US2197041A - Electron discharge device - Google Patents

Description

April 16, 1940.

squnc: OF asnscrmc VOLTAGE mew/vs VOLTAGE F. GRAY 2,197,041

smcmou DISCHARGE DEVICE Filed Feb. 4, 19:58

I 2 |Ill 72 [6 I5 I I9 v 1 l? 73 H I 55 5/ v OUTPUT SOURCE OF T 52 I I 55 INVENTOR l-T GRAY A T TORNE V Patented Apr. 16, 1940 ELECTRON DISCHARGE DEVICE Frank Gray, New York, N. Y., assignor to Bell Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New York Application February 4, 1938, Serial No. I88,648

'1 Claims.

This invention relates to electron discharge devices and more specifically to devices of this character which operate by controlling the deflection of an electron beam.

In ordinary vacuum tubes, the emission of electrons from a cathode is controlled by the voltage supplied to a grid to thereby control the output current. The output current of such a tube, however, is not directly proportional to the input voltage over much of the operating range of voltages and not strictly proportional over any of the range. Cathode ray tubes, on the other hand, ordinarily operate by deflecting a beam of electrons which electrons, for example, have been emitted by a cathode and focused and accelerated toward a target by one or more electrodes at positive potentials with respect to that of the cathode. The deflection may be caused by electrostatic or electromagnetic means. In tubes employing electrostatic deflection, the deflection is directly proportional to the deflecting voltage. This characteristic has been utilized in this invention to provide a tube suitable for many purposes. In its preferred form, the invention comprises a centrally located elongated cathode around which there are concentrically arranged portions of a divided or split anode and means for controlling the emitted electrons.

It is an object of this invention to provide an improved cathode ray device of the divided or split target type.

It is another object of this invention to provide forms of cathode ray,devices in which two or more of the functions of modulating, focusing and deflecting the beam are performed by the same element or elements.

Other and ancillary objects will be apparent from the description below.

In accordance with this invention in a preferred form, an electron discharge device is pro- In an embodiment of this preferred form of the invention, an electron discharge device is provided which comprises an elongated cathode surrounded by a cylindrical plate which is split into an even number of sections or segments as.

for example, four, as shown in the accompanying drawing. Between the cathode and the anode segments are a number of wires parallel to the axis of the cathode and equidistant therefrom, one for each anode segment, in part performing the function of a grid in the ordinary vacuum tube. They will therefore be referred to as grid wires. The grid wires are all similarly biased negatively with respect to the potential of the cathode and form the electrons into four wedge-shaped beams each of which, in the absence of deflection signals, impinges upon the narrow elongate-d area between adjacent plate or anode segments. The potential of all the grid wires in common may be varied to control the intensity of the beam. The grid wires are connected into two groups, opposite grid wires being electrically connected together, with separate leads for each group. 'A varying voltage, which may be, for example, an alternating current voltsegments, depending on the amplitude of the 26,

varying voltage. Opposite segments of the anode or plate are connected in common; in effect, there are thus two electrically separate plates in the tube, and the electron stream (considered as a composite of the four beams) divides its 80 energy between or among the plates in accordance with the switching voltage. The grid wires thus serve to focus the electron beams, control the strength of the beam currents (if desired), and. to deflect the beams. A tube of this type may be used in high frequency switching operations serving, for example, as a high frequency commutator for dividing the transmission time between two image currents which are alternately transmitted over the line. be apparent from the detailed description below that it may be used for amplifying, for detecting, for the modulation of a high frequency carrier wave with voice or image currents, etc.

The invention will be more readily understood by referring to the following description taken in connection with the accompanying drawing forming a part thereof in which:

Fig. 1 is a perspective view of an electron 5o discharge device embodying the principles of this invention; a

Fig. 2 shows a circuit in which a tube of the type shown in Fig. 1 may be used; and

Fig. 3 is an enlarged view ofan electrode as- 5 It will also 0 suitable for shown in Fig. l.

Referring more cally to the drawing. Fig. 1 shows in perspective an electron discharge device embodying the principles of this invention, the envelope being partly broken away in order to show more clearly the electrode structure therein. The device comprises a gas-tight envelope Id of, for example, glass, containing a press II, in which are held in position a cathode I2, four anode sections or segments I3, I4, IS and I6, and four grid wires or elements I1, I8, I9 and 20, the grid elements being located between the anode elements and the cathode.

The cathode I2 is preferably a metallic cylinder of either the open-end or closed-end type. It is heated by any suitable means (not shown). Coated on the outside of the cathode is a layer of electron emissive material. The connection to the cathode from an external circuit is made through the terminal 2i. Terminals 22 and 23 are connected to the heating means of cathode I2 and these terminals are adapted to be connected to a source of potential to produce the heating current. Preferably, the terminal 2i is connected to the mid-point of the current supply for terminals 22 and 23 to prevent the possibility of a "free input or floating element.

Anode segments I3, I4, I5 and It may either be segments of a single cylinder as shown in Fig. l or each may have two portions one of which is ofiset from the other, all the offset portions lying in one cylindrical surface, and all the remaining portions in a second concentric cylindrical surface somewhat nearer the cathode, these segments being so positioned that the oflset portion of each plate overlaps one end of an adjacent plate. In this latter case each of the anodes I8. I4, I5 and I6 comprises a portion. which is a segment of one cylinder and a portion which is a segment of a somewhat larger cylinder. The purpose of the overlapping arrangement is to avoid open spaces between the segments through which projected electrons can pass.

The grids I'I, I8, I9 and preferably comprise single wires located between the cathode I2 and the plate or anode segments I3, I4, I5 and I6 and parallel to the axis of the cathode. The grids are located substantially 90 degrees apart and are preferably placed on lines drawn through the cathode to the center lines of the plate or anode segments I3, I4, I 5 and It, respectively. Anode segments I3 and I5 are electrically connected together by a wire 24 which also serves to help support these plates in their proper positions. Anode segments I4 and I 6 are electrically connected together by a wire 25 which has a supporting function similar to that of the wire 24. Wires 26, 27, 28 and 29 serve to support the anode segments I3, I4, I5 and I6 from the press II.

External terminals 30 and 3i are connected to the support wires 27 and 26, respectively. Grid wires I7 and I9 are electrically connected together by wire 32 and grid wires I8 and 20 are connected together by wire 33. Wire I9 is connected to an external connection 34 and wire 20 is connected to an external connection 35.

From a consideration of the arrangement de-. scribed above, it will be immediately apparent that there are two electrically separate plates or anode assemblies or structures) in the tube, that is, I3 and I5 taken together constitute one plate (electrically) and I4 and I6 taken together constitute the second plate, and two'electrical grids,

electrical grid and It and 22 taken together make up the other.

Due to the symmetry of the grid wires and the anode segments with respect to the cathode, the capacity of each grid with respect to its anode is substantially equal to the capacity between each of the other grids and its corresponding anode.

Fig. 2 illustrates how the tube may be used. Adefiecting voltage, as for example, an alternating current voltage is applied between the two electrical grids by means of the terminals 40 and 4| which are connected to a source of deflecting voltage (indicated by the block 42). Across the terminals 60 and 4I are connected equal high resistances 43 and 84, the common terminal 45 of which is connected to a source of varying voltage represented by the source 46 and potentiometer 47 having a movable tap 48. It is obvious, of course, that the source of varying voltage may comprise a fixed direct current bias with a super imposed alternating voltage, such as image or voice signals. The positive terminal of the source it is connected to the cathode I2 and thus a negative bias is placed on all of the grid wires I9,-20, 2I and 22 together and causes the electron stream from the cathode I2 to be formed into four beams each having a substantial line focus as indicated in this figure, or the beams may be less convergent so that each of them may impinge partly upon' one plate and partly upon another. The latter would be used wherever it is desired to have the energy of each of the beams divisible between two of the plates. For convenience of description these beams have been designated A, B, C and D.

Equal high resistances 49 and 50 are connected in series with plates I6 and I3. The common terminal 5! of the resistances 49 and 50 is connected to the positive terminal of a-source of potential 52, the negative terminal of which is connected I to the cathode I2. The plate or anode segments source 42, each grid is placed at the same potential by means of the source of direct current 46 acting through the potentiometer resistance 41, assuming a stationary position for the tap 48. In this condition, the axes of the beams B and D are at right angles to those of beams A and C and each beam strikesthe division line between adjacent anodes I3, I 4, I5 and I6. If now a deflecting voltage, which may be, for example, a square topped alternatingwave generated by the source 42, a wave suitable for switching, is applied between the terminals 40 and 4|, the potential of the grids I9 and I! will swing from that of the grids I8 and 20. If it is assumed that the potential of the grids I7 and I9 is swinging positive with respect to that of the grids I8 and 20, beam C will swing toward grid I9, beam B will swing toward grid I9, beam A will swing toward grid I1 and beam 1) will swing toward grid I1. If the switching signal is large enough, beams B and C will both entirely impinge upon plate or anode segment I5 and beams A and D will both entirely impinge upon plate segment I 3. In this condition,

that is, I1 and I9 taken together constitute one all of the current flows through resistance 50 and enough to cause the beams to impinge wholly I upon one anode assembly on the positive half waves and wholly upon the other on the negative half waves. The respective output currents are taken off the terminals 53 and 56 of resistance 49 and terminals 56 and 54 of resistance 50.

If it is desired to use the tube as an amplifier, for example, then'each beam is wide enough to bridge the gap between plates, which gap may be small or may be eliminated by overlap as explained above. Then in general the beams A, B. C and D divide their energy between the plates l3, l4, I5 and I8. In this case a portion of the plate current flows through resistance 49and a portion through resistance 59, the outputcircuit connected between the'outside terminals 53 and '54 of the resistances 49 and 50 receiving the differential current flowing through these resist- As only a very small deflecting voltage is required to move the beam and this controls a relatively large beam current, an amplified out- I put is obtained in the output circuit between terminals 53 and 54. Typical operating constants which have been used for a tube operating as above described are: plate voltage, 124 volts; grid bias, 22 volts; amplification constant a 3.8; voltage for complete deflection, volts; beam current, 1.7 milliamperes. However, a wide variety of operating constants may obviously be used.

It may be noted that the type .of tube herein described is suitable for so-called "push-pull operation, the circuit shown in Fig. 2 being a push-pull circuit. In the ordinary vacuum tube push-pull circuit, as one grid or grid assembly swings in the positive direction, the other grid or grid assembly swings in the negative direction. The current in one of the differential output circuits' is thus increased while that in the other is correspondingly decreased. By combining the currents of these differential circuits an amplifled current is obtained. The principle is that of the well-known Colpitts amplifier disclosed for example in Patent 1,128,292, February 16, 1915. See also Principles of Radio Communication, by J. H. Morecroft, 1933, page 1004, for a description of push-pull amplification.

When a suitable feedback is provided, the arrangement becomes a push-pull oscillator, the circuit connection being, for example, like that shown in Scriven 1,396,786, November 15. 1921, or Carson 1,463,796, August 7, 1923.

Obviously, the arrangment shown in Fig. 2 may be employed as a modulator of high frequency. current as in the well-known push-pull modulator circuits employing ordinary vacuum tubes. The source 42 isthen the source of carrier frequency and the modulating signals are applied in the common portion of the divided input circuit. For a description of push-pull modulating circuits like that here shown and modified forms in which a tube of the type here disclosed may be employed, if desired. see for example page 824 of Principles of Radio Communication, by Morecroft or Carson 1,463,796, August 7, 1923.

When the deflecting voltage is a modulated carrier and the source of varying voltage inthe common-branch of the input circuit is of carrier frequency the arrangement functions in the reverse manner and becomes a detector. Any of the well-known push-pull detector circuits may be used.

It will be obvious to one skilled in the art of vacuum tubes how'this tube may be used in push-pull circuits for usesother than those men-' tioned above.

It will be apparent that the grid wires ll, l8 l9 and 29 ordinarily serve the triple function of focusing the electron beams, deflecting the beam so that the current or energy of the composite beam is divided between the effective parts of the anode, and controlling the strength of the beam current.

Condensers may be shunted across resistances 43 and 44, respectively, when the varying voltage applied in the same phase to all the grids is higher in frequency than the switching or defleeting voltage from the source 42, the function of the condensers being to offer a low impedance path to the high frequencies.

, Electrons striking a plate will normally cause an emission'of secondary electrons with a consequent flow'of cross-current from this plate to other plates. If these cross-currents are troublesome they may be substantially suppressed by coating the plates with a material that gives only a small secondary emission, such as carbon, for example.

The arrangement shown in Fig. 3 has not only the advantage of suppressing the secondary electron currents but also causing the beams to switch more sharply from one plate to another. The arrangement is like that shown in Fig. 1 with the addition of electrode elements 19, II 12 and 13 located respectively in the openings between adjacent plate segments. These electrodes are placed at a negative potential with respect to the cathode I2, or at the same potential as that of the cathode. They may be supported in any suitable manner, the arrangement shown in Fig. 3 being merely illustrative. As shown, these electrodes are supported from and electrically connected to a metal ring 14 which is held in position in the press H (notshown in this figure, but which is similar to the press II in Fig.1), by support members I5 and 16, the support member 15 being electrically connected to cathode 12 by the connection 11. The structure of Fig. 3 is otherwise similar to that of Fig. 1. Inasmuch as the members 10, ll, 12 and 13 have-a negative potential with respect to the plate or anode segments l3, 14, I5 and I6 adjacent thereto, they tend to repel secondary electrons emitted by'each anode segment back to the anode segment from which they were emitted and thus substantially prevent secondary electron cross-currents.- Furthermore, as the electrons of a beam directed to the region between anodes approach the edge of one of these elements, they are deflected laterally by the element because of its negative potential, that is, the beam is split and the two portions are deflected laterally as it passes on to the plates. As the beam moves laterally over the edge of the auxiliary electrode there is a continual relatively rapid shift in the direction of the electrons in the portion of the beam near the edge of the auxiliaryelectrode. .This action is somewhat analogous-to a snapswitch action, but there is no actual sweep of any elemental portion of the beams across the openings between the plates. As .oneelemental portion after another of the beam reaches the edge of the auxiliary electrode,

.tween the cathode and anode plates, the results of such modifications of the exact illustrated arrangement described herein being obvious to one familiar with ordinary vacuum tube and cathode ray tube design. It is also obvious that there may be six, eight, ten, twelve or more anode segments and grid elements in a single tube instead of the number shown in the drawing. Other modifications of the embodiment herein described may obviously be made without departing from the spirit of the invention.

What is claimed is:

1. A cathode beam device comprising a cathode capable of emitting electrons, an anode structure. a plurality of electrostatic electron control elements between said cathode and said anode structure and substantially equidistant from said cathode, each of said elements being spaced from an adjacent element by the same distance, means electrically connecting a group of said elements together to form a unitary control member, and means electrically connecting together a second group of said elements to form a second unitary control member, each element of one of said groups being adjacent an elemen of the other of said groups.

2. A cathode beam device comprising an elongated cathode, two anode structures insulated from each other, all efiective portions of which lie in a cylindrical surface coaxial with said cathode, portions of one of said anode structures being positioned in said surface adjacent similar portions respectively of the other of said anode structures, and two grid structures insulated from each other, all effective portions of which lie on a cylindrical surface between said cathode and said anode structures and coaxial therewith, portions of one of said grid structures being positioned in said second surface adjacent corresponding portions respectively of the other of said grid structures.

3. A cathode beam device comprising a cathode, a plurality of elongated parallel anode members mounted in a cylindrical boundary encompassing said cathode, electron beam forming and controlling means including a plurality of elongated elements mounted between said cathode and said boundary, each of said elements being opposite a corresponding one of said anode members, and means electrically connecting alternate elements into two groups.

4. A cathode beam device comprising an elongated cathode, two anode structures insulated from each other, each comprising an even number of plates each of which is of segmental cylindrical shape, means supporting said anodes in position surrounding said cathode with narrow openings parallel to said cathode between the tioned in said surface adjacent corresponding portions respectively of the other of said grid structures.

5. A cathode beam device comprising an elongated cathode, two anode structures insulated from each other, each comprising an even number of plates each of which is of segmental cylindrical shape, means supporting said anodes in position surrounding said cathode with narrow openings parallel to said cathode between the edges of adjacent ones of said plates, each plate of one anode structure lying-between plates of the other, and two grid structures insulated from each other, each consisting of two linear elements parallel to said cathode, means supporting said elements in a cylindrical surface between said cathode and said anode structures with each element of one grid structure lying between elements of the other along said surface.

6 A cathode beam device comprising an elongated cathode, two plate-likeanodes positioned in a cylindrical surface concentric with said cathode with one edge of each anode parallel to said cathode and also to an adjacent-edge of said other anode, two elongated grid elements positioned between said cathode and said anodes respectively, each element being parallel to and equidistant from said cathode, for causing electrons emitted from said cathode to pass therebetween in a converging path and to reach said surface at difi'erent positions thereon dependent upon the potentials of said grid elements, and a said anodes.

7. In combination, anode members and two groups of grid structures in respective concentric cylindrical surfaces, a cathode axially positioned with respect thereto, the respective grid structures being spaced with respect to each other and shield member between the adjacent edges of to the anode members to form beams projecting outwardly from the cathode through the spaces between the grid structures toward the anode members, said 'grid structures when properly biased serving to form the beams normally toward points between the respective anode members and serving to shift the beams away from certain anode members toward other anode members under the influence of applied electromotive forces, said grid structures consisting of elongated elements parallel to said cathode and the grid structures of one of said groups being positioned between corresponding grid structures of

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