JPH02123564A - Demodulator for magnetic disk device - Google Patents

Abstract

PURPOSE:To execute accurate viterbi demodulation by taking in a read out waveform at a sampling point as digital data and comparing the digital data for several bits with previously stored reference pattern data. CONSTITUTION:Before the first operation of the title magnetic disk device, a prescribed reference pattern is written by a pattern writing means 1 at the sampling point at every prescribed track. This reference pattern is read out by a pattern reading out means 2, and the data of the reference pattern are stored in a storing means 3 together with track position information. Thus, after the operation of the magnetic disk device, the data of the reference pattern stored in the storing means 3 can be used as the reference pattern to be used at demodulation time. Consequently, the data of an isolated wave or the reference pattern in each track from the innermost periphery to the outermost periphery of a disk can be accurately and highly speedily fetched, and the accurate viterbi demodulation can be executed at the demodulation time.

Description

[Detailed Description of the Invention] [Summary] Regarding a demodulator for a magnetic disk drive that digitally demodulates data from a magnetic disk drive using the Viterbi decoding method, the present invention relates to a demodulation device for a magnetic disk drive that digitally demodulates data from a magnetic disk drive using the Viterbi decoding method, which uses solitary wave data or a reference pattern in each track on the disk during demodulation. The purpose of the present invention is to provide a demodulator for a magnetic disk drive that is capable of accurately and quickly capturing data and performing accurate Viterbi demodulation.The aim is to capture the readout waveform at a sampling point as digital data, and to combine it with several bits of reference pattern data and pre-stored reference pattern data. In a demodulating device for a magnetic disk device that reproduces read information by comparing the Before the disk device operates for the first time, pattern reading means reads the reference pattern written by the writing means, and data of the reference pattern at the sampling point read by the reading means is stored together with track position information. After the magnetic disk device starts operating for the first time, the data of the reference pattern stored in the storage means can be used as a reference pattern used at the time of demodulation.

[Industrial Application Field] The present invention relates to a demodulating device for a magnetic disk device, and particularly to a demodulating device for a magnetic disk device that digitally demodulates data from the magnetic disk device using the Viterbi decoding method.

Demands for magnetic disk devices include higher density and higher speed. Recently, the circumferential recording density per inch is 200008 PI, the radial track density per inch is 1200 TPI, and the transfer rate is 4.5 MB/S.
, an average access time of 12m5 has been achieved, but these demands will only increase in the future. In order to meet this demand for higher density, efforts have been made to improve magnetic recording media, improve magnetic heads, and reduce circuit noise. Furthermore, in a magnetic recording/reproducing device in which the magnetic head floats above the disk, the flying height of the magnetic head above the disk is also an important factor for achieving high density. In other words, the smaller the flying height of the head, the higher the output and resolution, but conversely,
If dust or the like gets between the head and the disk, there is a high probability that the head will be damaged, and there will naturally be a limit to the minimum value of the flying height.

Therefore, there is a limit to the improvement in output and resolution in the magnetic head-medium system, and there is a need for a demodulator for magnetic disk drives that can handle low S/N ratios and low resolutions and has a high demodulation speed. .

[Conventional technology]

Conventionally, in a demodulation circuit of a magnetic disk drive, a waveform read from a disk is subjected to analog differentiation, and the zero crossing point is detected as the peak position of the waveform. However,
As shown in Figure 4, in a system with poor resolution, that is, a system in which the solitary waves in the reproduced signal are adjacent to each other, the reproduced waveform is actually As shown by the solid line C, a peak shift occurs in which the peak of the reproduced waveform deviates from the peak of the actual solitary wave, leading to the mistaken impression that information has been written to adjacent bits.

Therefore, as a method of improving when reading data, we emphasize the high frequency components of the signal and improve the resolution as shown in Figure 15 (a).
A pulse slimming (cosine equivalent) circuit as shown in Figure 1 is sometimes introduced. This cosine equivalent circuit consists of a delay line DL with a delay time τ, a voltage divider, and a differential amplifier DA. When a voltage as shown in FIG. 5(b) is applied to the input terminal IN, the voltage of the amplifier DA is The voltage shown in Figure 5 (C) delayed by τ is input to the human power, and the voltage at the peak value as shown in Figure 5 (d) is input to the human power, and the voltage is activated via the delay line DL. A voltage having a peak value having a delay of 2τ that is reflected and input by the amplifier DA is input.

Therefore, the voltage appearing at the output terminal 011T of this cosine equivalent circuit is a slimmed version of the voltage in FIG. 5(C), as shown in FIG. 5(e). When this cosine equivalent circuit is used, a frequency characteristic with emphasized high frequencies can be obtained as shown in FIG. 5(f). However, if the high-frequency components of the signal are emphasized, the high-frequency components of the noise are also emphasized at the same time, resulting in an increase in jitter.

On the other hand, as a method of improving data writing, the amount of peak shift is predicted from the beginning, and the data is alternately delayed and advanced at the time of writing data to the medium. Write compensation (Write Comp) that makes the data interval narrower than the waveform (solid line E)
ensation) is also being carried out.

However, narrowing the data interval is the same as writing at a higher recording density on the medium, which leads to a reduction in the SZN ratio and resolution.

Therefore, there is a need for a circuit or method that can accurately read signals even in systems with reduced resolution. A system in which waveform interference affects adjacent bits can be considered a type of convolutional code, and research is underway to apply the Viterbi decoding method, which is a maximum likelihood decoding method for convolutional codes, to the field of magnetic recording. There is. In conventional demodulation methods, the gradient (d/dt) of the waveform over a short period of time on the time axis is observed using a differentiating circuit, but in Viterbi demodulation, a several-bit pattern is captured as digital data and pre-stored or calculated reference pattern data is used. It is used to compare and demodulate. The Viterbi algorithm is used as a method to select the most probable pattern from a large number of reference patterns.

Since the Viterbi algorithm is well known in the field of communications, its explanation will be omitted, but here we will explain the reading of waveform values and the comparison of reference pattern data when applied to a magnetic disk drive.

(2) First, an isolated waveform is sampled at a certain interval (bit interval or 172 bit intervals), A/D converted, and taken in as a digital value.

■ Based on the data imported in ■, the value at the sampling point for the pattern waveform (reference pattern data)
Calculate. The number of patterns to be calculated varies depending on how many bits are looked at, but if it is 4 bits, 2'=16 patterns will be calculated.

■ On the other hand, the readout waveform is sampled every moment, and
/D conversion and import as a digital value.

(2) Compare the value of several bits acquired in (2) with the value of the reference pattern data calculated in (2), and compare the reference pattern with the closest value with the pattern of the read waveform. Although the comparison is performed for several bits, the information determined is bit by bit. In other words, the Viterbi decoding method is different from peak detection using a conventional differentiation circuit, in that one bit is determined from information of several bits before and after. Since the reference pattern data incorporates waveform interference, the data can be reproduced no matter how much peak shift there is in the readout waveform.

[Problem to be solved by the invention]

As mentioned above, the Viterbi decoding method is basically advantageous in low-resolution systems, but when considering actually applying it to magnetic disk drives, the problem is how to determine the value of the solitary wave at the sample point. The problem is how to import it or how to create a reference pattern. Generally, the recording density differs between the inner circumference and the outer circumference of a magnetic disk device, and the shape of the solitary wave also differs. Therefore, in order to perform accurate Viterbi demodulation, there remains the problem of how to accurately and quickly capture solitary wave data or reference patterns in each track from the innermost track to the outermost track.

In other words, because the shape of the isolated waveform and the calculation pattern are different between the outside and inside of the disk, the solitary wave (data) was written on the first track, and this data was read and calculated before reading the next data. Because the speed of A/D conversion performed at the sampling point to capture it as a digital value is slow,
The problem remains that it takes a lot of time just to create the reference pattern, making it impossible to speed up decoding. Moreover, since the signals read from the head are buried in noise, they must be averaged. Therefore, several kilobytes must be reserved as a reference area, and immediately before the original data is reproduced, A It is extremely difficult to perform /D conversion and import digital data.

The present invention provides a demodulator for a magnetic disk drive that can accurately and quickly capture solitary wave data or reference patterns in each track from the innermost track to the outermost track during demodulation, and that can perform accurate Viterbi demodulation. The purpose is to provide

[Means to solve the problem]

The configuration of a demodulator for a magnetic disk drive according to the present invention that achieves the above object is shown in FIG. A demodulator for a magnetic disk drive according to the present invention captures a read waveform at a sampling point as digital data and reproduces read information by comparing several bits with reference pattern data stored in advance. A pattern writing means 1 writes a predetermined reference pattern at the sampling point for each predetermined track before the magnetic disk device starts operating for the first time. Reference numeral 2 denotes a pattern reading means' which reads out the reference pattern written by the writing means 1 before the magnetic disk device starts operating for the first time. 3 is a storage means, which stores the data of the reference pattern at the sampling point read out by the reading means 2 together with the track position information. As a result, after the magnetic disk device starts operating for the first time, the reference pattern data stored in the storage means 3 can be used as a reference pattern used during demodulation.

[Function] According to the demodulator for a magnetic disk drive of the present invention, patterns at all sampling points necessary for reference are written in the memory before the device is shipped, and read data is stored therein. When reading data when the disk device is used by a user, information is reproduced by referring to only necessary data among the data stored in the memory based on positioning information (track number).

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 2 shows the configuration of an embodiment of a demodulator for a magnetic disk drive according to the present invention. The magnetic disk 10 is provided with a data head DH and a servo head SH.
Data is written to the magnetic disk 10 by a read/write amplifier 11. A control circuit 14 is connected to the read/write amplifier 11 and switches read/write and sends write data from the host model to the read/write amplifier 11. The control circuit 14 also stores write data for a reference pattern. The signal read by the data head DH is input to a first clock recovery circuit 12 including a filter, AGC, equalizer, pulse shaper, etc., and a sampling circuit 15 including an A/D converter. The output of the first clock recovery circuit 12 is input to a second clock recovery circuit 13 including a VFO, and the sampling clock CK of this system is output from the second clock recovery circuit.

This sampling clock C has a sampling circuit 15.
．． Register 16. Memory 20. and is input to the comparator 21.

On the other hand, the signal input to the sampling circuit 15 is A/D
A converter digitizes the signal at every sampling point and inputs it to a register 16 and an averaging circuit 17. The register 16 bundles several bits (the same number of bits as the reference pattern data, for example 4 to 8 bits) including the data input immediately before, and outputs it to the comparator 21 as read data. The averaging circuit 17 averages the input data, assuming that a repetitive pattern of several bits long (the number of bits of the reference pattern) has been written. A control circuit 19 is connected to the memory 20,
When reading the reference pattern from the data head D11, the input from the averaging circuit 17 is written into the memory 20.

For other readings, reference pattern data is output from the memory 20. In addition, the current position (track number) of the data head D11 is stored in the servo circuit 1 as track information.
8 to the memory 20.

A comparator 21 including a differential circuit compares the data read from the register 16 and the reference pattern data in the memory 20 read based on the track information. Then, the pattern with the closest value is output from the detector 22, and at this time, only one bit of data at the oldest point in time is determined as reproduced data.

In the demodulator configured as described above, before the demodulator is shipped, the control circuit 14 writes/reads necessary pattern data to the magnetic disk 10, and the read values at sampling points and track information are stored in the memory 20. It is captured. The pattern data can be taken in by writing the pattern in the data area on the circumference of the disc and performing normal data reproduction. However, the sampled data is written into the memory 20 by a memory write/read signal from the control circuit 19.

Therefore, in a demodulator for a magnetic disk drive configured as shown in FIG. 2, reference pattern data that has been reproduced in advance in a predetermined area of the magnetic disk 10 before the device is shipped is stored together with the values and track information at that time. . Therefore, in this device, the comparator 21 compares the data read by the data head D)l when the device is in operation with the reference pattern data stored in the memory 20 based on the track information before the device is shipped. Reference patterns with similar values are selectively detected by the detector 22 and output as reproduced data.

Note that it is sufficient to store the reference pattern data in the memory 20 not for all tracks of the magnetic disk 10 but for every few tracks.

FIG. 3 shows the structure of another embodiment of the demodulator for a magnetic disk drive according to the present invention. The device of this embodiment takes into consideration the compensation of reference pattern data when off-track, in which the data head Dll deviates from the actual track trajectory, occurs in a magnetic disk device. Therefore, the device of FIG. 3 has the memory 2 of the device of FIG.
In addition to storing the amplitude value of the reference pattern during on-track when the data head D)I traces the track of the magnetic disk 10 without deviating from the track trajectory, the reference pattern comparator 31 is used in addition to the device shown in FIG. and counting multiplier 32
has been newly established.

The reference amplitude from the memory 20 and the amplitude value of the reference pattern at the time of data reading from the averaging circuit 17 are input to the reference pattern comparator 31 , and the comparison result between the two is output to the counting multiplier 32 . The counting multiplier 32 is provided in the middle of the reference data path connecting the memory 20 and the comparator 21, and depending on the comparison result from the reference pattern comparator 31, it changes the reference pattern from the memory 20 to the comparator 21. Multiply by a count less than 1 to lower the level of the reference pattern.

The operation of the demodulator of the magnetic disk device configured as described above is almost the same as the device shown in Figure 2, but in this device, all the patterns necessary for reference are written/read before the device is shipped, and the sampling points are Read the value at as the on-track value. The read reference pattern data, track information, and the amplitude value of the standard pattern (appropriately the gap pattern immediately after Index) are stored in the memory 20 as a reference standard amplitude. During data demodulation after shipment (normal data read), memory 2 is
Of the data stored in 0, only necessary data is referenced. In addition, in order to take into account a decrease in the amplitude value due to off-track, the amplitude value of the reference pattern is held at its peak, and the ratio with the reference reference amplitude stored in the memory 20 is calculated in the reference pattern comparator 31. Then, the reference pattern data is multiplied by a coefficient by this value in the counting multiplier 32 and compared with the read data to reproduce the information.

Therefore, in the apparatus shown in FIG. 3, reference data when the head is off-track can be easily obtained, and the difference in waveform between the inner and outer peripheries of the disk device can be taken in, and accurate demodulation can be performed. Further, it is not necessary to calculate data of several bit patterns from a solitary wave one by one, and the speed of demodulation can be increased.

[Effects of the Invention] As explained above, according to the demodulation device for a magnetic disk drive of the present invention, it is possible to accurately obtain solitary wave data or reference patterns in each track from the innermost circumference to the outermost circumference of the magnetic disk during demodulation. and can be imported at high speed.
This has the advantage that it is possible to perform Viterbi demodulation of 1.

[Brief explanation of the drawing]

FIG. 1 is a principle block diagram of a demodulating device for a magnetic disk device of the present invention, FIG. 2 is a diagram showing the configuration of an embodiment of the demodulating device for a magnetic disk device of the present invention, and FIG. 3 is a block diagram of the principle of a demodulating device for a magnetic disk device of the present invention. A diagram showing the configuration of another embodiment of the demodulator of the device, FIG. 4 is a diagram showing a peak shift due to waveform interference, FIG. 5 is a diagram showing a cosine equivalent circuit and its operation, and FIG. 6 is a diagram showing the write compensation method. FIG. ■... Pattern writing means, 2... Pattern reading means, 3... Storage means, 10... Magnetic disk, 12, 13... Clock regeneration circuit, 15... Sampling circuit, 17.・Averaging circuit,
20...Memory, 21...Comparator, 22
...Detector, 31...Reference pattern comparator, 32...Coefficient multiplier.

Claims (1)

[Scope of Claims] 1. A demodulator for a magnetic disk device that reproduces read information by capturing a read waveform at a sampling point as digital data and comparing several bits with reference pattern data stored in advance. pattern writing means (1) for writing a predetermined reference pattern at the sampling point for each predetermined track before the magnetic disk device operates for the first time; pattern reading means (2) for reading out the reference pattern written by step 1); and storage means (2) for storing data of the reference pattern at the sampling point read out by the reading means (2) together with track position information. 3), and after the magnetic disk device operates for the first time, the data of the reference pattern stored in the storage means (3) can be used as a reference pattern used at the time of demodulation. Demodulator for magnetic disk drives. 2. The device according to claim 1, wherein the storage means (3
) further stores the amplitude value of the reference pattern during normal demodulation, and the amplitude value of the reference pattern read by the reading means (2) is stored in the storage means (3). An amplitude value comparing means (4) for comparing the amplitude value and the storing means (4) according to the comparison result of this comparing means (4) at the time of demodulation.
3) A demodulating device for a magnetic disk device, comprising: coefficient multiplication means (5) for multiplying a reference pattern read from and used by a coefficient of less than 1.