JP2000090450A - Focus bias setting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To highly precisely obtain optimum focus bias for every loaded disk independently of secular change of an optical system and dispersion of conditions due to dispersion for every disk. SOLUTION: On the assumption that a device corresponds to an optical recording medium having an emboss-pit region L1 and an over-write region L2, reproduction is performed varying focus bias for the emboss-pit region L1, and first focus bias being optimum by corresponding to the emboss-pit region L1 is obtained based on a jitter value obtained at this time. Second focus bias being optimum by corresponding to the over-write region L2 is obtained by giving offset quantity obtained by a previous measured result to the first focus bias.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides an offset to a focus position of a converged laser beam when irradiating a converged laser beam, for example, for recording or reproducing on an optical recording medium. And a focus bias setting device for setting an optimal focus bias as the focus bias.

[0002]

2. Description of the Related Art CD (Compact Disc) and CD-ROM (Com
Disc-shaped optical recording media such as pact Disc-Read Only Memory) have become widespread. These CDs and CD-ROMs
At the time of manufacturing, a minute concave portion (physical pit) is formed on the surface of the plastic substrate, and information is recorded by this pit row. The pit train itself is used as a track, and the light beam spot for signal reproduction traces the track based on the pit train. That is, media such as CDs and CD-ROMs are read-only media, and cannot be added or rewritten after manufacturing.

On the other hand, in recent years, a write-once CD-R (R
Discs capable of recording and reproducing data, such as ecordable and rewritable CD-RWs (ReWritable), have become widespread. In these recording media, grooves as guide grooves are formed in a manufacturing process so that a light beam spot can properly trace in a recording area. In the case of a CD-R, data recording is performed by modulating the intensity of a light beam spot, thereby deforming the recording layer on the groove to form physical pits. Also CD
In the case of -RW, this is performed by forming phase pits by a so-called phase change method.

In recent years, DVDs (Digital Versataile Discs or Digital
l Video Discs), read-only discs such as DVD-ROMs, etc., have also been known.
A recordable disk medium (for example, a DVD-RAM) having a recording capacity substantially equivalent to that of a D-ROM has also been proposed. For example, a DVD-RAM or the like has a read-only area in which data about various kinds of information fixed with respect to the disc is recorded by physical emboss pits,
A recording area in which a groove is formed and data can be rewritten.

[0005] In a disk drive apparatus corresponding to these disk media, a disk rotated by a spindle motor is irradiated with laser light from an optical pickup to a track on the disk, and the reflected light is detected. In this way, data is read out, or data is recorded by irradiating a laser beam modulated by recording data.

In order to perform a recording or reproducing operation using a laser beam, the spot of the laser beam must be kept in focus on the recording surface of the disc. A focus servo circuit system for controlling a focus state by moving an objective lens, which is an end, in a direction approaching and separating from the disk is mounted. As the focus servo circuit system, usually, a two-axis mechanism having a focus coil for moving the objective lens in the direction of moving toward and away from the disk and a tracking coil for moving the disk in the disk radial direction, and information reflected from the disk are used. A focus error signal (i.e., a signal indicating the amount of deviation from the in-focus state) is generated, and a focus drive signal is generated based on the focus error signal.
It is composed of a focus servo control system that applies a voltage to the focus coil of the two-axis mechanism.

As a basic operation of the focus servo circuit system, a focus drive signal is applied to a focus coil of a two-axis mechanism so that a distance between an objective lens and a signal surface is adjusted so that a focus error signal level becomes zero. Adjusted. That is, when the focus error signal level is 0, the objective lens is in focus on the signal surface, that is, the best imaging state is obtained for the laser light irradiated on the signal surface. It is said.

[0008]

In an actual disk drive device, the best focus state may not always be obtained when the focus error signal level is 0, which often occurs. This is due to, for example, changes in the position or characteristics of a laser light source, a photodetector that detects laser light as reflected light from a disk, and other optical components over time. Further, the disk-shaped recording medium may be, for example, a disk D (see FIG. 16) shown in FIG. 16 for the purpose of properly performing recording / reproduction even if dust or scratches are present on the medium surface, or for protecting the signal surface. As shown in (partial sectional view), a signal surface 201 is generally formed on the back surface of a transparent layer 202 formed of resin or the like. The thickness T of this transparent layer 202
H may be slightly different for each recording medium even if they are of the same type. Due to the variation in the thickness TH of the transparent layer 202, even if the detected focus error signal level is 0, the laser beam actually emitted from the objective lens 300 has the best result on the signal surface 202. It has been found that a phenomenon in which an image state is not obtained can occur.

In view of these circumstances, it is necessary that the target value of the focus error signal level is not set to 0, but can be shifted and set by another appropriate value. That is, it is necessary to give an offset (bias) to the focus error signal. Also, this bias is not fixed,
Depending on the aging of the optical system and variations from disk to disk,
It is necessary to set it appropriately.

[0010] In the above-mentioned disk medium of a large capacity and good recording density, such as a DVD system, the groove interval (track pitch) and pit length are as small as the order of the wavelength of the light source, so that the laser beam can be accurately formed in the groove (or In order to trace the land formed between the grooves) and accurately record or reproduce data, the light beam spot is
So-called diffraction-limited quality is required. For this reason, high precision is also required for the above-described focus servo circuit system, and accordingly, a high-precision value must be obtained as the bias as described above.

[0011]

In view of the above problems, the present invention considers at least a first area where data is recorded by forming physical pits, and pits other than the physical pits as recording data. Is formed so that it corresponds to an optical recording medium having a second area on which data is recorded, and then, the recording and reproduction is performed by irradiating the converged laser light to the optical recording medium. A recording / reproducing apparatus capable of performing the optical recording while setting the focus bias variably as a focus bias setting apparatus for setting a focus bias for giving an offset with respect to the focal position of the converged laser light. Trial reproduction means for performing trial reproduction of performing data reproduction on the first area of the medium; A predetermined signal characteristic of the obtained reproduction data is measured, and the measurement result is obtained as sample information in association with a focus bias set at the time of trial reproduction, and sample information obtained by the sample means is obtained. A first focus bias which is optimized individually for the first region, or which is optimized for the first region and the second region in common, and an individual focus bias which is optimized for the second region. Focus bias setting means for setting the second focus bias which is optimized correspondingly is provided.

[0012] According to the above configuration, the optical recording medium corresponds to an optical recording medium having a first area in which data is recorded by physical pits and a second area having a groove or the like and capable of recording data. On the basis of the characteristics of the signal obtained by reproducing the first area under the condition that the focus servo is executed by the variable focus bias, the first and second areas are optimized. It is configured to set a focus bias to be set. That is, it is possible to obtain the optimum focus bias based on the characteristics of the reproduction signal for each recording medium.

[0013]

Embodiments of the present invention will be described below. The focus bias setting device of the present embodiment is, for example, a case where the focus bias setting device is mounted on a disk drive device that is connected to a personal computer or the like as a host and employs a configuration that enables recording and reproduction of a predetermined type of disk. . Here, the type of the disk that can be recorded and reproduced by the disk drive device according to the present embodiment is not particularly limited, but in addition to a disk having a read-only area in which physical pits are formed in tracks as recording pits, A disk having a recording / reproducing area capable of recording / reproducing by a method or a phase change method,
Further, a disk or the like having a write-once (write-once) recording / reproducing area using an organic dye for a recording film is applicable. The following description will be made in the following order. 1. 1. Disk structure Disk drive device 3. Jitter detection Focus bias setting

1. Disc Structure First, a disc structure to which this embodiment corresponds will be described. FIG. 14A shows an example of a disk D which is assumed to correspond to the present embodiment. This disc D has an embossed pit area Aep in which data is recorded by physical embossed pits and is exclusively used for reproduction.
Are formed on the inner circumference side, and an overwrite area Aov in which data can be overwritten (or may be simply rewritable) is provided on the outer circumference.

The embossed pit area Aep stores, for example, disc-specific and fixed management information specific to the disc. That is, it is treated as a so-called TOC (Table Of Contents) area.

The recording / reproducing method corresponding to the overwrite area Aov in this case is not particularly limited, but a magneto-optical method or a phase change method can be adopted.

In the overwrite area Aov, for example, as shown in an enlarged view in FIG. 14B, a groove Gr as a concave part as a guide groove is formed so that the irradiated light beam can properly trace the track. Is done. Further, a land Ld as a convex portion is formed between a certain groove Gr and an adjacent groove Gr. These grooves Gr and lands Ld are formed concentrically or spirally with respect to the signal surface. Data is, for example, groove Gr
Is recorded as a track. There is a method of recording data on the land Ld, but in the following description, unless otherwise specified, the data is recorded on the groove Gr. Although not shown in this figure, meandering corresponding to the signal modulated by the address data is represented by groove Gr as address information on the disk.
And the land Ld.

As the disc D shown in FIG. 14, there are two types of discs, one having a single-layer structure (single-layer disc) and the other having a two-layer structure (double-layer disc), particularly with respect to the overwrite area Aov. 15 (a) and 15 (b) show cross-sectional structures of these discs.

First, both the single-layer disc and the double-layer disc shown in FIGS. 15A and 15B have a total disc thickness of 1.2 mm. The single-layer disk 110 shown in FIG. 15A has a transparent synthetic resin such as a transparent polycarbonate resin, a polyvinyl chloride resin, or an acrylic resin having high light transmittance and mechanical resistance or chemical resistance. The disk substrate (transparent layer) 121 is formed by the material. Then, the back side of the disk substrate 121 (upper side in the figure)
Signal surface 124 is formed. On the signal surface 124, for example, a recording track as a groove (or land) is actually formed as shown in FIG. 14B. Disk substrate 121 on which signal surface 124 is formed
Aluminum or the like having a high light reflectance is vapor-deposited on the surface to form a reflection layer 125. Adhesive surface 1 on reflective layer 125
26, through which the dummy plate 127 is bonded. Laser light from a disk drive device is incident on the single-layer disk 110 from the disk surface 128 side, and information recorded on the signal surface 124 is detected from the reflected light.

Similarly, in the two-layer disk shown in FIG. 11B, a disk substrate 121 is arranged from the disk surface 128 side, and a signal surface is formed on the back surface side of the disk substrate 121. However, in this case, since the signal surface has two layers, first,
A first signal surface 122 and a first signal surface 122 corresponding to the first signal surface 122;
The data recording surface of the first layer is formed by the reflective layer 123. The second signal surface 124 and the second reflective layer 125 corresponding to the second signal surface 124 form a second layer data recording surface. The upper surface of the second reflective layer 125 is an adhesive surface 126, through which the dummy plate 127 is adhered.

The first reflection layer 123 is a semi-transparent film, and is formed so as to reflect a certain ratio of laser light. As a result, if the laser beam is focused on the first signal surface 122, the first signal surface 122
When the laser light is focused on the second signal surface 124, the laser light passes through the first reflection layer 123 and is focused on the second signal surface 124. The signal recorded on the second signal surface 124 can be read from the light reflected by the second reflection layer 125. That is, in the case of the single-layer disc 110 shown in FIG. 15A, only the signal surface 124 and the reflection layer 125
It can be seen that the second signal surface 124 and the second reflection layer 125 in FIG.

As can be seen from FIGS. 15A and 15B, these single-layer discs and double-layer discs
22 (124) is formed at a position near the center of the thickness of the disk when viewed from the disk surface 128 side (the signal surface 122 (124) where the laser spot should be focused at a position approximately 0.6 mm from the disk surface 128 side. ) Is located).

2. FIG. 1 is a block diagram showing a configuration of a main part of a disk drive device according to the present embodiment. Disk D shown in this figure
Is mounted on a turntable 7 and rotated at a constant linear velocity (CLV) or a constant angular velocity (CAV) by a spindle motor 6 during a reproducing operation. Then, the data recorded on the signal surface of the disk D is read by the optical pickup 1.

The optical pickup 1 is provided with a laser diode 4 as a light source of laser light, an optical system including a deflection beam splitter and an objective lens 2, a photodetector 5 for detecting laser light reflected on a disk, and the like. It is configured. Here, the objective lens 2 is movably supported by the biaxial mechanism 3 in the tracking direction and the focus direction.

FIG. 2 shows an example of the structure of the optical system in the optical pickup 1. In the optical system shown in this figure, a laser beam output from a laser diode 4 is collimated by a collimator lens 51 and then reflected 90 degrees by a beam splitter 52 to a disk D side. Is irradiated. The light reflected by the disk D is passed through the objective lens 2 to the beam splitter 5.
2, the light passes through as it is, and reaches the condenser lens 53.
After being condensed by the condensing lens 53, the photodetector 5 passes through a cylindrical lens (cylindrical lens) 54.
Is incident on.

Here, the center wavelength of the laser diode 4 is set according to the type of the disk to be actually reproduced, and the numerical aperture NA of the objective lens 2 is also set according to the type of the disk to be actually reproduced. Is set.

The laser light reflected from the disk D by the reproducing operation of the disk drive device is detected by the photodetector 5 as a light receiving current. And
This light receiving current is output to the RF amplifier 9 as an information signal read from the disk. The RF amplifier 9 includes a current-voltage conversion circuit, an amplification circuit, a matrix operation circuit (RF
And a necessary signal based on a signal from the photodetector 5. For example, an RF signal as reproduction data, a push-pull signal PP for servo control, a focus error signal FE, a tracking error signal TE, a pull-in signal PI as a so-called sum signal
Generate etc.

The photodetector 5 is provided with a four-divided detector 5a including detectors A, B, C, and D in the direction shown in FIG. 3A. In this case, the focus error signal FE is supplied to the detectors A, For the outputs of B, C, and D,
It is generated by the calculation of FE = (A + C)-(B + D).

FIG. 4 shows a quadrant detector 5a according to the focus state of the objective lens 2 with respect to the disk signal surface.
2 shows a pattern example of a beam spot SP as reflected light, which is obtained by (1). For example, when the focus state of the objective lens 2 with respect to the disk signal surface is a just-focus state, the light receiving elements A, B, C, and D transmit beams as shown in FIG. The spot SP is received. That is, the light receiving elements A, B, C,
A substantially uniform amount of received light is obtained for D. On the other hand, when the focus state of the objective lens 2 with respect to the disc signal surface is closer to the focus state than the focus state,
As shown in FIG. 4B, the beam spot SP is received such that a larger amount of light is received by the light receiving elements A and C than the light receiving elements B and D. In addition, when it is located at a position farther than the focused state, as shown in FIG. 4C, a larger amount of light is received by the light receiving elements B and D than by the light receiving elements A and C. The beam spot SP is received.

In this manner, the light receiving area in the light receiving elements A, B, C, and D changes according to the focus state. The result of performing the above-described calculation for such light receiving elements A, B, C, and D is as follows. The focus error signal FE is obtained. In this case, if it is closer to the just focus state, it fluctuates in a positive region with respect to the reference value corresponding to the 0 level according to the defocus. Conversely, if it is farther than the just focus state, it changes according to the defocus. ,
The signal fluctuates in a negative region with respect to the reference value.

Further, the pull-in signal PI
= (A + B + C + D). When the push-pull signal PP is generated by the four-divided detector 5a, as shown in FIG. 2B, the detectors A, B,
Regarding the outputs of C and D, the differential amplifier 5b outputs (A + D) −
It can be generated by performing the operation of (B + C). Further, considering the so-called three-beam method, the tracking error signal TE is provided with detectors E and F for side spots separately from the quadrant detector shown in FIG.
It may be generated by an EF operation.

Returning to FIG. Various signals generated by the RF amplifier 9 are supplied to a binarization circuit 11, a servo processor 1
4 is supplied. That is, the reproduced RF signal from the RF amplifier 9 is supplied to the binarization circuit 11, and the push-pull signal PP, the focus error signal FE, the tracking error signal TE, and the pull-in signal PI are supplied to the servo processor 14.

The reproduction RF signal output from the RF amplifier 9 is binarized by the binarization circuit 11 to generate a binarized signal (for example, an EFM signal (8-14 modulated signal) or an EFM + signal).
The signal is branched and supplied to the encoder / decoder 12, the PLL (Phase Locked Loop) circuit 20, and the jitter detection circuit 21.

In the PLL circuit 20, the reproduction clock P synchronized with the channel bit frequency of the input binary signal
Generate LCK. The reproduction clock PLCK is used as a reference clock for signal processing or the like at the time of reproduction, and is supplied to, for example, the encoder / decoder 12 as shown in FIG. . In the present embodiment, the reproduction clock PLCK is also supplied to the jitter detection circuit 21.

At the time of reproduction, the encoder / decoder 1
In the decoding unit 2, EFM demodulation or EFM + demodulation, and error correction processing (RS-PC scheme,
The information read from the disk D is reproduced by performing the CIRC method or the like. The data decoded by the encoder / decoder 12 is supplied to a host computer (not shown) via the interface unit 13. Further, the encoder / decoder 12 obtains disk rotation speed information from the reproduction clock PLCK. This disk rotation information indicates the relative speed between the laser spot output from the optical pickup 1 and the track on which the recording pit is formed.

The jitter detection circuit 21 detects the amount of jitter of the binarized signal using the input binarized signal and the reproduction clock PLCK as described later, and outputs information on the detected amount of jitter. , And a jitter value JT to the system controller 10. Here, the jitter refers to the fluctuation of the binarized signal along the time axis.

When data is recorded on the disk D, for example, data supplied from a host computer (not shown) is sent to the encoder of the encoder / decoder 12 via the interface 13.

In the encoding section, the data input from the interface section 13 is subjected to addition of an error correction code according to a predetermined method and encoding processing.
Further, predetermined modulation processing for recording on the disk D is performed to generate recording data WD. Here, for example, assuming that the overwrite area Aov of the disk D corresponds to the magneto-optical method and the recording is performed by the light modulation overwrite method, the recording data WD is transferred to the laser driver 18.
Output to The laser driver 18 generates a laser diode drive voltage modulated based on the supplied recording data, and drives the laser diode 4 of the optical pickup 1. As a result, the laser diode 4 emits a pulse light modulated by the recording data WD. On the other hand, for example, the system controller 10
By controlling the magnetic head driver 22, the magnetic head 23 generates, for example, a required constant level magnetic field and applies it to the disk D. Thus, data recording by the light modulation overwrite method is realized.

If recording is performed by a magnetic field modulation overwriting method (here, a simple magnetic field modulation method is taken as an example), the recording data WD generated by the encoder of the encoder / decoder 12 is transferred to the magnetic head driver 2.
2 to be supplied. The magnetic head driver 22 outputs a drive signal corresponding to the input recording data WD to the magnetic head 23, thereby generating an N or S magnetic field corresponding to the recording data from the magnetic head 23 and applying the magnetic field to the disk. I do. At the same time, the system controller 1
In the case of 0, laser drive control data in which a laser power corresponding to a required recording level is set is generated and output to the laser driver 18 as a laser drive signal via the servo processor 14, for example. As a result, light is emitted from the laser diode 4 with the laser power corresponding to the recording level. In this manner, by applying the external magnetic field modulated by the recording data and irradiating the laser beam with the laser power of the recording level, the recording can be performed by the magnetic field modulation overwriting method. As a magnetic field modulation overwrite method, a so-called laser strobe magnetic field modulation method has been proposed which achieves a higher recording density than the simple magnetic field modulation method. The system controller 10 may perform control so that the modulated external magnetic field is applied and the laser light is pulsed according to the clock timing of the recording data.

As can be said in any of the above-described magneto-optical recording methods, the laser diode 4 of the optical pickup 3 at the time of recording has a power enough to raise the temperature on the recording surface of the disk D to the so-called Curie point. The magnetic head 23 applies a magnetic field to the recording surface of the disk D whose temperature has risen to the Curie point due to the laser light, and then applies a magnetic field to the recording surface with the rotation of the disk D. When the temperature is lowered, the applied magnetic field remains, which means that recording has been performed.

The overwrite area A of the disk D
When recording is performed on the overwrite area Aov on the assumption that ov corresponds to the phase change method, for example, the recording data WD generated by the encoding unit of the encoder / decoder 12 is supplied to the laser driver 18. In this case, for example, the laser driver 18 performs modulation based on the input recording data WD, generates a laser diode driving voltage in which a required recording level and erasing level are combined, and drives the laser diode 4. Thus, data recording is performed according to the phase change method. When adopting only the recording / reproducing configuration based on this phase change method,
The magnetic head driver 22 and the magnetic head 23 may be omitted.

The servo processor 14 generates various servo drive signals for focus, tracking, thread, and spindle from the focus error signal FE, tracking error signal TE, push-pull signal PP, and the like from the RF amplifier 9, and executes the servo operation. . That is, a focus drive signal FDR and a tracking drive signal TDR are generated in accordance with the focus error signal FE and the tracking error signal TE, and are supplied to the biaxial driver 16.

The biaxial driver 16 includes, for example, a focus coil driver 16a and a tracking coil driver 16b. The focus coil driver 16a supplies the drive current generated based on the focus drive signal FDR to the focus coil of the biaxial mechanism 3 to drive the objective lens 2 in the direction of moving toward and away from the disk surface. The tracking coil driver 16b supplies the drive current generated based on the tracking drive signal TDR to the tracking coil of the biaxial mechanism 3 to drive the objective lens 2 to move in the disk radial direction. Thereby, the optical pickup 1, the RF amplifier 9, the servo processor 1
4. A tracking servo loop and a focus servo loop by the two-axis driver 16 are formed.

The servo processor 14 supplies a spindle drive signal generated from the spindle error signal SPE to a spindle motor driver 17 described later. The spindle motor driver 17 applies, for example, a three-phase drive signal to the spindle motor 6 in accordance with the spindle drive signal, and drives the spindle motor 6 to rotate at a required rotational speed. Further, the servo processor 14 generates a spindle drive signal in response to a spindle kick (acceleration) / brake (deceleration) signal from the system controller 10, and the spindle motor driver 1
7 to start or stop the spindle motor 6.

The servo processor 14 generates a thread drive signal based on, for example, a thread error signal obtained from a low-frequency component of the tracking error signal TE and an access execution control from the system controller 10 and supplies the thread drive signal to the thread driver 15. . The thread driver 15 responds to the thread drive signal by the thread mechanism 8.
Drive. The sled mechanism 8 is a mechanism for moving the entire optical pickup 1 in the radial direction of the disk. The sled driver 15 drives a sled motor inside the sled mechanism 8 in accordance with a sled drive signal, so that the optical pickup 1 can slide properly. Is performed.

Further, the servo processor 14 also performs light emission drive control of the laser diode 4 in the optical pickup 1. The laser diode 4 is a laser driver 18
The servo processor 14 generates a laser drive signal for performing laser emission at the time of recording / reproduction based on an instruction from the system controller 10, and generates a laser drive signal based on an instruction from the system controller 10.
To supply. In response, the laser driver 18 drives the laser diode 4 to emit light.

Various operations such as servo and encode / decode as described above are controlled by a system controller 10 including a microcomputer and the like. For example, operations such as reproduction start, end, track access, fast forward reproduction, and fast reverse reproduction are realized by the system controller 10 controlling the operation of the optical pickup 1 via the servo processor 14. The table 10a shown in FIG.
The information is stored in an internal ROM or the like, and includes the emboss pit area Ae set corresponding to the overwrite area Aov for each disc type.
This is an offset value for the focus bias corresponding to p, which will be described later.

FIG. 5 shows a configuration in which the focus servo system is extracted from the configuration shown in FIG. In this figure, the same parts as those in FIG. The light receiving signal detected by the photo detector of the optical pickup 1 is supplied to the RF amplifier 9 as described above. The RF amplifier 9 generates a focus error signal FE as one of the generated signals,
Supply to the focus servo system inside. As a focus servo system in the servo processor 14 shown in this figure, a target value control circuit 41, a differential amplifier 42, and a phase compensation circuit 43 are provided. The target value control circuit 41 generates and outputs a voltage level as a focus bias to be superimposed on the focus error signal as a target value for the convergence of the circuit system by the focus servo loop. The value of the focus bias is set based on a bias setting control signal output from the system controller 10.

The focus error signal FE is input to the non-inverting input of the differential amplifier 42, and the voltage level as the focus bias output from the target value control circuit 41 is supplied to the inverting input. As a result, the focus error signal FE on which the focus bias set by the target value control circuit 41 is superimposed is output from the differential amplifier 42.

The output of the differential amplifier 42 is supplied to a phase compensation circuit 43
And the focus coil drive signal F
DR is supplied to the focus coil driver 16a. The focus coil of the biaxial mechanism 3 is driven according to the input focus coil drive signal FDR from the focus coil driver 16a to move the objective lens 2 in the direction of coming and coming from the disk.

In the configuration shown in FIG. 5, if the focus offset value to be output from the target value control circuit 41 is "0", the focus error signal level becomes 0 so that the focus servo loop circuit system Will work. If the focus bias value is set as the value “x”, the operation is performed so that the zero level of the focus error signal converges to the level shifted by the focus bias value “x”. .

As described above in the conventional example, a state occurs in which the focus state when the focus error signal is at the 0 level is not the best image formation state due to various factors. Focus error signal FE
By setting the focus bias, it is possible to always obtain an appropriate imaging state as the focus servo control by the closed loop. In addition,
As the present embodiment, a configuration for determining a focus bias to be set for the target value control circuit 41 will be described later.

3. Jitter Detection In the disk drive device having the configuration described above, the amount of jitter in data reproduced from the disk can be detected. In the present embodiment, this amount of jitter is
It is used to set a focus bias that is optimized at least in response to focus servo control in at least the emboss pit area. Then, in the present embodiment,
A configuration for detecting jitter will be described.

FIG. 6 is a block diagram showing a configuration example of the jitter detection circuit 21. The jitter detection circuit 21 shown in this figure comprises a multiplier 30, a ΔT detection circuit 31, and a jitter value calculation circuit 32.

For the ΔT detection circuit 31, the binarized signal from the binarization circuit 11, the reproduction clock PLCK, and the reproduction clock PLCK are multiplied by the multiplier 30 by a predetermined multiple n. nxPLCK) is input. Here, it is assumed that the multiple n = 10 and the multiplied clock MCK is a frequency signal obtained by multiplying the reproduction clock PLCK by about 10 times. Note that the actual multiple n
May be arbitrarily set to a value so that the counting of the period of ΔT described later can be performed as accurately as possible.

FIG. 7 is a timing chart showing signals input to the ΔT detection circuit 31, and FIG.
(B) and (c) show the input binary signal, reproduced clock PLCK, and MCK, respectively. here,
As the binarized signal shown in FIG. 7A, an inversion interval based on the H level of 3T is shown. As described above, the reproduction clock PLCK shown in FIG. 7B is a signal having the channel bit frequency of the binary signal and synchronized with the binary signal. Further, the multiplied clock MCK shown in FIG. 7C is a frequency signal obtained by multiplying the reproduced clock PLCK, and thus becomes a frequency signal synchronized with the reproduced clock PLCK.

By the way, ideally, the edge timing of the binarized signal and the edge timing of the reproduced clock PLCK should coincide with each other on a time axis. Period t
As shown in 0 to t1 and the subsequent periods t2 to t3, a phase error represented by ΔT may occur.

Here, the amount of jitter refers to the phase error Δ
This refers to the range of fluctuation of T. So, for example,
ΔT, ΔT, sampled each time the binary signal is inverted,
If ΔT... Is constant, the jitter is set to zero. On the other hand, ΔT, ΔT,
If ΔT... Is not constant and a change is observed, a jitter exists, and the larger the change amount, the larger the jitter amount. Although several factors can be considered for the generation of such jitter, mainly the variation of the recording pit length itself formed as data on the disk D is cited. In addition, including defocusing of the laser beam irradiated during reproduction,
It occurs depending on the operation performance of the reproducing system including the optical system.
That is, the jitter amount can indicate the formation state of the recording pit length, and can also be used as information indicating the good reproduction characteristics.

The .DELTA.T detecting circuit 31 detects the phase error amount as .DELTA.T each time the edge position is obtained by inverting the binary signal waveform. The detection is performed, for example, as follows. be able to.

FIG. 8 is an enlarged view showing the vicinity of the periods t0 to t1 in FIG. In the jitter detection circuit 21,
For example, when the rising (or falling) edge position of the input binary signal waveform (FIG. 8A) is detected at time t0, the earliest PLCK (see FIG. 8 (b)), the period (that is, the period during which the phase error ΔT occurs) between the time points t1 at which the rising edge is obtained, and the cycle (for example, the number of inversions) of the multiplied clock MCK shown in FIG. I do. The multiplied clock MCK is a signal synchronized with the reproduction clock PLCK.

FIG. 8 shows a state in which three cycles of the multiplied clock MCK are obtained in the period t0 to t1 and "6" is obtained as the number of inversions.
The detection circuit 31 outputs, for example, the counted value of the number of inversions to the jitter value calculation circuit 32 as the value of the phase error ΔT. Here, the value of the phase error ΔT is used as the number of inversions, but the present invention is not particularly limited to this as long as the value is as accurate as possible, and may be, for example, the number of appearances of an H-level pulse. is there.

The jitter value calculating circuit 32 obtains information on the value of the phase error ΔT every time the binary signal is inverted. Therefore, the jitter value calculation circuit 32 obtains the jitter value JT by taking a predetermined m number of samples for the value of the phase error ΔT sequentially obtained each time the binary signal is inverted, and performing the following operation. To be. Here, m sampled phase errors ΔT are represented as ΔTi (1 ≦ i ≦ m) according to the sampled time axis. First,

(Equation 1) By performing the calculation represented by, an average value of m sampled ΔTi, ΔTi, ΔTi... Is obtained. Then, using this average value,

(Equation 2) The jitter value JT is obtained by executing the calculation represented by. The jitter value JT expressed by (Equation 2) indicates a fluctuation width between the m sampled ΔTis, ΔTi,.... The jitter value JT calculated in this way is input to the system controller 10.

The number of samples m is the jitter value J
T can be obtained with the highest possible accuracy and the jitter value J
It may be arbitrarily set in consideration of preventing the time required for calculating T from becoming unnecessarily long. In addition, since various internal configurations of each unit forming the jitter detection circuit 21 are conceivable, detailed illustration is omitted here. For example, the ΔT detection circuit 31, the jitter value calculation circuit 32, and the like can easily realize the above operation by combining various digital circuits and logic circuits. Also, the method of calculating the jitter value JT shown in the above (Equation 1) and (Equation 2) is merely an example, and may be performed using other arithmetic expressions or the like.

4. Focus Bias Setting In the present embodiment, the focus bias is set as follows. Here, it is assumed that the disk D having the structure shown in FIG. 14 is loaded. That is, the disc has an emboss pit area Aep and an overwrite area Aov. First, in the present embodiment, assuming that the disc D is loaded, trial reproduction is performed on a predetermined recorded area in the emboss pit area Aep. However, at this time, as the focus bias, the focus bias is sequentially changed at a predetermined timing within an appropriately set range.

Here, performing reproduction while changing the focus bias means that the goodness of the focus state obtained by the focus servo loop control changes. The signal reproduced at this time includes:
This will affect the quality of the characteristics. In other words, the focus bias set when the signal characteristics are in the best state is at least the emboss pit area A
The focus bias can be optimized to correspond to ep. In the present embodiment, the signal characteristic serving as this judgment material is the jitter value JT described above. That is, in the present embodiment, the jitter value JT obtained during the period of the trial reproduction is monitored.

FIG. 9 shows an example of the relationship between the focus bias obtained as a result of the trial reproduction and the jitter value JT. In this figure, the horizontal axis is the focus bias, and the vertical axis is the jitter value. Further, the crosses in the coordinates in the figure indicate sample points (measurement points). In this case, six sample points (-3, -2, -1, 0,
The case where the jitter value is measured by 6 points (1, 2) is shown.

For example, in the case where the result shown in this figure is obtained, the focus bias as the optimum value can be obtained as follows. One is the lowest jitter value (best value) among sample points.
Is a method of setting the focus bias at the time when is obtained as an optimum value. In the case of FIG. 9, the coordinates (−1,
1) is an extreme value. Therefore, in this case, focus bias = −1 is set as the optimum value. One is to find a region where the change rate of the jitter value is the lowest according to the measurement result, and set the focus bias corresponding to this region as the optimum value. In the case of FIG. 9, the change rate of the jitter value is the lowest near the coordinate (-1, 1). Therefore, also in this case, the focus bias = −1 is set as the optimum value.

One is that the jitter value at the coordinates is close to a predetermined value and the average value or the arithmetic mean value of two sample points sandwiching the extreme value as the jitter value is calculated as the focus bias. This is a method of setting as an optimum value. Here, in the case of FIG. 9, assuming that the preset jitter value is “2”, two sample points close to the jitter value 2 and sandwiching the extreme value coordinates (−1, 1) are: , Coordinates (-2,1.8) (1,2)
Becomes Then, when an average value is obtained by using the focus bias values of these two sample points, (−2 + 1) /2=−0.5, and the focus bias = −0.5 is obtained. In addition, in the case of FIG. 9, if the arithmetic mean value is obtained, as in the case of obtaining the average value, if the preset jitter value is set to “2”, the coordinates of the extreme value (−1, 1) and a jitter value close to 2 and 2
Coordinates (-2,1.8) as one sample point
(1, 2). Then, when the arithmetic mean is obtained from the values of these two coordinates, (−2 / 1.8 + 1/2) / (| −2 + 1 |) ≒ −0.
6, and a focus bias of -0.6 is obtained. It should be noted that other arithmetic expressions for calculating the arithmetic mean can be considered.

One is to use the fact that the focus bias and the jitter value have a certain degree of correlation (for example, the result shown in FIG. 9 has a quadratic function). By performing a required numerical calculation process using all or a part of the measurement results of the points, a value assumed that the jitter value is an extreme value is calculated, and it is further estimated that the jitter value corresponds to this extreme value. The focus bias value is calculated. Then, the calculated focus bias value is set as an optimum value. In the case of FIG. 9, a numerical operation process is performed by using all or a part of the sample information (focus bias and the jitter value measured corresponding to the focus bias) obtained at the six sample points. Is performed, and a focus bias which is assumed to correspond to the jitter value calculated as an extreme value at this time is calculated, and this is set as an optimum value.

The focus bias set in this manner is obtained by performing trial reproduction on the emboss pit area Aep, and therefore, directly, the focus bias is directly set in the emboss pit area. The focus bias becomes optimal when the focus servo control is performed on Aep. Therefore, the focus bias obtained in the steps up to this point (hereinafter also referred to as “first focus bias”) is set as a focus bias as at least an optimum value when reproducing the embossed pit area Aep of the disc. You can do it. That is, when the actual emboss pit area Aep is reproduced, the focus servo loop control may be performed by superimposing the first focus bias on the focus error signal FE. To do this, as mentioned above,
The system controller 10 controls the bias setting control signal S1.
, The control should be executed so that the first focus bias obtained by the detection operation so far is set to the target value control circuit 41.

As characteristics of a certain type of disc D, the emboss pit area Aep and the overwrite area A
If it is known that the focus bias with the same value may be set in ov and ov, the first focus bias is set in common and the focus servo loop control is executed even when the overwrite area Aov is reproduced. It should be good.

However, depending on the type of disc, the optimum focus bias may be different between the emboss pit area Aep and the overwrite area Aov. Therefore, in such a case, the focus bias which is optimized for each of the emboss pit area Aep and the overwrite area Aov is determined as follows.

Here, the focus bias optimized for the emboss pit area Aep is determined by the first bias described above.
Since it is sufficient to use the focus bias, first, FIG.
May be the first focus bias obtained by trial reproduction of the emboss pit area Aep described with reference to FIG. Then, the focus bias (hereinafter referred to as “second bias”) which is optimized for the emboss pit area Aep.
Focus Bias))
After obtaining the focus bias, the first focus bias is used to obtain the focus bias as described below.

FIG. 10 shows the measurement results of the focus bias and the jitter value when trial reproduction was performed on the emboss pit area Aep and the overwrite area Aov for a specific type of disc. ing. The disc shown in this figure is a single-layer disc (see FIG. 15B), and has an overwrite area A
In the case of ov, the disc is recorded on the groove Gr as a track. In this case, a curve L1 is a measurement result of the emboss pit area Aep, and a curve L2 is a measurement result of the overwrite area Aov.
According to this figure, for example, the offset amount of the focus bias (between B1 and B2) corresponding to each extreme value of the curves L1 and L2 is represented by (x).

Although the offset amount (x) has a certain slight error, it can be regarded as unique and unique to this type of disc. Therefore, when obtaining the focus bias for this type of disc, first, the first focus bias is obtained by trial reproduction of the emboss pit area Aep as described above, and then the value of the first focus bias is set to m, and the second focus bias is set to m. Assuming that the focus bias is n, n = m + x is obtained. Thus, the first focus bias corresponding to the emboss pit area Aep and the second focus bias optimized for the overwrite area Aov are obtained. In actuality, the target value control circuit 41 sets the first focus bias when reproducing the emboss pit area Aep and sets the second focus bias when reproducing the overwrite area Aov.

The disc type is a single-layer disc, and in the overwrite area Aov, recording is performed using the groove Gr and the land Ld as tracks (here, a land / groove disc). ) Is also conceivable. In such a disc, it is conceivable that the optimal focus bias differs between the groove area and the land area in the overwrite area Aov. In such a case, the optimum focus bias is determined for each of the emboss pit area Aep, the groove area, and the land area as follows. FIG. 11 shows a measurement result (a relationship between a focus bias and a jitter value) when trial reproduction is performed on a certain type of land / groove disk. In this figure, a curve L1 is an emboss pit area Aep, a curve L2 is a groove area,
A curve L3 is a measurement result of the land area. According to this figure, for example, the offset amount of the focus bias (between B1 and B2) corresponding to each extreme value of the curves L1 and L2 is (x1)
It is represented by Further, for example, the offset amount of the focus bias (between B1 and B3) corresponding to each extreme value of the curves L1 and L3 is represented by (x2).

Also in this case, the offset amount (x1)
Although (x2) has some slight errors, it can be regarded as unique and unique to this type of disc. Therefore, when a focus bias is determined for this type of disc, first, the first focus bias is determined by trial reproduction of the emboss pit area Aep described above. Then, thereafter, the value of the first focus bias is set to m, and the second focus bias corresponding to the groove area is set to n1, so that the second focus bias optimized for the groove area is obtained by the calculation of n1 = m + x1. To be. Similarly, when the value of the first focus bias is set to m and the second focus bias corresponding to the land area is set to n2, the calculation of n2 = m + x2 is performed.
A focus bias is obtained. It should be noted that the second focus bias can also be obtained by performing the above-described calculation of n2 for a disk having a format in which recording is performed only on the land Ld. In this manner, following the first focus bias corresponding to the emboss pit area Aep, two second focus biases which are optimized corresponding to each of the groove area and the land area are obtained.

Further, in a two-layer disc as shown in FIG. 15B, in the overwrite area Aov,
Further, it is conceivable that the focus bias differs between the first signal surface and the second signal surface. Even in such a case, it is possible to obtain the optimum focus bias for each of the first signal surface and the second signal surface in the emboss pit area Aep and the overwrite area Aov as follows.

FIG. 12 shows a measurement result (a relationship between a focus bias and a jitter value) when trial reproduction is performed for a specific type of two-layer disc. In this figure, the curve L1 corresponds to the emboss pit area Aep and the curve L1
0 is the measurement result of the first signal surface, and curve L11 is the measurement result of the second signal surface. According to this figure, for example, the focus bias (between B1 and B10) corresponding to each extreme value of the curves L10 and L11
Is represented by (x10). Further, for example, the offset amount of the focus bias (between B1 and B11) corresponding to each extreme value of the curves L1 and L11 is represented by (x11). It is assumed that the measurement results shown in this drawing correspond to a disc defined to record the groove Gr as a track on both the first signal surface and the second signal surface.

Also in this case, the offset amount (x10)
Although (x11) has a certain slight error, it can be regarded as unique and unique to this type of disc. Therefore, when a focus bias is determined for this type of disc, first, the first focus bias is determined by trial reproduction of the emboss pit area Aep described above. After that, the value of the first focus bias is set to m and the second focus bias corresponding to the first signal layer is set to n10.
A focus bias is obtained. Similarly, when the value of the first focus bias is set to m and the second focus bias corresponding to the second signal layer is set to n11, the calculation of n11 = m + x11 is performed to optimize the second signal bias for the second signal layer.
A focus bias is obtained.

By doing so, the emboss pit area A
In addition to the first focus bias optimized for ep, two second focus biases optimized for each of the first signal layer and the second signal layer in the overwrite area Aov are obtained. Can be Note that the groove of the second signal layer is optically first placed in FIG.
In some cases, the land / groove disk may be equivalent to the land described in 1 above. In this case, the focus bias setting can be handled in the same manner as the land / groove disk.

In the present embodiment, for example, as described with reference to FIGS. 10 to 12, in order to enable an appropriate focus bias to be obtained for each disc type, for example, the present embodiment Measurement is performed in advance for each disc type that is assumed to be reproduced by the disc drive device of the embodiment, data of an offset value with respect to a first focus bias for obtaining a second focus is obtained, and this information is used as a parameter. It is stored in a set of disk drive devices. This is the table 10a shown in FIG. At the time of actual focus bias setting, the offset value corresponding to the currently loaded disc type and the area to be reproduced is read out, and as described above, it is determined that the offset has already been obtained by the previous trial reproduction. By performing an operation of giving an offset value to the first focus bias,
An optimal second focus bias is determined.

Next, a processing operation for actually realizing the above-described operation for obtaining the focus bias will be described with reference to FIG.
This will be described with reference to the flowchart of FIG. The processing shown in this figure is executed by the system controller 10.

In this routine, first, in step S101, the process waits for a disk to be loaded. If it is determined that a disk has been loaded, the process proceeds to step S102. In step S102, a control process for performing a seek on a predetermined area of the emboss pit area Aep is executed. Then, step S10
In 3, control for executing the trial reproduction described above is performed. That is, reproduction is performed on a predetermined area of the embossed pit area sought in step S102. At this time, for example, a focus bias that is stepwise changed at a predetermined timing is set in the target value control circuit 41 (see FIG. 5). To be. Then, the jitter value JT of the binarized signal reproduced at this time is fetched and held in the internal RAM corresponding to each changed focus bias.

At the stage where the trial reproduction in step S103 is completed, data indicating the relationship between the focus bias as a sample point and the jitter value JT as shown in FIG. 9 is obtained in the internal RAM. Therefore, in the subsequent step S104, the first focus bias is obtained by using, for example, an arbitrary calculation method set in advance among the calculation methods described with reference to FIG. Then, the value of the first focus bias obtained here is held in the internal RAM.

Subsequently, in step S105, disc type is determined. The determination here is
For example, the identification information of the disc type recorded in the emboss pit area Aep is read, and the identification can be performed based on the identification information. When the disk type is determined in step S105, in a succeeding step S106, a parameter (offset value) corresponding to the disk of the determined type is read from the table 10a and the internal RA is read.
M. Then, the following step S1
In step 07, the second focus bias as described above is obtained by using the parameter (offset value) taken in step S106. Then, the calculated second focus bias is held in the internal RAM. When the process of step S107 is completed, the process for setting the focus bias ends.

As described above, step S107
As the second focus bias to be obtained by the above, a plurality of values may be calculated in accordance with each area to be used, depending on the disc type. Further, in the case where the same focus bias may be used in the emboss pit area Aep and the overwrite area Aov depending on the disc type, for example, the table 10
In a, 0 may be set as the offset value. As a result, as a result, the second focus bias is made to be the same as the first focus bias. Further, when the same focus bias may be used between different areas (or signal planes) in the same overwrite area Aov, the same value may be set as these offset values.

As described above, the values of the first and second focus biases calculated in steps S104 and S107 and held in the internal RAM are determined according to the area to be reproduced in the subsequent disk reproduction. The target value control circuit 41 is read out and set as described above. As a result, at the time of actual reproduction, the focus servo control in a closed loop is executed under a state in which a focus bias set appropriately for each loaded disc is applied. That is, an appropriate focus servo control operation can be obtained.

Note that the present invention is not limited to the configuration described above. For example, as the recording area, C
There is also a write-once type in which recording data is formed as physical pits (emboss pits), like a recording layer of DR.
In the above description, the emboss pit area Aep
Is a read-only area. From the viewpoint that an emboss pit is formed and data is to be recorded in this area, the emboss pit area Aep may be, for example, such as the recording layer of the CD-R. It is conceivable to set a write-once recording area. Even in such a case, the present invention can be applied if any data is recorded in the write-once emboss pit area Aep. vice versa,
This is defined as a groove Gr as an overwrite area Aov.
If the write-once area is considered as a write-once area, the overwrite area Aov should be set as such a write-once area since the write-once recording layer such as the CD-R also has a groove. Is also conceivable.

In the above embodiment, a recording / reproducing apparatus capable of recording / reproducing is taken as an example of a disk drive apparatus. However, the disk drive apparatus to which the present invention is applied may be a reproduction-only apparatus. It doesn't matter. Further, the disk drive device of FIG. 1 only shows a general configuration to a certain extent, and each unit is appropriately changed, for example, necessary or necessary functional circuit units are added or deleted according to the type of the corresponding disk. Is what is done.
In addition, a jitter value is employed as a signal characteristic for obtaining a focus bias, but other signal characteristics such as a signal amplitude and a modulation degree may be employed as long as the signal characteristic depends on a defocus state. Things.

[0091]

As described above, according to the present invention, a first area (emboss pit area) in which data is recorded by forming physical pits, and pits other than the physical pits are formed as recording data. As a result, reproduction is performed while changing the focus bias with respect to the first area on the assumption that the optical recording medium has a second area (overwrite area) in which data is recorded. On the basis of the obtained signal characteristics, the first region and the second region are individually optimized or optimized (the first region and the second region are commonly optimized). (When the bias characteristics are the same) and a second focus bias that is optimized for each of the second regions. According to this configuration, the focus bias is set appropriately for each loaded disc. In other words, it is possible to obtain the optimum focus bias for each loaded disk, regardless of the variation of the condition due to the aging of the optical system or the variation of each disk.
Therefore, it is possible to execute appropriate focus servo control regardless of what kind of disk is loaded. Further, by using a reproduction signal, it is possible to obtain, for example, a highly accurate focus bias value. In particular, even in a system in which a margin for defocus is reduced by supporting a medium having a high recording density. High reliability is obtained. Further, by using the reproduced signal, there is no need to add a functional circuit unit or the like for obtaining a focus bias, and a relatively simple configuration is realized. Also, even if no data is recorded in the second area, which is generally rewritable, if the first area (emboss pit area) is set as a read-only area, The focus bias can always be obtained by using the first area in which some data is recorded.

Further, as a configuration for setting an optimum focus bias corresponding to each of the first region and the second region individually, a trial bias is set so as to be optimum corresponding to the first region by trial reproduction. By setting the first focus bias and giving an offset value to the first focus bias, the second focus bias which is optimized for the second region is set. Even with a simple configuration, it is possible to obtain a focus bias with high accuracy corresponding to each recording area. Further, at this time, if the second focus bias is obtained by giving an offset value set according to each disc type to the first focus bias, the accuracy can be adjusted in accordance with the disc type. A high focus bias can be obtained.

In determining the focus bias based on the signal characteristic, the focus bias set when the predetermined signal characteristic is optimized or when the rate of change thereof is minimized is determined by the first. If the focus bias is set, the focus bias can be obtained by relatively simple processing. Further, an arithmetic mean or an average value of the focus biases set so that the predetermined characteristic is close to the extreme value as the best and corresponding to two or more samples sandwiching the extreme value is set as the first focus bias. , And even based on the sample values,
If the first focus bias is obtained by performing a numerical operation process for obtaining a focus bias corresponding to the extreme value of the signal characteristic, the first focus bias can be obtained with high accuracy even with a required minimum number of samples. Focus bias can be obtained.

When the amount of change in jitter is detected as a predetermined characteristic of a reproduction signal used to obtain an optimum focus bias, for example, the jitter of the original disk drive device is used as a characteristic. When a configuration for detecting the amount of change is provided, this can be used, and it is not necessary to add a functional circuit unit, so that cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a disk drive device according to an embodiment of the present invention.

FIG. 2 is a structural diagram conceptually showing a structural example of an optical system of the optical pickup.

FIG. 3 is an explanatory diagram showing a detection operation by a photodetector of the optical pickup.

FIG. 4 is an explanatory diagram showing a beam spot shape received by a photodetector according to a focus state.

FIG. 5 is a block diagram illustrating a focus servo system according to the present embodiment.

FIG. 6 is a block diagram illustrating a configuration example of a jitter detection circuit according to the present embodiment.

FIG. 7 is a timing chart for explaining an operation of detecting a phase difference between a binarized signal and a reproduced clock, which is required for jitter detection according to the present embodiment.

FIG. 8 is a timing chart for explaining an operation of detecting a phase difference between a binarized signal and a reproduced clock, which is required for jitter detection according to the present embodiment.

FIG. 9 is an explanatory diagram showing an example of a relationship between a focus bias and a jitter value obtained by trial reproduction of an embossed pit area.

FIG. 10 is an explanatory diagram showing an example of a relationship between a focus bias and a jitter value in a case where an emboss pit area and an overwrite area are reproduced.

FIG. 11 is an explanatory diagram showing an example of a relationship between a focus bias and a jitter value when reproducing an emboss pit area and an overwrite area (groove area / land area).

FIG. 12 illustrates a case where an emboss pit area and an overwrite area (first signal surface / second signal surface) are reproduced.
FIG. 3 is an explanatory diagram illustrating an example of a relationship between a focus bias and a jitter value.

FIG. 13 is a flowchart illustrating a processing operation for obtaining first and second focus biases.

FIG. 14 is a perspective view showing a disk structure to which the present embodiment corresponds.

FIG. 15 is a sectional view showing a disk structure to which the present embodiment corresponds.

FIG. 16 is an explanatory view conceptually showing a state of a laser beam irradiated on a signal surface of a disk.

[Explanation of symbols]

1. Optical pickup, 2. Objective lens, 3. Biaxial mechanism, 4. Laser diode, 5. Photodetector, 5.
a split detector, 5b differential amplifier, 6 spindle motor, 7 turntable, 8 thread mechanism, 9
RF amplifier, 10 system controller, 10a
Table, 11 binarization circuit, 12 decoder, 13
Interface section, 14 Servo processor, 15
Thread driver, 16 two-axis driver, 16a focus coil driver, 16b tracking coil driver, 17 spindle motor driver, 18 laser driver, 20 PLL circuit, 21 jitter detection circuit, 22 magnetic head driver, 23 magnetic head, 3
0 multiplier, 31 ΔT detection circuit, 32 jitter value calculation circuit, 51 collimator lens, 52 beam splitter, 53 condenser lens, 36 cylindrical lens, 41
Target value control circuit, 42 differential amplifier, 43 phase compensation circuit, 110 single-layer disk, 120 double-layer disk, 1
21 disk substrate, 122 (first) signal surface, 123
(First) reflective layer, 124 second signal surface, 125 second
Reflective layer, 126 bonding surface, 127 dummy plate, 128
Disk surface, Aep embossed pit area, Aov
Overwrite area, D disk, Gr groove,
Ld Land

Claims (9)

[Claims] At least a first area in which data is recorded by forming physical pits and a second area in which data is recorded by forming pits other than the physical pits as recording data. Is provided for a recording / reproducing apparatus capable of performing recording / reproduction by irradiating the optical recording medium with a converged laser beam after being adapted to the optical recording medium having As a focus bias setting device for setting a focus bias for giving an offset to a focal position of a laser beam, a trial reproduction of performing data reproduction with respect to a first area of the optical recording medium while variably setting a focus bias is performed. Measuring a predetermined signal characteristic of the reproduction data obtained by the trial reproduction means. Sample means for obtaining the measurement result as sample information in association with the focus bias set at the time of the trial reproduction, and individually corresponding to the first area based on the sample information obtained by the sample means. A first focus bias that is optimized for the first region and the second region that is optimized for the second region, and a second focus bias that is optimized for the second region individually. A focus bias setting device, comprising: a focus bias setting unit configured to set the focus bias of the focus bias setting. 2. The method according to claim 1, wherein the focus bias setting unit sets a first focus bias and a second focus bias that are optimized individually in the first area and the second area. A configuration in which the first focus bias is directly set based on the sample information, and the second focus bias is set by giving a specific offset value to the first focus bias. The focus bias setting device according to claim 1, wherein: 3. A medium type discriminating means for discriminating a type of a recording medium loaded in a recording / reproducing portion capable of recording or reproducing, wherein the focus bias setting means is discriminated by the medium type discriminating means. Wherein the second focus bias is set by giving the specific offset value set according to the type of the recording medium to the first focus bias. Item 3. The focus bias setting device according to Item 2. 4. The focus bias setting means, based on the sample information, specifies a focus bias set at the time of the trial reproduction corresponding to reproduction data whose predetermined signal characteristic is determined to be the best. 2. The focus bias setting device according to claim 1, wherein the focus bias setting device is configured to set the first focus bias. 5. The focus bias setting means according to claim 1, wherein said focus bias setting means sets a focus bias set at said trial reproduction in accordance with reproduction data whose change rate of said predetermined signal characteristic is determined to be minimum based on said sample information. The focus bias setting device according to claim 1, wherein the first focus bias is set by specifying the first focus bias. 6. The method according to claim 1, wherein the focus bias setting means is configured to determine, based on the sample information, that the predetermined signal characteristic is close to a predetermined value and is an extreme value of the measured predetermined signal characteristic. An average value is calculated by using a focus bias as sample information obtained at two measurement points sandwiching the point, and the calculated average value is set as the first focus bias. Item 2. The focus bias setting device according to Item 1. 7. The method according to claim 7, wherein the focus bias setting means is configured to determine, based on the sample information, that the predetermined signal characteristic is close to a predetermined value and is an extreme value of the measured predetermined signal characteristic. Calculating an arithmetic mean value for the focus bias using sample information obtained at two measurement points sandwiching the point, and setting the calculated arithmetic mean value as the first focus bias. The focus bias setting device according to claim 1, wherein: 8. The focus bias setting means performs a required numerical calculation process for obtaining a focus bias corresponding to an extreme value as a signal characteristic based on the sample information, and obtains the calculation result. 2. The focus bias setting device according to claim 1, wherein the first value is set as the first focus bias. 9. The focus bias setting device according to claim 1, wherein said focus bias setting means is configured to measure a variation of jitter as said predetermined signal characteristic.