Note: Descriptions are shown in the official language in which they were submitted.
~03~07~7
The invention relates generally to the field of mag-
netic bubble technology (MBT) and, more particularly, to means
for propagating or transmitting magnetic bubbles, especially in
recirculating closed loops~
This application is a divisional of copending Canadian
Application Serial Number 212,765, filed October 31, 1974.
Briefly, MBT involves the creation and propagation of
magnetic bubbles in specially prepared magnetic materials. The
word "bubb1e", used throughout this text, is intended to encom-
pass an~ single-walled magnetic domain, defined as a domain
having an outer boundary whichcloses on .itself. The applica-
tion of a statlc, uni~orm magnetic bias field orthogonal to a
sheet of magnetic materiAl havilly ~u:itable un:laxtal antsotropy
causes the normally random serpentine pattern of magnetic domains
to shrink into short cylindrical conigurations or bubbles whose
co~non polarity is opposite that o~ the bias field. The bubbles
repel each other and can be moved or propagated by a magnetic
field in the plane of the sheet.
Many schemes exist for propagating bubbles along pre-
determined channels. These techniques can be classed generally
as conductor-accessed and field-accessed. In conductor-acces-
sed propagation systems, loops of electrical conductors are dis-
posed in series over the magnetic sheet. A propagation system
has been proposed using a "serpentine" conductor criss-crossing
a erromagnetic rail defining stable complementary bubble posi-
tions. In field-accessed propagation systems electrical con-
ductors are not disposed on the magnetic sheet for propagation;
inst.ead, an overlay pattern of ferromagnetic elements estab~
lishes a bubble propagation channel in which a sequence of
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~(~3~7
attracting poles is caused to be formed in the presence of a
continuous, uniformly rotating magnetic drive field in the
plane of the sheet. A major distinction in function between
conductor-accessed and field-accessed circuits is that several
conductor--accessed circuits can be disposed on the same sheet
or 'lbubble chip" and operated completely separately and ex-
clusively from each other, while field-accessed circuits on
the same chip ~1 operate at the same time under the control
of an ubiquitous, uniformly rotating, common drive field.
One attempt at providing field-accessed circuit selection
in the prior art is shown in U.S. Patent No. 3,543,25~ to
Perneski illustrating several variations on the famillar T~bar
circuit driven by diffexent perrnutations of pulsed orthogonal
drive fields.
MBT can be used in data processing beca~se magnetic bubbles
can be propagated through channels, whether field accessed or
conauctor-accessed, at a precisely determined rate so that uni-
form data streams of bubbles are possible in which the presence
or absence of a bubble at a particular position within the
. stream indicates a binary "1" or "0". Because of its potential
for low cost, low power consumption and extremely high bit
density, MBT is under active consideration for use in large
scale relatively low speed memories. One of the prime design
elements of many memory systems utilizing field-accessed magnetic
bubbles is the provision of a seriai closed loop bubble path
which can be used as a recirculating "shift registerl'. Many
memory arrangements of this type employ a plurality of "minor"
loops selectively interconnectibl~ with a "major" loop such
that bubbles can be transferred between the major and minor
loops on command. The ability to propagate bubbles in
~Q3~
one recirculating loop without operatin~ other loops on the same
chips has in the past been con~ined to systems employing conduc-
tor-accessed circuitsO
Another consideration to~hich this application is dir-
ected is the desirability of providing a segmented continuous
overlay rather than discrete spaced e].ements such as those used
in chevron and T-bar circuits. U. S. Patent No. 3,518,643 to
Perneski illustrates zigzag and crenellated forms of continuous
overlay patterns based on right angles, driven by a pulsed ortho-
gonal coil arrangement.
In a preEerred embodiment o~ the p~es~nt .~nvention
there is prov.~ded a closed loop magnet.ic bubb.le propa~tion clr-
cuit comprising a sheet Oe magnetic hubble material, means ~or
applying a magnetic bias ield orthogonal to said sheet to pro-
duce and maintain magnetic bubbles therein, a continuous ferro-
magnetic overlay circuit operatively disposed on said sheet
forming a closed bubble propagation path, and ~ans for applying
a pre-determined sequence of pulsed discrete drive field orienta-
tions in the plane of said sheet for propagating bubbles around
said closed path.
In a further embodiment of the present invention there
is provided a closed loop continuous magnetic bubble propagation
circuit, comprising a sheet of magnetic bubble material, means
for applying a bias field orthogonal to said sheet to produce
and maintain bubbles therein, and a continuous magnetic bubble
propagation overlay circuit on said sheet in the orm of a con-
tinuous zigæag pattern crisscrossing the sides of a reference
triangle such that the zlgzag elements o said pattern on any
given side of said crisscrossed triangle are parallel to the other
two sides o said reference triangle, and means for applying a
predetermined sequence of pulsed magnetic drive fields in the
~ ~ 4 ~
plane of said sheet in fi~st/ second and third directions res-
pectively parallel to the sides of said reference triangle for
propagating bubbles around said closed path.
In a still furthe~ embodiment of the present invention
there is provided field-accessed mutuall~ exclusive closed bubble
propagation paths, comprising means defin.ing a first many-sided
closed bubble propagation path in which the sides of said path
are parallel to corresponding sides of a first equilateral ref-
erence triangle.having a first orientation, means for applying a
se~uence of three pulsed drive fields aligned respectively with
the sides o said first equilateral tr.iangle ~or propagati.ng
bubbles around sa.id :Eirst alosed path r each s.ide of said .E.irst
closed path being ~ormed by a circu.it pa~tern overlay for propa-
gating bubbles along said side in response to alternating align-
ment of said first se~uence of drive fields with the other two
sides o said first reference triangle, a second many-sided
closed bubble propagation path the sides of which are parallel
to corresponding sides of a second equilateral reference triangle
having a second orientation such that the sides of said second
triangle are nonparallel to the sides of said first triangle,
means for applying a second sequenceof three pulsed drive fields
aligned respectively with the sides of said second triangle, each
side of said second closed path being formed by a circuit pattern
overlay for propagating bubbles along said s.ide in response to
alternating alignment of said second sequence of pulsed drive
fields with the other two sides of said second triangle.
One of the objects of the invention is to provide
closed loop bubble propagation channels, field-accessed by means
of nonrotating, i.e. discretely orientedl pulsed fields. An-
other object of the invention is to provide mutually exclusive,
closed loop circuits, field-accessed by means ofdifferent sets
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of pulsed field orientations. A further object of the invention
is to improve continuous overla~ ~ield~accessed circuits, which
ensure uniform bubble size by maintaining uniform bias field
strength due to the absence of discrete, spaced circuit elements.
The applicants have discovered that these and other
objects of the invention are accomplished by providing a closed
loop
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~Q3~0~77
bubble propagation circuit driven by a pulsed drive field
assuming discrete orientations in a predetermined repeating
se~uence. In the preferred embodiment, subsets of a sequence
of nonorthogonal field orientations are effective to drive
bubbles on corresponding sides o~ the closed loop path. A
continuous zigzag form overlay circuit traverses sides of the
closed path parallel to the sides of an equilateral triangle.
The drive field sequence includes three discrete orientations
corresponding to the sides of the triangle. Any two of the
orientations are effective to drive bubbles along one side of
the closed path. More complex forms of closed loops based on
; the equilateral triangle can be generated by usin~ any closed
loop zigzag circuit design as a constructional l:in~ on which
to build successive zigzag circuits in the nature of a "Peano
diagram".
Pulsed field-accessed, closed loop circuits are applied,
in another important aspect of the invention, to the problem
of field-accessed circui~ selection. A pair of closed loop
pulsed field-driven circuits are oriented relative to each
other such that a sequence of pulsed field orientations effec-
tive to circulate bubbles on one of the closed loops is inef-
fective to operate the other closed loop, and vice versa.
Hence, the closed loops, while field-accessed, are mutually
exclusive.
A semihexagonal continuous overlay circuit is driven by
discrete pulsed field orientations repetitively realigning
with consecutive angled segments of the overlay circuit.
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3~7
BRIEF DESCRIPTION OF THE DR~WINGS
Fig. 1 is a fragmentary perspective view of a bubble chip
furnished with a conventional chevron circuit.
Fig. 2 is a schematic drawing illustrating a semihexagonal
continuous overlay and the associated drive field sequence
according to the invention.
Fig. 3 is a schematic drawing illustrating a zigzag con-
tinuous overlay circuit and the associated drive field sequence
according to the invention.
Fi~. 4 is a schematic diagram illustrating a closed loop .
zigzag continuous overlay circuit and its associated drive
field acaording to the invention.
Fig. S is a schematic diagram illustrating a variation on
the closed loop zigzag circuit of Fig. 4.
Fig. 6 is a schematic diagram indicating a technique for
generating successively more complex closed loop zigzag cir-
cuits.
Fig. 7 is a schematic diagram illustrating a pair of
mutually exclusive field-accessed closed loop circuits and
their respective drive field sequences according to the
invention.
~ ig. ~ is a graph indicating the hysteresis curve for a
particular overlay material.
DESCRIPTION OF P:REFERRED E~ DIMENTS
Fig. 1 illustrates the basic components of a field-accessed
garnet bubble chip haviny a conventional chevran circuit~ A
substrate 10 of nonmagnetic garnet supports an epitaxial
magnetic bubble garnet layer 12 and spacing la~er 14 of silican
C 07-2~ ?37
~38~
oxide to which conventional permalloy chevron circuit elements
16, 18 and 20 are bonded. The chip is subjected to a static
magnetic bias ~ield orthogonal to the plane of the magnetic
bubble garnet layer 12. In the presence of a bias field of
suitable strength, cylindrical magnetic bubbles (not shown in
Fig. 1) are mai~tained in the bubble garnet layer 12. Conven-
tionally, a rotating, in-plane magnetic drive field, produced
by an orthogonal pair of Helmholtz coils, causes bubbles to pro- I~
pagate from chevron circuit element 16 to element 18, for
example.
~,~ Many parameters affect the performance of che~ron circuits
such as the number of parallel chevrons per bubble position
(single chevrons are illustrated in Fig~ 1), thc spacing of
adjacent chevron elements, their width, the magnetic properti~es
of the overlay material, and the strengths of the magnetic bias
and drive ~ields.
One of the problems with discontinuous circuit overlays of
spaced elements, like the chevron circuit ~Fig. 1), or the
familiar T-bar circuit is that bubbles propagating along the cir-
; cuit channel are subjected to varying bias field strength as they
move from under one circuit element through a gap region to the
next circuit element. A continuous circuit overlay avoiaing this
problem is shown in Fig. 2. The circuit overlay 22 is composed
o~ a series of parallel semihexagonal, three-segment sections,
each comprising an angled straight line segment 24 coupled by a
horizontal straight segment 26 to another angled straight segment
28, to form a truncated sawtooth pattern. Segments 24 and 2~ ¦
make an angle of 120 with respect to the horizontal segment 26
and the angled segments make an angle ~-60 with respect to each
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~ 0380~77
other. Thus the segments 24, 26 and 28 together outline one
half o~ a hexagon. The semihexagonal sections are continuously
interconnected by joining adjacent angled end segments 24 and 28.
A pulsed field sequence 30 for propagating bubbles along
the continuous overlay 22 in Fig. 2 comprises three discrete
pulced field orientations parallel to the elements 24, 26 and
28, respectively. The field sequence 30 occurs in the order
indicated by the numerals associated with the field vectors.
The first field orientation is aligned with segment 24, the
second orientation is aligned with segment 26 and the third
is aligned with segment ~28. The three orientations all point
in the same general direction of travel along consecutive seg-
ments in the circuit 22~ The alignment and diraction o the
pulsed fields orms attrac~ing poles along the line segments of
the semihexagonal overlay in the sequence indicated by the
numerals 1, 2 and 3 adjacent to the circuit 22. Bubbles ~not
shown) under the circuit overlay 22 are attracted to the pole
positions in the order indicated and thus traverse first the
segment 24 to the position 1, next the segment 26 to the position
2 and finally the segment 28 to the position 3. This motion is
repeated for each repetition of the fîeld sequence 30 as bubbles
move over successive semihexagonal sections in the circuit 22. '
Fig. 3 illustrates a zigzag continuous overlay channel 32
comprising alternately angled straight line segments 34 and
36 forming a regular sawtooth pattern. ~he segments 34 are
parallel, as are the segments 36 which meet the segments 34
preferably at a 60 anglej 0. The pulsed drive field sequence
38 comprises a pair of discrete, alternate orientations labeled
1 and 2 separated by the angle 180 minus ~ or preferably 120.
~ C-07-21-0237
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~L~380~7
These orientations are parallel respectively with segments
34 and 36. Bubbles (not shown) under the overlay channel 32,
attracted to'the changing poles formed by the drive field 38,
are propagated to the right, the direction of the drive field
38 as viewed in Fig. 3, through the bubble positions labeled
,1 and 2 form~d at the upper and lower vertices of the circuit
respectively.
Fig. 4 illustrates the manner in which, closed loop con-
tinuous zigz-ag type circuits are constructea. The equilateral
tr;angle 40 in Fig. ~ is drawn for reerence as a construc-
tion,al diagram. The overlay c.ircu.it itse.l.~ is represented by
the closed xiyzag patt~'rn ~2 consccu~iv~ly cri.s.scrossing khe
sides of the triangle 40. The z.igzag cixcuit 4Z, itself has
three sides or sections 4~, 46 and 48 corresponding to the
sides a, b and c of the equilateral triangle 40. For each
section 44, 46 or 48 the straight line segments of the zigzag
pattern traverse or crisscross one side of the triangle 40, and
' the segments are alternately parallel to the other two sides of
; the-same triangle. Thus section 44 of the zigzag circuit 42 .
crisscrosses side a of the triangle and every other parallel
indiviaual element of the ~igzag section 44 is parallel to
side b or side c. Th,e section 46, on the other hand, criss-
crosses side b and is alternately parallel 'to sides a and c.
Similarlyt,section 48 cr;sscrosses s.ide c and is alternately
parallel to sides a and b.
Pulsed drive field 50, shown in Fig. ~ to the right of
the closed zigzag circuit 42, comprises a sequence o~ three
pulsed field orientations, labeled arbitrarily 1, 2 and 3,
which are aligned with sides b, a and c respectively of the
` C-07 21-n237
construction triangle 40. Recalling from Fig. 3 that alter-
nately pulsed ~rive fields parallel to the individual straight
line segments composing a zigzag overlay channel and pointing
in the same direction down the channel will drive bubbles in
that direction along the channel, it can be seen in Fig. 4
that for any given section, 44, 46 or 48 only two of the three
pulsed field orientations successfully propagate bubbles in
tha~ section. For example, in section 44 the drive field
orientation labeled 2, parallel to side a of triangle 40, has
little effect on the propagation of bubbles in section 42.
However, ield orientations 1 and 3 are effective to drive
bubbles to the right (clockwise) along section ~4 in the man-
ner shown .in Fig. 3. ~n sec~ion 46, sirnil~rly, the ~field
orientation 1 parallel to the traversed side b is ineffective
to propagate bubbles while the other field orientations 2 and
3 are effective to propagate bubbles along this section.
Section 48 operates in the same manner driven by field orienta-
tions 1 and 2. Hence, the effective field orientations for
each-side or section of the closed loop circuit 40-are inter--
lacea in the drive sequence. The fact that bubbles in one sec-
tion of the circuit 42 are not in motion during the application
of one of the three pylsed drive field orientations has no
adverse effect upon the running of the circuit.
The equilateral triangle 40 on which the circuit 42 is
based is employed hecause it provides maximum isolation of the
three field orientations. That is, this arrangement perm;ts
the field orientation parallel to the traversed side to have
mi~imum effect on a zigzag circuit section corresponding to
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C-07-21-0237
.
~ 380~q
that side. ~ile 60 is beli~ved to be the best angle for
: achieving this type of circuit, clearly analogous circuits with
angles di~fering from 60 are possible in achieving closed
loop configurations. In adaition, constructional figures, like
triangle 40 in Fig. 4, do not have to be triangles but may be
any polygon having any number o~ sides restricted to three
orientations, preferably at 60 angles, where circuit sections
along any parallel sides will not be required to propagate in
opposite direction~. .
Another example of the closed loop, continuous zigzag cir-
cuit based on a 60 angte is sho~n in ~ig. 5 in which the
; construct.ional fiyure 52 consists o a hor.izontal line .int~r-
connecting the ends of a sexies of thrcc sawtee~h. q'he ziyzag
~ircu;t S4 is drawn so as to crisscross the respective sides
of the figure 52 to form a closed loop. The resulting circuit
is driven by pulsed drive field 50 in Fig. 4 in a manner simi-
lar to that for the regular triangular circuit 42.
. - Another closed loop circuit is shown in Fig. 6 dr.iven by
the pulsed drive field sequence 50, where the circuit 42 of
~0 Fig. 4 itself forms a constructional figure 42 to generate a
more complex form of.zigzag circuit 56. Again all of the
elernents of the resulting zigzag circuit 56 are alternately
parallel to respective ones of the sides o~ the original
triangle 38 and propagation along parallel sections is in the
same direb~ion. In a sirnilar manner the co~nplex æigzag circuit
56 can be used itself as a constructional figure to produce a
third generation closed loop zigzag circuit still more complex.
This process of producing successive constructional figures
for successive generations o~ zigzag circuits can be carried
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C-0~-21-0237
~(~3!3i~
out as far as desixea, in the nature of Peano diagrams in
the field of topology, in oraer to efficiently utilize the
space available on the bubble chip. No matter how complex
the closed zigzag pattern becomes, it will be composed of
zigzag sections whose general direction o~ propagation is
parallel to one of the sides of the original equilateral
triangle, and thus propayation over this section will be
affected by two of the three pulsed field orientations 48.
It is important to note that these closed loop circuits can
not be driven by a uniformly, rotatlng magnet.ic field; they
must be driven by a se~uence of pulsed fields such as .ield
sequence 50.
Fig. 7.illus~rates the pri.nciple o~ mu~ually exclusive
field-accessed, closed loop circu.its. In this embodiment,
a pair o closed loop zigzag circuits 58 and 60 are based
respectively on equilateral triangles A and B, symbolizing
the two closed loop circuits. Because of the offset angulax
~orientations of the circuits A and B, when these Cil^cUits are
placed on the same chip, one may be driven by one sequence of
. pulsed dirve fielas while the other is inoperative and vice
versa. In particular, circuit B is tipped approximately 30
relative to the orientation of circuit A. Because the cir-
cuits A and B are both built on 60 angles, the three sides
of circuit B each make an angle of 30 with the three corre-
sponding sides of circuit A. Expressed differently, the
sides of triangle B are orthogonal to the sides of triangle A.
This angular separation is sufficient to render the subset lA,
2A and 3A of the pulsed arive field sequences 62 inoperative
to drive bubbles on the circ~it B while it suc~essfully
c-07-2l-n2 37
1~3~07q .
propagates bubbles on the circuit A. Conversely, the subset
lB, 2B and 3B, offset by 30 from the A subset, is ineffective
to propagate bubbles in circuit A while successfully moving
bubbles around the circuit B. Hence circuits A and B are
mutually exclusive, field-accessed closed loop circuits~
The reasons why these particular circuits in Fig. 7 are
mutually exclusive can be explained, for example, in terms of
the action of the A sequence on the B circuit. Assume that the
vectorial projections of the A orientations on corresponding
segments of the B circuit are sufficient to affect the magnetic
polarity of these segments. When the ~ield 3A ig applied to the
righthand section ~illustxated) o~ circuit 60(B), the field 3A,
as the bisector of the anyles rnade by the segments, affects
adjoining segments equally. Thus a bubble 64 at an inner vertex,
for example, will experience zero net attraction to move to an
outer vertex. The next consecutive field orientations. lA and
2A, will leave the bubble 64 where it is because they (i.e.,
their strongest vectorial projections) point along the adjoining
segments toward the location already occupied by the bubble 64.
2Q . This method of analysis holds true for any section of circuit B
under consideration, and extends by direct analogy to the effect
of field sequence B on circuit A.
While the embodiments diagrammed in Fig. 7 indicate a
so-called "first generation" zigzag circuit configuration or
circuits 58 and 60 with sections corresponding directly to the
sides of the original constructional triangle, it should be
; clear that more complex forms can be used so long as the
individual line segments making up the closed circuit zigzag
overlay are parallel to the sides of a triangle,
`\
~ C-~7~21-~237
.
pre~erably equilateral, parallel sections propagate in the
same direction and the triangles are sufficiently skewed
relative to each other. As in the description of Figs. 4
through 6, 60 angles are preferred although operative embodi-
ments are not limited strictly to 60 angles, triangular con-
figur~tions other than equilateral being feasible. Similarly,
the principle of mutual exclusivity in field-accessed, closed
loop circuits illustrated in Fig. 7 is not necessarily limited
to continuous overlay zigzag circuits. ~iscre~e circuit el~ment,
closed loop overlay patterns mu~ually exclusively op~rable by
means of pulsed field orientations represent a feasible exten-
sion of the underlying principle of field-accessed closed loop
mutual exclusivity.
. As illustrated in the pulsed drive field sequences 62 in
Fig. 7 the angle between sequence A and sequence B is 60. Thus,
for example, field 3A has a vectorial projection in the direction
of field 3B whose magnitude is the cosgin of 30. Thus the
field strengt~ in the direction 3B attributable to a pulsed field
in the direction 3A would be 86% of the full magnitude in the
field in the direction 3A.
To enhance the exclusive operation of circuits A and B, the
circuit material used for the continuous zigzag circuit, or
whatever type of circuit is employed, is chosen with the right
hysteresis curve such that saturation occurs in the presence
of full field strength when the field is strictly aligned
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~)38~7
with the element in circuit ~ for example, while 86% field
strength operating on t~e correspond~ng elements of circuit B
is insufficient to saturate these elements, that is, it is not
enough to switch the magnetic polarity of the corresponding
elements. One example of a suitable hyste~esis curve is shown
~n ~igure 8. A material whose magnetic properties approximate
the h~steresis curve in Figure 8 is the material known under
the trade name Perminvar.
The same general hysteresis property may also be ob-
tained by depositing materials for the circuit overlay which
have a tendency to remain magnetized perpendicular to their long
axes. Such materials will evidence magnetization parallel to
their long axes only above a certain critica:L eield strength~
~ccoxdingly, the magnetic behaviour of such materials would also
approximate the hysteresis loop shown in Figure 8.
Yet another way of enhancing mutual exclusivity would
be to drive the circuits A and B at the highest possible speed
to take advantage of the restrictive operating margins of the
c~rcu~ts. Thus the A sequence of pulses might be well within
the operat~ng margins of-circu~t A. At-the same time, because
o~ reduced components o~ sequence A projected on circuit B, in
combinatl-on with the hi~h operating speed, circuit B would not
; be withi~n its operating margins and thus would fail to function
properly. All of these efforts described above have in common
the pxinciple of improving mutual exclusivity by enhancing the
criticality o~ the drive ~ield strengthsuch that the fully
aligned field will cause saturation of parallel circuit elements
while a field misaligned by as much as 30 will have an aligned
component or projection which is not sufficient to saturate
parallel circuit elements. Any parameter which trims the
opexat~ng margins may be useful in this regard.
~ 15 -
C-07~ 0237
~338~77
The invention may be embodied in other specific forms
without departing from its spirit or central characteristics.
The present embodiments are therefore to be considered in all
respects as illustrative and not restrictive, the scope of the
invention being indicated by the claims rather than by the
foregoing description, and all changes which come within the
meaning and range of equivalence of the claims are therefore
intended to be embraced therein.
