JP3064860B2 - Focus control device and recording medium - Google Patents

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 for controlling a light beam to be focused on a recording medium and a recording medium. More specifically, information is recorded / recorded on a recording medium having land tracks and groove tracks.
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 on which information can be recorded are:
Since it can hold a large amount of data, it has become important as a medium for storing information representing audio, video, and the like. Generally, a concave portion and a convex portion are formed in a spiral shape in an optical recording medium. The optical recording medium is usually in the shape of a disc, and hence the optical recording medium is referred to here as a “disk”.
Call it. The concave and convex portions of the disc are generally called lands or grooves. The disk is rotated at high speed to read information recorded on spiral lands or grooves. In order to read information without touching, a light beam such as a semiconductor laser is focused (focused) on a disk and reflected by the disk. The amount of light reflected gives the recorded information.

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

Referring to FIGS. 16A to 16E, the principle of the astigmatism method will be described. In the astigmatism method, reflected light from a disc focused by a pair of focusing lenses and a cylindrical lens is applied to a four-divided detector 160. FIGS. 16A to 16E show the shapes of the light beam 161 on the quadrant detector 160 when the distance between the focal point of the light beam 161 and the disk changes. FIG. 16A shows a state where the focal point of the light beam 161 is farthest from the disk, and FIG.
FIG. 16C shows a just-focus state, and FIG. 16E shows a state where the focal point of the light beam 161 is closest to the disk. FIGS. 16 (b) and 16 (d) show FIGS. 16 (a) and 1
16 (c) and the intermediate state between FIG. 16 (c) and FIG. 16 (e). In FIGS. 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 crossing the track (hereinafter referred to as “radial direction”) is the figure. It corresponds to the left-right direction. Quadrant detector 160-2
The orthogonal dividing lines of the book are respectively along the circumferential direction and the radial direction. To obtain a focus error signal, that is, a signal indicating how much and in which direction the focus is deviated, the following is performed. The sum of the light amounts of two pairs of detectors located at the diagonal of the four-divided detector 160, that is, (A + D) and (B + C) 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. For example, "Optical Disc Technology" supervised by Morio Onoe, Radio Engineering Co., Ltd., Chapter 1.2.5 Focusing, Detection of Tracking Error, No. 83 Since it is described on pages 85 to 85, a detailed description is omitted here.

In recent years, there has been a demand for higher recording densities for optical disks. As one method for increasing the recording density of an optical disk, there is a method of reducing the interval between tracks on which information is recorded (hereinafter, referred to as “track pitch”). In order to reduce the track pitch, a land having a land track and a groove track /
Groove format optical disks (hereinafter referred to as “L / G disks”) have been proposed.

FIG. 17 is a view schematically showing an L / G disk. In a conventional optical disk, recording / reproduction of information is performed on either a groove for tracking control or a land which is an area sandwiched between adjacent grooves. On the other hand, in an L / G disc, both lands and grooves are used as tracks on which information is recorded / reproduced. 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 disk include a groove track 170 using a groove (a portion indicated by dots in FIG. 17) and a land track 171 using a land.
(A portion sandwiched by adjacent groove tracks) are alternately arranged for each rotation. The tracks on the L / G disk are groove track 170 and land track 1
Since this is a single spiral shape formed alternately, data can be continuously recorded / reproduced without interruption over the entire surface of the disk.

FIG. 18 is an enlarged view of a “boundary in the radial direction between the land track 171 and the groove track 170” 180 (hereinafter referred to as “boundary” for simplicity) surrounded by a circle in FIG. The figure is shown. The “boundary” 180 is provided 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 in a concave or convex structure that substantially satisfies d = λ / 8. The land track is a flat portion 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 every rotation.

At the edge where the optical depth is λ / 8, the light beam is diffracted. For this reason, it is widely known that the interference pattern of the light reflected by the optical disk at the detector changes. For example, for a groove, the interference pattern changes due to diffracted light due to a circumferential edge. The push-pull tracking method utilizes this change in the interference pattern to detect a tracking error and output a tracking error signal.
It is also well known that diffracted light by an edge affects an astigmatic focus error signal. (See “Optical Disc Technology”, supervised by Morio Onoe, Radio Engineering Co., Ltd., Chapter 1.2.5 Focusing, Tracking Error Detection, pages 85-87). This is because the light diffracted by the groove is not output uniformly from each of the diagonal pairs of the quadrant detector.

One of the causes of the unevenness of the diffracted light is as follows.
There is light beam aberration. 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 disk is not completely symmetric 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, instead of a step shape that is stood up exactly vertically. . In addition, this inclination differs not only for each disk but also for the position on the same disk. In other words, when looking 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 shape difference. When the light beam is located on the groove and when it is located on the land, the edge of the groove is switched left and right with respect to the light beam. When the cross section of the optical disc 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 unequal diffracted light due to the edges described above, the interference pattern on the quadrant detector is asymmetric even when the light beam is focused with zero focus error. That is, the above-mentioned focus error signal does not become zero in spite of the just focus. This focus error signal, which does not correspond to the actual focus shift (hereinafter, referred to as “true defocus”), is herein referred to as a “pseudo defocus” signal. 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”)
It is about 0.1 μm. On the other hand, a focus error signal caused by pseudo defocus has a magnitude corresponding to “true defocus” of about 2 μm.

When the light beam is in the just-focus state, for example, when the light beam is in the just-focus state on the groove, the focus error signal becomes zero so that the focus error signal becomes zero. 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, the focus control is not affected by the pseudo defocus, and stable information recording / reproduction can be performed.

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, even when the focus error is substantially zero, that is, even when the light beam is positioned on the land in the just-focus state, pseudo defocus occurs.

FIGS. 19 (a) to 19 (c) plot changes of the focus error signal ER and the tracking error signal TR when the light beam 161 crosses tracks in the radial direction of the disk. 19 (b) and 19 (c) show the magnitude of the focus error signal ER and the tracking error signal TR, respectively, and the abscissa shows the position of the light beam 161 in the radial direction of the optical disc. As shown in FIG. 19B, in the groove track 170, when the focus error signal ER is adjusted to be zero, the land track 171 has a 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 sufficiently fast. Therefore, the frequency of the focus error signal ER generated when the light beam 161 traverses the track (that is, the reciprocal of the number of tracks traversing per unit time) is much 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 on the track in the radial direction can be ignored. The amount of pseudo defocus generated by the radial movement of the track is out of phase by about 90 ° with respect to the tracking error signal TR.

FIGS. 20 (a) and 20 (b) show how the focus error signal ER changes when the light beam 161 moves from the groove track 170 to the land track 171. FIG. FIG. 20 (a) schematically shows the relationship between the light beam 161 and the track when the optical disc is viewed from above, and FIG.
20 plots a change 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. 20B, the light beam 1
Reference numeral 61 is located completely on the groove track 170, and the focus error signal ER is at the zero level. This is because the focus error signal ER due to pseudo defocus, which is generated when the light beam 161 is positioned on the groove track 170 as described above, is adjusted to be zero.

At position X2 in FIG. 20B, the light beam 1
61 is passing through a boundary 180 between the groove track 170 and the land track 171. Again, as shown in FIG.
The magnitude of the pseudo defocus signal generated by the light beam 161 moving on the track in the radial direction is represented by DF.
And At the moment when the light beam 161 reaches the position X2, a focus error signal ER is generated due to pseudo defocus.
Indicates the DF. However, in practice, the light beam 161
Reaches the position X2, the focus state is substantially the same as that at the position X1, ie, just focus. In other words, true defocus does not occur even if the focus error signal ER is DF due to pseudo defocus. This is because the above-described “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 defocus amount is negligibly small.

In an L / G disk, the light beam is
It is located on the land track and groove track for each rotation of the disk. The pseudo defocus occurs while the light beam is positioned on the land track, that is, during a 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 disc is much lower than the response frequency of the focus control system. Specifically, the rotation frequency of the disk is at most about several tens Hz (that is, the rotation cycle is about several tens ms).
It is. Therefore, when the light beam scans the land track and the groove track alternately, several kilohertz
A focus control system having a response frequency of about z
It responds to a focus error signal due to pseudo defocus having a frequency of about Hz. In addition, the amount of defocus caused by pseudo focus is about 2 μm. From the above, true defocus occurs.

As shown in FIGS. 20A and 20B, until the light beam 161 reaches the position X3 from the position X2 (about several milliseconds in time), the focus control system outputs the focus error signal. By performing negative feedback on ER, control is performed so that the focus error signal ER becomes zero. as a result,
At the position X3, the focus error signal ER converges to zero. As described above, the light beam 161 changes from X2 to X3
Is longer than the response time of the focus control system, that is, the time required for the focus control system to perform control and settle the focus error signal ER to substantially zero. At the position X3, the focus error signal ER is zero. However, since the focus control was performed to reduce the level DF of the focus error signal ER based on the pseudo defocus to zero, actually,
True defocus corresponding to pseudo defocus has occurred. True defocus caused by pseudo defocus differs depending on a focus error signal detection method, a focus control system, an optical head, and the like. But,
Compared to the depth of focus of the light beam (about ± 1 μm), the true defocus due to the pseudo defocus is several μm.
Since it is large, the recording and reproduction of signals becomes difficult, and the focus control is lost.

[0019]

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

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and an object of the present invention is not to be affected by a focus error signal caused by pseudo defocus. An object of the present invention is to provide a focus control device and a recording medium that can be controlled.

[0021]

According to the focus control apparatus of the present invention, a land track and a groove track are provided.
A recording medium which is alternately arranged in series, wherein
Information on both the track and the groove track.
Focus the light beam on a recordable recording medium
A focus control device for controlling the
Focusing means for focusing a beam on the recording medium;
Detecting the convergence state of the light beam on the recording medium,
Focusing state detecting means for outputting a signal indicating the focusing state
And a comparison between the output value of the focusing state detecting means and a target value.
And moving the focusing means according to the comparison result.
By this, the convergence state of the light beam on the recording medium
Control means for maintaining a desired state; and
When the land track is irradiated, the target value
Is set to a first target value, and the light beam is
When irradiating the track, the target value is
Target value setting for setting a second target value different from the first target value
Means for determining whether the light beam is
After passing the boundary with the lube track,
Sampling means for sampling the output of the detecting means;
Wherein the first target value and the second target value are smaller.
At least one is sampled by the sampling means.
Is set based on the ringed value ,
The above object is achieved. The sampling means is
The light beam is directed to the land track and the groove track.
The response of the control means from the time at which the
Within a predetermined time shorter than the time,
The output may be sampled. With the land track
An identifier indicating the position of the boundary with the groove track
Is provided on the recording medium, and the sampling means
The stage is responsive to a signal generated by the identifier,
The output of the focusing state detecting means may be sampled.
No. The identifier identifies the track from other tracks.
Address may be used.

[0022]

[0023]

[0024]

[0025]

[0026]

[0027]

[0028]

[0029]

[0030]

[0031]

[0032]

[0033]

[0034]

[0035]

[0036]

[0037]

[0038]

[0039]

[0040]

According to the focus control apparatus of the present invention, the target value of the focus control is changed depending on whether the light beam is irradiated on the land track or the groove track. By setting a target value having the same value as the generated focus error signal even if a focus error signal due to "pseudo defocus" occurs even though the light beam is in a substantially just focus state. The pseudo defocus can be prevented from affecting the focus control.

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

[0042]

[0043]

[0044]

[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 the focus control device according to the present invention. Semiconductor laser 1
Generates a light beam 161 for recording and reproducing information. The generated light beam 161 is collimated by the collimator lens 2 and then reflected by the polarization beam splitter 3 to pass through the λ / 4 plate 4 (λ is the wavelength of the light beam 161). The focusing lens 5 has a light beam 161 that has passed through the λ / 4 plate 4.
Is focused on a disk 7 and irradiated. The disk 7 is rotated by a motor 6.

The reflected light from the disk 7 is converged by a detection lens 15 and a cylindrical lens 16 via a converging lens 5, a λ / 4 plate 4 and a polarizing beam splitter 3, and then irradiated to a four-divided detector 8. You. The detection lens 15 and the cylindrical lens 16 intentionally generate astigmatism. The quadrant detector 8 is used for detecting a focus error amount by an astigmatism method and generating a focus error signal. The principle and configuration of the focus error signal detection of the astigmatism method are well known to those skilled in the art. For example, “Optical disk technology” (supervised by Morio Onoe, Radio Engineering, Chapter 1.2.5 Focusing, Tracking Error Detection, pages 83-85).

The output of the quadrant detector 8 is used by an adder 17 and an adder 18 to calculate the sum of the light amounts of the pair of detectors at diagonal positions. The differential circuit 9 includes an adder 17 and an adder
The focus error signal ER indicating the convergence state of the light beam 161 on the disk 7 is output by receiving the outputs from 18 and calculating the difference between them. The focus error signal ER output from the differential circuit 9 is applied to a non-inverting input of a differential amplifier 31 having an amplification factor of 1. The output of the differential amplifier 31 is input to a phase compensation circuit 10 for ensuring the control stability of the focus control system. The output of the phase compensation circuit 10 is input to a drive circuit 12 via a gain compensation circuit 11 for securing a loop gain required for focus control. The focus actuator 13 drives the focusing lens 5 in a direction substantially parallel to the optical axis of the light beam 161 in accordance with the output of the drive circuit 12 in order to focus the light beam 161. The above elements shown in FIG. 1 constitute a loop of the focus control system.

The inverting input and the non-inverting input of the differential amplifier 31 are both set so as to be output at an amplification factor of 1. The target value of focus control (usually expressed by a constant voltage) is given to the inverting input. Here, let us consider a case where the focus control system has reached a steady state by operating the focus control. At this time, the focus error signal output from the differential circuit 9 is
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 of the focus control can be set freely.

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

The outputs of the adders 17 and 18 are
Added by 19. An output signal of the adder 19, which represents the amount of reflected light from the disk 7, is input to an address reading circuit 21 and an address recorded on the disk 7 described later.
ID0 to ID3 are read. The address reading circuit 21
When ID0 described later is read from the address, the ID0 detection signal
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 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. On disk 7,
For the wavelength λ of the light beam 161 emitted from the semiconductor laser 1, the optical depth (considering the refractive index) is approximately λ /
8. Groove track 170 using concave groove
(Parts indicated by dots in FIG. 2) and a land track 171 (a part sandwiched between adjacent groove tracks 170) using lands that are convex portions are formed. The land tracks 171 and the groove tracks 170 are alternately arranged every one rotation. As a result, one spiral connected in series is formed over the entire surface of the disk 7. On the track, a boundary between the land track 171 and the groove track 170 exists every one rotation of the disk. The position of the boundary is provided so as to match regardless of the position of the track in the radial direction. Each track of the disk 7 has four address 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 a track address for track identification and a sector address for identifying which one of the four address parts (ID0 to ID3) present in one rotation corresponds to the track address. I have.

FIG. 3 shows an example of the format of a track on the disk shown in FIG. Each track is divided into four sectors from sector 0 to sector 3.
Each sector includes an address part and a data part for recording and reproducing information. In the address part, a sector mark SM indicating the beginning of a sector, a single frequency area VFO for pulling in a PLL for reading a signal, an address mark AM indicating the beginning of an address, a track address TR-ID, a sector address SC- ID, cyclic redundancy check code CR for error check
C, a postamble PA indicating the end of the address portion is arranged to be read in this order. The address reading circuit 21 reads the track address TR-ID and the sector address SC-ID, thereby obtaining the light beam 161.
At which track is located, and at the same time, which sector in one track is located. The address portions ID0 to ID3 of each track are arranged on the same radial line.

Referring back to FIG. 2, ID0 is the last address read in each track. That is, after passing through the IDO, the light beam does not pass through the other address portions ID1 to ID3 before passing through the boundary. ID0 is located on the opposite side of the boundary from the direction in which the light beam scans on the track. Here, "the light beam scans on 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 portion ID0 and the boundary 180 surrounded by a circle in FIG. The address portion is generally formed of a pit row having a concave-convex structure, and the pit row having the concave-convex structure stores address information. The address reading circuit 21 receives a signal indicating a 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 smaller 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 diffraction in the pit row is very small as compared with the fluctuation of the focus error signal due to pseudo defocus. As shown in FIG. 4, ID0 is provided at a distance w before the boundary 180. Here, “before” the boundary 180 means “in the direction opposite to the direction in which the light beam scans” with respect to the boundary 180. Between the address part ID0 and the boundary 180, the land track 171 located before the address part ID0 is located.
Alternatively, it is configured such that a track of the same type as the groove track 170 exists.

FIG. 5 is a sectional view of a disk 7 which is an embodiment of the recording medium according to the present invention. The disk 7 has a substrate 510 made of polycarbonate or the like, on which uneven tracks are formed by a method such as injection molding, and a dielectric layer 520 for heat insulation. A recording film 530 made of a phase-change type recording material for recording / reproducing by the light beam 161, a reflection film 540 for preventing the transmission of the light beam 161, and for protecting the above layers from scratches and the like. Including 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 convenience, a track protruding toward the side where the light beam 161 is incident on the disk 7 is referred to as a “land track” 171, and a track sandwiched between adjacent land tracks 171 is referred to as a “groove track” 170. Call it. However, a track protruding toward the side where the light beam 161 is incident may be referred to as a “groove track”, and a track sandwiched between adjacent groove tracks may be defined as a “land track”. Further, a magneto-optical recording layer may be used as the recording film.

FIG. 6 is a sectional view of a double-sided disk for realizing a larger storage capacity. The double-sided disk is formed, for example, by bonding two single-plate disks of FIG. 5 with an adhesive layer 600 such that the protective layers 550 are in contact with each other. When recording / reproducing on a double-sided disc having such a configuration, not only from the bottom as shown in FIG.
The light beam 161 can be emitted from above. As a result, one double-sided disk has the storage capacity of two single-plate disks. Regardless of whether the disk to which the present invention is applied is a single-plate disk or a double-sided disk, there is no significant difference in the configuration and effects. Therefore, in the following description, only a single-plate disk 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 can be applied to a double-sided disk.

FIGS. 7A to 7G show the operation of focus control in the focus control device and the recording medium according to the present invention. FIG. 7A shows that the light beam 161 scans along the groove track 170 due to the rotation of the disk 7, and the address part ID0, the groove track 170 and the land track 17
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 the ID0 when the light beam 161 scans the 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 / hold circuit 27 are shown, and the horizontal axis is time. The horizontal axes in FIGS. 7B to 7G are displayed so as to correspond to the horizontal axes in FIG. That is, FIG.
And the time T on the horizontal axis in FIGS. 7B to 7G.
When b is represented by the same length, the relationship between the distance Xa and the time Tb is Xa = v · Tb, where v is
The light beam 161 represents the linear velocity at which the track is scanned.

7A to 7G, for the sake of simplicity, for the sake of simplicity, no defocus has occurred in the groove track 170 (that is, just focus), and as a result, the focus error signal ER Assume that it has been adjusted to indicate zero. The hold signals SH20 and SH27 from the timing generator 23 are set to LOW level and 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 open, the sample / hold circuit 27
Outputs the voltage held in the capacitor 29. For the sake of simplicity, 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 / hold circuit 27 is also zero. Therefore, at this time, the input value to the inverting input terminal of the differential amplifier 31 for setting the target position of the focus control, that is, the target value of the focus control is zero.

When the light beam 161 is positioned 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 are determined by the light beam 161.
Smaller than the diameter of 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 slight. The distance w between the address part ID0 and the boundary 180 is the address part ID.
It is provided that a minute change in the focus error signal ER due to 0 converges sufficiently before sampling the focus error signal ER described later. That is, the distance w satisfies w> v · Tr, where v is the linear velocity at which the light beam 161 scans the disk, 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 end of address portion 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 delay circuit 22
T is equal to the time required for the light beam 161 to travel the distance w and 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-described pseudo defocus
Occur stepwise. One of the features of the present invention is that a focus error signal corresponding to this pseudo defocus
ER is sampled and used as a 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 at which the light beam 161 passes the rear end of ID0
And the difference between the time T2 passing through the boundary 180 and AT,
At least AT <DT. That is, the delay time DT has a lower limit. Further, when the control system is realized by actual hardware, the light beam 161
At the same time as the track reaches the land track 171, pseudo defocus is not reflected on the focus error signal ER, and a slight time lag occurs. In other words, a focus error signal indicating pseudo defocus
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 in the land track 171 is replaced with the target value in the groove track 170 after the time T2 and before the control system completely follows the focus error signal ER due to pseudo defocus. Because it must be done. FIG.
Referring to (e), when a focus error signal DF due to pseudo defocus occurs at time T2, the focus control system responds to pseudo defocus. As a result, at time T3, the focus error signal ER due to the pseudo defocus decreases to DF '. If the target value of the focus control is the focus error signal ER in the groove track 170 (in this case, a signal of zero level), the control system operates so that the focus error signal ER becomes zero, and true defocus occurs. Would. 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 DF and DF 'can be regarded as substantially equal. If the difference between DF and DF 'is too large, the target value of the focus control will be shifted, and as a result,
A pseudo defocus effect 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
More preferably, it is shorter than 0.

In this embodiment, the delay time DT is given by AT = w
/ V <DT <AT + Tr. Here, AT is the light beam after the ID0 detection signal DET is output.
161 is the time required to reach the land track, and Tr is the response time of the control system. Here, when the distance w differs depending on the position of the light beam 161 on the disk, that is, the track being scanned, the distance w may be calculated based on the track information (track position) obtained from the address portion. 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 receiving the ID0 detection signal DET delayed at time T3, the timing generator 23 sets the hold signal SH20 to a high level from time T3 to time T5 (period HT1). As a result, during the HT1, the sample and hold circuit 20 outputs the focus error signal ER at the time T3.
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 pseudo defocus generated in the land track 171. The timing generator 23 sets the hold signal SH20 to the HIGH level at the time T3, and simultaneously sets the hold signal SH20 to the time T4 from the time T3 (for a period
HT2), the hold signal SH27 is changed from HIGH level to LOW
Set to level. When the hold signal goes low, the switch 28 is short-circuited and charging of the capacitor 29 is started, and the output OUT27 of the sample / hold circuit 27 eventually becomes equal to its input. At time T4 when the period HT2 has elapsed from time T3, the hold signal SH27 goes high again, and the sample-and-hold circuit 27 holds the input, that is, the focus error signal ER due to the pseudo defocus generated 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 time T4, the focus error signal ER due to the pseudo defocus on the land track 171 is output. The value becomes the target value of the focus control. Therefore, the focus control system is not affected by the focus error signal ER reflecting the pseudo defocus on the land track 171, and as a result, it is possible to prevent the occurrence of true defocus.

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 without holding it. Therefore, the relationship between periods HT1 and HT2 is
It is set so that HT2 <HT1.

FIGS. 8A to 8G show the operation of the focus control when the light beam 161 moves from the land track 171 to the groove track 170 in the focus control apparatus and the recording medium according to the present invention. FIGS. 8 (a) to 8 (g) are diagrams when a time period of substantially one rotation of the disk has elapsed from times T1 to T5 in FIGS. 7 (a) to 7 (g). FIG. 8A shows a state in which the light beam 161 moves along the land track 171 due to the rotation of the disk 7 and passes through the address portion ID0 and the boundary 180 to reach the groove track 170. 7 is schematically shown. FIG.
(b), (c), (d), (e), (f), and (g) show the ID0 detection signal DET, sample hold when the light beam 161 moves as shown in FIG. Hold signal SH20 to circuit 20, hold signal SH27 to sample and hold circuit 27, focus error signal ER, output signal OU of sample and hold circuit 20
Output signal OUT27 of T20 and sample and hold circuit 27
Are shown, and the horizontal axis is time. Fig. 8 (b)
The horizontal axis of (g) is 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 pseudo defocus sampled and held by the sample and 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 a just-focused state on the disk 7.

Before time T8, the timing generator 23
Accordingly, 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, and the sample and hold circuit 20
Numeral 27 outputs a focus error signal ER caused by pseudo defocus, which is sampled at a time just before the time when the disk makes one rotation. When the light beam 161 is located at the address portion ID0, the focus error signal ER fluctuates due to diffraction by edges along the circumferential direction of the address portion ID0. However, since the change of the focus error signal ER is slight, a large defocus caused by the address portion ID0 does not occur.

The address reading circuit 21 has an address 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 outputs the period HT1 as described above.
, The hold signal SH20 is set to HIGH. As a result, the sample and hold circuit 20 holds the focus error signal ER at time T8. Then the light beam
The reference numeral 161 indicates a position immediately after being located on the groove track 170 after passing through the boundary between the land track and the groove track.
Therefore, the pseudo defocus that has occurred on the land track 171 no longer occurs, and the focus error signal
ER returns to near zero level. Therefore, the sample and hold circuit 20 samples and holds a signal of almost zero level.

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

At time T10 when the period HT1 has elapsed from time T8, 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 without holding it. After approximately one revolution of the disk, the light beam 161 again crosses the boundary and moves from the groove track 170 to the land track 171 again. Thereafter, the operations described with reference to FIGS. 7A to 7G and FIGS. 8A to 8G are repeated every two rotations of the disk.

With the above-described configuration, even a disk in which land tracks and groove tracks are alternately arranged for each rotation of the disk is not affected by pseudo defocus. That is, by using a biased sample value as the target value of the focus control, it is possible to prevent the focus error signal caused by the pseudo defocus from becoming zero. As a result, it is possible to configure a focus control device that can always maintain the just focus state in all tracks.

In the above embodiment, the hold signals SH20 and SH27 to the sample / hold circuits 20 and 27 are generated by using the ID0 detection signal indicating that the address section ID0 has passed as a trigger of the timing generator. I have. 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 by configuring as follows. The address reading circuit 21 detects the address portion ID3 and outputs an ID3 detection signal to the delay circuit 22. The delay circuit 22 delays the ID3 detection signal and outputs the signal 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 by the rotation of the disk 7, instead of the above-described delay time DT1. . That is, assuming that the period of one rotation of the disk 7 is TROT and the number of addresses passing during one rotation of the disk is N, DT3 = DT1 + TROT / N. For example, in the case of the disk 7 according to the present embodiment, N = 4.

By setting the delay time as described above, the timing of the ID3 detection signal coincides with that of the above-described 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 n-th 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) =
What is necessary is just to set so that it may become 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 differs depending on the position of the track, the position of the track is obtained from the address portion, and the linear velocity on the track is calculated. If the delay time is set according to the linear velocity obtained in this way, sampling can be performed at an 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. The focus error signal sampled and held immediately after the boundary is set as a target value of focus control by a target value setting circuit. As a result, even when the pseudo defocus between the groove track and the land track affects the focus error signal, the focus position that becomes the just focus can be set as the target value of the focus control system. As a result, according to the present invention, it is possible to realize focus control that is not affected by 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 depends on (1) the environment where the disc is placed (temperature, humidity, etc.), and (2) the position on the disc (inner track or outer track). And (3) even if it changes due to manufacturing errors and deformations of individual disks, it is possible to sample and use an appropriate target value for each track, thereby improving the accuracy of focus control. Having.

In the above-described 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 of the focus control is not necessarily limited to the value obtained by the above method. For example, if the pseudo defocus amount generated between the land track and the groove track is a substantially constant value, DF2, the following method can be applied. That is, instead of the sampled and held focus error signal value, two constant voltage generators may be used and selectively given to the control system as target values.

FIG. 9 is a block diagram of a focus control device according to a second embodiment of the present invention. 9, the description of the same components as those in FIG. 1 is omitted. The disk used in the present embodiment is almost the same as the disk 7 used in the first embodiment, so that the configuration diagram is omitted. FIG.
In, the constant voltage generators 40 and 41 give, as outputs, target values for focus control on land tracks and groove tracks. The outputs of the constant voltage generators 40 and 41 are provided to two inputs of an 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) according to an input signal to a 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 focus control target value. When the control signal is at the high level, the output of the constant voltage generator 40 is supplied to the inverting input of the differential amplifier 31 when the control signal is at the low level. The constant voltage generator 40 outputs a zero level signal. Constant voltage generator 41
Outputs a signal of a defocus amount DF2 caused by pseudo defocus generated on a land track.

On the other hand, the output of the address reading circuit 21
DET is input to the land / groove identification circuit 43. The land / groove identification circuit 43 determines whether the light beam is located on a land track or a 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 includes:
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 are used. Land / groove identification circuit
Reference numeral 43 can easily determine whether the light beam 161 is located on a land track or a groove track depending on whether the read track address is an even number or an odd number. The output of the land / groove identification circuit 43 is at a high level when the light beam 161 is located on a groove track, and is at a low level when the light beam 161 is located on a land track.
Set to W level, this output is
Output to 2 control terminal. As described above, the inverting input of the differential amplifier 31
When 161 is located on the groove track, the output of constant voltage generator 40 is provided, and when 161 is located on the land track, the output of constant voltage generator 41 is provided. Therefore, similarly to the first embodiment, even when the pseudo defocus affects the focus error signal, the focus error signal corresponding to the focus position that becomes the 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 when 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 be zero when the light beam 161 is positioned on the land track, the output levels of the constant voltage generators 40 and 41 need only be DF2 and zero, respectively. In this embodiment,
The target value of the focus control was changed by selectively switching the outputs from the two constant voltage generators. However, if the target values can be set to different levels, the effects of the present invention can be obtained, 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 is omitted.

The method for obtaining the timing for sampling the focus error signal is not limited to the method using the address described above. 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 portion.
00 ") on each track. Figure
The identifier 100 shown in 10 does not necessarily need to include information on a track, a sector, or the like, 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" for the other data on the disk. This is a condition necessary for the identifier 100 to exist 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 that is longer than the maximum length of a continuous bit string that can be taken by data other than the identifier 100 is used as a unique mark.
For example, a continuous "1" that can take data other than an identifier
Suppose that the number of is at most 16. At this time, if the bit error is not considered, 17 consecutive “1” s
Can be uniquely distinguished from data other than the identifier 100, and can be said to be a unique mark.
As in the disc shown in FIG. 2 described above, the identifier 100 exists “before” the boundary 180. That is, the light beam 161 is
It first passes through the identifier 100 and then through the boundary 180.

In the disc shown in FIG.
It is preferable that the distance between 0 and the boundary 180 be as large as the distance w described above. Because the change of the focus error signal by the identifier 100 is
Is settled at the time when the light beam 161 scans.

FIG. 11 is a block diagram of a focus control device using the disk shown in FIG. In the configuration of FIG. 11, the output of the adder 19 is used as 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 identifying that an identifier exists, the identifier supplies an identifier detection signal IDT to the timing generator 23 via the delay circuit 22. When the identifier detection signal IDT is input, the timing generator 23 outputs two hold signals to the sample / hold circuits 20 and 27 at predetermined timings as in the embodiment shown in FIG. Thus, also in the focus control device shown in FIG. 11, similarly to the focus control device shown in FIG. 1, it is possible to realize focus control that is not affected by pseudo defocus generated on land tracks and groove tracks. The delay circuit 22 outputs the identifier detection signal ID.
The time for delaying T is v, where v is the scanning linear velocity of the light beam, and w is the distance between the rear end of the identifier 100 and the boundary 180.
It can be determined in the same manner as in the first embodiment.

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

FIG. 13 is a block diagram of a focus control device using the disk shown in FIG. In the focus control device of FIG. 13, the photocoupler 45 detects the identifier. The photocoupler has a light emitting unit and a light receiving unit (not shown),
The light beam 161 from the light emitting unit irradiates the non-data area of the disk 7, and the light receiving unit reflects the light beam 16 reflected by the disk.
One is arranged to receive. The output of the photocoupler 45 is provided to the non-inverting input of the differential amplifier 46. The predetermined voltage output from the constant voltage generator 47 is given to the inverting input of the differential amplifier 46 as a comparison signal. The differential amplifier 46 compares the two input signals, and applies a HIGH level when the output of the photocoupler 45 is larger and a LOW level when the output is smaller, to the input of the edge detector 48. The edge detector 48 detects a rising edge of the output from the differential amplifier 46. As mentioned above, the reflectivity of the identifier is
For example, it is higher than the reflectance of other regions. Therefore, FIG.
The identifier can be detected by the focus control device having the above configuration. The output of the edge detector 48 is supplied 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 / 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 focus control that is not affected by pseudo defocus similarly to the focus control device of FIG.

If information on the distance between the identifier and the boundary is also recorded in the above-described identifier, the distance between the identifier and the boundary can be determined at the same time as reading the identifier. From this distance and the linear velocity at which the light beam 161 scans, the time required for the light beam 161 to scan from the identifier to the boundary can be determined, 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 technique can be applied not only to a disc having an identifier but also to a disc having an address portion. That is, by recording information on the distance w between the address part and the boundary in the address part, information for obtaining the sampling timing can be obtained in the same manner. The identifier may include address information, for example, information on a track address or a sector address.

It is preferable that the address part or the identifier (in the following description, represented by the identifier) for determining the sampling timing described above exists before the “neighbor” of the boundary. The angle at which the disk rotates between the time when the light beam 161 passes through the identifier and the time when the light beam 161 passes through the boundary is referred to as a “difference angle” here for convenience.
To be present in front of the “neighbor” means that the “difference angle” is small here. The reason why the identifier is preferably present before the neighbor is as follows. If the difference angle is too large, an error in the rotational angular velocity of the disk will cause
This is because the timing for sampling the target value is shifted. In practice, the difference angle is preferably smaller than 0.5 rad, and more preferably smaller 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 portion 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 a focus control device using no identifier according to the present invention. In the focus control device of FIG. 14, the boundary is detected by examining a change in the focus error signal itself. To enable this, the focus error signal ER output from the differential circuit 9 is also supplied to the non-inverting input of the differential amplifier 49. A predetermined voltage output from the constant voltage generator 50 is supplied 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 when the focus error signal is large, and outputs a LOW level when the focus error signal is small as the output OUT49. The level of the comparison signal output from constant voltage generator 50 will be described later. The output OUT49 of the differential amplifier 49 is connected to 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 supplies the 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.
The SH27 is output at a predetermined timing.

FIGS. 15 (a) to 15 (h) show the position of the light beam 161 and the waveforms of various parts for explaining 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 as the disk 7 rotates. Light beam 1
61 is located first on the groove track 170, passes through the boundary 180 between the land track 171 and the groove track 170, reaches the land track 171, makes another rotation, passes through the boundary 180 again, Reach the groove track 170. The vertical axes of FIGS. 15B to 15H are the focus error signal ER, the output OUT49 of the differential amplifier 49, and the edge detector 5, respectively.
1 shows the output OUT51, the hold signal SH20 supplied to the sample-and-hold circuit 20, the hold signal SH27 supplied 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 in FIG. 15A, that is, the position of the light beam 161 on the track.

In the description after (a) to (h) of FIG. 15, for the sake of simplicity, no defocus occurs in the groove track 171 (that is, just focus), and as a result, It is also assumed that the focus error signal ER on 171 (output from the differential circuit 9 in FIG. 14) is also at the zero level. The hold signals SH20 and SH27 from the timing generator 23 are LOW level and H level, respectively.
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 and hold circuit 27 is open, the sample and hold circuit 27 outputs the voltage held by 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 of level / 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 level changes from the LOW level to the HIGH level. The edge detector 51 detects the 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.
It is set to the time needed to be on top. The timing generator 23 outputs the edge detection signal OUT51 at time T12.
Is received, as described with reference to FIG.
The hold signal SH20 is set to the high level and the hold signal SH27 is set to the low level for one time. The following operation is the same as that of the above-described embodiment, and a detailed description thereof will be omitted. However, it is possible to remove the influence of the pseudo defocus on the focus control.

When the disk makes another rotation, at time T15
In, 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 has been adjusted. Therefore, the level of the focus error signal ER is
Becomes zero. As a result, the output OUT49 of the differential amplifier 49 becomes HIGH.
Change from H level to LOW level. The edge detector 51
The falling edge is detected and the edge detection signal OUT51 is output. Hereinafter, similarly, the time T16 delayed by DU from the time T15.
After that, 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 the details of the following operation are omitted, the influence of the pseudo defocus on the focus control can also be removed. 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, which is generated when the light beam 161 passes through the boundary, can be prevented.

In the above embodiment, it is assumed that a disk in which land tracks and groove tracks are alternately arranged in series is used. However, the present invention can be applied to a disk in which pseudo defocus occurs in recording / reproducing even if land tracks and groove tracks are not alternately arranged in series. For example, a single land track and a single groove track are formed in a spiral shape without a boundary for each rotation of the disk, and information is recorded / reproduced on both the land track and the groove track. The present invention can also be applied to 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 of the focus control is changed depending on 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, it is possible to prevent the focus control from being affected. Therefore, high-precision focus control can be realized even on an optical disc on which information is recorded / reproduced on a land track and a groove track.

According to the focus control device of the present invention, a 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 information giving the timing of sampling on the recording medium itself. Therefore,
The capacity that can be stored on the optical disk can be increased, and the configuration of the focus control device can be simplified.

[0095]

[0096]

[Brief description of the 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 a structure of a disk 7 used in the focus control device of the present invention.

FIG. 3 is a diagram showing a format example of a track of the disk shown in FIG. 2;

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 sectional view of a disk 7 which is an embodiment of the recording medium according to the present invention.

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

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

FIGS. 8A to 8G are diagrams showing focus control operations 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 disk 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 disk shown in FIG.

FIG. 14 is a block diagram of a focus control device that does not use an identifier according to the present invention.

FIGS. 15A to 15H are diagrams illustrating the operation of the focus control device in FIG. 14;

FIGS. 16A to 16E are diagrams showing the shape of a light beam on a four-segment detector when the distance between the light beam converging point and the disk changes.

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

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. 17;

FIGS. 19A to 19C are diagrams illustrating changes in a focus error signal and a tracking error signal when a light beam crosses a track in a disk radial direction.

FIGS. 20A and 20B are diagrams illustrating a change in a focus error signal when a light beam moves from a groove track to a land track.

[Explanation of symbols]

 REFERENCE SIGNS LIST 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 / hold circuit 21 Address reading circuit 22 Delay circuit 23 Timing generation circuit 31 Differential amplifier

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Shinichi Yamada 1006 Kadoma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. In-house (72) Inventor Yoshihiro Kanda 1006 Kazuma, Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (56) References JP-A-7-141701 (JP, A) (58) Fields investigated (Int. .7, DB name) G11B ^7/ 09-7/095 G11B 7/007

Claims (4)

(57) [Claims] 1. Land track and groove track
There a recording medium which is serially arranged alternately, the information on both the La <br/> command tracks and the groove track
On a recording medium capable of recording, a focus control unit that controls so as to focus the light beam, a focusing means for focusing the light beam onto the recording medium, the light beam of said recording medium detecting a focused state on a comparison between the focusing state detecting means for outputting a signal representing the focusing state, the value and the target value of the output of the focusing state detecting means,
By moving the focusing means according to the comparison result, a control means for maintaining the converging state on the recording medium of the light beam to a desired state, the light beam is irradiated onto the land track setting the target value to the first target value when you're, second target value different from the target value and the first target value when the light beam is irradiated onto the groove track <br/> Target value setting means for setting the land track and the groove track
After passing through the boundary with the focus,
Sampling means for sampling an output , wherein at least one of the first target value and the second target value
One is sampled by the sampling means.
A focus control device that is set based on the input value . 2. The method according to claim 1 , wherein said sampling means includes a light beam.
Is the land track and the groove track
From the time of passing the boundary, the response time of the control means
Short within a predetermined time, sampling the output of the focusing state detecting means, a focus control apparatus according to claim 1. 3. The land track and the groove track.
Identifier indicating the position of the boundary with the
Provided, the sampling means is generated by the identifier
In response to the signal, the output of the focusing state detecting means is sampled.
To pulling focus control apparatus according to claim 1. 4. The method according to claim 1, wherein the identifier is a track.
4. An address according to claim 3, wherein
Focus control device.