US2727228A - Pulse generator - Google Patents

Description

Dec. 13, 1955 c. H. HoEPPNER ETAL 2,727,228

PULSE GENERATOR Filed Sept. 17, 1945 All wvvm/Lo'm CONRAD H. HOEPPNER ALBERT G. HUBBY @MQML United States Patent PULSE GENERATOR Conrad H. Hoeppner, Washington, D. C., and Albert G. Hubby, Waco, Tex.

Application September 17, 1945, Serial No. 616,944

15 Claims. (Ci. 340-345) (Granted under Title 35, U. S. Code (1952), sec. 266) This invention relates to a pulse generating system and particularly to a system for generating a series of accurately known time duration and spaced pulse signals.

An object of this invention is to provide a means for producing a controllable number of electrical pulses.

Another object of this invention is to provide a pulse generating circuit in which a single artificial line may be used as a time determining element for accurately fixing the duration of each pulse of a series of pulses as well as the time interval separating the pulses.

Another object of this invention is to provide a pulse generator of the foregoing type whose standby, i. e., before operation, power consumption is reduced to a minimum.

Other objects and features of the present invention will become apparent upon a careful consideration of the following detailed description when taken together with the accompanying drawing, the single figure of which is a schematic diagram of a typical embodiment of the invention.

in general, the circuit of the drawing constitutes a specific embodiment of the invention and is arranged to produce a controllable number of accurately known time duration and time spaced pulses. According to the single embodiment of the invention, an input pulse obtained, forexample, from an external generator 10, is used to key a switching circuit 4t) into operation, the purpose of which is to enable or render the rest of the circuit operative for a controllable period of time by means of a controllable time duration pulse. The leading edge of this pulse, after being amplified, for example, by a number of stages 18, 22 and 24 is applied through a suitable vacuum tube 29 to an artificial line 30 which for purposes of illustration is shown as short circuited at oney end 41. The applied voltage surge travels down the line* to the short circuited end where it is inverted and reected and after a period of time required for two trips through the line appears as a negative voltage surge at the input end of the line. The resulting negative surge is reapplied to the line through amplifier 18, for example, where a regenerative action is started causing the input end of the delay line to be driven further negative. Again, after an interval of time required for two trips through the line, the negative voltage surge returns as a positive surge, which is similarly re-applied through amplifier 18 to the line. lt is apparent that this action could continue indefinitely if desired, with the result that a series of accurately known time spaced and time duration pulses would be produced at a number of points between the plate of tube 18 and the plate of tube 34. Each pulse and the spacing between the pulses is equal to the time required for a voltage surge to travel down the line and back again. Therefore, in the case where a limited numer of pulses is to be generated, a switching or enabling circuit such as that shown at 40 must be provided for permitting or suppressing the regenerative action of the circuit by controlling, for example, the operation of the feedback tube 18. The period of the switching circuit is adjusted so that after the production of a double pulse signal, for example, it will return to its initial condition sometime after the second pulse but before the start of a third pulse thus blocking the operation of the feedback tube 1S as hereinafter described in detail.

Since only a finite number of pulses is to be generated, the switching circuit liti is preferably of the self-returning type. For instance, in the drawing the switching circuit 4t) comprises tubes 11 and 12 connected as a multivibrator which is provided with one stable state of operation in which the pulse generating circuits are held quiescent. ln particular, the stable state of the multivibrator exists when tube 11 is conducting and tube 12 is non-conducting and is attained by connecting the grid of tube 11 through resistances 13 and 14- to a positive potential and the grid of tube 12 to a potential divider comprising resistances 15, i-A connected between the plate of tube 11 and a source of negative potential. In the standby condition, before operation of the system is instituted, the grid of tube 12 is maintained suliiciently negative, with respect to its cathode, by the voltage divider action of resistances 15, id-A and l2 so as to prevent conduction by tube 12. The time constant of the grid circuit of tube 11, de termined essentially by capacitance 16 and resistances 13, and 38, is made such that tube 11 will remain cut off, subsequent to the application of a negative pulse to its grid, for an interval of time slightly longer than that over which the desired number of output pulses is to occur. If, for example, a series of two output pulses each of 10 microseconds duration and spaced in time by a 10 microsecond period is desired, it would be suitable to adjust the multivibrator 1l, 12 to remain in the unstable condition with tube 12 conducting and tube 11 non-conducting for approximately 35 microseconds to allow 5 microseconds leeway in timing in either direction.

ln controlling the operation of the feedback tube 18 from the switching circuit 4l), the grid of tube 12 is directly connected to the control grid 17 of tube 18. Thus, by making the negative potential applied to the grid of tube 12 of sufficient value, tube 18 can also be held cutolf when tube 11 of the gating circuit is conducting. When, however, tube 12 of the gating circuit becomes conducting as a result of the application of a negative trigger puise to tube 11, the potential at the grid of tube 12 and at grid 17 of tube 18 will rise together to thus cause tube 18 to become conducting. As tube 18 is rendered conducting, a negative voltage swing appears across its plate load resistance 19 and is coupled by means of capacitance 2li and resistance 21 to the grid of tube 22. The latter tube is plate loaded by resistance 23 and acts primarily as an inverter and amplier having its grid returned to the positive supply through resistance 21 so that it is normally biased conducting except when tube 18 becomes conducting, at which instant it is rendered nonconducting thus producing a sharp positive voltage swing at its plate. The voltage variations produced across the plate load resistance 23 of tube 22 are in turn applied to the grid of a cathode loaded vacuum tube 24.

Tube 24 serves as a low impedance driving source for tube 29 and is biased normally non-conducting as a result of a negative bias maintained at its grid by way of the voltage divider action of resistances 25, 26, 27 connected between a negative potential and ground. The grid of tube 29 is likewise maintained at a negative potential slightly greater than cut-off potential by its connection to the cathode of tube 24, the cathode of tube 29 being returned to ground through delay line 20. Thus, tubes 2d and 29 are normally held in a cut-off condition and like tubes 12 and 18 are of low average power consumption.

For practical reasons, the artificial line 30 has a low characteristic impedance, for example, 250 ohms. Thus,

to produce a voltage pulse of an appreciable magnitude, considerable line charging current is required to flow therethrough. To produce this high current flow, the dual cathode loaded amplifier arrangement consisting of tubes 24 `and 29 with the line Sii placed in the cathode circuit of tube 29 is employed. The loW output impedance ci the cathode loaded tube 24 and the direct connection to tube 429 permits the grid of tube 29 to be driven highly positive on large amplitude positive pulses without the development of an additional biasing voltage as a result of the charging of a coupling capacitance. This positive grid condition produces high conductivity by the plate of tube 29 as well as by the grid of that tube so that a peak current of approximately l ampere (with tubes 24 and 29 as a 6SN7) 4may be drawn under certain operating conditions.

To complete the regenerative action necessary in the production kof a series of pulses, the cathode ot tube 29 is connected by means of a coupling circuit comprising capacitance 31 and resistance 32 to the second control grid 33 vof the feedback amplifier tube i8.

Aidescription of the operation of the circuit when used .to .produce a series of two pulses upon application of a ksingle negative pulse to the grid of tube 1i is as follows:

A negative keying pulse produced by the signal generator 10 trips the gating circuit il, l2 causing tube 12 to conduct and thereby removing the cut-od bias from tube 18. Conduction by tube 18 causes a sharp drop in its plate potential -which is communicated to the grid of tube 22, where it is amplitied, inverted and applied through tube ,24 to the grid of tube 29 as a positive voltage surge. Thelowimpedance of the line 3G causes the amplilication of tube 29 to be considerably less than unity, therefore, thegrid of that tube is actually driven positive on large amplitude signals producing a heavy flow of grid current 4which is suppiied by tube 2d. The resulting heavy conduction by tube 29 produces a voltage surge which travels down the delay line 39. This voltage surge is also applied through a capacitance 31 to grid .'33 of tube 18 to assure .heavy conduction by 18. The positive voltage surge is reected and inverted when it reaches the closed end of the delay line 33 and, after a period of time equal tothe time required for the surge to travel down line 36 and return, appears at the cathode of 29 as a negative .voltage surge. This negative surge is applied through capacitance 31 to grid 33 of tube 1S and is of surlcient amplitude to cut-oit tube 13, producing a positive voltage swing at the plate of that tube. Tube 22 is thereby returned to conduction producing a negative voltage swing at `its plate which cuts ott tubes 2d and` 29. rThus, a regenerative etect or reenforcement of the negative and positive pulses appearing at the cathode of 29 is produced and will continue until tube 12 of the gating circuit di) returns to non-conduction. At this instant the control grid 17 of tube i8 is returned to a negative potential thus disabling the circuit and preventing further regenerative action.

An output signal can be obtained from a number of points in the circuit with the low output impedance of tube 24 providing the most convenient source from which to drive a shaping and output amplitier 34. Therefore, the grid of tube 34 is direct connected to the cathode of tube 24 through a limiting resistance 35. Normally tube 34 is held non-conducting by the same negative voltage holding 29 cut off, as previously discussed. During the positive pulses at the cathode of 2d, the grid of tube 34 is driven positive resulting in a ow of grid current. Since it is desirable to produce a large voltage output from 34, taken across the plate load resistance 36, 37, it vis desirable to drive the grid of 34 relatively tar positive. Therefore, the limiting resistance 3S is made somewhat larger than the minimum value which would cause excessive loading of the cathode follower 24 by grid current drawn by tube 34. A representative value for the size of this resistance where 65N? tubes are used would be 250 ohms. It should be noted, however, that unequal pulse width and pulse spacing may be obtained by connecting the grid of tube 34 to various points along the line 36 rather than to the cathode of tube 24 and by proper adjustment of the bias on tube 34. An asymmetrical voltage waveform is produced at intermediate sections of the delay line 30 in which the maximum pulse voltage is attained at a period of time after the surge of current to the line 30 is initiated and this maximum voltage is terminated somewhat before the flow of current is stopped by regenerative action through tube 18. In this case the spacing between leading edges of the pulses in multiple pulse waveforms remains the same as with the output connection to the cathode of tube 24, only the pulse duration being altered.

The operation of the invention to produce a dual pulse signal may be illustrated more fully with the aid of the waveforms placed ou the drawing in proximity to the circuits to which they apply. Waveform A is representative of a negative input trigger which is applied to tube 1l to initiate Vthe ,multiple pulse signal. Waveform B shows the gating pulse generated at the grid of tube 12 and applied to the grid 17 of Vtube 18. Waveform C shows the dual pulse output of vtube 1S after coupling to the grid of 22 through .the circuit comprising capacitance 20 and resist- ,ance 21. Waveform D shows the squared dual pulse voltage produced at the cathode of tube 24. The sloping tops of waveform C have been removed in this waveform by plate current cut-off in tube 22 on the lower portions of thenegative pulses. The inverted, negative dual pulse output voltage is shown in waveform E.

Where .an output signal consisting of a large number of pulses is desired, for `example l0, the adjustment of the length yof .the gate produced .by tubes 11, 12 is quite critical to assure production of ten pulses without clipping of the tenth `er production of a part or" an eleventh. This would place an accuracy requirement of better than 5% on each `oi the elements which comprise the time constant circuit `for the gatingcircuitt. To reduce this stringent requirement, a synchronizing signal taken from a part or" the load `resistance of tube 34 is applied through a capacitance 39 to the grid resistances 13, 14 of tube 11. By this means the accuracy requirement of the aforementioned critical components is greatly reduced. Other synchronizing means such as a countercircuit would also be suitable where a waveform consisting of many pulses is to be produced.

The time constants of the coupling circuits 2i), 2l and 31, 32 are ypurposely selected to permit an appreciable charge or discharge during the period of a pulse. A suitable value of the R-C product for each of these coupling circuits would beone equal to twice the pulse period, permitting a 30 percent change in voltage during a single pulse. This ,is done to provide a greater degree of abruptness on the pulse edges and hence faster triggering on and oit" ofthe tubes 18 and22. If long time-constant circuits .were used at theaforementioned points, it would be necessary for the .entire pulse voltage to be developed before the-gridaiected was returned to the quiescent potential. Since ldistributed capacitance cannot be eliminated entirely, slopingifleadingand trailing edges cannot be avoided. These sloping edges wouldrepresent considerable time delay at the crest of the pulses whereas the delay is much less .at 'the.lower, sharply rising, leading edges. Thus, by permittinga partial discharge of the coupling capacitances 20 and 3l,.a faster on-off action of tubes i8, 22 will result. ln this connection, it is possible to vary respectively the :pulse width and pulse spacings by small amounts by varying the time-constants of the coupling circuits 20, 2i and '31, 32. As previously shown, the pulses have sloping leading and trailing edges, therefore it follows that by changing the point on bothedges at which triggering on or off of the tubes 18, v22 takes place, a slight variation in timing is possible. Thus, slight tolerances in the construction off-the Vdelay -line 30 may be allowed-with subsequent compensation by a variation in the sizes of the resistances 21, 32.

Although one specific embodiment of the present invention has been shown and described, it is apparent that many modifications of this basic idea can be made without exceeding the scope of this invention. Therefore, this invention is not to be limited except by the spirit of the prior art and the scope of the appended claims.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed is:

l. An arrangement for generating a plurality of timespaced pulses comprising, pulse-generating means includinc a delay line responsive to a control signal for genratin a first pulse, said delay line controlling the time duration of said pulse, means responsive to said control signal for deriving a first control potential having a time duration greater than that of said pulse, means responsive to the pulse output of said pulse-generating means for deriving at predetermined times after the generation of each pulse thereof second control potentials having time durations less than that of said first control potential, and means responsive to said first control potential and each of said second control potentials at the times of coincidence thereof for causing said generating means to generate a series of pulses following said first pulse.

2. An arrangement for generating a plurality of timespaced pulses comprising, pulse-generating means responsive to a control signal for generating a first pulse, multivibrator means responsive to said control signal for deriving a first control potential having a time duration greater than that of said pulse, means responsive to the pulse output of said generating means for deriving at predetermined times after the generation of each pulse thereof second control potentials having time durations less than that of said first control potential, means responsive to said first control potential and each of said second control potentials at the times of coincidence thereof for causing said generating means to generate a series of pulses following said first pulse, and means for controlling the time duration of said first control potential to provide a series of any predetermined number of pulses.

3. An arrangement for generating a plurality of timespaced pulses comprising, pulse-generating means responsive to a control signal for generating a first pulse, means responsive to said control signal for deriving a first control potential having a time duration greater than that of said pulse, means including a delay line responsive to the pulse output of said generating means for deriving at predetermined times after the generation of each pulse thereof second control potentials having time durations less than that of said first control potential, and means responsive to said first control potential and each of said second control potentials at the times of coincidence thereof for causing said generating means to generate a series of pulses following said first pulse with a time spacing between each of said pulses effectively corresponding to the time delay characteristics of said delay line.

4. An arrangement for generating a plurality of timespaced pulses comprising, pulse-generating means responsive to a control signal for generating a first pulse, means responsive to said control signal for deriving a first control potential having a time duration greater than that of said pulse, means responsive to the pulse output of said generating means for deriving at predetermined times after the generation of each pulse thereof second control potentials having time durations less than that of said first control potential, and an electron tube normally maintained in a nonconductive condition and rendered conductive by said first control potential and each of said second control potentials at the times of coincidence thereof for causing said generating means to generate a series of pulses following said first pulse.

5. An arrangement for generating a plurality of timespaced pulses comprising, pulse-generating means responsive to a control signal for generating a first pulse, means responsive to said control signal for deriving a first control potential having a time duration greater than that of said pulse, means responsive to the pulse output of said generating means for deriving at predetermined times after the generation of each pulse thereof second control potentials having time durations less than that of said first control potential, an electron tube normally maintained in a nonconductive condition and having an anode and a cathode and at least two electrodes in the space-current path therebetween, and means for applying said rst control potential to one of said electrodes and said second control potential to the other of said electrodes to render said electron tube conductive at the times of coincidence of said first and second control potentials to cause said generating means to generate a series of pulses following said first pulse.

6. A multiple pulse generating circuit comprising arnplifier means having two operating conditions and responsive to a control signal to initiate operation in the first of said two conditions, delay line means responsive to the output of said amplifier means to derive a rst control potential of predetermined time duration, means for applying said first control potential to the input of said amplifier means to maintain said ampifier means in said first operating condition for a period of time equal to said predetermined time duration, said amplifier means assuming the second of said operating conditions upon the termination of said first control potential, said delay line means operatively responsive to the output of said amplifier means in said second operating condition to derive a second control potential of predetermined time duration, said second control potential operative to maintain said amplifier means in said second operating condition for a period of time equal to the last-mentioned predetermined time duration, said amplifier means returning to the first of said operating conditions upon termination of said second control potential to reinitiate a new cycle of operation, means responsive to said control signal for deriving a third control potential having a time duration greater than that of said first and second control potentials, and means for operatively coupling said third control potential to said amplifier means to prevent operation thereof upon termination of said third control potential.

7. A multiple pulse generating circuit comprising, amplifier means having two operating conditions and responsive to a control signal to initiate operation in the first of said two conditions, delay line means responsive to the output of said amplifier means to derive a first control potential of predetermined time duration, means for applying said first control potential to the input of said amplifier means to maintain said amplifier means in said first operating condition for a period of time equal to said predetermined time duration, said amplifier means assuming the second of said operating conditions upon the termination of said first control potential, said delay line means operatively responsive to the output of said amplifier means in said second operating condition to derive a second control potential of predetermined time duration, said second control potential operative to maintain said amplifier means in said second operating condition for a period of time equal to the last-mentioned predetermined time duration, said amplifier means returning to the first of said operating conditions upon termination of said second control potential to reinitiate a new cycle of operation, means responsive to said control signal for deriving a third control potential having a time duration greater than that of said first and second control potentials, means for operatively coupling said third control potential to said amplifier means to prevent operation thereof upon termination of said third control potential, and

means for controlling the time duration of said third control potential.

8. A multiple pulse generating Circuit comprising, rapid-acting vacuum tube means -responsiveto a control signal to initiate atirst voltage impulse, means regenerativelycoupling the output of `said rapid-acting -means to the input thereof to sustain said first voltage impulse, delay line means responsive-to lthe output of said rapidacting means to derive after a period of time a-rst control impulse, said iirst control impulse being coupled to the input of said rapid-acting means to terminate said first voltage impulse, said delay line means being responsive to the termination of said iirst voltageimpulse to derive after a period of time a second-control impulse, said second control impulse being inverted iu `polarity with respect to said first control impulse to initiate a second voltage impulse in the output of said rapid-acting means and thereby begin another cycle of operation, means responsive to said control signal for deriving a control potential having a time duration of at least several cycles of operation, and means for operatively coupling said control potential to said rapid-acting means to interrupt the operation thereof upon termination of said control potential.

9. A multiple pulse generating circuit comprising, rapid-acting vacuum tube means responsive to a control signal to initiate a iirst voltage impulse, means regeneratively coupling the output of said rapid-acting means to the input thereof to sustain said first voltage impulse, delay line means responsive to the output of said rapid-acting means to derive after a predetermined period of time a lirst control impulse, said rst control impulse being inverted in polarity with respect to said iirst voltage impulse and being coupled to the input of said rapid-acting means to terminate said tirst voltage impulse, said delay line means being responsive to the termination of said lrst voltage impulse to derive after a predetermined period of time a second control impulse, said second control impulse being inverted in polarity with respect to said first control impulse to initiate a second voltage impulse in the output or" said rapid-acting means and thereby begin another cycle of operation, means responsive to said control signal for deriving a control potential having a time duration at least equal to several of said cycles of operation, and means for operatively coupling said control potential to said rapid-acting means to interrupt the operation thereof upon termination of said control potential.

l0. A multiple pulse generating circuit comprising, rapid-acting vacuum tube means responsive to a control signal to initiate a iirst voltage impulse, means regeneratively coupling the output of said rapid-acting means to the input thereof to sustain said first voltage impulse, delay line means responsive to the output of said rapid-acting means to derive after a predetermined period of time a iirst control impulse, said first control impulse being inverted in polarity with respect to said lirst voltage impulse and being coupled to the input of said rapid-acting means to terminate said first voltage impulse, said delay line means being responsive to the termination of said lirst voltage impulse to derive after a predetermined period of time a second control impulse, said second control impulse being inverted in polarity withrespect to said first control impulse to initiate a second voltage impulse in the output of said rapid-acting means and thereby begin another cycle of operation, multivibrator means responsive to said control signal for deriving a control potential having a time duration at least equal to several of said cycles of operation, and means for operatively coupling said control potential to said rapid-acting means to interrupt the operation thereof upon termination of said control potential.

ll. A multiple pulse generating circuit comprising, rapid-acting vacuum tube means responsive to a control signal to initiate a first voltage impulse, means regeneratively 'coupling the output of said rapid-acting means to the input thereof to sustain said first voltage impulse, a

delay line having one end coupled Ito th'eoutput of said rapid-acting means and the other end Athereof shorted, said delayline deriving,`fter`a period'of time determined by the characteristics-of saiddelayline,arst control impulse of inverted polar-ity 'with trespect to ythe impulse applied thereto, said `Iiirstcontrol impulse being coupled to the inputof'said rapid-acting means to terminate said rst voltage impulsa-said delay/"line being responsive to the terminationof said rstivo'ltageiimpulse to derive after said period of Etime a lsecond control impulse, said second control impulse 'being inverted 1in polarity With respect to said rst 'control impulse to initiate a second voltage impulse in the output of saidrapid-acting means and thereby begin vanothercyclelo'f foperation, means responsive to said control -signalfor deriving a control potential having a time duration-atleast equal to several of said cycles of operation, and means for operatively-coupling said control potential to `saidtrapid-acting means to interrupt vthe operation thereof upon `,termination of said control potential.

l2. A multiple pulse .generating circuit comprising, rapid-acting vacuum tube .imeanszresponsive to a control signal to initiate a first voltage iimpulse, means regeneratively coupling the 'output of said'rapid-acting means to the input thereof to sustain Lsaidiirstvoltage impulse, a delay line having one endicoupled-to theoutput of said rapid-acting means and the .other end thereof shorted, said delayline deriving, after a period of time determined by the characteristics of vsaid delay line, a vfirst control impulse of invertedfpolarity with respect to the impulse applied thereto, said first control. impulse being 'coupled to the input of said rapid-acting means to terminate said tirst voltage impulse, lsaid delay line being responsive to the termination of said rst voltage impulse-to derive after said period of time a second .control impulse, said second control impulse being :inverted in polarity with respect to said iirst `control-impulse'tofinitiate a second voltage impulse in the output l of. saidsrapid-acting means and thereby beginanother cycle fof operation, means responsive to said control signal for deriving a control potential having a time duration .atleast equal to several of said cycles of operation, .means for operatively coupling said control potential to -said rapid-acting means to interrupt the operation `thereof upon termination of said control potential, and output imcans'associated with said rapid-acting vacuum tubemeansvwhereby a train of output pulses of predetermined' number can be obtained,

i3. A multiple pulse gener-atingl .circuit comprising, rapid-acting vacuum tube vmeans responsive toa control signal to initiate a lirst voltage impulse, means regeneratively coupling the output of saidrapid-acting means to the input thereof to sustain saiditirst voltage impulse, a delay line having one end coupled to the output of said rapid-acting means and the other =end thereof shorted, said delay line deriving, after a period Ioftime determined by the characteristics of said delayline, a iirst control impulse of inverted polarity With-respect to the impulse applied thereto, said iirst control limpulse being coupled to the input of said rapid-acting means to terminate said first voltage impulse, said delay :line `being responsive to the termination of said first voltage impulse to derive after said period of time a secondcontrol impulse, said second control impulse being inverted in polarity with respect to said tirst control impulse to initiate a second voltage impulse in the output of said rapid-acting means and thereby begin another cycle of operation,-means responsive to said control signal for deriving la control potential having a time duration at least equal to several of said cycles of operation, means for-operatively coupling said control potential tosaid rapid-acting means to interrupt the operation thereof upon termination of said control potential, and output `means yconnected to said delay line at a predetermined ,point between the ends thereof.

i4. A multiple pulse generatingeircuit comprising,

multivibrator means responsive to a control signal for deriving an output control potential of predetermined time duration, a coincidence circuit coupled to the output of said multivibrator means, amplifier means responsive to said control signal to initiate a rst voltage impulse, means including said coincidence circuit for regeneratively coupling the output of said amplifier means to the input thereof to sustain said rst voltage impulse, a delay line having one end coupled to the output of said amplier means and the other end thereof shorted, said delay line deriving, after a period of time determined by the characteristics of said delay line, a rst control impulse of inverted polarity with respect to the impulse applied thereto, said first control impulse being coupled to the input of said amplifier means by means of said coincidence circuit to terminate said rst voltage impulse, said delay line being responsive to the termination of said rst voltage impulse to derive after said period of time a second control impulse of inverted polarity with respect to said rst control impulse to initiate a second voltage impulse in the output of said amplifier means and thereby begin another cycle of operation, the termination of the output control potential from said multivibrator means interrupting the aboverecited operation after a predetermined number of cycles, and means for varying the time of duration of said control potential.

15. An arrangement for generating a plurality of timespaced pulses comprising, pulse-generating means responsive to a control signal for generating a first pulse, means responsive to said control signal for deriving a first control potential having a time duration greater than that of said pulse, means responsive to the pulse output of said generating means for deriving at predetermined times after the generation of each pulse thereof second control potentials having time durations less than that of said rst control potential, and means responsive to said first control potential and each of said second control potentials at the times of coincidence thereof for causing said generating means to generate a series of pulses following said first pulse.

No references cited.

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