US2909659A

US2909659A - Pulse shaping circuits

Info

Publication number: US2909659A
Application number: US681726A
Authority: US
Inventors: Woo Way Dong
Original assignee: Raytheon Co
Current assignee: Raytheon Co
Priority date: 1957-09-03
Filing date: 1957-09-03
Publication date: 1959-10-20
Anticipated expiration: 1976-10-20

Description

Oct 20 1959 WAY noNG woo 2,909,659

PULSE SHAPING CIRCUITS Filed Sept. 5. 1957 United States Patent gO PULSE SHAPING CIRCUITS Way Dong Woo, Newton Center, Mass., assignor to Raytheon Company, a corporation of Delaware Application sepfembers, 19s7serialNo.6s1,7'26

6 claims. (ci. 25o-27) This invention pertains to pulse shaping circuits and more particularly relates to an electronic circuit responsive to a pulse or train of input pulses of lvaryingamplitudes for generating a corresponding pulseorl train of output pulses of uniform and predetermined amplitude. The novel circuit is capable of generating rectangular pulses having steep leading and trailing edges.

The invention makes use of the properties of certain magnetic materials characterized by a rectangular hysteresis loop providing two identifiable stable states of magnetization and providing a highly nonilinear ilux density-coercive force relationship whereby the state of magnetization can be definitely and quickly changed. The invention utilizes a magnetic'core transformer having its secondary winding connected in series with the load and having a constant DC. biasing current applied to its primary winding to cause the magnetic core to be held at one of its two stable states of magnetization. An input pulse causes a rapidly increasing current to flow in the secondary winding until the magnitude of that current causes the magnetic core to commence changing its state of magnetization. At this point a large change in magnetic ux occurs in the core inducing aback in the secondary winding which tends to oppose any further increase of current and maintain-the secondary winding current at a constant value. After vtermination of the input pulse, the D.C. biasing current vin ythe primary winding causes the magnetic core to return to its initial state of magnetization. By virtue of this action, the n ovel pulse shaping circuit is capable ofproducing an output pulse having steep leading and trailing edges and having a predetermined amplitude. By adjustment of the D.C. biasing current flowing in the primary Winding, the amplitude of the output pulse may be changed. The ease and rapidity with which the amplitude of the output pulse may be changed is an important attribute of this invention.

The invention and its mode of operation can be apprehended by reference to the following exposition when considered in conjunction with the drawings wherein:

Fig. l is a schematic representation of the preferred embodiment of the invention;

Fig. 2 is a diagram showing a rectangular hys-teresis loop; and

Fig. 3 is a schematic representation of another embodiment of the invention. y

Referring now to Fig. 1, there is illustrated `a circuit for regulating the amplitude of a current pulse. A vacuum tube, here shown as a triode 1, has its cathode connected to ground through a resistor 2 in series with the secondary winding 3 of a transformer 4 having a core fabricated of magnetic material characterized by a rectangular hysteresis loop. In the primary winding 5 of the transformer, there is a large biasing current ID@ supplied from a constant current DC. source connected to terminals 6'. A constant current generator may be any current generator whose internal impedance is high `in lrelation to the impedance of the load supplied. The dots adjacent the windings of transformer d, in accordance With conveny 2,909,659 Patented Oct. 20, 1959 ICC -tion,.indicate that the primary and secondary windings are positioned around the core so that the same electrical polarity obtains at the dotted ends of those windings. A diode 7 is shunted yacross 'the ends of secondary winding 3 to permit electron lflow to ground. The plate of tube 1 is connected to a source of B+ voltage through the load which is connected across output terminals 8. The control grid of tube 1 is connected through resistor 9 to input terminali() and a diode 11 is provided to clamp the grid to ground when the input signal exceeds ground potential.

lPig. 2 shows the type of rectangular hysteresis'loop which characterizes the magnetic core of transformer 4. The magnetic properties of the core material are dened by the way the ux density B is related to the applied magnetic field H. VWhen the core` is magnetized by an applied field, in the negative direction., for example, of suflicient magnitude to cause saturation, the core will retain the larger part of its magnetization when the applied lield is removed. lf the rectangularity were perfect the magnetic flux density -Br would vbe equal to the saturation flux density .-Bm and when once driven to saturation there would be no further change in the state of magnetization duetto additional negative lields'of any magnitude. Certain materials such as magnesium man- -ganese ferrites, permalloy, nickel-iron alloys, and others exhibit a high degree of rectangularity. Because the magnetic core of transformer 4 ischaracterized by a rectangular hysteresis 1oop,.the current IDCi in primary winding 5 causes flux density saturation of the core and the initial operational point is established at the point 12 by the magnitude of the direct current. H1 is the coercive force established by .current flow in the primary winding, i.e.

where k is a constant characteristic of the .geometrical dimensions of the core, and N1 is the number of turns in the primary winding.

Inorder to cause the magnetic core toV change its state of magnetization, it is necessary to provide an opposing coercive force H2 somewhat greater in magnitude than H1. When such an opposing coercive yforce is applied, a large and rapid change influx occurs in the core. The opposing coercive force H2 is generated in the circuit of Fig. l bycausing current I2 to ilow in the proper direction in secondary winding 3 and H2=kN2l2 Where N2 is the number of turns in the secondary winding, and I2 is the current tlowing in the secondary winding.

In the circuit of Fig. 1, tube 1 is cut oif in the quiescent state by impressing'a fnegative bias potential Ec., on the control grid. Because of the D.C. biasing current iiowing in primary Winding 5 the operating point of the core of transformer 4 is at point 12 of the hysteresis diagram. When a positive pulse `ec is applied at input terminal 1), the control grid is driven to ground potential and kept at that potential by clamping diode 11. Current rapidly commences to flow through the tube since the secondary winding 3 oifers but slight impedance due to saturation of the magnetic core. As tube current flow increases the operating point shifts to the right from point 12 and when `the rcurrent I2 in the secondary winding causes `the coercive force H2 to ,exceed H1, the operating point moves up the knee of |the hysteresis curve toward point 13. When this occurs a high voltage develops across the secondary winding because of the rapid change in flux density in the magnetic core and consequently the voltage of the cathode is raised. The grid-cathode bias is thereby reduced ,sufficiently to cause the output current I2 to remain almost constant. The .output current will now tend to increase .slowly but before the operating point reaches saturation in the positive direction (-l-Bm) the grid driving pulse ecshould be completed. The pulse@c in the drawing is of such duration that the operating point moves to point 13 on the hysteresis diagram before the pulse is terminated. Upon termination of the input pulse the tube 1 is again cut oif and the collapsing iield about the windings causes the diode 7 to conduct whereby the cathode is rapidly returned to ground potential. The biasing current in primary winding 5 concurrently causes the operating point to return to the initial point via path l13, 14, and 12 so that the circuit will be ready for another input pulse. Diode 7 is employed to prevent the cathode from dropping below ground level during the fall of I2. Because of the rapid collapse of the magnetic field, ringing may be encountered in the cathode circuit and in this circumstance a resistor of appropriate value placed in .series with diode 7 will damp out the undesired oscillations. The pulse shaping circuit provides a high degree of degeneration during the peak of the output current, and extremely small degeneration during the rise and fall of the output current, giving fast rise and fall times. Resistor 2 in the cathode circuit provides some degeneration and its function is to protect tube 1 from excessive plate current in the event that the control grid should be driven up for too long an interval.

The peak output current attained is JWM. H. I2 N2 LICN,

where Hc is the coercive force of the core.

Using a core of low coercive force this is essentially NrDo N2 The output current can be varied by changing ID C which determines the initial operating point 12. By decreasing Inca the initial operating point is moved to the right and the amplitude of the output pulse is decreased. As a corollary, increasing IDC, causes the initial operation point to be moved to the left and the amplitude of the output pulse is increased. Since the output of a constant current generator may, in general, be easily regulated, the initial operating point of the core is readily changed to control the amplitude of the output pulse.

fFig. 3 illustrates a current amplitude regulatingcircuit which may be used where Ithe impedance of the load and the input signal source are both very low. A biasing current ID C supplied by a constant current generator connected to terminals 15, is caused to flow in the primary Winding 16 of transformer 17. The core of the transformer is constituted of a magnetic material of the type previously described having a rectangular hysteresis loop. The secondary winding 21 of transformer 17 is shunted by a rectiiier 25 in series with a resistor 26. YThe input signal pulse ec is applied at terminals 18 and a low impedance load, here indicated as a resistor l19, is connected across terminals 20 whereby the secondary winding 21 is in series with the load. The direction of current liow to and from the load is indicated by `arrows labeled IL. A rectifier 22, in series with secondary winding 21, prevents load current IL from reversing. Where a rectifier may already be present in the load or the signal source, rectifier 22 may be eliminated.

The current Inc. iiows in the primary winding 16 in such direction as to cause the magnetic core of transformer 17 to besaturated in the plus direction and the initial operating point to be established at the point 23 indicated in Fig. 2. When the positive input pulse ec is applied at terminals `18, it causes a rapidly increasing current IL to flow in secondary winding 21 and when the coercive force due to the current flow in that Vwinding exceeds the coercive force due yto current IDC. flowing in the primary winding, the operating point of the core moves down the knee of the hysteresis curve toward point 24. At this time a high back is induced across the secondary winding because of the rapid change in ux density in the core thereby opposing any additional increase of the current IL. The current IL will now tend to increase slowly but before the operating point reaches saturation in the negative direction (-Bm) the input pulse ec is completed. The diode 25 will now conduct current due to the collapse of the magnetic eld about the transformer windings and the resistor 26 acts to prevent ringing or oscillations in the secondary winding 21. The diode 25 also acts as a safety device inasmuch as it pre- 'vents a high inverse voltage from being impressed across the rectifier 22 upon collapse of the magnetic ield. The biasing current in primary winding 16 causes the operating point of the core to return to its initial position to prepare the circuit for the next input pulse.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the electronic circuit art that various changes and modications may be made therein without departing from the scope of the invention as set forth in the appended claims.

What is claimed is:

1. A pulse shaping circuit comprising a transformer including a primary and a secondary winding and having a magnetic core characterized by a rectangular hysteresis loop, means for impressing a potential on said primary Winding to cause a biasing direct current to iiow therein, a unilateral impedance and a load connected in series with said secondary winding, and means for connecting an input signal source in series with said secondary winding.

2, A pulse shaping circuit comprising a primary and a secondary winding and a magnetic core, said magnetic core having a rectangular hysteresis loop, a direct current generator coupled to said primary winding whereby a biasing current flows in said primary winding causing flux density saturation in said core, a unilateral impedance and a load connected in series with said secondary winding, and means for connecting a source of input signals in series with said secondary winding, said input signals causing current to flow in said secondary winding in a direction such that the coercive force attributable to that current opposes the coercive force due to said biasing current in said primary winding.

3. An electronic circuit comprising a transformer including a magnetic core having a rectangular hysteresis loop, a direct current generator coupled to the primary winding of said transformer, an electron tube having a cathode, anode, and control grid, said cathode being connected throughsaid secondary winding of said transformer to a reference potential, means coupled to said control grid for applying input signals, unilateral impedance means connected to said control grid for clamping said grid to said reference potential when said input signals exceed a predetermined potential, and means for connecting a load in series with said secondary winding.

4. A pulse shaping circuit comprising a transformer including a magnetic core of the type having a rectangular hysteresis loop, a constant current generator coupled to the primary winding of said transformer, a vacuum tube including a cathode, an anode, and a control grid, said cathode being connected through the secondary winding of said transformer to a reference potential, means connected to said control grid for clamping said grid to said reference potential, means for connecting said anode to a potential source, and means for connecting a load in series with said anode.

5. A pulse shaping circuit comprising a transformer having a primary and a secondary winding positioned on a magnetic core of the type characterized by a rectangular hysteresis loop, a constant direct current generator coupled to theprimary winding of said transformer, a vacuum tube including a cathode, anode, and control grid, said cathode being connected through sai-d secondary winding toa reference potential, a unilateral impedance means connected to said control grid for clamping said grid to said reference potential, a unilateral impedance means shunted across said secondary winding, means for connecting .a load in series with said secondary winding,

having a primary and a secondary winding positioned on a reference potential, means coupled to said control grid 10 for impressing input signals, a unilateral impedance coupled to said control grid for clamping said grid to said reference potential when said input signals exceed a predetermined potential, means for connecting a load in series with said secondary winding, a unilateral impedance shuntcd across said secondary winding, and means for coupling said anode to a plate voltage source.

References Cited in the le of this patent UNITED STATES PATENTS 2,688,075 Palmer Aug. 31, 1954 2,825,820 Sims Mar. 4, 1958 FOREIGN PATENTS 763,734 Great Britain Dec. 19, 1956 1,116,389 France Ian. 30, 1956