US3036238A

US3036238A - High resolution c.r. tube

Info

Publication number: US3036238A
Application number: US25596A
Authority: US
Inventors: Elmer O Stone; Alan T Kuryla
Original assignee: Sylvania Electric Products Inc
Current assignee: GTE Sylvania Inc
Priority date: 1960-04-29
Filing date: 1960-04-29
Publication date: 1962-05-22
Anticipated expiration: 1979-05-22

Description

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3. .,.H. ...u nvvv A TTORNE Y United States Patent Ofiice 3,036,238 Patented May 22, 1962 3,036,238 HIGH RESOLUTION C.R. TUBE Elmer 0. Stone, Seneca Falls, and Alan T. Kuryla, Ge-

neva, N.Y., assignors to Sylvania Electric Products Inc., a corporation of Delaware Filed Apr. 29, 1960, Ser. No. 25,596 6 Claims. (Cl. 315-16) This invention relates to cathode ray tubes and in particular to the gun construction thereof to produce a high resolution cathode ray beam on the screen of the tube.

The resolution of a trace or picture on the face of a screen is determined in part by the cross sectional size and shape of the electron beam. The trace on the screen can be no finer than the image of the cathode spot itself, or, Where a convergent electron lens is employed, of the image of the cathode spot at a cross over point of the rays from opposite diametrical points on the cathode. To maintain the beam against spreading and the spot image on the screen as small as possible, a convergent electronic lens is placed close to the cathode, and Wehnelt cylinders are employed to keep the resultant beam confined; in general, the longer these cylinders are, the better the resolution of the picture. However, in order to shorten the overall length of cathode ray tubes, the gun, too, has to be shortened. Various expedients have been employed to obtain a proper beam form and cross section with the shortened gun. Also to reduce cost and simplify the circuitry involving the formation of a picture on the screen of the tube, electrostatic focusing of the beam has been resorted to. This involves the creation of a second electron lens at a distance from the lens close to the cathode.

One form of gun involving the dual lens structure wherein the second lens is designed to have excellent focus characteristics regardless of changes in anode voltage and to have increased depth of focus over a simple bipotential lens, is exemplified in the patents to Hoagland Re. 24,673, granted July 28, 1959, and Collins et al. 2,922,072, granted January 19, 1960.

The optimum sizes of parts and spacing between them is given in these patents to which reference may be had for further details.

It is found that with a different arrangement of potentials on the various electrodes then previously known in the art, the spot size as cast on the screen and therefore the resolution of the image may be greatly improved.

It is an object of this invention to provide a cathode ray tube with a gun structure and circuitry such as to produce a beam of electrons of very small diameter at the screen of the tube.

More specifically, it is an object of this invention to provide a fine .trace or picture 011 the screen of a cathode ray tube of the type having spaced electron lenses and wherein the lens most remote from the source of elec trons or cathode is surrounded by a focusing anode with different potentials applied to each part of the most remote lens.

Other objects will become apparent upon further consideration of the following specification and claims, when taken in connection with the accompanying drawing in which the figure diagrammatically illustrates a cathode ray tube with a gun structure and associated circuitry, in accordance with the invention.

On the figure, 10 represents the glass envelope with aquadag coating 12, as is usual in the art, extending to a high voltage button 14 to which a direct current high voltage lead 16 is connectible. The aquadag coating extends some distance into the neck 18 of the envelope. The gun is comprised of a cathode and first grid assembly 22 such as is shown, for example, at 10 in the Johnson et al. Patent 2,864,935, granted December 16, 1958.

Spaced longitudinally from the first grid of the assembly is a second grid 24 and spaced longitudinally from that is the first or accelerating anode 26. The gun structure may include a bent gun or slash gun feature to trap ions as is known in the prior art. Spaced from the accelerating or first anode 26 is a third anode 28 and surrounding and overlapping the first and third anodes or riding saddle on the first and third anodes is the second, cylindrical anode 30.

The whole group comprised of cathode assembly with its first grid, the second grid and the anodes are supported Within the tube neck by suitable supports, not shown, and all of the grids and anodes are held in proper spaced relation to each other by means of a number of insulator bars 32 of glass or equivalent insulating material connected by pins 34 to the various electrodes. All the electrodes are individually connected to terminals; the third anode 28, in contradistinction to the prior art, is connected to a terminal independently of the first anode 26. As here shown, the third anode is connected via conductive snubbers or springs 36 to the conductive coating 12 within the envelope. If desired, the third electrode may be connected via a lead to a pin terminal extending from the base of the tube. A conventional deflecting coil assembly 38 surrounds the neck of the tube.

For the gun to operate to bring the spot size on the screen to approximately one half of that which results thereon where

anodes

26 and 28 are at the same potential, it is desirable to apply a much higher voltage to the third anode than to the first anode. In actual practice, with the proportions of parts set forth in the Hoagland and Collins et al. patents referred to above, the voltage applied to the first anode should be approximately one-fourth to onefifth the voltage applied to the third anode. With 16 kv. applied to the third anode, 3500 v. would be suitable for application to the first anode; the focus control voltage on the second anode could be anywhere between Zero "olts and 1500 volts, as required to obtain a suitable spot on the screen. With these voltages, a normal voltage of 300 or approximately onefiftieth of that applied to the third anode is applied to the second grid with one of the pair including cathode and control grid at zero potential and the other of the pair at signal potential.

As stated before, by the arrangement described and with the voltages applied to the electrodes as set forth, a spot size on the screen is attained which is much smaller than could be attained where the first and third anodes are at the same potential.

As an explanation of this, consider the analogy between the electron lenses of the invention and optical lenses. The lens formed by grid 22 and grid 24 creates a cross over point between the two or a virtual image of the cathode closely in front ofthe bottom 40 of the second grid. The second lens formed by the three

anodes

26, 28 and 30 can be regarded as seeing either this cross over or the virtual image. Let one of these be regarded as lying in the object plane. The image plane of the second lens is on the screen. The magnification of the object in the object plane on the screen is the ratio of the distance between the object and lens and the distance between the lens and the image plane. If a be the distance between the object plane and the effective center of the second lens and b be the distance between the eifective center of the lens and the image plane, then the magnification is equal to the inverse ratio of these distances. This can be expressed as b magnification Thus to secure a small spot on the screen it is advantageous to make the distance a as large as possible. This can be achieved, in the prior art, by lengthening the first anode but this would lengthen the neck of the tube, which is undesirable. Actually, in the prior art, the voltage on the first anode was much higher than the voltage on the second grid, making a very strong lens which drove the object plane closer to the first lens and therefore shortened the distance a and made the magnification larger. With the applied voltages of the invention to the

arrangement arrangement

26, 28 and 30. Furthermore, in order to lengthen the efiective distance a as much as possible the first lens, that is, the lens formed between the second grid and first anode, is weakened by reducing the voltage on the first anode to about one fourth of that on the third anode.

Thus while retaining the desirable features of a saddle type of lens, i.e., one utilizing an anode overlapping two other anodes with the attendant advantages of constant focus regardless of normal anode voltage changes and with the advantage of its depth of focus, by applying the different voltages to these anodes, increased spot resolution is attained. This is enhanced by decreasing the voltage on the first anode, thereby increasing the distance from the object plane to the second lens.

Having thus described the invention, what is claimed is:

1. A cathode ray tube system including a gun having electrodes including a cathode, a grid, a second grid, and first, second and third anodes, said first, second and third anodes being spaced in that order in the direction away from the second grid; said first and third anodes being in axial alignment and spaced from each other with the second anode riding saddle over the first and third anodes, leads to each of the electrodes, the leads to the grids and the first and third anodes being independent ofeach other,

and means for coupling voltages to the various electrodes, the voltage to the third anode being higher than that applied to the first anode.

2. A cathode ray tube system including a gun having dependent of each other, and means for coupling voltages to the various electrodes, the voltage to the third anode being higher than that applied to the first anode.

3. A cathode ray tube system including a gun having electrodes including a cathode, a grid, a second grid, and first, second and third anodes, said first, second and third anodes being spaced in that order in the direction away from the second grid; said first and third anodes being in axial alignment and spaced from each other with the second anode riding saddle over the first and third anodes, leads to each of the electrodes, the leads to the grids and the first and third anodes being independent of each other, and means for supplying voltages to the various leads, the voltage to the leads of the thirdanode being four to five times that applied to the lead of the first anode.

4. A cathode ray tube system including a gun having electrodes including a cathode, a first grid, a second grid, and first, second and third anodes, said first, second and third anodes being spaced in that order in the direction away from the second grid; said cathode, grids, first and third anodes being in axial alignment and spaced from each other with the second anode riding saddle over the first and third anodes, leads to each of the electrodes, the leads to the grids and the first and third anodes being independent of each other, and means for supplying voltages to the various leads, the voltage to the leads of the third anode being four to five times that applied to the lead of the first anode. V I

' 5. A cathode raytube system including a gun having electrodes including a cathode, a grid, a second grid, and first, second and third anodes, said first, second and third anodes being spaced in that order in the direction away from the second grid; said first and third anodes being in axial alignment and spaced from each other with the second anode riding saddle over the first and third anodes,

leads to each of the electrodes, the leads to the grids and the first and third anodes being independent of each other, the voltage to the lead of the third anode being approximately five times that applied to the lead of the first anode and the voltage applied to the lead of the second grid being approximately one-fiftieth of the voltage applied to the third anode.

6. A cathode ray tube system including a gun having electrodes including a cathode, a first grid, a second grid,

and first, second and third anodes, said first and second third anodes being spaced in that order in the direction away from the second grid; said cathode, grids, first and third; anodes being in axial alignment and spaced from each other with the second anode riding saddle over the first and third anodes, leads to each of the electrodes, the leads to the grids and the first and third anodes being independent of each other, the voltage to the lead of the third anode being four to five times that applied to the lead of the first anode and the voltage applied to the lead of the second grid being approximately one-fiftieth of the voltage applied to the third anode.

' References Cited in the tile of this patent UNITED STATES PATENTS 2,719,243 Hoagland Sept. 27, 1955 2,732,511 Dichter a; Jan. 24, 1956 2,839,703. Niklas June 17, 1958 2,902,6Q3 Knechtli Sept. 1, 1959 2,963,608;

Benda et al. Dec. 6, 1960