JPH07320285A - Focus control device and recording medium - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide a focus control device and a recording medium capable of accurately recording and reproducing a large-capacity land / groove format optical disc. A focusing means for focusing a light beam on a recording medium, a control means for controlling the focus of the light beam,
It has a focusing state detection means for detecting the focusing state of the light beam, and a target value setting circuit for setting a target value for focus control. By switching the target value of focus control depending on whether the position of the light beam is a land or a groove, even if a pseudo defocus occurs in the focus error signal between the groove track and the land track,
The focus control system is not affected by the pseudo defocus.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus control device and a recording medium for controlling a light beam to be focused on the recording medium. More specifically, information is recorded / recorded on a recording medium having a land track and a groove track.
The present invention relates to a focus control device and a recording medium that are not affected by pseudo defocus during reproduction.

[0002]

2. Description of the Related Art In recent years, optical recording media capable of recording information have been
Since it can hold a large amount of data, it has become important as a medium for accumulating information representing audio, video, and the like. Generally, in an optical recording medium, a concave portion and a convex portion are formed in a spiral shape. Since the optical recording medium usually has a disc shape, the optical recording medium is referred to as a “disk” here.
Call it. The concave and convex portions of the disc are generally called lands or grooves. The disc is spun at high speed to read the information recorded on the spiral land or groove. To read information without contact, a light beam such as a semiconductor laser is focused (focused) on the disc and reflected by the disc. The amount of light reflected reflects the recorded information.

As a conventional focusing control technique, there is an astigmatism type focus control device used in an optical "recording / reproducing device". In the following, "Record /
The term "reproduction device" is a general term for a recording device, a reproduction device, and a device capable of both recording and reproduction. The term “recording / reproducing” is a general term for performing only recording, only reproducing, and both recording and reproducing.

The principle of the astigmatism method will be described with reference to FIGS. 16 (a) to 16 (e). In the astigmatism method, the reflected light from the disc focused by the pair of focusing lenses and the cylindrical lens is applied to the four-division detector 160. 16 (a) to 16 (e) show the shapes of the light beam 161 on the four-division detector 160 when the distance between the focusing point of the light beam 161 and the disk changes. FIG. 16 (a) shows a state in which the focal point of the light beam 161 is farthest from the disc.
16C shows a just focus state, and FIG. 16E shows a state in which the focal point of the light beam 161 is closest to the disc. Figures 16 (b) and 16 (d) show Figures 16 (a) and 1 respectively.
An intermediate state between 6 (c) and an intermediate state between FIG. 16 (c) and FIG. 16 (e) are shown. 16 (a) to 16 (e), the longitudinal direction of the track (hereinafter referred to as "circumferential direction") is the vertical direction of the figure, and the direction traversing the track (hereinafter referred to as "radial direction") is shown in FIG. Corresponds to the left-right direction. 2 of the quadrant detector 160
The orthogonal dividing lines of the book are along the circumferential direction and the radial direction, respectively. To obtain a focus error signal, that is, a signal indicating in what direction and in which direction the focus is deviated, the following is performed. If the sum of light amounts of the two sets of detectors located diagonally of the four-division detector 160, that is, (A + D) and (B + C) is calculated, and then the difference between the obtained sums of light amounts is calculated, the calculated focus error signal 162 is obtained. There is {(A +
D)-(B + C)} is obtained. The principle and configuration of the astigmatism method are well known to those skilled in the art, and are described in, for example, “Optical Disk Technology”, supervised by Morio Onoue, Radio Technology Co., Chapter 1.2.5 Focusing, Tracking Error Detection, No. 83. Since it is described on page 85, detailed description is omitted here.

In recent years, there is a demand for higher recording density in optical discs. One method for increasing the recording density of an optical disc is to reduce the interval between tracks on which information is recorded (hereinafter referred to as "track pitch"). Land / groove with land track and groove track to reduce track pitch
A groove format optical disk (hereinafter referred to as "L / G disk") has been proposed.

FIG. 17 is a diagram schematically showing an L / G disc. In a conventional optical disc, information is recorded / reproduced in either a groove for tracking control or a land which is an area sandwiched between adjacent grooves. On the other hand, in the L / G disc, both the land and the groove are used as tracks for recording / reproducing information. As a result, the track pitch is equivalently halved, so that the capacity of the optical disk can be doubled. The tracks of the L / G disc are a groove track 170 using a groove (a dotted portion in FIG. 17) and a land track 171 using a land.
And (parts sandwiched by adjacent groove tracks) are alternately arranged every one rotation. The tracks of the L / G disc are groove track 170 and land track 1
Since 71 and 71 are formed in a spiral shape alternately, data can be continuously recorded / reproduced without interruption on the entire surface of the disc.

FIG. 18 is an enlarged view of the "boundary in the radial direction between the land track 171 and the groove track 170" 180 (hereinafter referred to as "boundary" for simplicity), which is enclosed by a circle in FIG. The figure is shown. The "boundary" 180 exists for each rotation of the disk, and its circumferential position is provided so as to match regardless of the radial direction of the track. When the wavelength of a light source such as a semiconductor laser is λ, the optical depth d of the groove is formed to have a concave structure or a convex structure that substantially satisfies d = λ / 8. The land track is a flat part without a groove. Therefore, when the light beam 161 moves along the spiral track, the light beam 161 is positioned on the groove track and the land track for each rotation.

At the edge where the optical depth is λ / 8, the light beam is diffracted. Therefore, it is widely known that the interference pattern at the detector of the light reflected by the optical disk changes. For example, for the groove, the interference pattern changes due to the light diffracted by the edge in the circumferential direction. The push-pull tracking method detects a tracking error by using the change in the interference pattern and outputs a tracking error signal.
It is also well known that the diffracted light by the edge affects the astigmatic focus error signal. (See "Optical Disc Technology" Morio Onoue, Radio Technology Co., Ltd., Chapter 1.2.5 Focusing and Tracking Error Detection, pages 85-87). This is because the diffracted light due to the groove is not evenly output from each diagonal pair of the quadrant detector.

As one of the causes of the unevenness of the diffracted light,
There is aberration of the light beam. It is impossible to process or assemble the optical components used in the optical head with zero error. Therefore, the light beam focused and irradiated on the disc does not have a perfect symmetry with respect to the optical axis, and aberration occurs. Another cause is that in an actual optical disc, the edge portion between the land and the groove is formed in a ramp shape having a certain degree of inclination, not in a step shape that is exactly vertically raised. . Moreover, this inclination varies depending on the individual discs, and also varies depending on the position on the same disc. In other words, when you look at the cross section of the disc,
It is impossible to generate both edges of the groove completely symmetrically, and the left and right edges have a slight difference in shape. When the light beam is located on the groove and when it is located on the land, the edges of the groove are left / right interchanged with respect to the light beam. When the cross section of the optical disk is viewed, for example, if the right edge of the groove is located on the right side of the light beam on the groove, the right edge of the groove is located on the left side of the light beam on the land.

Due to the uneven diffracted light due to the above-mentioned edge, the interference pattern on the four-division detector becomes asymmetric even when the light beam is focused with zero focus error. That is, the focus error signal described above does not become zero even though the focus is just. This focus error signal that does not correspond to the actual focus shift (hereinafter referred to as "true defocus") is referred to as a "pseudo defocus" signal here. The amount of “true defocus” depending on whether the light beam is applied to the land or the groove is about 0.1 μm. That is, the difference between the distance between the focusing lens and the land and the distance between the focusing lens and the groove (hereinafter referred to as “groove depth”) is
It is about 0.1 μm. On the other hand, the focus error signal caused by the pseudo defocus has a magnitude corresponding to the “true defocus” of about 2 μm.

When the light beam is in the state of just focus, for example, when the light beam is in the state of just focus on the groove, the focus error signal becomes zero so that the four-division detector of the optical system is divided. Adjust the position. In this case, if the light beam is focused on the groove, a focus error signal due to pseudo defocus does not occur. As a result, on the groove, focus control is not affected by pseudo defocus, and stable recording / reproducing of information is possible.

However, the interference pattern on the detector due to the diffracted light from the disk changes depending on whether the light beam is applied to the land or the groove. As a result, pseudo defocus occurs even when the focus error is substantially zero, that is, even when the light beam is positioned on the land in the just-focused state.

19 (a) to 19 (c) are plots of changes in the focus error signal ER and the tracking error signal TR when the light beam 161 crosses a track in the disk radial direction. The vertical axes in FIGS. 19B and 19C indicate the magnitudes of the focus error signal ER and the tracking error signal TR, respectively, and the horizontal axis indicates the position of the light beam 161 in the radial direction of the optical disc. As shown in FIG. 19 (b), in the groove track 170, if the focus error signal ER is adjusted to zero, in the land track 171 by pseudo defocus,
The maximum value of the focus error signal ER is DF. The speed at which the light beam 161 traverses the track is fast enough. Therefore, the frequency of the focus error signal ER generated when the light beam 161 crosses a track (that is, the reciprocal of the number of tracks crossing in a unit time) is sufficiently higher than the response frequency of the focus control system. Therefore, the response of the focus control system due to the pseudo defocus when the light beam 161 moves along the track in the radial direction can be ignored. The pseudo defocus amount generated by the radial movement of the track is out of phase with the tracking error signal TR by about 90 °.

20 (a) and 20 (b) show changes in the focus error signal ER when the light beam 161 moves from the groove track 170 to the land track 171. As shown in FIG. FIG. 20 (a) schematically shows the relationship between the optical beam 161 and tracks when the optical disc is viewed from above, and FIG.
20A and 20B plot changes in the magnitude of the focus error signal ER corresponding to the position of the light beam 161 in FIG.

At position X1 in FIG. 20 (b), the light beam 1
61 is completely located on the groove track 170, and the focus error signal ER is at zero level. This is because the focus error signal ER due to the pseudo defocus generated when the light beam 161 is positioned on the groove track 170 as described above is adjusted to zero.

At position X2 in FIG. 20 (b), the light beam 1
61 passes through the boundary 180 between the groove track 170 and the land track 171. Again, as shown in Figure 19 (a),
The magnitude of the pseudo defocus signal generated by the light beam 161 moving in the radial direction on the track is DF.
And At the moment when the light beam 161 reaches the position X2, the focus error signal ER is generated due to the pseudo defocus.
Indicates the DF. But in reality, the light beam 161
Even when reaches the position X2, the focus state is substantially the same as that at the position X1, that is, just focus. In other words, true defocus does not occur even if the focus error signal ER is DF due to the pseudo defocus. This is because the above-mentioned “groove depth” is about 0.1 μm, whereas the focal depth of the light beam 161 is about ± 1 μm. Compared to the depth of focus, the true amount of defocus is negligibly small.

In an L / G disc, the light beam is
It is located on the land track and the groove track for each rotation of the disk. The pseudo defocus occurs while the light beam is located on the land track, that is, during the period in which the light beam scans one rotation of the disk. Unlike when the light beam traverses the track, that is, when the light beam moves in the radial direction, the rotation frequency of the disk is much smaller than the response frequency of the focus control system. Specifically, the rotation frequency of the disc is about several tens Hz (that is, the rotation cycle is about several tens ms).
Is. Therefore, when the light beam is scanning the land track and the groove track alternately, several kH
A focus control system having a response frequency of about z is given by
It responds to a focus error signal due to pseudo defocus having a frequency of about Hz. Moreover, the amount of defocus caused by the pseudo focus is about 2 μm. From the above, true defocus occurs.

As shown in FIGS. 20 (a) and 20 (b), during the time until the light beam 161 reaches the position X2 from the position X2 (about several ms in time), the focus control system keeps the focus error signal. The focus error signal ER is controlled to be zero by negatively feeding back ER. as a result,
At the position X3, the focus error signal ER converges to zero. As described above, the light beam 161 emits light from X2 to X3.
The period of several ms for moving to is much longer than the time required for the focus control system to control and set the focus error signal ER to almost zero, that is, the response time of the focus control system. At the position X3, the focus error signal ER is zero. However, since the focus control is performed so that the level DF of the focus error signal ER based on the pseudo defocus is set to zero, actually,
True defocus corresponding to the pseudo defocus has occurred. The true defocus caused by the pseudo defocus differs depending on the focus error signal detection method, the focus control system, the optical head, and the like. But,
Compared with the depth of focus of the light beam (about ± 1 μm), the true defocus due to pseudo defocus is several μm
Since it is relatively large, recording / reproducing of a signal becomes difficult, or focus control is lost.

[0019]

The above-mentioned prior art has the following problems. That is, a pseudo defocus occurs due to diffraction at the edge along the circumferential direction of the track. The focus control system of the light beam corresponds to this pseudo defocus,
True defocus occurs.

The present invention has been made in order to solve the above problems, and an object thereof is not to be influenced by a focus error signal due to pseudo defocus, and as a result, a highly accurate focus can be achieved. An object is to provide a controllable focus control device and a recording medium.

[0021]

A focus control device according to the present invention is a spiral track having a land track and a groove track, and both the land track and the groove track record / reproduce information. A focus control device for controlling a light beam to be focused on a recording medium having the focusing means for focusing the light beam on the recording medium, and detecting a focusing state of the light beam on the recording medium. Then, the focusing state detecting means for outputting a signal indicating the focusing state is compared with the target value and the value of the output from the focusing state detecting means, and the focusing means is moved to record the light beam. Control means for maintaining a focused state on the medium in a desired state, and the target value is set to a first value when the light beam is irradiated on the land track. And a target value setting means for setting the target value to a second level different from the first level when the light beam is focused on the groove track. The above object is achieved.

Preferably, the land tracks and the groove tracks are alternately arranged in series.

The target value setting means switches the target value between the first level and the second level when the output from the focusing state detecting means changes by a predetermined value or more. May be configured as.

Further, the target value setting means switches the target value between the first level and the second level in response to a signal generated by the identifier recorded on the recording medium. May be.

The target value may be switched between the first level and the second level after a predetermined time has elapsed after receiving the signal generated by the identifier.

The target value setting means switches the target value between the first level and the second level in response to a signal generated by an address pit provided on the recording medium. Good.

The target value may be switched between the first level and the second level after a predetermined time has elapsed after receiving the signal generated by the address pit. The predetermined time may be determined based on the information recorded by the address pits.

In one embodiment, the target value setting means is
Sampling means for sampling the output from the focusing state detecting means is provided, and at least one of the first level and the second level is a value of the output from the focusing state detecting means sampled by the sampling means. It is set based on. Preferably, the sampling means samples the output from the focusing state detecting means within a predetermined time from the time when the light beam passes through the boundary between the land track and the groove track on the track. Preferably, the predetermined time is shorter than the response time of the control means.

In one embodiment, the time DT from the passage of the light beam through the address pit to the sampling of the output of the focusing state detecting means is w.
/ V <DT, the scanning linear velocity of the light beam in the track irradiated with the light beam is v, and the distance between the address pit and the boundary is w.

In one embodiment, the distance w between the address pit and the boundary is determined based on address information generated by the address pit provided on the recording medium.

The sampling means is based on a predetermined scanning linear velocity of the light beam and a signal generated by an identifier which is provided on the recording medium and which indicates a position of a boundary between the land track and the groove track. ,
The output from the focusing state detecting means may be sampled.

The recording medium according to the present invention is a spiral track in which land tracks and groove tracks are alternately arranged in series, and both the land tracks and the groove tracks record / reproduce information. A recording medium having:
It has an identifier indicating the position of the boundary between the land track and the groove track, and the identifier is provided at a distance from the boundary, whereby the above object is achieved.

Preferably, the identifier is provided near the boundary. Preferably, the identifier is located with respect to the boundary in a direction opposite to the direction of movement of the light beam relative to the track.

Preferably, a settling area is provided between the identifier and the boundary, and in the settling area, a signal corresponding to a focus error of a light beam with which a track is irradiated is transmitted by the light beam. The state before the identifier is reached is substantially restored. The identifier may have a track address for identifying the track as information. A track address pit may function as the identifier.

In one embodiment, the length W of the settling region is
Satisfies the relation of W> v · Tr with respect to the scanning linear velocity v of the light beam on the track irradiated with the light beam and the rising time Tr of the control means for controlling the focusing of the light beam.

The identifier may include information about the length of the settling area.

Preferably, the recording medium is disc-shaped, and the tracks are formed on both sides of the recording medium. The recording medium may be formed by laminating at least two disc-shaped recording media.

[0038] In one embodiment, the recording medium includes a base material and a recording layer.

In one embodiment, the recording layer is a phase change recording layer.

[0040]

According to the focus control apparatus of the present invention, the target value for focus control is changed depending on whether the light beam is applied to the land track or the groove track. By setting a target value that has the same value as the generated focus error signal, even if a focus error signal due to "pseudo defocus" that occurs even when the light beam is in a state of being just focused is generated. , It is possible to prevent the pseudo defocus from affecting the focus control.

When the target value of the focus control is set by sampling the focus error signal due to the pseudo defocus, the sampling timing can be determined by detecting the change of the focus error signal itself. Therefore, it is not necessary to record the information that gives the sampling timing on the recording medium itself.

According to the recording medium of the present invention, the timing for sampling the focus error signal as the target value for focus control can be determined by the identifier indicating the boundary position between the land track and the groove track. As a result, an appropriate focus error signal can be sampled before the focus control system is affected by the pseudo defocus, that is, before the focus error signal does not reflect the pseudo defocus.

A predetermined space is provided between the identifier and the boundary, and as a result, the pseudo error defocus occurs after the fluctuation of the focus error signal caused by the influence of the identifier (for example, the address portion) disappears. Only the focus error signal corresponding to can be sampled.

When information for determining sampling timing, for example, the distance between the identifier and the boundary between the land and the groove is recorded on the recording medium itself,
Even if this distance varies depending on the position on the disk, sampling can be performed at an appropriate timing.

[0045]

Embodiments of the present invention will be described below with reference to the drawings. In the following description, the same reference symbols represent the same elements.

FIG. 1 is a block diagram of a first embodiment of a focus control device according to the present invention. Semiconductor laser 1
Generates a light beam 161 for recording / reproducing information. The generated light beam 161 is collimated by the collimator lens 2, reflected by the polarization beam splitter 3, and passes through the λ / 4 plate 4 (λ is the wavelength of the light beam 161). The focusing lens 5 receives the light beam 161 passing through the λ / 4 plate 4.
Are focused on the disk 7 and irradiated. The disk 7 is rotated by the motor 6.

The reflected light from the disk 7 is focused by the detection lens 15 and the cylindrical lens 16 through the focusing lens 5, the λ / 4 plate 4 and the polarization beam splitter 3, and then is irradiated on the four-division detector 8. It The detection lens 15 and the cylindrical lens 16 intentionally generate astigmatism. The four-division detector 8 is used to detect a focus error amount by an astigmatism method and generate a focus error signal. The principle and configuration of the focus error signal detection of this astigmatism method are well known to those skilled in the art, and, for example, “optical disc technology” (supervised by Morio Onoue, Radio Technology Co., Chapter 1.2.5 Focusing, Tracking error detection, pages 83-85).

With respect to the output of the four-divided detector 8, an adder 17 and an adder 18 calculate the sum of the light amounts of the pairs of detectors at diagonal positions. The differential circuit 9 includes an adder 17 and an adder.
The focus error signal ER indicating the focused state of the light beam 161 on the disk 7 is output by receiving the output from 18 and calculating the difference between them. The focus error signal ER output from the differential circuit 9 is given to the non-inverting input of the differential amplifier 31 having an amplification factor of 1. The output of the differential amplifier 31 is input to the phase compensation circuit 10 for ensuring the controllable stability of the focus control system. The output of the phase compensation circuit 10 is input to the drive circuit 12 via the gain compensation circuit 11 for securing the loop gain necessary for focus control. In order to focus the light beam 161, the focus actuator 13 drives the focusing lens 5 in a direction substantially parallel to the optical axis of the light beam 161, according to the output of the drive circuit 12. A loop of the focus control system is configured by the above elements shown in FIG.

Both the inverting input and the non-inverting input of the differential amplifier 31 are set so as to be output with an amplification factor of 1. The target value for focus control (normally expressed by a constant voltage) is given to the inverting input. Here, consider a case where the focus control system has reached a steady state due to the operation of the focus control. At this time, the focus error signal output from the differential circuit 9 is the differential amplifier 31.
It converges to an offset value equal to the target value given to the inverting input of. That is, by changing the input to the inverting input terminal of the differential amplifier 31, the DC voltage level at which the focus error signal ER should converge, that is, the target value for focus control can be freely set.

The focus error signal ER output from the differential circuit 9 is input to the sample / hold circuit 20 for holding the focus error signal ER. The output of the sample and hold circuit 20 is the sample and hold circuit.
The output of the sample and hold circuit 27 is input to the inverting input of the differential amplifier 31 as a target value for focus control.

The outputs of the adders 17 and 18 are the adders.
Added at 19. The output signal of the adder 19, which represents the amount of reflected light from the disk 7, is input to the address reading circuit 21, and the address recorded on the disk 7 described later is recorded.
ID0 to ID3 are read. The address reading circuit 21
When ID0, which will be described later, is read from the address, the ID0 detection signal
The DET is output to the timing generator 23 via the delay circuit 22. When the ID0 detection signal DET is input, the timing generator 23 outputs hold signals to the sample and hold circuits 20 and 27 at predetermined timings, which will be described later. As described above, the sample and hold circuits 20 and 27 hold the respective input signals while the hold signal is at the high level and output the sampled input values as they are while the hold signal is at the low level. The delay time of the delay circuit 22 will be described later.

FIG. 2 schematically shows the structure of the disk 7 used in the focus control device of the present invention. In the disk 7,
The optical depth (refractive index is taken into consideration) is approximately λ / with respect to the wavelength λ of the light beam 161 emitted from the semiconductor laser 1.
Groove track 170 using groove of 8 concave structure
(A dotted portion in FIG. 2) and a land track 171 (a portion sandwiched between adjacent groove tracks 170) using a land that is a convex portion are formed. The land tracks 171 and the groove tracks 170 are alternately arranged every one rotation, and as a result, one spiral connected in series is formed over the entire surface of the disk 7. On the track, the boundary between the land track 171 and the groove track 170 is present for each rotation of the disk. The positions of the boundaries are provided so as to match regardless of the positions of the tracks in the radial direction. Also, each track on the disk 7 has four address section IDs for track identification.
0 to ID3 are arranged at equal intervals in the circumferential direction of the disk 7. The address parts ID0 to ID3 are provided with track addresses for track identification and sector addresses for identifying which of four address parts (ID0 to ID3) that exist in one rotation correspond. There is.

FIG. 3 shows an example of the format of tracks on the disc shown in FIG. Each track is divided into four sectors from sector 0 to sector 3.
Each sector is composed of an address part and a data part for recording / reproducing information. In the address part, a sector mark SM indicating the beginning of the sector, a single frequency domain VFO for pulling in the signal reading PLL, an address mark AM indicating the beginning of the address, a track address TR-ID, a sector address SC- ID, cyclic redundancy check code CR for error checking
C and the postamble PA indicating the end of the address part are arranged so as to be read in this order. The address reading circuit 21 reads the track address TR-ID and the sector address SC-ID to obtain the light beam 161.
It is possible to determine which track is located at the same time as which sector is located in one track. The address parts ID0 to ID3 of each track are arranged on the same line in the radial direction.

Referring again to FIG. 2, ID0 is the last read address in each track. That is, the light beam does not pass through the other address parts ID1 to ID3 after passing through the IDO and before passing through the boundary. ID0 is located on the opposite side of the boundary from the direction in which the light beam scans the track. Here, “the light beam scans the track” means “the irradiation spot of the light beam on the disk scans the track in the circumferential direction of the disk”.

FIG. 4 is an enlarged view showing the vicinity of the address part ID0 and the boundary 180 surrounded by a circle in FIG. The address portion is generally formed by a pit string having an uneven structure, and the pit string having the uneven structure stores address information. The address reading circuit 21 receives a signal indicating the change in the amount of reflected light due to the pit row, and detects the position of the light beam. The width of each pit is narrower than the track width, and the length of the pit is about the radius or diameter of the light beam. for that reason,
The fluctuation of the focus error signal due to the diffraction in the pit row is very small compared to the fluctuation of the focus error signal due to the pseudo defocus. As shown in FIG. 4, ID0 is provided at a distance w before the boundary 180. Here, “in front of” the boundary 180 means “in the direction opposite to the scanning direction of the light beam” with respect to the boundary 180. Between the address section ID0 and the boundary 180, the land track 171 located in front of the address section ID0
Alternatively, the same type of track as the groove track 170 exists.

FIG. 5 shows a sectional view of a disk 7 which is an embodiment of a recording medium according to the present invention. From the bottom to the top of FIG. 5, the disk 7 is composed of a substrate 510 made of polycarbonate or the like on which uneven tracks are formed by a method such as injection molding, a dielectric layer 520 for heat insulation, and information. A recording film 530 made of a phase change type recording material for recording / reproducing with the light beam 161, a reflective film 540 for preventing transmission of the light beam 161, and for protecting the above layers from scratches and the like. Includes a protective layer 550. Light beam 1
61 is irradiated from the base material 510 side of the disk 7 to record / reproduce information. In this specification, for the sake of convenience, a track protruding toward the side where the light beam 161 is incident on the disk 7 is called a “land track” 171, and a track sandwiched between adjacent land tracks 171 is a “groove track” 170. Call it. However, a track protruding toward the side where the light beam 161 is incident is called a “groove track”, and a track sandwiched between adjacent groove tracks may be defined as a “land track”. A magneto-optical recording layer may be used as the recording film.

FIG. 6 shows a sectional view of a double-sided disk for realizing a larger storage capacity. The double-sided disc is formed, for example, by laminating two single discs shown in FIG. 5 with an adhesive layer 600 so that the protective layers 550 are in contact with each other. When recording / reproducing on a double-sided disc having such a structure, as shown in FIG. 6, not only from below,
The light beam 161 can be emitted from the upper side. As a result, one double-sided disc has a storage capacity of two single-plate discs. Whether the disc to which the present invention is applied is a single plate disc or a double-sided disc, there is no great difference in the configuration and the effect. Therefore, in the following description, only a single plate disc will be described, but it will be apparent to those skilled in the art that the focus control device and the recording medium of the present invention are also applicable to a double-sided disc.

FIGS. 7A to 7G show the focus control operation in the focus control device and the recording medium according to the present invention. In FIG. 7A, the light beam 161 scans along the groove track 170 by the rotation of the disk 7, and the address portion ID0, the groove track 170, and the land track 17 are displayed.
The position of the light beam 161 on the track when passing through the boundary 180 with 1 and reaching the land track 171 is schematically shown. 7 (b), (c), (d), (e), (f), and (g), the vertical axis represents ID0 when the light beam 161 scans a track as shown in FIG. 7 (a). Detection signal DET, hold signal SH20 to sample and hold circuit 20, hold signal SH27 to sample and hold circuit 27, focus error signal ER, sample
The output signal OUT20 of the hold circuit 20 and the output signal OUT27 of the sample and hold circuit 27 are shown, respectively, and the horizontal axis represents time. The horizontal axes of FIGS. 7B to 7G are displayed so as to correspond to the horizontal axis of FIG. That is, FIG. 7 (a)
Xa on the abscissa and time T on the abscissa of FIGS. 7B to 7G.
When b and the same length are expressed, the relationship between the distance Xa and the time Tb is Xa = v · Tb, where v is
The linear velocity at which the light beam 161 scans the track is represented.

In the description from FIG. 7A to FIG. 7G, for the sake of simplification, defocus does not occur in the groove track 170 (that is, just focus), and as a result, the focus error signal ER is Suppose that it is adjusted to show zero. The hold signals SH20 and SH27 from the timing generator 23 are set to the LOW level and the HIGH level, respectively. At this time, since the switch 24 of the sample-hold circuit 20 is short-circuited, the sample-hold circuit 20 outputs a signal equal to the input signal. Since the switch 28 of the sample hold circuit 27 is opened, the sample hold circuit 27
Outputs the voltage held in the capacitor 29. For simplification, it is assumed that the initial value of the hold voltage of the capacitor 29 is zero and the initial value of the output of the sample and hold circuit 27 is also zero. Therefore, at this time, the input value to the inverting input terminal of the differential amplifier 31 that sets the target position for focus control, that is, the target value for focus control is zero.

When the light beam 161 is located at ID0, the focus error signal ER fluctuates due to diffraction by the edge of the address portion along the circumferential direction. However, the address part
The width and length of the edge of the pit row of ID0 is
Small compared to the diameter. Therefore, usually the address part
The pseudo defocus amount due to the diffraction of ID0 is extremely small, and the fluctuation of the focus error signal ER is small. The distance w between the address part ID0 and the boundary 180 is the address part ID
It is provided that a minute fluctuation of the focus error signal ER due to 0 is sufficiently converged before the sampling of the focus error signal ER described later. That is, the distance w satisfies w> v · Tr, where v is the linear velocity with which the light beam 161 scans the disc, and Tr is the response time determined by the response characteristics of the focus control system.

The address reading circuit 21 includes a light beam 161.
Is located at the rear end of the address section ID0, at time T1, ID0
The detection signal DET is output to the delay circuit 22. ID0 detection signal DET
Is delayed by the delay circuit 22 and input to the timing generator 23 at time T3. Delay time D of the delay circuit 22
T is equal to the time required for the light beam 161 to travel the distance w and to be positioned on the land track 171 beyond the boundary 180, that is, (T3−T2). At time T2, the focus error signal ER corresponding to the above-mentioned pseudo defocus is generated.
Occurs stepwise. One of the features of the present invention is a focus error signal corresponding to this pseudo defocus.
The purpose is to sample ER and use it as the target value for focus control. Therefore, at time T3, the focus error signal ER on the land track 171 is sampled.
It needs to be sampled by the hold circuit 20. Therefore, the time T1 when the light beam 161 passes the rear end of ID0
And AT is the difference between time T2 when the boundary 180 is passed,
At least AT <DT must be satisfied. That is, the delay time DT has a lower limit. If the control system is realized by actual hardware, the light beam 161
At the same time as the land track 171 reaches the land track 171, the pseudo defocus is not reflected in the focus error signal ER, and a slight time lag occurs. That is, the focus error signal that represents the pseudo defocus
In order to sample ER, there must be some margin between time T2 and time T3.

On the other hand, the delay time DT has an upper limit. This is because the target value for focus control on the land track 171 is replaced with the target value on the groove track 170 after the time T2 and before the control system completely follows the focus error signal ER due to the pseudo defocus. It must be done. Figure 7
Referring to (e), when the focus error signal DF due to the pseudo defocus is generated at time T2, the focus control system responds to the pseudo defocus. As a result, at time T3, the focus error signal ER due to the pseudo defocus is reduced to DF '. If the target value of the focus control is the focus error signal ER (zero level signal in this case) in the groove track 170, the control system operates so that the focus error signal ER becomes zero, so that true defocus occurs. Will end up. That is, the delay time DT must be set sufficiently short so that the response of the focus control to the pseudo defocus can be ignored. In other words, it is necessary to sample the focus error signal ER in a range where it can be considered that DF and DF ′ are substantially equal. If the difference between DF and DF 'is too large, the target value for focus control will deviate, and as a result,
The effect of pseudo defocus occurs. From the above, at least the period (T3-T2) must be shorter than the response time Tr of the focus control system. Period (T3−
T2) is preferably shorter than Tr / 3, and Tr / 1
It is more preferable if it is shorter than zero.

In this embodiment, the delay time DT is AT = w
/ V <DT <AT + Tr is set. Here, AT is a light beam after the ID0 detection signal DET is output.
Tr is the time required for 161 to reach the land track, and Tr is the response time of the control system. If the distance w differs depending on the position of the light beam 161 on the disc, that is, the track being scanned, the distance w may be calculated based on the track information (track position) obtained from the address section. By doing so, even when the distance w is proportional to the radius of the track, the distance w can be determined using the track position.

When the timing generator 23 receives the ID0 detection signal DET delayed at the time T3, it sets the hold signal SH20 to the HIGH level from the time T3 to the time T5 (period HT1). As a result, the sample and hold circuit 20 keeps the focus error signal ER at the time T3 during the HT1.
Hold. Since the delay time of the delay circuit 22 is set as described above, the sample and hold circuit 20 holds the focus error signal ER due to the pseudo defocus generated in the land track 171. The timing generator 23 sets the hold signal SH20 to the HIGH level at time T3, and at the same time, from time T3 to time T4 (period
HT2) hold signal SH27 from HIGH level to LOW
Set to level. When the hold signal goes low, switch 28 is short-circuited and charging of capacitor 29 begins and the output OUT27 of sample and hold circuit 27 eventually equals its input. At time T4 when the period HT2 has elapsed from time T3, the hold signal SH27 becomes HIGH level again, and the sample and hold circuit 27 holds the input, that is, the focus error signal ER caused by the pseudo defocus occurring in the land track 171. And output.

Since the output of the sample and hold circuit 27 is input to the inverting terminal of the differential amplifier 31 as described above, after the time T4, the focus error signal ER due to the pseudo defocus on the land track 171 is generated. The value becomes the target value for focus control. Therefore, the focus control system is not affected by the focus error signal ER that reflects the pseudo defocus in the land track 171, and as a result, the true defocus can be prevented from occurring.

At time T5 when the period HT1 has elapsed from time T3, the hold signal SH20 is set to the LOW level again. As a result, the sample and hold circuit 20 outputs the input focus error signal ER as it is without holding it. Therefore, the relationship between period HT1 and HT2 is
It is set so that HT2 <HT1.

8A to 8G show the focus control operation when the light beam 161 moves from the land track 171 to the groove track 170 in the focus control device and the recording medium according to the present invention. FIGS. 8 (a) to 8 (g) are diagrams when the time for rotating the disk almost once has elapsed from the times T1 to T5 in FIGS. 7 (a) to 7 (g). FIG. 8A shows a disk on the track when the light beam 161 is moved along the land track 171 by the rotation of the disk 7, passes through the address section ID0 and the boundary 180, and reaches the groove track 170. The position of 7 is shown schematically. Figure 8
(b), (c), (d), (e), (f) and (g) are the ID0 detection signal DET and the sample and hold when the light beam 161 moves as shown in FIG. 8 (a). Hold signal SH20 to the circuit 20, hold signal SH27 to the sample and hold circuit 27, focus error signal ER, output signal OU of the sample and hold circuit 20
Output signal OUT27 of T20 and sample and hold circuit 27
Are shown respectively, and the horizontal axis is time. Figure 8 (b)
The horizontal axes of (g) to (g) are displayed so as to correspond to the horizontal axis of FIG.

On the land track 171, the focus error signal ER is DC offset by the focus error signal ER due to the pseudo defocus sample-held by the sample-hold circuit 27 before one rotation of the disk. However, at this time, true defocus has not occurred, that is, the light beam 161 is in the just-focused state on the disk 7.

Before the time T8, the timing generator 23
The hold signals SH20 and SH27 are set to the LOW level and the HIGH level, respectively, as described above.
Therefore, the sample-and-hold circuit 20 outputs a signal equal to the input signal.
The reference numeral 27 outputs a focus error signal ER due to the pseudo defocus, which is sampled at a time before the time when the disk makes almost one rotation. When the light beam 161 is located at the address section ID0, the focus error signal ER fluctuates due to diffraction by the edge of the address section ID0 along the circumferential direction. However, since the change in the focus error signal ER is slight, a large defocus due to the address part ID0 does not occur.

The address reading circuit 21 uses the address part ID
At time T6, which is the rear end of 0, the detected ID0 detection signal DET is output to the delay circuit 22. The delay circuit 22 delays the ID0 detection signal DET and inputs it to the timing generator 23 at time T8. The timing generator 23 operates as described above for the period HT1.
The hold signal SH20 to HIGH. As a result, the sample and hold circuit 20 holds the focus error signal ER at time T8. At this time the light beam
Reference numeral 161 is immediately after passing the boundary between the land track and the groove track and being located on the groove track 170.
Therefore, the pseudo defocus that has occurred on the land track 171 does not occur, and the focus error signal
ER returns to almost zero level. Therefore, the sample and hold circuit 20 samples and holds a signal of almost zero level.

The timing generator 23 controls the times T8 to T9 (period
HT2) hold signal SH27 from HIGH level to LOW
Set to level. The signal held by the sample and hold circuit 20 is held and output by the sample and hold circuit 27 after time T9. As a result, the target value for focus control on the groove track is set to almost zero level, which is the just focus state, without depending on the pseudo defocus signal on the land track 171.

At time T10 when period HT1 has elapsed from time T8, hold signal SH20 is set to the LOW level again. As a result, the sample and hold circuit 20 outputs the input focus error signal ER as it is without holding it. After another further rotation of the disc, the light beam 161 again passes through the boundary and moves again from the groove track 170 to the land track 171. After that, the operation described with reference to FIGS. 7A to 7G and FIGS. 8A to 8G is repeated every two rotations of the disk.

With the above-described structure, even in a disc in which land tracks and groove tracks are alternately arranged for each rotation of the disc, there is no influence of pseudo defocus. That is, by using the biased sample value as the target value of the focus control, it is possible to prevent the control in which the focus error signal due to the pseudo defocus becomes zero. As a result, it is possible to configure a focus control device capable of always maintaining the just focus state in all the tracks.

In the above-mentioned embodiment, the hold signal SH20 and SH27 to the sample and hold circuits 20 and 27 are generated by using the ID0 detection signal indicating that the address section ID0 has been passed as a trigger of the timing generator. There is. However, the trigger is not limited to the ID0 detection signal. When using an address other than ID0, for example ID3,
The same effect can be obtained with the following configuration. The address reading circuit 21 detects the address section ID3 and outputs an ID3 detection signal to the delay circuit 22. The delay circuit 22 delays the ID3 detection signal and outputs it to the timing generator 23. The delay time DT3 of the delay circuit 22 is set to be equal to the time required for the light beam 161 to be positioned from the rear end of the address part ID3 to immediately after the boundary due to the rotation of the disk 7, instead of the delay time DT1 described above. . That is, if the cycle of the disk 7 making one rotation is TROT and the number of addresses passing during one rotation of the disk is N, then DT3 = DT1 + TROT / N may be set. For example, in the case of the disk 7 according to this embodiment, N = 4.

By setting the delay time as described above, the timing of the ID3 detection signal coincides with the above-mentioned detection signal ID0. By using the ID3 detection signal as a trigger, the timing generator 23 and the sample and hold circuits 20 and 27 can be operated as in the above-described embodiment, and the same effect can be obtained. More generally,
An address portion located as the nth address from the boundary between the land track and the groove track may be used. The delay time DT (n) of the delay circuit 22 at this time is DT (n) =
It should be set so that it becomes DT1 + n ・ TROT / N.

Even if the scanning linear velocity of the light beam 161 is not constant, the scanning linear velocity can be obtained based on the track information. For example, when the linear velocity varies depending on the position of the track, the position of the track is obtained from the address part, and the linear velocity on the track is calculated. If the delay time is set according to the linear velocity thus obtained, sampling can be performed at appropriate timing even when the linear velocity is not constant. As described above, the present invention provides a target value setting circuit for setting a target value for focus control, a detector for detecting a boundary between a land track and a groove track, and a sample / hold circuit for sampling and holding a focus error signal. Are provided, the focus error signal that is sampled and held immediately after the boundary is set as the target value for focus control by the target value setting circuit. As a result, even if the pseudo defocus on the groove track and the land track affects the focus error signal, the focus position that is the just focus can be set as the target value of the focus control system. As a result, according to the present invention, it becomes possible to realize focus control that is not affected by the pseudo defocus.

In the first embodiment, the focus error signal is sampled each time each track is scanned. As a result, the magnitude of the focus error signal due to the pseudo focus is (1) the environment in which the disc is placed (temperature, humidity, etc.), (2) the position on the disc (inner track or outer track). (3) and (3) The effect that the correct target value for each track can be sampled and used even if it changes due to manufacturing errors and deformation of individual disks, etc., and focus control accuracy improves Have.

In the above-mentioned embodiment, the target value of the focus control on the land track and the groove track is set by sampling and holding the focus error signal immediately after the boundary. However, the target value for focus control is not necessarily limited to the value obtained by the above method. For example, when the pseudo defocus amount generated on the land track and the groove track is a substantially constant value, DF2, the following method can be applied. That is, instead of the focus error signal value sampled and held, two constant voltage generators may be used and selectively given to the control system as target values.

FIG. 9 is a block diagram of the focus control device according to the second embodiment of the present invention. In FIG. 9, description of the same components as those in FIG. 1 will be omitted. Further, the disk used in this embodiment is almost the same as the disk 7 used in the first embodiment, and therefore its configuration diagram is omitted. Figure 9
In, the constant voltage generators 40 and 41 give, as outputs, target values for focus control in the land track and the groove track. The outputs of constant voltage generators 40 and 41 are provided to the two inputs of analog switch 42. The analog switch 42 selectively outputs two input signals to the switch (here, outputs from the constant voltage generators 40 and 41) in response to an input signal to the control terminal of the analog switch 42. The output of the analog switch 42 is given to the inverting input of the differential amplifier 31 as a target value for focus control. The output of the constant voltage generator 40 is supplied to the inverting input of the differential amplifier 31 when the control signal is HIGH level, and the output of the constant voltage generator 41 is supplied when the control signal is LOW level. The constant voltage generator 40 outputs a zero level signal. Constant voltage generator 41
Outputs a signal of the defocus amount DF2 caused by the pseudo defocus generated on the land track.

On the other hand, the output of the address reading circuit 21
DET is input to the land / groove discrimination circuit 43. The land / groove identifying circuit 43 determines whether the light beam is located on the land track or the groove track according to the read address value. As described above, the disk 7 is provided with groove tracks and land tracks alternately for each rotation, and the address portion has
A track address and a sector address are provided.
As the track address, for example, a series of addresses in which integer values are sequentially assigned from the outer track to the inner track is used. Land / groove identification circuit
43, it is possible to easily determine whether the light beam 161 is located on the land track or the groove track depending on whether the read track address is an even number or an odd number. The output of the land / groove discrimination circuit 43 is high when the light beam 161 is located on the groove track, and is LO when the light beam 161 is located on the land track.
Set to W level, this output is analog switch 4
Output to the 2 control terminal. From the above, the inverting input of the differential amplifier 31 is
The output of the constant voltage generator 40 is provided when the 161 is located on the groove track, and the output of the constant voltage generator 41 is provided when the 161 is located on the land track. Therefore, as in the case of the first embodiment, even when the pseudo defocus affects the focus error signal, the focus error signal corresponding to the focus position that is just focus can be set as the target value of the focus control system. Therefore, it is possible to realize a focus control device and a recording medium that do not cause an error in focus control even if a pseudo defocus occurs. The levels of the output signals of the constant voltage generators 40 and 41 described above are not limited to zero and DF2. When the focus error signal is adjusted to zero when the light beam 161 is located on the land track, the output levels of the constant voltage generators 40 and 41 may be DF2 and zero, respectively. In this embodiment,
The target value for focus control was changed by selectively switching the outputs from the two constant voltage generators. However, the effect of the present invention can be obtained if the target value can be set to different levels, and a single voltage generator whose output level can be changed may be used. The method of generating the timing for switching the target value is the same as that in the first embodiment, and thus the description thereof is omitted.

The method of obtaining the timing for sampling the focus error signal is not limited to the above-mentioned method using the address. FIG. 10 shows an identifier 100 (hereinafter simply referred to as “identifier 1” used to identify the boundary 180 between the land track 171 and the groove track 170 instead of the address part).
"00") in each track. Figure
The identifier 100 shown in 10 does not necessarily need to include information about a track, a sector, etc., but may include such information. The only requirement for the identifier 100 is that it be distinguished from other data by having a "unique mark" with respect to other data on the disc. This is a condition necessary because the identifier 100 exists in the data area 110. The case where the identifier 100 is located in the non-data area 120 will be described later.
The "unique mark" is a mark that can be uniquely distinguished from other data recorded on the disc. In this embodiment, a continuous bit string longer than the maximum length of a continuous bit string that can be taken by data other than the identifier 100 is used as the unique mark.
For example, consecutive "1" that data other than identifier can take
Suppose that the number of is up to 16. If bit error is not taken into consideration at this time, 17 consecutive "1"
The bit string consisting of can be uniquely distinguished from the data other than the identifier 100, and thus can be said to be a unique mark.
Similar to the disc shown in FIG. 2 above, the identifier 100 is “front” of the boundary 180. That is, the light beam 161 is
The identifier 100 is passed first, and then the boundary 180 is passed.

Also in the disc shown in FIG. 10, the identifier 10
The distance between 0 and the boundary 180 is preferably separated by the distance w described above. Because the focus error signal changes due to the identifier 100,
This is because the distance between and is settled at the time when the light beam 161 scans.

FIG. 11 is a block diagram of a focus control device using the disc shown in FIG. In the configuration of FIG. 11, the output of the adder 19 is the address reading circuit of FIG.
Instead of 21, it is input to the identifier detector 44. The identifier detector 44 has a function of receiving the output of the adder 19 and detecting a continuous bit string longer than a predetermined length,
This identifies the presence of the identifier. Identifier detector 44
When the presence of the identifier is recognized, the identifier detection signal IDT is given to the timing generator 23 through the delay circuit 22. When the identifier detection signal IDT is input, the timing generator 23 outputs two hold signals to the sample and hold circuits 20 and 27 at predetermined timings, as in the embodiment shown in FIG. As a result, also in the focus control apparatus shown in FIG. 11, similar to the focus control apparatus shown in FIG. 1, it is possible to realize focus control that is not affected by the pseudo defocus occurring in the land track and the groove track. The delay circuit 22 detects the identifier detection signal ID
When the scanning linear velocity of the light beam is v and the distance between the rear end of the identifier 100 and the boundary 180 is w, the time to delay T is w
It can be determined in the same manner as in Example 1.

FIG. 12 shows a disc in which an identifier 130 is provided in an area (non-data area) 120 other than the data area in which data is recorded / reproduced. The disc identifier 130 shown in FIG.
Are located in the non-data area 120 existing on the inner circumference side of the disk with respect to the data area 110. Therefore, in order to identify the position of the boundary 180 while recording / reproducing data, the light beam 161 for recording / reproducing data is used.
In addition to the detector and the like, a light beam and a detector (not shown) for detecting the identifier are used. Similar to the disc shown in FIGS. 2 and 10, with respect to disc rotation, the identifier 130 is located before the boundary 180. In the disc of FIG. 12, the radial position of the identifier 130 is
It is located in the non-data area. Therefore, the area occupied by the disc identifier 100 of FIG.
It can be used for recording and reproducing data as 10. As a result, the storage capacity of the disc can be increased. Figure 12
Since the disc identifier 130 is provided outside the data area 110, it need not be a unique mark like the disc identifier 100 of FIG. For example, data area 11
Only by providing an area having a reflectance different from that of 0 (for example, an area having a high reflectance), the function as the identifier 130 is achieved.

FIG. 13 is a block diagram of a focus control device using the disc shown in FIG. In the focus control device of FIG. 13, the photocoupler 45 detects the identifier. The photo coupler has a light emitting portion and a light receiving portion (not shown),
The light beam 161 emitted from the light emitting portion is applied to the non-data area of the disc 7, and the light receiving portion 16 is reflected by the disc.
It is arranged to receive 1. The output of the photocoupler 45 is given to the non-inverting input of the differential amplifier 46. The predetermined voltage output from the constant voltage generator 47 is applied to the inverting input of the differential amplifier 46 as a comparison signal. The differential amplifier 46 compares the two input signals and gives a HIGH level to the input of the edge detector 48 when the output of the photocoupler 45 is larger and a LOW level when the output of the photocoupler 45 is smaller. The edge detector 48 detects the rising edge of the output from the differential amplifier 46. As mentioned above, the reflectance of the identifier is
For example, it is higher than the reflectance of other regions. Therefore, Figure 13
The identifier can be detected by the focus control device having the above configuration. The output of the edge detector 48 is given to the input of the timing generator 23 via the delay circuit 22. When the edge detection signal is input, the timing generator 23 outputs two hold signals to the sample and hold circuits 20 and 27 at predetermined timings, as described with reference to FIG. As described above, the focus control device shown in FIG. 13 can also realize the focus control which is not affected by the pseudo defocus as in the focus control device of FIG.

If the information on the distance between the identifier and the boundary is also recorded in the above-mentioned identifier, the distance between the identifier and the boundary can be known at the same time when the identifier is read. From this distance and the linear velocity with which the light beam 161 scans, the time required for the light beam 161 to scan from the identifier to the boundary can be known, and the sampling timing can be determined according to this time. As a result, even when the light beam 161 does not scan at a constant speed, timing information can be obtained in real time, and the configuration of the focus control device itself can be simplified. Such a method can be applied not only to a disc having an identifier but also to a disc having an address part. That is, also by recording the information of the distance w between the address portion and the boundary in the address portion, the information for obtaining the sampling timing can be obtained in the same manner. Further, the identifier may include address information, for example, information regarding a track address and a sector address.

It is preferable that the address portion or the identifier (which will be represented by the identifier in the following description) for determining the sampling timing, which has been described so far, exists before the “neighborhood” of the boundary. For the sake of convenience, the angle at which the disk rotates between the time when the light beam 161 passes through the identifier and the time when it passes through the boundary is referred to as a “difference angle”.
Being in front of the "neighborhood" here means that this "difference angle" is small. The reason why it is preferable for the identifier to exist in the vicinity is as follows. If the difference angle is too large, the disc rotation angular velocity error causes
This is because the timing of sampling the target value is shifted. In practice, the difference angle is preferably less than 0.5 rad, and more preferably less than 0.2 rad. In each of the above-described embodiments, the boundary between the land track and the groove track is detected using the address part or the identifier. Hereinafter, a focus control device that realizes focus control without using an identifier will be described. FIG. 14 shows a block diagram of an identifierless focus control device according to the present invention. In the focus control device of FIG. 14, the boundary is detected by checking the change of the focus error signal itself. To enable this, the focus error signal ER output from the differential circuit 9 is also applied to the non-inverting input of the differential amplifier 49. A predetermined voltage output from the constant voltage generator 50 is given to the inverting input of the differential amplifier 49 as a comparison signal. The differential amplifier 49 compares the two inputs and outputs a HIGH level as the output OUT49 when the focus error signal is large and a LOW level when the focus error signal is small. The level of the comparison signal output from the constant voltage generator 50 will be described later. The output OUT49 of the differential amplifier 49 is the edge detector 51
And to the input of the timing generator 23 via the delay circuit 52. The edge detector 51 is a double-edge detection type detector, and outputs an edge detection signal OUT51 when detecting either a rising edge or a falling edge in its input signal. When the edge detection signal OUT51 delayed by the delay circuit 52 is input, the timing generator 23 outputs two hold signals SH20 and SH20 to the sample and hold circuits 20 and 27 in the same manner as described with reference to FIG.
SH27 is output at each predetermined timing.

FIGS. 15A to 15H show the position of the light beam 161 and the waveform of each part in order to explain the operation of the focus control device of FIG. FIG. 15A shows the position of the light beam 161 on the track when the light beam 161 scans along the track due to the rotation of the disk 7. Light beam 1
The 61 is first located on the groove track 170, passes the boundary 180 between the land track 171 and the groove track 170, reaches the land track 171, and then makes another rotation and passes the boundary 180 again. Reach groove track 170. The vertical axes in FIGS. 15B to 15H indicate the focus error signal ER, the output OUT49 of the differential amplifier 49, and the edge detector 5, respectively.
1 output OUT51, the hold signal SH20 applied to the sample and hold circuit 20, the hold signal SH27 applied to the sample and hold circuit 27, the output OUT20 of the sample and hold circuit 20 and the output OUT27 of the sample and hold circuit 27. The axis corresponds to the horizontal axis of FIG. 15 (a), that is, the position of the light beam 161 on the track.

In the description after (a) to (h) in FIG. 15, for the sake of simplification, defocus does not occur in the groove track 171 (that is, just focus), and as a result, the groove track It is also assumed that the focus error signal ER on 171 (output from the differential circuit 9 in FIG. 14) is also at zero level. The hold signals SH20 and SH27 from the timing generator 23 are low level and high level, respectively.
It is set to IGH level. At this time, since the switch 24 of the sample-hold circuit 20 is short-circuited, the sample-hold circuit 20 outputs a signal equal to the input signal. Since the switch 28 of the sample hold circuit 27 is opened, the sample hold circuit 27 outputs the voltage held in the capacitor 29.

When the light beam 161 reaches the boundary 180, the focus error signal ER indicates the defocus amount DF due to the pseudo defocus as described above. As shown in FIG. 15 (b), the constant voltage generator 50 outputs almost DF 'as a comparison signal.
A voltage at the level of / 2 is applied to the inverting input of the differential amplifier 49. Therefore, the output OUT49 of the differential amplifier 49 is the light beam 1
At time T11 when 61 is located at the boundary, the LOW level changes to the HIGH level. The edge detector 51 detects this rising edge and outputs an edge detection signal OUT51 to the delay circuit 52. At time T11 when passing the boundary,
The detected edge detection signal OUT51 is input to the timing generator 23 at time T12 via the delay circuit 52. The delay time DU of the delay circuit 52 is such that the light beam 161 passes through the boundary 180 and the entire light beam 161 is completely land track 171.
Set to the time needed to be on top. The timing generator 23 detects the edge detection signal OUT51 at time T12.
Upon receipt of the period HT, as described with reference to FIG.
Set the hold signal SH20 to HIGH level and the hold signal SH27 to LOW level for 1. Since the following operation is the same as that of the above-mentioned embodiment, the detailed description thereof will be omitted, but the influence of the pseudo defocus on the focus control can be eliminated.

When the disk further rotates once, time T15
At, the light beam 161 moves from the land track 171 to the groove track 170. In the groove track 170, the focus error signal ER becomes zero,
The position of the quadrant detector with respect to the light beam 161 is adjusted. Therefore, the level of the focus error signal ER is
It becomes zero. As a result, the output OUT49 of the differential amplifier 49 becomes HIGH.
Changes from H level to LOW level. The edge detector 51 is
Detects the falling edge and outputs edge detection signal OUT51. Similarly, at time T16, which is delayed by DU from time T15
From then on, the hold signal SH20 is set to the high level for the period HT1, and the hold signal SH27 is set to the low level for the period HT2. Although details of the following operation are omitted, the influence of the pseudo defocus on the focus control can be eliminated. The comparison signal is not limited to DF '/ 2. If the differential amplifier 49 has a hysteresis characteristic,
Spike noise included in the focus error signal ER that occurs when the light beam 161 passes through the boundary can be blocked.

In the above embodiments, it is assumed that a land track and a groove track are alternately arranged in series. However, the present invention can be applied even if the land tracks and the groove tracks are not alternately arranged in series as long as the disk causes a pseudo defocus during recording and reproduction. For example, there is no boundary for each revolution of the disc, and a single land track and a single groove track are spirally formed, and information is recorded / reproduced on both the land track and the groove track. The present invention can be applied to the above. In such a disc, for example, the groove track is scanned from the outermost circumference to the innermost circumference, and then the land track is scanned from the outermost circumference to the innermost circumference. Therefore, also in this case, the influence of the pseudo defocus on the focus control can be eliminated.

[0093]

According to the focus control device of the present invention,
The target value for focus control is changed according to whether the light beam is located on the land track or the groove track. Therefore, even if the focus error signal changes due to the pseudo defocus, the focus control can be prevented from being affected. Therefore, highly accurate focus control can be realized even in an optical disc for recording / reproducing information on the land track and the groove track.

According to the focus control device of the present invention, the change in the focus error signal is detected, and the focus error signal is sampled based on the detected timing. As a result, it is not necessary to record the information that gives the sampling timing on the recording medium itself. Therefore,
The capacity that can be stored in the optical disc can be increased, and the configuration of the focus control device can be simplified.

According to the recording medium of the present invention, the timing at which the focus error signal is sampled can be determined by the identifier recorded on the recording medium. Therefore, an appropriate focus error signal can be sampled before the focus control system is affected by the pseudo defocus. Therefore, highly accurate focus control can be realized.

According to the recording medium of the present invention, a predetermined space is provided between the identifier and the boundary, and as a result,
The focus error signal can be sampled after the fluctuation of the focus error signal due to the influence of the identifier disappears. Therefore, highly accurate focus control is possible.

[Brief description of drawings]

FIG. 1 is a block diagram of a first embodiment of a focus control device according to the present invention.

FIG. 2 is a diagram schematically showing the structure of a disk 7 used in the focus control device of the present invention.

FIG. 3 is a diagram showing an example of a format of tracks on the disc shown in FIG.

FIG. 4 is an enlarged view showing an address part ID0 surrounded by a circle in FIG. 2 and the vicinity of a boundary.

FIG. 5 is a diagram showing a cross-sectional view of a disk 7 that is an embodiment of a recording medium according to the present invention.

FIG. 6 is a diagram showing a cross-sectional view of a double-sided disc.

7A to 7G are diagrams showing the focus control operation when the light beam moves from the groove track to the land track in the focus control device and the recording medium according to the present invention.

8A to 8G are diagrams showing a focus control operation when a light beam moves from a land track to a groove track in the focus control device and the recording medium according to the present invention.

FIG. 9 is a block diagram of a focus control device according to a second embodiment of the present invention.

FIG. 10 is a diagram showing a disc having an identifier in each track instead of an address part.

11 is a block diagram of a focus control device using the disc shown in FIG.

FIG. 12 is a diagram showing a disc provided with an identifier in a non-data area.

13 is a block diagram of a focus control device using the disc shown in FIG.

FIG. 14 is a block diagram of an identifierless focus control device in accordance with the present invention.

15A to 15H are diagrams illustrating the operation of the focus control device in FIG.

16A to 16E are diagrams showing the shapes of the light beams on the four-division detector when the distance between the focusing point of the light beams and the disc is changed.

FIG. 17 is a diagram schematically showing an L / G disc.

18 is an enlarged view of a radial boundary between a land track and a groove track, which is surrounded by a circle in FIG.

19A to 19C are diagrams for explaining changes in a focus error signal and a tracking error signal when a light beam traverses a track in a disc radial direction.

20 (a) and 20 (b) are diagrams illustrating how a focus error signal changes when a light beam moves from a groove track to a land track.

[Explanation of symbols]

 1 Semiconductor Laser 2 Collimator Lens 3 Polarizing Beam Splitter 4 λ / 4 Plate 5 Focusing Lens 6 Lens 7 Disk 8 Quadrant Detector 9 Differential Circuit 10 Phase Compensation Circuit 11 Gain Compensation Circuit 12 Drive Circuit 13 Focus Actuator 15 Detection Lens 16 Cylindrical Lens 17, 18, 19 Adder 20, 27 Sample and hold circuit 21 Address reading circuit 22 Delay circuit 23 Timing generation circuit 31 Differential amplifier

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinichi Yamada 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Toshiyuki Kino 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. (72) Inventor Yoshihiro Kanda, 1006 Kadoma, Kadoma-shi, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (26)

[Claims] 1. A spiral track having a land track and a groove track, both the land track and the groove track recording information.
A focus control device for controlling a light beam to be focused on a recording medium having a track to be reproduced, the focusing means for focusing the light beam on the recording medium, and the focusing means for focusing the light beam on the recording medium. Detect the focusing condition,
Focusing state detecting means for outputting a signal indicating the focusing state, and a value of an output from the focusing state detecting means and a target value are compared and the focusing means is moved to move the light beam on the recording medium. Control means for maintaining the focused state at a desired state, and setting the target value at a first level when the light beam is radiated onto the land track so that the light beam is focused on the groove track. And a target value setting means for setting the target value to a second level different from the first level. 2. The focus control device according to claim 1, wherein the land tracks and the groove tracks are alternately arranged in series. 3. The target value setting means sets the target value between the first level and the second level when the output from the focusing state detecting means changes by a predetermined value or more. The focus control device according to claim 1, which is switched. 4. The target value setting means is responsive to a signal generated by an identifier recorded on the recording medium,
The focus control device according to claim 1, wherein the target value is switched between the first level and the second level. 5. The target value setting means switches the target value between the first level and the second level after a lapse of a predetermined time after receiving the signal generated by the identifier. Item 5. The focus control device according to item 4. 6. The target value setting means sets the target value between the first level and the second level in response to a signal generated by an address pit provided on the recording medium. The focus control device according to claim 1, which is switched. 7. The target value setting means switches the target value between the first level and the second level after a lapse of a predetermined time after receiving the signal generated by the address pit. The focus control device according to claim 6. 8. The focus control device according to claim 7, wherein the predetermined time is determined based on information recorded by the address pits. 9. The target value setting means includes a sampling means for sampling an output from the focusing state detection means, and at least one of the first level and the second level is sampled by the sampling means. The focus control device according to claim 1, wherein the focus control device is set on the basis of the value of the output from the focused state detecting means. 10. The sampling means samples the output from the focusing state detecting means within a predetermined time from the time when the light beam passes through the boundary between the land track and the groove track on the track. The focus control device according to claim 9. 11. The focus control device according to claim 10, wherein the predetermined time is shorter than a response time of the control means. 12. The sampling means samples an output from the focusing state detecting means in response to a signal generated by an address pit provided on the recording medium, and the light beam causes the address pit to be sampled. The time DT from the passage to the sampling of the output of the focusing state detecting means is w / v <DT,
The focus control device according to claim 11, wherein a scanning linear velocity of the light beam on a track irradiated with the light beam is v, and a distance between the address pit and the boundary is w. 13. The focus control device according to claim 12, wherein the distance w between the address pit and the boundary is determined based on address information generated by the address pit provided on the recording medium. 14. The sampling means is provided on the recording medium at a predetermined scanning linear velocity of the light beam.
10. The focus control device according to claim 9, wherein the output from the focusing state detecting means is sampled based on a signal generated by an identifier indicating a boundary position between the land track and the groove track. 15. A recording medium having a spiral track in which land tracks and groove tracks are alternately arranged in series, both the land tracks and the groove tracks recording and reproducing information. The track has an identifier indicating a position of a boundary between the land track and the groove track, and the identifier is provided at a distance from the boundary. 16. The recording medium according to claim 15, wherein the identifier is provided near the boundary. 17. The recording medium according to claim 16, wherein the identifier is located with respect to the boundary in a direction opposite to a moving direction of a light beam with respect to the track. 18. A settling region is provided between the identifier and the boundary, and in the settling region, a signal corresponding to a focus error of a light beam with which a track is irradiated is the light beam. The recording medium according to claim 15, wherein the recording medium substantially returns to the state before reaching the identifier. 19. The identifier has a track address for identifying the track as information.
The recording medium described in. 20. The recording medium according to claim 19, wherein a track address pit functions as the identifier. 21. The length w of the settling region is set with respect to a scanning linear velocity v of a light beam in a track irradiated with the light beam and a rising time Tr of a control means for controlling the focusing of the light beam. The recording medium according to claim 18, which satisfies the relationship of w> v · Tr. 22. The recording medium according to claim 18, wherein the identifier includes information regarding a length of the settling area. 23. The recording medium according to claim 15, wherein the recording medium is disc-shaped, and the tracks are formed on both sides of the recording medium. 24. The recording medium is formed by laminating at least two disc-shaped recording media.
The recording medium according to item 3. 25. The recording medium according to claim 15, wherein the recording medium includes a base material and a recording layer. 26. The recording medium according to claim 25, wherein the recording layer is a phase change recording layer.