JPH0514972B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a skew error correction circuit suitable for use in detecting the skew angle of a rotating disk such as an optical video disk.

BACKGROUND TECHNOLOGY AND PROBLEMS In an optical disc reproducing device, a laser beam is converged by an objective lens to reproduce a signal. As a light source, a semiconductor laser is used because it is inexpensive and suitable for downsizing the device.

Semiconductor lasers have a wavelength of 780nm, which is longer than the helium-neon laser's wavelength of 623.8nm. For this reason, if you try to make the spot diameter so that you can obtain the same resolution as when using a helium neon laser as a light source, the NA of the objective lens
(Numerical Aperture) value must be increased to 0.5.

When the NA value of the objective lens is increased in this way, crosstalk from adjacent tracks becomes a problem when the optical axis of the laser beam is not perpendicular to the recording surface of the disk.

That is, when the optical axis 2 of the laser beam is perpendicular to the recording surface of the disk 1 as shown in _FIG. Although the crosstalk from adjacent tracks T ₁ and T ₂ is sufficiently small relative to the output, as shown in Figure B, the optical axis 2 is no longer perpendicular to the recording surface of disk 1 (hereinafter referred to as disk 1).
(referred to as skew) and crosstalk from the adjacent track at the detection output D, in this case _T1 , becomes large.

This crosstalk level L _C is: L _C ∝Wcmα (NA ³ /λ・α) ^2However , as is clear from the relational expression, W _C is the amount of comatic aberration, λ is the laser beam diameter, and α is the skew angle in the radial direction of the disk. Furthermore, when the NA value becomes large, it cannot be ignored. For example, λ=
780nm, track pitch 1.67μm, NA=0.5
To ensure a crosstalk level L _C =-40 dB in this case, the condition α≦0.5 is required.

The cause of disk skew, where the disk surface and optical axis are not perpendicular, is the bending of the spindle axis.
There are various causes, such as bending of the disk holder and skew of the disk itself, but the main cause is skew of the disk itself, and the current radial skew angle α of the disk itself is 1°≦α≦2°. Therefore, when a semiconductor laser is used as a light source, it is necessary to detect skew in the radial direction of the disk (including causes other than the skew of the disk itself (the same applies hereinafter)) and take measures against increased crosstalk.

An example of the skew detection means will be explained below.

In the example shown in FIG. 2, a skew detection means 5 is provided separately from the light source of the optical pickup 3. The figure shows the detection means 5 as seen along the radial direction of the disk 1, and FIG.
FIG. 4 is a view seen from the top side of the disk 1 (however, the disk is not shown).

A diffused light source is used as the light source, and in the examples shown in FIGS. 3 to 5, a light emitting diode 9 whose light emitting surface diffuses light is used.

Further, a photodetector 10 is provided which receives the light reflected by the disk 1 from the light emitting diode 9 via a lens 11. This photodetector 10 is a two-split photodetector in which the photodetection area is divided into two.

Light emitting diode 9, photodetector 10 and lens 1
1 is attached to a housing member 12 made of a cylindrical body. That is, the lens 11 is disposed on one open end side of the housing member 12, and the light emitting diode 9 and the photodetector 10 are disposed on the other open end side at the focal plane position of the lens 11. They are arranged on the left and right with the plane including the optical axis 11A serving as the center.

As shown in the figure, the housing member 12 is installed so that the lens 11 is on the disk 1 side and the light emitting diode 9 and the photodetector 10 are aligned in a direction perpendicular to the skew detection direction of the disk 1. .

In this example, the radial skew of the disk 1 is detected, so the light emitting diode 9
and the photodetector 10 are arranged in a direction perpendicular to the radial direction of the disk 1. Further, in this case, the optical axis 11A of the lens 11 is installed so as to be perpendicular to the recording surface of the disk 1 when the optical axis to the optical pickup is perpendicular. Further, the dividing line 10C of the two-split photodetector 10 is perpendicular to the skew detection direction, that is, the direction perpendicular to the radial direction of the disk 1, and the optical axis 11
It is made to intersect with the plane containing A.

Figure 5 shows a light emitting diode 9 and a two-split photodetector 1.
0 is shown in a perspective view.

With this configuration, a real image of the surface portion of the light emitting diode 9 is formed on the photodetector 10 as an image 13 shown with diagonal lines in FIG.

That is, if the optical axis 11A of the lens 11 and the recording surface of the disk 1 are perpendicular to each other, the optical paths of the incident light and the reflected light to the recording surface of the disk 1 are completely symmetrical.
It will look like Figure 6. Therefore, the real image of the light emitting diode 9, which includes the optical axis 11A of the lens 11 and is on the left side of the plane along the radial direction of the disk 1, is formed on the focal plane of the lens 11 on the right side of the plane. In FIG. 6, the portion above disk 1 is the portion that is reflected by the recording surface of disk 1, so when it is folded back by the recording surface of disk 1, it becomes as shown in FIG. 7, and the light emitting diode 9
A real image of the surface portion of is formed just at the position of the photodetector 10.

Then, the optical axis 11A of the lens 11 and the disk 1
When the recording surface of the image 13 is perpendicular to the recording surface as shown in FIG. forms an image. Therefore, the photodetection outputs from each divided area 10A and 10B are equal, and the difference between them is zero.

When the optical axis 11A of the lens 11 and the recording surface of the disk 1 are no longer perpendicular to each other due to the skew of the disk 1, as shown in FIG. Because of this tilted disk 1, it is shifted in the direction perpendicular to its radial direction, and therefore, the image 13 of the photodetector 10 is formed to include more of the image on the area 10B side as shown in FIG. 9C. I come to do it.

When the disk 1 has a skew that is on the opposite side to the state shown in FIG. 8, that is, the right side of the figure is downward, the image 13 of the photodetector 10 is shifted toward the area 10A side, as shown in FIG. 9A. Form the image so that it includes a lot of it.

From the above, each area 10 of the photodetector 10
The direction and amount of skew of the disk 1 can be detected by the detection outputs of the optical images 13 from the optical images A and 10B. This skew error signal is used as a servo signal for the movable part 40 shown in FIG.

FIG. 11 shows an example of the configuration of a movable part including an optical pickup and a skew detection part.

In the figure, reference numeral 20 denotes an optical block, which houses an optical pickup optical system for detecting information recorded by the pits of the disk 1 and an optical system for detecting skew. The focus servo and tracking servo for the optical system of the optical pickup are operated by a two-axis optical drive section 21.
This is done in the same manner as before.

Then, the optical axis position 2 of the optical system of the optical pickup
1A, the housing member 12 serving as the aforementioned skew detection means is attached to this block 20 in the longitudinal direction of the recording track T. Therefore, the surface including the optical axis of the lens 11 is
It is configured to also include the optical axis 21A of the optical pickup.

The optical block 20 is entirely supported by an axis 23 extending perpendicular to the radial direction of the disk 1, and is tilted in the radial direction of the disk 1.

That is, in this example, a worm gear 24 is attached to the bottom surface of the optical block 20, and two side plates 28A, 28B shaft hole 2
The shaft 23 is rotatably inserted through the shafts 9A and 29B, and when the worm 27 is rotated by the motor 26, the worm gear 24 is rotated by a rotation angle corresponding to the rotation, and thereby the optical block 20 is moved in the radial direction of the disk 1. be tilted. Therefore, by controlling the motor 26 using the skew detection output of the disk 1, it is possible to control the optical axis 21A of the optical pickup so that it is always perpendicular to the recording surface of the disk 1.

By the way, if the skew is such that the disk 1 is bent axially symmetrically with respect to the rotation axis as shown in FIG. 11, the skew is constant in the rotation direction of the disk 1, so the As shown, a skew error signal (DC component) S _E corresponding to the radial skew angle α is obtained. At this time, the skew servo is applied so that the skew error signal _SE becomes a predetermined level _V1 .

On the other hand, if the skew angle in the radial direction is not constant, the average level (DC component) of the skew angle α in the radial direction when the disk 1 makes one revolution is )
A skew error signal S _E is generated in which the skew error signal S E is superimposed. When disk 1 is rotated at 1800rpm, AC
Since the fundamental wave of the component is 30 Hz, in this case, for example, a skew error signal S _E as shown in FIG. 13 is detected.

Therefore, in the skew servo system, the skew servo is applied so that the DC skew error component of the skew error signal S _E is at a predetermined level, and the skew servo is simultaneously activated to cancel the AC skew error component. Movable part 4
Since the skew servo motor 26 provided at 0 is generally an inexpensive motor, if the skew servo system is configured to respond even to the AC skew error component included in the skew error signal S _E , Since the motor 26 is driven all the time, the life of the motor 26 is shortened, making it not very practical.

Therefore, in the past, attempts were made to cut out the AC skew error component contained in the skew error signal S _E and construct a skew servo system that responded only to the DC skew error component, but the AC skew error component was only 30 Hz. is the fundamental wave, so a normal low-pass filter cannot sufficiently cut out this AC component, and if you try to completely cut it out, the response time will be slow and excessive servoing will occur.

In order to solve these drawbacks, the present applicant previously proposed the following configuration.

In other words, as mentioned above, the skew angle α is
If it is 0.5° or more, crosstalk will occur and it will not be possible to pick up satisfactory information. However, if the skew is less than α<0.5°, information without crosstalk can be picked up without setting α=0. Furthermore, if skew occurs in the rotational direction of the disk 1, skew servo with α=0 is impossible.

Therefore, as shown in Fig. 14, the skew angle that becomes the threshold is set so that skew servo is performed only when the skew error is greater than or equal to the skew angle ±α (0.5° or less, in this example, about 0.4°) where no adverse effects due to crosstalk occur. Define α ₁ . If the skew error signal (DC skew error level V _D ) when the skew angle α is ₁ is V ₁ , then the skew angle is -
At α ₁ , a DC skew error of −V ₁ is detected.

FIG. 15 shows an example of the skew servo circuit 50, and 60 is a detection circuit for detecting the DC skew error corresponding to the skew angle α from the skew error signal S _E , which is configured digitally. Ru. 70 is a motor 26 that performs skew servo
drive system.

Skew error signal S _E obtained from photodetector 5
is connected to a pair of voltage comparators 62 via an input terminal 61,
63. The first voltage comparator 62
As shown in Figure 1, the reference plane X- of the rotating disk 1
A threshold hold level V ₁ corresponding to the skew angle α ₁ is used to detect a skew error when this disk 1 is skewed below X′.
is set to the reference level. On the other hand, the second voltage comparator 63 is for detecting a skew error when the disk 1 is tilted above the reference plane X-X', and its threshold level is -V ₁
It is. The following description will first be made regarding the configuration and correction when α>0.

As shown in Fig. 11, if the skew angle is α and this skew changes uniformly in the direction of rotation, then the DC skew error V _D1 (V _D1 > V ₁ ), a skew error signal S _E having an AC skew error Sq with a fundamental wave of 30 Hz is input, so the first voltage comparator 62 outputs the first voltage signal shown in FIG. Comparison output
P _C1 is obtained, which is determined by the first pulse width discrimination circuit 6 composed of a counter 65A and a latch circuit 65B.
5.

The counter 65A uses the pulse FG obtained from the frequency generator FG provided in connection with the disk drive motor (not shown) as a clock, and in this example, 32 pulses FG are obtained per disk rotation. It will be done. The first comparison output P _C1 is supplied to the counter 65A as an enable pulse,
The counter 65A operates only during the interval W in which the first comparison output P _C1 is at a high level.

The MSB bit data of the count output is latched by the latch circuit 65B. This latch is performed every rotation of the disk, and a pulse _PX (16th C) obtained by dividing the pulse FG by 1/32 (synchronized with the rotation period of the disk 1) is supplied as the latch pulse.

Therefore, the latch circuit 65B outputs the first comparison output.
The MSB bit data at the falling edge of _PC1 is latched. As shown in Figure 16, V _D1 >
When V ₁ , W>T/2 (T is 1 of the disk
Since the MSB bit data at this time is "1", the latch output _R1 becomes "H" (FIG. 16D).

The latch output _R1 is supplied as a switching pulse to the power switch 72 provided in the drive power supply 71 of the motor M, and the latch output _R1 is set to "H".
When this is the case, the power switch 72 is turned on and the motor 26 is driven in normal rotation.

Here, as long as V _D1 > V ₁ , the counter 65A
The MSB bit data from is set to “1”.
Since the motor is continuously driven while the latch output _R1 is "H", the direction of the light source 3 shown in FIG. 11 is changed in the direction of the arrow by this normal rotation drive, and the disk The illumination angle of the light source 3 relative to the light source 1 is continuously changed.

If the direction of the light source 3 is controlled to be perpendicular to the surface of the disk 1, the level of the DC skew error V _D1 included in the skew error signal S _E will also decrease, and V _D1 = V ₁ , therefore, When W=T/2, the MSB bit data of the counter 65A changes from "1" to "0". Therefore, the latch output that is latched every rotation of disk 1
_R1 becomes "L" and the power switch 72 is turned off.

Therefore, at the time when the skew error is detected such that V _D1 =V ₁ , the forward rotation of the motor 26 is stopped, and the light source 3 is stopped at the moving position. Since skew error detection is always performed during disk rotation, if V _D1 >V ₁ again, the above-mentioned skew servo will operate.

Depending on the disk 1 used, there may be a skew opposite to that described above. The DC skew error -V _D1 (not shown) at this time is detected by the second voltage comparator 63, and the DC skew error -V D1 (not shown) is detected by the second voltage comparator 63.
A second comparison output with a pulse width corresponding to V _D1
P _C2 is supplied to a counter 68A constituting the discrimination circuit 68, and a counter output corresponding to the pulse width of the second comparison output P _C2 is obtained.

The MSB bit data of the counter output is similarly latched by the latch circuit 68B.

MSB bit data of counter 68A is “1”
This occurs when −V _D1 <−V ₁ , and at this time, the latch output R ₂ is set to “H”.
This latch output _R2 turns on the power switch 74, and the reverse drive power source 73 is supplied to the motor 26.
The light source 3 is moved in a direction opposite to that shown in FIG. As a result, the irradiation angle of the light source 3 with respect to the disk 1 is changed in a direction that reduces the DC skew error. And −V _D1 =
-V ₁ When the skew error is detected, motor 2
6 stops, and the light source 3 stops at that moving position.

As is clear from the above operation description, the discrimination circuits 65 and 68 output the first and second comparison outputs having pulse widths W corresponding to the DC skew errors V _D1 and -V _D1 .
It has a function of determining the magnitude of P _C1 , P _C2 and the pulse width T/2 related to the rotation period of the disk 1.

By the combination of these discrimination circuits 65 and 68 and the first and second voltage comparators 62 and 63,
It is possible to configure a circuit system that does not respond to the AC skew error Sq included in the skew error signal S _E , but only responds to the DC skew error.

Furthermore, since the skew error within the threshold level ± _V1 is treated as a dead zone, the motor 26 will not be overloaded, and even an inexpensive motor 26 can have a significantly longer service life.

As described above, the skew error detection circuit previously proposed by the present applicant can extend the life of the motor 26 and improve the response characteristics, but the period of one rotation of the disk 1 is longer than the above. When applied to a long, slow-rotating optical disc playback device, the following problems arise.

For the sake of simplicity, it is assumed that the skew of disk 1 is uniform in the rotational direction and that there is no 30 Hz AC skew error signal Sq. Then, at a certain latch timing, a voltage is applied to the motor 26 in the servo-on state when the period greater than the reference level V ₁ is more than half (T/2) of one rotation period, and as a result, a DC skew error V _D occurs. It is assumed that it decreases linearly (FIGS. 18A to 18C).

Therefore, at latch timing a, the first comparison output P _C1 of the previous cycle is latched. In the case shown in the figure, since V _D >V ₁ throughout one period, the servo-on state continues even after latch timing a (FIG. 18D).

At the next latch timing b, even though the DC skew error V _D is actually lower than the reference level V ₁ , in one cycle before the latch timing b, W>T/2 Therefore, it is determined that the servo is on even at latch timing b. As a result, even if V _D <V ₁ , the motor 26 continues to work, and the polarity of the DC skew error V _D further increases in the opposite direction, so that the servo actually turns off at the latch timing of c.

Therefore, if the above-mentioned skew error detection circuit is applied to a device where the rotation speed of disk 1 is slower than the current case, the latch timing will be even longer than the current case, so the latch timing c
There is a possibility that the DC skew error V _D exceeds the other reference level -V ₁ , and in some cases, a problem may occur in which the skew servo system oscillates.

In particular, if the absolute values of the reference levels V ₁ and -V ₁ are made smaller in order to improve the accuracy of the skew servo system, the probability of oscillation will increase.

This is due to the fact that the comparison outputs P _C1 and P _C2 are sampled only once per rotation of the disk 1, and the data is latched.

Purpose of the Invention Therefore, in this invention, even with a low-speed rotating disk,
In addition to extending the life of the motor as described above, it is possible to construct a stable skew servo system that does not cause oscillation.

Summary of the invention Therefore, in this invention, for example, the first
As shown in Fig. 9, there is a comparison circuit 62 that compares a skew error signal S _E consisting of a DC component and an AC component corresponding to the skew angle of the rotating disk with a DC skew error threshold level, and this comparison circuit. A counter 8 counts the reference clock FG related to disk rotation based on the comparison pulse P _C1 corresponding to the DC skew error obtained from 62.
1, an up-down counter 82 to which the count value of this counter 81 is loaded, and a comparison pulse.
The data corresponding to P _C1 is compared with the data P _RG corresponding to the value of the comparison pulse P _C1 one cycle before the rotation of the disk, and only when the two data differ, the count value of the up-down counter 82 is changed to the reference clock FG.
Count value control circuit 8 that controls according to
3, 84, and drive means control circuits 71, 7 that control the drive means 26 for correcting the skew error according to the count value _R1 of the up-down counter 82.
2.

With this configuration, data is compared with data from one cycle before every reference clock cycle, so the servo-off timing becomes faster than before, making it possible to avoid oscillation phenomena. can.

Embodiment Next, an example of the skew error correction circuit according to the present invention will be explained in detail with reference to FIG. 19 and subsequent figures.

FIG. 19 is a system diagram of the main parts showing an example of this, and in this invention also, in order to obtain comparison pulses P _C1 and P _C2 corresponding to the DC skew error, the first and second voltage comparators 62 , 63 are provided.

The first comparison pulse P _C1 is supplied to the first control signal forming circuit 80A. The first control signal forming circuit 80A has a counter 81,
The first comparison pulse P _C1 is supplied as an enable pulse and the reference clock pulse FG is counted. Count data of counter 81 is 1
It is loaded into the up-down counter 82 every rotation period. Therefore, the pulse Px obtained by dividing the pulse FG by 1/32 by the frequency divider 67 is supplied to the up-down counter 82 as a load pulse.

On the other hand, the first comparison pulse P _C2 is supplied to a 32-bit (corresponding to the number of pulses FG in one cycle) shift register 83, and the data of the first comparison pulse P _C1 is taken in at the timing of the pulse FG. For example, as shown in FIG. 18A, in one cycle between a and b, the first half period W is "H" and the remaining period is "L", so the "H" period is "1" data. However, during the "L" period, "O" data is taken into the shift register 83, and all data immediately before sampling timing b, one cycle before point b, is taken into the shift register 83. The output data _PRG of the shift register 83 is output at the timing when the pulse FG is obtained.

The first comparison pulse P _C1 is then supplied to the up-down counter 82 as an up-down control pulse. In this example, it is controlled so that when it is "H" it is an up count and when it is "L" it is a down count.

Up-down mode is executed only when an enable pulse is input. Therefore, the first comparison pulse _PC1 and the output data _PRG of the shift register 83, which is data from one cycle before, are supplied to the exclusive NOR circuit (control circuit) 84, and its output is sent to the up-down counter 82 as an enable pulse. Supplied as.

The operation of the first control signal forming circuit 80A configured in this way will be explained using FIGS. 20 and 21.

Now, as a result of the skew servo, the DC skew error V _D has decreased as shown in Figure 20A, and is just a
It is assumed that the DC skew error V _D decreases below the reference level V ₁ between .about.b and that W>T/2 in this section. In this case, if the sampling point b is used as a reference, the data of the counter 81 is loaded into the up-down counter 82 at the timing b.

The loaded count data is exactly "16" when converted into analog data when W=T/2, so in the above case W>T/2, the count data at this time is larger than "16". For the sake of explanation, let's assume that count data "19" is loaded.

Since the output data PRG is obtained from the shift register 83 in synchronization with the input timing of the pulse FG, the exclusive NOR circuit 84 obtains the output data _PRG in synchronization with the input timing of the pulse FG.
Comparison of input levels is performed in synchronization with the input timing of the FG.

If the input timings of the pulse FG after sampling point b are b ₁ , b ₂ , ..., then the input timing b ₁
Then, the output data P _RG at the same input timing a ₁ one cycle before is obtained, so the data and output data at each input timing of the first comparison pulse P _C1 are obtained.
The relationship with _PRG is shown in Figure 21. As a result, at the input timings b ₁ , b ₂ , . . . , the enable pulses P _EN are all “L”, and the first comparison pulse P _C1 at this time is “L”, so the counter 82 is in the down-count mode. As a result, the count data loaded into the counter 82 decreases, and the count data decreases to "16" at input timing _b3 .

Therefore, the MSB bit data of this counter 82 changes from "H" to "L" at the input timing _b3 , and the switching pulse _R1 as a motor control signal changes from "H" to "L" and the motor The drive of 26 is stopped (FIG. 20C). After the motor 26 stops, the DC skew error V _D remains constant (Fig. 20A).

In this way, if the data from one cycle before is compared with the data currently obtained, and if the count data is 16 or more, the count data loaded into the counter 82 is decreased, then the next sampling The loaded count data always becomes "16" or less before reaching timing c. Therefore, the skew servo can be turned off earlier than before, and as a result, even if the original sampling period is longer than the current one, the skew servo can be realized without causing oscillation.

When count data “32” at sampling point a is loaded into the counter 82, each input timing a ₁ after sampling point a
Since the data of the first comparison pulse P _C1 at a _{2 ,} . After the period W has passed, the first
The data of the comparison pulse P _C1 changes to "L" and enters the down count mode, but since the remaining period is less than T/2, the loaded count data cannot be less than "16". , therefore motor 2
6 maintains the normal rotation drive state.

The formation circuit 80B for the control signal _R2 that performs reverse drive is also similar to the first formation circuit 80A, so its explanation will be omitted.

Effects of the Invention As explained above, according to the configuration of the present invention, the data loaded to the up-down counter is controlled by comparing the data obtained one cycle ago with the data obtained at the present time, so that the apparent Since the sampling period is shortened, oscillations will not occur even when used for detecting skew errors in low-speed rotating disks. Therefore, always stable skew servo can be realized.

In addition, DC within the threshold level ±V ₁
Since it is possible to immediately detect that the skew error V _D has converged, even if the absolute value of the threshold level ±V ₁ is reduced in order to improve the accuracy of the skew servo, the skew servo system will not oscillate, so the high Accurate skew servo can be realized.

Of course, according to the configuration of the present invention, since there is a dead zone for skew errors within the threshold level ±V ₁ , it is possible to avoid overloading the motor 26, prolong the life of the motor, and achieve a 30Hz Since the AC skew error signal Sq is digitally filtered, the response characteristics are improved.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the adverse effects caused by disk skew, FIG. 2 is a diagram showing an example of a skew detection means, and FIGS. 3 and 4 are diagrams showing an example of the configuration of a main part of the skew detection means. 5 is a perspective view of an example of the main part of the skew detection means, and FIGS. 6 to 9
The figure is a diagram for explaining the operation, Figure 10 is a diagram showing an example of a mechanism for controlling the optical axis of the optical pickup to always be perpendicular to the recording surface of the disk, and Figure 11 is an illustration of skew. , Figures 12 and 13
14 is a diagram illustrating the relationship between the skew error angle and the skew error detection voltage. FIG. 15 is a system diagram showing an example of the skew error detection circuit used to explain the present invention. Figure, 16th
18 are waveform diagrams for explaining its operation, FIG. 19 is a system diagram showing an example of the skew error correction circuit according to the present invention, and FIGS. 20 and 21 are diagrams for explaining its operation, respectively. be. 1 is a disk, 9 is a light emitting diode as a diffused light source, 10 is a two-split photodetector, 11 is a lens,
13 is an image of a diffused light source, 50 is a skew servo circuit, 60 is a skew error detection circuit, 70 is a motor control system, 62 and 63 are voltage comparators, 65 and 68
is a discrimination circuit, 80A and 80B are control signals
R ₁ and R ₂ forming circuits, 81 and 82 are counters, 8
3 is a shift register, and 84 is an exclusive NOR circuit for control.

Claims (1)

[Claims] 1. A skew error signal consisting of a DC component and an AC component corresponding to the skew angle of the rotating disk.
a comparator circuit that compares the threshold level of the skew error; a counter that counts a reference clock related to disk rotation based on a comparison pulse corresponding to the DC skew error obtained from the comparator circuit; The up-down counter into which the count value is loaded is compared with the data corresponding to the above-mentioned comparison pulse and the data corresponding to the value one cycle before the rotation of the disk of the above-mentioned comparison pulse, and the above-mentioned up-down counter is loaded only when the two data are different. A count value control circuit that controls the count value of the down counter according to the reference clock; and a drive means control circuit that controls the drive means that corrects the skew error according to the count value of the up-down counter. A skew error correction circuit characterized by: