US2459724A - Astatic cathode-ray tube - Google Patents

Description

Jan. 18, 1949. SELGlN 2,459,724

I ASTATIC CATHODE-RAY TUBE Filed Nov. 27, 1946 2 Sheets-Sheet 1 SIIGNAL SOURCE UTILIZ TION 1|||n| f INVENTOR PAUL J. SELGIN ATTORNEY Jan. 18,1949.

Filed Nov. 27, was

2 Sheets-Sheet '2 FIG.2

SIGNAL SOUR-OE UTILIZATIO CIRCUIT fl3 r48 J 1 jl l lk 38 INVENTOR PAULJSELGIN ATTORNEY Patented Jan. 18, 1949 ASTATIC CATHODE-RAY TUBE Paul J. Selgin, Fort Wayne, Ind.,-assignor, by mesne assignments, to Farnsworth Research Corporation, a corporation of Indiana Application November 27, 1946, Serial No. 712,566

This invention relates to cathode ray tubes and particularly to devices of this character which are capable of operating independently of the influence of stray fields.

Cathode ray tubes wherein one or more electron beams are deflected over a target electrode have been used for many purposes such as signal modulation, signal detection, etc. Usually in tubes of this character the target electrode has either a particular form or consists of a number of separated parts arranged in a particular manner and over which the one or more electron beams are deflected. Depending upon the amplitude of such deflection, a signal voltage is developed in an output circuit coupled to the target electrode which is representative of the signal by which the beam deflection is controlled.

.It is well known, however, that such devices do not always reproduce signals in the output circuit which are completely free from distortion. Usually the greatest signal distortion is caused by a spurious deflection of the beam as a result of its being subjected to stray fields. It is not always possible, and generally it is not convenient, to shield the tube and the electron beam from stray fields.

It is an object of the present invention, therefore, to provide a novel deflection type of cathode ray tube which is capable of operating entirely independently of stray fields whether they are produced within the tube or exterior to it.

In accordance with the present invention, there is provided a cathod ray tube having facilities for generating at least one pair of electron beams. The tube also includes a deflecting system for each beam. Both deflecting systems are subject to control by the signal which it is desired to reproduce in the output circuit. The deflecting systems are so constructed and arranged that signal-controlled deflections of the two beams of each pair are in opposite senses. The tube also includes a target electrode system for each beam. The target electrodes are so constructed and arranged that signal-controlled deflection of the two beams of each pair influences each target electrode in the same manher. The target electrodes are both coupled to the same output circuit in such a manner that they both contribute to the output signal.

For a better understanding of the invention, together with other and further objects thereof, reference is made to the following description, taken in connection with the accompanying drawings and its scope will be pointed out in the appended claims.

7 Claims. (Cl. 250-27 In the accompanying drawings:

Fig. 1 is a diagrammatic illustration of one illustrative embodiment of the invention; and,

Fig. 2 is a diagrammatic representation of another embodiment of the invention employing a specific form of electron beam and an electron multiplier.

Referring now to Fig. 1 of the drawings, the cathode ray tube is provided with evacuated envelope I. Atone end of the tube, within the envelope, there are provided two electron guns 2 and 3. It will be understood that each electron gun is provided with a cathode sourceof electrons and is capable of developing a stream of electrons and for directing the electron stream toward a target electrode. In'the present case, the target electrode associated with the electron beam 4 comprises a pair of plates 6 which are separated vertically from one another by a relatively narrow gap. Also, there is provided for the electron beam 5, a target electrode comprising a pair of I plates 1 which are separated vertically from one another by a relatively narrow gap. The target plates 6 and i also are separated horizontally from one another. The spacings between the target electrode plates provide electrical insulation among the plates. The target plate spacing may be effected by an air gap as shown herein, or by any other suitable insulating structure as desired.

In order to obtain optimum results from such a device, it is preferred to couple the target electrodes differentially to the output circuit. The upper and lower plates of each set of target electrodes are cross-connected as shown, and are connected to the terminals of an output circuit impedance device such as a resistor 8. The midpoint of the output circuit resistor is connected to the positive terminal of a source of unidirectional voltage such as a battery 9. The negative terminal of thisbattery is connected to the cathodes of the electron guns 2 and 3, as-

indicated, so that the target electrodes are at all times maintained at a positive potential with respect to the cathode electron sources. The terminals oi the output circuit resistor 8 may also be coupled to any desired utilization circuit ill.

Between the electron guns and the target electrodes there is mounted within the tube envelope a deflecting system for each of the electron beams i and 5. In the present instance; these de fleeting systems consist of a pair of horizontal plates ll associated with the beam 4 and a pair 7 of horizontal plates l2 associated with beam 5.: Upper and lower ones of the two pairs of the detrodes 6 and 1 respectively. A signal voltage of. one polarity, derived from the source 13, which, when impressed upon the deflecting..:plat'es? [2,"

causes upward deflection of the beam 5, will, by

reason of the cross-connection :of. the platesilt and I2 cause a downward deflection of the beam.

4. If the target electrode plates 6 and I are the strength of the stray field, it is seen that the total collection of the electrons by the lower plate 6 and the upper plate 1 on the one hand, and the upper plate ii and the lower plate 1 on the other hand is substantially the same as in the case where no stray field exists. The signal voltage developedin the output resistor 8 then is substantially. identical to the signalvoltage which would be developed in the absence of a stray field.

Obviously, in order to neutralize a device of this character against the efi'ects of stray fields,

it is not'essential to employ a target electrode of closely spaced, as in the casewheresclass -A operation is desired, the upward deflection. of the. beam 5 will cause fewer electrons to strike the lower plate 1, and more electrons to strike the upper plate 1. At the same time the downward deflection of the beam 4 causes the upper'plate 6 to collect fewer'electrons,"andthe lower plate 6 to collect more electrons: The described crossconnection of the targetzelectrode plates-connects both of the plates receiving'more electrons to the upper terminal of the resistor. 8 and connects the two plates receiving fewer electrons to the lower terminalof the resistor '8. Thus, it is seen that in the output 'circuit,'inasmuch' as .all signalproduced variations in the electron collection, by

these plates, is additive'in the output circuit.

It will be obvious that'a signal'voltage of opposite polarity-derived from the source 53 will cause. the downward 'deflectiomof the beam 5 and the, upward defiectioniofthe beam 4, whereby an increased. numberof electrons are caused to flowto the lower terminalof the resistor 8 and a decreased number to the upper terminal:

Theforegoing description. of. the operation of the illustrated device is predicated on .the' absence of anystray. fields-which might affect'the deflection of theelectron ,beams.

assumethat. the electron beams-are exposed to the influence of, a. stray field which.causes 'both' beams to be deflected upwardly. Ifnowa signal. voltage. isimpre'ssedmpon the deflection plates quently, the. increase. inthe. electroncollection by the lower plate! and the-.correspondingdecrease in the electron collection; by. the ,upper. plate 1 is less..by..the .degreeof. difference in the strength. of. the deflecting. field produced. by the. deflecting plates.l2 and the strengthofthestray. field.. On..the2 other..hand,,the.'.upward. deflection of the beam .4; is greater in. an. amountequal. .to the. sum ofv theistrength .of thefield produced by the defiecting'electrodes. LI and. the strength of the-stray-field;v .In this casethe increase inthe' electroncollection by theupper plate 6 andthe corresponding. decrease. in the. electron collection inthe-lower plate 6 is greater than, in the .case where. no stray fieldexists. Inasmuch as the diflerencesinthe electron collectionsby theltarget.

electrodes 6 and 1 are directly proportional to Inorderto appre: ciatethe advantage of the present arrangement;

the particular form illustrated and described. A modification of the target electrode of Fig. 1, for exampla'is one having only an upper plate asso- 'ciated with one electron beam and only a lower shown a modified embodiment of the present invention. The cathode ray tube is provided with an evacuated envelope I l. Adjacent one end of' thetube'envelope isan electron-emitting cathode l5 of elongated form extending generallyin a vertical direction. The cathode may be c0ndi-' tioned for the emission of electrons in any conventional manner, not shown, such as by heating,

eith'erdirectly or indirectly. In front. of the cathode there is located electrode 16 which is provided with two substantially circular aper-- tures 1'! and 23 in alignment with the cathode; These apertures, when properly energized, in a manner to be described, function to form two pencil-like electron beams 19 and 2| from the electron emission by the cathode.

The tube also is provided with a deflecting systemfor controllingthe direction of the two electron beams. The deflection system in this case comprises upper and lower plates 22 'and'23, respectively, arranged in two spaced substantially horizontal planes. The deflecting system also includes a box-like electrode 24 having upper and lower flat surfaces spaced from, andfacing,

respectively, the upper and lower plates 22 and 23. These electrodes are so locatedrelative to the apertures H and it, that the electron beams it and Zi are directed respectively in alignment between the electrodes 22 and 24 on the one hand and electrodes 23 and 24 on the other hand. Also, there is provided a plurality of focusing electrodes, such as a first pair of rods 25 and 26 associated-with the upper deflecting system and a second pair of rods 2? and 28 associated with the lower deflecting system. The respective rods of each pair are mounted adjacent the longitudinal" edges of the deflecting plates and are generally coextensive therewith. When these focusing electrodes are'suitably energized, in a manner to be described. the penoil-like electron beams l9 and 21' are formed respectively into electron sheets 29 and 3i whichlie generally in two horizontally placed planes, approximately coinciding with the central axes 'of' the two deflecting systems.

Adjacent the "right hand end of the tube en-" velope M, there is provided a target electrode structure. In the present illustrative embodiment of the invention, this structure comprises'a two-stage electron multiplier. Associated with the electron sheet 29' and in substantiallyum' deflected alignment therewith, there is provided a rod-like secondaryelectron-'emissive electrode Similarly, there is provided asecondrod like secondary electron-emissive electrode 33 in substantial alignment with the undeflected electron sheet 3|. In back of the electrodes 32 and 33, there is mounted a substantially vertical plate electrode 34, the front surface of which is conditioned for the liberation of secondary electrons. The target electrode structure additionally includes a pair of rod-like electron collecting electrodes 35 and 36 located respectively, above and below the secondary electron emitting electrodes 32 and 33. Another rod-like electron collecting electrode 31 is mounted substantially mid-way between the secondary electron emitting electrodes 32 and 33.

The electrode structures of the tube areconnected to suitable sources of voltage and to the signal source and utilization circuit in the following manner. There may be provided a source of unidirectional voltage, such as a battery 38. In order to suitably dis'lribute the voltages derived from this battery among the various tube electrodes, there also may be provided a voltage divider 39 comprising a series connection of a plurality of impedance elements, such as resistors.

The cathode I5 is connected to the negative terminal 4| of the voltage divider and the beamforming electrode 16 is connected to a more positive point 42. The upperand lower deflecting plates 22 and 23 are connected together and to terminal of which is connected to the center deflecting electrode 24. An intermediate, preferably the center, point of the input resistor 43 is connected to a still more positive voltage divider 28 are connected to a higher positive potential point 45. The secondary electron emitting rod electrodes 32 and 33 are connectedto a still more positive point 46 and the secondary electronemitting plate 34 is connected to an even higher positive potential point 47. The upper and lower collecting electrodes 35 and 36 are connected together and to one terminal of an output resistor 48, the other terminal of which is connected to the center collecting electrode 31. The resistor 48 is provided with an intermediate tap, preferably at the mid-point thereof, which is connected to the positive terminal 49 of the voltage divider 39. 3

A source of signals 5! is connected to the terminals of the input resistor 43 so that suitable voltages, varying in accordance with the signals, are impressed upon the beam-deflecting system. A utilization circuit 52 is coupled to the terminals of the output resistor 48 so as to receive the signal voltages derived from the electron collecting electrodes. Referring now to the operation of the modifi: cation of the invention shown in Fig. 2, consideration first will be given to the formation of the electron beam. The electrons emitted by the cathode l5 are drawn through apertures IT and I8 of the'plate It by reason 'of'this plates more positive potential relative to the cathode. The electrons emerging from the apertures H and I8, are in the form of relatively small pencil-like beams l9 and 2|. These beams are directed respectively through the upper and lower sets of deflecting elements. connection of the deflecting elements and the focusing rods adjacent thereto, all of the deflecting electrodes are at negative potentials relative to the positive potentials of the focusing rods 25, 26, 2'1 and 28. Each of the electron beams It By reason of the described i and 2! therefore, in passing through the deflecting system, is spread horizontally under the influence of the positive focusing rods. As a consequence, these beams emerge from the deflecting system as relatively thin horizontal electron sheets 29 and 3!.

The impingement of the electron sheets 29 and 3! respectively, upon the econdary electron-emitting electrodes 32 and 33, efiects the liberation of a multiplied number of secondary electrons. These secondary electrons are drawn toward the plate electrode 34, the impingement upon which produces a greater number of secondary electrons. These secondary electrons in turn are drawn to, and collected by, the electrodes 35, 36 and 3?. The numbers of electrons collected by these respective electrodes aredependent upon the manner in which the electron sheets impact the target electrodes 32 and 33. For example, the deflection of the electron stream 29 upwardly, causes a greater number of electrons to be collected by the collecting electrode than by the center electrode 31. Similarly, a downward deflection of the electron stream 3! causes the lower collecting electrode 33 to receive a greater number of electrons than are received by the center electrode 3'1. Conversely, a downward deflection of the electron stream 29 and an upward deflection of the electron stream 3!, causes a greater one terminal of an input resistor 43 the other number of electrons from the respective streams to be collected by the central electrode than by either the upper or lower collecting electrodes 35 and 36 respectively.

The deflections of the electron stream are unpoint 44. [The hne f0cusing rods 25 26 21 and der the control of the signals derived from the source 5!. Assume that a given signal derived from this source is impressed upon the input resistor 33 in such a manner that the upper and lower deflecting plates 22 and 23 respectively,

,w, are of positive potential relative to the center electrode 24. In this case the electron stream 29 is deflected upwardly and the electron stream 3i is deflected downwardly. As a result, the collecting electrodes 35 and 33 receive from the respective beams, more electrons than are received by the center collecting electrode 31. A signal voltage is developed in the output resistor 48 of such a character that the right-hand terminal of the resistor is more positive than the left-hand terminal.

If now a signal of opposite polarity, derived from the source 5!, is impressed upon the input resistor 43, the center deflecting electrode 24 is positive relative to theupper and lower deflecte ing plates 22 and 23 respectively. In this case the electron stream 29 is deflected downwardly and the electron stream 3! is deflected upwardly. The central collecting electrode 37 therefore, will receive more electrons from the two streams than the upper and lower collecting electrodes 35 and 35, respectively. A voltage of opposite polarity is thereby developed by the output resistor 48.

As in the previously described embodiment of the invention, the deflection of the electron beams in opposite directions under the control of intelligence signals renders the device substantially independent of the effects of stray fields. Any stray fields which may cause deflection of the electron beams will move the beams in the same direction. In view of the previously given detailed description of the manner in which a tube of this character operatesto eliminate distortion of the signals derived therefrom, it should be obvious that in the present instance the beam deflections from fields other than those produced under zthe contnoliof the, input signals. are. substantia-lly nullified: in the output circuit.

W'hile-there-has been. describedwhat is at present-considered'the preferred embodiment of theinvention itwill be obvious to those skilled in the art that various changes and modifications may be made thereinwithout departing from the invention, and it is, therefore, aimed in the appended claims to cover all. such changes and modifications as. fall within the true. spirit and scope of the invention.

What is claimedsis:

1. Signaling. apparatus comprising, a source of signals an output circuit forsaid signals, a cathode ray-device comprisingmeans for producing twoelectron beams, deflecting systems located adjacent to the'respectivepaths of said beams and connected to saidsignal source in a manner to causesaid-beains to be deflected in response to said signal to the same degree butin opposite senses, an electron collecting system including two targets-electrodes. located in the respective paths of said electron beams, and means coupling said target electrodes differentially to'said output circuit in-a manner 'whereby'signabpro duced variations. in'the electron collection by said electron collecting system is" additive in said output circuit.

,2. Signaling apparatus comprising, a source of signals, an ouput circuit for said signals, a cathode ray devicecomprising means for producing two independent electron beams, two deflecting systems located adjacent to the respective paths of saidbeams and connected in opposite polarity to said signal source, whereby to cause said beams to be deflected in response to said signals to the same degree but in opposite senses, and two electron. collectingsystems locatedin the respective pathsof. said electron beams and connected in opposite polarity to said output circuit, whereby signal-produced variations in the electron collection by saidcollecting systems is additive in said output circuit.

3. Signaling apparatus comprising, a source of signals, an output circuit -for said signals, a cathode ray device comprising two electron guns for producing two independent electron beams, two pairs of deflecting-plates. similarly-located adjacent to .the respectivepaths of said beams and connected in opposite polarity to said signal source, whereby to cause saidbeams to be deflectedin response to said signals to the same degree butin opposite senses, and two pairs of co-planar. electron collecting anode plates located inthe respective paths .of said electron beams and connected in opposite polaritytosaid output circuit, whereby signal-produced variations in the electron collection'by said anode plates is additive. in said output circuit.

4. Signaling. apparatuscomprising, a source of signals, anoutput circuit for said signals, a cathode ray. devicecomprising two electron guns for. producing two independent electron beams, two pairs of deflecting plates horizontally located adjacent-tothe respective pathsof said beams and .connectedin opposite polarity tosaid. signal source, whereby, tocause-said beams to be deflected vertically in response to said signals to the same degree.but.-in.opposite senses, and two pairs of electron collecting anode plates vertically located in the-respective paths of said electron beams. and connected in opposite. polarity to said output circuit,v whereby signaleproduced. variations in the electron collection by. saidcanode plates is additive insaid output circuit.

5. Signaling apparatus comprising, asourceof signals, a utillzationcircuit for said signals, a cathode ray device comprising means for producing two electron beams, two deflecting systems located adjacent to. the respective. paths of. said beamsv and connectedin opposite polarity to said signal source, whereby to cause said beams to be deflectedoppositely in response to said signals, and two secondary electron-emissive electrodes located in the respective paths .of said electron beams and coupled in opposite polarity to said utilization circuit, whereby thesignal-controlled variations in. the deflections of said beams is additive in said utilization circuit.

6.v Signalingapparatus comprising, a source of signals, a utilizationcircuit for said signals, a cathode ray device comprising means for producing two electronbeams, two. deflecting systems comprising three plates horizontally locatedad jacent to the. respective paths of said beams with the center one of said plates being common to both deflecting systems, means for connecting, the upper and lower plates of each of said deflecting systems in opposite polarity to said signal source, wherebyto cause said beams to be deflected vertically in response to said signals to the same degree but in opposite senses, a secondary electron-emissive target electrode located in the path of each of said electron beams, two electron collecting systems comprising three electrodes, said collecting systems being coupled in opposite polarity to said utilization circuit, whereby signal-produced variations in the electron collection by said two collecting systems is additive in said utilization circuit.

7. Signaling apparatus comprising, a source of signals, a utilization circuit forsaid signals, a cathode ray device comprising means for producing two electron .beams, two deflecting systems located adjacent to the respective ,paths of said beams and connected in opposite polarity to said signal source, whereby to cause said beams to be deflected oppositely in response to said signals, two focusing systems located adjacent to the respective deflectingsystems and energized in opposite polarity to said deflecting systems, whereby to convert said electron beams into electron sheets, and two target electrodes located in the respective paths of said electron sheets, said target electrodes each having one dimension at least as great as the width of said electron sheets and being coupledto said utilization circuit in a manner whereby signal-produced variations in the electron impingement upon said two target electrodes is additive in said utilization circuit. v

PAUL J SELGIN.

" REFERENCES CITED The following references are. of recordin the file of this patent:

UNITED STATES. PATENTS Number Name Date 2,170,944 Glass et'al Aug. 29, 1934 2,183,634 Zoorykin Dec. 19, 1939 2,276,359 Van Arderne Mar. 17, 1942 2,402,758 Leverenzy June 25, 1946

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