US3723786A

US3723786A - Flat cathode-ray tube for direct viewing spot display

Info

Publication number: US3723786A
Application number: US00121076A
Authority: US
Inventors: D Charles
Original assignee: Thomson CSF SA
Current assignee: Thales SA
Priority date: 1970-03-10
Filing date: 1971-03-04
Publication date: 1973-03-27
Anticipated expiration: 1990-03-27
Also published as: DE2111438A1; FR2082304A5; GB1290993A

Abstract

The present invention relates to a cathode-ray tube designed for point display. The tube comprises an electron-gun embodying a series of cathodes 2 arranged on a conductive band A, an electrode C for the individual control of each of said cathodes in said series, and two additional parallel electrodes running along the band A over the whole of its length, one of then,F carrying a cathodoluminsecent coating and the other, E,metal strips 11. By combining the control voltages applied to C, on the one hand, and the potential exhibited by the strips 11 in relation to that of the cathodoluminescent coating, on the other hand, spot display on the cathodoluminescent layer is achieved.

Description

OR 397239786 SR nited States Patent @191 Charles 1 Mar. 27, 1973 54 FLAT CATHODE-RAY TUBE FOR 3,198,976 8/l965 Starr ..313/86 DIRECT VIEWING SPOT DISPLAY 3,558,967 1/1971 Miriam ..3l3/69 R X [75] Inventor: Daniel R. Charles, Paris, France Primary Examiner Robert Sega] [73] Assignee: Thomson-CSF, Paris, France Almmey cu5hman, Darby & Cushman PP 121,076 The present invention relates to a cathode-ray tube designed for point display. [30] Foreign Application Priority Data The tube comprises an electron-gun embodying a series of cathodes 2 arranged on a conductive band A, Mar. l0, 1970 France ..7008540 an electrode C for the individual control of each of said cathodes in said series, and two additional parallel [52] US. Cl. ..3l3/70 R, 313/78 electrodes running along the band A over the whole of [51] Int. Cl ..H0lj 29/50, HOlj 31/12, HOlj 29/74 its length, one of then,F carrying a cathodolumin- [58] Field of Search "313/70, 69, 92 F secent coating and the other, E,metal strips 11. By combining the control voltages applied to C, on the [56] References Cited one hand, and the potential exhibited by the strips 1 l in relation to that of the cathodoluminescent coating, UNITED STATES PATENTS on the other hand, spot display on the cathodolu- 2,506,627 5/1950 Barford ..3l3/69 R x mmescem acheved- Roberts 4 i Drawing Figures 2,879,446 3/1959 Aiken 2,978,608 4/1961 Gaffney ..3l3/69 R X FLAT CATIIODE-RAY TUBE FOR DIRECT VIEWING SPOT DISPLAY Cathode ray tubes, although possessing a large number of qualities which have led to them being universally adopted in all kinds of applications for the display of various phenomena, nevertheless exhibit drawbacks when it is desired to apply them to the display of symbols, for example the presentation of letters and numbers.

These drawbacks consist primarily in the fact that:

the deflection imparted to the electron beam has a substantially analogue character, that is to say it varies continuously with the control signals applied to the deflection elements;

the length of the tube is in the order of the length of the diagonal of the effective part of the screen.

The present invention, which relates to cathode ray tube for display applications, is intended to overcome these drawbacks.

The invention will now be further described, by way of example, with reference to the accompanying drawings:

FIG. 1 schematically illustrating a perspective view in connection with a cathode ray tube in accordance with the invention;

FIGS. 2, 3, 4, 5, 6, 7 illustrating plan or elevational views of the elements of FIG. 1;

FIG. 8 providing an explanatory diagram of the operation of the tube of FIG. 1, utilizing a section taken in a plane perpendicular to the major dimension thereof; and, 7

FIGS. 9 and 10 illustrating an embodiment of the cathode ray tube schematically illustrated in FIG. 1.

FIG. 1 is a perspective viewshowing schematically the relative dispositions of the constitutive electrodes of a tube in accordance with the invention. In the embodiment of FIG. 1, which is given solely by way of example, there are shown six electrodes referenced A B C D E and F, each of which will be described more in detail hereinbelow. It goes without saying, that, without departing from the scope of the preset invention, it could be subtracted from or added to the device of FIG. 1, one or more electrodes provided that such subtraction or addition produce no fundamental modification in the principles of operation of the tube in accordance with the invention, as staded hereunder.

FIGS. 2, 3, 4 and 5 are plan views of the electrodes A, B, C and D of FIG. 1, as seen by an observer located above them, whilst FIGS. 6 and 7 provide elevational views of the electrodes E and F as seen by an observer located between them. i

The dimensions of the different elements of these figures have been selected to comply with the requirements of the drawing but arbitrarily in relation to their real sizes.

The electrode A (FIG. 2) is constituted by a flat conductor strip 1, for example of tungsten, upon which there are deposited at intervals, small identical equidistant square spots 2, of an electron-emissive material such as the type known generally as a cathode oxide.

Heating by the passage of current through the strip 1, will, under given conditions, give rise to electronic emission from the spots 2, which latter are, for this reason, referred to as cathodes, just as strip 1, in the following description.

The electrode B (FIG. 3) is constituted by a flat conductor strip 3, for example of non-magnetic nickel alloy, exhibiting a series of openings 4 in the form of squares substantially equal in size to the aforesaid spots, spaced apart from one another at the same spacing as the aforesaid spots 2.

The electrode C (FIG. 4) is constituted by a flat insulating strip 5, for example of ceramic, containing square openings whose number is equal to the number of the spots 2 and at the same spacing thereas, bordered by conductive eyelets 6 delimiting orifices substantially equal in size to the openings 4 and to the spots 2; the connections to the eyelets 6 are marked 7.

The electrode D (FIG. 5) is identical with the electrode B: a flat conductor strip 8 containing openings 9.

At the time of assembly, the electrodes A, B, C, and D are located parallel with one another andtheir position is adjusted so that the openings in the electrodes B, C, D are aligned'with the spots 2 of the electrode A, in the direction perpendicular to said electrode A.

E (FIG. 6) is an insulating plate 10, for example of glass, perpendicularly disposed in the example of FIG. 1, with regard to the electrodes A B C and D, bearing, on one of its faces, conductive coatings 11 in the form of mutually parallel equidistant strips, the long side of which is parallel to the plane of the strip A; these conductive strips are connected with the external circuit by connections 12. That face of the plate E which carries these coatings, is disposed towards the electrodeF.

The electrode F (FIG. 7) is constituted by a flat transparent plate 13, of glass for example, parallel to the plate E and entirely covered on that of its faces which is disposed towards the electrode E, firstly with a transparent conductive coating 15, for example tin oxide, this being connected with the external circuitry by the connection 14, and secondly by a coating of cathodoluminescent material marked '16. In a general manner, the preparation of the electrode F, as of all the other electrodes, is carried out using prior art techniques and, for this reason, no further discussion in this respect is required. I

The number of spots 2 on the electrode A and of corresponding openings in the electrodes B, C, D, is limited, for sake of clarity, to a few in the figures, but will be practically largely more numerous: there will be provided, spots 2 and 250 strips 11, for instance.

All the points on the electrode A, or cathode, are

placed at the same potential, which we will consider in the following to be the zero or reference potential, the other voltage values being given solely by way of nonlimitative example.

The electrode B is permanently at a potential which is some few volts positive with respect to the reference potential i.e., the potential of the electrode A.

The conductive eyelets 6 of the electrode C are placed in some cases at a voltage V of 30 to 50 volts and in other cases at a voltage which is a few volts negative, in accordance with a program which will depend upon the application of the tube.

The electrode D is permanently at a positive voltage of V,, of some few hundreds of volts, for example.

If the voltage applied to an eyelet 6 is positive and equal to the positive voltage V hereinbefore referred to, the cathode A being in condition for electronic emission, an electron beam will be emitted by thespot '2 of the electrode A which is located vis-a-vis with the eyelet 6 in question. This beam will pass through the space defined between the electrodes E and F via the hole 9 located vis-a-vis with the eyelet 6.

If, on the other hand, the voltage applied to the eyelet 6 becomes slightly negative, the emission from the corresponding spot 2, will cease.

The conductive coating 15 of the electrode F is permanently maintained through the connection 14, at a voltage substantially equal to V By contrast, the conductive strips 11 deposited upon the plate E are in some cases placed at the voltage V and in some cases at a voltage which is less, by a quantity V than the voltage V namely V V in accordance with a program in connection with the program relating to the eyelets 6.

Assuming that all the conductive strips 11 of the plate E are raised simultaneously to the potential V,,, the electron beam emitted by a spot 2, for an appropriate bias voltage V on the opposite eyelet 6 30 to 50 volts in the example under consideration), will pass through the space defined between the plates E and F, which will be practically an equipotential space due to equality of their voltages, in a direction substantially parallel to said plates.

If such is not the case, however, the electron beam coming from a spot 2 will be deflected towards the electrode F when it arrives at the level of a strip 11 raised to the potential V V hereinbefore referred to, as a consequence of the positive difference between the voltage V of the electrode F and the voltage of the strip in question. lts impact upon the layer 16 which covers the electrode, will gives rise to the luminescence of a point in said layer.

This has been illustrated in FIG. 8, the latter being an explanatory diagram of the operation of the tube of FIG. 1, in which, for reasons of clarity, the conductive strips 11 have been enlarged and their number limited to 4. In this figure, 17 represents the trajectory of the electron beam coming from a spot (not shown) and passing in front of the three lower strips 11 which are at the voltage V,,, the arrow findicating the direction in which the beam is deflected on arriving in the neighborhood of the fourth strip which is at the voltage V V The display of a light spot on the luminous layer 16 is obtained by switching the voltages V and V V respectively of the eyelet 6 and the strip 11, which define said point in accordance with the diagram of FIG. 8.

The voltages V and V are respectively referred to as the line control voltage and the column control voltage.

In operation, the conductive eyelets 6 of the electrode C and the conductive strips 11 of the plate E, are connected to a switch which enables the voltages applied to be varied from V to some few volts negative for the eyelets 6, and from V to V V for the strips 11, depending upon what point on the luminescent layer is to be excited.

The voltage V is currently some few tens of volts.

This point is worth underlining, since it embodies a major significance in so far as the invention is concerned.

In other words, thanks to the use ofa large number of cathodes, the spots 2 in FIG. 2, in accordance with the invention (as many cathodes as there are lines), the same luminosity on impact of the electron beam upon the cathode-luminescent layer 16 (FIG. 7) can be obtained, other things being equal, at a much lower beam acceleration voltage than in conventional cathode-ray tubes.

This accelerating voltage is the column control voltage V as this results from the foregoing; in the case of the tubes in accordance with the invention, this voltage can be limited to some few tens of volts, a value compatible with the use of compact solid state switches which are increasingly being used in display techniques.

Another advantage of the invention rests in that the size of the cathode-ray tube of the invention, is substantially reduced with respect to that of known cathoderay tubes because of the bent trajectory of the electron beam between the cathodes 2 and the cathodoluminescent layer. This size is virtually limited only by the breakdown voltage between the plates E and F, and it appears from what has been said hereinbefore that this voltage will not exceed more than some few tens of volts; it goes without saying that in this case the cathode strip A (FIG. 1) and consequently the spots 2, must be reduced in the same proportions, and E located close to F.

In the embodiment of FIGS. 1 to 7, given solely by way of example, the spots of the electrode A, and consequently the openings in the electrodes B, C, D, have been assumed to be regularly spaced. However, and without departing from the scope of the invention, the spacings between two successive spots may be arranged to vary throughout the electrode A. The same remark applies to the conductive strips of the plate E.

An electrode B, at a slightly positive potential in relation to the cathode A, is present, in the embodiment of FIG. 1. Such an electrode being not necessary for a satisfactory operation of the tube in accordance with the invention, the latter applies also to a structure which does not comprise such an electrode. Likewise, a structure comprising several other electrodes in addition to the electrodes A, C and D provided for electronoptical reasons for example, as already remarked hereinbefore, is also within the scope of the present invention.

Lastly, it should be emphasized that a collector or catcher, no mention of which has been made until this point since it forms part of the prior art of electronic tubes, is essential in order to pick up the electrons of the beam which, in the absence of the voltage V will be propagated, without deflection, from the cathode A to the opposite end of the tube. This catcher may furthermore, be formed quite simply by an additional conductive strip placed at a slightly higher potential than V and located on the plate E beyond the strips 1 1.

FIGS. 9 and 10 provide an exploded view of an example of a cathode-ray tube in accordance with the invention, in which the plates E and F form part of the tube envelope. In the example shown in these figures, the envelope is constituted by two U-shaped components, both of glass for example; the plates E and F are constituted by the legs of one of the U-shaped components, respectively carrying the strips 11, on the one hand, and the

layers

15 and 16 on the other hand,

whilst the base of the other U-shaped component carries the electrodes A, C and D. The two U-shaped components, separately manufactured, are attached together around the whole of their peripheries a and b, by a vacuum-tight bond, using one of the prior art techniques. I

The attachment of the electrodes to their supports and the design of the electrode connections, which again form part of the prior art, have merely been schematically indicated in FIG. 10. In FIG. 9, 70 are leadin-wires each of which is in electrical contact with one of the connections 7.

In a general manner, the invention is open to other variant embodiments than those described and illustrated and which, open to one having ordinary skill in the art, all fall within the scope of the invention.

What we claim, is:

l. A cathode-ray tube which comprises, inside an evacuated envelope, at least a portion of which is transparent, an electron-gun and an electron collector, said gun comprising a cathode in form of a first elongated surface, and at least one control electrode and comprising two additional flat plates extending in the direction of said cathode and perpendicularly to its surface, one of which called the first electrode plate, visible through said transparent portion, is transparent and is covered, on that face disposed towards the other of said two additional plates with a thin, transparent, conductive film itself coated with a cathodoluminescent material, and the other of which, called the second plate, carries parallel conductive strips insulated from one another and extending across the large side of said surface, in the form of rectangles whose large sides are parallel to the large side of said surface, wherein said cathode is a flat rectangular metal strip covered at intervals with small areas of an electron-emissive material and said control electrode is a flat rectangular strip of insulating material parallel to said cathode and pierced by spaced holes said holes being ordered by conductive eyelets electrically insulated from one another, a further flat rectangular metal electrode also parallel to said strip on the side thereof corresponding to electron flow pierced by spaced holes, said emmissive areas, eyelets and holes all respectively aligned and substantially equal in size with each other and disposed in a direction substantially perpendicular to said cathode, each of said eyelets, provided with a separate connection, enabling separate individual control of the emission of one of said small areas to be effected; all of these electron beams emitted by these areas propagating in the same direction perpendicular to this surface and wherein are provided means for applying a fixed voltage to said film and for separately applying voltages to said eyelets and to said strips with regard to said cathode to bend the electron beams into scanning said first plate.

2. A cathode-ray tube as claimed in claim 1, in which said electron-gun is composed of the successive arrangement of a cathode constituted by a flat, rectangular metal strip covered, at intervals, with small elements of an electron-emissive material, by a flat rectangular electrode of insulating material parallel to said strip and pierced by spaced holes, said holes being bordered by conductive eyelets, and by a flat rectangular metal electrode parallel to said strip and pierced by spaced holes, said holes in said electrodes all being substantially equal to the said elements and the relative positions of said electrodes being such that said holes are in alignment with said elements in the direction perpendicular to said strip, and in which said two additional plates are two flat plates perpendicular to said strip, and said conductive strips carried by said second electrode plate are rectangles whose large sides are parallel to the large side of said strip.

3. A cathode-ray tube as claimed in claim 1, in which said two additional electrodes are parts of said envelope.

4. A cathode-ray tube as described in claim 1 further comprising: An additional flat rectangular metal electrode also parallel to said strip on the side thereof corresponding to electron flow and pierced by spaced holes alligned with the holes emissive areas and eyelets.

Claims

1. A cathode-ray tube which comprises, inside an evacuated envelope, at least a portion of which is transparent, an electron-gun and an electron collector, said gun comprising a cathode in form of a first elongated surface, and at least one control electrode and comprising two additional flat plates extending in the direction of said cathode and perpendicularly to its surFace, one of which called the first electrode plate, visible through said transparent portion, is transparent and is covered, on that face disposed towards the other of said two additional plates with a thin, transparent, conductive film itself coated with a cathodoluminescent material, and the other of which, called the second plate, carries parallel conductive strips insulated from one another and extending across the large side of said surface, in the form of rectangles whose large sides are parallel to the large side of said surface, wherein said cathode is a flat rectangular metal strip covered at intervals with small areas of an electron-emissive material and said control electrode is a flat rectangular strip of insulating material parallel to said cathode and pierced by spaced holes said holes being ordered by conductive eyelets electrically insulated from one another, a further flat rectangular metal electrode also parallel to said strip on the side thereof corresponding to electron flow pierced by spaced holes, said emmissive areas, eyelets and holes all respectively aligned and substantially equal in size with each other and disposed in a direction substantially perpendicular to said cathode, each of said eyelets, provided with a separate connection, enabling separate individual control of the emission of one of said small areas to be effected; all of these electron beams emitted by these areas propagating in the same direction perpendicular to this surface and wherein are provided means for applying a fixed voltage to said film and for separately applying voltages to said eyelets and to said strips with regard to said cathode to bend the electron beams into scanning said first plate.