US2686275A - Art of storing or delaying the transmission of electrical signals - Google Patents

Description

Aug. 10, 1954 M COHEN 2,686,275

ART 0F STORING OR DELAYING THE TRANSMISSION OF ELECTRICAL SIGNALS Filed March 31, 1951 INVENTOR Patented Aug. 10, 1954 UNITED STATES PATENT OFFICE ART F STORING 0R DELAYING THE OF ELECTRICAL TRANSMISSION SIGNALS Martin J. Cohen, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware 9 Claims.

This invention relates to improvements in the art of storing or delaying the transmission oi electrical signals.

The prior art offers many examples of storage tubes of the electro-mechanical and electrostatic varieties. Irrespective of the advantages claimed for a given tube it may be said generally that it possesses certain disadvantages inherent to its class. Thus, if the device is of the electromechanical variety, its ability to handle electrical signals without distorting them is adversely affected by the necessity of translating the signalsinto mechanical vibrations, and back again. On the other hand, if a storage device is of the electrostatic type its ability to maintain a number of signals in storage is limited by the leakage characteristics of the material (e. g. mica) upon which the signal-bearing electrostatic charges are stored.

Accordingly, the principal object of the present invention is to obviate the foregoing and other less apparent objections to electro-mechanical and electrostatic types of storage devices and to provide a novel, relatively distortionless, method of and apparatus for storing electrical signals.A

Another object of the invention is to provide a storage device having an adjustable storage or delay time, and one capable of handling a multi plicity of discrete signals withouty cross-talk or leakage.

Stated generally, they foregoing and other objects are achieved in accordance with the invention by producing small groups of ions, say at one end of a gas-filled tube, and then collecting the ion groups at the other end after they have travelled the length of the tube. The delay due to the transit time of the ions, and consequently the memory or delay time of the tube, depends upon the choice of operating parameters such as; applied voltages, nature and pressure of the transit medium, etc.y It may range from a fraction .of a second to several seconds, or even longer if output signals are fed back into the input in a continuous process.

The invention is described in greater detail in connection with the accompanying single sheet of drawings wherein:

Fig. l is a longitudinal section of a storage device constructed in accordance with the principle of the invention and including an evacuated gun-chamber and a gas-nlled storage chamber;

Fig. 2 is a longitudinal .section of the storage ory ionization chamber of the deviceof Fig. 1,

said' storage chamber containing analternative` form of output electrode-assem'bly';v

Fig. 3 is a side view of a tube, cut away in part to show a schematic presentation of the electron gun, and a longitudinal section of the ionization chamber which affords many simultaneous corridors of information; and

Fig. 4 is a fragmentary View, partly in section, showing an alternative output electrode assembly for the tube of Fig. 3.

The tube shown in Fig, l comprises a gas-tight envelope II divided into a first chamber i3 and a second chamber I 5 by an hermetically sealed-in wall I 'l with an electron permeable window I9.

The Wall I1 is constructed of copper so that it may serve as an electrode offering a conductive path to ground. The electron-permeable window I9 is of the Lenard type, i. e. it holds a vacuum but is permeable to an electron beam. It may comprise a thin sheet of aluminum foil. The first chamber I3 is evaculated and contains an electron-beam source comprising: an electron emitter 2! a control electrode 23, and an accelerating and focusing electrode 25. These members are so positioned that the electron beam produced by them is directed toward the electron permeable window I9. The second chamber I5 contains under pressure a pure gas (argon is suitable), and has a collector electrode 2'! situated at the opposite end from, andy directly in line with, the electron permeable window I9. The pressure of the gas is in the neighborhood of one atmosphere, but it may be varied over wide ranges consistent with other properties and functioning of the tube.

The electron beam from the iirst chamber i3 travels at suicient velocity to pass through the window I9 into the second chamber I5 and, by knocking electrons from their orbits within individual gas molecules, produces positive ions in the immediate vicinity of the Window i9. The extent of this ionization is explained more fully below under the heading, Transit Time, Diffusion, etc. The electrons which the beam drives out of the gas molecules are collected on the electrode I1, and the resulting positive ions drift in a substantially straight path through the gas toward the collector electrode 21 under the influence oi an electro-static eld set up by a source oi variable potential, represented by the battery 26, between the wall electrode I1 which .1 is at ground potential and the collector electrode 2l' which is at a negative 10,000 volts. The time that it takes these ions to complete their transit through the gas depends upon variable factors and may be calculated by formula in a manner which will be more fully explained below. It is this drift time which introduces into the tube the delay that makes it useful as a memory device. The electron beam which creates the ions in the chamber l5 is controlled by input signal voltages applied to the control grid 23 of the beam source in chamber I3.

Standard techniques are used to detect the arrival of ions at the collector electrode 2l' and derive output signals therefrom, e. g. differentiating circuit external to the tube and not shown in the drawing.

Instead of the single electrode shown in Fig. 1, Fig. 2 shows the combination of a screen electrode 29 and a solid electrode Si as a signal pickup means. The screen electrode 29 is located slightly in front of the solid electrode 3l in the path of approaching ions. 'Ihe output from the tube is taken across the resistance 42 in the circuit connecting these two electrodes. This circuit includes a variable source of potential indicated by the 1000 volt battery lili which keeps the solid electrode 3l more negative than the screen electrode 29. While the ions are in the area between the electron permeable window I9 and the screen electrode 29 there is no signal current in this circuit, but when ions pass through the region between the screen electrode 29 and the solid electrode 3i current flows in the circuit between them and a signal voltage appears across the resistance 42.

The tube shown in Fig. 3 comprises an evacuated compartment 28 and a gas-filled compartment 30. 'I'he evacuated compartment 28 has an electron beam source comprising: an electron emitter 32, a control electrode 3G and an accelerating and focusing electrode 3E which function in conventional manner to produce an electron beam 38. The two compartments 28 and 30 are separated by a target electrode 33 which comprises a light-transparent supporting member 35 with a fluorescent coating 3l on the side presented to the beam 38 and a photo emissive coating 39 on the side presented to the ionizable gas. Deecting elements 5,! associated with the evacuated compartment 28 cause the electron beam 38 to scan the fluorescent surface 3l of the target 33.

Instead of the single collector electrode shown in Figs. 1 and 2, this tube has a plurality of collector electrodes 43. Six are shown but any convenient number may be used within limitations which are discussed below under the heading, Multiplicity of information.

As the electron beam 38 scans successive areas of the phosphor side 3l of the target electrode 33, it causes the phosphor immediately under electron bombardment to give off light. This light passes through the transparent supporting member 35 and when it arrives at the photo emissive side 39 of the target 33 it causes the photoemissive material in that area to emit electrons which attach themselves to the gas molecules in the immediate vicinity, thereby creating negative ions. These negative ions then drift in separate groups toward the collector electrodes 43 which are at a positive 10,000 volts with respect to the target electrode 33. As the electron beam 98 scans across the target 33, many such paths or corridors are activated. The maximum number of corridors available depends upon crosstalk due to lateral diffusion of the ionized gas. This lateral diffusion is discussed below under the heading, Multiplicity of information.

Because ions travel in a straight line toward the closest electrode of opposite potential under the influences of a uniform potential eld, this type of structure can be utilized to provide any number of corridors of ion travel and consequently of electrically stored information.

The field in which the ions travel is kept uniform by means of a potential gradient device 45 comprising alternate electrically conducting rings 4l and resistance elements 49. The effect of this device is to divide the potential drop between the target electrode 33 and the collector electrodes 133 into even steps and keep straight the lines of potential gradient between the target 33 and the collector electrodes 43. The rings 41 are embedded into the walls of the chamber 30 so that they have a surface exposed to the interior. An alternative method of securing an even distribution of potential is to coat the inner surface of the envelope with a high resistance conductive material.

rThe arrival of ions at the collector electrodes i3 may be detected by a diierentiating integrating circuit, as mentioned in connection with the description of Fig. 1. Alternatively, a take-off cathode ray beam may be used, as shown in Fig. 4. In the latter case, the electrically separate electrodes 5i upon which the ions are collected are individually sealed into the glass wall 53 of the gas-filled chamber with an exposed surface on each side of the wall. Sealed against this wall 53 is an evacuated envelope structure 55 containing an electron gun 5l, defiecting means 59 and a signal electrode 6l. Following a known technique in the pickup tube art, the electron beam 62 travels from the gun 5l and bombards the target or wall 53 at a voltage above rst crossover. The eiect is to raise the potential of the elements 5| to that of the screen 6l (10,000 volts). Once the elements 5l are so charged, the entire beam 62 is reflected back to the screen 0i. ts electron content is aflected by the negative ion charges which have accumulated on the individual electrodes 5|. In the circuit between the signal electrode 6l and ground is an output resistance Sli. The changes in electron content of the beam 62 as it is intercepted by the electrode 5i and conducted to ground cause voltage variations across the resistance 64 and become the signal output of the tube.

Multiplz'city of information The amount of information which can be stored per electron beam in a tube of the type shown in Fig. 3 is limited by three factors: (a) the number of storage paths available, (b) the amount of information which can be stored in each path, and (c) the number of individual ion groups which the scanning electron beam can start down the separate corridors of the tube during the transit time of an ion between electrodes. In this specication the storage paths (separate parallel paths of ion travel) are referred to as corridors and each time or space division capable of carrying information Within a corridor is termed a channel As previously mentioned, ions travel in substantially straight lines to their collector electrodes making possible a great number of parallel corridors in a single tube. One limitation on the number of corridors which is practicable is a possible lateral difusion of the ions in transit. This makes some physical separation between neighboring circuits necessary to prevent crosstalk. Co-axial magnetic iields (not shown) around the tube, or insulating partitions within the tube (also not shown) can be used to cut down on the physical separation necessary between corridors. As demonstrated later in the specification under the title, Transit .TimemDiiusiom etc., however, even without the co-axial "elds and insulating partitions suggestedabove, the physical separation .necessary to: prevent crosstalk is not too serious a limitation. In argon, for example, aanion will;.cliff-usefoniy --.'036 cm. in .01 second which=is a vpracticable transit time between electrodes.

The number of separate items of information '.'Whiohfican be written into a tube ofzthe type shown in Fig. 3 isa function of the transit, or drift time, of an ion in the tube, and the scanning speed of the electron beam which produces the ions. Theseparateitems can'v beufwritten in separatecorridors or they .can be. channeled into 'a vsingle, `or relativelyfew corridors. 'Inany 'event their number, ior a'given scanning speed,

can be :calculated ,from the formula:

where n=the number of items of informationpossible. `t=thel transit time of ions travellingbetween electrodes down a corridon (This `-`istthe effective time available `for laying Vdown or =writing :signals l'in a .total number oiifcor- .;ridors, because there .is u no point iin ihaving A.more corridors -than can Vvbe :used A.simultaneously.)

t=.'0l is selected asa-"desirable delay time. fw1=thettime it takes the"fwritingelectron beam to ionize suflicient molecules of gas within a corridor` to produceasignal.

w1=025 106- is convenient to. (secure. a .satisfactory band width and .anamplesignalto-noise ratio at the collector electrode. It is also consistentwithaasuitablessize for the instrument and accepted scanning techniques. w12=the time intakes the'writingfelectron beam to traverse the .space between corridors (or the spacing betweenppulses within a corridor). w2=0-5 106 is selected as representative, if, :in order to get #adequatefseparationythe -space'between corr-idorsfr pulses) Iis to equal approximately'the .width of-la corridor, or *the time it takesto write a signal.

When the values suggestedfabove.-arecapplied .to s theformula,

or .10,000 vpossible .items `of :information :If .the 10,000 .separate items of informatien .referred to above .y are 'i to be carried in separate corridors within the tubetthe question oi lphys-ical sizeof :the tube ,required arises, 'This question involves. such considerations 'as the dian-ieterro'f the .ion lgroups `.as :they s are initially f 'createdl'by the writing electron beam and the extent to which 'they diffuse in transit .down fa corridor. The 4electron beamsspot area'` onfthe gtargetH33 maybe .assumedto be vapproximately i008 lsq.: cm. (Cf Spangenberg, Vacuum .'Iubes, :page 11427..) 'As a. result, lan iongroupfas itstartathrough the drift. mediuml is 5.008 It, as: issnientionedaabove, ions willrdiffuse. only `about .036vc1n. in alltr-ansit time/of :0l seconoLithen ilxsqcm. loi-=area wculii provideampie 'crossv section .to contain :a v:single corridor. 'This would permit105000fdiierentfcor- Ariders to be carried with a margin ofsaietyfin al2icm.: diameter i-tube. 'The num-ber of "foer- 6 ,f-ridorsavailablef'in-aztube of-.ia-givenidiameter ris a .f function l.of the tubes icrossz-sectional xarea and may be calculated from the formula:

Number -of corridors available1,7%2

l.where r lis given.v in.. cmrandthe .Olis thearea ofr a, .1: cm. square corr-iden y.The -amounttoi .information 'which can .be ,channeiled into each .corridor.depends upon several factors. The first limitation fis -the transittime of the-iongroups through the tube. This ydetermines, how: much thetube can held Many-,given time. ,.But :Within this ,periodxof transit time therer-mayf be a greatnumber .of pulses: of information and each ion group can .represent -a separate channel of .information within its own corridor .If we-assurne a transit -tiine of .01.sec., a .great number is prac- ..tioable) of micro-,second .pulses with .adequate Vspacing between .them to Aprevent interference can be utilized. .The spacinginust be sufieiently .Wide to take'careotdiiusion of the .ions in .transit toward the collector` electrode. .(This diffusion problem is discussed below.)

A proper combination of corridors, and channels Within corridors makes it possible to store many times 10,000 different elements of binary information. Furthermore, since the col- `lector electrode and its associated circuitry can bemade sensitive to the degree of amplitude of a vpulse as well as to its mere presence, inter- -niediate information as well as binary OIT-on Yconditions can be indicated and stored. 1t has been explained. aboveihow`l`0g000 ^corridorsfcan be contained in aiigfcmxdiameterftube. @This .wou-ld.. call. lfor asoanning speed. of 1.01 .secondper raster. By increasing the speed. offthescanning beam, however, ..so..that.. .it lays down. 1a succession of ion pulsesineach corridor.bef.ore..the .rst ,pulse .has y.completed .r its `transit yto the collector electrode, it..is.possi-ble to.multiplethese110,000 corridors= by agreatnumber of. channels-within corridors The -numberof Achannels .possible within .a .single Ycorridor .is in .the .hundreds as shown in the chart. below. .Thus itis .conceivable that more than a inillioneleinents .of..information can be stored if .the writing beam scans fast 'enough to complete ia hundred `or 'more rasters during'the ion'transititime. Asexplained above, this scanning time: isiimitedamong other`things fby'thetime necessary-to lgive each ion group-Jan ladecuiate signal to-'noise i ratio.

Trnsitftz'me, diffusion, etc.

(References: Cork, rRadioactivityY.and Nucleai-.Physics;

Loeb, Fundamental Processes of:ElectricaLDischargeiin Gases.)

When ions are produced I;by `bornbaniment throughafLenard window.' the depth oi ionization is a function of the energy excess of the electrons after they have penetrated Vthrough the diaphragm-of the window. 'Anexcess'f2500 v. will ionize to a depth oi about .Ofi om. and' 1000 v. to about .003 om. (Rei. Cork). (A chart, onpage 293, vol. 4 of the RCA Review publication Television shows the percentage o1 available energy after a cathode ray pierces a Lenardewindow as a function of window thickness and beam voltage.) For each electron which penetrates into the gaseous region several electrons'and positive ions are formed, and the excess energy (i. e. the energy above that which is necessary to 'pierce the window) is dissipated at arate oi approximately 30 electron volts per ionizedpai-r. .These are the factors which along with the time duragroups which can be channeled through its corridors.

As explained above, the depth of these groups is affected, not only by the time duration of the electron beam which accomplishes the ionization, but also by the degree to which that beam penetrates into the gaseous region to be ionized. There is another factor which has an iniuence on the depth of the ion group as it passes through the gas filled chamber. This is the tendency oi' the ionized gas molecules to diffuse gradually throughout the gaseous region. This tendency of gas ions to diiuse must be taken into consideration in calculating the amount of information which can be channeled along any given (6) .DL-.0235 K N-e) (8) N= i (using Equation 5)= 2x (ft Vc (using Equations 2 and Equation 8 shows that the number of channels within a corridor is independent of the size of the instrument and volume of the gas but increases with the square root or" the voltage (V) between electrodes. 'This is based on the assumption that the pulse has a width diffusion width upon formation.

The chart below shows the number of channels increasing V and approximately at the rate N :2.9 V

(dividing Equation 2 by Equation 4) corridorf Voltage Distance Transit No. of across between gds'g go/051,133 time, Cgtrn Chantube electrodes t sec. nels 0m. Mcrosec.

In performing these calculations the ollowing approach is helpful. Let:

the extent to which the input pulse has been widened by diffusion of its ion (assuming pulse of zero width at beginning). E is the distance the pulse is widened from the central aXis therefore the total widening is 252-) Tim 3Jt 1 atm. pressure (k for argon-l.3 cin/sec.

volts/cm., with positive ions) (International Critical Tables, vol. 6, p. 111). D=difiusion parameter (.0235 k.) (Ref. Loeb supra).

d (2) 15:; (3) v=k Using the rst case stated in the chart the diffusion of an ion group in .0092 second is calculated as follows:

25;(f0r i=.oo92 sec.)

2(.19)(.o092)1/2=.036 cm.

Gases In the gas-lled tubes described above there are two diierent types of ionization calling for two diierent types of gas.

In the first type (Fig. 1) ionization is accomplished by electron bombardment through an electron permeable window which bombardment separates electrons from the gas molecules to produce positive ions. In order to prevent the free electrons from combining with other molecules of the gas to form negative ions, a gas is selected which has a small co-efcient for electron attachment. (E. g. the probability of a free electron attaching to a molecule with which it collides is less than 105 to one.) Some suitable gases are: the rare gases helium, neon, argon, krypton, xenon, hydrogen, nitrogen, carbon monoxide, and carbon dioxide. Ihe excess electrons are eliminated by attraction to the wall-electrode Il.

In the second type (Fig. 3) ionization is accomplished by activating an electron emitter which sends forth electrons to combine with individual molecules of the gas to form negative ions. Here the situation is opposite to the above case where the object was to eliminate electrons. Instead, we want to add them to the gas molecules. So a gas is selected with a high co-enicient for electron attachment. (E. g. the probability of a free electron attaching to a molecule with which it colli'des is more than i0-4 to one.) Considerable portions of the gas should be one of the following: afhalogen, oxygen, waterovapor, hydrogen-- suln'de, ammonia,. andI nitrous oxide. Fior. the. secondftype ofoperation only, gasv selected .from the 1 above. may.. be. mixed withl one of the: gases suggested for the..nrstv type. But it isrecoinmended that gaseswithin the same.l group. should notib'e. mixed'zin .either type` of `'operation because this'. would result. inv ions .of f diierent gases. with different.characteristics. .and .transit times..

The delays introduced in a device of the sort described are of the order of a few seconds or fractions thereof. Longer memory may be achieved by running information back through the tube by means of associated circuitry connecting output to input. In this manner a signal may be stored indefinitely. rlhe ei'ects of diffusion are oiiset by appropriate circuitry to sharpen the pulses each time they are fed back through the tube.

One of the corridors or given pulses within any of the corridors, can be utilized for synchronization or control purposes indicating when one of the parameters should be changed in order to operate the device at the desired delay time. Thus voltage and temperature irregularities etc., can be compensated for. Response to the indicated change can by appropriate auxiliary 'devices be made automatic.

The storage tubes and delay devices of the invention have been described as feeding into differentiating circuits for deriving a signal output. It will be understood that they may also be fed into other types of circuits and used for other purposes, e. g. they can be used as counting devices in cooperation with integrating circuits.

The invention has been presented as embodied in a gas lled discharge tube. The disclosure in this respect is to be interpreted as being illustrative and not in a limiting sense. rThe ionizable medium may comprise any iluid material wherein the elementary particles or molecules are capable of changing their electrical charge characteristics (i. e. add r subtract an electron relatively easily). Among such ionizable media are dust particles in air, oil droplets in various emulsions, etc.

What is claimed is:

l. A storage device for electrical signals comprising, an envelope containing an ionizable medium at a pressure of the order of one atmosphere, a plurality of electrodes mounted to define the terminals of a path in said ionizable medium, means for creating a signal-modulated localizeddischarge in said ionizable medium adjacent to one of said terminals, means for establishing a potential difference between said electrodes of an intensity and sign calculated to draw said localized-discharge in a substantially straight path away from its area of origin through said ionizable medium in the direction of said other terminal electrode, means including said other terminal electrode for deriving signals from said signal-modulated localized discharge, and at least one other electrode intermediate said terminals of said path.

2. The invention as set forth in claim 1 and wherein means are provided for varying the potential-diiference between said terminal electrodes, whereby to regulate the transit time of said signal-modulated discharge through said ionizable medium.

3. The invention as set forth in claim 1 and wherein said means for creating a signal-modulated localized discharge in said ionizable medium comprises an electron-gun.

4; The inventionzas.setorthinclaimil andi wherein said envelope comprisesY an. electron?. permeable gas-tighty partition vrwhich divides,` said;- envelope into. a gas-chamber and'. an.-` evacuated chamber; and wherein said met-mentioned means` comprises a .grid-controlled .f electron-.gun mounted within said evacuated chamber in line with said eleotrora-permeableA partition..

5. An electrical delay-device comprising a gastight envelope having two chambers having a,l common gastight wall, an electron permeable window in`said-wall5 a beam-source of electrons mounted in one of said chambers in a position to bombard said window, the other of said chambers containing a gas of a 'type and pressure capable or" localized ionization in response to the impress thereon of said electrons, a collector electrode in a part of said gas-lled chamber remote from said electron permeable window, and a foraminous auxiliary electrode mounted in the gaseous space between said window and said collector electrode.

6. The invention according to claim 5 wherein said ionizable fluid consists essentially of a gas having a low coefiicient of electron-attachment.

'7. An electrical delay device comprising an envelope having a translucent gas-tight partition 'dividing the interior thereof into an evacuated compartment and another compartment containing an ionizable uid, a beam source of electrons mounted in said evacuated compartment in a position to scan said translucent partition, an electron-sensitive photo-emissive coating on the scanned surface oi said partition, a photo-sensitive electron-emissive coating on the opposite surface of said partition and within said other compartment, a plurality o1 collector electrodes immersed in the ionizable uid in said other compartment remote from said partition, means for establishing a potential diilerence between said partition and at least one of said collector electrodes of an intensity and sign calculated to draw a localized-discharge in a substantially straight path away from said partition through said ionizable fluid in the direction of said collector electrodes, means including said collector electrodes for deriving signals from said localized discharge, and at least one electrode intermediate said partition and said collector electrodes.

8. The invention according to claim 7 and wherein said ionizable fluid consists of gas having a high coeincient for electron attachment.

9. An electrical discharge device comprising an envelope containing two spaced apart gas-tight partitions dividing the interioi of said envelope into a central compartment and two oppositely located evacuated compartments, an ionizable huid in said central compartment, a beam source of electrons mounted in each of said evacuated compartments in a position to scan the adjacent surface of its partition, the scanned surface of one of said portions comprising an electronsensitive, light-emissive coating, the opposite side of said partition having an electron-emissive coating sensitive to the light emitted by said rst mentioned coating, the scanned surface of the other partition comprising a plurality of discrete electrodes for collecting ions resulting from the release within said gas of electrons from said light sensitive electron emissive surface means for establishing a potential difference between said partition having said electron emissive coating thereon and at least one of said electrodes of an intensity and sign calculated to draw a localizeddischarge in a substantially straight path away References Cited n the le of this patent UNITED STATES PATENTS Name Date Null Feb. 21, 1928 Number Number 12 Name Date Schroter et al June 11, 1935 Applebaum Feb. 11, 1936 Barthelemy Aug. 11, 1936 Thomas Jan. 10, 1939 Strubig June 6, 1939 Farnsworth Aug. 27, 1940 Lubszynski et a1 Oct. 7, 1941 Ponte Dec, 4, 1951

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