US3654627A - Plated wire memory - Google Patents

Abstract

A plated wire core memory array is described in which the core wires are divided into two sets which are placed on either side of word conductors. The flux emanating from one core during excitation passes through another core on the other side of the word conductors so that fluctuations in the switching fields due to changes in the pattern of stored information, are reduced or suppressed.

Description

United States Patent 3,654,627 Snyder [4 Apr. 4, 1972 541 PLATED WIRE MEMORY 3,397,394 8/1968 Maeda ..340/l74 PW [72] Inventor: l:Rlichard L. Snyder, New Smyrna Beach, Primary Examiner stanley MurynowiczJn 22 Filed: June 30,1970 ABSTRACT 21 Appl. No.: 51,175

US. Cl. ..340/174 PW, 340/174 QB, 340/174 DC Int. Cl ..G1lc 11/14 Field of Search ..340/l74 PW, 174 PC, 174 QB, 340/174 DC References Cited UNITED STATES PATENTS 2/1968 Fedde ..340/l74 PW 0.. WRITE -3s AMPLIFIER WORD A plated wire core memory array is described in which the core wires are divided into two sets which are placed on either side of word conductors. The flux emanating from one core during excitation passes through another core on the other side of the word conductors so that fluctuations in the switching fields due to changes in the pattern of stored information, are reduced or suppressed.

1 Claims, 3 Drawing Figures SENSE AMPLIFIER SELECTOR PLATED WIRE MEMORY This invention is concerned with static magnetic core memories of the type in which the core is a section of magnetic material deposited as a thin film on a wire, such as that described in U.S. Pat. No. 3,390,383, issued to the applicant on June 25, 1968. The magnetic material is usually a nickel iron alloy deposited in an electroplating bath and so treated that it is oriented having uniaxial anisotropy with the easy axis in the circumferential direction.

Bits of information are stored in the memory by magnetizing sections of the film along a circumferential path in either a clockwise or counterclockwise direction depending on the value of the bit. Storage is effected by passing a current through the wire having its polarity determined by the value of the bit. This current generates a circumferential magnetic field which, acting alone, is somewhat less than that required to reverse the polarity or to disturb the field in a magnetized section of the wire. While this current is flowing, a magnetic field parallel to the axis is generated by passing current through a short coil, called the word coil, around the wire. Its conductors have straight sections positioned near each side of and substantially perpendicular to the wire. The width of the coil is approximately equal to the length of the section of the film and wire in which a bit is stored. The combination of the circumferential and axial fields in the selected bit section causes the field in the magnetic film to reverse by coherent or rotational switching if the film is not initially magnetized in the direction of the field established by the bit wire current.

Information is read from a bit position by pulsing a current through the word coil equal to that used during recording. The magnetic field so produced partially rotates the field stored in the bit section. This partial rotation of the field changes its coupling to the core wire thereby generating a voltage across the bit section which is detected across the terminals of the core wire. The polarity of the voltage so produced is determined by the polarity of the stored bit. The field from the read pulse is limited to a value which, when the pulse subsides, allows the field in the film of the bit section to return to its initial condition so that any number of read operations may be executed without destroying the stored information.

The current through the core wire during recording is supplied through a bridge circuit which is arranged so that the sensing circuit is protected from excessive disturbance during recording. It is not intended that any discussion of ancillary equipment or circuits connected to the memory array to be described are to be considered as entering into this invention. Such equipment is well known to those skilled in the art. Only the array itself, including the core wires and word conductors and shields, are new.

In memories of this type, a number of bit wires are arranged in a parallel array and are served in parallel by a number of recording and sensing circuits. The array is also provided with a number of work coils, each of which encloses all of the wires. A number of bits are therefore served by each word coil and a number of words are served by each bit wire. When a large number of bits are being switched simultaneously, a considerable magnetic field is developed near them. This field is variable depending on how many bits in a word are switched. For this reason, it is usually necessary to space the bit wires relatively far apart to prevent bits adjacent to those being switched from being disturbed.

For example, consider an array composed of bit wires, 0.005 inches in diameter, a common size, having a magnetic film 10,000 angstroms thick. The circumference of the wire is therefore approximately 0.040 centimeters. The total area of film is, in a cross section perpendicular to the axis, then 4 X 10 X 10 4 X 10 square centimeters. The saturated flux density in these films is approximately 1.25 X 10' gauss. Therefore, a total of X lines would exist if the film were saturated in the axial direction. This condition exists during rotational switching of a core. If the array has its wires spaced on 0.010 inch centers or four wires per millimeter and, due to shielding, the fields external to the core sections are confined to a space I millimeter thick, the flux density when all of the cores switch, will then be 4 X 5 X 10 0.2 lines per square millimeter or 20 gauss. A magnetic field of 20 oersteds in addition to that required for overcoming the reluctance of the material would then be needed. However, if none of the cores switch, less than half the 20 gauss must be accommodated. Since the difference between the field required for switching and that for no switching is nearly as large as the usual cross fields from the word coils, such a system is inoperative. For this reason, the core wires are arrayed with much greater spacing.

Even with relatively large spacing between the bit wires variations in the fields caused by changes in bit patterns place severe requirements on the tolerances that can be permitted in variations in the characteristics of the magnetic films. These requirements can be considerably relaxed if field variations are eliminated.

The present invention overcomes this problem of variable fields by employing two cores per bit, placed close to one another and arranged so that during switching the field emanating from one core is provided with a return path through its mating core. By this means, fluctuating fields about the switching cores are eliminated which also eliminates pattern sensitivity. Mention should be made of the fact that a compromise can be made in which only one core per bit is used and pattern sensitivity can be greatly reduced. In this scheme, cores are arranged in pairs independently. The flux due to the word coil field is therefore cancelled. By arranging matters so that neighboring cores cannot switch together, interference is reduced.

It is accordingly an object of this invention to provide an improved thin film memory.

Another object of this invention is to eliminate pattern sensitivity in a thin film memory.

A further object of the invention is to provide a means of making a more compact plated wire memory array.

Still another object of the invention is to provide a memory structure more compact than those presently available but to retain the economy of a single core per bit.

One more object is to provide a structure for plated wire memories which will function with cores having less uniform magnetic characteristics than are now required.

The foregoing and other objects and features of this invention will be more clearly understood from consideration of the detailed description of embodiments thereof which follows when taken in conjunction with the accompanying drawings in which:

FIG. 1. is a diagram which illustrates how the magnetic field in and about the cores of a conventional plated wire memory behaves during reading and writing.

FIG. 2 illustrates the behavior of cores in a memory made in accordance with the present invention.

FIG. 3 is a semi-schematic diagram of a plated wire core memory having two core sections to store each bit.

As mentioned above, the magnetic films of which the cores are made are so oriented that they have uniaxial anisotropy with the easy axis forming a circumferential path. In the absence of an externally applied magnetic field, this material can only be magnetized in the direction of the easy axis except where two magnetic domains meet. At the domain walls for a distance of a few hundred molecules, the field undergoes a reversal. FIG. 1 shows a bit wire 1 l on which for convenience are indicated four bit storage positions as discreet sections of film. In practice, the films are usually continuous with the ends of the bit positions comprised of domain walls. At A in FIG. 1 is shown a section of film magnetized in one polarity indicated by the arrow 0. Its field will be undisturbed even if it is subject to a reverse magnetizing current IWI having the magnitude required to write a bit of the opposite polarity. The Section at B is shown enclosed by the conductors of a word coil 12. It is initially magnetized in the same direction as section at A but is then subject to a magnetomotive force from current in the word coil generating the field H indicated at 4. H, causes the field in the film to tilt into a helical direction indicated by the arrow 2. Some of the flux emerges from the core and encircles the conductors of the coil 12, as shown by the line 5, instead of the core wire 11. This change of flux linkage generates a voltage across the section at B. When the field from the coil 11 is allowed to collapse, the flux returns to its initial path and in so doing, generates another voltage of opposite polarity across the section at B. At C the same set of circumstances prevails as at B except that the polarity of the field in the core is reversed as indicated by the arrow 1. When the core at C is subject to the same magnetizing force as at B, the flux tilts as shown by the arrow 3. The polarity of the emerging flux is the same as at B. However, the voltages induced across the section are opposite because the flux linking the wire has been reduced from the opposite polarity. The direction of the field from the coil is immaterial, the polarity of the output signals is subject only to the polarity of the field in the film.

At D is shown a film initially magnetized in the direction. It is then subject to a magnetizing force from the word coil 12 which tilts the field in the direction of the arrow 2. The section is next subject to the additional field from current lWl in the bit wire which causes the flux to swing to the position indicated by the arrow 3. When both magnetizing forces subside, the field in the core swings to the position indicated by the arrow 1 being completely reversed.

As described above, the fields which emerge from the cores during a reading or writing operation have magnitudes that are comparable to those produced by the controlling currents. Because the magnitudes of these fields depend on whether a core switches or not, which is in turn determined by the information being stored, no compensating changes in the control currents can be employed to reduce the effects of the variation.

Complete compensation can be obtained by using a structure like that shown in FIG. 2. The word coil is replaced by a single conductor 23 and two shield plates 24 which provide space for two bit wires 21 and 22. All of the wires in the array are electrically insulated from one another and from the word conductors and the shields. The word conductors are also insulated from the shields except that one end of each word conductor may be connected to the shields which then serve as a ground return. This insulation is not shown in the drawings. Current through the word conductor 23 which may return through the shield plates 24 generates a magnetic field parallel to the axis of 21 and 22 but in opposite directions so that a north pole formed by flux leaving the core on 21 is adjacent to a south pole formed at the end of the core on 22. Since the cores are of reasonably uniform magnetic characteristics, very little field develops beyond them. When the cores switch, the increased field from each core compensates that from the other and no variation in field outside the region occurs. The direction of magnetization for the cores representing zero and ones relative to one another is immaterial. Thus, if 1 is used to record a zero in the core on 21, either 1 or I. may be used to record a zero in the core on 22. Of course, the convention, once selected, must be maintained.

The independence of the core convention between pairs of cores make it convenient to use either a series or a parallel system of excitation of the bit wires. FIG. 3 is a schematic diagram of a memory using two cores per bit. It consists of two arrays of word conductors 23 served by a word selector 39, four sets of bit wires 30,31,32, and 33 which are connected to the primaries of four coupling transformers 34 which having center taps 35 connected to four write circuits 38 only one of which is shown. The bit wires connected to each side of the primary of a transformer have substantially the same impedance. The secondaries 36 of the four transformers are connected to four sense amplifiers 37, only one of which is shown. Shields which are normally placed on either side of each array are here omitted to simplify the diagram.

To record a word, the word selector 39 controlled by an external circuit, delivers a current pulse to one of the word conductors 23. Each write amplifier delivers a pulse of current to the center tap 35 of one of the transformers. The polarit of the pulse 18 determined by the value of the bit to be recorded.

The current to each center tap divides between the two bit wires of each pair in substantially equal amounts. The magnitude of the current is selected to cause no disturbance in any core except adjacent the selected word conductor.

To read a word, one of the word conductors is excited by the word selector. The magnetizing force from the current in the word line tilts the field in all of the cores under its influence causing a voltage to be generated across each bit section which excites the transformer primary connected to its word line and causes a signal to be delivered by the secondary to the sense amplifier. The polarity of the signal indicates the value of the bit stored in the disturbed cores.

It will be noticed in FIG. 3 that the branches of the bit wires 30 and 31 are connected in parallel on either side of the transformer primary whereas bit wires 32 and 33 are connected so that their branches are connected in series. The parallel connection is suitable for large arrays where it is desirable to keep current paths short to minimize signal propagation time. The series connection is used in small arrays where propagation time is negligible because less current is required.

The structures so far described achieve nearly complete suppression of stray fields from switching cores. In very large memories, complete suppression may sometimes be unnecessary. in very large memories, the number of bit wires in an array may be many times the number of bits in a word. Consequently, only a small fraction of the bit wires will be excited during the recording of a word.

If the bit wires to be selected for any word are uniformly distributed in the array, the spacing between the active bit wires may be great enough to reduce interaction to negligible levels. By placing half the bit wires on one side of an array of word conductors and half on the other side, all stray fields due to word selection currents will be suppressed. Also switching of two of the most closely spaced cores which will be on opposite sides of the array will cancel each others stray fields.

A structure for a plated wire memory has been described in which it is possible to store information at high density. Although the embodiment and its variations which have been described in detail above is one form of the invention, other configurations and embodiments may be made by one skilled in the art without departing from the spirit, scope, or principle of this invention.

What is claimed is:

1. A magnetic core memory array of the type in which the cores are formed in a ferromagnetic film deposited on a wire called a bit wire said cores consisting of magnetic flux in a path in the film which encircles the wire and extends axially along the wire for a distance substantially equal to the core width; said memory array being comprised of a group of said bit wires arranged in a parallel configuration wherein each wire passes an assembly of parallel word conductors said bit wires to be arranged to be substantially perpendicular to and equally spaced from said word conductors; said group of bit wires divided into two sets one of which passes on one side of said word conductors and one on the other side; said sets arranged so that the wires in one set are as close as it is practical to place them to corresponding wires in the other set; said corresponding pairs of wires from each set electrically connected in parallel so that the cores of a pair on either side of a word conductor are subject to substantially equal electrical excitation, changing their magnetic fields in a complementary manner and so suppress or reduce the effect of said fields on neighboring cores.

Claims (1)

1. A magnetic core memory array of the type in which the cores are formed in a ferromagnetic film deposited on a wire called ''''a bit wire'''' said cores consisting of magnetic flux in a path in the film which encircles the wire and extends axially along the wire for a distance substantially equal to the core width; said memory array being comprised of a group of said bit wires arranged in a parallel configuration wherein each wire passes an assembly of parallel word conductors said bit wires to be arranged to be substantially perpendicular to and equally spaced from said word conductors; said group of bit wires divided into two sets one of which passes on one side of said word conductors and one on the other side; said sets arranged so that the wires in one set are as close as it is practical to place them to corresponding wires in the other set; said corresponding pairs of wires from each set electrically connected in parallel so that the cores of a pair on either side of a word conductor are subject to substantially equal electrical excitation, changing their magnetic fields in a complementary manner and so suppress or reduce the effect of said fields on neighboring cores.

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