JPH10188203A - Magnetic disk drive - Google Patents

Abstract

PROBLEM TO BE SOLVED: To early discover minute protrusions of a medium by increasing the low cutoff frequency of a read amplifier, eliminating the low frequency components of a thermal asperity(TA) and suppressing the increase in an error burst length. SOLUTION: Read waveforms from a magneto.resistive MR head 1 are inputted to a read write IC 17 and amplified by a read amplifier 2. Transmission systems 4, 5 and 6 are selected by a disk controller 16 through a switch 3. The system 4 is used for the medium defective/protrusion inspection prior to a shipment and accelerates the error occurrence frequency caused by the minute TAs which are not detected prior to the AGC input. Moreover, the systems 5 and 6 are used for a normal operation. Especially, the system 6 suppresses the low frequency region gain during a retry while a unrecoverable error occurs by a TA, reduces the error burst length and transforms it to a recoverable error burst length. Then, the signals are passed through a buffer amplifier 7, and AGC circuit 8 and a low pass filter/equalizer 9 and used to discriminate the data in a signal processing circuit 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic storage technology, and more particularly to a technology which can be applied to a means for suppressing a deterioration of an error rate due to a thermal asperity in a magnetic disk device equipped with an MR head.

[0002]

2. Description of the Related Art In recent years, as the density of magnetic disk devices has increased, an MR (Magneto-Resistive) head utilizing a magnetoresistance effect has begun to be used instead of a conventional inductive head. MR heads use the characteristics of elements whose electrical resistance changes according to the amount of magnetic flux, and have higher electromagnetic conversion efficiency than conventional inductive heads. Normally
A constant current is applied to the MR element, and the MR accompanying the magnetic flux change on the medium
An output waveform is obtained by converting a resistance change of the element into a voltage change. TA
(Thermal Asperity) is a phenomenon peculiar to this MR head, in which the MR element comes into contact with a projection on the medium and the temperature of the MR element rises, and the element resistance changes. This is superimposed on the waveform. TA
The change in resistance due to the change in magnetic flux is much larger than that due to the change in magnetic flux, and includes a low frequency component. Therefore, if such a waveform is superimposed on the read signal, correct data discrimination cannot be performed over several to several tens of bytes. In addition, since a waveform having a large amplitude is temporarily input to the reproducing circuit, the AGC circuit narrows the output amplitude, and thus it takes time to recover the waveform.

Conventionally, to solve such a problem, the response of the AGC is made as slow as possible, or the envelope component of the readout waveform is extracted as described in JP-A-07-57204 and subtracted from the waveform to reduce the TA. Methods such as shortening the period during which data cannot be compensated have been adopted. However, the response of the AGC cannot be set to an excessively slow response because the write / read recovery time needs to be shortened. Further, the extraction of the envelope waveform has a problem that the circuit scale becomes large.

[0004]

In the above situation, there is a need to develop a means for shortening the error burst length due to the TA and a means for early detecting and replacing the minute projections of the medium having the potential of the TA. there were. An object of the present invention is to provide a means for shortening the error burst length by TA to a byte length or less that can be compensated by ECC, and a means for early detection and replacement processing of minute protrusions of a medium having a TA potential. It is.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0006]

The following is a brief description of an outline of typical inventions disclosed in the present subject matter. That is, in the present invention, the low-frequency cutoff frequency of the read amplifier is increased to remove low-frequency components from the frequency components of the TA, thereby suppressing an increase in the error burst length due to waveform undulation. Also AGC
It has a function of fixing a gain of the AGC when detecting a TA by providing a certain slice level for the output amplitude.

Conversely, by lowering the low-frequency cut-off frequency of the read amplifier or boosting the low-frequency gain, the detection sensitivity of the TA by the fine protrusion is amplified, and the fine protrusion having the potential of TA is reliably replaced. The processing can be performed.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a magnetic disk drive according to an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a data reproducing circuit in a magnetic disk drive, including a function devised by the present invention. The read waveform reproduced from the recording medium by the MR head 1 is input to the read / write IC 17. The input read waveform is amplified by the amplifier 2 and output from the buffer 7 through any of the transmission systems 4, 5, and 6. The transmission systems 4, 5, and 6 are those in which the low-frequency band is boosted 4, those in the normal band 5, and those in which the low-frequency cutoff frequency is raised 6, and the transmission system used by the disk controller 16 passes through the switch 3. Selected. The criteria for selecting the transmission system to be used are, for example, as follows.

The transmission system 4 is used for inspection of medium defects / projections before shipment. TA due to microprojections has small amplitude and AGC
Due to the action of the coupling capacitor before input, it may not be detected as a data error. The transmission system 4 is used to accelerate the error occurrence frequency due to such a small TA. Next, the transmission systems 5 and 6 are used in a normal operation, but since the transmission system 6 has an increased cutoff frequency in the low frequency range, a distortion may occur in a reproduced waveform (particularly a low frequency), which may degrade the read margin. There is. Therefore, the transmission system 6 is mainly used during the retry operation. That is, when an unrecoverable error due to the TA occurs, the error burst length is reduced by suppressing the low-frequency gain during the retry, and the error burst length is recoverable by the ECC. If the low-frequency cutoff frequency of the transmission system 6 can be set to an appropriate value that does not cause waveform distortion and suppresses the error burst length of TA, it is ideal to select the transmission system 6 even in normal operation. Needless to say,

Next, the waveform output from the read / write IC 17 is input to the AGC circuit 8, passes through the filter circuit 9, and is subjected to data discrimination in the signal processing circuit 10. The gain control potential 15 used in the AGC circuit 8 is controlled by using the charge pump circuit 11 from the charge / discharge pulse created for the output waveform of the filter circuit 9, and keeps the output of the filter circuit 9 constant. The comparator 12 has a threshold value several times as high as the waveform peak output value of the filter circuit.
Whether the C control potential 15 is connected to the constant potential circuit 14 for a certain time,
Alternatively, the switch 13 is turned off. That is, the gain of the AGC is set to a fixed value or a value immediately before the occurrence of TA.

[0012]

Advantageous effects obtained by typical ones of the inventions disclosed in the present application will be briefly described.
It looks like this:

(1) FIG. 2 shows a read waveform generated by TA. At this time, the transmission system 5 is selected in the read / write IC 17. AGC gain is not fixed. In Figure 2, TA
Low frequency component is superimposed on the lead waveform, and TA
The error burst length 18a is long because the AGC circuit narrows the gain due to the large vibration of the waveform at the time of occurrence. Figure 3
Is a TA waveform when the transmission system 6 is selected. Although the low frequency components after the occurrence of the TA are removed, the error burst length 18b is not reduced so much because the gain is narrowed down by the AGC. FIG. 4 shows a TA waveform when all the functions shown in the present invention are applied. When the low frequency component is removed by the transmission system 6 and the TA is detected by the slice level 20, the AGC gain is fixed for the time 19, so that the output does not decrease due to the narrowing of the gain. Therefore, it is understood that the read waveform after the occurrence of the TA is quickly recovered, and the error burst length 18c is within the shortest time.

(2) FIG. 5 shows a TA waveform generated by the minute projection. At this time, the transmission system 5 is selected in the read / write IC 17. When the transmission system 4 is selected for the same waveform, the result is as shown in FIG. With the waveform as shown in FIG. 5, it is easy for the detection of the minute TA to be missed in the inspection process, and effective replacement registration cannot be performed. On the other hand, in FIG. 6, since the low frequency component due to TA is amplified and the slice level margin is deteriorated,
Can be detected relatively easily.

[Brief description of the drawings]

FIG. 1 is a data reproducing system in a magnetic disk drive according to an embodiment of the present invention;

FIG. 2 is a read waveform when TA occurs when the present invention is not used.

Fig. 3 Read waveform when TA occurs when transmission system 6 is used

FIG. 4 is a read waveform when a TA occurs when the function of the present invention is applied.

FIG. 5: Read waveform by small TA

FIG. 6 is a waveform read by a small TA when the transmission system 4 is used.

[Explanation of symbols]

1 MR head, 2 read amplifier, 3 switch, 4 transmission system, 5 transmission system, 6 transmission system, 7 buffer amplifier, 8 AG
C (Auto Gain Control) amplifier, 9… Low-pass filter / equalizer, 10… Signal processing circuit, 11… Charge pump circuit, 12
... Comparator, 13 ... Switch, 14 ... Constant voltage circuit, 15 ...
AGC gain control potential, 16: Hard disk controller, 17: Read / write IC, 18a: Error burst length, 18b
… Error burst length, 18c… Error burst length, 19… AGC
Fixed gain time, 20 slice levels

Claims (9)

[Claims] 1. A magnetic storage system comprising: a magnetic storage medium; a magnetic head for performing a recording and reproducing operation of information on the magnetic recording medium; and an information recording and reproducing circuit connected to the magnetic head. For magnetic heads used for reproduction
A magnetic disk drive equipped with an MR head and using a reproducing circuit having at least two transfer functions per head. 2. The magnetic disk drive according to claim 1, wherein the higher-level control device changes the transfer function of the reproducing circuit to one having a lower cut-off frequency that is sufficiently larger than a value used in normal operation. A magnetic disk drive characterized in that the influence of a low frequency signal due to the above can be reduced. 3. A magnetic disk drive according to claim 2, wherein a low cut-off frequency of a read amplifier for controlling amplification of a read signal of a magnetic head is increased. 4. A magnetic disk drive according to claim 2, wherein AGC (A
A magnetic disk device characterized by increasing the low-frequency cutoff frequency of an analog signal processing circuit such as an auto gin control circuit, an equalizer, and a low-pass filter. 5. The magnetic disk drive according to claim 1, wherein a transfer function of a reproduction circuit is changed from a higher-level control device to a transfer function having a low-frequency cut-off frequency sufficiently smaller than a value used in a normal operation. Increases the effect of low-frequency signals,
A magnetic disk drive characterized in that disturbance can be easily detected. 6. A magnetic disk drive according to claim 5, wherein the low cut-off frequency of a read amplifier for controlling amplification of a read signal of a magnetic head is reduced. 7. A magnetic disk drive according to claim 5, wherein a low-frequency cutoff frequency of an analog signal processing circuit such as an AGC circuit, an equalizer, and a low-pass filter is reduced. 8. A magnetic disk drive according to claim 1, wherein a comparator having a slice level several times as large as the waveform amplitude value is inserted into an input section or an output section of the AGC circuit. A magnetic disk drive characterized in that the gain of the AGC circuit can be fixed to a certain value when the value exceeds. 9. A magnetic disk drive according to claim 8, wherein when the waveform amplitude exceeds the slice level, the differential input section or the differential output section of the AGC circuit is short-circuited and the AGC waveform amplitude control can be stopped. Characteristic magnetic disk drive.