US2551280A - Pulse delay circuit - Google Patents

Description

May 1, 1951 l R. E. MOE 2,551,280

PULSE DELAY CIRCUIT Filed Jan. 29, 1949 2 Sheets-Sheet l PULSE SOURCE 49 f TRIGGER Hf,

cmcun' PULSE SOURCE TRIGGER CIRCUIT Inventor: Rbert, EMOe;

bym 0% His Attorney.

May 1951 R. E. MOE

PULSE DELAY CIRCUIT 2 Sheets-Sheet 2 Filed Jan. 29, 1949 Fig.3.

TIME

t, tzt t t t 13 -13 Ihventor: RobePtEMoe, b A) M His Attorney.

Patented May 1, 1951 Robert E. Moe, Syracuse, N. Y, assignor to General Electric Company, a corporation of New York Application January 29, 1949, Serial No. 73x41 *Claiiin's. 1

This invention relates generally toelectrical multivibrator circuits and more particularly to a circuit for accurately determining the time-duration of a voltage pulse.

An object of this invention is to provide an improved circuit for generating a rectangular pulse of voltage having a time-duration accurately determined as a multiple of the interval between repeated marking pulses.

Another object of this invention is to provide a circuit for generating a rectangular pulse whose time-duration is a sub-multiple of the period of an applied alternating current wave. 7

A further object of this invention is to provide a stable multivibrator circuit for generating a square wave upon the occurrence of a voltage pulse and for terminating the duration of said wave at a predetermined time after the occurrence of said pulse, said time being determined by an external circuit.

For further objects and advantages and for a better understanding of the invention, attention is now directed to the followingdesc'ription and accompanying drawings, and also to the appended claims, in which the features of the invention believed to be novel are more particularly pointed out.

In the drawings, Fig. 1 illustrates schematically a type of multivibratorcir'cuit, known iii the art as a cathode-coupled multivibrator; Fig. '2 illustrates schematically a c'athode coupled multivibrator with certain improvements embodying my invention; and Fig. 3 shows a series ofcurve's illustrating, on a common time scale, voltage variations and wave forms occurring at various designated points in the circuit of Figs. 1 and 2.

Referring to Fig. 1, there is shown a source I adapted to supply pulses of voltage, through a capacitor 2, to the control electrode or grid 3, of an electron discharge device *4, which in conjunction with another ele'ctrondis'charge device 5, constitutes a multivibrator circuit of the cathode-coupled type. The anodes '6 and I of devices 4 and 5 are connected through resistances 8 and 9 respectively to a source of operating potential indicated by B-+. The cathodes l0 and H 'of both devices have a commoncon'nection to ground through a resistor l2. A potentiometer 13, connected between the source of operating potential 3+ and ground, provides, at an adjustable tab 14-, a positive bias potential for the grid 3"of device 4. The connection from grid 3 to tap it is made through a resistor l'5 which has a sufliciently high resistance to "prevent any substantial dissipatioiiof pulse energy 'ily be 'thec se To obtains'uchan integral relathe basic "circuit and the pulse source l fope' ted in the potentiometer. The anodeB of device it is coupled to the grid I'G of device {through a capacitor IT, and a positivebias is a ppli 'ed to grid l6 througha resistor lil providing-a 'connection to the source of operatingpotentia l l3+r.

A trigger circuit l9 has an input terminal connected to source "and an output terj a1 connected to the grid [:6 of device "5. The-f r tion of the trigger circuit is to provide, f mediately after the occurre'ncebfa pulse the source I, a series of pulsesof predetermined shorter time-duration. Any of the inful'tivibrator circuits known in the art and capable 'of pro} viding a series of pulses, occurring "at short time intervals immediately a ftertl ie o'ccurrende of an input pulse which isrep'eatjed at time intervals, may be used for the purpose. Such a circuit, for instance, is described in the publication Principles of Radar the B91 r School of the Massachusetts Institutepf ch;-

nology, published by the McGraw- "Company of NEW York in 1946, and again *U. 5. Patent No. 2-,423-,304-Fi c issued July 1,

1947, and entitled fPulse Producing "Syst'e While I have not shown-in the curves of' any rate era relationship bat-eta the repea rateof t e trigger circuit a d that of the use source, it wiut pparent that suchpoulfd tionship, the trigger circuit-l9 could he as therefrom. With such an arrangement, 'p s'e source I may take theformof a counter 51 t, and give for example, one (in ut- 3 1156 01 "every ten pulses supplied to it from the trigger circuit.

A description of the operation of the electrical multivibrator circuit 'otFig. 1 will now segues,

reference being made to 'tl'le curves of Fig, 3.

The inultivibrator circuit 'compri'sing device and 5 is 'oi the type having one condition lof stability in which device 4 is normally no onjidu'cting and device 5 is n rm uyeprraueusg. 12 1 i e i p rt o t fa t th .th i'd return of deviceE is made through resistor (8 to the positive source 13+, whereas the grid retu n oi d evice 4 is made to a source egress positive potential, as determined'by the setting of tap M on potentiometer I3. Also, due to the common cathode eo'nne'ctmn through resistor 12, the current through aevice 5 "serves to biasthe cathode l0 or device 4 in a positive enemies,

thus producing a negative bias on grid 3'o'ft'li'at device, thereby rendering it completely 'ii'o'n conductive.

device 4, a series of pulses occurring at the relatively long time interval h to tn, as illustrated by curve 30 of Fig. 3. A positive pulse as grid 3 initiates a first pulse of current through device 4 causing a decrease in voltage at the anode 6, which is coupled back to grid 6 of device 5 as a negative increment of voltage. The negative increment of voltage at the grid of device 5 reduces the current through that device, thereby reducing the voltage drop across resistor 2 and further increasing the positive increment of voltage at the grid of device 4, over and above that originally supplied from the source This further increase in the positive increment at the grid of device 4, in turn initiates another similar succession of changes, and thus a switching process occurs which proceeds very rapidly to the point where device 4 is conducting very heavily and device 5 has become completely non-conductive. The voltage at the anode l of device 5 is shown by curve 3| of Fig. 3, which illustrates a positive increment of voltage occurring at a time h, and again at time tn, as determined by the occurrence of pulses from source A negative increment of voltage, which is the inverse of the positive increment illustrated in curve 3|, occurs at the anode 6 of device 4, and supplies, through coupling capacitor [1, a negative increment of voltage at the grid I6 of device 5. The charge coupled through capacitor H is dissipated or discharged through resistor H at a rate dependent upon the time-constant of the combination, as illustrated by curve 32 of Fig. 3. In normal course, device 4 remains conducting, and device 5 non-conducting, until the charge across capacitor I! has decreased to the critical value where conduction through device 5 is just on the point of beginning. At that instant, a switching process in the reverse direction occurs, causing device 4 to become non-conducting and device 5 to become conducting. The positive increment of voltage at the anode of device 5 is thereby terminated, resulting in the generation of a square pulse of voltage, as illustrated by a curve 3| of Fig. 3.

The time-duration of the square pulse depends vupon the magnitudes of capacitor l1 and resistor l8, and also upon the circuit constants of .the associated elements and the operating voltages. The time-duration, as can be appreciated from an inspection of curve 32; is determined by the intersection of a sloping exponential curve with a certain horizontal voltage level and, acfcordingly, is not accurately and positively fixed.

For instance, referring to Fig. 3, curves 3| and :32 represent respectively the anode output voltage, and the control electrode voltage of device 5 for a certain set of operating voltages and circuit constants. Curves 3|f and 32' represent similar operating characteristics when capacitor l1 and may be anywhere within certain limits such as tb to to in Fig. 3. Thus, any slight change in supply voltages or any drift in circuit constants -due to temperature changes may shift the actual I time ta of the occurrence of the reverse switching process.

To provide a more definite fixation or determination of the time-duration of the rectangular output pulse, it, has been customary heretofore to apply to the grid of device 5 a sharp pulse which will increase the voltage on the grid of device 5 to a value sufficient to initiate the reverse switching process. Thus, the function of the trigger circuit I9 is to provide a series of trigger pulses occurring at definite time intervals after the original input pulse. While the period between trigger pulses is normally an integral sub-multiple of the period between pulses from the source there is no necessity that such be the case, and the trigger pulses may have any desired repetition rate. The output pulses from the circuit l9 are illustrated by curve 33 of Fig. 3. When these pulses are applied to the grid of device 5, they are superimposed on the exponential discharge curve and establish definite instants in time at which the switching action may occur, as illustrated by curve 34 of Fig. 3. For instance, the switching action would normally occur at time t7, and the time-duration of the rectangular output pulse of curve 3| would then be the interval ii to t7, which is equal to 6 of the periods of the trigger pulses from the circuit [9.

While the circuit which has been described provides results which are adequate for some applications, the circuit suffers from a considerable measure of instability, since it has been found in practice that the switching action may occur at the instants is to ts, rather than at the instant 157. This is due to the fact that the timing pulses from the trigger circuit are superimposed on a gently curving exponential. Accordingly, there is not a great deal of difference in the absolute potential or voltage to which the grid of device 5 is raised by successive trigger pulses. The result is that the reverse switching action definitely occurs at an instant determined by one of the trigger pulses, but the number of the trigger pulse or in other words the particular individual pulse is not definitely and positively selected. Thus, referring to curve 34, the reverse switching occurs at time t7, but any slight disturbance or variation in circuit constants may make it occur at times ts or is, and also may cause the switching instant to shift continuously back and forth from one to the other.

My invention resides particularly in an improvement in the circuit for applying the trigger pulses of curve 33 in a modified form to the grid of device 5, as illustrated in Fig. 2. Referring to Fig.2 in which circuit elements performing the same function as in Fig. 1 bear the same numerals, the grid I6 of device 5 is no longer connected to the source of operating potential B+ through a resistor |8, but instead is connected to ground through a capacitor 2|. The output terminal of the pulsing circuit I9 is now connected to the grid 16 of device 5 in series with a resistor 22, a capacitor 23, and a diode 24, which is connected to conduct current from capacitor 23 to grid l6. Another diode 25 is connected to conduct current from a point of potential, which is negative with respect to ground, to the junction of diode 24 and capacitor 23. The point of negative potential is provided by a tap 26 on a potentiometer 21, of which one terminal is grounded and the other terminal is connected to a source of negative potential provided by a battery 28. A capacitor 29 connected between ground and tap 26 provides a low impedance path for pulsating currents flowing through diode 25.

When a positive pulse of voltage is supplied to grid 3 of device 4 in the circuit of Fig. 2, the sequence of events is very similar to that occurring in the circuit of Fig. 1. Immediately upon the-occurrence of the pulse-at times t1 and 1511, as illustrated in curve 3ll, a switching action occurs which renders device 4 conducting and device 5' non-conducting. This 'resultsin a Y positive increment of voltage at the anode of device 5, as illustrated by curve 3!, and also by curve 36, of Fig. 3. Simultaneously, a negative increment of voltage is produced at the grid 55 of device 5 through the coupling capacitor 9, as illustrated by the negative increment in curve 35 occurring at times t1 and tn. Trigger pulses, as illustrated in curve 33, are applied to the charging circuit comprising diode 24, from the trigger circuit i9. These pulses cause small increments of charge to flow through the diode 24, thereby incrementally raising the initial negative potential at'gridlt of device 5 toward zero. The voltage at grid 1 6, or in other Words the charge developed across capacitors I? or 2 l, increases in a series of small increments or steps, as illustrated by curve 35 of Fig. 3. For each pulse of voltage supplied from the trigger circuit, an increment of voltage appears at grid E6. The size or magnitude of this increment is dependent upon the ratio of the values of capacitors 23 and I? and upon the ratio of resistance 22 to the anode resistance of device 4. The function of capacitor 2| is simply to stabilize the operation of the circuit, and its value may be approximately of that of capacitor l1.

The voltage developed across capacitor i! increases in a number of increments or steps until it reaches a value sufficient to initiate the reverse switching process and thereby determine the time-duration of the output pulse at terminal "20, as illustrated in curves 35 and 3.6. When the reverse switching process occurs at time t7, diode .25 conducts and restores, across capacitor 23, a reference voltage whose magnitude is dependent upon the setting of potentiometer 21. The length of time, or the number of pulses or steps, required to initiate the reverse switching process in the multivibrator is dependent upon both the setting of potentiometer 21, which determines the reference negative bias at grid 16 of device '5, and upon the setting of potentiometer l3, which determines the anode current of device 4 and, therefore, the magnitude of the negative pulse supplied to grid 16 of device 5 at the initiation of a switching process. In practice, either potentiometer 2! or potentiometer I3 is permanently set, and the other is varied to determine the length or timeduration of the rectangular output pulse.

In operation, the time-duration of the rectangular output pulse is always an exact multiple of the time between trigger pulses. With the circuit of my invention, the count or number of periods comprised Within the time-duration of the rectangular pulses is definitely fixed. The operation remains stable because the number of trigger pulse periods contained within one rectangular output pulse is determined largely by the voltage divider action of potentiometer 53 which remains constant regardless of temperature drift. With my invention, the tendency of the switching process to shift in occurrence between adjacent pulses from the timing circuit is largely eliminated.

While a certain specific embodiment has been shown and described, it will, of course, be understood that various modifications may be made without departing from the invention. The appended claims are therefore intended to cover 6. any suchimodificationsiwithin the truespiritsand scope of the invention.

7 What I claimas new and desire to secure by Letters Patent of the United States is:

1. A system for generating a voltage pulse of predetermined time-duration after an initiating impulse, comprising a multivibrator, said multivibrator comprising time constant-circuits providing said multivibrator with one condition of stability, means for applying saidimpulse to said multivibrator to. disturb said condition of stability, means responsive to said impulse for generating a series of triggering pulses at predetermined time intervalsafter saidoccurrence, a unilateral charging circuit comprising said multivibrator time constant circuits responsive tosaid triggering pulses for generating a stepvoltage which increases by one step at a time for each of saidtriggering pulses, said multivibrator being responsive to a predetermined level of said step voltage for returning to said condition of stability.

2. A system for initiating an increment of voltage upon the occurrence of successive electrical impulses and for terminating said increment after a fixed number ofequal time intervals beginning with said occurrences, comprising a multivibrator, said multivibrator comprising time constant circuits providing said multivibrator with one condition of stability, means for applying said impulses to said multivibrator to disturb said condition of stability and to cause an increment of voltage in said multivibrator upon the occurrence of said impulses,said voltage increment maintaining said multivibrator in said disturbed condition for a given interval, means responsive to said impulses for'generating a series of triggering pulses at predetermined relatively short time-intervals after said occurrences, a unilateral charging circuit comprising said multivibrator time constant circuits responsive to said triggering pulses forgenerating a step voltage by the accumulation of a 'definiteamount of charge in response to each one of said triggering impulses, said multivibrator responsive to a predetermined level of said step voltage for returning to said condition of stability and to terminate said increment before the expiration of said given interval.

3. A system for initiating an increment of voltage upon the occurrence of successive electrical impulses and for terminating said increment after a fixed number of equal time intervals beginning with said occurrences, comprising a multivibrator, said multivibrator comprising time constant circuits providing said multivibrator with one condition of stability, means for applying said impulses to said multivibrator to disturb said condition of stability and cause an increment of voltage in said multivibrator upon the occurrence of said impulses, said voltage increment maintaining said multivibrator in said disturbed condition for a given time interval, a trigger circuit responsive to each of said impulses for generating, a series of triggering pulses at time-intervals substantially less than said given interval, said trigger circuit having an output terminal connected in series with an impedance and a rectifier to said multivibrator, time constant circuits, said impedance rectifier and time constant circuits forming a storage circuit to produce a step voltage increasing by a small increment in response to each of said triggering pulses, and said multivibrator responsive to a predetermined level of said step voltage for returning to said condition of stability, thereby terminating said increment of voltage.

4. A pulse generating system comprising a source of initiating impulses, a pair of electron discharge devices each having an anode, a cathode and a control electrode, a common resistive connection from both said cathodes to a common point of fixed potential, separate resistive connections from said anodes to a point of positive potential with respect to said fixed potential, a voltage bias source, means to apply said bias to the control electrode of one of said devices to maintain said one device normally non-conducting, a capacitive connection from the anode of said one device to the control electrode of said other device, a connection from said impulse source to the control electrode of said one device to render said one device conducting and said other device non-conducting upon the occurrence of an initiating impulse, a trigger circuit connected to said source for generating, in synchronism with the occurrence of an initiating impulse, a series of triggering pulses at time intervals substantially less than the intervals between said initiating impulses, said trigger circuit having an output terminal connected in series with an impedance and a rectifier to the control electrode of said other device, said rectifier poled to produce at said control electrode a step voltage increasing by a small increment in response to the positive going portion of each of said triggering pulses, a second rectifier biased to a negative potential with respect to said fixed potential, said second rectifier connected to the junction of said first rectifier and impedance and poled to be conductive in response to the negative going portion of each triggering pulse, said step voltage being of a polarity to render said other device conducting after the attainment of a predetermined magnitude by step voltage.

5. A pulse generating system comprising a source of initiating impulses, a pair of electron discharge devices each having an anode, a cathode and a control electrode, a common resistive connection from both said cathodes to a common point of reference potential, separate resistive connections from said anodes to a point of positive potential with respect to said reference potential, a voltage bias source, means to apply said bias to the control electrode of one of said devices to maintain said one device normally conducting, a capacitive connection from the anode of said one device to the control electrode of said other device, a connection from said impulse source to the control electrode of said one device to render 1 said one device conducting and said other device non-conducting upon the occurrence of an initiating impulse, a trigger circuit connected to said source for generating, in synchronism with the occurrence of an initiating impulse, a series of triggering pulses at time intervals substantially less than the intervals between said initiating impulses, said trigger circuit having an output terminal connected in series with an impedance and a first rectifier to the control electrode of said other device to produce thereat a step voltage increasing by a small amount in response to each of said triggering pulses, said first rectifier being poled to conduct on a positive going voltage, a second rectifier connected between the junction of said first rectifier with said impedance and a point of negative potential with respect to said reference potential, said second rectifier being poled to conduct on a negative going voltage.

ROBERT E. MOE.

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

UNITED STATES PATENTS Number Name Date 2,405,237 Ruhlig Aug. 6, 1946 2,411,648 Brauer Nov. 26, 1946 2,420,516 Bischofi May 13, 1947 2,430,547 Anderson Nov. 11, 1947 2,444,036 Crost June 29, 1948

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