EP0461205A1 - Canon a electrons a deplacement reduit du point de croisement a des niveaux eleves du courant de faisceau, et ses procedes d'exploitation - Google Patents

Canon a electrons a deplacement reduit du point de croisement a des niveaux eleves du courant de faisceau, et ses procedes d'exploitation

Info

Publication number
EP0461205A1
EP0461205A1 EP90908899A EP90908899A EP0461205A1 EP 0461205 A1 EP0461205 A1 EP 0461205A1 EP 90908899 A EP90908899 A EP 90908899A EP 90908899 A EP90908899 A EP 90908899A EP 0461205 A1 EP0461205 A1 EP 0461205A1
Authority
EP
European Patent Office
Prior art keywords
electrons
electrode
cathode
emitting surface
point
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP90908899A
Other languages
German (de)
English (en)
Other versions
EP0461205A4 (fr
Inventor
Thomas A. Dunbar
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Mirion Technologies IST Corp
Original Assignee
Imaging and Sensing Technology Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Imaging and Sensing Technology Corp filed Critical Imaging and Sensing Technology Corp
Publication of EP0461205A4 publication Critical patent/EP0461205A4/fr
Publication of EP0461205A1 publication Critical patent/EP0461205A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
    • H01J29/46—Arrangements of electrodes and associated parts for generating or controlling the ray or beam, e.g. electron-optical arrangement
    • H01J29/48—Electron guns
    • H01J29/488—Schematic arrangements of the electrodes for beam forming; Place and form of the elecrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
    • H01J29/46—Arrangements of electrodes and associated parts for generating or controlling the ray or beam, e.g. electron-optical arrangement
    • H01J29/48—Electron guns

Definitions

  • the present invention relates generally to the field of electron guns, such as used in cathode ray tubes and the like, and, more particularly, to an improved electron gun having a smaller cross-over or object point, and in which movement of such cross ⁇ over point relative to the cathode as a function of beam current is reduced, all with the object of improving the resolution of a reformed image point on a dfeplay screen.
  • Electron guns are in common use. Such guns are typically used in cathode ray tubes (CRT) to create a beam of electrons which is then focused on, and selectively deflected relative to, a display screen.
  • the screen typically has a phosphor coating on its inner surface, which is illuminated by the incident electron beam.
  • the ambient or back ⁇ ground light in the room in which the CRT is located varies within a relatively-small bandwidth.
  • the electron gun may be designed to produce a, .reason ⁇ ably well-defined spot on the display screen within a range of anticipated beam currents.
  • the level of ambient light may vary significantly.
  • a CRT or heads-up display (HUD) in the cockpit of an aircraft On the one hand, the aircraft may be flying at an altitude of, say, 30,000 feet [9.144 kilometers] in brilliant sunshine. If the pilot sits beneath a transparent canopy, the intensity of such ambient or background light may literally "wash out" the readability of the screen. On the other hand, the aircraft may be flying in conditions of darkness. This problem is amplified in projection-type devices in which the beam current required to produce a screen image of acceptable relative intensity, varies with the area of the projected display.
  • the pilot typically adjusts the brightness and contrast of the CRT in an attempt to produce a readable image under the existing light conditions.
  • the pilot would typically reduce the brightness and contrast of the CRT.
  • the pilot is adjusting the beam current of the electron gun within the CRT. While this sounds reasonably innocuous, in such electron guns as have been developed heretofore, the axial position of the cross-over point is believed to have changed as a function of the magnitude of the operator-selected beam current.
  • the fineness or quality of that resolu ⁇ tion might well be affected if the beam current were to be changed.
  • the level of ambient light may change drastically (Le., for conditions of darkness to conditions of brilliance).
  • the CRT might produce an image point of acceptable resolution under one condition, but an unacceptable "fuzzy" image point under another condition.
  • an improved electron gun having a more precisely defined cross-over or object point, and in which axial move ⁇ ment of the cross-over in response to varying beam currents, is reduced, with the object of improving the resolution of the reformed image point on the display screen under various background lighting conditions.
  • the improved gun e.g., 40
  • the improved gun broadly includes a cathode (e.g., 41) having an emitting surface (e.g., 58); a first electrode (e.g., 42) arranged in spaced facing relation to the emitting surface and having a first aperature (e.g., 45) axially aligned with an imaginary line (e.g., x-x) extending normally (Le., perpendicularly) from a point on the surface; a second electrode (e.g., 43) arranged in spaced facing relation to the first electrode and having a second aperture (e.g., 46) axially aligned with the
  • the electrons exhibit less of a space charge effect at the cross-over point, and the cross-over point will therefore be of higher resolution (Le., finer or of smaller diameter) and will be less susceptible to axial movement relative to the emitting surface in response to changes in the beam current.
  • the invention provides an improved method of operating an electron gun (e.g., 40) having a cathode (e.g., 41) and having three sequentially-spaced electrodes (e.g., 42,43,44) associated with the cathode.
  • Each of the electrodes has an aperature (e.g., 45,46,48) aligned with an imaginary line (e.g., x-x) extending away from a point on the emitting surface (e.g., 58) of the cathode.
  • the improved method broadly includes the steps of: applying a first voltage (V j ) to a first of the electrodes (e.g., elec ⁇ trode 42); applying a second voltage (V 2 ) to a second of the electrodes (e.g., electrode 43); applying a third voltage (V 3 ) to a third of the electrodes (e.g., electrode 44); and selectively controlling the respective voltages to cause a desired flow of electrons to be emitted from the cathode to cause the electrons to be accelerated to a velocity at the cross-over greater than in prior art electron guns, and to focus the emitted electrons on a cross-over point which remains substantially stationary along the imaginary line (Le., at a substantially fixed distance from the emitting surface), independent of the magnitude of the electron flow.
  • the general object of the invention is to provide an improved electron gun.
  • Another object is to provide an improved electron gun in which the elec ⁇ trons are accelerated to a velocity at the cross-over greater than in prior art guns. Another object is to provide an improved electron gun in which the cross ⁇ over is smaller and more precisely defined than in prior art guns.
  • Still another object is to provide an improved method of operation an elec ⁇ tron gun so as to reduce axial movement of an object point in response to changing beam currents.
  • Fig. 1 is a fragmentary view, partly in section, partly in elevation and partly schematic, of a prior art display-type cathode ray tube.
  • Fig. 2 is an enlarged fragmentary vertical sectional view of the electron gun used in the prior art CRT shown in Fig. 1, this view depicting the cross-over as being spaced from the cathode emitting surface along line x-x by a horizontal distance x c when one set of voltages is applied to the grids.
  • Fig. 3 is a view similar to Fig. 2, but showing the cross-over as being spaced from the emitting surface along line x-x by a greater horizontal distance x c when another set of voltage conditions is applied to the grids.
  • Fig. 4 is a fragmentary vertical sectional view of the improved electron gun, showing the three electrodes arranged in sequentially-spaced relation to the cathode, and showing the control means for supplying individual voltages to the cathode and the grids.
  • Fig. 5 is a plot of resolution (ordinate) vs. beam current (abscissa), compar ⁇ ing the general shapes of the curves of the prior art and improved guns.
  • Fig. 6 is a plot of resolution (ordinate) vs. beam current (abscissa) of the improved gun, for different voltages applied to the grids, and demonstrates how the resolution may be confined within a desired bandwidth by dynamically switching the grid voltages at different desired beam currents.
  • the terms “horizontal”, “vertical”, “left”, “right”, “up” and “down”, as well as adjectival and adverbial derivatives thereof simply refer to the orientation of the illustrated structure as the particular drawing figure faces the reader.
  • the terms “inwardly” and “outwardly” refer to the orientation of a surface relative to its axis of elongation, or axis or rotation, as appropriate.
  • the improved gun affords the desirable capabilities of forming a physically-smaller object point or cross-over, and maintaining the cross-over at a substantially-fixed distance from the emitting surface, with accompanying improvement in the resolution of a reformed image point on the screen, notwithstanding widely-varying beam currents.
  • a prior art CRT is shown as broadly including a horizontally-elongated evacuated envelope having a leftward , neck portion 21, an intermediate funnel-shaped portion 22, and a rightward face-plate or dis- play screen 23.
  • This type of CRT is generally disclosed in U.S. Patent No. 4,334,170, the aggregate disclosure of which is hereby incorporated by reference.
  • a plurality of cathodo- luminescent phosphor targets (not shown) are provided on the inner surface of the screen.
  • a shadow mask represented by dashed line 24, is positioned within the envelope in close proximity to the face-plate.
  • An electron gun 25 is positioned within the neck portion and is arranged to produce or generate a rightwardly-directed beam of electrons along the horizontal center- line x-x of the tube.
  • a power supply 26 is arranged to supply various voltages to gun 25, and to other parts of the tube. This power supply may be operated to cause the gun to produce a stream of electrons of variable beam current, and to selectively deflect the beam either on-axis or off-axis to different desired parts of the face-plate.
  • an off-axis deflected beam of electrons is schematically represented by line 27.
  • Fig. 2 is a schematic vertical sectional view of pertinent portions of the electron gun 25 shown in Fig. 1.
  • the gun is similarly elongated along tube axis x-x, and is shown as including a leftward thermionic cathode 28 and two sequentially-spaced verti ⁇ cal plate-like electrodes 29,30 having apertures 31,32, respectively, aligned with axis x-x.
  • Plates 29,30 are shown as having annular vertical surfaces 33,34 and 35,36 facing toward and away from the cathode, respectively.
  • Plate 29 is sometimes referred to as grid G
  • plate 30 as grid G 2 .
  • Power supply 26 is arranged to supply various individual volt ⁇ ages to the cathode and to grids G 7 ,G 2 , inter alia, for varying the beam current issuing from the rightwardly-facing vertical emitting surface 38 of the cathode.
  • grids G ,G 2 also form an electrostatic lens for focusing such electrons on a cross-over or object point, indicated at 39.
  • the various voltages applied to the cathode and grids G ⁇ G would be selectively varied to controllably alter the beam current.
  • variations in the desired beam current would also affect the axial distance (Le., distance x c ) of the cross-over from the emitting surface, as comparatively illustrated in Figs. 2-3.
  • Fig. 2 illustrates the cross-over as occurring at one distance from the emit ⁇ ting surface along line x-x when one set of voltages is applied to the cathode and grids G ⁇ G ⁇
  • Fig. 3 depicts the cross-over as occurring at a greater distance from the emitting surface along line x-x when another set of voltages is applied to the cathode and grids.
  • the cross-over typically occurred somewhere between grids G j and G
  • the position of the cross-over relative to the emitting surface was a function of the voltages applied to the cathode and the two grids, inter alia.
  • the beam current was also a function of these voltages.
  • the cross-over was relatively large.
  • the size (Le., diameter) of the cross-over was a function of the velocity of the electrons at the cross-over.
  • Persons skilled in this art will readily appreciate that such electrons have a zero velocity at emitting surface 38, but are quickly accelerated as they leave this surface and pass through the grid apertures en route to their impingement on the phosphor targets.
  • the cross- over point typically occurred between the first and second grids, as shown fct IJ ⁇ gs. 2 and 3.
  • the space charge effect (Le., the fact that negatively- charged electrons tend to repel one another) limited the formation of a* precisely-defined point-like cross-over.
  • the resolution of the image point reformed on the display screen was, of course, dependent upon the size ofthe object point. Therefore, upon information and belief, the prior art electron gun suffered from three principal drawbacks: (1) the maximum velocity of the electrons at the cross-over was relatively slow, (2) the space charge effect had a greater influence where the cross-over was formed before the elec ⁇ trons had reached their maximum velocity, and (3) the axial position of the cross-over from the emitting surface varied with changes in the magnitude of the beam current.
  • the present invention overcomes these deficiencies by providing an improved electron gun in which the electrons are accelerated to a greater velocity prior to forma ⁇ tion of the cross-over, in which the faster moving electrons are less susceptible to the space charge effect at the cross-over, and in which the cross-over point remains substan ⁇ tially-stationary on line x-x despite changing beam currents.
  • the improved gun is fragmentarily illustrated as being elongated along horizontal axis x-x, and as having a thermionic cathode 41.
  • Three vertical plate-like electrodes 42,43,44, provided * ith aper ⁇ tures 45,46,48, respectively, are sequentially spaced along axis x-x. More particularly, electrodes 42,43,44 are shown as having annular vertical surfaces 49,50, 51,52 and 53,54, facing toward and away from the cathode, respectively. Surfaces 49,51,53 are shown as being arranged at distances x , x 2 , x 3 from the cathode, respectively.
  • Electrode 42 may be regarded as grid G 7 , electrode 43 as grid G j , and electrode 44 as grid G 3 .
  • Grids G j .G ⁇ G j form an electrostatic focusing lens.
  • an annular groove is shown as extending leftwardly into grid G 2 from its right face 52, immediately about aperture 46. This groove is bounded by an inwardly-facing cylindrical surface 55 extending leftwardly into the grid from right surface 52, and a rightwardly-facing annular vertical surface 56 extending radial ⁇ ly inwardly therefrom to join aperture 46.
  • a suitable power supply or control means, generally indicated at 60 is arranged to supply respective voltages to the cathode and to the three grids, possibly inter alia.
  • control means or power supply is arranged to supply selected voltages (V C ,V 7 ,V 2 ,V 3 ) to the cathode and to grids G 7 ,G 2 ,G 5 , respectively.
  • V C ,V 7 ,V 2 ,V 3 selected voltages
  • grid G may be at -40 volts, grid G 2 at +1000 volts, and grid G 5 at +7000 volts.
  • the third grid serves to accelerate the electrons to a velocity not obtained with the prior art triode.
  • electrons issue from the rightwardly-facing vertical emitting surface 58 ofthe cathode as a substantially-laminar flow parallel to axis x-x, and are focused by the G 2 -G 5 lens on cross-over 59.
  • this cross-over is located farther from emitting surface 58 than in the prior art. In fact, such cross-over occurs farther from the emitting surface than grid G 3 .
  • the electrons are accelerated to a velocity greater than with prior art guns, and the cross-over occurs after the electrons have substantially reached their maximum velocity attributable to the voltages supplied to the cathode and the three grids. Since the velocity of the electrons is greater at the cross-over than in prior art guns, the space charge effect has less of an effect on the fineness or preciseness (Le., smallness of diameter) of the focused cross-over.
  • Fig.5 is a graph of resolution or screen spot size (ordinate) vs. beam current (abscissa), showing the general forms of the curves for the prior art and improved elec ⁇ tron guns.
  • the prior art curve appears to fit the general equation:
  • R the spot size at the screen (measured in terms of its diameter)
  • i the beam current
  • the resolution of the improved gun is shown as having greater amplitude swings between i — 0 and i « 0.5/, ⁇ than with the prior art gun.
  • Fig. 6 is a plot of screen resolution (ordi ⁇ nate) vs. beam current (abscissa) for the improved gun, showing two different curves representing different voltage conditions applied to the cathode and the grids'.
  • Curve A was obtained by holding the cathode at ground, by holding G 2 and G j at +550 and +7000 volts, respectively, and by varying G 2 from -140 to 0 volts.
  • Curve B cm the other hand, was obtained by holding the cathode at ground, by holding G 2 and G 3 at +450 and +7000 volts, respectively, and by varying G 7 from -110 to 0 volts.
  • Curve./! is shown as having a maximum current of i ⁇ , ⁇
  • curve B is shown as having a maximum current
  • the screen resolution may be maintained within a predetermined bandwidth throughout the entire operating range of possible beam currents.
  • the control means may be selectively operated to dynamically switch between other voltage conditions as well.
  • the present invention expressly contemplates than many changes and modifi ⁇ cations may be made.
  • the emitting surface of the cathode need not necessarily be planar, but may be convex or have some other shape if desired.
  • the relative spacings of the grids may be changed.
  • the sizes and shapes of the apertures may also be changed as well.
  • the power supply or control means may be operated to supply desired voltages to the cathode and the three grids. If desired, the control means may be opera- tively arranged to dynamically switch the respective voltages applied to the cathode and the three grids, to maintain the resolution of a reformed image point on the screen within a predetermined bandwidth.

Landscapes

  • Cathode-Ray Tubes And Fluorescent Screens For Display (AREA)

Abstract

Un canon à électrons (40) comprend une cathode (41) et trois électrodes (42, 43, 44) plates espacées successives. Chaque électrode comprend une ouverture (45, 56, 58) alignée avec une ligne (x-x) normale par rapport à un point de la surface d'émission (58) de la cathode. Une alimentation (60) applique des tensions respectives (Vc, V1, V2, V3) à la cathode et aux trois électrodes. Les électrons sortent de la surface d'émission en un flux essentiellement laminaire et sont focalisés sur un point de croisement (59) situé au-delà de la troisième électrode, une fois que les électrons ont été accélérés jusqu'à leur vitesse maximale. La vitesse des électrons au point de croisement est sensiblement supérieure à celle atteinte avec des canons de l'état antérieur de l'art. Le point de croisement a une résolution accrue à cause de la réduction de l'effet de charge d'espace. Le point de croisement reste à un endroit essentiellement fixe par rapport à la surface d'émission à tous les niveaux du courant de faisceau. Un procédé amélioré d'exploitation d'un canon à électrons comprend la commutation dynamique des différentes tensions appliquées à la cathode et aux trois électrodes, de façon à maintenir la résolution d'un point d'image reformé sur l'écran dans une largeur de bande prédéterminée dans toute la plage possible de courants de faisceau.
EP90908899A 1989-12-28 1989-12-28 Canon a electrons a deplacement reduit du point de croisement a des niveaux eleves du courant de faisceau, et ses procedes d'exploitation Withdrawn EP0461205A1 (fr)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/US1989/005853 WO1990009675A1 (fr) 1989-12-28 1989-12-28 Canon a electrons a deplacement reduit du point de croisement a des niveaux eleves du courant de faisceau, et ses procedes d'exploitation

Publications (2)

Publication Number Publication Date
EP0461205A4 EP0461205A4 (fr) 1991-08-19
EP0461205A1 true EP0461205A1 (fr) 1991-12-18

Family

ID=22215441

Family Applications (1)

Application Number Title Priority Date Filing Date
EP90908899A Withdrawn EP0461205A1 (fr) 1989-12-28 1989-12-28 Canon a electrons a deplacement reduit du point de croisement a des niveaux eleves du courant de faisceau, et ses procedes d'exploitation

Country Status (5)

Country Link
EP (1) EP0461205A1 (fr)
JP (1) JPH04504631A (fr)
KR (1) KR920702896A (fr)
DK (1) DK152091A (fr)
WO (1) WO1990009675A1 (fr)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0589522B1 (fr) * 1992-09-25 1997-03-05 Koninklijke Philips Electronics N.V. Tube à rayons cathodiques
FR2803431B1 (fr) * 1999-12-30 2002-05-03 Thomson Tubes & Displays Structure de canon a electrons pour tubes a rayons cathodiques

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4496877A (en) * 1982-04-06 1985-01-29 Zenith Electronics Corporation Unipotential electron gun for short cathode ray tubes

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CA1196677A (fr) * 1982-02-26 1985-11-12 Sony Corporation Canon electronique
US4724359A (en) * 1986-10-17 1988-02-09 General Electric Company Laminar flow guns for light valves

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4496877A (en) * 1982-04-06 1985-01-29 Zenith Electronics Corporation Unipotential electron gun for short cathode ray tubes

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See also references of WO9009675A1 *

Also Published As

Publication number Publication date
DK152091D0 (da) 1991-08-28
KR920702896A (ko) 1992-10-28
WO1990009675A1 (fr) 1990-08-23
JPH04504631A (ja) 1992-08-13
DK152091A (da) 1991-08-28
EP0461205A4 (fr) 1991-08-19

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