US2486491A - Gate distributor circuits - Google Patents

Description

Nov. l, 1949.

L. A. MEACHAM GATE DISTRIBUTOR CIRCUITS Filed Feb. 8, 1946 2 Sheets-Sheet 1 /Nl/ENTOR l.. A. MEACHAM NOV- l, 1949. A. MEACHAM 2,486,491

GATE DISTRIBUTOR CIRCUITS Filed Feb. 8, 1946 2 Sheets-Sheet 2 /A/l/ENTOR L. A. MECHAM @7l/@EMM ATTORNEY Patented Nov. 1, 1949 U N I TED STATES PAT EN GF F 2,486,491

GATEDISTRIBUTOR CIRCUITS Lamed A. -Meacham Summit, N. J., assignorwto Bell Telephone Laboratories, Incorporated, New." Yrk,.'N. YL; a corporation of NewYork ApplicationFebruary 8. 1946, ASerial-No. 646,455'

2 claims.. (01.250427) This invention relates toe-,electronicswitching or gating circuitsal` The `invention .particularly contemplates an electronic: switching ycircuitof the so-'called .chain typen;N

A fundamental process vappearing .frequently Yin electric circuits and devices is that-ain which the members of a group oflsimiiarcircuits areoperated-in sequence at-.accurately prescribed times. Such instances arise-,ciers exampldt-.in connection with timing and coordinating'the operations of various portions of radar. equipment; in the conu nection of a number 'offaudio .channels *to-transmission equipment. used. -in-L common. onf a time'- division basis; in the cycliczrecognition ofnthe presence or absence of Icharges upon.storagecon densers in certain forms of pulse signaling ,"in .the sorting of received pulse signalsinto separate circuits; and in other .timingg-.Lcoordinatingg and synchronizing circuits and systems: r

Control of such sequential.operationimaybea complished by means '-oftin'fied pulses orgates" generated or distributed in commutator fashion to a desired number: of vseparate lpathsxfhe isequence of gates appearingin anyzoneeoffthese paths controls the operation sof apparatusV associated with the 'particular'path.'v Th'egate fdistributor has the nature'of -commonsynchronizng equipment, and it can .supplyfanyl numbersfof groups of circuitsrequiring 'sequential'. control.

Conveniently, each oixthe gate'srequired.for i the sequential operation of-a desiredinumber of circuits or devices may 'comprise a changegfat the proper time, of the polarity ormagnitude orboth of a voltage or current applied-.to .eachicircuit or device. comprise electronic switching meansz'capableof The gate distributork may',l therefore;

distributor or-electronicfswitchtwhich will deliver accurately timed rectangularpulses in sequence toanumber of--separateoutputs and to increase the precisionottimingover thatrnormally-attainable through the use of chain type' switching circuits of-the type re-ferred-toabove.\ I

In viewfoil thelabove objectsfand-` in accordance with the invention, a pulse distributor is provided which comprises means for precisely timing the operation-oi -achain-type. electronic switching circuit. In general, such means include, in addition to oneoramorechains-or trains of a single lpulse generators,-means--iorgenerating two or more controlcurrentsof substantially constant, `harmonically related-frequencies.' One of these control currentsiswemployed tcp-initiate successive cycles of operationof the chain, while another, of higherfirequency, is utilized precisely to time lin turntheLoperation-ofeach of the individual single pulse generators' inrthve chain.

In an exemplary embodiment of the invention, the requiredfsinglesquare'pulses orgates are generated anddistributed'-to -a1plurality' of outputs in precisely timedrelation by-.a system in effecting the required number of voltagefor our;

rent changes in the `proper timed relationship; There have heretororebeenproposed a number of sequential electronicswitching circuitsiof the co-called chain type which are in .general cal pable of fulllingthese requirements: Infsuch switching circuits, a control -pulsel-initiates-the' operation by ring or triggering the :first switching stage (a lvacuum tube or combination of vacuum tubes). Thereaitenpthe remaining stages are fired successively along ithe chaingieach by the action of the preceding stage." Such icirn cuits, While possessing suiicient precision of timing for many purposes,\may not be suiiiciently precise for high speed switchingin caseswh'ere each vof the "control circuitsor devicesis to be rendered operative. for times of .the orderr of microseconds.

Objects: oi this. -inventionvarelV to provide fafgate which the' outputofva sine-wave oscillator having'high-frequency@stabilitytis appliedvto a square wave generator to-obtainJavsquare wave output of the same fundamental" frequency as that of the oscillator. This-square Wave signal-controls the operation I. of a 'series of -m-ulti-v-ibrators ar ranged ina frequency -dividingnetwork to obtain square Wave outputs Vhaving fundamental frequenciesWhichfare'submultiples-'of that of the sine Wave -osci11lator;- The square-wave outputs from theirequency dividing -network are used to control the'operationofone'or-more pulse distributor chainseachL-comprisinga number of single square pulsex generators/of v'the type-some times known `as Isingletr-ip multi-vibrators. It will be 'understood that -thefexactv number oi such single squareA pulse generator-sl usedjin each pulse distributorrchain depends upon the-desired nunkber Vof Ygates desired lto be Vobtained.`

Each of the singlersquare pulse'generatorsor single trip multivibrator-s l'comprises-a --vacuum tube switching' circuit Which- Imay be triggered from a'res't-.rorfnormal conditionto aneactuated condition from'fiwhich--fit automatically-returns after an interval determined by-thefparameters of the circuit. -The sing-lesquare pulse generators forming `a -pulse distri-butonchai-n are so v@inter-- connectedthatrthe'rstfgenerator ofthe chain may be triggered byanfexter-nal signal to produce a single squarepulsef fvIvfhetermination ei'thi's squarepu-lse is vthen effectiveto trigger! the next 3 generator of the chain and this process is repeated to the end of the chain, each generator except the first being triggered by the preceding generator of the chain. The circuit constants of the single pulse generators are adjusted to obtain square pulses of equal periods but in accordance with the invention more precise timing both as to duration and time of occurrence of the pulses is obtained by introducing into each of the pulse generator circuits of the chain a square Wave synchronizing signal derived from the frequency dividing 'network and having a higher frequency than that of the signal used to initiate the operation of the chain. More specifi cally, the synchronizing signal in the exemplary arrangement described in detail herein is chosen as a harmonic of the initiating signal and its period is made twice the desired pulse duration.

The above and other features of the invention will be better understood from the following detailed specification taken in connection with the drawings in which:

Fig. 1 is a block diagram of a pulse or gate distributing system in accordance with the invention;

Fig. 2 shows typical wave forms of the voltages and currents occurring at various points in the system of Fig. 1;

Fig. 3 is a circuit diagram of a frequency dividing network suitable for use in the system of Fig. 1; and

Fig. 4 is a circuit diagram of a chain of single trip multivibrators suitable for use as the pulse distributor of the system of Fig. 1.

In the block diagram of Fig. 1, there is shown a gate distributor arranged for purposes of illustration and in accordance with the invention to provide two sets of gates, each set being capable of controlling the operation of or supplying pulses to eight channels or paths. For this example it has been assumed that the gate frequency is to be 64 kilocycles per second for the eight channels of one set and 8 kilocycles per second for the eight channels of the other set.

Accordingly, two gate distributor chains are provided, that for operation at 64 kilocycles com prising single trip multivibrators l through 8 and that for operation at 8 kilocycles comprising single trip multivibrators I through 8'. The required 8- and 64-kilocycle square wave control signals and the synchronizing signals are provided by a frequency dividing network comprising six multivibrators 26 through 36 controlled in tandem by a sine-wave master oscillator 22 operating at 1,024 kilocycles and driving a square wave generator 24 arranged to produce a square wave output of the same fundamental frequency. Multivibrators 26, 28, 30, 32 and 34 are arranged in a well-knownmanner as frequency dividers to obtain submultiple frequencies at a 2:1 ratio while the final multivibrator 36 is arranged to obtain Ya submultiple output at a 4:1 frequency ratio. Thus, there are provided square wave outputs of 512, 256, 128, 64, 32 and 8 kilocycles, respectively. It will be understood that the sine wave oscillator, the pulse generator, and the frequency dividing circuit may each be of any well-known type. For example, United States Patent 2,022,969, Meacham, December 3, 1935, shows a suitable type of frequency changing circuit. The disclosure of this Meacham patent is hereby made a part of this application as if fully included herein. The sine wave oscillator may, for example, comprise a crystal-controlled vacuum tube oscillator delivering a substantially pure sine wave output of high frequency stability. Suitable types of oscillators are disclosed in United States Patents 1,788,533,

Marrison, January 13, 1931; 1,931,873, Marrison,

October 24, 1933; 2,087,326, Marrison, July 20, 1937; 2,163,403, Meacham, June 20, 1939; and 2,275,452, Meacham, March 10, 1942. The square wave generator may conveniently comprise one or more vacuum tubes operated as overloaded amplifiers which are driven alternately into saturation and beyond cutoff by the sine Wave output of the master oscillator to obtain an output of fundamental frequency, having a substantially square wave form. In the system of Fig. 1 all of the single trip multivibrators comprising each of the chains are arranged to produce single square pulses or gates of equal duration and circuit constants are so chosen that the distributor chains are not triggered for a second cycle of operation until the last gate of the preceding cycle has been completed. Under these conditions in the exemplary system described herein, the pulse duration in the chain controlled by the 64-kilocycle multivibrator is approximately 2 microseconds while that for the chain controlled by the S-kilocycle multivibrator is approximately 16 microseconds.

Inasmuch as the two pulse distributing chains of the exemplary system operate in substantially identical fashion but at different frequencies, only the distributor controlled by 64-kilocycle multivibrator 32 and comprising single trip multivibrators I through 8 will be described in detail. As pointed out above, the first single pulse generator of the distributor chain is triggered by the 64kilocycle square wave output from multivibrator 32 and the circuit parameters of the pulse generator are so chosen that a single square top pulse is generated having a period equal to approximately one-eighth the period of the 64- kilocycle control signal or approximately 2 microseconds. The termination of this square top pulse is used to trigger the next generator 2 of the chain'and this process is repeated until the eighth generator has been operated.

In the operation of the circuit thus far described, the duration of each of the single square pulses or gates is controlled approximately by adjustrnent of the RC elements determining the time constant of the' `single trip multivibrators. For

high speed switching, however, greater precision of timing than that so obtained is often necessary. For this purpose and in accordance with the invention, the output of that multivibrator of the frequency dividing network which has a fundamental frequency of 256-kilocycles is utilized to control precisely the ending of each of the gate pulses and the initiation of the succeeding gate pulse of the chain. Recalling that the gates are to be generated in each path or channel at a gate frequency of (i4-kilocycles, it will be recognized that the half period of this 256-ki1ocycle synchronizing signal is precisely the desired gate length. It should be understood that a 512-kilocycle synchronizing signal could be used, the whole period of this signal being equal to the desired pulse length, and that other synchronizing frequencies might also be used.

It will be noted in Fig. 1 that multivibrators 28 and 34 utilized to provide the synchronizing signals for the two pulse distributor chains are each provided with two output terminals labeled A and B, and A and B', respectively. Conveniently each of these multivibrators is provided with means for generating two outputs degrees out of phase with each other and alternate cycle square wave generator 24 (Fig. 1) at a2:1 ratio while multivibrator 28 is controlled at the same ratio by the 512-kilocycle output of multivibrator 26.

Similarly, multivibrators 38, 32 and 34 are each respectively controlled by the preceding multivibrators of the network at a 2:1 ratio giving fundamental output frequencies of 128, 64 and 32 kilocycles per second, respectively, while multivibrator 38 is controlled by multivibrator 34 at a 4:1 ratio to produce a fundamental output frequency of 8 kilocycles. Control signals at 8 and 64 kilocycles per second are obtained from the plate circuits of multivibrators 36 and 32, respectively. Multivibrators 28 and 34 are slightly modied to provide two outputs which are in phase opposition of 180 degrees out of phase, for the synchronizing signals which are advantageously employed in the operation of the pulse distributor circuits as will be explained hereinafter. Thus, for example, in multivibrator 28, resistors 88 and 68, respectively, are connected in the cathode circuits of multivibrator tubes 10 and 12 and 180 degrees out of phase outputs are obtained at terminals A and B, respectively.

It will be understood that the number of multivibrators in the frequency dividing network and the ratios at which they are controlled may be varied as required to provide output signals of the frequencies necessary for control and syni It will be recognized, for example, that when two or more pulse distributor chains are included in the system, the control signals for one chain and the synchronizing signals for another may be obtained from the plate and cathode, respectively, of a single multivibrator operating at the proper frequency.

Pulse distributor circuits chronization purposes.

Circuit details of an exemplary pulse distributor chain are shown in Fig. 4 to which reference is now made. Each of these chains in the system of the example comprises eight single square pulse generators of the type sometimes referred to as single trip multivibrators because, like multivibrators, the circuits have two conditions of stability, acquired alternately. But whereas the two conditions are both in the case of the ordinary multivibrator, the present circuits have a normal condition of permanent stability in which they remain until actuated to the other condition. These circuits will remain in this other or activated condition for only a short interval of time after which they automatically return even in the absence of applied control currents. Three of these generators are shown in detail in Fig. 4. i

The first single trip multivibrator of the pulse distributor chain is typical of all eight and comprises two triodes or in this case a dual-triode type vacuum tube 14 and associated circuit elements. The plates of the left and right-hand sections of this tube are respectively connected through load resistors 18 and 18 to the positive terminal of battery 80, the negative terminal of which is connected to ground. The cathodes of the two sections are connected together and through resistor 82 to input terminal A which in turn is connected to output terminal A of multivibrator 28 (Fig. 3). The grid of the left-hand section of vacuum tube 14 is connected through capacitor 84 to input terminal C which is connected to output terminal a of multivibrator 32 (Fig. 3), the grid return being through resistor only temporarily stable to the normal conditionk 86 to the junction of voltage divider resistors 88 and 90 which are connected together andin series with resistor 92 between the positive potential at 80 and ground. The plate of the left-hand section of vacuum tube 14 is connected through capacitor 94 to the grid of the right-hand section and grid return resistor 96 lis connected to the junction of voltage divider resistors 88 and 92 described above. Inductor 98 is so connected that it by-passes cathode resistor 66 of multivibrator 28 (Fig. 3) to reduce the flow of direct current through resistor 66 and thus to reduce changes in bias or operating conditions of tubes 10, 12, 14 and the other tubes in the chain which, like tube 14, are associated with terminal A.

The operation of single trip multivibrator 14 will now be considered with reference to the wave forms of applied voltage shown in Fig. 2. Let it be assumed that in the rest condition the righthand section of single trip multivibrator tube 14 is conducting a current determined by the bias voltage derived from voltage divider resistors 92, 88 and 90 w-hile the left-hand section of that tube is cut off by a more negative bias also derived from the divider. At the beginning of a cycle of pulse distributor operation the positive half cycle of a l-kilocycle square wave control signal (shown at 32 in Fig. 2) is applied to the left-hand section of single trip multivibrator 14 through input terminal C. At the same time a negative square pulse of a synchronizing signal having a frequency of 256 kilocycles as shown in trace A (Fig. 2) is applied through terminal A and cathode resistor 82 to the cathodes of vacuum tube 14. The control grid of the left-hand section of this tube is thus made positive relative to the cathode thereof and this section of the tube begins to conduct current. The voltage drop thus produced across load resistor 16 causes capacitor 94 to discharge applying a negative voltage to the control grid of the right-hand section of the same tube to cut off that section. As capacitor 94 discharges and after a period predetermined by the values of capacitor 94 and resistor 96 the potential on the control grid of the right-hand section rises, in the absence of a synchronizing signal or pulse, to such a value that this section of tube again becomes conducting. The large increase in total current through cathode resistor 82 then increases the cathode potential relative to the grid of the left-hand section of the tube to such a value that this section is again cut oi, capacitor 94 is recharged,

` carrying the grid of the right-hand section momentarily strongly positive, and the cycle of operation of the single trip multivibrator is completed.

The grid bias applied to the right-hand section of multivibrator tube 14 is so chosen that this section of the tube operates as a cathode follower which is not overloaded during the rest portion of the cycle. This assures uniformity of cathode potential at the rest condition and thus contributes to accuracy of triggering despite reasonable tube and circuit changes.

From the above, it is apparent that in the absence of any controlling or synchronizing signals, the multivibrator circuit comprising both sections of tube 14 has an activated or temporarily stable condition and a normal condition. When the anode current of any of these tubes is changed from the normal condition, it will be returned to the normal condition automatically after a predetermined interval of time.

It has been discovered, however, that the time required to return. to the normal condition `varies depending upon many factors including characteristics `o f individual tubes, potentials applied thereto, ambienty temperatureand temperature of circuit components, as well as other factors.

In order to more accurately and with greater precision control the time at which the circuits are restored to their normal condition, synchronizing or control pulses are applied to all; theV so-called single trip multiyivbrators,y in such a manner that any circuits which are inthe activated condition are returned to their normal condition and theV succeeding ones switched to their opposite or activated condition.

At a time prior to the time at which the circuits of tube 14 would normally revert to their normal condition as described above, synchronizing orcontrol pulses are applied to control leads A r B. At this. time lead A is made more positive and lead B'more negative. When lead A becomes more positive the cathode of both sections of tube '14 are likewise made more positive. This change in the cathode potential is suicient to cause the anode current of the left-hand section of tube 14 to be decreased. The anode ofthe left-hand section, therefore, will rise in potential or voltage and cause the grid of the righthand section likewise to rise in voltage due to the coupling capacitor 94. As a result the righthand section of tube 'I4 starts to conduct current and causes the two cathodes to rise to a relatively high positive value, thus completely interrupting conduction in the left-hand section of tube 14, and restoring this circuit to its normal condition. When the cathodes of tube 14 rise in potential they cause a positive potential to be applied to the grid of the left-hand section of tube |02 of the next single trip multivibrator through capacitor |00. Simultaneously with the application of the positive synchronizing potential to lead A a more negative potential is applied to the synchronizing lead B. Synchronizing leads A and B extend respectively to the cathodes of the tubes of alternate pulse generators or single trip multivibrator circuits. In making lead B more negative, therefore, the effective grid-to-cathode potential of the lefthand section of the tube |02 of the second single trip multivibrator is made more positive. However, this change in voltage is not suicient to cause current to flow through the left-hand section of this tube or those of any of the tubes to which lead B extends.

However, the grid of the left-hand section of tube |02 in the second single trip multivibrator will have applied to it a positive pulse from the cathode of the previous tube through the capacitor as described above. Consequently, tube |02 which is thus Conditioned by the applica-, tion of a positive potential to its grid in addition to the negative synchronizing potential applied to its cathode through lead B will be changed from its normal condition to its activated condition thus causing current to ow in its output circuit. When it is desired to terminate this current, the synchronizing potentials applied to the leads A and B are again reversed and the multivibrator circuit in its activated condition is returned to its normal condition. In this maner each one of the tubes or pulse generaton circuits causes a succeeding tube or pulse generating circuit' to be conditioned so that it will be actuated to its activated condition in response to the next control condition applied to synchronizing or control leads A and B.

Thus, after one-half cycle of the synchronizing signal, at Iwhich time 'the first single trip multivibrator has completed a full cycle of. operation, a negative signal lis applied to the cathode of vacuuin tube |112` simultaneouslyfwith the application of the positive voltage appearing at the cathode outputpfvacuum tube 14' tothe control gridY of the left-hand section of vacuum tube |02. This section oi the tube is then triggered on and this' single trip multivibrator operates in the same fashion asthat of the preceding. pulse generator rtoproduce a secondwsquare pulse as shown in tr-acei 2 of Fig. 2 inaccurately. timed relationship vto that produced by the rst multivibrator of the chain Iand shown at trace I. of Fig. 2. The

remaining single trip multivibrators of the' chain operate in identical fashion, the two. out-of-phase `outputs A and B of the synchronizing multivibrator being applied to alternate single trip multivibrators as'. shown preciselyl to time the initiation' and completi'onlofthe 'gate pulses in the eight channels.

In anwalternative arrangement, the two leads A and B of Fig. 4 may be eiectively connected together to forma sing-le synchronizing lead, this single lead being supplied with a synchronizing square wave of twice the frequency, that is rto say, 'of a period equal to the period of each single trip multivibrator. Sucha square wave may, for example, be 'obtained from the preceding stage of the multivibrator frequency dividing network.

By lproviding two separate synchronizing leads A and B, however, and connecting them Ito alternate ones of the pulse generating circuits and then applying synchronizing or .controlling .potentials to these leads in phase opposition, more time is provided to permit the currents to establish themselves in the manner described above, and greater protection is secured against causing more than one tube to change from its normal to its temporarily activated condition. Furthermore, the change from the normal to the activated condition and vice versa is more accurately and stably controlled by the synchronizing signals and is thus more completely independent of variations of the type referred to above.

While there has been described above one embodiment of tlhe invention it will loe understood that changes in the particular circuit arrangements, in the types of vacuum tubes used, and in circuit parameters may be made within wide limits. For example, each of the single trip multivibrators may comprise two separate tri-odes while the multivibrators of the frequency dividing network may each comprise two sections of a dual triode.' The multivibrator-s of the frequency dividing network may be of the common triode type in which the control grids and plates of a pair of triodes are cross-connected througlh 'appropriate resistors and capacitors Iin the wellkn-own multivibrator circuit. Changes may also be made in the number of pulse generators in each gate distributor chains and in the number of chains provide-d.

What is claimed is:

1. A gate distributor comprising a substantially constant .frequency oscillator, a series of frequency-dividing multivibrators driven thereby, a train of single pulse generators, the end of a pulse in one generator being effective |to trigger the next generator of the train, means for applying the output of one of the frequency-dividing multivibrators to trigger the first generator of the train, connections for obtaining two degrees out-of-phase outputs from a frequency-dividing multivibrator of higher frequency and means for 11 applying these two outputs respectively to alternate single pulse generators of the train.

2. A pulse distributor comprising a yplurality of sources of :control current Voi? harmonically related frequencies, a train of single pulse lgenerators each adapted to be triggered by the en-d `of a lpulse from the preceding generator of said rents being equal to the frequency lof said one control current multiplied fby one-half the number of single pulse generators in said train.

LARNED A. MEACHAM.

- REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,262,838 Deloraine etal Nov. 18, 1941 2,410,883 Larsen et al Nov. 12, 1946 2,426,454 Johnson Aug. 26, 1947 FOREIGN PATENTS Number Country Date 357,532 Great Britain Sept. 14, 1931 363,403 Great Britain Dec. 18, 1931

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