JPH11273098A - Focus servo circuit and optical disk recording and reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To calculate the variable range of focus bias values in which a tracking servo is not ruptured by reproducing an optical disk while changing a focus bias value in a state in which a tracking servo system is made OFF and detecting tracking error signals from these reproduced signals. SOLUTION: When an interlock switch SW is made OFF so that the tracking servo is not operated, an amplitude detector is operated. Here, amplitude values of tracking error signals are detected in the detector by supplying the signals to the detector while successively incrementing the focus bias value by ΔF from -Fx to +Fy and measured amplitude values and focus bias values at those times are stored. Next, an amplitude value which is lowered by a prescribed value from the maximum value of these measured amplitude values is calculated and focus bias values -Fa, +Fb becoming limits of an optimum variable range are calculated. Thus, it is eliminated that the tracking servo is to be locked.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a focus servo circuit and an optical disk recording / reproducing apparatus. More specifically, a variable range of the focus bias value within a range in which the tracking servo is not broken can be obtained from a tracking error signal detected while varying the focus bias value with the focus servo system turned off. Further, an optimum focus bias value can be set by controlling the focus servo within the above-mentioned variable range of the focus bias value while the tracking servo system is turned on. As a result, it is possible to reliably prevent the measurement from becoming impossible due to the inability to perform the tracking servo before the optimum focus bias value is set.

[0002]

2. Description of the Related Art In an optical disk recording and reproducing apparatus such as a magneto-optical disk, data is reproduced while adjusting the focus of an optical pickup with respect to the optical disk. At this time, in order to obtain optimum reproduction characteristics, a process of determining an optimum focus servo signal for performing optimum focus servo immediately before reproducing data is performed.

[0003] In order to realize an optimum focus servo, an optimum focus bias value must be determined, but a jitter component of a reproduced signal may be used as a parameter for the evaluation. When the amount of jitter is used as an evaluation parameter, for example, a point where the amount of jitter is minimum can be set as a just focus point, and a focus bias value at that time can be set as an optimum focus bias value.

In order to determine the minimum jitter amount, for example, the focus jitter value obtained by changing the focus bias value is plotted by a second approximation or the like. The vertex is set as the optimum focus bias value.

[0005]

By the way, even when the vertex of the curve obtained by the quadratic approximation is obtained as the optimum focus bias value, if the jitter amount does not change to some extent by the focus bias value,
The plotting accuracy of the quadratic curve deteriorates.

Therefore, it is desirable to widen the variable range of the focus bias value in order to make the jitter swing to some extent. However, in such a case, since the swing width of the objective lens constituting the optical pickup system also becomes large, the tracking servo may deviate and measurement may become impossible. That is, the tracking servo may break.

When the tracking servo is unlocked, an optimum focus bias value cannot be obtained, so that the standby time for transition to a normal state when data is actually recorded and reproduced is lengthened.

Therefore, the present invention solves such a conventional problem. As a pre-stage for setting the optimum value of the focus bias, a variable range of the focus bias value which does not cause the tracking servo to break is set in advance. It is exactly what is required.

[0009]

According to a first aspect of the present invention, there is provided a focus servo circuit for reproducing an optical disk while changing a focus bias value with a tracking servo system turned off. A tracking error signal is detected from the reproduction signal, and a variable range of the focus bias value is set from the tracking error signal.

According to the present invention, even when the tracking servo is turned off, the optical disc is reproduced while changing the focus bias. A tracking error signal is obtained from the reproduced signal. This is because, in most cases, the optical pickup has a disk eccentricity, so that the optical pickup travels across the tracks by removing the tracking servo.

If the focus is not sufficient, the amplitude of the tracking error signal becomes small, and if the tracking servo is deviated, the amplitude becomes considerably small. Therefore, the variable range of the focus bias value for preventing the tracking servo from being deviated from the amplitude value can be known. Experience has shown that the maximum amplitude is -3 dB
The range that falls is set as the optimal variable range.

According to a fifth aspect of the present invention, there is provided an optical disk recording / reproducing apparatus for outputting a focus bias value for focus servo, an amplitude detector to which a tracking error signal is supplied, A memory means provided in the control unit for writing down a bias value and reproducing the optical disk while varying the focus bias value in a state where the tracking servo system is turned off. The tracking error signal is detected and a variable range of the focus bias value is set from the tracking error signal.

In the present invention, focus servo is performed based on the optimum variable range of the focus bias, and the just focus point is obtained from the reproduction jitter amount at that time. The focus bias value at the just focus point is used as an optimum value. Actually, the focus servo operates by adding the focus error signal to the focus bias value. As a result, the rise of the focus servo becomes faster, and the time required to shift to the actual focus servo operation can be reduced.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of a focus servo circuit and an optical disk recording / reproducing apparatus according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a system diagram of a main part showing an embodiment of an optical disk recording / reproducing apparatus to which the present invention is applied. In the figure, light emitted from a laser 11 is used as a beam splitter (BS) 1 constituting optical pickup means.
2, the traveling direction is separated, a part of the light enters a photodetector (MPD) 13 for monitoring the emission power, and the other part irradiates the surface of an optical disk 16 via a reflection mirror 14 and an objective lens 15. Is done.

The light emission power detected by the light detector 13 is converted into a current (Im) and supplied to an error amplifier (APC amplifier) 21 for light emission power control. On the other hand, from the laser power controller (LPC) 21, a current Iout, which is a reference of the emission power, is input to the error amplifier 21, and the output of the amplifier controls the impedance of the control transistor 25. As a result, the current flowing to the laser 11 is adjusted so that the emission power always becomes Im = Iout, and the laser power is controlled to be constant. Reference current Iout output from laser power controller 22
Can rewrite a register or the like provided inside the controller 22 in accordance with an instruction from the main control unit (MPU configuration) 30, and can output a waveform having various values as a reference current waveform. . Thereby, for example, it is possible to control so that the laser powers correspond to the erasing mode, the recording mode, and the reproducing mode, respectively.

The laser light reflected by the optical disk is transmitted through a beam splitter 12 to a photodetector (P) for signal reproduction.
D) Light enters 20. The photodetector 20 is constituted by four divided photodetectors, and each photodetection signal is supplied to a first current / voltage converter (IV) 24. A plurality of servo signals are generated from the current / voltage converter 24. In the example shown in the figure, a combined signal SUM, which is a signal obtained by adding the focus error signal FESO, the tracking error signal TESO, and all four photodetectors, is generated.

The focus error signal FESO and the tracking error signal TESO are supplied to AGC circuits 25 and 26 and are normalized by the combined signal SUM in order to avoid the values from changing due to the light emission power. The normalized focus error signal FES is output from the A / D converter 2
After being converted into a digital signal by 7, it is supplied to a control unit 30 having an MPU configuration.

The control unit 30 generates an optimum focus bias signal (focus servo signal).
After being converted into an analog signal by the A-converter 31, the signal is supplied to the driver 28 of the focus coil 29, the gap between the objective lens 15 and the disk surface is adjusted, and focus adjustment is performed. That is, focus servo is applied. Therefore, the circuit system up to the driver 28 including the AGC circuit 25 and the control unit 30 functions as a focus servo control unit.

FIG. 5 shows a partial configuration of the control unit 30. A memory 82 is connected through a bus 81 connected to an MPU 80, and a variable range of an optimum focus bias value is set in the memory 82. For this purpose, a plurality of focus bias values (-Fx to + Fy) shown in FIG. 4 are stored. The difference is obtained from the focus error signal FES fetched via the bus 81 and the focus bias value fetched from the memory 82, and the difference is similarly supplied to the digital filter 83 via the bus 81 and filtered. After that, it is converted into an analog focus servo signal FS by a D / A converter 31 provided outside the control unit 30.

In the process of setting the optimum variable range of the focus bias value, the tracking error signal TES is used.
The focus error signal FES is used for the process of setting the optimum focus bias value, and details of each will be described later.

The tracking direction of the optical disk 16 is controlled in the same manner as the focus, and a normalized tracking error signal TES is supplied to a tracking servo system (not shown) via the control unit 30 so that the optical disk 16 is always controlled. A tracking servo is applied so that the light is focused on the track.

The tracking error signal TES is further supplied to the amplitude detector 36 via the interlock switch SW.
A tracking error signal TES 'when the tracking servo is off is detected. The tracking error signal TES 'at this time is also supplied to the control unit 30 shown in FIG.

The output of the photodetector 20 is supplied to a second current / voltage converter 32 and converted into a data signal including an address signal. After the data signal is optimized in amplitude by a variable gain amplifier (VGA) 33, it is supplied to a slicer 34 through an equivalent filter (supposed to be included in the variable gain amplifier 33), and is sliced by a reference voltage 35. This is binarized (digitized).

The binarized digital signal is supplied to a PLL circuit 40. This PLL circuit 40 has a phase comparator 41, a variable voltage oscillator (VCO) 42 and a low-pass filter 44,
The phase is compared with the read clock signal RC output from 2 by the phase comparator 41, and the phase error is converted into a voltage by the low-pass filter 44 to obtain a phase error signal. The oscillation frequency of the variable voltage oscillator 42 is controlled by the phase error signal, and a read clock signal RC synchronized with the digital signal is obtained.

The extracted read clock signal RC is supplied to the flip-flop circuit 43 together with the digital signal, and a read data signal RD completely synchronized with the read clock signal RC is generated.

The read data signal RD and the read clock signal RC are supplied to the optical disk controller block (ODC)
50. Optical disk controller block 5
0 is provided with an address decoder 51, and the address signal is decoded by supplying the read data signal RD and the read clock signal RC to the address decoder 51.

The read data signal RD and the read clock signal RC are further supplied to the data decoder 52, and the reproduced data is decoded while performing address management based on the decoded address signal. The decoded reproduced data passes through the read buffer circuit 53 and is
The data is supplied to an interface 54 such as a CSI controller and output to the host terminal.

On the other hand, when recording data on the optical disk 16, the controller 22 sets an optimum write power based on a power setting signal from the main control unit 30. Also, data to be recorded and address information to be recorded are received from the host side, and are encoded by a data encoder 56 via a write buffer circuit 55. When a laser scans an address to be recorded, a timing signal from a gate signal generator 58 provided in the optical disk controller block 50 is output.
(Write gate) WG is output. In synchronization with this, the write data WD and the write clock signal WC which is a data synchronization clock are supplied to the controller 22, respectively.

Therefore, the controller 22 converts the recording data into the recording current Iout at that timing. The laser 11 is modulated by the recording current, and pits are formed on the optical disk 16. When a phase change disk is used as the optical disk 16, data can be recorded only by modulating the laser power. When a magneto-optical disk is used as the optical disk 16, an external magnetic field is also used for recording data, so it is necessary to generate an external magnetic field using an external magnet.

When erasing data, the control unit 3
Erase processing is executed based on a command from 0. First, the controller 22 sets an erase mode (erase power) in response to a command from the control unit 30. And
When a target address comes from the optical disk control block 50, the designated erase power is changed based on the write gate timing.
The data is erased by being irradiated on the upper side. Optical disk 1
When a magneto-optical disk is used as 6, the external magnet is simultaneously controlled as described above.

In the present invention, as described above, the optimum variable range of the focus bias value is found with the tracking servo turned off. Then, a process of obtaining an optimum focus bias value within the bias variable range calculated with the tracking servo turned on is performed.

The optimum variable range of the focus bias value is obtained as follows. First, with the tracking servo turned off, the optical disc is reproduced while changing the focus bias value. A tracking error signal is obtained from the reproduced signal. This is because, in most cases, the optical pickup has a disk eccentricity, so that the optical pickup travels across the tracks by removing the tracking servo. As a result, a tracking error signal TES as shown in FIG. 3 is obtained.

If the focus is not sufficient, a defocused state will occur, and the reproduced signal level at that time will be low. As a result, the amplitude of the tracking error signal becomes smaller, so that when the tracking servo is deviated, the amplitude becomes smaller.

Therefore, as shown in FIG. 4, the variable range of the focus bias value is selected from the range of -Fx to + Fy which is the defocus mode. This range is wider than a variable range (-Fa to + Fb) which is considered appropriate.

When the amplitude value of the tracking error signal at each focus bias value is plotted, a curve as shown in FIG. 4 is obtained, and the amplitude value at the just focus point becomes maximum.

Normally, when the maximum amplitude value is used as a reference, the range in which the tracking servo is applied is up to a range of an amplitude value lower by about -3 dB. This is empirically required. Therefore, the variable range FBN (−Fa to + Fb) of the focus bias value for preventing the tracking servo from being deviated from the amplitude value can be known.

FIG. 5 is a processing flow for obtaining the appropriate variable range FBN. This processing is a pre-processing for actually reproducing data. The control program is shown in FIG.
Is built in the MPU 80.

First, the interlock switch SW is turned off so that the tracking servo does not operate (step 6).
1). Thus, the amplitude detector 36 operates. Next, the reproduction mode is set in a state where the focus bias value is -Fx, and a reproduction signal at that time, that is, a tracking error signal is supplied to the amplitude detector 36 and the amplitude value TES 'thereof is supplied.
Is detected (steps 62 and 63). The measured amplitude value and the focus bias value at that time are stored in the memory 82 in the control unit 30 (step 64).

After this operation, the focus bias value is incremented by ΔF (this value is arbitrary), and
The amplitude value and the focus bias value at that time are respectively memorized (step 65, step 65).
66, 63, 64).

The focus bias value is the maximum variable value + Fy
Is exceeded, the maximum value of the amplitude value is determined next, and an amplitude value lower than the maximum value by a predetermined level (in this example, an amplitude value falling by -3 dB from the maximum value) is determined (step 67).
Thus, the focus bias values -Fa and + Fb, which are the limits of the appropriate variable range, can be obtained.

The focus bias values -Fa and + Fb, which are appropriate variable ranges, are stored in the memory 82 (step 68). When the storing process is completed, the interlock switch SW is returned, and the tracking servo returns to the on state (step 69). At the same time, the process of setting the appropriate variable range ends. If a focus bias value within this variable range is used, the tracking servo will not be locked and measurement will not be disabled.

When an appropriate variable range of the focus bias value is set, the next process shifts from this focus bias value to a process of setting an optimum focus bias value.

In this example, the amount of jitter of the reproduced signal is used as a parameter used to set an optimum focus bias value. The measurement of the jitter amount uses test pattern data, but conventionally, nothing is recorded on the tracks on both sides where the test pattern data is recorded. However, in this case, when an optical disk for high-density recording is used, the optimum focus state changes due to leakage (crosstalk) from an adjacent track.

Therefore, in the embodiment described below, in addition to the test pattern data, at least one side of the track on which the test pattern data is recorded, preferably both sides of the track, so that the amount of crosstalk from the adjacent track can be taken into consideration. Is recorded with pattern data (for example, pattern data different from the test pattern data).

Since the jitter component increases when the crosstalk from the adjacent track is mixed in the reproduced signal, the optimum focus servo point in consideration of the crosstalk, that is, the just focus point can be determined by monitoring the jitter amount. You can find out.

Here, the influence of the presence or absence of crosstalk on jitter will be described with reference to FIG. The curve La shows the jitter amount when only the test pattern data is recorded and no data is recorded on the adjacent track.
The curve Lb shows the jitter amount when pattern data different from the test pattern data is recorded on both adjacent tracks.

As is clear from the curve La, when there is no crosstalk from the adjacent track, the focus position is -1.5 μm with respect to the surface of the optical disk 16.
The jitter amount hardly changes in the range from to 0.5 μm. Here, the plus (+) value indicates that the just focus point is on the near side (the optical pickup side) with respect to the surface of the disc, and therefore, the minus (−) value is the just focus on the far side from the disc surface. It means that a point exists. Therefore, if the focus bias value at that time is a value between -Fa and + Fa ', it can be said that there is almost no effect on the reproduction characteristics. Since the focus bias value Fo is just focus, all other areas are defocus areas.

On the other hand, when data is recorded on an adjacent track, the influence of crosstalk appears remarkably, and the crosstalk not only greatly changes the original jitter amount, but also depends on the focus point. It can be seen that the amount changes greatly.

The reason why the amount of jitter changes due to the crosstalk and the amount of jitter greatly changes even in the defocus state is considered to be due to the following physical phenomena.

FIG. 7 schematically shows the state of a beam spot focused on the optical disk 16 when the focus is changed. Tracks T1 to T3 are prepared on the outermost peripheral side of the optical disc as tracks on which test patterns can be recorded, for three tracks. The test pattern data is recorded on the center track T2, and no data is recorded on the adjacent tracks T1 and T3. This corresponds to a conventional example.

FIG. 7A shows an example of the case of just focus, and the beam shape (spot shape) is substantially circular. On the other hand, FIG. 6B shows a case where the objective lens 15 is defocused on the near side (near side) with respect to the optical disc 16,
The beam spot has an elliptical shape whose long side is the traveling direction.
This state occurs when the focus bias is weak.

FIG. 7C shows the opposite side of the optical disk 16 (far side).
Side), when the focus bias is too strong, and the beam spot becomes an elliptical beam spot having a long side in a direction perpendicular to the traveling direction.

The beam spot becomes elliptical because astigmatism exists in the optical pickup system including the optical system such as the laser 11 and the objective lens 15. The jitter amount in these cases is as shown by the curve La in FIG. 2, and the jitter does not deteriorate much because there is no crosstalk from the adjacent track.

FIG. 8 shows a case where pattern data is recorded on adjacent tracks on both sides, which corresponds to FIG. FIG. 8A shows just focus and FIG.
Indicates the relationship between the track and the beam spot at the time of defocus.

In FIG. 7A, since the beam spot is just focused, the beam spot is circular, the resolution in the beam traveling direction is high, and crosstalk from an adjacent track does not significantly affect the beam spot. Therefore, in this case, the amount of jitter is minimized.

However, when the optical disk 16 is defocused on the near side (near side) (FIG. B) and when it is defocused on the back side (far side) (C in FIG. 3), both of the long sides are defocused. The beam spots have different ellipses, and the beam spot spreads in the reading direction or in a direction perpendicular to the reading direction. As a result, the reading resolution decreases and the jitter amount increases. It can be seen from the shape of the beam spot that the jitter amount is larger in FIG.

Therefore, in the present invention, the focus servo is determined in advance in consideration of the crosstalk, and the best focus point is searched for in the balance between the resolution in the reading direction and the crosstalk.

In the present invention, as shown in FIG. 8, test pattern data is recorded on a center track T2 using three tracks on which a test pattern can be recorded. The test pattern data is increment pattern data for sequentially increasing the mark length. The increment pattern data includes the mark lengths of all lengths.

The tracks T1 and T adjacent to the track T2
3, pattern data other than this is recorded. Specifically, the pattern data is such that the amount of leakage into the track T2 is large, such as 6T pattern data. A similar leakage amount can be expected by recording data other than 6T pattern data with, for example, a larger write power than usual.

All of these pattern data use pattern signals from a pattern generator 59 provided in the optical disk control block 50, and the control unit 30 instructs when to output the pattern data.

The memory 82 shown in FIG. 2 has a focus bias value (-Fa to + Fb) indicating the above-described appropriate variable range.
Is stored. The difference is obtained from the focus error signal FES fetched via the bus 81 and the focus bias value fetched from the memory 82, and the difference is similarly obtained via the bus 81 by the digital filter 83.
After being supplied to the control unit 30 and filtered, the data is converted into an analog focus servo signal FS by a D / A converter 31 provided outside the control unit 30.

Therefore, focus servo is applied to the objective lens 15 by the focus servo signal corresponding to the focus bias value. The amount of jitter is calculated from the reproduced data at this time, and the calculated amount of jitter is stored in the jitter storage area of the memory 82 via the bus 81 together with the focus bias value.

This processing is performed when the focus bias value is + Fb.
Is performed while incrementing the focus bias value until the following condition is satisfied, and the focus bias value and the jitter amount at that time are stored.

When the jitter amount is measured while the data is reproduced while sweeping the focus bias value stepwise, the minimum value of the jitter amount is obtained.
The focus servo signal at the focus bias value that has become the initial jitter amount is used as an optimum focus servo signal thereafter.

FIG. 9 shows a specific example of a jitter amount calculator 70 which is a jitter amount measuring device. The jitter amount calculator 70 is configured based on the so-called root mean square concept.

In FIG. 9, the phase error signal sampled and digitized by the A / D converter 60 at the timing of the read clock signal RC is digitally squared by the squarer 71. Since the digital phase error signal is squared in order to eliminate the sign processing, an absolute value may be taken and averaged.

The squared digital phase error signal is supplied to the adder 72, where it is integrated with the output of the memory 73. Squarer 71, adder 72, and memory 73
Operate at the timing of the read clock signal RC.

On the other hand, the counter 75 counts the number of read clocks.
Is supplied to the level shifter 76, and the integrated data is shifted and averaged by the count number of the read clock. Thereafter, the averaged output is supplied to the square root calculator 77 and subjected to square root processing. The value subjected to the square root processing is the amount of jitter to be obtained.

The counter 75 and the memory 73 are cleared at the fall of the read gate pulse from the gate generator 58 (see FIG. 1). The level shifter 76 is controlled to shift by the count output from the counter 75 at the rise of the read gate pulse. The above-described square root processing and normalization processing can be omitted.

An example of a process for obtaining a focus bias value serving as a basis for an optimum focus servo signal will be described with reference to FIG. The control program for this process is MP
Built in U80. The optimum focus bias processing is performed every time the optical disk 16 is loaded into the optical disk recording / reproducing apparatus.

First, a test pattern (increment pattern) is recorded on the track T2 (step 91), and similarly, 6T pattern data is recorded on the adjacent tracks T1 and T3 (steps 92 and 93). Next, the focus bias is set to -Fa, and the data of the track T2 is reproduced in the focus servo state at that time to measure the jitter amount (steps 94 and 95). The measured jitter amount and the focus bias value at that time are stored in a table of the memory 82 (step 96).

Next, data is reproduced in a focus servo state in which the focus bias value is incremented by ΔF, and the jitter amount and the focus bias value at that time are stored (steps 97, 98, and 95). As described above, the focus bias value is changed until the focus bias value reaches + Fb. When the focus bias value reaches + Fb, the jitter amount measurement mode ends.

After that, a focus bias value at which the minimum jitter amount is obtained is obtained, and this focus bias value is stored in the memory 82 so as to be used as an optimum focus bias value, that is, as a reference focus bias value thereafter, and then, The optimal focus bias setting process is terminated (steps 99 and 100).

The optimum focus bias value obtained in step 99 is obtained by approximating a quadratic curve based on the obtained jitter amount,
The bottom value of the approximated quadratic curve can be set as the optimum focus bias value.

[0076]

As described above, in the focus servo circuit according to the present invention, based on the tracking error signal obtained when reproducing the optical disk while varying the focus bias value with the tracking servo system turned off. The variable range of the focus bias value is set.

According to this, since the tracking error signal in a state where the tracking servo is turned off is used, it is possible to reliably avoid a situation where the tracking servo is disconnected and the tracking error signal cannot be measured.
This has the characteristic that an appropriate variable range of the focus bias value can be set.

Further, according to the optical disk recording / reproducing apparatus of the present invention, since the variable range of the appropriate focus bias value is determined, the rise of the focus servo is accelerated, and the time until the actual focus servo operation is started. You can save time.

Therefore, the present invention is suitable for application to an optical disk recording / reproducing apparatus using a magneto-optical disk or the like.

[Brief description of the drawings]

FIG. 1 is a system diagram of a main part showing an embodiment of a disk recording / reproducing apparatus according to the present invention.

FIG. 2 is a diagram showing a configuration of a part of a control unit constituting a focus servo control unit.

FIG. 3 is a diagram showing a tracking error signal when tracking servo is not applied.

FIG. 4 is a characteristic diagram showing a relationship between a focus bias value and a tracking error signal.

FIG. 5 is a diagram illustrating an example of a processing flow for setting an appropriate focus bias range.

FIG. 6 is a diagram illustrating a relationship between crosstalk and a jitter amount.

FIG. 7 is a diagram showing a relationship between defocus and a beam spot when data is not recorded on an adjacent track.

FIG. 8 is a diagram illustrating a relationship between defocus and a beam spot when data is recorded on an adjacent track.

FIG. 9 is a system diagram showing an embodiment of a jitter amount calculator which is a jitter amount measuring device.

FIG. 10 is a flowchart illustrating an example for setting an optimum focus bias.

[Description of Signs] 10 ... Disc recording / reproducing device, 11 ... Laser,
16 ... optical disk, 20 ... photodetector, 22 ...
.Laser power controller, 30 ... control unit, 40
... PLL circuit, 44 ... low-pass filter, 50
... Optical disk control block, 61 ... A
/ D converter, 70... Jitter amount calculator, 71.
Multiplier, 72 ... Adder, 73 ... Memory, 75 ...
・ Counter, 76 ・ ・ ・ Shifter

Claims (5)

[Claims] An optical disk is reproduced while varying a focus bias value while a tracking servo system is turned off, a tracking error signal is detected from the reproduced signal, and a variable range of the focus bias value is set from the tracking error signal. A focus servo circuit characterized in that: 2. The tracking error signal according to claim 1, wherein the tracking error signal is an error signal associated with the eccentricity of the optical disc, and the focus bias value is set using an amplitude value of the tracking error signal. The focus servo circuit according to claim 1, wherein 3. The variable range of the focus bias value in which the tracking servo does not deviate is set to -3 dB from the maximum amplitude value of the tracking error signal.
2. The focus servo circuit according to claim 1, wherein the focus bias value is selected as the focus bias value until the drop. 4. A control unit for outputting a focus bias value for a focus servo; an amplitude detector to which a tracking error signal is supplied; and a control unit for recording the amplitude value and the focus bias value. The optical disk is reproduced while changing the focus bias value while the tracking servo system is turned off, a tracking error signal is detected from the reproduced signal, and a variable range of the focus bias value is obtained from the tracking error signal. An optical disc recording / reproducing apparatus, wherein 5. A jitter amount calculator, wherein a variable range of a focus bias value is set based on a tracking error signal obtained when the tracking servo is turned off, and the tracking bias is set by turning on the tracking servo. 5. The optical disk recording / reproducing apparatus according to claim 4, wherein the jitter amount of the reproduction signal is measured by the jitter amount calculator while varying the value of the reproduction signal, and the optimum focus bias value is set based on the jitter amount. .