JPS6043205A - Magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To reproduce an analog signal and a digital signal with one head by varying the intensity of a bias magnetic field impressed to a magneto-resistance effect element according to whether a recorded magnetic signal is the analog signal or digital signal. CONSTITUTION:The intensity of the bias magnetic field impressed to the magneto-resistance effect (MR) element is varied by switching values of the impressed DC current. Amplifiers 7 and 8 are amplifiers which supply the DC currents for applying optimum magnetizing biases to the MR element. Then, both amplifiers are switched manually in reproduction with a changeover switch 9 according to whether the recorded signal is analog or digital, and the optimum DC current is supplied to the MR head 10 so that the optimum bias magnetic field is produced in either case. Thus, the resolution in the reproduction of a digital signal, specially, of short-wavelength recording is improved, and both analog and digital signals are reproduced excellently with the one MR head.

Description

[Detailed Description of the Invention] (a) Industrial Application Field The present invention reproduces magnetic signals recorded on a magnetic recording medium with a magnetoresistive thin-film magnetic head using a magnetoresistive element. The present invention relates to a magnetic recording/reproducing device.

(b) Prior Art In general, conventional magnetic heads, that is, bulk structure magnetic heads, are often used in the fields of analog recording or digital recording. however,
Particularly in the field of digital recording, progress is being made towards shorter wavelength recording and narrower track widths, that is, higher density recording. Thin-film magnetic heads, which are superior to conventional magnetic heads in terms of high-density recording, have recently attracted attention. Thin film magnetic heads have recently developed rapidly with the development of engineering technology, and are now used in magnetic disk devices for computer computers, PCM recording and reproducing devices using magnetic tape, and the like.

Thin-film magnetic heads include an inductive type capable of recording and reproduction, and a magnetoresistive type using a magnetoresistive element for reproduction only. The structure and principle of an inductive thin film magnetic head is the same as a conventional bulk structure magnetic head, but because the manufacturing process does not allow for a large number of windings, when used as a recording magnetic head. However, it has the disadvantage of requiring a large current during recording. However, compared to conventional magnetic heads, because the pole face base is shorter, the magnetic field distribution generated in the gap becomes steeper, making it suitable for high-density recording. However, since this inductive thin film magnetic head is a magnetic flux change responsive type with few windings, it can only be used as a reproduction magnetic head when the relative speed between the magnetic recording medium and the magnetic head is high. First, when the relative speed between the magnetic recording medium and the magnetic head is slow, for example, a deck using a compact cassette or a reel-to-reel type deck (tape speed 19ff/EtθC1%cs
/SeO) etc., it was not possible to reproduce the signals recorded on the magnetic tape with a sufficient S/N ratio at the relative speed between the magnetic tape and the magnetic head. Therefore, when the relative speed between the magnetic recording medium and the magnetic head is slow, a magnetoresistive thin-film magnetic head (hereinafter referred to as ML head) that utilizes the magnetoresistive effect, which is insensitive to magnetic flux, is used as a magnetic head for reproduction. The structure of such an MR head will be briefly explained below.

Here, FIG. 1 shows the structure of a conductor bias type MR head, and FIG. 1 (a7) is a diagram schematically showing the internal structure of the head.
(hereinafter referred to as an MR element), (2) is a conductor for flowing a bias current to the MR element in order to detect the magnetic signal recorded on the magnetic recording medium with the MR element (1), and (3)
is a conductor for passing a direct current to provide a bias magnetic field to the MR element. Figure 1 (bl is the same figure (al is x-
In this cross-sectional view when cut as shown by the x' line, (4) is a substrate on which a thin film magnetic head pattern is formed by a method such as sputtering, and (5) is a layer of magnetic insulator. be.

Further, FIG. 2 shows a hard film (ferromagnetic material, ie, permanent magnet) bias type MR head. Figure 2 (al is a diagram schematically showing the internal structure of the head, (1) is the MR element, (2)
(6) is a conductor for passing a bias current to the MR element for detecting magnetic signals, and (6) is a hard film for applying a bias magnetic field to the MR element. Figure 2 (bl is the same figure (a)
of'! This is a cross-sectional view taken along the line -Y', in which a thin film magnetic head pattern is formed on the substrate (4) by sputtering or the like, as in the case of FIG. 1. Other MR' heads include a barber pole type MR head, but a description thereof will be omitted.

Next, the principle of the MR head will be explained. First, the magnetoresistive effect is a phenomenon in which the electrical resistance of an MR element changes when a magnetic field is applied to the MR element. The magnetoresistive effect of the -axis anisotropic ferromagnetic thin film changes symmetrically with respect to the direction of the applied magnetic field, as shown in FIG. Δrmax in the figure indicates the maximum value of the resistance change of the MR element. Therefore, as shown in Figure 3, if a constant DC current is applied, a resistance change Δr caused by the magnetic field applied from the magnetic recording medium to the M and R elements will occur at both ends of the MR element. It is detected as a voltage change.If the voltage change occurring at both ends of the MR element is 8E, then 8E - Δr
・Work... [1]. However, as is clear from Figure 6 (al), the resistance change Δr of the MR element with respect to the applied magnetic field is nonlinear. Therefore, from equation [1], with respect to the magnetic field applied to the MR element, Therefore, the voltage change Δl?j becomes nonlinear.

Therefore, in order to provide linearity to changes in the minute signal magnetic field from the magnetic recording medium, the MR element is used with a bias magnetic field applied thereto. The bias magnetic field at this time is shown in Figure 5 (
It is set to H'b as shown in al. The current flow direction and the M
The angle formed by the magnetization inside the R element is set to 45°. This kind of M Jl head is
It is used in audio equipment such as C cassette decks and open decks, where the relative speed between the magnetic tape and the magnetic head is slow. It is also used as a magnetic head for analog recording and playback devices and PCM recording and playback devices. ing. In the case of an analog recording/playback device, in order to play back low-level to high-level analog signals recorded on magnetic tape over a wide dynamic range with little distortion, it is necessary to follow a straight line of resistance change as shown in Figure 6 fat. Use good parts. For this purpose, the angle between the direction of internal magnetization of the MR element and the bias current flowing through the MR element is set to 45°. if,
When this angle becomes larger or smaller than 45°, a phenomenon occurs in which the resistance change becomes saturated with respect to a unidirectional magnetic field applied from the recording medium to the MR element. The reproduced signal at this time is shown in FIG. 4(a)(1)). Figure 4 (al
is when the angle between the direction of magnetization inside the MR element and the bias current flowing through the MR element is 45°. It can be seen that it is collapsed on one side. Therefore, when reproducing an analog signal, the bias magnetic field applied to the MR element is M
The direction of magnetization inside the R element is 45% with respect to the bias current.
It must be set so that

On the other hand, in the case of digital recording, progress is being made toward shorter wavelength recording, narrower track widths, and higher density recording.

When reproducing a digital signal recorded on a recording medium, the position of magnetization reversal is detected and demodulated to the original digital signal. As shown in FIG. 5, when reproducing with an MR head, a pulse waveform is generated corresponding to the magnetization reversal position. Therefore, when demodulating to the original digital signal, it is necessary to accurately read out the peak position of this pulse waveform. As shown in FIG. 5, when the half-widths of the response waveforms of the M and R heads are narrow relative to the magnetization reversal interval, the peak position of the reproduced waveform relative to the magnetization reversal position does not deviate.

However, as shown in Fig. 6, when the half-width of the response waveform of the MR head becomes similar to the magnetization reversal interval, the peak position is affected by interference from the response waveform at the adjacent magnetization reversal position. A so-called pattern peak shift occurs (ie, the position of the solid line). This pattern peak shift becomes larger as the wavelength becomes shorter, making it impossible to demodulate the original digital signal No. 44.

Now, when using such a single MR head to reproduce analog and digital signals recorded on a magnetic recording medium, in the conventional method, the bias magnetic field applied to the MR element is controlled by the magnetization of the MR element. Generally, the angle between the direction and the bias current flowing through the MR element is set to be 45°. At this time, when reproducing analog signals, the setting of the bias magnetic field is optimal, resulting in the least distortion and a maximum dynamic range of 1. However, in the case of reproducing digital signals, if the half-width of the response waveform generated at the magnetization reversal position of the MR head is sufficiently narrow compared to the magnetization reversal interval during long wavelength recording, the original digital signal can be demodulated without any problem. However, when the recording wavelength becomes shorter and the half-width of the response waveform of the MR head becomes similar to the magnetization reversal interval, a pattern peak shift occurs, making it difficult to demodulate the original digital signal. This made it difficult to demodulate digital signals recorded at short wavelengths.

(c) Purpose of the Invention The present invention has been made in view of the above points, and it is possible to suitably reproduce analog signals recorded on a recording medium and reproduce short wavelength recorded digital signals using one MR head. The object of the present invention is to provide a magnetic recording/reproducing device that can perform the following operations.

B) Structure of the invention, that is, according to the present invention, the above object should be achieved (MR
This is a magnetic recording and reproducing apparatus that reads magnetic signals recorded on a recording medium using an MR head that applies a bias magnetic field to an element using a magnetic field generated by a direct current.

A switching means is provided for switching the strength of the magnetic field generated by direct current to change the strength of the bias magnetic field applied to the MR element depending on whether the recorded magnetic signal is an analog signal or a digital signal.

(e) Examples Embodiments of the present invention will be described below with reference to the drawings.

That is, according to the present invention, when reproducing an analog signal recorded on a magnetic recording medium, the current is applied so that the direction of magnetization of the MR element and the direction of the current flowing through the MR element are at an angle of 45 degrees, as in the conventional case. However, when reproducing digital signals recorded with short wavelengths, a so-called pattern peak shift occurs (this pattern peak shift is a response waveform of the MR head generated corresponding to the magnetization reversal position on the magnetic recording medium). This problem arises when the half-width of the magnetization reversal interval becomes close to the same extent as the magnetization reversal interval, so the bias magnetic field is set to be sufficiently stronger than this. To make the bias magnetic field strong enough during digital signal reproduction is to make the bias magnetic field applied to the MR element strong enough so that it is sensitive only to the minute part of the tip of the MR element on the side that contacts the magnetic recording medium. This is because if the magnetization direction of the central portion is completely oriented in the direction of the bias magnetic field, the reproduction output will be small, but the half width of the response waveform of the MR head will be narrow. If the half-width of the response waveform of the MR head becomes narrower than the magnetization reversal interval, even when reproducing digital signals recorded at short wavelengths, the reproduced waveform of the MR head will become as shown in Figure 7, and a pattern peak shift will occur. It can be seen that this is significantly improved compared to Figure 6. Since the present invention uses a magnetic field generated by direct current as the bias magnetic field to change the strength of the bias magnetic field,
Specifically, this is done by switching the DC current value.

That is, FIG. 8 is a block diagram showing one embodiment of Mok Hyungju, and (7) is a block diagram for giving an optimal magnetization bias to the MR element when reproducing an analog signal recorded on a magnetic tape. This is an amplifier that supplies direct current. Also, (8
] is an amplifier that supplies a direct current to give an optimum magnetization bias to an MR element when reproducing a digital signal recorded on a magnetic tape. Switching between both amplifiers is done manually during playback using a changeover switch (9) depending on whether the signal recorded on the magnetic tape is an analog signal or a digital signal. It is designed to supply the optimum DC current to the head (1α).

(F) Effects of the Invention As described above, according to the present invention, the strength of the bias magnetic field applied to the MR element is changed when reproducing an analog signal using an MR head and when reproducing a digital signal. Since it is possible to obtain the optimum reproduction signal, the resolution can be improved, especially when reproducing digital signals recorded with short wavelengths, and one M
The R head can suitably reproduce analog signals and digital signals.

Schematic diagram and x-x' sectional view, Figure 2 (al (1)
l is a schematic diagram of a hard film bias type MR head;
-Y' cross-sectional view, Figure 6fat (bl is a diagram showing the resistance change of the MR element with respect to the applied magnetic field and its schematic diagram, Figure 4 (aHb+ is the reproduction waveform diagram of the MR head, respectively, Figure (a) is the reproduction waveform diagram of the MR head with the optimum via,
Figure fl) l is M at insufficient bias or optimal bias,
Figure 5 is a reproduction waveform diagram of the R head. Figure 5 is a reproduction waveform diagram of the MR head when the half width of the response waveform of the MP head is narrow relative to the magnetization reversal interval. Figure 6 is the response of the MR head to the magnetization reversal interval. Figure 7 is a reproduction waveform diagram of an MR head when the half-width of the waveform is approximately the same, Figure 7 is a reproduction waveform diagram of an MR head when the bias magnetic field is strengthened compared to the one in Figure 6, and Figure 8 is a diagram of reproduction waveforms according to the present invention. FIG. 1 is a schematic block diagram showing an example.

fi+...MR element, (3)...conductor, (9)...
・Choice switch, a■...Mal (head.

Applicant: Sanyo Electric Co., Ltd.

Claims (1)

[Claims] (1) Magnetic recording/reproduction that reproduces magnetic signals recorded on a magnetic recording medium using a magnetoresistive magnetic head that applies a bias magnetic field to a magnetoresistive element using a magnetic field generated by a direct current. A switching device that switches the strength of a magnetic field generated by a direct current to change the strength of a bias magnetic field applied to a magnetoresistive element depending on whether a magnetic signal recorded on a recording medium is an analog signal or a digital signal. A magnetic recording/reproducing device characterized by being provided with means.