JPH10134307A - Magnetic disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the positive and negative asymmetrical wave form of a reproducing signal from an MR head by controlling a sense current supplied to the MR head. SOLUTION: In order to make optimal a sense current supplied to an MR head 5 so as to eliminate the positive and negative asymmetry of the reproducing analog signal from the MR head 5 with respect to a reference signal level to create equal amplitudes, this magnetic disk device is composed of a recording signal reproducing section 1 for peak-identifying 14 and amplitude-identifying 15 a reproducing signal from the MR head 5, a wave form asymmetry detecting section 2 for detecting asymmetry between the positive and negative amplitudes of a wave form and making a gate signal for controlling a sense current and a sense current control section 3 for setting a sense current. By correcting asymmetry between the positive and negative amplitudes of an MR head reproducing signal, a read margin is increased during data discrimination and the reliability of the magnetic recording device is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording / reproducing apparatus equipped with a magnetoresistive head (MR head).
The present invention relates to determination of a sense current for correcting an asymmetric positive / negative amplitude of an analog reproduction signal from an MR head.

[0002]

2. Description of the Related Art In the field of magnetic recording, high-density recording has been progressing in recent years, reflecting the trend of miniaturizing and increasing the capacity of magnetic disk drives. In response to this demand, the magnetic head performs a conventional recording / reproducing operation with a single head, and from a magnetic induction type head whose output characteristics change according to the speed of the recording medium,
A recording / reproducing separation type head in which a recording operation is performed by a conventional magnetic induction type head and a reproducing operation is performed by a magnetoresistive head (MR head) whose output characteristics do not depend on the speed of a recording medium has been increasingly used.

An MR head is a reproducing head using the magnetoresistance effect. The magnetoresistive effect utilizes a characteristic in which the electric resistance of the MR element changes according to the signal magnetic field of the recording medium. That is, the output waveform of the MR head is obtained by converting a change in resistance into a voltage by flowing a constant current (sense current). The resistivity of the MR element is represented by ρ = ρ ₀ + Δρ _m cos ² θ. Where ρ ₀ is the resistivity in the absence of a magnetic field, Δ
ρ _m is the maximum resistivity change. θ is the angle between the direction of the constant current (sense current) vector and the direction of the magnetization vector of the MR element.

[0004] The output waveform of the MR head is obtained by converting the change in resistance into a voltage by passing a constant current (sense current). In this case, the direction of the magnetization vector becomes the same value in both positive and negative directions, and it becomes impossible to determine the polarity of the signal magnetic field applied to the MR element from the recording medium. Therefore, it is designed to operate in a linear region by applying a predetermined bias magnetic field Hb so that the magnetization vector and the current vector have a predetermined angle (usually 45 °) in advance.

The method of applying the bias magnetic field Hb is as follows.
Various methods have been proposed by changing the structure of the R head. As one of them, a method of applying a bias magnetic field by a magnetic field generated by a sense current is used because of its simple structure and easy manufacture.

[0006]

In the MR head having the above-described characteristics, if the sense current flowing through the MR head is improper as shown in FIG. 2, positive and negative asymmetry of the reproduction output amplitude occurs. The positive / negative asymmetry of the reproduced waveform is also one of the causes for reducing the read margin in data discrimination.

In a magnetic disk drive equipped with an MR head, the same current value is set in any head for setting the sense current. However, the asymmetry of the reproduction signal from the MR head differs depending on each head due to the variation of the film in the MR head. In fact, it takes a great deal of effort to individually set appropriate values for the sense currents flowing through all the MR heads of a mass-produced magnetic disk drive.

Also, the asymmetry of the reproduction signal of the MR head may change due to external factors, and an appropriate sense current is always supplied to the MR head to improve the reliability of the apparatus by improving the asymmetry of the reproduction signal. It is possible.

SUMMARY OF THE INVENTION It is an object of the present invention to improve the reliability of a magnetic disk drive equipped with an MR head by optimizing a sense current flowing through the MR head.
It is intended to improve the asymmetry of the reproduced signal from the head.

[0010]

In order to solve the above problems, the present invention employs the following configuration.

[0011] In a magnetic disk drive having at least a head for recording or reproducing information on or from a magnetic recording medium and a recording / reproducing means for processing an information signal to or from the head, the information is reproduced from the magnetic recording medium. A magneto-resistive head as a recording head, and correcting means for correcting the asymmetry of the positive and negative amplitudes of an analog reproduced signal obtained by reproducing the reference signal recorded on the magnetic recording medium by the magneto-resistive head. Magnetic disk drive.

The asymmetry correcting means includes a circuit for flowing a sense current to the magnetoresistive head, a reproducing unit for reproducing an information signal from the head, and detecting a positive / negative amplitude asymmetry of the analog reproduced signal. A magnetic disk drive comprising: an asymmetry detection unit; and a sense current control unit that controls the sense current based on the detection of the positive / negative amplitude asymmetry.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The outline of the present invention will be described with reference to FIGS. FIG. 1 shows the principle configuration of the present invention, and FIG. 2 is a waveform diagram for explaining the asymmetry of the reproduction signal from the MR head. Here, 1 indicates a recording signal reproducing unit, 2 indicates a waveform asymmetry detecting unit, and 3 indicates a sense current control unit.

The principle configuration of the present invention is to optimize the sense current flowing to the MR head so that the analog reproduced signals having different positive and negative amplitudes with respect to the zero level by the MR head have the same positive and negative amplitudes. As shown in FIG. 1, a recording signal reproducing unit 1 amplifies an analog reproduction signal from an MR head and removes noise to shape a signal waveform. And outputs whether or not the signal is asymmetric. Further, the sense current control section controls the set value of the sense current of the MR head based on the output from the asymmetric detection section.

As shown in FIG. 2, when there is a recording signal having a positive and negative waveform biased by a magnetic field corresponding to the sense current and reproducing the recording signal, the waveform of the reproduction signal changes according to the characteristics shown in FIG. can get. Here, if a reproduced signal is obtained using the linearity portion of the characteristic curve in FIG.
Although asymmetry of the positive and negative waveforms does not occur, generally, since the characteristic curve shown in FIG. 2 does not have ideal linearity, an asymmetric waveform occurs in the reproduced signal. Therefore, it is necessary to control the bias value of the sense current so as to operate in a characteristic curve portion as close as possible to the linearity portion.

The specific structure of the present invention is shown in FIGS. FIG. 3 shows an isolated waveform signal of a specific frequency recorded in advance on a magnetic recording medium in order to determine a sense current, and also shows a waveform diagram in which the signal is reproduced. FIG. 4 is a circuit diagram showing a specific configuration of the present invention. FIG. 5 is a diagram showing input / output waveforms of the amplitude discrimination circuit. FIG. 6 is a diagram showing input / output waveforms in the EOR circuit in the waveform asymmetry detector.

The embodiment of the present invention will be described by taking, as an example, a reproduction system of a magnetic disk device that reads data from a magnetic disk using an MR head as a circuit for processing an analog signal.

It is assumed that an isolated waveform having a specific frequency as shown in FIG. 3 is written on the magnetic recording medium 4 before the servo area. This signal is read when the magnetic disk drive starts. At this time, the switch SX in the recording / reproducing unit 1
17, the switch SY18 is closed. This signal has a symmetrical positive and negative signal amplitude with the reference level being zero. When this recording signal is read by the MR head 5, if the setting of the sense current is inappropriate, the signal is reproduced as an analog signal having different positive and negative amplitudes. Hereinafter, the description will be made on the assumption that the signal waveform has positive / negative asymmetry.

Here, 1 is a recording signal reproducing unit, 2 is a waveform asymmetry detecting unit, 3 is a sense current control unit,
Is a magnetic recording medium, 5 is an MR head, 6 is a read / write I
C and 7 are preamplifiers, 11 is an AGC amplifier, 12 is a low-pass filter, 13 is an equalizer, 14 is a peak detection circuit, 15 is an amplitude discrimination circuit, 16 is a data discrimination circuit,
7, 18 are switches, 21 is a delay circuit, 22 is an EOR circuit, 31 is a pulse detection circuit, and 32 is a sense current control circuit.

The analog signal reproduced by the MR head 5 passes through the read / write IC 6, is amplified by the preamplifier 7 with a specific gain value, and is input to the recording signal reproducing unit 1. The configuration of the recording signal reproducing unit 1 includes waveform shaping 11, 12,
13, peak detection 14, amplitude discrimination 15, and data discrimination 16 functions.

The analog signal input to the recording signal reproducing unit 1 is amplified to a signal of a constant amplitude by an auto gain control (AGC) amplifier 11, and low-frequency noise is removed by a low-pass filter 12.
3 performs waveform shaping. The analog signal subjected to the waveform shaping is branched into two signals. One is input to a peak detection circuit 14 and the other is an amplitude discrimination circuit 15
Is input to

The peak detection circuit 14 performs time differentiation on the shaped analog signal waveform, finds the peak position of the reproduction pulse from the zero cross point, and determines the magnetization reversal position of the magnetic recording medium. In the present invention, since the output signal from this circuit is not used, detailed description is omitted.

The amplitude discrimination circuit 15 sets a fixed discrimination level (slice level) for the shaped analog signal waveform. If the reproduction pulse amplitude exceeds this, it is determined that there is a magnetization reversal on the magnetic recording medium. Deciding. From this amplitude discrimination, a determination that there is magnetization reversal on the magnetic recording medium is output as a digital signal (gate signal). This output signal and the output from the peak detection circuit 14 are input to the data discrimination circuit 16 and reproduced. Since the subsequent reproduction function is not the intention of the present invention, description thereof will be omitted.

The present invention uses a signal obtained by splitting the output signal from the amplitude discrimination (level slice) circuit 15 into two. When the amplitude discrimination is described in detail, as shown in FIG.
The waveform-shaped analog reproduction signal is subjected to amplitude discrimination based on the slice level. The slice level can be determined with respect to the positive and negative amplitudes of the reproduced signal, and is defined as a slice level (+) and a slice level (-), respectively. In the present invention, both are set at the same level. The digital signal whose amplitude is discriminated at the slice level (+) is converted to a gate signal X.
L, and a digital signal whose amplitude is discriminated at the slice level (-) is a gate signal YL. As shown in FIG. 5, each of the gate signals is a digital signal having a pulse width of a waveform width of a reproduced waveform at a certain specific level.

That is, as shown by the gate signal XL, the digital signal has a pulse width of the waveform width Pw + at a certain slice level (+) of the reproduced waveform. On the other hand, as shown by the gate signal YL, the signal becomes a digital signal having the pulse width of the waveform width Pw- at a certain slice level (-) of the reproduced waveform. These two digital signals are input to the waveform asymmetry detector 2.

The configuration of the waveform asymmetry detector 2 is the same as that of the delay circuit 2
1. EOR circuit 22 is provided. The gate signal XL and the gate signal YL deviate from each other by a half cycle (T / 2) of a fixed cycle isolated waveform recorded on the recording medium 4.
The delay circuit 21 has a function of delaying one of the signals by a half cycle in order to compare the pulse widths of the two digital signals. When the gate signal XL is input to the delay circuit 21, a digital signal having the same cycle as the gate signal XL, that is, the gate signal XH is output as shown in FIGS. The gate signal YL and the gate signal XH are EO
Input to R circuit.

The EOR circuit is for taking an exclusive OR of the gate signal XH and the gate signal YL. The EOR circuit digitally determines the difference in pulse width between the gate signal XH and the gate signal YL. That is, as shown in FIG. 6, both the gate signal XH and the gate signal YL are at High level or L level.
When the signal is at the low level, a low-level pulse is output. When one of the gate signal XH and the gate signal YL is at a high level or a low level, a high-level pulse is output. An output signal from the EOR circuit is referred to as a gate signal Z. The gate signal Z is input to the sense current control unit 3.

The sense current control section 3 comprises a pulse detection circuit 31 and a sense current control circuit 32.
The pulse signal detection circuit 31 includes the waveform asymmetry detection unit 2.
The gate signal Z which is an output signal from the EOR circuit 22 is input.

The sense current control circuit 32 has a function of setting a sense current step by step and supplying the sense current to the MR head. When the magnetic disk drive is started, an appropriate current value given as an initial value is supplied to the MR head. Then, the sense current is increased stepwise at certain time intervals, and when the sense current reaches the set maximum value, the sense current is gradually decreased in a loop so as to be set to the next set minimum value. If the gate signal Z is present in the pulse detection circuit 31 during the stepwise increase or decrease, or if the pulse has a certain width or more, the stepwise setting is continued. However, when the gate signal Z does not exist in the pulse detection circuit 31 or when the pulse is a pulse having a certain width or less, the setting is kept at that point.

The sense current setting at this time is selected as a sense current value for eliminating the waveform asymmetry of the reproduction signal of the MR head. After an appropriate sense current is set, the recording / reproducing unit 1
The switch SX17 and the switch SY18 are opened, and the adjustment of the sense current ends.

[0031]

By eliminating the positive / negative asymmetry of the reproduction waveform of the MR head, the read margin at the time of data discrimination can be increased, and the reliability of the disk device can be improved. By optimizing the sense current flowing through the MR head, it is possible to correct the positive / negative asymmetry of the reproduction waveform of the MR head.

According to the present invention, the above-described adjustment of the sense current can be automatically performed every time the magnetic disk device is started, and the reliability of the magnetic disk device can be improved. Further, since the operation is performed by branching from the reproduction circuit, it is not necessary to configure a complicated circuit, so that the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic configuration of the present invention.

FIG. 2 is a waveform diagram illustrating asymmetry of a reproduction signal from an MR head.

FIG. 3 is a diagram showing an isolated waveform signal of a specific frequency previously recorded on a magnetic recording medium and a signal obtained by reproducing the signal.

FIG. 4 is a circuit diagram showing a specific configuration of the present invention.

FIG. 5 is a diagram showing input / output waveforms of the amplitude discrimination circuit.

FIG. 6 is a diagram showing input / output waveforms in an EOR circuit in a waveform asymmetry detection unit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Recording signal reproduction part 2 Waveform asymmetry inspection part 3 Sense current control part 4 Magnetic recording medium 5 MR head 6 Read / write IC 7 Preamplifier 11 Auto gain control (AGC) amplifier 12 Low pass filter 13 Equalizer 14 Waveform discrimination circuit 15 Amplitude discrimination (Level slice) circuit 16 data discrimination circuit 17, 18 switch 21 delay circuit 22 EOR circuit 31 pulse detection circuit 32 sense current control circuit

Claims (4)

[Claims] 1. A magnetic disk drive having at least a head for recording or reproducing information on or from a magnetic recording medium and a recording / reproducing means for processing an information signal to or from the head. Using a magnetoresistive head as a head for reproducing the data, and correcting means for correcting the asymmetry of the positive / negative amplitude of the analog reproduced signal obtained by reproducing the reference signal recorded on the magnetic recording medium with the magnetoresistive head. A magnetic disk drive comprising: 2. The magnetic disk drive according to claim 1, wherein the asymmetry correcting means includes a circuit for flowing a sense current to the magnetoresistive head, and a reproducing unit for reproducing an information signal from the head. A magnetic disk drive, comprising: an asymmetry detection unit that detects the positive / negative amplitude asymmetry of the analog reproduction signal; and a sense current control unit that controls the sense current based on the detection of the positive / negative amplitude asymmetry. . 3. The magnetic disk drive according to claim 2, wherein the reproducing section slices positive and negative amplitudes of the analog reproduction signal at a predetermined level and extracts respective waveform widths corresponding to the positive and negative amplitudes. A magnetic disk drive, comprising: a circuit; and the asymmetry detection unit includes a circuit for comparing the respective waveform widths. 4. A magnetic recording medium on which a reference frequency for symmetrical positive and negative signal amplitudes is recorded for detecting asymmetry of positive and negative amplitudes of an analog reproduction signal.