- Project Runeberg -  Elteknik : Tidskrift för elektrisk kraftteknik, teleteknik och elektronik / Årgång 2. 1959 /
100

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Full resolution (JPEG) - On this page / på denna sida - A Method of Storing Binary Information in Ferrite Memory Cores Facilitating Non-Destructive Read-Out, by Alvar Olsson

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Fig. 2. 1-signal and O-siynal versus read-out current for
General Ceramics’ memory core F-39A, material
S-5. Read-out current has a rise time of 0.2 /us
and a duration of 10 jus. 1-signal measured on a
reference core with a low 1-signal (high
coerci-tivity). O-signal measured on a reference core with
a high O-signal (low coercitivity).

Fig. 3. The shape of 1-signals and O-signals. Current rise
time about 0.2 us. All pictures 0.5 jusldiv, signals
5 mV/div.

tion of a current pulse of sufficient amplitude and
duration. They were demagnetized to 1 with a
damped sinusoidal current-wave. For read-out use
was made of rectangular current pulses. A negative
pulse followed by a positive pulse of the same
amplitude and duration is used as a pulse cycle. The
induced voltage in one turn around the core was
measured, when the core was set to the remanent
state, O-signal, and when it was set to the
demagnetized state, 1-signal.

Fig. 2 shows the peak value of the 1- and O-signals
as functions of the read-out current for a General
Ceramics’ memory core, size F-394, i.e. 2 mm
outside diameter. Material S-5 was found to be the most
suitable for this application.

The shape of the signals at three different values
of the read-out current is seen in fig. 3. The peak
value of signals is obtained during the rise time and
is dependent on the reversible permeability. The
irreversible domain wall movement gives the
1-signals a certain width, which, at higher currents
is limited by the length of the read-out pulses. It is

obvious from fig. 3 that the minor loops used at
higher currents arc much larger than the loops used
at smaller currents.

Figs. 2 and 3 are based on a rise time of 0.2 |is.
The duration of read-out pulses is 10 (.is in fig. 2
and 0.5 us in fig. 3. The amplitude of the 1-signal is,
however, not affected by the duration of the
readout pulses. This is important with regard to speed
since the duration of the read-out pulses may be
chosen without having to take the switching time
of the core material into account. A very short
cycle time may therefore be used even with
materials having a low coercitivity. In contradistinction
to conventional core memories, this means that
a rapid memory can be obtained with low pulse
currents so that transistor drive circuits may easily
be used. Thus 2 mm cores of General Ceramics’ low
coercitivity material MF-3876 permit about 100 mA
read-out current.

In the 0-signal curve, a knee is obtained, which
determines the magnitude that the read-out current
may have without the core being driven out of the
remanent state. The position of the knee depends
upon the magnitude of the current pulse, Is, which
has driven the core to the remanent state as also
could be seen from the hysteresis loop family in
fig. 1. With shorter pulses the knee in the 0-signal
curve comes up considerably, a phenomenon already
known3.

With the long pulses used in fig. 2 almost "static"
conditions are achieved. This means that, provided
the read-out current is below the knee in the
0-signal curve, the information is not destroyed even
if either of the read-out pulses is missing.

The symmetry between the positive and the
negative component of the read-out pulse is not critical.
When magnitude of read-out current is mentioned,
that component tending to drive a core in 0-state
out of its remanent state, is meant. The opposite
component of the read-out current may of course
be considerably higher, resulting in the use of an
unsymmetrical minor loop.

The memory and the writing procedure

The proposed method is best suited for matrix
systems with direct word selection (sometimes also
called linear selection systems or word-organized
memories, fig. 4). The problem involved in the
proposed method is then chiefly the writing into the
memory which must take place with coinciding
currents in row and column.

Several methods for writing have been tested. The
one found to give the best margins in drive currents
and signals uses the damped sinusoidal wave for
writing of 1 and is based on the fact that a memory
with non-destructive read-out usually permits a slow
writing procedure. It may, for example, be arranged
in the following manner.

First the entire word is erased with a high
saturating current pulse, Is, on the row. Since there are no
coincidence conditions in this process, Is may be
of arbitrary amplitude and cores that are to store
0 can get the knee in their 0-signal curve at as high
a current as possible.

In order to write 1 in certain cores of the word
the row is continously pulsed with read-out current

.100 ELTEKNIK 1959

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