JPH0696543A - Magnetic recording and reproduction apparatus - Google Patents

Abstract

PURPOSE:To reduce the amplitude error of servo data due to a noise component in a high region and a low region and to enhance the positioning control of a head in a data face servo system. CONSTITUTION:A low-pass filter 25a, for ordinary data use, provided with a cutoff frequency matched to ordinary data and a bandpass filter 25b in which the frequency of servo data is set as a passing band are installed, and the ordinary data and the servo data are reproduced. Thereby, when the ordinary data is passed through the low-pass filter 25a, a high-frequency component is cut and an error rate in a read operation can be maintained. In addition, when the servo data is passed through the bandpass filter 25b, a noise component in a low region and a high frequency can be removed and an accurate amplitude can be detected.

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 device such as a magnetic disk device using a data surface servo system.

[0002]

2. Description of the Related Art Conventionally, in a magnetic disk device using a data surface servo system, burst data is generally used as servo data for head positioning control. This burst data is, as shown in FIG.
In the servo write at the time of manufacturing, the burst pattern is recorded at a position shifted by 1/2 track from the center position of the track in the radial direction of the recording medium.

By the way, the burst data has a repeating frequency so that peak shift due to waveform interference or the like does not occur. Also, burst data is easier to read at low frequencies, so we want to make the frequency as low as possible. However, if the frequency is too low, the burst pattern area increases and the original data recording area is reduced.
Therefore, in general, when the lowest frequency of the normal data is 1f, the repetition frequency of the burst data is 8 / 3f.

FIG. 4 is a block diagram showing the structure of a conventional magnetic recording / reproducing apparatus. In FIG. 4, information recorded on the recording medium 10 is an analog signal of the magnetic head 1.
The data is read by 1, and amplified by the head amplifier (AMP) 12, and then further amplified by the gain set by the AGC control circuit (AGC CONT) 14 in the AGC amplifier 13. Here, since the read waveform has high-frequency noise, the low-pass filter (LPF) 15
To remove this. The cutoff frequency of the low-pass filter 15 is determined by the characteristics of the magnetic head 12 and the recording medium 10 and the S / N ratio of the entire device.

FIG. 5 shows the gain characteristic of the low-pass filter 15. In the figure, a is a gain curve. In this example, the cutoff frequency is 8f (when the lowest frequency is 1f). The frequency range of the read waveform is 1f to 4f, though it varies depending on the modulation method. The data that has passed through the low-pass filter 15 is the differentiation circuit (D
IF) 16, comparator (COMP) 17, pulse generation circuit (PULS) 18, phase synchronization circuit (PLL) 19
It is converted into digital read data through and is given to the control circuit 21.

On the other hand, here, burst data is 8 / 3f.
And the repetition frequency. The burst data that has passed through the low-pass filter 15 is sent to the sample & hold circuit (S & H) 20. Sample and hold circuit 2
0 is a burst pattern A to form burst data.
Each amplitude of D is detected, and the coded signal is output to the control circuit 21. The control circuit 21 detects the head position deviation amount based on the amplitudes of the burst patterns A to D.

That is, for example, the burst AGC shown in FIG.
When the amplitude of the read signal in the area is "100", the amplitude of the burst patterns A and B in the cylinder "0" is "50", the amplitude of the pattern C is "0", and the amplitude of the pattern D is "100". . Here, assuming that the position of the magnetic head 11 is deviated to the cylinder "1" side by 1/4 track, the burst data on the cylinder "1" side is read, and the amplitude of the burst pattern A in this case is "75". ",
The amplitudes of patterns B and C are “25”, and the amplitude of pattern D is “75”. In this way, burst patterns A to D
The amount of head position deviation is detected from the change in each amplitude.

[0008]

By the way, since normal data (data in the data area) has a wide band frequency, as shown in FIG. 5, it is considerably higher than 8 / 3f which is the frequency of burst data. Is the cutoff frequency. Here, if it is assumed that 5f is the optimum value as the cutoff frequency of the burst data of 8 / 3f, for example, in the gain characteristic as shown in FIG. 5, the shaded portion is insufficiently attenuated. In the case of normal data, its peak value becomes a problem, but in the case of burst data, its amplitude value becomes a problem, so if there is a high-frequency noise component that changes the amplitude, it is incorrect. Therefore, the amount of misalignment will be detected.

Further, in the sector servo type magnetic disk device, CDR (Constant Density) is used.
There is a recording medium using a recording system. This is because the data surface of the recording medium is divided into a plurality of zones in the radial direction by taking advantage of the fact that the outer circumference of the recording medium is longer than the inner circumference, and the recording frequency is changed from the inner circumference to the outer circumference for each zone. This is a system in which the recording density per unit length on the entire surface of the recording medium is made substantially constant by configuring the sectors in which the height becomes high, thereby increasing the capacity of the device. When this CDR method is used, the use frequency differs for each zone, so it is necessary to change the cutoff frequency of the low-pass filter. Generally, a low-pass filter having a cut-off frequency switching function is used, and the optimum cut-off frequency is switched according to each zone.

However, since the frequency of burst data is the same in each zone, as shown in FIG. 5, when the cutoff frequency of normal data changes to 8f ', the gain characteristic of the low-pass filter is shown by a'. As a result, there occurs a phenomenon that the S / N ratio in the high frequency range of burst data is further deteriorated.

Further, the AGC amplifier is usually effective in removing low frequencies. Therefore, the low frequency noise can be cut by passing the normal data through the AGC amplifier. However, since the amplitude value of burst data is of course a problem, AGC cannot be applied, and during that time, the gain of the AGC amplifier is held and the AG
The C amplifier is not allowed to follow. Therefore, burst data is weaker than low-frequency noise components as compared with normal data.

The present invention has been made in view of the above points, and in a data surface servo system, it is possible to reduce an amplitude error of servo data due to noise components in a high band and a low band and improve head positioning control. It is an object of the present invention to provide a magnetic recording / reproducing device that can be used.

[0013]

According to the present invention, in a data surface servo type magnetic recording / reproducing apparatus, a low pass filter for normal data having a cut-off frequency matched with normal data and a frequency of servo data as a pass band are used. A bandpass filter for set servo data is provided to reproduce normal data and servo data.

Further, according to the present invention, in a CDR type magnetic recording / reproducing apparatus, a low pass filter for normal data having a plurality of different cut-off frequencies matched with normal data for each zone, and a frequency band of servo data in a pass band. A bandpass filter for servo data set as is provided to reproduce normal data and servo data.

[0015]

According to this structure, by passing normal data through the low-pass filter, the high frequency component can be cut and the error rate at the time of reading can be maintained. Further, by passing the servo data through the bandpass filter, it is possible to remove low-frequency and high-frequency noise components and perform accurate amplitude detection.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A magnetic recording / reproducing apparatus according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the structure of a sector servo type magnetic disk device. In FIG. 1, servo data for positioning control of the magnetic head 21 is previously recorded on a part of the data surface of the recording medium 20. In the same embodiment, the servo data is composed of burst patterns A to D as shown in FIG. 3, and is recorded at a position shifted by 1/2 in the radial direction of the recording medium 20 from the center position of the track. The servo data has a repetition frequency of 8 / 3f when the lowest frequency of the normal data is 1f.

Further, in this embodiment, this recording medium 20 is used.
Uses the CDR method. That is, the data surface is divided into a plurality of zones in the radial direction, and sectors having different recording frequencies are formed in each zone.

The magnetic head 21 moves in the radial direction of the recording medium 20 to record / reproduce data. The head amplifier (AMP) 22 amplifies a read signal of the magnetic head 21. The AGC amplifier 23 is an AGC control circuit (AGC
CONT) 24 according to the gain set by
The output of the head amplifier 22, that is, the read signal of the magnetic head 21 is amplified. The AGC control circuit 24 monitors the output of the low-pass filter (LPF) 25a, controls the gain of the AGC amplifier 23 so that the output amplitude is constant, and holds the gain in the servo pattern area. The low-pass filter 25a is a filter for normal data and has a gain characteristic as shown by a in FIG. Also,
In the CDR method, this low pass filter 25a
It has a function of switching the cutoff frequency for each zone as shown in a'of FIG.

In this embodiment, a bandpass filter (BPF) 25b for servo data is provided in addition to the lowpass filter 25a. As shown in FIG. 2B, the band pass filter 25b has a characteristic that the frequency of servo data (burst data) is set as a pass band and cuts low and high frequencies.

As shown in FIG. 1, the low-pass filter 25
The output of a is the AGC control circuit 24 and the differentiation circuit (DI
F) 26. The differentiating circuit 26 differentiates the read signal that has passed through the low-pass filter 25a. The comparator (COMP) 27 detects the zero-cross point of the output of the differentiating circuit 26. Pulse generation circuit (PULS) 28
Generates a pulse signal according to the peak position of the read signal based on the output signal of the comparator 27. The phase synchronization circuit (PLL) 29 synchronizes the pulse signal from the pulse generation circuit 28 with the read clock in phase.

The output of the low pass filter 25b is given to the sample & hold circuit (S & H) 30. The sample & hold circuit 30 detects the amplitude of the servo data and outputs a coded signal to the control circuit 31. A control circuit (CONT) 31 controls the entire disk drive, and here, the phase synchronization circuit 2 is used.
The read data is obtained from No. 9, the amplitude signal of the servo data is obtained from the sample & hold circuit 30, and the positioning control of the magnetic head 21 is performed based on this amplitude signal. Further, in the CDR system, the control circuit 31 outputs a signal S for switching the cutoff frequency of the low pass filter 25a for each zone. Next, the operation of the embodiment will be described.

The read signal of the magnetic head 21 is amplified by the head amplifier 22, and then further amplified by the gain set by the AGC control circuit 24 in the AGC amplifier 23. Of this read signal, normal data (data in the data area) passes through the low-pass filter 25a and is sent to the data reproducing system including the differentiating circuit 26, the comparator 27, the pulse generating circuit 28, and the phase synchronizing circuit 29. At this time, the cutoff frequency of the low-pass filter 25a is set to an optimum value according to the frequency band of the normal data regardless of the burst data. This makes it possible to cut off high-frequency noise components and obtain an optimum signal.

Further, when the CDR method is used, the cut-off frequency is switched for each zone based on the signal S from the control circuit 31, because the used frequency is different for each zone. As a result, the gain characteristic of the low-pass filter 25a changes as indicated by a'in FIG. 2, and the error rate can be optimized by the S / N ratio at the time of reading.

In fact, the read signal of the magnetic head 21 is read by the low-pass filter 25a and the band-pass filter 2.
The control circuit 31 is reached through both paths of 5b. Control circuit 3
In No. 1, the signal from the low pass filter 25a and the signal from the low pass filter 25b are selectively input at a predetermined timing. That is, the control circuit 31 inputs the signal from the low-pass filter 25a when reproducing the normal data, and inputs the signal from the low-pass filter 25a when reproducing the servo data.
Input the signal from b.

The normal data passed through the low-pass filter 25a is differentiated by the differentiating circuit 26, and then the comparator 2
At 7, it is compared to the reference voltage. A pulse signal corresponding to the peak position of the read signal is generated in the pulse generation circuit 28 by the output signal of the comparator 27. The phase synchronization circuit 29 synchronizes the pulse signal with the clock signal to generate read data.

On the other hand, servo data (burst data)
Passes through the band pass filter 25b and is sent to the servo reproduction system including the sample and hold circuit 30. The frequency of servo data depends on the balance between the efficiency of the data recording area and the characteristics of the head.
3f). In this case, if the gain characteristic of the band pass filter 25b is set as the pass band of the frequency of the servo data as shown in FIG. 2b, the noise in the high and low frequencies indicated by the diagonal lines is cut, and the S / N ratio of the burst data is reduced. The ratio improves.

By using the CDR method,
Even if the gain characteristic of the low pass filter 25a changes like a ', the S / N ratio of the servo data is always constant.
Therefore, by changing the gain characteristic of the low-pass filter 25a, it is possible to prevent a high-frequency noise component from being transferred to the servo data.

The servo data passed through the band pass filter 25b is given to the sample & hold circuit 30. The sample & hold circuit 30 detects the amplitude of the servo data, that is, the amplitude of each burst pattern constituting the servo data, and encodes it with an internal A / D converter. The control circuit 31 positions the magnetic head 21 based on the change in the amplitude of the servo data.
In this case, the band pass filter 25b cuts noise in the high band and the low band, so that accurate positioning can be performed.

In FIG. 1, the remaining electric circuits except the head amplifier 22 and the control circuit 31 are integrated into a one-chip IC.
When it is built in, the low-pass cut component by the bandpass filter 25b reduces the DC offset of the differential output generated by the lowpass filter 25a, so the coupling capacitor between the lowpass filter 25a and the bandpass filter 25b is reduced. it can.

[0031]

As described above, according to the present invention, in the data surface servo system, the cutoff frequency of the low pass filter is set in accordance with the frequency band of normal data, and the band pass filter is adjusted in accordance with the frequency band of servo data. By setting the cutoff frequency of, the high frequency component can be cut to maintain the error rate at the time of reading, and the low frequency and high frequency components can be cut to reduce the amplitude error of the servo data. As a result, the head can be positioned with high accuracy based on the accurate change in the amplitude of the servo data.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a magnetic recording / reproducing apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing characteristics of a filter in the example.

FIG. 3 is a diagram for explaining a servo data recording method.

FIG. 4 is a block diagram showing a configuration of a conventional magnetic recording / reproducing apparatus.

FIG. 5 is a diagram showing characteristics of a conventional filter.

[Explanation of symbols]

20 ... Recording medium, 21 ... Magnetic head, 22 ... Head amplifier, 23 ... AGC amplifier, 24 ... AGC control circuit, 25
a ... low-pass filter, 25b ... band-pass filter,
26 ... Differentiation circuit, 27 ... Comparator, 28 ... Pulse generation circuit, 29 ... Phase synchronization circuit, 30 ... Sample & hold circuit, 31 ... Control circuit.

Claims (2)

[Claims] 1. A magnetic recording / reproducing apparatus comprising a recording medium in which servo data for head positioning control is previously recorded on a part of a data surface, and reproducing the servo data and normal data from a read signal of the head, A low-pass filter for the normal data having a cut-off frequency matched to the normal data, a band-pass filter for the servo data set with the frequency of the servo data as a pass band, and the head obtained through the low-pass filter The normal data reproducing means for reproducing the normal data based on the read signal of the head, and the servo data reproducing means for reproducing the servo data based on the read signal of the head obtained through the band pass filter. And a magnetic recording / reproducing apparatus. 2. A data surface which is divided into a plurality of zones in the radial direction, and a sector having a different recording frequency is formed for each of the zones of the data surface, and a head is previously formed on a part of the data surface. In a magnetic recording / reproducing apparatus that includes a recording medium on which servo data for positioning control is recorded, and that reproduces the servo data and normal data from a read signal of the head, a plurality of magnetic recording / reproducing devices that match the normal data for each zone. Based on the low-pass filter for the normal data having different cut-off frequencies, the band-pass filter for the servo data set with the frequency of the servo data as a pass band, and the read signal of the head obtained through the low-pass filter. A normal data reproducing means for reproducing the normal data, and the bandpass filter. Through based on the read signal of the head obtained by the magnetic recording and reproducing apparatus characterized by comprising a servo data reproducing means for reproducing said servo data.