US2185239A - Cathode ray tube - Google Patents

Description

19401 M. VON ARDENNE 2,185,239

CATHODE RAY TUBE Original Filed May 24, 1954 a 7 l C l 1 '1 6 7D C3 I 5 f 1/3 l b-El I f- I lfil l l F-" l l l l /00[ I000! [0001! I N V EN TO R M4A/FRED VONARDEA/IVE f MW ATTORNEY Patented Jan.

CATHODE RAY TUBE Manfred von Ardenne, Berlin, Germany, assignor to Radio Corporation of America, a corporation of Delaware 6 Claims.

This application is a divisional of my co-pending application Serial No. 727,206, filed May 24,

1934 and entitled Cathode ray tube.

My invention relates to improvements in and methods of operation of cathode ray tubes, in particular for use as oscillographs and in cathode ray television systems. The general form of cathode ray tubes heretofore known in the art used for oscillographs or in cathode ray television comprises the three essential parts: a thin beam or pencil of electrons, a fluorescent target or luminous screen for the electron pencil to strike against to produce a recording light spot, and a mechanism for deflecting the electron beam and varying the intensity of the luminous spot on the screen for producing an image or pattern of desired configuration and charac- .teristics.

In the ordinary cathode ray tubes as known in the art used for oscillographic and television purposes, deflecting potentials of several hundred volts are necessary to move the electron beam over the entire surface of the fluorescent screen. This low sensitivity of deflection necessitates the use of very high anode voltages and high ampliflcation in the sweep or control circuits for producing the deflecting potentials.

It is a main object of my invention to provide a novel method of and means for deflecting the electron beam in a cathode ray tube which is characterized by considerably increased sensitivity of the deflection While enabling the use of very high electron velocities required for insuring a brilliant luminous spot upon the fluorescent screen produced by the impact of the electron ray.

As is well known, the sensitivity of deflection of an electron ray may be increased if the deflection takes place at a place Where the electrons travel at low speed. In recognition of this fact it has already been attempted to construct tubes in which the electron beam is initially accelerated to a fraction only of the desired final speed and is then passed through the deflecting system whereupon a final acceleration is applied to secure sufficient kinetic energy of the electron beam striking the fluorescent surface to produce a bright luminous spot thereon. By this scheme the further advantage is obtained especially in tubes containing a gaseous atmosphere that on account of the low velocity in the ray producing system, the destruction of the cathode by gaseous ions is limited to a minimum.

60 lected to a large deflection in both coordinate However, it has not been possible in practicedirections, without causing serious interference with the proper operation of the tube.

Accordingly it is a further object of my invention to provide a means in the path of a concentrated electron ray for additionally accelerating or decelerating the electrons substantially independent of the direction and/ordegree of deflection of the electron pencil relative to a normal or zero position and without any additional impairment of the proper functioning of the tubes.

It was furthermore found especially in the case of gas filled cathode ray tubes, that the electron speed in the ray-producing and reflecting space had to be of comparatively high value (several hundred volts) in order to secure a sufficient current intensity at the top of the ray or in turn a. sufficiently brilliant luminous spot on the fluorescent screen.

Accordingly, a further object of my invention consists in-a novel method and means whereby an extremely low electron speed may be employed within the space of the deflecting system, resulting in a considerably increased sensitivity of reflection while maintaining simultaneously high velocity of the electron ray at the place where the ray strikes against the fluorescent screen.

Still a further object of my invention is the provision of a novel electrode construction in a cathode ray tube for deflecting the beam at a place immediately near the cathode where the electrons move with the lowest velocity, resulting in greatly increased sensitivity of the deflec- One of the diificulties experienced with cathode ray tubes as known heretofore in the art is the fact that a substantial reaction, especially capacitative reaction, may take place between the deflecting systems used for deflecting the beam in both a vertical and horizontal direction, in particular if two pairs of capacitative deflecting plates are used. This deflection may result in substantial decrease of the sensitivity of deflection, in distortion, and otherwise greatly interfere with the proper operation of the tube.

Accordingly it is a further object of my inven tion to provide efficient screening means between the deflecting systems in a cathode ray tube for substantially eliminating interaction between defleeting systems.

These, as well as further objects and aspects of my invention, will be better understood by reference to the following detailed description taken together with the accompanying drawing wherein I have shown several cathode ray tube constructions embodying my invention. The embodiments shown are to be taken as being illustrative only of the underlying principle and novel features of the invention which, as will become obvious, is subject to various modifications and variations coming within the broadest scope thereof as expressed in the appended claims.

In the drawing, in which similar reference numerals identify similar parts in the different views;

Figure 1 schematically illustrates a cathode ray tube having an electrodeacccrding to Figure 2 embodied therein;

Figure 2 illustrates an electrode construction for accelerating or decelerating an electron beam in accordance with my invention;

Figure 3 illustrates another form of cathode ray tube embodying an electrode system enabling the deflection of the cathode ray immediately near the cathode, resulting in greatly increased sensitivity of the reflection;

Figure 4 illustrates a bottom View of the tube according to Figure 3 and the connections to the deflecting plates from a controlling source;

Figure 5 is a front view of the anode or shielding electrode provided in the tube shown by Figure 3; and

Figures 6, 6a and '7, 7a schematically illustrate electrode systemsvfor cathode ray tubes employing the shielding element in accordance with my invention.

In accordance with my invention, I provide a means in a cathode ray tube for accelerating an electron ray from either an initial very low velocity or a reduced velocity obtained by previous deceleration to a desired final acceleration without otherwise impairing the operating characteristics and sensitivity of deflection of the electron ray.

In accordance with the preferred embodiment of my invention, I have devised an accelerating electrode insuring a gradual potential variation from the place of the initial or starting potential to the final potential to which the ray is to be accelerated. According to a preferred con struction, I use a tubular shaped unit'as an accelerating electrode comprising substantially two cylindrical elements provided with wedge-shaped teeth engaging each other whereby the acceleratingpotentialis applied to one of said elements.

This construction is shown in more detail by Figure 2 of the drawing. This illustrates the cylindrical metallic unit, or unit provided with a metal coating, used as an accelerating means in which the cylinder is shown to be cut open lengthwise and spread out into a plane. I have shown the one element at M provided with wedgeshaped teeth i l and the second cylindrical element at l2 provided with similar wedge-shaped teeth l2 engaging the teeth of the first element as shown. The embodiment as shown by Figure 2 is of a specific and preferred form to be used for both final acceleration and previous deceleration of the electron beam, and for this purpose I have shown further wedge-shaped teeth l4. connected to the other side of the cylindrical element Mand a'further cylindrical element 11 5 provided with teeth It engaging teeth M of the element Hi. The arrangement and function of this construction will be explained further in connection with Figure 1.

By providing a' sufficient number of teeth in the cylindrical elements forming the acceleration or deceleration electrodes, the conditions obtained are such that a highly homogeneous electric field consists for both undeflected and largely deflected rays passing inside the cylindrical unit.

Generally, the electrode structure for accelerating or decelerating an electron beam in accordance with the invention is of such configuration and design as to produce an accelerating or decelerating electric field which exerts a substantially equal force upon the electrons independent of the direction of the beam through the field. In this manner both the deflected and undeflected beam is accelerated or decelerated in an equal manner without in any way affecting the characteristics of the beam, such as its initial velocity, degree of concentration, etc. liable to produce distortion of the pattern or image produced by the beam upon the luminescent screen.

I have furthermore discovered that obviously on account of conditions prevailing in. the ray generating a concentrating space in gas filled cathode ray tubes and furthermore due to the high stray losses of slow electron rays even within ranges of only 5 centimeters, it is impossible to maintain the electron velocity within the deflecting space at very low values in order to obtain a very high sensitivity of deflection.

I overcome this defect by using a higher initial acceleration voltages in the ray producing sys tem equal to, about one-half to one-eighth of the desired electron Velocity at the luminous screen. I then provide means for decelerating the electrons within the deflecting space and in this manner I have found it possible to secure extremely high degrees of sensitivity of deflection especially in gas filled cathode ray tubes. The'deceleration may be carried out to substantially lower electron volt velocities as would be possible in the above mentioned case where low initial velocity is employed in the space where the ray is produced and initially concentrated, such as by means of a negatively biased concentration cylinder.

When using an initial high electron velocity and subsequently decelerating the electrons to a lower velocity in the deflecting space, the deceleration may be carried out by means of ordinary electrodes, such as by the provision of a pair of circular plates with central openings for passing the electron ray whereby the braking or decelerating voltage is applied to the second electrode. However, I have found that in the case of very high decelerating voltages that the ray is deviated from its central. position and deflected more or less in a lateral direction so that it is finally prevented from passing through the opening of the decelerating electrode.

In accordance with a further feature of the invention, I prevent the aforementioned deviation of the beam by the decelerating field by the prcvision of a similar shaped cylindrical electrode system with mutually engaging wedge-shaped teeth as hereinbefore described for efiecting a final or re-acceleration of the electron beam to the desired final velocity.

Referring to Figure 1 of the drawing, I have shown a cathode ray tube embodying an electrode system as described by Figure 2 used for both decelerating and subsequently accelerating an electron beam for the purpose as described. Referring to the drawing, I have illustrated a cathode ray tube comprising a glass bulb l having a neck shaped portion housing the electrode systems for producing and deflecting the electron ray and a spherical shaped end portion including an inclined luminous screen it as described in my ccpending application entitled Improvements in and methods of operatingcathode ray tubes of even date. Numeral 2. represents a cathode which maybe a thermionic filamentary cathode as shown, but it is understood'that any other type of cathode may be provided, such as an indirectly heated cathode of known design in the art. The cathode is shown to be heated by a battery 1 and is surrounded by a cylindrical or concentration electrode 3 negatively biased to the cathode by means of a biasing battery as shown at 8 for concentrating the electron stream into a sharply focused pencil. At 15 I have shown a positive or anode electrode for producing an initial acceleration of the electron beam emanating from the cathode and the concentration cylinder 3. The electrode I5 may be of ring-shape with a central opening and provided with a cylindrical unit having wedge-shaped teeth #5 similar to the unit i5 as described by Figure 2. The electrode I 5 is connected to a high positive operating potential of about 1000 volts such as shown by the battery 9 to initially accelerate the electron beam. Numeral I represents a breaking or deceleration electrode having a lower positive potential applied to it than the electrode 55, such as by means of battery I! as shown. The electrode i0 may also be of circular shape with a central opening for passing the electron ray and connected to the cylindrical unit M with teeth It engaging the teeth iii of element l as shown in more detail in Figure 2. In this manner a decelerating electric field is produced within the space between the electrodes 55 and H) of favorable potential distribution to enable the electron ray previously accelerated by the electrode 2 to be decelerated to a very low electron velocity without deviating from the central position. In this manner high sensitivity of deflection is obtained, such as by means of the usual deflecting mechanism such as the two pairs of electrostatic deflecting plates 5 and 6, respectively, arranged at right angles to each other as shown in the drawing.

The thus deflected electron ray is subsequently reac-celerated to its final velocity by means of the tubular accelerating electrode i2 provided with wedge-shaped teeth l2 engaging the teeth Id of the electrode M. In this manner as pointed out, a i e-acceleration of the electron beam even when deflected to its fullest degree in both coordinates is insured without any substantial impair ment of its characteristics.

I have shown the accelerating potential which may be of the same value as the breaking potential (1000 volts in the above example) applied by a battery !3 connected to the element it. It was furthermore found that the conditions and the operation can be improved by biasing the screen It to a potential equal to the accelerating potential such as shown by the connection of the screen to the plus pole of the battery I3. In the example as illustrated the potential of the battery i may be within the order of 100 volts or less.

In an arrangement for gas filled cathode ray tubes as described, it is possible to decrease the velocity of the electrons down to almost the ionization potential of the gas, especially if the deflecting system is so constructed that the path over which the electrons travel at the lowest velocity through the gas does not exceed two to three centimeters. If still lower voltages are employed, this will result in an impairment of the definition or sharpness of the luminescent spot on the screen. Thus, it is preferable to use gases with very low ionization potential in order to secure very high degrees of sensitivity of deflection as is understood. It has furthermore been found advantageous to use heavy gases with the added advantage of increased ray intensity or correspondingly decreased losses caused by stray electrons.

While I have described a specific arrangement comprising both deceleration and acceleration of the electron ray, it is obvious that I am not limited to the specific combination as shown. Thus, it is possible to use the decelerating mechanism in connection with any other accelerating arrangement.

In acordance with a further feature of the invention, it is advisable to provide the electrode NJ with a very small aperture through which the low speed electrons pass, especially in the case of very high deceleration to very low electron velocities. In some cases I found it advantageous to cover the opening of the electrode I0 with a fine wire net or grid to secure as straight a course of the lines of field as possible.

Referring to Figure 3 of the drawing, I have shown another cathode ray tube construction for deflecting the electron beam immediately at the source or cathode where the electron speed is a minimum, thus obtaining a maximum sensitivity of the deflection, as is obvious. This type. of construction is especially suited for partly or highly evacuated tubes in which the electron velocity at the cathode may be of a very low value as compared with gas filled tubes hereinabove mentioned.

I have shown a special electrode construction mounted at the cathode serving both for deflecting the electron beam preferably in one direction and at the same time acting as a means for concentrating and focusing the electron stream into a sharp beam together with a specially con" structed anode electrode, as will be described hereinafter.

Referring to the drawing. Figure 3, I have again shown a cathode ray tube comprising a glass bulb I mounted upon a base I1 and provided with an inwardly projecting press [8 for carrying the cathode, anode and the deflecting system. The cathode ray tube shown in this figure differs from Figure 2 by the arrangement of the luminous screen I9 directly applied to the inner end wall of the tube in accordance with well known constructions in the art. Numeral 20 represents the cathode similar as described by Figure 2 connected to terminals 20' mounted at the sides of the base 11. I have furthermore shown a boxlike system comprising four plates 2!, 22, 23 and 24 arranged in square shape close to each other and surrounding the cathode. Each of the plates is connected to a connecting terminal or prong 2|, 22', 23' and 24,- respectively, mounted at the bottom of the base I I, as shown by Figure 4. Figure 4 also shows a cross-section of the plate system and the connection to the prong terminals. By the use of an arrangement of this type the electron beam can be deflected in one direction by applying the controlling potential supplied from a transformer or other source is shown in Figure 4 to a pair of opposite plates, in the example illustrated plates 23 and M. In order to obtain deflection in both directions from the central or zero position of the electron beam, the remaining plates 2| and 22 should be connected to the mid-tap point of the controlling source l8, in the example the secondary of the transformer winding as illustrated.

In order to increase the sharpness of the beam which has already been focused by the proper choice of the cathode and by the action of the electrode system 2i to 24 acting similar to a. concentration cylinder, I have found it advisable to provide an anode 25 surrounding the cathode structure on all sides, such as by means of a circular anode plate 25 covering the cylinder 2? surrounding the entire cathode structure.

In order to insure large deflections of the oathode ray by the deflecting plate system as shown and preventing the ray from being obstructed by the anode plate 25, I have shown the latter provided with a. lengthwise slit 25" to allow the beam to sweep over the entire surface of the luminous screen in a horizontal direction according to the specific example as shown in more detail by Figure 5. If it is further desired to sweep the beam in a vertical direction, a pair of ordinary deflecting plates as shown at 255 may be arranged behind the anode 25.

In an arrangement as described, the anode 25 furthermore acts as a screen between the two defleeting systems for preventing decrease of sensitivity of the deflection and distortion caused by electrostatic interaction between the deflecting systems.

It is furthermore understood that a shielding electrode as shown at 25 in Figure 3 may be employed in connection with any other electrode system in cathode ray tubes and is not limited to the particular construction according to Figure 3 in which the shielding electrode simultaneously acts as an anode for the electron stream.

Thus, referring to Figures 6 and Go I have indicated schematically an electrode system of usual construction in combination with a shielding electrode according to the invention. Numeral 28 indicates the cathode ray source such as the concentration cylinder surrounding a cathode. Numeral 29 represents the usual anode which may be in the form of a disc with a central opening for passing the cathode ray. Numeral 3B shows a first pair of deflecting plates to sweep the beam in a vertical direction. Numeral 3! represents a shielding electrode in accordance with the invention comprising a disc provided with a vertical slit to allow the beam to sweep vertically between the upper and lower deflecting positions, and numeral 32 indicates a second pair of deflecting plates for sweeping the beam in a horizontal direction.

Figures and 7a illustrate a similar system with the succession of the deflection reversed, in which case the shielding electrode 3! is arranged with its slit in a horizontal position, as will be understood.

Having described my invention, what I claim is:

1. In combination with a cathode ray tube comprising a means for producing a concentrated electron beam, a luminescent screen for said beam to strike against, a first deflecting system for sweeping beam over said screen in one direction, a further deflecting system for sweeping said beam in different direction, a screening member arranged between said deflecting systems provided with a lengthwise slit for allowing passage of said beam while being swept over the entire surface of screen by said first deflecting n'zeniiher, and electrode means for accelerating the said beam following the two deflecting systems.

2. In combination with a cathode ray tube comprising means for producing a concentrated electron bearn, a luminescent screen for said beam to strike against, a first deflecting system comprising a pair of electrostatic deflecting plates for sweeping said beam over said screen in one direction, a second deflecting system comprising a pair of electrostatic deflecting plates for sweeping said beam over said screen in a direction at right angle to said first direction, a metallic screen separating said deflecting systems and provided with a slit to allow passage of said beam while being swept over the entire surface of said screen by said first deflecting system, and electrode means for accelerating the said beam following the two deflecting systems.

3. A cathode ray tube comprising a cathode, a first cylindrical electrode surrounding the cathode, a second cylindrical electrode coaxial with and spaced from the first cylindrical electrode, a third cylindrical electrode coaxial with and spaced from the second cylindrical electrode, a fourth cylindrical electrode intermediate the second and third cylindrical electrode said second, third and fourth electrodes being serrated and interleaved at their adjacent boundaries, cathode ray deflecting means positioned within the fourth electrode, and a luminescent screen positioned in register with and spaced from the third cylindrical electrode.

4. A cathode ray tube comprising a cathode, a cylindrical electrode surrounding the cathode, a second cylindrical electrode coaxial with and spaced from the first cylindrical electrode, a third cylindrical electrode coaxial with and spaced from the second cylindrical electrode, a fourth cylindrical electrode intermediate the second and third cylindrical electrodes, an apertured electrode Within the fourth cylindrical electrode, said electrode having an elongated aperture to permit a beam of electrons to pass without hindrance, while said beam is deflected over substantially the entire width of the luminescent screen, cathode ray deflecting means positioned within the fourth cylindrical electrode, and a luminescent screen positioned in register with and spaced from the third cylindrical electrode.

5. A cathode ray tube comprising a cathode, a cylindrical electrode concentric with the oathode, a first cylindrical saw-tooth electrode coaxial with and spaced from the cathode, a second cylindrical saw-tooth electrode spaced from the first saw-tooth electrode, an apertured disk electrode intermediate and in register with the first and second saw-tooth electrodes, a third cylindrical sawtooth electrode intermediate the first and second saw-tooth electrodes and surrounding the disk electrode, cathode ray deflecting means intermediate the first and second saw-tooth electrodes, and a luminescent screen in register with and spaced from the second saw-tooth electrode.

6. A cathode ray tube comprising a cathode, a cylindrical electrode concentric with the cathode, a first cylindrical saw-tooth electrode coaxial with and spaced from the cathode, a second cylindrical saw-tooth electrode spaced from the first sawtooth electrode, an apertured disk electrode intermediate and in register with the first and second saw-tooth electrodes, a third cylindrical sawtooth electrode intermediate the first and second saw-tooth electrodes and surrounding the disk electrode, two pairs of parallel plane electrodes mutually perpendicular to each other intermediate the first and second saw-tooth electrodes, and a luminescent screen in register with and spaced from the second saw-tooth electrode.

MANFRED VON ARDENNE.

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