US2193959A - Electron discharge device - Google Patents

Description

March 19, 1940. E

c. s. BULL :1- AL ELECTRON DISCHARGE DEVICE Filed Oct. 30, 1936 OUTPUT OSC/LIAwB l/VPl/T' Mam/Mme wPl/r.

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Patented Mar. 19, 194i) are rice f f ELECTRGN DISCHARGE DEVICE Cabot Seaton Bull, Uxbridge, and .iohn Edgar Keyston, Hiliingdcn, England, assignors t0 Electrio d; Musical Industries Limited, Hayes, I Middlesex, England, a British company Application October so, 1936, Serial In Great Britain November 2,

8 Claims.

The present invention relates to electron discharge devices.

The invention is particularly concerned with discharge devices of the kind which comprise means for producing a beam of electrons, one or more collecting electrodes, and. means for defleeting the electron beam in accordance with an. applied controlling signal in such a manner that the electron current passings to the collecting electrode or electrodes varies in dependence upon the controlling signal.

Most known devices of the kind referred to above have the disadvantage in practice that the ratio of extent of variation of collecting electrode current to the amplitude of the controllin signal-that is, the deflection sensitivity of the device-is undesirably low. In an attempt to overcome this clifficulty, it has been proposed to provide means, such for example as a reflector,

for causing electrons on their Way to the collecting electrode to follow paths which are longer than the distance between the electron source and the collecting electrode measured directly, whereby the extent of the deflection of electrons over the collecting electrode in a linear direction which corresponds to a certain angular deflection produced by the deflecting means is in creased; the arrangement is, however, such that the angular defiectionoi the electron beam mains substantially constant at all points in the electron path, or at least is not greatly increased, the angular deflection being the angle made with the direction of the beam in the undeflected condition, by the beam, when a deflecting signal of unit strength is applied to the deflecting means.

It is an object of the present invention to provide new or improved discharge devices of the kind referred to which have a greater deflecting sensitivity. than known arrangements of that kind.

The present invention accordingly provides an electron discharge device having means comprising a source of electrons ior emitting an electron beam, a collecting electrode or system of collecting electrodes for receiving said beam, and first deflecting means for deflecting said beam in response to applied electric deflecting signals, wherein there are provided second defleeting means for increasing the angular deflecticnof the beam produced by the first defleeting means, the arrangement being such that, over a part only of the range of deflection of the beam by the first deflecting means, the second deflecting means give to the beam a coml lo. 108,466 1935 ponent of motion in a direction opposite to that of the electrons leaving the first deflecting means.

It may be arranged that if a given deflecting signal causes theelectron beam to be deflected by the first deflecting means through an angle A, the effective angular deflection of the beam ai'te-r deflection by the second deflecting, means is given approximately by (BA) over a range or" values of A; the angle 3 can be made greater than 96, and can be arranged to approacho closely to 188; the angle A can convenientlybe arranged to have a maximum value of the order of 4:5", and it will thus be clear that the second deflecting means can be arranged to produce an effective increase in the angular deflection produced by the first deflecting means of at least twice; in general, an increase of much more than twice can be obtained.

The second deflecting means may be so constituted and arranged that, in operation, they; produce a deflecting field the equipotential surfaces of which are substantially of saddle-back shape. As will appear hereinafter, however, the second deflecting means may be arranged to produce fields of other forms, for example, holds the equipotential surfaces of which conform to the surfaces of co-axial cylinders.

Other features of the invention will appear from the following description and appended claims. I

Various embodiments of the invention will now be described, by way of example, with reference to the accompanying drawing, in which,

Fig. l. is an explanatory diagram to which reference will be made for the purpose of eluci datingthe principles of the invention.

Fig. 2 illustrates a modification of a detail of the arrangement of Fig. 1.

Fig. 3 is a diagrammatic drawing of a dis charge device according to the invention, and a circuit therefor.

Fig. 4 is an explanatory diagram.

Fi 5 illustrates further construction or" the device according to the invention and a circuit therefor, and t Fig. 6 is a cross-sectional View of the electron discharge device of Fig. 5, the cross-section being a median one along the broken line in Fi 5.

Referring to Fig. 1, four electrodes P, P,-N, N are arranged as shown to form four sides of a 50 rectangular box, each electrode being insulated from the two adjacent electrodes. The electrode N is provided with an aperture at itscentr'e, and outside the box and facing this aperture there is located an electron-emitting cathode C.,- Q

Means (not shown) which may take any suitable form are provided for directing a beam of electrons from the cathode C towards the aperture in electrode N. Between the cathode and the aperture there are provided first deflecting means for deflecting the beam in a plane perpendicular to the planes of the four electrodes which form the box, these deflecting means cenveniently taking the form of a pair of plates D and D adapted to provide electrostatic deflection; the first deflecting means may alternatively comprise coils adapted for electromagnetic deflection. The deflecting means D, D are coupled in operation, to a source (not shown) of deflecting signals; the apertured electrode N and the electrode N opposite thereto are both maintained at or near to cathode potential and the electrodes P and P are maintained at suitable positive potentials with respect to the oathode.

It will be assumed that the incident direction of the electron beam is normal to the electrode N when the deflecting means D, D are inoperative. When the deflecting means produce only slight deflection of the beam to the left (it being assumed that the observer is looking into the box through the aperture in electrode N) the beam follows an almost straight path to a point close to the opposite low potential electrode. It then suffers a rapid deflection to the left in a substantially parabolic curve (this deflection may be about 150 for example) after which it follows another almost straight path and terminates on that edge of the high potential electrode P which is nearer the apertured electrode N. The path followed by the beam in these circumstances is indicated by the dotted line A. When the cleflecting means D, D produce greater angular deflection, the beam tends to travel up the potential saddle formed between the electrodes P, P, N, N by the potentials thereon, and when the deflection due to plates D, D exceeds a critical value, the beam is deflected through less than a right-angle and follows a path such as that indicated by the full line B.

The electrodes P, P, N, N constitute the second deflecting means, the deflecting field which they produce being one of saddle back form. The arrangement is such that the deflection produced by the second deflecting means varies inversely in dependence upon that produced by the plates D, D; electrons which are deflected by the plates through an angle which is less than a critical value are given, by the influence of the saddle back field, a component of motion in a direction opposite from that in which they leave the oathode, and electrons which are deflected by the plates D, through an angle greater than the critical value continue in motion in a direction having a component in the direction of emission. Thus a small change in the deflection due to the deflecting plates D, D produces a considerable change in the deflection which the beam suffers within the box P, P, N, N. When the plates deflect the ray to the right, the effect with respect to the high-potential electrode P is the same as for the high-potential electrode P in the case described above.

The device described with reference to Fig. 1 may be modified for use in amplifying electrical oscillations; for this purpose a part of one or both of the high-potential electrodes P, P may be insulated from the remainder thereof and connected to its associated source of potential through a load impedance.

Fig. 2 illustrates a part of the device of Fig. 1 modified in the manner suggested; the electrode P of Fig. 1 is replaced in Fig. 2 by two plane electrodes S and T, electrode S being biassed to a positive potential by battery B, and electrode T being connected through a load resistance R to battery B. By virtue of the shape of electrode T a portion of the beam of varying magnitude falls in operation, on this electrode. The potential across or the current in the load impedance R may be used to control a further stage of arnplification or may be used directly for many other purposes.

If it is desired to operate the device of Fig. l as a simple relay, the output may be taken from the whole of one of the high potential electrodes P, P or from both these electrodes in pushpull.

A further arrangement according to the invention is illustrated in Fig. 3; referring to Fig. 3, a cathode C and first deflecting means in the form of a pair of electrostatic deflecting plates D, D are enclosed within a cylindrical electrode The axis of the electrode E is coincident with the undeflected direction of the electron beam and the cylinder is maintained, in operation, at or near cathode potential. In front of the cylinder E and intersecting the axis thereof at right-angles, is located a rod-shaped electrode F which is arranged perpendicular to the plane in which the electron beam is deflected and is also maintained, in operation, at or near cathode potential.

Five part cylindrical electrodes P1, P2, P2, P4. P5, are arranged in a cylindrical surface the axis of which is parallel to the rod F and is situated substantially mid-way between the rod F and the end of the electrode E adjacent the rod. At least a part of the cylindrical electrode E is located within the cylindrical surface in which electrodes P1, P2, P3, P4, P5 lie. The part-cylindrical electrodes P1, P2, P3, P4, P5 are bounded in part by lines parallel to the axis of the cylinder of which each forms a part. Measuring angles from the centre of the cylindrical surface, taking the direction from which the beam normally enters as axis and measuring in a clockwise direction, the edges of the part-cylindrical electrodes occupy approximately the following positions: P1, 30 and P2, and P3, and 210, P4, 225 and 255; P5, 270 and 330. The part-cylindrical electrodes are all maintained at suitable positive potentials with respect to the cathode. As in the arrangement of Fig. l, the electrons, after deflection by the first deflecting means, enter a saddle-shaped potential field and are deflected in a manner similar to that described with reference to Fig. l, the electrodes by which the saddle-shaped potential field are generated serving as second deflecting means. When the deflecting plates D, D are inoperative, the beam is reflected by the field in the neighbourhood of the rod F and terminates on P1; with maximum deflection by the deflecting plates D, D, the beam terminates on P3, and interniediately the beam falls on P2. Thus the curve showing the relation between the current flowing to P2 and the deflection produced by the deflecting plates D, D has the form shown at X in Fig. 4; the curve starts at zero current for small angular deflection, rises to a maximum current for a certain intermediate deflection and falls to zero at a greater deflection. By suitably shaping electrode P2 (for example by making this electrode of triangular outline instead of rectangular) or by adjusting the current density in various parts of the beam, the characteristic curve X can be madesubstantially para-bolic over a considerable range, and the device is then suitable for use in a variable gain ampli- The gain controlling bias may be applied to the first deflecting means D, D alone or to the low potential rod F or to both the first defiectingmeans-and the rod. Further, the deflecting signals may also be applied to the rod. Instead of using P2 as output electrode, P1 and Ps may be connected together to serve this pur-' The relationship between angular defiec a maximum) in theneighborhood of a boundary (which may be defined by one .or more electrodes) and does not therefore continue beyond this minimum (or maximum).

In the arrangement according to the invention which is illustrated in Figs. 5 and 6, the cathode C is in the form of an elongated shallow rectangular box containing a suitable heater (not shown) and coated on its major surface a with electron- For the sake of description the electron emitting surface will be considered.

emitting material.

as being so disposed that its longer edges extend downwardly into the paper, and the median horizontal line passing normally through the centre cathode lie near the plane. containing the electron emitting surface. Extending between the plates M, M2 in a plane at right angles to the axis of the arrangement-is located a diaphragm MD of length equal to that of the plates M, M2, the diaphragm having a slot therein as shown. The slot is located symmetrically about the axis and extends almost thevwhole length of the diaphragm MD. The width of the slot is considerablyless than the distance between the plates M, M2 constituting the modulating electrode.

On the side of the modulating electrode remote from the cathode a first anode is located; the first anode comprises two plates G, G2 arranged coplaner respectively with and spaced a small distance from the two plates M, M2 of the modulating electrode. Extending centrally between the first anode plates is a diaphragm GD similar to that of the modulating electrode, except that the slot GD of the first anode is somewhat wider than the slot MD of the modulating electrode.

' The width of the plates G, G2 of the first anode In some cases, instead of respectively with and spaced a small distance from the plates of the first anode. The width of the plates ofthe second anode may be about twice the width of the plates of the first anode. A diaphragm HD similar to that in the modulating electrode extends between the ends remote from the cathode of the plates H, H2 of the second anode. Two electrostatic deflecting plates D, D2 are located within-the second anode, the plates lying in planes parallel to and equidistant from 10 the axis of the arrangement and being more remote from the cathode than the centre of the second anode.

Beyond the second anode a rod-shaped electrode F is arranged to lie in a plane extending vertically downwards into the paper through the axis of the arrangement. The distance between the end of the second anode I-I, H2 and the rodshaped electrode F may be somewhat less than the length of the second anode.

Five part cylindrical electrodes P1, P P3, P4 and P5 are arranged in a cylindrical surface about the rod-shaped electrode F as axis, the radius of the cylinder being slightly less than the distance of the rod-shaped electrode from the end nearer thereto of the second anode H, H2. The part cylindrical electrodes are bounded in part by lines passing vertically downwards into the paper, the angles which the planes through these lines and the rod-shaped electrode make with the axis of the arrangementzero direction being that of a line from the rod-shaped electrode towards the cathode-being as follows: P1,

10 and 55"; P2, 70 and P3 and 210; P4, 225 and'290; P5, 305 and 350.

It will be seen that the adjacent edges of P1 and P5 form a slot close to and parallel with the slotin the diaphragm HD in the second anode.

In operation, the modulating electrode M, M2 is used to control the'intensity of the electron beam leaving the cathode and is maintained at a negative biasing potential with respect to the cathode. I The first and secondanodes G, G2 and H, H2 are maintained at suitable positive potentials with respect to the cathode and serve as anelectron lens to cause a narrow elongated or ribbon like beam of electrons to'pass out through the diaphragm HD in the second anode. This beam of electrons may be deflected by applying a deflecting potential difference between the de-" fiecting plates'D', D2;

The rod shaped electrode Fis maintained at or near cathode potential and the electrodes P1.

P2, P3, P4, P5 are maintained at suitable positive I potentials with respect to the cathode.

The arrangement described with reference to Figs. 5 and 6 operates in a manner similar to that of the arrangement of Fig. 3; the arrangement of Figs. 5 and 6 has, however, several imequipotential surfaces conform to coaxial cylin- I ders the common axis of' which isco-incident with the rod-shaped electrode F. The angle between the direction of electrons entering the field within electrodes P1 to P and the direction of the lines of force of this field (which may be considered as the direction in which an electron tends?! to move due to the field at the point considered may be almost as great as 180.

In the arrangement of Figs. 5 and 6 there are three methods of controlling the magnitude of the electron stream impinging on any one of the electrodes P1, P2, P3, P4 and P5. In the first of these, controlling signals are applied to the modulating electrode M, M2 (which, instead of being formed with an apertured diaphragm may contain a grid constructed of wire mesh or the like). In the second, deflecting signals are applied to the deflecting plates D, D2. In the third, controlling signals are applied to the rod-shaped electrode F.

Inter-modulation between two signals may be obtained by controlling the electron stream by the two signals, for example, by applying one signal to the deflecting plates D, D2 and the other signal to the rod electrode F. The term intermodulation is intended to cover arrangements in which a signal is caused to beat with a second signal of different frequency (such as modulating and superheterodyne arrangements), arrangements in which a modulated carrier is caused to beat with an oscillation of the same frequency as the carrier (homodyne reception) and arrangements in which the signal is caused to beat with itself, thereby producing square law rectification.

It is also possible to mix two signals by applying them simultaneously either to the deflecting plates or to the rod-shaped electrode; in this case, when the arrangement is such that working on a parabolic characteristic takes place, modulated signals free from undesired signals are given.

The sensitivity of the arrangement can be further increased by so coupling the deflecting plates D, D2 and the rod electrode F that. as the plates produce less deflection, the rod electrode becomes more negative relative to the cathode. This yields a greater degree of control than that obtained by applying the controlling signal to the deflecting plates only.

In a further modification the electrode system P1 to P5 is replaced by a fluorescent screen held at a suitable positive potential with respect to the cathode so that the point of incidence of the deflected beam is rendered visible, the fluorescent screen acting as a collecting electrode. Such an arrangement can be used as a sensitive electrostatic voltmeter or as a tuning indicator for a wireless receiver, deflection control being effected either by direct or alternating potentials.

It will be appreciated that, in many cases, the current proceeding to the collecting electrode system P1 to P5 does not remain in a focused beam after being deflected by the rod electrode F. In some cases the deflection produced by this electrode may be so sensitive that electrons of the incident beam which have different original emission velocities are deflected through appreciably different angles. In this case the electrons which proceed to the collecting electrode system may be spread out into a spectrum according to their initial velocities. In this case a beam of electrons having a substantially homogeneous velocity may be separated. from the main beam by providing a suitably shaped narrow slit in the collector system.

The arrangement of Figs. 5 and 6 may be adapted for the generation of oscillations in the following manner; collecting electrodes P4 and P5 are connected to a common load impedance, and are coupled to one of deflector plates D and D2. Electrodes P1 and P2 also have a common load impedance, and are coupled to the other deflecting plate. The arrangement is made such that when current passes to electrodes P4 and P5, the beam is deflected by plates D, D2 so that it falls on electrodes P1 and P2, whereupon it is deflected to the right to fall on plates P4 and P5 and so on. An output circuit is coupled to the electrodes P1, P2, P4 and Pa in such a manner that an oscillation is set up in the output circuit. The frequency of the oscillation can be adjusted by variation of the time constants of the external circuits.

Screening grids, which are maintained in operation at positive potentials relative to the cathode, may be provided if desired to prevent variations in the potentials of the collecting electrodes from causing a distortion of the field within the collecting electrodes, and from influencing adversely the operation of the device. When screening grids are employed, means may also be provided for preventing the passage of secondary electrons from the collecting electrodes to the screening grids; these means conveniently take the form of one or more suppressor grids maintained in operation, at or near cathode potential.

It is to be understood that the second deflecting means may take other forms than those described; thus, instead of the single electrode N of Fig. 1 or F of Fig. 3, second deflecting means comprising any desired arrangement of more than one electrode which produces a suitable deflecting field may be employed.

The invention is not limited to the arrangements described by Way of example above, and many modifications within the scope of the appended claims will occur to those versed in the art.

We claim:

1. An electron discharge device having an envelope containing a plurality of electrodes enclosing a space and including anodes for receiving electrons, two of the said plurality of electrodes being spaced to provide an aperture, means for projecting a beam of electrons into the space enclosed by said electrodes through said aperture, a control electrode in the path of the beam of electrons for deflecting said electrons and another-pair of oppositely disposed electrodes adjacent the beam supply means and on opposite sides of said beam and cooperating with said first control electrode for causing the beam of electrons to be shifted from one anode to another during operation of the electron discharge device,

2. An electron discharge device having an envelope containing a plurality of electrodes enclosing a space and including a pair of oppositely disposed anodes for receiving electrons, two of said electrodes being spaced to provide an aperture, means including a cathode for projecting a beam of electrons into the space enclosed by said electrodes through said aperture, a deflecting electrode in the path of said beam of electrons and maintained at cathode potential, 9. pair of oppositely disposed deflecting electrodes adjacent said cathode between which said beam passes, said first deflecting electrode and said pair of deflecting electrodes cooperating during operation of the tube for deflecting the electron beam between said oppositely disposed anodes.

3. An electron discharge device having an envelope containing a plurality of arcuate shaped electrodes enclosing a space, two of said elec trodes being spaced to provide an aperture, a deflecting electrode within said space, means including a cathode for projecting a beam of electrons through said aperture into said space towards said deflecting electrode and a pair of oppositely disposed deflecting electrodes between which the beam passes positioned adjacent the cathode, said pair of deflecting electrodes and said first deflecting electrode cooperating during operation of the tube for deflecting the beam of electrons between the electrodes enclosing said space.

4. An electron discharge device having an envelope containing a plurality of arcuate shaped electron receiving electrodes coextensive with each other and positioned around a common axis to enclose a space, a deflecting electrode positioned within the space enclosed by said arcuate shaped electrodes and at the axis of said space and parallel to said arcuate shaped electrodes, a beam forming device including a cathode for pro jecting an electron beam into the space enclosed by said arcuate shaped electrodes, a connection between the first deflecting electrode and said cathode, and a pair of deflecting electrodes between said cathode and said first deflecting elec-' trode between which the beam of electrons passes.

5. An electron discharge device having an envelope containing a plurality of rectangular shaped electrodes of arcuate cross-section enclosing a substantially cylindrical space, said electrodes being coextensive and parallel to each other, a control electrode parallel to said arcuate shaped electrodes positioned at the axis of the space enclosed by said arcuate shaped electrodes, means for projecting a ribbon like beam of electrons into said space towards said deflecting electrode and including a cathode, a pair of oppositely disposed beam deflecting electrodes adjacent the cathode through which the beam is directed, and a pair of focusing electrodes coextensive with the cathode and with said arcuate shaped electrodes for focusing the beam of electrons between said pair of deflecting electrodes.

6. An electron discharge device having an envelope containing a plurality of electrodes enclosing a space and including a pair of oppositely disposed anodes for receiving electrons, means electrode being connected to said cathode, and a source of voltage connected between the output circuit and said cathode.

'7. An electron discharge devicehaving an envelope containing a plurality of arcuate shaped electrodes surrounding a substantially cylindrical space and including a pair of oppositely disposed anodes, a deflecting electrode within said space positioned at the axis of said arcuate shaped electrodes, means including a cathode for projecting a beam of electrons into said space towards said deflecting electrode and a pair of oppositely disposed deflecting electrodes between which the beam passes positioned adjacent the cathode, said pair of deflecting electrodes and said first deflecting electrode cooperating during operation of the tube for deflecting the beam of electrons between the electrodes enclosing said space, an input circuit connected between said pair of deflecting electrodes and said cathode and an output circuit connected between said pair of oppositely disposed anodes and a source of voltage connected between the cathode and said output circuit, the other arcuate shaped electrodes not connected to said output circuit being connected to an intermediate point on said source of voltage supply, and a connection between said first deflecting electrode and said cathode.

8. An electron discharge device having an envelope containing a plurality of rectangular shaped electrodes of arcuate cross section enclosing a substantially cylindrical space, said electrodes being coextensive and parallel to each other, a control electrode parallel to said arouate shaped electrodes positioned at the axis of the space surrounded by said arcuate shaped electrodes, means for projecting a ribbon shaped beam of electrons into said space towards said deflecting electrode and including a cathode, a pair of oppositely disposed beam deflecting electrodes adjacent the cathode through which the beam is directed, and a pair of beam focusing electrodes coextensive with the cathode and with said arcuate shaped electrodes for focusing the beam of electrons between the first pair of deflecting electrodes, an input circuit connected between the cathode and one of said beam focusing electrodes, an oscillator circuit connected be tween said pair of deflecting electrodes and a connection between the cathode and said oscillator circuit,- anoutput circuit connected between a pair of oppositely disposed arcuate shaped electrodes, a source of voltage supply connected between the cathode and said output circuit, the remainder of said arcuate shaped electrodes being connected to an intermediate point on said I source of voltage supply, and a connection between the first deflecting electrode and said cathode,

CABOT SEATON BULL.

JOIN EDGAR KEYSTON.

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