US2436395A - Pulse generator - Google Patents

Description

Feb. 24, 1948. J. M. MANLEY ETAL 2,436,395

' PULSE GENERATOR Filed Sept. 14, 1943 2 Sheets-Sheet 1 HIIIIIIP .1 M MANLEY INVENTORS. E PETERSON Patented Feb. 24,1948

PULSE GENERATOR;

Jack M. Manley, East Orange, N. 1., and Eugene Peterson, New York, N. Y., aasignors to Bell Telephone Laboratories, Incor orated, New York, N. Y., a corporation of New York Application September 14, mascara No. 502,282

r cum (01. 171-97) This invention relates to pulse generators, particularly for keying or modulating ultra-high frequency radio transmitters for the transmission of recurrent, short pulses of high power.

Various systems, forexample, distance measuring and object locating systems, employ high power recurrent pulses of ultra-high frequency radio waves. Such pulsesmay be of very short duration compared to the interval between pulses.

Consequently, the average power demand on the prime ower source. is quite low even for high a peak power outputs. n the other hand. the system must be capable of meeting the high instantaneous power demands during the pulse interval.

An object of the invention is to provide an emcient and economical pulse generator.

One general type of pulse generating system that has been found useful in such applications is that of the copending application of William Shockley, Serial No. 460,328, filed October 1, 1942, Patent No. 2,416,718, of March 4, 1947. The basic principle of operation of this type of system is that of double energy storage, the energy from the prime source being first stored magnetically and then transferred to a capacitor from which it is discharged to the load circuit. This requires two discrete switching operations or their equivalent; one for the transfer of the energy from the magnetic to the electric storage, and the other for the ultimate discharge to the load. Efiicient operation requires a critical timing of the second switching or energy transfer so that the discharge oi. the capacitor occurs at the instant of maximum energy storage therein. One type of switching circuitfor accomplishing this function as shown in the Shockley patent employs a nonlinear inductor which is maintained in the nonsaturated condition during the capacitor charging period but saturates at the end of that period to provide a low impedance path for the discharge of the capacitor to the load.

In the Shockley system it is necessary to employ a blocking capacitor in serieswith the nonlinear coil in order to block the flow of current from the prime power source during the nonactive period of the operating cycle. As a result this blocking capacitor provides a source of stored energy that will discharge through the tube used for establishing an inductive charging circuit. If

uncontrolled this action not only results in a considerable waste of energy, but also, if the capacitor discharge is permitted to carry the non-linear coil into the saturated region may result in plate saturation of the tube and so limit the energy storage in the inductive system.

A further object of the invention is to improve the operation of such a non-linear inductor type of pulse generator.

In accordance with a feature of this invention 2 there is applied to the non-linear inductor a polarizing magnetizing force that magnetizes the core in the same sense as it is magnetized by the discharge current from the storage capacitor and to a degree sufficient to carry it into the saturation region. One eflect of such a polarization or bias in which the core of the non-linear inductor is biased into the saturation region is to increase the energy that may be stored in the inductive system during the time required to carry the nonlinear inductor through the non-saturated region; that is, from saturation in one sense to saturation in the opposite sense.

The amount by which the available inductive energy is augmented increases with the biasing current and, if the latter is made large compared with the current required to saturate the core and. comparable to the peak current passed by the tube in the charging interval, substantial increases in the stored energy may be had.

The property of increased energy storage due to bias of the non-linear inductor into the saturation region may be briefly explained as due to the fact that the presence of the biasing current causes the inductive system to operate between two finite limits rather than from a value of zero. Thus, with such a polarization, upon closure of the inductive charging circuit the current will rise almost instantaneously to a value equal to the difference between the bias and the saturation values and the inductive charging will lake p e as the current rises from that value to the value that it reaches at the time the inductive charging circuit is opened.

These and other objects, features and aspects of the invention may be better understood by reference to the following detailed description in connection with the drawing in which:

Fig. 1 is a schematic circuit diagram of one embodiment of the invention;

Figs. 2 and 3 are schematic circuit diagrams of modifications of the portion of the circuit of Fig. 1 between the dash-dot lines ll and 2-4; and

Figs. 4 to 7 are graphs illustrating the operation of the circuit of Fig. 1.

In the system of Fig. 1 the invention is employed for producing recurrent short pulses of high power ultra-high frequency radio waves.

For the purpose of illustration, the ultra-high frequency generator is shown as a multicavity magnetron iii of the type of United State Patent 2,063,342 to Samuel, December 8, 1936, for example. In this type of oscillator the anode H forms an external sheath or enclosure which it is desirable to maintain at ground potential. When the tube is subjected to a. magnetic field supplied by the magnet l2 and a high dircct current voltage is impressed between the anode ii and the electron emitting cathode Hi, there are produced high power oscillations of a frequency deteraccuses mined by theinal of the device as described in more detail in the Samuel patent. These oscillations may be picked up by a loop it and transmitted through a coaxial line is to an antenna (not shown).

The remainder of the circuit of Fig. 1 constitutes the pulse generator circuit for producing high power recurrent pulses of short duration nected through an inductor it to the anode of a vacu tube it, the cathode of which is connected to the grounded negative teral of the battery ll. A storage capacitor 2c is connected between the anode oi the tube i9 and the cathode is oi the magnetron i b.

The grid of the tube iii is normally biased to cut-on or beyond by a battery 26. The opera tion or the tube it is controlled by a positive square wave supplied from the source it. A charging diode 2b is connected in parallel to the space path oi the magnetron ill to provide a con= ductive path in the direction opposite to that pro-= vided by the magnetron space path.

Connected between the junction of the inductor it and the charging capacitor 2b, in parallel to the space path of the tube it. is a series circuit comprising the operating winding bi of a nonlinear inductor 3t! and the blocking capacitor The non-linear inductor it employs a core, of magnetic material of such characteristics that the inductance is high for very low magnetizing forces but is readily saturable so that at a comparatively low magnetizing game the inductance drops to a very low value. This inductor it is also provided with a biasing winding 32 to which biasing current is supplied through the inductor 35 from a battery 36. The sheet of this biasing current i to supply a polarizing magnetizing force to the core to pet operations over a desired portion or its characteristics. The value of the biasing current flowing under steady state condition will be deter mined by the voltage oi the source 36 and the resistance of the circuit.

Fig. 2 shows n variation in the portion of the circuit of Fig. l. between the dash-dot lines l--l and E d. This circuit shows a variation in the construction or the non-linear coil to with respect to the manner of supplying bias. In this modh ucation the non-linear inductor has only one winding and the biasing current is supplied there to from the battery it through the inductor 35. A filter capacitor 3?! is included to smooth out the demand on the bias supply 3%. As for as the system operation is concerned the circuits of Figs. 1 and 2 are equivalent. Fig. l is better suited to situations in which a high current, low voltage supply is available for bias and Fig. 2, where a high voltage. low current supply is available.

The operation will be described with particular reference to Fig, 2 since this somewhat simplifies the explanation with respect to the effectoi the biasing current for the non-linear inductor it. The same considerations are applicable to the circuit of Fig. l with proper weight given to the coupling between the operating winding iii and the biasing winding 32.

Li general the system operates by the periodical storage or energy in the inductive system, the to changes almost instantaneously to the saturation tr oi that ener'to the cancel and finally the discharge or that enerw to the load circuit. In the usual operation these energy transfers which constitute the working portion of the cycle occupyabout one-tenth to one-quarter of the entire operating cycle. The building-up of energy in the inductive system is initiated by the positive voltage supplied to the grid of the tube 8 9 causing the space path to become conductive. Plate current to this tube is supplied from two sources. namely from the battery through the linear inductor it and from the blocking capacitor so which has become charged by the battery it during the idle period. This latter current flows through the non-linear inductor 3b and the bias inductor 35in parallel. The plate current or the tube 89 is permitted to build up 'until the current through the inductor it reaches substantially the saturation point and then the tube is cut oh. During this period when the tube is conducting the inductor so is operating in the unsaturated region where its inductance is high. Also the current in the inductors it and 35 has been build== ing up with a consequent storage oi energy in the magnetic fields. At the instant the tube it is out ch this energy begins to be transferred to the capacitor 263 through the charging die 2%. During this period of energy transfer the change in current through the non-linear inductor 8E3 till causes it to approach saturation. The circuit is so designed that the saturation time oi the non-= linear inductor is equivalent to the charging time of the capacitor 2b. When the full volt%e is developed on the capacitor is the non hnear in doctor 36 saturates and its inductance drops to a very low value providing a low impedance path for the discharge of the capacitor 2b to the imag netron oscillator lb.

The operation will now be described in more detail with reference to the explanatory diagrams of Figs. 4-7. Figs. 4,5, 6 and 'i show various cur rents plotted against time. Fig. 6A shows an idealized magnetic characteristic of the non= linear inductor 3E3, hysteresis being neglected 1-; the'transition between the saturated and non saturated conditions being treated as though it occurred abruptly.

Beginning at a time prior to 1, a bias current (-13) is supplied from the battery 36 that causes the inductor 3b to operate at the point A of its idealized characteristic as indicated in Fig. 6A. Accordingly, there will be corresponding values of current flowing in the inductors 35 and lid as indicated by the curves I35 and In of Fig. 6.

shown in Fig. icausing the space path to becomev conductive. This establishes a path for the flow of current from the battery ill through the inductor it which takes place as shown in Fig. 5. This current (118) rises slowly as is the characteristic of an inductive circuit. At the same time the low impedance of-the space path of the tube 59 afiords a path for the discharge of the capacitor it through the inductors 3b and till in parallel. As shown in Fig. 6 the current 135 in the inductor 35 starts out at the value of the biasing current (In) and rises slowly. Since the inductor 39 is in the saturated region where its inductance is substantially zero, the current therethrough a isasss value -11. From that point it rises slowly through the region where the inductance is high until it reaches the opposite saturation point (-i-Ls) at the time in. The system is 'so designed that at that instant, t2, the voltage from the source 23 drops to zero and the tube I9 is cut oil, as shown by the curve of Fig. 4.

The dotted line in Fig. 6 represents the sum of the currents I30 and 135 which is, 01 course, the current drawn by tube l9 from the non-linear coil and the biasing choke 35 together. current, rises sharply at the time ii to a value equal to the diiierence between the biasing current and the current value corresponding to magnetic saturation'of the non-linear coil and after that time increases more slowly. Since the blocking condenser 35 may be made large enough so that the voltage across its terminals changes but little during the interval t1-i2, the growth of the total current takes place under a substantially constant voltage and the work doneduring this time is represented by the area under the curve. This work is done in changing the magnetization of the system and so represents en- 'ergy that is recoverable from the system. It is evident from the drawing that the amount of this energy is substantially greater than ii the total current were constrained to increase linearly from zero to same maximum value in the same time. Thus when the charging time and the maximum current are limited by other considerations, the use of a strong over-saturating bias provides a substantial increase in the stored magnetic energy,

At the instant ii at which the tube I9 is cut of! the path for the flow of current from the battery I! through the inductor i8 and for the flow of current from the capacitor 38 through the inductors 30 and 35 is opened. However, due to the inductive eifect, the current through these circuits tends to continue and accordingly flows through the capacitorZil and charging diode 26 inseries. The energy stored in the magnetic field of the inductive system is thus transferred to the electric field of the capacitor 20 and by the proper proportioning of the circuit elements the result ant surge voltage developed across the capacitor 20 may be made many times that of the battery il. This surge circuit is of an oscillatory char acter, being composed essentially of the capacitor 20 in parallel with the inductors i8, 30 and 35. Accordingly, the'iall of current in each of the inductors follows a cosine law as shown by the curves of Figs, 5 and 6 and the rise of the voltage across the capacitor 20 is of a similar form, Fig. '1. At the time t; the current through each of the inductors i8 and 35 has dropped to its original value and the energy stored in their magnetic fields during the period the tube i9 was conducting has been transferred to the capacitor 20 which, at the same instant has reached its maximum voltage. At this same instant (ta) the current in the non-linear inductor 30 will have changed to -I= corresponding to the other saturation point and the inductance of the inductor 30 will suddenly drop providing a low impedance path through which the high voltage charge on the capacitor 28 is discharged to the magnetron oscillator I0.

, In the interval from t: to t4 the system is essentially quiescent except for the restoration of the charge on the capacitor 36. At the time $4 another active period of the operating cycle is commenced.

The curves of Figs. 5 to 7 are based on some- Thiswhat idealized conditions and show qualitatively the nature of the operation of the circuit. Other factors such as the eflect of hysteresis on the inductor 30, surge currents through the inductor iaduring the cut-oil period of tube l9, etc. will produce effects of secondary character.

Fig. 3 shows a second modification of the manner-oi biasing the non-linear inductor 30. In this circuit the blocking capacitor 36 is shunted by a resistor 44. The biasing current is supplied to the single winding of the non-linear inductor as in the circuit of Fig. 2. However, the biasing current is drawn from the main source I! through the resistor 44. This circuit may be found useful in cases where a separate biasing source is not readily available and where the power capacity of the main source is adequate.

What is claimed is:

, 1. In an impulse generator, a. source of direct current, a storage capacitor, an inductor havin a readily saturable magnetic core. circuit connections for providing a path for the surge discharge of said capacitor to a load through said inductor, switching means for intermittently establishing a path for the flow or direct current from said source through an inductive circuit whereby said polarizing said core by a magnetizing force in'the same sense as that produced by the discharge of said capacitor through said inductor and of at least such value as to saturate said core.

2. In an impulse generator, a source of direct current, a storage capacitor, an inductor having a readily saturable magnetic core, circuit connections for providing a path for the surge discharge or said capacitor to a load through said inductor, switching means for intermittently establishing a path for the flow of direct current from said source through an inductive circuit whereby said capacitor is charged by the surge developed upon the interruption or said Path, and means for sup plying a direct current to said inductor to produce a polarizing magnetizing force in the sametions for providing a path for the surge discharge oi said capacitor to a lead through said inductor, switching means for intermittently establishing a path for the flow of direct current from said source through an inductive circuit whereby said capacitor is charged by the surge developed upon the interruption or said path, and means for polarizing said core by a magnetizing force in the same sense as that produced by the discharge of said capacitor through said inductor and ot a value at least several times that required to saturate said core.

4. In an impulse generator for supplying a unilateral conducting load circuit, a source 01 direct current, a storage capacitor, an inductor having a readily saturable magnetic core 01' high permeability and flux densities below saturation, circuit connections for providing a path for the discharge of said capacitor to said load circuit through said inductor including a blocking capacitor, switching means for intermittently es-- upon the interruption or said path. and means tor accuses polarizing said cdre by amagneti rorce in the same sense as that produced by said discharge of I said capacitorthrough said inductor and of at least such magnitude as to saturate said core.

5. An impulse generator-comprising a first in:

' readily saturable at higher magnetizing forces, a

load circuit, a blocking capacitor, circuit connec= tions establishing a series circuit including said storage capacitor, said load circuit, said second inductor and said blocking capacitor, circuit connections including intermittently operated switching means for supplying current from said source to said first inductor and for interrupting said flow of current, circuit connections tor charging said storage capacitor by the surge volt= age developed upon said interruption of said flow or current, and means for so biasing the core of said second inductor that at the instant or estab= lishing said flow 01 current from said source to said first inductor the magnetizing force is oithe order of at least ten times that required tor sat= uration.

8. in an impulse generator, a source oi direct current, a storage capacitor, inductor having a readily saturable magnetic core, circuit connec= tions for providing a path for the surge discharge of said capacitor to a load through said inductor, switching means for intermittently estalolisg a path for the flow of direct current from said source through an inductive circuit whereby said capacitor is charged by the surge developed upon d the interruption or said path, and mes for so polg said core that during the charging De riod of said capacitor the nun therein varies from substantial saturation in one sense to saturation in the opposite sense.

7. in arr-impulse generator for supplying a unilateral conducting load circuit, a source of direct current, a storage capacitor, an inductor having a readily saturable magnetic core or high permeiii : Number ability and flux densities below saturation, circuit connections for providing a path for the discharge oi said capacitor to said load circuit through said inductor inclug a blocking ca pacitor, switching means for intermittently establishins a path for the fiOW of current from said source through an inductive circuit whereby said capacitor is charged by the surge develonsn upon the interruption or said path, and means for so polarizing said core that during the period of charging said capacitor the magnetization varies from substantially the saturation point in one direction to the saturation point in the opposite rection.

JACK M. 7'. r Y.

EUGENE PETERSQN.

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

UNITED STATES PAS Name Date 2,157,929 Troger May 9, 1239 Prast Sept. 29, 1942

Images