US2212640A - Cathode ray system - Google Patents

Description

Aug. 27, 1940. J. v. L. HOGAN CATHODE RAY SYSTEM Filed July 7, 1934 7241 Vlflfo gaw INVENTOR NEY Patented Aug. 27, 1940 UNITED STATES PATENT orrica carnonn BAY SYSTEM Application July 7, 1934, Serial No. 734,144

9 Claims. (Cl. 250-275) This invention relates to cathode ray tubes and devices where a stream of electrical particles are made to impinge upon a screen coated with v fluorescent material, thus giving rise to a visible spot of light whose position may be changed by electrical and/or mechanical forces caused to act upon such stream.

More particularly this invention deals with a cathode ray tube applied to television transmission, as for purposes of image reproduction.

One object of the present invention is to provide a cathode ray television scanner or reproducer capable of operation with greater picture detail or picture contrast than is obtainable with such tubes operated in the fashion .at present known to the art.

Another object of this invention is to control the area and the shape of the fluorescent spot appearing on the screen of a cathode ray oscillograph tube.

A further object of this invention is to increase elementary resolving power of a cathode ray tube scanner without changing the number of scanning lines or the rates of scanning.

Yet another object of this invention is to increase such elementary resolving power of a scanning system using the cathode ray tube without loss of the photographic smoothness of the reproduced image, which latter quality is highly desirable.

Another object of this invention is to secure a reproduced image in a cathode ray tube scanner which will constitute a smooth and even picture possessed of crispness and detail to an unusually high degree.

Further objects of this invention will appear in the following detailed description and accompanying drawing where v Fig. 1 represents a typical form of cathode ray tube suitable for use with my invention, shown in a partially diagrammatic fashion.

Figs. 2 and 3 illustrate diagrammatically various forms of scanning spots which may be produced by the use of my invention.

Fig. 4 shows, partly schematically, certain portions of a cathode ray tube system according to my invention.

Fig. 1 illustrates one typical form of cathode ray tube where l0 represents an envelope of suitable material such as glass provided at its larger end'with an interior screen ll constructed of fluorescing material such as willemite or other suitable substance which will become fluorescent under bombardment by an electron stream.

At l2 there is indicated a hot cathode coated with suitable electron emitting material. Envelope Ill may be evacuated either moderately, or to a very high degree, in accordance with principles well known in cathode ray tube construction and the residual gas, if any, left therein may be an inert gas suitable for use in such tubes.

The electron stream leaving cathode I! may be controlled by a so-called grid l4 and may be focused or concentrated by an element l5 here represented as a cylinder but which may be made in other shapes. This is supplied with a suitable electric charge by means of an external connection l3. At l6 there is represented an anode which serves to accelerate the passage of electrons from cathode l2. The stream of electrons which passes through a suitable aperture IS in anode l6 impinges upon fluorescent screen ll, thus giving rise thereupon to the bright or luminous spot previously referred to. The various elements above referred to, except the screen, are connected by' conductors leading through envelope ID to suitable supplies of electric potential so that their various potentials relative to one another may be appropriatefor producing, focusing, and accelerating the passage of the electron stream from the cathode to the screen. These elements may be supported from one or more so-called "presses or in any other suitable fashion.

The size of the bright spot produced on the screen may not only be controlled by the choice of configuration of and potentials on the various elements within the tube, but may also be controlled in certain cases by the proper choice of pressure for such residual gas as may be left in the envelope, as well understood in the art.

During its passage from the anode to the screen, the electron stream may be subjected to electrostatic forces by passing it between a pair of vertical plates l1 and I8 and also between a pair of horizontal plates l9 and 20.

Electro-magnetic control of the electron stream may also be obtained by subjecting it to the magnetic field produced by a pair of coils 2i and 22 whose axes lie horizontally and between another pair of coils 23 and 24 whose axes lie vertically.

It is customary in cathode ray tube operation to deflect the electron stream in two dimensions at right angles to one another by applying appropriate potentials to these deflecting plates or passing appropriate currents through these deflecting coils above described.

While the deflecting plates have been indicated as lying within the tube and the deflecting coils as lying without the tube, it is to be understood that such relative location is susceptible of wide variation without changing the general operating action of these elements and this invention is equally applicable to tubes whose elements are located in a fashion different from that above described. j

It is also to be understood that electrical connections extending without the tube are provided for conducting suitable potentials and/or currents to the elements lying within'the tube.

In operating a cathode ray tube as a television scanner various sources of currentare applied to the elements within the tube and it is thought unnecessary to illustrate such sources of current supply since they are well known in the art, but the following brief description of the operationof this tube as a television scanner according to the usual practice may be found helpful in understanding this invention. In television it is customary to pp y a moderately high frequency saw-tooth wave-form of potentialto the plates (or of current to the coils) causing horizontal deflection, and a lower frequency saw-tooth wave-form to the plates or coils causing vertical deflection. If the television picture is to be scanned in 100 lines per frame and at the rate of 20 frames (or pictures) per second, the horizontal frequency will'be 100x20 or 2,000 periods per second and the vertical frequency 20 periods per second. The cathode beam when acted upon by these forces will sweep the fluorescent spot from side to side of the screen at the line-scanning rate, the successive lines thus described being progressively moved across (e. g. down) the screen so as to cause complete twodimensional scanning at the desired rates. In television reproduction the picture may be generated on the screen by modulating the intensity of the fluorescent spot in accordance with the picture content, as by means of the grid operating upon the electron stream within the tube.

The size of the fluorescent spot is ordinarily selected to be approximately equal in diameter to the height of the picture fleld divided by the number of scanning lines. Thus if the tube screen is nine inches in diameter, the vertical dimension of the picture field may be about six inches. If 100 scanning lines per frame are used, the spot will be about inch or ,5 inch in diameter.

If the spot is smaller, the fleld will show horizontal black lines which in reproduction will prevent obtaining a smooth photographic or pictorial effect. If the spot is larger, the lines will overlap too much, highlights in the picture will show horizontal bright lines, and detail will be lost.

In applying my invention I may use the well known cathode ray oscillograph tube above described, fltted with both the deflecting coils and the pairs of deflecting plates whose action has been explained. For television reproduction, I may apply the deflecting or sweep-producing forces by means of electric currents in the coils described, leaving the deflecting plates disconnected andthus available for the special purposes of my invention about to be described. I prefer that the tube potentials and evacuation shall be.

adjusted or chosen so that the round fluorescent spot on the screen is too small to give a smooth picture when used in the usual way, prominent horizontal black lines appearing across the screen under such usu'al conditions.

Referring now in addition to Figs. 2 and 8 certain principles of my invention which are there illustrated will be apparent from the following description of the operation of a cathode ray tube in accordance with my invention.

With the reproducer as described, I apply a controllable negative potential to each of the two vertical deflecting plates, which would normally be used to control horizontal deflection of the electron stream or spot position. These potentials are adjusted by trial to meet the conditions present in any particular tube, and if the tube is symmetrical may be identical on the two vertical plates. Thus, the plates may be connected together and, by means of a battery or a rectifler, the common potential of both may be brought to a value several hundred volts more negative than that of the anode, or of the electron stream passing between the plates.

I have found that the result of applying such negative potential to both plates is to repel the electrons therefrom in such a way as effectively to "squeeze the electron stream into a thin vane illustrated in cross section at CI of approximately rectangular or elliptical cross section, instead of its normal round cross section indicated at 32, the smaller dimension being horizontal. I flnd that the best potential may be determined by trial for each design of tube, and that if the tube is not symmetrical it is desirable to apply somewhat different values of potential (both ordinarily being negative with respect to the anode or electron-stream reference potential, however) to each of the two vertical plates, one on either I side of the electron stream.

The choice of the proper potential is not diflicult, for the shape of the fluorescent spot on the screen in general corresponds to the cross-section of the electron stream and it is only necessary to increase the two potentials (or the common potential) in the negative direction until the spot has been "squeeaed electrically into the desired elongated form without any substantial loss of brilliance.

I may further increase the vertical elongation of the spot, decrease its horizontal dimension, and at the same time increase its brilliance, by applying a similar but positive potential to the pair of horizontal deflecting plates (normally used to control vertical deflection of spot position). These plates may be connected together and a common potential, usually several hundreds of volts positive with respect to the anode or reference potential, applied to both, or, as in the case of the other pair of plates, separately adlusted but more or less equal positive potentials may be applied to each of the two plates, respectively above and below the electron stream. This results in making the spot horizontally still narrower as shown at 33 and vertically still longer, and in increasing the velocity of the electrons and consequently the brilliance of the fluorescent ellipse, rectangle or line on the screen,

While a cathode ray tube may be operated in several difl'erent fashions while utilizing the principles of this invention, there follows a brief description of one method of operation which I have found satisfactory for purposes of television scanning.

I may adjust the shape of the spot into the flnest or narrowest vertical line that can be obtained, with the highest possible brilliance, the

voltage adjustments for this purpose being made with the deflecting coils inactive and consequently with the spot standing in .one position on the screen. I may then start the deflecting voltage aaracso supply system, as in normal operation, which has the eiiect of moving the fluorescent line or spot rapidly from side to side and less rapidly from top to bottom of the screen, so that (no modulation having been applied) a rectangular field is illuminated.

Next I may slightly readjust the squeezing negative and elongating positive potentials applied to the plates and used to control the shapemake certain that after having selected the correct vertical length of fluorescent area I have not increased its width. If the spot is now of considerably less width (horizontally, or in the ,direction of fast-scanning) than height (vertically, or in the direction of slow scanning), the adjustments have been properly made and the value.

values thus determined need not be changed unless some other variation occurs in the system such as to require compensating re-adjustment.

The cathode ray system is now adjusted ideally for the reproduction of pictures with maximum brilliance, clarity, sharpness, detail and smoothness. Yet the scanning rates have not been changed. n restarting the deflecting system and applying picture-modulation in the usual way, the desired improved results are had.

In Fig. 4 I have shown certain portions of a system which embodies some of' the novel features of my invention. In this figure I have omitted the deflecting systems, including the electrical apparatus ancillary to the tube proper, and which forms a portion of such scanning systems.

Likewise I have omitted the fluorescent screen which may be of any suitable type. Both the deflecting systems and the fluorescent screen are well known in the art and since they have been indicated in Fig. 1 and since the particular type of system or of fluorescent screen used does not form an essential part of my invention, it is thought unnecessary to illustrate them in detail.

In Fig. 4 the hot cathode I2 is supplied by a suitable source of electrical energy, here indicated schematically by battery H2. The concentrating element I5 is maintained at a suitable potential by means of a battery H5. The control or grid element II is maintained at a suitable potential by battery Ill. By moving along this battery the connection indicated as a variable one and leading to element H, the charge upon the grid l4 with respect to cathode l2, may be made to assume either a negative or positive It can be seen that battery H4 may be replaced by any other suitable source of potential such as the picture signal output of a television receiver. Anode I8 is connected to a suitable source of relatively high potential 6, here indicated diagrammatically as a battery.

The vertical field-producing plates l1 and II! are provided with individual connections leading to a suitable source of potential, which is arranged so as to give these plates a negative charge with respect to cathode l2. The purpose of the individual leads from the two individual plates This means that the verof the pair is to allow any asymmetrical action arising from lack of symmetry in the various elements of the tube or from any other cause, to be compensated for by the application of slightly diiferent potentials to the two individual plates,

as previously described in detail. Similarly horizontal field-producing plates I9 and 20 are provided with individual taps leading to -a source of positive potential, diagrammatically indicated by battery I20.

The variable connections extending from the different tube elements to their respective sources of potential are designed to allow the electrical manipulation of the electron stream which is passing through the tube, by the operator thereof. The details of such manipulation have been previously described. Suitable relative quantitative values for the various sources of potential here indicated have been previously set forth and it is to be understood that such sources of potential are not necessarily electrochemical in nature, but may beconstituted by other devices well known in the art, such astransformer-rectitier-filter systems.

I have described my invention as applied to a television reproducer utilizing so-called horizontal progressive scanning but it is equally applicable, as will be understood by those skilled in the art, to television pickup apparatus, to systems using so-called vertical scanning, to oscillatory or simple Lissajous scanning, and to oscillograph operation. Further the desired control of spot shape may be had by impressing squeezing or elongating magnetic forces upon the electron stream, as by so locating a permanent magnet or a coil carrying a direct current that the magnetic lines of force extend substantially parallel to the electron stream but are of differing intensities in-perpendicular planes containing the central path of the electron stream.

It is also possible to use the same electrostatic plate system or magnetic coil system both for control of spot shape and size and for control of spot position or deflection, by superimposing the varying deflecting voltages upon the normally unvarying shape-control voltages or currents.

While I have chosen a certain type of cathode ray tube to illustrate the principles underlying my invention it is to be understood that this inby the use either of deflecting coils or deflecting plates which give rise to electrical forces of different character and therefore in the claims hereto appended, such phrases as electrical forces or electrical means are to be understood as applying either to electrostatic or electromagnetic forces or to the devices producing them.

By a consideration of the device above described, it will be seen that the electron stream is produced by the cojoint action of the cathode and the anode and that the part of the stream which passes through the aperture in the anode will remain substantially constant in electron content when acted upon by any structures which do not lie between the cathode and'the anode. My shape-controlling elements are located be-. yond the anode and wholly discrete therefrom,

sothatwhentheyactupontheelectronstream they will only change its shape and consequently theshapeofthespotonthescreemwhile they will not materially alter the total electron contentofthestream.

1 claim: I 1. In a cathode ray tube, means'forproducing an electron stream and means for changing h cross sectional shape of said stream so as to narrow said cross-sectional shape substantially in one dimension only, said last mentioned means including at least two magnets having like poles facing one another on opposite sides of said electron stream, substantially all said stream passing uninterruptedly through said shape changing 1 2. In a cathode ray system, means for producing a luminescent spot upon a fluorescent screen functioning solely as an energy conversion device and not as an anode, including the following elements, means for producing an electron stream, means for defining the cross section of said stream-means for causing substantially all of said stream, after definition thereof,.to impinge upon said screen, so as to produce thereupon a luminescent spot, and further discrete means in said system for controlling the shape of said luminescent spot without substantially altering the total quantity of electrons impinging upon said screen, said last means including means for applying electrical forces symmetrically upon opposite sides of said electron stream as'defined,

and means for altering and adjusting the value of said electrical forces, whereby the shape of said luminescent spot is altered, while its position remains substantially constant.

3. A cathode ray tube scanning device comprising means for producing an electron stream, means for applying symmetrical fields of force to the stream to modify the stream and cause its cross section thereof to be unequal in different transverse dimensions, meansfor moving said modified stream so asto scan an image and a fluorescent screen upon which substantially all of said modified stream impinges at substantially all times during its motion, so as to. produce thereupon a symmetrical non-circular luminous spot a scanning tube having a cathode, means for heating said cathode whereby free electrons are emitted therefrom, means for directing said electron into a non-eqmdimensional beam, said last v -means including means for producing a symmetrical electric field, means for controlling the shape of said field, means for controlling the intensity of said field, and means for causing said electron beam to pass through said field, a screen for changing at least a portion of the energy of said beam into luminous energy and means for moving said beam laterally so as to scan said screen.

5. In a cathode ray tube, a screen, means for producing an electron stream, means for causing 4. A cathode ray system for producing a sym-' metrical non-circular luminescent spot, including substantiallyallsaidstreamtoimpinl onsaid screen,soastoproducethereuponaluminescsnt spot, and further discrete means forcmtrollins theshapeofsaidspotinsaid-tubaw'hilem substantiallyall saidstreamimpiming onsaid screen,saidlastmeansinclndingmeansfcrapplyingtwodiiferentandadiustableelectrioforces' transverse directions and mutually substantially perpendicular thereto, whereby said luminescent spot is changed as to shape while remaining substantially constant with respect to the total number of electrons striking thereupon.

'7. In a cathode ray tube, a cathodic source of electrons, an apertured anode for cooperating therewith and establishing a stream of electrons, a luminescent screen upon which substantially all the electron stream passing through the aperture in said anode impinges to produce thereupon .a luminescent spot, and discrete spot shape controlling means, including means located between said anode and said screen, for applying transversely to said electron stream substantially pespendicular electric forces. I

8. A cathode ray tube including means for producing an electron stream, said means including a cathode and an anode, said anode being formed to pass at least part of said electron stream therethrough and therebeyond, shape controlling means acting upon the part of said stream which through said anode to change the crosssectional shape of said passed stream while maintaining the total electron content thereof substantially constant, and a fluorescent screen whereupon said electron stream impinges, said shape controlling means including means for applying electrical forces transvcrsely to said stream and upon opposite sides thereof.

9. In a cathode ray tube, means for producing 1 an electron stream including a cathode and an anode, said anode being arranged to allow at least a portion of said stream to pass therebe-' yond, a luminescent screen located beyond said anode for intercepting the portion of said stream which has passed said anode, and meansfor at least partially controlling the shape of the portion of said stream which reaches. said screen, said latter means including means located between said anode and said screen for applying electric forces to opposite sides of said portion of said stream. I

' JOHN V. L. HOGAN.

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