KR100295724B1 - Method and apparatus for using a thermal response of a magnetoresistive head - Google Patents

Abstract

The present invention relates to an apparatus and method for reading an information signal from a magnetic storage medium using a magnetoresistive (MR) head and for separating a column signal component when a magnetic signal component is provided from the information signal. The signal separation / restoration module eliminates distortion of the magnetic signal component of the readback signal generated by the column signal component of the readback signal. A finite impulse response (FIR) filter can be used within the signal separation / recovery module to remove distortion of the magnetic signal. A signal sepration / restoration module may be used to extract the thermal signal component from the readback signal. In one arrangement, the MR head is connected to an arm electronics (AE) module which performs a high-pass filtering operation and to a signal separation / decompression module comprising an inverse filter, And has a transfer function that is inverse to a valid high-pass filter. The inverse filter may be an infinite impulse response (IIR) filter. In another embodiment, the magnetic and thermal signal components of the readback signal are extracted and processed to correspond linearly to the head-to-disk spacing, respectively. Head-to-disk gap variations using thermal signals are used to detect disk surface defects, topography variations, and servo control surface variations.

Description

≪ Desc / Clms Page number 1 > METHOD AND APPARATUS FOR USING A THERMAL RESPONSE OF A MAGNETORESISTIVE HEAD &

The present invention relates generally to data storage systems and, more particularly, to a method and apparatus for using a thermal component of a signal generated in a magnetoresistive (MR) head.

Typically, a data storage system includes a magnetic medium that stores data in magnetic form, and a transducer that writes magnetic data to or reads magnetic data from the magnetic medium. For example, a disk storage device includes one or more data storage disks coaxially mounted on a hub of a spindle motor. Typically, a spindle motor rotates a disk at a rate of about several thousand times per minute. Typically, digital information is stored in the form of magnetic transitions on a series of concentrically spaced tracks comprising the surface of a magnetizable hard data storage disk. In general, a track is divided into a plurality of sectors, each sector including, for example, a field for storing data and a plurality of information fields including sector identification and synchronization information.

Typically, the actuator assembly includes one or more transducers mounted on flexible suspensions and a plurality of outwardly extending arms having a slider body. Typically, the slider body takes off the transducer head of the disk surface as the spindle motor rotational speed increases, and drives the take-off head to rotate on the disk on the air- It is designed as an aerodynamic lifting body. The distance between the head and the disk surface is typically about 50-100 nanometers (nm), and generally this distance is referred to as head-to-disk spacing.

Data writing to a data storage disk generally involves applying a current to a write element of the transducer assembly to cause a magnetic flux line to be generated that magnetizes a specific position of the disk surface. Typically, the reading of data from a particular disk location is done by a read element of a transducer assembly that senses magnetic or magnetic flux lines generated from the magnetized position of the disk. When the read element passes over the surface of the rotating disk and interacts between the read element and the magnetized position on the disk surface, an electrical signal, often referred to as readback signals, is generated in the read element.

Conventional data storage systems typically utilize a closed-loop servo control system to locate a read / write transducer at a particular storage location on a data storage disk. During operation of a typical data storage system, a servo transducer, typically mounted proximate to or read as a read / write transducer, reads information to track (track) a particular track, Is used to locate (search) specific track and data sector locations on the track.

According to one known servo technique, the built-in servo pattern information is generally written to the disk along a segment extending outward from the center of the disk. Thus, the built-in servo pattern is formed between the data storage sectors of each track.

Typically, a servo sector is data that is often referred to as a servo burst pattern, which is used to optimally align the read / write transducers on the center line of the track when data is read and written in a particular data sector on the track . In addition, the servo information may include a sector and a track identification code used to identify the position of the transducer.

In the data storage system manufacturing industry, there is a growing interest in using MR elements as read transducers. While MR heads, which typically include an MR read element and a thin film write element, offer many advantages over conventional thin film heads and the like, those of ordinary skill in the art will appreciate that many of the preferred It will be appreciated that the benefits provided by the MR head can not be fully realized, since it is not possible to accommodate non-MR head characteristics.

In particular, the sensed magnetic signal representing data or servo information typically stored on the magnetic storage disk can be distorted by the MR element transducer. The distortion to the magnetic signal is caused by a number of undesirable characteristics inherent in the MR element and by a number of factors including the specific configuration and orientation of the MR element when incorporated into the MR transducer assembly. For example, a typical MR element is known to vary its read responsivity along the width of the MR element, and the width of such an MR element has been detected to be a factor for varying severity of servo control errors. For example, depending on the magnitude of the magnetic signal distortion generated by the MR element, the servo sector information may be misinterpreted or unreadable, resulting in a loss of interrupt or servo control, or in some cases, It can lead to an impossible result.

There has been a continuing development of measures to directly reduce or eliminate the adverse effects associated with self-read signals that are significantly distorted by the amount of industry interest and resources. In a readback signal caused by an MR transducer, this distortion has been treated collectively as undesirable noise without analyzing the response of the MR element to the variable effects occurring within its operating environment. Nevertheless, a solution to eliminate or substantially reduce the distortion of the magnetic signal generated by the MR element has not yet been presented at a satisfactory level.

In a commonly manufactured data storage system, there is a need for an apparatus and method for eliminating undesirable distortion of a magnetic read signal generated in an MR element. There is also a need to provide an appropriate device and method for incorporation into existing data storage systems as well as new system devices. The present invention provides these and other needs.

The present invention relates to an apparatus and method for reading an information signal from a magnetic storage medium using a magnetoresistive (MR) element and for separating a thermal signal component and a magnetic signal component from the information signal. The magnetic signal is processed to remove the influence of the thermal signal component from the magnetic signal. The signal separation / restoration module removes the modulated signal of the magnetic signal component of the readback signal generated by the column signal component of the readback signal. To remove the modulated signal in the magnetic signal, a finite impulse response (FIR) filter may be used in the signal separation / recovery module. In addition, the signal separation / decompression module can be used to extract the thermal signal component from the readback signal.

According to a disk drive embodiment in which the MR element is coupled to an arm electronics (AE) module having a high pass filtering function, the signal separation / decompression module is inverse to the effective high pass filter transfer function of the AE module And an inverse filter having a transfer function. An infinite impulse response (IIR) filter can be programmed to invert the amplitude and phase distortion of the thermal signal generated by the high pass filter of the AE module.

According to another embodiment, the magnetic and thermal signal components of the readback signal are each extracted and processed to correspond linearly to the head-to-disk spacing.

The head-to-disk spacing can be used to detect defects and position changes in the disk surface by using thermal signals. The thermal signal can be calibrated by using magnetic spacing signals to directly measure head-to-disk spacing variations. The thermal head-to-disk spacing signal may be used for other systems and diagnostic purposes, including defect characteristics, error correction and predictive failure analysis (PFA).

In yet another embodiment, the servo control information may be provided in the form of geographic variations on the disk surface. A thermal servo signal may be generated in the MR element if the head ignores the geographic variations that are extracted and communicated, such as signals for actuator and spindle servo control. In addition, changes in the emissivity and / or absorptivity of the disk surface material can be sensed by the MR element and converted to corresponding thermal signals.

FIG. 1 is a block diagram of an apparatus for extracting a thermal signal and a magnetic signal from a readback signal generated in an MR head. FIG.

Figure 2 is a top view of the data storage system with the upper housing lid removed.

3 is a flow chart illustrating a method of acquiring and using a column signal component of a readback signal;

Figure 4 shows the distorted D.C. Fig. 5 is a diagram showing a readback signal generated in an MR head showing a baseline;

FIG. 5 shows the readback signal of FIG. 4 showing the D. C baseline restored after being processed by the signal separation / restoration module; FIG.

FIG. 6 shows a read signal obtained from the same track position after AC erasure of magnetic information and a column signal extracted from the read signal generated in the MR element at the specific track position.

7 is an enlarged side view showing a data storage disk showing various surface defects and characteristics and the thermal response and magnetic spacing response of the MR element to such defects and features;

Figure 8 shows a readback signal indicative of a head-to-disk contact event;

FIG. 9 is a diagram illustrating the extraction of a thermal signal and a magnetic signal from a readback signal derived from an MR element, and FIG. A block diagram of a signal separation / modulation module restoring a baseline.

FIG. 10 is a block diagram of the D.C. A block diagram of a signal separation / modulation module restoring a baseline.

Figure 11 is a block diagram of a system for selectively communicating a readback signal with a signal separation / decompression module.

12 shows the magnitude and phase response of the finite impulse response (RIR) filter used in the signal separation / decompression module;

FIGS. 13A, 13B, and 13C illustrate the readback signal derived from the MR head, the recovered magnetic signal component of the readback signal, and the unrecovered magnetic signal component of the readback signal, respectively.

14 illustrates the magnitude and phase response of a window-type FIR filter used in a signal separation / decompression module;

15 shows the magnitude and phase response of a highpass filtering operation of a typical AE module;

FIGS. 16 and 17 show magnitude and phase response comparisons of high pass filtering operations of an inverse filter having a transfer function that is inversely related to a typical AE module and the effective high pass filter of the AE module; FIG.

FIG. 18 is a signal flow diagram illustrating the inverse filter of FIGS. 16 and 17; FIG.

Figures 19a-19c illustrate three waveforms caused by disk surface pits generated at different processing points within the signal separation / decompression module.

20 shows a close correspondence between the magnetic head-disk spacing signal and the thermal head-disk spacing signal associated with the detection of disk surface defects;

21 is a block diagram illustrating another embodiment of a signal separation / decompression module using an infinite impulse response (IIR) filter.

FIG. 22 illustrates magnetic and thermal spacing signals associated with a head-to-disk contact event; FIG.

Figure 23 is a block diagram of the defect classification circuit.

24 is a flow chart of an error recovery process using a column signal of a readback signal;

Description of the Related Art

12: Suspension 18: Controller

20: Data storage system 22: Voice coil motor

24: Disk 26: Spindle motor

60: reverse read signal 63, 80: column signal

71: Positive peak-hold circuit 73: Negative peak-hold circuit

72: Magneto-resistive element 74: AE module

75, 77, 79: comparator 76: signal separation / restoration module

78: Self-read signal 81: Addition circuit

86: Delay device 88: Programmable filter

90: signal adding device 91: defect identification circuit

152: amplitude detector 154: logarithmic device

156: Inverse filter 157: Heat signal extraction filter

158: means filter 160: magnetic gap signal

162: column spacing signal

Referring to FIG. 1, an apparatus 70 for reading an information signal having a magnetic signal component and a thermal signal component from a magnetic storage medium, and separating the thermal and magnetic signal components from the information signal is illustrated. The magnetic signal is processed to remove the influence of the thermal signal component from the magnetic signal. Two independent magnetic and thermal signals can be used to improve the operation, performance and reliability of the data storage system.

As shown in FIG. 1, the magnetoresistive (MR) element 72 is located very close to the surface of the data storage disk 24. The information read from the disk 24 by the MR element 72 is generally referred to as a read signal. Typically, the readback signal generated in the MR element 72 is amplified by an arm electronics (AE) module 74. The readback signal may also be filtered by the AE module 74. As shown in graphic form at the output of the AE module 74, the analogue read signal 60, which includes the relatively high frequency magnetic signal component 61a, The baseline is shown because there is a low frequency modulated signal component. Those skilled in the art will appreciate that the modulated magnetic signal component 61a of the modulated readback signal 60, particularly the readback signal 60, includes servo control errors and inaccuracies, Storage and retrieval reliability is degraded and in some cases turned out to be one cause of adversely affecting multiple data storage systems such that data retrieval becomes impossible. As has already been described in the background of the invention, much of the industrial interest and resources have been invested to fully analyze the nature and causes of undesirable readback signal baseline modulation. As will be described in greater detail below, the Applicant has discovered that the readback signal 60 is a composite signal containing independent magnetic and thermal signal components, and in fact, the low frequency modulation in the readback signal is independent of the readout signal 60 And is a column information signal component. As will also be described in detail below, Applicants have found that the modulation of the undesired readback signal 60 can be eliminated or substantially reduced in magnitude, resulting in a substantially pure magnetic field representing data or servo information Signal can be provided.

In particular, the presently unnecessary thermal signal components of a readback signal, generally referred to herein as a thermal signal, also include information content, which is extracted from the readback signal 60, Can be used for a number of advantages that have not been appreciated by those who have the knowledge of the prior art. For example, the column signal 63 is used by the servo control to allow the track tracking and track seeking operations to be reliably provided, in contrast to the magnetic signal 61a used in accordance with the typical servo control scheme, . The thermal signal 63 includes information for determining the flight altitude of the MR element 72 relative to the disk surface 24 to be on the order of one nanometer and includes disk surface analysis and terrain mapping, disk defect detection and screen error correction, Prediction failure analysis (PFA), and the like. The apparatus shown in Figure 1 may be included as part of a new type of data storage system design that tracks the utilization of the reconstructed unmodulated magnetic read signal 61 and the independent column signal 63, May also be incorporated into an existing data storage system using it as part of a reconciliation program. As shown in FIG. 2, a data storage system 20, typically using an MR transducer, includes one or more hard data storage disks 24 that rotate about a spindle motor 26. Typically, actuator assembly 10 includes a plurality of interleaved actuator arms 11 and suspensions 12, each of which may be used to write information to or read information from data storage disk 24 One or more MR head transducers 72 are supported. The actuator assembly 10 includes a coil assembly 14 for use with a permanent magnetic assembly 16 to act as an actuator voice coil motor 22 in response to a control signal generated by the controller 18. The controller 18 controls the transfer of data to / from the data storage disk 24 and cooperates with the actuator voice coil motor 22 when writing data to the disk 24 or reading data from the disk 24. [ Thereby positioning the actuator arm / suspension 11/12 and the MR transducer 72 in the predetermined track 28 and sector 25.

In order to facilitate understanding of a number of useful applications for detecting the availability of thermal information signals, as well as the general process of separating the thermal and magnetic signal components from the readback signal, FIG. 3 illustrates one embodiment of the present invention A method of acquiring and using a column signal component of a read signal is illustrated in a flowchart. In step 30, the MR element 72 reads information from the magnetic storage disk and generates a readback signal, which is generated to indicate distortion or modulation, but the magnetic signal component and the thermal signal component are substantially . It should be noted that the magnitude of the magnetic signal component is zero when the magnetic information is not recorded on the disc. However, due to previously unknown phenomena that have been understood, characterized and practiced by the Applicant, thermal signal components are generally provided. In step 32, the column signal components are separated or extracted from the readback signal. The magnetic signal component of the readback signal separated in step 32 is often referred to as the D.C. It contains the baseline.

In step 34, baseline modulation of the magnetic signal is removed, thereby restoring the baseline of the magnetic signal. If it is determined at decision step 36 that a thermal signal is extracted for the servo control, the thermal signal is passed to servo control at step 38 and then processed. If a magnetic signal is used for servo control, the magnetic signal recovered in step 40 is transferred to the servo control. If it is determined at decision step 42 that a thermal signal is desired to perform the head flight altitude routine, then at step 44 the thermal signal is provided to the evaluated flight altitude processor. If it is determined at decision step 46 that a thermal signal is desired to analyze or inspect the disk surface, then at step 48 the thermal signal is passed to the disk surface analysis processor. In addition, if the thermal signal is used to perform an error recovery or prediction failure analysis (PFA) at decision step 50, the thermal signal is passed to the error recovery processor at step 52.

Referring to FIGS. 4 and 5, a distorted read signal and an undistorted read signal restored by the signal separation / restoration module 76, as shown in FIG. 1, are shown. (Modulation) of all the low frequencies can be compensated by the signal separation / restoration module 76, regardless of whether or not it is caused by operation of the thermal head-disk spacing or unwanted filtering from the AE module or both. For purposes of illustration, it is assumed that the readback signal 60 is a signal read from the servo sector on the data storage disk 24. In this example, the servo sector read signal includes a plurality of information fields, namely, a write recovery field 62 synchronous field 64, a gray code field 66, burst pattern field 68. It will be appreciated that the gray code field 66 typically includes a sector and a cylinder identification field.

Referring to FIG. 4, it can be seen that the baseline of the servo-controlled readout signal is heavily distorted and especially distorted in the gray code field 66. The low frequency distortion associated with the gray code field 66 may be caused by the thermal head-to-disk spacing variation, but may also be caused by the high-pass characteristics of the AE module 74. Typically, the gray code field 66 is the amplitude at which the interpretation of sector and cylinder information is detected to be unreliable, in the presence of amplitude distortion. This distortion of the amplitude causes a servo control error which changes the rigidity according to the distortion amplitude. It should be noted that this amplitude distortion of the readback signal 60 obtained from the data sector as opposed to the servo sector readback signal results in detection and interpretation errors that similarly cause soft or hard read errors. Up to 15% -20% of sectors formatted on the surface of the disk 24 are common to clearly indicate the level of readback signal distortion similar to that shown in FIG.

As described above, the cause of the readback signal 60 modulation, which is undesirable by a person having ordinary skill in the art, is that the noise of the MR element 72 or the instability or operation of the MR element 72 It has been misunderstood to be caused by other causes. However, due to the presence of an independent column signal component of the readback signal that modulates the magnetic signal component 61a, the distortion of the readback signal 60 causing the readback signal 60 to have a time varying baseline ≪ / RTI > has also been found to be present by the present applicant. The signal separation / decompression module 76 processes the readback signal 60 to recover the readback signal base line as shown in FIG. 5 and reconstructs the substantially pure magnetic signal 61b ).

The magnetic and thermal signals are illustrated in waveform in Fig. The waveform shown in Fig. 6 (a) is derived from a magnetic read signal by using a digital filter and an MR head configured as a local filter. When the waveform shown in Fig. 6 (a) is obtained, the track generating the waveform is magnetically AC erased. The same MR head was moved to the same position of the erased track to obtain the waveform shown in Fig. 6 (b). It can be seen that the extracted column signals in Fig. 6 (a) and the readback signals derived from the erased track in Fig. 6 (b) are substantially the same. The two waveforms shown in Fig. 6 are two columns and magnetic signals read at the same time, and are provided in the readout signal, and these signals are independent of each other and are separable.

Observing the readback signal for the two independent and separable components reveals previous undesirable information content in the readback signal obtained by using the MR head. In particular, information about the disk surface can be derived from the thermal signal. 7 shows an enlarged side view of the MR slider 67 and the MR element 72 close to the surface 24a of the magnetic data storage disk 24. As shown in Fig. Generally, the disk surface 24a has a varying topography at the microscopic level. It should be appreciated that surface features such as, for example, grooves, pits, and bumps may be intentionally provided on disk surface 24a to encode information on disk surface 24a.

7, the thermal response voltage level 119 of the MR element 72 is changed as a function of spacing as indicated by the parameter y between the MR element 72 and the disk surface 24a . The change of the self-read signal causes the resistance variation of the MR element 72. In particular, a typical MR element that is a resistor in response to the presence of a magnetic field is electrically connected to a current source between the positive and negative element leads. The bias current is applied to the MR element via a lead. In normal operation, the magnetic transition on the disk surface 24a affects the resistance of the MR element 72 causing voltage variations across the MR element 72. [ These voltages are generated at the magnetic data transition frequency recorded on the disk surface 24a. Is the basis for the magnetic signal component of the readback signal.

In addition, the resistance of the MR element 72 is affected by the head-disk distance. In particular, the head-disk gap variation is simultaneously varied during heat transfer from the MR element 72 heated by the positive bias current to the disk 24. Heat transfer is the inverse of the head-to-disk spacing. When the heat transfer from the MR element 72 increases (the distance becomes smaller), the temperature and the resistance of the MR element 72 decrease. When the heat transfer is reduced, the temperature and resistance of the MR element 72 increase (the distance becomes larger). Thus, variations in heat transfer between the MR element 72 and the disk 24 result in temperature variations in the MR element 72. [ Therefore, when the temperature of the MR element 72 is changed, the electrical resistance of the MR element 72 and the voltage across the MR element 72 provided by the positive bias current also change correspondingly. It should be noted that, typically, variations in slider flight altitude occur at frequencies much lower than magnetic transitions.

Thus, this temperature change of the MR element 72 occurs at a much lower frequency than the magnetic data transition, and is the unit of the column component of the readback signal.

As shown in FIG. 7, there is an inverse relationship between the topographic surface variations of the disk 24, and there is a magnitude variation of the thermal signal 119. The air space insulation between the MR element 72 and the disk surface 24a is correspondingly increased as the head-disk gap y is instantaneously increased. As a result, the temperature of the MR element 72 also increases . The increase in the temperature of the MR element increases the resistance of the MR element 72 because the positive temperature coefficient of the material of the MR element is typically used to manufacture the MR element 72. For example, permalloy is the preferred material used to make the MR element 72 and has a temperature coefficient of + 3 x 10 ^-3 / 캜. For example, if the MR element 72 passes over the bump 124 on the disk surface 24a, the heat transfer between the MR element 72 and the disk surface 24a increases, And cooled. When the MR element 72 is cooled, the resistance of the MR element is reduced, and then the voltage V _TH across the MR element 72 at the positive bias current is also decreased.

Referring to the pits 122 shown on the disk surface 24a as a result of the interaction between the MR element 72 and the disk surface 24A described above, It can be seen that the amplitude of the column voltage signal V _TH 119 across the MR element 72 increases. In addition, referring to the bump 124 shown on the disk surface 24a, the thermal voltage signal V _TH 119 decreases in amplitude as a function of the decreasing head-to-disk separation distance. For convenience, the disc surface (24a) changes in terrain, without inversion, it may be desirable to reverse the thermal voltage signal V _TH (119) in direct response to changes in the thermal voltage signal V _TH (119). Thus, the negative value -V _TH of the MR head voltage represents the property of the terrain of the disk surface 24a by representing "cooling areas" as peaks and "heating area" as valleys qualitative indication.

In addition, FIG. 7 shows magnetic spacing signals 121 that are in a state corresponding to the variation of the disk surface 24a. It can be seen that when the topography of the disk surface 24a changes, the magnetic spacing signal 121 improperly indicates the presence of some surface characteristics, such as magnetic voids. Also, compared to the disk surface image information provided by the use of the thermal signal 119, it can be seen that the magnetic spacing signal 121 provides a lower signal of other surface characteristics, such as the bump 24.

In general, it should be understood that when a thermal signal interacts with a disk, it includes a thermal response signal of the MR element. As the emissivity or absorptivity of the disk surface changes, the thermal signal can also change. As will be more readily understood with reference to the following description, changes in the disk surface, such as surface profile or emissivity / absorptivity, can be intentionally disclosed and used by using the information content of the components of the readback signal.

Another feature of the MR element 72 that affects the characteristics of the readback signal obtained from the disk surface is that the MR element 72 is in physical contact with the disk surface or other obstructions. For example, thermal asperity (TA) is generated when a temporary physical connection between the disk surface and the MR element 72 occurs. For example, as shown in FIG. 8, the negative (cooling) peak of the thermal voltage response to the bump 124 is largely replaced instantaneously, but the narrow positive spike response is quickly Continuously. The positive spike response is generated by the mechanical frictional heat between the MR element 72 and the local asperity on the disk surface 24A. Due to the mechanical friction associated with thermal asparity, the magnetic coating can be peeled away in the physical connection area. This can cause magnetic vacancies 126, but is not a source of voids.

Referring to FIG. 9, an embodiment of the signal separation / decompression module 76 described above with respect to FIG. 1 is shown. The signal separation / decompression module 76 may be used to perform a single task of separating the magnetic signal from the readback signal to remove low frequency modulation components of the readback signal that are considered to be influenced by the thermal signal or other cause. In another embodiment, the signal separation / decompression module 76 is used to separate the magnetic signal components from the two tasks, i.e., the readback signal 60, to remove low frequency thermal signal components, Can be used to extract the signal and continuously process the information of the magnetic signal and the thermal signal in a substantially independent form.

9, the readback signal is generated in the MR element 72 located in proximity to the magnetic data storage disk 24. As shown in FIG. As will be described in more detail below, the readback signal modulation varies with frequency and amplitude as the function of the column signal component operation.

In one embodiment, the readback signal received from the AE module 74 from the MR element 72 is converted from an analog form to a digital form by the A / D converter 84. The digital read signal is then communicated to a delay device 86 and a linear phase programmable filter 88. Programmable filter 88 is a finite impulse response (FIR) with length N, where N is the impulse response coefficient of the programmable filter 88 or the number of taps. When the readback signal passes through the programmable filter 88, the readback signal applied to the programmable filter 88 is subject to an integral signal delay corresponding to the length N of the programmable filter 88.

According to this embodiment, the programmable filter 88 is programmed with appropriate tap coefficients and weights so that the relatively low frequency column signal component of the readback signal is passed and the relatively high frequency magnetic signal component is filtered. As such, the programmable filter 88 is configured as a local pass filter and includes a thermal signal component that can be characterized as a generally medium frequency signal having a high energy in the frequency range from about 10 kHz to about 100-200 kHz Lt; / RTI > It should be noted that the magnetic signal component of the readback signal has a frequency range of about 20 MHz-100 MHz. At the output of the programmable filter 88, the column signal 80 is communicated to the signal adder 90. From the output of the programmable filter 88, the thermal signal 80 may be communicated to the servo control device to control other components of the data storage system, e.g., track tracking and track seeking operations.

The delay device 86 receives the readback signal from the A / D converter 84 and outputs a read signal to the signal tracing device 90 at a time interval equal to the delay time required for the readback signal to pass through the programmable filter 88 Thereby delaying the read signal transmission. As such, the readback signal comprising the magnetic and thermal signal components and the thermal signal 80 derived from the readback signal by the programmable filter 88 arrive at the signal adder 90 at substantially the same time. The signal adder 90 performs a modulating operation on the readback signal and the column signal 80 to cause the reconstructed readback signal 78 to be generated. Thus, the signal separation / decompression module 76 shown in the embodiment shown in FIG. 9 separates the magnetic and thermal signal components of the combined readout signal and adds the undistorted and reconstructed magnetic readout signal 78 to the additive .

Another embodiment of the signal separation / decompression module 76 for generating a recovered readback signal 78 after processing the readback signal modulated through the signal separation / . According to this embodiment, the amplitude-distorted readback signal comprising magnetic and thermal signal components is sensed by the MR element 72 from the magnetic data storage disk 24 and communicated to the AE module 74. The modulated readout signal is then digitized by a sampler 84 and passed through a suitably configured programmable filter 88 such that undistorted readout readout signal 78 is generated.

The programmable filter 88 is preferably a finite infinite response (FIR) filter programmed to pass the relatively high frequency magnetic signal component of the combined readout signal and removes the relatively low frequency thermal signal component of the combined readout signal. Although FIR filters and other filters can be used as the programmable filter 88, it is important for the filter 88 to have a substantially complete linear phase response to achieve optimal performance. This is easily accomplished by using a digital FIR filter. However, in some applications, the nonlinear phase operation of the filter 88 may be somewhat acceptable.

Generally, when a signal passes through a filter, the amplitude and / or phase of the signal changes. The nature and extent of the signal change depends on the amplitude and phase characteristics of the filter. The phase delay or group delay of the filter provides an effective way for the filter to change the phase characteristics of the signal. A filter having a non-linear phase characteristic accepts a phase distortion of a signal passing through the filter. This phase distortion is caused by the fact that the frequency components in the signal are each delayed to a magnitude that is not proportional to the frequency, thereby changing these harmonic relationships. Certain classes of FIR filters substantially eliminate all undesirable modulation of the readback signal generated due to the effects of the thermal signal components, and are required to provide a complete linear phase response required to generate the recovered readback signal 78 It turned out to be necessary.

Referring to the embodiment shown in FIG. 11, the function of selectively connecting and disconnecting the signal separation / decompression module 76 from the recording channel through which the readback signal typically passes is shown. The programmable filter 88 is connected to a read-only-memory (ROM) 94 that stores a plurality of sets of programmable filter parameters. In an embodiment that includes a FIR filter 88, the ROM 94 typically stores a number of tap weight sets 96 and also stores at least one restoration tab weight set . For example, for purposes of illustration, it is assumed that the write channel for a particular data storage system includes a single 10-tap FIR filter 88. [ The 10-tap FIR filter 88 is connected to a ROM 94 that stores a different set of tap weight sets 96, and any set of these sets is coupled to the FIR filter 88 to reprogram the response Can be loaded. As described above, when the servo controller tries to process a distorted read signal, the modulated read-out signal read from the servo sector may produce particularly bad results. For example, the sector and cylinder information contained in the gray code field 66 of the servo sector may be misinterpreted or difficult to read.

As shown in FIG. 11, the signal separation / decompression module 76 may be selectively used to process only the read signal information from the servo sector between the data sectors. According to this embodiment, a single programmable filter 88 contained within the recording channel of the data storage system is coupled to the signal separation / decompression module 76 and the servo channel via the data channel And may be time-divided between the readback signal processing corresponding to the data sector. When the data sector information is read, the read signal is selectively transmitted through the data channel in order to bypass the signal separation / restoration module 76.

11, according to an embodiment of data storage disk 24 employing embedded servo architecture, when data storage disk 24 typically rotates at thousands of RPM speeds, another series of data and servo The sector is advanced by the MR element 72. When the MR element 72 reads information from the data sector 102, the readback signal generated in the MR element 72 is passed to the AE module 74, the FIR filter 88 and the data channel, / Restore module 76 is bypassed. It should be noted that when processing the signal information obtained from the data sector 102, the FIR filter 88 is programmed with one of a plurality of tap weight sets 96.

When the servo sector 104 is brought close to the MR element 72 the restitution weight set 98 stored in the ROM 94 is loaded into the FIR filter 88, Lt; / RTI > is restored. The restoration tap weight set 98 constitutes the FIR filter 88 to remove the column signal component of the readback signal read out from the servo sector 104, And generates a read-out magnetic signal 78. Thereafter, the recovered magnetic read signal 78 is processed in communication with the servo control. When the data sector 106 adjacent to the servo sector 104 approaches the MR element 72, the selected set of tap weights 96 is applied to the FIR filter 88 . The readback signal derived from the data sector 106 is processed through the FIR filter 88 and the data channel to allow the signal separation / decompression module 76 to be bypassed. The process of selectively processing the readback signal derived from the servo sector is similarly repeated.

It should be appreciated that the embodiment illustrated in FIG. 11 is particularly suited for retrofitting a data storage system that includes a single programmable filter 88 within the read / write channel. It should be appreciated that a first programmable filter may be configured for operation of the servo channel and a second programmable filter may be desirable to incorporate a separate programmable filter so that it may be configured for operation of the data channel. According to the configuration using such an independent programmable filter, the error rate performance of the data storage system can be improved by restoring the readback signal derived from the data sector.

A process may be performed to load the set of restore tab weights 98 stored in the ROM 94 into the programmable filter 88 when a sync field 64 or other signal indicative of the start of the servo sector is detected . Similarly, to determine when the tap weight set 96 for a data sector is loaded into the programmable filter 88 to read information from the data sector, a synchronization field or other information signal indicating the start of the data sector Can be detected. References for designing, implementing, and programming a FIR filter suitable for use in the signal separation / decompression module 76 are described in E.C. Ifeachor, B.W. Digital Signal Processing " (Addison-Wesley Publishing Company, Inc. 1933) described by Jervis.

Referring to FIGS. 4 and 5, the modulated readback signal shown in FIG. 4 shows the readback signal before being processed by the signal separation / restoration module 76. The readback signal shown in FIG. 5 illustrates the readback signal of FIG. 4 after being processed by the signal separation / restoration module 76. By using a 9-tap FIR filter in the signal separation / decompression module 76 that generates the reconstructed magnetic read signal shown in FIG. 5, the undesirable effects of the column signal components on the readback signal shown in FIG. 4 are eliminated do. 12 illustrates the amplitude and phase characteristics of a 9-tap FIR filter used to generate the reconstructed magnetic readback signal 78 shown in FIG.

In particular, in FIG. 12 (b), it can be seen that the 9-tap filter exhibits a perfect linear phase response over the frequency range. FIG. 13 illustrates a 9-tap FIR filter that effectively removes baseline shift or modulation of the read signal. Fig. 13 (a) shows a readback signal indicating an unsafe amplitude-variable base line. Fig. 13 (b) shows that the modulation baseline of the read signal, which is shown in Fig. 13 (a), is removed after the read signal has passed through the appropriately programmed 9-tap FIR filter. The tap weights for the 9-tap filter used to recover the baseline of the readback signal are designed to include the following tap weights:

B (i) = (1/9) * (-1, -1, -1, -1, 8, -1, -1, -1, -1)

B (i) = (-111, -111, -111, -111, -889, -111, -111, -111,

It should be noted that the waveform shown in FIG. 13 (c) is generated by passing the modulated readout signal shown in FIG. 13 (b) through a typical highpass Butterworth filter. It will be appreciated that undesired modulation of the baseline of the readout signal is still present even after the readback signal has passed through a typical high-pass filter.

As described above, the amplitude and phase characteristics of the 9-tap FIR filter used to recover the baseline of the readback signal shown in Fig. 13 (b) are shown in Figs. 12 (a) and 12 have. Referring to Figure 12 (a), it should be appreciated that some degree of ripple may occur in the passband of the filter, which can be eliminated by providing the window function to the tap weights of the 9-tap FIR filter. For example, a Hamming window may be provided for the tap weights of a 9-tap FIR filter to form a windowed reconstruction filter with the following tap weights:

B (i) = (-.0089, -0.239, -.06, -.0961, .8889, -.0961, -.06, -0239,

The output signal of the 9-tap window type FIR filter having the above-mentioned tab weights is output with the ripple removed as shown in FIG. 14 (a). Further, as shown in Fig. 14 (b), the windowed 9-tap FIR filter includes a complete linear phase response. It should be noted that applying a window function, such as a Hamming window, to the tap weights of the programmable FIR filter 88 slightly increases the non-zero DC gain at low frequency response.

Referring to Figures 15-22, another embodiment of a signal separation / decompression module (also referred to as a < RTI ID = 0.0 > 76 are shown. This embodiment can be used in reconditioned systems as well as in modern designed data storage systems. The design of an analog AE module, such as the AE module 74 shown in Figure 1, sometimes includes a high pass filter with a preamplifier to remove the signal component of the readback signal that is less than the frequency range of the magnetic signal component . In the high pass filter of the AE module 74, the column signal component of the combined read signal is amplitude and phase distorted. This thermal signal distortion varies significantly with the frequency and phase response of the particular AE module being used.

For example, a high pass filter suitable for use in the AE module 74 may have a cutoff frequency of about 50 kHz and may exhibit non-linear phase operation.

However, the frequencies associated with the associated column signal information are typically less than 200 kHz, and have a range of 10 kHz-100 kHz. It should be appreciated that a high pass filter having a cutoff frequency of about 500 kHz significantly distorts the amplitude and phase of the column signal component of the readback signal. However, the magnetic signal component of the readback signal is also unaffected by the highpass filter because the frequency range for the magnetic signal is typically about 20-40 times larger than the highpass filter cutoff frequency.

Figures 15 (a) and (b) show graphs illustrating the amplitude and phase response of a typical analog AE module 74 representing a high pass filter. The high pass filter has a cutoff frequency of about 500 kHz. The digital formula of the analog transfer function of the effective high-pass filter of the AE module 74 having the single pole of 500 kHz and the amplitude and phase response shown in Fig. 15 is as follows:

Here, b _h (1) = 0.9876

b _h (2) = -0.9876

a _h (2) = -0.9752

The amplitude and phase distortion of the thermal signal derived by the high pass filtering of the AE module 74 is effectively eliminated by using an inverse filter having an inverse transfer function to the high pass filter. When the readback signal outputted from the AE module 74 passes through the inverse filter, the column signal is restored to its original amplitude and phase form. For example, the transfer function of the inverse filter for transforming the readback signal passed through the high-pass filter having the transfer function of the above-mentioned equation (1) is as follows:

The amplitude and phase responses for the effective high pass filter and the inverse filter of the AE module 74 in the above-described equation [2] are shown in Figs. 16 and 17, respectively. In particular, the amplitude response of the effective high pass filter of the inverse filter and AE module 74 is shown by curves 170 and 172, respectively, in FIG. The phase response of the inverse filter and the effective high-pass filter is shown as a curve 176 in Fig.

In one embodiment, the infinite impulse response (IIR) filter is used as an inverse filter in the signal separation / decompression module 76 to recover the column signal component of the high-pass filtered read signal. The impulse response of the IIR filter has an infinite duration in contrast to the FIR filter in which the impulse response has a finite duration. Unlike the FIR filter, which exhibits a perfect linear phase response, the phase response of the IIR filter is nonlinear, especially at the band edge. Although an analog filter can be used in another embodiment, the IIR filter provides many advantages that are suitable for use as an inverse filter to recover the amplitude and phase of a distorted thermal signal by high pass filtering of the analog AE module 74.

The signal flow diagram shown in Fig. 18 shows a first order IIR filter configured as an inverse filter. The coefficients associated with the signal flow diagram of FIG. 18 for a first order IIR inverse filter having a transfer function provided by the above equation [2] are:

a ₁ = 0.9876

a ₂ = -0.9876

b ₁ = 0.1

b ₂ = -0.9752

A more detailed description of designing and implementing and programming an IIR filter suitable for use as an inverse filter in the signal separation / decompression module 76 is given in E. C. Ifeachor, B.W. Jervis, " Digital Signal Processing " (Addison-Wesley Publishing Company Inc. 1993).

19 illustrates three waveforms used to verify the effectiveness of the inverse filter and recover the original amplitude and phase of the column signal components in the readback signal passed through the high pass filter. 19 (a) shows the readback signal detected by scanning the pits on the surface of the data storage disk using the MR head. The magnetic read-out signal shown in Fig. 19 (a) is detected from a track recorded at a recording frequency of 20 MHz.

The readback signal with 8-bit resolution is sampled at 100 MHz. The signal shown in Fig. 19 (b) represents the amplitude between the peaks measured in the readback signal in Fig. 19 (a). In addition, the signal shown in Fig. 19 (b) represents the magnetic signal component of the readback signal shown in Fig. 19 (a), which shows a significant amplitude reduction due to the MR read element moving on the pit. 19 (c) shows the column signal component of the readback signal of Fig. 19 (a) after passing through the effective high-pass filter of the AE module 74. Fig. 19 (b) and 19 (c), it will be understood that the magnetic and thermal signal components of the readback signal do not closely correspond to each other. As such, the poor correlation between the thermal and magnetic signals can be caused by distortion to the thermal signal, which is caused by the effective high-pass filter of the analog AE module 74 with effectively differential thermal signals do.

The inverse filter of the signal separation / decompression module 76 restores the amplitude and phase of the column signal 162 as shown in FIG. It should be noted that the thermal and magnetic signals shown in FIG. 20 are shown as head-to-disk spacing signals, as will be described in greater detail below. It will be appreciated that the magnetic signal and the recovered thermal signal closely correspond to each other after the high pass filtered thermal signal passes through the inverse filter.

As described above with respect to Fig. 7, the thermal signal included in the MR head changes as a function of the head-disk gap. Thus, the information contained in the thermal signal can be used to detect surface topography variations of the disk. Several surface features such as pits, gouges, bumps, thermal asperities, and specific contamination can be detected using thermal signals. It should be appreciated that in order to derive various types of information using thermal signals, these surface features may be intentionally included on the surface of the disk.

To detect the position of tracks and sectors using a thermal signal, concentric and radial elongated depressions may be included on the surface of the disk, for example, concentric and radial. Further, detailed terrain mapping of the disk surface can be achieved by using thermal signals. It will be appreciated that the column signal derived from the readback signal can be advantageously used in a variety of applications. On the other hand, for example, one or more depressions may be included up to a certain depth in the disk surface to derive the head-to-disk spacing using a thermal signal to measure the thermal response of the MR head.

It is well known to those skilled in the art to use the magnetic readout signal generated by the read / write transducer to detect variations in the spacing between the disk surface and the transducer. This method of measuring the head-to-disk spacing using a self-read signal is referred to as the Harmonic Ratio Flyheight (HRF) clearance test. HRF inspection is a well-known method, which uses a magnetic head-to-disk spacing signal to measure the flying height of a slider supporting a transducer carried in a data storage system housing. The HRF scheme is disclosed in U.S. Patent No. 4,777,544, assigned to the assignee of the present invention, which is incorporated herein by reference. The HRF measurement scheme is a method for continuously and simultaneously measuring the ratio of two spectral lines in the spectrum of the readback signal. The amplitude of the spectral lines of these synchronizations relates to the same volume element of the recording medium located just below the MR transducer. The HRF measurement scheme provides a method for simultaneously measuring head spacing on the disk surface using a magnetic read signal.

According to one embodiment, the thermal signal component of the readback signal derived from the MR head is used to qualitatively measure the head-disk gap variation. In another embodiment, the thermal signal is corrected using a magnetic signal to quantitatively measure the head-to-disk spacing. Referring to FIG. 21, a system for processing magnetic readback signals to derive magnetic and thermal head-to-disk space information is shown in block form. A readback signal is detected from the disk surface 24 by the MR element 72. [ Assuming that the readback signal is a composite signal that includes both magnetic and thermal signal components, it should be appreciated that the readback signal without the magnetic signal component contains a thermal signal component useful for measuring the head-to-disk spacing. The readback signal detected by the MR element 72 communicates with the AE module 74 and thereafter communicates with the highpass filter 150. The high pass filter 150 is shown as an element external to the AE module 74, but is generally provided to represent the high pass filter of the AE module 74. The transfer function of the effective high-pass filter 150 is shown as H ₀ . The signal output from the high-pass filter 150 is sampled by the A / D converter 151 to generate a digital sample of the read signal that is high-pass filtered.

As shown in Fig. 21, the column signal 159 at the output stage of the column signal extraction filter 157 can be generated by using one of the above-mentioned schemes. For example, a digital read signal may be communicated to an inverse filter 156, which corrects for distortion generated by the high pass filter 150 of the AE module 74. The transfer function of the inverse filter 156 is shown as H ₀ ^-1 . The thermal signal is then extracted by a thermal signal extraction filter 157, which may be an FIR filter. It should be appreciated that the inverse filter 156 and the column signal extraction filter 157 can be internal to the signal IIR filter such that the distorted thermal signal can be reconstructed by the high-pass filter 150. Also, the readback signal may be tapped to the front end of the high-pass filter 150 and input to the column signal extraction filter 157, and the column signal extraction filter 157 may be an FIR filter as described above. The thermal signal extracted by the thermal signal extraction filter 157 is communicated to an average filter 158 to generate a thermal spacing signal 162 that is linearly related to the head-disk spacing. The averaging filter 158 is a filter that gently averages the digital shift.

Also, the readback signal provided at the output of the A / D converter 151 is communicated to an amplitude detector 152, such as an FIR filter, which detects the amplitude between the peaks of the readback signal and extracts the magnetic signal component from the readout signal . The logarithm of the magnetic signal is derived by passing the magnetic signal through a log device 154 which generates a magnetic signal linearly related to the head-disk spacing. Since the magnetic calibration is well known and depends only on the wavelength of the recorded signal, if the magnetic spacing signal 160 and the column spacing signal 162 are derived, the column signal can be measured. It should be noted that the negative (or inverse) of the magnetic spacing signal 160 and the derived thermal signal 162 is linearly proportional to the head-disk spacing y.

20, the column spacing signal 162 processed by the column signal extraction filter 157 and the averaging filter 158 includes a magnetic spacing signal 160 that is processed through the amplitude detector 152 and the log device 154, Respectively. Typically, the linearized magnetic spacing signal 160 is corrected by taking the logarithm of the signal between peaks and multiplying by the known sensitivity of the output voltage variation versus the magnetic spacing variation in accordance with the well-known Wallace equation, . 20, the magnetic spacing signal 160 and the column spacing signal 162, except for the difference in signal height and a slightly longer time constant associated with the column spacing signal 162, It should be understood that it is a pit. As will be described in greater detail below, the column spacing signal 162 can be corrected by using a linearized magnetic spacing signal 160 to accurately reflect the head-to-disk spacing.

An important advantage of the present invention is that the head-disk gap variation can be detected by using the thermal response of the MR element 72. Using the thermal response of the MR element 72 to measure the head-to-disk spacing at the original location will provide disk manufacturing inspection and screening during the useful life of the data storage system in the field, PFA). In addition, the column spacing signal 162 may be used to detect a head in contact with the surface of the data storage disk.

Referring to FIG. 22, a magnetic spacing signal 160 and a column spacing signal 162 for head-to-disk contact are shown, such as a contact between an MR head and a local thermal asperity (TA). The magnetic spacing signal 160 has been linearized by taking the logarithm of the magnetic signal. The column spacing signal 162 is determined by using the inverse filtering scheme described above. It can be seen that when the disk asperity moves the MR head 72 upward from the disk surface, the MR element-disk gap increases. The magnetic spacing signal 160 and the column spacing signal 162 show that the head-to-disk spacing gradually increases between 0 and 25 microseconds. Some air-bearing (head-to-disk spacing) modulation occurs before the MR element 72 advances on the asperity and before the MR element 72 returns to the steady state flight altitude. Referring to FIG. 22, it can be seen that air-to-baying modulation is performed continuously from about 35 microseconds to 70 microseconds.

In the waveform characteristics for the magnetic spacing signal 160 and the column spacing signal 162, the column spacing signal 162 is applied to the head-to-head signal at the original position, without requiring a means of testing bench equipment or external tester, And can be used to detect disk contact. It should be noted that the characteristics of the inverse filter required for a particular data storage system are dependent on the pole position for the high pass filter 150 of the AE module 74. In the case of an embodiment using an IIR filter or FIR filter, only the coefficients or tap weights are required to be changed. In an embodiment using an IIR filter, such a change may be performed adaptively or dynamically in the case where the pole frequency of the high-pass filter 150 changes. Typically, this variation can occur, for example, as the temperature fluctuates. It should be understood that the inverse filter 150 described herein is not limited to a first order IIR structure.

Generally, the amplitude of the thermal signal generated in the MR head is a function of the particular MR element used in the MR head. For example, variations in the manufacturing process used and material variations will cause variations in the response of the MR device. Therefore, in order to accurately determine the head-disk gap variation using the thermal response of the MR head, it is desirable to measure the thermal response at the original position using a magnetic response. For example, accurate magnetic spacing information can be achieved by using the well-known Wallis interval loss equation. A measured depression, such as a radial trench or a pit, is formed in the landing zone and is used to perform thermal spacing measurements at the original location, generating both thermal and magnetic signal modulation. The magnetic spacing for the trench can be accurately determined and used to measure the thermal voltage response of the MR element.

Another option involves combining magnetic head-disk spacing measurements with thermal spacing measurements using an HRF scheme or other similar scheme. In accordance with this combination test, thermal and magnetic " spindown " are performed simultaneously, whereby the thermal voltage fluctuation between the two disk speeds is compared to the known (HRF) interval fluctuations between the two disk speeds. However, recovery of the thermal signal at the disk rotational speed is difficult to achieve in a system using the AE module 74 with highpass filtering because typically a highpass cutoff frequency is applied to the disk rotation Because it has several orders of magnitude than frequency.

The head-to-disk spacing measurement of the thermal response of the MR head is further complicated by the high-pass filtering nature of the AE module 74. In general, the transfer function H _AE (s) of the AE module 74 with the high-pass filtering operation can be expressed in a linear fashion as follows:

Where K _AE is the gain of the AE module 74 at the write frequency and " a " is the cutoff frequency for the effective highpass filter incorporated in the AE module 74. The typical value of the gain is K _AE = 170, but generally the gain of the AE module 74 has many variations. A typical cutoff frequency " a " is about 325 kHz, typically associated with many tolerances of +/- 125 kHz.

The corresponding frequency for surface detection similar to the bumps to be detected during surface analysis screening typically has a range of 10 kHz to 100 kHz. The thermal response of the MR head directly relays these frequencies, but the magnetic response shifts these frequencies within the 20 MHz range due to the magnetic recording carrier frequency. The highpass characteristic of the AE module 74 attenuates all bump disturbance amplitudes in the thermal response to frequencies below 400 kHz, but the magnetic response is not affected. To restore the attenuation of the thermal response, several types of integration methods are provided. This reconstruction process is accomplished by using an inverse filter having a transfer function H _INV (s) that is inverse (i.e., H _INV (s) = 1 / H _AE (s)) to the transfer function H _AE of the AE module 74 . For example, the lowest frequency provided from MR head read data from disk spinning at 7200 RPM is 120 Hz, and the lowest frequency for detecting disk surface bumps is about 10 kHz. A pseudo-inverse filter, such as a lead-lag filter with zero (" a ") at 400 kHz and a pole (" b ") at 5 kHz, Can be suitably used.

A pseudo-inverse filter can have a transfer function of the form:

The overall transfer function of the pseudo-inverse filter cascaded with the AE module 74 is as follows.

Thus, the compensation transfer function H (s) described above is a high pass filter with a cutoff frequency at 5 kHz, which is suitable for passing the frequency associated with the disk surface bump in an undistorted form.

Many variations of the high pass cutoff frequency " a " can cause many variations in the recovered thermal response. Accurate evaluation of the high pass cutoff frequency " a ", gain K _AE, and sensitivity [nm / mv] for each MR head is important for reliability of measurement. Due to the lack of a low frequency (i.e.,? 120 Hz) response signal of the AE module 74, the thermal measurement process can be supported in other ways such as the standard of reference. This support scheme is referred to herein as a readback signal modulation (RSM) scheme, which is a well-known magnetic measurement scheme for determining the variation of the head-disk magnetic spacing based on the Waliss spacing loss scheme. An effective thermal measurement procedure is based in part on the RSM approach and is initially performed, but the actuator can be a crash stop of the landing zone to inspect both the heat and magnetic components of the readback signal of the track containing the measurement depression, / RTI >

The correction depression is corrected on the surface of the disk blank and is subject to a polish and sputtering process so that the magnetic and thermal data are obtained from the corrected depression. It should be noted that the depression generated in the landing zone can be formed like a bump. However, the bumps are prone to cause head / disk interference (HDI) and can permanently damage the head or disk as a result of head-to-disk crashes. In addition, the bumps may cause head lift-off and air-bearing modulation, and thus may be unsuitable for use as a permanent calibration site. In contrast, " pure " pits do not cause head lift-off or air-bearing modulation. In addition, the correction trench on the disk substrate surface requires a low cost to manufacture.

Prior to describing one embodiment of the calibration procedure, it is desirable to define several variables associated with the calibration procedure. It should be noted that the term low frequency (LF) is referred to as a frequency in the order of the disk rotation frequency (RPM / 60) such as 120 Hz at a rotation speed of 7200 RPM. Referring to Equations (6) and (7), V _TH (LF) is the average per rotation of the restored column voltage (baseline) response of the AE module at the landing zone, excluding data obtained from the correction pit, Expressed in millivolts (mv). V _TH (Pit) is the recovered average thermal voltage peak of the AE module generated from the correction pit of the landing zone taken over several revolutions, typically expressed in millivolts (mv). δ _HRF (LF) is the average per rotation of the RSM head-to-disk distance in the landing zone, excluding data obtained from the correction pit, typically expressed in nanometers (nm). Finally, δ _HRF (Pit) is the average peak HRF head / disk spacing generated from the correction pits at the landing zone taken over several revolutions, typically expressed in nanometers (nm).

By following the crash stop of the landing zone and excluding the data obtained from the correction pit, the proposed thermal correction process is based on the average per rotation obtained with the actuator, i.e. the RSM value _HRF (LF) of the low frequency (LF) ) And the corresponding average thermal baseline voltage V _TH (LF). The average peak values of the excluded column and magnetic pit data generate V _TH (Pit) and 隆_HRF (Pit).

The " AC " correction factor C (i) for the i-th head can be determined as follows:

It should be noted that for a pit, a condition is provided that? _HRF (LF)>? _HRF (Pit) and? _TH (LF)>? _TH (Pit).

The formula for the i-th thermal head-disk spacing is:

Here,? V _TH = V _TH (defect) - V _TH (LF). In the case of a bump, assuming that there is no head-to-MR element connection, cooling is provided so that DELTA _VTH is set to less than zero. In the case of pits, when the head-disk separation increases, the MR element is heated, so that? V _TH exceeds 0. At the position of the correction pit (that is, in this case, the inner diameter landing zone, but in the case of a load / unload disk drive, the outer diameter may be located), the equation of the thermal head- Updating the average RSM head-disk spacing δ _HRF (LF) can improve accuracy. To achieve this during manufacturing screening, a magnetic track can be recorded on a magnetic track at a defect radius.

Even if the thermal response of the MR head is not corrected, the thermal signal component of the readback signal can be used to provide qualitative analysis instead of quantitative analysis of the disk surface characteristics. Thus, disk surface analysis screening can be performed to detect disk defects using a unique regular scheme. This approach is predicted when using the unique " background " column signal information on the disc track as a reference to derive the clip levels (i.e., failure threshold). It should be noted that the quantitative and qualitative evaluation of disk surface topography can be performed without the magnetic coating to be provided on the disk surface. Thus, disc blanks without magnetic coating, whether intentional or unintentional, prior to processing the disc blanks, can be fully analyzed for surface defects and properties. This makes it possible to prevent an excessive processing cost of the defect disk blank.

A thermal back ground signal for a typical magnetic data storage disk can consist of five major frequency groups. The first group includes the main servo pattern frequency, typically ranging from 2.5 MHz to 10 MHz. The second group includes the servo-length frequency defined from the beginning to the end of each servo burst, typically ranging from 60 kHz to 70 kHz. The third group includes an inverse of the time between the inner-servo frequency or the servo burst at about 10 kHz. The frequency of the fourth group is a data pattern frequency exceeding 10 MHz. When the track is erased, the magnetic data pattern can be removed.

The frequency of the fifth group is the broadband frequency and is associated with the disk topography, and the head-disk spacing varies as the disk surface varies. The upper end of the fifth group is typically limited to a thermal time constant of the MR response of about 1 microsecond. Once properly filtered, the readback signal amplitude modulation effects of these five " noise " sources can be selectively suppressed. In the case of head-to-disk contact, the signal-to-noise ratio typically exceeds the ratio of 10: 1 (20 dB) and can be easily detected.

A number of filtering schemes can be used to filter the five noise sources described. Such filtering schemes include the use of an elliptical filter to filter the readback signal. Bandstop elliptic filters provide higher attenuation than Butterworth filters or Chebyshev filters and provide less phase distortion than these filters. One useful filtering scheme uses two elliptic band-stop filters. Each fourth-order digital elliptical band-stop filter has two notches, which are generated by two pairs of composite zeros in a transfer function located on a unit circle in the z-plane. One " low notch " quadratic elliptical filter can remove frequencies below about 15 kHz. Indeed, the internal-servo pattern frequency has the most problems when it comes close to the desired detection bandwidth for disk surface defects. The low-notch elliptical filter may be designed to provide a notch at 120Hz and 10.8kHz providing a very high attenuation (e.g., 20-60db) in this frequency range. A second quadratic elliptic torch filter composed of a high-notch filter can attenuate the servo pattern frequency of about 5 MHz and the third harmonic of about 15 MHz. These two frequencies are dominant. A fourth order elliptical notch filter can provide very high attenuation in this frequency range. These frequencies are stable due to the precise speed of the spindles of typical data storage systems.

As described above, when the readback signal is read, the magnetic and thermal components of the readback signal include information about the surface characteristics of the disk surface. Table 1 below provides a comparison between various types of disk surface defects and magnetic and thermal spacing signal responses for permanently recorded servo sectors. By separating the composite readout signal into independent magnetic and thermal signal components, two independent responses of the MR head are simultaneously used to detect the same " unknown phenomenon " or surface defects. Two independent thermal and magnetic signals are used to significantly improve defect detection and reliability during disk surface analysis. Improved defect detection can be achieved by using a two-dimensional (2D) detection scheme rather than one-dimensional (1D). The one-dimensional detection scheme is referred to as a scheme that uses one of the magnetic or thermal signals but does not use all of these signals. At the same time, powerful means are provided for detecting and classifying unknown disk surface defects in using two independent magnetic and thermal signals obtained simultaneously from the same MR element.

Hereinafter, Table 1 schematically provides the difference between the simple disk surface defects shown in FIG. 7 and the magnetic and thermal MR head-disk spacing responses for permanent writing. It should be appreciated that multiple disk surface defects, such as scratches and gouge, are typically a complex combination of several simple defects and may result in more complex MR head responses.

Referring to Table 1, a method for performing disk surface defect analysis can be performed as follows. First, a thermal scan is performed on the surface of each disk provided in the data storage system. The thermal response results for the thermal voltage exceeding the predetermined positive and negative thresholds are then monitored. Since the thermal response is not sensitive to magnetic vacancies and pre-recorded servo sectors, this process will remove the magnetic patterns of the servo sectors and magnetic vacancies as effective surface defects. It should be noted that a defect analysis process that exclusively uses a magnetic signal may misrepresent the presence of surface defects in detecting magnetic pores or misplaced permanent recordings. Thereafter, the triggering of the thermal threshold detector during the column scan is caused by three basic types of surface defects, i.e., pits, bumps and thermal asperities (TA), or by combining these three defect types.

Then, to perform the magnetic defect verification procedure, such as using the HRF or RSM scheme using the magnetic response characteristics provided in Table 1 above, the magnetic information may be recorded at the disk surface location at which the thermal threshold is triggered . Both the thermal detector and the HRF / RSM detector must be triggered at the same time before the defective disk is rejected to the disk or data storage system in which it is housed, since the bump and thermal asperities only represent a valid failure condition.

Thus, heating and cooling of the MR element in response to head-to-disk spacing variations is not sufficient to mechanically damage the disk 24 to remove the disk and not have to remove the disk, such as pits and magnetic air, Can be used to detect and identify other less critical disk defects. Such coupling analysis of the disk surface can be performed in the original place or in a data storage system that can operate fully before shipment. Also, in order to perform a predictive failure analysis on a data storage system, at a pre-set time during the useful life of the in-field, a defect analysis of the disk surface can be performed at the original location. In addition, disc surface defect analysis can be performed on a disc blank without a magnetic coating to prevent the defect disc blank from being processed.

The way to classify disk defects can be formulated by using the negative and positive peaks of the thermal signal derived from the MR head. When the MR element is heated due to an increase in head-disk spacing, one embodiment of the defect classification scheme is derived by determining that the amplitude of the thermal signal for the disk depression (e.g., pit) increases.

In such a classification of the disk defects, there is rarely a predetermined cooling which allows the thermal head of the negative polarity to be generated by the MR head.

Under close head-disk contact conditions, the MR element is cooled. The MR element cooling generates a negative progressive thermal voltage signal V _TH . The criteria for disk inspection for mechanical damage are provided as follows:

Where V + is the positive peak of V _TH ;

V- is the negative peak of V _TH ;

T is a thermal voltage threshold that, if exceeded, indicates the presence of mechanical damage to the disk.

The inspection criterion in Equation [8] has been proven to be able to be used to accurately identify the presence of criterion or urgent mechanical disc damage. The application of Eq. [8] is suitable for determining the presence of disk mechanical damage, because this damage is due to the cooling caused by the MR element due to the proximity of the disk surface to the heating caused by disk defects that mis- It is related. In the case of other disk defects not associated with top disk surface overhang, such as plating pits, the thermal voltage signal can not exhibit a sufficiently large negative peak to show this relationship because the cooling value of the resulting MR element Is not large enough. In addition, disk defects, such as magnetic pores, that have a significant effect on magnetic signals do not generate a sensible thermal response. A typical screening procedure does not reliably detect the presence or absence of mechanical damage to the disk associated with magnetic voids or other, so removing or discarding non-fatal magnetic voids is primarily handled by manufacturers of magnetic data storage disks It came.

In general, curves can be used to distinguish between pass and fail screening criteria. An example of a screening curve is provided in the following manner:

Where V _- is the minimum column voltage; V ₊ is the maximum column voltage; n, m, C ₁ , and C ₂ are constants. For example, if n = m = 2 and C ₁ = 1, then the pass- Quot; is a section of a circle having the same radius as "

Identification of a specific type of surface defect can be set by using a disk surface defect detection circuit. 23, it is to be understood that although the defect identification circuit 91 is implemented by using analog circuitry, it is to be understood that the defect identification circuit 91 may also be implemented by digital circuitry or by digital signal processing do.

Fault detection identification circuit 91 is, for example, the negative thermal cooling peak V _TH (cool) and heat astro parity "heating" spark V _TH (warm), the total thermal voltage signal difference between the positive peak of △ V _TH (TA) To detect thermal affinity (TA), the total thermal voltage signal difference is:

The thermal voltage signal V _TH is derived from the read signal by the signal separation / restoration module 76 and is applied to the positive feed-and-hold circuit 71 and the negative peak-and-hold circuit 73. The positive peak-and-hold circuit 71 buffers the positive peak voltage V _TH (warm) of the column signal, while the negative peak-hold circuit 73 buffers the negative peak voltage V _TH (cool) of the column signal. The pit detector 75, implemented using an operational amplifier of the comparator arrangement, compares the appropriate input threshold voltage T _(PIT) with the positive peak voltage V _TH (warm) and then calibrated to calculate the surface pit .

Similarly, the bump detector 79 is implemented and calibrated to compare the appropriate input threshold voltage T _(BUMP) with the negative peak voltage V _TH (cool) to detect surface bumps. Similarly, the appropriate input voltage T _(TA) is compared to the thermal difference signal (V _TH (warm) - V _TH (cool)) generated by the adder circuit 81 to detect the thermal asperity A thermal asperity detector 77 is also implemented and corrected. In embodiments that do not use the positive and negative peak-and-hold circuits 71 and 73, the maximum positive and minimum negative peak values of the thermal response voltage V _TH for the preset threshold can be continuously monitored for fault identification .

The logic levels of the three comparators 75, 77 and 79 have three-bit words {TA, BUMP, PIT} used with a pass / fail decision table as shown in Table 2 below Lt; / RTI > As described above, the verification procedure may be executed in the case of a disc that has been rejected when the magnetic track is recorded on the disc and the HRF and / or RSM authentication check is performed.

Referring to FIG. 24, there are shown various steps for performing an error recovery routine using the column signal components of the readback signal. In general, the error recovery routine shown in the form of a flow chart in FIG. 24 is useful for recovering data with severe error conditions, typically after performing a number of standard error recovery routines. In step 530, a defective sector that contains damaged or unreadable information is identified. In step 532, the readback signal for the defective sector or disc area is sampled. At step 534, the sampled read signal is stored. The stored read signal corresponding to the defective sector is expressed as RS _(DEFECT) = M _(DEFECT) + T _(DEFECT) . Here, RS _(DEFECT) represents the entire readback signal derived from the defective sector, M _(DEFECT) represents the magnetic signal component of the readback signal obtained from the defective sector, and T _{(DEFECT) Represents} the column signal component of the read signal RS _(DEFECT) .

At step 536, the defective sector of the disk surface area is erased. After the defective disk surface location erase is complete, the readback signal is sampled for the erased defective sector, as shown in step 538. The read signal sample from the erased defect sector is indicated by RS _(ERASE) = T _(ERASE) . Here, RS _(ERASE) represents the total re-read signal sampled from the erased defective sector, and T _(ERASE) represents the column signal component of the re-read signal RS _(ERASE) obtained from the erased defective sector. It should be noted that since the erase process substantially removes all magnetic signal components from the defective sector, the read signal RS _(ERASE) does not include a magnetic signal component.

However, it should be noted that despite the erase procedure, a very small amount of magnetism may enter the fine gaps on the disk surface. Thus, as shown in step 540, it may be desirable to extract and store the column signal T _(ERASE) from the readback signal derived from the erased defective sector. It should be noted that T _(DEFECT) is substantially equal to T _(ERASE) , as evidenced by the thermal signal waveform described above with respect to Figures 6 (a) and 6 (b). In step 542, the readback signal obtained for the defective sector erased in step 538 from the readback signal derived from the defective sector in step 532 is subtracted. As shown in step 542, this subtraction generates a recovered magnetic signal component M _(RECOVERED) of the defective sector. Then, the recovered magnetic signal M _(RECOVERED) is stored in a memory or on a data storage disk. Then, at the last step 546, the recovered magnetic signal M _(RECOVERED) is passed through the regular data recording channel, from which information is decoded into binary words.

Therefore, when the present invention described above is implemented, the present invention can efficiently remove undesired distortion on the read-out signal generated in the MR element.

Of course, it should be understood that the present invention may be modified or added in various ways within the scope of the present invention without departing from the scope or spirit of the present invention. Accordingly, the scope of the invention is not to be limited to the specific embodiments described, but is defined by the scope of the appended claims.

Claims (59)

A method of processing a signal obtained from a storage medium using a magnetoresistive (MR) element proximate to the storage medium, (1) reading the signal from the storage medium using the MR element, (2) filtering the signal to generate a thermal signal component indicative of a thermal response of the MR element, And (3) outputting the column signal component. The signal processing method according to claim 1, wherein the thermal signal component indicates a distance between the MR element and the storage medium. The signal processing method according to claim 2, wherein the thermal signal component changes linearly in response to variation of the interval between the MR element and the storage medium. The method according to claim 1, (1) the signal includes a magnetic signal component, (2) the signal component is calibrated using the magnetic signal component so that the thermal signal component is used to evaluate an interval variation between the MR element and the storage medium. 2. The method of claim 1, wherein the signal comprises a magnetic signal component, the method comprising: generating a thermal spacing signal using the column signal component and the magnetic signal component, Varies in proportion to the variation of the gap between the MR element and the storage medium. 6. The signal processing method according to claim 5, wherein the column spacing signal linearly changes with the interval variation between the MR element and the storage medium. 2. The method of claim 1, comprising filtering the signal to degrade the thermal component of the signal prior to filtering the signal to generate the thermal signal component. 2. The method of claim 1, wherein the step of filtering the signal to generate the column signal component comprises filtering the signal using a finite impulse response (FIR) filter. 9. The method of claim 8, wherein the filtering comprises programming the FIR filter using a set of tap weights stored in a memory connected to the FIR filter. 10. The method of claim 9, wherein the filtering step comprises providing a window function to the set of tap weights when programming the FIR filter. 10. The method of claim 9, 1) programming the FIR filter using a first set of tap weights to read data stored on the storage medium; 2) programming the FIR filter using a second set of tap weights to read servo information stored on the storage medium. 2. The method of claim 1, further comprising using the signal to generate a magnetic component. 2. The method of claim 1, wherein the signal comprises the column signal component and the magnetic signal component, and the method further comprises subtracting the generated column signal component from the signal to extract the magnetic signal component from the signal / RTI > The method according to claim 1, (A) reading the signal from a defective portion of the storage medium, the signal being a composite signal comprising a magnetic signal component and a thermal signal component; Erasing the magnetic signal component from the defective portion of the storage medium; (3) extracting the thermal signal component from the erased defect portion of the storage medium; Subtracting the extracted thermal signal component from the composite signal to generate a reconstructed magnetic signal that substantially represents the magnetic signal component of the composite signal. 1. A signal separating apparatus for an information storage apparatus including an information storage medium, (A) a transducer including a magnetoresistive (MR) element, and A read channel connected to the transducer for reading a signal from the storage medium using the MR element in proximity to the storage medium, A filter connected to the read channel for filtering the signal to extract a column signal component of the signal, the column signal component representing a thermal response of the MR element and being provided at an output of the filter; Device. 16. The apparatus of claim 15, wherein the filter comprises a finite impulse response (FIR) filter. 16. The signal separation device according to claim 15, comprising a magnetic signal filter connected to the read channel and extracting a magnetic signal component of the signal read from the storage medium. 16. The apparatus of claim 15, further comprising a signal summing device connected to the read channel and the filter, wherein the signal adding device comprises: A subtracter for subtracting the column signal component from the composite signal using the extracted signal component to obtain a reconstructed magnetic signal component substantially representing the magnetic signal component of the composite signal, A signal separating device for generating a signal. An information storage apparatus comprising: (1) a transducer including a magnetoresistive (MR) element, (2) a storage medium, (3) means for moving at least one of the transducer and the storage medium to provide relative movement between the transducer and the storage medium, the transducer having a gap separating the MR element from the storage medium Arranged for the storage medium, (4) a read channel connected to the transducer and reading a signal from the storage medium using the MR element, A filter connected to the read channel for filtering the signal to extract a thermal signal component of the signal, the thermal signal component representing a thermal response of the MR element and being provided at an output of the filter; Device. 20. The apparatus of claim 19, wherein the filter comprises a finite impulse response (FIR) filter. 21. The apparatus of claim 20 including a memory coupled to the FIR filter, wherein the FIR filter is programmable using a set of tap weights stored in the memory. 21. The method of claim 20, The memory stores a set of window parameters, 2) The FIR filter is programmed using a set of tab weights and window parameters stored in the memory. 21. The method of claim 20, wherein when the MR element moves in close proximity to a data storage portion of the storage medium, a first set of tap weights is passed from the memory to the FIR filter, Wherein the second set of tap weights is transferred from the memory to the FIR filter when moving closer to the storage portion. 20. The information storage device according to claim 19, comprising a magnetic signal filter connected to the read channel and extracting a magnetic signal component of the signal read from the storage medium. The signal adding apparatus according to claim 19, further comprising: a signal adding device connected to the read channel and the filter, wherein the signal adding device adds the composite signal read from the storage medium including the column signal component and the magnetic signal component, Receive a column signal component and subtract the column signal component from the composite signal using the extracted signal component to generate a recovered magnetic signal that substantially represents the magnetic signal component of the composite signal. 20. The apparatus of claim 19, further comprising a signal adder and a write element, said MR element reading the signal from a defective portion of the storage medium, the signal being a composite signal comprising a magnetic signal component and a thermal signal component Wherein the recording element erases the magnetic signal component from the defective portion of the storage medium and the filter extracts the thermal signal component from the erased defective portion of the storage medium, And subtracting the extracted thermal signal component from the thermal signal component to generate a recovered magnetic signal. 27. The information storage device of claim 26, wherein the recovered magnetic signal is decoded in the read channel. A method of inspecting a medium using a signal derived from a magnetoresistive (MR) device spaced from the medium, (1) when the MR element moves relative to the medium, reading the signal using the MR element, (2) detecting a variation of a thermal signal component of the signal read by the MR element, And (3) determining a variation in the characteristic of the medium from the variation of the thermal signal component. The method according to claim 28, wherein the detecting step includes detecting a variation in the distance between the media of the MR element. 30. The method of claim 29, (1) determining the interval at a plurality of locations on a portion of the medium, ≪ Desc / Clms Page number 11 > (2) mapping a topographic representing the portion of the medium using the gap determined at the plurality of locations. 30. The method of claim 29, Detecting a variation of the thermal signal component at a plurality of locations on a portion of the medium; And (2) using the variation of the thermal signal component at the plurality of locations to map the terrain representing the portion of the medium. 31. The method of claim 30, wherein the characteristic of the medium is a surface profile of the medium, the method comprising generating a column spacing signal from the column signal component, And the dimension of the gap between the surfaces. 31. The method of claim 30, wherein the property of the medium is a surface profile of the medium, (1) detecting a variation in a magnetic signal component of the signal read from the medium using the MR element, Generating a magnetic gap signal from the magnetic signal component, the magnetic gap signal representing a measure between the MR element and the surface of the medium, Generating a thermal spacing signal from the thermal signal component, wherein the thermal spacing signal is corrected using the magnetic spacing signal to indicate a spacing dimension between the MR element and the surface of the medium; Way. 31. The method of claim 30, wherein the property of the medium is a surface profile of the medium, 1) determining the frequency of the thermal signal component; (B) associating the thermal signal component frequency with a surface profile feature of the medium. 32. The method of claim 30, wherein the method comprises detecting a variation in a magnetic signal component of the signal read from the medium using the MR element, wherein the characteristic of the medium is a surface profile of the medium, Wherein the determining includes determining the variation of the surface profile of the medium using the thermal signal component variation and the magnetic signal component variation. 32. The method of claim 30, wherein the property of the medium is a surface profile of the medium, and the method includes detecting a feature of the surface profile using a variation of the thermal signal component . 37. The method of claim 36, Recording a magnetic signal at a location on the medium corresponding to the position of the feature; (2) reading the magnetic signal using the MR element, And (3) detecting the feature of the surface profile using the read magnetic signal using the MR element. 29. The method of claim 28, wherein the property of the medium is a surface profile of the medium comprising depressions provided on a surface of the medium, the method comprising: And detecting the depression provided on the surface. An information storage apparatus comprising: (1) a transducer including a magnetoresistive (MR) element, (2) a storage medium, Means for moving at least one of the transducer and the storage medium to provide relative movement between the transducer and the storage medium, the transducer being configured to move relative to the storage medium to separate the MR element from the storage medium, Is arranged - (4) a read channel connected to the transducer for reading a signal from the storage medium using the MR element, A filter connected to the read channel and transmitting a thermal signal component of the signal, the thermal signal component representing a thermal response of the MR element, And a detector connected to said filter for detecting a variation of said thermal signal component corresponding to a variation of a surface profile of said storage medium. 40. The apparatus of claim 39, wherein the thermal signal variation detected by the detector corresponds to a dimension variation of the spacing between the MR element and the surface profile of the storage medium. 41. The information storage device of claim 40, wherein the detector is adapted to detect variations in the spacing dimension at a plurality of locations on a portion of the storage medium, thereby indicating the variation of the surface profile of the portion of the storage medium. 40. The information storage device of claim 39, wherein the detector detects the thermal signal component variations at a plurality of locations on a portion of the storage medium, thereby indicating the surface profile variation of the portion of the storage medium. 40. The apparatus of claim 39, further comprising a mean filter coupled to the filter and for changing the column signal component to a column spacing signal, Corresponding to the dimension of the gap. 40. The apparatus of claim 39, further comprising: a magnetic signal filter connected to the filter; and a log filter for changing magnetic signal components of the signal read from the storage medium to a magnetic gap signal using the MR element And the magnetic spacing signal corresponds to a dimension of the spacing between the MR element and the surface of the medium. 45. The apparatus of claim 44, further comprising: a magnetic signal filter connected to the filter; and a log filter for changing magnetic signal components of the signal read from the storage medium using the MR element to a magnetic gap signal, Wherein the signal and the column spacing signal substantially correspond to a dimension of the spacing between the MR element and the surface of the medium. 40. The apparatus of claim 39, comprising a defect characterization circuit that associates the frequency of the thermal signal component with a surface profile feature. 40. The method of claim 39, wherein the detector detects a magnetic signal component variation of the signal read from the storage medium using the MR element corresponding to a surface profile characteristic of the storage medium, And the corresponding thermal signal component variation is detected. 40. The information storage device of claim 39, wherein the detector detects a surface profile feature of the storage medium as the thermal signal component. A method of reading a signal from a medium using a single magnetoresistive (MR) element of a transducer, the method comprising: using the MR element to simultaneously write first type information and second type information contained in the signal from the medium Wherein the first type of information is represented within a magnetic component of the signal and the second type of information is represented within a column component of the signal; filtering the signal; And outputting the column signal component together with the magnetic signal component. 50. The method of claim 49, wherein the first type of information comprises data and the second type of information comprises transducer location information. A method of processing a signal obtained from a storage medium using a magnetoresistive (MR) element, comprising: reading the signal from the storage medium using the MR element proximate to the storage medium; Modifying the signal so that a thermal component of the signal indicative of a thermal response of the signal is degraded; and modifying the modified signal to generate a reconstructed column signal that substantially represents the thermal component of the signal read from the storage medium So as to generate a signal. 52. The method of claim 51, wherein the signal read from the storage medium comprises a magnetic component and the thermal component, and wherein the modifying comprises transmitting the magnetic component of the signal and causing the thermal component of the signal to deteriorate And filtering the signal, wherein the modifying comprises filtering the modified signal to produce the reconstructed column signal. The signal processing method according to claim 51, wherein the restored thermal signal indicates a separation interval between the MR element and the storage medium. The signal processing method according to claim 53, wherein the recovered thermal signal varies in proportion to variation of the separation interval between the MR element and the storage medium. 52. The method of claim 51, wherein the reconstructed thermal signal represents a surface profile of the storage medium. 52. The method of claim 51, further comprising generating a magnetic component using the signal. A signal processing apparatus for an information storage device comprising an information storage medium, the signal processing apparatus comprising: a transducer including a magnetoresistive (MR) element proximate to the storage medium; and a controller coupled to the transducer, Circuitry for modifying a signal read from the storage medium using the MR element such that a thermal component of the signal representing the stored signal is degraded; And a filter that generates a recovered thermal signal that substantially represents the thermal component of the signal read from the medium. 58. The apparatus of claim 57, comprising a magnetic signal filter coupled to the circuitry for delivering magnetic signal components of the signal read from the storage medium. 11. An information storage device comprising: a transducer including a storage medium and a magnetoresistive (MR) element proximate to the storage medium; and at least one of the transducer and the medium, A circuit coupled to the transducer for modifying a signal read from the storage medium using the MR element so that the thermal component of the signal indicative of the thermal response of the MR element is degraded; And a filter coupled to the circuitry to generate a reconstructed column signal substantially representative of the column component of the signal read from the storage medium using the modified signal received from the circuitry, .