Output timing arrangement for single-wall magnetic domain apparatus

An output timing arrangement for single-wall magnetic domain apparatus for ensuring the concurrence of a domain-generated output signal and the output strobe. Voltages generated at the detector array of the apparatus by its in-plane rotating drive field are employed prior to readout to control the timing of the strobe signal. More specifically, the voltages generated by the rotating field at the second harmonic frequency of its fundamental frequency are filtered out to generate timing data indicative of the precise time at which a domain-generated signal may be expected during a subsequent readout operation. The occurrence of the output strobe signal is thus caused to track variations in the phase angle of the rotating field, which variations in the past frequently affected the strobe timing and hence the reliability of readout.

BACKGROUND OF THE INVENTION 
This invention relates to a single-wall magnetic domain arrangements and 
more particularly to detection circuits adapted for use in such 
arrangements. 
The advancements in the single-wall magnetic domain technology in recent 
years have resulted in the realization of various and numerous data 
processing, memory, and other applications. The control of domain 
propagation in a thin film magnetic medium and the novel circuits achieved 
thereby are wellknown and have been extensively treated in the general and 
patent literature. The manner in which the domains (or "bubbles", as they 
are familiarly termed) are initially created in a thin film medium is also 
wellknown. An external bias field of suitable polarity is applied 
perpendicularly to the plane of the medium to reduce randomly oriented, 
elongated domain patterns to the individual, cylindrical, bubble-like 
domains employable as binary bit representations. Once generated, the 
domains are propagated from point to point within the medium of a system 
by arrays of magnetic elements such as the familiar Permalloy chevrons, or 
"T's" and bars, which are magnetized by an externally generated in-plane 
rotating magnetic field. This rotating field is frequently employed in a 
single-wall domain system as the timing basis for controlling the various 
operations of the system. In one prior art system disclosed in U.S. Pat. 
No. 3,997,877, issued Dec. 14, 1976, to R. A. Naden, for example, the 
propagation of domains in a magnetic medium is synchronized by counting 
the number of rotations of the rotating field to determine the proper 
instant of transfer of the domains from one point to another in the 
medium. The same rotating field also functions to control the readout of 
the domain apparatus which is accomplished in one typical arrangement by 
propagating a domain from the apparatus along a detector path comprising 
Permalloy propagation elements to a detection array of elements having 
magnetoresistive characteristics. The presence of a domain in the array is 
detected magnetoresistively in that the resistance of the array to a 
current varies in response to the magnetic flux of the domain. When a 
domain is propagated to a point under the array, the resistance is changed 
thereby generating an output signal across the array. 
The output signal generated by the presence of a domain under the array is 
a function of the position of the domain relative to the detection array. 
The output signal waveform is a function of the domain position under the 
array, that position in the detector array being determined by the 
direction of the field at the time of readout. In one typical readout 
arrangement, a domain generated output signal has an amplitude of 
approximately 700 microvolts and has a duration of approximately 300 
nanoseconds of a rotating field cycle of 2800 nanoseconds. In this typical 
arrangement, the waveform of the output signal is not specified, only the 
integral of the voltage over the 300 nanoseconds is determined. 
Accordingly, in such and other arrangements it becomes important to 
determine the precise times to begin and terminate the integration period 
to an accuracy commensurate with the output signal duration, in the 
foregoing illustrative case, a duration of 300 nanoseconds. The direction 
of the rotating field which determines the position of a domain in the 
detector array is not precisely determined in time, however. The rotating 
drive field is generated by causing two nominally sinusoidal currents to 
pass through two coils with perpendicular axes which encircle the magnetic 
medium carrying the domains. In the ideal case, where current waveshapes, 
physical alignment of the structural elements, winding and wiring 
dimensions, and the like, are perfect, the angle (direction) of the 
rotating field vector would be precisely linearly proportional to time. In 
practice, however, none of these ideal conditions are met. As a result, 
the time relationship between the timing clock of the system which 
controls the rotating field circuits and the ultimate output signal of the 
system is uncertain to a degree comparable to the duration of the output 
signal. As a result, where, for the foregoing reasons, the arrival time of 
an output signal at the detector is not precisely determined and, on the 
other hand, the output strobe is controlled to occur at a fixed time, the 
reliability of readout of a magnetic domain system may be seriously 
affected. It is to this problem that the detection circuit of this 
invention is chiefly directed. 
SUMMARY OF THE INVENTION 
One illustrative single-wall magnetic domain readout timing arrangement 
according to the principles of this invention, in one of its aspects, is 
based on the aforementioned fact that the magnetic interaction of the 
rotating drive field with the detector array elements causes a voltage to 
appear at the detection array terminals. The magnetoresistive effect is a 
magnitude effect; accordingly, the generated output voltage has a 
component at the second harmonic frequency of the rotating field 
frequency. The phase of the rotating field component of the detector 
output voltage is thus directly related to the direction in which the 
rotating field vector lies with respect to the Permalloy elements of the 
detector array. Since both the domain position at the detector readout 
point and the phase of the second harmonic component of the detector 
voltage output are determined by the rotating field direction, the second 
harmonic output is advantageously employed, in accordance with one aspect 
of this invention, to provide timing information for the detector output. 
In one implementation of the invention, a phase detector circuit is 
provided to gate into a register the clock time at which one of the zero 
crossings of the second harmonic frequency of the rotating drive field 
occurs. A known, predetermined characteristic delay of the particular 
domain medium and supporting structure under consideration is added to the 
time determined by the phase detector circuit to generate signals for 
controlling the output strobe of the detector circuit. This timing 
operation advantageously does not introduce additional delay for its 
accommodation and hence does not increase the time required for the 
readout of the apparatus. The timing operation of the invention is 
accomplished during the delay normally encountered after a readout 
decision is made. In a memory application, for example, the domain content 
of the magnetic medium is first transferred to a path leading to the 
detector array before the actual readout at the arrays is accomplished. 
Having determined the time at which the domain output signal will arrive at 
the detector, the effect of the uncertain time relationship between the 
system clock and the rotating field is advantageously reduced to a 
negligible magnitude. Further, the buses which distribute timing 
information for the rotating field coil and which transmit the detector 
array signals to the detector circuit are sufficiently long to contribute 
significant delay. This delay is also compensated for by the timing 
arrangement of this invention; since the timing information, that is, the 
second harmonic component of the rotating field, and the domain signal to 
be detected are both transmitted over the same path, they both suffer 
approximately the same delay. As a result, in accordance with the 
principles of the present invention, domain generated output signals are 
advantageously detectable notwithstanding tolerance variations and 
variable delays introduced by other frame and system factors.

BRIEF DESCRIPTION OF THE DRAWING 
The organization and operation of a single-wall magnetic domain timing 
arrangement according to the principles of this invention together with 
its features will be better understood from a consideration of the 
detailed description of one specific illustrative embodiment thereof which 
follows when taken in conjunction with the accompanying drawing in which 
the single FIGURE thereof depicts in block symbol form the organization of 
one specific illustrative timing arrangement according to this invention 
shown as operating in conjunction with a generalized magnetic domain 
apparatus which may comprise, for example, a major-minor loop domain 
memory. 
DETAILED DESCRIPTION 
The organization of one specific timing arrangement according to this 
invention is shown in the drawing as employed as an adjunct to a 
single-wall magnetic domain apparatus 10, which apparatus may typically 
comprise, for example, a well-known minor-major loop memory. The output of 
apparatus 10 conventionally comprises a detector array 11 in turn 
comprising a plurality of Permalloy chevron elements 12 arranged to expand 
single-wall domains as they appear during a readout operation. As finally 
expanded, a domain appears in a chevron detector 13 where an output signal 
is magnetoresistively generated thereby all in a manner well-known in the 
art. The Permalloy elements of detector array 11 and final detector 13 are 
assumed to be affixed to a thin film layer also known, in which 
single-wall domains can be created and propagated, which layer is not 
shown in the drawing as not being essential to a complete understanding of 
the invention. 
The propagation of magnetic domains from point to point within the magnetic 
media of apparatus 10 and its output section is conventionally 
accomplished by an in-plane rotating field generated by a field source 14. 
Source 14 is shown in block symbol form only, the details thereof being 
readily envisioned by one skilled in the art. Typically, a rotating field 
is generated by causing two nominally sinusoidal currents to pass through 
two coils with perpendicular axes which enclose the magnetic media of the 
domain apparatus. The frequency of the rotating field is controlled by 
periodic clock pulses generated by a system clock pulse source 15 
transmitted to field source 14 via conductor 16. These periodic clock 
pulses are conventionally generated by counting the occurrence of a 
predetermined number of output pulses of a higher frequency oscillator. 
Returning to the output section of domain apparatus 10, the output of 
detector 13 is seen as being applied to a first filter circuit, rotating 
field frequency filter 17, the output of which filter is in turn applied 
at two subsequent stage circuits. A first stage comprises a second 
harmonic of the rotating field frequency filter 18 and the second is a 
second harmonic phase detector 19. For reasons which will appear 
hereinafter, filters 17 and 18 are functionally interposed between output 
detector 13 and a conventional integrator circuit 20 which in a manner 
well-known in the art is employed to integrate significant output signals 
generated by domains appearing at detector 13. 
At the second harmonic phase detector 19, an output is applied to a 
reference time register 21, which register serves simply to count output 
pulses of the previously mentioned high frequency oscillator occurring 
between clock pulses received from clock pulse source 15 and phase 
detector 19. Time interval data is applied from the output of register 21 
to a fixed time delay generator 22, the outputs of which serve both to 
reset integrator 20 and to act as an output strobe for strobing output 
signals due to domains read out of domain apparatus 10. The strobing 
operation is accomplished by an output comparator 23 to which both the 
strobe output of delay generator 22 and the signal output from integrator 
20 are applied. Finally, a logic level output indicative of a binary "1" 
or "0" is applied to utilization circuits 24 which may comprise any data 
processing circuits requiring the binary information to be read out of 
domain apparatus 10. The operation of the domain apparatus 10 is 
controlled by control circuit 25 via a conductor 26 and also controls the 
rotation of the in-plane rotating field through clock pulse source 15. 
Thus, control circuit 25 controls the time of read out of apparatus 10 and 
determines when the time interval data of register 21 is applied to delay 
generator 22. The circuits referred to in the foregoing are shown in block 
symbol form only, their details being readily envisioned by one skilled in 
the art considering the functions to be ascribed thereto hereinafter. 
Indeed, circuits and devices 14, 15, 20, 23, and 25 are assumed as being 
already present in connection with domain apparatus 10 with which the 
timing arrangement of this invention may be associated. Accordingly, these 
circuits need not be described other than to consider their functions for 
a complete understanding of this invention. 
With the foregoing organization of a timing arrangement according to this 
invention in mind, illustrative operations thereof may now be considered. 
Once a decision originating at control circuits 25 to read the contents of 
a particular address of domain apparatus 10 is made, the stored data is 
transferred or replicated onto a path leading to detector array 11 and 
output detector 13. The delay time required for a domain to appear at 
detector 13, which may typically comprise 50 propagation cycles of the 
rotating field, is advantageously employed in accordance with this 
invention, to determine the precise time at which an information signal 
may be expected at comparator 23 and hence when the strobe operation must 
be accomplished. During this delay time and at nonreadout times, a number 
of noninformation significant voltages appear at output detector 13. A 
first such voltage is generated by electromagnetic coupling from the 
continuously rotating field coil structure. The same rotating field 
interacts with detector 13 to generate the second harmonic voltage. 
Finally, the output of detector 13 includes random noise voltages 
generated, for example, by the manipulation of domains in domain apparatus 
10. 
As the foregoing voltages appear at detector 13 output, the voltages 
generated by the rotating field coupling at its fundamental frequency are 
suppressed by filter 17 which filter permits the voltages at the second 
harmonic frequency of the rotating field and the ramdom noise voltages to 
pass. Filter 18 is next provided to suppress the former voltages at the 
second harmonic frequency and prevents the latter voltages from obscuring 
any significant domain generated signals during readout. The output of 
filter 17, that is, the voltages generated by the coupling of the rotating 
field at the second harmonic of its fundamental frequency, is also applied 
to second harmonic detector 19. At this point the zero crossings of the 
second harmonic voltages are detected and signals indicative of the fact 
and times of the crossings are generated and are applied from the output 
of detector 19 to the input of reference time register 21. 
Time register 21 is adapted to count time intervals between each periodic 
clock pulse from source 15 and the arrival of a phase input from detector 
19 and operates under the control of the system control circuits 25. Under 
this control, register 21 retains its time data until such time as a 
decision to read data from domain apparatus 10 is made; at that time the 
time data is transmitted to time delay generator 22. At the latter stage, 
data representing an additional, fixed delay as determined by the geometry 
of the particular magnetic media of apparatus 10 is added to the time data 
to control the generation of an output strobe signal. The latter signal is 
applied under the control of a clock pulse from source 15 to both 
integrator 20 and output comparator 23. At the former stage, a domain 
generated signal (if one is present) is integrated and its output voltage 
level (which may be representative of a binary "1") is transmitted to 
comparator 23. The latter circuit which may conventionally comprise a high 
gain amplifier, conventionally operates under the control of an enabling 
strobe pulse from generator 22 to distinguish between voltage levels 
received from integrator 20 to generate a "1" or "0" output signal as 
determined by those levels. 
Advantageously, and in accordance with one feature of a timing arrangement 
of this invention, the same factors, that is, rotating field phase angle 
variations and propagation delays characteristic of magnetic apparatus 
geometries, which control the arrival times of domain generated signals at 
the output comparator, also control the timing of the output enabling 
strobe pulse. As a result, the concurrence of an information signal and 
its strobing at comparator 23, and hence the reliability of readout is 
assured. Information representative signals generated at comparator 23 are 
transmitted to utilization circuits 24 which may comprise any circuits of 
a data processing system with which the timing arrangement of this 
invention may be adapted for use requiring the information provided by 
magnetic domain apparatus 10. 
What has been described is considered to be only one specific illustrative 
timing arrangement according to the principles of this invention and it is 
to be understood that various and numerous other arrangements may be 
devised by one skilled in the art without departing from the spirit and 
scope thereof as defined by the accompanying claims.