US 3754274 A
Current driver circuitry for magnetically saturable loads, such circuitry including feedback means for monitoring the time rate of change of flux in such load and disconnecting such circuitry when such rate of change of flux indicates that a saturation condition has been reached.
Description (OCR text may contain errors)
United States Patent 11 1 Auger Aug. 21, 1973 CURRENT DRIVER CIRCUITRY FOR  References Cited Inventor: Ernest g Billerica. Mass- 3,154,763 10/1964 13611111611561 340/174 LA 3,175,098 3/1965 Grace 307/288 x  Assgnee' 33 Lexmgmn 3,446,984 5/1969 Shukla 340 174 LA 3,521,079 7/1970 Kuck 307/270 x  Filed: July 31, 1972 211 App]. No.: 276,627 i iinw,fi t fykfisnflet 7 u Att0rney-Philip J. McFarland, Richard M. Shar- Related U.S. Appllcatlon Data k k et l I  Continuation of Ser. No. 130,124, April 1, 1971, V V v abandoned- 57 ABSTRACT 521 vs. (:1 343/854, 307/262, 307/270, current drive circuitry magnetically San-"able 307/88 333/241, 343/754 loads, such circuitry including feedback means for 1511 1111. C1. H01q 3/26 Innnitnring the time rate change flux in Such Field 61 Search 333/241; 307/101, and disconnecting such cnwiny when such 307/270, 88 314 343/100 SA 100 TD, change of flux indicates that a saturation condition has 854; 340/174 LA been reached.
3 Claims, 4 Drawing Figures r 1: I I 4W l l 3 i I I 405 l -280 42s 1 l 414$ 36 l V, I Z 1r- 538$ I 1 46s +v l l 1 FROM J 1 BEAM M G T I 260 STEERING 1 COMPUTER, /5 l f 250 l l b /30 PAIENIEmuw ms 3.754.274
SHEET 1 BF 2 TRANSMITTER RECEIVER SYNCHRONIZER \2/ STEERING ,COMPUTER INVENTOR ERNEST R AUGE/P PAIENIEDMISZI I975 3.75427 SHEET 2 OF 2 FROM BEAM STEERING COMPUTER, l5
FROM BEAM STEERING COMPUTER/5 Zea/i 260 lNVENTOR ERNEST P. AUGER CURRENT DRIVER CIRCUITRY FOR FERRITE PHASE SHIFTERS This is a continuation of application Ser. No. 130,124 filed Apr. 1, 1971 now abandoned.
BACKGROUND OF THE INVENTION This invention relates generally to current driver circuitry for magnetically saturable loads and more particularly to current driver circuitry for ferrite phase shifter elements of the type employed by phased array radar antennas.
As is known in the art, phased array radar antennas generally employ many thousands of ferrite phase shifter elements, such elements being used to electronically steer the beam of an antenna to a desired direction in response to electrical signals supplied by a beam steering computer. As is also known in the art, each ferrite phase shifter element normally is made up of a waveguide containing at least one ferrimagnetic toroid, each one of such toroids having at least one current drive wire passing through the center thereof. The hysteresis curve (sometimes referred to as the 8-H loop) associated with each ferrimagnetic toroid is substantially rectangular so that remanent flux in the toroid may be made to be dependent on the time integral of a pulse of voltage applied across a wire passing through the center of such toroid. Either an analog or a digital signal may be used to achieve a proper remanent state. With an analog approach one ferrimagnetic toroid is used for each phase shifter element, such toroid being initially reset to a reference remanent state by driving the toroid into saturation of predetermined polarity, and secondly, set to a proper remanent state by applying a pulse of voltage of proper time integral across the current drive wire. With a digital approach, a number of ferrimagnetic toroids are used for each phase shifter element, the numbercorresponding to the number of bits in a binary word supplied by the beam steering computer. Each one of such ferrimagnetic toroids is driven into one of two remanent states by driving the toroid into one of its two saturation conditions, the particular condition to which the toroid is driven being in accordance with the binary state of the particular control bit controlling such toroid. These conditions are generally called set" and reset." The proper saturation condition is achieved by passing current of sufficient level through a drive wire to saturate the toroid, the direction of current flow through the drive wire being in accordance with the binary state of the control bit.
Therefore, for reason described above, it is necessary to drive the ferrimagnetic toroids into saturation to properly control the amount of phase shift required by the phase shift elements in directing the beam of the phased array antenna employing such elements regardless of whether the analog or digital approach is used. As is well known, however, when a ferrimagnetic toroid is driven into saturation, the power dissipated in the current driver greatly increases because of the reduction in the inductive load impedance presented by the ferrimagnetic toroid. Such increases in power may cause the phase shifter element to be heated excessively and, possibly, destroyed. Different techniques have been employed to prevent such power increases and, at the same time, to reduce the capacity required of the attendant power supply employed by the antenna system. With a digital approach additional timing means may be provided for disconnecting the current driver from the toroid before thev undesirable large power condition occurs; however, this technique has been found lacking because of the variation in ferrite saturation time from toroid to toroid. Therefore, the duration of the pulse of voltage applied across the drive wire must be designed for worst case" conditions. Further, to permit a toroid to be driven only from one saturation condition to the other, logic circuitry may be provided to enable the control signal to be effected only when the sense of the control bit changes and to inhibit the control signal when the sense of the control bit does not change. This solution is subject to the reliability of the logic circuitry. In the analog scheme means may be provided to sense the magnitude of the current passing through the current drive wire so that, as the driver current approaches a predetermined maximum level, the driver current is reduced. Such an arrangement is described in Microwave Journal, Mar. 1967, Latching Ferrite Phase Shifter For Phased Ar rays, J. Frank, J. H. Kuck and C. H. Shipley. However, because all toroids are not identical, each .one requires a different amount of current to actuate it; therefore, the predetermined maximum level must be set high enough to account for that toroid requiring the maximum amount of current to drive it into saturation.
SUMMARY OF THE INVENTION It is, therefore, a primary object of the invention to provide improved current drive circuitry for a magnetically saturable load, such circuitry being designed to drive such load into saturation with minimum power dissipation by the load.
It is another object of the invention to provide improved current driving circuitry for a magnetically saturable load, such circuitry being extremely reliable, and being adapted to prevent excessive current from being drawn during operation.
These and other objects of the invention are achieved generally by providing means for supplying sufficient current to a magnetically saturable load to drive such load into saturation, and means for first sensing the magnetization state of the load and then disconnecting the load from the current supplying means when such magnetization state is as desired. The invention takes advantage of the fact that the voltage induced in a ferrimagnetic load is proportional to the time rate of change of magnetic flux density (i.e., dip/d!) generated by the current supplied to such a load, and that, in saturation, dqb/dt decreases significantly in magnitude as the load saturates. Therefore, in a preferred embodiment, the sensing means are provided to couple the voltage developed across the load to the current driving means in such a manner that the magnitude of the voltage so coupled determines whether or not the current driving means is connected to the load.
BRIEF DESCRIPTION OF THE DRAWINGS For a more complete understanding of the invention reference is now made to the following description of the accompanying drawings in which:
FIG. 1 is a simplified sketch of .a radar system using an array of radiating elements, each one thereof being connected to a ferrite phase shifter element which is driven by drive circuitry according to this invention to radiate a collimated beam of radio frequency energy and to receive echo signals from targets illuminated by such radiated energy;
FIG. 2 is a cross-section of a ferrite phase shifter element of the type shown in FIG. 1;
FIG. 3 is a schematic diagram of a current driver circuit embodying the invention, such circuit being adapted to drive a ferrimagnetic toroid employed by the phase shifter element shown. in FIG. 2; and,
FIG. 4 is a schematic diagram of an alternative embodiment of a current driver circuit for driving a phase shifter element of the type having two current drive wires.
DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, it may be seen that an antenna according to this invention includes a number of phase shifter elements 11, each such element having associated therewith a current driving circuitry 13. The phase shifter elements 11 and associated current driving circuitry 13 may be mounted in a conventional manner (not shown in detail) to form a space-fed planar array. Appropriate connections are made as indicated between each current driving circuitry 13 and the conductor for each ferrimagnetic toroid (shown in FIG. 2) of each phase shifter element 11 to drive each phase shifter element 11 in accordance with digital control signals from a beam steering computer 15. As is known, such an arrangement permits radio frequency energy from a feed born 17 to be collimated and directed in a beam as desired and echo signals returning to the individual phase shifters of the antenna array to be focused on the feed horn 17. The feed horn 17 is connected in any convenient manner, as by waveguide (not numbered) to a transmitter/receiver 19. The operation of the transmitter/receiver 19 and the beam steering computer is controlled by a conventional synchronizer 21.
Each one of the phase shifter elements Ill includes a section of waveguide 23 with the ends (not numbered) thereof matched to free space by conventional matching devices 25, 25'. In the particular embodiment illustrated, each one of the phase shifter elements ll includes three serially arranged ferrimagnetic toroids 26a, 26b, 26c (FIG. 2) to operate in response to a three-bit control signal. Obviously, however, the number of toroids may be changed without departing from any inventive concepts.
A different bit of a three-bit control signal is applied to a different one of three identical current drivers l3a-c, which together make up the current driving cir cuitry 13. A different one of the drivers 13a-c is coupled to a different one of the ferrimagnetic toroids 26a-c via current drive lines 28ac.
Referring now also to FIG. 3, an exemplary one of the current drivers l3a-c (here current driver 13a), it may be seen that the beam steering computer 15 transmits one bit of each one of the control signals to current driver 13a via either line 42s or 42r. That is, a set signal is transmitted as a positive-going voltage square wave, i.e., a binary zero, on line 42s and a reset" signal is transmitted as a negative-going voltage square wave, Le, a binary one," on line 42r. Exemplary current driver 13a is seen to comprise set circuitry 30s and reset circuitry 3dr, such circuitry being connected to lines 42s and 42r, respectively, and being powered by a positive and negative power supply marked +V and v79 The reset circuitry 30r and set circuitry 305 are each comprised of an input transistor 32r, 32s and an output transistor 3dr, 34s, the electrodes of such input and output transistors being coupled, as shown, by a base resistor 36;, 36s, a bias resistor 38r, 38s and a feedback resistor 41hr, 40s. The collector electrodes of output transistors 34s, 34r are also connected together and to current drive line 28a, such current drive line passing through the approximate center of ferrimagnetic toroid 26a, to ground as shown. Differentiatcrs, made up of capacitors 44s and 441* and resistors 46s and 46r as shown are connected across the base and emitter electrodes of the input transistors 32:, 32s. To complete the reset circuitry Elllr, the emitter electrode of input transistor 32r and the emitter electrode of output transistor 3dr are connected, as shown, to ground and to the negative power supply, -V. Similarly for the set circuitry 30s, the emitter electrodes of the input and the output transistors 32s, 34s are connected to ground and to the positive power supply, +V.
In operation, when a binary zero is applied to line 42s, capacitor 44s and resistor 46s differentiate such signal in such a manner that the input transistor 32s is immediately turned on." As the amplitude of such differentiated pulse decreases the voltage across the base and emitter electrode decreases until, absent any other effects, such voltage becomes insufficient to maintain such transistor on. It will be observed, however, that an effect does take place which latches input transistor 32s on, provided the ferrimagnetic toroid 26a is not in its set" state. The reason for such latching is that when input transistor 32s turns on during the initial portion of a set" signal, transistor 34s also turns on, thereby supplying current to the base electrode of input transistor 32s via feedback resistor 40s. Therefore, the input transistor 32s is latched on as long as the voltage across its base-emitter electrodes is greater than approximately +0.7 volts. When output transistor 34s turns on, a self-induced voltage is generated in current drive wire 280, the magnitude of such voltage being proportional to the time rate of change of flux (i.e., drb/dt) through the ferrimagnetic toroid 26a. Therefore, the magnitude of the voltage on the collector electrode of output transistor 34s will be a function of ddw/dt. When ferrimagnetic toroid 26a saturates, dqb/dt is essentially zero. Therefore, as the ferrimagnetic toroid 26a approaches its set saturation condition, the voltage on the collector electrode of output transistor 3% drops in magnitude and tends toward ground potential. Hence, the base-emitter electrode voltage of input transistor 32s drops to less than 0.7 volts. Such input transistor therefore turns off, cutting output transistor 34.: off" so that current no longer flows through drive wire 28a. If, however, the ferrimagnetic toroid 26a is in its set" saturation condition when a set signal appears, such a signal would be differentiated to turn transistor 32.: on as before; such transistor would not be latched on" by output transistor 34s because ddz/dt in the ferrimagnetic toroid 26 a would be zero and no current could be fed back to input transistor 32.: through feedback resistor 40s. Reset circuitry 3dr operates in the same manner as set circuitry 3%- except that the reset circuitry operates in response to a negative-going voltage square wave on line 42r and any current flowing through line 28a is in the opposite direction from the direction of current flow produced by set circuitry 30s.
Referring now to FIG. 4, another current driver I3'a embodying the features of the invention is shown, such driver requiring that two current drive lines pass through the approximate center of ferrimagnetic toroid 26a. Such a driver may be used when it is desirable to use a power supply of only one voltage polarity, here +V volts, and also where it is desirable to have such driver turn on in response to binary signals of one voltage polarity, here positive (i.e., the set circuitry 30's and reset circuitry 30'r both respond to positive voltage pulses applied to lines 42's and 42'r). It is noted that the set circuitry 30's and reset circuitry 30'r are similar in construction to each other and, with but one difference, to the set circuitry 30s shown in FIG. 3. The difference is that reset circuitry 30's and reset circuitry 30'r require a blocking diode 50s and a blocking diode 50r respectively. The anode of each one of the blocking diodes 50s and 50r is connected, as shown, to the collector electrode of input transistor 34's and 34r. Such diodes are necessary to eliminate any effect of mutual inductance between current drive wires 28'a and 28"a. Thus, when current flows into one such wire, say 28'a,
a voltage is induced in wire 28"a. In the absence of blocking diode 50r, input transistor 32r might thereby be turned on and latched on by feedback from output transistor 34'r. Conversely, when current flows through current drive wire 28"a, block diode 50s prevents input transistor 32's from being turned on and latched.
Numerous variations in the described embodiments, within the scope of the appended claims, will occur to those skilled in the art. For example, while a digital arrangement has been described, the current drivers can be used in an analog arrangement. Also, while a ferrimagnetic toroid load was employed in the described embodiments, other magnetically saturable loads can be employed, such as Faraday-rotation phase shifter devices. These variations are merely illustrative and hence it will be understood that the invention is not limited in scope to the particular embodiment here shown, but only by the appended claims.
What is claimed is:
1. In a phased array antenna assembly for collimating and directing a beam of electromagnetic energy by actuating, in accordance with control signals from a computer, each one of a plurality of magnetically saturable phase shifters, each one of such phase shifters including at least one magnetizable element having a first and a second saturation condition determined by the direction of electric current through an energizing coil, the improvement comprising:
a. separate first and second switching means, disposed in circuit between each energizing coil and the computer, for passing electric current through each energizing coil in a direction determined by a signal from the computer; and
b. switching means control circuitry, disposed in operative relationship to each one of the switching means and responsive to the saturation condition of the associated magnetizable element when a signal is applied by the computer, for permitting operation of the switching means in operative relationship with such element only when the signal from the computer commands a change in the saturating condition of the magnetizable element.
2. In a phased array antenna system wherein an antenna beam is collimated and directed in accordance with beam steering signals produced by a computer, the combination comprising:
a. a plurality of magnetically saturable phase shifter elements, a portion thereof being in a saturation condition; and
b. a plurality of means, each one thereof being coupled to a different one of the plurality of magnetically saturable phase shifter elements and responsive to the beam steering signals to establish a saturation condition in selected ones of such elements by supplying current to the selected ones of such magnetically saturable phase shifter elements which are in an unsaturated condition and by inhibiting current from being supplied to the selected ones of such magnetically saturable phase shifter elements which are in the saturation condition, each one of such plurality of means comprising:
i. driving means having an input terminal in circuit with the computer and an output terminal in circuit with one of the plurality of magnetically saturable phase shifter elements, such driver means being responsive to the beam steering signals to vary the rate of change of flux in the magnetically saturable phase shifter element in circuit therewith in accordance with the initial state of the flux therein; and
disabling means, coupled between the input terminal and the output terminal, and responsive to the rate of change of flux in such magnetically saturable phase shifter element to disable the driving means when the rate of change of flux produced therein reaches a saturation level.
3. In a phased array antenna system wherein an antenna beam is collimated and directed in accordance with beam steering signals produced by a computer, the combination comprising:
a. a plurality of magnetically saturable phase shifter elements; and,
b. a plurality of driver means, each one thereof being coupled to a different one of the plurality of magnetically saturable elements and having means responsive to the beam steering signals, to vary the rate of change of flux, and thereby establish a saturation condition, in selected ones of such elements in accordance with such signals by supplying current to those of the selected ones of such elements which are in an unsaturated condition and by inhibiting current from being supplied to the selected elements which are in the saturation condition by means disabling each one of the plurality of driver means coupled to such remaining ones of the selected elements when the rate of change of flux produced therein reaches a saturation level.
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