JPH06290407A - Equalizer for magnetic recorder - Google Patents

Abstract

PURPOSE:To provide an equalizer having an amplitude characteristic and a group delay characteristic optimal for partial response class IV, relating to the equalizer for a magnetic recorder. CONSTITUTION:This equalizer is constituted by cascade-connecting a booster filter parallel connecting 4 secondary HPF 1 and a secondary LPF 2, a notch filter parallel connecting the secondary HPF 3 and the secondary LPF 4, the secondary LPF 5 and an all pass filter 6. Further, the equalizer is constituted by connecting a cosine equalizer 7 to that, at need, and is provided with the characteristics optimal for equalizing a magnetic recording and reproducing signal to the partial response class IV. The amplitude characteristic and the group delay characteristic more suitable are realized by forming these filters with active filters.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an equalizer used for reproduction signal processing of a magnetic recording device such as a magnetic disk device, a magnetic drum device or a magnetic tape device. In recent years, magnetic recording devices such as magnetic disk devices are required to have a large capacity and a high speed transfer. With the increase in capacity and high-speed transfer of such a magnetic recording device, it is necessary to correct the demodulation by correcting the inter-code interference of the reproduction signal and the output reduction of the signal caused by the weak reproduction signal read from the recording medium. I have to.

[0002]

2. Description of the Related Art A partial response (part) response is an effective method for correcting and demodulating a reproduction signal of a magnetic recording device.
ial response PR) method and maximum likelihood detection method (maximum likelihood detection method)
ing) have already been proposed (JD Coker, RL Galbraith,
G. J. Kerwin, J .; W. Rae, P .; A. Zi
perovich "Implementation o
f PRML, in a Rigid Disk Dr
IVE ”THE MAGNETIC RECORDING
G CONFERENCE July 7, 1991).

FIG. 6 is an explanatory diagram of equalization of an isolated reproduction wave by a partial response system. FIG. 6A schematically shows a state in which recorded information is reproduced from a magnetic recording medium by a magnetic head, and FIG. An isolated reproduction wave is shown, and (C) shows the result of equalization by the partial response method. In this figure, 11 is a magnetic recording medium, and 12 is a reproducing magnetic head.

The equalization of the isolated reproduction wave by the partial response system will be described with reference to this figure. The magnetic recording medium 1
When recording digital information on the magnetic recording medium 1, the magnetic recording medium 1
1 is relatively moved (rotated) with respect to the recording magnetic head 12, and a pulsed current is passed through a coil of the recording magnetic head to magnetize the surface of the magnetic recording medium 11 for writing.

When reading the written information, the reproducing magnetic head 12 is brought into contact with or close to the surface of the magnetic recording medium 11 and the magnetic recording medium 11 is moved relatively to the reproducing magnetic head 12. (Rotation), the magnetization information magnetically recorded on the magnetic recording medium 11 is picked up by the coil of the reproducing magnetic head 12 and read as a current signal.

As described above, when reading the magnetization information recorded on the magnetic recording medium 11, the magnetic recording medium 1 is read.
At the magnetization reversal position of 1, one isolated reproduction wave as shown in FIG. 6 (B) is generated. Black dots in this figure indicate sampling points.

When detecting information from this isolated reproduction wave, a discriminating level of an appropriate magnitude is set, and when the amplitude is larger than this discriminating level is set to "1", and when the amplitude is smaller than this discriminating level. By detecting the amplitude of "0" (amplitude discrimination), the signal of "0001000" can be extracted. However, if this method is adopted, erroneous reading cannot be avoided when the recording density per track is increased, which causes a peak shift and a decrease in the amplitude value due to the subsequent isolated reproduction wave.

Therefore, when this isolated reproduction wave is converted into a 1 + D (D is one sample delay) waveform shown in FIG. 6C through an equalizer having a certain characteristic, the signal at the sampling point is "00011000". Therefore, it is possible to reproduce a waveform that is not affected by the isolated reproduction wave that occurs subsequently. In this case, "00011000" is replaced by "0001
If you promise to read "000", the recorded information can be read correctly. In this equalization method, since the reproduction signal when the information is read from the storage medium has a differential waveform of (1-D), the whole is (1-D) (1 + D).
= 1-D ² and partial response method class I
This means that V is equalized.

FIG. 7 is an amplitude characteristic diagram of the partial response equalizer. In this figure, the horizontal axis represents frequency and the vertical axis represents gain. The characteristics shown in this figure correspond to the partial response class I from the magnetically recorded isolated reproduction wave.
These are the amplitude characteristics of the equalizer necessary for equalization to V. Letting Y (ω) and G (ω) be the respective amplitude characteristics, the equation Y
(Ω) / G (ω) ... (1). However, Y (ω) = k / 2 · π · exp (−kω / 2) G (ω) = 2 · cos (ωT / 2) k is the half-value width of the isolated reproduction wave, and T is the sampling period.

FIG. 8 is an illustration of an example of a conventional partial response equalizer. In this figure, 21 is a notch filter, 22 is an all-pass filter, 23 is a low-pass filter, and 24 is a cosine equalizer.

The equalizer used in the case of equalizing to the conventional partial response class IV is, as shown in this figure, a notch filter 21 having an amplitude of 0 point,
An all-pass filter 22 having a flat gain frequency characteristic for adjusting the group delay time and a low-pass filter 23 that passes the low frequency band are connected in series, and further, if necessary, for fine adjustment of the amplitude characteristic. Cosine equalizer 2
4 are cascade-connected, and passive filters are all used for these filters that constitute this equalizer.

[0012]

However, it is difficult to realize an equalizer having an amplitude characteristic and a flat group delay characteristic suitable for the partial response class IV shown in FIG. 7 by this conventional equalizer. However, the performance that can be achieved is limited even if the trade-off between the amplitude characteristic and the group delay characteristic is emphasized. It is an object of the present invention to provide an equalizer having optimum amplitude characteristics and group delay characteristics for partial response class IV.

[0013]

In an equalizer of a magnetic recording apparatus for equalizing a magnetic recording / reproducing signal to a partial response class IV according to the present invention, a booster filter, a notch filter, a low pass filter and an all pass filter are subordinate to each other. The connected configuration is adopted.

In this case, the booster filter, the notch filter, the low-pass filter and the all-pass filter can be composed of active filters.

In this case, the booster filter can be formed by a second-order filter, the notch filter can be formed by an even-order filter, and the low-pass filter can be formed by a second-order or higher-order filter. The all-pass filter can be composed of filters of the first order or higher, and the booster filter can be
It can consist of the following lag leads.

In this case, a cosine equalizer type equalizer may be added to correct the variation of the frequency characteristic of the magnetic recording / reproducing signal so that the frequency characteristic can correspond to the transmission line.

Further, in this case, each characteristic of the equalizer can be approximated on the frequency axis and evaluated on the time axis to determine each parameter.

Further, in this case, when the ideal frequency characteristic for determining each parameter and the designed frequency characteristic are approximated on the frequency axis, it is possible to design by weighting within the used frequency band.

In this case, the clocking at the time of evaluation can be determined by comparing the square error for all combinations of sampling points.

[0020]

In the equalizer of the magnetic recording apparatus of the present invention,
By constructing a booster filter, a notch filter, a low-pass filter, and an all-pass filter in cascade connection, it is possible to approximate the ideal amplitude characteristic shown in FIG. 7 necessary for equalizing a magnetic recording / reproducing signal to a partial response class IV. However, by equalizing the group delay, it is possible to realize an equalized waveform in which distortion is not generated by the frequency component of the reproduction signal.

In this case, by constructing the booster filter, the notch filter, the low-pass filter and the all-pass filter by active filters, it is possible to realize more appropriate amplitude characteristics and group delay characteristics by utilizing the characteristics of the active filters.

Further, by constructing the booster filter by a second-order filter, the frequency amplitude characteristic up to 20 MHz in FIG. 7 can be approximated. Further, by constructing the notch filter by an even-order filter, the frequency amplitude characteristic from 20 MHz to 27 MHz in FIG. 7 can be approximated.

Further, by constructing the low-pass filter by a filter of second order or higher, 20 in FIG.
It is possible to approximate the frequency amplitude characteristic above MHz. Further, the group delay characteristic can be flattened by forming the all-pass filter by a filter of the first order or higher.

Further, by forming the booster filter with the first-order lag leads, the circuit can be made simpler than the circuit formed with the second-order filter. Further, a cosine equalizer type equalizer is added to correct the variation in the frequency characteristic of the magnetic recording / reproducing signal.

Also, each characteristic of the equalizer is approximated on the frequency axis and evaluated on the time axis to approximate each parameter of each filter. Also, when the approximation of the ideal frequency characteristic that determines each parameter and the designed frequency characteristic is performed on the frequency axis, by designing by weighting within the used frequency band, it is designed as a filter with less equalization error. be able to.

In this case, the clocking at the time of evaluation can be designed separately from the equalization error caused by the data clocking error by comparing the squared errors for all combinations of sampling points.

As described above, by approximating the amplitude characteristic to the ideal characteristic as shown in FIG. 7 and flattening the group delay characteristic, it is possible to provide an equivalent waveform in which distortion does not occur due to the frequency component of the reproduced signal. .

[0028]

EXAMPLES Examples of the present invention will be described below. Figure 1
It is explanatory drawing of the partial response equalizer of this invention.
In this figure, 1 is a secondary high-pass filter (HP
F), 2 is a secondary low pass filter (LPF), 3 is a secondary high pass filter (HPF), 4 is a secondary low pass filter (LPF), 5 is a secondary low pass filter (LPF),
6 is an all-pass filter (APF), 7 is a cosine equalizer, and 8 and 9 are adders.

In the partial response equalizer of the present invention, the secondary high-pass filter (HPF) 1 and the secondary low-pass filter (LPF) 2 are connected in parallel, and the adder 8 subtracts the output of the secondary high-pass filter 1. Then, the output of the second-order low-pass filter 2 is added to form a booster portion having a high-pass characteristic, and the low-frequency side is approximated from the maximum amplitude frequency of the equalizer.

A second-order high-pass filter (HPF)
3 and a secondary low-pass filter (LPF) 4 are connected in parallel,
The adder 9 adds the outputs of the second-order high-pass filter 3 and the second-order low-pass filter 4 to form a notch portion having an amplitude of 0 point to approximate the curve on the high frequency side from the maximum amplitude frequency of the equalizer.

Then, the frequency characteristic is approximated by cutting the high-frequency amplitude characteristic by a first-order or higher-order, for example, a second-order low-pass filter (LPF) 5. Then, the all-pass filter (APF) 6 is approximated so that the group delay characteristic becomes sufficiently flat to realize a target partial response equalizer. In addition, if necessary, the cosine equalizer 6
The amplitude characteristic can be further finely adjusted by.

(First Embodiment) FIG. 2 shows the PR of the first embodiment.
FIG. 3 is a frequency gain characteristic and frequency group delay characteristic diagram of a (1,1) type equalizer. The horizontal axis of this figure is the frequency (MH
z), the vertical axis represents the group delay time (ns) and the gain (1/10).

The gain in the range of 0 to 45 MHz in this figure corresponds to the frequency gain characteristic of 0 to 27 MHz in FIG.
The gain of Hz to is negligible because of its low level. Also, 0
Group delay time in the range of ~ 45MHz is almost constant,
However, since the gain in this frequency range is low, the influence is small. After all, the frequency characteristic of FIG. 2 is almost the same as the ideal frequency gain characteristic of FIG. 7, and it can be said that the group delay characteristic is constant in this range.

The equalizer whose frequency characteristic and group delay characteristic are shown in FIG. 2 is configured by combining a first-order lag lead, a second-order notch filter, a fourth-order low-pass filter and a fourth-order all-pass filter. Is. This first-order lag lead is an approximation of the frequency amplitude characteristic up to 27 MHz in FIG. 2, the second-order notch filter is an approximation of the frequency amplitude characteristic from 27 MHz to 47 MHz in FIG. 2, and the fourth-order low-pass filter is , An approximation of the frequency amplitude characteristic of 27 MHz or more, and the fourth-order all-pass filter is for flattening the group delay forcing up to 47 MHz.

The numerical value of each parameter is set to 10 [MB / S] as the transfer rate in the 8/9 code, and the magnetic disk device having a solitary half-value width of 1.25 times the sampling period is considered as a condition. When determining each parameter, the frequency characteristics up to the maximum amplitude value are approximated by the filter that approximates the low-frequency side curve, and the maximum amplitude of the equalizer is then approximated by the filter that approximates the high-frequency side curve. The characteristics near the frequency are approximated, and finally, the band above the cutoff frequency is blocked by the LPF. These operations roughly estimate the value and perform approximation.

Finally, the total transfer function is G (s) = (P
Ds²+ PEs + PF) / (PAs ²+ PBs + PC)
, And within 1 / 8T to 1 / 2T, which is the used band
Bandwidth over 1 and less than 1 / 8T, 0.85 and over 1 / 2T
Then multiply by 0.001 (T is the sampling frequency)
Period), the squared error between the ideal value of each amplitude value and the calculated value is the evaluation function
Is optimized by the mountain climbing method using a computer as
Designed.

The clocking for this evaluation was determined by evaluating and selecting the square error of all possible combinations of sampling points. The optimized design results are as follows. LPF First stage denominator s ² coefficient PA = 1.0000 First stage denominator s ¹ coefficient PB = 0.93254 First stage denominator s ⁰ coefficient PC = 0.39486 First stage numerator s ² coefficient PD = 0.00000 1st stage molecule s ¹ coefficient PE = 0.00000 1st stage molecule s ⁰ coefficient PF = 0.62682 0.627 / (s ² + 0.933s + 0.395)

LPF Second stage denominator s ² coefficient PA = 1.00000 Second stage denominator s ¹ coefficient PB = 0.49572 Second stage denominator s ⁰ coefficient PC = 1.05151 Second stage numerator s ² Coefficient PD = 0.00000 Second stage molecule s ¹ coefficient PE = 0.00000 Second stage molecule s ⁰ coefficient PF = 1.19579 1.196 / (s ² + 0.496s + 1.052)

LPF Coefficient of the third stage denominator s ² PA = 1.000 Coefficient of the third stage denominator s ¹ PB = 0.43618 Coefficient of the third stage denominator s ⁰ PC = 0.86406 Third stage denominator of s ² Coefficient PD = 1.01404 Third stage molecule s ¹ coefficient PE = 0.0000 Third stage molecule s ⁰ coefficient PF = 1.06450 1.014 / (s ² + 0.436s + 0.864)

Laglead Coefficient of 4th stage denominator s ² PA = 1.0000 Coefficient of 4th stage denominator s ¹ PB = 1.0000 Coefficient of 4th stage denominator s ⁰ PC = 0.39400 4th stage denominator s ² Coefficient PD = 0.00000 4th stage molecule s ¹ coefficient PE = 1.0000 4th stage molecule s ⁰ coefficient PF = 0.19133 (s + 0.191) / (s + 0.394)

APF Coefficient of 5th stage denominator s ² PA = 1.00000 Coefficient of 5th stage denominator s ¹ PB = 0.87325 Coefficient of 5th stage denominator s ⁰ PC = 0.16681 of 5th stage numerator s ² Coefficient PD = 1.0000 5th stage molecule s ¹ coefficient PE = 0.87325 5th stage molecule s ⁰ coefficient PF = 0.16681 (s ² -0.873s + 0.167) / (s ² +0.8
73s + 0.167)

APF Coefficient of 6th stage denominator s ² PA = 1.000 Coefficient of 6th stage denominator s ¹ PB = 0.71760 Coefficient of 6th stage denominator s ⁰ PC = 0.46644 of 6th stage numerator s ² Coefficient PD = 1.0000 6th stage molecule s ¹ coefficient PE = -0.71760 6th stage molecule s ⁰ coefficient PF = 0.46644 (s ² -0.718s + 0.466) / (s ² +0.7
18s + 0.466)

The cosine equalizer is 1-2 Kc.
It is represented by os (ωT). At this time, the cosine equalizer is not used (used at 2K = 0), but it is necessary when the solitary wave fluctuates. In addition, the standardized frequency at this time is 45 MHz.

FIGS. 3 and 4 show PR (1,
It is a circuit diagram of a 1) type equalizer. PR of the first embodiment
The (1,1) type equalizer is constituted by an active filter using an operational amplifier as shown in this circuit diagram. The circuit constants of the active filters shown in FIGS. 2 and 3 can be calculated from the above transfer function.
That is,

R ₁₁ = 10.6 kΩ, R ₁₂ = 10 kΩ, R
₁₃ = 10 kΩ, R ₂₁ = 11.5 kΩ, R ₂₂ = 24.5 k
Ω, R ₂₃ = 24.5 kΩ, R ₂₄ = 5.73 kΩ, R ₂₅ =
10 kΩ, R ₂₆ = 10 kΩ, R ₂₇ = 10 kΩ, R ₂₉ = 1
0 kΩ, R ₂₁₀ = 10 kΩ, R ₃₁ = 13.9 kΩ, R ₃₂
= 14.6 kΩ, R ₃₃ = 14.6 kΩ, R ₃₄ = 6.95
kΩ, R ₃₅ = 10 kΩ, R ₃₆ = 10 kΩ, R ₃₇ = 10 k
Ω, R ₃₉ = 10 kΩ, R ₃₁₀ = 10 kΩ, R ₄₁ = 10.
7 kΩ, R ₄₂ = 15.9 kΩ, R ₄₃ = 15.9 kΩ, R
₄₄ = 10 kΩ, R ₄₅ = 10 kΩ, R ₄₆ = 10 kΩ, R ₅₁
= 20.2 kΩ, R ₅₂ = 9.75 kΩ, R ₅₃ = 9.75
kΩ, R ₅₄ = 8.58 kΩ, R ₅₅ = 10 kΩ, R ₅₆ = 1
0 kΩ, R ₆₁ = 22.9 kΩ, R ₆₂ = 10.8 kΩ, R
₆₃ = 10.8 kΩ, R ₆₄ = 9.17 kΩ, R ₆₅ = 10 k
Ω, R ₆₆ = 10 kΩ C ₁₁ = 4.93 F, C ₂₁ = C ₂₂ = C ₃₁ = C ₃₂ = C ₄₁ = C
₄₂ = C ₅₁ = C ₅₂ = C ₆₁ = C ₆₂ = 100 μF

FIG. 5 is an explanatory view of pattern equalization results by the PR (1,1) system equalizer of the first embodiment.
(A) is a signal read from the magnetic medium, and (B) is a signal after equalization. The black circles are sampling points, but from the signal (B) after equalization, “000101101101000
1100011000110000 ". The recording signal can be determined from this signal. In this case, since the solitary wave is converted to (1 + D), if the recorded information is "0", it is "0", and if it is "1", it is "11". Therefore, this recording signal is "00011011.
01100001000010000100 ".

[0047]

As described above, according to the present invention,
It is possible to realize an equalizer having more ideal frequency characteristics and group delay characteristics, and it is possible to effectively suppress the occurrence of equalization error.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a partial response equalizer of the present invention.

FIG. 2 is a frequency gain characteristic diagram and a frequency group delay characteristic diagram of the PR (1,1) type equalizer of the first embodiment.

FIG. 3 is a circuit diagram (1) of the PR (1,1) type equalizer of the first embodiment.

FIG. 4 is a circuit diagram (2) of the PR (1,1) type equalizer of the first embodiment.

5A and 5B are explanatory diagrams of pattern equalization results by the PR (1,1) system equalizer of the first embodiment, FIG. 5A is a signal read from a magnetic medium, and FIG. It is a signal.

FIG. 6 is an explanatory diagram of equalization of an isolated reproduction wave by a partial response method. FIG. 6A schematically shows a state in which recorded information is reproduced from a magnetic recording medium by a magnetic head,
(B) shows an isolated reproduction wave, and (C) shows the result of equalization by the partial response method.

FIG. 7 is a frequency amplitude characteristic diagram of the partial response equalizer.

FIG. 8 is an explanatory diagram of an example of a conventional partial response equalizer.

[Explanation of symbols]

 1 2nd-order highpass filter (HPF) 2 2nd-order lowpass filter (LPF) 3 2nd-order highpass filter (HPF) 4 2nd-order lowpass filter (LPF) 5 2nd-order lowpass filter (LPF) 6 All-pass filter (APF) 7 Cosine equalizer 8 , 9 Adder 11 Magnetic recording medium 12 Magnetic head for reproduction 21 Notch filter 22 All pass filter 23 Low pass filter 24 Cosine equalizer

Front page continuation (72) Inventor Kiichiro Kasai 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited

Claims (11)

[Claims] 1. A magnetic recording device comprising a booster filter, a notch filter, a low-pass filter, and an all-pass filter connected in cascade, and having a characteristic of equalizing a magnetic recording / reproducing signal to a partial response class IV. Equalizer. 2. The equalizer for a magnetic recording apparatus according to claim 1, wherein the booster filter, the notch filter, the low-pass filter and the all-pass filter are constituted by active filters. 3. The equalizer for a magnetic recording apparatus according to claim 1, wherein the booster filter is a second-order filter. 4. The equalizer for a magnetic recording apparatus according to claim 1, wherein the notch filter is constituted by an even-order filter. 5. The equalizer for a magnetic recording apparatus according to claim 1, wherein the low-pass filter is composed of a second-order or higher-order filter. 6. The equalizer for a magnetic recording apparatus according to claim 1, wherein the all-pass filter is composed of a first-order or higher-order filter. 7. The equalizer for a magnetic recording apparatus according to claim 1, wherein the booster filter is composed of a first-order lag lead. 8. The magnetic recording medium according to claim 1, wherein a cosine equalizer type equalizer is added to correct fluctuations in the frequency characteristic of the magnetic recording / reproducing signal, and the magnetic field is obtained corresponding to the transmission path. Recording device equalizer. 9. The equalizer for a magnetic recording apparatus according to claim 1, wherein the approximation of each characteristic of the equalizer is performed on the frequency axis and evaluated and designed on the time axis. 10. The ideal frequency characteristic for deciding each parameter and the designed frequency characteristic are approximated on the frequency axis by weighting within the frequency band used for the design. Equalizer for the described magnetic recording device. 11. The equalizer for a magnetic recording apparatus according to claim 9, wherein the clocking at the time of evaluation is determined by evaluating squared errors at all sampling points.