 41, and 42, 43 and 44, respectively. The second electron lens of the central gun comprises electrodes 45, 46 and 47. As will be seen, the width of the electrode 46 exceeds that of the anode 45 of the central gun. This results in a better lens. However, since the lenses are arranged so as to be staggered, the axes of the guns may be nearer each other than the sum of the radii of the electrodes 41 and 46 or 44 and 46 respectively. In this embodiment, additional deflector electrodes 48 and 49 and 50 and 51, respectively, for the outer guns are arranged at the level of the second electron lens of the central gun. With the aid of these sets of deflector electrodes, the two outer electron beams can be converged to the point at which the central electron beam strikes the image screen. By the use of the invention, a very compact construction of the electrode system is obtained, as may be seen from the drawing.

Although the figures only show electron guns comprising an accelerating anode, this does not mean that this acceleration anode forms an essential part of a tube in accordance with the invention. Use may be made without further expedients of a so-called triode gun, or a greater number of electrodes may, for example, be arranged between the anode and the cathode. When in describing the invention second electron lenses have been referred to, only those lenses are meant which are produced between the anode and the deflecting field, but not the electron lens produced between the anode and the accelerating anode.

The description of one specific embodiment similar to that shown in Fig. 1 will illustrate the invention. In that embodiment the crossover was formed approximately at the aperture in the control grids 6 and 15. The thin lens constituted by electrodes 8, 9 and 10 of the outer guns was spaced about 60 mms. from the crossover, and about 497 mms. from the screen 4. Therefore, the ratio was 60 The thin lens constituted by electrodes 17, 18 and 19 was spaced about 87 mms. from the crossover, and about 470 mms. from the screen. Thus, its ratio of image to object distance was which, of course, is smaller than the ratios for the outer While we have described our invention in connection with specific embodiments and applications, other modifications thereof will be readily apparent to those skilled in this art without departing from the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. A system for reproducing color television images comprising a cathode-ray tube, said tube including an electron-receiving screen and a plurality of electron guns, each of said guns including a cathode, a control grid and an anode and producing an electron beam having a crossover point, and a plurality of second electron lenses each associated with one of said electron guns, the second lens associated with one of said guns being positioned so that said one gun exhibits a smaller ratio of lens to screen distance and lens to crossover distance than that exhibited by the other guns, a source of color signals including at least two separate signals of which one has a larger bandwidth than the other, and means for applying the signal of larger bandwidth to said one gun.

2. A system for reproducing color television images comprising a cathode-ray tube, said tube including an electron-receiving screen and a plurality of electron guns, each of said guns including a cathode, a control grid and an anode and producing an electron beam having a crossover point, and a plurality of second electron lenses each associated with one of said electron guns, the second lens associated with one of said guns being closer to the electron-receiving screen than the second lenses of the other guns so that said one gun exhibits a smaller ratio of lens to screen distance and lens to crossover distance than that exhibited by the other guns, a source of color signals including at least two separate signals of which one has a larger bandwidth than the other, and means for applying the signal of larger bandwith to said one gun.

3. A system as set forth in claim 2 wherein the distance between the crossover and the electron-receiving screen is the same for all the guns.

4. A system as set forth in claim 1 wherein the second electron lenses for all the guns are spaced the same distance from the electron-receiving screen.

5. A system as set forth in claim 1 wherein the second electron lenses are unipotential lenses.

6. A system as set forth in claim 1 wherein the second electron lenses each contain one electrode whose diameter is greater than another of its electrodes, said one electrode having a diameter at which a projection thereof on to a plane at right angles to the tube axis will produce partially overlapped images.

7. A system as set forth in claim 1 wherein three guns are provided having parallel axes and all lying in the same plane, the second lens of the central gun being closer to the electron receiving screen than the second lenses of the outer guns, the latter two guns being spaced the same distance from the image screen.

8. A system for reproducing color television images comprising a cathode-ray tube, said tube including a fluorescent screen containing a plurality of color-producing-components and a plurality ofi electron guns each producing an electron beam adapted to cooperate with one of said color-producing-components of said fluorescent screen, each of said guns including a first immersion lens producing a crossover point of said electron beam and a second electron lens adapted to project said crossover point onto said fluorescent screen, the ratio of the spacings between said second lens and said screen and said second lens and said crossover point for one of said guns being smaller than the corresponding ratio for the other guns, a source of color signals including a signal of larger bandwidth and another signal of smaller bandwidth, and means coupling said signal of larger bandwidth to said one gun and said signal of smaller bandwidth to another of said guns.

9. A system as set forth in claim 8 wherein said second lens is a unipotential lens, and the color-producingcomponent of said screen cooperating with said one gun produces green.

10. A cathode-ray tube for reproducing color television images comprising an image screen having difierent, color-producing, electron-responsive areas, at least two electron guns each including an electron lens for producing two electron beams directed at the screen, the lenses of the two guns having difierent ratios of image-to object spacings with respect to the whole of the screen, said guns producing differently-sized picture elements over said screen, and means for coupling to said guns color signals possessing different bandwidth characteristics.

References Cited in the file of this patent UNITED STATES PATENTS 2,459,790 Busignies Jan. 25, 1949 2,549,072 Epstein Apr. 17, 1951 2,570,858 Rajchman Oct. 9, 1951 2,728,025 Weimer Dec. 20, 1955 2,728,872 Smith Dec. 27, 1955 CERTIFICATE OF CORRECTION Patent N06 2,825,845

March 4, 1958 Johan Lodewijk Hendrik Jonker et all,

It is hereby certified that error appears in the printed of the above numbered patent specification requiring correction and that the said Letters Patent should read as corrected below Column 2, line 4, for "means" read mean column 6 line 35, for "image" read electron-receiving Signed and sealed this 20th day of May 1958o (SEAL) Attest:

KARL H, AXLINE Commissioner of Patents v t'\. H

UNITED STATES PATENT OFFICE CERTIFICATE OF (IQRRECTION Patent No, 2,825,845

March 4 1.958

Johan Lodewijk Hendrik Jonker et al.,

It is hereby certified that error appears in the printed specifica ion of the above numbered patent requiring correction and that the said Le ers Patent should read as corrected below Column 2, line 4, for "means" read mean column 6, "image" read electron-receiving 1111a 35 for Signed and sealed this 20th day of May 1958o {(SEAL) Attest:

KARL Ha AXLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents

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