US2930931A - Electronic device - Google Patents

Description

March 29, 1960 w. R. AIKEN 2,

ELECTRONIC DEVICE Filed Sept. 28, 1955 2; iii im-l C-l l4 l5 I6 RECEIVER INVENTOR.

WILLIAM ROSS AIKEN United States Patent ELECTRONIC DEVICE William Ross Aiken, Los Altos, Califi, assignor, by mesne assignments, to Kaiser Industries Corporation, a corporation of Nevada Application September 28, 1955, Serial No. 537,098

4 Claims. (Cl. 315-16) This invention relates generally to the control of electron beams, and more particularly to a system for controlling the focus of the electron beam within a cathode ray tube.

The cathode ray tubes known in the art as the Aikentype fiat tube, as described in co-pending applications Serial No. 355,965, filed May 19, 1953, now abandoned; Serial No. 396,120, filed December 4, 1953, now Patent No. 2,795,731; and Serial No. 521,201, filed July 11, 1955, now Patent No. 2,864,970, as well as the conventional elongate cathode ray tubes, employ electron gun arrangements wherein the cathode is heated by a heater filament in order to cause the cathode surface to emit electrons. These electrons, having been driven olf the surface of the cathode, first pass through a control elec trode and then through a series of accelerating and focussing electrodes which serve to accelerate the emitted electrons and to cause the electron beam to assume a desired size and shape.

In one use of a cathode ray tube, as for example in the television field, the video signal voltage containing the picture information to be displayed which arises from the television scanning process is electrically connected to the control electrode of the electron gun of the tube. In such an arrangement the control electrode is physically disposed about the cathode and is provided with an aperture through which the electrons emitted from the cathode must pass. The electrode is capable of controlling the number of electrons which flow therethrough toward the accelerating and focussing electrodes. When a more negative potential than the cathode potential is placed on the electrode, it decreases the number of electrons which pass through the aperture in the electrode. When the charge on the electrode is varied, the number of electrons passing through the aperture in the electrode also varies. The electrode can therefore be used to control the number of electrons in the beam, and for this reason, is generally referred to as the control electrode. If the charge on the electrode is sufiiciently negative relative to the cathode, the electron beam will be entirely cut oif. Therefore, it will be manifest that as the potential applied to the control electrode becomes more positive with respect to the cathode potential more electrons emitted from the cathode will be permitted to travel therethrough and toward the accelerating and focussing electrodes containing apertures formed therein permitting the passage of the electron beam therethrough. These electrodes serve both to collimate and accelerate the electron beam which has been emitted from the cathode. The accelerated beam of electrons then is caused to be directed toward the fluorescent target area and recreate the picture information. In cathode ray tubes employed in the field of television, the tonal values of the image displayed are recreated by applying the video frequency voltage signal to the control electrode to vary the beam density in 2,930,931 Patented Mar. 29, 1960 accordance withthe signal; the more negative the video signal the less dense will be the impinging beam.

In the type of operation of a cathode ray tube electron gun to which this invention more specifically relates, the signal voltage is applied to the cathode rather than to the control electrode. The control electrode is maintained at a negative voltage with respect to the cathode potential during the operation of the tube and the amount of beam current or energy is controlled by the video frequency voltage supplied to the cathode. As the cathode voltage becomes less positive with respect to the control electrode, the speed of the electrons being emitted is increased. This increase in beam velocity causes a corresponding change in the focus of the electron beam. Ordinarily, an optimum value is selected for the focusing: and accelerating electrodes so that during mean condi-- tions, the beam is best focused. In other words, the: voltages on the accelerating and focusing'electrodes are: not adjusted for each change in voltage to the cathode but: are adjusted for an over-all or average beam velocity' in order to obtain what most nearly resembles a goocfl focus for the beam.

The instant invention has produced a means for auto-- matically changing the voltage on at least one set of the: focusing electrodes to compensate for the change in voltage applied to the cathode so that it is possible to have the electron beam in correct focus at all times during the operation of this type of electron gun. This principle of operation may be utilized within an electron gun in a number of various manners which will be obvious with reference to the following description of one embodiment of the invention.

This invention will now be described in detail with respect to the figure which is a schematic representation of an electron gun arrangement employing one embodiment of said invention.

With reference to the drawings, there is shown an electron gun including a heater or coil 11, cathode 12, and a plurality of electron beam forming and controlling electrodes 13, 14, 15, and 16. It will be noted that the heater filament 11 is disposed in the cavity formed within the cathode 12 and is electrically coupled to a source of electrical energy. The cathode 12 is electrically coupled to a television receiver 10 through a conductor 12a. The cathode 12 is also electrically coupled to the electrode 15 through a capacitor C-1. Also, the electrode 15 is maintained at a predetermined potential through a variable resistor R and resistor R from a battery 17.

The electrode 13 is coupled to a power supply within the television receiver 10 through an electrical conductor 13a. The electrodes 14 and 16 are coupled together and connected to the battery 17.

, In operation, the sole function of the heater coil, or filament 11, is to heat the cathode 12 to its proper oper ating temperature. No useful electron emission takes place from the heater coil 11. The heater filament 11 converts the electricity or current passing therethrough. into heat. The heat thus generated by the filament 11 is radiated to the cathode 12. The cathode is suitably insulated from the filament 11 so that no electrical interaction may take place. The intensity of electron emis-- sion from the cathode 12 is controlled by the voltagesignal impressed thereon from the television receiver 10- through the conductor 12a.

The electrons thus emitted from the cathode 12 must; pass through an aperture formed in the next adjacent. electrode 13. In order to obtain the desired operation. of the device, the electrode 13 is supplied with a D.C. restoring potential or bias generated by a power supply within the television receiver through an electrical conductor 13a and the electrons emitted from the cathode 12 are attracted through the electrode 13 due to the relatively positive potential of the more remote electrodes 14, 15, and 16. A portion of the electrons will pass through the aperture formed in the electrode 13 and due to their forward velocity will travel along an axis toward the electrodes 14, 15, and 16 in succession. The electrons which pass through, because of the pulling forces exerted by the positive charges on the electrodes 14, 15, and 16, converge into a narrow beam.

It will be readily discerned that if the apertures formed in these electrodes are in axial alignment With that of the initial axis of travel of the electron beam, a large portion of the beam may therefore travel therethrough if there are proper potentials impressed thereon.

In actual practice, after the electron beam passes through the aperture formed in the electrode 13, there is a tendency for the electrons of the beam to scatter. In order to militate against this scattering or spreading out of the beam, suitable forces are applied to the beam to cause the electrons to return toward the initial axis of the beam travel. These forces which may be referred to as focusing and accelerating forces are established by impressing suitable potentials on the electrodes 14, 15, and 16. Manifestly, the potentials applied must be such as to cause the beam of electrons to converge at certain points along its axis of travel. The electrostatic focusing forces referred to above may be readily understood by referring to an optical analogy of the action of an electric field on an electron beam. With a lens, light rays can be made to converge at a point and afterwards they will commence to diverge again. By substituting lenses of different curvatures, the distance to the converging or crossover point can be varied. If a screen is disposed a certain distance away, the light rays can be made to cross over, or focus, at the screen by the proper selection of lens curvature.

If an electrostatic lens and an electron beam are substituted for the optical system and light beam, this electrostatic focusing can be readily understood. The electrodes 14 and 16, which are electrically coupled together and in turn coupled to the plus terminal of the battery 17, are maintained at a potential positive with respect to the cathode potential, and the forces established thereby will continuously attract and accelerate the electron beam in a direction away from the source, the cathode 12. Electrode 15 is connected to cathode 12 through condenser C-1 and is operated at a potential less positive than that of electrodes 14 and 16. It is manifest that the electrostatic focusing action must take place for many different beam currents. These differences are caused by the potentials impressed on the cathode 12 from the television receiver 10 through the conductor 12a. If a potential positive with respect to electrode 13 is impressed on cathode 12, the resultant electron beam passing through the system will be sparse in cross-sectional density and thereby the beam will have a relatively small current characteristic.

If the signal impressed on the cathode 12 from the signal source within the television receiver 10 were of a relatively less positive value with respect to the potential on the electrode 13, the resultant electron beam achieves greater density proportions and therefore may be referred to as having greater beam current. It must be understood that as the beam current or density is increased, the resultant beam velocity is simultaneously increased. In order to compensate for this so as to maintain the beam in proper focus, the signal fed to the cathode 12 from the signal source is likewise fed through the condenser C1 to the electrode 15. It can be readily ascertained that when an electrical signal of varying character is impressed on the cathode 12, it is simultaneously passed by the condenser C-1 and onto the electrode 15. If the signal impressed on the cathode 12 is such as to cause a large velocity beam to be emitted, the potential impressed on the electrode 15 will be in direct relation thereto and will establish a corresponding change in the focusing force. This focusing force is a consequence of the electric field established by the impression of the voltage signal on the electrode 15. In some cases, it may be desirable to amplify by several times the potential impressed on electrode 15 in order to obtain a greater focusing on the electron beam. This can easily be accomplished by those skilled in the art through the use of electronic amplifiers in the circuit between the cathode 12 and electrode 15.

It may be expeditions to set forth at this point in the description, the fact that as a general rule, there is a direct relation between the beam current and the velocity of the electron beam; thus, as the beam current approaches a higher value, the velocity of the electron beam likewise approaches a higher value. Thus, when the instant invention is employed in connection with a television reproduction or receiving system, the changes in the electron beam current and velocity, created by the varying potential signals impressed on the cathode 12, will be reflected in changes in the potential signals impressed on the electrode 15 and thereby result in concurrent changes in the focusing of the electron beam passing through the field established thereby.

As a result of the instant invention, it will be obvious that a system has been devised for maintaining fine focusing characteristics of any devices wherein the electron guns of the type hereinabove described are employed.

From the foregoing description of the instant invention, it will be readily discernible to those skilled in the art that certain other modifications of the preferred embodiment can be accomplished without avoiding the spirit of the invention and the scope of the appended claims.

What is claimed is:

1. In an electron discharge device, an electron emissive member for delivering an electron beam along a given path, signal means for applying signals of variable values to said electron emissive member to vary the intensity of the electron beam, and means for applying forces to said beam including a plurality of electrodes disposed along said path wherein at least two alternate ones of said electrodes are electrically coupled to a source of positive potential with respect to said beam and at least one of the other of said electrodes is capacitively coupled to said electron emissive member for providing variable focusing forces for said beam simultaneuosly with the variations of said beam intensity.

2. In a electron discharge device, an electron beam source means for delivering a beam along a given path, including an electron emissive cathode means for coupling alternating current signals to said cathode to vary the intensity of said beam and means located along said path for applying focussing forces to said beam including at least one focussing electrode coupled to a source of constant potential and at least one addtional focussing electrode capacitively coupled to said cathode to provide variable focusing forces for said beam simultaneously with variation of said beam intensity.

3. In an electron discharge device, an electron beam source member for delivering a beam of electrons along a given path, signal input means for applying alternating current signals of various values to said source member to vary the intensity of said beam, focusing means located along said path, and capacitive means coupling said source member to said focusing means to provide variable focusing forces for said beam simultaneously with variation of said beam intensity by said alternating current signals.

4. In an electron discharge device as set forth in claim 3 which includes a high impedance circuit connected to couple a biassing potential to said focussing means to prevent shorting of the alternating current sig- References Cited in the file of this patent UNITED STATES PATENTS Rajchman June 8, 1954 6 Keyston et a1. July 5, 1938 Schlesinger July 5, 1938 Faudell Dec. 1, 1942 Skellett Sept. 10, 1946 Boyle Jan. 11, 1949 Kirkpatrick May 23, 1950 'Fyler et a1. Sept. 16, 1952

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