US3155872A

US3155872A - Flat display tube utilizing voltage gradient deflection layer

Info

Publication number: US3155872A
Application number: US141862A
Authority: US
Inventors: Svend E Havn; Harry T Freestone
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1961-09-29
Filing date: 1961-09-29
Publication date: 1964-11-03
Anticipated expiration: 1981-11-03
Also published as: NL283750A; ES281160A1; DE1232273B; GB997576A

Description

Nov. 3, 1964 s. E. HAVN ETAL 3,155,872

FLAT DISPLAY TUBE UTILIZING VOLTAGE GRADIENT DEFLECTION LAYER Filed Sept. 29, 1961 3 Sheets-Sheet l FIGJ. g

SOURCE OF HORIZONTAL DEFLECTION SIGN AL INVENTORSI svsmo E. HAVN,

HARRY T. FREESTONE BY QMMMM THEIR ATTORNEY.

I Nov. 3, 1964 Filed Sept. 29, 1961 5. E. HAVN ETAL 3,155,872

FLAT DISPLAY TUBE UTILIZING VOLTAGE GRADIENT DEFLECTION LAYER .5 Sheets-Sheet 2 SOURCE OF HORIZONTAL DEFLECTION SIGNAL INVENTORS SVEND E. HAVN, HARRY T. FREESTONE,

BQJ

THEIR ATTORNEY.

Nov. 3, 1964 s. E. HAVN ETAL FLAT DISPLAY TUBE UTILIZING VOLTAGE GRADIENT DEFLECTION LAYER.

Filed Sept. 29, 1961 (5 Sheets-Sheet 5 FIG.3

SOURCE OF VERTICAL DEFLECTION VOLTAGE INVENTORS'.

N W Am. HF- am D N Evln VR R THEIR ATTORNEY,

United States Patent 3,155,872 FLAT DESELAY TUBE EJ'HLEZENG VQLTAGE GRAEHENT BEi-FLECTEfiN LAYER Svend E. Havn, Syracuse, NP! and Harry 'll. Freestone,

I'laoli, Fa assignors to General Electric Company, a

corporation of New Yorlr Filed dept. 2% 19st, No. raises to Gim'ms. (Cl. 315-423) This invention relates to an image display system and in particular to a relatively shallow cathode ray tube and circuit for energizing it.

It is one object of this invention to provide a shallow cathode ray tube system in which scansion of the beam in one direction may be obtained by the application of a beam deflection waveform to but a single point on an electrode structure of the tube.

It is another object of the invention to provide a shallow cathode ray tube system in which scansion of the beam in any direction can be effected with a beam deflection waveform having a relatively small peak to peak amplitude.

Still another object of this invention is to provide a shallow cathode ray tube .system in which dynamic focusing in the direction of beam scansion is effected without additional circuitry and in such manner as to maintain a relatively constant spot size in the scanning direction.

A further object of this invention is to provide a shallow cathode ray tube which can be energized and operated with circuits of the same type as employed with conventional cathode ray tubes instead of using relatively complicated and expensive circuits.

Another object of this invention is to provide a shallow cathode ray tube useful in attaining the above objectives.

Briefly, in accordance with certain aspects of this invention, electron beam deflection means are spaced opposite a target and extend along one dimension thereof and, when suitably electrically energized, the deflection means establishes a deflection field opposite the target. An electron beam is projected into the field and is caused to scan the target by the deflection means, one extremity of which is maintained at a certain fixed potential rela tive to that of the target and the potential of the other extremity is varied. In addition, means may be provided for varying the angle of entry of the beam into the varying deflection field. Various structures are provided in accordance with the present invention for effecting the type of action just described in a highly desirable manner. It is also possible by provision of certain relationships between the voltages applied to the structure just described and the region from which the beam emerges prior to its entry into the structure just described to obtain highly desirable deflection and focusing action.

The invention will be explained in more detail in connection with the drawings in which:

FIG. 1 is a front view of the cathode ray tube;

FIG. 2 is an external bottom view of FIG. 1; and

FIG. 3 is a side view of FIG. 1 at section 22.

Briefly, one way of obtaining these objectives in accordance with the principles of this invention is now described. The top portion of the cathode ray tube is an image section in the form of a rectangular box having greater height than depth. At the bottom of the image section is a vertical deflection section, and below this in a horizontal deflection section. This invention is directed to the vertical deflection and image section, and whereas various types of horizontal deflection sections may be used, the one that is the subject matter of US. patent application No. 141,863, filed in the name of Havn, one of the inventors of this application, is preferable. A target, capable of forming an image when scanned by a modulated electron beam, is mounted on the inside of one vertical Wall of the image section, and on the inside of an opposite wall a coating of highly rcsistive material provides a means for establishing a voltage gradient from the top of the coating down to a point where the resistive coating is joined by a lining of highly conductive material. The front wall of the vertical deflection section curves downwardly and to the rear from the lower front edge of the image section and is spaced at its lower extremity from an extension of the back wall with its conductive lining so as to form a slit like entrant section or throat. Means are provided for establishing the inside wall of the curved section at the same potential as the target or at least at some fixed positive potential. Means are provided for maintaining the upper edge of the resistive coating within a range of potential that is below the potential of the target and vertical er'lection waves 01": generally sawtooth configuration are applied to the conductive coating on the back wall.

The overall operation of the tube and system is as follows. The particular horizontal deflection system to be described projects a beam of electrons into the lower opening of the throat of the vertical deflection system in such manner that it moves along the slit in vertical collimated paths. A vertical deflection field is estab lished between the conductive back plate and the curved front wall of the vertical deflection section and is of sutlicient range to cause the beam to scan from the bottom of the target where it joins the curved section to a point beyond the top of the target. In other words, the vertical deflection thus produced overscans the target at the top. The voltage gradient established by the resistive coating between the fixed potential at its top and the deflection voltage wave at its bottom provides an automatic vertical focusing action by causing the beam to bend so that it will strike the target at an angle closer to normal than would otherwise be the case. The fixed potential at the top of the resistive coating is important as, for reasons which will subsequently be discussed in detail, it makes it possible for a cross sectional area of the beam of electrons to maintain a minimum vertical dimension.

In the specific form of the invention shown in FIGS. 1 and 2 the portion of the tube opposite the bracket 1 is the image section; the portion opposite the bracket VD, the vertical deflection section; and the portion opposite the bracket HD is the horizontal deflection and collimaling section. As seen in FIG. 1, an electron gun 2 projects a beam of electrons 3 between pole plates 4, only one of which is visible in the view; and the magnetic field set up between the pole plates 4 in a well-known manner by a yoke 6,. deflection coil 8 and source 1d of horizontal deflection waves causes the beam to scan in a plane parallel to the paper from one extreme position, 3/, to another, 3". Pole plates 12, only one of which is seen in FIG. 1, are mounted adjacent the outside wall of the horizontal deflection section HD. The pole plates 12 are joined at their right-hand ends by a magnet 14, and they are so shaped that the beam of electrons emerges along parallel vertical paths all in the same plane regardless of where the beam first enters the space between the pole pieces 12.. The collomated horizontally scanned beam thus formed enters the vertical deflection section VD and scans the target 16.

Reference is now made to FIG. 3 in order to obtain a clearer understanding of the operation of the cathode ray tube. These components previously described are indicated by the same numerals. The tube is shown as being made of glass. In the following discussion the term resistive coating or resistive means refer to a means having sufilcient resistance so as to not unduly load any source a) of varying voltage applied across it, and conductive coatings, means or surfaces refer to means which have an insignificant amount of voltage drop when different potentials are applied at different points. The target 16 may be comprised of the customary phosphor layer 18 dea conductive lining 26 which extends down along the back wall into the vertical deflectionsection VD. The conductive lining 26 is a means for applying deflection voltage Waves to the resistive coating 24 and to the means for deflecting the beam in the lower region of the target 16. A conductor 28 makes electrical contact with the resistive coatings 22 and 24 all along their intersection at the top right corner. The conductor 28 may be moved a small amount without upsetting the desired results.

In this particular embodiment of the invention, one part of the vertical deflection section VD is formed by a coat ing 21 which may be an extension of the metallic coating 20. The shape of this coating may vary, but in general it is desirable that it be parabolic. The coating 21 includes a horizontal portion shown as a strip 23. The other side of the vertical deflection system is formed by the extension of the conductive layer 26 and a portion thereof shown as astrip 25 that is parallel to the strip 23. The vertical deflection sensitivity is largely determined by the spacing between the

strips

23, 25. Other constructions of the front portion of the vertical deflection systems are possible. The curved section of glass could be replaced by an L-shaped section connecting the front wall of the image section I and the strip 23 and a conductive coating like the coating 21 could connect the strip 23 and the metallic coating 20. It is not essential that the potential of the strip 23 be the same as the target 16, and it would be possible to use other potentials but this would require another lead through the glass wall. The parabolic section is to be preferred as it lies adjacent to the path 54 and aids in guiding the beam to the target 16. Furthermore, if this coating 21 were not present, it would be desirable to substitute for it a high resistive coating so as to prevent random charges from collecting and disturbing the paths of the beam terminating at the lower end of the target 16. Any of the constructions described provide means for establishing a fixed potential at the front of the vertical deflection system, and the extended conductive lining 26 and the strip 25 provide means for applying a variable potential to the rear of the vertical deflection system.

The inner walls of the horizontal deflection section HD are lined with a conductive coating 3% which is connected internally as by a lead 32 to the final electrode of the electron gun 2 so as to insure that the entire horizontal deflection section HD, external to the gun, exists at an equipotential.

In order to simplify the drawings, the horizontal deflection components 4, s, 8 and 1d of FIGURE 1 have not been shown in FIG. 3.

It is, of course, necessary to provide leads through the glass wall of the tube to the various elements therein so as to apply potentials, voltage waves, and signals necessary to the operation of the tube. Thus a lead 34* makes connection with the corner conductor 28, a lead 36 makes connection with the conductive lining 26, a lead 38 makes connection with the conductive coating 34?, and a plurality of leads generally designated by .the numeral 42 make connection in the usual manner to the various elements (not shown) of the electron gun 2. One of these leads wardly until. it makes an electrical. connection at 2'7 with (g. is considered to connect to the cathode of the gun 2 and it is shown as being grounded.

Certain voltages and voltage ranges in FIG. 3 and all the drawings are to scale, in order to make the disclosure of one embodiment of the invention clearer, but it will be understood from the following discussion that these voltages, ranges and dimensions may be changed in various W21 S.

The manner in which the horizontal deflection section HD causes a collimated beam of electrons to scan back and forth, as it enters the vertical deflection section VD, in a plane generally perpendicular to the plane of the paper and in a generally vertical direction as indicated by the beam path 3 in FIGJ, has already. been explained. We now turn to the operation of the vertical deflection section VD and the image section I. .A source 44 of periodically recurring vertical deflection waves 46 having a period T is connected to the lead 36, and for illustrative purposes only, is assumed to vary between a peak value of 7 kv. and 1.6 kv. Inasmuch as the deflection lining 21 is maintained at a constant potential, herein shown as being 10 kv., which is the potential of the target 16, a varying electrostatic field is formed between the strip 23 of deflection lining 21 and the strip 25 of the rear conductive lining 26. This field is of such a nature as to deflect the beam and to cause the angle of entry of the beam into the deflection field existing in the image section 1 to vary and consequently cause the beam to scan the target 16 in a vertical direction. In fact, if the effects of the focusing resistive lining 24 are neglected, this vertical deflection field would direct the beam from a path '50, when the voltage wave 4-6 is at 7 kv. to a path 52, at a lower voltage, and to a path 54 when the wave 46 is at its lowest value of 1.6 kv. It will be noted that the angle of approach of the path 52 to the target 16 is rather shallow, and that consequently the vertical spot size will be too large. The voltage gradient extending vertically along the resistive coating 24 from the junction 27 to the conductor 28 produces an electrical field between itself and the target 16 that varies in strength. This field bends the beam from the path 50 along a path 50' which approaches the top of the target 16 at an angle much closer to normal than the path 52. This action continues but with decreasing effect as the beam scans downward, and somewhere in the vicinity of the level of the junction 27, it probably has very little eifect. However, a good approach angle is maintained at the lower positions because the angle of approach brought about by the vertical deflection section VD alone improves as the beam scans downwardly. In fact, path 54 shows an approach that is normal for all practical purposes.

Another factor that contributes in a significant manner to bending the beam more and more as it progresses along its path is the shape of the varying field produced in the upper region of the tube. The curved dotted lines illustrate equipotential surfaces at a particular position of the ield, and the vector P indicates the direction of the electrostatic fields at a point chosen at random. The resistive coating 24, the fixed potential applied to its top and the deflection waves 46 applied to its bottom and the potential applied to the target 15 are means for forming an electrostatic field defined by equipotential surfaces that remain relatively fixed in the vicinity of one extremity of the target 15 and rotate during the scanning cycle until the target is scanned from one extremity to the other. 0f course, during the relatively steeper portion of the detection wave 46 the equipotential surfaces quickly rotate back to their initial position. It can be seen that there is asubstantial downward component P which will act to slow the electrons down and give the normal component F more time to act. These field vectors are most pronounced when the deflection wave 46 is at its maximum value and when the beam is deflected by the section VD into the upper region of the tube. When the deflection wave at its lower value, the direction of the field may be such as to have an upward component, but this will be of little eficct as the beam is not in the upper region of the tube cavity when this occurs.

We now turn to a consideration of the reasons for maintaining the upper edge of the resistive coating 24 at a potential within a ran e that lies between the reference potential to which the cathode of the electron gun is referred, herein indicated as being ground, and the high voltage applied to the target 16. As the beam 3 emerges from the electron gun 2, the important dimensions as far as vertical focus or spot size at the target 16 is concerned, is that measured between the left and right hand edge of the beam, because the beam turns in planes parallel to the paper toward the target 16. By proper selection of the horizontal dimension of the beam as it emerges from the gun 2, the angle at which the left and right extremities of the beam converge and the shape of the vertical deflection field between the

conductive linings

21 and 25, the beam is made to have a sufficiently small vertical dimension at the target 16 when it strikes it at the bottom, as for example when it follows a path 54. As the beam scans toward the top of the tube, it is desired that the curvature of the path gradually reduce until it strikes the top of the target along a path 56. When this result is achieved the vertical dimension of the beam at the target lo remains constant from top to bottom because even though the change in convergence is less per unit length of path, the path is longer.

With this in mind, observe what happens as the potential of the corner conductor 28 varies. As its potential is lowered, the beam is deflected more strongly toward the target 15 by the field produced primarily between the re sistive coating 24 and the target 16, thus requiring that the deflection wave 46 be more positive than it was before in order to strike the same point. If the potential of the corner conductor 2% is reduced too much, the beam must follow a path such as 55 in reaching the top of the target. It may even be necessary to make the peak of the wave more positive than the target 15 to even reach the top. Observe that the curvature of the path 56 in its upper region is as great or greater than that of the path 54 so that the curvature of the path is not gradually reduced. The vertical spot size increases because the left and right edges of the beam cross over before they reach the target 16. It is true that the desired path Ell does not approach the target 16 as close to normal as the less desirable path 56, and it might seem, therefore, that the vertical spot size would be enlarged. The fact is, however, that little change in size is produced for angles of approach reasonably near 90.

The maximum limit of the range of voltages within which the conductor 28 need be maintained is easily determined by determining what value will cause the beam to just reach the top of the target 15 when the deflection wave 46 is at its maximum positive value. As the voltage of the conductor 28 is increased, the maximum positive value of the wave 46 may be decreased, in order to cause the beam to strike the top of the target 16, but the trajectory followed will approach the trajectory 52, which it is recalled was the path followed as a result of action by the vertical deflection section VD acting alone. Thus increasing the potential of the conductor .23 permits the reduction in the positive peak of the deflection wave 4-6 with a consequent more shallow approach of the beam to the target 16.

The lining so, the strips 23, 25' and the

surfaces

21, 26 with voltages applied thereto, constitute a lens system which deflects the beam at a vertical rate and also provides a dynamic focus action that is very weak when the beam strikes the top portion of the target 16, and gradually increases as the beam scans toward the bottom. Optimum dynamic focal characteristics are achieved by suitable design of the length of the gaps till, es, the height of the

strips

23, 25, their spacing and the voltages applied.

It would be possible to connect the front portion of the lining 39 to the strip 23, thus establishing the horizontal deflection zone at the same potential as the screen. However, this would necessitate an increase in the horizontal deflection power as the beam within the horizontal deflection section would have a higher potential.

From an examination of FlGURE 1 it will be seen that there is a considerable difference in the path lengths 3' and 3 to a given height in the target lid. Thus the convergence of the beam in a plane perpendicular to the paper in FIGURE 1 is significant, the focusing actions that control vertical spot size cannot produce constant vertical spot size along horizontal lines on the target to, unless some sort of dynamic control is used at the electron gun 2. Thus in accordance with this invention the convergence of the beam as leaves the gun 2 is maintained slight, 2 minutes having been found satisfactory. Smaller converge-cc may be used.

it is contemplated that if any problems arise by virtue of random collection of electrons in the areas where the glass is exposed that they can be eliminated by application of a high resistive coating such as chromic oxide. Such a coating has not been shown in the drawings.

In place of the resistive coatings 22 and Z4 arrays of horizontally disposed wires interconnected by resistors and mounted in the respective plane of the resistive coatings in such manner that the wires are parallel to the target 16. The purpose of the coating 22 is to establish definite potentials between the target lo and the conductor 23 and thus to prevent the random collection of charge from upsetting the terminal lines of the equipotential planes. If collection of charge does not take place, the coating 22 could be dispensed with. However, the coating 24 or some means such as the wires interconnected by resistors must be provided for supporting, maintaining or establishing a voltage gradient, at least in the vertical direction, in a surface parallel to the target, between the fixed potential applied to the top and the deflection voltage wave an applied to the bottom.

Consideration is now given to the factors determining the vertical position of the junction 27 between the resistive coating 2 that establishes the dynamic focusing field and the conductive coating 26. As 27 approaches the top of the tube, the angle of approach of the beam in the central portion of the screen becomes very shallow and poor focus results. Also the deflection lens and subsequent focal lens in the upper region becomes overly strong and results in over focus of the beam at the top of the picture. As 2-7 is lowered along the back the required drive voltage increases and consequently increases the deflection power required. Then too the angle of approach of the beam at the top or" the picture becomes excessively shallow and degenerates focus.

If the junction 27 is located at the top of the tube so that the entire rear wall is a conductive surface, the focusing action discussed in connection with the resistive lining Z4 and the potential applied thereto is eliminated, but the advantages of that portion of the invention relating to the vertical deflection section VB and the horizontal deflection section l-iD are retained. On the other hand, if the junction 27 is moved to the bottom of the tube so that the entire back wall is lined with highly resistive material, more drive voltage may be required, but in order to retain the focusing action described with reference to the resistive coating 24, it may be necessary to vary certain parameters such as the depth of the tube and the potential of the corner conductor 23.

Whereas the coating 24 and the conductive lining have been shown as lying in a plane that is parallel to and rearward of the plane of the target 16 it is to be understood that these surfaces could be curved or inclined toward one another to some extent without upsetting the operation. Therefore, when a planar surface or surface is set forth in the claims, such terminology should not be interpreted as being restricted to a true plane.

it will be apparent to one skilled in the art that the 1 junction 27 may be eliminated and that separate connections could be made to the coating 24 and to the conductive lining 25. It should also be apparent that other internal connections could be eliminated by this technique. However, it is desirable that the number of leads extending through the walls of the tube be reduced to a minimum.

What we claim is:

1. In an image display device, a target capable of producing an image when scanned by a beam of electrons, means for supporting a voltage gradient, at least in a given direction, on a surface that is generally parallel to and spaced opposite said target, means for applying a potential to said target, means for applying a lower potential to one extremity of said voltage gradient supporting means, means for applying a cyclically recurring deflection voltage waveform to another extremity of said voltage gradient support means, one cycle having a period T and said waveform having an amplitude which varies continuously throughout the period T, and means for proiecting a beam of electrons into the space between said target and said voltage gradient supporting means.

2. In an image display device comprising a planar target having an area with top and bottom edges, means for supporting a potential gradient between a first line parallel to and spaced from said top edge and a second line, parallel to and below the first line, said second line being opposite an intermediate portion of said target, a conductive surface direct current coupled to said voltage gradient supporting means at said second line and extending downward at least as far as the bottom edge of said target, and means including said conductive surface for producing an electrostatic deflection field in the region of said lower edge of said target between the plane of said target and said conductive surface.

3. In an image display device, a target capable of producing an image when scanned by a beam of electrons, resistive means for supporting a voltage gradient in at least a vertical direction along a surface opposite to and to the rear of said target and generally parallel thereto, a first highly conductive surface direct current coupled to said resistive means along an extremity of said resistive means, said first highly conductive surface extending below said target, a second conductive surface having a portionthereof parallel to and disposed forwardly of the portion of said conductive surface that is below said target.

4. In an image display device as set forth in claim 3, an electrical connection between said second conductive surface and said target.

5. In an image display device, a target capable of producing an image when scanned by a beam of electrons, resistive means for supporting a voltage gradient in at least a vertical direction along a surface opposite to and to the rear of said target and generally parallel thereto, a first highly conductive surface direct current coupled to said resistive means along an extremity of said resistive means, said first highly conductive surface extending below said target, a second conductive surface making electrical contact with said target so as to be at the same potentialas said target, said second conductive surface curving rearwardly and downward to a line parallel to and spaced from the portion of said first conductive surface extending below said target.

6. An image display system comprising a planar target, means for establishing an electrostatic field in the vicinity of said target, said field being defined by equipotential surfaces that remain fixed in the vicinity of one extremity of the target and that rotate during a scarring cycle, means for projecting a beam along collimated paths in a plane, and means for deflecting the beam of electrons so as to cause it to enter said field from the other extremity of said target at varying angles with respect to said target.

7. An image display system comprising a planar target, means for establishing an electrostatic field in the vicinity of said target, said field being defined by equipotential surfaces that remain fixed in the vicinity of one extremity of the target and that rotate in one direction until the target is scanned from one extremity to the other, means for projecting a beam along collimated paths in a plane, and means for deflecting the beam of electrons so as to cause it to enter said field from the other ex 'emity of said target at varying angles with respect to said target.

8. A cathode ray tube comprising a two dimensional target, means for supporting a voltage gradient, when suitable potentials are applied thereto, said means being disposed in a plane parallel to said target and opposite a first portion thereof, a highly conductive surface, said highly conductive surface being disposed opposite to a second portion of said target, means for establishing, when energized, a varying electrical field transverse to the plane of said target within a region adjacent to the portion of said highly conductive surface that is remote from said means for supporting a voltage gradient, and means for projecting, when suitably energized, a beam of electrons along successive collimated paths into said region.

9, An image display system comprising a cathode ray tube as set forth in claim 8, means for applying a fixed potential that is more positive than the reference potential at which the electron beam originates to said means for supporting a suitable voltage gradient in a region remote from said conductive surface, and means for applying a deflection wave to said latter means in a region adjacent said conductive surface.

10. An image display system comprising a cathode ray tube as set forth in claim 8, means for applying a fixed potential that is more positive than the reference potential at which the electron beam originates to said means for supporting a suitable voltage gradient in a region remote from said conductive surface, and means for applying a deflection voltage wave to said latter means in a region adjacent said conductive surface and to said conductive surface. 7

11. An image formation system comprising a two dimensional target, means disposed in a plane opposite to and spaced from said target for establishing an electrical field in the vicinity of said target of such nature as to urge electrons toward said target, means for varying the strength of said field in a cyclical manner, means for projecting a beam of electrons along collimate-d paths with a predetermined electron potential, means deflecting the beam following the coliimated paths in planes perpendicular to said target and for directing them into said field, said latter means being comprised of spaced conductors parallel to said target, means for applying a fixed potential to one of said conductors that is higher than said predetermined potential, means for applying to said other conductor a potential that varies in amplitude in synchronisrn with the variation in strength of said field.

12. A cathode ray tube comprising a two-dimensional target, means for establishing, when suitably energized, a voltage graident across a first two-dimensional surface that is opposite and parallel to said target, said voltage gradient extending in a direction parallel to one dimension of said target, means for providing an equal distribution of any potential applied to a second two dimensional surface throughout the second two-dimensional surface, said second surface lying in the same plane as said first surface and extending along said one dimension of said target, a third surface, means for applying, when suitably energized, a potential equal to at least a portion of a voltage appliec to said target to said third surface, said third surface having a portion thereof mounted parallel to a portion of said second surface and forming a slot therebetween that extends in a direction perpendicular to the direction of the voltage gradient in said first surface, an electron gun for forming an electron beam, and means for directing said beam through said slot along successive colli' mated paths when suitably energized.

13. An image display system comprising a cathode ray tube as set forth in claim 12, means for applying a fixed potential to said target, means for applying a relatively lower potential along the portion of said first surface that is remote from said second surface, a source of deflection voltage Waves, and means for applying said voltage Waves along the portion of said first surface that is adjacent said second surface.

14. A system for displaying images comprising a cathode ray tube haivng a two-dimensions, target, said target having first and second parallel edges, an electron gun for forming a beam of electrons, means for directing said beam in a direction that would cause electrons of the beam to cross over said first and second edges of said target in the order named, and means for causing said beam of electrons to scan said target in a cyclic manner between said first and second edges and beyond said second edge, means for supporting a potential gradient in a direction perpendicular to said first and second edges along a surface parallel to said target and opposite to at least a portion of said target that is adjacent said second edge, means for applying a fixed potential to said target, means for applying a fixed potential to the portion of said means for supporting a potential gradient that is adjacent said second edge of said target, a source of deflection voltage Waves that vary in synchronism with said cyclic scanning of said target, and means for applying the deflection voltage waves to a portion of said means for supporting a voltage gradient that is remote from and parallel to said second edge of said target so as to cause said beam to approach the portion of said target that is near said second edge at an angle that is closer to ninety degrees than would otherwise occur.

15. In a cathode ray tube having a target extending in at least one dimenision having two extremities, deflection means including a voltage gradient supporting means spaced opposite and in generally parallel relationship to said target, said deflection means extending in said one dimension for establis 'ing an electron beam deflection field opposite said target, means for generating an electron earn having a path extending between the target and said deflection means, and means for cyclically scanning the beam across the target in said one dimension, on scanning cycle occurring in a period of time T, said scanning means including means for maintaining one extremity of said dimension of said deflection means at a fixed potential relative to said target and means for applying a singular varying potential to the other extremity of said dimension of said deflection means, said varying potential having an amplitude which varies continuously through out the period T.

16. In a cathode ray tube havini a target extending in at least one dimension, deflection means spaced opposite said target and extending in said one dimension for establishing an electron beam deflection field opposite said target, means for maintaining one extremity of said deilection means at a fixed potential relative to said target, means for generating an electron beam having a path extending between the target and said deflection means, and means for cyclically scanning the beam across the target in said one dimension, one scanning cycle occurring in a period of time T, said scanning means comprising means for varying the angle of entry of the beam. into the deflection field in a plane perpendicular to sadi target, and means for applying a varying potential to another extremity of said deflection means, said varying potential having an amplitude which varies continuously throughout the period T.

References Cited in the file of this patent UNITED STATES PATENTS 2,880,365 Law et al -u Mar. 31, 1959

Claims

1. IN AN IMAGE DISPLAY DEVICE, A TARGET CAPABLE OF PRODUCING AN IMAGE WHEN SCANNED BY A BEAM OF ELECTRONS, MEANS FOR SUPPORTING A VOLTAGE GRADIENT, AT LEAST IN A GIVEN DIRECTION, ON A SURFACE THAT IS GENERALLY PARALLEL TO AND SPACED OPPOSITE SAID TARGET, MEANS FOR APPLYING A POTENTIAL TO SAID TARGET, MEANS FOR APPLYING A LOWER POTENTIAL TO ONE EXTREMITY OF SAID VOLTATE GRADIENT SUPPORTING MEANS MEANS FOR APPLYING A CYCLICALLY RECURRING DEFELECTION VOLTAGE WAVEFORM TO ANOTHER EXTREMITY OF SAID VOLTAGE GRADIENT SUPPORT MEANS, ONE CYCLE HAVING A PERIOD T AND SAID WAVEFORM HAVING AN AMPLITUDE WHICH VARIES CONTINUOUSLY THROUGHOUT THE PERIOD T, AND MEANS FOR PROJECTING A BEAM OF ELECTRONS INTO THE SPACE BETWEEN SAID TARGET AND SAID VOLTAGE GRADIENT SUPPORTING MEANS.