US2575559A - Impulse generating system - Google Patents

Description

Nov. 20, 1951 G. B, PARKINSON IMPULSE GENERATING SYSTEM 2 SHEETS-SHEET 1 Filed Jan. 22, 1946 3mm GEOFFREY B. PAR'KINSON Nov. 20, 1951 3, 5, PAKINSQN 2,575,559

IMPULSE GENERATING SYSTEM Filed Jan. 22, 1946 2 SHEETS-SHEET 2 A n F1 0 20 4'0 66 do 160 IZIO I40 lo GRID PULSE AMPLITUDE (VOLTS) GEOFFREY PARKINSON Patented Nov. 20, 1951 I IMPULSE GENERATING SYSTEM Geoffrey B. Parkinson, Washington, D. 0;, assignor to the Minister of Supply in His Majestys Government of the United Kingdom of Great Britain and Northern Ireland, London,

England Application J anuary 22, 1946, Serial No. 642,695

7 Claims.

This invention relates in general to an impuls generator and particularly to a gas tube type of impulse generating system.

It is an object of this invention to provide a simple, eflicient, ultra short duration impulse generating system.

It is another object of this invention to provide a method of and means for producing voltage impulses a fraction of a microsecond in duration.

It is another object of this invention to provide a system of the foregoing type for producing voltage impulses of a selectable duration.

Other objects and features of the present invention will become apparent upon a careful consideration of the following'detailed description when taken drawings.

Fig. 1 is a detailed circuit diagram of one embodiment of the invention;

Fig. 2 is a detailed circuit diagram of a'variant embodiment of the invention;

Figs. 3 and 4 show a series of waveforms useful in explaining the operation of Figs. 1 and 2 respectively, and

Fig. 5 shows a series of curves illustrating the starting time characteristic of a pair of well known gas tubes.

In the operating characteristics of grid controlled gas tubes, I have discovered that the ignition time of such tubes is determined by the trigger signal amplitude applied'to the tube'grid as well as by ambient temperature and plate voltage. Specifically, I have discovered that ignition time varies inversely with grid signal amplitude. Advantage is taken of this phenomena in practicing the present invention. Briefly, the system provided by the present invention comprises at least one gas tube arranged in such a manner that ignition thereof generates the trailing edge of the pulse. The time duration of this pulse is determined by the ionization time of the gas'tube, and is controlled by adjustment of the trigger signalamplitude applied to the gas tube. r

In the two embodiments of the invention which are herein illustrated, a pair of gas tubes are employed. The first is arranged to produce, upon ignition, the leading edge of a pulse and the second is arranged to produce the trailing edge of the pulse, upon ignition. The trigger signal for the second tube is produced by and obtained from the first tube in such a manner that pulse duration may be controlled by selectively varying the amplitude of the triggering together with the accompanying signal applied to the second tube. Incorporated in the invention is a suitable device for quenching the two gas tubes once the output pulse has been produced. For purposes of illustration this device has been represented as an artificial transmission line. It is to be understood, however, that any other suitable device may be used, if desired. It is also to be understood that even though I have shown two gas tubes as constitilting the preferred embodiments of the invention; a tube other than that of the gaseous variety, or other suitable device may be used to generate the leading edge of the pulse.

Reference is now had in particular to Fig. i where one typical embodiment of the invention is shown. The two gas tube components which comprise, in part, the circuit of the invention are illustrated at [0 and II, and as herein indicated are connected together at their anodes by lead 2|. In the quiescent state of the circuit both tubes are biased non-conducting and therefore consume no idle current. Bias for the first tube I0 is represented as a negative voltage [8 applied to the tube grid via resistance is. Bias for the'second tube H is represented as a positive voltage l3 applied to the cathode of the tube. The first tube In is plate loaded by resistance 20, and cathode loaded by the resistance of potentiometer 22. Across the latter resistance the output terminals I5 of the circuit are taken. The tube quenching device is represented as an open circuited transmission line It connected to the anodes of the tubes.

From the foregoing paragraph it becomes obvious that in order to institute the generation of a voltage pulse by igniting tube IE3, a positive trigger pulse must be applied to the tube grid via the input terminals l1. Upon the application of such a triggering pulse, tube IE! fires and line It, which is normally charged, commences to discharge at steady rate through the tube and the resistance of potentiometer 22. At this instant the voltage across the resistance of potentiometer 22' and hence the voltage across the output terminals 15 rises abruptly positive. The leading edge of the output pulse is thus formed. A- selectable portion of the voltage wavefront appearing across potentiometer 22 is communicated via movable arm M to the control grid of tube H. A fraction of a microsecond later, depending uponthe setting of movable arm at, tube i! will ionize and the potential at the'anodes of the tubes will fall abruptly negative to substantially that of the source indicated at [3, which is only a few volts positive of ground. At the same in- 3 stant the voltage appearing across potentiometer 22 falls abruptly to some voltage slightly less positive than source l3. This action generates the trailing edge of the impulse.

To quench the tubes, the reflection qualities of the artificial line It are utilized. In brief, as tube I is rendered conducting, current fiows out of the line and through the tube. This current represents the current of a positive voltage wave propagating in the same direction, right to left, along the line. Then if the line is terminated at the tube end, (essentially the resistance of potentiometer 22) in some impedance less than its characteristic impedance, reflection with inversion will occur and. the net result will be an abrupt drop in voltage at the anodes of the tubes. By selecting a value of resistance for potentiometer 22 something less than the characteristic impedance of the line the incident wave will be inverted, made negative in this case, and reflected back down the line to the open circuited end. At the open circuited end the wave will again be reflected, this time without inversion. Then after a time delay determined by the equivalent electrical length of the line this negative reflected wave will reach the tube end of the line. In the meantime, however, tube H -has been fired and the voltage existing at the anodes of the tubes is-substantially equal to the source 13 so that the reflected negative wave will actually drive the anodes negative relative to ground to thereby quench both tubes simultaneously. As afore-mentioned any suitable arrangement may be used to quench the tubes, but an artificial line is preferred because of its compactness, rapid action, and constant discharge rate as beneficial to pulse definition.

From close observation of the circuit in Fig. 1 it will be recognized that the value of plate resistance 2B is selected so that the time constant formed by it and the capacitance of line [6 is great enough to hold the tubes anodes negative relative to ground long enough to permit deionization to occur.

To facilitate a comprehensive understanding of the exact action of the circuit in Fig. 1 during a cycle of operation, reference is now had to the waveforms shown in Fig. 3. In Fig. 3, time is plotted along the horizontal axis and voltage along the vertical axis. Waveform A represents a trigger signal applied to tube Ill via input terminals l'i. Waveform B represents the voltage variation which occurs at the anode of the tubes in response to the trigger signal shown in waveform A. As shown by waveform B the voltage at the anodes of the tubes drops abruptly from 13+ coincident with the leading edge of the trigger signal. This is due to the fact that the incident wave propagating along line it is inverted and reflected by the mismatch in terminating impedances at the tube end of the line. As shown in waveform C, which represents the signal appearing across the output terminals l5, ignition of tube It! generates the leading edge F of the output pulse. A short time thereafter tube fires and the anode voltage for the tubes drops abruptly negative to substantially the voltage of source voltage I3. This action is represented by reference character G in waveform B.

At this instant the trailing edge of the output pulse shown in wave form C is generated. Thereafter the negative wave reflected from the open end of the line returns to the tube end of the line and drives the anodes abruptly negative relative to ground, as shown at H in waveform B.

4 The tubes deionize and the line starts to recharge through resistance 20 to produce the exponential rise of the anode voltage indicated at I.

From the foregoing it may be clearly recognized that the time of duration of the output pulse depends on the ignition time of tube H.

In Fig. 5, to which reference is now had, the ignition time characteristic versus grid signal amplitude of a pair of gas tubes is shown. In particular curves X and Y typify the ignition time characteristic of a 2050 type of gas tube. Curve X represents the ignition time of this tube with 120 volts at its anode and 10 volts cathode bias. Curve Y represents the ignition time of this tube with 600 volts at its anode and 16 volts cathode bias.

Curve Z represents the ignition time of an 884 type of gas tube with volts at its anode and 15 volts cathode bias. The ignition time, as herein indicated, decreases inversely with the trigger signal amplitude. Consequently the movable arm M of potentiometer 22, through which the trigger signal for tube H is communicated, provides an ideal control of impulse duration.

In the embodiment of Fig. 1 the action of line It was such as to simultaneously quench both tubes. If, however, it is desired to have tube H quench tube l0 and the line 16 quench tube H the arrangement shown in Fig. 2 may be employed. Herein reference characters similar to those used in Fig. 1 are employed to designate corresponding elements in the two circuits. The major difierence in the circuits of Fig. 1 and Fig. 2 is that the grid of tube H is A. C. coupled to the movable arm Hl'of potentiometer 22, thus permitting the cathode of tube II to be returned to a negative potential 24. Bias for tube II, in this case is provided by a negative voltage'indicated at 23 and applied to its grid.

The action of Fig. 2 is essentially the same as that of Fig. 1 except tube It in this case is deionized as tube 1 i is ionized, and the impulse generated at terminals 15 contains a trailing edge that falls abruptly to ground or slightly below ground depending on the cathode bias of tube H. The waveforms illustrating the action of Fig. 2 are shown in Fig. 4. Herein, waveform A again represents the trigger signal applied at terminals ll. Waveform B represents the anode voltage variation in response to the trigger signal of wave form A. From waveform B it will be recognized that as tube H fires, the anode voltage of the tubes drops abruptly to ground or slightly below ground (as indicated by portion G) depending on the cathode bias of tube H. Hence tube ill will deionize in response to ionization of tube ii, while the latter tube will again deionize in response to the negative reflection (as indicated at H) from line l6. Waveform C again represents the signal impulse generated at the terminals 15.

Although I have shown and described only limited and specific embodiments of the present invention I am fully aware of the many modifications possible thereof. Therefore this invention is not to be restricted except insofar as is necessitated by the spirit of the prior art and the scope of the appended claims.

What is claimed is:

l. A gas tube generator comprising, a source of operating potential, first and second grid controlled gas tubes connected together at their anodes and to said source of operating potential, an impedance element connected to said first tube and across which output terminals for the circuit are taken, an artificial line connected to said tubes for quenching the same, the grid of said second tube so associated with said output terminals as to receive a selectable amplitude of the signal variation which appears thereacrosswhen said first tube is rendered conducting, and means for impressing a triggering signal to the grid of said first tube.

2. A gas tube generator comprising, a source of operating potential, first and second grid controlled gas tubes connected together at their anodes and to said source of operating potential, an impedance element connected to said first tube and across which output terminals for the circuit are taken, an open circuited artificial line connected to the anodes of said tubes for quenching the same, the grid of said second tube so associated with said output terminals as to receive a selectable amplitude of the signal variation which appears thereacross when said first tube is rendered conducting, and m ans for impressing a triggering signal to the grid of said first tube.

3. A pulse generator comprising, a source of operating potential, first and second grid controlled gas tubes connected to said operating potential, an output circuit connected to said first tube to receive an abrupt potential variation of one sense in response to conduction by said first tube, and further connected through said first tube to said second tube to receive an abrupt variation in potential of the opposite sense in response to conduction by said second tube, means for applying a triggering signal to the grid of said first tube, and means for applying a controllable amplitude triggering signal to the grid of the second tube simultaneously with the establish} ment of conduction in said first tube.

4. A pulse generator comprising, a source of, operating potential, first and second grid controlled gas tubes connected to said operating potential, an output circuit connected to said first tube to receive an abrupt potential variation oi one sense in response to conduction by said first tube, and further connected through said first;

tube to said second tube to receive an abrupt variation in potential of the opposite sense in re-' sponse to conduction by said second tube, means for applying a triggering signal to the grid of said first tube, and means coupling the-grid of} said second tube to said output circuit, said last named means operative to couple a controllable portion of the potential variation received by said output circuit in response to conduction by said,

trolled gas tubes connected to said operating poi,

tential, an output circuit connected to said first tube to receive an abrupt potential variation of one sense in response to conduction by said first tube, and further connected through said first tube to said second tube to receive an abrupt variation in potential of the opposite sense in response to conduction by said second tube, means for applying a triggering signal to the grid of said first tube, means for applying a controllable amplitude triggering signal to the grid of the second tube simultaneously with the establishment of conduction in said first tube, and a quenching circuit operatively associated with said tubes for deionizing the same subsequent to the establishment of conduction in said second tube.

6. A pulse generator comprising, an impedance element, means including a switch circuit connected to said element operative upon closure of the switch circuit to produce a potential variation of one sense across said element definitive of the leading edge of a pulse, a gaseous discharge device connected to said element through said switch and operative upon conduction to produce an abrupt potential variation of the opposite sense across said element, and means coupling a portion of the leading edge of the pulse appearing across said impedance element to said gaseous discharge device as a triggering signal whereby the ionization time of said device functions to control the time duration of the pulse.

7, A pulse generator comprising, an impedance element, means including a switch circuit connected to said element operative upon closure of the switch circuit to produce a potential variation of one sense across said element definitive of the leading edge of a pulse, a gridcontrolled gaseous discharge device connected to said element through said switch and operative upon conduction to produce an abrupt potential variation of the opposite sense across said element, means coupling a portion of the leading edge of the pulse appearing across said impedance element to the grid of said device as a triggering signal whereby the ionization time of said device functions to control the time duration of the pulse, and a quenching circuit operative to deionize said device following th establishment of conduction therein. i

GEOFFREY B. PARKINSON,

REFERENCES CITED The following references are of record in the file of this patent: 1

UNITED STATES PATENTS Number Name Date 1,691,395 Langmuir Nov. 13, 1928 2,236,015 Sonnentag Mar. 25, 1941 2,394,389 Lord Feb. 5, 1946

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