JP2003045050A - Magneto-optical recording medium reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magneto-optical recording medium reproducing device which performs an offset correcting operation for track control while improving accuracy without obstructing a data reproducing operation. SOLUTION: The magneto-optical recording medium reproducing device having a means for reproducing data recorded on a recording medium by light tracking-controlled on the basis of tracking error signals is provided with a means 6 for outputting the result of comparing the tracking error signals with a reference level provided beforehand and a means 7 for measuring the quality of reproducing data corresponding to output and adding an offset value calculated on the basis of the result to the tracking error signals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium reproducing apparatus for performing tracking control based on a tracking error signal.

[0002]

2. Description of the Related Art Generally, a tracking method for an optical disk is controlled by using a tracking error signal detected by a detection method such as a push-pull method or a wobble pit of a sample servo. In both cases, tracking control is performed with the center point of the tracking error signal amplitude as a reference.

However, in recent years, the density of optical discs has been increased by narrowing the track pitch and the like, and the demand for improving the accuracy of tracking control has been increasing. In addition to simply controlling the center point of the tracking error signal amplitude, the center of tracking control is set to the maximum amplitude point of the RF signal or the best point such as jitter and error rate so that the reproduction signal is in an optimum state. Control is being performed by appropriately adding an offset or the like so that a point comes. (Japanese Patent Laid-Open No. 2000-1492
No. 95, etc. )

In the process of obtaining the value of the offset or the like, any method such as the method of obtaining the maximum amplitude point of the RF signal and the method of obtaining the optimum point of the jitter, the error rate, etc. can be used to set a predetermined offset amount in the tracking control system. For example, the operation of searching for the best point of the RF signal is repeated, or the best point is calculated from the state of the RF signal when an offset of about several points is given.

[0005]

However, in the method of searching for the best point while giving such an offset, since the actual data reproducing operation cannot be performed during the best point detecting operation, it is not possible to perform the data reproducing operation every time. When I went there, it took a long time to play the data. In addition, when it is performed for each disc, or when the disc is divided into a plurality of areas and the division is performed for each area, an optimum offset cannot be given due to a difference in the disc position or data recording conditions. It was

Further, in a device for reproducing an optical disc recorded at high density such as a DWDD type magneto-optical disc device, further improvement in accuracy in track control is required.

The present invention has been made in view of the above points, and provides a magneto-optical recording medium reproducing apparatus for performing offset correction operation for track control while improving accuracy without hindering the data reproducing operation. It is intended to be provided.

[0008]

In order to solve the above problems, the present invention provides a magneto-optical recording medium having means for reproducing data recorded on a recording medium by light tracking-controlled based on a tracking error signal. In the reproducing device, means for outputting a result of comparing the tracking error signal with a reference level provided in advance,
Means for measuring the quality of the reproduced data according to the output and adding an offset value calculated based on the result to the tracking error signal.

[0009]

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

(First Embodiment) FIG. 1 is a block diagram showing the configuration of the present embodiment. In FIG. 1, 1 is an optical head, 2 is a reproduction RF signal detection circuit, 3 is a tracking error detection circuit, 4 is a tracking servo circuit, 5 is an offset addition circuit, 6 is an error level comparator, and 7 is an RF signal quality discriminator. Is.

A laser beam is emitted from the optical head 1 to an optical disk (not shown), and the return light is received by a sensor (not shown) in the optical head, and a signal based on the light is generated. Of the generated signals, the reproduction data signal is supplied to the reproduction RF signal detection circuit 2 and the reproduction servo signal is supplied to the tracking error detection circuit 3.

Although not shown, the reproduction servo signal is also supplied to a focus error detector to perform focus control so that the data surface of the optical disk is in focus. The tracking error detection circuit 3 generates a tracking error signal based on the supplied servo signal, and the tracking error signal is supplied to the tracking servo circuit 4 after a predetermined offset is added by the offset adder 5. .

In the tracking servo circuit 4, a tracking control signal is generated based on the supplied tracking error signal, and the tracking control signal is supplied to a tracking actuator (not shown) in the optical head.
Tracking servo is applied based on this, and the laser light applied to the optical disk is controlled so as to follow the data track.

In the first state, the offset added by the offset adder 5 is zero. Before giving a detailed description, the relationship between the amount of track deviation and the reproduction RF signal quality in a DWDD type magneto-optical disk, which is a large-capacity, high-density optical disk, will be described. FIG. 2 is a diagram showing the relationship. In FIG. 2, the horizontal axis represents the track shift amount and the vertical axis represents the reproduction RF signal quality. As an index indicating the reproduction RF signal quality on the vertical axis, there is an error rate of the reproduction signal or the like, but even if other indexes are used, there is a difference in detection sensitivity, but the characteristics are almost the same. The lowest part has the best quality of the reproduced signal, and the quality becomes worse regardless of which point around that point. Such a tendency can be seen even in a normal optical disc, but it is more remarkable in a DWDD type disc, which is a high-density optical disc, and the difference in quality with respect to a track deviation becomes larger.

In the present embodiment, the tracking control accuracy is improved by utilizing such characteristics. Assuming that a reproduction RF signal is detected in a state in which the disc (not shown) is under focus and track control, the signal output from the tracking error detection circuit 3 is, as shown in FIG. It is in a state of swinging up and down, with the level being normally 0). this is,
It is the control error amount due to the servo band and the disturbance resulting from applying the servo with the reference level of the servo as the target value.

FIG. 3 shows an example of the error level comparator.
The low-pass filter 16 removes the high-frequency component of the tracking error signal after the offset addition, and is sent to the comparator 17. The comparator 17 compares it with a reference level provided in advance, and outputs a signal from the comparator 17 based on the result.

FIG. 4 is a graph showing the relationship between the input tracking error signal and the output signal. In each figure of FIG. 4, the upper solid line shows the input tracking error signal, and the lower rectangular pulse shows the output signal of the comparator 17. FIG. 4A shows a waveform when the reference level and the magnitude are simply compared and output. A binary signal of 1 is output when the input tracking error signal is higher than the reference level, and 0 when it is smaller than the reference level.

FIG. 4B shows a waveform when the comparator 17 is provided with hysteresis of a predetermined width. When the tracking error signal enters the hysteresis region, 1 is output after exceeding it, and when it exits the hysteresis region, 0 is output after passing through it. By adding hysteresis, the influence of noise can be removed. The amount of hysteresis may be set to an appropriate value according to the magnitude of the tracking error level.

FIG. 4 (c) shows a dead zone having a predetermined width with respect to the reference level and not outputting an output signal for a tracking error signal in the dead zone.
In the case of FIG. 4 (c), since there are three output states, the output signal may be increased by another to be a 2-bit signal. That is, it is possible to add an output signal that becomes 1 while in the dead zone and set the RF signal quality discriminator 7 in the next stage so that the discrimination operation is not performed when this signal is 1.

The output of the error level comparator 6 is input to the RF signal quality discriminator 7. The RF signal quality discriminator 7 takes in the signal quality when 1 and the signal quality when 0 according to the output value of the error level comparator 6 for a predetermined time. As a result, when the output of the error level comparator 6 is 1 or 0, the quality is compared. When the output is 1, the tracking error signal is larger than the servo reference level. Therefore, the offset value to be output is given to the − side. 0
When is good, the offset on the + side is given. The output offset value is added to the tracking error signal by the offset adder 5 to perform tracking control.

FIG. 5 is a block diagram showing the RF signal quality discriminator of this embodiment. In FIG. 5, 8 is an A / D converter, 9 is a PRML circuit, 10 is a demodulator, and 11 is an ECC.
The circuit, 12 is an error count circuit. These components are components almost required for demodulation of a general reproduction signal. The output of the error level comparator is input to the error count circuit 12.

The error count circuit monitors the error correction status in the ECC circuit and counts the error status at the position according to the output of the error level comparator. When the output of the error level comparator is 1, the first counter (not shown) counts, and when the output is 0, the second counter (not shown) counts. Which is better is determined from the result of the predetermined time.

The predetermined time is set to an appropriate time so that the numbers of errors can be compared. Depending on the result of the determination, the error count circuit 12 gives an offset of a predetermined polarity to the offset addition circuit. The amount of the offset to be given may be changed according to the difference in the comparison result, but if it is performed by a predetermined amount for each determination, malfunction due to noise or the like can be prevented.

Further, if the LPF 16 of the tracking error signal to the error level comparator is made to have only the frequency component which tracking control can follow, and it is outputted by comparing with the reference level, malfunction of the comparison output due to noise or the like will occur. Can be prevented.

In this way, while reproducing the data,
By adding an offset value to the tracking error signal in the direction in which the quality of the reproduced signal is good, it becomes possible to always obtain the optimum reproduced signal.

(Second Embodiment) FIG. 6 shows the RF of the present embodiment.
It is a block diagram showing a signal quality discriminator. Other configurations are
Since it is the same as the first embodiment, only FIG. 6 will be described.
In FIG. 6, 8 is an A / D converter, 9 is a PRML circuit,
Reference numeral 10 is a demodulator, and 13 is a level jitter measuring circuit.
The output of the error level comparator is input to the level jitter measuring circuit 13. The level jitter measuring circuit 13 has P
From the RML circuit 9, a signal after PR (after filtering) is used as an input signal and its signal level distribution is measured.

FIG. 7 is a diagram showing the level distribution, in which the vertical axis is the amplitude level and the horizontal axis is the appearance frequency of the level. Assuming that the PR characteristic is PR (1, -1), three peaks are formed in the distribution of the input signal level as shown in FIG. The + -side peaks or −-side peaks on the vertical axis represent the change points of the waveform before PR, and the part without change is the center (0) peak.

The level jitter measuring circuit 13 measures each distribution according to the output of the error level comparator 6. That is, the distribution when the output of the error level comparator 6 is 0 and the distribution when the output is 1 are measured. The higher the quality of the reproduced RF signal, the more the three peaks are separated, and the smaller the minimum value of the frequency distribution such as the level a and the level b in FIG. 7 is. The relationship between the minimum value and the track deviation is also as shown in FIG.
Which is better is determined from the result of the predetermined time. The predetermined time is an appropriate time that allows the distributions to be compared. According to the result of the determination, the level jitter measuring circuit 13 gives the offset adding circuit an offset of a predetermined polarity. In this embodiment, the minimum value is used, but the standard deviation value of each mountain may be used. In this case, the minute value detection circuit 13 is used as shown in FIG.

According to this embodiment, the offset value can be updated at a time interval shorter than the time interval required to measure the error rate as in the first embodiment, and the real-time property is further improved. .

(Embodiment 3) FIG. 8 shows the RF of this embodiment.
It is a block diagram showing a signal quality discriminator. Other configurations are
Since it is the same as the first embodiment, the configuration of FIG. 8 will be described. In FIG. 8, 8 is an AD converter, 9 is a PRML circuit, 10 is a demodulator, and 14 is an amplitude measuring circuit.

The output of the error level comparator 6 is input to the amplitude measuring circuit 14. The amplitude measuring circuit 14 measures the signal amplitude of the signal from the AD converter 8 as an input signal. The amplitude measuring circuit 14 measures each amplitude according to the output of the error level comparator. That is, the amplitude when the output of the error level comparator is 0 and the amplitude when the output is 1 are measured.

Which is better is determined from the result of the predetermined time. The predetermined time is an appropriate time with which the amplitudes can be compared. Depending on the result of the determination, the amplitude measuring circuit 14
An offset of a predetermined polarity is given to the offset addition circuit 5. In this embodiment, the amplitude value is used, but the jitter value at the signal change point may be used. In this case, the amplitude measuring circuit 14 is the jitter measuring circuit 14 as shown in FIG.

According to the present embodiment, the number of samples (input signal from the AD converter 8) required for measurement is smaller than that in the case of measuring the level jitter as in the second embodiment, so that the time interval is further shortened. With this, the offset value can be updated, and the real-time property is improved.

(Embodiment 4) FIG. 9 shows the RF of this embodiment.
It is a block diagram showing a signal quality discriminator. Other configurations are
Since it is the same as the first embodiment, FIG. 9 will be described. Figure 9
In the figure, 8 is an AD converter, 9 is a PRML circuit, 10 is a demodulator, and 15 is an amplitude measuring circuit.

The output of the error level comparator is input to the amplitude measuring circuit 15. The amplitude measuring circuit 15 measures the signal level of the signal after the PR (after the differential filter) from the PRML circuit 9 as an input signal. Amplitude measuring circuit 15
Measures the respective amplitudes according to the output of the error level comparator 6. That is, the amplitude when the output of the error level comparator 6 is 0 and the amplitude when the output is 1 are measured. Which is better is judged from the result of the predetermined time. The predetermined time is
The time is set so that the amplitudes can be compared. Depending on the result of the determination, the amplitude measuring circuit 15 gives the offset adding circuit an offset of a predetermined polarity.

According to the present embodiment, the offset value can be updated at a time interval shorter than the time interval required to measure the level jitter as in the second embodiment, and the real-time property is further improved.

[0037]

As described above, according to the present invention,
Since it is configured to determine the offset value to be added to the tracking error signal based on the result of measuring the quality of the reproduction data corresponding to the output signal by comparing the tracking error signal with the reference level provided in advance, It has become possible to perform an offset correction operation for track control for data reproduction while improving accuracy without hindering the data reproduction operation.

Further, the quality of the reproduced data is set to the amplitude of the reproduced data signal, the jitter, the amplitude of the post-PR signal, the dispersion of the amplitude level distribution, the minimum value of the distribution, etc., so that the tracking control with the real-time property further improved. It can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of a configuration of an embodiment of the present invention.

FIG. 2 is a graph showing a relationship between a track deviation amount and a reproduction RF signal quality.

FIG. 3 is a block diagram showing an example of an error level comparator.

FIG. 4 is a graph showing a relationship between an input signal and an output signal of the error level comparator.

FIG. 5 is a block diagram of an RF signal quality discriminator according to the first embodiment of the present invention.

FIG. 6 is a block diagram of an RF signal quality discriminator in Embodiment 2 of the present invention.

FIG. 7 is an example of a distribution of signal levels after PR according to the second embodiment.

FIG. 8 is a block diagram of an RF signal quality discriminator in Embodiment 3 of the present invention.

FIG. 9 is a block diagram of an RF signal quality discriminator in Embodiment 4 of the present invention.

[Explanation of symbols]

1 Optical head 2 Playback RF signal detection 3 Tracking error detection 4 Tracking servo circuit 5 Offset addition circuit 6 Error level comparator 7 RF signal quality discriminator 8 A / D converter 9 PRML circuit 10 demodulator 11 ECC circuit 12 Error count circuit 13 level jitter measurement circuit or minimum value detection circuit 14 Amplitude measurement circuit or Jitter measurement circuit 15 Amplitude measurement circuit 16 LPF 17 Comparator

Claims (7)

[Claims] 1. A magneto-optical recording medium reproducing apparatus having means for reproducing data recorded on a recording medium by light tracking-controlled based on a tracking error signal, wherein the tracking error signal and a reference level provided in advance. And a means for outputting the result of comparison between and, and means for measuring the quality of the reproduction data according to the output and adding the offset value calculated based on the result to the tracking error signal. Characteristic magneto-optical recording medium reproducing apparatus. 2. The magneto-optical recording according to claim 1, wherein the quality of the reproduced data is an error rate of the reproduced data, and the smaller the error rate of the reproduced data, the better the quality. Media playback device. 3. The quality of the reproduction data is a minimum value of a signal amplitude level distribution of the reproduction data after filtering, and the smaller the minimum value of the signal amplitude level is, the better the quality is. The magneto-optical recording medium reproducing apparatus according to claim 1. 4. The quality of the reproduced data is the standard deviation of the signal amplitude level distribution of the reproduced data after filtering,
2. The magneto-optical recording medium reproducing apparatus according to claim 1, wherein the smaller the standard deviation of the signal amplitude level distribution is, the better the quality is. 5. The magneto-optical recording medium reproduction according to claim 1, wherein the quality of the reproduction data is a jitter of the reproduction data, and the smaller the jitter of the reproduction data is, the better the quality is. apparatus. 6. The magneto-optical recording medium reproduction according to claim 1, wherein the quality of the reproduction data is an amplitude of the reproduction data, and the larger the amplitude of the reproduction data is, the better the quality is. apparatus. 7. The quality of the reproduction data is an amplitude of the reproduction data after differentiation, and the higher the amplitude of the reproduction data after differentiation is, the better the quality is. Magneto-optical recording medium reproducing apparatus.