US2923846A

US2923846A - Electrical systems

Info

Publication number: US2923846A
Application number: US625734A
Authority: US
Inventors: Melvin E Partin
Original assignee: Philco Ford Corp
Current assignee: Maxar Space LLC
Priority date: 1956-12-03
Filing date: 1956-12-03
Publication date: 1960-02-02
Anticipated expiration: 1977-02-02
Also published as: NL247954A; GB872607A; DE1230453B; FR1248229A

Description

Feb- 2, 1960 M. E. PARTIN ELECTRICAL SYSTEMS Filed DSO. 5, 1956 United States Patent O ELECTRICAL SYSTEMS Melvin E. Partin, Philadelphia, Pa., assignor lto Philco Corporation, Philadelphia, Pa., a corporation oftPenn- Sylvania Application December 3, 1956, Serial No. 625,734

Claims. (Cl. 313-92) This invention relates to improvements in cathode ray tubes and in particular to improved screens for cathode ray tubes used to reproduce scenes `televised in colors.

There are systems for the reception of color television signals which employ a cathode ray tube having an image-forming, beam-intercepting structure constituted in part of a screen having a plurality of sets oftstrips of phosphor materials which are disposed substantially parallel to one another. 'Each of the sets of phosphor strips emits light of a particular color when bombarded by an electron beam. .An electron beam, Whose intensity is modulated by signals representative Aof 'the colors of the "scanned elements of a televised scene, is caused to scan :such structure in amanner such that, at a time when it is modulated in intensity by a signal `representative of, say.the 'red colored elements of the scene,itwill impinge only on a phosphor strip emissive of `red light. The Astrips are :made very line and positioned close together, so that the eye'merges the light emitted, when they are scanned, into 'a continuous color picture. An indexing system for coordinating the intensity modulation ofthe beamwith the position of the latter on the beam-intercepting structure is usually employed because of beam `scanningirregularities and `for other reasons. Theindexing systemfhelps 'tomaintain thecolors of the reproduced image faithful to those of the original televised scene.

One type of indexing system vthat `has "hitherto been employed involvesthe detection of radiant energy signals of a particular Wavelength 'which are generated at Apredetermined points on the screen in 'response to the impingement of thebearn thereupon. Detection of these signalsmay be accomplished by placing a photosensitive device,responsiveto theparticular type of radiant energy 'generated,insuch aposition that Whenlthe beam imping'es upon predetermined elements ofthe screen, the device will generate electrical indexing signals `which may `be used to coordinate the beam modulation `with its "position. This coordination may be achieved eitherby shiftingthe beam to the fproper strip or `by :modulating 1the beam with a video signal correspondingto the Vcolor of the fareaon Whichthe beam is impinging.

In the past some indexing `systems employed a photosensitive device positioned external to, and in front of the faceplate of the cathode rayttube. In suchla ysystem it'isipossible to deposit on the rear surface ofthephosphor strips.anielectron-permeable layer of a reflective and conductive material `such as `aluminum which, `in general, serves three purposes. MFirst, this layerhelps to increase the `brightness of the reproduced image by reilecting back tothe viewer-.light otherwise lost toward the rear of the phosphortscreen. Secondly, this layer, being impervious to ions, also obviates the-need Vfor ion traps or other expedients Vaimed attreducing ion spot-that`is, the 'discoloration of the yiluorescent screen caused by .negative `ions ipresent within .an electromagnetically deected cathode ray tube being accelerated into `conta`ct`vvith the by the second crossover point voltage.

er ICC fluorescent screen. Thirdly, the reflective layer 'helps to increase brightnessby enabling the uorescent screen to be maintained at a higher positive potential with respect to the cathode than would be possible if the reflective layer Were omitted. In this latter connection, if the iluorescent screen is oating-that is, not connected lto a source of potential-and electrons are accelerated into impingement thereupon by a voltage which is higher than the so-called second crossover point of the particular phosphor used (i.e., the point at which the application of a higher positive potential to the screen results in a ratio of secondary incident electrons of less than l) the potential on the screen cannot be made more positive than the voltage of the second crossover point. This is due to the fact that the screen will be charged increasingly negative by the secondaries falling back upon it so that in the latter case the attainable brightness is limited However, if a reective, conductive layer is used which is at a positive potential, the secondary electrons, emitted in response to the impingement on the screen of the primary electrons of the beam, are collected by the layer so that the potential on the screen may be maintained much'higher than if the Alayer were omitted.

Indexing systems are also known in which the photosensitive device is mounted behind the liuorescent screen. In such systems, if the reflective layer is omitted, the rear mounted photosensitive device can be constructed to respond to light emitted by just one of the sets of phosphor strips, but the above enumerated advantages of the reflective layer are lost. If it is desired, on the other "hand, to include a reflective layer in such an arrangement ithas hitherto been necessary to deposit appropriate electron-sensitive indexing strips productive of light of the wavelength to which the photosensitive device responds ontherrear surface of the reilective layer. This involves an extra manufacturing step.

`It would therefore be highly desirable, in indexing systems employing rear-mounted photosensitive devices, to arrange all of the electron-sensitive elements, including the indexing elements, on the inner surface of the tube faceplate, and to deposit on the rear of these elements a rellective coating of such construction that the rear-mounted device can be actuated in response to the scanning of the screen so as to perform the required indexing function.

Accordingly, it is an object of the invention to provide improved systems for reproducing images of scenes televisedtin color.

`It `is another object of the invention to provide improved screen `structures for use in television display assemblies employing photo-indexing scanning systems in which thepho-tosensitive devices are placed to the rear of the fluorescent screen.

`Still another object of the invention is 'to increase the intensity of images produced by cathode ray tube display assemblies using indexing systems in which a rearmounted photosensitive device is employed..

Another object o-f the invention is to permit the use of a conductive and reflective llayer in display assemblies which employ rear-mounted photosensitive devices for indexing the scanning `position of the beam with the intensity modulation thereof.

These objects, as `ovell as others which will appear, are achieved according to my invention by an improved beamintercepting structure Vfor cathode ray tubes which are used with rear-mounted `photosensitive devices to coordinatetheposition of the scanning electron beam with the intensitymodulation thereof.

'This structure comprises la number of sets fof imageproiducing phosphor `lelements respectively emissive fof radiant energy of a first predetermined range of wavelengths when struck by an electron beam, and a number of indexingphosphor elements which uoresce upon electron-excitation to produce radiant energy of a second predetermined range of wavelengths substantially different from the first range. All of the phosphor elements are deposited on an appropriate transparent substrate such as the interior surface of the faceplate of a cathode ray tube. On the rear surface of the phosphor elements a layer of an electron-permeable and conductive material is deposited which reflects radiant energy having Wavelengths in the first range and transmits the radiant energy having wavelengths within the second range. When such a structure is embodied in a color television display tube of the type previously mentioned, the brightness of the image produced thereby is considerably enhanced and the position of the scanning electron beam may be` signalled to the indexing system because the radiant energy emitted by the indexing phosphors, which is ordinarily chosen to be invisible to the human eye, passes through the reective layer and impinges on the photosensitive device mounted to the rear of the beam-intercepting structure.

In accordance with one form of the invention as used in color television display apparatus, a plurality of elongated, image-forrning phosphor elements vrespectively emissive of light of selected component colors of a televised scene are deposited on the interior surface of the faceplate of a color television reproducing tube. Mixed with elements emissive of light of one of the image colors are indexing phosphors which emit invisible light, i.e., ultraviolet light having a wavelength or wavelengths substantially different from the light emitted by the sets of image-producing phosphors. Behind the phosphor elements and desirably in contact therewith is deposited an electron-permeable and conductive layer, which may be made of silver, for example, and which reflects visible light of the selected component image colors toward the viewer through the glass faceplate of the tube, and which transmits ultraviolet light emitted by the indexing phosphors toward the rear of the tube to actuate a photosensitive device responsive to the ultraviolet light. A1- ternatively, instead of mixing indexing phosphors with one set of image-producing phosphors, a phosphor may be chosen which emits both visible light of one of the selected image colors and invisible light for generating the indexing signals. In another form of the invention indexing phosphors are chosen which uoresce in the infrared region, and the electron-permeable conductive layer is constructed so as to reflect the visible light emitted by the image-producing phosphors and to transmit the infrared light emitted by the indexing phosphors.

The sole figure is a block, schematic and partially sectional view of a color television receiver which utilizes a cathode ray tube having a beam-intercepting structure in accordance with my invention.

Referring to the sole gure, a part of a color television receiver is shown which includes a cathode ray tube 20 incorporating a beam-intercepting structure 30 according to the present invention. A conventional thermionic cathode 16 generates a beam 18 of electrons which is impelled by an accelerating electrode 22 (to which a positive potential is applied) and focussed by a focussing coil 24 positioned about the neck of the tube 20. The focussing coil 24 is energized by current from an appropriate source 26 of focussing current. The beam is deected in response to deflection fields created by the deflection yoke 28 which may be of conventional construction and which moves the beam 18 in horizontal and vertical directions forming a scanning pattern. The yoke is energized by currents supplied by the horizontal and deflection circuits 32. In order to mpel the beam 18 toward the beam-intercepting structure 30 a positive potential is applied to a conductive layer 34 which. is

deposited on the internal surface of the bell portion of the cathode ray tube 20 as shown. A potential of about -|30 kv. is a typical value of voltage which may be used for this purpose.

In scanning each line the beam 18 is deflected in a direction generally transverse to that in which the

phosphor strips

46, 42 and 44 are disposed. These strips respectively emit red, green and blue light in response to electrons of the beam 1S impingent thereupon. The red and blue emissive strips may be compo-sed of any conventional and appropriate phosphors for this purpose which are well-known in the color television art.

In accordance with my invention the phosphor strips 44 are constructed so as to emit light of two distinct ranges of wavelengths, one visible and the other invisible. In a preferred form of the invention as shown in the sole figure the invisible light is ultraviolet and the visible light isl green. In order to obtain the visible green light the strips '44 may be composed in part of the zinc orthosilicate phosphor manufactured by Du Pont under the designation of Q65-2823. When this zinc orthosilicate phosphor is properly activated by manganese it emits green light in response to electrons impingent thereupon. When zinc orthosilicate is unactivated, however, it emits ultraviolet light. Therefore the strips 44 include a mixture both of activated and unactivatedzinc orthosilicate. The mixture also serves another purpose-Le., the addition of unactivated zinc orthosilicate to the activated phosphor helps to reduce the efficiency of the green emissive phosphor so as to balance its light output relative to that of the other phosphors and thereby maintain, in the manner described and claimed in copending application of M. Sadowsky and R. E. Waggener, Serial No. 364,398, led June 26, 1953, now Patent No. 2,862,- 130, proper color values in the reproduced image. Alternatively the phosphor strips v44 may be made from a single phosphor having two different peaks of emission, one within the visible band of wavelengths and another Within the invisible. For example, the phosphor known by the Radio and Television Manufacturers Association designation P-15, i.e., activated zinc oxide, peaks around 3900 A. which is near the ultraviolet region and also at about 5000 A. which is the green region of the spectrum.

In accordance with the invention a reflective, electronpermeable layer 50 of silver, for example, is deposited on the rear surface of the

phosphor strips

40, 42 and 44 which helps to prevent ion spot, and which also tends to increase brightness by reflecting toward the viewer light ordinarily lost toward the rear of the tube and by enabling the potential of the phosphor strips of the structure'to be more positive than is possible withoutsuch a layer. While the layer 50 reflects red, blue and green light toward the viewer, it is essentially transparent to ultraviolet light. Therefore, when the beam 18 traverses the green emissive strips 34 containing the mixture of activated andl unactivated zinc orthosilicate phosphor as mentioned above, the latter will emit ultraviolet light, a direct ray of which is indicated by the broken line 66, which will pass through the layer 50 and impinge upon the rear-mounted photosensitive device 65 as shown. A window 70 is formed in a portion of the wall of the tube 20 which permits the passage of ultraviolet light of the desired wavelength. In response to the ray 66 the device 65 will generate a current or a voltage which is applied to the indexing system 72 via the leads 74. The indexing system thereupon applies a corrective signal to the color signal processing circuits 12 so that the coordination between the beam position and the beam modulation may be maintained. There are a number of particular ways `in which this coordination can be effected, but since this aspect of the system does not directly concern the present invention, further description of any particular indexing orv control system'is believed unnecessary and will be` omitted herefrom. p

If the radiant energy contained in the unactivated zinc orthosilicate is relatively feeble, the anode layer 34 may be so Vconstructed that it reflects light in the ultraviolet region so that the other rays indicated at the number 76 will be reflected back and forth along the layer 34 until they finally pass through the window 70 and fall upon the `photosensitive device65 in the manner explained in U.S. Patent No. 2,749,449 issued to W. E. Bradley and D. E. Sunstein on June 5, 1956.

It is also possible to increase the amount of ultraviolet light which reaches the photosensitive device 65 by making the faceplate 60 of the tube 20 of glass which reflects ultraviolet light and which transmits red, blue and green light. This reiiected ultraviolet light will pass through the layer 50 and will eventually impinge on the photosensitive device 65. This type of faceplate will also prevent stray ambient ultraviolet light originating outside the tube from generating signals in the photosensitive device 65. i

In anotherform of my-invention the layer 50 can be composed of a material which reflects red, blue and green light but transmits infrared rays. Within one of the phosphor strips such as the green emissive strip 44 for example a phosphor material is inserted which fluoresces and emits light in the infrared region when impinged upon by an electron beam. One such phosphor is known as P-13 and comprises magnesium silicate (MgSiOazMn) which emits light in the infrared region when impinged upon by an electron beam.

The layer 50 in this form is composed of a material which will reiiect the Visible colors of the image and transmit infrared. The layer 50 may be composed of silicon or germanium evaporated upon the rear surface of the phosphor elements. The amount of infrared radiation collected by the photosensitive device may be increased by employing the invention taught in the previously mentioned U.S. Patent No. 2,749,449, or by making the faceplate 60 reliective of the infrared light and transmissive of the visible colors. In all other respects, the operation of the tube containing such a beam-intercepting structure would be substantially identical to the operation of the tube shown in the sole figure.

It should be appreciated that the indexing phosphor can be placed anywhere on the front side of the conductive and reliective layer, not just in one of the phosphor strips. For example, the indexing phosphor may be inserted in spaces between selected adjoining ones of the image-forming phosphor strips.

While the invention has been described with reference to screens for cathode ray tubes for reproduction of televised scenes in color, it should be understood that the advantages of employing screens constructed `according to my invention are also to be gained in cathode ray tubes for monochromatic image production in which it is desired that the linearity of the sweep of the electron beam, for example, be improved by the generation of indexing signals indicative of the rate at which the beam traverses the screen. These indexing signals can then be used to stabilize the sweep so that the quality of the image reproduced is improved thereby.

It will be understood that still other embodiments and applications of apparatus constructed according to my diverse forms of the invention described herein will occur to those skilled in the art. Consequently, I desire the scope of this invention to be limited only by the appended claims.

What I claim is:

1. A beam-intercepting structure for a cathode ray tube comprising: a Iirst electron-sensitive fluorescent portion constmcted and arranged so as to emit radiant energy within a first range of wavelengths, a second electronsenstive portion constructed and arranged to emit radiant energy of a second range of wavelengths substantially different'vfrom said first range,` 'and a layerof a electron-permeable `material deposited on saidv rst and second portions, said layerbeing constructed so as to transmit substantially only radiant energy having wavelengths within said second range. p

2. A beam-intercepting structure for a cathode ray tube comprising: a first electron-sensitive fluorescent portion constructed and arranged so as to emit radiant energy within a first range of wavelengths, a second electronsensitive portion constructed and arranged to emit radiant energy of a second range lof wavelengths substantially different from said first range, and a layer of an electrically conductive electron-permeable material deposited on said first and second portions, said layer being constructed so as' to transmit radiant energy having wavelengths Wi-thin said second range.

`3. The structure according to claim 2 wherein said layer is also constructed so as to reflect radiant energy having wavelengths within said first range.

4. A beam-intercepting structure for a cathode ray tube comprising: a iirst electron-sensitive uorescent portion deposited upon a substrate, said first portion being constructed and larranged so as to emit light within a rst range of wavelengths, a second electron-sensitive portion constructed and arranged to emit light of a second` range of wavelengths substantially dilferent from said first range; and a layer of an electrically conductive and electronpermeable material deposited upon said lirst and second portions, said layer being constructed so as to retlect light having wavelengths within said iirst range and to Itransmit light having wavelengths within said second range.

5. A beam'intercepting structure for a cathode ray tube comprising: a iirst electron-sensitive portion constructed and arranged so as to emit visible radiant energy within a first range of wavelengths, a second electron-sensitive portion constructed and arranged to emit invisible radiant energy of a second range of wavelengths substantially diiferent from said lirst range, and a layer of an electrically conductive and electron-permeable material deposited on said lirst and second portionsu said layer being constructed so as to reflect said visible radiant energy and to transmit said invisible radiant energy.

6. A beam-intercepting structure according to claim 5 wherein said invisible radiant energy is light in the ultraviolet region of the spectrum.

7. A beam-intercepting structure according to claim S wherein said invisible radiant energy is light in the infrared region of the spectrum.

8. A beam-intercepting structure for a cathode ray tube usedA to reproduce images of scenes televised in color, said structure comprising: a rst electron-sensitive fluorescent portion constructed and arranged so as to emit light of selected colors, a second electron-sensitive portion constructed and arranged so as to emit invisible radiant energy, and a layer of an electrically conductive and electron-permeable material deposited on said iirst and second portions, said layer being constructed so as to reect said light and to transmit said invisible radiant energy.

9. In a cathode ray tube assembly for reproducing images of scenes televised `in color, said assembly comprising a cathode ray tube and a photosensitive device positioned to the rear of the faceplate of said cathode ray tube which generates signals in response to a pre determined form of radiant energy, a beam-intercepting structure for said cathode ray tube comprising: a plurality of sets of phosphor elements respectively emissive of selected colors in response to the impingement thereupon of said electron beam, said elements being deposited on the inner surface of said faceplate, a plurality of electrcn-sensitive fluorescent elements deposited on said faceplate constructed and arranged to emit said predetermined form of radiant energy, and a layer of an electron-permeable material deposited on the rear surface of said elements, said layer being constructed S0 as to reect light of said selected. colors and to transmit said predetermined form of radiant energy. y

10. A beam-intercepting structure for a cathode ray tube, said structure comprising: a plurality of sets of electron-sensitive tluorescent elements deposited on the inner surface of said faceplate, one of said sets of elements comprising a phosphor which has a radiant energy emission characteristic having peaks at two different wavelengths, and a layer of an electron-permeable and conductive material deposited on said elements which transmits radiant energy of only one of said wavelengths. 11. The structure according to claim 10 wherein said layer reflects radiant energy of the one of said `two wavelengths which is not transmitted by it.

12- A beam-intercepting structure for a cathode ray tube used to reproduce images of scenes televisedfin color, said structure comprising: a plurality of sets of elongated, electron-sensitive phosphor strips deposited on a substrate, said sets of strips respectively being emissive of light of the additive primary color components of said televised scene when traversed by an electron beam, the material of one of said sets of strips also being emissive of detectable invisible light when traversed by an electron beam, and a layer of an electron-permeable and conductive material deposited on said strips which reects said colors Vand transmits said invisible light.

. color components of s aid televised scene, one of said sets of strips also containing material which emits de- |tectable invisible light when traversedl by an electron beam, and a layer of an electron-permeable and 'conductive material deposited on such strips which reects said colors and transmits said invisible light.

15. A beam-intercepting structure according to claim 14 in which said invisible light is inthe ultraviolet regon of the spectrum and said layer comprises silver particles.

References Cited in the tile of this lpatent UNITED STATS PATENTS sziklai Mar. 6, 1956 Wallmark Dec. 18, 1956 n Mlm

Claims

1. A BEAM-INTERCEPTING STRUCTURE FOR A CATHODE RAY TUBE COMPRISING: A FIRST ELECTRON-SENSITIVE FLUORESCENT PORTION CONSTRUCTED AND ARRANGED SO AS TO EMIT RADIANT ENERGY WITHIN A FIRST RANGE OF WAVELENGTHS, A SECOND ELECTRONSENSITIVE PORTION CONSTRUCTED AND ARRANGED TO EMIT RADIANT ENERGY OF A SECOND RANGE OF WAVELENGTHS SUBSTANTIALLY DIFFERENT FROM SAID FIRST RANGE, AND A LAYER OF AN ELECTRON-PERMEABLE MATERIAL DEPOSITED ON SAID FIRST AND SECOND PORTIONS, SAID LAYER BEING CONSTRUCTED SO AS TO TRANSMIT SUBSTANTIALLY ONLY RADIANT ENERGY HAVING WAVELENGTHS WITHIN SAID SECONDD RANGE.