JP2823664B2 - High density magnetic recording method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Industrial Application Field) The present invention relates to a magnetic layer used for a card-shaped recording medium such as a prepaid card, a credit card, and other magnetic recording media. And a high-density magnetic recording method capable of magnetically recording information at a high density.

(Prior Art) Conventionally, information is recorded on a magnetic layer of a card-shaped recording medium by:
Although binary recording is performed using the two states A and B shown in FIG. 16, recording is generally performed by a method called F-2F. That is, as shown in FIG. 15, when a frequency twice as high as the frequency for recording “0” is used, “1” is recorded, and the clock signal is automatically generated based on the width of the data signal. It is created at the time of reading (self-clock), and returns to the original binary value according to this clock. In this method, it is not necessary to provide a track for the timing signal separately from the data track. However, in order to record a binary value of “0” or “1”, a length twice as long as the minimum magnetization reversal length required is required. Need and
Recording density is low. In this case, the recording density is 2 ⁿ (the index n represents the number of digits per fixed length of the recording medium).

On the other hand, if a timing track is separately provided, recording can be performed with half the length of the F-2F system, but even in this case, recording itself can be performed only in two values using two states, and furthermore, the timing track ( Extra track).

(Problems to be Solved by the Invention) However, recently, the amount of information recorded on a card-shaped recording medium has been increasing greatly, and there is a strong demand for higher density and higher security of magnetic recording.

For a card-shaped recording medium having a magnetic layer, it is more secure to perform falsification by performing multi-level recording than to perform binary recording, and security is improved. However, multi-level recording is performed for one type of magnetic material. Although it is theoretically possible to do it, it is almost impossible as a practical matter. This is because, when recording information, it is difficult to keep the degree of contact on the contact surface between the magnetic head and the magnetic layer completely uniform due to limitations in mechanical and processing accuracy. Maintaining the current with high accuracy has a problem in cost, so in the case of a magnetic layer composed of one type of magnetic material,
As shown in FIG. 16, even if a change ΔH in magnetizing force, which is a deviation of the magnetic field at the time of recording, cannot be avoided to some extent, this deviation of ΔH results in a large deviation such as ΔΦ in the residual magnetic flux Φ. Regarding the magnetic hysteresis curve C indicated by the various types of magnetic materials, even if an attempt is made to record multi-values (hereinafter, multi-value refers to three or more values) using multi-states of three or more states as the residual magnetic flux, the residual magnetic flux is accurately detected. This is because unreasonable multi-value recording that cannot be held only impairs the stability of reading. For this reason, multi-value recording is considered to be virtually impossible. However, at present, binary recording using two states is used while leaving problems in recording density and security.

Therefore, the magnetic layer of the card-shaped recording medium is made into two layers, and two magnetic layers are constituted by magnetic materials having different coercive forces, respectively.
There is one that can record on each layer. But,
Information recording of each layer is limited to binary recording in two states, and true recording of one magnetic layer and false recording of the other magnetic layer are performed. This is because false recording is performed on the low coercivity magnetic layer, so that a true recording can be read by applying a bias magnetic field to the magnetic head, for example, to erase the recording on the low coercivity layer. Still, it leaves a problem in terms of security.

The present invention has been made in view of the above circumstances,
SUMMARY OF THE INVENTION It is an object of the present invention to enable multi-value recording using magnetic layers composed of various kinds of magnetic materials having different coercive forces, and perform high-density magnetic recording with high security by performing writing by a special modulation method. An object of the present invention is to provide a high-density magnetic recording method which enables the method.

Means for Solving the Problems The present invention relates to a high-density magnetic recording method, and an object of the present invention is to provide m types (m is a natural number of 2 or more) of magnetic materials having different coercive forces. The residual magnetic flux can be in the (m + 1) state by using one mixed magnetic layer, and the residual magnetic flux in the write area of the magnetic layer is previously set to the lowest or highest state in the (m + 1) state. This is achieved by recording binary data as m-valued multi-valued data according to a predetermined algorithm when recording data. In addition, m types (m
Data is synchronized with the timing signal to a magnetic recording medium having a magnetic layer made of a magnetic material of 2 or more natural numbers) and a timing track on which a timing signal for reading magnetic recording is recorded. This is achieved by recording as a multi-value of the (m + 1) value.

(Function) In the present invention, in order to enable multi-value recording of information at a high density, the magnetic layer is composed of at least two kinds of magnetic materials having different coercive forces from each other, and reading of magnetic recording is performed as necessary. A timing track on which a timing signal is recorded is provided, and data is binary- or multi-valued recorded on the magnetic layer in a self-clocking manner or in synchronization with the timing signal. This is because the magnetic properties of a single magnetic material have two states of residual magnetic flux in the magnetic hysteresis curve, while the magnetic layers having different coercive forces are mixed (or provided) to form a magnetic layer. This is because multi-state magnetic flux can be obtained. Note that the larger the difference in coercive force between magnetic materials, the easier multi-value recording is, but a difference of about three times or more is sufficient.

(Embodiment) The magnetic layer used in the present invention is not formed of one kind of magnetic material, but is formed by mixing or forming two or more magnetic materials having different coercive forces from each other. First
The figure shows the magnetic hysteresis characteristics of this magnetic layer.
From the magnetization characteristics given by the magnetic flux Φ with respect to the magnetization force H,
Magnetizing force H _d or H residual flux maximum or smallest when _a D1
Or not only two values of the positive and negative D3, the residual magnetic flux D2 appears by magnetizing force H _b or H _c. H _b or H _c has a width of low coercive force portion saturation magnetic field more [Delta] H. The residual magnetic flux has three states in total. FIG. 2 shows an example of the magnetic characteristics of the magnetic material of the magnetic layer. The magnetic characteristics are shown by the relationship between the magnetic force H and the magnetic susceptibility x. In this example, the magnetic material A has a larger coercive force than the magnetic material B. By adjusting the current of the write head from the magnetization characteristics shown in FIG. 5 by about 5 times, multi-valued residual magnetic fluxes D1 to D3 can be recorded, for example, as shown in FIG.
The magnetic layer can also be formed by laminating (multilayering) magnetic materials in addition to mixing and forming a plurality of magnetic materials.

By the way, when a magnetic layer is formed by using magnetic materials having different coercive forces, a magnetic hysteresis curve showing its magnetization characteristics usually shows a residual magnetic flux in a 2m state for m kinds of magnetic materials. That is, in the case of the two magnetic body mixed generated magnetic layer, a residual magnetic flux D1 or D4 corresponding to the magnetizing force H _d or H _a as shown in FIG. 3, corresponds to the magnetizing force H _c or H _b There are four statistical states with the residual magnetic flux D2 or D3, but from a practical point of view, it is desirable to use only the residual magnetic flux in the (m + 1) state. For example, residual flux D3 (Fig. 1) or D4
(FIG. 3) is assumed to be an initial state, and (m) in FIG.
+1) state and the 2m state in FIG. 3, (m +
1) is in a state to record the residual magnetic flux D2 (FIG. 1) is multiplied by the magnetic field of the magnetizing force H _c, in order to record the residual magnetic flux D1 (FIG. 1) is multiplied by the magnetic field of the magnetizing force H _d It is sufficient to remove each magnetic field, but in the 2m state, for example, the residual magnetic flux D3 (third
Figure) When recording, thus once subsequently after applying a magnetic field of force H _d over the magnetic field of the magnetizing force H _b, then must be to remove the magnetic field, in logging method laborious Because. Therefore, it is better not to use the D3 state when using the characteristics as shown in FIG. Further, in the case where the magnetic layer is formed by mixing or layering with three kinds of magnetic materials, it suffices to configure so that residual magnetic fluxes in four states (# 1 to # 4) can be obtained as shown in FIG. .

To the magnetic layer configured as described above, by adjusting the magnetic head in the initial state, deprived of the magnetic field after applying a magnetic field of force H _a on a magnetic hysteresis curve shown in FIG. 1, the residual leave the state of the magnetic flux D3, obtain residual magnetic flux D2 or D1 respectively over magnetizing force H _c or H _d in recording. Also in the case of rewriting, after reading the three-state information, it is sufficient to initialize by applying _a magnetic field of the magnetizing force Ha and then apply _a magnetic field according to the hysteresis curve. In the above description, the residual magnetic flux in the initial state is the lowest state among the (m + 1) states, that is, D3, but D1 in the highest state may be the initial state.

The reading of such ternary information is performed by self-clocking F-2F.
In the case where the method is performed by the method, a description will be given with reference to a time chart shown in FIG. 5, assuming that the residual magnetic flux D3 shown in FIG. First, a recording medium provided with the above-mentioned magnetic layer is conveyed at a constant speed to obtain a dΦ / dt signal as shown in FIG. 2A by a magnetic head, and the signal is supplied according to a self-clock.
By reproducing the dΦ / dt signal as shown in FIG. 3, reproduction information is obtained in three values of “0”, “1”, and “2” as shown in FIG. That is, 1
"0" if there is no inversion in the bit, "1" if there is a half-level inversion (D1D2 or D2D3) in one bit, "2" if there is an inversion of all levels (D1D3) in one bit ". The recording density of the F-2F 3 value recording scheme is 3 ^n. When recording information in three values, an input signal to the magnetic head may be given in the reverse process of the above (B) and (C).

As a recording method for further increasing the density, when the integrated signal corresponding to (B) in FIG. 5 is as shown in FIG. 6, D3 and D2 immediately after D3 are set to binary “0”. , D1 and
If D2 immediately after D1 is binary "1", the self-clocking method
2F-2 value recording is possible. In this method, magnetic flux reversal is not required within one bit, and recording of one bit per minimum magnetization reversal length is possible. Therefore, higher density recording is possible than in the F-2F method.

FIG. 7 shows an example of a block diagram of the recording / reproducing circuit, in which the writing head 2 and the reading head 3 are provided so as to contact the card 1 having the above-mentioned magnetic layer. The write data WS and the write clock CL1 are modulated by the modulator 11 via the parallel / serial conversion circuit 10 as described later, and the write data are modulated on the magnetic layer of the card 1 by the write head 2 via the amplifier 12. WS is recorded. The data recorded on the magnetic layer is read by the read head 3 and the amplifier
The playback signal RA amplified by 25 is a peak position level detection circuit
The differential signal RB differentiated by the differentiating circuit 23 is input to the differential signal 23, and the zero-cross detecting circuit 24 detects the zero-cross. The detected zero-cross signal ZC is input to the peak position level detecting circuit 22. Peak position level detection circuit 22
The output PS is compared with a predetermined threshold value by the comparator 21, and the output CS (2F signal) is input to the demodulator 20 and output as the read data RS and the clock CL2.

The operation will be described with reference to time charts of FIGS. 8 (A) to (J). The write data WS has the timing shown in FIG. 8A, and the write clock shown in FIG.
Input to the parallel / serial conversion circuit 10 together with GL1,
The write data and clock converted into a serial signal are input to modulator 11. The operation of the modulator 11 is as shown in FIG. 9. First, it is determined whether the write data WS synchronized with the write clock CL1 is “0” or “1” (Step S1).
In the case of “0”, the first “0” or the immediately preceding data is “1”
Is determined (step S2). If the determination is YES, the input signal is set to low level (step S3). If the determination in step S2 is NO, it is determined whether or not the continuous "0" is an even-numbered "0" (step S4). If it is an even number, it is set to a middle level (step S5), and if it is an odd number, it is set to a low level (step S3). Also, the above steps
When it is determined to be "1" in S1, it is determined whether the first data is "1" or the immediately preceding data is "0" (step S6), and YES
If so, the level is set to the high level (step S8). If NO is determined in step S6, it is determined whether or not this continuous “1” is an even-numbered “1” (step S7). If the number is even, the middle level is set (step S5). Is high level (step S8). Thereafter, it is determined whether or not the data length has reached a predetermined value (step S9). If the data length has not reached the predetermined length, the process returns to step S1, and if the data length has reached, the operation ends.

The three-state (low, middle, high) modulated signal DM as shown in FIG. 8C modulated by the modulator 11 as described above is
The data is written into the magnetic layer of the card 1 by the write head 2 via the amplifier 12. The write current of the write head 2 is as shown in FIG. The low level is the write current 0, and the write current increases as the level becomes middle or high. The magnetic layer is magnetized in advance to “D3”. The data written in the magnetic layer is thereafter read by the read head 3, and the reproduced signal RA shown in FIG. 8 (E) amplified by the amplifier 25 is input to the peak position level detection circuit 22 and the differentiation circuit 23, and is differentiated. Circuit 23
The differential signal RB differentiated by is as shown in FIG. 8 (F).
Then, if the position where the zero crossing of the differential signal RB is detected, the peak position of the reproduction signal RA can be detected.
Therefore, the differential signal RB is input to the zero-cross detection circuit 24 to detect the zero-cross, and the detected zero-cross signal ZC is input to the peak position level detection circuit 22. In addition, although the circle portion in FIG. 8E has a zero cross in the differential signal RB in FIG. 8F, it is determined that this is not the peak position of the reproduction signal RA. This is indicated by a cross in FIG. 8 (G). The peak signal PS as shown in FIG. 8 (G) output from the peak position level detection circuit 22 is input to the comparator 21 and is compared with predetermined thresholds L1 and L3. The comparison by the comparator 21 is performed based on whether or not the value of the reproduced signal RA in the zero-cross portion (the value of the waveform is sampled and stored) exceeds the predetermined thresholds L1 and L3 in absolute value. At the same time, depending on whether it is above or below the intermediate threshold value L2 ', L2 ". In this case, an upward peak halfway between the threshold value L2" and the 0 level, and the threshold value L2' and the 0 level The middle downward peak is removed. That is, the judgment is made based on the relationship between the polarity of the peak and the threshold values L2 ', L2 ". The comparator 21 outputs a total of four types of a large positive peak, a small positive peak, a small negative peak, and a large negative peak. A signal CS as shown in Fig. 8 (H) obtained by integrating the peak signal PS composed of the peaks by hardware or software is output, and this signal CS is input to the demodulator 20. The demodulator 20 outputs D3. And D2 immediately after D3 is 2
The value “0” is set, D1 and D2 immediately after D1 are set to the binary “1”, and the eighth
The read data RS shown in FIG. 7J and the clock CL2 shown in FIG. Further, the differential signal RB does not necessarily need to be obtained, and a peak search is performed from the reproduction signal RA by some other method, and the peak height and the threshold values L1, L2 ′, L
The peak signal PS may be obtained by distinguishing four types of peaks by 2 ″ and L3. Further, the writing head and the reading head can be shared by one head. This realizes 2F-2 value recording / reproduction, and the recording density in this case is 2 ²ⁿ = 4 ⁿ because the magnetization reversal within one bit is unnecessary, which is higher than that in FIG. .

Using the magnetic layer composed of the two types of magnetic materials and the timing signal TS from the timing track as described above,
As shown in the figure, for example, D3 is ternary “0”, D2 is ternary “1”, D1
Corresponds to the ternary "2", and ternary recording can be performed. Recording density in this case is 3 ²ⁿ = 9 ^n.

Then, by mixing or laminating the three magnetic obtain a magnetization characteristic shown in FIG. 11, the residual magnetic flux _{-M F, -M H, + M} H, recording 2F-3 values when taking + M _F Will be described. Recording format of this case is as shown in FIG. 12, + M _F 3 value immediately after the -M _F and _{-M F "0", - +} M F immediately following M _H and -M _H 3 the value "1", + + M _F immediately following M _H and + M _H is a ternary "2", and thereby obtain a recording density of 3 ²ⁿ = 9 ^n. + M in this method
Using the _F as a spare for self clock, the -M _F If you want to express 0, if 0 is followed by several consecutive -
Generating a clock pulse by M _F and + M _F. Also, 1
The -M _H when expressing the a, if one is consecutive -M _H
And + M _F by generating a clock pulse. Here, although the spare self clock is + M _F, it may be set other conditions as spare.

With a timing signal TS from the timing track even for a magnetic layer composed of three kinds of magnetic material in above, -M _F
Four values "0", - the M _H 4 value "1", + M _H 4 value "2", it can be recorded as four values "3" + M _F. In this case, the recording density is 4 ²ⁿ = 16 ⁿ .

Further, FIG. 13, the residual magnetic flux -M _F when mixed with four _{magnetic, -M H, 0, + M} H, shows how the + M _F is obtained, the recording mode of Figure 14 4 0 immediately after the -M _F and -M _F is
The value "0", - 0 4 value immediately after the M _H and -M _H and + M _H "1",
+ 0 4 value immediately after the M _H "2", + M 0 immediately after the _F and + M _F is 4 value "3", and thereby obtain a recording density of 4 ²ⁿ = 16 ^n. Here, 0 is used as a spare for the self-clock, but a state other than 0 may be used as a spare for the self-clock. Using the timing signal from this timing track also 5 value -M _F "0", - the M _H 5 value "1", 0 5 values "2", 5 value + M _H "3", + M _F can quinary recording by corresponding to the 5 values "4", 5 ²ⁿ = 2
A recording density of 5 ⁿ can be obtained.

In the above description, the case where the present invention is applied to a card-shaped recording medium has been described, but it is needless to say that the present invention is not limited to a card-shaped recording medium but can be applied to other general magnetic recording media.

Effects of the Invention As described above, according to the magnetic recording method of the present invention, if m-value recording is performed using magnetic layers composed of m kinds of magnetic materials having different coercive forces, the conventional method can be used without providing a timing track. Higher density recording can be performed than in the F-2F system. When a timing track is separately provided, multi-level recording of (m + 1) values can be performed, and high-density magnetic recording can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a magnetic hysteresis curve of the magnetic layer of the present invention, FIG. 2 is a characteristic diagram of the magnetic material, FIG. 3 is a diagram showing a magnetic hysteresis curve of another magnetic layer, FIG.
FIG. 5 is a magnetic hysteresis curve diagram for explaining residual magnetic flux relating to another magnetic layer, FIG. 5 is a time chart for explaining reading of multi-value information from the magnetic layer, and FIG. 6 is an example of an integration signal. FIG. 7 is a block diagram showing an example of a recording / reproducing apparatus, FIG. 8 is a flowchart showing an operation example thereof, FIG. 9 is a flowchart showing an example of modulation operation, and FIG. 11 and 13 are diagrams each showing another magnetization characteristic, FIGS. 12 and 14 are diagrams each showing a recording form thereof, and FIG. 15 is a diagram showing a conventional recording method. FIG. 16 is a diagram for explaining binary recording of F-2F, and FIG. 16 is a general magnetization characteristic diagram. 1 ... Card, 2 ... Write head, 3 ... Read head,
10: Parallel / serial conversion circuit, 11: Modulator, 20
... demodulator, 21 ... comparator, 22 ... peak position level detection circuit, 23 ... differentiation circuit.

Claims (2)

(57) [Claims] 1. A magnetic layer comprising a mixture of m kinds (m is a natural number of 2 or more) of magnetic materials having different coercive forces so that a residual magnetic flux can take a (m + 1) state by using one magnetic layer. The residual magnetic flux in the write area of the layer is set to the lowest or highest state among the (m + 1) states, and the binary data is multiplied by a predetermined algorithm according to a predetermined algorithm at the time of data recording in accordance with the write clock. A high-density magnetic recording method characterized by recording as value data. 2. A magnetic recording medium having m types of magnetic layers (m is a natural number of 2 or more) having different coercive forces and a timing track on which a timing signal for reading magnetic recording is recorded. On the other hand, a high-density magnetic recording method characterized in that data is recorded as multi-valued (m + 1) values in synchronization with the timing signal.