US3579010A

US3579010A - Elongated aperture electron gun structure for flat cathode-ray tube

Info

Publication number: US3579010A
Application number: US772232A
Authority: US
Inventors: Robert C Jones
Original assignee: Philco Ford Corp
Current assignee: Space Systems Loral LLC
Priority date: 1968-10-31
Filing date: 1968-10-31
Publication date: 1971-05-18
Anticipated expiration: 1988-05-18
Also published as: GB1292966A

Abstract

An electron gun for a flat cathode-ray tube wherein the control electrode and the screen electrode of the gun each have an elliptical aperture therein, and a flat cathode-ray tube employing such a gun. The major axes of the two elliptical apertures lie in a common plane which is oriented with respect to the faceplate of the tube so that an electron beam emitted by the cathode of the gun produces a substantially circular spot on said faceplate.

Description

United States Patent I Filed Robert C. Jones Elkins Park, Pa. 772,232

Oct. 31, 1968 May 18, 1971 Philco-Ford Corporation Philadelphia, Pa.

inventor Appl. No.

Patented Assignee ELONGATED APERTURE ELECTRON GUN STRUCTURE FOR FLAT CATHODE-RAY TUBE 9 Claim, 6 Drawing Figs.

U.s.c| 313/86, 313/299 Int.Cl H0lj 1/46, H0lj29/46 FieldofSearch 313/86.85

[56] References Cited UNITED STATES PATENTS 2,836,752 5/1958 Berthold 3 l 3/86X 2,884,559 4/1959 Cooper. Jr. et a]. 3 l3/86X Primary Examiner-Roy Lake Assistant Examiner-V. Lafranchi Attorney-Herbert Epstein ABSTRACT: An electron gun for a flat cathode-ray tube wherein the control electrode and the screen electrode of the gun each have an elliptical aperture therein, and a flat cathode-ray tube employing such a gun. The major axes of the two elliptical apertures lie in a common plane which is oriented with respect to the faceplate of the tube so that an electron beam emitted by the cathode of the gun produces a substantially circular spot on said faceplate.

Patented May 18, 1971 3,579,010

2 Sheets-Sheet l INVENTOR. 05597 (3 JO/Vff fMWQ 3%..

Patented May 18, 1971 3,579,010

2 Sheets-Sheet 2 .ra J4 f6 f6 37 45 J6 46 INVENTOR.

BY QK M ATTORNEY ELONGATED APER'IURE ELECTRON GUN STRUCTURE FOR CATHODE-RAYTUBE Cathode-ray tubes in which the viewing faceplate is substantially flat and thebeam deflection system of tube is positioned so that a line from the center of deflection of the tube to the center of the faceplate of the tube makes an acute angle with the faceplate (hereinafter referredto as flat cathode-ray tubes" or flat tubes") are advantageous because they have flat viewing screens and occupy lessspace in a direction perpendicular to the faceplate than do cathode-ray tubes in which the line from the center of deflection to the center of the faceplate is perpendicular to the faceplate. The latter tubes are referred to hereinafter as conventional tubes." I-Iowever, flat tubes have beam-focusing problems not found in conventional cathode-ray tubes. Because of the aforedescribed angular relationship iii 'a-' flat tube, an electron beam of circular cross section produces; wherever it impinges on the faceplate, an elliptical spot elongated in substantially a single direction. By contrast, in a conventional cathode-ray tube, an electron beam of circular cross section produces a circular spot of light when perpendicular to the faceplate of the tube and, when not perpendicular, produces a spot elongated in a direction which changes as the point of impingement of the beam is changed.

In both kinds of tubes it is desirable that a sharply focused circular spot of light be produced wherever the beam impinges the viewing screen. To this end, focus correction systems for altering the cross-sectional shape of the beam have been proposed for conventional tubes. However, since the way in which spots elongate in flat tubes is considerably different from the way in which spots elongatein conventional tubes, the focus correction systems applicable to conventional tubes are useless in flat tubes. 7

An object of the presentinvention is to provide a cathoderay tube short in a direction perpendicular to the viewing screen.

Another objectis to provide a flat cathode-ray tube with an improved electron gur for providing defocusing correction. A

A further object is to provide an electron gun the beam of which produces a substantially circular spot wherever it impinges the faceplate of a flat cathode-ray tube. y

In general, these and other objects of the present invention are achieved in a flat tubeby use therein of an electron gun the control electrode and the screen electrode of which have respective elongated apertures therein. I

Preferably, the apertures in the controlelectrode'and the screen electrode are elliptical with coplanar major axes. Such electrodes supply an electron beam of elliptic cross section to the main focusing lens of the electron gun. The major axes of the elliptical apertures are oriented so that the plane defined by said major-axes intersects the screen'of the tube along a line which extends in'a direction transverse to the direction of elongation of the spots which would be produced on, the screen if a beam of circular cross section were incident thereon. Preferablythe aforementioned plane intersects the screen of the tube along a line which is perpendicular to the aforementioned direction of elongation. Due to the orientation of the elliptical apertures and the acute angle that exists in a flat cathode-ray tube between the line extending from the center of deflection of the tubeto the center of the faceplate of the tube, theregion of the faceplate impinged by the elliptically shaped beam is substantially circular, and therefore a high resolution image can be formed by the beam on the faceplate of the tube. a 7

Other objects and features of the invention will become apparent in the course of the following detailed description of the accompanying drawings, of which: e

FIG. I shows a perspective view of a flat cathode-ray tube incorporating an electron gun structure according to the invention; v j

FIG. 2 is asectional view of the tube'shown in FIG. 1 taken along the line 2-2and viewed in the direction indicated by the arrows; 7

FIG. 3 is a perspective view, partlyin section, of

the electron gun of the present invention;

FIG. 4 is a side elevation in section of the electron gun of FIG. 3; and v i j FIGS. 5 and 6 illustrate respectively the shape of spots produced on a section of faceplate of a flat cathode-ray tube comprising an electron gun which produces a beam of circular cross section and the shape of spots produced on a section of the faceplate of a flat cathode-ray tube comprising the electrode gun structure of FIGS. 3 and 4.

' FIGS. I and 2 show a flat cathode-ray tube in accordance r faceplate forms an acute angleG withfaceplate 25. An

electron gun 26 in neck section 22 is adapted to project an electron beam onto a target 28 which in the embodiment of the invention shown is a luminescent screen on faceplate 25. Screen 28 may comprise a layer 30 of phosphor material with a film 32 of aluminum thereon. Alternatively, screen 28 may be any other type of electron-beam-responsive screen such as the type of screen used in a storage tube. Beam deflection apparatus 34 is disposed between the electron gun 26 and the viewing section 12 for deflecting the electron beam across the screen 28. Beam deflection apparatus 34 may comprise a first pair of electrostatic plates and a second pair of electrostatic plates oriented perpendicular to the first pair of plates. Alter natively, apparatus 34 may comprise a first pair of coils whose axes extend in one direction and a second pair of coils whose axes are perpendicular to the axes of the first pair of coils. Where electrostatic plates are used deflection of the electron beam is achieved by applying appropriate potentials to the plates. Where coils are used deflection of the electron beam is achieved by passing appropriate currents through the coils. While the r deflection apparatus 34 is depicted as located within envelope 10, it is to be understood that deflection apparatus 34 may be located outside envelope [0.

Neck 22 is closed at its free end with a stern structure 35 which includes a plurality of lead-in conductors 36 for applying suitable voltages to the electrodes of the electron gun.

FIGS, 3 and 4 show the principal elements of electron gun 26 of FIG. I. Gun 26 comprises a tubular control electrode cup 38, a tubular screen electrode cup 40, and a focusing-accelerating lens comprising

tubular electrodes

42 and 44. A tubular thermionic cathode 46 (FIG. 4) is mounted in a centrally apertured insulating disc 48 which in turn is fixed within the control electrode cup 38. Cathode 46'is closed at one end, and is coated on the other end with an electron-emissive material to provide a circular electron-emissive surface 47. To heat cathode 46 a heater of conventional form (not shown) may be provided therefor. The electrodes of the electron gun are rnou nted in coaxial spaced relationship along a pair of

insulating rods

52 and 54 by mounting studs 56 which are fixed to the electrodes and embedded in the insulating rods 52 and .54. Typically

electrodes

38, 40, 42 and 44 are made of 305" stainless steel, and

rods

52 and 54 are made of glass.

In operation both electrode 42 and electrode 44 are supplied with potentials hig hly positive with respect to the potential of cathode46. The potential supplied to electrode 44 is higher than that supplied to electrode 42.

Electrode

42 and 44 accelerate the electron beam passing through screen electrode 40 and produce a focusing field which causes the electron 'bea rn passing through screen electrode 40 to converge to a by passage through aperture 41. To this end, aperture 41 preferably is made slightly larger than aperture 39. Preferably the ratio of the length of the major axis to the length of the minor axis, hereinafter referred to as axial ratio, of each

apertures

39 and 41 is between about 1.3 and about 2.5. The optimum axial ratio depends on the value of the impact angle 2 (F162). As the value of D is decreased, the axial ratio of

apertures

39 and 41 is increased.

The major axes of

apertures

39 and 41 are oriented so that the plane defined thereby intersects screen 28 along a line transverse to the direction in which the spot of light produced on screen 28 by the electron beam from gun 26 would be elongated if gun 26 produced an electron beam of circular cross section instead of a beam of elliptical cross section, or if a beam of circular cross section were projected along the line extending from the center of deflection of the tube to the center of the faceplate of the screen. Preferably, said plane intersects screen 28 along a line which is perpendicular to the aforementioned direction of elongation.

FIG. 5 illustrates the shape of spots 58 that are produced on screen 28 when the electron beam 60 incident thereon is of circular cross section. Spots 58 are elongated in the direction of dashed line 62. Such elongated spots are undesirable because they cover unnecessarily large areas of the screen and hence degrade the image resolution obtainable with the tube.

FIG. 6 illustrates the results realized by utilizing the electron gun of the present invention positioned as described hereinbefore. in accordance with the invention, elliptical beam 64 produced by the electron gun of FIGS. 3 and 4 is oriented so that substantially circular spots 66 are produced on screen 28.

In the embodiment of the invention shown in FIGS. 1 and 2, that is, with the neck section 22 of tube 10 attached opposite a vertical panel 14 of viewing section 12, the common plane containing the major axes of

apertures

39 and 41 is a vertical plane. However, neck section 22 of tube 10 alternatively may be attached opposite a horizontal panel of viewing section 12, e.g. where panel 18 not located. In such a case the major axis of each aperture is horizontal and the major axes of both apertures are coplanar.

in the embodiment of the invention wherein the structure of the electron gun is that shown in FIGS. 3 and 4, the various electrodes typically may have the following dimensions and spacings:

Outside diameter of all electrodes, in 395 Inside diameters of all electrodes, in- 375 Axes of elliptical apertures:

Electrode 38 Major axis, in .036 Minor axis, in 018 Electrode 40 Major axis, in 044 Minor axis, in 022 Spacing between cathode 46 and electrode 38, in 006 Spacing between

electrodes

38 and 40, in 007 Spacing between

electrodes

40 and 42, in. 040 Spacing between

electrodes

42 and 44, in. 100

Length of electrode 38, in Length of electrode 40, in Length of electrode 42, in Length of electrode 44, in Distance from center of deflection 23 to the Dizsfitalnce from cathode emitting surface 47 to the center of so 11 Suitable D.C. voltages for operating such a gun are as follows:

Electrode 38 65 v. below cathode potential. Electrode 40... 400 v. above cathode potential. Electrode 42. 400 to 800 volts above cathode potential. Electrode 44 kv. above cathode potential.

rfiicamiic'faig as? such a gun are as follows:

production of an electron beam of elliptical cross section by the electron gun may be facilitated by providing one or more of the electrodes thereof with an elliptical internal cross section and/or by using a cathode that emits an electron beam of elliptical cross section. The major axis of each such electrode and such electron beam should lie in the plane defined by the major axes of

apertures

39 and 41.

Moreover, where circularity of the spots formed on the faceplate of the tube is not essential, elongated apertures other than elliptical apertures may be provided in

electrodes

38 and 40. For example, the apertures in

electrodes

38 and 40 can be rectangular with the long sides of one rectangular aperture parallel to the long sides of the other rectangular aperture. I

Furthermore a three electrode einzel lens can be submitted for the focusing-accelerating

lens comprising electrodes

42 and 44. An einzel lens comprises a pair of electrodes each maintained at a potential highly positive with respect to the cathode and a third electrode intermediate the pair of electrodes and at a potential intermediate the cathode potential and the potential of the pair of electrodes. Accordingly, I desire the scope of my invention to be limited only by the appended claims.

lclaim:

1. in a cathode-ray tube comprising an electron-beamresponsive screen, means for projecting a beam of electrons thereagainst, and electron beam accelerating-focusing apparatus, said means comprising an electron-emissive cathode, a control electrode and a screen electrode, said tube having a center of deflection for said beam, said beam-responsive screen being oriented at an angle acute with respect to a line connecting said deflection center and the center of said screen, the improvement comprising an elliptical aperture in said control electrode and an elliptical aperture in said screen electrode, the major axes of both said apertures lying in a common plane.

2. The tube of claim 1 wherein said apertures are coaxial.

3. The tube of claim 2 wherein said apertures are oriented so that said common plane intersects said screen in a direction transverse to the direction in which a spot would be elongated if produced on said screen by a beam of circular cross section projected along said line.

4. The tube of claim 3 wherein said direction of intersection is perpendicular to said direction of elongation.

5. The tube of claim 4 wherein said aperture in each of said control electrode and said screen electrode has an axial ratio ofbetween 1.3 and 2.5.

6. An electron gun comprising an electron-emissive cathode, a control electrode and a screen electrode, the improvement comprising an elliptical aperture in said control electrode and an elliptical aperture in said screen electrode, said elliptical apertures being coaxial and having coplanar major axes.

7. The electron gun of claim 6 wherein each of said apertures has an axial ratio of between 1.3 and 2.5.

8. In a cathode ray tube comprising an electron-beamresponsive screen, means for projecting a beam of electrons thereagainst, and electron beam accelerating-focusing apparatus, said means comprising an electron-emissive cathode, a control electrode and a screen electrode, said tube having a center of deflection for said beam, said beam-responsive screen being oriented at an angle acute with respect to a line connecting said deflection center and the center of said screen, the improvement comprising an elongated apcrturein said control electrode and an elongated aperture in said screen electrode, the major axes of both said apertures lying in a common plane.

9. An electron gun comprising an electron-emissive cathode, a control electrode and a screen electrode, the improvement comprising an elongated aperture in said control electrode and an elongated aperture in said screen electrode, said elongated apertures being coaxial and having coplanar major axes.

Claims

1. In a cathode-ray tube comprising an electron-beam-responsive screen, means for projecting a beam of electrons thereagainst, and electron beam accelerating-focusing apparatus, said means comprising an electron-emissive cathode, a control electrode and a screen electrode, said tube having a center of deflection for said beam, said beam-responsive screen being oriented at an angle acute with respect to a line connecting said deflection center and the center of said screen, the improvement comprising an elliptical aperture in said control electrode and an elliptical aperture in said screen electrode, the major axes of both said apertures lying in a common plane.

2. The tube of claim 1 wherein said apertures are coaxial.

5. The tube of claim 4 wherein said aperture in each of said control electrode and said screen electrode has an axial ratio of between 1.3 and 2.5.

8. In a cathode ray tube comprising an electron-beam-responsive screen, means for projecting a beam of electrons thereagainst, and electron beam accelerating-focusing apparatus, said means comprising an electron-emissive cathode, a control electrode and a screen electrode, said tube having a center of deflection for said beam, said beam-responsive screen being oriented at an angle acute with respect to a line connecting said deflection center and the center of said screen, the improvement comprising an elongated aperture in said control electrode and an elongaTed aperture in said screen electrode, the major axes of both said apertures lying in a common plane.