US2178093A

US2178093A - Television system

Info

Publication number: US2178093A
Application number: US597898A
Authority: US
Inventors: Vladimir K Zworykin; Gregory N Ogloblinsky
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1932-03-10
Filing date: 1932-03-10
Publication date: 1939-10-31
Anticipated expiration: 1956-10-31
Also published as: DE618975C

Description

Oct. 31, 1939. v. K. ZWORYKIN ET AL 2,178 0 3 TELEVISION SYSTEM Filed larch 10, 19:52

I I 9 k 1 18 l l l a4 i "42 Generator- Generator f'orsam- Toorh For-saw- Tool J V currerzr wave ,4 urrenr wa ve Rad i 0 58 .52 5,000 10 Transmitter ll AA/AAA- D H v v v v v v 6 8 1 E 'V 40 70 W\! vvvv/ :5 66 E; ==V52 9 Generator Genemfor For-5171a Wave ForS/rze Wave 07000 10 70 I Phase Freouelzcy Shifter Doubler- INVENTOE'S. Vladzmzrl'. Z wor ylfm, Flume Fre uency Gregory 0g 11723121], 3 H177 Doubler 82 CJ 0 l3 ATTORNE Patented st. i958 PATENT OFFICE TELEVISION SYSTEM Vladimir K. Zworykin, Haddonfleld, and Gregory N. Ogloblinsky, Collingswood, N. J., assignors to Radio Corporation of America, a corporation of Delaware Application March 10, 1932, Serial No. 597,898

5 Claims.

Our invention relates to television systems, and more particularly to systems of the type includ- 11:55 an electron tube for developing picture sign In using television transmission tubes of the general type disclosed in Patent No. 1,773,980 of August 26, 1930, to Philo T. Farnsworth, an image of the object is projected onto a cathode plate coated with light-sensitive material. A beam of. electrons is thereby developed, in which the electrons move with considerable velocity from the cathode plate to an anode plate having a central aperture back of which an anode element is supported. The degree of electron emission at any instant from a particular elemental area of the cathode plate is dependent directly upon the light intensity at that instant on this elemental area. For the purpose of preventing dispersion of. the electrons in their travel from the cathode plate to the anode plate, a focusing coil is disposed about the tube and operates to develop a magnetic focusing field having lines of force extending in a direction generally axially of the tube.

Scanning is accomplished by so deflecting the entire electron beam both horizontally and vertically that the electrons from the elemental areas, in a transverse section of the beam at the anode plate, pass successively through the central aperture to the anode element referred to. Picture signals are thereby developed and supplied to suitable apparatus for transmission.

It has been found expedient to deflect the beam electromagnetically, for which purpose horizontal and vertical deflection coils are used to develop deflecting fields transverse to the focusing field. The advantages of the combination of electromagnetic focusing and electromagnetic deflection, however, have heretofore been offset by several disadvantages. In the first place, the deflection of the beam, instead of being at right angles to the transverse electromagnetic deflecting fields, is at an oblique angle, the angular difierence depending upon the relation between the intensities of the focusing and deflecting fields. In the second place, the focusing is appre- (Cl. IVS-7.2)

disclosed in the patent referred to, and which is 15 effective to develop picture signals for transmission. Such a tube comprises a photosensitive cathode I2, upon which is projected an image of an object Hi being televised, the latter being illuminated by a suitable light source 16. In operation, electrons are emitted from the cathode l2 and move at high velocity in the form of a beam l8 directed at an anode plate which is maintained at a high positive potential with respect to the cathode by a battery 22 or other potential source.

The anode plate is provided at the center thereof with a small aperture 25, back of which is supported an anode element 26 connected as shown to one end of a resistance 28.

For the purpose of focusing the beam 118 on the plate 20, an electromagnetic coil 30, supplied by a battery 32, is so disposed as shown about the tube, that the flux lines extend substantially parallel to the tube axis. The strength of the focusing electromagnetic field is so adjusted by a resistance 36 that the electrons emitted from any elemental area of the cathode H, such as the area 36, normally come to a focus on the anode plate 20. That is, the electrons emitted from the elemental area 36, for example, travel at high velocity along paths generally axially of the tube, and under the influence of the focusing electromagnetic field come to a focus at the opposite, corresponding elemental area 38 of. the anode plate 20. The degree of electron emission at the instant from the photosensitive area 36 is a direct function of the light intensity on this area at this instant. In like manner, there is electron emission from each of the elemental areas of the cathode i2, the degree of emission depending directly upon the light intensity on the particular area at the instant. The focusing electromagnetic field is efiective to focus the electrons emitted'from any elemental area on the anode Plate 20.

Scanning is accomplished by so deflecting the entire beam l8 transversely in both horizontal and vertical directions that during each pictureframe period the electrons at the individual elemental regions in a cross-section of the beam, taken at the anode plate 20, pass successively through the aperture 24 and strike the anode element 26. This action is effective to develop picture signals in the resistance 26, and these are amplified and transmitted in the well known manner by a suitable amplifier and radio transmitter 46.

For the purpose of deflecting the beam is in the manner aforesaid,

electromagnetic coils

42 and 44 operate to develop electromagnetic fields wherein the flux lines are transverse to the tube axis. The coils 42 are connected to the output of a suitable generator 46 which causes, for example, a saw-tooth current wave at five thousand cycles to pass through these coils, the resultingfield operating to deflect the beam l8 five thousand times a second, horizontally. The coils 44 are connected to the output of. a suitable generator 48 which causes, for example, a sawtooth current wave at ten cycles to pass through these coils, the resulting field operating to deflect the beam I8 ten times a second, vertically.

The combination of electromagnetic focusing and electromagnetic deflection of the beam l8 has well known advantages. There is, however, a serious disadvantage which will now be explained, for which purpose consideration will be given to the electrons emitted from one of the individual elemental areas of the cathode l2, such as the area 36. As the beam I8 is deflected, and when the ray IQ of electrons issuing from the elemental area 36 is in the position indicated by dash lines, whereat this ray is directed at the aperture 24, the electrons are focused at the point 50, an appreciable distance in front of this aperture. This causes the electrons from the particular area 36 to be out of focus in some degree with respect to the anode element 26.

The various rays of electrons, propagated from elemental areas on the cathode I2 further removed from the center thereof than the area 36, will be out of focus a greater degree with respect to the anode element 26, during the scanning action. The result of this action is that the transmitted picture has substantially less degree of detail around the outside portion than at the central portion. The degree of focusing on the aperture 24 may be made more uniform over the entire picture area by causing the beam to be focused normally on a plane slightly to the right of the anode plate 20, so that when the various electron rays are deflected to be directed at the aperture 24, they are more nearly at a focus with respect to the anode element 26. This expedient, however, is a compromise, and does not provide for the best operating action in the way of picture detail.

For the purpose of avoiding the difficulty outlined above, we propose to superimpose upon the electromagnetic focusing field a corrective wave form whereby the point at which the electrons in any ray come to a focus is varied as the beam I8 is deflected, the resulting action being that when any ray is deflected to the position whereat it is directed at the aperture 24, the electrons meet at a focus on the anode element 26. For this purpose, a resistance 52 and a condenser 54 are connected as shown to the output 01. the

'by an auxiliary electromagnetic coil 56 which is connected to the resistance-

condenser combination

52, 64 through a suitable coupling tube 58. The focusing field is thereby varied in a manner dependent upon the characteristic wave-shape of the electromagnetic field for horizontal de flection of the beam l8.

In like manner, another corrective wave form is superimposed upon the normal focusing field by means of a resistance 60 and a condenser 62 connected as shown to the output of the generator 48. For this purpose, a second auxiliary electromagnetic coil 64 is disposed about the tube l0 and is connected to the resistance-condenser combination 60, 62 by a suitable coupling tube 66. The focusing fleld is thereby varied in a manner dependent upon the characteristic wave-shape of the electromagnetic field for vertical deflection of the beam I 8.

In operation, the corrective wave forms operate automatically to vary the focusing fleld in a manner similar to the characteristic waveshapes of the horizontal and vertical deflecting fields so that, at any instant during the scanning action, the electrons are focused on the aperture 24 and the anode element 26 immediately back of the same. The corrective electrical waves in the

coils

56 and 64 can be said to approximate in shape the integrals of the respective wave-shapes developed by the

generators

46 and 48.

In systems wherein scanning is accomplished by passing sine waves through the

deflecting coils

42 and 44, modification is made as shown in Fig. 2. In this case, the generator 68 develops a sine wave at flve thousand cycles, and the integral of this wave is obtained, as an approximation, by doubling the frequency by means of a suitable frequency doubler 10. It is proposed to use a suitable phase shifter 12 to compensate for a possible discrepancy in phase incident to the use of the frequency doubler 10. The auxiliary coil 56 is connected to the output of the phase shifter 12 through a suitable coupling tube 14.

The corrective wave form is developed and supplied to the auxiliary coil 64 by a similar and operate to vary the focusing in such manher that, at any instant during the scanning action, the electrons are focused on the aperture 24 and the anode element 26.

In lieu of using independent

auxiliary coils

56 and 64, the corrective wave forms may be superimposed on the normal focusing fleld by induction, as shown in Fig. 3. In such case,

suitable transformers

84 and 66 are connected as shown between the coupling tubes and the exciting circuit for the focusing coil 36.

We claim as our invention:

1. In electron apparatus of the character described, anode structure provided with an aperture, an anode element supported on one side of said structure and in proximity to said aperture, photosensitive cathode structure supported on the other side of said anode structure and in spaced relation with respect thereto, means for focusing an image on said cathode structure to develop a beam of electron rays directed at said anode structure, means for focusing said beam on said anode structure, means for deflecting said beam in scanning fashion with respect to said aperture, and means controlled by said deflecting means and operating to vary the point of focus of the individual rays to a point substantially at said aperture.

2. The combination with electron apparatus of the character described comprising a tube, electrodes supported in said tube in spaced relation with respect to each other, said apparatus being characterized by the fact that in operation a beam of electrons is developed at one of said electrodes and is directed at the other electrode, means for deflecting the electrons, and an electromagnetic coil disposed about said tube and coaxially therewith for developing an electromagnetic field; of an auxiliary electromagnetic coil disposed about said tube and co-axially therewith for developing an electromagnetic field superimposed upon said first-named field, and means controlled by said deflecting means and operating to cause an electrical wave to pass through said auxiliary coil.

3. The combination with electron apparatus of the character described comprising a tube, electrodes supported in said tube in spaced relation with respect to each other, said apparatus bein characterized by the fact that in operation a beam of electrons is developed at one of said electrodes and is directed at the other electrode, means for deflecting the electrons, and an elec trcmagnetic coil disposed about said tube and co-axially therewith for developing an electromagnetic field for focusing the beam of electrons with respect to said other electrode; of means controlled by said deflecting means and operating to develop a second electromagnetic field superimposed upon the focusing field.

4. The combination with electron apparatus of the character described comprising a tube, electrodes supported in said tube in spaced relation with respect to each other, said apparatus being characterized by the fact that in operation a beam of electrons is developed at one of said electrodes and is directed at the other electrode, electromagnetic means for focusing said beam with respect to said other electrode, and electromagnetic means for deflecting said beam in scanning fashion with respect to said other electrode; of means controlled by said deflecting means and operating in turn to control the focusing action of said first-named electromagnetic means in such manner that during deflection the focus of the electrons at a fixed elemental zone at said other electrode is maintained.

5. The combination with electron apparatus of the character described comprising a tube, electrodes supported in said tube in spaced relation with respect to each other, said apparatus being characterized by the fact that in operation a beam of electrons is developed at one of said electrodes and is directed at the other electrode, means for developing an electromagnetic field for focusing said beam on said other electrode,

' means for developing an electromagnetic field for deflecting said beam horizontally, and means for developing an electromagnetic field for deflecting said beam vertically; of means for superimposing on the focusing field a wave form dependent upon the characteristic wave form of the horizontal deflecting field, and means for superimposing on the focusing field a wave form dependent upon the characteristic wave form of the vertical deflecting field.

VLADIMIR K. ZWORYK'IN. GREGORY N. OGLOBIINSKY.