US3038101A

US3038101A - Deflection controlled tube

Info

Publication number: US3038101A
Application number: US725270A
Authority: US
Inventors: Schlesinger Kurt
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 1958-03-31
Filing date: 1958-03-31
Publication date: 1962-06-05
Anticipated expiration: 1979-06-05

Description

June 5, 1962 K. SCHLESINGER DEFLECTION CONTROLLED TUBE Filed March 5l. 1958 RJ swam 2 sheets-sheet;

INVENTOR. lem' June 5, 1962 K. scHLl-:slNGER 3,038,101

- DEFLECTION CONTROLLED TUBE PMM/ @MJU United States Patent O 3,038,101 DEFLEC'HQN CNTRQLLED TUBE Kurt Schlesinger, La Grange, lll., assigner to Motorola, luc., Chicago, Ill., a corporation of Illinois Filed Mar. 3l, 1958, Ser. No. 725,270v il Claims. (Cl. 315-22) This invention relates to a new and improved crossedeld modulation system for use in cathode-ray tubes to modulate Iand focus a beam and thereby control the intensity of a spot on a viewing screen. y

Cathode-ray tubes in present use include an electron gun having a small area or point cathode modulated by an adjacent grid, which together with a first anode converges the beam into a crossover. A lens is provided to image the crossover on a viewing screen so that a spot is formed thereon, and the grid-modulation controls the intensity of the spot.y

Some generally recognized standards for a good electron gun are that it should provide high beam current and resolution, good halftone rendition, high modulation sensitivity, and minimum interaction between control voltage and spot size. For many applications, and particularly those in which the control voltage is developed by transistor circuits, it is desirable for the control characteristic to permit modulation with low voltages of the order of 12 volts or less. It has been found that cathode-ray tubes with conventional grid-modulation control cannot meet all of the above general requirements; there has to be a compromise between brightness and resolution.

Accordingly, one object of this invention is to provide a new and improved system for modulating and focusing an electron beam.

Another object of the invention is to provide a cathoderay tube with a new and improved intensity control system which has high modulation sensitivity at low beam voltages.

Still another object is to provide an improved deflection control using beam interception in which scattered electrous resulting from such interception are collected separately in order to reduce halation on the screen.

A feature of the invention is the provision of a cathoderay tube with a large area cathode providing a high current beam which is concentrated by a focusing modulator into a small image-defining aperture which presents a stable size and shape with controlled illumination.

Another feature of the invention is the provision of a focusing modulator assembly having electrostatic electrodes generating crossed-fields simultaneously providing strong focusing elds and weak superimposed deecting fields, thereby permitting intensity control of a high current electron beam with low control voltages.

Another feature of the invention is the provision of a crossed-field modulator including a slotted-cylinder unit providing two electric fields in a cavity; one field being coaxial for Ifocusing an electron beam, and the other being transversal for deflection modulation of the beam.

A further feature of the invention is the provision of a focusing modulator including two separate bifocal fieldgenerator systems arranged in quadrature along the tube axis, with each system having four pole-pieces shaped .as

rectilinear hyperbolae, and with the first system receiv' ing the modulating signal along its positive focal plane.

A further feature of the invention is the provision of a new and improved deflection modulation system having a beam intercepting anode, and wherein scattered electrons and secondary emission from the interceptor anode are drawn backward to a collector anode which is positively biased.

A still further feature is the provisionl of a focusing modulator having a post-focuser at its exit end including rice a concave profile immediately following an intercepting aperture for concentrating the lbeam in the presence of post-accelerating elds.

The invention is illustrated in the accompanying drawings in which:

FIG. 1 shows a cathode-ray tube including a crossedeld modulator in accordance with one embodiment of the invention;

FIG. Z is ya slightly enlarged cross-sectional view of the modulator structure shown in FIG. 1; l

FIG. 3 shows a printed ceramic construction forrthe modulator of FIG. l;

FIG. 4 is a diagram of a control circuit suitable for use in the cathode-ray tube shown in FIG. 1;

FIG. 5 is a curve illustrating the control characteristic of the modulator of FIG. 1; l

FIG. 6 shows a modification of the crossed-field modulator structure shown in FIG. l; and

FIGS. 7 and 8 show a cathode-ray tube including a focusing modulator in accordance with another embodiment of the invention.

The invention is a modulation system for cathode-ray tubes in which a high current beam of electrons passes through a focusing modulator including adjacent electrode groups, each having a plurality of pole-pieces bounding a common cavity. The pole-pieces generate crossed electric fields in the cavity which simultaneously exert focusing and deflecting action on the beam.- In a slottedcylinder embodiment, the pole-pieces have a semi-cylindrical shape. In another embodiment, the pole-pieces are shaped as rectilinear hyperbolae. In either case, two or more groups of pole-pieces are closely spaced coaxially to form the common cavity in which deflection and lfocusing take place. The radial distance from the axis of the cavity to the active faces may vary from one group to another. A form of insulating material is provided to locate the pole-pieces in the proper positions, and the pole-pieces may be provided as coatings of conductive material on the form. In the slotted-cylinder embodiment, the focusing action is provided by a field which acts coaxially of the modulator while deflecting action is provided by fields which act transversely and are, therefore, crossed with respect to the focusing field. In

ythe hyperbolic embodiment, simultaneous deflecting and focusing action is obtained with a single pair of electrostatic 4-po1e systems arranged in quadrature along the same axis, with only the rst system being connected to the modulating signal. In both embodiments, an apertured interceptor anode is positioned at the exit end of the cavity. The beam of electrons passes through the cavity with little loss since it is converged to form a sharp, small crossover right at the interceptor. The deflecting field causes part of the beam to impinge yon an edge portion of the interceptor, while the remainder of the beam passes through the aperture and thus varies with the modulating signal. Electrons which are intercepted tend to scatter, and this may cause undesirable halation of the picture background. To prevent this, a collector anode is positioned behind the interceptor to pull the scattered electrons backward. The collector anode may be a separate apertured disc, or may even be one of the groups of pole-pieces if the cavity therethrough is made to have a suiiiciently small diameter at its exit end.

In FIGS. 1 and 2 there is shown part of a cathode-ray tube having a focusing modulator of the slotted-cylinder type. Electrons are emitted from the large area cathode 1t). The electrons are accelerated away from the cathode 1-0 into the modulator cavity 33 where they are focussed into a crossover. This crossover is placed right in the spot defining aperture 44 in -the interceptor anode 43. The beam is deflected in response to a modulating signal applied to half of the slotted-cylinder so that the portiony of the beam passing through aperture '44 is' con- `trolled. A positively biasedcollector plate. 5.1 havingy f -t-entialsto each half vof the cylinder, a transverse Afield: l

an aperture l52y is positioned behind the interceptor with they edgev of aperture 52 closely spaced kfrom they intercepting edge houndingaperture 44. in order to` pull back yscattered'electrons which tend to cause halation 'on the Screen. f

The beamdiverges after passing through the aperture 20 by the interactionof a concave meniscus 45. at low :voltage andthe main llen-s barrel` 17 at higher voltage.y

f 44, and is re-converged into an image-forming 'section l Since the interceptor presents `a beam of deiinite shape potentialv electrostatic, un-potential electrostatic, ,mag-l ynetic, and others. The image forming section is pref- .erablyl of large; diameter to reduce spherical aberrations. vThein'xaging lensintyv also include asecond anode 18 i l which is preferably acoating -18 .of conductivematerial v 1 kon ith: lwall 19 ofl the tube.: f .This liens vsection is adjust- .ed to focus the image of the aperture 44 into a well: de-i i fined spot on theviewing screen .21. f f

. The cathode ;10.is provided with a comparatively large emitting 4surface. 26, and since beam current. is propori tional to cathode areahigh beam currents rmay therebyv be provided.` .The -cathodeisurface 26 is concave ito preiocusing end-plate 41. provide a ield which preconwith varying illumination, the image forming section 1 may be any of several conventional types, ysuch as ybiisv established between the halves'. Thus, the bcamis deflected `slightly from the centcr of the aperture 44.

lThis isy accomplishedv by moving the arm .iliileither above or below the center position. Thenr when a ymodulating Signal isapplied toene-half of the unit, theerieet is to f f shift the position of the beam focus transverselyl in rcl sponse tothe variations ofthe signal. v f

; The picture displayy from a'givenv signal will be a positive or negative image, depending on the oit-center position of the focusvvith respect to aperture ,44. Accordzingly, the `crossed-held modulator tube is capable kof handling picture signals of either polarityl by reversing the l bias across the cavity. 'Since' thev beam-voltage .in the :cavity isrcomparatively slow, thev deflecting field can ,be` weak, and eiiicient-modulation canbehad at aloW signall .level of theorder. of 12 volts'and less. A control .char- :actenistic for a .modulator in .accordance vwith FIG. 1 is Shown in FIG. 5 `to illustrate the; high modulation sensi.'r c fil/ity `and the positive-negative picture control describedA labovepmf.. l

, The followingdimensions for :a :cathode-rayA tube built f n in accordance with FIGS'. l and-2 arey giveny by yway of f facilitate focusing. vThe collimating aperture 27 andA the verges/the *beamprior to itsentry into the modulator cavity 33.r .Relative placement of cathode 10, collimator d2, 30

and end-plate 41 maybe chosen such thaty thev collimator lbiasoptirnizes atl ground potential.` y

v The modulator vlrincludesthree pairs of pole-pieces:r .l

glass, or other insulating material. The inner faces 8l and 82 of the pole-

pieces

38 and 39 respectively, and the manner in which they bound the slotted cavity 33, may be seen clearly here.

The poles 34-39 are shown in FIGS. l and 2 as halfrings of metal, but may also be constructed by applying coatings of conductive re paint to an insulating form such as is illustrated in FIG. 3. The pins 132, preferably of Kovar, extend through the semicylinders 130 and make contact with the inner surfaces 3439. In either type of construction, the pole-pairs are separated by narrow insulating gaps 40.

The circuit diagram of FIG. 4 illustrates how electric potentials may be applied to the elements of a modulator structure n accordance with FIG. l. A potential of about 250 volts may be applied to the two end-

plates

41 and 51 in parallel. A slightly lower potential is applied to the interceptor 43 and also to the pole-pairs 34-35 and 38-39. A low voltage bias is applied to the central pole-pair 36--37, and the latter pair may even be grounded. A structure of this type provides a non-linear spatial potential distribution which exerts strong focusing action with low spherical aberration, especially if this spatial potential variation is parabolic. By judicious choice of pole-piece length and bias, the focal length of this modulatormay beadjusted so as to focus the beam into a sharp `crossover right at the spot dening aperture 44 of the interceptor 43.

When opposing pole-pieces are at the same potential, the field `formed thereby has circular symmetry. Therefore, the crossover is centered with aperture 44 and most of the beam passes through it. This symmetrical field distribution exists when the arm 100 on potentiometer 102 is at the center position. By applying different poiilustration'and 'arel not intended to limit the lscope of the y invention in any lway:

Separation lbetween cathode 10 and grid 12 Separation between poles 344-35, 36--37, 38--39 i 0.030 Transverse spacing betweenl pole-pairs 34: and 35;, l f 36-and k3'7, .and 38-and 39 f 0.030

Diameter ofprefocusier aperturel 42 0.100 Diameter of grid aperture 27 l f 0.150

Diameter of collector aperturev 52 0.060

-Diameterof interceptor aperture 44 0.025 Diameter of emitting surface 26 0.060 Diameter of cathode '10 0.125 DiameterE of meniscus 45-.; c 0.250 Radius of meniscusl 4'5 l 0.125 Diameter of cavity 3'3 '.f.'. 0.250 Length of pole-pieces 34-35 4/16 Length of pole-pieces 364:9 5716 Thickness of

end plates

41 and 51 0.010 Thickness of disc 43 0.062

The following circuit values are given for the circuit shown in FIG. 4 only by way of illustration:

Such a cathode-ray tube has been found to have the following characteristics:

Modulation voltage 12 volts and less.

Maximum transconductance 150 microamperes per volt.

Maximum beam current G-1200 microamperes.

Highest voltage needed for modulator 250 volts. Resolution Better than 400 lines.

In FIG. 6 there is shown a modification of the modulator of FIG. 1 in which the cavity diameter tapers down towards the exit. In the tapered structure shown here, the faces 91 of pole-pair 61--62 at the cavity exit have a diameter `which corresponds roughly to that of edge 52 shown in FIG. 2. Pole-pair `61--62 is maintained at a slightly higher potential than the interceptor 71 to pull Inch i i .030 Separation between grid 12 and prefocuser 41 f 0.100 f sessant' back scattered electrons, and thus no separate collecting structure is required.

A cathode-ray tube provided with a focusing modulator in accordance with another embodiment of the invention is shown schematically in FIGS. 7 and 8. It may be seen that in this embodiment the modulator 14) includes two

adjacent quadrapoles

138 and 139 on a common axis and forming a common cavity 153. The active yfaces of the ypole-pieces 141-143 are of hyperbolic shape. The polepieces are held in position by a common cylinder 149 of insulating material such as lava, as may be seen in FIG. 8. Slots 151 are provided in the cylinder 149 to locate the edges of the pole-pieces. A broad beam of electrons from the large area cathode 10 passes through the composite system, and will converge to a crossover at the exit end of cavity 153 when .proper bias is applied to the pole-pieces. An apertured interceptor 43 is placed at the eXit of the cavity. A collector anode 51 is interposed between the interceptor 43 and the cavity.

The action of the modulator 140 is somewhat different from that of modulator 13 of FIG. l, but there is an overall similarity in construction and the beam passing through the cavity is simultaneously focussed `and deiiected by crossed-fields. the cavity 153; one exerting a positive focusing action, and the other exerting -a negative focusing action. Voltages are applied to each quadrapole in a balanced-to-anode fashion, as shown at X and Y in FIG. 7. As a result, the average beam velocity stays constant throughout the system. Moreover, experience shows that the potential difference -and length of the respective electrodes are inversely proportional. If used independently, each qua rapole would tend to produce a line focus. It has been found, however, that by employing only one pair of quadrapoles with the polarities of one rotated 90 with respect to the other, it is possible to obtain an overall positive focusing action, and under certain conditions of bias this system can produce a point focus. The conditions for obtaining point focus can be described by the equation Where f1 is the focal length of the first quadrapole 138, f2 is the -focal length of the second quadrapole 139, and a is the distance between them. The system can be biased to pass the beam through the narrow aperture 44, and the focus is then shifted transversely by a modulating signal applied to one of the poles 142 and 144.

The potentials required to provide this simultaneous focusing and deflecting action are applied to the various elements of the modulator by the circuit shown therewith in FIG. 7. The prefocuser 41 and collector 51 are placed at about 200 volts, and the interceptor 43 is placed at a VSomewhat lower potential to insure that scattered electrons are collected. Opposite pole-pieces within each quadrapole system are placed at the same potential, with .the pairs 141--143` and 146--148 being positive with respect to beam voltage, and pairs 142-144 and 14S- 147 being negative with respect to beam voltage. The pairs of like polarity in :

groups

138 and 139 are rotated 90 with respect to each other in order to provide the composite crosSed-ield effect previously described.

The modulating signal is applied lfrom the signal source 155 to pole-piece 144 to initiate deflection modulation. VIt is important to apply the signal to one of those electrodes in quadrapole system 138 which is negative with respect to beam voltage so that the first quadrapole system receives the signal along its positive focal plane. If this is done, the beam -Will 4move in a plane for which the second quadrapole system is divergent, its corresponding polepieces being positive with respect to `anode voltage, as shown. Under these conditions, the second quadrapole 139 lprovides additional defiection even though it is not directly connected to the signal source.

Each quadrapole generates two fields in It is apparent from the foregoing description that the crossed-field modulation system of the invention provides a high current gun yielding a spot of denite size and shape. This system has a nearly linear modulation characteristic, and it runs on very low signal voltage. Consequently, a tube provided with such a crossedeeld modulator may be operated in a television receiver wtih a low level of video signal, and is especially suited vfor use with transistorized circuits which provide signals of only 12 Volts or less. The modulation off the beam by partial interception has little effect on spot size. Spurious halation by scatter electrons can be eliminated by the provision of a separate collector anode in back of the intercepting anode. A tube having a control system of this type is capable of displaying positive or negative modul-ation. This 1oiiers the practical advantage of handling signals of either polarity with out the need for a separate inverting ampliiier.

I claim:

1. In a cathode-ray tube including a viewing screen, and an electron source for directing a beam in a predetermined path against the screen, a crossed-field modulation system for controlling t-he intensity of a viewed spot formed by the beam on the screen, said system including in combination, a beam intercepting anode located between the electron source and the screen and having a spot defining aperture in alignment with the predetermined bearn path, a plurality of adjacent electrode groups located between the electron source and said intercepting anode and each including a plurality of electrostatic poles positioned on opposite sides of the predetermined beam path, said poles having transversely curved active faces extending longitudinally and defining a common cavity for passage of the beam, circuit means having a iirst portion for applying different biasing potentials to said poles to establish a focusing field in said cavity for converging the beam into a crossover at said edge of said intercepting anode, said circui-t means having a second portion for applying a modulating signal to certain of said poles for superimposing a transverse -deiiecting field on said focusing field which is effective to deiiect said beam between one extreme condition wherein the beam is directed at said spot defining aperture and another extreme condition wherein substantially the entire beam is directed on said beam intercepting anode about said aperture, whereby the modulating signal is effective to control the portion of the beam passing through said aperture and striking said screen, thereby controlling the intensity of the viewed spot.

2. In a cathode-ray tube having a viewing screen, and an electron source for directing a beam in a predetermined path against the viewing screen, a crossed-field modulation system as defined in claim l having at least three adjacent electrode groups each including two opposed poles, said poles having active faces of semi-cylindrical [shape forming a slotted cavity, and said first portion of said circuit means applying a lower potential to the intermediate pole-pair than to the other two to provide a non-linear spatial potential distribution exerting strong positive focusing action.

3. In a cathode-ray tube including a viewing screen and an electron source for directing a beam in a predetermined path against the viewing screen, a crossed-held modulation system as defined in ciaim 1 having two coaxially adjacent electrode groups arranged sequentially in quadrature and each including four poles, said poles having active faces shaped as rectilinear hyperbolae, with the biasing potentials applied thereto by said first portion of said circuit means being selected to provide a composite crossed-field exerting positive focusing action, and with the rst electrode group in the sequence receiving the modulating signal along a `focal plane for which the second electrode groups is divergent.

4. In a cathode-ray tube including a viewing screen, and an electron source yfor directing a beam in a predetermined path -against the viewing screen, a crossed-field modulation system as defined in claim 1 with one of said poles in the electrode group positioned nearest to said beam intercepting anode having a portion closely spaced from the surface on said interceptor anode impinged by the deflected beam, and with the potential applied to said closely spaced pole-portion by said circuit means being more positive than the potential of said interceptor anode, whereby electrons which are scattered from said interceptor anode are separately collected by `said pole-portion.

5. In a cathode-ray tube including a viewing screen, and an electron source for directing a beam in a predetermined path against the viewing screen, a crossed-field modulation system as dened in claim l and further including a collector anode interposed between said beam intercepting anode and the electrode group positioned nearest thereto, said collector anode having a portion closely spaced from a surface on said beam intercepting anode impinged by the detlected beam, and with said circuit means having a portion for biasing said collector anode positively with respect to said beam intercepting anode for separately collecting electrons which are scattered therefrom.

6. In a ctahode-ray tube having a collimator and a cathode for emitting a high current beam of electrons in a predetermined path, a focusing modulator including in combination, an interceptor anode having a spot defining aperture therein of a diameter smaller than the diameter of the beam emitted by said cathode, a multiple electrode structure positioned between the cathode and said interceptor anode, said electrode structure including a least three closely spaced electrode groups each including a pair of semi-cylindrical electrostatic pole-pieces defining a common cavity for passage of the beam, a collector anode between said interceptor anode and the electrode group at the beam exit end of said cavity, said collector anode having an aperture aligned with said image defining aperture and larger than said image dening aperture, circuit means for applying different predetermined biasing potentials to said pole-pieces thereby establishing in said cavity a focusing field having a non-linear spatial potential distribution exerting strong focusing action for converging said beam at the position of said interceptor anode, said circuit means having a portion for applying a modulating signal to half of said pole-pieces for superimposing a transverse field on said focusing field providing a composite field of variable transverse asymmetry, with such composite field being effective to deflect the beam between one extreme condition in which the beam is directed against said interceptor anode and another extreme condition in which the beam is directed through said aperture therein, thereby providing deflection intensity control, and said circuit means having a further portion for biasing said collector anode positively with respect to said interceptor anode for drawing scattered electrons back from said interceptor anode to said collector anode.

7. In a cathode-ray tube, a focusing modulator as defined in claim 6 and further including an apertured prefocusing anode between the collimator and the electrode group at the beam entrance end of said cavity, and said circuit means applying a positive potential to said prefocuser anode for preconverging the beam before entry into said cavity.

8. in a cathode-ray tube, a focusing modulator as defined in claim 6 with said circuit means including a variable control for adjusting the biasing potentials applied to said pole-pieces, said control being adjustable to invert the sense of modulation for converting between a positive and a negative picture.

9. A focusing modulator for use in a cathode-ray tube having a collimator and a cathode for emitting a high current beam of electrons in a predetermined path, said modulator including in combination, a prefocuser anode adjacent the collimator and having an aperture therein aligned with the predetermined beam path, a multiple electrode structure adjacent the exit side of said prefocuser anode and including two groups of electrostatic polen pieces arranged in sequence and defining a common cavity aligned with the predetermined beam path, each of said groups comprising four pole-pieces arranged in opposed pairs about the predetermined beam path and having active faces shaped as rectilinear hyperbolae bounding said cavity, a collector anode at the exit end of said cavity and having an aperture aligned with the predetermined beam path, an interceptor anode closely spaced from the exit side of said collector anode and having a spot defining aperture therein of a diameter smaller than that of the beam emitted by said cathode and larger than that of said aperture in said collector anode, said spot defining aperture being aligned with the predetermined beam path, and circuit means having a first portion for applying predetermned biasing potentials to said pole-pieces with said opposite pole-pairs in each of said groups being of opposite polarity, one of said groups being rotated with respect to the other for providing a composite crossed electric field in said cavity for focusing the beam at the position of said interceptor anode, and said circuit means having a second portion for applying a modulating signal to one of said pole-pieces in said first group for superimposing a dellecting field on said composite field effective to deliect the beam between one extreme condition in which the beam `is directed substantially entirely against said interceptor anode and another extreme condition in which the beam is directed lthrough said spot defining aperture, thereby providing deflection intensity control.

l0. In a cathode-ray tube, the combination including, a large area cathode for emitting a high current beam in a predetermined path, an interceptor anode spaced from said cathode and having a spot defining aperture smaller than the diameter of the beam emitted 'by said cathode, focuser means lbetween said interceptor anode and said cathode for focusing said high current beam into a crossover at said spot defining aperture, said focuser means including a multiple electrode structure providing a composite focus ing field having a variable transverse component for deecting the entire focused beam in one lateral direction substantially entirely out of said aperture and onto said interceptor anode about said aperture, means for providing modulation potential at said electrode structure effective to vary the deliection of the beam with respect to said spot dening aperture and said interceptor anode about said aperture so that the total beam current supplied to said interceptor anode and said aperture therein is substantially constant and the portion of the beam current which passes through said aperture varies from a cut-oli Value to a maximum value, an image forming lens spaced from the beam exit side of said interceptor anode, and concave post-focusing means at the exit side of said spot defining aperture lfor concentrating the beam before it enters said image forming lens.

11. In a cathode ray tube, the combination including, a large area cathode for emitting electrons in a predetermined path, an interceptor anode spaced from said cathode and having a spot defining aperture therein, electrode means positioned between said interceptor anode and said cathode, said electrode means including a plurality of poles providing a composite electric :field having both axial and lateral components in the path of the electrons, said poles of said electrode means being positioned so that said field is effective to focus electrons from said cathode into a crossover at said spot defining aperture and to deflect substantially all of such electrons laterally away from said spot defining aperture and onto said interceptor anode about said aperture, and means for applying modulation potential to said electrode means to vary the deection of the electrons with respect to said spot defining aperture to thereby control the portion of the electrons which passes through said aperture, said large area cath ode providing substantially constant electron current to said interceptor anode and through said aperture therein, with the portion of the electron current passing through said aperture varying yfrom a Ieut-off value to a. maximum value.

References Cited in the le of this patent UNITED STATES PATENTS 10 Sziklai Feb. 26, 1952 Smith Dec. 27, 1955 Williams Sept. 24, 1957 McNaney Oct. 29, 1957 Kompfn-er May 13, 1958 Laerty Sept. 16, 1958 Logue Apr. 28, 1959 Beam May 26, 1959 Glaser Dec. 29, 1959