JPH07220212A - Equalizer for magnetic disk unit - Google Patents

Abstract

(57) [Abstract] [Purpose] Regarding an equalizer for a magnetic disk device that equalizes a reproduced signal into a waveform corresponding to the partial response system,
Equalize with emphasis on group delay characteristics. A delay flat filter unit 1 such as a linear phase filter 6 for inputting a reproduction signal of a magnetic disk device and an adaptive filter unit 2 such as a cosine equalizer 7 are provided. The linear phase filter 6 includes a boost filter 3 that determines a low-frequency side characteristic, a notch filter 4 that determines a high-frequency side characteristic, and a low-pass filter 5 that blocks a band equal to or higher than a cutoff frequency. When the adaptive filter unit 2 is composed of a digital circuit, an AD converter 8 is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an equalizer for a magnetic disk device which equalizes a reproduced signal in the magnetic disk device into a waveform corresponding to the partial response system. With the increase in capacity and high-speed transfer of magnetic disk devices, the level of the reproduction signal read from the magnetic disk is low,
In addition, the inter-symbol interference occurs. In order to reproduce the recorded data using such a reproduced signal, it is necessary to correct and demodulate the reproduced signal.

[0002]

2. Description of the Related Art As an effective means for correcting and demodulating a reproduction signal of a magnetic disk device, a partial response (P
R; Partial Response) method and maximum likelihood detection method (ML; Maximum Likelihood Decod)
ing) is known (for example, “JD Coker, RL Galbraith, G.
J. Kerwin, J .; W. Rae, P. A. Ziperovich
"Implementation of PRML in a Rigid Dis
k Drive ", July 7, 1991").

FIG. 6 is a diagram for explaining the equalization of an isolated reproduction wave and shows an outline of the above-mentioned partial response system. FIG. 3A shows a schematic configuration in which the head 32 is moved and positioned by the actuator 33 on a designated track of the magnetic disk 31. A reproduction signal read from the magnetic disk 31 by the head 32 is amplified, equalized, identified,
By demodulating, the data stored in the magnetic disk 31 is reproduced. The isolated reproduction wave in that case is shown in (b), and the black circles indicate sampling points. When this isolated reproduction wave is equalized by the equalizer 34 by the partial response method corresponding to, for example, 1 + D (D is a delay time of one sample), an equalized output signal shown in (c) is obtained. This partial response method is usually class I
~ V is adopted, and class I is 1
It corresponds to + D and becomes a three-valued signal. Class IV is 1-D
It corresponds to ^2, and also in this case, it becomes a ternary signal.

FIG. 7 is an explanatory view of a conventional example. 41 is a notch filter, 42 is an all-pass filter, 43 is a low-pass filter, 44 is a cosine equalizer, 51-54 are respective frequency characteristics, and 55 is a synthesized frequency characteristic. Indicates. In the frequency characteristics 51 to 55, G on the vertical axis indicates gain, and f on the horizontal axis indicates frequency. The notch filter 41 is
The frequency characteristics on the high frequency side as an equalizer are approximated, and the frequency characteristics of the gain G of the all-pass filter 42 are flat, and the group delay characteristics are flattened. Further, the low-pass filter 43 blocks the high frequency side above the cutoff frequency as an equalizer. Also Cosine Equalizer 4
4 has a frequency characteristic 54 and is adjusted so as to obtain a frequency characteristic 55 as an equalizer.

[0005]

The ideal frequency characteristic when the reproduction signal of the magnetic disk device is equalized by the partial response system is, for example, as shown in FIG. The vertical axis represents the normalized gain and the horizontal axis represents the frequency [MHz]. When such frequency characteristics are realized by the configuration of the conventional example shown in FIG. 7, the amplitude characteristics are realized by the notch filter 41 and the low pass filter 43, and the group delay characteristics are flattened by the all pass filter 42. It is difficult to completely flatten the group delay characteristics by passing through the notch filter 41 and the low pass filter 43.

Therefore, the present applicant has proposed an equalizer that satisfies the amplitude characteristic and the group delay characteristic in Japanese Patent Application No. 5-74923.
Filed as an issue. However, since the equalizer attaches importance to both the amplitude characteristic and the group delay characteristic, the filter order becomes large, for example, 10th order or more,
As a result, there is a problem that the circuit scale also increases.

Therefore, according to the present invention, since the group delay characteristic has a slightly larger specific gravity in view of the characteristic as an equalizer, FIG.
The purpose is to approximate the ideal frequency characteristic shown in (1) and to flatten the group delay characteristic.

[0008]

An equalizer for a magnetic disk device according to the present invention will be described with reference to FIG. 1. An equalizer for a magnetic disk device which equalizes a reproduced signal into a waveform corresponding to a partial response system. A delay flat filter unit 1 having at least a 6th order or more for inputting a reproduced signal and having a flat group delay characteristic, and an adaptive filter unit 2 for correcting the frequency fluctuation of the reproduced signal. Composed by.

The flat delay type filter unit 1 can be constituted by a linear phase filter 6 including a boost filter 3, a notch filter 4 and a low pass filter 5.

Further, it is possible to provide means for setting respective parameters of the boost filter 3, the notch filter 4 and the low pass filter 5.

Further, the adaptive filter section 2 can be constituted by a cosine equalizer 7. The AD converter 8 is provided when the cosine equalizer 7 is realized by a digital circuit.

[0012]

The flat delay type filter section 1 has characteristics that emphasize the flattening of the group delay characteristics. In that case,
Since the amplitude characteristic changes due to the frequency fluctuation of the reproduction signal,
The adaptive filter unit 2 adaptively corrects the frequency fluctuation. As a result, the group delay characteristics below the cutoff frequency can be flattened and can be approximated to the ideal frequency characteristics shown in FIG.

Further, the flat delay type filter section 1 is constituted by a linear phase filter 6, the boost filter 3 of the linear phase filter 6 approximates the low frequency side from the maximum amplitude frequency of the equalizer, and the notch filter 4 is equal. The high frequency side is approximated from the maximum amplitude frequency of the rectifier, and the cutoff frequency or higher is blocked by the low pass filter 5. In that case, it is possible to have a second-order filter configuration, and therefore, the flat delay type filter unit 1 has a sixth-order filter configuration.

Further, the boost filter 3 and the notch filter 4
The parameters of the low-pass filter 5 and the low-pass filter 5 are set by an external setting input, and when the setting means causes a change that cannot be absorbed by the adaptive filter section 2, the parameter or the like is changed to cope with the change. You can

The adaptive filter unit 2 is composed of a cosine equalizer 7 to adaptively control the frequency characteristic with respect to the frequency fluctuation of the reproduced signal. The frequency characteristic is approximated to the ideal frequency characteristic and the magnetic disk rotates. It is possible to cope with the frequency fluctuation of the reproduction signal due to the fluctuation and the temperature fluctuation.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, when an analog reproduction signal is input to a flat delay type filter unit 1 and a digital equalized output signal is output from an adaptive filter unit 2, an AD converter 8 shown by a dotted line is used. Is connected and the analog filter output signal is output from the adaptive filter unit 2, the AD converter 8 is omitted. Further, the flat delay type filter unit 1 is configured to emphasize flattening the group delay characteristic, and various configurations can be adopted. In particular, when the linear phase filter 6 is used, the frequency characteristic can be set more easily than when the Bessel type filter is used. The adaptive filter unit 2 is for correcting the frequency fluctuation of the reproduction signal, and a cosine equalizer 7 for adaptively controlling is suitable.

FIG. 2 is an explanatory view of a linear phase filter according to an embodiment of the present invention. Reference numerals 10 and 12 are conversion circuits, 11 is an input side buffer circuit, 13 is a boost filter, 14 is a notch filter, and 15 is a low pass filter. , 16 is a buffer circuit on the output side, and 17 is a gain controller.

A linear phase filter as an example of the flat delay type filter unit 1 has a boost filter 13, a notch filter 14 and a low pass filter 15 as main parts, and each filter has a parameter (filter constant) whose setting is changed. Is possible.

The reproduction signal of the magnetic disk device is applied to the buffer circuit 11 on the input side. Further, the boost value setting signal is converted into a control signal for controlling the boost characteristic by the conversion circuit 10 and added to the boost filter 13.
The cut-off frequency setting signal is converted into a control signal for setting the cut-off frequency by the conversion circuit 12 and added to the boost filter 13, notch filter 14 and low-pass filter 15. The output signal of the low-pass filter 15 is applied to the adaptive filter section 2 via the buffer circuit 16 on the output side and fed back via the gain controller 17.

The boost filter 13 approximates the low-frequency characteristic of the equalization characteristic, the notch filter 14 approximates the high-frequency characteristic of the equalization characteristic, and the low-pass filter 15 The configuration is such that frequency components above the cutoff frequency are blocked. These filters can be realized by a known circuit configuration such as an active filter biquad circuit. The boost characteristic of the boost filter 13 in this case can be changed by the boost value setting signal.
The frequency characteristic of 15 can be changed by the cutoff frequency setting signal.

FIG. 3 is an explanatory view of the cosine equalizer of the embodiment of the present invention, in which reference numerals 21 and 22 are delay circuits and 23 and 24.
Is a multiplication circuit, 25 is an addition circuit, and 26 is a gain controller. This embodiment shows a cosine equalizer as an example of the adaptive filter unit 2 in FIG.

The delay circuits 21 and 22 have a delay time of one sample time, and the adder circuit 25 inverts and adds the output signals of the multiplication circuits 23 and 24 to the output signal of the delay circuit 21, and the like. The converted output signal. The gain controller 26 controls the coefficient applied to the multiplication circuits 23 and 24 corresponding to the equalized output signal, and corrects the equalization error due to the linear phase filter corresponding to the frequency fluctuation of the reproduction signal.

Further, in FIG. 2, a linear phase filter is constituted by the second-order boost filter 13, the second-order notch filter 14 and the third-order low-pass filter 15, and 8 /
The function of each filter is as follows in the case where the 9-code system is adopted, and the transfer rate is 10 MB / s and the magnetic disk device has a solitary-wave full width at half maximum of 2.5 times the sampling period.

The boost filter 13 has a (-2.2S ²
+ 1.317S ⁰ ) / (S ² + 1.685S ¹ +1.3
17S ⁰ ), and the notch filter 14 is (S ² +5.3).
71S ⁰ ) / (S ² + 1.145S ¹ +5.371)
S ⁰ ), and the first-stage low-pass filter is 5.163S
⁰ / (S ² + 1.542S ¹ + 2.951S ⁰ ), the second-stage low-pass filter is 0.862S ⁰ / (S ¹ +
0.862S ⁰ ). Also, the cosine equalizer is 1
-2Kcos (ωT). In this case, 2K = 0.6
Set to 1. Further, T is a sampling period, and ω is an angular frequency. The coefficients of each filter described above are as follows.

In boost filter 13, coefficient PA of S ² of denominator PA = 1.0000 coefficient of S ¹ of denominator PB = 1.68500 coefficient of S ⁰ of denominator PC = 1.31680 coefficient S ² of numerator PD = -2.20000 coefficient of S ¹ of molecule PE = 0.0000 coefficient of S ⁰ of molecule PF = 1.31680

In the first-stage low-pass filter, the coefficient PA of S ² of the denominator PA = 1.0000 the coefficient P of S ¹ of the denominator PB = 1.54150 The coefficient PC of S ⁰ of the denominator PC = 2.95050 S of the numerator Coefficient of ² PD = 0.00000 S ¹ coefficient of molecule PE = 0.00000 S ⁰ coefficient of molecule PF = 5.16338

Further, in the notch filter 14, the coefficient of S ² of the denominator PA = 1.00000 the coefficient of S ¹ of the denominator PB = 1.14540 the coefficient of S ⁰ of the denominator PC = the coefficient of S ² of the numerator PD = 1.0000 The coefficient of S ¹ of the molecule PE = 0.0000 The coefficient of S ⁰ of the molecule PF = 5.337080

In the second-stage low-pass filter, the coefficient PA of S ² of the denominator PA = 0.0000 the coefficient P of S ¹ of the denominator PB = 1.0000 The coefficient PC of S ⁰ of the denominator PC = 0.86150 S of the numerator Coefficient of ² PD = 0.0000 Coefficient of S ¹ of molecule PE = 0.0000 Coefficient of S ⁰ of molecule PF = 0.86150

However, the above-mentioned parameter has a normalized frequency of 25.3 MHz. With this setting, the characteristics shown in FIG. 4 were obtained. That is, the curve A shows the ideal frequency characteristic curve shown in FIG. 8, the curve B shows the calculated value of the frequency characteristic obtained by setting the above parameters, and the curve C shows the group delay characteristic curve. The frequency at which the phase changes in this group delay characteristic is about 57 MHz or higher, and the frequency is flattened in the frequency band below that frequency. In addition, it is preferable to set the region for cutting the frequency on the frequency characteristic to be about 1 to 1.5 times as large as the region for cutting the frequency of the ideal value, and about 1.3 times in the above case. .

The secondary boost filter 13, the secondary first-stage low-pass filter, and the secondary notch filter 1
4 and the first-order second-stage low-pass filter form a seventh-order linear phase filter. It is also possible to use a linear phase filter having a sixth-order configuration including the second-order boost filter 13, the second-order notch filter 14, and the second-order low-pass filter 15.

FIG. 5 is an explanatory diagram of the equalized output signal according to the embodiment of the present invention, in which the vertical axis represents voltage [V], the horizontal axis represents time [ns], and (A) and (C) are reproduction signals. , (B), (D) show equalized output signals by the equalizer having the above-mentioned configuration. The black circles on the waveform indicate sampling points. The equalized output signal in this case corresponds to 1 + D of the partial response system, and the distortion of the waveform due to the group delay of the equalization error could be suppressed. Therefore, an identification signal by the partial response method is obtained by amplifying by the AGC amplifier or the like in the subsequent stage and performing level identification, and correct data can be restored by decoding the identification signal by the maximum likelihood detection method. .

In the above-mentioned equalizer design, the boost filter 13 that approximates the frequency characteristic curve on the low frequency side
The notch filter 14 approximates the frequency characteristics of the solitary wave so as to be Nyquist equalization, and also approximates the characteristic curve near the maximum amplitude frequency as an equalizer by the notch filter 14 that approximates the frequency characteristic curve on the high frequency side, and also the low-pass characteristic. Each parameter is set by the filter 15 so as to block the band above the cutoff frequency. In that case, the initial value is set and the characteristic is calculated to obtain the evaluation function.

The evaluation function for the approximation in this case is (1) 1 / 8T to 1/2 corresponding to the used band as the entire evaluation function.
T, (2) less than 1 / 8T, and (3) more than 1 / 2T, divided into 1 for the (1) band, 0.85 for the (2) band, and (3 ) For the band
It is possible to multiply the weight of 1 to find the squared error between the ideal value and the calculated value of each amplitude value, and proceed with the approximation processing so that the error is minimized. Here, T is a sampling period.

[0034]

As described above, according to the present invention, the delay flat type filter unit 1 having a flat group delay characteristic and the adaptive type filter unit 2 are provided, and the reproduction signal of the magnetic disk device is changed to the group delay characteristic. The equalization is performed in accordance with the partial response method with an emphasis on, and the delay flat filter unit 1 can be realized with a filter configuration of about the sixth order.
The circuit scale can be reduced.

Further, the flat delay type filter unit 1 is formed by a linear phase filter 6, and setting means capable of changing the respective parameters of the boost filter 3, notch filter 4 and low pass filter 5 is provided, and the frequency fluctuation of the reproduced signal is large. In such a case, there is an advantage that it is possible to deal with it by changing the parameter when the correction cannot be performed even by the cosine equalizer 7 forming the adaptive filter unit 2. It should be noted that the present invention is not limited to the above-described embodiments, but various additions and modifications can be made.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is an explanatory diagram of a linear phase filter according to the embodiment of this invention.

FIG. 3 is an explanatory diagram of a cosine equalizer according to the embodiment of this invention.

FIG. 4 is a characteristic explanatory diagram of an example of the present invention.

FIG. 5 is an explanatory diagram of an equalized output signal according to the embodiment of this invention.

FIG. 6 is an explanatory diagram of equalization of an isolated reproduction wave.

FIG. 7 is an explanatory diagram of a conventional example.

FIG. 8 is an explanatory diagram of an ideal frequency characteristic.

[Explanation of symbols]

 1 Delay Flat Filter 2 Adaptive Filter 3 Boost Filter 4 Notch Filter 5 Low Pass Filter 6 Linear Phase Filter 7 Cosine Equalizer 8 AD Converter

Claims (4)

[Claims] 1. An equalizer of a magnetic disk device for equalizing a reproduced signal into a waveform corresponding to a partial response system, having an order of at least 6th order or more for inputting the reproduced signal, and having a group delay characteristic. Flat delay flat filter section (1)
And an adaptive filter section (2) for correcting the frequency fluctuation of the reproduction signal, the equalizer for a magnetic disk device. 2. The flat delay type filter unit (1) is constituted by a linear phase filter (6) including a boost filter (3), a notch filter (4) and a low pass filter (5). An equalizer for a magnetic disk drive according to claim 1. 3. A means for setting respective parameters of the boost filter (3), the notch filter (4), and the low-pass filter (5) is provided.
An equalizer for the magnetic disk drive described. 4. An equalizer for a magnetic disk drive, wherein the adaptive filter section (2) is composed of a cosine equalizer (7).