KR100713545B1 - Method and device for tracking of optical disk - Google Patents

Abstract

An apparatus for tracking an optical disc according to the present invention includes: means for generating a high frequency signal by the sum of signals output from the photodetector; Means for detecting a space portion from the high frequency signal of the high frequency signal generating means and outputting a gate control signal; Means for generating first and second tracking signals by combining left and right of the signals sampled and held by the quadrature photodetector by the gate control signal of the space detecting means; Means for integrating a magnitude of each tracking signal of the tracking signal generating means for a predetermined time and detecting a tracking level with an average size of the maximum and minimum signals thereof; And means for detecting the difference between the maximum and minimum values of the tracking level detected by the tracking level detecting means and adding the sums thereof to detect the tracking error signal.

According to the present invention, a tracking signal for left and right boundaries is generated using a wobble signal in a space when an optical disc is reproduced, and a difference signal with respect to an average magnitude is generated for a predetermined time and the tracking signal is summed at the boundary surface. By outputting a tracking error signal to the tracking servo that corrects the offset by the tracking level difference, there is an advantage that the light beam can go along the center of the signal track.

Description

Method and device for tracking of optical disks

1 is a block diagram showing a tracking device of a conventional optical disk.

2 is a view showing a tracking error due to a position pattern of a light beam when tracking an optical disc.

Figure 3 is a block diagram showing an embodiment of the tracking device of the optical disk according to the present invention.

4 is a diagram illustrating an example of a tracking signal waveform when an offset occurs according to the present invention.

<Explanation of symbols for the main parts of the drawings>

1 ... optical disk 2 ... spindle motor

3 ... optical pickup 4 ... tracking error detector

5 ... tracking servo PD ... photodetector

OL objective lens 110.High frequency signal generator

120 ... Space detector 130 ... Tracking signal generator

140 ... tracking level detector 150 ... tracking error detector

131a ~ 131d ... sample / hold section 132a ~ 132d ... low filter

133a, 133b, 153 ... adder 141a, 141b ... max / min detector

142a ~ 142d ... Integrator 143a ~ 143d ... Average detector

151a, 151b ... Subtractor 152a, 152b ... Absolute Value Circuit

The optical disc tracking method and apparatus according to the present invention particularly relates to an effective tracking method and apparatus for a wobbled signal track in an optical record carrier having a wobbled groove.

Recently, optical recording media, magneto-optical recording media, and the like have been developed and used as recording media for recording various kinds of information such as video and audio information. Such optical recording media include CD-ROM (Read Only Memory) and DVD (Digital Versatile Disc) -ROM, including generalized CD (Compact Disc), CD-R (Recordable) and DVD-R, etc. WORM (Write Once Read Memory) type discs and rewritable discs such as CD-RW (Rewritable) and DVD-RAM (Random Access Memory) are widely spread or developed.

When reproducing such an optical disk, a condensing laser beam is irradiated to the center of the track to follow the track on which the information is recorded at a constant speed, and the change of the amount of reflected light by the track is converted into the form of an electrical signal by a photodetector. By signal processing the converted electrical signal, information is reproduced.

At this time, the condensing pattern of the laser beam irradiated to the track is controlled according to the distribution of reflected light irradiated to the photodetector, and the tracking (whether or not the laser beam leaves the track) is also adjusted to the distribution of reflected light irradiated to the photodetector. . The rotational speed of the optical disk is detected by processing the electrical signal converted by the photodetector, and the rotational speed of the optical disk is controlled according to the detected rotational speed. Further, the reproducing position on the optical disc by the playback information (i.e., the laser beam irradiated position of a track) is known since the optical disk is to be accessed randomly.

However, since the above signals are not recorded on the recording disk, they must be manufactured in a structure of a signal track that enables recording of information. This signal track should be formed in the form of hills and valleys to indicate the tracking state, and an auxiliary signal indicating the rotational speed should be recorded on the signal track.

Accordingly, CD-R and CD-RW and so on and the optical disc is formed to a spiral signal track of a row in the form of peaks and valleys, the signal tracks of a conventional acid used as a signal track to record information. The wobbling signal of a certain period including an address indicating the physical position of the signal track is recorded on the signal track of the goal. By this wobbling signal, the rotational speed of the optical disc and the recording position (that is, the position of the signal track on which the laser beam is located) are detected.

In order to precisely follow the center of the signal tracks of the mountain and valley formed on the recording medium as described above, a three-beam and a one-beam tracking control apparatus called a push-pull method are commonly used. The 1-beam tracking control device is used in most information recording / reproducing devices because the configuration of the optical pickup can be simplified and the optical efficiency can be increased during recording as compared with the 3-beam tracking control method. A one-beam tracking control device having these advantages will be described in detail with reference to FIG. 1.

In Fig. 1, the one-beam tracking control apparatus includes a spindle motor 2 for rotating the optical disc 1, an optical pickup 3 for accessing the optical disc 1, and a serial to the optical pickup 3. The tracking error detector 4 and the tracking servo 5 which are connected are provided.

The optical pickup 3 includes a beam lifter BS for guiding the light beam from the laser diode LD toward the objective lens OL and the light beam from the objective lens OL toward the photodetector PD, respectively; An actuator AC is provided to move the objective lens OL up, down, left, and right to perform focusing and tracking.

The objective lens OL condenses a light beam directed toward the optical disc 1 via the beam splitter BS. The beam splitter BS causes the light beam from the laser diode LD to be irradiated to the signal track of the mountain or the valley of the valley of the optical disc 1 via the objective lens OL, and also by the optical disc 1. The reflected reflected light beam is directed toward the photodetector PD.

The actuator AC moves the objective lens OL left and right so that the light beam follows the center line of the signal track of the mountain or valley. The photodetector PD converts the amount of reflected light incident from the optical disk 1 via the objective lens OL and the beam splitter BS into an electrical signal. The photodetector PD is composed of four photodetectors A, B, C, and D for detecting the light distribution diagram irradiated onto the signal track. The tracking error detector 4 for inputting electrical signals from these four photodetectors A, B, C, and D is a sum signal A of electrical signals from the two photodetectors A and B on the left. The difference signal of the sum signal C + D of the electrical signals from the two photodetecting pieces C and D on the right side is detected and supplied to the tracking servo 5 as the tracking error signal.

For this purpose, the tracking error detector 4 is composed of a four input differential amplifier 4a and a low pass filter (LPF) 4b. The differential amplifier 4a differentially amplifies electrical signals from the four photodetectors A, B, C, and D to detect a difference signal from the sum signal of the electrical signals. The low filter 4b generates a tracking error detection signal by filtering the output signal of the differential amplifier 4a. The tracking servo 5, which inputs the tracking error signal Te from the low-pass filter 4b, uses the actuator AC in response to the tracking error signal Te to the left and right of the objective lens OL (i.e., the optical disc). The light beam is positioned at the center line of the signal track.

However, in the conventional tracking control apparatus, since the DC error is generated in the tracking error signal as the objective lens OL is moved in the horizontal direction, it is difficult to cause the light beam to follow the center line of the signal track. This DC offset occurs when the track center of the objective lens OL deviates from the rigid axis as shown in ⓐ and ⓒ of FIG. 2, while the center of the objective lens OL is positioned at the center of the optical axis as in ⓑ. It does not occur if it is located.

In detail, when the center of the objective lens OL deviates to the left (②) or the right (③) of the optical axis as shown in ⓐ, ⓒ of FIG. 2, the reflected light beam reflected by the optical disc 1 is Since the light is separated from the center, the light distribution irradiated to the two light detection pieces A and B on the left side of the photodetector PD and the two light detection pieces C and D on the right side are not symmetrical. This causes a DC offset. At this time, the tracking servo determines that there is no error and performs tracking along lines ② and ③.

On the other hand, when the center of the objective lens OL is located at the optical axis as shown in ⓑ of FIG. The light distribution irradiated to the detection pieces A and B and the two light detection pieces C and D on the right side become symmetrical. As a result, a DC offset occurs.

Therefore, in the 1-beam tracking control device, when the center of the objective lens is shifted left and right, crosstalk with adjacent tracks occurs and jitter becomes worse, so that the tracking error signal is generated in order to perform accurate tracking control. DC offset must be corrected.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problem, and generates a tracking signal for the left and right boundary using a wobble signal in space during optical disc playback, and a difference signal with respect to the average magnitude for a predetermined time of the tracking signal. It is an object of the present invention to provide a tracking method and apparatus for an optical disc, in which a light beam can travel along the center of a signal track, by outputting a tracking error signal to the tracking servo by correcting the offset by the tracking level difference at the interface.

Tracking method of an optical disc according to the present invention for achieving the above object,

Each of the wobble signals at each interface output from the photodetector is sampled in a space section and a tracking error signal is output from the sum of the left and right magnitude differences of the sampled wobble signals.

The left and right magnitudes of the wobble signal are characterized by being the difference signal of the maximum levels and the minimum level having the average magnitude of the sum by integrating the wobbled signal for a predetermined time.

Tracking apparatus for an optical disc according to the present invention,

High frequency signal generating means for generating a high frequency signal by the sum of the signals output from the four-segment photodetector;

Space detecting means for detecting a space from the high frequency signal of said high frequency signal generating means and outputting a gate control signal;

Tracking signal generating means for generating a left and right tracking signal by the sum of the signals sampled and held by the gate signal of the signal at each interface output from the four-segment photodetector by the gate control signal of the space detecting means; ;

Tracking level detection means for detecting the magnitude of each of the tracking signals of the tracking signal generating means to detect the average magnitude of the maximum and minimum signals for a predetermined time;

It is characterized in that it includes tracking error detecting means for detecting and outputting a tracking error signal by calculating the average magnitude difference between the signals output by the tracking level detecting means and adding them .

In the present invention, the tracking signal generating means integrates a plurality of sample / hold portions for sampling and holding the output signal of the photodetector according to the gate signal of the space detecting means, and the signals output from the sample / hold portions, respectively. And a plurality of low-pass filters and first and second adders for adding the integrated signals output from the low-pass filters and outputting the left and right tracking signals.

In the present invention, the tracking level detecting means includes a maximum / minimum detector for detecting the maximum / minimum magnitude of the tracking signal output from the tracking signal generating means, and a maximum / minimum magnitude output from the maximum / minimum detector. The first to the fourth integration unit for outputting the signal accumulated for a predetermined time, respectively, and the first to fourth average value detection unit for detecting the average magnitude of the signal integrated from the first to fourth integration unit.

In the present invention, the tracking error detecting means includes: first and second subtracting parts for obtaining a difference between maximum and minimum values with respect to the average signal size detected by the tracking level detecting means, and from the first and second subtracting parts. And first and second absolute value circuits for obtaining absolute values of the maximum and minimum values to be output, and an adder for adding signals output from the first and second absolute value circuits.

Hereinafter, with reference to the accompanying drawings as follows. 3 is a block diagram showing an embodiment of an optical disk tracking device according to the present invention, Figure 4 is a view showing an example of the tracking signal waveform when the offset occurs in accordance with the present invention.

As shown in FIG. 3, the optical disc tracking apparatus according to the present invention includes a high frequency signal generator 110 for generating a high frequency signal RF by adding each boundary signal of the quadrature photodetector PD, and the high frequency signal. The four-part photodetector PD is detected by the space detector 120 that detects a space section from the output high frequency signal of the signal generator 110 and outputs a gate signal, and the gate control signal of the space detector 120. Sampling, holding and integrating each of the signals (A, B, C, D) output from the) and add the left and right signals to the tracking signal generator 130 to generate a tracking signal And a tracking level detector 140 for obtaining a maximum / minimum size of the tracking signal generated by the tracking signal generator 130 and detecting an average size of the tracking signal accumulated over a predetermined time period, and the tracking level detector 140. Average signal amplitude Obtaining a difference of the addition to this, the tracking error signal, is configured to include a tracking error detection unit 150 for detecting (Se Shift error) and output.

The tracking signal generation unit 130 includes a plurality of parallel connected sampling and holding output signals A, B, C, and D of the four-segment photodetector PD, respectively, according to the gate signal of the space detector 120. Sample / hold units (S / H) 131a to 131d, a plurality of low pass filter (LPFs) 132a to 132d for integrating each of the signals output from the sample / hold units 131a to 131d, and The first and second adders 133a and 133b output the left and right tracking signals S1 and S2 by adding signals output from the low pass filters 132a to 132d to the left and right signals.

The tracking level detector 140 detects first and second maximum / minimum values of the maximum and minimum magnitudes of the tracking signals S1 and S2 output from the first and second adders 133a and 133b, respectively. 141a and 141b, first to fourth integrators 142a to 142d for outputting a maximum / minimum sum signal obtained by integrating the maximum / minimum value for a predetermined time, and an average magnitude of the maximum / minimum sum signal. It is the structure containing the 1st-4th average value detectors 143a-143d to detect.

The tracking error detector 150 obtains first and second subtractors for obtaining difference signals between the first and third average detectors 143a and 143b and difference signals between the second and fourth average detectors 141b and 143d. First and second absolute value circuits 152a for obtaining absolute values of the difference signals of the first and second subtractors 151a and 151b, and the first and second absolute value circuits. The adder 153 which adds the signal output from 152a, 152b, and outputs the tracking error signal Se is comprised.

The tracking method and apparatus for an optical disk according to the present invention configured as described above will be described with reference to the accompanying drawings.

First, the output signals A, B, C, and D of the four-segment photodetector PD are input to the high frequency signal generator 110 and added (A + B + C + D) to generate a high frequency signal (RF). This high frequency signal is input to the space detector 120 to detect a zero crossing and detect only a space section. The space signal is output to the tracking signal generator 130 as a gate signal.

In addition, the tracking signal generator 130, which receives the signals A, B, C, and D at each interface output from the four-segment photodetector PD, corresponds to the gate signal of the space detector 120. After sampling in the space section and integrating the held signal in the other section, the first and second tracking control signals S1 and S2 which are left and right signals are generated.

To this end, the tracking signal generator 130 includes a sample / hold unit (S / H) 131a to 131d, a low pass filter 132a to 132d, and adders 133a and 133b, and the sample / hold unit 131a. 131d) is connected in series to the quadrature photodetector PD to sample and hold each of the signals A, B, C, and D at the interface by the gate signal Gate. The signals output from the sample / hold sections 131a to 131d are inputted to the low pass filters 132a to 132d, respectively, and then integrated at a level corresponding to the wobble frequency, and among the integrated signals, the left signals A and B. Is the first tracking signal S1 after being added (A + B) by the first adder 133a, and the right signals C and D are added by the second adder 133b and then added by the second tracking signal S1. It is output as the tracking signal S2.

Here, signals S1 (A + B) and signals S2 (C + D) are wobble signals at left and right boundaries that are sampled and held only in space. The level change of the first tracking signal S1 and the second tracking signal S2 is shown in FIG. 4, and (a) of FIG. 4 is the signal S1 and S2 signal waveforms when tracking is performed as shown in FIG. 4 (b) and 4 (d) show signals S1 and S2 waveforms when they are tracked as shown in 1 and 3 in FIG. 2, respectively.

The first and second tracking signals S1 and S2 generated from the tracking signal generator 130 are input to the tracking level detector 140, and the tracking level detector 140 is the maximum / minimum size of the signal level. After obtaining the output signal to the tracking error detector 150 as the average value of the integrated signal for a predetermined time.

 To this end, the tracking level detector 140 includes first and second maximum / minimum value detectors 141a and 141b, first to fourth accumulators 142a to 142d, and first to fourth average value detectors 143a to 143d. Having a

The first maximum / minimum value detector 141a detects the maximum value S1_Max and the minimum value S1_Min of the first tracking signal and outputs the first and second accumulators 142a and 142b, respectively. The two integrators 142a to 131d integrate the maximum value and the minimum value for a predetermined time and output the sum SUM to the first and second average value detectors 143a and 143b, and the first average value detector 143a The average value S1_Min_av of the integrated sum signal of the minimum value and the second average value detector 143b detect the average value S1_Max_av of the integrated sum signal of the maximum value, respectively.

Meanwhile, the second maximum / minimum value detector 141b detects the maximum value S2_Max and the minimum value S2_Min of the second tracking signal and outputs the third and fourth accumulators 142c and 142d, respectively. The fourth accumulators 142c and 142d integrate the maximum and minimum values for a predetermined time and output the sums to the third and fourth average value detectors 143c and 143d, respectively, and the third average value detector 143c is the minimum value. The average value S2_Min_av of the integrated sum signal is detected and output, and the fourth average value detector 143d detects and outputs the average value S2_Max_av of the maximum sum signal.

Referring to FIG. 4A, the values S1_Max, S1_Min, S2_Max, and S2_Min are determined from the first and second tracking signals S1 and S2 detected by the first and second maximum / minimum value detectors 141b. Each signal is detected, and the sum signal accumulated over a predetermined period (time) is detected from each signal to detect the maximum / minimum average level of the two signals, so that each level according to the movement of the two signals S1 and S2 is a space level GL. ; Average size at (Space Level).

The tracking error detector 150 detects the difference signal between the minimum average sizes of the two signals and the difference signal between the maximum average magnitudes, calculates the absolute value of the difference signal, and adds the absolute value to the tracking error signal (Se; Shift error). do.

To this end, the tracking error detector 150 includes first and second subtractors 151a and 151b, first and second absolute value circuits 152a and 152b, and an adder 153.

The first subtractor 151a receives the minimum average level of the first tracking signal of the first average value detector 143a as a non-inverting terminal (+), and applies it to the second tracking signal of the third average value detector 143c. The minimum average level is input to the inverting terminal (-) to detect the difference signal between the two levels, and the second subtractor 151b determines the maximum average level of the first tracking signal of the second average detector 143b as the non-inverting terminal. The signal is input as (+) and the maximum average level of the second tracking signal of the fourth average value detector 143d is input to the inverting terminal (−) to detect the difference signal.

The first absolute value circuit 152a takes an absolute value (| S1_Min_av-S2_Min_av |) of the difference signal of the first subtractor 151a, and the second absolute value circuit 152b takes an absolute value of the difference signal of the second subtractor 151b. (| S1_Max_av-S2_Max_av |), and outputs to the adder 153. The adder 153 adds the output values of the first and second absolute value circuits 151a and 151b to generate and output a tracking error signal Se, which is a final error signal.

As the tracking error signal Se is detected, the left and right tracking is always spaced apart from the space level GL at a constant level interval in FIG. 4.

Therefore, when the tracking error signal Se is minimized and applied to the tracking servo, the tracking servo can remove the offset amount according to the movement of the objective lens by using the actuator according to the tracking error signal, so that the light beam is objective. By correcting the DC offset according to the movement of the lens can follow the wobbled signal track and indicate its direction.

As described above, the present invention is capable of recording by correcting the offset of the signal track by the sum of the left and right magnitudes of the wobble signals sampled and held with respect to the space level using the wobble signals generated from an information recording medium such as an optical disc. It is possible to perform effective tracking by space section regardless of the header of the format of the disc.

Claims (9)

The light reflected from the optical disk is detected as the first to fourth signals using a quadrature photodetector, the first and second signals are summed to output the first tracking signal, and the third and fourth signals are summed to the second tracking. And a tracking error signal is obtained by summing the difference between the maximum value and the minimum value of the first tracking signal and the second tracking signal after outputting the signal. The method of claim 1, The first and second signals are optical disc tracking method, characterized in that the output signal from the optical detector located on the left or right with respect to the traveling direction of the optical pickup The method of claim 2, And the third and fourth signals are signals output from an optical detector located opposite to the photo detectors outputting the first and second signals. The method of claim 1, In outputting the first to fourth signals using the four-segment photodetector, the optical disc tracking method outputs a signal by sampling only a space portion. The method of claim 1, And in calculating the difference between the maximum value and the minimum value, the difference between the average value of the maximum value of the first tracking signal and the second tracking signal and the average value of the minimum value. Means for generating a high frequency signal by the sum of the signals output from the four-segment photodetector; Means for detecting a gate control signal by detecting only a space portion from the high frequency signal of the high frequency signal generating means; Means for sampling and holding a signal output from the quadrature photodetector by a gate control signal of the space detecting means to generate first and second tracking signals; Means for integrating magnitudes for each of the first and second tracking signals of the first and second tracking signal generating means for a predetermined time period and detecting a tracking level having an average magnitude of the maximum and minimum signals thereof; And means for obtaining a difference between the maximum and minimum values of the tracking levels detected by said tracking level detecting means and adding the sums to detect a tracking error signal. The method of claim 6, The tracking signal generating means includes a plurality of sample / hold parts for sampling and holding each interface output signal of the photodetector according to the gate signal of the space detecting means, and a plurality of low ranges for integrating each of the signals output from the sample / hold parts. And a first and second adders for adding the filter and the integrated signal outputted from the low pass filter and outputting the integrated signal as the first and second tracking signals. The method of claim 6, The tracking level detecting means includes: a maximum / minimum value detector for detecting a maximum / minimum magnitude for each of the first and second tracking signals of the first and second tracking signal generating means, and a maximum output from the maximum / minimum value detector. The first to fourth integrators respectively outputting signals obtained by integrating the minimum / minimum magnitudes for a predetermined time, and the first to fourth average value detectors respectively detecting the average magnitudes of the signals integrated from the first to fourth integrators. Tracking device for an optical disc comprising the. The method of claim 6, The tracking error detecting means includes first and second subtracting parts for obtaining a difference between maximum and minimum values with respect to the average signal size processed by the tracking level detecting means, and maximum and output values from the first and second subtracting parts. And first and second absolute value circuits for obtaining absolute values of minimum values, and an adder for adding signals output from the first and second absolute value circuits.

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