FR2895145A1 - Tricolor CRT for tricolor picture tube, has electromagnetic deflection unit with dynamic electromagnetic four terminal network located between electron gun and unit, and supplied with current to render CRT completely self-convergent - Google Patents

Abstract

The CRT has an electron gun (CN) emitting electron beams to excite different phosphor lands of a screen (EC). An electromagnetic deflection unit (DV) deflects the beams to sweep a surface of the screen, and has a dynamic electromagnetic four terminal network (QE) located between the gun and unit, and supplied with current to render the CRT completely self-convergent. The network has electromagnetic coils arranged along a same plane perpendicular to an axis (ZZ`) of the gun. The respective coil pairs have their axes located along vertical and horizontal planes.

Description

L'invention concerne un tube de television a rayons cathodiques trichromeThe invention relates to a trichromatic cathode ray television tube

integrant un systeme de correction de la convergence.  integrating a convergence correction system.

ETAT DE LA TECHNIQUE Dans un tube de television couleurs pour que les trois faisceaux d'electrons (correspondant aux trois couleurs rouge, vert et bleu) emis par le canon a electrons trichrome permettent d'obtenir sur 1'ecran une bonne reproduction d'une image, it faut que les trois faisceaux electroniques convergent aussi parfaitement que possible en un meme point de 1'ecran, afin qu'ils frappent les points correspondants de la mosaique de 1'ecran dans un meme triplet TR de 1'ecran. La figure 1 represente la convergence des trois faisceaux de couleurs au centre de 1'ecran. Cependant, la convergence doit normalement titre assuree eg alement en taus points de la surface de 1'ecran. Si ce reglage est realise, les pastilles de luminophores des differents triplets de 1'ecran, excites successivement par les trois faisceaux, produisent une image de couleurs correctes. Par contre, si ce reglage n'est pas realise, les electrons des trois faisceaux (correspondant aux trois couleurs rouge, vert et bleu) ne wont plus adresser respectivement des luminophores rouges, verts et bleus. On va avoir une modification des couleurs de 1'image affichee sur 1'ecran. En 1'absence d'une convergence parfaite des trois faisceaux sur 1'ecran, les trois images colorees rouge, verte et bleue ne se superposent donc pas et 1'image est alteree. Par exemple, si le faisceau correspondant au rouge vient exciter partiellement les luminophores verts voisins aux luminophores rouges, on obtiendra, au lieu de la reproduction du rouge, une teinte jaune. La purete de la couleur ne sera donc pas respectee. La figure 2a represente de facon schematique un tube de television dans lequel les trois faisceaux FR1, FV1 et FBI focalisent au centre 01 de 1'ecran. Chaque faisceau FR1, FV1, FBI a ete represente par 1'axe du faisceau. A noter que pour des raisons de simplifications, le point 01 represente un triplet comportant trois pastilles de luminophores rouge, vert et bleu sur lesquels sont focalises les faisceaux FR1, FV1 et FBI respectivement. Cependant, les faisceaux FR1, FV1 et FBI n'ont pas ete regles pour converger vers le bord de 1'ecran comme le montre les faisceaux FRn, FVn, FBn dont le lieu des points de convergence On est une surface courbe representee en trait mixte. Selon les techniques couramment utilisees, on effectue un reglage de la convergence des faisceaux d'electrons au centre de 1'ecran. Pour obtenir une convergence en tout point de 1'ecran, on utilise un systeme auto-convergent. Pour cela, un deviateur auto-convergent DV (figure 2b) assure une convergence au moyen de champ de deflection quadripolaire qui induit un effet quadripolaire approprie sur les faisceaux d'electrons FRn, FVn, FBn. La structure du champ magnetique d'un deviateur auto-convergent est telle que la convergence des trois faisceaux d'electrons est conservee sur tout 1'ecran. Le deviateur genere un effet quadripolaire qui a pour effet de deplacer les points de convergence vers 1'ecran lorsqu'on s'ecarte du centre de 1'ecran. Cela est schematise par la figure 2b.  STATE OF THE ART In a color television tube so that the three electron beams (corresponding to the three colors red, green and blue) emitted by the trichrome electron gun can obtain on the screen a good reproduction of a image, it is necessary that the three electron beams converge as perfectly as possible in one and the same point of the screen, so that they strike the corresponding points of the mosaic of the screen in the same triplet TR of the screen. Figure 1 shows the convergence of the three color beams in the center of the screen. However, convergence is normally ensured evenly at all points on the surface of the screen. If this adjustment is made, the phosphor pellets of the various triplets of the screen, excited successively by the three beams, produce an image of correct colors. On the other hand, if this adjustment is not achieved, the electrons of the three beams (corresponding to the three colors red, green and blue) will no longer address respectively red, green and blue luminophores. We will have a modification of the colors of the image displayed on the screen. In the absence of a perfect convergence of the three beams on the screen, the three red, green and blue colored images are not superimposed and the image is altered. For example, if the beam corresponding to red partially excites neighboring green phosphors red phosphors, will be obtained, instead of the reproduction of red, a yellow tint. The purity of the color will not be respected. Figure 2a schematically shows a television tube in which the three beams FR1, FV1 and FBI focus in the center 01 of the screen. Each beam FR1, FV1, FBI was represented by the axis of the beam. Note that for reasons of simplification, the point 01 represents a triplet comprising three pellets of red, green and blue phosphors on which the beams FR1, FV1 and FBI are respectively focused. However, the beams FR1, FV1 and FBI have not been set to converge towards the edge of the screen as shown by the beams FRn, FVn, FBn whose location of the convergence points On is a curved surface represented by a dotted line . According to commonly used techniques, the convergence of the electron beams in the center of the screen is adjusted. To achieve convergence at any point on the screen, a self-converging system is used. For this purpose, a self-converging DV diverter (FIG. 2b) converges by means of a quadrupole deflection field which induces an appropriate quadrupole effect on the electron beams FRn, FVn, FBn. The structure of the magnetic field of a self-converging deviator is such that the convergence of the three electron beams is preserved throughout the screen. The deviator generates a quadrupole effect which has the effect of moving the points of convergence towards the screen when one deviates from the center of the screen. This is schematised by Figure 2b.

Dans ces systemes, les faisceaux d'electrons forment des spots de bonne resolution au centre de l'ecran. Par contre, quand on se rapproche des bords lateraux de l'ecran, les spots des faisceaux sur l'ecran sont elargis horizontalement ce qui est du d'une part a l'angle des faisceaux par rapport au plan de l'ecran (les faisceaux etant incidents de facon oblique par rapport au plan de l' ecran) et d'autre part a l' effet quadripolaire du deviateur qui est equivalent a une lentille divergente dans le plan horizontal. De plus, les spots des faisceaux presentent des halos (flares en anglais) dans le sens vertical. Les systemes auto-convergents presentent donc les inconvenients de degrader la resolution des spots selon la direction horizontale de l'ecran et de creer un halo sur les bords des spots selon la direction verticale. On observe donc une degradation des spots aux bords de l'ecran qui est due a l'oblicite des faisceaux par rapport au plan de l'ecran et a l'effet de divergence dans le plan horizontal qui est genere pour obtenir la convergence des faisceaux. Ce defaut augmente avec l'angle de deviation du tube. Lorsque l'angle de deviation du tube augmente, pour une dimension d'ecran determinee, la resolution au centre de l'ecran s'ameliore. On a donc une deterioration des spots sur les bords de l'ecran et une amelioration au centre ce qui donne une diminution de l'uniformite de l'affichage de l'ecran, l'image devenant de meilleure qualite au centre de l'ecran qu'aux bords de l'ecran.  In these systems, the electron beams form spots of good resolution in the center of the screen. On the other hand, when one approaches the lateral edges of the screen, the spots of the beams on the screen are widened horizontally which is of on the one hand at the angle of the beams with respect to the plane of the screen (the beams being incidentally oblique to the plane of the screen) and on the other hand to the quadrupole effect of the deviator which is equivalent to a diverging lens in the horizontal plane. In addition, beam spots have halos (flares in English) in the vertical direction. The self-converging systems therefore have the disadvantages of degrading the resolution of the spots in the horizontal direction of the screen and creating a halo on the edges of the spots in the vertical direction. There is therefore a degradation of the spots at the edges of the screen which is due to the oblicity of the beams with respect to the plane of the screen and the divergence effect in the horizontal plane which is generated to obtain the convergence of the beams. . This defect increases with the angle of deviation of the tube. As the deviation angle of the tube increases, for a given screen size, the resolution at the center of the screen improves. There is therefore a deterioration of the spots on the edges of the screen and an improvement in the center which gives a decrease in the uniformity of the display of the screen, the image becoming better in the center of the screen only at the edges of the screen.

L'invention concerne donc un systeme de correction de la convergence pour tube de television couleur plus facile a mettre en oeuvre et permettant d'ameliorer la qualite des formes des spots des faisceaux notamment en bords d'ecran. L'invention est plus particulierement applicable dans les tubes grands angles. Elie prevoit des deviateurs non auto-convergents. Le but est de diminuer le phenomene de halo (flare) et de diminuer la taille des spots en bords d'ecran selon la direction horizontale tout en conservant une bonne qualite de spots au centre de 1'ecran.  The invention thus relates to a convergence correction system for color television tube easier to implement and for improving the quality of the shapes of the spots of the beams, especially at the edges of the screen. The invention is more particularly applicable in wide angle tubes. Elie provides for non-self converters. The goal is to reduce the phenomenon of halo (flare) and reduce the size of the spots at the edges of the screen in the horizontal direction while maintaining a good quality of spots in the center of the screen.

RESUME DE L'INVENTION L'invention concerne donc un tube a rayons cathodiques couleurs comprenant: a.un canon a electrons emettant trois faisceaux 15 d'electrons destines a exciter des pastilles de luminophores differentes d'un ecran, b.un systeme de deflexion permettant de deflechir les trois faisceaux d'electrons de facon a balayer la surface d'un ecran, 20 Dans ce tube a rayon cathodiques, le systeme de deflexion n'est pas auto-convergent et le tube comporte, en outre, un quadripole electromagnetique dynamique situe entre le canon a electrons et le deviateur electromagnetique de part et d'autre du tube a rayons 25 cathodiques. Le quadripole est alimente en courant pour rendre le tube a rayons cathodiques globalement auto-convergent Selon une forme de realisation preferee de l'invention, le quadripole electromagnetique comporte 30 quatre bobinages electromagnetiques disposees sensiblement selon un meme plan qui est perpendiculaire a l'axe du canon a electrons. Deux bobinages ont leurs axes situes dans un plan vertical du tube et deux autres bobinages ont leur axe situe selon un plan horizontal du tube. Selon 1'invention, le quadripole electromagnetique est alimente en courant en synchronisme 5 avec le deviateur electromagnetique. BREVE DESCRIPTION DES FIGURES Les differents objets et caracteristiques de 1'invention apparaitront plus clairement dans 10 la description et dans les figures annexees qui illustrant la convergence cathodiques trichrome connu deja decrites precedemment, - la figure 3, un exemple schematique du systeme de 1'invention, - la figure 4, un exemple de realisation d'un tube a rayons cathodiques selon 1'invention. DESCRIPTION DETAILLEE En se reportant a la figure 3, on va donc decrire un exemple de realisation d'un systeme de correction de convergence selon 1'invention dans un tube de television couleur. 25 Un tube de television comporte un tube a rayons cathodiques TRC muni d'un canon a electrons CN capable d'emettre des faisceaux d'electrons destines a titre diriges sur la face d'un ecran EC du tube lequel ecran est muni de pastilles 30 (pixels) de luminophores. Le canon a electrons est un dispositif electronique permettant d'emettre, dans le cas d'un tube de television trichrome, trois faisceaux representent: - les figures 1, 2a et 2b, des schemas d'un tube a rayons dans la technique et 15 20 d 'electrons (rouge, vert et bleu). Le canon a electrons comporte une succession d'electrodes permettant de former les trois faisceaux d 'electrons, de les accelerer et de les focaliser sur la face l'ecran EC. Un deviateur electromagnetique DV permet de devier les faisceaux d'electrons pour qu'ils balayent toute la surface de l'ecran. Comme cela a ete decrit precedemment, la surface de l'ecran etant quasiment plane, lors du balayage de l'ecran, si les faisceaux des trois couleurs convergent sensiblement au centre de l'ecran, la convergence des trois faisceaux est difficile a obtenir lorsqu'ils se rapprochent d'un bord de l'ecran. Dans les techniques connus, on realise des systemes appeles auto-convergents qui assurent la convergence en taus points de l'ecran a l'aide du deviateur qui est concu pour titre "auto- convergent" et qui agit sur la convergence des differents faisceaux en induisant un effet d 'astigmatisme sur les faisceaux. Cependant, cela a pour effet de degrader la resolution des spots des faisceaux sur l'ecran 25 selon la direction horizontale. C'est pourquoi, le systeme de la figure 3 comporte un quadripole electromagnetique QE situe de part et d'autre du tube TRC dans une zone localisee entre le canon a electrons et le 30 deviateur electromagnetique. Egalement, dans ce systeme, on reduit l'astigmatisme induit par le deviateur lorsqu'il induit un effet de correction de la convergence.  SUMMARY OF THE INVENTION The invention thus relates to a color cathode ray tube comprising: an electron gun emitting three electron beams for exciting phosphor pellets different from a screen, a deflection system This deflection system is not self-converging and the tube further comprises an electromagnetic quadrupole, which deflects the three electron beams so as to scan the surface of a screen. dynamic located between the electron gun and the electromagnetic converter on both sides of the cathode ray tube. The quadrupole is supplied with current to make the cathode ray tube generally self-converging. According to a preferred embodiment of the invention, the electromagnetic quadrupole comprises four electromagnetic coils disposed substantially in the same plane which is perpendicular to the axis of the electromagnetic coil. electron gun. Two coils have their axes located in a vertical plane of the tube and two other coils have their axis located along a horizontal plane of the tube. According to the invention, the electromagnetic quadrupole is supplied with current in synchronism with the electromagnetic generator. BRIEF DESCRIPTION OF THE FIGURES The various objects and features of the invention will appear more clearly in the description and in the accompanying figures which illustrate the known trichrome cathodic convergence already described above, FIG. 3, a schematic example of the system of the invention - Figure 4, an embodiment of a cathode ray tube according to the invention. DETAILED DESCRIPTION Referring to FIG. 3, an exemplary embodiment of a convergence correction system according to the invention in a color television tube will be described. A television tube comprises a CRT cathode ray tube provided with a CN electron gun capable of emitting electron beams for directing onto the face of an EC screen of the tube which is screened with pellets. (pixels) of phosphors. The electron gun is an electronic device for emitting, in the case of a trichromatic television tube, three beams represent: - Figures 1, 2a and 2b, schemas of a ray tube in the art and 15 20 electrons (red, green and blue). The electron gun has a succession of electrodes for forming the three electron beams, accelerating them and focusing them on the face of the EC screen. An electromagnetic deviator DV makes it possible to deviate the electron beams so that they sweep the whole surface of the screen. As has been described previously, the surface of the screen being almost flat, during the scan of the screen, if the beams of the three colors converge substantially in the center of the screen, the convergence of the three beams is difficult to obtain when they are getting closer to one edge of the screen. In the known techniques, we realize systems called auto-convergents which ensure the convergence in all points of the screen with the help of the deviator which is conceived for title "auto-convergent" and which acts on the convergence of the different beams in inducing an effect of astigmatism on the beams. However, this has the effect of degrading the resolution of the spots of the beams on the screen 25 in the horizontal direction. Therefore, the system of Figure 3 comprises an electromagnetic quadrupole QE located on either side of the TRC tube in a zone located between the electron gun and the electromagnetic deviator. Also, in this system, we reduce the astigmatism induced by the deviator when it induces a correction effect of the convergence.

Le quadripole electromagnetique QE est commande en synchronisme avec le deviateur DV de telle facon qu'a chaque pas de balayage, le quadripole electromagnetique corrige la convergence des faisceaux avant qu'ils ne soient devies par le deviateur DV. On constate que la reduction de l'astigmatisme du deviateur et la realisation de la convergence par le quadripole electromagnetique QE permet d'obtenir une amelioration substantielle de 1'uniformite horizontale de l'image sur 1'ecran. La correction de convergence realisee avant la deflexion permet ainsi d'ameliorer la taille horizontale des spots des faisceaux d'electrons en bords d'ecran. Il s'agit, en fait, d'une nette amelioration par rapport aux systemes connus. Ce faisant, ce systeme permet de minimiser les differences entre les spots en bords d'ecran par rapport au spot au centre de 1'ecran, lesquelles differences, conduisent, dans les tubes grands angles, a deteriorer rapidement la resolution trichrome. Bien que le deviateur ne soit pas auto-convergent, l'ensemble du systeme, comprenant notamment le quadripole electromagnetique situe entre le canon a electrons et le deviateur, est globalement auto-convergent. Le focus horizontal se conserve en taus points de 1'ecran et la modulation, qui await pour but de pre-compenser l'astigmatisme, a tendance a diminuer. La figure 4 represente un exemple de realisation d'un tube a rayons cathodique selon 1'invention.  The electromagnetic quadrupole QE is controlled in synchronism with the DV deviator in such a way that at each scanning step, the electromagnetic quadrupole corrects the convergence of the beams before they are deviated by the DV deviator. It is found that the reduction of the astigmatism of the deviator and the realization of the convergence by the electromagnetic quadrupole QE makes it possible to obtain a substantial improvement in the horizontal uniformity of the image on the screen. The convergence correction performed before the deflection thus makes it possible to improve the horizontal size of the spots of the electron beams at the edges of the screen. This is, in fact, a marked improvement over known systems. In doing so, this system makes it possible to minimize the differences between the spots at the edges of the screen relative to the spot in the center of the screen, which differences lead, in the wide-angle tubes, to rapidly deteriorate the trichromatic resolution. Although the deviator is not self-convergent, the entire system, including the electromagnetic quadrupole located between the electron gun and the deviator, is generally self-converging. Horizontal focus is conserved at all points on the screen, and modulation, which is intended to pre-compensate for astigmatism, tends to decrease. FIG. 4 represents an example of embodiment of a cathode ray tube according to the invention.

Le deviateur electromagnetique a ete represents en traits mixtes. On voit donc que le quadripole est situe entre le canon a electrons CN et le deviateur DV.  The electromagnetic deviator has been represented in phantom lines. We can see that the quadrupole is located between the CN electron gun and the DV converter.

Le quadripole electromagnetique comporte quatre bobines electromagnetiques B1, B2, B3, B4 situees sensiblement selon un plan (YX) perpendiculaire a 1'axe ZZ' du tube. Deux bobines B1 et B3 sont situees en vis a vis de part et d'autre du tube et ont leur axe contenu dans un plan vertical (YZ). Les deux autres bobines B2 et B4, egalement en vis a vis de part et d'autre du tube, ont leur axe contenu dans un plan horizontal (XZ) du tube.  The electromagnetic quadrupole comprises four electromagnetic coils B1, B2, B3, B4 located substantially in a plane (YX) perpendicular to the axis ZZ 'of the tube. Two coils B1 and B3 are located facing each other on either side of the tube and have their axis contained in a vertical plane (YZ). The other two coils B2 and B4, also facing each other on either side of the tube, have their axis contained in a horizontal plane (XZ) of the tube.

Les quatre bobines B1 a B4 sont alimentees de facon dynamique en synchronisme avec le balayage de 1'ecran du tube.  The four coils B1 through B4 are dynamically powered in synchronism with the scanning of the screen of the tube.

Claims (3)

REVENDICATIONS 1.Tube a rayons cathodiques couleurs comprenant: a. un canon a electrons (CN) emettant trois 5 faisceaux d'electrons destines a exciter des pastilles de luminophores differentes d'un ecran (EC), b. un systeme de deflexion (DV) permettant de deflechir les trois faisceaux d'electrons de facon a balayer la surface d'un ecran, 10 caracterise en ce que ledit systeme de deflexion (DV) n'est pas auto-convergent et en ce qu'il comporte un quadripole electromagnetique dynamique (QE) situe entre le canon a electrons (CN) et le deviateur electromagnetique (DV) de part et d'autre du tube a 15 rayons cathodiques, ledit quadripole etant alimente en courant pour rendre le tube a rayons cathodiques globalement auto-convergent.  1. Color cathode ray tube comprising: a. an electron gun (CN) emitting three electron beams for exciting phosphor pellets different from a screen (EC), b. a deflection system (DV) for deflecting the three electron beams so as to scan the surface of a screen, characterized in that said deflection system (DV) is not self-converging and in that it comprises a dynamic electromagnetic quadrupole (QE) located between the electron gun (CN) and the electromagnetic converter (DV) on either side of the cathode ray tube, said quadrupole being supplied with current to make the tube cathodic rays globally self-convergent. 2.Tube a rayons cathodiques couleurs selon la revendication 1, caracterise en ce que ledit quadripole 20 electromagnetique (QE) comporte quatre bobinages electromagnetiques (B1, B2, B3, B4) disposees sensiblement selon un meme plan qui est perpendiculaire a 1'axe (ZZ') du canon a electrons, deux bobinages (B1, B3) ayant leurs axes situes dans un plan verticale (YZ) du 25 tube et deux autres bobinages (B2, B4) ayant leur axe situe selon un plan horizontal (XZ) du tube.  2.The color cathode ray tube according to claim 1, characterized in that said electromagnetic quadrupole (QE) comprises four electromagnetic windings (B1, B2, B3, B4) arranged substantially along the same plane which is perpendicular to the axis ( ZZ ') of the electron gun, two coils (B1, B3) having their axes located in a vertical plane (YZ) of the tube and two other coils (B2, B4) having their axis located in a horizontal plane (XZ) of tube. 3.Tube a rayons cathodiques couleurs selon 1'une des revendications 1 ou 2, caracterise en ce que ledit quadripole electromagnetique est alimente en courant en 30 synchronisme avec le deviateur electromagnetique.  3. Color cathode ray tube according to one of claims 1 or 2, characterized in that said electromagnetic quadrupole is fed current in synchronism with the electromagnetic converter.