Output signal detectors of magnetic bubble memory devices

In a detector of an magnetic bubble memory device of the type comprising a magnetic bubble memory element having a detector, a source of constant current for passing constant current through the detector for producing a bubble output signal according to the magnetoresistive effect of a detector, a preamplifier for amplifying the output signal, a DC regenerator for regenerating an output signal of the preamplifier and a discriminator for converting the DC regenerated signal into a binary code, there is provided a holding circuit connected between the DC regenerator and the discriminator for holding a peak value of the DC regenerated signal for a predetermined time.

BACKGROUND OF THE INVENTION 
This invention relates to an output signal detector of a magnetic memory 
device capable of gaining a sufficient margin of the logical conversion 
for one bubble output signal. 
In a magnetic bubble memory device, magnetic bubbles are generated in a 
magnetic bubble memory element made up of a thin magnetic film so as to 
store information according to the presence or absence of the magnetic 
bubbles. The detection of the magnetic bubbles, that is, the bubble output 
is made by applying a rotating magnetic field to the magnetic bubble 
memory element to move the magnetic bubbles along a propagation pattern, 
causing the magnetic bubbles to pass by a detector provided at a portion 
of the magnetic bubble memory element, causing the resistance value of the 
detector to vary, and detecting such a resistance variation. 
FIG. 1 shows one example of a conventional output signal detector of a 
magnetic bubble memory element 1 comprising a magnetic film. A detector 2a 
is provided along a propagation path, not shown, of the magnetic memory 
element and a dummy detector 2b is provided at a portion of the magnetic 
bubble memory element 1, one end of the respective detectors 2a and 2b 
being grounded. Constant current sources 3a and 3b are provided for 
passing constant currents for detection of the resistance variations of 
both the detectors 2a and 2b. There are also provided a preamplifier 4 for 
amplifying a variation in the potential across the detectors 2a and 2b 
corresponding to the variation in the resistance values of the detectors 
2a and 2b, a DC regenerating circuit 5 which, in response to an external 
DC regeneration control signal W.sub.ST, DC regenerates a bubble detection 
signal variation from an amplified potential variation, and a 
discriminator 6 which, in response to an external strobe pulse N.sub.ST, 
converts a DC regenerated signal into a "1" or "0" logical signal. 
In the magnetic bubble detector having a construction as described above, 
the bubble output signal superimposed on a noise waveform N as shown in 
FIG. 2 is detected and converted into a logical output signal. In this 
case, one bubble output signal tends to undergo phase shifts due to the 
variation in the intensity of the rotating magnetic field, a minute change 
in the magnetic body utilized as the detector, and variation in the 
manufacturing steps, resulting in a waveform S.sub.1, S.sub.2 or S.sub.3 
as shown in FIG. 2. Therefore, the bubble output signal detection must 
cover any one of the waveforms S.sub.1, S.sub.2 and S.sub.3 in order to 
prevent failure of detection of one bubble output signal. Thus, a DC 
regeneration control signal W.sub.ST as shown in FIG. 2 is externally 
applied which has a sufficient duration for DC regeneration of any one of 
the bubble output signal waveforms S.sub.1, S.sub.2 and S.sub.3. In 
synchronism with the control signal W.sub.ST, the waveforms N, S.sub.1, 
S.sub.2 and S.sub.3 are DC regenerated to produce corresponding waveforms 
N', S.sub.1 ', S.sub.2 ' and S.sub.3 ' as well known in the art. At the 
same time, a threshold level Vth is set which is about half the level 
difference between a maximum and a minimum (a positive peak of the 
waveform S.sub.3 ' and a negative peak of the waveform S.sub.2 ' in this 
example). In the discriminator 6, within the duration of a strobe signal 
N.sub.ST, portions of the DC regenerated waveforms S.sub.1 ', S.sub.2 ' 
and S.sub.3 ' falling below the threshold level Vth are converted into 
logical signals of high level S.sub.10, S.sub.20 and S.sub.30 as shown in 
FIG. 2. Obviously, the margin of the logical conversion is small for the 
DC regenerated waveform S.sub.3 ', and the logical high level signal 
S.sub.30 has the smallest duration of the three signals and is critical 
because if the bubble output signal S.sub.3 shifts slightly to the right 
in the drawing, the high level signal S.sub.30 will disappear, resulting 
in failure to detect one bubble output signal represented by the waveform 
S.sub.3. Of course, prolongation of the duration of the control signal 
W.sub.ST is not a practical solution to this problem in view of the 
resolution of the bubble output signal detection. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of this invention to provide an improved 
output detector of a magnetic bubble memory device capable of gaining a 
sufficient margin of the logical conversion for one bubble output signal 
without degrading the resolution of the bubble output signal detection. 
According to this invention, there is provided a detector of a magnetic 
bubble memory device of the type comprising a magnetic bubble memory 
element having a detector, means for passing constant current through the 
detector so as to produce a bubble output signal according to the 
magnetoresistive effect of the detector, a preamplifier for amplifying the 
output signal, circuit means for DC regenerating an output signal of the 
preamplifier and a discriminator for converting the DC regenerated signal 
into a logical signal, characterized by a holding circuit connected 
between the preamplifier and the discriminator for holding a peak value of 
the DC regenerated signal for a predetermined time.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In FIG. 3 showing a preferred embodiment of this invention, circuit 
elements corresponding to those shown in FIG. 1 are designated by the same 
reference numerals. As shown, an amplifier 7 is connected to the output 
terminals of a DC regenerating circuit 5 for decreasing common mode noise 
at the time of the DC regeneration, and to the output terminal of the 
amplifier 7 is connected a peak value holding circuit 8 which holds for a 
definite time the maximum value of the DC regenerated output wave from the 
amplifier 7. The peak value holding circuit 8 is constituted by an emitter 
follower circuit 8a which effects a current amplification of the output of 
the amplifier 7 at a high fidelty, a peak holding circuit 8b for holding 
the peak value of the DC regenerated waveform for a definite time, a bias 
circuit 8c for applying a predetermined bias voltage to the emitter 
follower circuit 8a and the peak holding circuit 8b, and a releasing 
circuit 8d which releases the peak holding circuit 8b after a definite 
time. The time constant of the peak holding circuit 8b, determined by a 
resistor R and a capacitor C, is selected such that it maintains the same 
potential between positive and negative peaks of the bubble output signal, 
that is between 500 ns and 1 (one) microsecond when the frequency of the 
rotating magnetic field is 100 KHz. The descriminating circuit 6 is 
connected to the output of the peak voltage holding circuit 8. Thus, the 
output terminal of the emitter follower circuit 8a is connected to one 
input terminal 6a of the descriminating circuit 6, while the output 
terminal of the peak holding circuit 8b is connected to the other input 
terminal 6b of the descriminating circuit 6. 
In operation, as in the previous example, bubble output signal waveform 
S.sub.1, S.sub.2 or S.sub.3 superimposed on a noise waveform N is DC 
regenerated at the DC regenerating circuit 5 within a duration of a DC 
regeneration control signal W.sub.ST. A corresponding DC regenerated 
signal N.sub.1 ', S.sub.1 ', S.sub.2 ' or S.sub.3 ' is obtained as shown 
in FIG. 4. In contrast to the prior art detector previously described with 
reference to FIGS. 1 and 2, this embodiment comprised of the peak value 
holding circuit 8 holds a positive peak of the DC regenerated waveform 
N.sub.1 ', S.sub.1 ', S.sub.2 ' or S.sub.3 ' to provide a holding level 
N.sub.0 ', S.sub.10 ', S.sub.20 ' or S.sub.30 ' for the predetermined 
time. In the discriminating circuit 6, for the DC regenerated waveform 
S.sub.1 ', a threshold level V.sub.th1 is set which is about half the 
level difference between the holding level S.sub.10 ' and a negative peak 
of S.sub.1 '; for the DC regenerated waveform S.sub.2 ', a threshold level 
V.sub.th2 is set which is about half the level difference between the 
holding level S.sub.20 ' and a negative peak of S.sub.2 '; and for the DC 
regenerated waveform S.sub.3 ', a threshold level V.sub.th3 is set which 
is about half the level difference between the holding level S.sub.30 ' 
and a negative peak of S.sub.3 '. Now, within a duration of a strobe 
signal NsT applied to the discriminating circuit 6, a portion of the DC 
regenerated waveform S.sub.1 ', S.sub.2 ' or S.sub.3 ' falling below the 
threshold level V.sub.th1, V.sub.th2 or V.sub.th3 is converted into a 
logical signal of high level S.sub.10, S.sub.20 or S.sub.30. Since, in 
this embodiment, a sufficient margin of the logical conversion for one 
bubble output signal is obtained, the duration of the logical high level 
signal S.sub.10, S.sub.20 or S.sub.30 is relatively uniform and sufficient 
for prevention of failure of the bubble output signal detection.