KR19990011987A - Tracking Servo Device of DVD System - Google Patents

Abstract

The present invention relates to a tracking servo device of a DVDR system which drives and controls an optical pickup unit so that a laser beam of an optical pickup unit is accurately followed along a track of the optical disc using a tracking error signal detected corresponding to the amount of light reflected from the optical disc. The tracking error signal is detected by the DPD method in the recording and erasing mode of the DVDR in which the pit is already formed in the optical disc. The tracking error signal is detected by the push pull method in the recording mode of the DVDR without the pit previously formed in the optical disc. By providing the DVDR tracking servo device that can be detected, there is an effect that the reliability of the DVDR system can be enhanced by the stable tracking servo.

Description

Tracking Servo Device of DVD System

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tracking servo device of a DVDR system (Digital Video Disc Recoder System). In particular, during playback and erasing, a tracking error signal is detected by a DPD method (Differential Phase Detection Method) and a push signal is recorded. The present invention relates to a tracking servo device of a DVDR system capable of detecting a tracking error signal by a push-pull method.

In general, optical discs are read-only type in which the user can only play the information according to its function and purpose, and additional recording type and repetitive recording of information that the user can record once and read the recorded information many times but cannot erase and re-record It can be divided into erasing rewritable type that can be erased and reproduced. Among such optical discs, a system capable of recording, erasing and playing on an erasable rewritable optical disc is commonly referred to as a DVDR system.

On the other hand, when recording, erasing, and reproducing certain data on such an erased rewritable optical disc, the laser beam of the optical pickup unit accurately follows the signal surface of the optical disc in order for the optical pickup unit of the DVDR system to accurately record, erase, and reproduce the data on the optical disc. Should be. As such, adjusting the laser beam of the optical pickup portion to accurately follow the track of the optical disc is commonly referred to as tracking servo, and such tracking servo is performed by the tracking servo device.

The tracking servo device measures the extent to which the laser beam of the optical pickup part deviates from the track center, that is, the tracking error signal, by using the light reflected from the optical disk, and then compensates for the error. In this case, a three spot method, a DPD method, a push-pull method, and the like are commonly used as a method for detecting a tracking error using light reflected from an optical disk.

Among these tracking error detection methods, the three-spot method uses a diffraction grating to make two servo spots symmetrical about the main beam, and then detects the tracking error signal by using the difference in the amount of light detected at the two servo spots. As a reliable method, the optical system has a complicated structure, and high precision is required for the angle of the diffraction grating.

FIG. 1 is a principle diagram illustrating a method of detecting a tracking error signal by a push-pull method in a DVDR playback mode. The push-pull method includes a two-segmented photodiode and one beam, and an optical pickup unit (not shown). A method of detecting a tracking error by detecting the reflected light reflected from the disk reflected by the disk in each of the two divided photodiodes and comparing the difference of the detected amounts of light, as shown in FIG. When the amount of light detected by the photodiodes D1 and D2 coincides, a tracking error signal is generated to zero, indicating that the beam is exactly coincident with the track, and as shown in Figs. 1A and 1C, a two-divided photodiode ( If the amount of light detected at D1 and D2 is different, it can be seen that the beam is off the track in the direction in which the amount of light is detected.

While the push-pull method is simple in configuration, there is a problem in that a DC offset appears in the tracking error signal due to various factors such as the objective lens deviating from the optical axis or the radial direction of the disk.

Accordingly, a DPD method in which the push-pull method is improved in two directions has been developed, and a principle for explaining a method of detecting a tracking error in the playback and erase modes of a DVDR using the DPD method is shown in FIG. 2.

As shown in FIG. 2, in the DPD method, the reflected light reflected from the optical disk is detected using a four-divided photodiode, and the relative of two tones D1 and D3, D2 and D4 located in the diagonal direction of the four-divided photodiode. The tracking error is detected by detecting the time difference. Such a tracking error detection method by the DPD method has been mainly used in the conventional reproducing optical disc player because of the small influence of the offset current.

However, since the DPD method uses the intensity distribution according to the relative positional change of the beam and the mark, a relatively accurate tracking error can be detected in the playback mode or the erase mode of the DVDR in which the mark is formed on the optical disc. There was a problem that a tracking error signal cannot be detected when trying to record predetermined data on an optical disc that is not in use.

FIG. 3 illustrates a method of detecting a tracking error signal by a DPD frame in the recording mode of the DVDR. When the laser beam coincides with a track as shown in FIG. 3A, FIG. 3B and FIG. 3C are shown. As described above, even when the laser beam deviates to the left and right sides of the track, the tracking error signal cannot be detected because the sum of the amount of currents detected in the photodiode in the diagonal direction is always constant. This is because the difference in reflectance is not determined by the difference in reflectance between the portion where the mark is formed and the portion where the mark is not formed, but by the difference in reflectance between the land and the groove. This is because the sum of the amounts of reflections detected by the photodiode located at is always constant.

Therefore, in order to accurately record predetermined data on an optical disc on which no mark is formed, a tracking servo apparatus capable of detecting a tracking error and performing a tracking servo is required even on an optical disc on which an mark is not formed.

Accordingly, the present invention has been made in view of the above-described problems, and an object of the present invention is to provide a DPD method with less influence of offset current in the recording and erasing mode of a DVDR in which a mark is already formed on an optical disc. The tracking error signal can be detected and the tracking error signal can be detected by using a push pull method that can detect the tracking error signal with or without a mark in the recording mode of a DVDR without a mark previously formed on the optical disc. To provide a tracking servo device of the DVDR.

In order to achieve the above object, in the present invention, the amount of light reflected from the optical disk is detected by each photodetector divided into a predetermined number, and the tracking error signal corresponding to the amount of light detected by the photodetector is measured. A tracking servo device of a DVDR system for driving control of an optical pickup unit by using an error signal so that the laser beam of the optical pickup unit follows the tracks of the optical disc in the recording, erasing, and reproducing modes of the DVDR system; A photodetector for detecting an amount of light reflected from the optical disk by the photodetector divided into a predetermined number and generating a current corresponding to each amount of light detected by the divided photodiode; A current-voltage converter for converting and outputting each current generated by the photodetector into a predetermined voltage; A first tracking error detector for detecting a tracking error signal using a time difference between the voltages output from the current-voltage converter; A second tracking error detector for detecting a tracking error signal by using a voltage difference between the voltages output from the current-voltage converter; An error correction unit for correcting a tracking error signal applied by the first tracking error detector or the second tracking error detector; A switching unit for connecting and switching the error correction unit to a first tracking error detection unit or the second tracking error detection unit; The present invention provides a tracking servo device for a DVDR system, comprising a microcomputer for controlling switching of the switching unit in response to recording, erasing, and reproducing modes of the DVDR system.

1 is a principle diagram for explaining a tracking error detection method by a push-pull method in a playback and erase mode of a DVDR system;

2 is a principle diagram for explaining a tracking error detection method by a DPD method in a playback and erase mode of a DVDR system;

3 is an exemplary diagram for explaining a problem of a tracking error detection method by a DPD method in a recording mode of a DVDR system;

4 is a circuit diagram showing a tracking servo device of the DVDR system according to the present invention;

Degree. 5 is an exemplary view showing a method of detecting a tracking error signal in a recording mode of a DVDR by using a tracking servo device of a DVDR system according to the present invention;

6 is an exemplary view showing a method of detecting a tracking error signal in a playback and erase mode of a DVDR using a tracking servo device of a DVDR system according to the present invention;

FIG. 7 is a waveform diagram illustrating an output waveform of a current-voltage converter in a process of detecting a tracking error signal in a playback and erase mode of a DVDR using a tracking servo device of a DVDR system according to the present invention; FIG.

FIG. 8 is a waveform diagram illustrating output waveforms of a first comparator, a second comparator, and a time difference detector in a process of detecting a tracking error signal in a playback and erase mode of a DVDR using a tracking servo device of a DVDR system according to the present invention; FIG.

* Explanation of symbols for main parts of the drawings

100: key input unit 200: microcomputer

300: photodetector 400: current-voltage converter

500: first tracking error detector 600: second tracking error detector

510: first comparator 520: second comparator

530: time difference detector 540: integrator

600: differential amplifier 700: switching unit

800: error correction unit 810: phase compensation unit

820: pickup drive unit

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

4 is a circuit diagram illustrating a tracking servo device of the DVDR system according to the present invention, and includes a key input unit 100, a microcomputer 200, a photodetector 300, a current-voltage converter 400, and a first tracking error detector. 500, a second tracking error detection unit 600, a switching unit 700, and an error correction unit 800.

Hereinafter, the function and structure of each component constituting the tracking servo of the DVDR system according to the present invention will be described.

First, the key input unit 100 includes a plurality of function keys including a recording key, an erasing key, and a reproducing key, and generates a key signal for controlling the operation of the DVDR system as desired by the user.

The microcomputer 200 controls the overall operation of the DVDR system and, in particular, controls the switching of the switching unit 700 in response to the key signal generated from the key input unit 100.

The photodetector 300 is composed of four divided photodiodes D1, D2, D3, and D4, and detects the reflected light reflected from the optical disk, respectively, and generates a current corresponding to the detected reflected light.

The current-voltage converter 400 includes four current-voltage converters 410, 420, 430, and 440, and the first current-voltage converter 410 and the second current voltage converter 420 The sum of the currents detected by the photodiodes D1 and D3, D2 and D4 positioned diagonally to each other among the four divided photodiodes, is converted into a predetermined voltage, and the third current-voltage converter and the fourth current-voltage converter The units 430 and 440 convert the sum of the currents detected by the photodiodes D1 and D4, D2 and D3 located in the same direction among the four divided photodiodes into a predetermined voltage.

The first tracking error detector 500 includes a first comparator 510, a second comparator 520, a time difference detector 530, and an integrator 540, and each performs the following functions.

The first comparator 510 and the second comparator 520 convert a voltage output from the first current-voltage converter 410 and the second current-voltage converter 420 into a predetermined pulse signal, respectively, and time difference. The detector 530 detects a time difference between the pulse signals converted by the first comparator 510 and the second comparator 520, and the integrator integrates the pulse signal output from the time difference detector 530 to detect a tracking error at a predetermined voltage level. Output the signal.

The second tracking error detection unit 600 is composed of a differential amplifier having two input terminals and one output terminal, and is converted from the third current-voltage converter 430 and the fourth current-voltage converter 440. The difference between the voltages is amplified and output.

The switching unit 700 connects either the first tracking error detector 500 or the second tracking error detector 600 to the error correction unit 800 under the control of the microcomputer 200.

The error correction unit 800 compensates, amplifies, and outputs a phase of the tracking error signal provided by the first tracking error detector 500 or the second tracking error detector 600 through the switching unit 700. 810 and a pickup driver 820 for driving the optical pickup unit to compensate for the tracking error signal.

An operation process of the tracking servo device of the DVDR system according to the present invention, which includes the above-described constituent members, will be described with reference to FIGS.

The gist of the present invention is to perform tracking servo using the DPD method in the playback and erase mode of a DVDR system in which an optical disc on which an existing mark is formed is used, according to whether a mark is formed, and an existing mark is formed. Since the push-pull method is used in the recording mode of a DVDR system that uses an optical disc that does not have an optical disc, the following description will be given to the case where the DVDR system is in the recording mode and the DVDR system is in the play and erase mode.

First, when the DVDR system is in the play and erase mode, the operation and effects of the tracking servo device according to the present invention are the same.

In order to read predetermined information from the optical disc mounted on the optical disc, when a user presses a reproduction key provided in the key input unit 100, the key input unit 100 generates a reproduction key signal, and the generated reproduction key signal is a microcomputer ( 200).

The microcomputer 200 receiving the playback key signal 200 from the key input unit 100 controls the entire DVDR system so that the mounted optical disc can be played, and the switching unit 700 controls the first tracking error detection unit 500. The controller 700 is connected to the integrator 540, and the switching unit 700 is connected to the integrator 540 under the control of the microcomputer 200, and subsequently receives a tracking error signal output from the integrator 540. ) Is provided to the phase compensator 810.

On the other hand, under the control of the microcomputer 200, the optical pickup unit (not shown) irradiates the signal surface of the optical disk with a laser beam of a predetermined level for reproduction, thereby reading the information recorded on the signal surface of the optical disk. . At this time, a part of the laser beam irradiated to the optical disk signal surface is reflected from the signal surface of the optical disk, the reflected light of the laser beam reflected in this way is a photodetector consisting of four divided optical diodes (D1, D2, D3, D4) Detected at 300, each photodiode D1, D2, D3, D4 generates currents I1, I2, I3, I4 corresponding to the detected amount of light, respectively.

As such, the currents I1, I2, I3, and I4 generated by the photodetector 100 are in the diodes D1, D3, D2, and D4 located in the diagonal direction of the four-divided photodiodes D1, D2, D3, and D4. The generated currents are added together, and the added current I1 + I3 is provided to one end of the first current-voltage converter 410, and I2 + I4 is provided to one end of the second current-voltage converter 400.

The first current-voltage converter 410 converts the addition current I1 + I3 provided by the photodetector 100 to a predetermined voltage V1 and provides the converted current to the non-inverting input terminal (+) of the first comparator 510, and the second current- The voltage converter 420 converts the addition current I2 + I4 into a predetermined voltage V2 and provides it to the non-inverting input terminal (+) of the second comparator 520.

In this case, as shown in FIG. 6, the voltages V1 and V2 have different waveforms according to the positions of the marks and beams, and the waveforms are as follows.

If the laser beam coincides with the track as shown in Fig. 6B, along the path the laser beam travels along the signal plane of the optical disc, the mark will pass from the center of D 1 and D 2 to the center of D 3 and D 4, As a result, since the voltages V1 and V2 have the same phase as the two voltages as shown in FIG. 7B, no time difference will occur as shown in FIG. 8B, and a zero pulse will be output from the time difference detector 530.

On the other hand, as shown in FIG. 6A, if the radar beam is moved to the right side of the track, the mark will pass through D1 through D4. Therefore, as shown in FIG. 7A, the phase of the voltage V2 becomes faster than V 1, and the phase difference at this time is a time difference. The time difference Δt will be generated as shown in FIG. 8A, and the time difference detection unit 530 outputs a high signal in the section in which the time difference occurs.

In addition, as shown in FIG. 6C, when the radar beam deviates to the left side of the track, the mark will pass through D2 through D3. Thus, as shown in FIG. 7C, the phase of the voltage V1 becomes faster than V2, and at this time, the time difference detector 530. Outputs a low pulse in a section in which a time difference Δt occurs, such as 8c.

As described above, in each case, the pulse signal detected by the time difference detector 530 is provided to the integrator 540, and the integrator 540 integrates the pulse signal output from the time difference detector 530 into an analog signal. Output the made tracking error signal.

On the other hand, since the switching unit 700 connects the first tracking error detection unit 500 and the error correction unit 800 under the control of the microcomputer 200, the tracking error signal output from the integrator 540 is phase compensated. Provided in section 800.

The phase compensator 810, which receives the tracking error signal from the integrator 540, compensates the phase of the tracking error signal, amplifies it, and provides it to the driver 900. In the driver 500, the phase compensator 400 performs the compensation. The driving signal for driving the tracking actuator coil is generated by the output drive control signal, and the tracking actuator coil (not shown) is driven by the driving signal generated by the driving unit 500.

The objective lens is moved left and right by driving the actuator coil, and the laser beam of the optical pickup unit is adjusted to follow the track of the optical disc accurately by the movement of the objective lens.

The operating process of the tracking servo device according to the present invention when the DVDR system is in the playback mode has been described above. Hereinafter, the operation process of the tracking servo device according to the present invention when the DVDR system is in the recording mode will be described. do.

First, when a recording key signal is generated from the key input unit 100 by a user's key manipulation, the generated key signal is applied to the microcomputer 200, and the microcomputer 200 switches the second tracking error detection unit. The switching unit 700 is controlled to switch the connection to 600.

Therefore, the switching unit 700 is connected to the second tracking error detection unit 600 by switching the connection if previously connected to the first tracking error detection unit 500 under the control of the microcomputer 200, and previously, the second If it is the state connected to the tracking error detection part 600, the state will be maintained.

On the other hand, under the control of the microcomputer 200, the optical pickup unit (not shown) irradiates the signal surface of the optical disk with a laser beam of a predetermined level for recording, thereby recording predetermined information on the signal surface of the optical disk. Done. At this time, a part of the laser beam irradiated to the optical disk signal surface is reflected from the signal surface of the optical disk, the reflected light of the laser beam reflected in this way is a photodetector consisting of four divided optical diodes (D1, D2, D3, D4) Detected at 300, each photodiode D1, D2, D3, D4 generates currents I1, I2, I3, I4 corresponding to the detected amount of light, respectively.

As such, the currents I1, I2, I3, and I4 generated by the photodetector 100 are in the diodes D1, D4, D2, and D3 located in the same direction of the four-divided photodiodes D1, D2, D3, and D4. The generated currents are added together, and the added current I1 + I4 is provided to one end of the third current-voltage converter 430, and I2 + I3 is provided to one end of the fourth current-voltage converter 440.

The third current-voltage converter 430 converts the addition current I1 + I4 provided from the photodetector 300 into a predetermined voltage, and provides it to one end of the second tracking error detector 600, and the fourth current-voltage converter 440 converts the addition current I2 + I3 provided from the photodetector 300 into a predetermined voltage and provides them to the other input terminal of the second tracking error detection unit 600, respectively.

Here, according to the positions of the mark and the beam, as shown in Fig. 5, the amount of light to be detected varies, respectively, whereby a tracking error signal is detected.

For example, when the beam passes through the center of the track, that is, the center of the land, grooves having a difference in reflectivity compared to the land appear the same on both sides of the beam, so that the diodes are located in the same direction. The two addition currents I1 + I4 and I2 + I3 become equal, and therefore no tracking error occurs.

On the other hand, when the beam follows the right side of the track, the currents of the two addition currents I1 + I4 of the diodes located in the same direction become smaller than I2 + I3, so that the tracking error is positive.

On the other hand, when the beam follows the left side of the track, the currents of the two addition currents I1 + I4 of the diodes located in the same direction become larger than I2 + I3, so that the tracking error is negatively generated.

The second tracking error detector 600 includes a differential amplifier having two input terminals and one output terminal, and includes two input voltages provided by the third current-voltage converter 430 and the fourth current-voltage converter 440. The difference is detected and a tracking error signal is generated.

At this time, since the switching unit 700 connects the second tracking error detection unit 600 and the error correction unit 800 under the control of the microcomputer 200, the tracking error output from the second tracking error detection unit 600. The signal is provided to the phase compensator 800 via the switching unit 700.

Thereafter, the phase compensator 800 phase-compensates, amplifies, and provides the tracking error signal provided from the differential amplifier 600 to the driver 900.

The driver 500 generates a drive signal for driving the tracking actuator coil by the drive control signal output from the phase compensator 400, and the tracking actuator coil is driven by the drive signal generated by the driver 500.

The objective lens is moved left and right by driving the actuator coil, and the laser beam of the optical pickup unit is adjusted to follow the track of the optical disc accurately by the movement of the objective lens.

As described above, according to the present invention, in the tracking servo device of the DVDR system, in order to record predetermined information on an optical disc on which no mark is formed, the tracking error signal is detected by using the push-pull method, and the mark is When the playback and erasing operation is performed on the formed optical disc, the tracking error signal is detected by the DPD method which has little influence on the offset or the depth of the mark, and the tracking servo is performed to improve the reliability of the DVDR system by the stable tracking servo. It can be effective.

Claims (7)

The amount of light reflected from the optical disc is detected by each photodetector divided into a predetermined number, the tracking error signal corresponding to the amount of light detected by the photodetector is measured, and then the recording error signal is used to record the DVDR system. A tracking servo device of a DVDR system for controlling driving of an optical pickup unit so that the laser beam of the optical pickup unit follows the tracks of the optical disk in the erase and reproduction mode; A photodetector for detecting an amount of light reflected from the optical disk by the photodetector divided into a predetermined number and generating a current corresponding to each amount of light detected by the divided photodiode; A current-voltage converter for converting and outputting each current generated by the photodetector into a predetermined voltage; A first tracking error detector for detecting a tracking error signal using a relative time difference between the voltages output from the current-voltage converter; A second tracking error detector for detecting a tracking error signal by using a voltage difference between the voltages output from the current-voltage converter; An error correction unit for correcting a tracking error signal applied by the first tracking error detector or the second tracking error detector; A switching unit for connecting and switching the error correction unit to a first tracking error detection unit or the second tracking error detection unit; And a microcomputer for controlling switching of the switching unit in response to the recording, erasing, and reproducing modes of the DVDR system. 2. The tracking servo device of a DVDR system according to claim 1, wherein said photodetector comprises four divided photodiodes D1, D2, D3, and D4. The method of claim 2, wherein the current-voltage converter, A first current-voltage converter for converting a sum of currents generated in photodiodes D1 and D3 disposed diagonally among the four divided photodiodes into a predetermined voltage; A second current-voltage converter for converting a sum of currents generated in photodiodes D2 and D4 positioned diagonally from each of the four divided photodiodes into a predetermined voltage; A third current-voltage converter for converting a sum of currents generated in photodiodes D1 and D4 located in the same direction among the four divided photodiodes into a predetermined voltage; And a fourth current-voltage converter for converting a sum of currents generated in photodiodes D2 and D3 located in the same direction among the four divided photodiodes into a predetermined voltage. The method of claim 3, wherein the first tracking error detector, A first comparator for converting the voltage output from the first current-voltage converter into a predetermined pulse signal; A second comparator for converting the voltage output from the second current-voltage converter into a predetermined pulse signal; A time difference detector for detecting a relative time difference between the pulse signals converted by the first comparator and the second comparator; And an integrator for generating a signal detected by the time difference detector as a tracking error signal having a predetermined level. The method of claim 3, wherein the second tracking error detector, And a differential amplifier for amplifying and outputting a difference between two voltages converted by the third current-voltage converter and the fourth current-voltage converter. The tracking servo device according to any one of claims 1 to 5, wherein the switching unit is connected to the first tracking error detection unit when the DVDR system is in a play and erase mode. 7. The tracking servo apparatus of claim 6, wherein the switching unit is connected to the second tracking error detection unit when the DVDR system is in a recording mode.