JPH10255284A - Focus controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control a focus with high precision without the influence of a focus signal caused by a quasi-defocus by a method wherein the focus control target values of a land track and a groove track are so set as to have focus error signals zero on a mirror part on a disc where there is no land and no groove. SOLUTION: A differential amplifier 4 calculates a difference between the outputs of an adder 2 and an adder 3 which calculate the respective summations of the luminous powers of pairs of detectors provided on respective orthogonal positions and outputs a focus error signal FE which shows the conversion state of a light beam on a disc. The output is inputted to a differential amplifier 5 which calculates and outputs a difference between the focus error signal FE and the output of a selection circuit 12. When a focus control system reaches a steady state, the error signal outputted from the differential amplifier 4 is converged into an offset value equal to the output of the selection circuit 12. A focus control target value is set by changing the output of the selection circuit 12 as the target value of the focus control.

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 focus on a recording medium and a recording medium.

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus control device and a recording medium which are not affected by pseudo defocus when recording / reproducing information on / from a recording medium having land tracks and groove tracks.

[0003] In recent years, an optical recording medium capable of recording information has become important as a medium for storing information representing audio, video and the like since it can hold a large amount of data.
Generally, a concave portion and a convex portion are formed in a spiral shape in an optical recording medium. Since the optical recording medium is usually in the shape of a disc, the optical recording medium is referred to herein as a “disk”. The concave and convex portions of the disc are generally called lands or grooves. In order to read the information recorded on the spiral land or groove,
It is rotated at high speed. 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. 9A to 9C, 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 (not shown) and a cylindrical lens is applied to the four-split detector 1. FIGS. 9A to 9C show the shapes of the light beam 60 on the quadrant detector 1 when the distance between the focal point of the light beam 60 and the disk changes. FIG.
9A shows a state where the focal point of the light beam 60 is separated from the disk, FIG. 9B shows a just focus state, and FIG. 9C shows a state where the focal point of the light beam 60 approaches the disk. State. In order to obtain a focus error signal signal, that is, a signal indicating how much and in which direction the focus is shifted, the following is performed. If the sum of the light amounts of two sets of detectors located on the diagonal of the four-division detector 1, that is, (A + C) and (B + D), is obtained, and then the difference between the obtained sums of the light amounts is obtained,
{(A + C)-(B + D)}, which is 2, 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., 1.2.5 focusing, tracking error detection, Since it is described on pages 83 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. 10 is a diagram 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. In contrast, with L / G discs,
Both lands and grooves are used as tracks on which information is recorded and reproduced. As a result, the track pitch becomes equivalently halved, so that the capacity of the optical disc is reduced to 2
It can be doubled. The track of the L / G disk is a groove track 201 using a groove (FIG. 10).
And a land track 202 (a portion sandwiched between adjacent groove tracks) using lands is alternately arranged every one rotation. Since the track of the L / G disk is a single spiral in which groove tracks 201 and land tracks 202 are alternately formed, data can be continuously recorded / reproduced without interruption over the entire surface of the disk. Becomes

FIG. 11 is an enlarged view of a “boundary in the radial direction between the land track 202 and the groove track 201” 203 (hereinafter referred to as a “boundary” for simplicity) surrounded by a circle in FIG. The figure is shown. The "boundary" 203 exists every one 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 as a concave structure or a convex structure that substantially satisfies d = λ / 6. The land track is a flat portion without a groove. Therefore, when the light beam 60 moves along the spiral track, the light beam 60 becomes 1
It will be located on the groove track and the land track every rotation.

At the edge where the optical depth is λ / 6, 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 detects a tracking error using this change in the interference pattern and outputs a tracking error signal. It is also well known that diffracted light due to edges affects astigmatic focus error signals. (See "Optical Disc Technology", supervised by Morio Onoe, Radio Engineering Co., Ltd., Chapter 1.2.5, Focusing, Detection of Tracking Error, 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, an edge portion between a land and a 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. That is, when looking at the cross section of the disk, 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 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.

[0011] 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, despite the just focus, the focus error signal described above does not become zero.
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 signal due to “pseudo defocus”. 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 objective lens and the groove (hereinafter referred to as “groove depth”) is 0.1
It is about μm. On the other hand, the focus error signal caused by the pseudo defocus has a magnitude corresponding to “true defocus” of about 1 μm.

When the light beam is in a just-focus state, for example, when the light beam is in a just-focus state on a mirror portion having no concave and convex grooves which is not affected by diffraction, the focus error signal becomes zero. The position of the quadrant detector in the optical system is adjusted in advance. in this case,
In the mirror section, the focus control is not affected by the pseudo defocus, and the light beam is focused on the disk as shown in FIG. 9B.

[0013] The interference pattern on the detector due to the diffracted light from the disk changes depending on whether the light beam is irradiated on the land or on the groove.
As a result, even when the focus error is substantially zero, that is, even when the light beam is located on the land or the groove in the just-focus state, pseudo defocus occurs.

FIGS. 12 (a) to 12 (c) show the case where the light beam 60 crosses the track in the radial direction of the disk.
Focus error signal FE and tracking error signal T
It is a plot of the change in E. 12 (b) and 12 (c) respectively show the magnitude of the focus error signal FE and the tracking error signal TE, and the horizontal axis shows the position of the light beam 60 in the radial direction of the optical disk. As shown in FIG. 12B, when the focus error signal FE is adjusted by the mirror unit to be zero,
In the groove and land tracks 201 and 202, the maximum value of the focus error signal FE takes DFL and DFG due to pseudo defocus. The speed at which the light beam 60 traverses the track is sufficiently fast. for that reason,
The frequency of the focus error signal FE generated when the light beam 60 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 light beam 60
The response of the focus control system due to the pseudo defocus when moving 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 by about 90 ° with respect to the tracking error signal TE.

FIG. 13 is a plot of the change of the focus error signal FE with respect to the true defocus amount in the mirror section, groove track, and land track. In the mirror section, the defocus amount becomes 0 when the focus error signal FE is 0. On the other hand, in the land and groove tracks, pseudo defocus error signals DFL and DFG are generated at positions where the defocus amount is 0. In the focus control system, the focus error signal FE
Is controlled to be 0, focus control is performed at a position where the focus error signal FE in the land and the groove portion becomes 0, that is, a position shifted by ΔFL, ΔFG.

FIGS. 14A and 14B show how the focus error signal FE changes when the light beam 60 moves from the groove track 201 to the land track 202. FIG. FIG. 14A schematically shows the positional relationship between the light beam 60 and the track, and FIG.
A change in the magnitude of the focus error signal FE corresponding to the position of the light beam 60 in FIG. 14A is plotted.

At a position X1 shown in FIG.
0 is located on the groove track 201, and the focus error signal FE is at the zero level. However, since the focus control is performed so that the focus error signal FE due to the pseudo defocus becomes zero as described above, the true focus corresponding to ΔFG from the position of XG in FIG. It is operating at the position where focus is occurring.

At the position X2 in FIG.
0 is the groove track 201 and the land track 202
Is passing through the boundary 203 between the two. At the moment when the light beam 60 reaches the land portion, a large error signal is generated in the focus error signal FE due to pseudo defocus, but the band of the focus servo system is several KHz and does not respond immediately. . Therefore, at the moment when the light beam reaches the land portion, the focus is defocused by ΔFG from just focus. For this reason, when the light beam enters the land, a focus error signal of approximately (DFL + DFG) is generated.

As shown in FIGS. 14A and 14B, until the light beam 60 reaches the position X3 from the position X2 (about several ms in time), the focus control system controls the focus error signal. By performing negative feedback on FE, control is performed so that the focus error signal FE becomes zero. As a result, at the position X3, the focus error signal FE
Converges to zero. As described above, the light beam 60 is X2
The period of several milliseconds to move from to X3 is much longer than the time required for the focus control system to perform control and settle the focus error signal FE to substantially zero, that is, the response time of the focus control system. At the position X3, the focus error signal FE is zero. However, the level DFL of the focus error signal FE based on the pseudo defocus
Since the focus control has been performed to reduce the value to zero, a true defocus ΔFL corresponding to a pseudo defocus actually occurs. True defocus due to pseudo defocus differs depending on the focus error signal detection method, focus control system, optical head, and the like. However, when compared with the focal depth of the light beam (about ± 1 μm), the true defocus due to the pseudo defocus is as large as about several μm, which makes it difficult to record and reproduce a signal and causes the focus control to shift.

[0020]

In the above-mentioned prior art,
There were 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, resulting in true defocus.

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.

[0022]

A focus control apparatus according to the present invention is a spiral track having a land track and a groove track, wherein both the land track and the groove track have tracks for recording and reproducing information. Focusing means for focusing a light beam on the recording medium, using a recording medium having a mirror portion having no groove in a part of the land track and the groove track,
A focus state detection means for detecting a focus state of the light beam on the recording medium and outputting a signal indicating the focus state; and an output of the focus state detection means in the mirror section when the light beam follows a groove track and a land track. By moving the focusing means by comparing the output value of the focusing state detecting means with the output of the target value setting means, and comparing the output value from the focusing state detecting means with the output of the target value setting means. Control means for maintaining a focused state of the light beam on the recording medium in a desired state, and a focus control system for a land track and a groove track so that the true defocus detected by the mirror unit becomes zero. By setting the target value, the pseudo defocus can be prevented from affecting the focus control.

[0023]

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 an embodiment of a focus control device according to the present invention. The light reflected from the disk is applied to the quadrant detector 1. The quadrant detector 1
The focus error signal amount is detected by the astigmatism method,
Used to generate a focus error signal. The principle and configuration of this astigmatic focus error signal detection are well known to those skilled in the art, for example,
"Optical disk technology" (supervised by Morio Onoe, Radio Engineering,
1.2.5 Focusing, tracking error detection, pages 83-85).

The output of the quadrant detector 1 is used by an adder 2 and an adder 3 to calculate the sum of the light amounts of the pair of detectors at diagonal positions. The differential amplifier 4 receives the outputs from the adders 2 and 3 and calculates a difference between them, thereby outputting a focus error signal FE indicating the focusing state of the light beam 60 on the disk. The focus error signal FE output from the differential amplifier 4 is input to the differential amplifier 5. The output of the differential amplifier 5 is input via a sample-and-hold circuit 6 to a phase compensation circuit 7 for ensuring the control stability of the focus control system. Phase compensation circuit 7
Is input to a driving circuit 9 via a gain compensation circuit 8 for securing a loop gain necessary for focus control. The focus actuator 10 drives the objective lens 11 in a direction substantially parallel to the optical axis of the light beam 60 according to the output of the drive circuit 9 in order to focus the light beam 60. The above elements shown in FIG. 1 constitute a loop of the focus control system.

The differential amplifier 5 calculates and outputs the difference between the focus error signal FE output from the differential amplifier 4 and the output of the selection circuit 12. 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 amplifier 4 converges to an offset value equal to the output of the selection circuit 12. That is, by changing the output of the selection circuit 12 input to the differential amplifier 5 as a focus control target value (usually expressed by a constant voltage), the DC of the focus error signal FE to be converged is changed.
The voltage level, that is, the target value of the focus control can be freely set.

The focus error signal FE output from the differential amplifier 4 is input to a sample / hold circuit 13 for holding the focus error signal FE. The output of the sample and hold circuit 13 is input to the A / D conversion circuit 14 and is input to the output microcomputer 15 of the A / D conversion circuit 14.

The outputs of the adders 2 and 3 are added by an adder 18. The output signal of the adder 18, which represents the amount of light reflected from the disk, is input to an address reading circuit 19, which reads addresses ID0 to ID17 recorded on the disk described later. Upon reading ID0 to ID17, the address reading circuit 19 outputs an ID detection signal DET to the timing generator 23. When the ID0 detection signal DET is input, the timing generator 20 outputs hold signals to the sample and hold circuits 6 and 13 at predetermined timings described later. As described above, the sample and hold circuit 6
And 13 indicate that while the hold signal is at the HIGH level,
Each input signal is held, and during the LOW level, the sampled input value is output as it is.

FIG. 2 schematically shows the structure of the disk 200 used in the focus control device of the present invention. Disk 20
0 is a groove track 2 using a concave groove having an optical depth (considering the refractive index) of approximately λ / 6 with respect to the wavelength λ of the light beam 60 emitted from the semiconductor laser.
2 (a portion indicated by dots in FIG. 2) and a land track 202 (a portion sandwiched between adjacent groove tracks 201) using a land as a convex portion. The land tracks 202 and the groove tracks 201 are alternately arranged every one rotation.
A single spiral connected in series is formed over the entire surface of. Land truck 202 on the truck
A boundary 203 between the disk and the groove track 201 exists every one rotation of the disk. The position of the boundary 203 is provided so as to match regardless of the position of the track in the radial direction. In each track of the disk 200, 18 address portions ID0 to ID17 are arranged at equal intervals in the circumferential direction of the disk 200 for track identification. The address sections ID0 to ID17 are provided with a track address for track identification and a sector address for identifying which of the 18 address sections (ID0 to ID17) exist in one rotation. I have.

FIG. 3 shows an example of the format of a track on the disk shown in FIG. Each track is divided into 18 sectors from sector 0 to sector 17. Each sector includes an address part and a data part for recording and reproducing information. The address portion includes a sector mark SM indicating the beginning of a sector, a single frequency region VFO for pulling in a signal reading PLL, an address mark AM indicating the beginning of an address, and track and sector addresses of lands and grooves. After the indicated IDL and IDG are repeated a plurality of times to ensure reliability, the postamble PA indicating the end of the address portion is arranged to be read in this order. A mirror portion MIRR without a groove is provided behind the address portion.
By reading the address ID, the address reading circuit 19 can determine at which track the light beam 60 is located, and at the same time, which sector in one track is located. Address portions ID0 to ID17 of each track are arranged on the same radial line.

FIGS. 4 and 5 are enlarged views of the vicinity of the address portion ID0 and the boundary 203, and the vicinity of the address portion ID1, which are circled 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. Address reading circuit 19
Receives a signal indicating a change in the amount of reflected light due to the pit train, and detects the position of the light beam. The length of each pit is on the order of 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 smaller than the fluctuation of the focus error signal due to pseudo defocus. In addition, the address portion is arranged so as to be shifted in the disk radial direction by a 1/4 track pitch from the track center of the land and the groove. When the land track 202a and the groove track 201a are reproduced, the signal of the address portion output from the adder 18 becomes the same. However, when the land track 202a is reproduced, the IDL indicating the address of the land portion is used as the signal of the groove track 201a. Is reproduced, the track and the sector can be determined from the IDG indicating the address of the groove track. Thus, one address portion is shared by the land track and the groove track. Mirror part M without groove immediately after address part
An IRR is provided. The land track and the groove track are switched before and after the address portion ID0 in FIG. 4, and the land track and the groove track are switched from the groove track to the land track. However, the land track and the groove track are not switched before and after ID1 to ID17 other than ID0 in FIG.

FIGS. 6A to 6G show the operation of focus control in the focus control device and the recording medium according to the present invention. FIG. 6A schematically shows the position of the light beam 60 on the track when the light beam 60 scans along the land track 202 by the rotation of the disk 200 and passes through the address portions ID1 and ID2. . 6 (b), (c), (d), (e), (f)
The vertical axis of (g) indicates the light beam 6 as shown in FIG.
0 indicates a focus error signal F when scanning a track.
E, output signal SHO1 of sample / hold circuit 6, output signal SHO2 of sample / hold circuit 13, output SLO of selection circuit 12, signal SHC1 for controlling sample / hold operation of sample / hold circuit 6, sample / hold circuit 13 , And a signal SHC2 for controlling the sample-and-hold operation is shown, and the horizontal axis is time. The horizontal axes in FIGS. 6B to 6G are displayed so as to correspond to the horizontal axes in FIG.

At time T1 in FIG.
LO is zero, and the output FE of the differential amplifier 4 is output from the differential amplifier 5 as it is. At this time, the focus error signal FE is almost zero, which is the level DFL of the focus error signal FE based on the pseudo defocus.
Since the focus control has been performed to reduce the value to zero, a true defocus ΔFL corresponding to a pseudo defocus actually occurs. When the focus error signal FE is located at ID1, the focus error signal FE fluctuates due to diffraction caused by edges along the circumferential direction of the address portion. Therefore, the sample and hold control signal SHC1 from the timing generator 20
Thus, in the address portion, the immediately preceding focus error signal F
E is held so as not to be affected by this fluctuation. The time when this light beam passes through the address section (T5
−T2) is sufficiently short at about several tens of μs, and the focus shift occurring during this time can be almost ignored. Immediately after the address part ID1, a mirror part MIRR without land / groove grooves is provided. Since the mirror section MIRR is not affected by diffraction, a true focus error signal FE is output. Therefore, at time T3 when the light beam 60 reaches the mirror unit MIRR, the true defocus ΔF
The level DFL of the focus error signal FE based on L is generated in the focus error signal FE. During the period when the light beam 60 passes through the mirror section MIRR from the timing control circuit 20, the sample-and-hold circuit 13 outputs a signal SHC2 for sampling the focus error signal FE. As a result, the focus error signal FE based on the defocus ΔFL is supplied to the sample / hold circuit 13.
Is held. The output of the sample and hold circuit 13 is converted into a digital signal by an A / D converter 14 and then input to a microcomputer 15. Address information is input from the address reading circuit 19 to the microcomputer 15, and a signal indicating the mirror unit is input from the timing generation circuit 20. Thus, the microcomputer 15 detects the level DFL of the focus error signal FE based on the defocus ΔFL output from the sample and hold circuit 13. The microcomputer 15 detects the focus error signal F
A target value of focus control is calculated from the level DFL of E such that the focus error signal FE in the mirror unit becomes zero, that is, true defocus becomes zero.
Output to the D / A converter 16. The output of the D / A converter 16 is input to the selection circuit 12. The selection circuit 12 outputs zero in the address section and the mirror section in response to the selection signal SLC from the timing generation circuit. When the light beam 60 is located at the land, the output of the D / A converter 16 is output. Section, the output of the D / A converter 17 is selected and output. Time T
The microcomputer 15 calculates the target value of the focus control at 6, and outputs it to the D / A converter 16. Selection circuit 1
2 is input to the differential amplifier 5 as described above, so that after time T6, the land track 202
Focus error signal F due to the above pseudo defocus
The value DFL of E becomes the target value of the focus control. Therefore, the focus control system is not affected by the focus error signal FE reflecting the pseudo defocus on the land track 202, and as a result, it is possible to prevent the occurrence of true defocus. In this state, a DC voltage of only the DFL is generated in the focus error signal output from the differential amplifier 4, but the DC level of the signal after the output of the differential amplifier 5 is zero. The light beam 60 has the address part ID2
(T10-T)
In 8), since no true defocus has occurred,
The focus error signal FE is substantially zero.

FIG. 7 shows the operation when the light beam 60 scans along the groove track 201 by rotating the disk 200 and passes through the address portions ID1 and ID2, similarly to FIG.

At time T1 in FIG.
LO is zero, and the output FE of the differential amplifier 4 is output from the differential amplifier 5 as it is. At this time, the focus error signal FE is almost zero, but this is the level DFG of the focus error signal FE based on the pseudo defocus.
Since the focus control has been performed to reduce the value of to zero, a true defocus ΔFG corresponding to a pseudo defocus actually occurs. The light beam 60 is reflected by the mirror MI.
At time T3 when RR is reached, a level DFG of the focus error signal FE based on the true defocus ΔFG is generated in the focus error signal FE. Timing control circuit 20
Thereafter, the sample and hold circuit 13 outputs a signal SHC2 for sampling the focus error signal FE during the period when the light beam 60 passes through the mirror unit MIRR. As a result, the level DFG of the focus error signal FE based on the defocus ΔFG is held in the sample and hold circuit 13. The output of the sample and hold circuit 13 is converted into a digital signal by an A / D converter 14 and then input to a microcomputer 15.
The microcomputer 15 is a sample and hold circuit 1
3 detects the level DFG of the focus error signal FE based on the defocus ΔFG output. The microcomputer 15 calculates the focus error signal FE in the mirror unit from the level DFG of the detected focus error signal FE.
Is calculated as zero, that is, a target value of focus control such that true defocus becomes zero.
Output to the A converter 17. The output of the D / A converter 17 is input to the selection circuit 12. The selection circuit 12 receives the light beam 6 based on the selection signal SLC from the timing generation circuit 20.
When 0 is located in the groove portion, the output of the D / A converter 17 is selected and output. At time T <b> 6, the microcomputer 15 calculates a target value of the focus control and outputs it to the D / A converter 17. Since the output SLO of the selection circuit 12 is input to the differential amplifier 5 as described above, after the time T6, the value DFG of the focus error signal FE due to the pseudo defocus on the groove track 201 becomes the target of the focus control. Value. Therefore, the focus control system is not affected by the focus error signal FE reflecting the pseudo defocus in the groove track 201, and as a result, it is possible to prevent the occurrence of true defocus. In this state, a DC voltage of only the DFG is generated in the focus error signal output from the differential amplifier 4, but the DC level of the signal after the output of the differential amplifier 5 is zero. The period during which the light beam 60 passes through the mirror unit MIRR immediately after the address unit ID2 (T10-T
In 8), since no true defocus has occurred,
The focus error signal FE is substantially zero.

FIG. 8 shows that the rotation of the disk 200 causes the light beam 60 to scan along the land track 202 and pass through the boundary 203 between the groove track 201 and the land track 202 and the address section ID0 to reach the land track 202. The operation at the time is shown.

In FIG. 8, it is assumed that the focus error signal FE at the mirror section has been adjusted to zero. Therefore, when the light beam 60 is positioned on the land track, the value DFL of the focus error signal FE due to the pseudo defocus on the land track 202 becomes
Is located on the groove track 201, the value DFG of the focus error signal FE due to pseudo defocus on the groove track 201 is output from the selection circuit 12 as a target value of focus control. For this reason, the focus control system is not affected by the focus error signal FE reflecting the pseudo defocus on the land track 202 and the groove track 201, and as a result, true defocus does not occur. At time T1 when the light beam 60 is located in the land groove 171, the selection circuit 12
From the land track 17 as the focus control target value.
The value DFL of the focus error signal FE due to the pseudo defocus on 1 is output to the differential amplifier 5. At this time, a DC voltage of only DFL is generated in the focus error signal output from the differential amplifier 4,
The DC level of the signal SHO1 after the output is zero. In a period (T5 to T3) during which the light beam 60 passes through the mirror unit MIRR immediately after the address unit ID0, since true defocus has not occurred, the focus error signal FE is substantially zero. At time T5 when the light beam 60 reaches the groove portion, the signal from the timing generation circuit 20 outputs the output of the selection circuit 12 as the target value of the focus control as the value DFG of the focus error signal FE due to the pseudo defocus on the groove track 201. Is output to the differential amplifier 5. As a result, a DC voltage of only DFG is generated in the focus error signal output from the differential amplifier 4, but the DC level of the signal SHO1 after the output of the differential amplifier 5 remains zero. In the period (T8-T6) during which the light beam 60 passes through the mirror section MIRR immediately after the address section ID1, since true defocus has not occurred, the focus error signal FE is substantially zero.

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, if the disc causes false defocus during recording / playback,
The present invention can be applied 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 spirally without a boundary for each rotation of the disk, and a disk on which information is recorded / reproduced on both the land track and the groove track is also used. The present invention can be applied. 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. Further, in the above embodiment, the focus error signal FE in one mirror unit is used.
The focus control target values in the land and groove tracks are determined based on the above, but the focus control target values in the land and groove tracks are determined based on the focus error signals FE in the mirror unit a plurality of times. Is also good.
Further, when the focus error signal FE at the mirror unit when the target value of the focus control is output is not zero, the previous target value may be changed at any time according to the level of the focus error signal FE.

[0039]

According to the focus control device of the present invention,
By setting the target value of the focus control of the land track and the groove track so that the focus error signal becomes zero at the mirror portion having no land and groove of the disk provided on the disk, true defocus does not occur. be able to.

The target value of the focus control is changed depending on whether the light beam is located on a land track or a groove track. Therefore, even if the focus error signal changes due to pseudo defocus on the land track and the groove track, it is possible to prevent the focus control from being affected. Therefore, even with an optical disc on which information is recorded / reproduced on a land track and a groove track, highly accurate focus control can be realized.

According to the recording medium of the present invention, the amount of true defocus can be detected by providing the disk with a mirror portion having no land / groove grooves.

[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 an explanatory diagram of a structure of a disc 200 used in the focus control device of the present invention.

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

FIG. 4 is an explanatory diagram showing, in an enlarged manner, an address portion ID0 surrounded by a circle in FIG. 2 and the vicinity of a boundary;

FIG. 5 is an explanatory diagram showing, in an enlarged manner, the vicinity of an address part ID1 surrounded by a circle in FIG. 2;

FIG. 6 is an explanatory diagram showing an operation of focus control when a light beam follows a land track in the focus control device and the recording medium according to the present invention.

FIG. 7 is an explanatory diagram showing a focus control operation when a light beam follows a groove track in the focus control device and the recording medium according to the present invention.

FIG. 8 is an explanatory diagram 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 an explanatory diagram showing the shape of a light beam on a four-segment detector when the distance between the focal point of the light beam and the disk changes.

FIG. 10 is an explanatory view schematically showing an L / G disk.

FIG. 11 is an explanatory diagram of a radial boundary between a land track and a groove track that are circled in FIG. 10;

FIG. 12 is an explanatory diagram of changes in a focus error signal and a tracking error signal when a light beam crosses a track in a disk radial direction.

FIG. 13 is an explanatory diagram showing a relationship between a defocus amount and a focus error signal in a mirror section, a land track, and a groove track.

FIG. 14 is an explanatory diagram showing how a focus error signal changes when a light beam moves from a groove track to a land track.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... 4 division | segmentation detector 4, 5 ... Differential amplifier, 7 ... Phase compensation circuit, 8 ... Gain compensation circuit, 9 ... Drive circuit, 10 ... Focus actuator, 11 ... Objective lens, 2, 3, 18 ... Adder , 6, 13: sample and hold circuit, 14: A / D converter, 15: microcomputer, 16, 17: D / A converter, 19: address reading circuit, 20: timing generation circuit.

Claims (3)

[Claims] 1. A spiral track having a land track and a groove track, wherein the land track and a part of the groove track have a mirror portion that does not have the land and the groove of the groove. And a focus control device for controlling the light beam to be focused on a recording medium having a track for recording and reproducing information on both of the groove tracks, focusing means for focusing the light beam on the recording medium, A focusing state detecting means for detecting a focusing state of the light beam on the recording medium and outputting a signal indicating the focusing state; and comparing the output value from the focusing state detecting means with a target value to determine the focusing state. Controlling means for maintaining a desired state of focusing of the light beam on the recording medium by moving
A target value for setting a target value for focus control of the land track and the groove track such that an output of the convergence state detecting means when the light beam is positioned on the mirror portion of the land track and the groove track becomes zero. A focus control device including a setting circuit. 2. The apparatus according to claim 1, wherein said target setting means includes a sampling means for sampling an output from said focusing state detecting means, and outputs a plurality of times of said convergence state detecting means when said light beam is positioned on said mirror section. 2. The focus control device according to claim 1, wherein sampling is performed, and a target value is set based on the average value. 3. A spiral track having a land track and a groove track, wherein the land track and a part of the groove track have a mirror portion having no groove of the land and the groove, and And record information on both of the groove tracks
A recording medium having a track to be reproduced.