US2212396A

US2212396A - Cathode ray tube

Info

Publication number: US2212396A
Application number: US223089A
Authority: US
Inventors: Gabor Dennis
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1936-07-31
Filing date: 1938-08-04
Publication date: 1940-08-20
Anticipated expiration: 1957-08-20
Also published as: FR48958E; GB479064A; BE422914A; BE431937A; FR50137E; FR824875A; GB488188A; DE914878C; US2197523A; GB508520A

Description

Aug. 20, 1940. GABQR 2,212,396

CATHODE RAY TUBE 7 Filed Aug. 4, 1958 2 Sheets-Sheet l A9 X III v 27 I u f a T /6 Inventor: Dennis Gabon is A torn ey.

CATHODE RAY TUBE Filed Aug. 4, 1938 2 Sheets-Sheet 2 is Attorney.

Patented Aug. 20, 1940 CATHODIE RAY TUBE Dennis Gabor, Rugby, England, assignor to General Electric Company, a corporation of New York Application August 4,

1933, Serial No. 223,089

in Great Britain January 3, 1938 9 Claims.

The present invention relates to cathode ray tubes employed in the art for oscillographic and television purposes.

For deflecting an electron beam across a cathode ray tube it is customary to employ one or more pairs of oppositely positioned plates. These plates are usually of concave configuration with the concavity facing the beam so as to increase the homogeneity of the electric fields between the plates. The electrodes may have a uniform curvature so that when mounted in the tube, they form the outline of a circle. Sometimes, they take an angular shape so as to define the outline of a square or rectangle. However, while noticeable improvement by way of increased homogeneity of field is obtainable by electrodes of the character pecified, there is still a sufficient lack of uniformity of field over the entire path taken by the beam to give rise to distortion of the deflecting forces which act on the beam.

An object of the present invention is to provide an improved deflecting structure by which the electrostatic deflecting field presented to an electron beam over its entire length of travel is of a homogeneous character in order that the amount of deflection throughout the path of the beam will very accurately in accordance with the electric potential applied to the deflecting electrodes. This object is attained in brief by providing within the deflecting structure additional electrodes, the field of which combines with and modifies the field of the structure to the extent necessary to give complete homogeneity to the deflecting field over a large area.

The invention will be better understood when reference is made to the following specification and the accompanying drawings in which Fig. 1 is a cross-sectional view of an oscillograph tube employed in accordance with the present invention; Fig. 2 is a circuit diagram showing electrical connections to the tube in accordance with one form of the invention; Fig. 3 is a graph of the equipotential lines obtained when the tube is connected in accordance with the circuit of Fig. 2, and Fig. 4 is a graph of equipotential lines obtainable when the electrodes are connected in a modified manner.

Referring specifically to Fig. 1, numeral l designates the glass envelope of a typical form of cathode ray tube which has a portion of uniform diameter and a long, flared portion closed by an arcuate portion 2. On the interior of this arcuate portion there is provided a layer of material 3, such as willemite, which fluoresces when struck by electrons. The other end of the envelope terminates in a reentrant stem 4. With in the envelope and mounted from the stem l there is an indirectly heated cathode 5 which is heated by a filamentary member 6 and serves as a source of electrons. This stem also carries an apertured disk l positioned directly in front of the cathode 5 and the function of which is to focus or otherwise control the electrons. There is a metal disk 8 positioned on the opposite side of the grid 1 from the cathode 5, this disk having an opening through which the electrons emerge. The purpose of the disk 8 is to provide additional control of the focus, also to give high acceleration to the electrons emitted from the cathode so that the elements 5, l and 8 constitute a so-called electron gun. Obviously, any other suitable form of electron gun may be employed.

The interior of the flared portion of the envelope is coated with a layer of metal 9 such as copper, the outer edge of the coating terminating short of the fluorescent layer 3. A conductor if! is taken from this coating to the electrode 8. The purpose of the coating 9 isv to maintain the velocity of the electrons through the flared portion of the envelope. g I

For deflecting the beam as it emerges from th opening in the electrode 8, there is provided a deflecting structure which consists preferably of two pairs of electrodes ll, l2, l3, and M positioned diagonally opposite one another. These electrodes, when assembled, are spaced from one another and are flared outwardly in the longitudinal direction to give the appearance of a horn. These electrodes are of marked concave shape in cross-section, and this shape may extend from an ordinary curvilinear configuration to an L-shape having corners. -If the electrodes are of an arcuate shape, they form, when assembled, the outline of a circle, and when they are of an L-shape, they form the outline of a square or rectangle. The last-mentioned shape is illustrated in Fig. 2.

The deflecting electrodes may be mounted within the envelope in any suitable manner, for example, by means of conductors 15 (Fig. 1) which insulatingly pass through the coating 9 and are sealed in the glass envelope. A deflecting electrode structure such as described up to However, it

as been found that electrodes of this character 3 not give that high degree of homogeneity of eld which is found to be necessary, and in ac- )rdance with the present invention, I provide an nprovement in the structure by which a much igher degree of homogeneity of fleld can be obtined and the field is homogeneous over a much .rger area. The improvement consists essenally in providing a plurality of charged conduc- )IS it (see Fig. 2), positioned within the in- :rior of the deflecting structure and respectively :ljacent the median line of each electrode. These )lldllCtOlS therefore are located near each corer of the rectangular deflecting structure. The inductors should be of concentrated form, as aown, and in this connection may be described s being of generally filamentary character. should be understood, however, that the foreoing quoted phrase, as used herein and in the ppended claims, is not to be construed as limed to conductors of a circular cross-section but a, on the contrary, to be interpreted as includig all small-sectioned conductors regardless of neir configuration.

Fig. 2 illustrates a typical circuit arrangement 'hich might advantageously be employed in conection with the tube such as described. As will e seen in this figure, the heater is energized y a battery it, and the cathode 5 is connected 3 one side of the heater. The grid member 11 connected to the cathode 5 through a battery 9 and an alternator it which is intended geerically to indicate a source of control or signal urrent, which may be alternating current or inerrupted or continuous direct current. The acelerating electrode 8 and the coating 9 con- .ected thereto derive positive potential from a attery 2!. It will be noted that the electrodes l, l2, l3, and id of the deflecting structure and he contained conductor is are shown in a diferent plane from the remaining electrodes in or- .er to illustrate more clearly the connections to hese various electrodes. It will be understood lowever, that the deflecting electrodes actually xtend lengthwise of the tube and in the same .irection as the electron gun, similarly to that hown in Fig. 1.

As the electrons emerge from the opening in he electrode 8, they are caused to be deflected ietween the oppositely positioned electrodes l2 .nd M of the deflecting structure by means of he variable potentials applied to a transformer 2. The remaining pair of oppositely positioned :lectrodes H and i3 does not have a deflecting :otential applied thereto but instead these elecrodes are electrically connected together by a :onductor 23. The electrodes are also electri- :ally connected by means of a conductor 2% to L mean potential tap 25 on the transformer sec- )ndary. The electrodes it and it are preferably maintained at a positive potential with respect .0 the cathode 5 by a battery 2t, and serve to give the electrons within the deflecting structure L11 accelerated velocity. As stated hereinbefore, is the electrons leave the deflecting structure, ;hey continue to move forward at a high velocity, lue not only to the initial speed acquired in passng through the electrode 8 and between the eleczrodes H, is but also due to the positive poten- ;ial applied to the conical electrode or metal ayer 9. As these electrons reach screen 3 which ;hey strike with considerable force, a light trace .s produced on the screen. The length of this ;race at any particular time is of course dependent on the potential conditions within the tube and particularly the magnitude of the voltage applied across electrodes 12, M.

As stated hereinbefore, conductors It are provided for the purpose of increasing the homogeneity of the field within the deflecting structure. These conductors are preferably brought out from the deflecting structure by separate taps to a common conductor Zl' which is connected through the conductor 2 to the mid-point or mean potential tap of the transformer 22. The connection'between conductor 2? and each conductor it has been diagrammatically illustrated in Fig. 2 as a wire passing through all of the conductors, but it will be understood that the conduct'ors iii have their own individual connection leading to the common conductor 2? and preferably brought out from the deflecting electrode in such a manner as to interfere as little as possible with the electric fields produced by the electrodes ll, i2, i3, and M.

It is apparent that in addition to the function described hereinbefore of accelerating the electrons through the deflecting structure, electrodes i i, it also serve to modify the deflecting field set up by the electrodes 82, M, resulting in what may be termed a composite fleld. It has been found that when the conductors it are additionally provided, this composite field is still further modifled by the field of the conductors to the extent of providing a fleld of remarkable homogeneity in which the equipotential lines of force are uniformly distributed throughout an area almost as large as the area contained within the deflecting structure. The composite field as modified by thev field of the conductors it is illustrated in Fig. 3 in which the reference characters designate elements similar to those carrying the same designations in Fig. 2. The transformer 22 serves to apply across the electrodes l2, i i a deflecting potential which causes the electrons to move in the direction indicated by the arrow. Electrodes H, it are connected by the conductor 23 to the midtap on the transformer secondary, and the conductors it are electrically connected together to the same mid-tap.

A consideration of the potentials applied between the electrodes ll, i2, i3, and it with respect to one another and with respect to the conductors it will show that there is a potential difference between the ends of the adjacently positioned electrodes ll, l2, l3, and hi, also a potential difference between the upper right-hand conductor 56 and the electrode !2, and between the lower left-hand conductor l6 and the electrode M. However, there is no potential difference between the upper left-hand conductor 16 and the electrode l i nor between the lower righthand conductor l6 and the electrode 53. These potential differences are obtained from the voltages applied either across the entire secondary 22 or across one-half of the winding 22, as will be readily apparent from a study of this figure. The electrostatic lines of force due to the various potentials will form a pattern similar to that shown in Fig. 3. It will be noted that the area enclosed by the dotted square 28, in which the equipotential lines are almost equidistant and have small curvatures, is almost as large as the entire space contained within the deflecting that each of the equipotential lines represents a fixed potential diiference from the next adjacent line. Consequently a series of equally spaced lines represents a condition in which the deflecting-voltage gradient is constant throughout the region of equal spacing. Furthermore, in any region in which the equipotential lines are straight or have small curvature, the direction of the beam deflection will be the same irrespective of the portion of the region in which such deflection is initiated. Ithas been found that if the conductors It be omitted, the area over which the field is homogeneous is considerably reduced, and in some cases, entirely eliminated. The advantage of the increased homogeneity of field brought about by my improved deflecting structure is that the beam will be deflected proportionately to the variations in control potential over a considerable distance in the deflecting direction. Consequently, when it is desired to deflect the beam in two directions at right angles to one another as in the case of scanning a picture or image, the area over which the beam can be deflected throughout a homogeneous field is similarly increased and this tends to reduce distortion in the reproduction of the picture or image. This distortionless two-directional field can be obtained if desired, in accordance with my invention, by providing two complete sets of the deflecting structures shown in Fig. 3 and arranged adjacent one another, both structures being provided with the additional conductors i6 and the proper potentials to eliminate distortion in each of the two directions in which it is desired to deflect the beam.

The actual size of the deflecting electrodes and the spatial distances therebetween, also the distances between the conductors l6 and the electrodes, and the size of the conductors, as well as the other spatial and dimensional sizes and applied potentials, can best be determined by ex periment and will obviously depend onthe extreme areas or distances over which it is desired to deflect the beam. I have found that particularly good results are obtainable when the wires l6 have a diameter of about 1.5% of the side of the square formed by the deflector electrodes and are positioned a distance apart equal to about 78%. of the distance between the corners of. the

square.

It is obvious that any means may be employe to give the proper potential difference between the various electrodes, for example, continuous or interrupted direct-current voltages obtained from batteries or from any'other source of control voltage connected in such a manner that the equipotential lines of force contained within the deflector structure will have substantially the configurations shown in Fig. 3. Instead of using two sets of deflecting structures for deflecting the electrons in two directions, it is obvious that only one of the improved deflecting structures may be used for deflecting the electrons in one direction, and a magnetic form of deflectimg structure used for deflecting the elctrons in another direction. V arious other modifications will occur to those skilled in the art.

Another form which my invention might take and one in which the deflection is in the horizontal rather than in the diagonal direction is shown in Fig. 4. As in the case of Fig. 3, the conductors 16 are all connected together to the mid-tap of the transformer 22 which provides the deflecting voltage. But the electrodes II and M are now connected together, and similarly, electrodes l2 and I 3, so that the deflectingpotential is applied between two groups of electrodes, of which one group is constituted of electrodes H and i l and the other group is constituted of electrodes l2 and It. A study of the circuit diagram will show that there is a potential difference between electrodes ll and i2, also between electrodes l3 and Hi, but no potential difference between electrodes H and M nor between electrodes l2 and 13. But there is a potential difierence between all of the conductors and all of the electrodes. The fields introduced by these potential differences are roughly those illustrated in the figure, and it will be noted that a large square with its apexes vertical or horizontal can be drawn over an area in which the equipotential lines occur in a homogeneous array. Due to the manner in which the deflecting electrodes are connected, the direction of deflection is horizontal as indicated by the arrow. It will be noted that the length of the diagonal of the square 29 which encloses the area over which the equipotential lines are uniformly distributed is approximately 80% of the distance betwen any two opposite deflector plates, that is, 80% of the maximum deflection that is geometrically possible. This fact has been verified experimentally.

While I have described my invention more particularly in connection with deflector plates of a square or L-shaped cross-section, it will be understood that the increase in homogeneity of the static field introduced within the deflecting structure by the conductors it may also be advantageously employed in connection with deflector electrodes of other shapes than those illustrated and described. The spacing between the electrodes and between the conductors and the elec- 1 the electrons, said structure including a plurality,

of separate concave electrodes arranged to form an enclosure, means for applying a cyclically varying potential between at least certain ones of said electrodes to establish a deflecting field within the enclosure, and means within the enclosure for modifying the deflecting field to produce uniform deflecting gradients over substan-.

tially the entire region of deflection of the electron beam, said last named means comprising a plurality of discrete conductors of generally filamentary character charged to such potential as to produce local distortion of the deflecting field in the vicinity of each conductor.

2. In combination, a cathode ray tube comprising a source of electrons, means for accelerating said electrons, and a structure for deflecting the electrons, said structure comprising a plurality of L-shaped electrodes arranged to form a generally rectangular enclosure, means for applying a potential between at least certain ones of said electrodes to establish a deflecting field within the enclosure and within the enclosure for modifying the deflecting field to produce uniform deflecting gradients over substantially the entire region of deflection of the electron beam, said last mentioned means comprising a plurality of discrete conductors which are respectively positioned adjacent to the various L-shaped electrodes and which are charged to such a potential as to produce local distortion of the deflecting field inthe vicinity of each conductor.

3. A cathode ray tube comprising a source of electrons, means for accelerating 'said electrons, and a structure for deflecting the electrons, said structure including a plurality of separate concave electrodes arranged to form an enclosure, and a plurality of discrete conductors of generally filamentary dimensions respectively positioned within the concavities of the various electrodes, said conductors being adapted during the operation or the tube to modify the electrostatic field within the said enclosure.

4. In combination, a cathode ray tube including an electron gun and an electron deflecting structure, said structure comprising a plurality of pairs of oppositely positioned electrodes to form a common enclosure, means for applying a cyclically varying potential between the oppositely positioned members of one'of said pairs to provide a deflecting field for the electron beam Within the enclosure, means for maintaining another oi said pairs of electrodes at a relatively fixed potential to produce a first desired modification of the deflecting fieldand means for further modifying the deflecting field to produce uniform deflecting gradients over substantially the entire region of deflection of the electron beam, said last named means comprising the combination of a plurality of discrete conductors of general filamentary character positioned Withthe said enclosure and means for maintaining said conductors at a relatively fixed potential.

5. In combination, a cathode ray tube comprising an electron gun and an electron deflecting structure, said structure comprising a plurality potential to produce a first desired modification.

of the deflectin field and means for further modifying the deflecting field to produce uniform deflecting gradients over substantially the entire region of deflection of the electron beam, said last named means comprising the combination of a plurality of discrete conductors of general filamentary character respectively positioned Within the concavities of the various electrodes and means for maintaining said conductors at the mean potential of said alternating current source.

6. In combination, a cathode ray tube comprising an electron gun and an electron deflecting structure, said structure including a plurality of pairs of oppositely positioned L-shaped electrodes arranged toform a generally rectangular enclosure, asource of alternating current for applying a cyclically varying potential between the oppositely positioned members of one of said pairs to provide a deflecting field for the electron beamwithin said enclosure, means for maintaining the other of said pairs of electrodes at the mean potential of said alternating current source, a plurality of discrete conductors of generally filamentary character respectively positioned in each corner of the rectangular enclosure and meansfor maintaining said conductors at the same potential as the said other of said pairs of electrodes.

'7. In combination, a cathode ray tube comprising a'source of electrons, means for accelerating said electrons and an electrode deflecting structure, said structure including four concave electrodes arranged'to form a substantially closed configuration, alternating current means for applying a deflecting voltage between one pair of adjacent electrodes and the other pair of electrodes and means for modifying the deflecting field within the electrodes to increase its uniformity, said last mentioned means comprising a plurality of discrete conductors of generally filamentary character positioned Within the said hollow configuration and respectively adjacent each of said electrodes, andmeans for charging said conductors to a relatively fixed potential.

8. In combination, a cathode ray tube comprising a source of electrons, means for accelerating said electrons and a structure for deflecting the electrons, said structure including four L-shaped electrodes arranged to form a substantially rectangular enclosure, a plurality of discrete conductors of generally filamentary character positioned respectively in each corner of the said rectangular enclosure, means for applying a cyclically varying deflecting voltage between one pair of adjacently positioned electrodes and the other pair of electrodes, and means for maintaining said conductors at a common potential dififerent from the potential of each of said L'- shaped conductors.

9. In combination,'a cathode ray tube comprising a source of electrons, means for accelerating said electrons, and a structure for deflecting the electrons, such structure including four L-shaped electrodes arranged to form a substantially rectangular enclosure, a plurality of discrete conductors of generally filamentary character positioned respectively in each corner of the rectangle, an alternating current source for applying deflecting voltage-between one pair of adjacently positioned electrodes and the other pair of electrodes, and means for maintaining all the said conductors at the mean potential of the said alternating current source.

DENNIS GABOR.

CERTIFICATE OF CORRECTION.

Patent No. 2,212,596. August 20, 191m.

DENNIS GABOR.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 5, sec- 0nd column, line 214., for betwen" read -betwe en-; line 68, claim 2, before the word "within" insert "means"; page 1+ first column, line 17, claim )4, after "electrodes" insert --arranged-; and that the said Letters Patent should-be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 8th day of" October, A. D. 19).;0.

, Henry Van Arsdale, (Seal) Acting Commissioner of Patents.

v CERTIFICATE OF CORRECTION. Patent No. 2,212,596. August 20, 19m.

DENNIS GABO'R.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 5, second column, line 211., for "betwen" read "between"; line 68, claim 2, before. the word "within" insert "means"; pag'e ip first column, linelT, claim 14., l after "electrodes" insert -arranged-; and that the said Letters Patent should-be read with this correction therein that the same may conform to the record of the case in the Patent Office.

, Signed and sealed this 8th day or October, A. D. 191w.

x l I Henry Van Arsdale,

(Seal) Acting Commissioner of Patents.