US 2846576 A
Description (OCR text may contain errors)
g- 5, 1958 H. G. PURINTON ,Mfifi? v SHORT PULSE GENERATOR Filed Sept. 20, 1954 HAROLD s. PURINTON 2 .INVENTOR.
M ATTORNEYS snonr PULSE GENERATOR Harold G. Purinton, Baltimore, lVId., assignor to Bendix Aviation Corporation, Towson, Mi, a corporation of Delaware Application September 20, 1954, Serial No. 456,989
Claims. (Cl. 250-27) This invention relates to pulse generators and more particularly to a pulse generator capable of producing pulses of very short duration.
In some situations it is desirable to produce pulses of durations of a half microsecond or less and having fast rise and decay times. Among other expedients which have been tried for this purpose, use has been made of a thyratron oscillator having a series resonant circuit connected between the plate and cathode thereof. While such circuits have been able to produce pulses satisfactory for some purposes they are, however, subject to the defect that when coupled to a load circuit which has substantial capacity to ground the very high frequency components of the pulse are lost and the form of the pulse is thus altered so that it has rise and decay slopes less steep than might be desired.
It is an object of this invention to provide a pulse generator capable of producing extremely short pulses having very fast rise and decay times.
It is a further object of the invention to improve the thyratron oscillator type of pulse generator circuit in a manner which enables it to provide pulses of shorter duration and having faster rise and decay times than has heretofore been possible.
These and other objects of the invention are realized by a circuit in which the series resonant circuit is connected for R. F. across the load impedance of the thyra tron, rather than across the plate cathode space of the tube. Two forms of the circuit may be utilized, in one of which the load resistor is in the plate circuit, and the other of which it is in the cathode circuit of the thyratron. In the former version a negatively polarized output pulse will be obtained, whereas in the latter version the output pulse will be positive going. The capacity of the series resonant circuit is so selected that it, in conjunction with the capacitance to ground of the load circuit into which the output of the generator is coupled, will cause the formation of a pulse of the desired duration. in practice the lumped inductance is made small so that the ratio of lumped capacitance to load capacitance will be large, thus producing stability in pulse duration with varying load capacities.
in the drawing, Fig. 1 is a schematic diagram of a circuit embodying the invention and arranged to produce negatively polarized output pulses;
Fig. 2 is a schematic diagram of a circuit similar to that of Fig. l, but arranged to produce positively polarized output pulses.
Referring now more particularly to the drawing, there is shown in Fig. 1 a thyratron 1. Triggering voltage is applied to the thyratron from a terminal 2 by way of a resistor 3. The terminal 2 is also connected to ground by a resistor 4. The cathode is connected to the positive terminal of a source of supply voltage by Way of a resistor 5'. The cathode is also connected to ground through a resistor 6, the lower terminal of which is connected to a slider '7 for varying the value of the resistor 6. The anode is connected to a load resistor 8, the remaining 'thyratron.
terminal of which is connected to the positive terminal of the supply voltage source. A connection is returned from the latter terminal to a slider 9 for varying the value of the resistor 3. The anode is also connected by way of a capacitor 10 and a coil 11 to the cathode. The junction of the coil 11 and the cathode is connected to ground by way of a capacitor 12. The coil is by-passed by a diode 13. The junction of the coil 11 and the capacitor 10 is indicated as the point 14, at which the output of the generator appears and from which it is applied to a load circuit indicated by the box 17. The capacity to ground of this circuit is indicated by the dashed line capacitor 18.
In the operation of the above described circuit a triggering pulse having a waveform as indicated in the graph 15 is applied to terminal 2. This pulse should have a duration at least as great as the ionization time of the thyratron being used and its application causes ionization to occur within the tube. The ionization causes the anode to rapidly lose its positive potential because of the IR drop across the resistor 8. This sharp voltage drop is applied to the series resonant circuit consisting of the capacitor 10 and the coil 11 and the action of that circuit in conjunction with the capacitance 13 forms the negative going output pulse having a waveform as indicated by the graph 16, which pulse appears at 14 and is applied to the load circuit 17. The value of the capacitor 12 connecting the junction of coil 11 and the cathode of the thyratron to ground is so selected as to provide an R. F. ground for that end of the coil. The voltage supply source must be shunted by sufiicient capacity to provide a low impedance to ground for R. F. The diode l3 shunting the coil 11 has the effect of damping out the positive going swing of the waveform so that only the initial half cycle of the oscillation is recovered as indicated by the graph 16. In operating with a load circuit having a small value of capacity to ground the value of the inductance of the coil 11 can be made quite small and the ratio of the capacitance 10 to the load capacitance 13 can be made large. A choice of values of 10 and 11 in conjunction with capacitance 38 can be made, such that the pulse duration is very small and stable in length. The capacitor 12 furnishes a high frequency ground reference to series circuit 10, 11 and a low impedance source of electrons to the thyratro-n cathode. The dashed line capacitor 25 represents the low impedance of the power supply to R. F. currents.
in the form of the invention illustrated in Fig. 2 the load impedance of the tube has been changed from the anode circuit to the cathode circuit and appears as a resistor 19, made variable by means of a slider 26 connected to its grounded terminal. The resistor 5 is in this form of the invention connected to a slider 21 on a resistor 22, which is connected between the positive terminal of the supply voltage and ground. The anode of the thyratron is connected to ground by way of a capacitor 23. The series resonant combination of capacitor 10 and coil 11 are connected across the cathode load resistor 19. The coil is shunted as before by a diode 13 which has its cathode connected to the junction of capacitor 10 and coil 11.
In the operation of this circuit the positive triggering voltage 15 is applied as before to the input circuit of the The resulting ionization of the thyratron causes an IR rise in the cathode circuit resulting in the formation of an output pulse 2 having the same shape as the pulse 16 but being of a positive polarity. Otherwise, the operation of the circuit is the same as the operation described above for the circuit illustrated in Fig. 1. The duration of the pulse is controlled as before by the selection of the values of capacitor 10 and coil 11 in conjunction with load capacitance l8.
In each of the circuits of Figs. 1 and 2 the equivalent circuit of the pulse forming network is constituted by the series resonant circuit connected in series with the load resister of the thyratron. Thecapacitors 12 and 25 of Fig. 1 and 23 of Fig. 2 act to form a low impedance path for R. F. currents across the bias resistor 6 and the power supply respectively, acting to provide a low impedance.
path for radio frequencies around all elements of impedance in series with the gas discharge path of the tube, except those in the pulse forming network thus afiording the utilization of the higher frequency components of the generated pulse which would otherwise be unavailable.
By the use of the circuits described above pulses having extremely short durations may be obtained. These pulses may be clipped to any desired height by the use of cathode coupled clippers or biased diodes in a manner known to the art, thus producing square waves of extremely short duration and of very low rise and decay times.
What is claimed is:
1. A pulse generator comprising a gas discharge tube having a plate, a cathode and a control grid, a load resistor and a power supply connected in series with the gas discharge path of said tube between said plate and said cathode and constituting elements of impedance in said path, a series resonant circuit connected between said plate and said cathode to constitute a pulse forming network, a load circuit connected to said series resonant circuit, said load circuit having a capacity to ground, said capacity to ground acting as an integral part of the pulse forming elements of said resonant circuit, means damping the output of said series resonant circuit only after the first half cycle of the oscillation thereof, means forming a low impedance path for radio frequencies across all elements of impedance in series with the gas discharge path of said tube except those of the said pulse forming network, thus aifording greater utilization of the high frequency components of the generated pulse, and means applying a pulse of energy to said control grid of said gas discharge tube.
2. A pulse generator as claimed in claim 1, said load resistor being in the plate circuit of said gas discharge tube.
3. A pulse generator as claimed in claim 1, said load resistor being in the cathode circuit of said gas discharge tube.
4. A pulse generator as claimed in claim 1, said means forming said low impedance path for radio frequencies across said elements comprising a capacitor connected across each of said elements.
5. A pulse generator comprising a serially connected capacitor, inductor and switching device for initiating a predetermined change of state of charge on said capacitor, a unilaterally conductive damping device connected across said inductor, the connection between said inductor and said clamping device being so poled that said damping device will conduct only upon reversal of the potential across said inductor initially established by the operation of said switching device, an electrical biasing network serially connected with said switching device, said network having at least two impedance segments, a load circuit connected to the junction of said capacitor and said inductor and a junction of said two segments of said biasing network and a by-pass capacitor having avalue of capacity larger than said first named capacitor, one terminal of which is connected to the last named junction and the other terminal of which is connected to the junction between said biasing network and said switching device most remote from the connection between the first named capacitor and said switching device.
References Citedin the file of this patent UNITED STATES PATENTS 2,391,894 Gorham et a1 Jan. 1, 1946 2,398,701 Firestone Apr. 16, 1946 2,464,279 Zarem et al Mar. 15, 1949 2,555,305 Alty June 5, 1951