US2428819A - Secondary electron emission type of pulse generator - Google Patents

Description

AMPL VIDE- Oct. 14, 1947. A, M, SKELLETT 2,428,819

SECONDARY ELEcTRoNEMIssIoN TYPE OF PULSE GENERATOR l Filed Dec. 15, 1942 F/G. 3,4 F/G. 35

E /Ni/ENTOR y AM. SKL-LHT ATT R/vfy Patented Oct. 14, 1947 SECONDARY ELECTRON EMISSION TYPE OF PULSE GENERATOR Albert M. snellen, Madison, N. J., assigner to Bell Telephone Laboratories, Incorporated,

New York, N. Y., a corporation of New York Application December 15, 1942, Serial No. 459,047

4 Claims. 1 This invention relates to pulse generators. An object of the invention is to generate high power, short duration pulses of electric energy at a desired time interval or frequency.

A feature of the invention comprises a pulse' generation circuit arrangement embodying secondary emission electronic devices,

A further feature comprises utilizing a secondary electron trigger type vacuum tube or device to generate a square-topped output wave in-response to a control signal or voltage, and a second such device to generate a pulse of the desired magnitude and duration in response to the steep front only of the square-topped wave.

In the practice of the invention, electronic devices of the type described in my Patent 2,293,177, issued August 18, 1942, may be employed. The device of the aforenoted patent is asecondary electron emission, trigger type vacuum tube. In general, it comprises a triode or primary electron section and a secondary electron section. The triode section comprisesA a primary electron source or cathode, an input control grid, and a primary anode the latter is provided with an aperture or slot for the escape of a preassigned percentage of the primary electrons arriving at the anode from the cathode. The secondary electron section comprises a secondary anode having a surface treated for emission of electrons in ratio greater than unity when bombarded with escaped primary electrons, and a secondary electron collector electrode or grid, the secondary grid and anode being positioned out of the direct path of the escaped primary electrons so that the secondary electron emitting surface will not be contaminated by cathode particles. directed onto the secondary anode by a deilector electrode positioned in the path of the escaped electrons, and which may be maintained at cathode potential. As explained in greater detail in Patent 2,293,177, if the input grid is initially biased beyond primary anode current cut-01T and the secondary anode and the input grid are interconnected and the collector grid is maintained at a potential more positive vthan the secondary anode, a positive pulse of small order of magnitude applied to the cathode-input grid circuit to initiate primary electron flow in the triode section, will cause the secondary anode to rise quickly to a high and stable oating potential which, applied to the input grid through the interconnection between the input grid and secondary anode, drives the input grid more positive with respectfto the `cathode and accelerates The escaped primary electrons are.

2 establishment of a high magnitude of primary electron flow between the cathode and primaryV In the absence of an interconnection anode. between the input grid and the secondary anode, the establishment of primary electron ow between the cathode and primary anode and the bombardment of the secondary anode with escaped primary electrons willcause the secondary anode to rise to a high and stable floating potential at which it will remain so long as primary electron ow and the appropriate collector grid potential are maintained.

In accordance with the invention, two such electronic devices are `arranged inV a circuit such that one of the devices produces or'generates a square-topped output Wave of the same frequency as and in responseA to an input signal thereto, and the second produces a single pulse at the time of the steep front of the squaretopped wave. The output of the second device is independent, over Wide limits, of the amplitude and Wave shape of the input signal or control voltage.

A more complete understanding of the invention will be obtained from the description that follows, taken in conjunction with the appended drawing, wherein:

- Fig. 1 illustrates a circuit arrangement embodying the invention;

Fig. 2 illustrates the electric Wave shapes present during operation of the circuit of Fig. 1, Fig. 2d having an expanded time axis so as to show in better detail the shape of the output pulse;

"Figs, 3A to.5B show cathode ray oscillograph tracings illustrative of pulse shapes obtainable with the pulse generator of the invention.

The circuit comprises a pair of secondary' electron trigger type vacuum tubes or devices TI, T2, such as described more fully in my Patent 2,293,177. Tube Tl comprises a cathode l'l, an input control electrode or grid I8, a primary anode I9 containing an aperture for the egress or escape oi some of the primary electrons that Imay .arrive at the anode from the cathode, an

3 more positive than the secondary anode, the latter has the characteristic, when bombarded by escaped primary electrons, of rising rapidly to a stable potential somewhat less than the collector grid potential. Tube T2 comprises similar electrodes torwhich the same designations primed are applied.

The input grid and secondary anode of tube Tl are interconnected through capacitor C1, so that, for such operation of thertube TI as ,causes the anode 22 to rise in potential, tlie gridV I8 will be caused simultaneously to become more positive with respect to the cathode. The latter and the deflector electrode may be maintainedl at groundl or reference potential. The gridY I8., is biased negatively to beyond primary anode current cutits off, the bias being provided by the sourceCAof- 4 anode, to the secondary anode of tube TI. As described in detail in my Patent 2,293,177, the anode 22 Will rise to a stable potential determined by the magnitude of resistor R3 and the potential on the collector grid, and will remain in such high potential state until;the primary electron flow is, interrupted asnares'ultjof rthe excursion ofthe grid I8 sufliciently negative with respect to the cathode. Cessation of primary electron bombardment of the anode 22 restores `the Vlatter to the potential determined by its connectionto the source B;

The resulting electric wave that appears across the resistor R3 is illustrated by curve b of Fig. 2.

YThe steepness of` the front of this wave and its of gric l ,2ll and the Ref-C2network.V Figs. 3A`

and 3B 'show cathode ray` oscillog'raph p tracings vof this steep front vfortwosets@ofucogjnditions witlrl primary anode and-high potential terminalgof sinirceln may be'foun'dy desirable when high primary anode potentials YareY involved. In a specic arrangement, itwas included when the potential Y(V5) exceeded about 250 volts. time constant yofthe network should b e such that the secondary anode may riseto its high stable potential before the potentialx ofl the /present in the steep front'o'f avsquare-toppefdj Wave. Grid 18' is also biased by s cnirceAC1-throwngh` resistor R4 to a potential beyondjprimaryanode current cut-off. Primary anode Jlilf n 'iayk be connected directly to the high potentiaijterrninalof source, B., or, asshown in; the drawing, a resistor Rtrnaybe interposed'thereby, enabling the don'nlnnonA of. n nognnvo., polso in onosoutpnt of' the circuit at terminal I l. The collector grid 2^lf is `alsorconnectedA to` the high potential terminal of source B with a resistance-condenser Vnets- Work Rif@ inioppoSod Tnooonotnnio onosoln] for therlatter networkA will determinel the duration of thepositive pulses. The higher the value of the resistancefRs, the shorter the pulse, the time constantofjth'e network`A (tl'lat is,4 R5 C4 being held'constant.Y Thesecondaryy anode 211' iS oonnootod. to positive pulsotorrninol I2 and', through a resistor' Reto a point'onisourceuB oufv lower vWPQa.1. than.. that. Of. the. conecto? grid-f. The operating features vof thegcircuit willjnow. be described. The inputrsignal or control voltage Y iS appliod-io tno ooinodofinpnt grid ononi of.;

The

' detectableA atterm-inal I-2,tl[1esymmetryoff who Ti threonine transformer lo:v The input Y signalmight be anaalternating currentofrsine wave character suchk asis illustratedjby curved of Fig. 2,` fraiieyfgriri1|ay win-'swing in instantaneous potential aboveV and below clit-nig` On Vvits' e'XW-" cursion above cutfoi, primary electronsemitted from thecathode have acces/sitothenprirnary' anode and; through the aperture in the primary a circuitsuchas is shownin 1. For-Fig. 3A",-

Vs was equal toj 250 volts and the .Raf-:.Cznet? work wasvomitted. For Eig. 3.B, V5 was equal tog. Y 400 volts, R2 was 50,00Qolnn'sand C2 was .009,023 microfarad. Y AsV already.y indicated, resistor Rfi prevents the-grid I8, vfro'rnY going toolfar plositivev for large vinput voltages. The capacitorv C1 feeds f back to the'. grid l.y the upward surgeoiv the secondary anodepotentials@V fas to accelerate,thel potential riso of the Sooondnrfy opodofloir onnoing.. doo input ond. to. booonlo ,more positivo-and.- to.Y permitr an increased now;y ofi, primaryneiectrons t0 Athe Primary an@ ,Sengaryfallod This 1re-jgenerative notionohifiooontrol offtno npntsrim to ino; Sooondnlrzonodol, nndossiston making tno-1 used only to trigger on the electroncurrent..

Y The capacitor 0 3 is ofsmall, ,capacity so that; only the higher `frequencies are transferred tothe` grid- IBI, and since Vthese .high frequenciesA have.

appreciable magnitude. only atr` the4 steep front of the ,square-topped wave,d grid I 8 receives a sharp.; i, input pulse at that time,V the inputzvwavefto thercathode-input gridcircuit of-` tube T2ybeing as illustrated by curvec lof Fig. 21;,V the dotted. line-g Y shows the. relativen potentialof primary anode! current cut-coiffer tubeTZ, the primary.'electrons*` being allowedto flow. -inthesecond tube forY a! veri/. shortinterval, for example, amicrosecond orless. Byvchoicel of constants for capacitor-C5- and77 resistor Rn the pulseduration may be varied;A

itive swing of -thergrid 1| 8-f will besufficiently rap.-l

id.: If the network Rs-Ct 4were not-present,,tliatM is, if`thecol1ector grid .2ll were connected dijre'ctly to theY high potentialgterminalof the .,SQl-llfe` B,Y the tubev T- Zwould produce a, square-vtoriloerl` wave such as is illustrated -by Ycuri/jed-oifeliigi 2; thQ sides. oi the wave being effectedby selectionloff a` suitable value of lV4 so that at-itheitopof Y p iuse the potential-0f the anode zzi'v-wnrbe'irlf tho positivo resistono@ pornonoi no1onornotop-`Y isdof'` Sino@v tho potential to Wnion f tnospoondary. c nnodo. rioosds. determined primarily .by the' potsnlr..V tiel. of. the collector grid 2l.' and tlnogmagnitudo-i 'ofVY resistor Ro; the heightv of the pulse may beV varied by changing v4 without altering the width of the baseA of the pulse.

In a pulse generator constructed in accordance with Fig. 1 for the generation of positive pulses, the circuit components had the following values:

R1=1 megohm R2=50,000 ohms R3=2 megohms R4=200,000 ohms R6=10,000 ohms C14- 2.5 micromicrofarads C2 .0O025 microfarad rC3=;00001 mi'crofarad 04:.00002 microfarad Figs. 4A, 4B and 4C illustrate cathode ray oscilloscope tracings of the output pulse of tube T2 for three different potential conditions of the tubes. That of Fig. 4A was obtained for potential settings on sources B and C of V1=35 volts, V2=55, volts, V3=55 volts, V4=295 volts and V5=4G0 volts. To give Fig. 4B, V1=-35 volts, Vz=25 volts, V3=50 volts, V4=180 volts and V5=250 volts. To give Fig. 4C, V1=35 volts, V2=-55 volts, Va=50 volts, V4=350 volts and V5=400 volts, and resistor R4 was changed to 20,000 ohms. The amplitude of the pulse for these respective conditions was 65, 40 and 30 volts. In each case the collector grid 2l and the primary anode I9' were connected directly to the high potential (V5) terminal of source B, resistors R5 and R1, condenser C4 and the negative pulse terminal being omitted.

An output pulse from tube T2 shaped more or less like a right triangle is obtainable by selecting a lower value for V4 than in the previous cases. Figs. 5A and 5B illustrate cathode ray oscilloscope tracings for the following conditions. Fig. 5A: V1=35 volts, V2=,-55 volts, V3=65 volts, V4=140 volts, V5=250 volts. Fig. 5B: Vi=35 volts, V2=25 volts, V3=65 volts, V4=165 volts and V5=400 volts. To obtain the more symmetrical Fig. 5B tracing, the R5--C4 network was included in the collector grid lead from the source B with the values Rs=1 megohm and 04:20 micromicrofarads. In each case, the pulse amplitude was of the order of 142 volts.

The pulses referred to hereinabove are the positive pulses that appear across the resistor Rs. If negative pulses are also desired, instead of connecting the primary anode I9 directly to the high potential terminal of source B, anode I9 is connected to negative pulse terminal H, and through a resistor R7 to source B as shown in Fig. 1. The shape of th'e negative pulses will be the Same as those impressed on the grid I8 since anode i9 does not have the negative resistance characteristic of anode 22. The triode structure comprising cathode l1', grid I8 and anode I9 functioning as an amplifier will produce amplified negative pulses. Because of the diierent magnitudes of the electron currents in the primary and secondary electron sections of the tube T2, the magnitudes of resistors Re and R7 should be different if-it is desired to have the positive and negative pulses of the same order of magnitude.

The circuit arrangement described has been found to operate at input voltages as low as one or two volts and over a wide band of frequencies. The amplitude and shape of the output pulses are substantially independent of the frequency, amplitude and wave shape of the input to the circuit. Although the circuit arrangement of Fig. l is of utility wherever a single high power, short duration pulse of either sign per cycle of 6 the signal wave or control'voltage is desired, it is apparent 'that it may beemployed as a direct reading frequency meter in that a current meter maybe inserted in place of the resistor Rv, to provide a current reading linear with frequency from zero to the megacycle range.

AlthoughV disclosed with reference to a single embodiment, .it 'is obvious that the invention is not limited thereto but that modifications and other applications will occur to those skilled in the art without departing from thev inventive concept.

What is claimed is:

l. An electronic device circuit comprising a pair ofl electronic devices', each of which comprises a primary electron section and a secondary electron section, means including a regenerative connection between the primary and secondary electron sections of one of said devices for convertingsignal wave input to the primary electron section of said one device into a square-topped electric wave in the secondary electron section of said one device, means for deriving the higher frequency content from said square-topped wave and for applying it to the primary electron section of the second device to establish a high power, short duration pulse of electric energy in the secondary electron section of the second device.

2. A pulse generator comprising a pair of vacuum electronic devices, each` device comprising a cathode, an anode, a control grid containing an aperture for the escape of Some of the primary electrons originating in said cathode, a control grid between said cathode and anode, a second anode for emitting secondary electrons when bombarded by escaped primary electrons, and a collector electrode forl collecting the electrons emitted by said second anode, a signal wave input circuit connected to the grid and cathode 0f one of said devices, a reactive coupling between the second anode and the grid of said one device, means connecting the second anode-collector electrode circuit of said. one device to the grid and cathode of the second device, and a utilization circuit connected to the second anode and collector electrode of said second device.

3. A pulse generator comprising a pair of vacuum electronic devices, each device comprising a cathode, an anode containing an aperture for the escape of some of the primary electrons originating in said cathode, a control grid between said cathode and anode, a second anode for emitting secondary electrons in ratio greater than unity when bombarded by escaped primary electrons, and a collector electrode for collecting the electrons emitted by said second anode, an input circuit for each device comprising the cathode and grid of the respective device, an output circuit for each device comprising the second anode and collector electrode of the respective device, means for applying a signal wave to the input circuit of one of said devices, a regenerative coupling between the input and output circuits of said one device, and means for connecting the output circuit of said one device to the input circuit of th'e second of said devices.

4. An electronic device circuit comprising a pair of electronic devices, each of which comprises a primary electron section and a secondary electron section, the primary section comprisingv a cathode, a primary anode and a control grid between the cathode and anode, the secondary section comprising a second anode adapted to emit secondary electrons in ratio greater than unity when bombarded with electrons from said pri- 7, mary section v'and ai .grid Vfor .coiecting' 'said sec; ond'ary electrons, lmeans including a .regenerative connection between the .fcontrol gridv'an'd the secondV anode. of Ysaid Vdevices 4for :converting a.- sinusoida'l electric `Wave appliedto the control.V

grid-cathode circuit .of :saidone device into a square-topped electric Wave in 'the'c'ollector gridsecond .anode kcircuit rofxsaid zone device, vmeans for yderiving the Yhigher frequency .contentioniy from said square=topped Wave `and. ,'forwapplying I0' Number itlto the control Agrid-'cathode icircuit of ythe second of said devices to establish, independent of vany connection between the second anode and rcontrol grid of -the second device, a :high power,

short durationipulseof `electric:energyin the col- 1:5 2,299,252

The following-references are of record in the file of this patent:

UNITED STATES PATENTS Name Date 2,086,918 Luck July 13,1937 2,168,165 'Koller et a1. 1 Aug. 1, 1939 2,274,369 Janssen Feb. 24, 1942 2,230,926 Bingley Feb. 4, 1941 Pierce Y Oct. 20, 1942

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