US2428149A - Impulse generator - Google Patents

Description

Sept. 30, 1947. A. E; FALK IMPULSE GENERATOR Filed Oct. 18, 1943 GAS FILLED s DELAY NETWORK TRIGGER PULSE GENERATOR INVENTOR ALFRED E. FALK ATTORNEY Patented Sept. 30, 1947 1 UNITED STATES. PATENT OFFICE HWPULSE GENERATOR Alfred E. Falk, Fort Wayne, Ind., assignor to FarnsworthTelevision and Radio Corporation, a corporation of Delaware 7 Application October 18, 1943, Serial No. 506,641

. 6 Claims. 1

This invention relates to impulse generators and particularly to relatively high frequency generators of this character.

According to conventional practice, impulse generators frequently comprise one or more electronic devices having trigger operating characteristics. By this term is meant the facility of the device to initiate and terminate substantially instantaneously the flow of current therethrough. In one well known device of this character one or more gaseous discharge devices are employed. These devices are fired, or the discharges therein are initiated, under the control of a series of triggering impulses derived from some form of mm s-. It ,is characteristic of this type of tube that, so long as 'a' 'predetermined anode-to-cathode potential is maintained, the

discharge initiating grid loses itscontrol of the v discharge once it has been initiated.

Numerous expedients have been utilized to extinguish the'discharge inthe tube. One of these has been the employment of a delay network connected to theganode of the discharge device. Concurrently with theinitiation of the discharge an impulsive voltage is impressed upon the delay network for propagation therethrough at a rate determined by the network parameters. A delayed voltage is derived from a predetermined point on the network for impression upon the anode of the discharge devicein a polarity to reduce the anode-to-cathode voltage thereof below the value required to sustain the discharge. The repetition rate of the impulses is determined by the frequency at which the triggering impulses are impressed upon the grid of the discharge device. The time durations -or widths of the generated impulses aredetermined by the delay network parameters.

As is well understood in the art, however, devices of this character are not capable of operating satisfactorily for the generation of impulses at repetition rates greater than a definite maximum value. As the repetition rate of the generated impulses is increased it is necessary to decrease the value of the load impedance connected to the anode of the discharge tube in order to obtain impulses of appreciable useful amplitude. Thus, the time constant of the discharging circuit for the delay network is so reduced that the delayed voltage derived from the network does not always remain sufiiciently negative for a long enough time to eiiect the complete deionization of the tube. This situation exists regardless of the widths of the impulses. Additionally, when it is attempted to generate relatively wide impulses at relatively high frequencies by means of prior art generators of this character, it is found thatsuch apparatus is incapable of operating satisfactorily for the reason that there is not sufficient time between successive impulses to enable the tube to deionize completely.

An object of the present invention, therefore, is to provide a novel impulse generator of an improved form which is capable of producing impulses at relatively high rates of repetition.

Another object of the invention is to provide an impulse generator in which the time durations of the generated impulses are determined by a novel arrangement which includes a delay net- ,wor k and which controls the development of voltages SilItZblGfOFGfiflCtiIlE' invariably the impulse terminations at predetermined'times.

e In accordance with the present invention there is provided a pair of gaseous discharge tubes arranged with the anodes thereof connected in parallel. The output circuit of one of the tubes includes a relatively high impedance device in which there is developed the generated impulses.

ranged to initiate a discharge in the tube having the low impedance device connected in its output circuit at a predetermined time following the initiation of the discharge in the first tube. The

discharge in the second tube is employed to develop a voltage for impression upon the first tube in a manner to depress the discharge-sustaining voltage in the first tube sufficiently to effect deionization thereof.

More specifically, in accordance with the illustrative embodiment of the invention disclosed herein, the timing means is connected to the input circuit of the tube having the relatively high impedance output circuit and also to one terminal of a non-reflecting delay network. The other terminal of the delay network is connected to the input circuit of the tube having the relatively low impedance output circuit so as to initiate a discharge therein after the lapse of a time interval determined by the parameters of the delay network.

In addition, the output terminals of the delay network may be connected to the input circuit of an electron discharge device having the output For a better understanding of the invention;

together with other and further objects thereof, reference is had to the following description,

" taken in connection with the accompanying draw-,

ing, and its scope will be pointed out in the appended claims.

In the accompanying drawing, the single figure is a circuit diagram, partly schematic, of an impulse generator embodying the present invention.

Having reference'now particularly to the drawing, there is shown a discharge tube I, to the cathode of which is connected a resistor 2 having a relatively high value. To the terminals of this resistor connections are made to a pair of output circuit terminals 3. The anode of the tube I is connected through load resistors 4 and 5 to the positive terminal of a source of direct current such as a battery 6, of which the negative terminal is connected to ground.

The discharge initiating grid of the tube I is connected through a current limiting resistor I and a coupling condenser 8 to the output terminals of a trigger pulse generator 9. This generator serves .as the timing means for determining the frequency of the generated impulses and may be of any conventional type, such as, for example, a multivibrator. The input'circuit" o1- the tube I is negatively biased by means of a connection to the grid circuit which includes a grid leak resistor I I connected to a suitable point on a potentiometer I2. The terminals of the potentiometer are connected to a source of biasing potential such as a battery I3. The battery is poled in a manner to effect a negative biasing of the tube grid with respect to its associated cathode.

A second gaseous discharge tube I4 is provided and includes the connection to the cathode of a resistor I5 having a relatively low value. The

anode of the tube I4 is connected to the anode .of the tube I, thereby to provide a parallel connection of the output circuits of the two gaseous discharge tubes. Preferably, although not absolutely essential to the successful operation of the device, the tubes I and I4 should be of a type having a shield grid between the anode and the control grid and which is operated at cathode potential.

The discharge initiating grid of the tube I4 is connected through a current limiting resistor I6 and a coupling condenser I! to the output terminals of a non-reflecting type of delay network I8. The input circuit of the tube I4 also is negatively biased by a connection of a grid leak resistor I9 to a suitable point on a potentiometer 2I. The potentiometer is connected across the terminals of a source of negative biasing potential such as a battery 22.

The input terminals of the delay network I8 are connected to the terminals of the trigger pulse generator 9. Also, there is connected across the output terminals of the network an energy absorption resistor 23. The function of this resistor is to completely absorb the energy transmitted through the network so that no reing resistor 23 4 flection occurs. The network itself may be of any well known form such as a two-wire transmission line having a suitable length to produce the desired delay in the propagation of a voltage impressed upon the input terminals thereof. Also, the network may comprise a number of lumped circuit elements such as condensers and inductors, arranged in any one of a number of well known configurations.

The output terminals of the delay network I8 also are coupled to the input circuit of an electron discharge device 24. This device may be any well known high vacuum tube in which the space current at all times is under the control of the grid of the tube. This device is provided with a self-biasing arrangement of a resistor 25 connected to the cathode of the device. The selfbiasing resistor 25 is shunted by the usual bypass condenser 26. The anode of the device 24 is connected to the junction point of resistors 4 and 5.

A condenser 21 is connected between the anodes of the tubes I and I4 and ground. Thus, it is in a position to be subjected to anode voltage changes and to influence the anode-to-cathode potentials of these tubes in a manner to be described.

Referring now to the operation of the impulse generator disclosed in the drawing, assume that the discharge tubes I and I4 and the electron discharge device 24 are non-conducting. In this condition there is no voltage developed across the output resistor 2 for impression upon the output circuit terminals 3. A positive impulse from the generator 8 is applied to thedischarge initiatlnggrid ef'the'tfibe I and is of sufficient magnitude to overcome the biasing of the tube. A discharge, therefore, is initiated substantially instantaneously to produce a current flow through the resistor 2, thereby to develop a voltage which is applied to the output terminals 3. By reason of the substantially instantaneous nature of the discharge initiation, the wave front of the voltage developed in the resistor 2 is sufliciently steep to be regarded as vertical with respect to a horizontal time base.

The discharge in the tube I also efiects the flow of current through the load resistors 4 and 5. The voltage drop thus produced in these resistors is effective to reduce the anode-to-cathode voltage of the tube I to a relatively low value which is not appreciably greater than the voltage required to sustain the discharge in the tube.

The positive impulse derived from the generator 9 for the initiation of the discharge in the tube I also is impressed upon the delay network I8. This impulsive voltage appears, after the lapse of the predetermined time required for its propagation through the network, across the terminat- This predetermined time is substantially equal to the desired time duration of one of the impulses to be generated. This volt age also is of a positive polarity and is of suincient magnitude to overcome the biasing of the gaseous discharge tube I4 whereby to initiate a discharge therein. Additional current is drawn from the battery 6 through the load resistors 4 and 5 as a result of the discharge in the tube I4. This additional current effects a greater voltage drop across the resistors 4 and 5 whereby to depress the anode voltage of the tube I. As a result of this voltage depression, the anode-to-cathode voltage of the tube I, by means of which the discharge in this tube is sustained, is reduced, thereby tending to extinguish the discharge.

will cease. l

, However, in cases where the apparatus is to be used for the generation of impulses having extremely shorttime durations and at extremely high repetition rates, it may be desirable to em- 6 condenser 21 for the extinguishing of a discharge in the tube I4 is entirely. satisfactory. The impulse generating apparatus will perform as desired even though the .discharge'in the tube l4 not always is extinguished at the same time following the initiation thereof. The only requirement is that the discharge in this tube be extinguished before the impression of the succeeding trigger pulse upon the discharge tube While it will be understood. that the circuit specification of the impulse generator disclosed herein may vary. according to the particular service requirements, the following specifications for a generator capable of producingimpulses havploy additional facilities to efl'ect the extinguishing time durationsof as'little as 0.25 microsecing of the discharge in the tube l. One such arrangement includes an electron discharge device such as the triode 24. The delayed impulsive voltage derived from the generator 9 and detFEreinr---9rdinarhy this votage reduction also will be suflicient to depress the anodeet athode voltage of the tube I4 sufficiently to extirfifiishi the discharge therein.

In any case the discharges in these tubes, and

particularly intube [4, are extinguished by the action of the condenser 21. The connection of this condenser to the anode circuits of the dis charge tubes is a well known one, particulary in cases where such tubes are used for the generaonds at repetition rates up to a maximum of 3600 impulses per second are'included, by way of example only.

veloped across the terminating resistor 23 is im- 0 TubFs l and M 20.50 pressed upon the control grid of the triode 24 Res{stor 2 "O 300 concurrently with the impression thereof upon Resstor 4 5000 the discharge tube 14. The magnitude of this Reslstor 5 10,000 positive impulsive voltage is sufiicient to overcome Battfery 6 300 the self-bias of the triode 24 and to initiate the 25 Reslstors 7 and conduction of space current therein. This cur- Condensers 8 and rent is supplied by the battery 6 and flows through Reslstrs I i 270000 resistor 5. A still further voltage drop thus is potentflwmeters and 2 1 produced across the load resistor -5 to reduce the Batteries and 22 "r 45 voltage at the junction point of this resistor with 3 Resistor 18 the load resistor 4. The effect of this voltage re- Resistor 23 k duction is applied, through the resistor 4, to the 24 "f 6v GT anodes of the tubes I and I4. In all cases the Reslstor 25 2 anode-to-cathode voltage of the tube I will be de- Condenser 26 "mlcrofamds" 0 0 pressed sufficiently to extinguish the discharge 35 Condenser 21 While there has been described what, at prescut, is 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 'fromthe invention, and therefore, it is aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention. i

What is claimed is:

1. An impulse generator comprising, a first gaseous discharge tube having an input circuit and a relatively high impedance output circuit for the development therein of said generated impulses, a second gaseous'discharge tube having an input circuit and a relatively low impedance output circuit, means for connecting the output circuits of said tubes in parallel, a circuit including a load impedance device and a source of 51 extinguish th d sc es therein. However, direct current connected in the output circuits since the transition of the condenser charge from one voltage value to another occurs in an exponential manner with respect to time, such a device cannot be relied upon solely to effect the terminaof said tubes, a source of timing impulses coupled to the input circuit of said first tube t initiate a discharge therein, a delay network having a propagation time substantially equal to the tion of the discharge in the-tube l. Obviously. time durations of the impulses to be generated very slight changes in the conditions of the various circuits, such as voltage variations of the battery 6, for example, will effect corresponding changes in the times at which the condenser 21 and coupled between said impulse source and the input circuit of said second tube to initiate a discharge therein whereby to effect current conduction in the output circuit of said second tube,

produces an extinguishing voltage for the tube I, 55 means including the current conducting output following the initiation of a discharge therein. The performance of the condenser 2'! as a discharge extinguishing means also is determined by the time constant of the charging and dischargcircuit of said second tube to depress the discharge-sustaining voltage of said first tube sufiiciently to extinguish the discharge therein, and means controlled by said timing impulses to exing circuits for the condenser. It is impractical -7o tinguish' the discharge in said second tube.

to attempt the design of such a circuit having the rigid requirements as to the time constant thereof, for example, where it is desired to produce impulses of extremely short time durations.

2. An impulse generator comprising, a first gaseous discharge tube, a relatively high impedance device connected in series with said first tube for the development therein of said generated However, the conventional functioning of the impulses, a second gaseous discharge tube, a

relatively low impedance device connected in series with said second tube, a circuit including a load impedance device and a source of direct current connected in parallel with said two series connections, a, source. of timing impulses coupled to said first tube to. initiate a discharge therein, a. delay network having a propagation time substantially equal to the time durations of the impulses to be generated and coupled between said impulse source and said second tube to initiate a discharge therein, means including the series connection of said second tube and said low impedance device to depress the discharge-sustaining voltage of said first tube suificiently to extinguish the discharge therein, and means coupled to said delay network to extinguish the discharge in said second tube.

3. An impulse generator comprising, a first gaseous discharge tube having an anode, a cathode and a discharge initiating grid, a relatively high impedance device connected to the cathode of said first tube for the development therein of said generated impulses and to form a first series circuit with said first tube, a second gaseous discharge tube having an anode, a cathode and a discharge initiating grid, a relatively low impedance device connected to the cathode of said second tube to form a second series circuit with said second tube, a circuit including a load impedance device and a source of direct current connected in parallel with said two series circuits, a source of timing impulses coupled to the grid of said first tube to initiate a discharge therein, a delay network having input and out put terminals and having a propagation time substantially equal to the time durations of the impulses to be generated; means for coupling said impulse source to the input t network, mea mg the output tcrmi- .nalg of siid'network to the grid of said second to initiate a discharge therein, means ineluding said second series circuit todepress the discharge-sustaining. voltage of said first tube sufficiently to extinguish the discharge therein, and means coupled between the output circuit of said delay network and the anode of said second tube-to extinguish the discharge in said second tube.

4.An impulse generator comprising, a first gaseous discharge tube, a second gaseous discharge tube having an output circuit, an electron discharge device having an output circuit, means to initiate a discharge in said first tube,

means operative a predetermined time after the initiation of the discharge in said first tube to 8 cuits, a relatively high impedance device connected in the output circuit of a firstone of said tubes, a relatively low impedance device connected in the output circuit of the second one of said tubes, an electron discharge device having an input circuit and an output circuit coupled to the output circuits of said discharge tubes, a delay network having a propagation time substantially equal to the time durations of the impulses to be generated, a source of timing impulses coupled to-the input circuit of said first discharge tube to initiate a discharge therein, means for coupling said delay network between said impulse source and the input circuits of said second discharge tube to serving to depress the discharge-sustaining voltinitiate a discharge in said second tube whereby to effect current conduction in the output circuit of said second tube, said operative means also serving contemporaneously to initiate current conduction in said electron discharge device and its output circuit, means including the current conducting output circuit of said second discharge tube to depress the discharge-sustaining voltage of said first discharge tube sufficiently to extinguish the discharge therein, and means including the current conducting output circuit of said electron discharge device to depress the discharge-sustaining voltage of said second discharge tube sufli'ciently to extinguish the discharge therein.

5. An impulse generator comprising, a pair of gaseous discharge tubes having unassociated input: circuits and parallelly connected output cirage in said first tube sufficiently to efiect deionizetion thereof and the current conduction in said electron discharge device serving to depress the discharge-sustaining voltage in said second discharge tube suiliciently to effect deionization thereof.

6. An impulse generator comprising, a pair of gaseous discharge tubes having unassociated input circuits and parallelly connectedoutput circuits, a relatively high impedance device connected in the output circuit of a first one of said tubes, a relatively low impedance device connected in the output circuit of the second one of said tubes, a source of direct current and two serially connected impedance devices coupled to the output circuits of said discharge tubes, an

electron discharge device having an inputcir uiLpand an output circuiteonnected to a point betweerr safd'serially connected impedance devices, a delay network having input and output terminals and having a propagation time substantially equal to the time durations of the impulses to be generated, a source of timing impulses coupled to the input circuit of said first discharge tube to initiate a discharge therein and also to the input terminals of said delay network, and means for coupling the output terminals of said delay network to the input circuit of said second discharge tube to initiate a discharge therein and also to the input circuit of said electron discharge device to effect current conduction therein, the discharge in said second. tube serving to depress the discharge-sustaining voltage in said first tube sufficiently to effect deionization thereof and the current conduction in said electron discharge device serving to depress the discharge-sustaining voltage in said second discharge tube sufficiently to effect deionization thereof.

ALFRED E. FALK.

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

UNITED STATES PATENTS Hall Apr. 28,

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