JPH05314653A - Magnetic recording / reproducing device - Google Patents

Abstract

(57) [Summary] [Object] The present invention captures digital data at a sampling point after equalization of a head read waveform,
A magnetic recording / reproducing apparatus for reproducing read information by comparing with pre-stored reference pattern data is to instantaneously obtain an equalization constant for waveform equalization and equalize the waveform. [Configuration] A signal waveform obtained by reproducing specific information is equalized by an equalizer 11. The subtractor 26 and the microcomputer 27 are arranged so that the error after the waveform equalization is minimized.
To adjust the equalization constant. The adjusted equalization constant is stored in the memory 28 together with the reproduction track position information of the input reproduction signal. During normal reproduction after shipment, waveform equalization is performed by reading out the equalization constant from the memory 28 according to the reproduction track position.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording / reproducing apparatus, and in particular, read information is obtained by comparing head read waveforms as digital data at sampling points after equalization and comparing them with reference pattern data stored in advance. The present invention relates to a magnetic recording / reproducing device for reproducing.

When a magnetic recording medium is a magnetic disk, a magnetic recording / reproducing apparatus is currently realized with a circumferential recording density of 50,000 BPI, a track density of 2,000 TPI, a transfer speed of 4.5 MB / S, and an average access time of 12 ms. In the future, demand for higher density and higher speed will continue to grow.

In response to the demand for higher density, measures such as improvement of the magnetic head and the magnetic recording medium and reduction of circuit noise are naturally taken, but the most problematic is the HDI (head disk interface). How to reduce the head flying height. The smaller the head flying height,
Although the output and resolution are high, the probability that the magnetic head collides with the magnetic recording medium is high, so there is a limit to reducing the head flying height.

Therefore, there is a need for a magnetic recording / reproducing apparatus capable of accurately reproducing signals even in a head / medium system having low S / N and resolution.

[0005]

2. Description of the Related Art Conventionally, in a magnetic recording / reproducing apparatus, digital data recorded on a magnetic recording medium is reproduced by a magnetic head, and when the recorded digital data is as shown in FIG. After obtaining the reproduction waveform (readout waveform) as shown in FIG. 4), it is passed through an analog differentiating circuit to generate the differential waveform shown in FIG.

Then, the pulse shown in FIG. 5D is generated at the zero-cross point of this differential waveform, and based on the separately generated data window pulse shown in FIG. 5E, demodulation as shown in FIG. Obtain data (readout information).
This is a reproducing operation from a region having a good resolution such as the outer circumference of the magnetic disk. However, when the resolution is poor such as the inner circumference of the magnetic disk, the magnetic recording medium on which the digital data shown in FIG. 6A is recorded. The waveform obtained by reproducing the magnetic field from the magnetic head is as shown by the solid line in FIG. 7B, and a peak shift occurs.

Therefore, when this reproduced waveform is subjected to analog differentiation, a waveform as shown in FIG. 7C is obtained, so that the zero-cross detection pulse becomes as shown in FIG. 7D and the data shown in FIG. The demodulated data obtained by the window pulse and the zero-crossing detection pulse is different from the original recorded digital data as shown in FIG. 7F, and is erroneous as if "1" was written in the bit adjacent to the original bit. Will be replayed.

Therefore, in the conventional magnetic recording / reproducing apparatus, the reproduced waveform is first inputted to the input terminal 1 of the cosine equalizing circuit shown in FIG. 7 and supplied to the delay line 2 and the gain adjuster 3, respectively. The input terminal 1 is also grounded via a resistor having a characteristic impedance Z ₀ . As a result, when the reproduced waveform delayed by the time τ in the delay line 2 is a solitary wave as shown in FIG. 8A, the output signal of the gain adjuster 3 becomes as shown in FIG. Signal to differential amplifier 4
By passing through the signal, as shown in FIG. 7C, a signal having a waveform whose skirt of the reproduced waveform is sharpened can be output to the output terminal 5.

This cosine equalization circuit has a frequency characteristic for emphasizing high frequency components as shown by the solid line in FIG. 9, and can improve the resolution. However, demodulating the high-frequency components of the signal also emphasizes the high-frequency components of the noise at the same time, so there is a trade-off between improved peak shift (resolution) and increased noise, and the high-frequency components There is a limit to the enhancement of.

Also, conventionally, write compensation has been performed in which the peak shift amount is predicted and the data interval is narrowed at the time of writing data on the magnetic recording medium. However, narrowing the data interval is the same as writing by increasing the recording density on the magnetic recording medium, which leads to a decrease in S / N resolution.

Further, conventionally, partial response equalization that positively utilizes waveform interference is known. This partial response equalization is an equalization method that improves the S / N of the identification point, and can reduce the S / N deterioration in a system with poor resolution.

A system in which waveform interference affects adjacent bits can be regarded as a kind of convolutional encoder, and the Viterbi decoding method, which is the maximum likelihood decoding method for convolutional codes, is applied to the field of magnetic recording and reproduction. Research is ongoing. This Viterbi decoding method takes in read information as digital data, compares it with reference pattern data stored or calculated in advance, and demodulates it, and selects the most probable pattern data from many reference pattern data as demodulation data.

When a magnetic recording medium on which an NRZI-modulated binary code is recorded is reproduced, the reproduced signal waveform becomes a ternary signal due to the differential characteristics of the magnetic head, as can be seen from the state transition diagram of FIG. 10B. In addition, the state bk of the current value is "-
When the input signal (recording signal) ak is "1" when the value is "1", the value zk of the output signal (reproduction signal) is "+2", and the state bk = + 1 is entered. In this state, ak is "1". , There is a rule that zk becomes “−2” and the state is changed to bk = −1, and no other state transition occurs.

Therefore, in the above case, the metric value L in the state (bk = 1 or bk = -1) up to the present in Viterbi decoding as shown in the dendritic representation of FIG. 10 (A).
_K-1 and the currently sampled value Y _K-1 and the expected data (0, 2 or -2), the metric value L _{K of the} next state
Select the most probable pattern by calculating.

[0015] At this time, state bk = + metric value in 1 L _K ⁺ is ^{_{L K-1 + - (Y}} K-1 -0) 2 and L _K-1 ^-
Select the larger _one of-(Y _K-1 -2) ² . L _K ^- also selects the larger Similarly two paths. When starting from the bk = + 1 or −1 state and successively selecting larger paths in this way, a plurality of paths initially exist, but over time, only a specific path survives. Then, the state transition until a certain time is fixed. If the state transition is known, the input signal can be known. In the above Viterbi decoding, as shown in the state transition diagram of FIG. 10B, when the input signal ak = + 1, the output signal zk is +2 or −.
The use of two impulses is used, but this is premised on an ideal magnetic recording / reproducing system having no waveform interference. However, in reality there are many waveform interferences,
There is an influence on the adjacent bit, which changes depending on the inner / outer peripheral position when the magnetic recording medium is a magnetic disk of constant angular velocity type.

In order to absorb this changing influence by Viterbi decoding, decoding requires complicated logic. Therefore, in order to cope with the influence of this change, some conventional apparatuses have an equalizer circuit that makes a constant waveform and then performs the above-mentioned Viterbi decoding by a simple logic.

As the above-mentioned equalization, for example, there is a partial response system shown in FIG. The write data shown in FIG. 9A is written as a magnetization reversal on the magnetic recording medium by passing a current through the magnetic head. When the recording medium is reproduced by the magnetic head, a reproduction signal corresponding to the peak of the write data "1" position shown in FIG. The partial response method is to equalize the waveform of this signal so that the signal output value at the sampling point becomes "0110" as shown in FIG. The reproduction of the write data is detected as "1" if the output value of the equalization circuit at the sampling point is a certain level (usually 0.5) or more and "0" if it is less than that (the same figure (D)). ).

[0018]

When digital data is recorded on a magnetic disk of the constant angular velocity system, the relative linear velocity between the head and the disk is different between the inner circumference and the outer circumference of the magnetic disk. Since the recording density is different between the outer circumference and the outer circumference, the shape of the reproduced isolated waveform is different between the inner circumference and the outer circumference.

Therefore, in order to obtain a constant waveform in the equalizing circuit, the data of the reproduced solitary wave in each track from the innermost circumference to the outermost circumference of the magnetic disk is accurately known, and the optimum equalization constant is determined accordingly. Must be set. However, in the conventional magnetic reproducing device, the magnetic head is
When positioned on a certain track, there is a problem that the waveform shape is instantly read and the optimum constant cannot be set.

The present invention has been made in view of the above points,
An object of the present invention is to provide a magnetic recording / reproducing apparatus which solves the above-mentioned problems by storing an equalization constant and track position information in advance and using them during reproduction.

[0021]

FIG. 1 is a block diagram showing the principle of the present invention which achieves the above object. In the present invention, a signal waveform obtained by reproducing digital data recorded on a magnetic recording medium by a magnetic head is equalized by an equalizer 11 based on an equalization constant, and the signal after the waveform equalization is leveled by a comparator 12. In the magnetic recording / reproducing apparatus for comparing with a reference pattern stored in advance to obtain demodulated data, the equalization constant varying means 13, the storing means 14, and the servo information reading means 15 are provided. Is.

The equalization constant varying means 13 equalizes a signal waveform obtained by previously recording / reproducing specific information with respect to the magnetic recording medium by the magnetic head by the equalizer 11 and outputs the signal waveform after the waveform equalization. The equalization constant of the equalizer 11 is automatically variably adjusted based on the input / output signal of the comparator 12 so that the error is minimized.

The storage means 14 stores the equalization constant adjusted by the equalization constant varying means 13 together with the track position information on the magnetic recording medium on which the specific information is recorded. The servo information reading means 15 reads the equalization constant from the storage means 14 based on the track position information reproduced from the magnetic recording medium and inputs it to the equalizer 11 during normal reproduction after the storage in the storage means 14 is completed. Waveform equalization.

[0024]

According to the present invention, the equalizer 11 to which the specific information is recorded and reproduced on the entire surface of the magnetic recording medium or in the unit of a predetermined number of tracks and the reproduced signal waveform is inputted through the input terminal 10 is the optimum waveform or the like. An equalization constant that can be used for conversion is obtained in advance and stored in the storage means 14 together with the track position information.
Therefore, at the time of normal subsequent arbitrary information reproduction, the optimum equalization constant can be instantaneously obtained from the storage means 14 according to the reproduction track position.

[0025]

FIG. 2 shows a block diagram of an embodiment of the present invention. In the figure, the same components as those in FIG. 1 are designated by the same reference numerals. In FIG. 2, for example, digital data recorded on a hard disk is reproduced by a magnetic head and input to the input terminal 20. The delay circuits 21 _{1 to} 21 _n , the gain adjusters 22 to 24, and the differential amplifier 25 form a transversal type equalizer 11.

Delay circuit 21₁~ 21_nEach recorded
Has a delay time equal to the bit period of digital data
It The gain adjuster 22 receives the reproduction signal from the input terminal 20.
Is input and the equalization constant G is input to this_-jMultiply and output. Gay
The circuit adjuster 23 is the delay circuit 21. ₁In the latter stage, and delay times
Road 21_nOutput reproduction signal of the delay circuit (not shown) in the previous stage
Is input and the equalization constant G is input to₀Multiply and output. Ge
The IN adjuster 24 is the delay circuit 21._nOutput playback signal is input
Then, this is multiplied by the equalization constant Gj and output.

Each equalization constant of the gain adjusters 22 to 24 is variably adjusted to a desired value by an output signal of the microcomputer 27 described later. The output signals of the gain adjusters 22 to 24 are supplied to the differential amplifier 25. The output signal of the differential amplifier 25 is a waveform-equalized signal, which is input to the comparator 12 and taken in as digital data at the sampling point, and then compared with the reference pattern data stored in advance and demodulated data (not shown). Output) to the terminal 30.

If the equalized waveform input to the comparator 12 from the differential amplifier 25 is indicated by I in FIG. 3, the comparison value in the comparator 12 is equalized as indicated by II in FIG. The comparator 12 has a comparison value II, which is a substantially central value of the amplitude of the latter waveform.
A larger input signal is output as "1" and an input signal smaller than II is output as "0" to the terminal 30.

In this embodiment, the subtractor 2 is used as shown in FIG.
6 and a microcomputer 27 are added, and an optimum equalization constant that minimizes intersymbol interference is obtained according to the hard disk track position according to the flowchart of FIG. Remember.

The operation of this embodiment in this case will be described with reference to FIGS. First, before the product is shipped, the equalizer 11
Information sequence "0 ... 01" for which an impulse response is obtained at the output terminal of
After moving the magnetic head to a required track position in order to record "0 ... 0" by the magnetic head in all tracks on the hard disk or in units of several tens of tracks (step 3).
1) Write the above information string in the hard disk (step 32).

Next, the written information sequence is reproduced by the magnetic head, the reproduction signal is input to the input terminal 20 of FIG. 2, and the equalization error E _k is _obtained from the subtracter 26 (step 3).
3). Here, if the above information string at time kt is ak, ak is a binary signal and is “1” or “0”. The output signal Y _k at the output terminal of the differential amplifier 25 at time kt is given by the following equation.

[0032]

[Equation 1]

However, h (k-1) t is the differential amplifier 25
Is an impulse response at time (k-1) t at the output end of. As shown in FIG. 2, the subtractor 26 subtracts the output demodulated data A _k of the comparator 12 from the output signal Y _k of the differential amplifier 25 to generate and output the equalization error E _k . Here, E _k = Y _k −A _k (2). A _k matches the recorded information string ak when there is no decoding error.

The microcomputer 27 calculates the equalization error evaluation function H _j from the equalization error E _k and the demodulated data A _k from the comparator 12 based on the following equation (step 3).
4).

[0035]

[Equation 2]

However, in the above equation, sgn indicates a sign of positive, negative or zero.

If this evaluation function H _j is positive, the equalization constant (gain) is increased by a minute amount Δ, and conversely, if it is negative, the equalization constant (gain) is decreased by a minute amount Δ, and the absolute value of the intersymbol interference is reduced. The sum D can be reduced.

Here,

[0039]

[Equation 3]

Therefore, the microcomputer 27 calculates the gain value based on the above-mentioned evaluation function H _j (step 35), and the gain adjuster 2 is set so as to obtain the calculated gain value.
The gains (equalization constants) of 2 to 24 are variably adjusted (step 36).

For example, the input signal ak is "00001000.
00 ”and considering the equalization of 3 taps (j = −1, 0, +1), the evaluation function H _j is as follows.

H-1 = sgn (A _{k-2 + 1} ) sgn (E _k-2 ) + sgn (A _{k-1 + 1} ) sgn (E _k-1 ) + sgn (A _{k-0 + 1} ) sgn ( E _k ) H 0 = sgn (A _k-1-0 ) sgn (E _k-1 ) + sgn (A _k-0 ) sgn (E _k ) + sgn (A _{k + 1-0} ) sgn (E _{k + 1} ). H + 1 = sgn (A _{k + 0-1} ) sgn (E _k ) + sgn (A _{k + 1-1} ) sgn (E _{k + 1} ) + sgn (A _{k + 2-1} ) sgn (E _{k + 2} ) Now Although there is interference in the waveform after equalization as shown in FIG. 3, assuming that "0001000" is obtained as the output A _k of the comparator 12, the evaluation function H _{j in} this case is as follows.

H-1 = 0 (+1) +1 (+1) +0 (0) = + 1 H 0 = 0 (+1) +1 (0) +0 (+1) = 0 H + 1 = 0 (0) +1 (+1) +0 ( +1) = + 1 Therefore, the gain adjuster 22 corresponding to H-1 and H + 1
And the gains (equalization constants) of 24 are increased by a small amount Δ.

Next, the sum of equalization errors obtained in this state |
The microcomputer 27 determines whether E _k-1 │ + │E _k │ + │E _{k + 1} │ is within the allowable range (that is, whether or not it is converged) (step 37), and it is converged. If not, the operations of steps 32 to 36 are repeated until they converge.

When the total sum of the equalization errors is within the allowable range, the microcomputer 27 then causes the internal memory 28 (which constitutes the storage means 14) to store the optimum gain (equalization constant) G obtained at that time. _-j , G ₀ , G _j are stored together with a value indicating the reproduction track position (step 38). Then, it is determined whether or not the storage of the above gains has been completed for all tracks (step 39), and if it has not been completed for all tracks, the processes of steps 31 to 38 are repeated, and the optimum gains for all tracks are obtained. The process ends when the storage of the gain ends (step 40).

When sgn│E _k-1 │ is taken as a value, when Y _k-1 = 0.4, H-1 = 0.4 and Y _k = 0.3.
Then, H-1 = 0.3. That is, H-1 has a larger value as the equalization error increases. Therefore, this value H-1
The larger the value is, the larger the gain is changed, so that the equalization error can be quickly converged.

After the equalization constant is stored in the memory 28 together with the track position information in this way, the hard disk device is shipped. Each time the user records and reproduces arbitrary digital data on this hard disk device, reproduction track position information is input to the microcomputer 27 as a read signal via the terminal 29 of FIG. As a result, the microcomputer 27 reads out the equalization constant corresponding to the input track position information from the memory 28 and supplies it to the gain adjusters 22 to 24, respectively.

Therefore, the equalizer 11 can perform accurate equalization and can always obtain the demodulated data accurately from the outer circumference to the inner circumference of the hard disk.

The partial response method shown in FIG. 11 can also be set to an equalization constant with the output waveform of the resistor shown in FIG. 2 as shown in FIG. 11 (C). Further, as the write information, the information string is “0 ... 010 ... 0”.
Thus, the impulse response can be easily obtained at the output terminal of the equalizer 11.

Further, the present invention is not limited to the above-mentioned embodiments, but can be applied in principle to a magnetic recording medium other than the hard disk.

[0051]

As described above, according to the present invention, the optimum equalization constant can be instantaneously obtained from the storage means in accordance with the reproduction track position, so that accurate data reproduction can be always performed.
Since the means for changing the equalization constant to the optimum value can be configured by a subtractor and a microcomputer, it can be configured inexpensively with less hardware, and further, information that becomes an impulse at the output end of the equalizer is recorded. Since it is reproduced, it has a feature that the optimum equalization constant for waveform equalization can be easily obtained, and the optimum equalization constant can be automatically generated.

[Brief description of drawings]

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

FIG. 2 is a block diagram of an embodiment of the present invention.

FIG. 3 is a diagram showing a waveform after equalization and a comparison value.

FIG. 4 is a flowchart for explaining the operation of one embodiment of the present invention.

FIG. 5 is an explanatory diagram of a conventional reproduced waveform.

FIG. 6 is an explanatory diagram of a conventional reproduced waveform.

FIG. 7 is a circuit diagram of a cosine equalization circuit.

8 is a time chart for explaining the operation of FIG.

FIG. 9 is a frequency characteristic diagram of a cosine equalization circuit.

FIG. 10 is an explanatory diagram of Viterbi decoding.

FIG. 11 is an explanatory diagram of an example of a partial response.

[Explanation of symbols]

11 Equalizer 12 Comparator 13 Equalization constant changing means 14 Storage means 15 Servo information reading means 21 _{1 to} 21 _n Delay circuit 22 to 24 Gain adjuster 25 Differential amplifier 26 Subtractor 27 Microcomputer 28 Memory

Claims (5)

[Claims] 1. An equalizer (11) for a signal waveform obtained by reproducing digital data recorded on a magnetic recording medium by a magnetic head.
In the magnetic recording / reproducing apparatus, the waveform equalization is performed on the basis of the equalization constant, the signal after the waveform equalization is taken in as digital data, and the reference pattern stored in advance is compared with a comparator (12) to obtain demodulated data. A signal waveform obtained by previously recording and reproducing specific information with respect to a magnetic recording medium by a magnetic head is waveform equalized by the equalizer (11) so that the error of the signal waveform after the waveform equalization is minimized. An equalization constant changing means (13) for automatically and variably adjusting the equalization constant of the equalizer (11) based on the input / output signal of the comparator (12), and the equalization constant changing means (13). ), The equalization constant adjusted by the above) is stored together with the track position information on the magnetic recording medium on which the specific information is recorded, and an arbitrary equalizer after the storage in the storage means (14) is completed. When playing information Reading means (15) for reading the equalization constant from the storage means (14) based on track position information reproduced from the magnetic recording medium and inputting the equalization constant to the equalizer (11) for waveform equalization. A magnetic recording / reproducing apparatus having: 2. The equalization constant varying means (13) includes a subtracter (26) for obtaining an error from a difference between an output signal of the equalizer (11) and an output signal of the comparator (12), A microcomputer (2) for varying the equalization constant supplied to the equalizer (11) based on the output signal value of the subtractor (26).
7. The magnetic recording / reproducing apparatus according to claim 1, comprising: 3. The specific information is the equalizer (11).
2. The magnetic recording / reproducing apparatus according to claim 1, wherein the output signal waveform of is a pulse train having an impulse. 4. The magnetic recording / reproducing apparatus according to claim 1, wherein the magnetic recording medium is a hard disk. 5. The changing of the equalization constant by the equalization constant changing means (13) and the storage of the equalization constant and the track position information in the storage means (14) are performed in advance before shipment of the apparatus. The magnetic recording / reproducing apparatus according to claim 1, wherein