US2516867A - Stabilized one-shot multivibrator - Google Patents

Description

A. S. HARRIS STABILIZED ONE-SHOT MULTIVIBRATOR Aug. 1, 1950 wmUT m Filed June 12, 1948 INVENTOR. ALBERT S. HARRIS ATTORN EY Patented Aug. 1,

STABILIZED ONE-SHOT MULTIVIBRATOR Albert S. Harris, Fort Wayne, Indl, assignor to F. A. R. Liquidating Corporation, a corporation Application June 12, 1948, Serial No. 32,582

This invention relates to impulse generators and particularly to the stabilization of app ratus of this character such as flip-flop circuits, multivibrators andt thelike.

In many types of signaling circuits employing impulses, it isdesirable to rigidly control the width of the impulses. For example, in signaling systems such as those employed in radio ranging apparatus particularly, it is necessary to develop impulses which. are relatively short in time and which arereproduced at a, relatively high periodicity. One type of impulse generator which has been used in apparatus of the class described with considerable success is a multivibrator. This type of impulse generator is quite well known in the art and consists essentially of a pair of vacuum tubes having the output circuit of one capacitively cross-coupled to the input circuit of the other in such a manner that the initiation of space current conduction in one tube operates to terminate theconduction of the space current in the'other tube The crosscoupling circuits between the tubes include leak resistors and the, natural frequency of oscillation of the multivibrator depends upon such factors as the time constants of the coupling circuits. t t

Another type of apparatus which is employed for the purpose of generating impulses is one which is substantially similar to the self-oscillating multivibrator. However, the input ircuits of the respective tubes are biased insuch a manner that normally the apparatus functions to oscillate foronly one cycle atQ-a'tlme in response to a triggering thereof by some external excitation. Such devicesfrequently are called flip-flop cilG11itS. f,, H

Apparatusof this general character functions quite well to generate impulses which are substantially rectangular, {but which may deviate from one another materially in width or time duration regardless of whether the repetition rate is high or low.. Conventional apparatus employing multivibrators, is not capable, of producing consistently satisfactory results, even when flip-flop circuits are used and the repetition rate of the generated impulses is controlledfromtan external source. Devices of this character are deficientin that the. time duration of thegenerated impulses varies considerably by reason of the, fact that the'impulse width or time duration is dependent not cnlyupon the timeconstants of the coupling circuits between the tubes, but

alsoupon such other jaotors as the tube char acteristics, the supply voltage regulation, etc.

3 Claims. (Cl. 250-27) It,,therefore, is an object of the present invention to provide an impulse generator with a stabilizing facility whereby it. is capable of operating to generate impulses having a relatively constant width or time duration.

Another object of the invention is to provide a multivibrator with a timing circuit which is independent of such variable factors as the time constants of. the coupling circuits between the tubes, the characteristics of the tubes, the voltage regulation ofthe power supply, etc.

Still another object of the invention is to provide a timing circuit for use with a multivibrator which includes an oscillatory circuit, the period of which may be closely controlled whereby the nultivi brator is capable of operating to generate impulses of substantially invariable time durations.

In accordance with the general aspect of this invention there is provided an impulse generator including a pair of vacuum tubes, each of which has an input circuit and an output circuit. Suitable control means is coupled to the generator in an appropriate manner to initiate operation thereof. The input circuit of a first one of these tubes is coupled to the output circuit of the second tube. There also is provided means which is responsive to an exciting voltage for producing a. voltage impulse having a predetermined polarity at a predetermined time following the initiation of operation of the generator, The voltage impulse producing means is of such "a character that its operation is substantially independent of the magnitude of the exciting voltage. The output circuit of one of the tubes is coupled to the voltage impulse producing means for the purpose of impressing the exciting voltage upon it. The voltage impulse producing means also is coupled to the input circuit of the second tube in such a manner that there is impressed upon, the input circuit of the second tube. the produced voltage impulses of predetermined polarity. More specifically in accordance witha preferred embodimentof this invention, there is provided an impulse generator in which thepair of vacuum tubes each is provided with an anode, a cathode and a space current control grid. The control, grid, of thefirst tube is coupled to the anode of thesecond tube in a conventional manner. The anode of the first tube is coupled to the controlgrid of the second tube bymeans including a unilaterally conducting device polarized sons to impress only voltage impulses of negative polarity upon'the control grid. of said which operates to terminate conduction therein;-

For a better understanding of the invention, together with other and further objects thereof, reference is made to the following description, taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

In the accompanying drawings:

Fig. 1 is a circuit diagram of apparatus embodying the present invention; and

Fig. 2 is a series of curves used in the explanation of the operation of the apparatus of Fig. 1.

Referring now particularly to Fig. 1 of the drawing, there is shown a multivibrator which includes a vacuum tube H of thedouble triode type. It will be understood by those skilled in the art that two equivalent single triode tubes may be used as an alternative arrangement. It, therefore, is intended that, where two vacuum tubes are referred to in the specification and claims, either of these alternative arrangements shall be considered as coming within the'scope of the invention. This tube functions as the usual dual space discharge type of device used commonly in multivibrator circuits. of the tube includes an anode, a cathode anda space current control grid. The cathodes l2 and i 3 of the tube are connected together and through a common resistor 14 to ground. The anodes l5 and N5 of the tubes are connected respectively through load resistors ll and IE to the positive terminal of a source of unidirectional energy such as a battery IS, the negative terminal of which is grounded.

As .a driving means for the impulse generator, there is provided a source 2| of triggering impulses. One terminal of the impulse source is grounded and. the'other terminal is coupled by a condenser 22 to the multivi-brator impulse generator. The triggering impulses derived from'the source 21 are impressed upon the anode I'B of the righthand portion of the tube I I. The anode I6 is coupled by a condenser 23 to-the control grid 24 of the left-hand portion of the tube. In this'manner the coupling circuit including the condenser 22 also is efiective to impress the triggering impulses upon the control grid 24. A leak resistor 25 which preferably is of the variable type is connected between the control grid 24 and the cathodes l2 and I3 of the tube ll. If desired, the resistor 25 may be connected, instead of to the tube cathodes, to some other point-of positive potential such as the positive terminal of battery I9. In such a case,'however, the resistor should be of a sufficiently high value to minimize the now of grid current. i

The anode 15 of'the left-hand tube portion is connected to a coupling condenser 26 whicha-lso' is connected to'an oscillatory circuit '21 includ' ing a parallel arrangement of a coil 28 and a con denser 29 which preferably is-made variable. The other terminal of the oscillatory 'circuit is grounded. The natural period of oscillation-of the circuit 2'! is substantially equal to twice the desired time duration of the impulses to be genvEach half erated. The coupling condenser 26 also is connected to the cathode of a diode 3|. The anode of this diode is connected to the control grid 32 or" the right-hand portion of the tube H. A leak resistor 33 is connected between the grid 32 and ground. A utilization circuit 34 is con nected between ground and the anode l5 of the tube H. I

In describing the operation of the apparatus shown in Fig. 1, reference will be made also to the curves of Fig. 2. The multivibrator employed in conjunction with the present invention is biased in such a manner that it does not operate to produce sustained oscillations. Instead, it normally .is in a. quiescent state. In this normal condition the left-hand portion of the tube H is conditioned for the conduction of space cur rent. At thistime no space current is permitted to flow in the discharge path of the right-hand portion. The right-hand ,portion of the tube is biased beyond cutoff by means of the voltage developed across the resistor M by reason of the space current flowing through it and the lefthand portion of the tube. The-voltage so developed is impressed upon the cathode and grid of the right hand portion of the tube in suitable polarity to effect the desired biasing.

A triggering impulse 35 of negative polarity with respect to ground is derived from the source 21. This negative impulse is impressed sirnultaneously upon the left-hand control grid. 24 and the right-hand anode 1.6 of the tube H. It is of sufficient magnitude to drive the control grid M in a negative direction, thereby decreasing the magnitude of the space current conduction in the left-hand portion of the tube su-fiiciently to initiate the conduction of space current in the righthand portion of the tube. .This operation is effected by means of the voltage developed in the cathode resistor 14. ,By decreasing the magnitude of the current traversing this resistor, the potential of the cathode I3 is driven in a negative direction; thereby decreasing the negative biasing of the control grid 32 to the point where space current begins to flow .inthe rightehand portion of the tube. Then, in a manner well known in the multivibrator art, the conduction of space current between the cathode l3 and the anode It drives the potential of the anode in a negative direction. ,This potentialis impressed by means of the "condenser 23 upon the control grid 2'4 to effect a still further reduction in the magnitude of the space current flowing in the left-hand portion of the tube. These operations are cumulative and occur in a very short space of time with the result that space current flow in the left-hand portion of the tube is interrupted andspace current flow .in the right-hand portion of the tube is initiated. abruptly... The curve 36.

of Fig. .2 is a representation or the voltage appearing at the control grid .24. Itis seen that this grid is drivenin a negative direction concurrently causes the voltage at the anode l6 to become less positive as represented .by the curve 38 of Fig. '2;

51 The positive voltage impulse derived from the anode l and represented by the curve 31 is impressed by the condenser 26 upon the oscil itive voltage impulse upon the oscillatory circult effects a shock excitation of this circuit whereby to produce oscillations. This oscillation is represented by the curve 39 of Fig. 2 and may consist of several cycles of successively diminishing amplitude. The oscillation produced.

in this circuit begins with a positive half cycle which is followed by a negative half cycle. The impression of the negative half cycle of the oscillation represented by the curve 39 upon the diode 3| causes this tubeto become conductive. Infthis manner a voltage impulse of negative polarity relative to ground which is represented by the curve 4| of Fig. 2 is impressed upon the control grid 32 of the tube II. This impulse is of suitable magnitude to decrease the magnitude of the space current flowing in the righthand portion of the tube suiliciently to produce a positive voltage impulse at the anode l6 having a suitable magnitude, when impressed upon the control grid 24 by the condenser 23, to initiate the conduction of space current in the left-hand portion of the tube. In this way the left-hand portion of the tube is restored to its condition of conducting space current at a time sooner than it normally would have been restored by the exponential decay of the wave 36 representing the discharge of the condenser 23. This condition results in the traversal of resistor M by a current of: greater magnitude, whereby the input circuit of the right-hand portion of the tube II is quickly biased beyond cutoff, thereby interrupting the conduction of space current in this portion of thetube. The described cycle of operation againis repeated at the occurrence of the nexttriggering impulse derived from the source 2|.

It has been found that a circuit of the character described is capable of stable operation for the generation of impulses varying in time duration from 2m 10 microseconds at repetition rates varying from to 9,000 pulses 'per second. Such stable operation is principally due to the timing facility provided by the use of the oscillatory circuit 21 and the diode 3|. In a conventional multivibrator the time duration of the impulse generated at the anode l5 of the tube II is determined principally by the time constant of the circuit including the components consisting of resistors l8 and 25 and condenser 23. The described timing circuit embodying the instant invention has been found to be much more reliable to produce impulses of substantially uniform time duration. In order to successfully employ the arrangement disclosed herein, the time constant of the circuit including resistors l8 and 25 and condenser 23 is chosen to be greater than the natural period of oscillation of the circuit 21. In this manner the negative impulse which is impressed upon the control grid 32 by the oscillatory circuit 21 serves to trigger the circuit back to its normally quiescent state substantially in the manner described.

It should be apparent to those skilled inthe art that the principles or the present invention are not limited necessarily to the particular circuit arrangement chosen for illustrative purposes herein. For example, the output circuit may be derived from either the anode l5 as shown or; alternatively from the anode IS, the control grid 24 or from the common cathode resistor l4.v Also, it is to be understood that the invention is not necessarily. limited to the use of a diode such. as the tube 3|. It is consideredto be within the scope of the invention that other types of unilaterally conducting devices may be used instead of the diode 3| with substantially equal facility. 1 Moreover, it will be appreciated that the invention is not necessarily limited to the use of.

any particular oscillatory circuit or device such" as that shown and described herein. The tuned circuit 21 is intended merely to be illustrative of a general class of apparatus which ordinarily is in a passive state but which, when shock excited, is capable of producing either an oscillatory voltage or a voltage impulse of suitable polarity at a predetermined time after the excitation thereof. The period of the oscillation or the delay of the impulse should be a function of the natural periodicity of the device or circuit and also should be independent of such extraneous factors as the magnitude of the exciting voltage. Apparatus other than that illustratively disclosed herein meeting these requirements and intended to be considered as within the purview of the instant invention includes a piez'o-electric crystal, a delay line, either of the reflecting or non reflecting type, and the like. I

Furthermore, it is not absolutely essential that the voltage impulse producing means such as the oscillatory circuit 21 be coupled to the left-hand portion of the vacuum tube I in such a manner as that disclosed so that the potential of the grid '32 is varied. Depending upon the characterisfrom the essential attributes of the invention.

Vacuum tube l, 6SN7 (RCA type) Resistor l4, 2,700 ohms Resistor 10,000 ohms Resistor l8, 12,000 ohms Power source I9, 300 volts Condenser 22, 27 micro-microfarads Condenser 23, 0.003 microfarad Variable resistor 25, 100,000 ohm potentiometer Condenser 25, 50 micro-mocrofarads Coil 28, 75 millihenrys Variable condenser 29, 20-425 micro-microfarads Diode 3|, 6H6 (RCA type) Resistor 33, 10,000 ohms While there has been described what is, at present, considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. An impulse generator comprising, a first 7 vacuum tube, a second vacuum tube, each of said vacuum tubes having a cathode, an anode and a control grid, a source of space current for said tubes, means coupling the anodes of said tubes to one terminal of said space current source, a common cathode resistor coupling the cathodes of both said tubes to the other terminal of said space current source, means capacitively couplingthe' anode of said second tube to the control grid of said first tube, an oscillatory circuit having a natural period of oscillation equal substantfal'ly to twice the desired time duration of the impulses to be generated, means capacitively coupling the anode of said first tube to said oscillatory circuit, a rectifier tube connected between said oscillatory circuit and the control. grid of said second tube in such polarity to impress only the negative half cycles of the oscillations .pl0- duced'. in said oscillatory circuit upon the control grid; of said second tube, a source of triggering impulses coupled to the control grid of said first tube, and a utilization circuit coupled t the" anode of said first tube.

2'. An impulse generator comprising, a first normallyconducting vacuum tube, a second normally nonconducting vacuum tube, each 01" said vacuum tubes having a cathode, an anode and a control grid, a source of space current for said tubes, means including load resistors coupling the anodes of said tubes to one terminal 01 said space current source, means including a biasing resistor coupling the cathodes of saidv tubes to the other terminal of said space current source, means includingv a first condenser coupling the anode of said second tube to the control grid of said first tube, a leak resistor for said first con denser connected to the control grid of said first tube, an oscillatory circuit having a natural period of oscillation equal substantially to twice the desired time duration of the impulses to be generated, means including a second condenser coupling. the anode of said first tube to said oscill'at'ory circuit, a half Wave rectifier tube connected between said oscillatory circuit and the control grid of said second tube in such polarity to impress only the negative half cycles of the oscillations produced in said oscillatory circuit upon the control grid of said second tube, a leak resistor for said second condenser coupled to the control grid of said second tube, a source of triggering impulses coupledto' the controfgrid of said first tube and td the anode of said second tube, and a utilization circuit coupled to the anode of said first-tube. f

3-. An impulse generator comprising, a: first nor mally'conducting vacuum tube, a secondnorrnally nonconduct'ing vacuum'tube, each of said vacuum tubes having'a cathode, an anode and a control grid, a source of space current for said tubes, a load resistor coupled' between the anode of each of said tubes and one terminal of said space cur rent source, a' biasing resistor coupled'between the cathodes ofboth' of saidtubes and the other terminal of Said space current source, a first 1 coupling condenser connectedbctween the anode of said second tube and the control 'grid of said first tube, a leak resistor connected between: the control grid and cathode of said first tubdyan oscillatory circuit having a natural period of 0'scillation equal substantially to twice the desired time durationor the impulsesito begenerated, a secondcoupling condenser connected between the anode of said first tube and said oscillatory circuit, a diodeconnected between said oscillatory I circuit andthecontrol grid of said second tubein such polarity to' impress only thenegative half cycles of the" oscillations produced in said oscill'atory cir'cuitupon the c'ont'rol grid of said second tube, a leak resistoncbuple d'. between the control grid of said second tube and said other terminal of the source of space current, a source of negative triggering impulses coupled to the control" grid of said first tube and to the anode of said secondtube, and autilization circuit coupled to the anodeotsaid fii'sttubc;

' ALBERTS. smears.

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

v UNITED STATES PATENTS Number 2,445-,448 Miller July 20, 1 48

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