JPH11238205A - Signal waveform controller for mr head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid instability by reading known data with an MR head while using plural sense currents and detecting a sense current with which the error rate of data decoded in a signal processing part becomes lowest in the read data to optimize asymmetry of the output amplitude and the half-value of the reproduced signal waveform of the head as the error rate of an actual magnetic recording device. SOLUTION: A PRML signal processing part 18 performs a wavefrom equalization and the decoding of a signal with respect to the reproduced wavefrom obtained from the sense current of an MR head 12. The recorded signal written on a magnetic record medium 32 is converted into the reproduced signal of the head 12 and it is decoded to be outputted to a comparator circuit 14. The signal inputted from the processing part 18 and the data series determined at first in a recording system signal processing part 22 are compared in the circuit 14 and, as a result, the number of obtained erroneous data is transmitted to a system controller 16, which controls a viterbi decoding circuit 183 so as to change a viterbi decoding threshold value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal waveform control device for an MR head (magnetoresistive head), and more particularly, to a signal waveform control device for realizing a magnetic recording device with high recording density and high reliability. Related to the device.

[0002]

2. Description of the Related Art In recent years, a magnetic recording device connected to a small-sized host or the like has been required to have a higher recording density. In order to realize this high recording density, an MR head or a PR using an MR element (magnetoresistive element) as a reproducing element is used.
New technologies such as ML signal processing technology are being introduced.

However, the reproduced signal waveform of a magnetic recording device using this MR head has an output amplitude and half width of a positive pulse and an output amplitude and half width of a negative pulse. There was a point of view (hereinafter referred to as "asymmetry") that would greatly differ. Therefore, it has been difficult to increase the density of the magnetic recording device. In particular, when the MR head and the PRML signal technology are used at the same time, the influence of this asymmetry has been remarkably exhibited.

A conventional technique for reducing this asymmetry is described in Japanese Patent Application Laid-Open No. 4-205903. This conventional technique detects a peak value of a positive pulse and a peak value of a negative pulse of one solitary wave, and takes a difference between them,
This is a method of optimizing the peak value of the positive pulse and the peak value of the negative pulse so that they have the same value.

[0005]

However, in this prior art, only one solitary wave or an individual solitary wave is considered. Therefore, when the condition or the state changes, or the characteristics of the solitary wave are changed by the average of the device. However, there is a problem that it is not possible to cope with characteristics that are not typical characteristics or characteristics of each part having different conditions in the apparatus. Further, since only the output amplitude of the solitary wave is considered, it is not possible to cope with a case where the half width or the like is different between the positive pulse and the negative pulse.

Further, with the recent trend toward narrower tracks, MR
There is a demand for miniaturization of the element, and as a result, fluctuations in asymmetry during operation of the device (hereinafter referred to as “instability”) have become a problem. The prior art described above could not cope with this instability at all.

Furthermore, it has been known that the error rate of a reproduced signal is reduced in a state in which a vertically symmetrical waveform is obtained in a magnetic head that has been widely used in the past. However, the MR head is characterized in that the output amplitude increases when the sense current is increased. Even if the output amplitude is somewhat asymmetric, the larger the output amplitude, the lower the error rate of the reproduced signal may be. The above-mentioned prior art cannot cope with this problem at all.

Therefore, the emergence of a new signal processing method and circuit has been desired.

[0009]

Accordingly, an object of the present invention is to optimize the asymmetry of the output amplitude and half-value width of the reproduction signal waveform of the MR head as an error rate of an actual magnetic recording apparatus, and to cope with instability. An object of the present invention is to provide a signal waveform control device for an MR head which realizes a magnetic recording device having a high recording density and high reliability.

[0010]

A signal waveform control device according to the present invention comprises: a sense current control means for causing an MR element to read known data recorded on a magnetic recording medium by using a plurality of sense currents; A signal processing unit that decodes a reproduction signal read by the MR element; and a comparison operation unit that detects, among the plurality of sense currents, the sense current that minimizes an error rate of data decoded by the signal processing unit. It basically has. Further, decoding control means for controlling a decoding threshold value in the signal processing unit, recording system control means for recording known data on a magnetic recording medium, and when causing the MR element to read data recorded on the magnetic recording medium. Any of off-track control means for intentionally off-tracking may be further provided.

For example, an arbitrary data series created by the recording system control means is output to a recording head and recorded on a magnetic recording medium. By passing a sense current through the MR head, a reproduced signal waveform of the recorded signal is obtained and output to the signal processing unit. The signal processing section decodes the data series using a certain threshold value and outputs the data series to the comparison operation means. The comparison operation means compares the decoded data series with the data series generated by the recording system control means, and calculates the coincidence rate and the like. Then, the threshold value is changed through the decoding control means in an arbitrary range, and the coincidence rate at the time of intentionally bad conditions is calculated,
The calculation result of each matching rate is obtained. This series of operations is performed with an arbitrary range of sense current, and finally, a sense current value having the best matching rate or an allowable sense current value is adopted. Also, instead of making the threshold of the decoding control means worse to calculate the match rate, the match rate may be calculated by intentionally off-tracking and reading the reproduced signal. Further, a switching circuit for outputting a reproduction signal to either the comparison operation means or the reproduction system signal processing unit may be provided.

[0012]

FIG. 1 is a functional block diagram showing an embodiment of a signal waveform control device according to the present invention. Hereinafter, description will be made based on this drawing.

The signal waveform control device 10 of the present embodiment
Comparison operation means (comparison circuit 14 and system controller 16) for comparing and operating the signal obtained from the RML signal processing unit 18 and the signal generated by the recording system signal processing unit 22;
Decoding control means for transmitting a control signal to a Viterbi decoding circuit 183 which is a part of the RML signal processing unit 18 (Vitervis threshold control circuit 15 and system controller 16)
And sense current control means (system controller 16 and sense current control circuit 17) for controlling the sense current of MR head 12, and recording system control means (system controller 16) for recording known data on magnetic recording medium 32
And a switching circuit 20 for outputting the signal waveform obtained from the PRML signal processing unit 18 to either the comparison circuit 14 or the reproduction system signal processing unit 24.

The system controller 16 is composed of an MPU and its program. In addition to functions as a comparison operation unit, a decoding control unit, a sense current control unit, and a recording system control unit, a PRML signal processing unit 18, a switching circuit 2
0, a function of controlling the recording system signal processing unit 22, the reproduction system signal processing unit 24, and the like.

[0015] The PRML signal processing unit 18 is provided with an MR head 1
A low-pass filter (LPF) 181 that removes high-frequency noise from the reproduced signal waveform and shapes it, and performs waveform equalization and signal decoding on the reproduced waveform obtained from the second sense current. And a Viterbi decoding circuit 183 for decoding the PR waveform into an original data sequence. n-value equivalent circuit 182
In, for example, the n value when equalizing to PR4 is 3, the n value when equalizing to EPR4 is 5, and the EEP
When it is desired to perform R4 equalization, the n value is 7.

The comparison operation means comprises the comparison circuit 14 and a part of the function of the system controller 16 for calculating the coincidence rate of the result obtained therefrom by an arbitrary method. The decoding control means uses the P in the Viterbi decoding circuit 183.
A vitervis threshold control circuit 15 for controlling a threshold value for Viterbi detection of the R waveform to an arbitrary value in accordance with an instruction from the system controller 16;
6 and some of the functions. The sense current control means includes some functions of the system controller 16 and M
And a sense current control circuit 17 for changing a sense current value supplied to the R head 12 according to an instruction from the system controller 16.

The recording system signal processing section 22 has an original function of converting a data series signal to be recorded and stored into a signal conforming to the magnetic recording apparatus, and also has a function of the system controller 16 (recording system control means). It also has a function of generating a signal converted from an arbitrary data series according to an instruction. The recording-system signal processing unit 22 is connected to an amplification circuit 30 for amplifying a recording signal and a recording thin-film head 34 for writing information on a magnetic recording medium 32 with the recording signal amplified by the amplification circuit 30. ing.

An amplification circuit 36 for amplifying a reproduction signal is connected to the MR head 12.

FIG. 2 is a waveform chart showing an example of the operation of the signal waveform control device of FIG. FIG. 2A shows the recording current input to the recording thin film head 34 of FIG. FIG. 2 (b) shows the MR input to the PRML signal processing unit of FIG.
3 shows a reproduction signal waveform of the head 12. FIG. 2 (c)
Indicates a reproduced signal waveform from which high-frequency noise has been removed by the LPF 181. FIG. 2D shows a reproduced signal waveform from which high-frequency noise has been removed by the LPP 181 similarly to FIG. 2C, but shows a reproduced signal waveform when the asymmetry is large.

In this embodiment, for the sake of simplicity, FIG. 2 shows a state when a data sequence having a single frequency is transmitted. Although this signal waveform may be used, signal waveforms having various periods are closer to the magnetized signal waveforms when a normal magnetic recording device is used, so an actual signal waveform controller uses such random period data. The affiliate is recommended.

FIG. 3 is a flowchart showing an example of the operation of the signal waveform control device of FIG. Hereinafter, FIGS. 1 and 2
The operation of the system controller 16 will be mainly described with reference to FIG.

First, the system controller 16, which controls the entire system, sends a control signal to the switching circuit 20, and shifts to the sense current optimization mode. Then, a control signal is sent to the recording signal processing unit 22 so as to generate an arbitrary data sequence. Then, the recording-system signal processing unit 22 generates a recording signal (FIG. 2A), and the recording signal is amplified by the amplifier circuit 30 and written to the magnetic recording medium 32 by the recording thin-film head 34 (Step 101). ). The system controller 16 determines a variable range, a step, and the like between the sense current and the decoding threshold value of the Viterbi decoding circuit 183, and first sends a control signal to input a certain value (initial value) (step 102).

The recording signal written on the magnetic recording medium 32 is converted into a reproduction signal by the MR head 12 and
6 (FIG. 2B), the PRML signal processing unit 18 (FIG.
(C), FIG. 2 (d)), the signal is decoded and output to the comparison circuit 14 via the switching circuit 20. Comparison circuit 14
Then, the signal input from the PRML signal processing unit 18 is compared with the data sequence initially determined by the recording system signal processing unit 22, and the number of error data as a result is sent to the system controller 16. After calculating the coincidence rate (error rate), the system controller 16 sends a control signal to the Vitervis threshold control circuit 15 to change to the next Viterbi decoding threshold (steps 103 to 105). By repeating this operation and calculating the match rate (error rate) at the previously determined Viterbi decoding threshold, the system controller 16 sends a control signal to the sense current control circuit 17 to change the sense current. . Then, the same operation is performed with the reproduction signal waveform of the MR head 12 obtained from the new sense current (steps 106 and 107).

After calculating the coincidence rates (error rates) for all of the previously determined sense current values, the system controller 16 searches for the best sense current value condition based on the operation results of the respective coincidence rates (error rates). (Step 108). Thereafter, if the reproducing operation is performed with this sense current, the optimum PRML signal processing can be performed with the reproduced waveform.

Also, a read error (Read error)
At the time of (Error), the operation shifts to the sense current optimization mode and the above operation is performed, and the instability of the asymmetry is confirmed and reduced, so that when the instability is large or a read error due to sudden asymmetry can be relieved. At this time, the magnetic recording medium 32
Using an area or system area that is not already recorded in
The same operation as described above is performed.

FIG. 4 is a graph showing an example of a sense current optimizing operation of the signal waveform control device of FIG. Less than,
Description will be made based on this drawing.

FIG. 4A shows a sense current 10.0 [mA].
FIG. 4B shows the bit error rate when the sense current is 12.5 [mA], and FIG.
(C) shows the bit error rate when the sense current is 15.0 [mA]. In FIG. 4, the plot is a value obtained as a result of the actual calculation, and the solid line is an approximate line of the plot. As shown in this figure, the optimum sense current value is calculated to be 12.5 [mA] in this case.

As another actual operation method, the width of the Viterbi decoding threshold value at a certain allowable bit error rate is calculated, and the sense current having the widest width is adopted. The sense current value having the largest number of matching Viterbi decoding threshold values may be adopted, and so on.

In this embodiment, the coincidence rate (error rate) is calculated by changing the Viterbi decoding threshold. Instead, the range and step size of the off-track of the MR head 12 are deliberately determined. May be read to calculate the coincidence rate (error rate). In this case, an off-track control unit (a head position control circuit and a system controller) for controlling the off-track of the MR head 12 is provided instead of the decoding control unit. Since the operation is the same, it is omitted.

The signal waveform control device according to the present embodiment
It may be built in as a function of the magnetic disk drive, or may be connected as needed as an external device.

[0031]

According to the signal waveform control device of the present invention, since the asymmetry of the reproduced signal waveform can be reduced by optimizing the sense current, the actual error rate in the magnetic recording device can be reduced. . Further, it is possible to immediately cope with the asymmetry fluctuation (instability) of the reproduced signal waveform caused by the transient response of the amplifier circuit or the like, and reduce the asymmetry of the reproduced signal waveform and transmit the signal to the signal processing unit. be able to. Furthermore, during normal operation of the magnetic recording device,
Even when asymmetric fluctuation (instability) occurs, the waveform signal can be returned to the optimal waveform signal and transmitted to the signal processing unit. Therefore, in a magnetic recording device using an MR head,
The problem that an error signal is generated due to a large difference in output amplitude and half width between a positive pulse and a negative pulse of a reproduction signal waveform or a fluctuation in instability of asymmetry during operation of the apparatus is extremely simple. It can be solved by the configuration. As a result, a high-density recording and high-reliability magnetic recording device can be realized.

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing a first embodiment of a signal waveform control device according to the present invention.

2A and 2B are waveform diagrams showing an example of the operation of the reproduction signal waveform control device of FIG. 1; FIG. 2A shows a recording signal output from a recording system signal processing unit, and FIG. FIG. 2C shows a good reproduction signal output from the head, and FIG.
FIG. 2D shows a good signal output from the circuit, and FIG.
7 shows a good signal output from the LPF circuit when an asymmetric reproduction signal is output from the R head.

FIG. 3 is a flowchart illustrating an example of an operation of a system controller of the reproduction signal waveform control device of FIG. 1;

4 is a graph of an operation result showing an example of the operation of the reproduction signal waveform control device of FIG. 1, and FIG.
FIG. 4 shows the bit error rate at 0.0 [mA].
4B shows the bit error rate when the sense electrodeposition is 12.5 [mA], and FIG. 4C shows the sense current 15.0 [mA].
The bit error rate at the time of is shown.

[Description of sign]

 Reference Signs List 10 signal waveform control device 12 MR head 14 comparison circuit 15 vitervis threshold control circuit 16 system controller 17 sense current control circuit 18 PRML signal processing unit 20 switching circuit 22 recording system signal processing unit 24 reproduction system signal processing unit 32 magnetic recording medium 34 Thin Film Head for Recording

Claims (7)

[Claims] 1. A signal waveform control device used in a magnetic recording device comprising: an MR element for reading data recorded on a magnetic recording medium; and a signal processing unit for decoding a reproduction signal read by the MR element. A sense current control means for causing the MR element to read known data recorded on the magnetic recording medium using each of the plurality of sense currents; and, of the plurality of sense currents, data of the data decoded by the signal processing unit. A comparison operation means for detecting the sense current having the lowest error rate; and a signal waveform control device for an MR head. 2. A signal waveform control device used in a magnetic recording device comprising: an MR element for reading data recorded on a magnetic recording medium; and a signal processing unit for decoding a reproduction signal read by the MR element. A sense current control means for causing an MR element to read known data recorded on a magnetic recording medium by using a plurality of sense currents; a decoding control means for controlling a decoding threshold in the signal processing unit; And a comparison operation means for detecting the sense current having the lowest error rate of the data decoded by the signal processing unit, out of the sense currents, and a signal waveform control device for an MR head. 3. A signal waveform control device used in a magnetic recording device comprising: an MR element for reading data recorded on a magnetic recording medium; and a signal processing unit for decoding a reproduction signal read by the MR element. A recording system control means for recording known data on a magnetic recording medium; and a plurality of sense currents, each of which is used to MR-record data recorded on the magnetic recording medium by the recording system control means.
A sense current control unit for causing an element to read; a decode control unit for controlling a decoding threshold in the signal processing unit; and an error rate of data decoded by the signal processing unit among the plurality of sense currents is the lowest. A signal waveform control device for an MR head, comprising: comparison operation means for detecting the sense current. 4. A signal waveform control device used in a magnetic recording device comprising an MR element for reading data recorded on a magnetic recording medium, and a signal processing section for decoding a reproduction signal read by the MR element. A sense current control unit for causing the MR element to read known data recorded on a magnetic recording medium by using a plurality of sense currents; and causing the MR element to read data recorded on the magnetic recording medium. Off-track control means for intentionally off-tracking; andcomparison operation means for detecting, among the plurality of sense currents, the sense current that minimizes an error rate of data decoded by the signal processing unit. A signal waveform control device for an MR head. 5. The comparison operation means detects a sense current by calculating a width of a Viterbi decoding threshold value at a certain allowable bit error rate and employing a sense current having the widest width. Item 5. The signal waveform control device for an MR head according to Item 1, 2 or 3. 6. The comparison operation means finely changes a Viterbi decoding threshold value and adopts a sense current value having the largest number of Viterbi decoding threshold values at which the bit error rate becomes zero,
4. The signal waveform control device for an MR head according to claim 1, wherein said sense current is detected. 7. The sense calculation unit according to claim 1, wherein the error rate of the data decoded by the signal processing unit is the lowest, or the error rate of the data decoded by the signal processing unit is allowed. The current is detected.
5. The signal waveform control device for an MR head according to 3 or 4.