Патент USA US2131892код для вставки
Oct. 4, 1938. 2,131,892 H. A. I‘AMS ‘ELECTRON DISCHARGE DEVICE Filed Oct. 1, 1936 Hall R m, INVENTOR HARLEY A. IAMS r , /, w,' ATTORNEY 2,131,892 Patented Oct. 4, 1938 um'rsp STATES PATENT OFFICE 2,131,892 ELECTRON DISCHARGE DEVICE Harley A. Iams, Berkeley Heights, N. J.,.assignor, by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application October 1, 1936, Serial No. 103,487 9 Claims. The present invention relates to television transmitting apparatus and particularly to ap (Cl. 178-12) tential slightly positive with respect to the second anode. Thus if the potential of the second anode is 1000 volts positive with respect to the cath ode, the scanned element may be at 1001 volts positive as the scanning beam passes from it to 6 adjacent elements, and it begins to collect second ary electrons emitted from the adjacent elements mosaic electrode consisting in general of an in sulating sheet with a great number of discrete then being scanned, so that its potential gradually falls. As soon as its potential falls below that light-sensitive elements on the front surface form 10 ing a mosaic screen on which the optical image is of the second anode (1000 volts) it emits photo- 10 formed and a conductive coating or signal plate electrons under the in?uence of light from the on the other surface, the front or illuminated sur-' object falling on the photo-sensitive surface of face being scanned by a cathode ray beam from an the elements, and these photo-electrons are col lected by the second anode. This emission of electron gun having at least two anodes to pro photo-electrons tends to make the potential of 15 ,15 duce currents which ?ow through an output re sistor connected between the signal plate of the the element rise, but the higher its potential, the mosaic electrode and ground to generate the more secondary electrons emitted from other parts of the screen does it tend to collect, to drive its picture signals. ' Now it has been found that parasitic signals potential more negative again. The ?nal po tential of the element before again being scanned .20 are developed superimposed upon the picture sig nals taken from the signal plate. These parasitic is that potential it acquired by the previous signals may take the form of base line wander at scansion, decreased by the secondary electrons the line scanning or picture scanning frequency acquired by it ‘from the secondary electrons or at both, or they may also develop an unnatural emitted from other parts of the screen and in .25 shading of the re-created picture. Thus if the creased by the photo-electrons lost by‘ the ele- 25 true picture signals are regarded as consisting of ment under the in?uence of the incident light. variations; corresponding to the brightness of the This ?nal potential may be of the order of 998 volts for an element illuminated with average mosaic elements scanned; in an upward direc tion from a base line corresponding to picture brightness. When the illuminated element is scanned its potential is instantly restored to 30 _,30 black, the parasitic signals may have the effect again 1001 volts,and the resulting discharge of the of causing the base line to assume a saw-tooth form. The base line may fall relatively suddenly condenser constituted by the element and the to a minimum value at the commencement of the signal plate causes in the circuit associated with scanning of a line of the image and may rise the signal plate an impulse which is ampli?ed and ’ 36 “35 steadily as the scanning of the line proceeds. In transmitted. Assume now that the cathode ray beam scans addition to this parasitic signal occurring at line frequency, there may also be found a parasitic the screen in a series of approximately parallel signal of similar general form occurring at the straight lines from left to right across the screen, and starts a complete scan of the screen in the top frame or picture frequency. left-hand corner. Now when, in scanning any 40 40 The reason for this is believed to be as follows: line, the beam‘ is on the left-hand end of a line In the operation of the cathode ray trans most of the secondary electrons emitted will ‘be mitting tube, the average potential of the ele ments of the mosaic screen is always in the collected by the second anode, but when the beam the right-hand part of the line, there will neighborhood of the potential of the second anode is on a number of positively charged elements to 45 545 'of the ‘electron gun. These photo-electrically be sensitive elements emit secondary electrons freely the left of the scanning beam, which collect when struck by the scanning beam, and. the secondary electrons emitted from the elements on paratus embodying cathode ray tubes. ' In one form of cathode ray transmitting tube 5 an optical image of an object of which a picture is to be transmitted is formed upon a target or second anode collects both the secondary elec trons and the photo-electrons emitted by the 59 ‘ mosaic screen. when an element is scanned by the cathode ray beam, the secondary electrons emitted .by the scanned element ?ow partly to the second anode of the gun and partly to neighboring elements on the mosaic'screen. and 5Q the scanned element becomes charged to a po the part of the line then being scanned. Thus there will be set up a field at the surface of the screen which is more positive at the left-hand‘ 50 side‘ of the screen than at other points on its sur face, and tend to attract electrons to the left hand side of the screen. The effect of this field is to cause the base line wander of the picture signals at line frequency. 55 2 2,181,89Q A similar effect will be produced as the beam’ moves down the screen from line to line, as the upper part of the screen will tend to attract elec trons emitted from the lower part‘and thus give a base line wander of the picture signals at frame frequency. . A further source of parasitic signals in a cath ode raytransmitting tube such as that considered above is in unequal secondary emission from all parts of the mosaic screen. This unequalemis sion results from the combination of the ?nite size of the mosaic particles, the non-uniform distribu tion of charges over the surface of the mosaic screen, variable charges on the glass wall of the 15 tube, and the non-uniform electrostatic ?eld pro duced by the second anode. It is the object of the present invention to pro vide means for removing or reducing these and other parasitic signals. According to the present invention a. cathode ray tube having a target or mosaic electrode com prising a mosaic screen of mutually-insulated ele ments capacitively associated with a common sig nal plate, an electron gun for directing a cathode 25 ray onto the screen, and de?ecting means for causing the ray to scan the screen, is provided with a compensating electrode system disposed between said gun and said screen and out of the path of the scanning beam and biased to produce .30 transverse to the scanned surface of said screen a potential gradient which serves to minimize para, ‘sltic signals generated in said signal electrode. The biasing potentials necessaryfor this purpose are usually small compared with the potential .35 difference between the cathode and secondanode of the electron gun.. The invention will now be described with refer ence to the accompanying diagrammatic drawing which shows in perspective a View of a transmit 40 ting tube of the kind previously referred to, incor porating an embodiment of the, present invention. Referring to the ?gure, the tube comprises a highly evacuated envelope or bulb 5 having a tubular arm or neck section enclosing a conven tional type electron gun and a bulbous section enclosing a parallelogrammic and usually rectan~ gular mosaic electrode of a well-known type. The mosaic electrode is so mounted in the envelope that an optical image may be projected on its. front surface by a lens system i 9, and the illumi nated surface scanned by the scanning beam from the electron gun in the neck of the envelope. The electron gun, of the conventional type, is shown as comprising a cathode 3, a control elec 585 trode 5 connected to the usual biasing battery, and ?rst anode ‘l associated with a second or beam focusing anode ‘i3, preferably a conducting coat ing on the inner surface of the envelope 5 near the neck, which acts as a collector electrode for 60 electrons from the mosaic electrode. These anodes are maintained positive with respect to the cathode 3 by a battery 9 and the electron stream leaving the ?rst anode ‘l is accelerated and vconcentrated into an electron scanning beam 65 focused on the mosaic screen by the second anode, which also collects any electrons emitted by the mosaic screen. Beam de?ecting means, such as the usual de?ection coils 2| and de?ection plates 22 sweep the beam in a horizontal and a vertical , 70 plane to scan the mosaic electrode. The mosaic electrode may be of the well-known type and may be constructed in various ways. In consisting of a multitude of oxidized silver glob ules 26 which are in effect discrete and are there fore insulated from one another, each made photo-electrically sensitive by being coated with caesium in accordance with the practice in make ing photocells. Themetal coating on the back of the mosaic electrode is connected to one end of an output impedance 30 and to the input circuit of a translating device such as the picture signal ampli?er 32, the opposite end of the impedance 10 being connected to the positive terminal of the > battery i5, usually through a ground. In accordance with my invention I provide for the mosaic screen a compensating electrode which is adjacent the mosaic electrode but out of the 15 path of the optical image focused on the mosaic screen and also out of the path of the cathode ray scanning beam, and which at suitable bias poten tial will suppress or eliminate parasitic signals which otherwise occur. Preferably the compen 20' sating electrode is close to the edge of the mosaic ' electrode and is insulated from it. I have found that a compensating electrode at one side and another at one end of the rectangular mosaic electrode will suppress'much of the parasitic sig nals at both line frequency and at picture fre ‘quency, but for more complete suppression I pre fer to use a compensating electrode system of four electrodes, 23, 2d, 25, and 26, two of which are mounted along the two parallel sides of the screen, and the other two along the top and bot~ - tom edges. Incompensatingsfor parasitic signals resulting from unequal secondary emission from the mosaic particles, I prefer to sub-divide the electrodes on two or more edges of the mosaic 35 screen. Thus two of the electrodes such as 23 and 26 may be divided as shown by the dotted lines resulting in individual electrodes 23a, 23b, 23c, and 26a, 26b, and 250. Electrodes 24? and 25 may be left continuous or these may likewise be 60 sub-divided in similar manner. - Each of the auxiliary electrodes is connected to a voltage divider 27, which serves as a source for the bias potential for the electrodes, through a lead and also through a resistor 28 which reduces the capacitance of the mosaic electrode to ground. The compensating electrodes may be biased pref erably a few volts positive or negative with re spect to the second anode it in compensating for parasitic signals arising from unequal secondary emission. The electrodes along any side of the @ill mosaic screen may be further biased positively or negatively with respect to each other to give the desired compensating or suppressing ?eld at the mosaic screen surface. With the tube as illustrated, scanning prefer ably takes place in a series of lines from side to side of the screen beginning at the left-hand top corner. The base line wander at line fre quency may be corrected by biasing to a few volts positive with reference to the second anode the compensating electrode 2d which is near the side of the screen on which the line scanning ends, and at frame frequency by similarly biasing the compensating electrode 23, near the bottom of the target. In this way there is produced 65 along the surface of the mosaic screen a field which compensates for the ?eld due to the scanned elements, and minimizes the parasitic signals. The positive electrode 2d at the right 70 hand 'end of each line of elements traversed by the scanning beam during line scanning attracts a preferred form it consists of a thin sheet of mica " the secondary electrons emitted by each scanned I8 having on the back a continuous metal coating element and counteracts the eifect of the posi $6 or signal plate is and on the front a mosaic screen tively scann‘ed elements in the line to the left 175 3 2,181,892 of the scanning beam. The positive electrode said compensating electrode at'a potential with 23 at the bottom of the screen likewise counter respect to said screen for producing in conjunc tion with said collector electrode along the sur face of said screen an‘ electrostatic ?eld by which the effects of the ?eld due to the scanned ele acts the e?ect of the positively oscanned elements above the line of scanning. I have obtained good results with a battery 9 of 250 volts, a battery ii of 750 volts, and a bias on the compensating ' ments of the series are minimized. 2. A cathode ray transmitting tube comprising electrode of about 5 volts positive with reference to the second anode I3. I have also found that resistors 28 of a value of about 100,000 ohms, are 10 suitable. a planar mosaic electrode including a mosaic screen of mutually insulated photo-electrically sensitive elements each capable of holding an 10 For suppressing parasitic signals resulting from non-uniform secondary emission from the mosaic screen I have found it desirable to bias the auxil iary electrodes either positively or negatively in electrostatic charge and a common signal plate back of said screen and capacitively associated with said elements, scanning means including an electron gun for directing a scanning beam to said such a manner that the transmitted picture when 715"'re-created'is of uniform shading? It has been screen and a collector electrode in front of said screen, a plurality of’ compensating electrodes'ad jacent and distributed along the edge of said screen and out of the path of the scanning beam and means to maintain each of said compensating electrodes at a potential which will equalize the 20 e?‘ect of the charges on said photoelectrically found that some tubes of this type are more'sub ject to parasitic signals of this nature than to parasitic signals resulting in base line wander. 20 I thus provide the potentiometer 21 which sup ' plies either positive or negative potential sources sensitive elements produced by scanning said as desired for the suppression of parasitic signals due to inequalities of secondary emission over the mosaic surface. The auxiliary or compensating electrodes may 25 screen. - 3. A cathode ray transmitting tube comprising a parallelogrammic mosaic electrode including a 25 mosaicscreen of mutually insulated photo-elec be’ used also to generate corrective signals which maybe mixed with the signals from the signal trically sensitive elements each capable of hold ing an electrostatic charge and a common signal plate back of said screen and capacitively asso ciated with said elements, scanning means includ 30 ing an electron gun for directing a scanning beam to said screen to liberate secondary electrons from said elements and a collector electrode in front of said screen, compensating electrodes adjacent one side and one end of said screen and means to maintain each of said compensating ture signal ampli?er. It is obvious that the compensating electrodes electrodes at a potential which will produce an - 23, 24, 25,'and 26 of the ?gure may be replaced electrostatic ?eld which in combination with the by compensating electrodes attached to the walls ' electrostatic ?elds produced by the collector elec of the bulbous portion of the tube | and arranged trode and the charged elements of the screen will between the cathode ray gun in the neck portion insure the uniform distribution over the surface plate either directly or after ampli?cation. For example the auxiliary electrodes, fed from a suit 30 able bias potential source through a high re sistance may be connected through a condenser to the mosaic electrode conductive coating, or to a tapon the impedance which is connected to the signal plate and across which the picture signals 35. are developed, or to a suitable point in the pic of the screen of secondary electrons produced by and the mosaic electrode assembly, that the elec trodes-may be in the form of wires let in through the glass walls, and that they may be perpen dicular to the glass, or may be arranged parallel scanning said screen. 4. A cathode ray transmitting tube as claimed in claim 3 having a plurality of compensating to the sides of the screen, as long as they are in proper relation to the screen and are given suit mosaic screen. . 5.,A cathode ray transmitting tube comprising able positive or negative biasing potentials. What I have indicated the preferred embodi ment of my invention of which I am now aware 50 and have also indicated only one speci?c appli cation for which my invention may be employed, it will be apparent that my invention is by no means limited to the exact forms illustrated or 55 the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without depart ing from the scope of my invention as set forth in the appended claims. electrodes along said side and said end of said , Having now particularly described and ascer a parallelogrammic mosaic electrode including a mosaic screen of mutually insulated photo-elec trically sensitive elements and a common signal plate back of said screen and capacitively asso ciated with said elements, scanning means in cluding an electron gun for directing a scanning beam to said screen, a plurality of compensating 55 electrodes adjacent and distributed along the sides and edges of said screen and means to main tain each of said compensating electrodes at a potential with respect to said screen for producing in conjunction with said collector electrode along tained the nature of said invention, and in what the surface of said screen an electrostatic ?eld by manner the same is to be performed, I declare which the e?ects of the ?eld due to the scanned that. what I claim is: elements of the said screen are minimized and the distribution of secondary electrons over the 65 surface of the screen made more uniform. ‘ 1. A cathode ray transmitting tube comprising 65 a mosaic electrode including a mosaic screen of mutually insulated photo-electrically sensitive 6; A cathode ray transmitting tube comprising elements and a common signal plate back of said ' a target electrode adapted to receive an optical screen and capacitively associated with said vele image, a. collector electrode in front of said target ments, scanning means including an electron gun electrode, and scanning means including an elec 70 for directing a ,scanning beam to said screen tron gun for directing a scanning beam over F and‘a collector electrode in front of said screen, said target in a series of parallel paths, a com a compensating electrode mounted out of the pensating electrode mounted out of the path of path of the scanning beam and adjacent one the scanning beam and adjacent one end of the . end of the paths followed by the scanning beam paths followed by the scanning beam, and means in scanning aseries of said elements maintaining to maintain said compensating electrode at a @ arsaeea predetermined potential with respect to said tar get electrode for producing in conjunction with said collector electrode along the surface of said screen an electrostatic ?eld by which the effects of the ?eld due to scanning the target electrode in one direction are minimized. 7. A cathode ray transmitting tube, comprising a parallelogrammic target electrode adapted to receive an electron image, scanning means in cluding an electron gun for directing a scanning beam to said target electrode to liberate second ary electrons from said target electrode and a collector electrode in front of said target elec_ trode, compensating electrodes adjacent one side and one end of said target electrode, and means to maintain each of said compensating electrodes at a predetermined potential with respect to said target electrode for producing in conjunction with said collector electrode along the surface of said 2% target electrode an electrostatic ?eld by which the effects of the ?eld due to the scanning of said target electrode are minimized and the distribu tion of secondary electrons produced by the scan ning beam on said target electrode over the sur face thereof made more uniform. - ' V 8. A cathode ray transmitting tube comprising ' a target electrode adapted to receive an optical . image, a collector electrode in front of said target electrode, and scanning means including an elec tron gun for directing a scanning beam over said target in a series of parallel paths, a compensat ing electrode mounted out of the path of the scanning beam and adjacent one end of the paths followed by the scanning beam, and means to maintain said compensating electrode at a posi tive potential of approximately ?ve volts with respect to said target electrode for producing in conjunction with said collector electrode along the surface of said screen an electrostatic ?eld by which the effects of the ?eld due to scanning the target electrode in one direction are mini mized. 10 9. A cathode ray transmitting tube comprising a parallelogrammic target electrode adapted ‘to receive an electron image, scanning means in eluding an electron gun for directing a scanning ' beam to said target electrode to liberate second 15 ary electrons from said target electrode and a collector electrode in front of said target elec trode, compensating electrodes adjacent one side and one end of said target electrode, and means to maintain each of said compensating electrodes 20 at a vpositive potential of approximately ?ve volts with respect to said target electrode for producing in conjunction with said collector electrode along the surface of said target electrode an electro static ?eld by which the effects of the ?eld due 95 to the ‘scanning of said target electrode are mini mized and the distribution of secondary electrons produced by the scanning beam on said target electrode over the surface thereof made more uniform. HARLEY A. .