[1]U, nited States Patent Office 31489,916 3,489,916 TRANSISTOR MAGNETIC AMPLIFIER PULSE CIRCUIT James R. Bacon, Philadelphia, George H. Barnes, West Chester, and Albert J. Meyerhoff, Wynnewood, Pa., assignors to Burroughs Corporation, Detroit, Mich., a corporation ofMichigan Filed Oct. 26, 1964, Ser. No. 406,267 Int. Cl. H03k 3126; Gllc 11106 U.S. Cl. 307-88 11 Claims ABSTRACT OF THE DISCLOSURE An electrical pulse circuit for reacting to an input trigger pulse and for maintaining said reaction for sufficient duration to be read as an output pulse and for returning itself to its initial electrical state. A first transistor amplifier having means to accept trigger inputs is connected in circuit to a second transistor magnetic amplifier, both amplifiers being inductively coupled through a common magnetic core of sqtiare hysteresis loop material. The operation of the first amplifier charges a trigger circuit, also coupled to the core, to cause the second amplifier to reset the core after the core is switched by the first amplifier. A temporary bias circuit connected with the first amplifier, and also inductively coupled to the core, prevents "free-running" of the pulse circuit after reset. This invention relates generally to transistor magnetic amplifier pulse circuits and, more particularly, to pulse circuits consisting of two transistor magnetic amplifiers wound on the same square loop magnetic core. Magnetic cores of square hysteresis loop material have found wide acceptance and use in electronic computer circuits since they can be made to asstime and maintain one of two magnetic states, arbitrarily defined as "O" and "1." Informationrepresented by the condition of magnetic cores may be processed through logic circuits using such cores. A transistor magnetic pulse amplifier is frequently used as a driver for magnetic core switching circuits. In such an amplifier, hereafter referred to as a TMA, a transistor is regeneratively connected through collector and base windings on a common square hysteresis loop magnetic core. When a pulse of proper polarity to forward bias the transistor is applied to the base, collector current begins to flow. The flow of collector current tends to switch the core to its opposite magnetic state and induces a voltage in the base winding of a polarity to increase the conduction of the transistor until the transistor saturates or bottoms. The switching process is now seifsustaining and the input pulse can be removed. The core will continue to switch until it approaches saturation. As core saturation is approached, the amou,t of collector current required to continue the switching increases sharply. The collector current can no longer maintain the core switching and the regenerating voltage begins to decrease thereby reducing the base current and quickly cutting off the transistor. The flux about the core rapidly collapses, and the core lapses to its new remanent state. Circuits which produce rectangular pulse paftern outputs of a given magnitude and duration for any short pulse input have wide application in electronic data processing apparatus and other electronic equipment. The ping-pong is a circuit involving square loop magnetic cores that develops such an output. When it is triggered by a pulse input, it operates to switch the cores from their original state of magnetization to the opposite state. The voltages generated in associated windings by this Patented Jan. 13, 1970 2 switching then act to reset the cores to their original state. The rectangular pulse pattern output is taken from an output winding on one of the cores. The ping-pong is a term sometimes applied to a dynamic storage element. In its operation, if the device starts in the ONE state, a drive or trigger pulse changes it to a second state, from which it is returned to the ONE state. Switching generates an output waveform indicating the stored ONE. If the device starts in the ZERO state, the drive produces no change of state and no resulting output is generated. 10 In the past, ping-pong circuits have required a plurality of magnetic cores. It was necessary that the switching of one core generate relatively large amounts of power in the windings since only passive element coupling existed between cores. The power generated by 15 the switching of one core was used directly to switch another core. Also, ping-pong circuits have shown a tendency to "free-run" by triggering themselves in the resetting portion of their operating cycle. These difficulties pre20 sented problems in design and the necessity for a plurality of cores increased costs for the circuit. It is, therefore, an object of our invention t(> provide a pin--pong circuit wound on a single square loop core. further object of our invention is to provide a ping21 @ong circuit wound on a single core in which an active ' rather than a passive element is the core switching mechanism. A further object of the invention is to provide a pingpong circuit which will not "free-run," using a single 30 core. A further object of the invention is to provide a dy@ namic storage element, which element switches to a reference state and back again in response t(> an input trigger only when the element initially is in a particular 35 one of its bistable storage conditions. In carrying out the objects of our invention, we provide two TMA's wound on the same square loop magnetic core with their windings in the opposite sense. When the core stores a particular one of its bistable values, the 40 triggering of the first TMA switches the core. Since the windings of the second TMA are wound in the opposite sense to those of the first, the flux generated in the core by the switching holds the second TMA off during the operation of the first. A trigger circuit for the second 45 TMA is provided. This circuit includes a winding on the core which charges a capacitor during the operation of the first TMA. At the collapse of the field generated by the switching of the first TMA, the voltage on the capacitor triggers the second TMA which resets the core. 50 When the field caused by the switching of the second TMA collapses, this collapse causes a fly-back phenomenon to be exhibited whereby a voltage of opposite polarity to that induced by the switching of the core is generated in the windings. This fly-back phenomenon tends to r e )5 cause the ping-pong to "free-run" by trig- ring the first TMA on the collapse of the field generated by the second TMA in resetting the core. This is prevented by providing a temporary bias circuit which holds the first TMA off during the fly-back portion of the second TMA's oper60 ation. When the core is already in its switched state, the trigger cannot cause the TMA to regenerate due to transformer coupling since the core is merely driven along the flat portion of the hysteresis loop. Thus the second TMA is never caused to turn on and no output is generated. Various objects, advantages and features of our inven65 tion will become more fully apparent from the follow. ing specification, appended claims, and accompanying drawing in which: FIGURE 1 is a schematic diagram of applicants'TMA 70 ping-pong circuit wound on a single core. FIGURE 2 is the outptit voltage waveform from the pingpong circuit of FIGURE 1.
[2]FFGURE 3 is the voltage waveform at the base of the first TMA transistor of the pin,-- pong circuit of FIGURE 1. Our invention can be best understood by referring to the following detailed description of the illustrated embodiment. In the following operation, it is understood that the core is storing a binary value and starts out in a switchable state. It is also understood that if the core starts out in its switched state, no output isgenerated. Referring to FIGURE I of the drawings, the windings are in a direction such that current into the dotted end of any coil will operate to set the core to the "O" state and will induce in the other coils a volta.-e havin.@ its positive polarity at the dotted end of the coil. TMA's 11 and 13 have all their windings on square loop magnetic core 15. TMA 11 consists of PNP transistor 17, winding 19 connected to the collector of transistor 17, and base winding 23 connected to the base of transistor 17. The free ends of collector winding 19 and base winding 23 are connected to a negative voltage supply 21 and the temporary bias circuit 25, respectively. The emitter of transistor 17 is grounded. The dotted ends of coils 19 and 23 are in the direction of the collector of transistor 17 and temporary bias circuit 25, respectively. The temporary bias circuit 25 includes a coil 27 wound upon core 15, the dotted end of the coil being grounded and the other end being connected to the anode of diode 29. The cathode of diode 29 is connected through resistor 35 to the parallel combination of resistor 31 and capacitor 33. The other end of the parallel combination is -rounded. The connection between winding 23 and temporary bias circuit 25 is made at the junction of resistors 31 and 35 and capacitor 33. Trigger input 37 for TMA 11 is connected to capacitor 39 and resistor 41. The other side of capacitor 39 is connected to resistor 43 and the cathode of diode 45. The free ends of resistors 43 and 41 are grounded. The anode of diode 45 is connected to the base of transistor 17. PNP transistor 47 of TMA 13 has the dotted end of its collector winding 49 connected to negative power source 21 and the undotted end connected to the collector. Its emitter is grounded. Base winding 51 of TMA 13 has its dotted end connected to the base of transistor 47 and its undotted end connected to one end of the parallel combination of capacitor 53 and resistor 55 of the trigger circuit 57, Tri.-ger circuit 57 also includes winding 59 on core 15 whose undotted end is connected to the cathode of diode 61. The anode of diode 61 is connected through resistor 63 to the juncture of the coil 51 and the parallel combination of capacitor 53 and resistor 55. The dotted end of coil 59 and the free end of the parallel combination are grounded. The output from the ping-pong is taken from output coil 65 wou - nd on core 15. Althotigh our circuit has been described using PNP transistors, it is, of course, obvious that NPN transistors or other suitable active elements could equally well be used if the appropriate changes were made in polarity sensitive components and volta,-e source values and polarities. For the purposes of our invention, an active element is one whose output power is at least supplemented by sources other than the input but whose output state is dependent on that of the input. In operation, a negative-going pulse 67 is impressed on trigger input 37. Any reasonable plilse with a fast-rise time will operate the circuit but its duration must not exceed the duration of operation of TMA 11 and should be somewhat less. If a longer pulse is used, capacitor 39 and resistor 43 should be adjusted to differentiate it. Capacitor 39 and resistor 43 also serve to decouple the trigger source 37 from TMA 11 thereby allowing temporary bias circuit 25 to work. The pulse is transmitted tbrough capacitor 39 and diode 45 and causes transistor 17 of TMA 11 to begin to conduct. Current enters the dotted terminal of collector winding 19 and generates a flux that begins to switch the core 15 to the "O" state. This change of flux induces a voltage in 31489y9l6 4 the other coils of the circuit. The volta.-e induced in base winding 23 drives the base of transistor 17 more negative thereby increasin.-- collector-to-emitter conduction. The current and voltage build up rapidly in the normal regenerative TMA fashion until core 15 has switched completely to the "O" state, at which time the flux collapses and th-, conduction of transistor 17 ceases. During the build-up of the flux due to the operation of TMA 11, coil 59 of trigger circuit 57 charges capacitor 53 through diode 10 61 and resistor 63. In order for the circuit to operate, the core must originally have been in the "I" state. If it were originally in the "O" state, the initial trigger pulse wotild merely drive the core further into saturation and only very small volt15 a@es would be generated in the other windings so the circuit would not operat@ regeneratively. TMA 13 is held off durin@@ the time of switching of TMA 11 since its windin.@s are wound in the opposite sense to the windings of TMA 11. Base windin.- 51 must 20 have at least as many turns as windin.- 59 so that the voltage induced in windin@@ 51 is greater than or equal to that induced in winding 59. Otherwise TMA 13 will trigger as soon as capacitor 53 charges sufficiently and will interfere with the switchin,@ of TMA 11. At the collapse 25 of the flux caused by the switching of TMA 11, the charge on capacitor 53 impresses a negative voltage on the base of transistor 47 and begins collector-toemitter conduction. TMA 13 then operates in the same manner as TMA 11 and resets the core to the "1" state. The flux generated in 30 the core by this resetting induces a voltage in winding 27 which charges capacitor 33 throu,-h resistor 35 and diode 29 of temporary bias circuit 25. This holds TMA 11 off during the fly-back portion of the operation of TMA 13. The output waveform generated in coil 65 is shown in FIGURE 2. .5 The fly-back portion of the operation of TMA 13 occurs because the top of the hysteresis characteristic 71 of core 15 is not flat but slanted. Therefore, when the core returns from its saturated state to the remanent state, 40 there is a decrease in the flux density in the core which induces in the windings a voltage opposite to that generated by the switching of the core. Temporary bias circuit 25 prevents this fly-back from retriggering TMA 11. The effect of the temporary bias circuit 25 on TMA 11 _ can be seen in FIGURES 2 and 3 depending, respectively, 4;) on whether or not temporary bias circuit 25 is included in the pin.--pong. If temporary bias circuit 25 is not included, the voltage waveform at the base of transistor 17 will be that of FIGURE 2. This is the same waveform as is induced in otitput winding 65. The fly-back portion 50 69 of the waveform will tend to cause TMA 11 to trigger spontaneously andd allow the ping-pong to free-run. FIGURE 3 shows the effect of the inclusic)n of temporary bias circuit 25 on the voltage waveform at the base of transistor 17. The fly-back re.-ion 69' remains well above 55 the zero voltage level thereby eliminating the tendency to free-run. An example of component values which were found to be suitable for our circuit is listed below: 60 Component: Value Resistor 31 ----------------------------- 5K Capacitor 33 ---------------------------- - 001 Resistor 35 ----------------------------- 470 Capacitor 39 ---------------------------- - 001 65 Resistor 41 ----------------------------- 91 Resistor 43 ----------------------------- 20K Capacitor 53 ---------------------------- - 002 Resistor 55 ----------------------------- 1K Resistor 63 ----------------------------- 470 70 All values of resistance given in ohms and all values of capacitance in microfarads. We
