US2416111A - Pulse generating circuit - Google Patents

Description

Feb. 13, 1947. D. E. MAXWELL 2,416,111

PULSE GENERATING CIRCUIT Filed June 19, 1944 SOURCE PULSE VOLTAGE Fig.3.

Inventor:- Donald E. Maxwell,

H is Attorney.

Patented Feb. 18, 194'? p 2,416,1ii

PULSE GENERATING CIRCUIT Donald E. Maxwell, Syracuse, N. Y., assignor to General Electric Company, a corporation of New York Application June 19, 1944, Serial No. 541,043

9 Claims.

My invention relates to electric pulse generating circuits, and more particularly to means for shaping the trailing edge of a pulse to provide a more nearly rectangular pulse wave form.

' Many radio communication and detection circuits in current. use employ pulse modulated rather-than continuous carrier waves for transmission. The modulating pulses are of very short duration, for example of the order of 1 microsecond, and preferably are of substantially rectangular wave shape. The pulsed carrier wave may be utilized in various ways, such as by transmission and reflection of a series of pulses for object detection, or by signal modulation of the pulse width, amplitude, or frequency to convey intelligence.

The pulse modulated carrier waves are commonly produced by generating voltage pulses of the desired characteristics and utilizing the pulses to modulate the output of a high frequency oscillator, such as a magnetron oscillator or the like. In such modulating circuits a pulse transformer is frequently interposed between the pulse generator and the magnetron oscillator, both to increase the voltage applied to the magnetron tube and to provide a charging path for the capacitive pulse-forming element.

In certain applications it is found desirable that a single apparatus be capable of supplying pulses of selectable duration or width, a typical variation in width being over a range of the order .of 5:1. For example,'a single pulse generator may be required to supply either a 0.5

mircosecond pulse or a 2.5 microsecond pulse. Heretofore, considerable difliculty has been encountered in providing such a versatile pulse generating apparatus, especially where the pulse load circuit is inductive, as it is when a pulse transformer is used. Such transformer may be designed to produce desirably shaped pulses of only one width. If the transformer is designed to produce a well-shaped wide pulse, an appreciably narrower pulse will exhibit a very slow decay of voltage at the trailing edge; while, if the transformer is designed to produce a wellshaped narrow pulse, the magnetizing current will be excessive on the wide pulse, resulting in,

poor pulse efficiency and voltage reversal at the trailing edge of each pulse. In either case, the trailing edge of each-pulse is characterized also by severe oscillations of very high frequency resulting from the leakage reactance and distributed capacitance within the pulse transformer itself. On the other hand, a pulse transformer designed for pulses of intermediate width leaves much to be desired, because both wide and" narrow pulses will then have unsatisfactory wave shapes.

Accordingly, it is one object of my: invention to provide a new and improved pulse generating .voltage decay atthe trailing edge of each pulse and means for suppressing trailing edge oscillations.

In accordance with my invention, I provide a pulse transformer designed particularly. to pro vide an optimum wave shape for the widest contemplated pulse. Such design demands; among other things, a transformer having a primary inductance sufficiently great that the magnetizing current and trailing edge oscillations will not be objectionably large for the wide pulse. Such a transformer, however, does not store suflicient energy during the shortest contemplated pulse interval to effect rapid decay of pulse voltage at the trailing edge of the pulse. Therefore, in order to provide sufiicient energy storage to avoid slow voltage decay at the trailing edge of a short pulse, I connect across the pulse transformer an inductive network arranged to increase the effective magnetizing current and ener yv storage for short pulses to a value suflicient to cause rapid decay of the pulse voltage at the trailing edge of a short pulse. Switching means are provided for disabling the auxiliary inductive circuit when wide pulses are desired. Preferably, energy dissipating means is also provided across the pulse transformer for preventing violent voltage oscillations at the trailing edge of the pulse, while permitting rapid voltage decay.

Myinvention will be more fully understood and its objects and advantages further appreciated by referring now to the following detailed specification taken'in conjunction with the accompanying drawing in'which Fig. 1 is a schematic circuit diagram of a pulse generating circuit embodying my invention and Figs. 2 and 3 are graphicalv representations of pulse wave shapes illustrating the operation and effect of my invention.

- Referringnow to the drawing, and particularly to Fig. 1, I have shown-a pulse generating circuit comprising a source I of substantially rectangular voltage pulses of selectable width or duration. The succession of pulses originating in the source I is supplied through a transformer 2 to the input circuit of an electron discharge device 3. The electron discharge device 3 comprises an anode 4,;a cathode 5, and acontrol vice or pulse triggering a tube 3 is periodically I rendered conductive by positive voltage pulses from the source I, thereby to connect the condenser I for pulse discharge through an output circuit including an autotransformer 9 anda magnetron oscillator tube 8 having an anode 8a and a cathode 8b.

As shown in the drawing, the magnetron oscillator tube 8 is connected across the secondary 'winding of the autotransformer 9, the primary winding! of which is connected in parallel circuit relation with the pulse discharge path through the magnetron oscillator 8. The primary winding II! of the autotransformer 9 serves as a direct current path for recharging the condenser 1- at the termination of each pulse. The condenser charging circuit also includes a high resistance II and a source of unidirectional electric current supply, such as the battery [2, connected in series circuit relation between the anode and cathode of the electron discharge device 3. The cathode 5 of the discharge device 3 and the anode 8a of the magnetron oscillator 8, as well as the negative terminal of the battery l2 and one terminal of the autotransformer 9, are connected together and grounded, as shown at Fig. 1.

The input circuit for the pulse triggering tube 3 comprises a secondary winding l3'of the input transformer 2 connected between the oathode 5 and control electrode 6 of the discharge device 9 through a suitable coupling capacitor M. The discharge device 3 is negatively biased to cut-off by any suitable means, such as, for example, a battery liand a grid resistor l6 connected'betweenithe cathode 5 and control electrode 6.

It is found in practice that the autotransformer 9 and the magnetron oscillator tube 8 have a certain amount of stray and distributed capacitance to ground. This capacitance is m dicated at it by dotted lines in Fig. l as capacitance between the anode and cathode of the magnetron 8. The stray and distributed capaci-i ties represented by the capacitor 8 form with the autotransformer 9 a resonant circuit having a natural frequency of oscillation relatively high with respect to therepetition rate of the pulses from the source, i. This natural oscillation frequency is ordinarily of the order of 100 kilocycles per second. The pulse repetition rate, on the other hand, is ordinarily of the order of 500 to 5000 pulses per second in radio detection apparatus or pulse communication apparatus. The autotransformer 9 has also a certain amount of internal leakage inductance and distributed ca:v

'pacitance.

In pulse transformers of the type commonly employed in the generation of pulses of the character described, these internal circuit constants tend to initiate a very high frequency.

trailing edge oscillation superposed upon the 100 kilocycle oscillation described above. These superposed high frequency oscillations are ordinarily of the order of 7 to 10 megacycles per second.

' The autotransformer 9 is designed to provide microseconds." Since the autotransformer is connected in parallel circuit relation with the- 4 tor tube 8, such design demands that the transformer be provided with sufiicient inductance so that the energy stored in the transformer during the relatively long pulse will not be so great as I to produce undesirably violent high frequency oscillations in the resonant circuit 9, It at the termination of 7 av pulse. On the other hand, the transformer inductance must permit sufficient magnetizing current and energy storage to effect a rapid decay of pulse voltage at the pulse termination. A transformer designed to meet these requirements in the optimum manner will have such a high inductance that appreciably shorter pulses, for example of the order of 0.5 microsecend, will not store sufiicient energy in the transformer to efiect a rapid decay of pulse voltage at.

the termination of the pulse. Accordingly; for

such short pulses, the trailing edge of the pulse will demonstrate a gradual decay of voltage,

an optimum pulse. wave shape for the pulses of; longest durationcontemplated, for example 2.5

rather than a sharp decay as desired.

In order to improve the characteristics of my pulse generating circuit for short pulses, I provide in parallel circuit relation with the primary winding I 9 of the autotransformer 9. an inductive circuit including an inductive impedance [9 connected in series circuit relation with a resistor 29 througha contact 2| of an electromagnetic relay 22. The relay 22 is controlled in any desired manner to connect the network 19, 29 in parallel circuit relation with the transformer primary winding lil when short pulses are being generated and to disable the network I 9, 29 when long pulses are generated. When the network [9, 20 is connected in circuit with the transformer, the effect of the network is to store additional energy in the inductive impedance l9 during the pulse intervals thereby to increase the effective magnetizing current and to increase the stored energy available for release at the termination of each pulse. The sum of the energy now stored in the transformer 9 and the inductor I9 is suflicient to produce a rapid decay of pulse voltage at the trailing edge of each pulse. The additional stored energy of course adds to the tendency to produce oscillations in the kilocycle range at termination of each pulse. In order to maintain .such oscillations within practical'limits, the resistor 29 is provided and is of such value that the trailing edge oscillations in, the 100 kilocycle range are rapidly damped out. 7 7

From the foregoing explanation, it is to be noted that it is necessary to design the autotransformer 9 itself so that, for long duration pulses with the network [9, 20 disabled, the energy storedin the transformer 9 itself is sufiicient to produce a rapid decay of pulse voltage at the trailing edge While the network I9, 29 is so designed kilocycles, additional means is necessary for suppressing the high frequency'oscillations at about Z to 10 megacycles arising from the internal circuit constantsof the pulse transformer 9. itself." 'F'or this purpose, an additional damping, resistor 23 may be'connected in seriescircuit relation with ablocking capacitor 24- across the primary tron discharge device 3 is normallybiased tocut" off by the battery Hi. When the discharge device 3 is not conducting, the condenser! is maintained charged to substantially the full voltage of the battery 12 througha charging circuit comprising the resistor H, the condenser 1, and the primary winding .ll! of the autotransformer 9. The voltage pulses applied from .the source I through'the transformer 2 are arranged periodically to impress positive potentialsupon the control electrode 6 for predetermined pulseperiods therebytorender the, discharge device 3 conduc-. tive. When the discharge device 3 becomes conductive, the condenser 1 .idischarges through a load circuit comprising the discharge device '13,

the magnetron oscillator tube '8, and the upper portion of the autotransformer 9 The voltage drop through the discharge device 3 is relatively small so that substantially the full .voltage of the condenser 1 is impressed across the magnetron oscillator tube '8 and the'upper portion of the autotransformerll. i

It will be noted, that there isconnected also across this load circuit the primary windingv H! of the autotransformerm However, since the autotransformer primary winding Innis highly inductive, very little magnetizing current flows through the primary winding during the pulse period. During the period of the pulse, however, a small amount of magnetizingcurrent is gradually'louilt up in the transformer winding! l3 so,

that at the termination of the pulse acertain amount of energy is stored in the windin I0.

This stored energy produces 'a rapid decay of voltage at the termination of the pulse discharge and initiates both' a relatively low frequencyLos-'- cillatory charge and discharge of the distributed and stray capacitance represented by thecondenser I8 and the high frequency oscillations characteristic of the internal transformer circuit constants. When the inductive reactor I9 is notconnected in thecircuit, the lower frequency oscillations .are'not of objectionable amplitude,-and the high frequency oscillations are damped by the network 23,24. When short pulses are received from the trigger voltage source I, the inductive network [9, 20 is connectedin circuitin order to store suflicient energy to efiect rapid trailing edge pulse voltage decay. The reactor l9 increases the tendency of the circuit to develop oscillationsin the range of 100 kilocycles, but-the-resistor 20 'effects satisfactory damping of suchoscillations; The network 23,24 functions as before to damp the high frequency oscillations at 7 to 10 megacycles, but is relatively ineffective for the lower frequency oscillations.

'To illustrate the effect of the networks I9, 29 and 23, 24 connected in parallelgcircuit relation 4 of shorter duration than said 'maximum, and

. v e I winding of the pulse transformer '9 when the transformer 9 is designed t'o-provide 2.5 microsecond pulses and the networks I9, 20 and 23', 24 are not connected in circuit with the transformer. At diagram b of Fig. 2, Ihave illustrated a typical wave shape for a 0.5 microsecond pulse'as obtained from the same transformer under similar conditions. Referring now to Fig.3, I have shown similar diagrams a; and b illustrating the waveshapes of 2.5 and 0.5 microsecond pulses, respectively, which are obtained from the same transformer 9 when the networks I9, 29 and 23, 24 are connected in parallel circuit relation primary winding [0. Y

While I have described only one preferred bodiment of my invention by way of illustration, many modificationswill' occur to those skilled in the art and'I therefore wish to have it understood that I intend in the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is z" 1. In combination, acapacitive pulse-forming energy storage element,.-a'load circuit including an inductive energy storagejelement, means for establishing a succession of pulse discharges of said capacitive storag'eelement through said load circuit, said means comprising switchingmeans.

and means for rendering said switchingmeans conductive for recurrent pulse interval of selectable duration, saidinductive element-storing sufiicient energy during pulse intervals of maximum duration to effect a rapid voltage decayat the termination of eachsuch pulse interval, and

an additional inductive energy storage element arranged to be connected inparallel circuit relation with said first inductive element to facilitate the'formation of pulses of shorter duration than said maximum.

2. In combinatiorua capacitive pulseiforining storage element, a load circuit including an in- .ductive energy torage element; mean's for establishing a succession of pulse dischargesof said capacitive storage element through said load circuit, said means comprising switching means and means for rendering said-switching means conductive for recurrent pulse intervals of selectable duration, said inductive element storingsuifi c'ient energy during pulse intervals of maximum dura tion to effect a rapid decay of voltage at the termination of each pulseint'erval', mean in cluding a-sourceof electric current supplyq'for charging said capacitivestorage element between said pulse intervals, an. additional inductive energy storage element arranged to be connected, in parallel circuit relation with said firstinductive elementto facilitate the formation of pulses means for damping electric oscillations'initiated by said stored energy at the termination. of each said Pulse discharges comprising a resistor connected in series circuit relation withsaidadwith the primary winding ID of the autotransformer 9, I have shown at'Fig. 2 a diagram a illustrating a typical pulse wave shape fora 2.5 microsecond pulse obtainedfrom the secondary ditional inductive energy storage element. 1

3. An electric pulsegenerating circuit comprising a capacitive pulse-dormingstorage element,

a load circuit including anjinductive energy storage element, means for establishing a succession of pulse discharges of said capacitive storage ele-' ment through said load circuit, said means com 1 prising switching means and means for rendering said switching means conductive for recurrent pulse intervals of selectable duration, said induc-"y I tive element storing sufficient energy during pulse intervals of maximumduration to. effectarapid' with the decayof voltagezatlthe termination of each pulse interval, :means iincluding a source .of electric current supply. for charging said capacitive storage element between said ,pulse intervals, and

means for facilitating the. formation oipu'lses of shorter duration thansaid maximum comprising an additional inductive energy storageelement and a'rresistor arranged selectably to beconnected in circuit with .said ,first inductive energy storage element. t

4. An electric pulse generating circuit-compris ing a: capacitive l pulse-forming energy: storage element, a ioadcircuit includinga unidirectional. conducting device, means for .es'tablishingia'suc cessionoflpulse discharges offsaid capacitiverstor age element through said load :circuit. including switching mean andmeans'forrecurrentlyrendering saidjswitching means conduc'ti've .iorpulse intervals of selectable duration, means including an inductive energy storage element connected across said unidirectional conductingdevice, said inductive element storing sufficient .energyduring pulse intervals of maximum duration to efiect a rapid voltagedecay at the termination of each pulse interval, and an :additional inductive en-i ergy storage element arranged selectably .:to be energy istorage :elementga :loadiciircizit iincluding an inductive 'zenergyrrstorage element, ,means for establishing :a succession of pulse discharges of said capacitive storage element through saidjload circuit, said :means comprising (switching means and means for rendering "said switching means conductive i011.reourrent'apulse intervals lot: so;-

lecta'bl'e Iduratio 11,, said inductive element storing sufiicient energy. during :pulse :intervals of maxi-i mumiselectable duration :to aeffecta rapid voltage dec'aylat ithe'itermination :of reach :such pulse interval, .a second :inductive energy storage .Iele

- ment, switching means formonnecting'said secconnectedinseriescircuit relation with a resistor across said "first inductive energy. storage element during theformationlof pulses oflshcrter duration than said maximum. r v

7 -75. In combination, an, electron dischargedevice including an anode, a cathodaand ascontrolJelec trode,'means for supplying to said control electrode a succession of voltagefpulses of selectable durations-arranged recurrently to render said dis- I charge device conductive forpredetermined se-v lectable pulse intervals, a capacitive pulse-formj ingenergy storage element, a load circuit icon? 0nd inductive energylstorage element in parallel circuit "relation with said first inductive energy storage element thereby to. increase the efi'ective I magnetizing'current ofcsaidyload circuit for pulses of shorter duration than said maximum, and means for damping electric oscillations initiated 1 by said stored energy-at the termination of each pulse discharge comprising a resistor connected in parallel Jcircuit relation with said first energy storage element. v l s j '8.I In combination, an :electron discharge :de-

"vice including antanode; a cathode, and a control electrode, :meansfor supplying tosaid icont'rol electrode a succession of voltagepulses of selectable duration arranged recurrently to render .said discharge device conductive for predetermined selectable pulse intervals, a capaci .tiveipulsefor'ming energy storage element, a load, 7 Q circuit includingan autotransformer 1 having av primarywinding connectedacross said capacitive pulse-forming element through said dischargedevice, said.v load cirouit gincluding also a unilateral conducting device connected across ithe second},

' ary win-ding'aof said transiormerjthe :magnetizing' :current 20fsaid transformer :being 'sufiicient nected to said capacitive storage element through said discharge device, said load circuit-including.v an inductive energy storage element having a magnetizing current sufiicient to provide a rapid voltage decay at the termination of pulses of,

maximum selectable duration, a second inductive energy storagegelement, and switching meangfor connecting said inductive storage elements in parallel circuit relation to increase the'eiiective vice including-an anoda-a cathodeQanida control electrode, means for supplying to said control electrode a succession of,voltage pulses off-so"- lectable duration arranged recurrently to renderv said discharge device conductive forpredeter- I magnetizing current in said load circuit thereby to facilitate the formation oiv pulses oi shorter duration than said maximum. 1 -s so 6. In combination, an electron discharge demined'selectable pulse intervals, a capacitive pulse-forming energystorage element, aload circuit connected ,to'jsaid capacitive storage element I 1 through said discharge device, 'saidload circuit 1 including an autotran-sformer and a unidirection-l ally conductingdevice connected across; the. 1 transformer-secondary winding, the magnetizing current of said transformer storing sufiicient en- Y j ergy in said transformer during pulses of maximum selectable duration to provide arapid volt- 1' age decay at the termination of eachsuch pulse, 1 and means for increasing the effective magnetizing current of saidtransformer for pulses of i shorter duration than said maximum comprising; 7 1 an inductiveenergystorage element and' an en- 1 ergy dissipating resistor arranged foriselecta'ble connection'in parallel circuit'relation' with the primary'windingiof said transformer.

T 3 In combination; a capacitive pulse-forming for pulses of maximum duration to effect rapid voltagev decaylof said pulses at the termination thereof, 'meansfor increasing the effective image,

netizing current of :saidtransformer vcomprising an inductive :energy storage element, switching means forzconnecting said inductive energy storage element in parallel circuit relationwith the primary winding of said 'autotransfiormerduring the occurrence of pulses of shorter said maximum; andilmea ns. for suppressing high frequency electric oscillations across said trans;

former atth'e termination of eachrpuls'e discharge yfor connecting said load circuit to, said pulse-J forming element for pulseiintervals of selectableduration, said inductive element storing sufficient energyduring pulses of maximum' duration to er feet Ia rapid voltage decay. atlthe termination'of I each such pulse, and means for selectably increasing the inductive energy storage capacity of said load circuit thereby to facilitate the formation of pulses of shorter duration'than said maximum.

DONALD 13.1 MAXW LL,

REFERENCES CITED The following references are of record inthe filelof thisipatentL V i 'FoREI-GNEPATENTSr Country Number :Date

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