US2803781A

US2803781A - Device comprising a cathode-ray tube

Info

Publication number: US2803781A
Application number: US362702A
Authority: US
Inventors: Jurgens Benno Frederik
Original assignee: US Philips Corp
Current assignee: US Philips Corp; North American Philips Co Inc
Priority date: 1952-08-13
Filing date: 1953-06-19
Publication date: 1957-08-20
Anticipated expiration: 1974-08-20
Also published as: GB746777A; FR1088280A; NL171800B; BE522075A; DE975071C

Description

Aug. 20, 1957 B. F. JuRGENs DEVICE CQMPRISNG A CATHODE-'RAY TUBE Filed June 19, 195s ,Il am wJ .w+ A

m m M y w Q/:J

2,803,781 DEVICE COMPRISIN G A CATHODE-RAY TUBE Benno Frederik Jurgens, Eindhoven, Netherlands, as-

signor, by mesne assignments, to North American Philips Company, Inc., New York, N. Y., a corporation of Delaware Application .lune 19, 1953, Serial No. 362,702 Claims priority, application Netherlands August 13, 1952 9 Claims. (Cl. 315-25) This invention relates to cathode-ray tubes, more particularly, to cathode-ray tubes which exhibit a linear relationship between the deilecting signal and the actual beam deflection. i

Some cathode-ray tubes comprise a pair of planar electrodes at the window end, between which an electrostatic field is produced for the purpose of dellecting a beam of electrons. One of these electrodes is a collecting electrode, and the other, which is parallel to and in front of the collecting electrode, may be in the form of a grid, or be constituted by a thin metal skin allowing the passage of electrons. An electrostatic field can be produced between the electrodes by applying suitable voltages thereto, the main direction of the lines of force being directed substantially at right angles to the surfaces of the two electrodes. Such an electrode system is useful to obt-ain the so-called post-acceleration of the electron beam. A further use is found in the production of television color images, in which the electron-permeable electrode is in the form of a grid parallel to the collecting electrode and a luminescent screen, which is divided into lines or points depending upon the type of television system employed.

An electron-beam entering the above-described electrostatic iield between the two electrodes at an angle with the lines of force is subject to a force making an angle with the direction of incidence, the electron beam thereby being deiiected along a curved path. This deflection results in a large deviation from the desired linear relationship between the shift of the point of impact of the electron beam, and the deflecting voltage or current which causes said shift, which deviation is dependent upon the angle between the direction of incidence of the electron beam and the lines of force and, hence, the extent of deflection. Since the deflection varies for different areas of the collecting electrode, so does the deviation vary.

The present invention has as its object to provide means for correcting the non-linear relationship, resulting from the above-mentioned deviation, between the shift of the point of the impact of the electron beam and the deflection voltage or current.

A device, according to the invention, comprises a cathode-ray tube having an electrode system which comprises an electron gun including at least a cathode and an accelerating electrode, a substantially planar collecting electrode, an electron-permeable electrode arranged in front of the collecting electrode parallel therewith, an electrostatic eld being produced between the latter electrodes, and means for deflecting an electron beam to scan the collecting electrode, which may be either electrostatic or electromagnetic. In front of the deflecting field produced by the deilecting means, there is provided shifting means for producing a iield to shift or displace the electron beam parallel to itself and in the plane of deflection, which means are coupled to the deiiecting means in a` manner such that the deflection of the electron beam is counteracted by the deflection due to the` eld produced between the collecting electrode and the electron-permeable electrode arranged in front thereof. The deilection should be adjusted so that there will result a complete compensation of the deviation. However, in certain cases, partial compensation will be adequate.

A shift of the electron beam parallel to itself may be effected in a simple manner by providing a pair of deilection fields which are identical, but oppositely directed, and which are provided in front of the iieid produced by the deilecting means. Such identical elds of opposite direction may be produced by either two pairs of deflection plates arranged after one another and interconnected in a crosswise manner, or two sets of magnetic coils traversed by current in opposite senses.

The shifting means for the electron beam should be coupled to the deflecting means. Such a coupling need not be a direct galvanic connection, but may include a network for bringing about the desired relationship between the deflection voltage or current and the voltage or current applied to the members for shifting the electron beam. Such a network may include, for example, cathode-ray tubes, resistors, capacitors, transistors and other elements.

' If the electrostatic or deflecting field between the collecting electrode and the electron-permeable electrode is produced by a voltage difference, and the collecting electrode has a positive potential relative to the other electrode, the electron beam, before entering the electrostatic or deilecting field, should be shifted in the same sense as the deection itself. lf the collecting electrode has a negative potential relative to the electron-permeable electrode in front thereof, the shift should be eifected in the opposite sense.

In the foregoing description, reference has been made 4 to one eld causing the deflection. In many cathode-ray tubes, for example, those for television purposes, there are provided, successively, two deflecting fields to permit deflection of the cathode-ray in two different directions, which are generally at right angles to one another. What has been said above with respect to the non-linear relationship between the shift of the point of impact and the current or voltage-applied to the deflecting means, applies equally well to both systems. Consequently, shifting means may be provided for both directions. In certain cases, however, shifting means for one direction or deection is sucient. This is the case for a device for reproducing television color images in which the luminescent screen is covered with parallel strips of material luminescing in different colors, and in which the electronpermeable electrode parallel to the luminescent screen is a grid comprising solely Wires parallel to the strips of luminescent material. In such a device, it is essential that there be accurate registration beteween the grid and the luminescent screen in a direction at right angles to the grid wires, which implies that the `deection of the electron beam at right angles to the grid wires must be in very exact linear relationship with the deilection voltages or currents. In the absence of accurate registration, particularly in the case of comparatively large angles of deflection, the correct color line will not be struck by the electron beam for a regular sequence of the color lines on the screen all with the same spacing and width. This difliculty might be eliminated other than by the invention by adapting the sequence of the color lines on the screen to the nonlinear relationship, but in this case there results a screen at the center of which lines of the same color do not have the same spacing as lines of the same color at the margin of the screen, which is extremely difficult to manufacture. On the other hand, pro` viding the shifting means according to the invention is a much simpler method for obviating the diiiiculty.- `Cor-l rection in a direction parallel to the color lines is not i `Patented uxg. 20, 1957Y accelerating electrode 3, and a conventionalv deection necessary since, with slight non-linearity, there willY belno change in color, but at most, relatively snialldistortionV ofthe image. Y

The invention is vapplicable to both the cathode-ray tubes containing. alumineseent screen, .andf tubes -crmtaining aplurality offanodes, thefsofcalled. switchingtubes. .The'invention will now bedescribed Y'with .reference .tov the aceompanying' drawing'yin which:A C Y Fig. l shows diagrammatically a Conventional cathoderay tubeA without the vshifting .means according to the.-v

invention, fc'sr the purpose. of. explaining the phenomena v1 of the deflection infront of` a collecting electrode;A

A Fig. 2. shows, on ,anv enlarged scale, adetail of `the tube shoWninTig; le;` Y, I.

Figl 3 shows'V diagrammatically an. electrodey system for4 `shifting.:an electron Vbeam; f

Fig. 4- lis ya diagrammatic viewof a-Vcathode-ray tube. in which the. electron beam is deile'cted as well as `shifted by, elec.trom-magnetic.means; Y Y

Eijg.5 is La View, similarto Fig. 4 of a modification;

Fig. z6VV showsA diagrammaticrallyv part of'a` cathode-ray.l 'tube adapted vfor reproducingtelevision color images.

i Referring now to^Fig. l a cathode-ray tube 1 cornprisesran electrodeV systemy includingV a cathode 2, `an` system constituted by

plates

4 and 5, which may be referred to as a first deecting means. A planar, con- Cil Fig; '3- shows, diagrammatically, one form of deflec-VY tion system according to the invention, in which in front of a lpairY of .coriven't'i'onal of rs't rdefiecting members and 16, there Vis provided an additional electrode sys- .tem in order to shift or displace the electronbeam parallel to itself and in the plane of the deflection eifected by the electrodes V15 andv 16. This electrode systemV is constituted'bry two pairsT of successively-arranged

deilection electrodes

17, 18, j19, '20, the

electrodes

17, 20

and 18, 19, respectively,"beingjdirectly connected gal- 'Y Y vanically in a crosswise manner. v In the absence'of this electrode system, Ythe electron beam would follow the path 21 and be deflected in the direction 22 bythe Voltage applied between the

electrodes

15 and 16. Due to the crosswise connection of the electrodes 17, and'18, 19, respectively, theV application 4of la voltage to the saidz electrode groups between the electrodes17 and 19 causes a deection of the electron beam which is compensated by the

electrode system

18, 20 eiecting la similar 'd e# ductive, collecting electrode 6 is provided 'at the Vend-ofVV the conical portion of the envelope. A grid 7, i. e., the Y electron-permeable electrode, is provided in -front of the- Y collecting electrode 6 and parallel therewith. A voltage difference provided by a Voltage source 8 is appliedbe,- tween the

electrodes

6 and 7 such that the electrode 6 has a positive potential relative to the electrodep7. ',The

'

electrode system

2, 3 produces an electron beam 9 Vwhich is deected by

theV deflection system

4, 5 inthe ldirection indicated by reference numeral 10. On passing through the grid4 7, the electronv beam 1 0 entersv the electrostatic eld between the electrodes 61and 7, inwhiehtheVV 'lines of force extend substantially parallel toy the 'axis'.

ofthe tube. The angle enclosed between the electron beam Itlandthe lines of force isindicated'by u.

may beV seen more vclearly froml IFig.' 2, in which part of. the,

electrode system

6, 7 is shown on an enlargedl scale. Due to the electron beam 10 Vintersecting the lines 'ofi lleotionbut in thebpposite sense. The direction' ofthe beam upon.emerging-from*thesystem- 18, 20 isthe`refore Y parallel to thedirection'fof originalbeam, but' is no longer located on the Yaxis,.but atthe position 23. The

. beam 23 now enters the deflection,

systemV

15, 16. ',When v this system -h'as applied' toit a. similar voltage as thatl causing a beam` on the axis to-"be deflected inY the directiorr 22, the Vbeam 23 vvi'lillfnow be deflected in the 'direci tionf 24, which -is `parallel`tothe directionl 22. By. applying suitablevoltagesito `the shifting

membersY

17, 18, 19,

20-by Ameans of a voltage Vdivider 42, it can be ensured that 'they distance between 'the directions 22 and 24V is force llat an angle a, a deection is produced, which Y will be referred to as a second deilection, so that the If the deecting the point of impact, per unit of shift of the/.point o'f'.'v y

impact as a .result of the deflecting voltage alone, i'ssmaller than with a comparatively large angle of'deecf tion, whereby the beam impinges upon a part ofthe? colf Y lecting electrode 6 located more towards the margin.

VIn order t'o reach the `point 14 in Fig; 2 at the -sam'edeection voltage, the electron beam must enter the lield' between the electrodes 6 "and 7 at a point further-re`A mote from. the axis of the tube; this results .from the.

fact that,V in Figs. Y1 and y2, the potential of the electrode 6::is :higherthan that ot theelectrode 7, `so that theelectron beam110 is bent towards the Vlines-of force.'y thereby describing thev curved path 12. :On the other hand,.it`,'theipotential` of. the electrode *6T is lower than.

that-of the grid 7, a1 deflection directed; away froml the. lines offforee will occur, .and =theielectron vbeam will ihave. to enter the eld'at a point closer to the. tube'faxisr: s r

exactlyy the amount required, so that the point' of theV collectingelectrode'struck would also be the point struck by a ray inthe direction 22 in the absence of therelectro-v stat-ic lield between the collecting electrode' and the electron-permeable electrode in front thereof.' By cou-V pling the shifting Ymea-ns 17 to 20 to thev 'deection'sysr tem 15, y16 as shown in the ligure, the proper correlation between the amount of detlection and the amount of shifting can be realized.

Fig. 4v shows a device according to the invention in. which ,the scanning 'deection is eiected Vby sets ofmagnetic coils 25, 26, shown diagrammatically.- The set of coils 25 is providedyat the cathode side, 'with two smallsets of coils 29,'30'whieh are .eonstructedV and` connected so thatthe Y'c l'etlection brought about by: the set of coils iscorrected.

i Fig'. -6 shows a cathode-raytube `adapted for reproduit Y I ingtel'evisitmY color images. -The electrode systemfof this tube comprises ascreen l31 'constituted by strips of mate-V rial"32'whieh become .luminescent inV different colors"V upon bombardment by electrons.V vIn front of theV electrede 311is'provided agrid 33 consisting of paralleli wires 34.` vIn order Vto, scan the/whole, screen 31, the beam 35v should be deected in a directionparallel to the grid wires'34 and ina direction at rightv angles thereto. For this purpose, use Vis made of sets of

coils

36, 37,. respectively. In the? direction at right angles Yto the grid wires, it is essential that the positions of the impact points Vof the beam 35.011 theelectrode 31 should be linearly dependent uponthe deflection voltage, that, is 'to say, that the imagej p Y of the grid-330m the luminescent4 screen 31 in a directionat right angles tothe imagesof the gridwires'should be' congruent to' the V'grid itself. VForthi's purpose, provi-V sionkis made of correcting or shifting sets of coils'. 38

and' 39. Y As explained before, a congruentimage isfno't particularly important ina direction .parallel to the grid.,V wires y34:Y Consequently, it will in -most cases, be suij.

cient tojutilizethe system shownin Fig. 6. If, however,

correcivon ofthe-,deection parallel to the-direction of the grid' wires is also desired, it is jp.ossible"to"provide two further' sets` of; coils .for shifting thebeam parallel withV ,thedirectionxof the grid wires.

. fltnisialsdmpossible, Vof course, nto.V either f'c'ombine. elee v tromagnetic dellection means and electrostatic means for shifting the beam or, conversely, to combine electrostatic members for the deflection with electromagnetic members for the shift.

The grid in front of the collecting electrode may, alternatively, be used for electing so-called post-acceleration. However, in many cases, use may be made of, instead of a grid, one or more annular electrodes commonly provided on the wall of the tube; in such a system, it is also possible to shift the point of impact of the beam on the collecting electrode by employing correcting members as described above.

It will be evident that the invention is not limited to the embodiments described, but is applicable to any device containing a cathode-ray tube having a collecting electrode and an electron-permeable electrode in front thereof. Thus, it is possible, or example, for the electron-permeable electrode 43 to be a thin, metal skin as shown in Fig. 5, or for the collecting electrode as well as the electrode in front thereof to be arranged in an inclined position with respect to the axis of the electrode system, which serves to produce and deflect the cathoderay. Furthermore, for example, in the case of a nonconductive luminescent screen, use may be made of a conductive electrode either before or after the screen, to which electrode the required voltage is applied instead of being applied to the screen itself.

What is claimed is:

l. A device comprising a cathoderay tube, said tube having an electrode system including a cathode, an accelerating electrode, a substantially planar, collecting electrode, and an electron-permeable electrode arranged in front of the collecting electrode and parallel therewith, first means for dellecting an electron beam disposed between the accelerating electrode and the electron-permeable electrode, means disposed in front of the rst dellecting means for shifting the electron beam parallel to itself and in the plane of deflection, means for maintaining an electrostatic eld between the permeable electrodes and at w 'ch a beam incident obliquely thereto is subject to a second deflection in one direction, and means interconnecting the shifting and rst deilecting means in such manner that the value of said rst detlection produced when a signal is applied to said rst dellecting means determines the magnitude of the shift produced by the shifting means in a direction opposite to said one direction, substantially to compensate for the second deflection produced by the electrostatic ield.

2. A device as claimed in claim l in which the electron permeable electrode is in the form of a grid.

3. A device as claimed in claim 1 in which the electron-permeable electrode is constituted by a thin metallic member.

4. A device as claimed in claim means include means producing a tlection fields which are identical in sitely directed and transverse to the 5. A device as claimed in claim ing means is constituted by two sets current in opposite senses.

6. An arrangement including a cathode-ray tube; said tube having an electrode system including at least a cathode, an accelerating electrode, an electron-permeable electrode, and a planar collecting electrode parallel to said permeable electrode arranged in that order; tirst means for deecting an electron beam disposed between the accelerating electrode and the permeable electrode, shifting means disposed in front of said rst detlecting means for shifting the electron beam parallel to itself and in the plane of dellection produced by said rst deilecting means, said shifting means including two pairs of successively-arranged deection electrodes intercon- 1 in which the shifting pair of successive demagnitude and oppobeam direction.

4 in which the shiftof coils traversed by collecting and electronnected in a crosswise manner, collecting electrode at a positive potential relative to the permeable electrode to thereby dellect the beam in one direction, and means connecting the pair of deection electrodes closer to said cathode in parallel with the rst detlecting means to shift the beam in a direction opposite to said one direction, said shifting and deilecting means producing deilections in the same direction.

7. An arrangement including a cathode-ray tube; said tube having an electrode system including at least a cathode, an accelerating electrode, an electron-permeable electrode, and a planar collecting electrode parallel to said permeable electrode arranged in that order; rst means for deilecting an electron beam disposed between the accelerating electrode and the permeable electrode, shifting means disposed in front of said first dellecting means for shifting the electron beam parallel to itself and in the plane of deilection produced by said deilecting means, said shifting means including two pairs of successively-arranged deflection electrodes interconnected in a cross-wise manner, means maintaining the collecting electrode at a negative potential relative to the permeable electrode to thereby detlect the beam in one direction, and means connecting the pair of dellection electrodes closer to said cathode in anti-parallel with the first detlecting means to shift the beam in a direction opposite to said one direction, said shifting and deilecting means producing deilections in the same direction.

8. A device comprising a cathoderay tube, said tube having an electrode system including, in order, a cathode, an accelerating anode, an electron-permeable, conductive electrode, and a substantially planar, conductive, co1- lecting electrode spaced from and arranged parallel with the electron-permeable electrode, means for maintaining a potential dilerence between the electron-permeable and collecting electrodes to thereby establish an electric tield therebetween whereby an electron beam intercepting said eld at an angle thereto will be subject to a second dellecton in a given direction, first deilecting means mounted between said electron-permeable electrode and said accelerating anode for causing an electron beam produced by said cathode to scan said collecting electrode, shifting means disposed between dellecting means and producing a pair of adjacent, successive, opposing elds for causing said beam to be displace parallel to itself and in a direction always opposite to said given direction, and means interconnecting said shifting and first delecting means whereby the magnitude of the first deilection produced by the first deilecting means determines the magnitude of the displacement produced by the shifting means to substantially compensate for the second beam deflection produced between the electronpermeable and collecting electrodes.

9. A device as claimed in claim 6 in which the electronpermeable electrode is a grid comprising solely parallel wires, the collecting electrode is a screen covered with strips of material which become luminescent in different colors and extend parallel to the `grid wires, and the shifting means are arranged to effect a shift in a direction at right angles to the direction of the grid wires so that the image of the grid on the collecting electrode in this direction is congruent to the grid.

means maintaining the References Cited n the tile of this patent UNITED STATES PATENTS said accelerating anode and lirst.