JP2002197603A - Magnetic disk device and head amplifier circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic disk device utilizing a perpendicular magnetic recording method, in which a practicable level is improved, by allowing the use of a signal processing circuit of a conventional longitudinal magnetic recording method by using a differentiation circuit and also realizing a head amplifier circuit conformable to the perpendicular magnetic recording method. SOLUTION: The head amplifier circuit 10 conformed to the perpendicular magnetic recording method is widely disclosed. A preamplifier circuit 100 includes a circuit 102 for adjusting a low range cutoff frequency for suppressing the waveform distortion of a rectangular read signal waveform. This rectangular read signal waveform is converted by the differentiation circuit 103 to the read signal waveform on the longitudinal magnetic recording method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to a magnetic disk drive of a perpendicular magnetic recording system, and more particularly to a head amplifier circuit suitable for the system and amplifying a read signal from a head.

[0002]

2. Description of the Related Art In recent years, a magnetic disk drive represented by a hard disk drive (referred to as a disk drive).
As a technique for exceeding the limit of the recording density in the longitudinal magnetic recording (in-plane magnetic recording) method, the perpendicular magnetic recording method has attracted attention. However, a conventional longitudinal magnetic recording type disk drive has been evaluated as a product having high reliability and stability as a result of various technical developments and technical improvements.

On the other hand, the disk drive of the perpendicular magnetic recording system has just reached a practical use level in recent years, and there are not a few problems to be solved as an actual product, and many technical Consideration is needed. In particular, as an important issue in commercialization, it is desirable to use the configuration of a conventional longitudinal magnetic recording type disk drive and minimize the number of change elements.

[0004] In the disk drive of the perpendicular magnetic recording system, as one of the technical problems of practical use, there is a signal processing system for generating a read signal read from a disk by a head into reproduction data. The read signal waveform read from the head is a Lorentz approximation waveform (a single peak waveform shape such as Lorenzian pulse) in the longitudinal magnetic recording method, but has a rectangular waveform shape in the perpendicular magnetic recording method. In this case, it is assumed that a disk having a two-layer structure is employed as a disk recording medium as a disk drive of the perpendicular magnetic recording system. A disk having a two-layer structure has a recording magnetic layer exhibiting perpendicular magnetic anisotropy, and a soft magnetic layer (also called a backing soft magnetic layer) between the recording magnetic layer and the substrate. Also, it is assumed that a giant magnetoresistive head (GMR) head is used as the read head.

In short, the signal processing system employed in the conventional longitudinal magnetic recording system cannot be applied to the perpendicular magnetic recording system as it is. Conventionally, the following technical proposals have been made as a method for solving the technical problem relating to such a signal processing method.

That is, as a first prior art, a recording / reproducing processing circuit of a disk drive of a perpendicular magnetic recording system includes:
A signal processing LSI to which the (1,7) RLL coding method and the positive coefficient PRML method are applied has been proposed (for example, see Japanese Patent Application Laid-Open No. 11-66755). Further, as a second conventional technique, a differentiating circuit is provided for differentiating once a rectangular reproduction waveform (read signal waveform) read from a disk on which perpendicular magnetic recording has been performed, and a signal using the differential waveform as a reproduction waveform is provided. A processing LSI has been proposed (see, for example, Japanese Patent Application Laid-Open No. 4-286702). In the second prior art, as a signal processing circuit following the subsequent stage, a PR (Partial Res) used in a conventional longitudinal magnetic recording system is used.
There is an advantage that the circuit of the class 4 system can be used as it is.

[0007]

As described above, in the conventional longitudinal magnetic recording type disk drive, since the read signal waveform is a Lorentz approximation waveform, a negative correction coefficient suitable for the read signal reproduction processing method is used. P using
An R4 signal processing LSI is used. On the other hand, in the perpendicular magnetic recording system, particularly when a disk having a two-layer structure and a GMR head are used as a read head,
The read signal waveform is a rectangular waveform type.

In the first prior art, a PR4 signal processing circuit using a positive correction coefficient suitable for a rectangular waveform reproduction processing method has been proposed as a signal processing LSI of the perpendicular magnetic recording method. However, in order to apply it to an actual perpendicular magnetic recording type disk drive, various technical developments and improvements including a waveform equalizing circuit and the like are required.
As a result, the signal processing LS of the conventional longitudinal magnetic recording system
A new signal processing LS suitable for a perpendicular magnetic recording type disk drive that cannot be used as it is and can be commercialized
It is required to design I. Therefore, at the present time, it is not at the stage where the disk drive of the perpendicular magnetic recording system can be easily put into practical use in consideration of the development cost and the development time.

On the other hand, in the second prior art, a differentiating circuit for differentiating a rectangular read signal waveform is used, so that a signal processing circuit at the subsequent stage uses a PR4 system employed in the longitudinal magnetic recording system. The circuit can be used as it is. In short, the differentiating circuit has a function of converting a read signal waveform in a perpendicular magnetic recording system into a read signal waveform in a substantially longitudinal magnetic recording system. Therefore, from the viewpoint of development cost and development time, the technology is close to the practical use level.

However, the configuration for incorporating the differentiating circuit into an actual signal processing LSI is not always concrete. Further, usually, a read head (GMR
In the case of a head), a read signal read out is amplified by a head amplifier circuit (preamplifier) and then processed by a signal processing LSI.
Sent to At this time, it was confirmed that when the read signal waveform of the rectangular waveform type in the perpendicular magnetic recording method was amplified by the conventional head amplifier circuit, the read signal waveform was distorted due to the influence of the low-frequency cutoff frequency. Have been. Therefore, the differentiating circuit differentiates the distorted read signal waveform, and outputs a differentiated read signal with reduced reproducibility. Therefore, it is not yet feasible.

An object of the present invention is to provide a head amplifier circuit which can use a signal processing circuit of a conventional longitudinal magnetic recording system by using a differentiating circuit and which can be adapted to a perpendicular magnetic recording system, and It is an object of the present invention to provide a perpendicular magnetic recording type magnetic disk drive capable of improving the level.

[0012]

SUMMARY OF THE INVENTION A first aspect of the present invention is as follows.
The present invention relates to a disk drive having a head amplifier circuit compatible with a perpendicular magnetic recording system, and more particularly to an improvement in a preamplifier circuit for amplifying a rectangular waveform read signal output from a read head. The head amplifier circuit has a differentiating circuit for differentiating the read signal waveform amplified by the preamplifier circuit, and converts the read signal waveform from the perpendicular magnetic recording method to the longitudinal magnetic recording method by the differentiating circuit. Send out. The preamplifier circuit of the present invention has a function of adjusting a low-frequency cutoff frequency, and the adjustment can suppress distortion due to a low-frequency cutoff frequency generated in a rectangular waveform read signal waveform in the perpendicular magnetic recording system. Amplify.

Specifically, the disk drive of the present invention
A head amplifier circuit including a preamplifier circuit including adjusting means for adjusting a low-frequency cutoff frequency, and a differentiating circuit for differentiating a read signal output from the preamplifier circuit and converting the read signal into a longitudinal magnetic recording type read signal It has.

The preamplifier circuit preferably has an adjustment function for adjusting the low-frequency cutoff frequency to 50 kHz or less, or 1/2000 of the maximum recording frequency on the disk to DC level. This adjusting function specifically comprises filter means such as a programmable filter circuit.

With the head amplifier circuit having such a configuration, it is possible to suppress the occurrence of waveform distortion when amplifying a rectangular waveform read signal in the perpendicular magnetic recording system.
Therefore, the differentiating circuit differentiates the rectangular waveform read signal in which the waveform distortion or the like is suppressed and outputs a differentiated waveform signal.
A high-quality read signal waveform suitable for the longitudinal magnetic recording method can be generated. Accordingly, when designing a disk drive of the perpendicular magnetic recording system, a signal processing circuit (signal processing LSI) for reproducing a read signal from a head amplifier circuit, for example, a PR4 compatible with a conventional longitudinal magnetic recording system. It becomes possible to adopt a system circuit.

A second aspect of the present invention relates to a head amplifier circuit having a selection means for selecting one of an output of the differentiation circuit and an output of the preamplifier circuit, in addition to the preamplifier circuit and the differentiation circuit.

In addition, when the output of the differentiating circuit is not selected by the selecting means, there is provided a power supply control means for cutting off the power supply of the differentiating circuit,
A low power consumption effect can be realized.

With such a configuration, in the disk drive conforming to the perpendicular magnetic recording system, the output of the differentiating circuit is caused to be transmitted to the signal processing circuit by the selecting means. In a disk drive conforming to the longitudinal magnetic recording method, the output from the preamplifier circuit is transmitted to the signal processing circuit by the selection means. Therefore, the present invention can be applied to either the perpendicular magnetic recording system or the longitudinal magnetic recording system.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a main part of a head amplifier circuit according to the embodiment. FIG. 2 is a block diagram showing a main part of the disk drive according to the embodiment.

(Structure of Disk Drive) The disk drive of the embodiment assumes a perpendicular magnetic recording system, and
As shown in FIG. 2, a disk 1 having a two-layer structure having a magnetic anisotropy in the vertical direction, a spindle motor (SPM) 2 for rotating the disk 1, and a head 3 are mounted and moved in a radial direction on the disk 1. And a control and signal processing circuit system.

The head 3 has a structure in which a read head composed of a GMR head and a write head composed of an inductive head are mounted on a slider. The actuator includes an arm (including a suspension) 5 on which the head 3 is mounted, and a voice coil motor (VCM) 6 for generating a driving force. The actuator positions the head 3 at a target position (target track) on the disk 1 by servo control of a microprocessor (CPU) 14.

The control / signal processing circuit system includes a head amplifier circuit 10, a read / write (R / W) channel 11, a disk controller (HDC) 12,
It has a CPU 14, a memory 15, and a motor driver 13. The head amplifier circuit 10 will be described later with reference to FIG.

The read / write channel 11 is a signal processing circuit (signal processing LSI) at the subsequent stage of the head amplifier circuit 10.
For example, PRML-based PRML (partial response
The reproduction signal processing of the maximum likelihood method is executed, and data (reproduction data including servo data) is decoded from the read signal (reproduction signal). Read / write channel 1
1 is an AGC (auto gain controller) for adjusting the amplitude of the read signal as shown in FIG.
l) an amplifier 111, a signal conversion circuit 112 including a noise removal filter (LPF) and an A / D converter, an equalizer (such as a digital filter) 113 for executing a predetermined waveform equalization process, and a decoder (Viterbi decoder and NR)
(Including a Z data demodulation circuit) 114. Lead /
The write channel 11 transmits the demodulated reproduced data to the HDC 1
Send to 2. Also, the read / write channel 11
It also has a function of executing, for example, RLL encoding of write data.

The HDC 12 constitutes an interface between the drive and a host system (personal computer or digital device) 16 and executes read / write data transfer control and the like.

The CPU 14 is a main control device of the drive, and is a main element of a servo system for executing positioning control (servo control) of the head 3. CPU
Reference numeral 14 controls a seek operation and a track following operation according to the servo data reproduced by the read / write channel 11. Specifically, the CPU 14 controls the drive of the actuator VCM 6 by controlling the input value (control voltage value) of the VCM driver 13A. The memory 15 includes a RAM, a ROM, and a flash EEPROM, and stores a control program of the CPU 14 and various control data. The motor driver 13 is a VCM driver 1
3A, an SPM driver 13B for driving the spindle motor (SPM) 3 is provided.

(Structure of Head Amplifier Circuit) As shown in FIG.
And a preamplifier circuit 100 for inputting and amplifying a read signal (rectangular waveform in the perpendicular magnetic recording system) 4 output from the read head. Further, the head amplifier circuit 10 is a circuit subsequent to the preamplifier circuit 100,
It has a differentiating circuit 103, a selecting circuit 104, a gain adjusting circuit 105, and a TA detecting circuit 106.

The preamplifier circuit 100 includes a differential amplifier 10
1 and an adjustment circuit (hereinafter sometimes referred to as an fc adjustment circuit) 102 for adjusting the low-frequency cutoff frequency. The differential amplifier 101 amplifies a read signal output from the read head. The fc adjustment circuit 102 is preferably 50 kHz or less or 1/2000 of the maximum recording frequency of the disk 1, in order to faithfully reproduce a rectangular read signal waveform read by the read head from the disk 1 in the perpendicular magnetic recording system. The low cutoff frequency of the differential amplifier 101 is set in the range from the following to the DC level. The fc adjustment circuit 102 includes, for example, the CPU 14
And a programmable filter circuit whose parameters can be adjusted.

The differentiating circuit 103 includes a preamplifier circuit 100
And a high-pass filter (HPF) for generating a differentiated waveform by differentiating the read signal waveform output from the LM and converting it into a substantially Lorentz-shaped read signal waveform suitable for the conventional longitudinal magnetic recording method. The gain adjustment circuit 105 includes a gain adjustment amplifier that performs gain adjustment for suppressing a saturation phenomenon of the read signal by the preamplifier circuit 100, and sends the read signal after the gain adjustment to the read / write channel 11.

The TA detection circuit 106 is a well-known circuit for detecting a thermal asperity phenomenon (TA phenomenon) generated by a GMR head used as a read head, and sends a detection signal to the read / write channel 11. Output.

In this embodiment, a head amplifier circuit 10 of a read amplifier system for amplifying a read signal from a read head is assumed. The head amplifier circuit 10 also includes a write amplifier system for converting write data into a write current.

(Operation of Head Amplifier Circuit) In a read operation of the disk drive, a read signal 4 read by a read head (GMR head) from a two-layer disk 1 on which perpendicular magnetic recording has been performed is input to a head amplifier circuit 10. Is done. Here, in the preamplifier circuit 100, as described above, the low-frequency cutoff frequency is adjusted by the fc adjustment circuit 102 to a range from 50 kHz or less or 1/2000 or less of the maximum recording frequency of the disk 1 to a DC level. . The read signal 4 is amplified by the preamplifier circuit 100 and sent to the differentiating circuit 103.

Here, the selection circuit 104 is operated by the CPU 14 according to the instruction to select the perpendicular magnetic recording system,
03 is selected and sent to the gain adjustment circuit 105. The gain adjustment circuit 105 sends the read signal converted from the rectangular waveform in the perpendicular magnetic recording system to the Lorentz waveform in the longitudinal magnetic recording system by the differentiating circuit 103 to the read / write channel 11 after performing predetermined gain adjustment. .

On the other hand, when the CPU 14 instructs the selection of the conventional longitudinal magnetic recording system, the selection circuit 104 naturally converts the read signal waveform output from the preamplifier circuit 100 through the gain adjustment circuit 105. It is sent to the read / write channel 11. However,
In this case, in the preamplifier circuit 100, in response to an instruction from the CPU 14, the fc adjustment circuit 102 adjusts the low-frequency cutoff frequency (fc) suitable for the longitudinal magnetic recording method to, for example, 500 kHz (or, for example, 350 kHz or more). The read / write channel 11 normally assumes a PRML signal processing method with a negative coefficient.

FIG. 5A is a diagram showing a result of calculation by computer simulation of a read signal waveform (rectangular waveform in the perpendicular magnetic recording system) corresponding to the low-frequency cutoff frequency (fc) in the preamplifier circuit. It is. Specifically, the read signal waveform 5 when fc is 1 MHz
Read signal waveform 5 when 0, fc is 500 kHz
1, Read signal waveform 5 when fc is 100 kHz
2. Read signal waveform 53 when fc is 50 kHz
Are respectively shown.

Here, in the conventional disk drive of the longitudinal magnetic recording system, the low cut-off frequency (fc) of the preamplifier circuit 100 is set to about 500 kHz. This is because, in general, in a disk drive, the transfer rate moves to a higher frequency with an increase in recording density, and accordingly, Fc also shifts to a higher frequency side. Therefore, Fc tends to further increase as the transfer rate of the disk drive increases. In a disk drive compatible with a high transfer rate, the low cut-off frequency (fc) of the preamplifier circuit is, for example, 1 to 3 MHz.
Set to obi.

However, as described above, in order to faithfully reproduce the read signal waveform of the rectangular waveform in the perpendicular magnetic recording system, at least 1/5 or less of the conventional one, that is, 1
00 kHz or less, ideally 1/10 or less, ie 5
It is desirable to set the frequency to 0 kHz or less. At the high-frequency low cut-off frequency (fc), the read signal amplified by the preamplifier has a high possibility of generating a waveform distortion exceeding an allowable range. FIG. 5B shows, for example, that fc is 1 MHz with respect to an ideal rectangular read signal waveform 61.
The read signal waveforms 60 and fc in the above-described case are set to 3
9 shows an actual measurement result of the read signal waveform 62 when the frequency is set to the 50 KHz band. As is clear from the actual measurement results, it can be confirmed that particularly when fc is set to 1 MHz or more, the waveform distortion generated in the read signal waveform 60 increases. When a read signal waveform having such a waveform distortion is transmitted to the read / write channel 11 at the subsequent stage, the probability of extracting erroneous reproduced data increases, and the read error rate deteriorates.

Therefore, the head amplifier circuit 10 suitable for the perpendicular magnetic recording system of the embodiment is adjusted to at least 1/5 or less of the conventional one, that is, 100 kHz or less, and ideally 1/10 or less, ie, 50 kHz or less. The read signal 4 having a rectangular waveform in the perpendicular magnetic recording system is amplified by the preamplifier circuit 100 thus constructed. Accordingly, the influence of the waveform distortion on the amplified read signal waveform is reduced, and the reproducibility of the rectangular read signal waveform can be improved. The differentiating circuit 103 can convert a read signal waveform of a rectangular waveform in the perpendicular magnetic recording system into a read signal waveform of a Lorentzian waveform in the longitudinal magnetic recording system so as to faithfully reproduce data. . Thereby, the read / write channel 11 can extract normal reproduction data from the read signal waveform faithfully reproduced from the head amplifier circuit 10. Therefore, by applying the head amplifier circuit 10 of the embodiment, the read error rate in the perpendicular magnetic recording system can be improved.

FIG. 6 shows the adjustment of the low-frequency cut-off frequency (fc) of the preamplifier circuit 100, and
The recording frequency (fs) and the read error rate (E
It is a figure which shows the relationship with R). Here, the ER characteristics 60 and 61 in FIG.
This is a case where a PR4 signal processing method of the PR4 class is assumed.

The low cut-off frequency (fc) of the preamplifier circuit conforming to the conventional longitudinal magnetic recording method is, for example, 3
The frequency is set to 50 kHz or more. Here, when the recording frequency (fs) is 200 MHz, “fc / fs = 1”
/ 570 ". On the other hand, assuming that the low-frequency cutoff frequency (fc) characteristic is linear, “fc / fs = １ ／
In the case of "000 or more", the read error rate deteriorates (see the characteristic 61 in FIG. 6). Further, assuming that the low-frequency cutoff frequency (fc) characteristic is quadratic, “fc / fs = 1”
In the case of "/ 3000 or more", the read error rate deteriorates (see the characteristic 60 in FIG. 6).

Therefore, in the E2PR4 class read / write channel, “fc / fs = 1/2000 or less”
Alternatively, it is desirable to adjust the low cut-off frequency (fc) of the preamplifier circuit so that “fc / fs = 1/4000 or less”. In the PR3 class read / write channel, “fc / fs = 1/1000 or less”
It is desirable to adjust the low-frequency cutoff frequency (fc).

Further, as a desirable specific example, when the recording frequency (fs) is 300 MHz, "fc / fs =
The low-frequency cutoff frequency (fc) of the preamplifier circuit is adjusted to 30 kHz so that the frequency becomes 1 / 10,000.

It should be noted that the head amplifier circuit 10 of the same embodiment
In TA, the TA detection circuit 106
This is a circuit for detecting the phenomenon A. The read / write channel 11 can include a predetermined compensation process for the TA phenomenon in the reproduction process in accordance with the detection signal from the TA detection circuit 106.

The head amplifier circuit 10 of the same embodiment
Has the gain adjustment circuit 105 as described above, and adjusts the gain of the whole amplifier. Generally, the output of the read head in the longitudinal magnetic recording system is about 1 to 2 mVpp. In consideration of the S / N ratio of the recording / reproducing system, the read / write channel at the subsequent stage has an input range of 200 mVpp.
It is designed to about 300 mVpp.

However, the head output can be considerably increased in the perpendicular magnetic recording system as compared with the longitudinal magnetic recording system. Specifically, the output of the read head can be, for example, up to about 4 mVpp. For this reason, the output of the head amplifier circuit is likely to be saturated with the conventional gain. Therefore, in the head amplifier circuit 10 of the embodiment, the gain adjustment circuit 105 increases the amplifier gain, which is
By lowering it to about 0 times, it is possible to suppress saturation in the whole amplifier. This makes it possible to avoid a situation where the input dynamic range is over in the read / write channel at the subsequent stage.

Further, the preamplifier circuit 100 of the same embodiment
Here, a differential amplifier 101 is used. Typically,
From the viewpoint of the S / N ratio, the differential amplification by the differential amplifier 101 is more preferable, but the present invention can be applied to the preamplifier circuit 100 of the same embodiment in the case of another type of amplifier.

(Modification) As a modification of the embodiment, the preamplifier circuit 100 may be constituted by a DC amplifier. However, a bias adjustment signal line 103 for adjusting the bias level of the DC amplifier with an adjustment signal from the read / write channel 11 is required. In addition, lead /
As the write channel 11, a PRML signal processing system having a positive coefficient suitable for the perpendicular magnetic recording system is desirable.

(Modification) As a modification of the embodiment, when the output of the differentiating circuit 103 is not selected by the selecting circuit 104, a power supply control circuit for cutting off the power supply of the differentiating circuit 103 is provided. Provide a configuration of a configured disk drive. With such a configuration, useless power consumption can be prevented by the differentiating circuit 103, so that a low power consumption effect can be realized.

[0049]

As described above in detail, according to the present invention, in a perpendicular magnetic recording system, when a rectangular waveform read signal output from a read head is amplified, occurrence of waveform distortion and amplifier saturation phenomenon is prevented. Can be suppressed. Therefore,
Since a differentiated waveform signal is output by differentiating a rectangular waveform read signal in which waveform distortion or the like is suppressed, a high-quality read signal waveform suitable for a longitudinal magnetic recording method can be generated. Accordingly, when designing a disk drive of the perpendicular magnetic recording system, a signal processing circuit (signal processing LSI) for reproducing a read signal from a head amplifier circuit
For example, PR adapted to a conventional longitudinal magnetic recording system
It becomes possible to employ four-system circuits. Therefore, since a signal processing circuit of the conventional longitudinal magnetic recording method can be adopted,
It is possible to improve the feasibility of the perpendicular magnetic recording type disk drive from the aspect of development cost and development time.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a main part of a head amplifier circuit according to an embodiment of the present invention.

FIG. 2 is an exemplary block diagram showing a main part of the disk drive according to the embodiment;

FIG. 3 is an exemplary block diagram showing a main part of a read / write channel according to the embodiment;

FIG. 4 is an exemplary block diagram showing a main part of a head amplifier circuit according to a modification of the embodiment;

FIG. 5 is a view showing a read signal waveform corresponding to a low-frequency cutoff frequency in a preamplifier circuit according to the embodiment.

FIG. 6 is a diagram showing a relationship between a low-frequency cutoff frequency and error rate saturation according to the embodiment;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Disc 2 ... Spindle motor 3 ... Head (including GMR read head) 4 ... Read signal (read head output) 5 ... Arm 6 ... Voice coil motor (VCM) 10 ... Head amplifier circuit 11 ... Read / write channel 12 ... Disk controller (HDC) 13 Motor driver 14 Microprocessor (CPU) 15 Memory 16 Host system 100 Preamplifier circuit 101 Differential amplifier 102 fc adjustment circuit 103 Differentiation circuit 104 Selection circuit 105 Gain adjustment circuit 106 ... TA detection circuit

Claims (11)

[Claims] 1. A perpendicular magnetic recording type magnetic disk device comprising: a disk on which a data signal can be recorded by a perpendicular magnetic recording method; and a head for reading a data signal recorded perpendicularly from the disk. An amplifier for amplifying a read signal output from the head, and a preamplifier circuit including an adjusting unit for adjusting a low-frequency cutoff frequency of the amplified signal output from the amplifier; and a read output from the preamplifier circuit. A magnetic disk drive, comprising: a head amplifier circuit including a differentiating circuit for differentiating a signal and converting the signal into a longitudinal magnetic recording type read signal. 2. A signal for inputting a read signal output from the head amplifier circuit, executing a reproduction signal process of various longitudinal magnetic recording systems, and outputting reproduction data of data perpendicularly magnetically recorded on the disk. 2. The magnetic disk drive according to claim 1, further comprising a processing unit. 3. The adjusting means comprises filter means having a function of adjusting the low-frequency cutoff frequency to 50 kHz or less, or 1/2000 of the highest recording frequency on the disk to a DC level. 2. The magnetic disk drive according to claim 1, wherein: 4. The magnetic disk drive according to claim 1, wherein the head amplifier circuit includes a TA detection circuit for detecting occurrence of a thermal asperity phenomenon from a read signal output from the preamplifier circuit. 5. The magnetic disk drive according to claim 2, wherein the head amplifier circuit includes a gain adjustment unit for adjusting a gain of a read signal output to the signal processing unit. 6. The head amplifier circuit includes a selector for selecting one of a read signal output from the differentiator circuit and a read signal output from the preamplifier circuit by a selection signal from the outside. 2. The magnetic disk drive according to claim 1, wherein: 7. A head amplifier circuit applicable to a magnetic disk device of a perpendicular magnetic recording system, comprising: an amplifier for amplifying a read signal output from a head of the magnetic disk device; and an amplified signal output from the amplifier. A preamplifier circuit including adjusting means for adjusting the low-frequency cutoff frequency of the above, and a differentiating circuit for differentiating a read signal output from the preamplifier circuit and converting the read signal into a longitudinal magnetic recording type read signal. A head amplifier circuit characterized by: 8. The adjusting means comprises filter means having a function of adjusting the low-frequency cut-off frequency to 50 kHz or less or from 1/2000 or less of the highest recording frequency on the disk to a DC level. The head amplifier circuit according to claim 7, wherein: 9. The semiconductor device according to claim 7, further comprising a selection circuit for selecting one of a read signal output from the differentiating circuit and a read signal output from the preamplifier circuit by an external selection signal. Head amplifier circuit. 10. The preamplifier circuit is constituted by a direct current (DC) amplifier circuit, and has an input unit for externally inputting a bias adjustment signal for adjusting a bias level of the DC amplifier circuit. The head amplifier circuit according to claim 7 or 9, wherein 11. A power supply control means for shutting off the power supply of the differentiating circuit when the read signal output from the differentiating circuit is not selected by the selecting means. The magnetic disk device according to the above.