US2220688A - Arrangement for receiving television images - Google Patents

Description

Nov. 5, 1940. F'. scHROTER ETAL ARRANGEMENT FOR RECEIVING TELEVISION IMAGES Filed May 27, 1957 s Sheets-sheaf. 1

' .l 'yw3a ATTORNEY Nov. 5 1940.

F. ISCHROTER ETAL ARRANGEMENT FOR RECEIVING TELEVISION IMAGES Filed May 27, 1937 5 Sheets-Sheet 2 Wi /ma INVEIVWIFS,

ATTORN EY Nov. 5, 1940. F. scHROTER HAL 2 5 ARRANGEMENT FOR RECEIVING TELEVISION IMAGES Filed. May 27, 1937 I S Sheets-Sheet 3 ATTORNEY in-case of a movie picture even when "its Patented Nov. 1940 UNITED, s r'A rEs 1 tion of Germany Application May 27, 1937, Serial No. 145,020

InGermany May 27,1936

in Claims. (01. Pia-7.5)

It is customary to employ Braun tubes in general for the reception of'television images transmitted'by'means of a'single transmission channel, for instance by meansof a modulated carrier 5 wave. Hereby, each image element is presented at the receiver side only during an extremely brief period when leaving out of consideration the after glow phenomena of the fluorescent screen. In view of such condition in the first place, the cathode ray in the'pBraun tube must be a very intensive ray, and furthermore, it is necessary to utilize a sufiiciently large number of image alternations, and at the line skip method,

a sufliciently large number'of vertical alternations in order to reproduce the receiving image with sufficient freedom of flickering. The luminous current' produced on the fluorescent mass unless extremely high voltages and amperages are I used, is so low that it is necessary in general to view the television image at least in reduced'daylight. The image on the fluorescent screen when.

projected on a surface having the size of a movie screen, i. e. a projection screen several m in size cannot be obtained with thesame brightness as using ourrents and voltages ofhigh value. p

a In accordance with theinvention, instead of reproducing the individual image points only at brief periods in the sequence in which they are I 30.. received, there will be assigned to each image element a special cathode ray system, having fluorescent screen and control grid, and during the entire time between two successive transmissions of brightness values assigned to the same image element,the controlgrid shall be maintained at constant potentiahso' that a constant current impinges on the fluorescent screen. In-

stead of assigning in this manner a. cathode ray 1 system having fluorescent" screen and control grid 40. to each image' element, cathode ray systems may also be provided only for the image elements of the one image coordinate, while the other image coordinate is established by means of a suitable photo-optical arrangement for instance by means of an oscillating mirror or mirror wheel. In both casesyi.v e. with a number of cathode ray sys-- items corresponding to the number of image elements of theentire image,or only of an image coordinate, it is possible to view the fluorescent screen directly, or also theprojectlon of the said screen. r The required potentials at th-control-grids ofi.

x '.the cathode ray systems can be produced in the I sense of the invention principally by means of any switch connecting the individual control grids in ary electron emission current and secondary emission surface of Fig. 3a.

succession with the amplifier of the'receiver. In

' the examples of construction described in the following a cathode ray switch shall be utilized to this end, whose contacts are formed by the control grids of the cathode ray systems, and by con- 5 trolling the current in the switching ray, the control grid potentialsshall be determined by the balance between switch ray current'and secondof' the switch contacts '(control grids). 10

Fig. 1 is a schematic diagram showing'the method of operation of a cathode ray secondary emitter. I

Fig. 2 shows the characteristic curves of the 1 1 device shown in Fig. 1.

Fig. 3a shows an image reproducer in which the emission from a thermionic surface is con trolled by a secondary emission surface.

Fig. 3b is a partial front View of the thermionic I Figs. 4 to 9 are views of other modifications of the invention.

.Before' describing in detail the arrangement according to the invention and its functioning,

there will again be reviewed the known facts re- 6 I garding the secondary electron emission and the balance between primary current'and secondary electron emission current upon which the invention is based.

In Figurel, item It designates a glow cathode, so

II is a control cylinder, item I2 is an anode, and I3 is an absorption plate to which is imparted ahigh secondary emission capacity forinstance by means of a cesium layer. Between the cathode 10 and the anode l2 a plate voltage source I 4 is 85 inserted and between the plate l3 and the anode l2, a direct voltage sourceU is placed. At the control cylinder Ii 'there'is at first assumed a certain constant potential determining the ray current leaving the cathode Ill and which is assumed to pass in its entirety the anode Ill. The current which can'be measured in the line-between'the plate l3 and the voltage source U, varies-in this arrangement in accordance with the value of the voltage U such as indicated in Figure 2. In Figure 2, the positive. abscissa axis corresponds with the polarity of thevolt'age source U as indicated in Figure 1. The ordinate axis indicates the current that can-be measured with the measuring instrument M. If the voltage U has the sign'reversed asfregards that in- .dicated in; Figure 1, 'a current flows onlyin the circuit designated"by"A;"'-and the measuring in----- strument M indicates the-same deviation in as a, measuring instrument mi in the lead-in to the and if it has the sign indicated in Figure 1, in

addition to the current in the circuit A, an electron. current fiows through the circuit B since the secondary electrons produced on the plate I3 pass to the anode I2 acting as secondary emission anode. In the measuring instrument mu the full value of this secondary emission current isi can be measured, while in the instrument M only the difference in1=(is1-ir1) can be measured. If the voltage U decreases without at first changing the sign the secondary emission current isi will be decreased, finally assuming the same value as the primary current in at the value U=a.-

In this case the instrument M points to zero. The entire curve I is then determined by a constant primary current im, and constant secondary emission factor (measure of the number of secondary electrons produced by a primary electron) which is greater than 1. At another, i. e. larger primary current the curve 2 is obtained having the values irz, isz, inz. This curve 2 ins tersects the abscissa at a higher voltage U, namely U=b. The secondary emission factor for the curve 2 is the same as for the curve I.

For a better understanding of the following, it should be kept in mind that the voltage U at which the curves I and 2 pass through the abscissa, is the higher the larger the primary current ip. These voltage values are ordinarily termed balance potential of secondary emission, since the number of secondary electrons leaving the plate I3 is at these potentials equal to the number of primary electrons impinging on the plate. The potential of the plate I3 thus is the more negative relative to the secondary emission anode I2, the larger the primary current.

In the mode of construction represented in Figure 3a, a glass vessel I5 contains a cathode ray switch consisting of the cathode IS, a control cylinder IT, a first anode l8, a second anode l9 and switch contacts to 22. Furthermore, there is accommodated within the glass vessel I5, cathode ray systems having fluorescent screen comprising the cathodes 23, 24 and a common anode 25 shaped as agrid embedded in the fluorescent substance 26. The contacts 20 to 22 of the cathode ray switch form at the same time the control grids for the individual cathode ray systems. The cathodes 23, 24 are connected to each other either in series (as shown in Figure 3a) or in parallel, and are passed by a heating current. The number of cathodes and control grids in the tube I5 may correspond to the number of image elements. As viewed from the side of the fluorescent screen the cathodes and control grids are situated for instance in the manner shown in Figure 317. Between the first anode I8 and the cathodeIIi a plate voltage source 21 is inserted, and a further plate voltage source 28 is placed between the second anode I9 and the first anode I8. Furthermore, a common plate voltage source 29 is inserted between the cathodes 23, 24 and the anode 25 common to all cathode ray systems. Regarding the .value and polarity of the voltage source between the second anode I9 and the cathodes 23, 24 it is referred to a later chapter.

The arrangement according to Figure 3a operates such that the voltage between the control cylinder I1 and cathode I6 of the cathode ray switch will be the more reduced the greater the brightness of the image point being transmitted at the moment. If in the usual manner dark image points are transmitted by a small amplitude of the carrier wave, and bright points by a large amplitude, it is therefore necessary to provide a corresponding phase reversal before the image signals are passed to the control cylinder I'I.v The cathoderay, in the course of a deviation across the switch contacts or control grids 20 to 22 corresponding to an image line, thus varies its intensity inversely proportional to the brightness distribution along this image line. As explained on hand of the Figure 2, the individual contact elements and control grids therefore, assume potentials (namely the balance potentials) which are the more negative relative to the second anode IS' acting as secondary emission anode,

the higher the amerage in the switching ray.

Thus for instance, as long as the switch ray rests upon the contact element 20 and a dark image point is thereby transmitted into distance, the amperage of the switching ray is high, and the contact 20 therefore receives a comparatively high negative potential (for instance the value c in Figure 2) relative to the secondary emission anode I9. In respect to the cathode 23 having a low negative potential (the value c for instance in Fig. 2) determined by the voltage source 30 relative to the secondary emission anode I9, the control grid therefore, has a relatively high negative potential, so that from the cathode 23 no current or only a very small current passes to the respective place of the fluorescent screen 26. The fluorescent mass therefore, will not be en'- ergized at all or but slightly and consequently the dark image point .will be correctly reproduced. If during the period in which the switch ray rests upon the contact element 2I, a bright image point is to be transmitted, the amperage in the switch ray will be comparatively small, in accordance with the above, and the switch contact 2| thus receives only a low negative potential (for instance the value a in Figure 2) relative to the secondary emission anode I9. The control grid 2I thus has only a low negative potential relative to the appertaining cathode 24, and therefore a comparatively large current will pass from this cathode to the appertaining surface of the fluorescent screen in accordance with the corresponding brightness of the appertaining image point. Thus on the fluorescent screen 26 the television image will be reconstructed point by point, with the brightness corresponding with the carrier amplitudes transmitted into distance. Whether the voltage source 30 is to be chosen with the polarity indicated in Figure 3a (corresponding with the value c in Figure 2), or whether it be chosen with another value, and eventually with the reversed polarity depends on the construction of the individual cathode ray systems and in particular on the through grip of the anodes 29.

An arrangement according to Figure 3a may also be constructed with a numberof cathode ray systems corresponding only to a single image line. The direct viewing or the projection of the fluorescent screen then takes place across moved mirrors or the like.

The mode of construction represented in Figure 5 differs from that according to Figure 3a substantially in that the individual cathodes are reproduced on the fluorescent screen 26 by means of an electron-optical reproducing device for instance a concentration coil 3|.

As regards the setting of the control grid po-- intensity is controlled and which is deviated in 7 aaa'dees the coordinate, the arrangement according to Figure 5 operates in -the same manner-as that accordingtoFigurev 3a. The arrangement in the surface of the individual cathodes and con- ,trol grids isshownin enlarged scale-in Figure-4. ' l'he cathodes 23, 24 can be formed by filaments arranged in the manner .of-a' cross shaped grid.

whereby the contactfelements and control grids to 22 .protrudeithrough the openings ofthe grid. v

vIn the mode of construction represented in Figure 6 the electron current'semanating from theindividual cathodeslikewise arrangedin the manner of a mesh, arepassed to the fluorescent screen by means of an electron-optical device in the same manner as in Figure 5. As compared withthe Figure; this arrangement :difiers only insofar as the" switching ray impinges i on the control grids from the same side towards which the electrons finally impinging on the fluorescent screen, leave the cathode.- In the arrangements according 7 to 9 in which likewise an electron-optical reproduction takes place on the fluorescent screen, the individual, glow cathodes or parts of a common glow'cathode are substituted by so-called virtual cathodes. This will at first be explained onhand of Figure 7.. Inthis figure, the arrangement situated below'the dot and dash lin .A-B is the same asin Figure 6. A grid 32 ormed of metal has an insulating cover-gfor instance of enamel whose bottomsurface contains a large numberflo'ff individual metal particles capable, of

secondary emission for instance composed of cesium. Above the line A'--B an arrangement is provided for producing. a difl'used cathode ray beam impinging the entire surface of the grid 32.

This arrangement consists of a cathode 33, a

directly as cathode.

first anode'3l, and a second anode 35 both of cylindrical shape. The voltage between the anode 35relative to the'cathode' 33 is supplied by the direct voltage source and is higher than the voltage of anode 34 originating with the direct voltage source 31. The grid 32 is connected to the cathode 33. The electrons penetrating the,

anode 35 at a high velocity are decelerated shortly before reaching the mesh-shaped electrode 32 forming at this place a space charge cloud acting of the metal particles 20'to 22 acting as control grid, which potential is adjusted to by the switchlng ray, determines the electron quantity passing through each individual gridopening.

The arrangement according to Figure 7 may 7 also be such that above the grid 32 a further grid electrode is provided having the same potential as the anode 35 in which case the retarding field for the production of the spacecharge cloud acts 7 between the mesh-shaped electrode 32 and the grid situated above said electrode.

Moreover, in the arrangement according to Fig. 7 the switch ray tube and the tube for producing the diffused cathode ray beam may be interchanged also if only a single grid electrode 32 is i provided, and likewise where a second grid electrode placed parallel to the first one, is provided. The arrangement for the last mentioned case is 1 shown in Fig. 8 in which the second grid electrode is designated by 38. The retarding of the difluse cathode ray beam originating with the cathode 32 takes place between the grid electrodes 32 and 38. The control grid elements is produced The anode 25 has a through grip through the meshes of the grid 32 thus being capable of withdrawing electrons from this space charge cloud, whereby the potential f sources comprises a electrode 32.

InFlgJQ a mode of construction is 'shown'inwhich'the arrangementfor producing the dif- 1 fuse cathode-raybeam, the switch ray tube and the, arrangement for the electron-optical repro duction' on the fluorescent screen are all situated; the control grid elements.

on the same side of arranged in a surface.- A'metalplate 39 is prof vided with an i insulating covering and covered with metal particles 20 grid elements. The space charge cloud obtained by the retarding ofthe difluse cathode ray beam each'point of the 'fiuorescent screen is influenced by the potentials assumedby the control-grid elements owing to the changing amperage. of the moving switch ray. 1

Also in the arrangements'according toFigures 4 to 9, provision can bemade that only the image I directiy in front .of'the control'grld elements, and the electron quantity impinging on 20 to 2: are situated in the meshes of the grid to ,22' actingas control of a single line appears on the fluorescent screen by photo-opticalimeans.

-What we claim is: Y 1. A tt'elevision reproducing device comprising while the secondimage coordinate isproduce d" means for developing an electron beam forma tion, meansfor deflecting said beam in at least I one co-ordinate, means'for modulating said beam in accordance with received television signals, means adapted to give off lightunder the impact of electrons thereon, a plurality of electron emis-'- sionw sourceseachfor reproducing one element,

of the image to be reproduced in at least one co fl grid elements" ordinate, a plurality ofgindividual interposed between said electron'e'mitting sources I and said means adapted to respondto electron impact, said gridelements having-a high secondary emission characteristic, said grid elements being adapted to be impinged upon by the deflected electron beam formation whereby thepotential thereof is governed by the equilibrium" .betwee'n the current of the deflected cathode ray,

beam and the secondary emission current ofithe 2. Apparatus inaccordance with claim '51,

individual grid elements.

wherein each individualgrid element is'. interposed between the plurality of electron emission means and the meansvresponsiveto electron im f pact, and is also positioned between the deflected cathode ray beam and the plurality of electron emission sources.

3. Apparatus in accordance with claim 1, wherein the plurality of electron emission sources comprises a plurality of virtual cathodes grid elements to the means responsive to electron impact are focussed thereon by eiectro-optical means.

4. Apparatus in accordance with claim 1,

66.. wherein electrons passing through the individual i wherein the plurality of electron emission response to signals representative of said images,

with claim 1,

comprising means for developing an electron beam formation, means for deflecting said beam in at least one coordinate of movement, means for modulating said beam in accordance with signals representative of the image to be reproduced, means adapted to give ofl light under the impact of electrons thereon, means for producing individual groups of electrons each for reproducing one element of the image to be reproduced, and a plurality of individual grid elements positioned adjacent said individual sources of electrons and adapted to have the potential thereof ontrolled in accordance with the value of the odulated cathode ray beam as it impinges thereon during its traversal. a

7. Apparatus in accordance with claim 6 wherein there is provided in addition means for focussing each of the produced individual groups of electrons for producing one element of the image to be produced onto the means adapted to give of! light under the impact of electrons thereon.

8. The method of reproducing an optical image which comprises providing a plurality of individual foci .of electron emission each adapted to reproduce one incremental element of the image to be reproduced and continuously producing electrons, and controlling the emission from each of said foci sequentially in accordance with the equilibrium potential produced during the control of each of said individual foci by the action of a modulated electron emission.

9. A television reproducing device comprising means for developing a cathode ray beam, means for modulating said beam in accordance with the optical values of the image to be produced, means adapted to produce light under the action of electron bombardment thereon, a plurality of cathode sources each for producing one of the image elements to be reproduced along at least one coordinate of said image, grid velements positioned adjacent said individual cathode sources and adapted to control the emission from said individual sourcesimpinging on said light reproducingmember, and means for directing the modulated-cathode ray beam sequentially onto said grid elements whereby the potential of said grid elements is controlled by the action-ct said cathode ray beam thereon.

10 An apparatus for reproducing signals representative of optical images comprising means for developing a cathode ray beam, means for modulating said beam in accordance with the values of the image to be reproduced, means for producing a plurality of individual virtual cathodes each adapted to produce an electronemission for reproducing one element 0! the optical image to be reproduced along at least one coordinate thereof, means responsive to electron bombardment for reproducing light, said latter means beingadapted to be impinged upon by the electrons from said virtual cathodes, a pmrality of individual grid elements' positioned adjacent said virtual cathodes and adapted to control the impingement of electrons from said virtual cathode onto said reproducing means, and means for directing the modulated cathode ray beam sequentially onto said grid elements.

FRITZ scrmb'rnn.

Images