KR20050062090A - Tracking servo controller using rotatable grating and method thereof - Google Patents

Abstract

The present invention provides an auxiliary beam and a main beam to perform tracking servo control by applying a differential push-pull (DPP) method to a read only memory (DVD-ROM) and a random access memory (DVD-RAM) having different track pitch sizes. A tracking servo control apparatus and a control method for adjusting the interval of a light by using a rotatable diffractive lens, comprising: a light source; Diffraction gratings; Rotating means for rotating the diffraction grating; Objective lens; Optical path converting means; A collimating lens positioned between the light path converting means and the objective lens to collimate the light source; The photodiode is located at the top or the bottom of the same line as the optical path converting means, and the area of the photodiode reaching the main beam to detect a tracking error signal from the three reflected light reflected from the disk through the optical path converting means is divided into four areas. A light splitting detector divided into two regions of each photodiode to which each auxiliary beam arrives; And tracking control means for performing tracking control according to the tracking error signal input from the light splitting detector, and determining the type of the disc to control the rotating means in the case of the DVD-RAM disc to rotate the diffraction grating at a predetermined angle. There is provided a tracking servo control device comprising a.

Description

Tracking servo controller using rotatable diffractive lens and its control method {Tracking servo controller using rotatable grating and method

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tracking servo control apparatus and a control method thereof, and in particular, applies a differential push-pull (DPP) method to a read only memory (DVD-ROM) and a random access memory (DVD-RAM) having different track pitch sizes. The present invention relates to a tracking servo control device and a control method of controlling a distance between an auxiliary beam and a main beam by using a rotatable diffractive lens to perform tracking servo control.

Discs are usually classified into CDs and DVDs. CDs are divided into CD-ROMs (Read Only Memory, hereinafter referred to as 'ROM') and CD-RAMs (Random Access Memory, hereinafter referred to as 'RAM'). It is divided into DVD-ROM and DVD-RAM.

In addition, the DVD is divided into DVD-S (Single) and DVD-D (Dual) according to the recording of information. Here, the CD is divided into a product that contains only audio information and video information and audio information, and the DVD is a DVD-S in which only one information is recorded in a single layer on one track, and one Two pieces of information on the track are divided into DVD-Ds recorded simultaneously in dual layers.

1A, 1B, and 1C show a layer structure as disc cross sections of CD, CD-R, and DVD, respectively. As recorded in each figure, the thickness of the whole disc is about 1.2 mm for CD, CD-R, and DVD.

In the CD 100 shown in Fig. 1A, a disc substrate (transparent layer) is made of a transparent polycarbonate resin, a polyvinyl chloride resin, an acrylic resin, or the like, having a high light transmittance and mechanical resistance or chemical resistance. ) 101 is molded.

In the disk substrate 101, a pit is transferred by a stamper assembled into a molding die on one main surface, and a signal surface 102 is formed. The pits on the signal surface 102 are formed in the disc substrate 101 as encoded small holes having different lengths in the circumferential direction corresponding to the predetermined information signals, respectively, to constitute a recording track.

On the surface of the disk substrate 101 on which the signal surface 102 is formed, aluminum or the like having a high light reflectance is deposited to form a reflective layer 103 as a signal recording layer, and a protective layer 104 is coated on the entire surface. 100 is formed.

For this CD 100, laser light from the disk drive apparatus is incident on the disk surface 105 side, so that the information recorded on the signal surface 102 is detected from the reflected light.

The CD-R 110 shown in FIG. 1B is an additional recordable medium. The CD-R 110 has the same physical characteristics (diameter, weight, thickness) and capacity as the CD 100. It is possible to use it, and the longevity is also long, which is suitable for data storage.

This CD-R 110 is also arranged with a transparent disk substrate (polycarbonate) 111 as seen from the disk surface 116 side. On the disk substrate 111, an organic dye layer 114 as a signal recording layer, a gold reflective layer 113, and a protective layer 115 are sequentially stacked to form a CD-R 110.

In this CD-R 110, grooves (groups) serving as irradiation guides of laser light are engraved in the recording, and the organic dye layer 114 covers this group. Then, the organic dye layer 114 and the disk substrate 111 made of polycarbonate react with the heat of the irradiated laser light to form a pit according to the information signal on the group, and the signal surface 112 on which the actual data is recorded. ) Is formed.

Likewise, in the DVD 120 shown in FIG. 1C, the disk substrate 121 is disposed from the disk surface 128, and a signal surface is formed on the other surface side of the disk substrate 121. In the case of DVD, it is called a one-layer disk having a single signal surface, and a two-layer disk having a two signal surfaces is proposed, but two types have been proposed, and FIG. 1C shows an example of a two-layer disk. That is, the data recording layer of the first layer is formed by the first signal surface 122 and the first reflective layer 123 corresponding to the first signal surface 122.

In addition, the second recording layer 124 and the second reflection layer 125 corresponding to the second signal surface 124 form the second data recording layer. The second reflective layer 125 is a bonding layer 126, through which the dummy substrate 127 is bonded.

The first reflective layer 123 is a translucent film and is formed to reflect a predetermined ratio of laser light. As a result, when the laser light is focused on the first signal surface 122, the signal recorded on the first signal surface 122 can be read from the reflected light by the first reflecting layer 123, and the laser light is read by the second light. When focusing on the signal surface 124, the laser light passes through the first reflective layer 123 and is focused on the second signal surface 124, and the second signal surface () is reflected from the reflected light by the second reflective layer 125. The signal recorded at 124 can be read.

In the case of a single-layer disc, the signal surface and the reflective layer are formed in the same manner as the second signal surface 124 and the second reflective layer 125.

As can be seen from Figs. 1A, 1B, and 1C, the CD 100 and the CD-R 110 have a signal surface 102, 112 viewed from the disk surface 105, 116, so that the thickness of the disk is usually different. (Signals 102 and 112 suitable for focusing the laser spot are located at a position approximately 1.2 mm on the disc surfaces 105 and 116 side).

On the other hand, in the DVD 120, the signal surfaces 122 and 124 are viewed from the disk surface 128 side, and are approximately 0.6 mm from the disk surface 128 side formed at a position near the center of the disk thickness. Signal planes 122 and 124 are positioned to focus the laser spot. As described above, the recording density due to the pits formed on the signal surfaces 122 and 124 is also higher than that of the CD 100 and the CD-R 110.

Due to this difference, a DVD having a wavelength of 650 nm or less is used for reproduction of the DVD 120, and the objective lens is approximately 0.6 on the disc surface 128 side while the aperture NA is raised to 0.6. An optimized optical pickup is used to focus the laser spot at the position of mm.

In addition, as a CD / DVD compatible device, it is not impossible to read the information on the signal surface 102 of the CD 100 by laser light having a wavelength of 650 nm or less.

It is also not impossible to focus the laser spot at a position of approximately 1.2 mm on the disk surface 105 side of the CD 100. However, it is not beyond the use of a pickup device in which various characteristics are optimized for the CD 100, which is advantageous in terms of reproduction characteristics.

In addition, the CD-R 110 is provided with an organic dye layer 114 having a wavelength dependency, and accurate data reproduction cannot be performed when laser light of 650 nm or less is used. That is, in the CD-R 110, the light absorption rate of the organic dye layer 114 increases with respect to the irradiated laser light of 650 nm or less, the reflectance decreases, and the modulation degree of the laser light by the pit of the signal surface 112 is reduced. Lowers. Moreover, when data is recorded, pits are formed with absorption and reflectances suitable for laser light having a wavelength of 780 nm. Thus, even if the data is read with laser light having a different wavelength, sufficient modulation is obtained.

Fig. 2 is a general block diagram of an optical disk recording and reproducing apparatus for recording data on such optical disks and reproducing the recorded data, wherein the optical pickup 202 condenses on the objective lens under the control of the servo control unit 204. The light beam is placed on the signal track of the optical disk 201, and the light reflected from the signal recording surface is again focused by the objective lens and then incident on the light detector for detection of the focus error signal and the tracking error signal.

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 203.

The RF and servo error generation unit 203 is an RF signal for reproducing data, a focus error (FE) signal for servo control, a tracking error (TE) signal from an electrical signal output from each photodetector of the photodetector. And the like.

The detected RF signal is output to a data decoder (not shown) for reproduction, and servo error signals such as FE and TE are output to the servo controller 204.

The servo controller 204 processes a focus error (FE) signal to output a driving signal for focusing control to the focus servo driver 205, and processes a tracking error (TE) signal to drive a signal for tracking control. Is output to the tracking servo driver 206.

At this time, the focus servo driver 205 moves the optical pickup 202 up and down by driving the focus actuator in the optical pickup 202 so that the optical disk 201 follows the vertical movement with rotation.

The tracking servo driver 206 drives the tracking actuator in the optical pickup 202 to move the objective lens of the optical pickup 202 in the radial direction to correct the position of the beam and track a predetermined track. .

In addition, when it is necessary to move the entire optical pickup, the sled servo driver 207 receives the sled control signal of the servo controller 204 and drives the sled motor 208 in the desired direction of the optical pickup body. Transfer directly.

In this case, the tracking control used for the CD and DVD-based optical discs in the RF and servo error generator 203 and the servo controller 204 is generally a three-beam method, a push-pull (PP) method, and a phase difference. There are various methods such as differential phase detection (DPD).

Here, the three-beam method arranges a pair of tracking side beam spots before and after the main beam spot for information decoding as shown in Figs. 3A to 3C. That is, the auxiliary beams are arranged in opposite directions from the track center by one quarter of the track interval as shown in FIG. 3C. At this time, arranging the auxiliary beams as described above is for preventing the omission of detection signals and for avoiding crosstalk from adjacent tracks.

3A illustrates an example in which the track cross direction of the main beam and the auxiliary beam is in the outer circumferential direction in the free running state, and FIG. 3B illustrates an example in the track cross direction of the main beam and the auxiliary beam in the free running state in the inner circumferential direction. Figure is shown.

In this case, the photodetector is generally composed of a center photodetector for detecting the amount of light of the main beam and an auxiliary photodetector for detecting the amount of light of the auxiliary beam. For example, as shown in FIG. It consists of four photodetectors (PDA, PDB, PDC, PDD), each of which is divided in a radial direction, i.e., divided into four, and the auxiliary photodetector includes two photodetectors each positioned at the top and bottom of the center photodetector. PDE, PDF). Here, the tracking error signal is obtained by processing the electrical signals E and F output from the auxiliary light detecting elements PDE and PDF (E-F).

In addition, the push-pull method divides the photodetecting element of the photodetector into two in accordance with the track direction and then detects the tracking error signal from the light quantity balance of both photodetecting elements. This utilizes the fact that the intensity distribution of light diffracted and reflected by the pit and then incident on the objective lens changes with the relative positional change between the pit and the spot.

If the shadow of the pit is equally detected by both photodetectors, the tracking error signal TE becomes zero, which is called tracking on (or on track). Conversely, a state in which the light error is shifted left and right from the track center and the tracking error signal TE has a + or-value is called tracking off (or off track).

If the optical detector comprises four optical detection elements (PDA, PDB, PDC, PDD) divided into four parts, i.e., divided into four directions in the signal track direction and the radial direction of the optical disc, the tracking error signal by the PP method is The electrical signals A, B, C, and D output from the photodetector of the photodetector can be obtained by (A + D)-(B + C). At this time, if the photo detector is divided into two in the track direction, the tracking error signal (= I1-I2) is detected from the light quantity balance of both photodiodes I1 and I2. That is, A + D of FIG. 4 corresponds to I1 and B + C corresponds to I2.

If it is assumed that the photo detector is the same as that of FIG. 4, the MPP (Main beam PP) signal corresponds to the electrical signals A, B, C, and D output from the center photodetection element of the photo detector (A + D)-(B + C), and a SPP (Side beam PP) signal can be obtained by (EF) the electrical signals E and F output from the auxiliary photodetecting element of the photodetector. In addition, DPP (Differential PP) signal can be obtained by MPP-SPP.

Here, the photo detector is divided into four optical detection elements (PDA, PDB, PDC, PDD), which are divided in four directions, i.e., in the signal track direction and the radial direction of the optical disk, or the optical detection element I1 divided into two in the track direction. PP2 and MPP signal are the same concept.

At this time, the MPP method described above has several conditions. One of them is called a wavelength of light, and when the depth of the pit is λ / 4, that is, when the diffraction by the pit is most effective and the modulation degree is maximized, the tracking error signal cannot be obtained by the MPP method. That is, since the pattern when the pit depth is λ / 4 becomes a symmetrical pattern, a tracking error signal cannot be obtained from the two-segmented photodetector.

On the other hand, the DPD method is an improvement of the MPP method. The DPD method receives a light detection element in which the light intensity distribution is divided into four and detects a phase difference in the radial (radius) direction to generate a tracking error signal.

Therefore, the effect of the pit depth is small, for example, a tracking error signal is generated even at a pit depth of λ / 4, and the effect is small even if the beam moves on the photo detector.

For example, a conventional CD generates a tracking error signal using a 3-beam method, and a CD recorder, particularly a CD-R / RW, generates a tracking error signal using a differential push pull (DPP) method. At this time, when the tracking error signal is detected by the MPP method by receiving the signal output from the center photodetector, the amount of the MPP signal is large, resulting in a DC offset due to lens shift.

Therefore, in the CD-R / RW, the DC offset in the MPP method is used to use the DPP method (DPP = MPP-SPP), that is, DC using signals obtained from MPP (Main Push Pull) and SPP (Side Push Pull). The tracking error signal is generated in a manner that minimizes the offset.

On the other hand, DVD-RAM optical systems up to now have a large numerical aperture of the objective lens to increase the recording density, and use a short wavelength light source of 650 nm, so that the DVD-RAM can be recorded and reproduced, while the CD-ROM is reproduced. It is also developed to play / record CD-RW. In addition, the DVD-ROM optical system was developed to be compatible with the DVD-ROM and CD-ROM.

In the optical disc market, DVD is rapidly spreading as an important element of a multimedia system. Therefore, it is essential to develop a pickup device that can cope with all kinds of DVDs such as DVD R / RW, DVD-RAM, DVD-ROM, and the like.

In general, in the DVD-ROM and the DVD-RAM, a DPP method using three beams is mainly used to generate a tracking error signal. Since the DPP method requires accuracy in positioning an auxiliary beam at a track boundary, the track pitch size is large. It is difficult to use to apply simultaneously to different media.

That is, the pitch size of the DVD-ROM is 0.74 µm while the pitch size of the 4.7 GB DVD-RAM is 0.615 µm, which makes it difficult to simultaneously apply the DPP method.

Therefore, the pickup apparatus for multi-DVDs must be equipped with a detection system for tracking error signals that can be applied regardless of the size of different track pitches of various DVDs.

Accordingly, the present invention provides a tracking servo control apparatus using a rotatable diffractive lens and a control method thereof, which are designed to meet the above needs, so that the track pitch can be tracked by rotating the diffraction lens of the DVD pickup device. It is for that purpose.

The present invention for achieving the above object is a light source for generating and irradiating light; a diffraction grating diffracts the incident light of the light source into three; Rotating means for rotating the diffraction grating; An objective lens for converging incident light so that light spots are formed on the recording surface of the disk; Light path converting means positioned between the light source and the objective lens to change a traveling path of incident light; A collimating lens positioned between the light path converting means and the objective lens to collimate the light source; The photodiode is located at the top or the bottom of the same line as the optical path converting means, and the area of the photodiode reaching the main beam to detect a tracking error signal from the three reflected light reflected from the disk through the optical path converting means is divided into four areas. A light splitting detector divided into two regions of each photodiode to which each auxiliary beam arrives; And tracking control means for performing tracking control according to the tracking error signal input from the light splitting detector, and determining the type of the disc to control the rotating means in the case of the DVD-RAM disc to rotate the diffraction grating at a predetermined angle. Characterized in that consisting of.

 The present invention also provides an optical pickup apparatus comprising: a first step of determining a type of a disc, whether a DVD-ROM or a DVD-RAM; A second step of performing tracking servo control if the determination result of the first step is a DVD-ROM; And a third step of performing tracking servo control after rotating the diffraction grating in the case of the DVD-RAM as a result of the determination in the first step.

Now, the preferred embodiment of the present invention will be described in detail with reference to the drawings of FIG. 5.

In the servo signal extraction method using the DPP method used in the present invention, the optical pickup apparatus, as shown in Fig. 5, the main beam 511 following the center of the track G of the bone, and the track of the bone to which the main beam 511 is irradiated; The auxiliary beams 512a and 512b following the center of the tracks L of the mountains adjacent to (G) are irradiated onto the optical disc 502.

The main beam 511 follows the center of the track G of the goal, which is a target signal track to be recorded or reproduced. The auxiliary beams 512a and 512b follow the center of the tracks L of the mountain adjacent to the target signal track.

When the track pitch (hereinafter referred to as 'TP') is the distance between the centers of the tracks G of adjacent valleys or the center of the tracks L of the mountains, the main beam 511 and the auxiliary beams The distance between the centers of 512a and 512b maintains TP / 2, and the distance between the centers of the auxiliary beams 512a and 512b maintains TP.

After the main beams 511 and the auxiliary beams 512a and 512b are focused on the optical disk 502, these light beams 511, 512a and 512b are reflected and focused on the photodetector as shown in FIG. 6.

Referring to FIG. 6, the photodetector includes a four-segment photodetector 622 in which the main reflection beam 611 'is focused, and a first and second two-split photodetector in which the auxiliary reflection beams 612a' and 612b 'are focused. 624a and 624b.

The four-segment photodetector 622 includes four photodetector pieces PDA to PDD divided radially and tangentially in the radial direction of the optical disk, and is focused on the track G of the goal signal track, which is reflected and then reflected. 611 'is converted into an electrical signal.

The first two-segment photodetector 624a includes tangentially divided photodetection pieces PDE, PDF, which are focused on the track L of the mountain adjacent to the target signal track and then reflected by the first auxiliary reflection beam. 612a 'is converted into an electrical signal.

In addition, the second two-segment photodetector 624b includes tangentially divided photodetection pieces PDG and PDH, and the second auxiliary reflection reflected after being focused on the track L of a mountain adjacent to the target signal track. The beam 512b 'is converted into an electrical signal.

The servo signal includes a tracking error signal detected in the normal mode, a focusing error signal and a sled error signal and a center error signal detected during data search.

The tracking error signal and the focusing error signal are detected in the normal mode at the time of recording / reproducing, and the tracking servo for causing the light beam focused on the optical disc from the objective lens to follow the center of the track and the focusing signal for focusing the servo to bring the light beam within the depth of focus. Used as

The data search is divided into rough search mode and fine search mode. In the rough search mode, the pickup pickup motor is driven in a moving range that exceeds the movable range of the tracking actuator while the sled servo and the tracking servo are turned off to transfer the entire optical pickup unit in the radial direction of the optical disc.

This rough search mode moves the optical pickup unit to the starting point of the fine search. The fine search mode drives the tracking actuator to move the objective lens to the final target position.

The center servo fixes the objective lens to the center of the optical pickup unit based on the center error signal detected during the optical pickup movement during data search to prevent the objective lens from flowing due to inertia due to acceleration and deceleration of the optical pickup unit. .

In order to detect such servo signals, the sub-signal extracting apparatus uses first to third adder amplifiers 628a to 628c for extracting the servo signal by using the output signal of the photodetectors 622, 624a and 624b as shown in FIG. ) And first to fourth differential amplifiers 626a to 626d.

The first adder amplifier 628a adds and amplifies the signals inputted from the PDA and the PDD photodetectors of the quadrature photodetector 622 to detect the push-pull signal of the first auxiliary beam 612a, thereby detecting a third differential amplifier. Supply to the positive input terminal (+) of 626c.

The second adder amplifier 628b adds and amplifies the signals input from the PDB and PDC photodetectors of the four-segment photodetector 622 to detect the push-pull signal of the second auxiliary beam 612b to generate a third differential amplifier. Supply to the negative input terminal (-) of 626c.

The first differential amplifier 626a differentially amplifies the signals input from the PDE and PDF photodetectors of the first two-segment photodetector 624a and supplies them to the third adder amplifier 628c. The second differential amplifier 626b differentially amplifies the signals inputted from the PDG and PDH photodetectors of the second two split photodetector 624b and supplies them to the third adder amplifier 628c.

The third differential amplifier 626c differentially amplifies the output signals of the first and second adder amplifiers 628a and 628b to generate a push-pull signal of the main beam 611. The output signal (A + D)-(B + C) of the third differential amplifier 626c, that is, the push-pull signal of the main beam, shows that the main beam 611 tracks the tracks GT and LT during data search as shown in FIG. Each jump results in a high frequency signal in which the polarity is reversed.

On the other hand, the push-pull signal EF of the first sub-beam 612a is delayed by 180 ° out of phase from the push-pull signals A + D- (B + C) of the main beam and is push-pull of the second sub-beam 12b. Since the signal GH is 180 ° out of phase with the push-pull signals A + D- (B + C) of the main beam, the push-pull signals GH of these first and second auxiliary beams 612b are in phase with each other. It is shown as the inverse of the push-pull signal (A + D)-(B + C) of the main beam.

The push-pull signals A + D- (B + C) of the main beam are commonly supplied to the input terminals of the low pass filter (hereinafter referred to as 'LPF') 640 and the fourth adder amplifier 626d. .

The LPF 640 low-pass filters the push-pull signals A + D- (B + C) of the main beam to generate a center error signal CE indicating the degree and direction in which the objective lens deviates from the center of the optical pickup unit. do.

The center error signal CE is supplied to the tracking coil 734 of the tracking actuator as shown in FIG. 7 during data search to cause the objective lens to follow the center of the optical pickup unit.

The third adder amplifier 728c adds and amplifies the push-pull signals E-F and G-H of the first and second auxiliary beams to supply the negative input terminal − of the fourth differential amplifier 726d.

The fourth differential amplifier 726d differentially amplifies the output signal of the third differential amplifier 726c and the output signal of the third add amplifier 728c to generate the tracking error signal TE. The tracking error signal TE is a push pull signal A + D- (B + C) of the main beam 711 having opposite polarity and antiphase, and a push pull signal EF of the auxiliary beams 712a and 712b. (GH) is a difference signal, and its amplitude becomes larger than the amplitudes of the push-pull signals A + D- (B + C) of the main beam 711.

The tracking error signal TE is amplified in the low pass by the low / high pass compensation circuit 730 as shown in FIG. 7 and phase compensated in the high pass, and then supplied to the power amplifier 732 and the LPF 736 in common. do. The power amplifier 732 amplifies the power value of the tracking error signal TE and supplies the tracking coil 734 to the actuator in normal mode. As a result, the main lens 711 and the auxiliary beams 712a and 712b focused on the optical disk 702 are driven by the tracking servo in the normal mode in the normal mode, so that the tracks GT, The center of the LT) can be followed.

The LPF 736 performs low pass filtering on the tracking error signal TE to extract the DC offset of the low frequency component included in the tracking error signal TE during data search. The output signal of the LPF 736 is amplified by a predetermined gain value by the amplifier 738 and then supplied to a pickup transfer motor (not shown).

The pickup transfer motor is driven in response to the sled error signal SE input from the amplifier 738 in the normal mode to move the entire optical pickup unit in the radial direction of the optical disc 702 so that the actuator is always centered in the radial direction of the optical disc. Keep it.

8 is a block diagram showing the configuration of a DVD-ROM optical system capable of reproducing a DVD-RAM according to the present invention, and FIG. 9 is an eight-segment photodetector of a DVD-ROM optical system capable of reproducing a DVD-RAM according to the present invention. A diagram showing the configuration.

8 and 9, first, the light source 801 is configured to generate a laser beam having a wavelength of 650 nm, and the beam splitter 802 is one diffused laser emitted from the light source 801. The beam is transmitted, and the reflected light reflected from the recording surface of the disk D is reflected.

The collimating lens 803 converts one diffused laser beam into parallel light when it is irradiated by the beam splitter 802 and the objective lens 804 is converted into parallel light. The laser beam of parallel light converted by the collimating lens 803 is focused and irradiated onto the disk D, and the focusing / cylindrical lens 805 reflects the laser beam reflected from the disk D to perform a focus servo. Is converted to astigmatism.

In addition, the diffraction grating 810 may convert the one beam generated from the light source 801 into three beams so that both the DVD-ROM and the DVD-RAM can be reproduced, the light source 801 and the beam splitter 802. It is located in between. At this time, the DVD-ROM optical system capable of reproducing the DVD-RAM determines whether the DVD-RAM disk is a DVD-ROM disk, and if the DVD-RAM disk is a DVD-RAM disk, rotates the diffraction grating 810 to position the auxiliary beam generated based on the main beam. Changes in the radial distance of the tracks allow tracking error signals to be detected on DVD-RAM discs.

The eight-segment photodetector 820 includes a main photodiode 821 divided into regions A, B, C, and D, and a sub photodiode 822 divided into regions of E, F, G, and H.

Here, the main photodiode 821 divided into areas A, B, C, and D uses the DPP method and the astigmatism method as described above by using the main beam and the auxiliary beam reflected from the recording surface of the DVD-ROM during the reproduction of the DVD-ROM. Focusing servo and tracking servo by detecting playback signals and error signals (focusing error and tracking error), and during the DVD-RAM playback, the main and auxiliary beams reflected from the recording surface of the DVD-RAM are DPP (Differential Push-Pull). And a reproduction signal and an error signal.

That is, a reproduction signal and a focusing error signal are detected by the main photodiode 821 divided into A, B, C, and D, and a reproduction signal and an error signal are detected by the subphotodiode 822 divided into E, F, G, and H. Detect.

Hereinafter, the operation of the compatible optical system of the DVD-ROM and the DVD-RAM according to the present invention will be described in detail with reference to FIGS. 8 and 9.

First, when a diffused laser beam having a wavelength of 650 nm is generated and emitted by the light source 801, it is divided into three beams by the diffraction grating 810, and the three beams divided by the diffraction grating 810 are transferred to the beam splitter 802. After being incident and transmitted by the beam splitter 802, the collimating lens 803 is converted into parallel light.

Then, the laser beam changed into collimated light in the collimating lens 803 is incident to the objective lens 804 through the phase retardation plate 806, and the objective lens 804 focuses the laser beam on the recording surface of the disk D. Investigate.

Thus, the three beams irradiated and reflected on the recording surface of the disk D are reflected by the beam splitter 802 through the objective lens 804, the phase retardation plate (λ / 4) 806, and the collimating lens 803. The reflected three beams are incident to the main photodiode 821 divided into A, B, C, and D of the eight-segment photodetector 820 via the focusing / cylindrical lens 805, and E, F, An auxiliary beam is incident on the auxiliary photodiode 822 divided into G and H.

In this state, when the disk D is recognized as a DVD-ROM in the system, the eight-segment photodetector 820 reflects the three beams split by the diffraction grating 810 on the recording surface of the DVD-ROM, so that the beam splitter 802 When incident via the focusing / cylindrical lens 805, the three beams of the main beam and the auxiliary beam are used to generate the reproduction signal, the focusing error signal, and the tracking error signal using the DPP method and the astigmatism method.

In addition, when the disk D is recognized as a DVD-RAM in the system, after the diffraction grating 810 is rotated, the eight-segment photodetector 820 uses the DPP method to divide three beams of the DVD-RAM into the diffraction grating 810. When reflected from the recording surface of the light incident on the beam splitter 802 and through the focusing / cylindrical lens 805, the incident signal and the focusing error in the main photodiode 821 and the subphotodiode 822 are incident to the incident three beams. Generate signals and tracking error signals.

10 is a view for explaining the rotation of the auxiliary beam according to the rotation of the diffraction grating according to the DVD-ROM and DVD-RAM.

Referring to FIG. 10, in the case of a DVD-ROM, the size of the track pitch is 0.74 μm, and thus, the distance between the main beam and the auxiliary beam is 20 μm, and θ is determined between the track where the main beam is located and the red line passing through the main beam and the sub beam. If the angle is cosθ = 0.74 / 20 = 0.037, θ is about 87.88˚.

In the case of DVD-RAM, the track pitch size is 0.615 µm, so that cosθ = 0.615 / 20 = 0.0307 and θ is about 88.24 °. Therefore, the rotation range of the diffraction grating is 87.88 ° to 88.24 °.

FIG. 11 is a diagram for describing a rotating apparatus according to an exemplary embodiment of the diffraction grating of FIG. 8.

Referring to the drawings, the angle of rotation can be adjusted by controlling the intensity of the current using the anode 1112 as an electromagnet, and the diffraction grating 1110 can be rotated using a mechanical mechanism.

12 is a view for explaining a rotation apparatus according to another embodiment of the diffraction grating of FIG. 8.

Referring to FIG. 12, the rotation of the diffraction grating of FIG. 8 inserts a reflective diffraction grating 1214 instead of an LD reflection mirror mounted on the hologram module 1210 and replaces the reflective diffraction grating 1214 with MEMS (Micro Electro Mechanical). Rotate using the device.

FIG. 13 is a block diagram showing the configuration of a DVD-ROM / DVD-RAM optical system capable of playing / recording a CD-RW according to the present invention, and FIG. 14 is a block diagram showing the configuration of an 8-segment photodetector applied to the present invention. .

13 and 14, first, the DVD-ROM / DVD-RAM optical system, the DVD laser diode 1300 is configured to generate a laser beam having a wavelength of 650nm.

The beam is split into three beams in the diffraction grating 1301 and then incident to the beam splitter 1302. At this time, the DVD-ROM optical system capable of reproducing the DVD-RAM determines whether the DVD-RAM disk or the DVD-ROM disk is a DVD-RAM disk and rotates the diffraction grating 1301 for the DVD-RAM disk. Changes in the radial distance of the tracks allow tracking error signals to be detected on DVD-RAM discs.

The beam splitter 1302 reflects three diffuse laser beams emitted from the diffraction grating 1301 and transmits the reflected light reflected from the recording surface of the DVD-ROM (D) / DVD-RAM (D), The collimating lens 1303 for the DVD is configured to convert three diffuse laser beams into parallel light.

The objective lens 1304 collects a laser beam of parallel light converted by the collimating lens 1303 for DVD, and irradiates the DVD-ROM (D) / DVD-RAM (D), and collects the focused / cylindrical lens ( 1305 converts the laser beam reflected from the DVD-ROM (D) / DVD-RAM (D) by astigmatism to perform a focus servo.

In addition, referring to the configuration of the CD-RW optical system, first, the laser diode for CD 1310 is configured to emit a 780nm laser beam capable of recording and reproducing the CD-RW (D ').

The plate beam splitter 1320 reflects the 780 nm laser beam of the CD laser diode 1310 to the objective lens 1304, transmits the light to the monitor photodetector 1360, and the laser diode for CD. The optical axis of the reflected light is interposed between the objective lens 1304 and the DVD collimating lens 1303 at the position where the 780 nm laser beam and the 650 nm laser beam intersect with each other to transmit the 780 nm laser beam and the reflected light. It is installed at an angle of 45 degrees to the left.

Here, the plate beam splitter 1320 has a thickness of 1.5 mm or less to minimize aberration generated when light is transmitted. Here, the reason why the plate beam splitter is installed after the collimating lens 1303 for the DVD is because the plate beam splitter is installed with an inclination of 45 degrees and is irradiated by the DVD laser diode 1301 so that the plate beam splitter ( The laser beam incident on the 1320 must be a parallel beam so that the 650 nm laser beam generated by the DVD laser diode 1301 is accurately incident on the objective lens 1304.

The diffraction grating 1330 is disposed between the CD laser diode 1310 and the plate beam splitter 1320 to enable recording and reproduction of the CD-RW (D ') by separating the 780 nm laser beam into three beams. .

The CD collimating lens 1340 is installed between the plate beam splitter 1320 and the diffraction grating 1330 to collimate the 780 nm laser beam emitted from the CD laser diode 1310.

On the other hand, the 8-segment photodetector 1350 used in both the DVD-ROM / DVD-RAM optical system and the CD-RW optical system is a recording surface of the DVD-ROM (D) / DVD-RAM (D) and the CD-RW (D '). The reflected signal reflected from the objective lens 1304, the plate beam splitter 1320, and the collimating lens 1303 for DVD is used to reproduce the reproduction signal of the DVD-ROM (D) / DVD-RAM (D). It is provided on the path of the reflected light to detect the error signal and the recording / reproducing signal of the CD-RW (D ') and the error signal.

The eight-segment photodetector 1350 is composed of a main photodiode 1351 divided into regions A, B, C, and D, and a sub photodiode 1352 divided into regions of E, F, G, and H. Here, the main photodiode 1351 divided into areas A, B, C, and D, and the sub photodiode 1352 divided into areas E, F, G, and H have a DVD-ROM (D) / DVD-RAM ( During playback of D), playback signals and error signals (focusing) are performed by the DPP (Differential Push-Pull) method and astigmatism method using the main beam and the sub beam reflected from the recording surface of the DVD-ROM (D) / DVD-RAM (D). Error and tracking error) to perform focusing servo and tracking servo, and to record the CD-RW (D ') using the main beam and the sub-beam reflected from the recording surface of the CD-RW (D'). The recording signal and the error signal are detected by the Differential Push-Pull method and the astigmatism method. When the CD-RW (D ') is reproduced, the main and sub beams reflected from the recording surface of the CD-RW (D') are used. The reproduction signal and the error signal are detected by the three-beam method and the astigmatism method.

The reason why the push-pull method is not used as a CD-RW reproducing / gippy 6-segment photodetector is that the difference in light distribution caused by the tilt of the disc and the shift of the objective lens, One of the beams is to prevent the tracking offset from occurring due to the difference in reflectivity when the other is recorded and the other is not recorded.

The monitor photodetector 1360 has a side surface of the plate beam splitter 1320 that is on the path of the 780 nm laser beam to adjust the intensity of light with the incident beam when the 780 nm laser beam transmitted from the plate beam splitter 1320 is incident. Is installed on.

The variable stop 1370 is provided between the objective lens 1304 and the plate beam splitter 1320 to adjust the diameter of the 650 nm laser beam or the 780 nm laser beam incident to the objective lens 1304. Here, a hologram element may be used to adjust the diameter of the laser beam incident on the objective lens 1304.

Hereinafter, the operation of the DVD-ROM / DVD-RAM optical system capable of playing / recording CD-RW according to the present invention will be described in detail with reference to FIG.

First, if a laser beam having a wavelength of 650 nm is emitted from the DVD laser diode 1300 at the time of reproduction of the DVD-ROM (D) / DVD-RAM (D), it is divided into three beams in the diffraction grating 1301 and then beams. It is reflected from the splitter 1302 to the collimating lens 1303 for DVD. At this time, the DVD-ROM optical system capable of reproducing the DVD-RAM determines whether the DVD-RAM disk is a DVD-ROM disk, and if the DVD-RAM disk is a DVD-RAM disk, rotates the diffraction grating 810 to position the auxiliary beam generated based on the main beam. Changes in the radial distance of the tracks allow tracking error signals to be detected on DVD-RAM discs.

Then, the 650 nm laser beam incident on the DVD collimating lens 1303 is converted into a parallel beam and then incident on the objective lens 1304 through the plate beam splitter 1320.

At this time, the variable stop 1370 adjusts the diameter of the laser beam of 650 nm so that the numerical aperture of the objective lens 1304 is adjusted to 0.6, which is the numerical aperture of the DVD-ROM / DVD-RAM.

Thus, the reflected light irradiated and reflected on the recording surface of the DVD-ROM (D) / DVD-RAM (D) through the objective lens 1304 is again reflected in the objective lens 1304, the variable aperture 1370, and the plate beam splitter. 1320, the collimating lens 1303 for DVD, and the beam splitter 1302 are sequentially passed to converge to the focusing / cylindrical lens 1305.

Then, the focusing / cylindrical lens 1305 converts the reflected beam into astigmatism so that the eight-segment photodetector 1350 can generate the reproduction signal and the focusing / tracking error signal by the DPP method and the astigmatism method.

Thus, the data recorded on the recording surface of the DVD-ROM (D) / DVD-RAM (D) can be reproduced by the eight-segment photodetector 1350.

Next, at the time of recording or reproducing the CD-RW (D '), the variable stop 1370 adjusts the laser beam of 780 nm to match the numerical aperture of the objective lens 1304 to 0.5, which is the numerical aperture of the CD-RW (D'). Adjust the diameter

In this state, when a laser beam having a predetermined intensity and a wavelength of 780 nm is emitted from the CD laser diode 1310, the laser beam is split into three beams in the diffraction grating 1330 and then incident on the collimating lens 1340 for CD.

Then, in the CD collimating lens 1340, the diffusion beam is converted into a parallel beam and incident on the plate beam splitter 1320.

Thus, the three parallel beams incident on the plate beam splitter 1320 are reflected by the plate beam splitter 1320 toward the objective lens 1304 and are incident on the monitor photodetector 1360. For this reason, the monitor photodetector 1360 detects the intensity of the incident light and adjusts the intensity of the light.

The 780 nm laser beam reflected by the plate beam splitter 1320 and incident on the objective lens 1304 through the variable aperture 1370 is irradiated and reflected from the recording surface of the CD-RW (D '), and the reflected reflected light is again reflected. The objective lens 1304, the variable aperture 1370, the plate beam splitter 1320, the DVD collimating lens 1303, and the beam splitter 1302 are sequentially passed through the focusing / cylindrical lens 1305. Converges to

Then, the focusing / cylindrical lens 1305 can generate the focusing / tracking error signal by the DPP method and the astigmatism method and the reproduction signal and the focusing / tracking error signal by the 3-beam method and the astigmatism method by the 8-segment photodetector 1350. Convert the reflected beam into astigmatism.

Thus, when recording the CD-RW (D ') in the eight-segment photodetector 1350, the recording signal and the focusing error signal and the focusing error signal and the pits can be formed on the recording surface of the CD-RW (D') by the DPP method and the astigmatism method. When a tracking error signal is generated and CD-RW (D ') is reproduced, a reproduction signal and a focusing / tracking error signal are generated by the 3-beam method and astigmatism method to reproduce the data recorded on the recording surface of the CD-RW (D'). Can be.

Therefore, it is possible to provide a compatible optical system that can use both CD-RW and DVD-ROM / DVD-RAM, and also uses a plate beam splitter that is less expensive than a cubic material beam splitter, thereby reducing the manufacturing cost of the optical system. Savings.

15 is a flowchart of a control method of a tracking servo control apparatus using a rotatable diffractive lens according to an embodiment of the present invention.

First, the optical pickup apparatus determines the type of disc (step S110), determines whether it is a DVD-ROM or a DVD-RAM (step S112), and if it is a DVD-RAM, rotates the diffraction grating (step S114).

Thereafter, after irradiating the laser beam to the disk (step S116), after extracting the tracking error signal (step S118), tracking servo is performed (step S120).

According to the present invention as described above, when the diffraction grating is rotated with respect to the optical axis, the position of the auxiliary beam generated by the diffraction grating also rotates with respect to the optical axis, that is, the main beam, and thus the radial distance between the main beam and the auxiliary beam is changed. By controlling the distance between the auxiliary beam and the main beam through a proper amount of rotation, it is possible to detect a tracking error signal that is not affected by the size of the track pitch.

What has been described above is only one embodiment for implementing the tracking servo control device and control method according to the present invention, and the present invention is not limited to the above-described embodiment, as claimed in the following claims. Without departing from the gist of the invention, anyone of ordinary skill in the art to which the present invention will have the technical spirit of the present invention to the extent that various modifications can be made.

1A, 1B, and 1C show a layer structure as disc cross sections of CD, CD-R, and DVD, respectively.

2 is a general block diagram of an optical disc recording and reproducing apparatus for reproducing recorded data.

3A illustrates an example in which the track cross direction of the main beam and the auxiliary beam is in the outer circumferential direction in the free running state, and FIG. 3B illustrates an example in the track cross direction of the main beam and the auxiliary beam in the free running state in the inner circumferential direction. FIG. 3C is a view showing a case in which they are arranged in opposite directions from the track center by a quarter of the track interval.

4 is a diagram showing an internal configuration diagram of a light detection element by a three beam method.

5 is a view for explaining a servo signal extraction method using the DPP method used in the present invention.

Fig. 6 is a detailed block diagram of the interior of the photodetector used in the present invention.

FIG. 7 is an internal block diagram of an amplifier of the tracking error signal of FIG. 6.

8 is a block diagram showing the configuration of a DVD-ROM optical system capable of reproducing a DVD-RAM according to the present invention.

Fig. 9 is a block diagram showing the configuration of an 8-segment photodetector of a DVD-ROM optical system capable of reproducing a DVD-RAM according to the present invention.

10 is a view for explaining the rotation of the auxiliary beam according to the rotation of the diffraction grating according to the DVD-ROM and DVD-RAM.

FIG. 11 is a diagram for describing a rotating apparatus according to an exemplary embodiment of the diffraction grating of FIG. 8.

12 is a view for explaining a rotation apparatus according to another embodiment of the diffraction grating of FIG. 8.

Fig. 13 is a block diagram showing the configuration of a DVD-ROM / DVD-RAM optical system capable of playing / recording a CD-RW according to the present invention.

14 is a block diagram showing the configuration of an eight-segment photodetector applied to the present invention.

15 is a flowchart of a control method of a tracking servo control apparatus using a rotatable diffractive lens according to an embodiment of the present invention.

Claims (8)

A light source for generating and irradiating light; A diffraction grating diffracting the incident light of the light source into three; Rotating means for rotating the diffraction grating; An objective lens for converging incident light so that light spots are formed on the recording surface of the disk; Light path converting means positioned between the light source and the objective lens to change a traveling path of incident light; A collimating lens positioned between the light path converting means and the objective lens to collimate the light source; The photodiode is located at the top or the bottom of the same line as the optical path converting means, and the area of the photodiode reaching the main beam to detect a tracking error signal from the three reflected light reflected from the disk through the optical path converting means is divided into four areas. A light splitting detector divided into two regions of each photodiode to which each auxiliary beam arrives; And Tracking control means for performing tracking control according to a tracking error signal input from the light splitting detector, determining the type of the disc, and controlling the rotating means for the DVD-RAM disc to rotate the diffraction grating at a predetermined angle. A tracking servo control device comprising a. The method of claim 1, And said rotating means rotates said diffraction grating by adjusting the intensity of an electric current with an anode as an electromagnet. The method of claim 1, And said rotating means rotates the hologram diffraction grating using a MEMS element. The optical pickup apparatus includes a first step of determining a type of a disc, whether a DVD-ROM or a DVD-RAM; A second step of performing tracking servo control if the determination result of the first step is a DVD-ROM; And And a third step of performing tracking servo control after rotating the diffraction grating if it is determined that the first step is a DVD-RAM. The method of claim 4, wherein The second step, A second step of dividing the laser beam into three and irradiating the disk on the DVD-ROM as a result of the determination in the first step; A step 2-2 after the step 2-1, receiving the three reflected disk lights and extracting a tracking error signal; And And after the step 2-2, the step of performing the tracking servo control according to the tracking error signal. The method of claim 4, wherein The third step, A third step of rotating the diffraction grating by a predetermined angle as the result of the determination in the first step as the DVD-RAM; After the step 3-1, the step 3-2 of dividing the laser beam into three and irradiating the disk; Step 3-3, after the step 3-2, extracts the tracking error signal by receiving three disc reflected light beams; And And after the third to third steps, performing a third to third tracking servo control according to the tracking error signal. The method of claim 6, The rotation of the diffraction grating of the step 3-1 is performed by varying the intensity of the current using the anode as an electromagnet. The method of claim 6, The rotation of the diffraction grating of step 3-1 comprises rotating the hologram diffraction grating using a MEMS device.