US2943231A - Storage tube target - Google Patents

Description

STORAGE TUBE TARGET Filed July 17, 1958 Y f. fs E I 12 11 II: i

s ,Hfl'blwl- 1 A i-W n 9 INVENTORS:

Francis .BOULET ATTORNEY United Sees Pachten@ 2,943,231` Patented Jurre l28, 1960v 2,943,231 Y STORAGETUBE TARGET .Francis Boulet and Jacques Toulemonde, France,

assignors to Compagnie Generale de Telegraphie Y Sans Fil, Paris, France v *Y p Filled July"17,`1a`ss, ser. No. 749,103

l Claims priority, application France AugrS, 1957 901m. -(cl. 'als- 12)A erasings of said signal. Theseperiods may,succeed'each` ,other without interruptions Aor be separatedby Vtime intervals. i"

i i 1 For practical technical application purposes these tubes t must present the following characteristics:

(l) lThe signals which have beenstored betweenthe moments O and T of a writing period must be reproduced without distortion of the curve of stored 'signals as a function of time and without relative shift relatively to the initial instant of each period, in one or several reading periods comprised between moments 11T and (Ir-ll T,

n designating an integer.

(2) This previous requirement is necessary for'the accurate reproduction of each signal being rea'd in accordance with the written signal as well as for the accurate comparison of several signals 'read consecutively with or without time intervals between the reading periods. Consequently,each preceding reading must notV modify the value of the charges written on thetarget during the writing period, the stored charges only controlling theY reading without being removed except during a period of intended erasing.

(3) The transfer characteristic mustallow theicorrect rendering of half-tones for a speed of inscription Ycorresponding to a sweeping periodofthe order of a 1,60 of Y a second.

It is an object of this invention to provide an improved storage tube of the above type satisfying the aforementioned requirements.

It is also an object of this invention to provide an iml proved combination of storage tube and circuitry therecircuitry for a tube operating as described above.

Still Ianother object of the present invention is to. providean improved combination of a specific `storage tube structure with a controlcircuit combined therewith ina ,novel manner.

- The tube according to .thehinvention comprises a single ne jctron gun in combination -with a target,` partof which isA constituted by a metallic layer or back plate to `which Edifferent potentials )are applied p during p the writing and ."r'eading periodsffDui-ing the same periods the potentials applied, tofthegil' electrodes remain the same. ,The [gun also comprises an `electrostaticsystem ofV electron "."o'p'tics such that theelectrons emitted by thegun during and reading periods are slow .with secondaryl enissionratillesslthan Iunity and impinging the target at According to `the invention, such tube is also charac terized by the construction of the target comprising a metallic layer or back plate mentioned above on which an insulating layer is deposited, which insulating layer supports ametallc grid oriented toward the gun and serving to deliver the output signal. 'n

In' `one embodiment of the invention the input signal is supplied to the Wehnelt or control electrodeof the gun in a manner :known in the art. In another embodiment of the invention, the input signal is supplied to the metallic back plate of the target.

These and other objects, featuresiandadvantages of the present invention will become more obvious from the followingdescription when taken in connection with the accompanying drawing, whichA shows, for purposes' of I illustration only, two embodiments inaccordance with the ving anode 5, and a second accelerating. anode 6 connected to the metallic layer 7 covering part of the inside of the Wall of enclosure A1.

p i To guide the target impinging electrons in parallel paths the tube includes a plurality of electrodes of collimation 8,'9, 10 either cylindrical or conical, electroderl() being provided with a transversal grid 11 parallel to and coextensive with the target.,

The target is composed of a very thin ne mesh grid -12 displayed on an electrically insulating back plate 13 mounted on a metallic layer 14, grid 12 facing grid 11, i.e., grid 12 is oriented toward the gun.

Vacuum-tight connections are provided in the enclosure 1 forthe purpose of connecting electrodes 2, 3, 4, 5, 6, 8, 9, 10, 11, 12 and 14 to the outside circuits.

A `direct current source 15 provides the potentials applied to-the gun elements. As an example, considering the cathode potential as a reference voltage, a negative potential of 70 volts is applied to the Wehnelt electrode 4, a positive potential of about 400 volts is applied to anode 5, a positive potential Yof about 1000 volts is applied to anode 6.

The heating filament 3 is fed by source 16. A direct current source 17 feeds potentiometerl 18 which supplies collimating electrodes 8, 9, 10 with successlvely `decreasing and adjustable positive potentials.

Said potentials can be, for instance, 500 volts to electrode 8, 300 volts to electrode 9, 30 volts toelectrode 10, the

cathode potential still being considered as the reference voltage.

The negative pole of source 17 is connected to the cathode 2, thus assuming the same potential. Y

The terminal of source 15 which is at the potential of the cathode is connected to switch 19 which, in the solid line position, connectsthe cathode to a potential at -or near ground and in the dotted position, connects the oatha potential of -400 volts for instance;

odej at a high negative potential relatively to the ground, This potential is supplied by. direct current source 20.

`-Itis understood that therepresentationof switch 19 as shown in the drawings is onlyv symbolic and that, in

practice, may correspond to any suitable switching means f 'Ihe target grid 12 is connected through a resistor Z1 to fa terminal of. adirecticurrent sourcerhaving a positive potential of a few volts, 5 volts for instance, relative to ground.

Metallic layer 14 of thetarget is connected to switch 23. yThe previous remarks relative to switch 19-also apply to switch. 23. Inthe solid line positionswitc-h23 connects layer lato ground, or a potential .very,.close thereto, .and in the dottedpositionlayer 14-is connected to direct current source 24 a positive potential of, for instance,v 20 volts relative .to .the ground.

Two. pairs of Adetlecting coils 25, energized by suitable sweeping sources (not shown), are.mounted around the neck of. enclosure 1 to provide respectively ,themagnetic deflection, horizontal and vertical, of electronbeam 26 produced by the gun.

An output :circuit 27 for. the readsignal` isconnected through-condenser .28 to grid 12 at a pointt betweenrgrid .12 .and resistor 21.

'Y Operation Initially, the target is fully erased, i.e., all the points of the surface` of .insulating layer` 13 adjacent to grid 12are at the same potentialsupplied to grid 12'bysource22, namely, 5 volts in the present example.

At the .beginning of the writing period, switch 19fis so oriented that. the cathode is grounded and switch. 23 isso positioned thata` positive potential of 20 volts is applied to layer 14. The writing signal source is connected at 29 to the WehneltV electrode 4 which is; so biasedthat theelectron beam is cutoff in the absence of a signal. Saidvsignal modulates beam 26 which sweeps the surface of grid 12 and insulating layer 13 under the action of deflective coils 25.

The beampaths 26 are rst angularly displaced during their passage through the gun, but are curved lunder lthe action of the co-llim-ating electrodes 8, 9, 10 andgbecome parallel to the axis of ,theA tube in their-last portionof travel.

The design ofv the .electronoptical system is such- Ythat the beamparallelism is `constantly maintained ythrough the entire sweepingperiod. Consequently the electrons pass through grid 11 in a perpendiculandirection; and .are

.impinging grid 12 in a direction perpendicular torthe target whatever thelocation of the impact may be.

The electrons of beam 26 are emitted by thecathode at a zero potential andare partly collected by grid 12 at, a potential of l-l-S volts and directed to resistory21. i Due to this small potential dilerence, they are slow electrons. Thev other beam electrons pass -throughthecmeshes of grid 12 and are intercepted bythe surface ofj'the'-r insulating layer 13 which isfat agreater potential .than-grid 12 since a 20 volt positivepotential has been applied-.to the metal supporting layer 14.

The impactofthe slow electrons on theinsulating layer causes a secondary emissionofelectrons from saidr layer with an emission coecientl lower than unity. Consequently, at a given point ofimpactg'the amount of electrons emitted is smaller than;the amount received,lthe point `of impact being'charged negatively, itsl potential` decreasing (orbecoming less positive) proportionally to the amount of electrons received, proportionally' that is to. thegmodulating signal applied at`-`29.v "Ifhe'circuit potentialswill be preferably chosen so-thaty the maximum' amplitude ofthe modulating inpu-t `sign-alt; lwill bring the-potenti`al ofthe Vpoint on impact to zero.

The sweeping Lvoff the surface v'of layery A:13, by beam -26 during the writing period thus produces on thisfsurface stable enough. As previously the reading beam-arriving at grid 12 is composed of slow electrons: and againimpinges the target penpendicularly regardless of the' locaanimpression of potential corresponding to the variations of the input signal within the limits of said period.

At the end of the writing period, switch 23 is moved to the position connecting the metal layer 14 to ground. The potentials of all the points of surface 13 then decrease 4an amount corresponding to the 20 volt reduction in potential of plate 14. The `points at which the potential did not change during the inscription because the signal was null are again` at a zero potential; the points brought to a zeropotential by action of theA maximum signal are now .,at, a `negative' potentialequal to the luniform potential decrease of plate 14.

'Ihe relative values of potential at the` charged points on surface 13`arenot disturbedby this operation, the signal being thus retained until a reading period is reached. Said period may or may not follow immediately the inscription period. Forlreading, the target is swept with a beam of constant intensity, provided, for example, by applying a signal of fixed amplitude applied at 29 during .the sweeping, the-potentials of all theV electrodes Vbeing .kept at the values they had at the.y end of the writing period.

At yany time of the reading period the pathof the beam -is exactly the same as at the correspondingtime of the writing'period provided the tube supplyingsources are tion of the impact.

However, as `opposed to the situation-fin the writing period, the electrons nowV find behind the grid an Vvinisulating surface having points which are either at a zero -potential in the areas corresponding to a null signalror --vat'a negative potential relatively to the ground, each :negatively charged point having a potential value corre- -sponding to the amplitude of a time related part of the t, signal.

In the areas of zero potentialall-clectrons are collected by grid 12. In the negatively charged areasthe points of the insulating surface which are negatively charged act like Wehneltv electrodes and repel -theelectrons,` the rejected electrons being divided into twoJ portions, the one of which being collected by the grid 12,

tand, the otherportion moving backward and `being col- -lected first by thegrid 11 and then by electrodes 1t), 9,--8. `The ratio iuwhich'the rejected electrons are thus' divided I depends upon the potential value-of thenegative charge at each point, that is to say 4upon the amplitude-of `the recorded signal at the corresponding point. At no time are the electrons collected by the insulating surface; fas a consequence the reading does not alter the Vvalue ofthe potential recorded onV the surface. vSuch reading can in theory be repeated an infinite number of times, and -in :practice itv is only limitedby the erosion oryleakage Vof the .stored potential occurring with time and due to the non-infinite resistivity of the insulating layer, such 1'esistiv1ty being-obviously kept as high as possible.

The electrons collected by grid 12 move through resistor '2.1; the currentin ythis -resistor is thusmaximum and the current diverted by electrodes 11, 10, 9, S is a minimum when the recorded signal is nulland the former current gradually decreases while the latter increases when the amplitude of said signal increases. For acertain value of the amplitude the current in resistor 21 willy become null; the system will-be so designedV that said .value 'of the amplitude will correspond tothe `crest'oi the amplitudes of the signal susceptible to be, brought to the tube input. In this manner, the crest is brought to coincide with an absolutelevel of current in theload resistor.

28 and the ground is equal to the bias of grid ,12,and

considering also thatA said voltage gradually Adecreases .when the current in resistor 21 increases, ,it,is noticed `thatthe voltage transmitted through condenserglsmto 5 the output circuit reproduces exactly the signal which was brought to the input during the writing period, the crest of this voltage being given by the bias of grid 12 determined by source Z2. t

When, after any desired number'of readings, it is de- "siredto erase1the target tohave it ready for a new inscription, the control handle'of switch 19 is moved toward the right `or dottedv position; the control handle of switch .7:3 ybeing kept in the left or solid line position asV it previously was. All potentials of the gun electrodes and of the collimating electrodes are then decreased of the same amount corresponding to the voltage of battery 20 which, according to the described example places the cathode at a potential of4 400` volts relative ground. The Wehnelt electrode receives from input 29 a constant signalwhich allows passage of the beam and the electrons reaching grid 12 at potential +5 v. are fast electrons.

They pass through the grid and hit the insulating layer 13 and sweep it under'the action of the decctive coils 25. VA secondary emission then occurs, originating from layer 13 Withan emissioncoeicient greater than unity. Consequently, at a given point of impact, the amount of electrons emitted is greater than the amount received, `the point is positively charged which destroys the negative charge if previously recorded and brings the potential "to a value near the potential of grid 12 which stays at volts. Finally, all the points of the insulating layer reach the same potential as the grid and the erasing is completed'.`

`If after onepsWeeping operation the erasing is not suficient` it can be Vrepeated,"several times, a new Writing period then followsand the same cycle as previously described occurs. t Y p Y When, according Vto the modified embodiment of the invention, thesignal to berecorded is not applied to Athe 'Wehnelt electrode 4, but modulates the potential of plate 14through the circuit indicated at 29-30', nothing changes in the operations of reading and Vof erasing as previously described. "The mechanism of writing is the only one to be affected-by the modification, however, the result is the same. p lnsuch a modification the control handle of switch 23 stays in the left position and plate 14 stays at a zero potential while the Wehnelt electrode receives such a bias that the electron beam is'emitted from the gun. The constant intensity ofthe beam sweeping the target is adjusted by a suitable Vchoice of Wehnelt bias such that the secondary emission will not alter the storage of charges on the insulatinglayer 1,3 so that the potential of each point of the surface will be brought to a zero value when irnpinged by the constant intensity beam. lf the signal appliedat 2i9f causes the potential of plate 14 to vary, the fluctuation is transmitted` to all the points of layer 13, but at the Vpoint corresponding to the impact of the beam the potential is maintained at a zero value by the beam. Consequently, a-stored potential appears on surface 13 and, at the end of the' writing period, when the plate 14 is again at a zero potential,- the potentials of the-points under'impact when the plate was receiving the signal become negative according -to the corresponding instantaneoushainplitude of the input signal when the respective points were under beam impact. The result is the same as the one obtained by modulation of the beam -by the Wehnelt electrode.

It has been noticed that during writing and reading periods the gun and the collimating electrodes were operated under the same supplied voltages. As a consequence, the reproduction of the recorded information is not affected by the geometrical defects of the tube and of the sweeping. The perfection of the time basis and the stabilization of the supply sources only intervene. It is seen that, as described, the apparatus answers the iirst requirements outlined at the beginning of the specification.

Since, also, the relief of the charges deposited during the inscription appears not to be disturbed by the reading operation the second requirements are also fulfilled.

Finally, since it is possible to have the maximum signal coincide with the threshold of cancellation of the current in the resistance 2'1, it is alsopossible to establish a univocal relationship between each intermediate value of the amplitude and a given current in the resistance, that is `to say to correctly reproduce the half-tones as mentioned in the third requisite.

` While We have shown and described two embodiments in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of y many changes and modifications within the scope and spirit gun, means for applying to said gun electrodes substantially the Vsame constant direct current potentials during both Writing and reading time intervals, said potentials being selected so that the electrons issued from said gun impinge said target substantially perpendicular thereto and provide a secondary emission ratio less than unity, `deilecting means for said electrons for sweeping said target surface, means for applying to said metal layer the Asame direct current potential during both said reading and Writing intervals, and input means connected to said metal layer for producing stored charges -at points on .said' insulatingrlayer corresponding .to the value of an input signal as at the moments the respective points are swept by the beam, and signal output meansV operatively vcoupled to said target grid.

2. A storage tube apparatus as claimed in claim 1,

'further comprising means for varying said direct current potentials applied to said gun electrodes to raise said electron velocity thereby erasing said input signal recorded on said target.

3. A storage tube apparatus for operation successively in input signal writing, reading and erasing conditions,

comprisingin combination a single electron gun having a plurality of electrodes including a control electrode and at leastone collimating electrode, `a target having a metal layer, an insulating layer on said metal `layer and a metal grid on said insulating layer, said grid facing said gun, means for applying to said gun electrodes substantially thesame constant direct current potentials during both Writing and reading time intervals, said potentials being selected so that the electrons issued from said gun impinge said target substantially perpendicular thereto and provide a secondary emission ratio less than unity,

`dellecting means for said electrons for sweeping said target surfacemeans for applying to said target metal layer different direct current potentials respectively in said writing and reading time intervals, signal input meansV coupled to said control electrode, and signal output means operatively coupled to said target grid.

4. Storage tube apparatus as claimed in claim 3, further comprising means for biasing said control electrode to prevent electrons from impinging said target except upon application of an input signal exceeding a predetermined value.

5. A storage tube apparatus as claimed in claim 3, further comprising means for varying the direct current potentials applied to said gun electrodes to raise said electron velocity thereby providing a secondary emission ratio greater than unity at said target for erasing signals recorded thereon.

6. An electronic storage tube apparatus for operation successively in signal writing, reading and erasing conditions, comprising in combination a target electrode composed of a metal back plate, an insulating layer disfposed onsaid back plate ,and a fine mesh metal grid on .said insulating layer, an electron gun including a cath- ;odefa control electrode, accelerating electrodes and col- -limating electrodes for forming a concentrated electron beam-directed toward said target grid, `deiecting means intermediate said accelerating electrodes and said collimating electrodes for deiiecting said beam to sweep the :Wholeasurfacevofrsaid target, means for bringing said =gun:electrodes topredetermined lined potentials relative Yto said vcathode for increasing the electron velocitytalong said accelerating electrodes and decreasing that velocity alongsaid collimating electrodes, a resistor connected to said'ine mesh grid-by `one of its terminals, alow voltage direct current sourceconnected between thesothertterminal of said resistor and ground so that saidngridr is at a lowspositivetpotential relativefto-ground, means `for, selec- :tivelybringing-saidcathode to substantially/aground potential for; both -writing-and readingfoperation. andto.V a highly negative potentialrelative -to ground for` erasing operation thereby --impingingsaid target by` slowfand fast electrons, respectively, means for .selectively bringingfsaid back -plate -to a-potential higher y than said grid potential for Writing operationaand Vto-substantiallyy ground poten- .tial forr'both readingl anderasing operation,input means -connectedlto said control electrode. and output means connectedf across said-resistor.

f7.l Anlelectronic-storagetube apparatus for operation successively inV signalgwwriting, readingand erasing conditions, comprisingein combination a target electrode composed-of a metal baclc plate, an insulating layer disposedon said backplate and a nemesh metal-grid on `said insulating layer, an electron gun including av cathode,

-aY control electrode,-accelerating electrodes and collimatingaelectrodes -forviorming a concentratedelectronbeam -directed-toward said--target-grid, deiiccting means intermediate said acceleratingelectrodes and said collimating electrodes for detlecting said-beamto-sweepthe whole suriaceof -said target, means for-bringing said gun electrodes, to-predetermined xed potentials relative to'qsaid cathode forincreasing' the velectron velocity along said accelerating electrodesvand:decreasing that velocity along said collimating electrodes, a resistor connected to said ne mesh' grid by one of its terminals, a-low.voltage direct l. current-source connected lbetween the other. terminal of said resistor and-ground so that saidgrid isat aV-lovv positive* `potential relative v to l ground,-' means l for. selectively bringing `said cathode to substantiallygroundpotential for bothwritingvand reading operation and to. a highly negative potential relative to yground` for erasing operation thereby impinging said targetbyslow and fast electrons,

respectively, means forfbringingl said back plate 'tory-substantially ground potential, input means connected to said kbackplate and output means connected across saidl resistort on said back plate and a-rine mesh metal grid on said insulating layer, an electron gun including a cathode, a control electrode,l accelerating electrodes and collimating electrodes Afor forming a concentrated beam directed to- .vvardsaid target grid, deecting means intermediate said accelerating electrodes and said collimating electrodes flor deecting said beam to sweep the Whole surface of said target, means for bringing said gun electrodes to predetermined iiXed potentials relative to said cathode for increasing the electron velocity along said accelerating electrodes and decreasing that velocity along said collimating-electrodes, av resistor connected to said line mesh grid -by one of its terminals, a direct current source connected between the other terminal of said resistor and ground, means for selectively bringing said cathode to a first potential withmrespectttoground for both Writing andnreading operation and to a second potential for erasing operatiom saidrst and second potentials being so Vchosen that/,Said target is struck by slow and fast electrons, respectively, andthe ,secondary electronl emission ratio of said insulating layer is s mallerand-greater than unity, respectively.

l9.,-An electronic storage tubesapparatus for operation successively in signal writing, reading Aand erasing conditions,` comprising in combination a target electrode composed of; a metal back plate, an insulatinglayer disposed onsaid back-plate anda tine mesh metalfgrid on said .insulatinglayen an electron., gun including a cathode, a v control electrode, accelerating electrodes and collimating electrodes for forming alconcentrated beam directed toward said target grid, deflecting means intermediate said acceleratingelectrodes y-andv said,V collimating 4electrodes fon deflecting saidbeamV to lsweep the whole surfaceof Said target, --means for bringing said gun electrodes to predetermined xed potentials relative to said cathode for KJincreasing the electron .velocity along said accelerating electrodes and decreasing that velocity along saidcollimating electrodes, a resistor connected to said tine mesh rgrid-by one of its terminals, a direct current source connectedbetween the` other terminal of said resistor and ground, means ,for selectively bringing said cathode to a iirstrpotentiallwith respect, to ground forbothvwriting andreadingoperation and to afsecond potential Lfor erasing-operatiomvsaid Ifirst/ and secondnpotentials being so Achosen that said target is struck by slow and fast electrons, respectively, and` theJ secondary electron emission ratio of said insulating layer is smallerand greater` than unity, respectively, means `for applying an input signal to said apparatus during said writing operation for producing,by means of said slow electrons, stored Acharges at points on said insulating layer Ycorrespondingto the value of the input signal at the moments the respective points are impinged by the beam, andmeans for abstractingan output Vsignal from said gridrduring said reading opera- Vtion.

References Citedl in the file of this patent UNITED STATES PATENTS 2,706,264 Anderson ..Y Apr. 12, 1955 2,844,722 Hines July 22, 1958 2,863,090 Young Dec.Y 2 1958

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