US 2784342 A
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March 5, 1957 A. J. w. M. VAN OVERBEEK 2784342 cmcun' FOR TELEVISION PICTURE TUBES F1ed April 1 1953 4. 5. INVENTOR ADRIANU5 Jormrmss VVILHELMUS MARIE VAN OVERBEEK 2,784,342 C!RCUIT FOR TELEVISION PICTURE 'IUBES Adrianus Johannes Wilhelmus Marie van Overbeek,
Eindhoven, Netherlands, assignor to Hartford National Bank and Trust Company, Hartford, Conu., as trustee Application April 1, 1953, Serial No.346,083
Claims priority, applieatiou Netherlands April 10, 1952 Claims. (Cl. 315-21) This invention relates to a circuit for a television picture tube of which the sereen is.composed of three strips of the same width which are cyclcally repeated and which reproduce the fundamental colours, which screen is scanned in two directions substantially at rght angles to one another, one directon coincidiug with the direction of length of the strips.
In knewn circuits of the above-mentioned kind the picture tube serves solely for the reproducton of colour television images. ode-ray beam of the tube is obtained in such manner that the cross-section of the beam at the area of the sereen scans one coiour strip at the same time, so that one colour only is reproduced,
The deflection of. the beam is chosen, for exarnple, to be such that at first a11 strips of one colour, subsequently all strips of the second colour and then allstrips of the third colour are scanned. It is alternatively possible for the strips to be scanned in succession, in which event, for example, a red strip, then a green strip, subsequently a blue strip and then again a red strip, etc. are scanned.
The object of the circuit according to the invention is to make the picture tube serviceable not only for reproducing colour irriages, but also for the reproduction of black-white images and, furthermore, for another method f reproducing colour television images which is suitable for a colour television system in which inforrnation is transrnitted about brightness, colour and degree of satuiation of the image to be reproduced.
The circuit according to the invention is characterised in that the cathode-ray beam exhibits astigmatism, the largest dimension of the crosssection of the beam at the area of the sereen being substantially equal to three tirnes the width of a strip and the smallest dimerls'ion of: the cross-section at the same area being sbstantially equai to the width of one strip, provision being made of means for varying the orientation and the dimensions of the cross-section of the beam with respect to the direction of iength of the strips.
In order that the invention may.be readily carriedinto effect, it will now .be. described with re ference to the accornpa-nying drawing showing, by way of example one embodirnent thereof.
Fig. 1 shows a piuraiity of strips of the sereen, some iorms of the crosssection of the beam at the areaof the sereen being shown, which is also the case in Fig. 2
Fig. 3 shows a picture tube comprising a sereen such as shows in Fig. 1 er Fig. 2, some control mens ofthe tube being shown diagrarnrnatically. 1
Fig. 4 is a secticnal view at the area of the dotted line iV IV in Fig. 3, Fig. 5 showing diagrammatically a circuit of a deflection coil and the supply circuits used therewith.
The part of the sereen 1 shown in Fig. 1 is constituted by groups of three strips 2, 3, 4 and5, 6,-7, which are cyclcally repeated and which reproducethe fundarnental colours, for exarnple red (r) green (g) and blue"(b).
Reference numeral 8 indicates one ob tainable cross Maximum anastigmatism of the cath- SGITICS Pareii section of the cathode-ray beam where it strikes the sereen, the main dimension of which lies in the direction of length of the blue strip 4. The smallest dimension of the cross-section of the beam is at the most equal to the width of the strip.
If the beam with this orientation of its cross-section is defleeted in the direction of length of the strip, a visible blue signal is reproduced.
Wheri the beam is rnoved tbrough a distance equal to the width of one strip in the vertical direction, for exa-mple upwards, the cross-section of the beam lies on agreen strip and a visibie green signal is reproduced upon horizontal deflection.
With this orientation of the cross-section of the beam the picture tube is thus suitabie for reproducng a colour television image, it being mentioned for the sake of compieteness that the resolving power in the horizontal direction is smaller than with the couventional scanning method, in which the dimension of the cross-section of the beam in the horizontal direction is substantially equai to that in the vertical direction.
Since the beam is astigrnatic, it is possible by varying the focai length of the electron-optical system of the tube to obtain also an orientation of the cross-section of the beam at the area of the sereen by which the largest dimension of the cross-section is directed verticaily, as indicated at 9. In this case, the beam strikes the strips 3 (g), 4 (b) and 5 simultaneously, so that a blackwhite signal is now reproduced by the tube.
If the beam is rnoved in the vertical direction, it is possible for the whole sereen to be scanned.
If the vertical position of the beam, after one strip has been scanned, varies only over the width of one strip or two strips, this also results in subsequent horizontal scannings partly overlapping, so that the structure of the strips is rendered substantialy invisible.
Fig. 2 shows three forms 10, 11, 12 of the cross-section of the beam in which the center of the beam is centered on the green strip 1.3, and furthermore three forms 14, 15, 16, in which the center of the beam is centered on the blue strip 17.
At the position 10, white instead of green is reproduced, since red, green and blue strips are struck by the beam. Consequently, the degree of saturation of the green is uil, since the reproduced colour is located at the white point of the colour triangle.
At the position 12, green only is reproduced, the saturation of the green signal thus being equal to 1.
If, starting from the position 10, the focal length of the electron-optical system is graduaiiy vared until the position 12 is reached, a plurality of intermediate forms of the cross-section of the beam oceur at the area of the sereen, one of which is indicated at 11.
At the position 11, the beam strikes the strip 13, but
at the same time it also strikes part of the red strip located above and the blue strip located below, which corresponds to a degree of saturation of the green which is comprised between 0 and 1 and which is, for exarnple, 6.5.
Consequently, if at a determined position on the sereen the focal length of the electron beam systerri is varied therebychanging the size of the electron beam in the vertical direction from the center of the cross-sectin of the beam, this causes the degree of saturaion of the reproduced colour to be varied.
If the deflection is varied in the vertical direction, so that the center of the cross-section of the beam lies for example, on the blue strip 17, blue can be reproduced with differingdegrees of saturation, the positions 14,15, 16 exhibiting f0r;examplegthedegrees ot-saturatioxrj In producing a white colcrby means of the verticall y eilngte eleetren beam "spot 10, as deseribeil 'abdve, there will be a slight predominanee of green color due to the greater spot area on the green color strip. Similarly, the spot 14 will produce a slight predominance of -blue eolor, and the spot en the neirt line Will produce a slight ipredominance of red eolor. These slight deviatio'ns -from pure white are seatcely notieeable, due to the wide color toleranee of the human eye. The efiect of pure white is produced, how'ever, iiue te integration by the eye of the slightly predomiatirig eolors of grieen, blue and red during -successive scnnings of the eolor strips.
Consequently, if a eolour television sgnal is supplied to a colour televison receiver and this signal eomprises the required info'rmatien: brightness, eolour and degree of saturation, this 'signal may be reproduced with the use of a circuit aecording to the inVention.
One embodim'ent -suitable for this purpose is shown dag'rammatically in :Fig. 3.
A cathode-ray tube 18 comprises a sereen 19 having Strips of the kind shown in Fig. 1 or Fig. 2.
Furthermore, the tube comprises a cathode 20, a Wehnelt-electrde 21 and a first anode 22, by whieh a cathode-ray beam is generated in kn0Wn manner with the use of suitable biassing potentials.
The beam is focussed with the use of a focussing coil 23 of known eonstruction. A's viewed in the direction of movement of the electrons of the bearn, a coil 24 fed with suitable direct-current is provided behind the focussing coil 23. A cross-section of coil 24 taken 'along the dotted line IVIV is shown in Fig. 4, reference numeral 25 indicating the wall of the tube 18 at the area IVIV.
As may be seen from Fig. 4, the coil 24 has a shape which is fiattened and, as the case may be, for example elliptie. The cathode-ray beam thus aequires the required astigmatism, and the cross-seeti0n shape of the beam al'ong a portion of the length thereof in the vicinity of the sereen varics from an-oval shape with the longest diameter perpendieular te the sereen strips, to an oval shape with the longest diameter parallel to the sereen strips. By varyng the focus eurrent in the focus coil 23, these diterently shaped cross-section areas of the beam Will shift along the length of the beam, and thus the beam ean be c'aused to have the desired cross-section at the point where it strikes the sereen.
The astigmatism of the cathode-ray beam may alternatively be ensured in a different way, as is Well-knownin the aim at avoiding this phenomenon whieh, as a rule, is undesirable.
Thus, for example, in the case of the deflecton coils, vhieh are not shown in Fig. 3, it is possible for the two halves of one deflect'ion coil to be supplied in oppo'site senses with direct eurrent, such as shcwn diagrammatieally in Fig. 5.
The deflection coil is in this case constituted by halves 26 and 27. The deflection current is supplied between earth and a terminal 28 via a capacitor 29 te thehalves of the coil. The latter are conneeted in series in opposite senses, the series-c0nnection inclucling -a battery 30.
A further method of obtaining astigmatism is to provide the eathode-ray tube with an eleetron-opticl system eomprising a cylindrical eleetrode of ellipticl section.
Furthermore, for example, when using a -eathode-r-ay tube in whieh use is made of electrostatic deflection, the mean voltage of a set of deflectionplatesmaybe dilerent from -the voltage of the seeondanode of this tube.
Referring again to Fig. 3, it is mentioned that a third coil 31 is provided around the neck of the tube. This coil serves to defiect the cathode-ray beain in the vertical direction and in this case through a distanee 'equal at most to twiee the wdth of the strips.
Information about the degree of saturation is suppled to the foeussing coil 23 at 33, nformation about the colour being applied to a defleetion coil 31 at 34.
The normal deflection of the beam in the horzontal and vertical directions is brought about in known manner. For the sake of co'mpleteness, it is mentio-ned that the nformation about eolour need not necessarily be supplied to a par't icu lar defliztion coil 31, but may alternatively be superposed en the saW-tooth oscillation supplied to the ordinary vertical deflection means.
Under control of the colour information supplied te the coil 31, it is thus determned whether the center of the beam must fall, for example, en strip 13 -01 on strip 17 of Fig. 2.
The information about "degree of saturatien supplied to the focussing coil 23 determines the orientation of t-he=cross-section of the beam in accordanee with the positions 10 and 12 of Fig. 2 and the intermediate transition shapes such, for example, as 11.
The brightness signal supplied tothe Wehnelt eleetrode 21 "determines the strength of the cathode-ray beam and hence the brightness ofsereen 19 of the tube.
For the sake of eompleteness, it is to be notecl that the eorrecting means usually employed in the known circuits may also be uscd in the circuit according to the nvention. If it shuld appear, for example, that variation in the current streugthof the cathode-ray beam results in variation of thefocal length, whieh would also eause variation in the shape of "the c'ross-sectioh of the beam, a signal derived from the brightness sgnal may be suppiied as a correeting voltage to the focussing coil 23, so that the focussingis -not aiected by the brightness.
What-I claim is:
1. LA color telvsion display system eomprising a picture tube eon'taining-a Sereen composed of eyelically re peated parallel greups of equal-width strips of materials whichprodueedifferent 'colors when struek by an electron beam,meansfr:prodbing an electren beam dreeted to ward said sereen, means for causing said beam to scan saidscreen in a direction.parallel to said strips and in a direction perpendicular to said strips, and means for selectively eausing variable astigmatism of said beam by such 'an amounttht at "said sereen the dimension of the eross-sectionpf the bearn in a direetion perpendieular to the length of said strips is selectively varied between the limits of substzntially the wdth of a group of said strips and the Widthof a single strip.
-2. A system as elaimed in claim 1, in whieh said means for causing Variable astgrnatism of the electron beam comprises a beam-shaping means for eausing the beam to have an oval-shapedcross-Section and means for focusing said b'eam whereby the eross-section shape of the beam along a -portion of the length thereof in the vicinity of said sereen varies from an oval shape with the longest diameter perpendieular to said sereen strips, to "en =oval sh'ape with the longest diameter parallel to said sereen strips, and means for varying "the focus of said electron beam to selectively focus the beam on said sereen at vanous points along said portion of the length thereof.
3. A system as elaimed in claim 2, in Whieh said beam-shaping means compn'ses a coil having an ovalshaped cross-sectibnandpositioned to surround said elee tron beam.
4. A system as clairnedin claim 2, in whieh saidmeans forca5ing said electronbeam to s'ean said sereen com prises a pair of magnetic deflection coils arranged to pro duce a magnetie defleetion field perpendcular to said beam, and in which said beam-shaping means comprises mearis 'for apply'ing -clireet current to the coils of said pairin- Gppoite serise.
"A"c olor' television display system eomprising a pieture -'tub ee"oit aining a sereen eomposec'l of cyclielly re.-
peated parallel groups of equal-width strips of materials which produee different colors when struck by an electron beam, means for producing an electron beam drected toward said sereen, means for causng said beam to scan said sereen in a direction parallel to said strips and in a direction perpendcular to said strips, means for eausng said eleetr0n beam to have ellptieal astigmatsm whereby the cross-section of said bearn along a porion of the length thereof in the vcinity of said sereen varies from an oval shape with the longest diameter perpendieular to said sereen strips, to an oval shape with the longest diameter parallel to said sereen strips, said longest diameter being substantially equal to the total width of a group of said sereen strips, means adapted to control the fucus of said electron beam in response to eolor saturation signals, means adapted t0 control the intensity of said electron beam in response to brghtness signals, and means f0r selectvely deflecting said electron beam in a 6 direetion perpendicular to said strips and by a maximun amount equal to the width of a group of said strips in response to eolor signals.
Referenees Cited in the file of ths patent UNITED STATES PATENTS 2,137,353 Schlesnger Nov. 22, 1938 2212640 Hogan Aug. 27, 1940 2,278478 Oliver Apr. 7, 1942 2,304163 Goldsmth Dec. 8, 1942 2,310,863 Leverenz Feb. 6, 1943 2,431,115 Goldsmith Nov. 18, 1947 2481,839 Goldsmith Sept. 13, 1949 OTHER REFERENCES Prineples of NTSC Compatible Color Television, page 99, Electronies, February 1952.