US 2108091 A
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- Patented Feb. 15, 1938 UNITED STATES PATENT orrice CATHODE an nsvrce Application June 4,1934, Serial No. 728,835 I Germany July 22, 1933 momma. (o1. 25o 2'n My invention relates to improvements in cathode ray tubes and a method for operating such or similar electronic devices using a concentrated electron beam.
5 The usual type of cathode ray tube as known in the art for oscillographs and in cathode ray television comprises the following essential parts: means. for producing a. concentrated electron beam or pencil, a fluorescent screen for the electrons to strike against to produce a recording light spot thereon, and a mechanism for deflecting the electron beam or pencil to produce a desired pattern or image on the fluorescent screen.
A main object of my invention is the provision of means in connection with a cathode ray tube for compensating or equalizing distortions and errors of the screen image or pattern caused by irregularities or distortions of the deflecting field, in particular an electrostatic field used for deflecting the electron pencil in one or more directions.
While my invention is paticularly applicable to cathode ray tubes including a gaseous filling for focusing the electron pencil and using electrostatic deflecting plates for moving the electron beam over the luminescent screen, it is understoodthat the novel features of the invention may be embodied with equal advantage in any other type of tube for the purpose of compensatt ing or equalizing distortions and errors caused by position of the electron beam. passing between the deflecting plates. This non-linear behavior of the deflection causes considerable distortions in a television image produced by such a tube and results in a greatly distorted pattern if the tube is used for oscillographic recording of wave shapes or other physical variations.
An explanation of the above eifect is the fact that positive ions formed by the, electron beam by ionization by collision move towards the negative deflecting plate at a very low speed, while st ay 'electronsmove towards the positive deflecting plate at considerably higher speed, whereby a considerable cathode or anode drop, respectively, is produced at the respective plates, resulting in asubstantial weakening of the field in the center region between the deflecting plates. The deviation of the field strength from the theoretical value, especially within the central region between the plates increases with the increase of the fleld strength produced by the controlling or deflecting voltage as compared to the electric field strength produced by the space charge;
On account of the aforementioned inhomoat a constant rate across the luminous screen.
Thus, assumingthe beam to be swept at a high speed from one end to'the other end of the screen, such as in a horizontal direction, the central portion of the luminous line thus produced by the movement of the luminescent spot will appear considerably brighter than the marginal portions due to the reduced speed of the beam through the center region of the screen. This is due to the well known eiiect of a light beam appearing the brighter to the human eye, the slower its movement on account of the psychological phenomenon of the persistance of vision or retentivity of the human eye. Thus; if the electron beam is moved both in the vertical and horizontal direction as in the case of television, a more or less brilliant cross-shaped disturbing pattern known as zero error will occur in the of light spot on the screen, the greater will be the error or disturbance thus produced.
It has already been attempted to obviate this drawback by constructing the tube in an oblique fashion in such a manner as to shiftthe zero error beyond one edge of the screen area. The attainment of the same eflfect, has been attempted by displacing the disturbance outside of the screen by using electrical means, such as deflecting plates, magnetic deflecting ,coils and the like. Besides greatly complicating the construction of the tube and otherwise greatly interfering with the proper function and operation, all these schemes have the common disadvantage that only one quadrant of the luminous screen is covered by the scanning beam, resulting in a great decrease of efliciency and utilization of cathode ray tubes of this type.
Accordingly it is an object of my invention to provide means in a cathode ray tube especially of the gas filled type and using electrostatic defiecting plates for moving the electron beam over the luminous surface by which the region of the zero error or distortion is either shifted to or beyond both edges of the screen or equally distributed over the entire screen area in such a manner as to substantially eliminate the appreciable distortion eflects appearing in the pattern or image recorded on the screen in television or oscillographic work, respectively.
According to the main principle of my invention, I provide means for establishing a predetermined potential distribution along at least one of the deflecting plates in such a manner as to remove the zone of zero distortion to the outsideof the recording screen or alternatively to distribute the distortion effect substantially equally over the entire screen area.
My invention will be better understood by the 1 following detailed description taken with reference to the accompanying drawing by which I grams illustrating the phenomena of the'operation taking place in a tube according to'Figure 1.
Figures 5 and 6 illustrate an alternative arrangement for carrying the invention into practice.
Figure 7 illustrates a modification of a cathode ray tube according to the invention utilizing two pairs of deflecting'plates for sweeping the electron beam in both horizontal and vertical directions over the luminescent screen.
Referring to Figure 1, I have shown a simple scheme for suppressing distortion caused by the irregularity of the field between the deflecting plates in a cathode ray tube. Numeral I represents a tube of known design mounted upon a base 2 and provided with an inwardly projecting stem 3 carrying the cathode 4 and a concentration cylinder 6 of known design. The cathode has been shown to be of thermionic type directly heated as by means of a pair of connecting prongs 4' connected with the cathode terminals and serving for applying'a proper heated voltage as is well known. But any other type of cathode may be provided, such as an indirectly heated cathode, without departing from the spirit of the invention, as is readily understood. The cylinder 6 normally negatively biased with regard to the cathode and connected to the prong 6', serves to concentrate the electron stream emitted by the cathode into a sharply focused beam, 'as is well known in the art. At 5 I have shown the usual anode electrode provided with a central opening for passing the electron beam. The
beam is further passed through a pair-of elecv trostatic deflecting plates in the example shown comprising a plate I in combination with an opposite split plate having two parts 8 and 8' .as shown. The plates 8 and 8' are connected to a direct current potential source 9 whereby the plate 8' in the example shown is made positive L and the plate 8 placed at a negative potential. I have furthermore shown means for applying thedeflecting or control voltage to the plate I and the center point of source 9 as by means of input terminals l2 and l3;'
While I have shown only one of the deflecting plates being split into two parts biased to relative positive and negative potential, it is understood that both plates may be equally split and biased, but I have found that for most practical purposes satisfactory results may be obtained by providing a single split plate, preferably the defleeting plate, usually connected to the ground terminal as shown at In. At II I have indicated the luminescent screen for the electron pencil to strike against to produce a recording light spot thereon,
In an arrangement as described by Figure 1, the. deflecting field produced by the deflecting voltage applied to terminals l2 and I3 is simultaneously superimposed-to two qual opposite electric flelds produced by the split plates 8 and 8' By properly choosing the voltage of the auxiliary battery 9 in such a manner that the biasing voltage is greater than the highest deflecting voltage, the zero distortion is shifted in both directions beyond the fluorescent screen image.
Referring to Figures 2 to 4, I have shown diagrams illustrating the path of the electron beam under various prevailing conditions.
Figure 2 shows the beam in case that no ,defiecting potential is applied; that is, if plate 1 is at-zero potential. By first considering one part of the deflecting system; that is, plate I in the example shown, it is seen that the electron beam would be deflected by an agle a as shown by the upper dotted line. By. similarly regarding the second deflecting system; that is, plate 8' in the example, separately, it is seen that the beam would be deflected in the opposite direction by an angle a" as shown by the lower dotted line in the diagram. Both angles will be equal provided that the deflecting plates 8 and 8' are of equal dimensions. If now the beam-passes the two deflecting fields in succession, as is actually the casein a construction as shown, a path will be obtained as shown by the full line and it is seen that the beam when leaving the deflecting system has again assumed its original direction with a slight parallel displacement by a distance 1 asshown. The displacement in most cases is inappreciable and may be neglected for practical purposes. Alternatively it may be compensated as will be readily understood by initially adjusting the beam so as to'be at a closer distance to one of the deflecting plates in such a manner that the beam when leaving the deflecting system is exactly in the central axis m---::, as
Referring to Figure 3, this shows the electro beam for the case of a deflecting voltage producing a field strength equal and opposite to the field strength produced by the first part of the deflecting system; that is, by the plate 8, while in Figure 4 I have illustrated the deflection of the electron beam in the case that the deflecting field strength has become equal to the biasing field strength produced by the second plate 8'.
If the voltage of the potential of the auxiliary battery 9 has a highervalue than above specifled, 'an excessive parallel displacement of the beam will take place. On the other hand, ii the potential has a lower value than specified, the distortion zone will move from the outer regions more and more towards the center of the screen.
Another explanation of the function of a defleeting plate structure according to the invention is the fact that the electron beam is held in its zero position by two opposite forces, causing a differential action by the deflecting voltage with the result of a considerably increased sensitivity of the deflection in the zero position and consequent suppression of the zero distortion existing in the case of ordinary deflecting plates used in tubes of hitherto known construction.
Referring to Figures and 6, I have shown another scheme for suppressing the distortion ef-v feet produced by an irregular deflecting field. For this purpose I have shown the lower deflecting plates I1 consisting of resistance material or alternatively comprising a plate having a coating of resistance material applied thereon, such as by means of a sputtering or precipitation method well known in the art. I have furthermore shown at l8 and I9 metallic electrodes mounted at opposite sides of the plate I! and connected to.the potential source 9 whereby a, gradually varying potential drop is obtained through the resistance from the left-hand edge to the right-hand edge of the plate ll. In this manner, it a deflecting voltage is applied between the plate, such as a voltage of saw-tooth shape gradually pulling the electron beam across the screen, it is seen that the zero distortion will be gradually shifted to ditferent zones across the deflecting condenser in such a manner as to become substantially evenly distributed over the entire screen area, whereby distortions of the image or pattern on the screen are substantially eliminated. The electrical resistance through a;- plate of this type should be. small as compared to the discharge impedance between the plates and also small as com-pared with the inner impedance of the deflecting potential source.
As pointed out before, the invention is especially useful in case that high light or current intensities are used, however, it is understood that the arrangement according to the invention may be used with equal advantage for compensating any kind of distorted or irregular defleeting force exerted on the electron beam for securing any desiredchange or variation of the sensitivity of the deflection for producing a desired correction or modification of the pattern or image on the luminous screen.
Referring to Figure 7 of the drawing, I have shown a cathode ray tube embodying two pairs of deflecting plates for moving the cathode ray in both a horizontal and vertical direction, such as used in the scanning of television pictures, the second deflecting system being arranged at right angles to the first system and comprised of a deflecting plate l5 and an opposite split plate system comprising plates l6 and It in a manner similar as described by Figure 1. In a tube of this type it is possible to use the same biasing voltage for both deflecting systems as shown, in such a manner that the connections may be carried out inside the tube, as shown, and only two terminals are required for the connection of the current source 9 similar as in an ordinary tube construction.
when using a construction as described, the dimensions of the plates will have to be increased, making it necessary to increase the distance between the plates, especially of the plates farther removed from the anode than the other pair '01 deflecting plates, so as to enable the cathode beam to sweep over the entire surface of the luminescent screen. Alternatively the plates may be inclined so as to allow a. wider sweeping angle. In both cases the length of the plates should be chosen in such a manner as to substantially for deflecting said beam; and means comprising a biasing potential source for said first means for exercising an auxiliary substantially constant electric field upon said beam of varying.
field strength distribution for different lengths of the beam for compensating irregularities of deflection for different deflecting angles.
2. A cathode ray tube comprising an envelope;
means for producing a concentrated electron beam therein; means including a pair of electrostatic electron plates for deflecting said beam; and biasing means for securing a predetermined electric-potential distribution over at least one of said deflecting plates to produce two additional substantially constant fields of opposite sign and normally perpendicular to the deflecting plates within the deflecting space enclosed by said deflecting plates for correcting irregularities of sensitivity of deflection for 'diiferent defleeting angles of said beam.
3. A cathode ray tube comprising an envelope; means for producing a concentrated electron beam therein; a pair of electrostatic deflecting plates, at least one of said plates being splitintotwo parts; and means for applying to each of said parts different electric potential measured relative to a fixed point of potential.
4. A cathode ray tube comprising an envelope; means for producing a concentrated electron trostatic deflecting plates for said beam, at least one'of said plates having electrical resistance;
.and means for applying electric potential difference to opposite sides of said last plate for producing an electric potential gradient in the direction of said electron beam.
6. In combination with a cathode ray tube comprising an envelope; means for producing a concentrated electron beam therein; a deflecting system including a first-deflecting plate; a pair of opposite deflecting plates, a-source of biasing potential connected to said opposite deflecting plates; and means for applying deflecting potential between the center point of said source and said first deflecting plate.
7. In combination with a cathode ray tube comprising an envelope; means for producing a concentrated electron beam therein; a deflecting system including a first deflecting plate, a pair of further deflecting plates of equal dimension disposed opposite and parallel to said first. deflecting plate; a biasing potential source connected to said opposite plates; and means for applying de- 7 flecting potential between the center point of said source and said first deflecting plate.
8. A cathode ray tube comprising an envelope; means for producing a concentrated electron beam therein; means for deflecting said be comprising a first deflecting plate; a second defleeting plate mounted opposite said first plate, said second plate constituting an, electrical resistance; a source of biasing potential connected to opposite ends of said resistance for producing a potential gradient in the direction of the electron beam; and means for applying deflecting potential between the center point of said source and said first deflecting plate.
9. A cathode ray tube as claimed in claim 7 including a luminescent screen placed in the path of said electron beam in which said deflecting plates are arranged at an angle to allow maxi mum deflection of said beam to cover the surface of said screen.
10. A cathode ray tube as claimed in claim 8 including a luminescent screen placed in the path or said electron beam in which said deflect-v ing plates are arranged at an angle to allow maximum deflection of said beam to cover the surface of said screen.
11. A cathode ray tube comprising an envelope;
means for producing a concentrated electron beam therein; a luminescent screen placed in the path of said beam; two pairs of electrostatic de flecting plates arranged at an angle to sweep the electron beam over said screen in diflerent direc-' tions, at least one plate 01' each pair of deflecting plates being split into two separate parts: and means including a pair oi. connecting terminals and circuit connections therefrom to said deflecting plates for applying different electric biasing potential to the difierent parts of each of said split plates.
12. A cathode ray tube comprising an envelope: means for producing a concentrated electron beam therein; a luminescent screen placed in the path of said beam; a pair of electrostatic deflecting systems each comprising a pair of deflecting plates for moving said beam over said screen in both horizontal and vertical directions, at least one plate of each system being split into two halves separated from each other; and means including a pair of connecting terminals for said tube and circuit connections therefrom to said split halves of said deflecting plates for applying positive and negative biasing potential between corresponding split plates.
13. In a cathode ray tube wherein a concentrated electron beam is developed, the method for correcting irregularities in deflection of the beam which comprises the steps of applying equal and opposite deflecting forces to hold said beam in an initial position, and superimposing upon the said forces a deflecting force to deflect the beam.
14. In a cathode ray tube wherein a concentrated electron beam is developed, the method of correcting for irregularities in deflection of the beam which comprises the steps or applying equal and opposite electrostatic deflecting flelds upon said beam whereby the beam 'is maintained in an initial position, and superimposing a deflecting electrostatic field to effect deflection oi the beam.
15. In a cathode ray tube wherein a concentrated electron beam is developed, the method of operating which comprises the steps of applying a varying electrostatic fleld along the axis 01' said developed beam, and superimposing upon said fleld a substantially constant deflecting electrostatic fleld of substantially equal intensity but varying in time to effect deflection of said beam.
16. In a cathode ray tube wherein a concentrated electron beam is developed, the method of operation comprising the steps of applying a gradually increasing and subsequently decreasing electrostatic field in the direction 01' the axis of the beam, and superimposing upon said field a deflectingfleld of substantially constant intensity but varying in time for effecting deflection of the electron beam.
17. In a cathode ray tube wherein a concentrated electron beam is developed, the method of.
operating which comprises the steps of applying a positive and negative electrostatic biasing field through which the developed-electron beam must pass, and superimposing upon the biasing fl'eld a deflecting field of substantially constant intensity but varying in time for eflecting deflection of the electron beam.
18. A cathode ray tube comprising means for producing a concentrated electron beam, means normally perpendicular auxiliary substantially constant electric flelds of opposite sign to said beam whereby irregularities of deflection sensitivity of the electrostatic means are corrected.
mumps: vow mm.