US2505542A - Triggered pulse generator - Google Patents

Description

April 1950 w. c. HAHN 2,505,542?

TRIGGERED PULSE GENERATOR Original Filed Dec. 30, 1943 Fi l.

PULSE OUTPUT TRIGGER PULSE.

INPUT GR: VOLTAGE OF 424 m 0 Ld I g 478| 479 3 C l ANODE VOLTAGE OF 424 VOLTAGE ON GRID 4Z6:

OUT PUT VOLTAGE PULSE Inventor": William CHahn,

M QM His Attorney.

Patented Apr. 25, 1950 NITED STATES PATENT OFFICE TRIGGERED PULSE GENERATOR William C. Hahn, Scotia, N. Y., assignor to General Electric Company, a corporation of New York 3 Claims.

The present application is a division of my application Ser. No. 516,239, filed December 30, 1943, now U. S. Patent No. 2,467,208 assgned to the same assignee as the present application.

In the automatic range tracking circuits of pulse echo systems of the type illustrated in the above parent application, it is necessary to generate very short pulses, commonly known as aperture pulses. These short pulses may have a duration, or width, of from only a fraction of a microsecond up to several microseconds. They must be very accurately initiated in response to a train of applied synchronizing pulses or transients, and their duration and wave shape must be readily and precisely controllable. It is a primary object of the present invention to provide an improved pulse generator meeting these requirements.

Specifically, it is an object of the present invention to provide an improved pulse generator which may be very accurately triggered by applied pulses and which may be readily adjusted to produce extremely short pulses of substantially rectangular shape, and of an accuratelv controllable width which is not afiected by the length of the triggering pulses.

It is a further object of the present invention to provide an improved triggered pulse generator which can be adjusted to produce extremely short pulses of less than one microsecond duration and which is not subject to false triggering even though the applied triggering transient may have a decay time, or discharge time constant, greater than the pulse duration.

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

In the drawings:

Fig. 1 is a circuit diagram of one form of pulse generator embodying the invention; and

Fig. 2 graphically represents several voltage wave forms, appearing at various lettered points in the circuit of Fig. 1, on a common time scale.

The pulse generating apparatus of Fig. 1 comprises an electron discharge device 424, represented as a pentode. and a second electron discharge device lid which is represented as including two separate tetrodes having a. common cathode. Device 424 is utilized as a trigger amplifier and polarity reverser, and the two sections of device 4 l 5 are connected in a circuit resembling a known form of single-pulse generator or multivibrator, as will appear more fully from the description of the circuits and their operation below The cathode of device 324 is connected directly. to ground and a positive bias is impressed upon its control grid from a suitable source of oper-l ating potential, represented conventionally by a bus connected to B+, through a resistor 443. Suitable anode and screen grid operating potentials are also supplied from B+ through resistors iii! and illi in conventional manner. The anode of device 62 i is coupled to the left-hand control grid 326 of device did through a coupling capacitor 42s. A potentiometer network, comprisingresistors and tilt and a variable resistor 440, is connected between the positive bus and ground. A bias potential is supplied to control grid 426 by a connection to the junction of resistors 438 and 339 through resistor M2. The lower end of resistor Eli is bypassed to ground through a capacitor MB.

A common cathode load resistor 421 is pro-1 vided between the cathode of device il and ground. The left-hand and right-hand anodes 63 i and are respectively connected to the p0si-' tive bus through individual resistors 529 and 430' and a common resistor 433. The right-hand control grid 43% is also connected to the positive. bus through an individual resistor 43! and the. common resistor The upper end of resistor it? is bypassed to ground through a capacitor illi. Control grid 36 is also coupled to anode. 13d through a capacitor 435. I

In operation, the trigger amplifier 42 is normally conducting by virtue of the relatively high, positive bias supplied to its control grid. The bias; on control grid 525 is adjusted with respect to the potential of anode iil l so that the left-hand section of device cm is normally non-conducting. However, the control electrode 436 is positive with respect to the cathode and the right-hand: section of the device M4 is normally conducting. The voltage drop thereby produced across the common cathode resistor 62? assists in main-j taining the required negative bias upon controlj rid M6.

Assume now that a positive trigger pulse, as represented by curve A in Fig. 2, is applied through conductor 37 and a coupling capacitor 323 to the control grid of amplifier 32$.

entiating network having a predetermined time constant. Therefore the resultant pulse wave applied to the control grid of device 32 1 may, for

example, be of the form illustrated by the curve B of Fig. 2. Since the device 325 is already con-- ducting, the initial positive transient 476 does not change the conducting state of the amplifier;

The capacitor 423 and resistor M3 comprise a difier- However, at the beginning of the trailing edge of the A pulse wave, at time t1, the sudden negative transient 4W applied to the control grid of device 424 drives the grid voltage below the cutoil value, represented by voltage e1, thereby abruptly reducing the anode current to zero. The anode voltage of device 424 immediately rises substantially to the voltage B+ of the operating source, as represented at 418 in curve C. The anode voltage of device 424 remains at this value until point 419, when the transient 41'? in the 13 pulse wave again rises abovethe cut oil value e1.

Capacitor 425 and associated resistors 438, 439, 440 and 410 comprise a diiferentiating circuit of relatively short time constant, with the result that the voltage applied to grid 42% has the shape represented by curve D in Fig. 2. The voltage level e2 represents the value at which the lefthand section of device M4 is cut oil. The lefthand section of device 4E4 now draws anode current and the potential of anode 434 drops abrupt- 1y; driving the controlgrid 43 of the right-hand section negative through capacitor 435. The anode current through the right-hand section of device 444 is thereby suddenly cut oil, initiating the pulse wave at the anode 474 of the form shown by'curve E in Fig. 2.

It will b recognized by those skilled in the art that the device M4 and associated circuits tend'to operate as a single-pulse multivibrator in which capacitor 435 tends to recharge through atime constant network primarily comprising the capacitor 435 and resistor 43'l, so that at the end of a" predetermined time the right-hand section of. device 444 would again begin to draw anode current and restore the initial operating conditions. However, it is important that the time constant of this multivibrator be adjusted so as to be relatively long compared to the desired output pulse duration. The time constant of the network associated with capacitor 425, which primarily consists of resistor 4W, capacitor 425 and resistor 4T2, is arranged to be very much shorter than the natural pulse period of the multivibrator, and thereby the time constant of this network determines the length of the E pulse in the following manner.

The'E pulse is terminated when capacitor 425 charges enough to drive the control grid 42S sufficiently negative to cause the right-hand section of device 4M again to become conducting. This corresponds to a voltage level e on curve D in Fig. 2. This terminates the E pulse at time 152. The length of the charging period required to cause control grid 426 to reach this potential may be varied by adjustment of resistor 44!].

The right-hand section of device 454 preferably passes a larger current through cathode resistor 421' than does the left-hand section, whenv conducting, which means that the potential on resistor 42? increases during the E pulse. Therefore, the pulse output may optionally be. taken from this resistor, as indicated by the dashed connection 488 in Fig. l.

' It will be observed from Fig. 2 that the length of the triggering transient 418 is also relatively great with respect to the width of the E pulse. Inother words, the E pulse also has a duration shorter than the time constant of the differentiating network comprising capacitor 423 and resistor 443. Consequently, although the capacitor 4'23 begins to charge upon the initiation of the E pulse, the discharge device 424 not only remains cut oil throughout the E pulse periodbut" until point 419 in curve C.

It will thus be apparent that the E pulse may be made of extremely short duration, determined primarily by the time constant of the coupling network between the trigger amplifier and the multivibrator circuit, even though the trailing edge of the incoming trigger pulse may have an appreciable tail both before and after differentiation. This is a distinct advantage over prior art circuits of the type in which a single-pulse generator is triggered directly by means of such a transient. because the maintenance of the transient voltage for a period longer than the duration of the desired pulse will normally tend to produce a false retriggering of a multivibrator.

While the present invention has been described as having particular utility in a pulse echo systcm of the type disclosed in the parent application referred to above, it will of course be obvious that it has general application to a triggered pulse generator wherever extremely short pulses of substantially rectangular wave form are required. It has been found in actual practice that pulses having a duration-as low as -microsecond or less may readily be produced.

While a particular embodiment of the invention has been shown and described, it will of course be understood that various modifications may be made without departing from the invention. tended to cover any such modifications within the true spirit and scope of the invention.

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

1. In combination, a pair or dischargev devices connected as a multivibrator, means to reverse the current conditions in said devices in response to a voltage transient having a predetermined period, said means including an electron dischargedevice having an anode, a cathode and control electrode, a condenser connected between said anode and said multivibrator, means to supply said transient between said control electrode and cathode to reverse the cur-- rent conditions in said first two devices upon initiation of said transient, and means to pro duce an opposite reversal of said current conditions at a time thereafter determined by said condenser and independent or and shorter than the period of saidtransient.

charge device having a control grid and an anode,

an anode load resistor connected in circuit with said anode, means for impressing a negative transient on said control grid through a resistance-capacitance difierentiating network having a time constant which is relatively long as compared to the desired duration of said pulses, said third device being rendered abruptly nonconductive by said transient for an interval longer than said desired pulse duration, a second resistance-capacitance differentiating network including said anode resistor and a coupling capacitor, said second network having a relatively short time constant as compared to that of said first network, and means for impressing voltage through said capacitor on said one device in a sense to render it non-conducting, said one de- 15 vice remaining non-conductive. for a pulse pe- The appended claims are therefore inriod determined by the time constant of said second network and independent of the duration of said transient.

3. A triggered pulse generator comprising, in combination, a pair of electron discharge devices connected in a single-pulse multivibrator circuit, said circuit being responsive to a triggering impulse supplied to one of said devices to initiate a single pulse of substantially rectangular waveform and of a normal duration determined by the time constant of a resistancecapacitance network in said circuit, a third, normally-conductive electron discharge device having an anode load resistor, a second resistsince-capacitance network comprising said resistor for supplying triggering potentials from said third device to said one device, said second network having a substantially shorter time constant than said first network, means for abruptly rendering said third device non-conductive for a REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,132,655 Smith Oct. 11, 1938 2,188,611 Norton Jan, 30, 1940 2,313,960 Wendt Mar. 16, 1943 2,408,078 Labin et a1 Sept. 24, 1946 2,425,600 Coykendall Aug. 12, 1947 2,438,910 Grieg Apr. 6, 1948

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