JPH08287403A - Magnetic recorder - Google Patents

Abstract

PURPOSE: To reduce regenerative waveform distortion and to eliminate a data error by making the number of turns of a coil of an inductive magnetic head a prescribed value and satisfying a specific relation between the input resistance and the input capacity of an amplifier circuit. CONSTITUTION: In the amplifier circuit of a MIG type magnetic head, for inducing no data error, it is necessary that the maximum waveform distortion factor is made 15% or below, and for satisfying the request, the matter that the inductance component Lh of the magnetic head among respective circuit constants is reduced is most effective. The reduction of the inductance component Lh is dealt with by reducing the number of turns of the coil 4. However, the number of turns of the coil 4 is limited to about 30 turns since a reproducing output is lowered. Further, when the input resistance of the amplifier circuit is defined Rin (Ω), and the input capacity is defined Cin (pF), the combination between the inductive magnetic head and the amplifier circuit satisfied with the relation of Rin<14300×Cin<-1.5> is required to be used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording device, mainly a magnetic head of a magnetic disk device and an amplifier circuit for amplifying a signal detected by the magnetic head.

[0002]

2. Description of the Related Art Various types of induction type magnetic heads are widely used as magnetic heads for magnetic disk devices. The main types of magnetic heads are thin film heads formed by using techniques such as photolithography and sputtering, and ferrite. It can be divided into bulk type heads that are created by cutting out magnetic materials by machining. The bulk type head, MIG forming a high metal magnetic film having saturation magnetic flux density in the magnetic gap facing surfaces of the ferrite core (M etal · I n · G ap) head is typical. The two types of magnetic heads differ in the inductance and the coil DC resistance due to the volume of the magnetic material and the coil winding form.

The thin film head has a small inductance (1
μH or less) and the coil DC resistance is large (around 30Ω), whereas the bulk type head has a large inductance (2
μH to 5 μH), and the DC resistance of the coil is small (10Ω or less). Therefore, from the viewpoint of impedance noise, a thin film head is conventionally used for a magnetic disk device having a wide frequency band, and a MIG type head is used for a magnetic disk device having a relatively narrow frequency band.

However, in recent years, the recording frequency has tended to increase due to the increase in the capacity of magnetic disk devices and the increase in the speed of data transfer, and there has been an increasing demand for the MIG type head to have a low inductance. In order to meet the demand for low inductance, the MIG type head reduces the volume of the magnetic body by downsizing the magnetic core, so that the number of coil turns is 30 to 40.
And an inductance of 1 to 1.8 μH has been realized (Japanese Patent Laid-Open No. 6-325314). The greatest advantage of the MIG type magnetic head is that the cost is lower than that of the thin film head.

By the way, a technique called zone bit recording is adopted as a method for increasing the capacity of a magnetic disk device. This is a method in which the radial direction from the inner side to the outer side of the disc is divided into a plurality of zones, and the recording frequency is switched for each zone so that the inner side and the outer side of the disc have the same recording density. It is an effective means for increasing the recording capacity per disc surface.

[0006]

However, in the zonal bit recording, when the MIG type head is used, the data error is higher at the outer circumference of the disk as compared with the thin film head as the signal reproduction is performed at a high speed. The number has increased, and there has been a problem that it will not be possible to cope with future high recording density.

[0007]

According to the present invention, in a magnetic recording apparatus using an inductive magnetic head, the inductive magnetic head faces a magnetic gap of at least one of a pair of magnetic core halves. A MIG type magnetic head having a metal magnetic film formed in its part, and the number of turns of the coil applied to the magnetic head is 30 turns or more, and a drive amplifier circuit for amplifying a signal detected by the magnetic head. It is characterized by satisfying the relationship of Rin <14300 · Cin ^-1.15 when the input resistance of Rin (Ω) and the input capacitance are Cin (pF).

[0008]

As a result of various analyzes of the cause of the data error, the present inventor has clarified that the data error is mainly affected by the waveform distortion generated on the outer peripheral side of the disk. When the reproduced signal of the MIG type head on the outer peripheral side of the disk recorded at a frequency of 1 MHz was observed, a reproduced waveform as shown in FIG. 5A was obtained. The reproduced signal of the thin film head under the same conditions is shown in FIG. 6B, and it can be seen that in the MIG type head, a large waveform vibration is generated in the rear part (right side of the peak) of the signal as compared with the thin film head. Therefore, when intensive research was conducted to investigate the cause of waveform distortion, waveform distortion occurs when a sudden output change occurs with time.
It was found that it was due to the transient response phenomenon of the head amplifier system circuit.

In order to improve such waveform distortion in the MIG type head, in the amplifier circuit for amplifying the output signal from the magnetic head, the input resistance of the amplifier circuit is set to Rin.
(Ω), when the input capacitance is expressed as Cin (pF)

[Formula 1] Rin <14300 · Cin ^-1.15 (1) It should be adjusted so as to satisfy the relationship.

The MIG type magnetic head according to the present invention has a structure as shown in FIG. A coil 4 is wound around the magnetic core halves 2 and 2'to read out magnetic information, and the magnetic core portion has a structure as shown in FIG. 2 and 2'in FIG. 2 (b) are Mn-Z.
It is a magnetic core half body made of single crystal ferrite such as n, and a metal magnetic thin film mainly made of iron is formed on the facing surface of the magnetic gap portion 5 as shown by 6. Magnetic core half 2
A coil 4 for obtaining the magnetic information wound on the magnetic head as an electric signal is wound, and is further input to an amplifier circuit for amplifying a weak signal output from the magnetic head.

The amplifier circuit has a circuit constant with an input resistance Rin
(Ω) and input capacitance Cin (pF) are specified, but if the MIG type head is replaced as a passive component, the circuit configuration will be
It is represented by an equivalent circuit as shown in FIG. Symbols Lh, Rh, R
p and Ch are the inductance component of the magnetic head, the direct current resistance component, the high frequency loss equivalent resistance component of the magnetic core, and the stray capacitance, respectively.

The relational expression of the equation (1) is derived by the following analysis. First, consider a magnetic head and an amplification circuit represented by the circuit constant specifications as shown in Table 1 based on the equivalent circuit model as shown in FIG. Lh and Rh are MI measured at a frequency of 1 MHz by an impedance analyzer
The value of the G type head is based.

[Table 1] As an output signal f (t) induced from the magnetic head, consider an ideal waveform approximated by a Lorentz function represented by the following equation. Here, the symbol T50 is the full width at half maximum of the signal waveform, and A is the amplitude.

[Formula 2]

When the waveform h (t) restored after transmission in the equivalent circuit of FIG. 3 is obtained with T50 = 20 ns and A = 1 in the above equation, the result of FIG. 4 is obtained. The solid line h (t) is the analysis result. A broken line g (t) is a signal waveform output when it is assumed that the output signal f (t) has passed only the amplifier circuit. h (t) and
The difference in g (t) is represented by the alternate long and short dash line Δ (t), and the amplitude at the time when the absolute value of Δ (t) is maximum is ΔMAX. At this time, the maximum waveform distortion rate is defined by the following formula.

[Formula 3] Maximum waveform distortion rate = △ MAX ÷ input amplitude A × 100 (%) (3)

The inventors of the present invention have also conducted an analysis based on the above equivalent circuit and found that the maximum waveform distortion rate must be 15% or less in order not to induce a data error. In the equivalent circuit of the magnetic head of FIG. 3, in order to satisfy this requirement, it is most effective to reduce the inductance component Lh of the magnetic head among the circuit constants.

In the MIG type head (FIG. 2) which is the object of the present invention, in order to reduce Lh, the magnetic material is cut off at the coil winding portions (magnetic core halves 2 and 2'in FIG. 2). This can be dealt with by reducing the area and the number of turns of the coil 4. However, the cross-sectional area is 2000 μm ^{2 in} view of mechanical strength and reproduction efficiency, and the number of turns of the coil is limited to about 30 turns because the reproduction output is reduced. Therefore, the lower limit of Lh is about 1 at a frequency of 1MHz.
It is expected to be μH, and a large reduction cannot be expected. Therefore, in order to reduce the waveform distortion in other than the magnetic head, we examined for the purpose of adjusting the input resistance Rin and the input capacitance Cin of the amplifier circuit.

The curve shown by the solid line in FIG. 1 is Lh of 1 μH.
The relationship between the input capacitance Cin and the input resistance Rin when the maximum waveform distortion rate is 15% is shown below. In other words, if Cin and Rin are in the range below the curve, waveform distortion will be 15
The relational expression (1) was determined based on the fact that it can be suppressed to less than or equal to%. To satisfy this relation,
This can be dealt with by connecting a resistor or a capacitor to the outside of a commercially available drive amplifier circuit, but it goes without saying that an amplifier circuit satisfying the relational expression may be used in advance. Hereinafter, the effects of the present invention will be described based on Examples.

(Embodiment 1) The magnetic head is a MIG type head in which magnetic core halves 2 and 2'are inserted into a non-magnetic 50% slider 1 as shown in FIG. 2A and fixed with glass 3. I was there. In FIG. 2B, the magnetic core is a sendust alloy magnetic thin film 6 having a thickness of 2 μm on both sides of the magnetic gap 5.
And the magnetic core half body 2 has a thickness of 50 μm.
The width Iw of the portion to which the winding wire 4 is applied is 50 μm. The track width Tw, which is machined in steps to be the surface facing the recording medium, is 6.0 μm. As the winding 4, a copper wire having a wire diameter of 20 μm was used and wound for 33 turns. At this time, the inductance component was 1.2 μH (at 1 MHz) and the DC resistance component was 10Ω.

The above magnetic head is connected to an amplifier circuit, and 3.
At a radius of 40 mm on a 5-inch (outer diameter 95 mm) magnetic disk, a rotation frequency of 4500 rpm and a magnetic head / disk gap height (flying height) of 0.05 μm will give a frequency of 1 MHz.・) Was recorded. Next, the recorded information was reproduced and the distortion rate of the reproduced waveform was measured. In this experiment, two general types A and B which are commercially available as an amplifier circuit were used. The input capacitance Cin of the amplifier circuit A is 15 pF and the input resistance Rin is 1000Ω. The input capacitance Cin of the amplifier circuit B is 25 pF and the input resistance Rin is 1000Ω.

In the present invention, Cin is 15p from the relational expression (1).
When F, Rin is 635Ω or less, when Cin is 25pF, Rin
Must be less than 353Ω. Therefore, the amplifier circuits A and B are not applicable to the present invention as they are. Therefore, an external resistance Ra was connected in parallel with Rin at the input end of the amplifier circuit to adjust the effective input resistance Rin '. Rin 'can be calculated by the following equation (4).

[Formula 4] Rin ′ = Rin · Ra / (Rin + Ra) (4) Therefore, Ra = 1740Ω or less in the amplification circuit A, amplification circuit B
The condition satisfying the present invention can be achieved by connecting an external resistance of Ra = 545 Ω or less to. Table 2 shows the results measured by changing the value of the external resistance Ra and changing the effective input resistance Rin 'of the amplifier circuit.

[0020]

[Table 2] In each of the examples in which Rin 'satisfied the condition * Rin of the present invention, the waveform distortion rate was 15% or less of the allowable amount.

[0021]

According to the present invention, the inductance is 1 μm.
The waveform distortion that occurs when the MIG type head of H (at 1 MHz) or higher is rotated at a high speed can be reduced, data error can be prevented, and the MIG type head can be applied to a magnetic disk device having a high recording density.

[Brief description of drawings]

FIG. 1 shows the relationship between input capacitance and input resistance according to the present invention.

FIG. 2 is an external view of a MIG type magnetic head and a magnetic core.

FIG. 3 is an equivalent circuit including a magnetic head and an amplifier.

FIG. 4 is an example of a transient response analysis calculation result of an input signal f (t).

FIG. 5 is a reproduction waveform measurement example according to the present invention and a conventional reproduction waveform.

[Brief description of reference numerals]

1 non-magnetic slider, 2 magnetic core half body, 2'magnetic core half body, 3 fixed glass, 4 windings, 5 magnetic gap, 6 metal magnetic film, 7 bonded glass.

Claims (1)

[Claims] 1. An induction type magnetic head having a metal-in-gap (hereinafter abbreviated as MIG) in which a metal magnetic film is formed on at least one magnetic gap facing portion of a pair of magnetic core halves with a magnetic gap interposed therebetween. In a magnetic recording device including an amplifier circuit, when the coil wound around the inductive magnetic head has 30 turns or more, the input resistance of the amplifier circuit is Rin (Ω), and the input capacitance is Cin (pF), Rin A magnetic recording device comprising a combination of the induction type magnetic head and an amplifier circuit satisfying the relationship of <14300 · Cin ^-1.15 .