Method and arrangement for the recording and playback of data

For the purpose of increasing storage density of data recorded on a magnetic recording medium, particularly on a magnetic tape, a coder stage is supplied with data signals allocated to the record data and with high-frequency magnetization signals. The coder stage generates write signals which are recorded with the magnetization signals. The pulse duration or the pulse pause of the respectively existing magnetization signal is lengthened given every change of the data signals. The magnetization signals and the data signals are preferably synchronized with one another such that the polarity of the magnetization of the recording medium changes at every change of the data signals. In the playback of the data, the peak values of the magnetization have zero axis crossings of the read output signals allocated to them. At the zero axis crossings, a detector stage generates data signals for a decoding of the recorded data.

BACKGROUND OF THE INVENTION 
The invention relates to a method for recording data on a magnetic 
recording medium wherein data signals output by a data source are coded in 
a coder stage and the coded data signals are supplied to a write amplifier 
which emits write signals to a data head for recording the data on the 
data recording medium. The invention also relates to an arrangement for 
the implementation of the method. 
In recording data on a magnetic recording medium, for example a magnetic 
tape or a magnetic disk, it is already generally known to supply data 
signals allocated to the record data to a coder stage which generates 
coded data signals, and to supply these to a write amplifier. The write 
amplifier generates write-in signals which are usually fashioned as write 
currents which are proportional to the coded data signals. Numerous 
writing methods, for example the NRZI, the MFM, or the GCR writing method 
are available for coding the data signals. 
When the write currents are supplied directly to a write head in the 
magnetic head, the magnetization of the recording medium corresponds to 
the chronological curve of the write currents. This method is generally 
referred to as a direct recording method. The implementation of this 
method is extremely simple, but it exhibits various disadvantages. When no 
premagnetization is employed and the write signal is the only excitation 
of the recording medium, the recording process is nonlinear and the 
recording sensitivity is low. A relatively high write current is required 
in order to magnetize the recording medium up to its saturation, and this 
results in the fact that modulation signals and cross-talk occur to a high 
degree. 
When the recording density is increased, the signal-to-noise ratio is also 
deteriorated and a shift of the rated point in time of the peaks of the 
read signals occurs, this being generally referred to as "bit shift". The 
principal reason for the peak shift lies in the a-symmetry of the 
magnetization of the recording medium, which depends on the appearance of 
the binary characters 0 and 1 in the data signals. This results from the 
fact that the recording medium is magnetized up to its saturation in both 
directions, and the remanence on the recording medium is a function of the 
spacing between two successive magnetization changes. The magnetization of 
the recording medium between two magnetization changes is redundant as 
viewed from the standpoint of data storage, and represents a principal 
reason for the peak shift. 
The read output signals have a maximum at that location at which the 
magnetic flux exhibits its greatest positive slope, and have a minimum at 
that location at which the magnetic flux exhibits its greatest negative 
slope. These points are employed in order to recover the data, and it is 
standard to differentiate the read output signals and to teen identify the 
successive zero axis crossings. Consequently, these locations have the 
same degree of peak displacement as is present in the magnetization of the 
recording medium. Every differentiation of the magnetic flux is connected 
with an increase of noise, which means that the signal-to-noise ratio is 
lower than is maximally prescribed by the magnetization. 
German OS No. 32 33 489, corresponding to U.S. Pat. No. 4,547,818, 
incorporated herein by reference, discloses that the write signals can be 
superimposed with high-frequency premagnetization signals and can be 
supplied to the magnetic head. The recording medium is alternately 
magnetized up to its saturation by the pre-magnetization signals having a 
frequency which lies far above the pass band of the read channel. 
As a result of employing pre-magnetization signals, the recording process 
is linearized and a more precise recording thus occurs. The recording 
sensitivity becomes greater, which means that a corresponding 
magnetization can be achieved with a significantly lower write current. 
The advantage is that fewer modulation signals and less cross talk appear 
in the read channel. 
SUMMARY OF THE INVENTION 
An object of the invention is to specify a further method for the recording 
and reproduction of data such that the data can be recorded with a high 
recording density, and wherein a low shift of the rated points in time of 
the peaks of the read output signals will occur. 
In accordance with the invention, the write signals for writing with the 
data head are formed from magnetization signals whose period duration is 
significantly smaller than a shortest spacing between two successive 
changes of binary values of the coded data signals. A duration of the 
respective magnetization signals is lengthened given every change of the 
binary values of the coded data signals. During the playback, the recorded 
data is recovered from zero axis crossings of the read output signals. 
In the method of the invention, magnetization signals, i.e. their pulse 
durations or pulse pauses, are respectively lengthened when the coded data 
signals change their binary values. The magnetization signals remain 
unaltered when the binary values of the coded data signals do not change. 
Differing from the known methods, the magnetization of the recording 
medium itself, and not the change thereof, represents the coded data 
signals. 
The lengthening of the magnetization signals at the points in time of the 
changes of the binary values of the coded data signals preferably occurs 
such that successive, lengthened magnetization signals have opposite 
polarities. 
It proves advantageous when the magnetization signals are synchronized with 
the data signals, and/or when the respective magnetization signals are 
lengthened to a duration which corresponds to n-times the period duration 
of the magnetization signal, whereby n is a whole number. 
In case the data signals are coded such as known from the NRZI or GCR 
methods wherein the binary value of the data signals changes given a 
respective, first binary character and the binary value remains unaltered 
given the second binary character, it is preferable when the duration of 
the respectively existing magnetization signals is lengthened given every 
recording of the first binary value, and the magnetization signal remains 
unaltered given every recording of the second binary value. 
The magnetization signals are preferably high-frequency magnetization 
signals whose frequency lies above the pass band of the read channel, and 
which correspond to the known premagnetization signals. 
For playback of the data recorded on the recording medium, the read output 
signals have zero axis crossings at the locations allocated to the extreme 
values of the magnetization. In order to be able to distinguish these zero 
axis crossings from the zero axis crossings between two magnetizations, it 
is advantageous to integrate the read output signals, and to only evaluate 
them when the integrated read output signals exceed prescribed threshold 
voltages. 
An advantageous arrangement for the implementation of the method contains a 
coder stage which is provided with a converter which generates the write 
signals from the coded data signals and from the periodic magnetization 
signals generated in an oscillator, these write signals being respectively 
lengthened when a change of the coded data signals exists. 
In a preferred embodiment, the converter contains a delay element which 
delays the coded data signals by at least one half a period duration of 
the magnetization signals and which generates a control signal given an 
inequality of the data signals. It also contains a flip-flop which, with 
every change of the magnetization signals, is flipped in one direction 
when it is not inhibited in its respectively flipped position due to the 
control signal. 
The delay element is preferably fashioned as a shift register at whose data 
inputs the coded data signals are adjacent and at whose clock inputs the 
clock pulses allocated to the magnetization signals are adjacent. 
It is favorable for the playback of the data when an integrating element is 
provided, the read output signals being supplied thereto and said 
integrating element always emitting evaluation signals when the 
corresponding integrated read output signals exceed prescribed threshold 
voltages. It is also favorable when a zero-axis crossing detector is 
provided which emits zero axis crossing signals allocated to zero axis 
crossings whenever the evaluation signals are present.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the arrangement shown in FIG. 1, a data source DS emits the binary data 
D to be recorded on a magnetic recording medium T by means of a magnetic 
head H. The data D are represented by the data signal D1, whereby these 
respectively assume a first binary value 1 or a second binary value 0 when 
the binary characters 1 or 0 are to be recorded as data D. 
FIG. 2 shows the data signals D1 belonging to a prescribed sequence of data 
D. The coder stage CD allocates coded data signals D2 to the data signals 
D1, these coded data signals D2 being coded in accordance with an employed 
recording method, for example the NRZI or GCR method. In this case, the 
data signals D2 shown in FIG. 2 always exhibit a change of their binary 
values, for example when binary characters 1 are recorded. The changes of 
the data signals D1 and D2 occur at respective prescribed points in time 
defined by clock pulses C1 or C2. The data signals D2 are present at a 
write amplifier WA which generates the write signals WS in the form of 
write currents which are proportional to the data signals D2. The write 
signals WS are supplied to the write head of a magnetic head H and effect 
a magnetization on the recording medium T, this magnetization being shown 
as magnetization MA in FIG. 2. 
When reading the recording medium T by means of a read head provided in the 
magnetic head H, read output signals RS are generated which have their 
extreme values at the locations of the greatest change of the 
magnetization MA. These read output signals RS are amplified by means of a 
read amplifier RA and are supplied to a detector stage DE as read output 
signals RS1. At the locations of the extreme values of the read output 
signals RS1, this detector stage DE respectively generates data pulses D3 
from which the recorded data are recovered in a decoder stage DC in a way 
known per se. 
As may be derived from FIG. 2, the points in time of the data pulses D3 
differ from the corresponding changes of the binary values of the data 
signals D2. This results because the magnetization MA is not symmetrical 
relative to the zero line, and thus the points of greatest possible slope 
of the magnetization MA and thus the extreme values of the read output 
signals RS or RS1 are shifted. This shift from the rated points in time is 
referred to as peak shift or bit shift B. 
Given the time diagrams shown in FIG. 3, the data signals D2 are not 
generated in accordance with a known recording method, but by use of a 
converter in a coder stage CD which is shown in FIG. 4, and the data 
signals D3 are generated by use of a detector stage DE shown in FIG. 5. 
The converter shown in FIG. 4 contains a shift register formed of two 
flip-flops F1 and F2. The data inputs of the shift register are supplied 
with first coded data signals D21 which, for example, correspond to the 
coded data signals D2 in FIG. 2 in case the coder stage CD codes the data 
signals D1 in accordance with the NRZI or GCR methods. The clock inputs of 
the shift register are supplied with clock pulses C3 which preferably 
represent high-frequency rectangular signals, and which are synchronized 
with the clock pulses C1. The output signals D22 or D23 at the flip-flops 
F1 or F2 of the shift register are supplied to an exclusive-OR element EX 
which emits a control signal S having the binary value 0, given inequality 
of the output signals D22 and D23. The shift register delays the output 
signals D22 and D23 by the period duration of the clock pulses T3 and 
represents a delay element with the assistance of which changes of the 
data signals D21 can be identified. 
The control signals S are present at the J inputs and K inputs of a 
flip-flop F3 which is always flipped by the clock signals C3 when the 
control signal S exhibits the binary value 1. When, however, the control 
signal S exhibits the binary value 0, the flip-flop F3 is inhibited until 
the control signal S again assumes the binary value 1. The second coded 
data signals D2' thus exhibit a curve as shown in FIG. 3. They exhibit 
periodic magnetization signals M which do not change between two changes 
of the data signals D22, and the duration of which is lengthened at every 
change of the data signals D22. The lengthening preferably occurs such 
that the polarity of the data signals D21 changes at every lengthening. As 
long as they are lengthened, the magnetization signals M in the second 
coded data signals D2' correspond, for example, to known pre-magnetization 
signals given a recording of data by use of high-frequency 
pre-magnetization signals. 
When the repetition frequency of the magnetization signals M is selected 
such that it lies outside of the pass band of the write-read channel, the 
recording medium T is only magnetized at the locations at which the 
magnetization signals M are lengthened and which, given the illustrated 
exemplary embodiment, are allocated to the binary character 1. As the 
curve of the magnetization MA in FIG. 3 shows, this occurs only at the 
binary characters 1 and respectively exhibits the value 0 between them. 
When reading the recording data, double pulses which respectively have a 
zero axis crossing at the extreme values of the magnetization MA arise as 
read output signals RS. 
The detector stage DE as shown in FIG. 5 generates zero axis crossing 
pulses ZC at the zero axis crossings of the read output signals RS or of 
the amplified read output signals RS1. The detector stage DE comprises an 
integrating element IN which integrates the read output signals RS1 in 
order to obtain the read output signals RS2. The integrating element IN 
also contains a threshold stage which compares the integrated read output 
signals RS2 to prescribed threshold voltages SW1 and SW2, and which 
generates evaluation signals PEC and NEC given upward or downward 
transgression of these threshold voltages SW1 or SW2. A switching stage SS 
which generates the zero axis crossing pulses ZC emits these to the 
decoder stage DC as data pulses D3 only when the integrated read output 
signals RS2 upwardly or downwardly exceed the corresponding threshold 
voltages SW1 or SW2, and the evaluation signals PEC and NEC appear. In 
this way, it is assured that zero axis crossing pulses ZC which appear 
between the read output signals RS1 as a consequence of disturbances are 
not interpreted as data signals D3. 
For the evaluation of the read output signals RS1, it is also conceivable 
to employ a circuit arrangement which, instead of comparing the integrated 
read output signals RS2 to prescribed threshold voltages, compares the 
read output signals RS1 themselves to prescribed threshold voltages. Such 
a circuit arrangement is known, for example, from German OS No. 33 23 336. 
A lengthening of the magnetization signals M in the coded data signals D2' 
to the factor 2 corresponds to a phase skip of the magnetization signals M 
by l80.degree.. It is also possible to execute the lengthening by some 
other factor. Preferably, however, the magnetization signals M are 
synchronized with the data signals D1 or first coded data signals D21 in 
this case as well. It is also preferable to execute the lengthenings of 
the magnetization signals M such that a differing polarity of the 
magnetization MA alternately appears. 
Although various minor changes and modifications might be proposed by those 
skilled in the art, it will be understood that I wish to include within 
the claims of the patent warranted hereon all such changes and 
modifications as reasonably come within my contribution to the art.