KR20000074744A - Method for recording/playing of optical record medium - Google Patents

Abstract

PURPOSE: A method of recording and reproducing an optical record carrier is provided to detect a defocus offset amount on a correct focus from a tracking error signal being detected in a free-running state with only a focus servo turned on, and to apply it to recording and reproduction process. CONSTITUTION: The method of recording and reproducing an optical record carrier(101), wherein a tracking error signal and a focus error signal is detected using an electrical signal of an optical pick-up(102) which irradiates a laser beam onto a specified position on the record carrier and picks up a reflected beam therefrom to perform a tracking servo and a focus servo, comprises the steps of: rotating the optical record carrier with only the tracking servo turned on to detect the tracking error signal; and judging an instant when the tracking error signal is the largest to be a focus-on state and detecting a defocus offset amount at the instant.

Description

Method for recording and reproducing an optical record carrier {Method for recording / playing of optical record medium}

The present invention relates to an optical recording medium system, and more particularly, to a method for detecting and compensating for defocus of an optical recording medium.

In general, optical recording media are largely divided into three types: read-only ROM, write-once worm type, and rewritable rewritable type. Lose.

Among these, freely and repeatedly rewritable optical recording media such as an optical disc include a rewritable compact disc (CD-RW) and a rewritable digital versatile disc (DVD-RW, DVD-RAM, DVD). + RW).

The above-described rewritable optical discs, especially optical discs such as DVD-RAM, have signal tracks having a structure of lands and grooves, so that tracking control can be performed even on a blank disc in which no information signal is recorded. Recently, in order to increase the recording density, information signals are recorded on the tracks of the hills and valleys, respectively.

That is, the wavelength of the laser light of the optical pickup for recording / reproducing is shortened, and the numerical aperture of the objective lens for condensing is increased to reduce the size of the light beam for recording and reproducing. In addition, in the above rewritable high density optical disc, the distance between signal tracks, that is, the signal track pitch, is reduced in order to increase the recording density.

In such an optical recording / reproducing apparatus, in order to record information or to reproduce the recorded information, focus control is performed through optical pickup.

At this time, if the optical focus is shifted from the disk surface during focus control, that is, the focus servo (hereinafter referred to as defocus), there is a problem in that data quality during recording and reproducing is deteriorated, resulting in unstable operation of the system.

Accordingly, the focus servo moves the optical pickup up and down by driving the focus actuator in the optical pickup so that the optical disk follows the vertical movement with rotation. That is, the focus actuator keeps the distance between the objective lens and the optical disk constant by driving the objective lens that focuses in accordance with the focus error signal in the vertical axis.

However, in an optical disc capable of recording data in both lands and grooves, such as a DVD-RAM, the focus offset is different depending on the depth difference between the lands and grooves, so that the focus error signal may be defocused even if zero.

That is, even if the focus is corrected on the track of the land by the depth difference between the land and the groove, the offset adjustment is not performed. Therefore, if it is applied to the track of the groove, the focus may not be performed. Similarly, when focusing is matched to the track of the groove, defocusing may occur in the track of the land due to the depth difference between the land and the groove.

In this case, the defocus state cannot be known only by the focus error signal. As a result, the jitter characteristic becomes worse and the bit error rate (BER) increases. If the recording is performed in this state, the recording characteristics of the land and the groove may be changed. As in the case described above, the quality of data may be deteriorated during recording and reproducing, resulting in an unstable operation of the system.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to detect a defocus offset amount during positive focus from a tracking error signal detected in a free running state in which only the focus servo is turned on, and apply it during recording and reproduction. The present invention provides a recording and reproducing method of an optical recording medium.

1 is a block diagram of a recording and reproducing apparatus of an optical recording medium according to the present invention;

2 is a diagram illustrating an example of the photo detector of FIG. 1;

3 is a graph illustrating an example in which the level of a tracking error signal changes due to a defocus offset change in a free running state.

4A to 4E are waveform diagrams showing the level change of the tracking error signal due to the defocus offset change.

Explanation of symbols for main parts of the drawings

101: optical disk 102: optical pickup

103: RF and servo error generation unit 104: defocus determination unit

104-1: LPF 104-2: level detector

104-3: Defocus Detection Unit 105: Servo Control Unit

106: focus servo driver

According to an aspect of the present invention, there is provided a method of recording and reproducing an optical recording medium, the method including: detecting a tracking error signal by rotating the optical disc in a state where only a focus servo is turned on; Determining a time point at which the image is to be focused and detecting a defocus offset amount at the time point.

The defocus offset amount detecting step may detect a time point when the level of the tracking error signal becomes maximum while changing the defocus offset amount.

In the defocus offset detection step, the defocus offset amount may be detected by obtaining an average value of the tracking error signal.

In the recording and reproducing method of an optical recording medium according to the present invention, the optical recording medium is rotated while only the focus servo is turned on to detect a tracking error signal, and then the amount of defocus offset at the point of time when the tracking error signal is maximized. Performing a process at each of a plurality of designated points of the optical recording medium, and performing focus servo of the corresponding point with the defocus offset amount detected in the step during data recording and reproducing.

Other objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments taken in conjunction with the accompanying drawings.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

According to the present invention, when the tracking error signal detected in the free running state in which only the focus servo is turned on is determined to be the focus on, the amount of defocus offset at the point in time is detected and the detected error is detected during actual recording and playback. This is to perform the focus servo with the defocus offset amount.

That is, when the focus servo is turned on and the tracking servo is turned off, when the pickup is fixed and the disk is rotated, a tracking error signal is detected by the eccentric amount of the disk, which is called a free running state.

1 is a block diagram of an optical disk recording / reproducing apparatus for defocus detection according to the present invention, in which an optical disk 101 capable of rewriting data and an optical pickup for recording and reproducing information on the optical disk 101 are provided. 102, from the RF and servo error generator 105 for generating RF and servo error signals from the electrical signal output from the optical pickup 102, from the tracking error signal output from the RF and servo error generator 105 A defocus discrimination unit 104 for detecting a defocus offset amount at the time of positive focus, a servo control unit 105 for generating a focus drive signal corresponding to the defocus offset amount detected at the defocus determination unit 104, and The focus servo driver 106 controls the optical pickup 102 according to the focus driving signal to compensate for defocus.

Here, the optical pickup 102 is provided with a photo detector for detecting the light amount of the beam and converting it into an electrical signal, the optical detector is an example of the signal track direction and the radial direction of the optical disk 101 as shown in FIG. In this case, it is possible to configure four specific photodetectors (PDA, PDB, PDC, PDD).

In addition, the defocus determining unit 104 performs a low pass filtering on the tracking error signal TE and averages the LPF 104-1, and a level detector detecting the level Vpp of the tracking error signal TE ( 104-2 and a defocus detector 104-3 which detects the defocus offset amount at the time of positive focus by using the output of the LPF 104-1 and the output of the level detector 104-2. .

In the present invention configured as described above, the optical disc 101 has a signal track structure of lands and grooves, and data can be recorded or reproduced not only on the tracks of the lands or grooves, but also on the tracks of the lands and grooves. have.

Thus, the laser light emitted by the laser diode of the optical pickup 102 during mounting or recording / reproducing of the optical disk 101 is placed on the signal track of the rotating optical disk 101, where the reflected light is directed to the optical detector. Incident.

The photo detector includes a plurality of photo detectors, and an electrical signal proportional to the amount of light obtained from each photo detector is output to the RF and servo error generator 103.

If the photodetector is configured as shown in FIG. 2, the photodetector outputs an electrical signal a, b, c, d proportional to the amount of light obtained from each photodetector element PDA, PDB, PDC, PDD. 103).

The RF and servo error generator 103 combines the electrical signals a, b, c, and d to generate an RF signal for data reproduction, a read channel 2 signal for servo control, a focus error signal, and the like. The RF signal may be obtained by (a + b + c + d) the electrical signal output from the photo detector, and the read channel 2 signal may be the (a + d) − electrical signal output from the photo detector. (b + c), and a tracking error (TE) signal can be obtained by processing the read channel 2 signal.

If the photo detector is divided into two in the track direction, the RF signal (= I1 + I2) and the read channel 2 signal (= I1-I2) are detected from the light amount balance of both photodiodes I1 and I2. That is, a + d in FIG. 2 corresponds to I1 and b + c corresponds to I2.

At this time, the defocus determination unit 104 detects the defocus using the tracking error signal TE processed by the read channel 2. FIG.

Such defocus detection is performed at a plurality of designated points of the inner and outer disks at the time of system initialization.

For example, when the disk is mounted, the RF and servo error generator 103 generates RF and servo error signals in the free running state in which only the focus servo is turned on, and then outputs the tracking error signal to the defocus discriminating unit 104. .

That is, if only the optical disk 101 is rotated while the optical pickup 102 is fixed while the focus servo is on and the tracking servo is off, the tracking error signal is detected by the disc eccentricity.

In this case, Table 1 below shows the level change of the tracking error signal that depends on the defocus offset while only the focus servo is turned on and the tracking servo is turned off in the tilt zero (ie, mechanism 0) state.

Defocus Offset [] TE level [V] 0.0 1.0 5.1 2.0 9.0 3.0 11.3 4.0 13.3 5.0 15.1 6.0 14.0 7.0 13.5 8.0 9.7 9.0 5.7 10.0 2.7

FIG. 3 is a graph of Table 1, wherein the level of the tracking error signal (Vpp) is not defocused, i.e., the maximum in the positive focus state, otherwise it is proportional to the degree of defocusing. Its size is reduced. For example, in Table 1, the point at which the defocus offset amount is 5.0 is the point at defocus zero.

Accordingly, the defocus determining unit 104 detects the level of the tracking error signal while changing the defocus offset at a designated point and determines the maximum time point as the focus-on and stores the defocus offset amount at the time point. .

To this end, the level detector 104-2 of the defocus determination unit 104 detects and outputs the level Vpp of the tracking error signal to the defocus detector 104-3, and defocus detector 104-3. Detects and stores the defocus offset amount at the point when the level Vpp of the tracking error signal becomes maximum while changing the defocus offset in the above-described process.

On the other hand, the tracking error signal is distorted and asymmetry occurs according to the defocus offset as shown in FIG. 3. For example, it can be seen that the waveform of the tracking error signal becomes unbalanced as the defocus offset becomes less than six.

Therefore, if the average value of the level Vpp of the tracking error signal is obtained and the defocus offset amount is detected using this average value, it is possible to detect a position without defocus, that is, a positive focus position in a short time. This is because the focus servo is performed only at the point at which the average value is not distorted.

In this case, when the tracking error signal is filtered by the LPF 104-1, an average value of the level Vpp of the tracking error signal may be detected. Here, if there is little distortion, the waveform corresponding to the average value is almost straight.

4A to 4E illustrate examples in which the level of the tracking error signal detected in the free running state in which only the focus servo is turned on and the tracking servo is turned off depends on the defocus offset. Since the level (Vpp) of the tracking error signal is the largest, it is determined at this time as the focus-on and the corresponding defocus offset amount is stored.

4 (d) shows an average value of the output of the LPF 104-1, that is, the level Vpp of the tracking error signal, but it can be seen that distortion is seriously generated. Therefore, the focus servo is not performed in a direction smaller than the defocus offset.

This process is performed at each of a plurality of designated points to store the defocus offset amount corresponding to the focus-on at each point.

At this time, the defocus offset amount at which the level of the tracking error signal becomes the maximum at each point is almost similar, but not the same. This is because the disc position deviation (e.g., reflectance, recording medium characteristics) is slightly different.

In addition, when the above process is performed in the land and the groove, the difference in focus offset between the land and the groove can be obtained by comparing the two defocus offset amounts.

Then, when the corresponding point designated during actual data recording / reproduction is reached, the focus servo is performed with the defocus offset amount stored at the point.

That is, the servo control unit 105 generates a focus driving signal corresponding to the defocus offset amount stored at a predetermined point during actual data recording / reproducing, and the focus servo driving unit 106 generates a focus driving signal in accordance with the focus driving signal. Drive the focus actuator.

Therefore, it is possible to shorten the time for finding the focus-on during the actual recording / reproducing, and thus, the focus servo is stabilized quickly so that the data recording / reproducing is performed accurately.

On the other hand, in the present invention, in the embodiment, the defocus offset to be positive focus is detected during system initialization, but this may vary depending on the type of the disk.

For example, since it is important for the DVD-RAM performing random access to stabilize the servo quickly, the de-focusing offset at the time of constant focus is performed in advance at the time of system initialization as described above. It is effective to perform the focus servo with the value, and DVD-R or DVD-RW which performs serial access does not have a big problem even if recording is a little late. Therefore, the defocus offset is changed by the above-described process during actual recording / playback. The focus servo may be performed by detecting a defocus offset amount that becomes a positive focus.

As described above, according to the recording and reproducing method of the optical recording medium according to the present invention, the level of the tracking error signal is maximized at a plurality of points of the inner circumference and the outer circumference of the disc in the free running state in which only the focus servo is turned on. By detecting and storing the focus offset amount, the focus servo is executed at the value stored at the corresponding point during the actual recording / playback to prevent the deterioration of data quality due to defocusing during recording and playback, and to stabilize the focus servo quickly so as to realize real time. At the same time, it is possible to record and to operate the system stably.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the spirit of the present invention.

Therefore, the technical scope of the present invention should not be limited to the contents described in the embodiments, but should be defined by the claims.

Claims (7)

A method of recording and reproducing an optical recording medium which performs tracking servo and focusing servo by detecting a tracking error signal and a focusing error signal by using an electrical signal of an optical pickup that receives a laser at a designated position of the optical recording medium and then picks up the reflected light. To Detecting a tracking error signal by rotating the optical recording medium with only the focus servo turned on; And determining the point of time when the tracking error signal is maximized to the focus-on state and detecting the defocus offset amount at the point of time. The method of claim 1, wherein the defocus offset amount detecting step is And detecting the point of time when the level of the tracking error signal is maximized while varying the defocus offset amount. The method of claim 1, wherein the defocus offset amount detecting step is And a defocus offset amount is detected by obtaining an average value of the tracking error signals. The method of claim 3, wherein the defocus offset amount detecting step is And a low pass filtering of the tracking error signal to obtain an average value of the tracking error signal. A method of recording and reproducing an optical recording medium which performs tracking servo and focusing servo by detecting a tracking error signal and a focusing error signal by using an electrical signal of an optical pickup that receives a laser at a designated position of the optical recording medium and then picks up the reflected light. To Rotating the optical recording medium with only the focus servo turned on to detect a tracking error signal and detecting a defocus offset amount at a point when the tracking error signal reaches a maximum at a plurality of designated points of the optical recording medium. Performing each step, And performing a focus servo of the corresponding point with the defocus offset amount detected in the step during data recording and reproducing. The method of claim 5, In the case of a random access optical recording medium, the defocus offset amount detecting step is performed in advance upon system initialization. The method of claim 5, In the case of a serial access optical recording medium, the defocus offset amount detecting step is performed during recording / reproducing.