US2359449A - Television system - Google Patents

Description

- Oct. 3, 1944. R. E. SHELBY TELEVISION SISTEM Filed sept. 29, 1942 2 sheets-sheet 1 Oct. 3, 1944. R, E, SHELBY 2,359,449

l TELEVISION SYSTEM Filed sept. 29, 1942 2 sheets-sheet 2/ Patented Oct. 3, 1944 TELEVISION SYSTEM Y Robert E. Shelby, Teaneck, N. J., asslgnor to Ra.- dio Corporation of America, a corporation of Delaware Application September 29, 1942, Serial No. 460,042

(Cl. TIS-7.2)

The present invention is directed to television s claims.

systems and particularly to a. form of television system wherein the eiect of Aincreased sensitivity of an electronic scanning tube may be attained.

In the prior art it has been known to use scanning tubes of the so-called Iconoscope, Image Iconoscope or the Orthi'con type, all of which have been described from time to time in literature. In such tubes there is included a mosaic electrodev which consists of al conducting signal plate and a layer of dielectric material supported thereupon. Upon the dielectric material is an arrangement of photo-electric particles or'globules which consists of a very sub,- stantial number of tiny particles of photo-electric material which are each mutually insulated` one from the other. Accordingly', when the particles are subjected to the light of an image, photo-electrons are released and the change in status of the mosaic particle potential relative to the signal plate causes an electrostatic charge to be developed across the insulator where the magnitude ofthe individual charges is proporitional to the brilliance of the optical image.

However, under many circumstances, with high detail of' scanning, such as, for instance, the 525 line scanning presently used in television systems and the relatively high repetition rate of the order of 60 picture elds or 30 frames of double interlace picture per second, it is apparent that the time within which charges may be accumulated for release to an external circuit bythe scanning action of a cathode ray beam scanning the mosaic is relatively short, and consequently the sensitivity of the scanning tubes is not as great as is often to be desired. If, however, provision is made for ways and means by which the time period between scannings may be lengthened out, then it is apparent that the effective sensitivity of any givenI elementary area of the mosaic would be increased, for it is substantially thel effect that would be achieved by decreasing the field frequency without the resultant loss inthe picture due toobof its component parts, other than to increase the number of individual scanning tubes.

Other objects of the invention are those of overcoming one or more defects known in the prior art, whereby the loss of sensitivity, due to high repetition rates of lscanning at the receiver, is not material at the transmitter.

Other objects and advantages of the invention will become apparent from a consideration of the following specication in connection with the accompanying drawings, wherein the figures thereof schematically 'represent Vways by which the invention may be practiced.

In the drawings, Fig. 1 represents one form of system for using the invention, while in Fig.. 2 a slight modification, using electronic switching, has been illustrated.

Referring now to the drawings, and ilrst to Fig. 1 thereof, there has been shown twoscanning tubes II and l2 which are each of the cathode ray type, and, for convenience of illustration only, those types of tubes known in the art as the Iconoscope, which have been devmany instances it is desirable to use the socalled Orthcon type of tube as a replacement for the Iconoscope or the Image Iconoscope. The Orthicon is shown particularly in conjunction with the system of Fig. 2, although it is to be understood that the system is to be in no way limited to any particular form of scanjectionable dicker, unless the picture reproducing device should have extremely long persistence. Accordingly, the present invention'comprises the system wherein it is an object to provide for\ increasing the effective sensitivity of scanning tubes 'of the cathode ray-type.

Other objects of the invention are to provide a `sys em wherein increased sensitivity may be obtained Without unduly increasing the compleXity\ of the system, nor yet the number ning tube. As an example of the use of the Orthicon tube, further reference to it has been made in the publications, for instance that entitled The Orthicon, and television pick-up tu by Rose and Iams, which Vappeared in the RCA Review, vol. IV, No. 2, on pages 186 to 199, for October, 1939, and also the same type of tube has -been described in an' article entitled Television pick-up tubes using low velocity electron beam scanning", published by Rose and Iams in the.Proceedings of the I. R. E., vol. 27, No. 9, for September, 1939, including pages 547, et. seq.

vFor purposes of illustration, the scanning tubes il and I2 comprise an evacuated envelope in which is included mosaic electrodes I3 and Il which, as above stated,- comprise signal plates dicated by the arrows thereadjacent.

and photo-electric surfaces formed in a number of droplets, globules or particles of photoelectric material separated from the signal plate by a dielectric, such as mica, for instance. 'I'he light of a'n optical image, not shown, isadapted to be directed upon the mosaic elements I3 andi I4 by way of suitable optical systems conventionally represented by the lenses I5 and IIi which aremovable in the directions conventionally in- Where the object to be televised is notlocated' -at substantially an infinite distance from the. camera or scanning tube, then it is, of course,

apparent that by utilizing vtwo physically separated scanningtubes II and I2 some objectionable introductions of parallax may result in the image, and for the purpose of correcting such distortion, systems of the general type shown by Burns Patents No. 1,931,890 and No. 1,968,476 may be relied upon for determining the position onthe mosaic of the tube I2 where the'impinging image is directed.

When the mosaics I3 and I4 are illuminated by the light of an image, photo-electrons are released therefrom which are collected by collecting electrodes, conventionally represented at I'I and. I8, with the result that in the form of tube illustrated the photo-electric side of the mosaic, that is, the side facing the light image acquires 1 a charge which is positive `relative to the signal plate'through suitable conductors I9 and 20 to .suitable pre-ampliilers conventionally representedat2Iand22. y

In a neck-of the scanningtubes II and I2 there is positioned an electron gun 23 and 24 which, under the application of suitable operating voltages supplied to the anode element thereof (notlspecically shown) by way of the con-` ductors 25 and 26,' will apply a voltage gradient between the anode element and the cathode (not .40

shown which is preferably `grounded at' 21. Consequently, when the yoltages are applied, electron beams 29'and 30.' are developed withinl the tube and directed as a cathode ray beam to impactthe photo-.electric surfacebf the mosaic-45 electrodes I3 and I4.

In order to cause the cathode ray beams 29 and 30 to traverse the, bi-dimensional' pattern Y of the mosaic elements; scanning yokes 3l and 32 are arranged to surround the neck portion 50 of the cathode ray -tube in order to deflect the developed 4cathode ray beams in a iii-directional pattern; For simplicity of illustration, the yokes are" not shown as consisting of separate yoke's u by the cathode ray 'beams 2s end so, 4as isw well known, releases the charges accumulated by the mosaics to represent the picture or image focused thereupon, with the result that the sisnals representative of the im'age are transmitted u via the conductorsl I9 and 20 to the pre-amplifiers 2| and 22 where the resultant signals are amplied to some-extent. 'I'he o utput energy`from the pre-amplifiers is fed by way of the conductors 33 and 34 to emerge 70 into a single conductor 35 which feeds its energy' into a combining ampliner unit 38. This ampliner is ot substantially conventional and weil known form and comprises suitable'thermionicj .for horizontal and vertical' deection, by .which 55 the scanningtubes I I and I2 to an extent desired for transmission to the suitable mixers, modulators and transmission channel .in known manner by way .of the conductor 31, for instance.

` In order to provide for the deflection of the cathode ray beams within the scanning tubesl II and I2, and at the same time to develop signals for synchronizing receiving apparatus with the transmitter scanning, tubes by providing av train of Isynchronizing signals to accompany the image signa1s,-a master oscillator 38, of known form, is provided. Generally speaking, this may consist of some suitable form of multi-vibrator or thel like, and. among the general forms of arrangements satisfactory iorcarrying out the purposes are those shown, for instance, in` the book entitled Principles of Television Engineering by Donald G. Fink, published by McGraw-Hill B ook Co., Inc., New York, 1940.

`The master oscillator serves to control hori-l zontal andvertical deilection control circuits.

.which are conventionally illustrated in block diagram at 4I, and the output energy from this generator unit is then fed by way of the conductor,

43 to energize the deflection coils 3| -and 32.- It

is to beunderstood, in this connection, that the schematic representation of the drawings illustrates .merely a single conductor and a singleunit for applying the horizontal and vertical deflectin energy to the coils, and again this illustration must be regarded as wholly and completely schematic and merely for the purpose of illustrating the general' principles of operation since the deection control unit and th'e like does not constitute a specific part of the invention.

Likewise', for blanking, the scanning beams 2l and 30 within the scanning tubes II and I2, during return motion, that is, during non-'picture producing periods.' there is provided a horizontal and vertical blaking signal generator unit '45 which is operated under the control of the master oscillator 39. The output energy from the horizontal and vertical blanking control unit 4I isthen'fed by way of the conductor 4I to supply' energy tothe control electrode (not shown) forming a part of the electron gun assembly ,(not shown) of-the scanning tubes II and I2, so that during the return line or snapback period the scanning beams may be suppressed under the iniluence of a negative cutoff potential applied to the control electrode element. Simultaneously, the master oscillato'i` 30' serves to control the production of line, fleld and 'frame synchronizing I impulses, which are herein assumed, ior purposes of illustration, to be developed within the unit 4'I, whose output is supplied by way of the conductor 48 to mix with that of the combining ampliiler 3B inthe conductor 3 1. In this way, and in accordance with 'standard practice, the synchcronizing' and control signals follow the image or eld signals -in ordinary sequence, al is standard practice in the art.-

In order to provide anode voltage for both the pre-ampliiiers .2| and 22 and the electron guns :send-zeef the scanning tubes Il man, e

source of anode voltage, conventionally represented at 49, is provided. 4This energy is thenv fed by wayoi a conductor 50 .to energize the anode voltage supply line 25 for the gun oi' the scanning tube I I and to energize the conductor 5I supplying anode voltage to the pre-amplifier Likewise, voltage from the source may be fed by way of a second conductor I2 to energize theanode voltage supply line 2O serving to amplifiers for amplifying the output signals from 7l supply theanode voltage oi the gun 24 to the scanning tube I2, and also to energize the supply line 53 for supplying anode voltage to the preamplier 22.

So as to provide the connection-of the source 49 to the conductors 50 and 52 alternately, thel contact points 54 and 55 are adapted 13o-alterAY nately bear upon the armature 56 of a relay unit l which is energized under the` control of 'an energizing coil 58. -When the relay is de-energized by lack of any currentV iiowing through' the relay Winding 58, the relay is biased by a spring 59, or-the like, so as to press the armature 56 against the lower contact 55 and energize the:

electron gun 24 of the scanning tube v|2 and the pre-amplifier. However, during time periods when the Winding 58 is supplied with energy, the

relay armature 56 4is carried "against the upper ,or link 62. The prime mover is preferably adapted to rotate at a rate coinciding withfthe frame frequency to bedeveloped which, for. a 2 to 1 interlace condition and with 60 fieldsl of transmission per' second, will amount to a rotational speed of 30 revolutions persecondor', wh're desired, the prime mover may be so gearedvas to rotate the commutator at this speed througheither step-down or step-up gearing. .In any event, to control the speed of the prime mover and to maintain it in synchronis'm with' the cathode ray-beams 29 and 30 Within the scanning tubes, the connection is made by way of they conductor 63.to the outputl from the horizontal and vertical deflection control circuit` unit 4|, so thatl the same energy that is supplied to deflect. the cathode ray beams in the transmitter scanner' tubes may also serve to controlvthe speed of rota tion of the prime mover in order that exact syn,- chronism be maintaincdwith the rate of beam deflection. e

The prime mover, in its rotation oi the commutator 6|, so provides that the source of voltage -49 Vmay energize the relay winding 58for a period corresponding to `180 of rotation of `each turn of the commutator. This is provided by reason of the provision of the" inner slip ri'ngmem` fective signal output, as supplied to thepre# amplifiers 2| and 22 is materially increased' for ipliedwith energyl from a source r 3 against its lower contact 55, and the scanning tube |2 and pre-amplifier 22 are energized. l

In this way it is apparent that alternate energization of two independent scanning tubes takes place and the time cycle of operation is such that the period permitted for charging of the mosaic elements, under the iniluence of the energizing light, is substantially increased, whereby the efany given light value. The result is that the objectionable noise is reduced substantially and the picture quality improved.

Now, making reference to the showing of Fig. 2, a modification of the system has been disclosed wherein the so-called .Orthicon .type of tubes I ||l and I I2 have been substituted for the Iconoscope tubes I| and I2 of Fig. 1. The Orthicon tubes herein illustrated have been shown merely.

in diagrammatic forni and include the mosaic structures ||3 yand ||4 positioned at the end of the tube and upon which the light of the image is directed by means of the optical systems such as those shown at I5 and I8.

As in the arrangement of Fig. l, the mosaic' structures ||3 and |'|4 of the "Orthicon tube comprise, generally speaking, the signal plate, the insulating member and the light sensitive yparticles supported uponY the insulator, as is well known. The light of the imageV projected through A the optical systems I5 and I6 is projected upon the mosaicelectrode of the Orthicon and elec-l trostatic charges are built up which are scanned, but in this case, the scanning is by a low velocity electron beam,'as explained in the publications cited.

For purposes of illustration, the focusing coils I |5'and I I6 have been shown as surrounding the complete length of the Orthicon tube and sup- The deiiecting coil for deflecting the electron beam within the tube in a verticaldirection is represented schematically by the coils ||9 and |20 surrounding the end of the Orthicon inthe region between the deflecting plate pair |2| and |22 to which the horizontal deiiection voltages ber 65 and the outer segmental'com-mutatorsece tions B1 and-68, of which it will be assumedthat the latter section connects to the slip ring member by way ofthe. connection 'wand-is Vinsulated from the section 61 by means of` the-insulator element 10. Thus,'by virtue of the connection of the brush 1| to the outer commutating ring' section'and the brush 12 to the inner slip ring mem- I ber, it will be seen that a circuit is closedalter nately through the source 49, vthe armature or winding 58, the brush 1|, the commutatorsection 68, the conductor 69,|the's1ip^ring 65,V the brush I2 and conductor I3 to ground 14,'and', u ny der such conditions, the scanning-tube II will serve to supply energy to the pre-amplifier 2|, whereas after Athe commutatorrotates to the position, as shown, whereby the brush 1| bears against the commutator segment 51, it is apparent that there is an open circuit as far as passing energy through the armature or windingSB is.

are applied. The vertical deecting coils are supplied with energy from the vertical deflecting control unit 44 which is to be understood as constituting a part ofthe vertical and horizontal d'ee'ction control unit shown in Fig. 1 as the unit.

4|. unit constituting another; part vofthe unit shown as 4|` in Fig. 1supplies its energy to the deflecting plate pairs |2|l and |22, as indicated. In order to developthe electron beam within the.."0rthicon tube for scanning ,the mosaicA y electrodes |13 and ||4, provision is made for an `electron gun element |23 and |24 whichcomprises the usual electron emitter accelerating anode and a suitable control anode. The accel'- erating 'anodes are supplied with energyfrom any suitable source of positive voltage, such as that represented schematically by the potential'source |25 which feeds its energy -by way of the conductors |21 and |28 to the. anode memberrof the electron gun. The cathode member isi'suitablyconnected to ground in well known manner, as indicated. Likewise, for convenience of illustra- Similarly, the horizontal defiection'control 'A tion, one end Aof the deilecting coils, thev focusing coils and the defiectingplate pairs is shown as connected to ground.

To control and modulate the intensity of the electron beam developed within the electron gun concerned, so that the relay armature 56 rests 75 .|23, as for instance -to provide for return line blanking,there is provided the usual control or grid electrode formed as one element of the gun structure.- The grid or control electrode of the gun |23 may be connected by Wayof a conductor |29 and |30 to an electron switch |3|, Similarly,

` the control electrode or grid f the gun element with the signal plates of the mosaic electrodes I3 and |4 of the two separate Orthicon tubes I and ||2 and serve in the same connection as did the pre-amplifiers 2| and 22 explained in connection with Fig. 1 to amplify the Output signals from the scanning tubes.' The output of the preampliers 2| and 22 is supplied by way of the output conductors 33 and 34 to the combining amplifier unit 36, all as explained in conjunction with the showing of Fig. 1.

The conductors |34 and |35 which feed energy 'from the electronic switch' will be assumed herein to supply cut-off biasing voltages on the amplifiers 2| `and 22 at predetermined points in' the operational cycle of the device. Similarly, the conductors |29 and |32, which derive energy from theA electronic switch |3|, will also be assumed to provide negative or cut-olf biasing voltages to the control or grid electrode of the electron guns |23 and |24 of the'tubes andllZ.

If now, it be assumed that a suitable source of biasing voltage |39 is-provided and arranged to feed its outputenergy into the electronic switch unit |3|, it can be understood readily that if the 'electronic switch is adapted alternately to connect the source |39 with the pre-amplier 2| and the control electrode of the gun |23 on the one hand, and the pre-amplifier 22 andthe control electrode of the gun |24 on the other hand,

' that each of these units may, when energized by the bias voltage |39 through the electronic switch,be carried toa cut-01T state.

The electronic switch herein is shownmerely in diagrammatic form although it is'to be understood that such switches are well known in the art and have been described, for instance, in the patents granted to Roys et al., No. 2,089,430,.`

granted August 10, 1937, and to Shumard, No. 2,146,862, granted February 14, 1939.

As was explained in the aforesaid patents, the electronic switch units, such as that now conventionally represented as |3|, are adapted to be triggered by some suitable source of energy which, in the arrangement of Fig. 2, is connected to the 'electronic switch by way of the, conductor |4|, and since it is desired, from what has been abo to provide a system, wherein the tubes and ||2are` alternately functioning, it is apparent that the., electronic switch unit |3| can readily be controlled from the vertical deilection control unit 44, which isdone by way of the connection established through the conductor |4| between 4the vertical 'deection control unit andthe electronic switch |3|, Accordative is to be carried to an operative state, the

bias is removed from the associated pre-ampli fler and electron gun and applied to the preamplifier and electron gun of the tube which is to be rendered in a negative state, so'that by a1- ternately switching the control from one "Orthicon" to another, it is apparent that the same effects secured by the switching unit 61, as driven from the unit 6|, are achieved in a purely electronic manner by the apparatus conventionally illustrated in Fig. 2.

Similarly, in the arrangrement of Fig. 1, horizontaland vertical blanking is applied to the Orthicon units and ||2 by way of the conductor |43, shown as supplying energy from the horizontal and vertical blanking unit 45 into 4the control electrode element of the electron gun of each of the "Orthicon tubes. In order to prevent any possibility of reaction between the electron switch |3| and the horizontal and vertical blanking unit 45, it is frequently desirable to include a buffer amplifier (not shown) in the lead |43 between the horizontal and vertical .blanking unit and the electron guns of the tubes, al1 as is cubtomarily practiced in the art.

For the purpose of supplying the line. eld and frame sync signal output to be combined with the output of the preampliers 2| and 22 as such outputs are fed by way of the conductors 33 and 34 to the combining ampliiier36, provision is made by way of the conductor 48 for mixing this line, eld and frame sync signal output in the output of the combining amplier 36 in the conductor 31. This combined signal output is then fed to the usual mixers, modulators and transmission channels in well known manner.

In order to supply the biasing cut-off voltages tothe pre-amplifier units 2| and 22, such units may frequently consist .of 'one or more tubes of the tetrode type, so that the signal output from the mixer elements of the Orthicon tubes may be fed to the #1 control grid of the amplier tube in the preamplifier unit and the biasing of the cut-01T voltage to be fed to the #2 grid of such tubes, and under conditions which the #2 L grid is maintained at a negative state, it is apparent that no output voltage will be derivedv from the pre-amplifier units.

In this way it is apparent that provision is made for controlling the control grid voltage in the -electron gun and pre-amplifiers, rather than by way of a control of the high voltage supply 'of the pre-amplier and electron gun as shown in Fig. 2.

It is understood, however, that both systems aregenerally equivalent and have been illustrated to show the wide variance in selection of circuit arrangements. It is to-be understood further that anyand all types ofelectronic switch elements may be utilized, and that for the purpose of these considerations the electronic switch and the mechanicalv switch are deemed to be the equivalent of one another, as are the various types of scanning tubes illustrated.

Furthermore, it is to be understood that the arrangements herein shown have all vbeen schematically represented and therefore the paringly, the electronic switch |3| serves, following the receipt of one signal showing the completion of one vertical traversalof the mosaic electrodes of the scanning tubes, to switch the bias voltage source cto-one pre-amplifier and its associated electron gun to render it inoperative -to produce signal output, and then immediately when the tube which has been previously rendered inopex'- 7,6"

- iiection energy source for alternately rendering the independent scanning tubes operative and in.v operative and simultaneously render the associated pre-amplifier operative and inoperative.

.3. In a television. scanning system, a pair of image scanning tubes each adapted to receive a substantially like light image, each of said image scanning tubes having a mosaic electrode upon which electrostatic charges representative of the impressed images are adapted to be accumulated upon the projection of an optical imswitching means for alternately renderingv the i independent scanning tubes and the, associated pre-amplifiers operative and inoperative.

2. In a television scanning system, a pair of image scanning tubes each adapted to receive a substantially like light image, each of said image scanning tubes having a mosaic electrode upon which electrostatic charges representative oi the impressed images are adapted to be accumulated upon the projection of an image thereon, means included in each of the scanning tubes for developing an electron beam, a source ofvbeam deection energy i'or deecting the developed electron beams to .cause said beams to scan the mosaic electrodes to produce signal energy output, a pre-amplifier connected with each of the moage thereon, means included in each of the scanning tubes for developing anelectron beam, a

source of beam deflection energy for deflecting saic electrode elements of the, tubes to receive the developed electron beams to cause said beams t0 scan the mosaic electrodes to produce signal energy output, a' pre-amplifier connected with each of the mosaic electrode elements of the tubes toreceive the output energy therefrom for amplification, a combining amplifier to receive the amplifiers, a source of bias voltage adapted when "applied to render the scanning tubes inoperative to produce a' scanning beam and `the preampliiiers inoperative to amplify signal energy output, and switching means for alternately ap plying the biasing' voltages to the individual scanning tubes and associated pre-amplifiers so that signal energy output vrepresentative of the impressed light image appears in the combining amplier alternately from each of the independent scanning tubes.

ROBERT E. SHELBY.

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