Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J31/00—Cathode ray tubes; Electron beam tubes
  • H01J31/08—Cathode ray tubes; Electron beam tubes having a screen on or from which an image or pattern is formed, picked up, converted, or stored
  • H01J31/10—Image or pattern display tubes, i.e. having electrical input and optical output; Flying-spot tubes for scanning purposes
  • H01J31/12—Image or pattern display tubes, i.e. having electrical input and optical output; Flying-spot tubes for scanning purposes with luminescent screen
  • H01J31/123—Flat display tubes
  • H01J31/124—Flat display tubes using electron beam scanning

Definitions

• the invention relates to a display device having a vacuum envelope which is provided with a transparent front wall with a luminescent screen, which display device comprises a number of electron sources, - a number of electron-transport ducts which cooperate with said sources, selection means for withdrawing each electron current from its transport duct via exit apertures and guiding it to pixels of the luminescent screen, and detector means for measuring a trial current transported through the transport duct.
• a display device is known from European Patent Application EP-A 0
• electrostatic sources is to be understood to mean herein sources for generating electrons
• electrostatic-transport ducts is to be understood to mean herein ducts for transporting electrons in the form of electron currents.
• Said Patent Application describes a flat-panel type display device. Such display devices relate to constructions having a transparent face plate and a rear plate, which is arranged at a small distance from said face plate, said face plate and rear plate being interconnected, for example, by side walls, and pixels in the form of a phosphor pattern being provided on the inner surface of the face plate. When (video-information controlled) electrons are incident on the luminescent screen, an image is formed which is visible via the front side of the face plate.
• the face plate may be flat or, if desired, curved.
• the display device described in European Patent Application EP-A 0 663 134 comprises a plurality of juxtaposed sources for emitting electrons, electron-transport ducts which cooperate with said sources and which serve to transport electron currents through the transport duct, and selectively energizable electrodes for withdrawing each electron current from its transport duct at predetermined extraction locations via exit apertures, and further means for guiding extracted electron currents to the luminescent screen for producing a picture composed of pixels.
• the known display device further comprises a detector for each transport duct to measure a trial current which is sent through the transport duct. If, during operation of the display device, non-uniformities occur in the electron currents flowing through the transport ducts, the picture displayed exhibits smears.
• a display device in accordance wim the invention is characterized in that the detector means comprise a measuring unit having an extraction means for extracting electrons from the transport duct through a measuring aperture in the transport duct, and - directing means for directing the extracted electron current from the measuring aperture towards a measuring element.
• the state-of-the-art detector means comprise measuring elements which measure the number of electrons which arrive at the top of the transport duct.
• the above document in accordance with the prior art mentions a number of causes of non-uniformity in the picture displayed. These causes all relate to drive-mode variations of a wire cathode, in the geometry of the wire cathode and in the position of the wire cathode relative to the transport ducts.
• the invention is also based on the recognition that non-uniformity will always occur, even if variations in the above properties do not occur.
• the electron currents which are directed towards the phosphor screen are extracted from a transport duct. This extraction process may cause variations in the brightness of the picture displayed.
• the measuring element By arranging the measuring element behind an extraction means, the term “behind” meaning in this respect "viewed in the direction of the electron current", the measuring element is sensitive to differences in the effectiveness with which the electron current is extracted from the transport duct.
• the measuring elements measure the number of electrons which arrive at the top of the transport ducts, i.e. if no electron currents at all are extracted. Consequently, the known measuring elements are incapable of determining differences in extraction efficiency.
• the detector means comprise a measuring unit for each transport duct.
• each transport duct is provided with a measuring element and the associated extraction means and further means.
• the exit apertures in a transport duct and the measuring aperture in said transport duct are similar in form.
• the display device comprises a perforated plate in which both me exit apertures and the measuring apertures are formed.
• the measuring aperture is one of the exit apertures
• the directing means comprise a drivable coupling channel with the means for guiding electron currents extracted through the relevant exit apertures to the luminescent screen.
• the electron current which is extracted from a transport duct through an exit aperture, is drawn off by the directing means via the drivable coupling channel, and the directing means guide said electron current to the measuring element.
• This embodiment has the advantage that a measuring element measures an electron current, which is extracted from the transport duct and, if the coupling is not activated, which actually contributes to the picture displayed. This enables the measurement to be improved.
• the above embodiment has the disadvantage, however, that the drive of the means for directing electron currents can disturb the measurements by capacitive interference.
• the measuring aperture is not an exit aperture and there is no coupling duct between the means for guiding the electron current and the directing means.
• the display device comprises further, perforated elements on which and/or in which the means for guiding the electron currents are secured, these perforated elements also include the directing means and the measuring element.
• the perforated elements comprise parts of the means for guiding electron currents to the luminescent screen as well as parts of the directing means and/or of the measuring element.
• the display device comprises shielding electrodes for electromagnetically shielding the measuring element.
• An electromagnetic shield reduces the disturbing influence on the measuring element, which may occur, in particular, as a result of capacitive coupling of different voltages which, in operation, are applied to other electrodes.
• Fig. IA is a schematic, perspective view, partly broken away, of a display device in accordance with the invention.
• Fig. IB is a cross-sectional view of a display device shown in Fig. IA
• Fig. 2A is a schematic, perspective view, partly broken away, of a display device which is provided with a pre-selection and a fine selection.
• Fig. 2B is a cross-sectional view of a display device as shown in Fig. 2 A,
• Fig. 2C is a cross-sectional view of a detail of a further embodiment of a display device in accordance with the invention.
• Fig. 3 is a sectional view of a detail of a further embodiment of a display device in accordance with the invention.
• Figs. IA and IB show a flat-panel type display device 1 having a display panel (window or face plate) 3 and a rear wall 4 which is located opposite said display panel.
• a luminescent screen 7 having a repetitive pattern (lines or dots), for example, of triads of phosphor elements luminescing in red (R), green (G) and blue (B), respectively.
• the luminescent screen may alternatively be a monochrome screen.
• the luminescent screen 7 is either provided on a transparent, electroconductive layer, for example a layer of ITO (indium tin oxide), or provided with an electroconductive layer (for example, an aluminium layer) to enable the necessary high voltage to be applied.
• ITO indium tin oxide
• the (dot-shaped) phosphor elements of a triad are situated at the vertices of a substantially isosceles or equilateral triangle.
• An electron-source arrangement 5 for example a line cathode which provides a large number (for example 600) of electron emitters by means of control electrodes, or a corresponding number of separate emitters, is arranged near a bottom portion 2 which connects the display panel 3 and the rear wall 4 with each other.
• Each individual emitter only has to supply a relatively small current, so that many types (either cold or thermionic) of cathodes can be used as emitters.
• the display device can be provided with a separate cathode.
• Each of me emitters can be arranged separately or, if the emitters are combined to form one line cathode, they can be arranged jointly.
• the electron-source arrangement 5 is arranged opposite entrance apertures 6 of a row of transport ducts which extend substantially parallel to the screen.
• each entrance aperture is provided with a first electrode GI and a second electrode G2.
• GI is a control electrode which can be driven for each individual duct
• G2 is an electrode which is common to several or all ducts.
• the line cathode and the electrodes GI and G2 togemer form a triode. Electrons are emitted in the relevant transport duct by heating the line cathode and applying a potential difference between cathode 5 and electrode G2.
• the transport ducts comprise ducts 11, 11', 11 ", for simplicity hereinafter also referred to as "the transport ducts 11, 11', 11", which are defined by the rear wall 4 and intermediate walls 12, 12', 12". At least one of said walls, preferably the wall opposite the exit apertures 8, 8', 8", is made of a material which is suitable for electron transport by means of secondary emission.
• the electric resistance of the wall material has a suitable high value in the longitudinal direction of the ducts, and a secondary emission coefficient above 1 across the area where electron transport should take place.
• the electric resistance of the wall material has such a value that, at a field intensity in the transport ducts of the order of several tens to several hundred volts per centimeter, which is necessary for the electron transport through the transport ducts, a small total amount of current, preferably less than 10 mA, will flow in the walls.
• a voltage is applied to a transport duct (in the longitudinal direction of the duct), which generates the field intensity necessary for transport.
• an electron current flows in the transport duct, the incoming current being equal to the outgoing current.
• An electron current can be withdrawn from the transport duct via exit apertures 8, 8' , 8" in a perforated plate 10.
• electrodes 9, 9' , 9" an electric field which draws the electrons towards the exit aperture 8 can be created locally, that is in the vicinity of an exit aperture 8. In the Figure, this is shown by means of a pulse sign.
• each transport duct is provided with a measurmg element which measures the number of electrons which arrive at the top of the relevant transport duct.
• Fig. IB shows a very simple embodiment of a display device m accordance with the invention.
• Measurmg aperture 21 is provided with an electrode 22. This enables electrons to be extracted from the transport duct 11.
• the extracted electrons are guided to a measurmg element 23.
• the measuring element may be, for example, an electrode to which a circuit for measuring the current received by the measu ⁇ ng element is coupled.
• This method of measuring a current has the advantage, relative to measuring the current which arrives at the end of a transport duct, as in the known display device, that an extracted electron current is measured. Extraction of electron currents from the transport duct may cause variations intensity on the screen.
• measurmg an extracted electron current for a number of transport ducts or, preferably, for each transport duct, it is possible to measure these variations and, if desired or necessary, said extracted electron current can be corrected for these variations.
• the measuring aperture and the exit apertures are substantially similar in form.
• substantially similar in form is to be understood to mean that the shape of the measurmg aperture does not deviate substantially from the average shape of the exit apertures m the relevant transport duct.
• a shape which does not deviate substantially from the shape of the exit apertures precludes that, due to a difference in shape, the efficiency with which the electrons are extracted from a transport duct is different for the measurmg aperture and the exit apertures. Said differences lead to inaccuracies in the measurements.
• the perforated plate 10 is provided with exit apertures 8, 8', 8" and the measu ⁇ ng aperture 21.
• Such an embodiment is preferred to an embodiment in which measuring apertures 21 are formed in a separate element.
• the number of necessary elements is reduced by using one and the same perforated plate 10.
• the position of the measuring apertures 21 relative to the exit apertures 8, 8', 8" can be accurately determined and does not depend on the accuracy with which an additional element is positioned relative to the perforated plate 10.
• a variation in the position of the measuring apertures 21 relative to the exit apertures 8, 8', 8" leads to variations in the correspondence between the measured currents and the currents which are guided to the display screen.
• Fig. IB shows that the measuring aperture, viewed from the entrance aperture of the transport duct, is the first aperture.
• the preferred positions for the measuring aperture are either the first aperture or the last aperture. When the measuring apertures are m these positions instead of between the exit apertures, the disturbing influences of the signals which are supplied, in operation, to electrodes 9, 9', 9" and other selection electrodes are reduced.
• the measuring aperture is the first aperture.
• the electron current which is emitted in a transport duct is governed by the potentials applied to the source 5 and the electrodes GI and G2.
• Fig. IB it is shown that the measuring aperture 21 and the next following exit aperture 8"' are situated at a distance from each other which is larger than the distance between the exit apertures in a transport duct.
• a blind aperture 27 that is an aperture which cannot be energized, is situated between the measuring aperture 21 and the exit aperture 8", which blind aperture is not provided with an electrode and hence electrons cannot be extracted through said aperture. If mis aperture is provided with an electrode, in operation, this electrode is not energized in such a way that electrons are extracted from the transport duct via said apertures.
• first aperture and last aperture are to be understood to mean the first aperture and the last aperture, respectively, through which electrons can be withdrawn from the transport duct. Consequently, the first "active" aperture and the last “active” aperture, respectively.
• Blind apertures (similar to aperture 27) may be situated between the entrance aperture and the measuring aperture, or further blind apertures may be situated beyond the last "active" aperture.
• Figs. 2A and 2B show a display device in accordance with the invention, in which multistage selection is used.
• multistage selection is to be understood to mean herein that the selection from the transport ducts 11, 11', 11 " towards the luminescent screen 7 is carried out in at least two steps.
• a first (coarse) step for example, the pixels are selected and in a second, fine step, for example, the color elements are selected.
• an active color-selection system 100 which comprises an (active) pre-selection plate 10a, a spacer plate 10b and an (active) (fine) selection plate 10c, is arranged in the space between the transport ducts and the luminescent screen, which is provided on the inner surface of the display panel 3.
• Plates 10a, 10b and 10c are perforated plates, i.e. they are provided with a pattern of apertures.
• a structure 100 is separated from the luminescent screen 7 by a spacer plate 101 , such as an apertured, electrically insulating plate.
• Fig. 2B is a schematic, sectional view of a part of the display device of
• Fig. 2 A in greater detail, in particular the active color-selection plate structure 100.
• This plate structure 100 comprises a pre-selection plate 10a with exit apertures 8, 8', and a fine- selection plate 10c with groups of holes R, G, B.
• the holes R, G, B are positioned so as to fo ⁇ n a triangle, but, in the sectional view of Fig. 2B, all three are represented schematically for the sake of clarity.
• a phosphor element R', G', B' corresponds to each aperture R, G, B.
• three fine-selection apertures R, G, B are associated with each exit aperture 8, 8'.
• Other numbers are also possible, for example 6 fine-selection apertures etc. for each pre-selection aperture.
• a spacer plate 10b is arranged between the pre-selection plate 10a and the fme-selection plate 10c.
• communication ducts 30, 30' are formed whose shape is chosen to be such that it corresponds with the shape of the phosphor color elements (for example circular or triangular triads).
• the apertures R, G, B are provided with electrodes 13, 13', 13" with which the electron current can be extracted from spaces 30.
• the electron-transport ducts 11, 11', 11 " are formed between the structure 100 and the rear wall 4.
• electrodes 9, 9', 9" are provided, in this example, on the surface of the plate 10a facing the screen.
• plate 10a comprises a measuring aperture 21 which is provided with an electrode 22 to extract electrons from the transport duct 11.
• plate 10b has a further measuring aperture 27 and an electrode 28 to extract electrons from space 30".
• a blind duct 8"' is situated between the measuring aperture 21 and the nearest active exit aperture 8. As a result, the distance between the electrodes 9, 13 and the measuring element 29 is increased.
• FIG. 2C shows a detail of a display device, in which a coupling duct is formed between space 30' and 30" via passages provided with electrodes 42 and 43. This enables the electron current actually supplied to a number of phosphor elements to be drawn off for the measuring process. This results in an improved accuracy of the measurement and, in this respect, such a construction is better than the constructions shown in Fig. 2B.
• the interferences which may occur as a result of capacitive coupling are generally greater in the construction shown in Fig. 2C than in the construction shown in Fig. 2B.
• Fig. 3 is a sectional view of a detail of a further embodiment of a display device in accordance wim the invention.
• the display device comprises a stack of plates 51, 52, 53, 54, 55, 56, 57 and 58.
• Plate 51 corresponds to plate 10a
• plates 52 and 58 are spacer plates and plates 53 to 57 are selection plates.
• Selection plates have apertures, for example aperture 61 in plate 53, which apertures have one input 63 and two or more ou ⁇ uts 64, 65 and associated selection electrodes 66, 67.
• a possible trajectory for an electron current is indicated by means of an arrow.
• Selection is accompanied by the application of varying voltages to the various electrodes around selection holes.
• Said varying voltages can induce a "false" signal on the measuring element, particularly as a result of capacitive coupling.
• Such a "false” signal reduces the accuracy with which the trial current can be measured.
• disturbances occur as a result of supply voltages.
• a blind duct 111 is situated between measuring aperture 21 and the nearest exit aperture 8'. This leads to a larger interspace between the electrodes around the selection holes and the detector, more particularly the measuring element of the detector.
• Plate 56 is provided with a measuring electrode 71.
• Plates 54, 56 and 58 are provided wim shielding electrodes 72, 73 and 74. Unlike the other electrodes, these shielding electrodes are not provided with drive voltages for driving electron currents, but serve to shield the measuring electrode 71.
• the impedance to high frequencies between the electrodes 72, 73 and 74 is small, which may be attained by interconnecting said electrodes.
• the assembly of shielding electrodes is preferably coupled capacitively to an earth point. Decoupling of disturbances now takes place very effectively as the electromagnetic "Faraday cage", which is formed by the shielding electrodes, provides a shield against capacitive disturbances. It is noted that the favorable effect obtained by the provision of detector means results in an improved measuring sensitivity of the detector, irrespective of the way in which the measuring current is generated, i.e. whether extraction takes place via a measuring aperture in the transport duct or not.
• This example also shows an alternative arrangement of the wire cathode.
• the wire cathode 5 is situated more or less next to the detector, and plate 51 comprises the electrodes GI and G2.
• the perforated plates comprise the exit apertures and the means for guiding the electron currents to the phosphor elements as well as the various parts of the measuring unit.
• the measuring unit is integrated in the perforated plates. The manufacture of additional parts is unnecessary, which is a big advantage.
• the measuring electrode measures the number of electrons incident on the electrode. This measurement can be used to analyze the operation of the apparatus, which analysis can be employed to send feedback signals to the wire cathode or to the electrodes GI and/or G2.
• the trial current is measured, for example, by measuring electrodes.
• the current impinging on the measuring electrode can be measured by means of a current or voltage measurement.
• this is a preferred way of measuring trial currents.
• it is not the only way.
• it is alternatively possible to make the electron current impinge on a trial-phosphor area or several trial-phosphor areas and measure the luminescence of said trial area(s).
• this is a more complicated construction, as it requires a photo-sensitive element, such a construction can determine possible differences in luminescence efficiency and is less sensitive to capacitive disturbances.
• electron-transport ducts in the form of channels are shown.
• transport ducts are to be understood to include any means by which, in operation, an electron current is passed, by means of secondary emission, from one or more starting points to the exit apertures.
• the directing means shown in the Figures are relatively complex directing means.
• "directing means" are to be understood to include all means which, in operation, guide a trial current from the measuring aperture to the measuring element.
• each measuring unit has a measuring electrode.
• a number of measuring units have a common measuring electrode. This results in a reduction of the number of measuring electrodes.

Landscapes

• Manufacture Of Electron Tubes, Discharge Lamp Vessels, Lead-In Wires, And The Like (AREA)

Priority Applications (1)

Applications Claiming Priority (4)

Publications (1)

Family

ID=8220935

Family Applications (1)

Country Status (3)

Family Cites Families (4)

• 1996
  • 1996-11-27 WO PCT/IB1996/001307 patent/WO1997022135A1/en not_active Application Discontinuation
  • 1996-11-27 EP EP96937473A patent/EP0808511A1/de not_active Withdrawn
  • 1996-11-27 JP JP9521881A patent/JPH11500862A/ja active Pending

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events