KR20000050390A - Tangential tilt detecting method of optical disc drive and apparatus therefor - Google Patents

Abstract

PURPOSE: A method for detecting tangential tilt of an optical disk drive and suitable apparatus thereof are provided not to necessary for an additional tilt detecting sensor by detecting a tangential tilt using a synchronous signal recorded in a header region of a disk. CONSTITUTION: A reproduction signal generator(140) generates signals, a subtracted signal and an added signal generated in light receiving devices of 4-divided optical detector. A header interval signal generator(152) generates a header interval signal for indicating a header region from a push-pool signal generated in the reproduction signal generator (140). A first synchronous signal level detector(144) detects a size (V1) of a synchronous signal among signals provided from a switch(S3) after being synchronized to the header interval signal(12) generated by the header interval signal generator(142). A second synchronous signal level detector(146) detects a size (V3) of a synchronous signal among signals provided from a switch(S1) after being synchronized to the header interval signal(34) generated by the header interval signal generator(142). A balance operating unit(154) operates a ratio between the V1 detected by the first synchronous signal level detector(144) and the V3 detected by the second synchronous signal level detector(146). A comparing unit(156) compares a balance value(T1) operated by the balance operating unit(164) with a predetermined reference value(T0) and outputs a difference of two values(T0,T1). A polarity inverting unit(160) inverts a polarity of the difference value outputted from the comparing unit(156). A tangential tilt adjusting unit(134) adjusts a tangential tile according to the polarity-inverted difference value. A mirror interval signal generator(150) generates a mirror interval signal for indicating a mirror region from the addition signal generated from the reproduction signal generator (140).

Description

Tangential tilt detection method and apparatus suitable for optical disc drive

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for detecting a tangential tilt of an optical disc drive, and more particularly, to an optical disc drive for recording and reproducing a recordable disc having a pre-pitted header for discriminating a physical sector. A method of detecting a tangential tilt using a header signal, and a tangential tilt adjusting device using the same.

In addition to playback-only discs such as DVD-ROMs, as well as recordable discs such as DVD-RAMs, as the recording density increases, signal quality deterioration due to the disc tilt increases.

In the recordable disc, if the tilt is present during recording, the recording quality is deteriorated due to the influence thereof. If the tilt is also present during the playback of the part, the quality of the reproduction signal is increased, causing data error.

There are two components of the disc's tilt: radial tilt and tangential tilt. Rial tilt refers to the tilt occurring in the radial direction of the disc, and tangential tilt refers to the tilt occurring in the track direction of the disc.

In the case of current DVD, if the tangential tilt is not adjusted, the performance during recording and playback is not significantly affected. However, in the case of a high density narrow tracked disc such as HD-DVD (High Definition DVD), the performance deterioration is caused by the tangential tilt. It is expected.

This requires the detection and adjustment of the tangential tilt.

An object of the present invention is to provide a method for detecting the tangential tilt of an optical disc drive, which has been devised to meet the above requirements.

Another object of the present invention is to provide a tangential tilt adjustment device suitable for the tangential tilt detection method described above.

FIG. 1A shows the physical shape of the land track, and FIG. 1B shows the waveform of the push-pull signal in the land track.

2A shows the physical shape of the groove track, and FIG. 2B shows the waveform of the push-pull signal in the groove track.

3 is an enlarged view of the header area illustrated in FIGS. 1A to 2A.

4A and 4B show a push-pull signal and a sum signal obtained when the laser spot passes through the header section of the groove track, respectively, in FIG. 3.

FIG. 5 shows a configuration of an apparatus for obtaining the push-pull signal and the sum signal shown in FIG. 4.

FIG. 6 is a waveform diagram illustrating reproduction signals generated in each light receiving element of a quadrature photodetector in the header area when there is no tangential tilt.

7 and 8 are waveform diagrams showing reproduction signals output from a light receiving element of a quadrature photodetector in the header area when there is a tangential tilt.

9 shows various signals and timings for detecting the magnitude of the synchronization signal from the reproduction signal output from the light receiving element.

10 is shown in FIG. and The configuration of the measuring device will be shown.

11 shows various signals and timings for detecting the magnitude of a mirror signal.

12 is a tangential tilt and balance value This graph shows the relationship of.

13 is a block diagram showing the configuration of a tangential tilt control device according to the present invention.

14 is a block diagram showing a detailed configuration of the tangential tilt control unit 162 shown in FIG.

15 and 16 is a waveform diagram showing the results of the experiment according to the invention /

In the method of detecting a tilt tilt according to the present invention, the recording area is divided into sectors, each sector has a header indicating an address, and the header is recorded in an address area and an address area in which the address of the sector is recorded. A tangential tilt detection method of an apparatus for reproducing an optical disc having a synchronization signal area in which a synchronization signal for detecting an address signal is recorded, the method comprising: light receiving elements located above or below a track direction among light receiving elements of a quadrant photodetector; It is characterized in that the tangential tilt is detected by the magnitude ratio of the signals obtained in the synchronization signal region.

Tangential tilt adjustment apparatus according to the present invention to achieve the above another object

The recording area is divided into sectors, each sector has a header indicating an address, and the header has an address area in which an address of a sector is recorded and a sync signal area in which a synchronization signal for detecting a signal recorded in the address area is recorded. 1. An apparatus for recording and reproducing a recording apparatus, comprising: a quadrant photodetector having two light receiving elements (B, C) located above the track direction and two light receiving elements (A, D) located below the track direction; And a reproducing signal generated from each light receiving element A reproduction signal generator for generating a push-pull signal RF_pp and a sum signal RF_sum; A header section signal generator for generating a header section signal indicating a header region from the push-pull signal RF_pp generated by the reproduction signal generator; Reproduction signals generated by the reproduction signal generator ( ) And playback signals in the synchronization signal region in synchronization with the header section signal generated by the header section signal generator. Size A synchronization signal level detector for detecting a signal; Detected by the synchronization signal level detector An operation unit for calculating a size ratio with; Difference value calculated by the operation unit And baseline Compare and compare the two values Comparator for outputting; And a tangential tilt control unit for adjusting the tangential tilt of the disc by the output of the comparing unit. Hereinafter, the configuration and operation of the present invention will be described in detail with reference to the accompanying drawings.

The tangential tilt detection method of the present invention generates a tangential tilt by a ratio of the reproduced reproduction signals generated from the light-receiving elements that are paired in the track direction in a quad split photodetector, and are detected from the synchronous signal regions regularly recorded on the disc. It is characterized by detecting a component.

In a DVD-RAM disc, information is recorded in a track, and the track is composed of a land track and a groove track, and the land track and the groove track intersect with each revolution of the disc. The reason why the land track and the groove track intersect in a DVD-RAM disc is to provide a tracking guide initially, and also to reduce crosstalk between adjacent tracks in a high density narrow track.

The track is composed of sectors divided into constant lengths. As a means for enabling physical division of such sectors, the header area is pre-pitted at the time of disc manufacture. The physical address of the sector is recorded in this header area.

That is, each sector is largely composed of a header area and a data area in which physical address information (hereinafter referred to as PID) is recorded.

1A shows the physical shape of the land track in a DVD-RAM disc, and FIG. 1B shows the waveform of a push-pull signal in the land track.

The header area is repeatedly arranged in a predetermined section (sector) of the track, and the so-called Complementary Allocation of Pit Address method in which four PIDs (PID1 to PID4) having the same value are alternately arranged from the center of the track to one header area is arranged side by side. Is recorded.

PID1 and PID2 are disposed away from the center of the track by a certain amount, and PID3 and PID4 are arranged away from the center of the track by a certain amount so that the laser spot 22 can accurately read the PID even if it is out of the center of the track. In the land track and groove track, the arrangement of PID1, 2 and PID3, 4 is reversed.

In the land track, a push-pull signal as shown in Fig. 1B can be obtained. In FIG. 1B, the large rectangles correspond to PID1 to PID4 from the left side, and PID1 and 2 are located at the bottom of the track center line (bottom header), and therefore have a low DC value and PID3 and 4 are upwards from the track center line. It has a high DC value because it is located at (peak header).

2A shows the physical shape of the groove track in the DVD-RAM disc, and FIG. 2B shows the waveform of the push-pull signal in the groove track. In FIG. 2B, the large rectangles correspond to PID1 to PID4 from the left side, and PID1 and 2 are located at the top of the track center line (peak header), and therefore have a high DC value and PID3 and 4 are lower from the track center line. It has a low DC value because it is located at (bottom header).

3 is an enlarged view of the header area illustrated in FIGS. 1A to 2A. In the structure of the header area, PID1,2 and PID3,4 are arranged to be shifted up and down with respect to the track center, and each PID has an ID indicating a physical address of a sector and a vfo signal of the same frequency for synchronization for ID detection. The signal is recorded. The vfo signal has a recording pattern of 4T (where T is the basic length of the recording signal).

As shown in Fig. 3, the header areas include vfo1 33 and ID1 34 (more than PID1), vfo2 35 and ID2 36 (more than PID2), vfo3 37 and ID3 38 (more than PID3). ), And vfo4 39 and ID4 40 (above PID4).

In FIG. 3, when the laser spot 32 passes through the header section of the groove track, the push-pull signal RF_pp as shown in FIG. 4A and the sum signal RF_sum as shown in FIG. 4B may be obtained. 4A and 4B, the vfo1 signal 42 corresponds to the vfo1 signal region 33 of FIG. 2, and the vfo3 signal 43 corresponds to the vfo3 signal region 37.

5 shows the configuration of a quadrant photodetector. In Fig. 5, reference numeral 50 denotes a four-part photodetector, 52 and 54 are adders, and 56 denotes a calculation unit.

The apparatus shown in Fig. 5 is a reproduction signal of the light receiving elements A to D of the quad split photodetector. , , , And Output the rule. In addition, the apparatus shown in FIG. 5 is a sum signal of the radial pairs B and C, A and D of the light receiving elements A to D of the quad split photodetector. , ), Wow Difference between Push-pull signal RF_pp, and Wow Sum of Outputs the sum signal RF_sum.

FIG. 6 is a waveform diagram illustrating reproduction signals generated in each light receiving element of a quadrature photodetector in the header area when there is no tangential tilt.

In Fig. 6, the signal on the uppermost side is the output of the light receiving element A located on the right side among the light receiving elements below in the track direction of the quadrature photodetector. The next signal is the output of the light-receiving element (D) located on the left And the next signal is the output of the light receiving element B located on the right among the light receiving elements above in the track direction of the quadrature photodetector. And the final signal is the output of the light receiving element (C) located on the left Will look.

Signals output from light receiving elements A and D as shown in FIG. Wow Shows the same directionality, and the signals output from the light receiving elements B and C Wow It can be seen that the same direction. That is, the signals output from the light receiving elements above or below the track direction of the 4-split photodetector have the same directivity.

The reason is that the tracking is adjusted so that the center line E-E 'of the quadrant photodetector 50 shown in FIG. 5 coincides with the center line of the track, and the header signals are shifted by a predetermined amount from the center of the track by a predetermined amount. Because it is.

In addition, the signal output from the light receiving elements (A and D) located on the upper side in the track direction. Wow Signals output from the light receiving elements B and C positioned upward in the track direction and the size of the Wow It can be seen that the size of the same.

7 and 8 are waveform diagrams showing reproduction signals output from a light receiving element of a quadrature photodetector in the header area when there is a tangential tilt.

As shown in FIGS. 7 and 8, when there is a tangential tilt, signals output from the light receiving elements A and D positioned upward in the track direction. Wow Signal output from the light receiving elements B and C positioned upward in the size ratio and track direction Wow It can be seen that the size ratio of is incorrect. That is, in the case of the tangential tilt, the magnitudes of the signals output from the light receiving elements above or below the track direction of the quad split photodetector in the header region are changed. This is because the intensity of light incident on the light receiving elements located on the left and right sides is different due to the tangential tilt.

Tangential tilt detection method of the present invention is characterized in that the tangential tilt is measured by the degree of balance of the signal output from the light receiving elements located in the upper or lower direction in the track direction of the four-segment photodetector in the sync signal interval of the disk do.

9 shows various signals and timings for detecting the magnitude of the synchronization signal from the reproduction signal output from the light receiving element. A detection output of header12 and a detection output of header34 of FIG. 9 are generated for a header section, and enable 12 and enable 34 of FIG. 6 are generated for a synchronization signal section.

When enable 12 of FIG. 9 becomes "high" If enable 34 becomes "high" Detect.

10 is shown in FIG. and As shown in FIG. 10, signals input to the enable terminal of FIG. 10 become enable 12 and enable 34 of FIG. 9. In the case of enable 12 is input to the device shown in FIG. If enable 34 is input, Outputs

If no tangential tilt occurs, the magnitude of the reproduction signal generated by the light-receiving elements located on the left and right sides of the quadrant photodetector is the same.

However, when the tangential tilt occurs, the magnitude of the reproduction signal generated by the light receiving elements located on the left and right sides of the quadrant photodetector is not the same.

Thus, the tangential tilt control can be measured by calculating the balance of the reproduction signal generated in the left and right light receiving elements of the quadrant photodetector.

Here, the tangential tilt is measured for the reproduction signal in the synchronization signal section for accurate comparison.

Where the balance value Is

or

or

or

here, Is the term for normalization.

or

here, Is the term for normalization.

or

Is determined.

here, Are signals output from the light receiving elements A, B, C, and D in the synchronization signal section, respectively. Is the size.

As another method, the balance value obtained by the equations (1) to (6) may be calculated in several successive header areas and averaged.

If there is no tangential tilt Value When tangential tilt occurs Value Is the difference between the two values Is defined as

In other words, The direction and magnitude of the tangential tilt can be known according to the value and the sign of.

here, May be a value measured in the absence of a tilt, a default value determined by the system controller of the recording / reproducing apparatus, or a value measured in a reference state determined by the system.

In land tracks and groove tracks, the top and bottom positions of the header area are reversed. To compute The polarity of must change from track to track.

Tangential tilt value in the system Is calculated as:

here, Is a proportional constant with a constant value.

The detected tangential tilt value Operate the tilt adjustment mechanism or change the recording / playback signal according to the direction and size of the. When operating the tilt adjustment mechanism or Control the value of to be zero. When changing the recording / playback signal Apply. Where proportional constant Has a constant value determined in accordance with the characteristics of the recording / reproducing apparatus and the method of manufacturing the disc.

Another example for tangential tilt detection is to change the normalization method shown in Equations 4 and 5 by using the magnitude of the reproduction signal in the mirror area immediately after the header period as follows.

here, Is a term for normalization and is the magnitude of the sum signal RF_sum measured in the mirror region.

At this time Can be obtained by applying the sum signal RF_sum to the input of FIG. 6 using the mirror interval detection signal and enable 5 shown in FIG.

12 is a tangential tilt and balance value This graph shows the relationship of. In Fig. 12, the vertical axis is a balance value and the magnitude of the tangential tilt. The graph shown in FIG. 12 used what is shown in Equation 6 to calculate the balance value. Tangential tilt and balance value as shown in FIG. It can be seen that has a linear relationship.

13 is a block diagram showing the configuration of a tangential tilt control device according to the present invention. The apparatus shown in FIG. 13 includes a reproduction signal generator 140, a header section signal generator 142, a first synchronous signal level detector 144, a second synchronous signal level detector 146, a mirror section signal generator 150, A mirror level detector 152, a balance calculator 154, a comparator 156, a land / groove detector 158, a polarity inverter 160, and a tangential tilt adjuster 162 are provided. The first switch S1 and the second switch S2 are selection switches.

The reproduction signal generator 140 generates signals generated by the light receiving elements of the quadrant photodetector. ), The difference signal RF_pp, and the sum signal.

The header section signal generator 152 generates a header section signal (header section signal 12, header section signal 34) indicating a header region from the push-pull signal RF_pp generated by the reproduction signal generator 130. Here, the header section signal 12 is a signal indicating the PID1, 2 areas, and the header section signal 34 is a signal indicating the PID3, 4 areas. Since the header region has a larger envelope than the data region, a header section signal representing the header region can be obtained using an envelope detector and a comparator for detecting the envelope of the reproduction signal.

The first synchronous signal level detector 144 is the size of the synchronization signal among the signals provided by the switch S3 in synchronization with the header interval signal 12 generated by the header interval signal generator 142. Is detected. Specifically, after generating the first enable signal enable 12 having a predetermined interval and a predetermined width from the start point of the header section signal 1, gating the push-pull signal RF_pp by the first enable signal enable 12 By detecting the peak-peak value of the gated reproduction signal Is detected.

The second synchronous signal level detector 146 is the size of the synchronous signal among the signals provided by the switch S1 in synchronization with the header section signal 34 generated by the header section signal generator 142. Is detected. In more detail, a second enable signal enable 34 having a predetermined interval and a predetermined width is generated from the start point of the header section signal 34, and the gate pull signal RF_pp is gated by the second enable signal enable 34, and then gated. By detecting the peak-peak value of the reproduction signal Detect. The first synchronous signal level detector 144 and the second synchronous signal level detector 146 are implemented with the apparatus shown in FIG.

The balance calculator 154 is detected by the first synchronous signal level detector 144 as shown in equations (1) to (6). Detected by the second synchronous signal level detector 146 Calculate the ratio of and. Here, the balance calculator 154 may output an average value of balance values obtained from several consecutive sectors.

The comparison unit 156 calculates the balance value calculated by the balance calculation unit 164 as shown in Equation (7). And the predetermined reference value Compare and compare the two values Outputs here, May be a value measured in the absence of a detrack, a default value determined by the system controller of the recording / playback apparatus, or a value measured in a reference state determined by the system.

The land / groove detector 158 introduces RF_pp to detect whether the current track is a land track or a groove track. As shown in Fig. 1B, the push-pull signal RF_pp in the land track is larger than the size of PID3,4, and in the groove track, the size of PID1,2 is smaller than the size of PID3,4. The land / groove detector 138 uses the same to determine a land / groove track.

The polarity inversion unit 160 outputs a difference value output from the comparator 156 according to a result detected by the land / groove detector 158. Invert the polarity of.

The tangential tilt adjustment unit 134 is a polarity inverted difference value output from the polarity inversion unit 160. Adjust the tangential tilt accordingly. Difference Since the sign and magnitude of represents the direction and magnitude of the radial tilt, the tilt is adjusted by feeding back the tilt.

The mirror section signal generator 150 generates a mirror section signal indicating a mirror area from the sum signal RF_sum generated by the reproduction signal generator 130. In the case of the push-pull signal RF_pp, since the mirror signal becomes zero, the mirror section signal cannot be obtained by the push-pull signal RF_pp.

Since the mirror signal has a very low envelope compared to the data region and the header region, the mirror signal may be generated by the envelope detector and the comparator.

The mirror signal level detector 152 detects the level of the mirror signal from the sum signal RF_sum based on the mirror section signal generated by the mirror section signal generator 150. The mirror signal level detector 152 generates a third enable signal enable 5 having a predetermined section and a predetermined width by the mirror section signal generated by the mirror section signal generator, and by the third enable signal enable 5. The sum signal RF_sum is gated and the peak-peak value of the gated sum signal RF_sum is detected. The mirror signal level detector 152 is implemented with the apparatus shown in FIG. 7.

The balance calculator 154 may level the sync signal detected by the first sync signal level detector 144. The level of the synchronization signal detected by the second synchronization signal level detector 156 Mirror signal level detected by mirror signal level detector 162. Balance value as shown in equations (9) to (10) by To calculate. Here, the balance calculator 164 may output an average value of balance values obtained from several sectors consecutive in the tangential direction.

Sum signal of radial pair instead of sum signal RF_sum , You can also use In this case, the first synchronous signal level detector 144 Is input to the second synchronous signal level detector 146. Enter.

14 is a block diagram showing a detailed configuration of the tangential tilt control unit 162 shown in FIG. The apparatus shown in FIG. 14 includes a tangential tilt servo 170, a tangential tilt driver 172, and an equalizer 174.

15 and 16 are waveform diagrams showing experimental results according to the present invention, and correspond to those shown in FIGS. 9 and 10, respectively.

That is, in FIG. 9, the size of A1 is reduced in A1 and D1, while in FIG. 15, the size of D1 is reduced. In FIG. 10, the size of B1 is reduced in B1 and C1, whereas in FIG. 16, the size of C1 is reduced. You can see it shrinks.

As described above, the tangential tilt method according to the present invention has the advantage of not requiring a separate tilt detection sensor because the tangential tilt is detected by using a sync signal recorded in the header area on the disk.

In addition, it is possible to increase the reliability by normalizing the synchronization signal, thereby enabling accurate tangential tilt adjustment.

Claims (22)

The recording area is divided into sectors, each sector has a header indicating an address, and the header has an address area in which the address of the sector is recorded and a sync signal area in which a synchronization signal for detecting an address signal recorded in the address area is recorded. In the tangential tilt detection method of a device for playing an optical disc, Tangential tilt detection method according to the magnitude ratio of the signals obtained in the synchronization signal region by the light receiving elements located above or below the track direction among the light receiving elements of the quad split photodetector. The method of claim 1, The quadrature photodetector comprises light receiving elements B and C positioned above the track direction and light receiving elements A and D positioned below the track direction, respectively, for detecting signals detected in the synchronization signal region by the respective light receiving elements. When Tangential Tilt Is Tangent tilt detection method, characterized in that determined by. The method of claim 2, wherein end Tangent tilt detection method, characterized in that normalized to. The method of claim 1, The quadrant photodetector includes light receiving elements B and C positioned above the track direction and light receiving elements A and D positioned below the track direction, respectively. When Tangential Tilt Is Tangent tilt detection method, characterized in that determined by. The method of claim 4, wherein end Tangent tilt detection method, characterized in that normalized to. The method of claim 1, The quadrant photodetector includes light receiving elements B and C positioned above the track direction and light receiving elements A and D positioned below the track direction, respectively. When Tangent tilt detection method, characterized in that determined by. The method of claim 1, The quadrant photodetector includes light receiving elements B and C positioned above the track direction and light receiving elements A and D positioned below the track direction, respectively. When Tangent tilt detection method, characterized in that determined by. The recording area is divided into sectors, each sector has a header indicating an address, and the header has an address area in which an address of a sector is recorded and a sync signal area in which a synchronization signal for detecting a signal recorded in the address area is recorded. In the apparatus for recording and playing back, A quadrant photodetector and a plurality of calculators each having two light receiving elements B, C located above the track direction and two light receiving elements A, D located below the track direction; Reproduction signals generated by the light receiving element A reproduction signal generator for generating a push-pull signal RF_pp and a sum signal RF_sum; A header section signal generator for generating a header section signal indicating a header region from the push-pull signal RF_pp generated by the reproduction signal generator; Reproduction signals generated by the reproduction signal generator ( ) And playback signals in the synchronization signal region in synchronization with the header section signal generated by the header section signal generator. Size A synchronization signal level detector for detecting a signal; Detected by the synchronization signal level detector An operation unit for calculating a size ratio with; Difference value calculated by the operation unit And baseline Compare and compare the two values Comparator for outputting; And Tangential tilt control device including a tangential tilt control unit for adjusting the tangential tilt of the disk by the output of the comparison unit The method of claim 8, wherein the sync level detector Signals generated by the light receiving elements A and B in synchronization with the header section signal ( A first switch for selecting one of Signals generated in the light receiving elements C and D and operated in synchronization with the first switch A second switch for selecting one of; A signal output from the first switch ( ), And the size of the reproduction signal in the synchronization signal region in synchronization with the header interval signal generated by the header interval signal generator A first synchronous signal level detector for detecting a; A signal output from the second switch ( ), And the size of the reproduction signal in the synchronization signal region in synchronization with the header interval signal generated by the header interval signal generator And a second synchronous signal level detector for detecting a signal. The method of claim 8, wherein the difference value output from the operation unit silver Tangential tilt adjustment device, characterized in that determined by. The method of claim 10, wherein the difference value output from the operation unit silver Tangential tilt detection device, characterized in that normalized to. The method of claim 8, wherein the difference value output from the operation unit silver Tangent tilt detection device, characterized in that determined by. The difference value output from the calculator. silver Tangential tilt adjustment device, characterized in that normalized to. The method of claim 8, wherein the difference value output from the operation unit silver Tangential tilt adjustment device, characterized in that determined by. The method of claim 8, wherein the difference value output from the operation unit silver Tangential tilt adjustment device, characterized in that determined by. The method of claim 8, wherein the reference value Is a balance value measured when there is no tilt. The method of claim 8, wherein the reference value Is a balance value measured in a prescribed reference state. The method of claim 8, wherein the reference value The tilt detection device, characterized in that the adjustment is made by the amount of tangential tilt during recording and reproduction. The method of claim 8, A mirror section signal generator for generating a mirror section signal representing a mirror region from the sum signal RF_sum provided by the reproduction signal generator; And The sum signal RF_sum provided from the reproduction signal generator is introduced, and the level of the mirror signal is synchronized with the mirror period signal generated by the mirror period signal generator. Further comprising a mirror signal level detection unit for detecting, Difference value output from the operation unit silver Tangential tilt adjustment device, characterized in that determined by. The difference value output from the operation unit of claim 19. silver Tangential tilt adjustment device, characterized in that determined by. The method of claim 8, wherein the disc is a DVD-RAM, Difference value output from the comparator according to land / groove track And a polarity inverter for inverting the polarity of the tilt sensor. 22. The apparatus of claim 21, further comprising a land / groove detector for introducing the push-pull signal RF_pp provided from the reproduction signal generator, detecting a land / groove track, and providing the land / groove track to the polarity inverter. .