JPH07320213A - Data recording/reproducing device and bias adjusting method of magnetic head - Google Patents

Abstract

PURPOSE:To reduce error rate of a data reproducing system and to improve reliability of the device by adjusting a bias current value to be properly set in the data recording/reproducing device using a magnetic head which requires the supply of a bias current like as an MR head, etc. CONSTITUTION:In an HDD(hard disk device) using MR head 1b, the bias current is supplied to the MR head 1b from a head amplifier 3 at the time of data reproducing operation. Margin of the reproduced data is calculated by a margin measuring circuit 6. By a controller 9, the bias current value is adjusted through a bias control circuit 7 taking a value in which the margin is maximum as the appropriate value based on the relation between the margin and the bias current value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data recording / reproducing apparatus, such as a hard disk drive, which uses a magnetoresistive magnetic head requiring a bias current.

[0002]

2. Description of the Related Art Conventionally, for example, a hard disk drive (HD
The data recording / reproducing apparatus such as D) is provided with a magnetic head (hereinafter simply referred to as a head) for recording / reproducing data on / from a disk which is a recording medium. The head includes an inductive head such as a thin film head and an MR (magneto re
It is roughly classified into a magnetic flux response type head such as a similar head.

In recent years, particularly in HDDs, the recording density has dramatically increased, and the reproduced signal per bit becomes weak, so that a highly sensitive head is required. The MR head is a magnetoresistive head that utilizes an anisotropic magnetoresistive effect to detect a magnetic field generated on the surface of a disk as a change in resistance value. The MR head has a high sensitivity with respect to an induction type thin film head and the like, and has an advantage that the magnitude of the reproduction signal does not depend on the running speed of the disk. Therefore, a high recording density HDD using an MR head as a head has been developed.

The MR head is a read-only head.
Therefore, in a data recording / reproducing device such as an HDD,
A write-only head is required in addition to the MR head. Specifically, an inductive thin film head is used as a write-only head, and a head having a composite head structure including this thin film head and an MR head is used.

By the way, the MR head is
A bias current (or a sense current) is required, and a resistance change due to a magnetic field is detected as a voltage change to reproduce the information recorded on the disc. The bias current is set to a predetermined value by the bias control circuit to generate the bias magnetic field and enable the operation in the linear region.

FIG. 8 shows the conversion characteristics of the MR head when the horizontal axis is the magnetic field H and the vertical axis is the output amplitude (voltage level). The magnetic field H indicates the strength of the recording magnetic field on the disc. With such a non-linear characteristic, the polarity of the signal magnetic field cannot be determined. Therefore, a bias current is supplied to apply a bias magnetic field to operate in a linear region of characteristics.

Now, as shown in FIG. 8, when the bias magnetic fields A and B are generated by the bias current, in the linear region of the bias magnetic field A, the positive and negative of the output amplitude are symmetrical with respect to the center. On the other hand, in the linear region due to the bias magnetic field B, the positive and negative of the output amplitude are asymmetric with respect to the center, which is inappropriate as the bias current value.

[0008]

In the data recording / reproducing apparatus using the MR head, it is necessary to adjust the bias current in the MR head to generate an appropriate bias magnetic field. In particular, as a signal processing system for data reproduction,
PRML (Partial Response Maxi)
In a method that requires amplitude detection processing, such as the mum Likelihood method, it is required that the output amplitude of the reproduced waveform be positive and negative, symmetrical, and have the same absolute value.
When the error in the output amplitude value is large due to an improper bias magnetic field, the error rate of the data reproducing system is deteriorated and the reliability of the device is lowered.

The object of the present invention is to reproduce data by adjusting the bias current value so that it can be set appropriately in a data recording / reproducing apparatus using a magnetic head such as an MR head which requires the supply of a bias current. It is to reduce the error rate of the system and improve the reliability of the device.

[0010]

SUMMARY OF THE INVENTION According to the present invention, in a data recording / reproducing apparatus equipped with, for example, a magnetoresistive effect type magnetic head which requires a bias current during a read operation, the data reproduced by the data reproducing means causes an error. The apparatus has a margin measuring unit that calculates a margin that is a margin up to a limit value and a bias current adjusting unit that determines a bias current that maximizes the margin.

[0011]

According to the present invention, the bias current is supplied to the magnetic head during the read operation for reading data from the recording medium. The data reproducing means reproduces the read signal output by the magnetic head into data. The margin measuring means calculates the margin of the reproduced data. Based on the relationship between the margin and the bias current, the bias current adjusting means adjusts the bias current so that the bias current value when the margin becomes maximum becomes an appropriate value.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a hard disk drive (HD
D) is a block diagram showing a main part, FIG. 2 is a block diagram showing a configuration of a margin measuring circuit according to the embodiment, FIG. 3 is a flow chart for explaining the operation of the embodiment, and FIG. FIG. 5 is a block diagram showing a modification of the margin measuring circuit concerned, and FIG. 5 is a block diagram showing a modification of the HDD according to the embodiment.

As shown in FIG. 1, the HDD of the embodiment is
A head 1 for reading / writing data from / to a disk 2 as a recording medium, a head amplifier 3, a read data reproducing circuit 4, a decoder 5, a margin measuring circuit 6, a bias control circuit 7, an encoder 8 and a controller (HDC).
9 and a memory 10.

The head 1 is a thin film head 1a for writing only.
And a read-only MR head 1b of the magnetoresistive type, which is a magnetic head having a composite head structure. The MR head 1b has a bias strip 1c for generating a bias magnetic field by supplying a bias current.

The thin film head 1a generates a recording magnetic field by the write current output from the head amplifier 3 to write data on the disk 2. The MR head 1b is
A read operation is performed in which a bias magnetic field is generated by the bias current supplied from the head amplifier 3 to the bias strip 1c and the recording magnetic field of the disk 2 is converted into a read signal.

The head amplifier 3 amplifies the read signal (read current) read by the MR head 1b and outputs it to the read data reproducing circuit 4. Read data reproduction circuit 4
Converts an analog read signal into digital read data. The decoder 5 is the read data reproducing circuit 4
The read data output from is decoded into, for example, NRZ code data.

The controller 9 constitutes an interface between the HDD and the host computer, and controls transfer of various interface signals and read / write data.
That is, the controller 9 saves the read data output from the decoder 5 in the memory 10 and transfers it to the host computer. Further, the controller 9 receives the write data transferred from the host computer and receives the write data from the memory 10
And output to the encoder 8. In this embodiment, the controller 9 executes the adjustment process of the bias current supplied to the bias strip 1c of the MR head 1b.
The memory 10 is a buffer memory accessed by the controller 9, and stores relationship information (table) between the margin and the bias current value in addition to the read / write data.

The bias control circuit 7 is a control circuit for causing the head amplifier 3 to output a bias current corresponding to the bias current value set by the controller 9.
The margin measuring circuit 6 calculates the margin of the reproduced read data based on the read data RM including the margin information given from the read data reproducing circuit 4, and outputs it to the controller 9. The read data RM including margin information is a signal that includes analog variations before completely becoming digital data.

Specifically, the margin measuring circuit 6, as shown in FIG. 2, includes subtraction circuits 11, 15, 17, a center value memory 12, a maximum value detection circuit 13, a minimum value detection circuit 14, an upper limit value memory 16 and It has a lower limit memory 18. The subtraction circuit 11 calculates an error between the waveform amplitude value of the input read data RM and the reference amplitude value (the ideal center value of the histogram shown in FIGS. 6 and 7) stored in the center value memory 12 in advance. . The subtraction circuit 11 inputs the read data R
Calculate the error for each sample of M. Maximum value detection circuit 1
3 detects the maximum value among the errors for each sample output from the subtraction circuit 11. On the other hand, the minimum value detection circuit 14 detects the minimum value. The subtraction circuit 15 has the upper limit memory 1 in advance.
The error between the upper limit value stored in 6 and the detected maximum value is calculated and output as the value of the upper margin. Further, the subtraction circuit 17 calculates an error between the lower limit value stored in advance in the lower limit value memory 18 and the detected minimum value, and outputs it as a lower margin value.

Next, the operation of the embodiment will be described. (Basic Operation of HDD) First, in the data write operation, as shown in step S1 of FIG. 3, when the controller 9 receives write data from the host computer, the write data is output to the encoder 8. The encoder 8 encodes the write data and outputs it to the head amplifier 3 (step S2).
The write-only thin film head 1a generates a recording magnetic field by the write current output from the head amplifier 3 to write data on the disk 2 (step S3). As a result, magnetic recording is performed on the disk 2 according to the write data from the host computer (step S
4).

Next, in the data read operation, the read-only MR head 1b converts the recording magnetic field corresponding to the data recorded on the disk 2 into a read signal (step S6). At this time, the MR head 1b is operated by the head amplifier 3
From the bias strip 1c, a bias current is supplied to generate a bias magnetic field (step S5).

The head amplifier 3 amplifies the read signal from the MR head 1b and outputs it to the read data reproducing circuit 4 (step S7). The read data reproducing circuit 4 converts the analog read signal output from the head amplifier 3 into digital read data (step S8). The decoder 5 decodes the read data output from the read data reproducing circuit 4 and outputs it to the controller 9. The controller 9 transfers the reproduced data to the host computer. (Margin measurement operation) In the present invention, the margin measurement is performed to measure the margin amount of the reproduced data in order to set the bias current supplied to the read-only MR head 1b to an appropriate value based on the margin amount of the read data. The action is executed. The principle of this margin measurement will be described with reference to FIGS. 6 and 7.

First, if the bias current value supplied to the MR head 1b is appropriate, a reproduced signal waveform having positive and negative symmetry can be obtained as shown in FIG. 6 (A).
FIG. 2B is an example of a reproduction signal including data, in which a circle indicates a data sample and corresponds to the read data RM input to the margin measuring circuit shown in FIG.

In this example, the data samples show seven kinds of levels in the amplitude direction, and are dispersed in the amplitude direction due to distortion of the signal waveform and mixing of noise. FIG. 6C is a histogram showing the dispersion state. The horizontal axis represents the signal amplitude, indicating that there are seven types of histograms. Figure 6
In (C), the dotted line is the threshold value, and no read error occurs in the reproduced data unless the variance exceeds the threshold value and enters another area. FIG. 3D is a collection of those histograms, which is for measuring the margin of the reproduced data. Same figure (D)
In the histogram, the narrower the dispersion of the amplitude value and the wider the gap with the threshold value, the larger the margin amount becomes.
Indicates that the read data error rate is low.

Here, the margin amount is expressed by the difference between the maximum and minimum values of the variance and the upper and lower limits of the threshold. In this case, an appropriate margin amount can be measured by giving a weight according to the degree of dispersion and obtaining the standard deviation of the distribution.

On the other hand, when the bias current value supplied to the MR head 1b is improper, the reproduced signal waveform becomes asymmetric between positive and negative as shown in FIG. 7 (A). 6A to 6D are diagrams corresponding to FIGS. 6A to 6D, respectively.

If the bias current value is improper, FIG.
As shown in (C), the shape of the negative histogram with large distortion is broken, and the dispersion is large. Similarly, the histogram of FIG. 7D shows that the variance is large. From the observation of the histogram shown in FIG. 7C, the negative side of the reproduced signal waveform is distorted due to saturation, so the bias magnetic field needs to be adjusted in the opposite direction. However, as shown in FIG. 8, the optimum point of the bias is not so wide, and in practice, fine adjustment is performed within a limited range.
Therefore, by observing the histogram in FIG. 7D, the bias current is slightly changed while measuring the margin amount, and the bias current value corresponding to the maximum value of the measured margin amount is set as the optimum value. According to the monotonous curve as shown in FIG. 8, the optimum value is concentrated on almost one value.

Based on such a principle, the margin measuring circuit 6 and the controller 9 calculate the margin amount from the data (data sample) RM reproduced by the read data reproducing circuit 4 (step S9). In particular,
In the margin measuring circuit 6 shown in FIG.
As shown in FIG. 6B or FIG. 7B, a data sample indicating the amplitude value of the reproduced waveform is input to the. When the distribution of the data samples is a plurality of histograms, the margin measuring circuit 6 is required for each histogram (data area).

The subtraction circuit 11 calculates an error from the reference amplitude value (ideal center value of the histogram) stored in the center value memory 12 in advance. The maximum value detection circuit 13 and the minimum value detection circuit 14 detect the maximum value and the minimum value from the output value from the subtraction circuit 11, respectively. By inputting a large number of data samples, the maximum and minimum values become the maximum and minimum values of the histogram of variance. The area in which this histogram should fit is determined by the upper limit value stored in advance in the upper limit memory 16 and the lower limit value stored in the lower limit memory 18. The subtraction circuit 15 calculates the error between the detected maximum value and the upper limit value, and outputs it as the value of the upper margin. Further, the subtraction circuit 17 calculates the error between the detected minimum value and the lower limit value, and outputs it as the value of the lower margin. The upper and lower margins are output by the number of data areas.
As shown in FIG. 7C, when the margin is deteriorated due to biasing only a specific histogram, it means that there is waveform distortion in that region.

The controller 9 totalizes the margin amounts calculated for each data area by the margin measuring circuit 6 and comprehensively evaluates them to determine the margin. Further, the controller 9 uses the memory 10 in the form of a table in which the determined margin and the bias current value at that time are associated with each other.
(Step S10). The controller 9 changes the bias current of the MR head 1b through the bias control circuit 7 and executes the read data margin measurement process at that time (step S13).

The controller 9 determines the maximum margin among the margins stored in the memory 10, and sets the bias current value corresponding to this maximum margin as the optimum value (YES in steps S11 and S12, S14). (Modification of Margin Measuring Circuit) FIG. 4 shows a modification of the margin measuring circuit of the embodiment. This margin measurement circuit
It has a determination circuit 19 for determining the data area of the input read data RM. The determination circuit 19 searches the center value memory 12 for a center value that matches the determined data area and outputs it. That is, as shown in FIG. 7 (D), it is a method of calculating a margin by using a histogram that is integrated in a certain data area. The other circuits are shown in Figure 2.
The description is omitted because it is similar to that shown in FIG.

In the case of the margin measuring circuit of such a system, the circuit shown in FIG. 2 requires a margin measuring circuit for each data area, but only one circuit is required. However,
Since the distortion of the reproduced signal waveform cannot be directly observed, it is necessary to measure while changing the bias current value so that the margin is maximized. However, since the range of the optimum bias point is not so wide, the maximum margin can be obtained by finely adjusting the bias current value. (Modification of HDD) FIG. 5 shows a modification of the HDD of the embodiment, which is an HDD having a read data reproducing circuit adopting the PRML method as a reproduction signal processing method. This read data reproducing circuit is a variable gain amplifier (VG
A) 20, low-pass filter (LPF) 21, A / D conversion circuit 22, digital equalizer (equalize)
er) 23, ML (Maximum Likeliliho)
od) circuit 24, gain controller 25, and timing controller 26.

The read signal read from the MR head 1b is amplified by the head amplifier 3 and further VGA2.
It is converted to an appropriate amplitude by 0. The output signal of the VGA 20 is subjected to noise removal and frequency characteristic adjustment processing by the LPF 21, and then is sampled by the A / D conversion circuit 22 and converted into a digital signal.

The digital signal from the A / D conversion circuit 22 is output as a data sample (RM) by the compensation process of the amplitude characteristic by the digital equalizer 23. This data sample (RM) is output to the margin measuring circuit (consisting of a plurality of circuit groups 6a to 6f) 6. The data sample (RM) is output to the timing controller 26 and the gain controller 25. The gain controller 25 is an adjustment circuit for adjusting the gain of the VGA 20. The timing controller 26 is a circuit for generating a sampling clock for the A / D conversion circuit 22.

On the other hand, the data sample (RM) is processed by the ML circuit 24 to reduce the influence of noise, and the decoder 5
Given to. The decoder 5 decodes the reproduced data,
Output to the controller 9. The operations of the margin measuring circuit 6 and the bias control circuit 7 according to the present invention are the same as those shown in FIG.

As described above, during the data reproducing operation,
The margin of the reproduced data (data sample) is measured, and the bias current value of the MR head 1b is finely adjusted so that this margin becomes maximum. As a result, the read-only head requires an MR that requires a bias magnetic field for the read operation.
An appropriate bias current can be supplied to the head 1b. The bias current adjusting operation based on the margin measuring operation is executed at the time of normal data reproducing operation or HDD startup. However, once the bias current is adjusted to an appropriate value, it does not have to be performed so frequently, so
Normally, it may be executed when the HDD is started or every time a fixed time elapses after the start.

Furthermore, as a bias adjusting method, it is effective to adjust the bias current according to the following temperature change or HDD power supply voltage change. First,
Since the conversion characteristic of the MR head 1b changes due to the temperature change, the internal temperature of the HDD is detected. That is, a temperature sensor is provided inside (or outside) the HDD, and when a significant temperature change that needs adjustment is detected, the bias current is adjusted. Specifically, the controller 9 monitors the temperature change by the detection signal of the temperature sensor, and when a significant temperature change is detected, the bias current is adjusted based on the margin measurement operation.

Secondly, the amplification characteristic of the head amplifier 3 changes due to the change of the power supply voltage, and as a result, the bias current value output from the head amplifier 3 changes. So HD
A power supply voltage monitoring circuit is provided at a predetermined position of the power supply line inside D, and when a change in the power supply voltage is detected, it is output to the controller 9. The controller 9 executes the adjustment of the bias current when it detects a significant fluctuation in the power supply voltage that needs to be adjusted.

[0039]

As described above in detail, according to the present invention, M
In a data recording / reproducing apparatus using a magnetic head such as an R head that requires supply of a bias current, a data margin is measured during a data reproducing operation, and a bias current value is adjusted so that the margin is maximized. . Therefore, the bias current of the head that executes the data reproducing operation can be appropriately set, and as a result, the error rate of the data reproducing system can be reduced and the reliability of the device can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a main part of a hard disk device (HDD) according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a margin measuring circuit according to the embodiment.

FIG. 3 is a flowchart for explaining the operation of the embodiment.

FIG. 4 is a block diagram showing a modification of the margin measuring circuit according to the same embodiment.

FIG. 5 is a block diagram showing a modification of the HDD according to the embodiment.

FIG. 6 is a diagram for explaining a margin measuring operation according to the embodiment.

FIG. 7 is a diagram for explaining a margin measuring operation according to the embodiment.

FIG. 8 is a diagram for explaining operating characteristics of a conventional MR head.

[Explanation of symbols]

1 ... Magnetic head, 1a ... Thin film head, 1b ... MR head, 1c ... Bias strip, 2 ... Disk, 3 ...
Head amplifier, 4 ... Read data reproducing circuit, 5 ..., Decoder, 6 ... Margin measuring circuit, 7 ... Bias control circuit,
8 ... Encoder, 9 ... Controller (HDC), 10 ...
Memory, 20 ... Variable gain amplifier (VGA), 21 ... Low-pass filter (LPF), 22 ... A / D conversion circuit, 2
3 ... Digital equalizer, 24 ... ML (Maxim
um Likelihood) circuit, 25 ... Gain controller, 26 ... Timing controller.

Claims (8)

[Claims] 1. A recording medium for recording data, a magnetic head for reading data from the recording medium and requiring a bias current during the read operation, and a read signal output by the magnetic head for reproducing data. Data reproducing means, a margin measuring means for measuring a margin of data reproduced by the data reproducing means, and a maximum margin based on the relationship between the margin measured by the margin measuring means and the bias current. And a bias current adjusting means for determining the bias current. 2. A recording medium for recording data, a magnetoresistive magnetic head for reading data from the recording medium and requiring a bias current during the read operation, and a read output by the magnetic head. Data reproducing means for reproducing a signal into data; margin measuring means for measuring a margin of data reproduced by the data reproducing means; and the margin and the bias current value measured by the margin measuring means, Bias current adjusting means for calculating a maximum value in the margin calculated by the margin measuring means in response to a change in bias current value and setting the bias current value corresponding to the maximum value as an optimum value. A data recording / reproducing apparatus characterized by being provided. 3. A data recording / reproducing apparatus having a recording medium for recording data and a magnetic head requiring a bias current during a read operation, wherein a read signal read from the recording medium by the magnetic head is reproduced as data. A step of measuring the margin of the reproduced data, a step of adjusting the bias current until the maximum value of the measured margin is measured, and a step of adjusting the bias current that maximizes the margin to an optimum bias current. And a bias adjusting method for a magnetic head. 4. A recording medium for recording data, a magnetoresistive magnetic head for reading data from the recording medium and requiring a bias current at the time of the reading operation, and a magnetic head according to a set bias current value. Bias current control means for supplying the bias current to the magnetic head, data reproducing means for reproducing the read signal output by the magnetic head into data, and dispersion of the amplitude of the reproduced signal reproduced by the data reproducing means. Margin measuring means for measuring the margin of the data based on the state; memory means for storing the margin calculated by the margin measuring means and the bias current value corresponding to the margin; and the bias current control. A plurality of margins stored in the memory means in response to changes in the bias current value of the means A data recording / reproducing apparatus, comprising: a bias current adjusting means for calculating a maximum value among the above, and setting the bias current value corresponding to the maximum value in the bias current control means as an optimum value. 5. The margin measuring means divides the reproduction signal into a plurality of data areas, and measures the margin amount for each histogram when the dispersion state of each data area is indicated by a plurality of types of histograms. 5. The data recording / reproducing apparatus according to claim 4, wherein the margin is determined based on the total of the margin amounts. 6. The margin measurement means divides the reproduction signal into a plurality of data areas, and when the dispersion state of each data area is indicated by a plurality of types of histograms, the reproduction reproduced by the data reproduction means. 5. A determination means for determining the data area of a signal is provided, the margin amount of a histogram corresponding to the determined data area is measured, and the margin is determined based on the margin amount. Data recording and reproducing device. 7. A recording medium for recording data, a magnetic head for reading data from the recording medium and requiring a bias current at the time of this reading operation, and the bias current according to a set bias current value. Bias current control means for supplying to the magnetic head, data reproduction means for reproducing the read signal output by the magnetic head into data, temperature change detection means for detecting a change in ambient temperature of the magnetic head, When it is necessary to adjust the bias current according to the detection result of the temperature change detecting means, the margin of the data reproduced by the data reproducing means is measured, and the measured margin and the bias current are Based on the relationship, the bias current value that maximizes the margin is set as the optimum value in the bias current control means. Data recording and reproducing apparatus characterized by comprising a bias current regulating means. 8. A recording medium for recording data, a magnetic head for reading data from the recording medium, which requires a bias current at the time of this reading operation, and the bias current according to a set bias current value. Bias current control means for supplying to the magnetic head, data reproducing means for reproducing the read signal output by the magnetic head into data, and voltage fluctuation for detecting fluctuation of power supply voltage supplied to the bias current controlling means. When it is necessary to adjust the bias current according to the detection means and the detection result of the voltage fluctuation detection means, the margin of the data reproduced by the data reproduction means is measured, and the measured margin and the margin are measured. The bias current value that maximizes the margin based on the relationship with the bias current is set as an optimum value. Data recording and reproducing apparatus characterized by comprising a bias current regulating means for setting the control means.