US2341764A

US2341764A - Cathode ray tube system

Info

Publication number: US2341764A
Application number: US421310A
Authority: US
Inventors: Gier Johannes De
Original assignee: Individual
Current assignee: Individual
Priority date: 1940-03-09
Filing date: 1941-12-02
Publication date: 1944-02-15
Anticipated expiration: 1961-02-15
Also published as: BE440981A; GB597468A; DE1077336B; FR874105A; GB549476A; NL58348C; CH223635A

Description

Feb. 15, 1944. J. DE GIER ,3

CATHODE RAY TUBE SYSTEM Filed Dec. 2, 1941 INVENTOR Jamie Gwr ATTORNEY Patented Feb. 15, 1944- chm-noon any 'runn SYSTEM Johannes de Gier, Eindhoven, Netherlands; vested in the Alien Property Custodian Application December 2, 1941, Serial No. 421,310 In the Netherlands March 9, 1940 8 Claims. (Cl. 315-22) My invention relates to electron discharge tubes and systems of the cathode ray type and particularly to an improved electrode structure for use in such tubes and systems.

In cathode ray tubes of the types utilized for recreation of television images and for oscillagraph purposes it is desirable to provide a structure capable of developing an electron beam of high electron density while atthe same time limiting the cross sectional diameter at the target to a value as small as possible. High electron beam current may be obtained while retaining a small beam cross section at the target or fluorescent screen by focusing the electron streams from the cathode with the'aid'of a pre-concentration system and by projecting a section of the beam thus formed on to the screen by means of an electrostatic lens system. In this case it is desirable to utilize an apertured diaphragm serving to limit the cross-sectional 'area of the beam of rays in order to avoid stray electrons impinging on the target or screen in the environment of the picture proper and producing additional light or halation over the target. Such a diaphragm has the disadvantage that the electrons which are intercepted produce secondary electron emission and if no particular provisions are made the secondary electrons thus liberated impinge not only on the target but also on other electrodes such as the deflecting plates and cause a variation of the potential of these plates if they are connected to a scanning circuit through a comparatively high resistance. This has the troublesome eifect that the picture point on the screen varies its position with the current and the figure described by this point is deformed. The influence of the secondary emission is reduced if the apertured diaphragm is placed nearer to the cathode. Thus if it is secured to the first electrode or anode of the electrostatic projection system, then nearly all the electrons liberated by secondary emission are collected by the electrodes of, the projection system, especially if the diaphragm is located in an electrostatic field free space. In this case, however, another dliliculty is encountered in that the electrons which impinge on the diaphragm have the effect of reducing the potential of the associated anode which is usually connected across a comparatively high resistance to a source of potential. This results in a fluctuation of the I anode potential and of the focal distance of the projection system and this causes defocusing of the image on the target screen. Consequently, with variation of the beam current, the voltage ratio between the electrodes varies. and must be adjusted subsequently, in order to keep the image sharp and in focus. g

It is an object of my invention to provide a cathode ray tube and system wherein the electron beam may be maintained in a focused condition notwithstanding wide variations in beam current. It is another object to provide a cathode raytube-system utilizing an electron gun having trol the variation of the focal distance of the electron beam in such a manner that the disadvantages referred to above are eliminated. These and other objects, features and advantages of my invention will become apparent when considered in view of the following description and the accompanying drawing, in which:

Figure l is a longitudinal view of a cathode ray tube system having electrode structure made and operated in accordance with my invention, and

Figure 2 is a cross sectional view of one of the electrodes shown in Figure 1 taken along the line 2-2.

I have found that it is almost exclusively those secondary electrons which emanate from the margin of a diaphragm in the and electrode which bring about troublesome phenomena, such as shift of the picture point and diffused screen light.

Therefore, in accordance with my invention, I provide a structure wherein the electron beam is limited by an apertured diaphragm which is located at such a point that it does not emit harmful secondary and reflected electrons but transmits only those primary electrons which cannot generate any appreciable harmful secondary radiation from further electrodes of the structure.

Further, in accordance with my invention I provide a diaphragm which collects only the stray electrons which directly adjoin the electron beam which is to be utilized to generate light on a target such as a fluorescent screen. .Thus the stray electrons can no longer impinge on a further electrode at a position which might cause further secondary electron emission and. therefore no serious trouble is encountered from secondary electrons emitted from this electrode. The potential of the apertured diaphragm, and associated anode limiting the rays and consequently the focal distance of the projection system are variable to a smaller degree since a great portion of the rays which are not used is not intercepted by the diaphragm and consequently does not contribute to the voltage variation of the diaphragm.

The invention will be more clearly understood with reference to Figure 1 wherein the highly evacuated envelope E is of elongated shape provided with a neck section enclosing an electron gun made in accordance with my invention and a frusto-conicai section enclosing a target elec- Due to the electric field between the cathode I and the first anode 3, the electrons are accelerated through the control electrode 2 which has a negative voltage relative to the cathode causing the electron paths to converge toward the electron gun axis to form an electron beam 6. In the tube represented in Figure 1 the voltages applied to the electrodes have such values that the paths of the electrons emitted from any point of the emitting surface of the cathode intersect or cross over each other in the vicinity of the first anode apertured disc 4. Consequently, the intersection of the electron paths to form the beam 6 is not at a mathematical point but over a small surface atwhich the beam has a minimum cross section. After the electrons of the beam 6 pass the cross-over point they follow divergent paths and are subsequently directed by the electrostatic fields between the first and second anodes on to the fluorescent screen S. While I have shown a structure in which the electrons converge from the cathode at a crossover point, the electrons may alternatively diverge from the cathode. The first anode 3 and second anode are maintained at positive potentials with respect'to the cathode I, preferably by a single potential source 8. Since the first anode is operated at a lower potential with respect to the cathode than the potential of the second anode, I provide a bleeder or potentiometer 9 of high resistance shunted across the source 8 to derive the potential applied to the first anode 4 such as by the variabl lead II) from the source 8.

In accordance with the invention, and in order to prevent excessive variation of the ratio of potentials existing on the first and second anodes, I provide a multi-apertured diaphragm II, which is so shaped as to intercept only part of the rays which are not used. As can be seen more clearly from Figure 2, the diaphragm II has a central aperture I2 which is aligned with the axis of the electron gun and a plurality of outer apertures I3 011' the electron gun axis. The central portion I4 of the diaphragm is preferably of annular shape and intercepts the rays in a region which directly adjoins the beam, transmitting through the apertures I3 the rays running in a marginal region I5 which is still further away from the axis. vThe latter rays consequently reach the electrode 5 but do not produce any harmful secondary emission since they impinge on the electrode at points from which the secondary electrons cannot penetrate through the aperture I6 in the diaphragm I. The secondary electrons which are produced at the central portion ll of the diaphragm II do not bring about disadvan tageous phenomena since the diaphragm is positioned in an almost field-free space so that the secondary electrons are not accelerated in th direction of the aperture I5. I

While wide fluctuations of the potential of the first anode 3 with varying beam intensities are eliminated, due to the particular shape of the diaphragm II, some residual variation in this potential due to the collection of electrons by the central annular portion is desirable. The intensity of the beam is controlled by setting up a voltage between points I! and I8 in the connection between the control electrode 2 and the cathode I, which voltage renders the electrode 2.

negative with respect to the cathode. The greater this potential difference, the weaker is the beam current but also the more are compressed the rays emanating from the cathode. Consequently, the cross-over point of the beam electrons adjacent the apertured disc 4 will be located nearer to the cathode at comparatively high modulation voltages. However, the residual variation of the first anode potential compensates for any defocusing of the electron beam and the focal distance of the lens system is rendered substantially constant with variation of electron beam intensity. It is very desirable that the area of the central portion I4 and of the apertures I2 and I3 of the diaphragm II should be chosen to collect a portion of the electron fiow thereby obtaining some slight variation of first anode potential with varying beam current. In conventional circuits this variation of the first anode potential and of focal distance is far too great with a diaphragm which intercepts all the marginal rays so that the displacement of the cross-over point of the electrons is overcompensated in this case. The ratio of the surface of the annular Portion I4 to aperture I3 area may be determined by trial but in any case apertures to allow marginal electrons to pass to the second anode must be provided to obtain the benefits of my invention. The diaphragm I I may also be constituted by a plurality of concentric rings or it may have a helical portion surrounding the annular central portion I4. The essential thing is that a central portion of the beam is transmitted and a portion of annular section about itis intercepted and outside the annular portion a quantity of rays is transmitted.

In the application of cathode ray tubes to oscillography it is often possible for the electrode voltage to be adjusted during use and thus to keep the beam in focus. In many cases, however, especially in recording of transient phenomena the short duration. of the surges to be measured necessitates an automatic control which makes the use of my invention particularly desirable.

While I have described my invention with particular reference to a cathode ray tube of the fluorescent screen type it will be understood that it is equally applicable to tubes of the television transmitting or light valve types wherein different targets are utilized and I, therefore, do not wish to limit my invention to the particular structure disclosed or the uses to which it may be applicable except as set forth in the following claims.

What I claim as new is:

1. A cathode ray tube system comprising a cathode to emit streams of electrons, a luminescent screen oppositely disposed from said cathode to receive electrons therefrom, a cylindrical anode surrounding and aligned with a portion of the path between said cathode and said screen, a multi-apertured disc supported within said anode one of the apertures of which is axially aligned with said anode, the remaining apertures of said disc surrounding said aligned aperture to minimize the collection of electrons by said disc, electrode means between aid anode and said screen in the path of electrons passing through said remaining apertures, and means to maintain said anode and said electrode means at diflerent positive potentials with respect to said cathode.

7 limit the,flow of electrons along said axis, a plurality of apertures surrounding said aligned aperture to allow electrons to flow beyond said collecting electrode and means between said. cy-

lindrical anode and said target in the path of electrons passsing through said plurality of apertures.

3. A cathode ray system comprising a source of cathode rays, a luminescent screen oppositely disposed from said source, a pair of axially aligned cylindrical anodes between said source and said screen to direct electrons along the axis of said anodes toward said screen, a multi-apertured disc in the anode nearer said source one of the apertures in said disc being axially aligned with said anodes, the remaining apertures surrounding the axially aligned aperture to allow the principal portion of electrons not flowing through said aperture to pass said disc in the direction of said screen, means between said nearer anode and said screen to intercept the electrons passsing through said remaining apertures, and means to maintain said anodes at difierent positive potentials with respect to said cathode.

4. A cathode ray tube system comprising a cathode to emit streams of electrons, a cylindrical anode to receive the electrons emitted by said cathode and focus said electron streams into a beam of'relatively large diameter, means within said anode to intercept electrons to form a central relatively small diameter beam of electrons and a plurality of streams of electrons surrounding said central beam, a luminescent screen to receive said central beam and means between said anode and said screen to intercept said plurality of streams of electrons and means to maintain said anode and said last-mentioned means at positive potentials with respect to said cathode.

5. A cathode ray tube system comprising a cathode to emit electrons, a pair or axially aligned cylindrical anodes to direct the electrons into a relatively large diameter electron beam within said anodes, means within the anode nearer said cathode to intercept electrons from an annular section of said beam, said means allowing electrons within and without said annular section to flow toward said other anode, an apertured disc within said other anode to intercept the electrons of said beam without said annular section, a high potential source connected between said other anode and said cathode, a high resistance connected across said potential source and an intermediate connection between said high resistance and said nearer anode to maintain said nearer anode at a substantially constant potential with respect to said cathode and said other anode. I

6. A cathode ray tube system comprising a cathode to emit streams oi electronaa cylindrical anode adjacent said cathode to direct electrons into a relatively large diameter beam, a target oppositely disposed from said cathode and anode, a second anode between said firstmentioned anode and said target, means to maintain said anodes at difierent positive potentials with respect to said cathode, means within said first anode to cut an annular section from said large diameter beam but to pass electrons within and without said annular section in the direction of said second anode whereby the electron current collected' by said first anode is limited to the electrons comprising said annular section and the potentialof said first anode is rendered-substantially constant, and means between said first anode and said target to collect the electrons of said beam without said annular section cut from said beam.

7. A cathode ray tube system comprising a cathode to liberate electrons, a target oppositely disposed from said cathode, a cylindrical anode to direct said electrons along diverging paths toward said target, a second anode to direct a portion of said electrons flowing along said divergent paths along converging paths toward said target, a single potential means connected between said second anode and said cathode, a bleeder resistance connected across said single potential source, an electrical connection between said-cylindrical anode and an intermediate point on said bleeder resistance whereby the electron current collected by said cylindrical anode flows through a portion of said bleeder, a multi-apertured disc within and connected to said cylindrical anode with one aperture axially aligned with said anodes and the remaining apertures surrounding said aligned aperture to limit the current collected by said disc whereby the current iiowing through the said portion of said bieeder is minimized.

8. A. cathode ray tube system comprising a cathode to liberate electrons, a cylindrical anode to accelerate the electrons from said cathode, an apertured electrode to control the quantity of electrons flowing therefrom in the direction of said anode along converging paths to a crossover point and thence along diverging paths within said anode, means to apply varying control potentials with respect to said cathode to said apertured electrode inherently causing said.

cross-over point to move in a direction along the axis of said cylindrical anode, a second anode to receive electrons from said cylindrical anode, means including a potentiometer to maintain said anodes positive with respect to the cathodeand said second anode positive with respect to said cylindrical anode, a multi-apertured disc having one aperture axially aligned with said anodes focused at a predetermined distance from said second anode irrrespective of'the movement of said cross-over point along said axis and means beyond said cylindrical anode in a direction from said cathode in the path of electrons flowing through said remaining apertures to prevent said last-mentioned electrons reaching the point 01 focus at said predetermined distance.

J OHANNES DE GIER.