US2899577A - Electron discharge device - Google Patents

Description

- J. A. M CARTHY ELECTRON DISCHARGE DEVICE Aug. 11, 1959 Filed March 27, 1957 5 Sheets-Sheet 1 INVENTOR By J. A. MC CARTHV ATTORNEY Aug. 11, 1959 J. A. M CARTHY ELECTRON DISCHARGE. DEVICE 3 Sheets-Sheet 3 Filed March 27, 1957 INIQ/ENTOR J. A. McO4R7'HV ATTORNEY ELECTRON DISCHARGE DEVICE .lolin" McCarthy, Monistown, N.J., assignbr to Bell Telephone, Laboratories, Incorporated, New York,

N.Y., a corporation of New York Application March 27, 1957, Serial No.- 648,802

SClaims. (Cl. 313-68) This invention relates to electron discharge devices and more particularly to target assemblies employed in electron discharge devices of the coder type.

A flash coder tube of one known type makes use of a wide, flat electron beam which is directed against an apertured coding plate. The apertures of the coding plate are arranged in parallel rows in an array corresponding to the particular form of digital code selected. The position of the beam in relation to the parallel rows of coding plate apertures is determined by deflecting means on which the input signal is impressed. The parts of the beam permitted to pass through the apertures thus represent a digital translation of the input signal.

In order to collect the output signal, a plurality of read-out electrodes or target electrodes are positioned behind the coding plate. Through a feedback arrangement from the output electrodes to the deflection system, accurate beam positioning may be realized. Tubes of this type are well known in the art and have been disclosed, for example, in R. W. Sears Patent 2,713,650, July 19', 1955. Such devices are useful in the monitoring of memory devices and are particularly suitable as elements in pulse code modulation systems.

Heretofore, one of the major problems arising in the construction of flash coder tubes is that of providing adequate shielding for the collector electrodes so as to reduce to a minimum the capacitive and electronic coupling between them. A further problem has-been the reduction of capacitance between each collector electrode and" ground. A still further source of difliculty encountered in the arrangements of the prior art is the complexityv of the target electrode array which has been found-necesary to produce acceptable results. The low output current of flash coder tubes has proved to be an additional factor limiting their usefulness. While attempts have been made in prior art devices to remedy the diflic-ulties noted, the best known target structures are still subject to the distinct disadvantages of high construction-cost brought about by the complexity of the electrode arrangements, interelectrode crosstalk caused by thelack of complete isolation between the electrodes, yground-to-collector capacitance limiting the speed of signal extraction from the electrodes, and low output current.

Itis-one object of this invention to reduce capacitive and electronic coupling between the target electrodes in an electron discharge device.

It is another object of this invention to limit capacitive coupling between the target electrodes and ground in such a device.

A further object of this invention is to provide a target arrayfor such a device which is of relatively simple construction and which is relatively easy to assemble.

A still further object of this invention is to increase the output current from electron discharge devices of the coder type.

A still further object of this invention is to provide an improved electron discharge device of the coder type.

Patent "ice These and other objects of this invention are realiied in one specific embodiment wherein the target electrode array comprises a single metallic block, which may advantageously be of aluminum. The targets in the direct path of the beam-are the sides of slantinggrooves which may be milled or otherwise formed into the block. The angle at which the parallel? sides of the milled grooves are slanted'permits each groove to house a. collector electrode wire which is held insulated from the aluminum block. By this arrangement the segments of the primary electron beam which are permitted to'pass through the coding plateirnpinge on one or more of the slanting surfaces of the grooves, but the electrode wires remain shielded from the direct path of the beam;

The sides of the grooves which serve as targets for the primary electron beam are partially oxidized or otherwise suitablytreated' in order to form-surfaces with high secondary emission properties. As a result, the bombarding beam current releases a larger secondary current which is then'collected bythepositivelyoperated collector wires; With the collector wires fully shielded from the primary beam; full use of the'secondary emission surface-for output current gainis-realized. Furthermore, the secondary emission from a bombarded surface is known to be greater with oblique bombardment than withnormal bombardment; For example, it is: known that electron bombardment with a (SO-degree angle of incidence will' increase secondary emission resulting from normalbomb'ardment by afactor of two. Consequently, two advantagesare gained'from the slanting configuration of the grooves; First, eflicient shielding between target electrodes is provided; and. second, the secondary emission of the groove walls is used to maximum advantage for output current gain.

It will be understood that the collector wires must be positioned with extreme accuracy in ordertobe in proper coincidence with the parallel rows of apertures on the'codin'g plate. This accuracy may advantageously beiachieved by feeding the wires through centering guides in ceramic'or other insulator end blocks which-are secured to the aluminum target block. The wires then fan out to individual inside terminal posts, each supported by the ceramic end blocks. Output connections for the tar-get wires are advantageously made through conventional button terminals which extend through the envelope of the tube.

The possibility of collector-to-target shorts which might occur, for example,.by the failure of an electrode wire whensubjected to undue stress by contraction or the like should advantageously be appreciably'red uced, as by mounting the wires under tension. Specifically, in one particular illustrative embodiment, each of the ceramic end blocks used to position the target electrode wires is held in place by a metal end plate. Integral with each end plate is a spring flap member, each of which bears against an insulating tension pin. Each tension pin in turn bears against the electrode wires, tending to force thewires to conform to the curvature of a groove in each end block. As a result, notwithstanding variations in length through contraction and expansion, tensionon the electrode Wires is kept relatively constant.

It is therefore one feature of this invention that the target assembly of an electron beam discharge device include collector electrodes individually shielded from each otherand from the direct electron beam by a single shielding' member. It is amore specific featureof thisinvention that'a grooved unitary block be used as a part of a target assembly'in order to provide shielding between in-- dividualelectrodes and to provide shielding of theelectrodesfrom the direct electron beam.

It'is a further feature of this invention that each of the grooves in the unitary block be obliquely disposed to the path of the electron beam.

It is a still further feature of this invention that a single electrode wire be positioned in each of the grooves of the unitary block.

It is a still further feature of this invention that the sides of grooves in a single metallic block be secondary electron emissive in order to provide output current gain.

It is a still further feature of this invention that the target array of an electron discharge device employ a plurality of relatively fine wires as electrodes.

It is a still further feature of this invention that the fine wire target electrodes be under tension in order to reduce the possibility of collector-to-target shorts.

A complete understanding of this invention together with additional objects and features will be gained from consideration of the following detailed description and accompanying drawing, in which:

Fig. 1 shows one specific illustrative embodiment of the invention, a flash coder tube, partially in cross section;

Fig. 2 is a cross section view of Fig. 1 along the line 22 taken in the direction of the small arrows;

Fig. 3 is a cross section of Fig. 2 taken along the line 33 in the direction of the small arrows;

Fig. 4 is an exploded perspective view showing details of the coding plate, the target block, target end blocks and retaining plates; and

Fig. 5 is a detailed perspective view of a strip electron beam partially intercepted by the coding plate and impinging on groove surfaces in the target end block.

Referring to Fig. 1, operating elements of the flash coder tube illustrated are enclosed in glass envelope 1. Glass envelope 1 is mounted on base member 3 through which extend terminal pins 2. Elements of the electron gun itself include deflecting and tilt correcting members, not shown, supported by a first set of insulating support rods 4; the electron gun may advantageously be of the type disclosed in the aforementioned Sears patent. The first set of support rods 4 in turn support a beam shield member 6. The beam shield member 6 is also supported by a first set of support brackets 7 bearing against braces 31 affixed to the inner wall of glass envelope 1.

Beyond the beam shield member 6 is a combination of elements comprising the target array. These elements are supported by a second set of support rods 5 which are in turn aflixed to the beam shield member 6. Elements of the target assembly shown include a rectangularly apertured shield plate 8, a coding plate 9 and a target block member 10. Secured to either end of the target block member 10 is a ceramic end block member 11, which may advantageously be of steatite, each of which is held in place by a metal retaining plate 14. Target electrode wires 19, best shown in Fig. 5, are positioned in but out of contact with milled grooves 24 in the end block 10. Each of the target electrodes is secured at each end to one of the end block terminals 12. One end of each target electrode is further connected to one of the peripheral button terminals 12 by means of an output lead 16. End button terminals 13 are shown connected to bias leads, one of which, 17, is shown connected to the rectangularly apertured shield plate 8.

Details of the relative positions of the various elements in the target assembly will best be gained from a study of Fig. 2. There it will be noted that the rows of apertures 18 in the code plate 9 are in parallel alignment with the target block grooves 24. Fig. 3 best illustrates the means employed to prevent shorting between the Wire target electrodes and the target block which might occur through failure of the wire if stretched too tightly by contraction, or by undue sagging of the wire if lengthened to any considerable degree of expansion. A rectangular flap 20 is cut out of each of the target end block retaining plates 14. Each flap 20 is, on its bottom edge, integral with each end block 11 while each top edge is free and curved. The curved portion of each of the spring flaps 20 accommodates a small cylindrical tension pin 21 of any suitable hard insulating material. Opposite each tension pin 21 is an accommodating groove 22 in the end block 11. Each wire target electrode 19 is secured to an end block terminal 12 and is stretched across the recessed area 25 as shown in Fig. 4, in the end block 11, thence across groove 22 through one of the end block guide slots 28, inside but out of contact with one of the milled grooves 24 and finally to similar connections at the opposite end.

When a target electrode wire 19 lengthens through expansion, the pressure of spring plates 20 bearing against electrode tension pins 21 will take up any slack by forcing the wire to follow more closely the contours of the grooves 22. Similarly, when an electrode wire contracts, it works against tension pins 21 and spring plates 20 so that it spans grooves 22 in a more nearly straight path. Thus, in either the case of expansion or contraction, tension on the electrode wires is kept relatively constant.

The functioning of a flash coder tube employing the features of the present invention will be best understood by consideration of Figs. 4 and S. The coding plate 9 operates to block off portions of the strip electron beam. Other portions 29 and 30 of the beam pass through the slotted apertures 18 of the coding plate and impinge upon the exposed sides 27 and 31, respectively, of the milled grooves 24. Each exposed side in each milled groove 24 is oxidized or otherwise treated in order to present a secondary electron emissive surface. It will be noted that each of the wire collector electrodes 19 is shielded by its associated groove 24 so as to be protected from direct impingement of the electron beam rays coming through the coded plate 9. Furthermore, the location of each wire electrode 19 in its groove 24 results in excellent shielding between the electrode wires. The only current reaching a collector wire is due to secondary electrons emitted when a segment of the electron beam strikes one of the groove walls.

Dependent upon the vertical position of the strip beam on the coding plate, various combinations of the collector electrodes are energized. These combinations represent digital codes of the beam position. The output current to any electrode wire, which is the result of secondary emission only, is, of course, proportional to the beam current contained within the width of the code plate slots and is advantageously in the order of 25 or 30 microamperes and may in fact be substantially greater.

In one specific illustrative embodiment the target block was constructed of aluminum, being 1% inches in width, 1% inches in height and A inch in depth. The shielding grooves were milled out of the block to a depth of .056 inch and inclined to the surface of the block at an angle of 63 degrees, as seen by the angle 40 in Fig. 5. Each groove was .023 inch in width and the Wall between adjacent grooves was .0145 inch thick. The target end blocks were manufactured from steatite with associated terminal pins of molybdenum. Target electrode Wires were of .008 inch monel. The use of relatively fine wire for the electrodes reduces capacitance between electrodes and ground to a satisfactory minimum. The specific dimensions noted are not to be considered as critical but rather as illustrative of one set of dimensional proportions which advantageously achieve the objects of my invention.

It is to be understood that the above-described embodiment of the invention is illustrative of the principles of the invention and is intended merely to teach the invention so that the art may utilize it in the construe tion of electron discharge device target arrays. Numerous other arrangements may be devised by those skilled in the art Without departing from the spirit, scope and teaching of the invention.

What is claimed is: v

1. An electron discharge device comprising a code plate having rows of apertures, means opposite thereto for projecting an electron beam towards said code plate, a target block having surfaces constituting the walls of recesses behind each of said rows of apertures, at least one of said surfaces in each recess having high secondary emission properties and being at an oblique angle to the path of said beam, and a fine wire collector electrode positioned in each of said recesses out of the path of said beam projected through said apertures.

2. In an electron discharge device employing an electron beam a target array comprising a single block, a plurality of projecting members integral with said block, at least one surface of each of said projecting members forming an oblique angle with said beam, a plurality of wire target electrodes, secondary emission means in the direct path of said beam, and means positioning each of said electrodes in the direct path of current from said secondary emission means out of the direct path of said electron beam, and in spaced relation to and between a pair of said projecting members.

3. An electron discharge device comprising an envelope, means for projecting an electron beam, an apertured coding plate, a target assembly located on the opposite side of said apertured coding plate from said electron beam projecting means, said target assembly comprising a unitary block, a plurality of grooves in said block, the planes defining the walls of said grooves being obliquely disposed in relation to the plane defined by said electron beam, secondary electron emissive surfaces in said grooves, a plurality of thin wire electrodes, each of said electrodes being housed in but in spaced relation to one of said grooves such that each of said electrode wires is shielded from the direct path of said electron beam, an end guide block mounted on each end of said target block positioning each wire electrode in its shielded position in its associated target block groove, a plurality of terminals mounted on each of said guide blocks, each of said electrode wires being connected to an associated one of said terminals on one of said end blocks and to a corresponding associated terminal on the other of said end blocks, and means for keeping the tension on said Wire electrodes relatively constant.

4. In an electron discharge device employing an electron beam a target assembly comprising a plurality of wire collector electrodes, a single target block, at least two of said shielding surfaces being interposed between each of said wire collector electrodes and every other of said electrodes and at least one of said surfaces being interposed between each of said electrodes and the direct path of said beam, and a plurality of shielding surfaces integral with said block, each of said wire electrodes being in spaced relation to said shielding surfaces.

5. In an electron discharge device means for forming a flat electron beam, a unitary target block member, an apertured coding plate between said beam forming means and said target block, a plurality of insulatedly separated wire collector electrodes, an equal plurality of grooves in said target block, the walls of each of said grooves defining substantially parallel planes intersecting the plane defined by said flat electron beam at oblique angles, said angles of obliquity, the width of said grooves and the depth of said grooves being such that one wall of each groove, the bottom of each groove and a part of the second wall of each groove are shielded from the direct path of said fiat electron beam, a secondary electron emissive surface on the walls of said grooves, and positioning and tensioning means for holding said wire collector electrodes in spaced relation to said grooves whereby the walls of said grooves shield each of said wire collector electrodes from each other.

6. An electron discharge device comprising an envelope,

means forming a flat electron beam, means for controlling the vertical position of said flat electron beam, a target assembly, an apertured coding plate comprising substantially parallel rows of apertures arranged in accordance with a selected code, said coding plate being positioned between siad beam forming means and said target assembly, said target assembly comprising a plurality of wire collector electrodes, an aluminum target block member, means integral with said block providing individual shielding surfaces for each of said wires whereby each of said wires is shielded from the remainder of said wires and from the direct path of said electron beam, a part of said shielding surfaces being out of the direct path of said electron beam, a part of said shielding surfaces being oxidized and exposed to the direct path of said electron beam and therefor secondary electron emissive, said wire electrodes being in the path of said secondary electron emission, and terminal means extending through said envelope, each of said wire collector electrodes being connected to said terminal means.

7. An electron discharge device comprising an envelope, electron gun means for projecting a flat electron beam, at target assembly, an apertured coding plate between said gun means and said target assembly, said target assembly comprising a plurality of wires, a metallic block with an equal plurality of grooves accommodating said wires, the walls of said grooves defining substantially parallel planes obliquely inclined to the plane defined by said flat electron beam, secondary electron emissive surfaces on one of the walls of each of said grooves, the width of said grooves, the depth of said grooves and the obliquity of the angles formed by the planes defined by the sides of said grooves and the plane defined by said electron beam being such that the inner bottom sections of said grooves and the walls of said grooves, except for said secondary electron emissive surfaces, are shielded from the direct path of said electron beam, each of said wire electrodes being in spaced relation to its said accommodating groove and spaced from the mouth of its accommodating groove so as to be shielded from the direct path of said electron beam, an insulating guide member positioned at each end of said block member having guide slots holding said wire collector electrodes in spaced relation to the grooves of said target block member, an end retaining plate member secured to each insulating guide member whereby each insulating guide member is affixed to one side of said metallic block, a plurality of terminal posts mounted in each of said insulating guide members and a plurality of terminals extending through said envelope, each of said electrode wires being connected to an associated one of said terminals ,on one of said end blocks and to a corresponding associated terminal on the other of said end blocks, each of said electrode wires being further connected to an associated one of said envelope terminals, and means tensioning side wires.

8. An electron discharge device comprising target means and electron gun means for projecting an electron beam against said target means, said target means comprising a single block member having a plurality of grooves in one surface thereof, a fine wire collector electrode positioned in each of said grooves, said grooves being oblique to the path of said beam and said wire electrodes being out of the path of said beam, the surfaces of said grooves impinged by said beam being secondary electron emissive, and means supported by said block member positioning and tensioning said wire electrodes in the path of the secondary electrons from said surfaces.

References Cited in the file of this patent UNITED STATES PATENTS 2,585,057 Vangeen Feb. 12, 1952 2,668,921 Jonas et a1 Feb. 9, 1954 2,713,650 Sears July 19, 1955

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