JPH04205903A - Method and device for reproducing signal by magnetoresistance effect type head and recording device using the same - Google Patents

Abstract

PURPOSE:To reduce asymmetry in a regenerative signal waveform and fluctuation of an output due to variations of head characteristics by providing a means for optimizing the magnetizing direction of a magnetoresistance effect film in changing the intensity of a bias magnetic field to be impressed upon the magnetoresistance effect film. CONSTITUTION:The subject device is provided with the means for optimizing the magnetizing direction of the magnetoresistance effect film in changing the intensity of the bias magnetic field to be impressed upon the magnetoresistance effect film. For example, a waveform reproduced by a magnetoresistance effect type head 2 is detected by a waveform asymmetry degree detecting part 4 in an unbalanced ant. between the plus side and minus side of the regenerative signal, and the unbalanced amt. and a reference symmetry degree signal are compared with each other by a comparing part 5 to detect their difference. An output of the comparing part 5 is given to a sense power source 6 for deciding a conductive current value to the magnetoresistance effect film, and a sense current value is varied according to the size of the output of the comparing part 5. By this method, the bias magnetic field is optimized, and asymmetry of the regenerative signal waveform and fluctuation of the reproducing output can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a signal reproducing method and apparatus using a magnetoresistive head exclusively used for reproduction, which is suitably used in a magnetic disk device or a magnetic tape device such as a VTR. Regarding the recording device used.

[Conventional technology]

With the increase in storage capacity of recent magnetic recording devices.

For example, in magnetic disk drives, the track width is becoming approximately several μm. In addition, recording devices have become smaller and have lower peripheral speeds. In this way, the narrowly recorded signal is converted into a high S (
As a magnetic head for detecting signal)/N (noise), a magnetoresistive head is being developed in place of the conventional inductive head. For example, the 13th Japanese Society of Applied Magnetics Academic Lecture Abstracts (1989), p. 228.

A magnetoresistive head has a structure as shown in FIG. 5, for example. The magnetoresistive head shown in the figure is called a shunt bias type head. The magnetoresistive head has a shield film 21 laminated on the upper and lower parts of the substrate. Magnetoresistive effect [I! 19. It is composed of a shunt bias film 20, an electrode 18, and the like.

To increase reproduction output and reduce signal waveform asymmetry in magnetoresistive heads.

A bias magnetic field must be applied to the magnetoresistive film 19. This will be explained using FIG. 6.

FIG. 6 is an output-magnetic field curve of the magnetoresistive film 19. The magnetoresistive head obtains a reproduction output 23 for a signal magnetic field 22 by using the steepest and most linear region of the output-magnetic field curve. For this purpose, a constant bias magnetic field H
It is used by applying b. In the shunt bias type head described above, a bias magnetic field Hb is applied by a magnetic field generated by a current flowing through the shunt bias 1I20.

However, in a shunt bias type head, for example, the shunt current value tends to change due to changes in the film thickness or specific resistance of the shunt bias film 20, and the bias magnetic field Hb also changes. This also applies to heads using other bias methods. For this reason, magnetoresistive heads with large rack widths have conventionally adopted a differential head structure.

FIG. 7 schematically shows a differential magnetoresistive head. One of these systems is a head having three terminals 24, 25, and 26 that divide one track into two. terminal 25
A current is passed from terminals 24 and 26 with the terminals being common. Thereby, bias magnetic fields in mutually opposite directions indicated by arrows can be applied to the magnetoresistive film 19 between the respective terminals. The signal magnetic field is.

Both are applied in the same direction. Therefore, the signals between the nine terminals have opposite phases, and by detecting the difference between the signals E□ and E2 between the terminals, the asymmetry of the signal waveform can be improved. However, as recording density increases and tracks become narrower, it is difficult to construct a head with narrower tracks due to the structure of the differential magnetoresistive head described above, and a new signal processing method is therefore desired. was.

[Problem to be solved by the invention]

As mentioned above, it is difficult to construct a narrow track head with a differential magnetoresistive head due to its structure, and in conventional magnetoresistive heads other than the differential type, it is difficult to set the bias magnetic field appropriately. No consideration was given to conversion. For this reason, the reproduced signal waveform becomes asymmetrical, and errors such as peak shifts occur in the reproduced signal, which tend to occur during signal reproduction. Further, there were also problems such as the playback output being easily fluctuated.

Although it is conceivable to establish a strictly controlled head manufacturing process, there are unavoidable variations in the film thickness and resistivity of the magnetoresistive film in that process, and in practice.

It is extremely difficult to strictly control the head manufacturing process, resulting in a problem of a decrease in product yield or an increase in cost.

An object of the present invention is to provide a signal reproducing system capable of suitably suppressing problems in the prior art described above, such as asymmetry of the reproduced signal waveform of the magnetoresistive head, peak shifts occurring in the reproduced signal, and fluctuations in the reproduced output. The object of the present invention is to provide a method, a device thereof, and an information recording device using the same.

[Means to solve the problem]

In order to solve the above-mentioned problems of the present invention, the magnetoresistive film is designed such that the magnetization direction of the magnetoresistive film is optimized by changing the intensity of the bias magnetic field applied to the magnetoresistive film of the magnetoresistive head. The energizing current value is configured to be variable,
This aims to optimize the bias magnetic field.

That is, in a shunt bias type head.

Changing the value of the current flowing to the magnetoresistive film (sense current) also changes the current value of the shunt bias film at the same time, making it possible to vary the bias magnetic field and optimize it. Become. Further, in a soft bias type head, by changing the sense current value to the magnetoresistive film as described above, the magnetization state of the soft bias film changes and the bias magnetic field can be optimized.

The present invention provides a signal reproducing device that reproduces information recorded on a recording medium using a magnetoresistive head, in which the direction of magnetization of the magnetoresistive film is changed by changing the intensity of a bias magnetic field applied to the magnetoresistive film. 2. For example, a means for detecting the degree of asymmetry of the reproduced signal waveform of a magnetoresistive head, and a means for optimizing the current flowing through the magnetoresistive film in accordance with the degree of asymmetry of the signal waveform. The present invention has means for optimizing the magnetization direction of the magnetoresistive film by changing the strength of the bias magnetic field. The means for detecting the degree of asymmetry of the signal waveform may be a means for detecting a difference between a positive peak value and a negative peak value of the signal waveform.

In addition, in the signal reproducing device using the magnetoresistive head of the present invention, information on the value of current flowing to the magnetoresistive film is
It is also possible to store the information in a read-only semiconductor memory and to optimize the magnetization direction of the magnetoresistive film by changing the strength of the bias magnetic field based on the information on the current value.

In the signal reproducing device using the magnetoresistive head of the present invention, the signal reproducing device is operated at least once to optimize the value of current flowing through the magnetoresistive film before use. A signal of 1 or 0 is recorded on the recording medium, and the difference between the positive peak value and the negative peak value of the signal waveform is detected using the signal, and the current value applied to the magnetoresistive film is controlled to optimize the bias magnetic field. It is possible to make changes. And the signal for optimizing the magnetization direction of the magnetoresistive film by changing the strength of the bias magnetic field.

It is a signal from essential data of a recording medium that is always stored on the recording medium or recorded for reproducing information.

Further, by combining a signal reproducing device using the magnetoresistive head of the present invention and an information recording device, a recording/reproducing device for recording and reproducing information can be constructed.

[Effect]

The following two effects of the present invention will be explained using FIG.

In the figure, a signal recorded on a recording medium 1 is reproduced by a magnetoresistive head 2. The reproduced signal is generally weak and is amplified by the amplifier 3 if necessary.

The output from the amplifier 3 enters a waveform asymmetry detection section 4.

Here, the amount of imbalance between the plus side and the minus side of the reproduced signal is detected. A comparison section 5 compares the unbalance amount with the reference symmetry degree signal.

Detect the difference. The reference symmetry degree signal is a signal corresponding to the degree of asymmetry allowed for driving the device, and the device operates normally if the degree of asymmetry is equal to or less than the reference symmetry degree signal. The output of the comparator 5 is applied to a sense power supply 6 that determines the value of the current flowing to the magnetoresistive film 19 (see FIG. 5), and the sense current value is varied depending on the magnitude of the output of the comparator 5. By the above operation, the noisy magnetic field Hb can be optimized, and asymmetry in the reproduced signal waveform and fluctuation in the reproduced output can be prevented. Note that the above series of operations must be performed before actually reproducing the recorded signal.

〔Example〕

Embodiments of the present invention will be described in more detail below with reference to seven drawings.

(Example 1) This will be explained using FIG. 1. The magnetoresistive head 2 used was a shunt bias type head, and the track width was 5 μm.
It is. As shown in FIG. 5, the magnetoresistive film 19. and the sense current value of the shunt bias film 20 are both 1
It was set to 0mA. First, continuous signals on recording medium 1.0 were recorded with an inductive thin film head. Next, the signal was reproduced using the magnetoresistive head. Such operations were automatically performed using software stored in the signal reproducing device. The degree of asymmetry of the reproduced waveform of this magnetoresistive head at the above sense current value was 30%. Furthermore, what is the degree of asymmetry of the reproduced waveform?

The plus side peak value IP, the minus side peak value, and the end of the reproduced signal.

Asymmetry of reproduced waveform (%) = (Ip I-)/(Ip
+I−)X100. The playback output value of the head used here is 7oμVp-p/μ per unit track width.
It was m. Therefore, tIp=45.5μV, ■
, =24.5 μV. Since the reproduced signal was very weak, amplifier 3 amplified it 100 times.

Next, the waveform asymmetry detecting section 4 detected the asymmetry of the reproduced signal waveform. The peak value detection method shown in FIG. 2 was used to detect the degree of waveform asymmetry. This peak value detection method uses the plus peak hold section 7. Minus peak hold section 8. and a differential amplifier section 9. That is, the plus side peak value IP of the reproduced signal waveform is held by the plus peak hold section 7.

Negative peak value ■1 and negative peak hold part 8
Detect with. The unbalance amount of Ip and (1) is detected by the differential amplifier section 9. The amplification degree of the differential amplifier section 9 is 10
It was doubled. As a result, the output of the differential amplifier section 9 is 21
mV was obtained. As the reference asymmetry signal (■), 3.5 mV, which corresponds to a waveform asymmetry of 5%, was given. As a result, the difference of 17.5 mV between both signals from the comparator 5 is the sense power supply 6.
Feedback was performed and the sense current value was adjusted to become smaller.

In order to measure the degree of waveform asymmetry, a signal of 1.0 was recorded in advance in this example, but it is also possible to use signals essential for signal reproduction such as address information and synchronization information recorded on the recording medium. be.

(Example 2) The above-mentioned Example 1 is a type that controls the sense current value in real time, but as the trunk width becomes narrower and the reproduction signal becomes weaker, the sense current is controlled more accurately due to the noise of the 9-circuit system. becomes difficult. In this embodiment, the influence of noise is reduced and the sense current is controlled more accurately.

This will be explained using FIG. In this embodiment, the waveform asymmetry detecting section 4 is divided into a plus side peak value detecting section 10°, a minus side peak value detecting section 13. Average value calculation unit 11.12. and a differential amplifier section 9.

In particular, the provision of the average value calculation units 11 and 12 is the first embodiment.
It is different from. With this configuration, a plurality of peak values within a certain period of time were detected, and the average peak value was determined.

In this example, the average of 1000 peak values was calculated. As a result, it was possible to sufficiently control the sense current value even in a head with a track of 1 μm. Although a shunt bias type head was used in the second embodiment, the same effect as described above was obtained with a soft bias type head.

(Third Embodiment) The first and second embodiments described above are examples in which the sense current value is not stored in the memory. For this.

If the sense current is to be lowered during head non-operation time, the sense current must be controlled again. About this.

In a magnetic recording device that requires high speed, this is undesirable as it results in a loss of time. This embodiment deals with the above problem and will be explained using FIG. 4. As shown in the figure, the output of the comparator 5 is digitized via an A (analog)/D (digital) converter 14 and further stored in a memory 15. Furthermore, the signal stored in the memory is converted again into an analog signal by the D/A converter 16, and is applied to the sense power supply 6.

Thereby, the sense current is always stored in the memory 15, and the above problem can be solved. Furthermore, by backing up the memory 15 with a battery, it is possible to cope with a power outage, and the time required to restart the apparatus can be shortened.

It is also effective to measure the optimum sense current value before installing the magnetoresistive head in the signal reproducing device, and to store the optimum sense current value information in a read-only semiconductor memory. In this case, an asymmetry detection system is provided on the signal reproducing device side.

Furthermore, a current value control system is not required, the signal reproducing device is simplified, and there are advantages such as cost reduction.

〔Effect of the invention〕

As described above in detail, according to the method and apparatus for reproducing signals using a magnetoresistive head according to the present invention.

Variations in head characteristics that are unavoidable during the head manufacturing process, especially asymmetry in the reproduced signal waveform due to fluctuations in the bias magnetic field.
Fluctuations in output can be reduced.

For example, in a conventional device, the degree of asymmetry of the reproduced signal waveform is 5.
However, with the device of the present invention, the degree of asymmetry could be reduced to 5% or less for all heads. Also, in a magnetoresistive head with a narrow track of 1 μm.

By using the signal reproducing method and device of the present invention,
The degree of asymmetry of the reproduced signal waveform could be reduced to the same level as above.

[Brief explanation of the drawing]

FIGS. 1 and 2 are system diagrams for controlling the asymmetry of the reproduced signal waveform illustrated in Embodiment 1 of the present invention. FIG. 3 is a system diagram for controlling the asymmetry of the reproduced signal waveform illustrated in the second embodiment, and FIG. 4 is a diagram showing the asymmetry control system for the asymmetry of the reproduced signal waveform illustrated in the third embodiment. Figure 5 is a schematic diagram showing an example of the configuration of a conventional shunt bias type head, Figure 6 is a graph showing the output-magnetic field curve of a conventional magnetoresistive head, and Figure 7 is a graph of a conventional differential type magnetic head. FIG. 2 is a schematic diagram showing an example of the configuration of a resistive head. 1... Recording medium 2... Magnetoresistive head 3... Amplifier 4... Waveform asymmetry detection unit 5... Comparison unit 6... Sense power supply 7...
Plus peak hold section 8・Minus peak hold section 9 ・Differential amplification section 10 . . . Plus side peak value detection section 11.12 .. Average value calculation section 13 . . . Minus side peak value detection section 14 . . A/ D converter↓5...Memory 16...D/A converter 17...Magnetic sensitive part 18...Electrode 19...
Magnetoresistive film 20... Shunt bias film 21...-Shield film 22... Signal magnetic field 23...
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Claims (1)

[Claims] 1. In a signal reproducing device that reproduces information recorded on a recording medium using a magnetoresistive head, the magnetoresistive effect is achieved by changing the intensity of the bias magnetic field applied to the magnetoresistive film. A signal reproducing device characterized by comprising means for optimizing the magnetization direction of a film. 2. A signal reproducing device using a magnetoresistive head according to claim 1, including means for detecting the degree of asymmetry of the signal waveform, and means for detecting the degree of asymmetry of the signal waveform, and a means for detecting the degree of asymmetry of the signal waveform. 1. A signal reproducing device comprising means for optimizing the magnetization direction of a magnetoresistive film by changing the strength of a bias magnetic field by changing the value of a current. 3. In the signal reproducing device using the magnetoresistive head according to claim 1 or 2, the means for detecting the degree of asymmetry of the signal waveform detects the positive peak value and the negative peak value of the signal waveform. A signal reproducing device characterized by comprising means for detecting a difference between the two. 4. In a signal reproducing device using a magnetoresistive head according to claim 1, 2, or 3, information on the value of current flowing through the magnetoresistive film is stored in a read-only semiconductor memory. The signal reproducing device is further provided with a means for optimizing the magnetization direction of the magnetoresistive film by changing the strength of the bias magnetic field based on the current value information. 5. In the signal reproducing device according to claim 1, 2, or 3, the value of the current flowing through the magnetoresistive film is optimized at least once before using the signal reproducing device. A signal reproducing device characterized in that it is provided with means for operating it. 6. Recording a 1, 0 signal on a recording medium using the signal reproducing device according to claim 5, and detecting the difference between the positive peak value and the negative peak value of the signal waveform using the signal. A signal reproducing method characterized by: 7. In the signal reproducing method according to claim 6, the signal for optimizing the magnetization direction of the magnetoresistive film by changing the strength of the bias magnetic field is always recorded and stored in the recording medium. Characteristic signal reproduction method. 8. In the signal reproducing method as set forth in claim 6, the signal used for optimizing the magnetization direction of the magnetoresistive film by changing the strength of the bias magnetic field is a record recorded for reproducing information. A signal reproduction method characterized in that the signal is from essential data of a medium. 9. A recording device comprising the signal reproducing device according to any one of claims 1 to 5, and comprising means for recording and reproducing information. 10. A recording method characterized by recording and reproducing information using the signal reproducing method according to any one of claims 6 to 8.