JPH0123844B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for reproducing magnetically recorded signals, and more particularly to a method for reproducing magnetically recorded signals in a magnetic recording device using a magnetoresistive magnetic head as a magnetic detection section. BACKGROUND ART Magnetic recording and reproducing devices such as home VTR devices have become widespread, and along with this, research on magnetic recording and reproducing methods has been actively conducted. For example, the magnetic recording method in a VTR device (1) rotates the magnetic head, (2) connects the recording signal to an external circuit via a rotary transformer, and (3) rotates the magnetic head in the tape running direction. The recorded area is constructed by recording diagonally, etc., and this method allows for (1) high-precision recording, (2) low-noise recording, (3) improved durability, and (4) image stillness. This recording and reproducing method is widely known as the helical scan method, and has many excellent features such as multiple functions such as double-speed feed. FIG. 1 shows the conventional structure of a magnetic recording/reproducing section employing such a helical scan method. 1st
In the figure, the reference numeral 1 indicates an upper cylinder, which is fixed to a rotating shaft 3 that passes through the lower cylinder 2 side and is guided. A plurality of magnetic heads 4 are attached to predetermined positions on the peripheral edge of the upper cylinder 1 while being supported by a fixing plate 5, and a magnetic tape is attached so as to span the upper and lower cylinders 1 and 2. Perform recording/playback for. The signal from the magnetic head 4 is guided via a lead wire 6 to an electrode plate 7 provided at the center of the upper cylinder 1, and further guided to the upper cover 9a of the rotary transformer 9 via a lead wire 8. There is. The rotary transformer 9 consists of an upper lid part 9a fixed to the upper cylinder 1 side and a lower lid part 9b fixed to the lower cylinder 2 side, and the signals collected between the upper and lower lid parts 9a and 9b are Processing circuit 11 via line 10
guided by. The upper cylinder 1 and lower cylinder 2 having the structure described above constitute a rotating head assembly 12 of a VTR. With such a VTR, the magnetic recording and reproducing system is
Although they have many advantages as mentioned above, recently there has been a noticeable trend toward higher density and smaller size. Regarding this tendency, the most important issues are the reproduction output of the magnetic head 4 and the diameter of the upper cylinder 1. That is, in the conventional magnetic head, although its recording characteristics are not so important, when attention is paid to reproduction, there are several points that should be improved as follows. (1) The conventional effective gap width of a magnetic head is 0.5μ.
This is the limit, and the limit has almost been reached at present. (2) It was difficult due to manufacturing technology to set the gap width to 0.5 μm and keep the accuracy to about 10%. (3) Output decreased due to gear loss. Recently, a magnetoresistive reproducing head has been proposed as a solution to these problems. This magnetoresistive read head (hereinafter referred to as MR head) has the following superior features when compared to conventional heads. Generally, when approximating the reproduction output of a conventional magnetic head, the following three points can be cited as main losses. They are (1) separation loss, (2) gap loss, and (3) thickness loss. These losses can be said to be almost the same for MR heads. Of these losses, the thickness loss depends on the thickness of the magnetic tape and has no relation to the MR head or the conventional head itself, so it is not evaluated here. To explain the separation loss in (1) above, the separation loss Ld depends on the distance d between the head and the magnetic tape, and also depends on the finishing accuracy of the sliding surface of the magnetic chip and the unevenness of the magnetic tape surface. It's decided. When the reproduction wavelength is λ, the separation loss Ld is expressed by the following equation (1). Ld=54.6d/λ [dB] (1) On the other hand, the gap loss Lg is the gap width g (MR
In the case of a head, it depends on the thickness of the magnetoresistive element, and similarly, if the reproduction wavelength is λ, it is expressed by the following equation (2). Lg=-20log|sin(πg/λ)/πg/λ|[dB] (2) By the way, the basic structure of the MR head is shown in FIG. 2. In FIG. 2, the reference numeral 13 indicates a substrate, and on the side surface of this substrate, a magnetoresistive element (MR element) 14 made of NiFe, NiCo alloy, etc. is deposited using a thin film deposition method, such as EB evaporation or resistance heating evaporation. It is formed by methods such as , sputtering, plating, and CVD. After film formation, the shape of the element 14 is adjusted by a method such as photoetching. Further, on the side surface of the substrate 13, a lead wire 15 made of a thin film of Au, Cu, Al, etc. is formed by a thin film deposition method, and is electrically connected to the MR element 14. Reference numeral 16 indicates a tape sliding surface. In an MR head having such a structure, the gap width corresponds to the thickness of the MR element 14, which is indicated by gm in FIG. This width gap gm can be controlled very accurately using a thin film deposition method and is usually formed to a value of 0.1 to 0.01 .mu.m. Now, the separation length gr is 0.2 μm, and the reproduction wavelength λ
is 1.0μm, and the gap width gm of the conventional head is
When the separation loss and gap loss are calculated assuming 0.05 μm, the results are shown in Table 1.

[Table] As is clear from Table 1, when an MR head is used, there is almost no drop in output due to gap loss, and the regeneration efficiency is approximately 1.5 times that of a conventional head (ring type head). While the effective gap of a conventional ring head is thought to be approximately 0.5 μm, the gap of an MR head has the potential to be reduced to less than 1/50 of that.
Therefore, considering the tendency for reproduction wavelengths to become even smaller, it is expected that MR heads will become the mainstream of reproduction heads in the future. On the other hand, if we turn our attention to miniaturization of devices, for example, the diameter of the cylinder of the rotary head of current household VCRs is 62 to 74 mm, but this diameter is gradually becoming smaller. Therefore, if the NTSC recording method is adopted, the rotation speed of the cylinder is constant at 30 revolutions per second, and as the cylinder diameter becomes smaller, the wavelength becomes shorter, and the relative speed of the magnetic head to the magnetic tape decreases. descend. As a result, when playing with a conventional ring-type head, output is output according to the rate of change of magnetic flux, so the smaller the size, the smaller the output, and considering the gap loss due to the shorter wavelength, the output becomes smaller. The decline is significant. On the other hand, since the reproduction output of the MR head is a magnetic flux response, it does not depend on the relative speed between the tape and the head, and the output decreases little due to a reduction in the diameter of the cylinder. Thus, considering the small gap loss of the MR head and the fact that it is responsive to magnetic velocity, it can be said that it is extremely suitable for reproducing short wavelength recorded signals. However, unlike conventional heads, MR heads read out signals through resistance changes, so it is necessary to constantly supply a detection current. This detection current is usually a direct current of several mA. In addition, the rotary transformer mentioned above has much superior characteristics in terms of brush noise and durability compared to the slip-ring type.
In order to combine it with an MR head, one possible method is to house the battery that supplies the aforementioned detection current in the upper cylinder and extract only the change in resistance value. However, if this method is adopted, (1) the battery is built-in, which hinders miniaturization, (2) the battery needs to be replaced at regular intervals, and the output changes due to fluctuations in battery voltage. There are disadvantages such as: The present invention has been made in order to eliminate the above-mentioned conventional drawbacks, and provides a magnetic recording system that eliminates the reduction in reproduction output due to gap loss, allows for miniaturization of the device, and enables faithful reproduction of high-density recording. The purpose is to provide a signal regeneration method. In order to achieve the above object, in the present invention, an alternating current is applied from the fixed member side to the magnetoresistive magnetic head attached to the rotating member through a rotary transformer, and the magnetoresistive magnetic head is A method was adopted in which the strength of the signal magnetic field applied to the magnetic recording medium is detected by the fixed member as a change in the amplitude or frequency of the alternating current voltage, and the recorded signal on the magnetic recording medium is reproduced by this detection. Hereinafter, details of the present invention will be explained with reference to the drawings. FIG. 3A is a circuit diagram illustrating the principle of the present invention. In the figure, the reference numeral 20 is an MR head, and the frequency of the reproduced signal is fr. 21 is a rotary transformer, 22 is a bridge circuit, and is connected to an AC oscillator 23 and an amplifier 24. An element 25 composed of an inductance and a resistor for balancing the bridge circuit is interposed in a part of the bridge circuit. Based on this configuration, in order to faithfully reproduce the recorded signal, it is necessary to adjust the oscillation frequency fc of the AC oscillator 23.
Then, the following condition (3) must be satisfied. fc＞fr (3) Specifically, since fr=2~6MHz, fc=
Approximately 12MHz is appropriate. In this way, the detection current for the MR head is supplied as an alternating current with a frequency higher than the frequency of the reproduction signal, and the MR element is used as an alternating current impedance due to the resistance change of the element due to the magnetic recording signal. The alternating current is amplitude modulated, and a faithful reproduction signal can be obtained according to the recorded signal. As a result, batteries etc. are accommodated in the upper cylinder,
It does not result in any hindrance to downsizing.
A reproducing method with excellent reproducing ability that combines the features of an MR head and those of a rotary transformer can be obtained. FIG. 4 explains a specific embodiment of a rotary head assembly for recording and reproducing to which the above principle is applied. In the figure, the same or equivalent parts as in FIG. 1 are designated by the same reference numerals. and the explanation thereof will be omitted. In this embodiment, the head attached to the upper cylinder 1 as a rotating member is an MR head 26. Further, unlike the structure shown in FIG. 1, the rotary transformer 9 has a structure in which it is divided concentrically not in the axial direction of the rotating shaft 3 but in the radial direction. That is, in the rotary transformer, the rotor 27 of the rotary transformer dedicated to the MR head is fixed to the rotating shaft 27 on the upper cylinder 1 side, and the stator 28, which is the fixed side of the rotary transformer, is attached to the lower cylinder as a fixed member on the outside. It is fixedly attached to 2. On the other hand, a write-only rotary transformer rotor 30 is fixed below the rotor 27 of the rotary transformer dedicated to the MR head via a nonmagnetic layer 29, and a stator 31 is connected to the lower cylinder 2 outside of the rotor 30. It is installed in a fixed position. A nonmagnetic layer 32 is arranged between this stator 31 and the stator 28 dedicated to the MR head. The presence of these nonmagnetic layers 29 and 39 ensures that the output from the MR head is not affected by the write head during reproduction. Note that the mounting position of the write head and its lead wire are omitted in FIG. In this way, the rotary transformer is divided into recording and reproducing parts, and by combining the rotor, which is attached to the same rotating shaft, and the stator fixed around the rotor, a helical transformer with a magnetic head for recording and reproducing is created. A scanning rotary head assembly can be obtained. Since this embodiment is configured as described above, it takes advantage of the advantages of the helical scan method and takes advantage of the characteristics of high-density recording, low noise, and multifunctionality, while also achieving the characteristics of the MR head (1) gear processing. (2) ease of manufacturing by thin film deposition method;
(3) There is little output loss even when downsized. (4) Excellent effects such as higher density recording can be obtained. In addition, FIG. 3B is shown as a modification of FIG. 3A.
By controlling the self-excited oscillator 23a with the output of the rotary transformer 21, the alternating current signal may be frequency modulated and faithful signal reproduction may be performed. As is clear from the above description, according to the present invention, in a magnetic recording signal reproducing method using a magnetoresistive element, in order to detect a magnetic signal recorded on a magnetic medium, An alternating current is applied to the magnetoresistive magnetic head from the fixed member side via the rotary transformer, and the strength of the signal magnetic field applied to the magnetoresistive magnetic head is expressed as a change in the amplitude or frequency of the alternating current voltage. Since the fixed member side detects the signal and the recorded signal on the magnetic recording medium is reproduced by the detection, the magnetoresistive magnetic head does not need to be provided with a power source for applying current to the magnetoresistive magnetic head on the rotating member side. Since the head can be used as a rotary head, the rotary head assembly can be downsized, and there are excellent effects such as high-density and stable recording and reproduction.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional side view of a rotary head assembly employing a conventional method, FIG. 2 is a partially enlarged perspective view showing the basic structure of the magnetoresistive element employed in the present invention, and FIG. 3A , B is a circuit diagram illustrating the principle of the present invention, and FIG. 4 is a longitudinal sectional side view showing an embodiment of a rotary head assembly to which the method of the present invention is applied. 20... Magnetoresistive playback head, 22...
Bridge circuit, 23... AC oscillator, 23a...
Self-excited oscillator, 27... Rotor for MR head, 28
... Stator for MR head, 29, 32 ... Nonmagnetic layer, 30 ... Writing rotor, 31 ... Writing stator.

Claims (1)

[Scope of Claims] 1. A magnetoresistive magnetic head is attached to a rotating member that is rotatable with respect to a fixed member, and an alternating current is applied to the magnetoresistive magnetic head from the fixed member side via a rotary transformer. The strength of the signal magnetic field applied to the magnetoresistive magnetic head is detected by the fixed member as a change in the amplitude or frequency of the alternating current voltage, and the recording signal on the magnetic recording medium is reproduced by the detection. A magnetically recorded signal reproducing method characterized by: 2. A patent characterized in that the magnetoresistive magnetic head is connected to one side of an AC bridge to which an AC signal is applied to detect the strength of the magnetic field applied to the magnetoresistive magnetic head. A magnetic recording signal reproducing method according to claim 1.