US2445448A - Electron discharge device trigger circuit - Google Patents

Description

y 1948. w. A. MILLER 2,445,448

ELECTRON DISCHARGE DEVICE TRIGGER CIRCUIT Filed July 27, 1944 4 Sheets-Sheet 1 ,9; F12 6 1/ l/ 154 ww 905.

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ELECTRON DISCHARGE DEVICE TRIGGER CIRCUIT Filed July 27, 1944 4 Sheets-Sheet 2 as. Temp/ms INVENTOR M164 4 Mam.

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ATTORN EY "111, 20, 1948. A, WLLER 2,445,448

ELECTRON DISCHARGE DEVICE TRIGGER CIRCUIT Filed July 27, 1944 4 Sheets-Sheet 3 Tlclfl Tlab.

BY f mm/ ATTORNEY July 20, 1948. w. A. MILLER 2,445,448

ELECTRON DISCHARGE DEVICE TRIGGER CIRCUIT Filed July 27, 1944 4 Sheets-Sheet 4 PM T PA? A ATTORNEY Patented July 20, 1948 uccubil FUUIT] ELECTRON DISCHARGE DEVICE TRIGGER CIRCUIT William A. Miller, Port Jefferson, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application July 27, 1944, Serial No. 546,890

13 Claims. I

This invention relates to improvements in electron discharge device trigger circuits.

An object of the invention is to provide a line controlled regenerative electron discharge device trigger circuit.

Another object is to provide an electron discharge device regenerative trigger circuit capable of producing pulses having time durations less than 1.0 microsecond and which are independent of the time-constants of the regenerative elements of the system.

A further object is to provide an electron discharge device trigger circuit having a stable state and an active state and having only one possible control of the duration of the output pulse.

Briefly stated, the present invention comprises a pair of electron discharge device electrode structures so interconnected as to produce a trigger circuit having a stable state and an active state. In the stable state one electrode structure draws maximum current while the other electrode structure draws minimum or no current. An initiating pulse of proper polarity and magnitude will fire or trip the trigger into its active state in which the aforesaid current conduction states of the two electrode structures are reversed. After a suitable time interval in the active state, the trigger circuit will restore itself to the stable state. It will thus be seen that the trigger circuit has one degree of electrical stability. A transmission line circuit suitably terminated is connected to one of the electrode structures for controlling the time duration of the active state of the trigger circuit.

In the practice of the invention, it is preferred that vacuum tube electrode structures be employed and that the transmission line circuit be short-circuited at the end remote from the line terminal which is connected to the electrode structure. This transmission line circuit may take several forms. It may be in the form of an artificial line having several sections of lumped series ind ictance and lumped shunt capacitance, or it may be a coaxial line, or spirally wound in the interest of compactness.

The following is a more detailed description of the invention, in conjunction with drawings, wherein:

Figs. 1 to 8 illustrate different embodiments of a line controlled regenerative trigger circuit in accordance with the invention.

Throughout the drawings the same reference letters have been used to designate the same or equivalent parts.

Referring to Fig. 1, there is shown (omitting for the present any consideration of transmission line circuit TL) a regenerative trigger circuit comprising a pair of vacuurri'tube trlodes VI and V2 whose grids and anodes are interconnected regeneratively by means of resistors RM and RM. Small condensers Chl and CM shunt the resistors RM and RM, respectively, to produce extremely rapid current increase and current decay in the trigger circuit, and are not essential. In other words, condensers CM and Ch! are used to speed up the transition or change over from the stable to the active state and return. The anodes are supplied with positive potentials from source +B through resistors RLI and RL2. Normally, tube VI is biased to cut-off by means of the negative potential supplied to its grid by source Ec over resistor Rdl. Tube V2 is normally conductive and has its grid connected to its cathode through resistor R112. The system is so designed that the resistors RLI=RL2; RdI=-Rd2 and Rhl=Rh2; if VI and V2 are identical tube structures. The normal condition where tube VI is cut-off (i. e.. non-conducting) and tube V2 conducting is called the stable state, while the reverse condition where tube VI is conducting and tube V2 non-conducting is called the active state. The trigger circuit is tripped from its stable state to its active state by an initiating or tripping input pulse of suitable polarity and magnitude applied to one of the electrodes of one of the tubes VI or V2. For example, a positive pulse applied to the grid of tube VI or a negative pulse applied to the grid of tube V2 will trip the trigger circuit, provided this pulse has a magnitude sufllcient to overcome the normal bias on these tubes. The duration of an output pulse, taken from either the anode of tube VI or the anode of tube V2, is only slightly longer than the duration of the tripping input pulse, the time difference between the two pulses (i. e., tripping and output) being due to the stray capacitance of the wiring, the sockets, and the interelectrode capacitances of the tubes. A positive output pulse may be taken from the anode of tube VI, or a negative output pulse may be taken from the anode of tube V2. In an ideal circuit of this type, the leading edge of a positive pulse applied to the grid of tube VI will cause VI to conduct current and cause V2 to cease conducting current, and when the tripping pulse vanishes the circuit will immediately return to its stable state due to the bias potential on the grid of tube VI.

An essential aspect of the present invention lies in the use of the transmission line circuit TL for controlling the duration of the active state of the trigger circuit and, hence, the duration of the output pulse. By suitably choosing the characteristics of this line so as to obtain a desired time delay therein, it is possible to vary the time of the active state of the trigger circuit. Line TL is here shown as an artificial line comprising a plurality of identical sections or series inductance L and shunt capacitance C. Line TL is shown connected at one end across resistor Rd2 through condenser C, and is short-circuited at its other end. Although an artificial line has been illustrated, it should be understood that for the purpose of the invention the line may be a coaxial type or one coiled up in suitable manner, reference being made to Lindenblad copending application Serial No. 459,497, filed September 24, 1942, as an example of a type of line circuit which can be used. The condenser C is a blocking condenser of suitable value which is used to prevent short-circuiting of resistor M2 for direct current, although if this short-circuiting efiect is not undesirable then this condenser may be omitted. Stated in other words, condenser C may serve to isolate the line TL from any direct current bias supply, as seen in more detail in the system of Fig. 3. When condenser C is used, its capacitance should be much greater than the value of C in the line circuit TL. It should be understood that it is a matter of operational expediency rather than circuit design whether or not the condenser C should be used.

The result of the short-circuiting termination on transmission line TL at the end remote from the electrode structure is that a positive or negative pulse applied to the sending end of the line (that is, the end connected to one of the electrode structures) will be transmitted as a wave over the line to the short-circuited end, and will charge the line to a voltage of magnitude and sign determined by the initial pulse. This pulse will be reflected at the short-circuited end as a pulse of opposite polarity relative to the polarity of the initial pulse and, if there is negligible attenuation along the line the reflected or echo pulse will have the same amplitude as the direct wave. As the reflected pulse travels back over the line to the sending end, it will remove the charge on the line produced by the direct wave or initial pulse. Thus, when the reflected pulse reaches the sending end of the line TL, the line will have no charge thereon. The characteristic impedance of the line TL is made to match or equal the resistor at the sending end of the line so as to ensure dissipation of the pulse and no recurrence of char e and discharge of the line until another pulse is applied to the sending end of the line. In the case of Fig. 1, the resistor Rd2 is equal to the characteristic impedance of the line TL.

The time delay due to an artificial line such as is shown, is t= /LC per section where L is the inductance and C the capacitance of the line per section. If the line has N identical sections, th en the total one way time delay of the line is NV'LC. In the present invention, however, the pulse must make a round trip over the line (twice the length or the line), and hence the total time delay of a pulse to travel down the entire length oflhe line and return to the sending end is 2N /LC.

A description of the operation of the line controlled regenerative trigger circuit of Fig. 1 will now be given: In the stable state, tube VI is cut oil (non-conducting) by the direct current bias supplied from -Ec, while tube V2 is conducting because of the slight positive potential on its grid. It, now, a very short positive pulse of such magnitude as to overcome the negative bias on the grid 04 tube Vi is applied to the grid of VI, tube VI will begin to conduct and tube V2 start to turn off the flow of current therethrough. This action takes place in a very short time. The decrease in anode potential of tube VI caused by the IR drop in resistor RLI as current starts to flow therein is transmitted to the grid of tube V2 by means of RM and CM in parallel. The leading edge of the negative pulse from the anode of tube VI will be transmitted without delay to the grid of V2 due to the use of condenser Ch2. This negative pulse arrives at the grid of V2 and the sending end of line TL while tube V2 is cutting off its flow of current, and the pulse travels over the length of line TL to the short-circuited end where its polarity is reversed and the pulse of reversed polarity positive now sent back to the sendin end of the line for dissipation in resistor R112. The negative pulse from the anode of tube VI will, of course, cut off tube V2, and by virtue of the regenerative action of resistor Rhl, the tube VI will conduct. The trigger circuit is now in its active state. As long as the line TL remains charged negatively due to the application of the negative pulse from the anode of tube VI, tube V2 will be held cut oil, but just as soon as the line TL is completely discharged by the reflected pulse arriving at the sending end of the line, this negative bias on the grid of tube V2 disappears and the bias Ec becomes effective to turn tube VI off (that is, cause Vi to cease conducting) in turn, turning tube V2 on (that is, cause V2 to conduct), hence ending the active period.

It will be seen from the foregoing that the active period of the trigger circuit is only controlled by the time during which the line TL remains charged. Since transmission lines can be designed to be as short as desired, it will be evident that very short pulses can be obtained from the trigger circuit. A practical limit is, however, set by the fact that the speed of change-over from one state to the other is affected by stray wiring and tube and socket capacitances. If the line TL has a one way delay time of T, the length of the output pulse is 2T. By means of the trigger circuit of the invention, it is possible to obtain pulses havin durations less than 0.25 microsec- 0nd.

Fig. 2 shows a line controlled regenerative trigger circuit in accordance with the invention. in which the line TL is in the grid circuit of tube Vl instead of in the grid circuit of tube V2, as illustrated in Fig. 1. The operation of the system of Fig. 2 is similar to that described above for Fig. 1, except that obviously the pulse impressed on the sending end of line TL in Fig, 2 is now positive, and this positive charge on the line holds the trigger in the active state until the positive charge is removed by the reflected pulse from the short-circuited end of the line and dissipated in resistor Rdl. In Fig. 2, the resistor Rdl is equal to the characteristic impedance of the line TL.

It is preferred in the case. of Figs. 1 and 2 that the characteristic impedance of the line TL be as high as is feasible since the larger Rdl and R112 can be made, the more voltage is available on the grid of the tube to which the line is connected to perform the control functions.

Where relatively low impedance transmission lines are necessary, it is preferred to employ the circuits of Figs. 3 and 4. This is because the load resistors RLI and RL2 may be. and generally are, smaller in value than the grid resistors Rdl and Rd2. I

In Fig. 3, when tube V2 ceases to conduct in Search Room response to conduction of tube VI (when the trigger circuit changes from its stable to its active state), a, positive pulse appears on the anode of tube V2 which travels down the line TL. The reflected pulse of reversed polarity from the short-oircuited end of line TL removes the positive charge on the line and is dissipated in resistor RL2 which equals the characteristic impedance of the line. As long as the line TL is charged positive, the tube Vi is maintained conducting. When the reflected pulse reaches the sending end of the line where it is dissipated in resistor RL2, the positive charge on the line is extinguished and the trigger will return to its stable state.

The foregoing description of the operation of Fig. 3 holds true for the operation of Fig. 4, except now a negative pulse appears on the anode of tube VI, travels down the line charging the same, and this negative pulse is reflected back from the short-circuited end with a positive polarity. The line terminating resistor RLI is equal to the characteristic impedance of line TL.

Figs. 5 and 6 show other line controlled regenerative trigger circuit embodiments of the invention having various other means for obtaining bias for the trigger circuit and for tripping the same from the stable to the active state. In Figs. 5 and 6 the line TL should have the proper characteristics, generally different for the difierent sending end locations, for controlling the active time of the trigger circuit.

In Fig. 5, the trigger circuit per se, without the line TL, follows the teachings otthe trigger circuit described in copending application Serial No. 492,872, flied June 30, 1943, jointly by me and E. R. Shenk, now abandoned. The diode M is provided in shunt to a high value resistor N in order' to'rapidly dissipate the negative input tripping pulse applied to the cathode of tube Vi. Small condensers can be connected across points A! and B5, and A6 and B6 to speed up the transition from the stables to the active state and return. The terminal A of line TL may be connected to any of the Al, A2 A9 points provided the terminal B of the line TL is connected to the corresponding Bl, B2 B9 terminal with the same subscript. For example, terminals A and B can be connected to points Al and BI or the A and B terminals can be connected to points A2 and B2, etc. Since there are nine different subscripts, the line can be connected to any one of nine different locations and still achieve the results of the invention. The line TL has been shown open ended at terminals A and B in the interest of simplicity, in order not to complicate the drawing by duplicating nine different circuits which would differ from one another merely in the location of the line.

The statements made above in regard to Fig. 5 generally apply to Fig. 6, except now the terminals of line TL have been designated C and D, and

the difierent points of connection to which C and D may be joined have been labeled Ci, C2 C9 and DI, D2 D9. The C and D terminals of line TL in Fig. 6 should be connected to any of the Ci C9 and Di D9 points having the same subscripts. Here again, line TL has been shown open ended at C and D in the interest of simplicity in order not to complicate the drawing with nine different circuits differing from one another only in the location of line TL. It should be noted that the trigger circuit per se of Fig. 6 does not show the negative bias source --Ec of the other figures, but instead shows a Voltage regulator tube VR. whose cathode is connected to ground and whose anode is conected to the resistor N and to the positive polarizing source +B through a resistor P. The voltage regulator tube VR will always be lit and the effect of supplying a positive potential to the cathode through resistor P is the same as supplying a negative potential to the grid of tube VI, thus biasing tube VI to cut oil in the stable state. Putting it in other words, the voltage regulator tube arrangement illustrates an alternative way of biasing tube VI to below its cut oil potential.

Fig. 7 shows another line controlled regenerative trigger circuit embodiment of the invention wherein a pair of pentode vacuum tubes V! and V2 are employed in the trigger circuit in conjunction with high frequency correction choke coils LI and L2 in the anode circuits for extreme speeds of operation, together with the proper choice of condensers Chi and Chi.

Fig. 8 illustrates another form of line controlled regenerative trigger circuit which differs from the trigger circuits of Figs. 1 to '7, inclusive, in employing a CR trigger circuit which has both a stable and an active state. The trigger circuit per se, omitting consideration of the line, is described in connection with Fig. 1 of copending application Serial No. 492,872, filed June 30, 1943, now abandoned. The line TL has here been shown as a coaxial line by way of example only, although it will be understood that an artificial line can be used instead. The preferred method of operating Fig. 8 is to have the time constants of C and R and its associated circuit elements so adjusted as to be longer than the time it takes a pulse to travel down the line and return to its sending end (round trip), but not too long so as to cause the production of multiple pulses for each tripping input pulse, in the event only one output pulse is desired for each input pulse. However, if it is desired to produce multiple output pulses for each input pulse, then the CR. network should be made to have a large time constant considerably longer than twice the delay of line TL.

What is claimed is:

1. An electron discharge device trigger circuit having one degree of electrical stability, comprising a pair of electrode structures each of which has an anode, a grid and a cathode, direct current passing impedance elements cross-connecting the anodes and grids of said structures in regenerative manner, sources of potential for said structures so connected thereto that the trigger circuit has a stable state and an active state, one electrode structure passing current while the other is non-conductive in the stable state, and vice versa in the active state, means for supplying an input pulse to one of said electrode structures of such magnitude and polarity as to trip said trigger circuit from its stable to its active state, and a transmission line having a. desired time delay connected at one end to the other of said electrode structures, and a connection short-circuiting said line at its other end, whereby said line controls the active time of the trigger circuit, and a resistor having a value substantially equal to the characteristic impedance of said line connected thereacross at said one end.

2. An electron discharge device trigger circuit having one degree of electrical stability, comprising a pair of electrode structures each of which has an anode, a grid and a cathode, direct current passing impedance elements cross-connecting the anodes and grids of said structures in 7 regenerative manner, sources of potential for said structures so connected thereto that the trigger circui t has a stable state and an active state, one electrode structure passing current while the other is non-conductive in the stable state, and vice versa in the active state, and a transmission line having a desired time delay connected at one end to one of said electrode structures and a connection short--circuiting said line at its other end, whereby said line controls the active time of said trigger circuit, and means connected to said one end of said line for substantially preventing the'rei'lection of a wave traveling over said line from the short-circuited end toward said one end.

3. An electron discharge device trigger circuit having one degree of electrical stability, comprising a pair of electrode structures each of which has an anode, a grid and a cathode, direct current passing impedance elements cross-connecting the anodes and grids of said structures in regenerative manner, sources of potential for said structures so connected thereto that the trigger circuit has a stable state and an active state, one electrode structure passing current while the other is non-conductive in the stable state, and vice versa in the active state, and a transmission line having a desired time delay connected at one end to one of said electrode structures, a resistor connected across said line at said one end and having a value equal to the characteristic impedance of said line, and a connection short-circuiting said line for direct current voltage at its other end, whereby said line controls the active time of said trigger circuit.

4. An electron discharge device trigger circuit having one degree of electrical stability, comprising a pair of electrode structures each of which has an anode, a grid and a cathode, a direct current passing impedance element cross-connecting the anode of each structure with the grid of the other structure, sources of potential for said structures so connected that one electrode structure passes current while the other is non-conducting in the stable state and vice-versa in the active state, said trigger circuit being responsive to a tripping input pulse of suitable polarity and magnitude for changing over from the stable to the active state for a temporary period of time after which it restores itself to the stable state, a resistor connected between the grid and cathode of one of said structures, and a transmission line having a desired time delay for energy passing thereover connected at one end across said resistor, said resistor having a value equal to the characteristic impedance of said line, and a connection short-circuiting the other end of said line.

5. An electron discharge device trigger circuit having one degree of electrical stability, comprising a pair of electrode structures each of which has an anode, a grid and a cathode, a direct current passing impedance element cross-connecting the anode of each structure with the grid of the other structure, sources of potential for said structures so connected that one electrode structure passes current while the other is non-conducting in the stable state and vice-versa in the active state, said trigger circuit being responsive to a tripping input pulse of suitable polarity and magnitude for changing over from the stable to the active state for a temporary period of time after which it restores itself to the stable state, a resistor connected between the anode of one structure and one of said sources of potential, and a transmission line having a desired time delay for energy passing thereover connected at one end across said resistor, said resistor having a value equal to the characteristic impedance of said line, and a connection short-circuiting the other end of said line.

6. An electron discharge device trigger circuit comprising a pair of electrode structures each of which has an anode, a grid and a cathode, a source of positive polarizing potential, separate resistors connecting said anodes to said source, impedance elements cross-connecting the anodes and grids of said structures, means biasing said grids such that one electrode structure passes current while the other is non-conducting in the stable state and vice-versa in the active state, said trigger circuit being responsive to a tripping input pulse of proper Polarity and magnitude for changing over from the stable to the active state for a temporary period Of time after which it restores itself to the stable state, and a transmission line having a desired time delay for energy passing thereover connected at one end across one of said anode resistors, said one anode resistor having a value equal to the characteristic impedance of said line, and a connection of low impedance to direct current connected across the other end of said line.

'7. A trigger circuit having one degree of electrical stability, comprising a pair of vacuum tube electrode structure each of which has an anode, a cathode and a grid, separate resistors of substantially equal value cross-connecting the anodes and grids of said structures, a source of positive polarizing potential, separate resistors of substantially equal value connecting said anodes to said source, and separate resistors of substantially equal value coupled between the grids and cathodes of said structures, means biasing said grids such that one electrode structure passes current while the other is non-conducting in the stable state and vice-versa in the active state, said trigger circuit being responsive to a tripping input pulse of proper polarity and magnitude for changing over from the stable to the active state for a temporary period of time after which it restores itself to the stable state, and a trans- 0 mission line having a desired time delay for energy passing thereover connected at one end across one of said resistors, said one resistor having a value equal to the characteristic impedance of said line, and a connection of low impedance to direct current connected across the other end of said line.

8. The combination with an electron discharge device trigger circuit having one degree of electrical stability-and including a pair of interconnected electrode structures so connected and ar ranged as to have a stable state and an active state, of a transmission line of predetermined electrical length connected at one end to one of said structures andshort-circuited for direct current at the other end, in order to control the active time of said trigger circuit.

9. The combination with a vacuum tube trigger circuit having one degree of electrical stability and including a pair of similar electrode structures so interconnected and arranged as to have a stable state and an active state, of a transmission line of predetermined electrical length connected at one end to one of'said structures and short-circuited at its other end for direct current energy, said one end of said line being terminated by a resistor of a value equal to the characteristic impedance of said line.

10. A vacuum tube trigger circuit comprising a. pair of electrode structures each having a. grid,

086 CH mom a cathode and an anode, a condenser connecting the anode of one structure and the grid of the othe'f'structure, a first resistor between the grid and cathode of said last structure, a second resistor between the anode of said last structure and the grid of said one structure, sources of potential for said structures so connected thereto that the trigger circuit has a stable state and an active state, one structure passing current while the other structure is non-conducting in the stable state and vice-versa in the active state, the time constants of said trigger circuit being primarily dependent upon the values of said condenser and said first resistor, and a transmission line having a predetermined time delay for energy passing thereover connected at one end across said first resistor, and a connection of low impedance for direct current connected across the other end of said line, said first resistor having a value substantially equal to the characteristic impedance of said line.

11. A vacuum tube trigger circuit in accordance with claim 10, characterized in this that the time constants of said condenser and said first resistor with its associated elements are has an anode, a grid and a cathode, direct current passing impedance elements cross-connecting the anodes and grids of said structures in regenerative manner, sources of potential for said structures so connected thereto that the trigger circuit has a, stable state and an active state, one electrode structure passing current while the other is non-conductive in the stable state, and vice versa in the active state, a, lead for supplying tripping input pulses to that electrode structure which is non-conductive when the trigger circuit is in the stable state, and a transmission line having a desired time delay connected at one end to that electrode structure which passes current when the trigger circuit is in the stable state, said line having a short-circuiting connection for direct current at its other end, whereby said line controls the active time of said trigger circuit.

WILLIAM A. MILLER.

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

UNITED STATES PATENTS Number Name Date 2,158,285 Koch May 16, 1939 2,188,970 Wilson Feb. 6, 1940 2,193,850 Andrieu et a] Mar. 19, 1940 2,212,173 Wheeler et a1 Aug. 20, 1940 2,212,967 White Aug. 7, 1940 2,221,666 Wilson Nov. 12, 1940 2,262,838 Deloraine et a1. Nov. 12, 1940 2,266,154 Blumlien Dec. 16, 1941

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