US2222957A - Television system - Google Patents

Description

' Nov. 26, 1940. R mm 2,222,957

' TELEvIsIbfi SYSTEM I Filed Jan. 14-, 1938 INVENTOR.

V v R. E. SHELBY Kg Mm ATTORNEY.

m t s, R Essig #2,0 2,122 of November 24, television pick-up or transmitter tube as well as "2 L alternating current components of the same freresides in t e'provision of means whereby the pic- 5' 5 fiire uencies upon the series ofpicture signals is Way of a cathode r a t by a cathode "a'o' I Patented Nov. 26, 1940 I a. I 2 22 957 I oirso STATES PATENT OFFICE TELEVISION SYSTEM Robert E. Shelby, Teaneck, N. J., assignor to Radio I Corporation of America, a corporation of Dela-5 ware t Application January 14, 1938, Serial No. 184,912

' 4 Claims. (c1. 178 7.2)

This invention relates to an improvement in means and the mosaic electrode or plate may be television systems. compensated for regardless ofwhether electroe More specifically the present invention relates static or electromagnetic deflection (or a comto an improvement in systems used for transmitbination of-these) is used.-

5 ting pictures by television in which a cathode ray A, Still'v further P p 0f Present e 5 transmitting tube is used'to transfer the visual tion resides in the p ev e m s whereby image that is to be televised into a series of electhe second anode of the telev s P D e trical signals. Sucha tube'is commonly known 0n0 0p m y be operated. at a positive p v as an Iconoscope" and is provided with a mosaic tential with respect to ground, n Orde that an electrode comprising a plurality of discrete phoimpedance 0r impedehee network y be 0011- 10 to-electric elements and a cathode ray generating eeted between the eco d de and ground p and deflecting means for scanning the mosaic to tential or between the second anode and a source produce a series of electrical signals from the sep- 01' potential less positive than the potential of the I arate charges on the individual photo-electric Second r the P p Of eliminating or i 5 elements of th i Th i l d iv d from counteracting the effect of electrostatic condition the television transmitting tube are then ampliwhich exists between the deflecting anode and the fled and modulated for subsequent broadcast. An mosaic electrode or P e.

7 example of the construction of the mosaic elec- A Still jp p the p vention 'trode'is clearly shown and described in the patresides i the D of means whereby e 1936, and #2,065,570 of December 29, 1936; e u put circuit for the tube may be shielded in In h e of t m employing h t sorder to reduce the efi'ect of the inherentdistribmitting tube it has not been uncommon to find nted eepeeitybetween these elements and grenndsuperimposed upon the series ofpicture signals A Still rther'p p 0f the P s nv n n quencies as the line and frame deflecting frequent s a d d f the television p -up. cies which" are impressed upon the deflecting tube may be applied: to a first video p fi r and means for the cathode'ray beam. It is believed means whereby s als f m this amp fi r may that this superimposition oi the line and frame b transferred to, additional p ifi staees by because of an electrostatic condition which excoupling- V ists between the beam deflecting unit and the I stiltfurther Pn poseof the present invention mosaic electrode or Signal plate; resides in the provision otmeans whereby the Also, in theuse of such a television transmiti l member which" surrounds the television 5 ting system, it has been found that the distribtubeend put circuit therefor may be v capacity between the fllconoscope" or connected to the cathode of the first video amplivision pick-up tube and ground,-'as well as the 1181 'P distributed capacity between the output circuit 5111i funnel Purpose Of h 'pr ent invention of the television pick-up tube and ground, has, resldee 111 the P n of means wherebythe some. instances caused-ascertain degree of a tpotential; of the second respect to tenuation and distortion of the series of picture FQ en the potentlal of the ld Of the tele signals with the result thatthe reproduced image. 'Vlslon PICK-up tube and Output it With reon the television receiver is not as clear in detail Spect teglound maybe at Substantially the same as might be if these distributed capacities were Potentlelk I i inat d, o Other purposesand advantages of the present 5' It is, therefore, one purpose of the present ininvention Will become more pp ent to those vention to provide means whereb-y'the presence Skilled in the alrtlfrom eleedihg t O OW Hg f impulses f line and fram v frequency which specificationand claims, particularly in connecare superimposed upon the series of picture sigtien Wi the drawing, wherein the s efi'gure o nals because of electrostatic conditions existing illustrates one form of the present inventions; 51 between the deflecting means the mosaic Referring mere pei'ticulerlyte e d n a electrode may be eliminated. 1 l r Y television. pick-up 'tubeor Iconoscope is shown Another purpose of the present invention 'regenerally at 10.1 'Ihetube comprises a glass ensides in'the provision of means whereby'the elecvelope which encloses amosaic electrode 12 "con- 55 trostatic field which exists between the deflecting sisting of a large number of discrete photo 'elec- '55 trio elements and a signal plate I4 to which an output circuit may be connected. The image to be televised is focused upon the mosaic I2 by means of an appropriate lens system 30.

For the purpose of scanning the mosaic in order to remove the potentials which exist on the separate photo-electric elements thereof in accordance with the light image projected thereon, a cathode ray gun structure is provided comprising a cathode I6, which may be heated by any appropriate means such as by an electrically operated heater. A grid structure I8 is also provided for controlling the intensity of the electrons which are emitted by the electron emitter I5, and a first anode 20 is provided for properly accelerating the electrons in the direction of the mosaic electrode 52. For further accelerating the electrons and for focusing the same into a narrow beam, a second anode 22 is provided which extends from a region adjacent the first anode to the interior of the television pick-up tube proper. The manner in which a cathode ray may be focused to a small elementary area is described and discussed in the patent to P. E. L. Chevallier #2,02l,252 and #2,021,253 of November 19, 1935, as well as in the patent to R. H. George #1086546 of July 13, 1937. This second anode also performs the function of attracting the secondary electrons and photo-electrons which may be emitted from the mosaic I2.

For the purpose of deflecting the cathode ray beam 2. deflecting unit 24 is provided. This unit may consist of two pairs of deflecting coils so arranged that their fields are at right angles to each other and are each at right angles to the direction of travel of the cathode ray beam. By appropriately energizing the deflecting coils the cathode ray beam may be caused to systematically scan the surface of the mosaic plate. Conductors for supplying energy to the deflecting coils are shown, and in order that the coils may be energized a current or voltage of appropriate wave form may be applied to the terminals 26 and 28. Instead of using electro-magnetic means for causing deflection of the cathode ray beam, electrostatic means may be used in which case two pairs of plates are ordinarily provided, the pairs being arranged in planes at right angles to each other and parallel to, but spaced from the path of the cathode ray beam in a manner which is well known in the art. By applying appropriate potentials to the deflecting plates an electrostatic field may be created between the pairs of plates with the result that the cathode ray beam is deflected horizontally and vertically in order to properly scan the mosaic electrode.

A further and more specific discussion of the construction and operation of the cathode ray television transmitting tube is believed to be unnecessary since its operation is well known to those skilled in the art and since a clear and concise description of the operation of the tube may be had by referring, for example, to a patent to V. K. Zworykin #2,021,907 of November 26, 1935.

In order that appropriate potentials may be applied to the elements of the cathod ray gun a potentiometer 23 is provided, to the ends of which is to be connected a source of current. The first and second anodes are, of course, positive with respect to the cathode whereas the grid of the gun structure is slightly negative with respect thereto. Some point along the potentiometer, preferably between the first and second anode terminals, is connected to ground as shown in the drawing. An impedance member 34 is provided, one end of which is connected to the second anode by conductor 32 and the other end of which is connected to a point along the potentiometer by conductor 33. Both the impedance connection and the ground connection to the potentiometer are adjustable and may occupy identical positions on the potentiometer or may occupy separate and different positions. In order to provide a convenient path to ground for alternating current which may appearin the impedance circuit, a condenser 35 is provided and is connected between the conductor 33 and ground. This condenser must, of course, be of sufiicient size to render little or substantially no impedance to the alternating currents which may be present in the impedance 34.

The impedance member 34 preferably consists of a parallel arrangement of a resistance and a variable condenser. It is to be understood, however, that other impedance networks may be used and that the value of the impedance network used may be so chosen as to properly compensate for signals which appear in the output circuit of the television pick-up tube as a result of the electrostatic condition which exists between the deflecting unit 24 and the mosaic electrode I2.

Connected to the signal plate I4 of the mosaic electrode I2 is an output circuit 36 which conducts the picture signals to the control electrode of the first video amplifier tube 4|]. The anode of this tube is connected to a terminal 48 to which may be applied a source of positive potential. The cathode and screen grid of the video amplifier tube 40 are connected to ground by way of a cathode resistance 46 and the control electrode of the amplifier tube is biased to appropriate operating potential by means of the source of current 42. In the connection between the source of current 2 and the control electrode is a grid resistor 44.

When the signals from the signal plate I4 of the television pick-up tube are applied to the control electrode of the video amplifier tube 40 a variation in the amount of current which is transmitted through the tube results. This variation in current causes a variation in potential drop to appear across the cathode resistance 46 and this potential is used to supply power to the control electrodes of the succeeding stages of video amplification. The following stages of video amplification are therefore connected between the terminal 50 and ground.

A certain distributed capacity is inherently present between the television pick-up tube I and ground, as well as between the output circuit 35 and ground. In order to compensate for this distributed capacity which electrically appears as a condenser between the control electrode of the video amplifier 40 and ground, a shield member 38 is provided and this shield member is connected by way of a conductor 39 to the cathode of the video amplifier tube 40.

In order for the secondary electrons and the photo-electrons which originate at the mosaic electrode to be attracted to the second anode to produce proper functioning of the television pickup tube, the second anode is preferably operated at a potential which is slightly positive with respect to ground. The amount of the potential is preferably equal to the positive potential of the mosaic signal plate I4 with respect to ground; i. e., the potential of the grid bias source of potential 42.

As stated above, there appears a certain electrostatic condition between the deflecting unit 24 and the -mosaic electrode I2 which may cause alternating current componentsof line and frame frequency to be superimposed upon the picture signal. There also exists a certain electrostatic condition between the deflecting unit 24 and the second anode 22 and as a result alternating curin, the net effect is to cause a compensation for the corresponding alternating current componentswhich 'mayappear in the output circuit of the television pick-up tube. Any alternating currents of line and frame frequency which may appear in the output circuit of the television tube as a result of the electrostatic condition existing between the deflecting unit 24 and the mosaic electrode l2 are thereby eliminated insofar as their effect is concerned.

Since it is known that triodes as a class are in general better than screen grid tubes for low level ly high effective input capacity it is not desirable to use a triode as the first input tube for video signal currents from a television pick-up tube.

Since it is known that the effective input capacity of a cathode coupled amplifier is lower than that of the same tube connected with output load in the anode circuit, a cathode coupled pentode is used to couple the television pick-up tube to the following triode amplifying stages. If such an arrangement is to be entirely satisfactory and used to its best advantage, the cathode coupled stage must not contribute appreciably to the total noise if a satisfactory noise level is to be maintained. When the first video amplifier tube is used in the manner shown in the drawing, the

cathode coupled stage may be considered as an impedance transformer for coupling the Iconoscope to the first amplifier stage which follows. In view of the fact that the inherent distributed capacity of the television pick-up tube'and the picture signal output circuit to ground has been appreciably reduced, it is possible to increase the value of the resistance 44 and thereby increase the amplification of the tube 40 as well as improve the signal to noise ratio. r

The inclusion of the impedance 34 and its con'-.

nection as shown in thedrawing provides means whereby any alternating current signals ,of the frequency of the line impulses or the frame impulses which appear in the output circuit of the I television pick-up tube (and which are undesirresult of the electrostatic condition, with respect to the phase relationship of the undesirable signals which appear in the grid circuit of the video amplifier tube 40. v

From the above it may therefore be seen that an improved television system has been developed wherein the signal to noise ratio has been increased by the substantial elimination of the distributed capacity between the cathode ray tube and ground as well as between the output circuit of the television pick-up tube and ground, and the further provision of means whereby undesirable superimposed alternating current impulses which may appear upon the picture series signal as a result'of the electrostatic condition existing between the deflecting unit and the mosaic electrode have been eliminated by means of cancellation. v

It is to be understood that although various modifications and. amendments may be made in the present invention, it is desired thatanyarid all such modifications be considered within the purview of the present invention, except as limited by the hereinafter appended claims.

1. A television system including a pick-uptube comprising an envelope, a photo-sensitive" mosaic in said envelope, a signal plate capacitively associated with'said mosaic, an electron gun structure in said tube including an electron emitter and an accelerating anode for developingand projecting a beam of electrons against said'mosaic, means including a deflecting yoke forfcausing the beam of electrons to systematically scan said mosaic, at least a portion of said accelerating anode being positioned between the deflecting yoke and. said signal plate, the relationship of the deflecting yoke, the accelerating anode and the signal plate being such that an inherent mutual capacity coupling exists therebetween, means connected to said electron emitter and to said anode to maintain the latter at a potential positive with respect to said emitter and to ground, an impedance network including a parallel resistance and condenser, and means to connect said impedance network between said anode and ground to substantially reverse the phase of the alternating current component of the current appearing in the accelerating anode circuit whereby the alternating current potential variations of the anode by reason of the capacity relationship between the deflecting yoke and the anode will be substantially out of phase with respect tothe potential variations of the deflecting yoke to thereby compensate for the capacity effect between the deflecting yoke and the signal plate. 2. A television system including a pick-up tube comprising an'envelope, a photo-sensitive mosaic in said envelope, a signal plate associated with said mosaic, an output circuit connected tosaid signal plate, an electro gun structure in said tube including an electron emitter and an accelerating anode for developing and projecting a-beam of electrons against said mosaicflneans including a deflecting yoke for causing'the beam of electrons to systematically scan said mosaic to produce a series of signals in said output circuit, the relationship of the deflecting yokefthe accelerating anode and the signal plate being such that an inherent mutual capacity coupling exists therebetween, an impedance network including a resistance and a condenser connected in parallel,

means for connectingsaid impedance network between said anode to groundto cause an alteration of the phase relationship of the alternating current voltage variations of the anode due to the proximity of the deflecting yoke and the capacity relationship between the deflecting yoke and the anode, and means to maintain said anode at a positive potential with respect to said electron emitter and with respect to ground whereby the presence of spurious signals of scanning frequency due to the capacity effect between the deflecting yoke and the signal plate are substantially eliminated from the output circuit.

. 3. A television system including a pick-up tube V comprising an envelope, a photo-sensitive'mosaic in said envelope, a signal plate cooperatively associated with said mosaic, an electron gun structure in said tube including an electron emitter and an accelerating anode for developing and projecting a beam of electrons against said mosaic, means including a deflecting yoke for causing the beam of electrons to systematically scan said mosaic, means for maintaining said anode at a potential positive with respect to ground and for maintaining the electron emitter at a potential negative with respect to ground, the position of the deflecting yoke, the accelerating anode and the signal plate being such that a slight amount of capacity coupling exists therebetween, and a phase reversing impedance network, including a resistance and a condenser connected betweensaid anode and ground for altering the phase relationship of the low amplitude alternating current voltage variations of the anode as induced therein from the deflecting yoke due to the capacity relationship between the deflecting yoke and the anode to prevent the presence of spurious signals of line and frame frequency from appearing at the signal plate because of the presence of the deflecting yoke.

4. A television system including a pick-up tube comprising an envelope, a photo-sensitive mosaic in said envelope, a signal plate associated with said mosaic, an electron gun structure in said tube including an electron emitter and an accelerating anode for developing and projecting a beam of electrons against said mosaic, means including a deflecting unit for causing the beam of electrons to sytematically scan said mosaic, the position of the deflecting anode, the accelerating unit and the signal plate being such that a slight inherent mutual capacity coupling exists therebetween, means including an impedance network comprising a resistance and a condenser for connecting said anode to ground in order to substantially reverse the phase of the alternating current compoent of the current appearing in the accelerating anode circuit and to thereby substantially reverse the phase of the low amplitude alternating current voltage variations of the anode whereby the capacity effect between the deflecting unit and the signal plate may be substantially nullified, and means to maintain said anode at a positive potential with respect to said electron emitter and with respect to ground.

ROBERT E. SHELBY.

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