JPH0714103A - Magnetic disk device and tap setting method - Google Patents

Abstract

(57) [Summary] [Object] The present invention enables automatic adjustment of the tap coefficient of an FIR filter to be optimum. [Structure] In the present invention, the magnetic disk 5 is composed of the head 3.
The reference data read from the reference data storage unit 1 is written in 0, and this is read by the head 3. Initially, since the FIR filter 4 is through, the reproduced data waveform from the head 3 is input to the characteristic calculation section 8 as frequency characteristic data in the frequency analysis section 6, where it is input from the reference frequency characteristic generation section 7. The ratio of the given reference data to the frequency characteristic data is taken. This ratio is converted into a time response waveform by the frequency domain / time domain conversion unit 9 and then the extraction circuit 1
At 0, the amplitude value near the time response is extracted, and this is set as a tap coefficient in the coefficient determination circuit 11 and set in the FIR filter 8. After that, the FIR filter 4 is used for the head 3
The distortion is removed from the reproduced data waveform read in step 1 and output to the peak detection circuit 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic disk device for recording / reproducing data on / from a magnetic disk using a thin film head.

[0002]

2. Description of the Related Art In a conventional magnetic disk device, when a thin film head is used for recording / reproducing data on / from a magnetic disk (magnetic recording medium), waveform distortion due to the contour effect of the thin film head is a major obstacle during data reproduction. Becomes Here, since the thin film head can form a minute pole / gap, it is advantageous in high density recording as compared with a monolithic head which has been widely used from the past. However, due to the contour effect due to the shape of the pole (the tip of the head for recording and reproduction) being thin,
At both ends of the peak of the signal waveform reproduced by the thin film head, a peculiar distortion like a groove having a polarity opposite to that of the peak occurs. Depending on the data pattern to be recorded, this distortion may be erroneously discriminated from the peak of the data and may cause a read error. Therefore, it is important to remove this distortion.

As one method of removing such distortion, it is possible to use an FIR filter (transversal filter) in a reproducing system using a thin film head, but the characteristics of the head / media system may vary depending on the device. It is not always constant and often varies depending on the position where data is recorded even within one device. Therefore, it is considered that the state of distortion also changes depending on the device and the data recording position,
The characteristics of the FIR filter also need to be changed accordingly.

Although the characteristics of the FIR filter described above are determined by the tap coefficient, it is a difficult problem to always determine the optimum tap coefficient of the FIR filter for the waveform distortion that is not fixed as described above. . Therefore, conventionally, the state of distortion of the signal reproduced by the thin film head was investigated in advance by a number of devices and evaluated, and the tap was set to an appropriate value at which the distortion of the reproduced signal was suppressed by a predetermined level or more in each device. I had no choice but to adjust the coefficient. However, in such a method, the effect of removing the waveform distortion of the reproduced signal by the FIR filter varies among the devices, and it is not possible to maximize the performance of each device. The drawback was that it would increase.

[0005]

In a magnetic disk apparatus for recording / reproducing data on / from a magnetic disk using a thin film head, an FIR filter is used to remove distortion of a reproduced signal due to the contour effect of the thin film head. However, the state of the distortion of the signal reproduced by the thin film head is investigated in advance by a number of devices and evaluated, and the above-mentioned F
The tap coefficient of the IR filter is adjusted uniformly. However, in this case, the effect of removing the waveform distortion of the reproduction signal by the FIR filter varies among the devices, and the distortion of the reproduction signal cannot be suppressed to the maximum in each device. The drawback was that it would increase.

In view of the above-mentioned drawbacks, the present invention automatically adjusts the tap coefficient of a predetermined filter to be optimum, and deletes harmful waveform distortion due to contour effects included in a reproduced waveform from variations in the apparatus or reproduction. An object of the present invention is to provide a magnetic disk device and a tap setting method that can always remove the maximum amount regardless of the position.

[0007]

According to the present invention, in a magnetic disk apparatus for inserting a predetermined filter into a reproducing system of data read from a magnetic disk by a head to remove distortion from the read data, a reference is provided by the head. Reference data read / write means for reading / writing data from / to the magnetic disk, and first analyzing means for frequency-analyzing the data read from the magnetic disk by the reference data read / write means to convert it into frequency characteristic data in a frequency domain, Second analyzing means for frequency-analyzing the reference data to convert it into frequency characteristic data in the frequency domain, frequency characteristic data obtained by the first analyzing means, and frequency characteristic obtained by the second analyzing means. The calculation means for obtaining the ratio with the data and the calculation result of this calculation means are the time response in the time domain. Inverse transforming means for inverse transforming into a data, tap coefficient creating means for creating a tap coefficient of the predetermined filter by extracting the level near the center of the time response data obtained from the inverse transforming means, and the tap coefficient And a setting means for setting the tap coefficient created by the creating means in the predetermined filter.

[0008]

In the magnetic disk apparatus of the present invention, the reference data read / write means reads / writes the reference data from / to the magnetic disk by the head. The first analysis means frequency-analyzes the data read from the magnetic disk by the reference data read / write means and converts it into frequency characteristic data in the frequency domain. The second analysis means frequency-analyzes the reference data and converts it into frequency characteristic data in the frequency domain.
The calculating means takes a ratio of the frequency characteristic data obtained by the first analyzing means and the frequency characteristic data obtained by the second analyzing means. The inverse transformation means inversely transforms the calculation result of the calculation means into time response data in the time domain.
The tap coefficient creating means creates a tap coefficient of a predetermined filter by extracting a level near the center of the time response data obtained from the inverse transforming means. The setting means sets the tap coefficient created by the tap coefficient creating means in the predetermined filter. As a result, the tap coefficient of the predetermined filter can be automatically adjusted to be optimum.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a magnetic disk device of the present invention. Reference numeral 1 is a reference data storage unit storing a reference data pattern, 2 is a head amplifier for amplifying data to be recorded / reproduced by a head 3, 3 is a head for recording / reproducing data on / from a magnetic disk 50, and 4 is a distortion from reproduced data. FIR filter for removing, 5 is a peak detection circuit for detecting the peak of the reproduced data, 6 is a frequency analysis section for analyzing the frequency of the reproduced data, 7 is a reference frequency characteristic of the frequency domain from the reference data given by the reference data storage section 1. A reference frequency characteristic generation unit for generating data, 8 is a characteristic value for determining the characteristic of the FIR filter 4 by taking the ratio of the frequency identification data obtained from the frequency analysis unit 6 and the reference characteristic data given from the reference frequency characteristic generation unit 7. And a frequency domain / time region 9 for converting the characteristic value given from the characteristic calculation unit 8 into a time response signal. Conversion unit,
Reference numeral 10 is an extraction circuit for extracting a necessary amplitude value near the origin from the time response signal waveform given from the frequency domain / time domain conversion unit 9, and 11 is an amplitude value near the origin obtained from the extraction circuit 10 for the FIR filter 4. This is a coefficient determination circuit that determines tap coefficients and obtains coefficient data by scaling the coefficients.

Next, the operation of determining the tap coefficient of the FIR filter 4 of this embodiment will be described. The reference data 101 read from the reference data storage unit 1 holding the reference data pattern is supplied to the head 3 through the head amplifier 2, and the head 3 writes the reference data on the magnetic disk 50. Next, the head 2 reads the reference data from the magnetic disk 50. The reproduced data waveform 102 thus obtained is input to the FIR filter 4 through the head amplifier 2 and the distortion is removed.
The FIR filter 4 has a reproduced signal waveform 103 from which distortion is removed.
Is output to the peak detection circuit 5 and the frequency analysis unit 6 in the subsequent stage. When the FIR filter 4 and the frequency analysis unit 6 are for digital processing, sampling means such as the A / D converter 11 is inserted at the position shown by the broken line in the figure to digitize the reproduced signal. . By the way, the FIR filter 4 has to adjust its tap coefficient so as to match its characteristic with the distortion state of the reproduction data. The operation of adjusting the tap coefficient will be described below.

Initially, the FIR filter 4 has its tap coefficient set to an initial value that allows the filter 4 to pass through. The frequency characteristic of the reproduction data waveform 103 that has passed through the FIR filter 4 is analyzed by the frequency analysis unit 6, and the reproduction data waveform is converted into the frequency domain, which is input to the characteristic calculation unit 8. Here, the frequency analysis unit 6 for analog processing performs Fourier transform (FFT) after sampling the reproduced data waveform, or performs frequency analysis by a filter bank method using a plurality of band pass filters (BPF) to reproduce the reproduced data waveform. To frequency characteristic data in the frequency domain. However, the frequency analysis unit 6 for digital processing generally uses a method of performing Fourier transform (FFT) on the reproduced data waveform.

On the other hand, the reference data pattern output from the reference data storage unit 1 is converted by the reference frequency characteristic generation unit 7 into a frequency domain by FFT, converted into reference frequency characteristic data, and output to the characteristic calculation unit 8. Since the reference frequency characteristic data can be calculated in advance when the reference data pattern is determined in advance, in this case, the reference frequency characteristic generation unit 7 may be a storage unit that holds the reference frequency characteristic data. When there are a plurality of reference data patterns, the reference data storage unit 1 holds a plurality of reference data, and switches the output data pattern as needed. In this way, when the reference data pattern changes arbitrarily, the frequency characteristic data of the reference data pattern can be obtained by performing FFT or the like by the frequency characteristic generation unit 7.

Next, the characteristic calculation unit 8 calculates the characteristic value required for the FIR filter 4 by taking the ratio of the output of the frequency characteristic data input from the frequency analysis unit 6 and the output of the frequency characteristic data of the reference frequency characteristic generation unit 7. And set this in the frequency domain /
Output to the time domain conversion unit 9. The frequency domain / time domain transforming unit 9 transforms the input characteristic value that the FIR filter 4 should have into a time response waveform by an inverse FFT or the like, and outputs this to the extraction circuit 10. The extraction circuit 10 extracts a plurality of necessary amplitude values near the origin from the input time response waveform, and outputs these amplitude values to the coefficient determination circuit 11. The coefficient determination circuit 11 scales the input amplitude value to F
After obtaining the tap coefficient data 104 of the IR filter 4, the obtained tap coefficient data is given to the FIR filter 4.
The above operation is repeated at least once to several times to optimally adjust the tap coefficient of the FIR filter 4.

If the time required for the adjustment operation of the tap coefficient of the FIR filter 4 becomes a problem, the adjustment operation is performed in advance when the apparatus is started. When an optimum difference in tap coefficient is expected depending on the recording position on the magnetic disk 50, the tap coefficient is adjusted in advance at a plurality of points on the magnetic disk 50, and the coefficient determined as a result is determined by a coefficient determining circuit. A plurality of them may be held in the disk 11, and the heads 3 may be switched depending on the position where the head 3 is accessing the magnetic disk 50.

FIG. 2 shows a general basic configuration of the FIR filter 4 described above. A plurality of delay circuits 41 are connected in series, and the signals delayed by each delay circuit 41 are input to a plurality of multipliers 42, multiplied by the tap coefficient given from the coefficient determining circuit 11, and then added by an adder 43. Then, the adder 43 outputs a signal from which distortion is removed.

FIG. 3 is a diagram showing a detailed example of the frequency analysis unit 6 and the characteristic calculation unit 8 based on the above filter bank method. The BPFs 51 to BPF5n are set so that their pass bands are slightly different from each other, and the reproduced data waveforms of the respective frequency bands output by these BPFs 51 to 5n are divided into reference frequency characteristic data supplied from the reference frequency characteristic generation unit 7 from the dividers 61 to 61. After division by 6n, the division result is output to the frequency domain / time domain conversion unit 9.

Here, the operation principle of the embodiment of the present invention shown in FIG. 1 will be described. FIG. 4A shows no waveform distortion when the head 3 writes / reads a data pattern having a constant frequency (corresponding to the reference data pattern stored in the reference data storage unit 1) to / from the magnetic disk 50. It is a reproduced waveform in the case. FIG. 4B shows the frequency characteristic (corresponding to the output of the reference frequency characteristic generation unit 7), and has a clean waveform in which the ratio of harmonics to the fundamental wave decreases at a constant ratio. On the other hand, FIG. 4C shows the reproduced data waveform (corresponding to the reproduced waveform data of the head 3) for the same data pattern when the waveform distortion due to the contour effect is included. FIG. 4D shows the frequency characteristic data (corresponding to the output of the frequency analysis unit 6). Compared to FIG. 4B, there are many higher harmonics, which represents waveform distortion. FIG. 4 (F) shows a ratio of the characteristics of FIG. 4 (B) and FIG. 4 (D) (corresponding to the output of the characteristic calculation unit 8) and shows the characteristic value of the filter necessary for removing the distortion. There is. Figure 4 (E)
4 is a response waveform on the time axis of FIG. 4F (corresponding to the output of the frequency domain / time axis domain conversion unit 9). This Figure 4 (E)
FIG. 4 (G) shows the amplitude of the signal extracted at the data time interval centered on the origin (corresponding to the operation of the extraction circuit 10). The amplitude of this pulse becomes the tap coefficient of the filter. Figure 4
In (G), the number of taps is limited within a certain range from the origin so that the number of taps is limited. FIG. 4 (H) is shown in FIG.
It is the frequency characteristic of (G) (the characteristic of the FIR filter 4 after adjustment). Here, the FI having the tap coefficient of FIG.
When the waveform having the distortion shown in FIG. 4C is input to the R filter 4, the waveform having the distortion removed as shown in FIG. 4I (the output of the adjusted FIR filter 4) is obtained. Figure 4 (J)
Shows the frequency characteristic of FIG. 4 (I), and it can be seen from the frequency characteristic that a waveform having no distortion and close to that of FIG. 4 (B) can be obtained.

Although the example of FIG. 4 was for a data pattern having a constant frequency, this is for explaining the basic principle. As actual data, we have to consider a random pattern. The example of FIG. 5 is for a case corresponding to a random pattern. FIG. 5 (A)-
(J) corresponds to FIGS. 4 (A) to (J). The procedure is also the same. However, the data pattern of FIG. 5A is a random pattern or a specific pattern having various peak intervals. However, in order to obtain FIG.
It is necessary to write / read on the magnetic disk 50 the same pattern as in FIG. If the pattern of FIG. 5 (A) is predetermined, the characteristic of FIG. 5 (B) can be calculated in advance.

FIG. 6 shows an example of distortion removal for a specific data pattern having a peak interval that is 2 to 8 times the data time interval. The reproduction data waveform for the random data pattern shown in FIG. This is an example of shaping by the filter 4. The waveform of FIG. 6B having distortion is shown in FIG.
The distortion is removed by shaping as shown in (C). FIG. 6D is an example of a reproduced waveform for the same data pattern when there is originally no distortion.

According to the present embodiment, since the tap coefficient of the FIR filter 4 can be automatically adjusted in each magnetic disk device, the optimum tap coefficient in consideration of variations in characteristics peculiar to the device is the FIR filter. Since it is set to 4, the reproduced data waveform distortion due to the contour effect by the FIR filter 4 can be almost completely removed, and the error rate can be reduced by this amount to maximize the performance of the apparatus. Further, even with respect to the reproduced waveform data distortion which differs depending on the data read position of the magnetic disk 50, the FI is corresponding to a plurality of positions on the magnetic disk 50.
By automatically setting the tap coefficient of the R filter 4 as described above, the distortion of the reproduced data waveform is almost completely removed irrespective of the position of the magnetic disk 50, and the performance of the apparatus is improved by reading the data from the magnetic disk. It can always be maximized regardless of position.

The present invention can be applied not only to the magnetic disk device but also to any device that magnetically records and reproduces data on the medium by using the head, and the same effect can be obtained.

[0022]

As described above, according to the magnetic disk device and the tap setting method of the present invention, the tap coefficient of the FIR filter is automatically adjusted to be optimum, and the harmful effect is caused by the contour effect included in the reproduced waveform. It is possible to always remove the maximum waveform distortion regardless of the variation of the device and the reproduction position.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a magnetic disk device of the present invention.

FIG. 2 is a circuit diagram showing a detailed example of the FIR filter shown in FIG.

FIG. 3 is a diagram showing a detailed example of a frequency analysis unit and a characteristic calculation unit shown in FIG.

FIG. 4 is a diagram illustrating the principle of the present invention.

FIG. 5 is a diagram for explaining the principle of the present invention with actually obtained data patterns.

FIG. 6 is a diagram showing an example of a waveform when distortion is removed from a specific data pattern by a filter with an adjusted tap coefficient.

[Explanation of symbols]

1 ... Reference data storage unit 2 ... Head amplifier 3 ... Head 4 ... FIR filter 5 ... Peak detection circuit 6 ... Frequency analysis unit 7 ... Reference frequency characteristic generation unit 8 ... Characteristic calculation unit 9 ... Frequency domain / time domain conversion unit 10 ... Extraction circuit 11 ... Coefficient determination circuit 50 ... Magnetic disk

Claims (2)

[Claims] 1. A magnetic disk device for removing distortion from the read data by inserting a predetermined filter into a reproduction system for reproducing data read from the magnetic disk by the head, wherein reference data is read from and written to the magnetic disk by the head. Reference data read / write means, first analysis means for frequency-analyzing the data read from the magnetic disk by the reference data read / write means, and converting it to frequency characteristic data in the frequency domain, and frequency-analyzing the reference data. Second analysis means for converting into frequency domain frequency characteristic data, and calculation means for obtaining a ratio between the frequency characteristic data obtained by the first analyzing means and the frequency characteristic data obtained by the second analyzing means. When,
The tap coefficient of the predetermined filter is obtained by extracting an inverse transforming means for inversely transforming the calculation result of the calculating means into time response data in the time domain, and a level near the center of the time response data obtained from the inverse transforming means. A magnetic disk device comprising: a tap coefficient creating means to be created; and a setting means to set the tap coefficient created by the tap coefficient creating means to the predetermined filter. 2. A tap setting method for a predetermined filter of a magnetic disk device, wherein a predetermined filter is inserted into a reproduction system of data read from a magnetic disk by a head to remove distortion from the read data. After writing the reference data to the magnetic disk by the head, reading the read data, converting the read data into frequency characteristic data in the frequency domain and the obtained frequency characteristic data, and converting the reference data into a separate frequency domain. Take the ratio with the obtained reference frequency data, extract the level near the center of the time response data obtained by inversely transforming this ratio into the time domain, create tap coefficients, and use this tap coefficient in the predetermined filter. A tap setting method characterized by setting.