JPH09265649A - Tracking error detecting circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To calculate almost the same offset component as an offset component actually generated in a pushpull signal taking the direction of lens shift into consideration by compensating the difference of dependency upon the lens shift generated in a detected wobble component. SOLUTION: Wobbling amplitude components Aw, Dw are obtained from a signal A from a PD on the left outside and a signal D from a PD on the right outside by a first wobbling amplitude detecting part 211 and a second wobbling amplitude detecting part 212, respectively, multiplied by coefficients KA, KD, respectively, dependency on the lens shift is compensated and the difference of compensated amplitude components (KA×Aw)-(KD×Dw) is obtained by a subtractor 213. The difference between the signal A and the signal D is also obtained by a subtractor 214 and a wobbling amplitude component (A-W)w for the resulted pushpull signal is obtained by a third wobbling amplitude detecting part 215. An offset signal PP0 =(KA×Aw)-(KD×Dw)/(A-D)w is obtained in a divider 216.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tracking error detection circuit used in a recording / reproducing apparatus for recording / reproducing a mini disk (MD), for example.

[0002]

2. Description of the Related Art In a recording / reproducing apparatus for recording / reproducing an optical disc such as a compact disc (CD) or a mini disc (MD), a tracking servo method for appropriately following a track is to sandwich a main beam. Comparing the amount of light reflected from the two sub-beams placed 3
The spot method is mainly used. However, the push-pull method capable of detecting a tracking error with one spot is drawing attention from the viewpoints of simplification, downsizing of the device, and reliability. The push-pull method utilizes the fact that the intensity distribution of light that is diffracted and reflected by the pits and grooves and re-enters the objective lens changes depending on the relative position between the pits and grooves and the spot. This is a method in which light is received by a plurality of divided photodetectors, and a tracking error is obtained based on the difference in the amount of light received by each photodetector.

In the push-pull method, however, there is a problem that the spot moves on the photodetector when the objective lens fluctuates, and a DC offset occurs in the tracking error signal. This DC offset occurs when a pickup having a configuration in which only the objective lens moves is used, or when the disk surface is displaced from 90 ° with respect to the optical axis of the beam due to disk skew. Therefore, when using the push-pull method, it is necessary to cancel this DC offset.

Various methods are conceivable for canceling the DC offset and appropriately detecting the tracking error, depending on the type of the disk-shaped recording medium to be tracked. When tracking servo is applied to a disk-shaped recording medium in which wobbles (states where the tracks meander) are formed on tracks, such as MD, WPP (Wo
The method called bble Push-Pull) is often used. The WPP method utilizes the fact that the amplitude of the wobble frequency component included in the output signal of the photodetector changes depending on the position of the objective lens, detects the amplitude of the wobble frequency component, obtains the position of the objective lens, and the offset that occurs in the tracking error. This is a method to cancel the value.

Specifically, assuming that the detection signals of the reflected light in the two directions are E and F, the wobble component amplitudes w (E) and w (F) are obtained from these signals. Further, a push-pull signal EF is obtained from the light detection signals E and F, and the amplitude w (EF) of the wobble component of the push-pull signal is obtained.
Ask for. Then, a offset component canceling weight PP _O by Equation 2 using a predetermined coefficient K.

[0006]

[Equation 2] PP _O = K × (w (E) −w (F)) / (w (EF)) (2)

Then, as shown in equation 3, push-pull
From the signal PP, this cancellation amount PP _OTo reduce the offset
Tracking component canceled T
Ask for E.

[0008]

[Equation 3] TE = PP-PP _O (3)

The push-pull signal PP is a signal I corresponding to the light detection signals E and F and the total reflection light amount.
Based on g, it can be obtained as shown in Expression 4.

[0010]

## EQU4 ## PP = (EF) / Ig (4)

[0011]

[SUMMARY OF THE INVENTION] However, the offset component canceling amount PP _O obtained by by example equation 2 based on the wobble component is for canceling quantity detected by the direction of the lens shift is changed, due to this As a result, there is a difference between the actual push-pull signal PP and the offset amount, and the offset amount cannot be obtained accurately, and as a result, an accurate tracking error signal may not be obtained.

The dependence of the push-pull signal PP on the lens shift direction shown in Equation 4 is symmetrical with respect to the lens shift 0, as indicated by d in FIG. That is, in FIG. 5, y1≈y2, and whichever shift the lens shifts to, regardless of the direction of the shift, an offset amount depending on the shift amount occurs. On the other hand, the wobble component obtained from the light detection signal has the characteristics shown in FIG. FIG. 6a shows the wobble component w (E) / w (E− corresponding to the first term of the offset component as shown in equation 2.
FIG. 6e shows the dependency of F) on the lens shift, FIG.
Is the wobble component w (F) / w (E corresponding to the second term.
It is a figure which shows the dependence with the lens shift of -F). When the offset component is obtained from such two signals having different dependences on the lens shift as shown in Expression 2, the obtained offset component is a signal depending on the lens shift direction, as shown in FIG. . That is, in FIG. 7, y3 >> y4, and even with the same shift amount, a large difference occurs in the offset components calculated according to the shifting direction.

As is apparent from the comparison between FIGS. 5 and 7, the offset actually generated in the push-pull signal shown in FIG. 5 when the lens shift is performed in the minus direction in FIGS. 5 and 7. The component and the offset component calculated by the equation 2 shown in FIG. 7 are significantly different from each other, that is, the correct offset component cannot be calculated, and as a result, a correct tracking error signal cannot be obtained.

Therefore, it is an object of the present invention to detect the tracking error signal with higher accuracy by accurately detecting the offset component by considering the dependency on the lens shift as in the actual case. To provide a circuit.

[0015]

In order to solve the above-mentioned problems, a difference in dependence on a beam shift direction between two amplitude components obtained corresponding to reflected light from two directions sandwiching a guide groove. Then, the offset component is detected based on the amplitude component.

Therefore, in the tracking error detection circuit of the present invention, the beam of one spot irradiated on the track of the disk-shaped recording medium having the guide groove formed in a meandering shape is detected from two directions sandwiching the guide groove. Detects reflected light,
A push-pull signal detection circuit that obtains a push-pull signal based on the detection signal of the reflected light and the guide groove sandwiched 2
The meandering amplitude component of the guide groove included in each of the reflected lights from the respective directions, corrects the difference in dependence of the two detected amplitude components on the beam shift direction, and corrects the amplitude component. And an offset component detection circuit for detecting an offset component included in the detection signal of the reflected light from the two directions, and a tracking error signal is obtained by removing the detected offset component from the obtained push-pull signal. And an offset signal cancel circuit.

Specifically, the offset component detection circuit is
A first amplitude component detection circuit for detecting the meandering amplitude components w (E), w (F) of the guide groove, which are included in the detection signals E, F of the reflected light from the two directions sandwiching the guide groove, respectively. Predetermined coefficients K _E and K are added to the generated amplitude components w (E) and w (F), respectively.
_A coefficient multiplication circuit for multiplying _F and a difference K _E × w between two amplitude components K _E × w (E) and K _F × w (F) multiplied by the coefficient
(E) −K _F × w (F) is included in the first subtraction circuit, the second subtraction circuit that obtains the difference E−F between the detection signals E and F, and the obtained difference E−F. The difference K _E × w (E) −K _F × w obtained by the second amplitude component detection circuit for detecting the meandering amplitude component w (E−F) of the guide groove and the first subtraction circuit.
(F) is a dividend, and a division circuit that performs division with the amplitude component w (EF) detected by the second amplitude component detection circuit as a divisor, and calculates the offset component PP _O shown in Expression 5. .

[0018]

[Number 5] _{PP O = (K E × w} (E) -K F × w (F)) / w (E-F) ··· (5)

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIGS. In the present embodiment, a tracking error detection circuit applied to an optical disc device for recording / reproducing a mini disc (MD) will be described. Further, the MD to be tracked is an optical disc having a meandering guide groove (wobble) along a data track as shown in FIG. The disc substrate 300 of the MD has a pre-groove 30 corresponding to a groove portion.
1 and land 302, which is the land part,
The edge portion meanders at a predetermined cycle. Then, the spot 303 follows the pre-groove 301 to record / reproduce data.

FIG. 1 is a block diagram showing the configuration of the tracking error detection circuit. The tracking error detection circuit 100 includes a photo detector PD and an adder 10
1, 102, 103, subtractors 213, 214, 219,
222, dividers 216 and 220, wobble amplitude detection unit 2
11, 212, 215 and coefficient multipliers 223, 2
24 are connected and configured as shown.

First, the structure of each part will be described. The photodetector PD is provided in the optical pickup (OP), detects the light diffracted / reflected by the recording medium, and outputs signals A to D corresponding to the amounts of light. The photodetector PD of the present embodiment includes four photodetectors PD-A to
A 4-division PD in which PD-Ds are arranged as shown is used. Of the four photodetectors PD-A to PD-D, two photodetectors PD-A and PD-B detect the first-order diffracted light reflected to the left side of the data track, and the remaining 2
The photodetectors PD-C and PD-D detect the -1st order diffracted light reflected on the right side of the data track.

The first adder 101 adds the output signal A from the photodetector PD-A and the output signal B from the photodetector PD-B, and outputs an output signal L (= A + B) corresponding to the total light amount of the first-order diffracted light. ) Is generated. Second adder 1
02 is the output signal C from the photodetector PD-C,
The output signal D from the photodetector PD-D is added, and the output signal R (= C + D) corresponding to the light amount of the all-first-order diffracted light is added.
Generate The third adder 103 is the first adder 10
The outputs of the first and second adders 102 are further added, and an output signal Ig (= A + B + C + D) corresponding to the total amount of light detected by the photodetectors PD-A to PD-D is output.

The first wobble amplitude detector 211 detects the wobble amplitude signal Aw on the photodetector PD-A side (left side) from the output signal A of the photodetector PD-A. The configuration of this first wobble amplitude detection unit 211 is shown in FIG.
Shown in The first wobble amplitude detection unit 211 has a bandpass filter 225, a full-wave rectifier 226, and a lowpass filter 227. First wobble amplitude detector 21
1, the input signal A is band-limited by the bandpass filter 225 and shaped by the full-wave rectifier 226.
The amplitude of the signal A is detected by passing through the low pass filter 227.

The second wobble amplitude detection section 212 has a first
The wobble amplitude signal Dw on the photodetector PD-D side (right side) is detected from the output signal D of the photodetector PD-D, similarly to the wobble amplitude detection unit 211 of FIG. The configuration and operation of the second wobble amplitude detection unit 212 are the same as the configuration of the first wobble amplitude detection unit 211 described above with reference to FIG.

The first coefficient multiplier 223 is a photodetector PD obtained by the first wobble amplitude detector 211.
The -A side (left side) wobble amplitude signal Aw is multiplied by a predetermined coefficient K _A and output to the first subtractor 213. The second coefficient multiplier 224 multiplies the wobble amplitude signal Dw on the photodetector PD-D side (right side) obtained by the second wobble amplitude detection unit 212 by a predetermined coefficient K _D , and then the first subtractor To 213. The coefficients K _A K _D multiplied by the first coefficient multiplier 223 and the second coefficient multiplier 224 are
A wobble component having a lens shift dependency as shown in FIG. 6a, for example, obtained by the first wobble amplitude detector 211, and a lens shift as shown in FIG. 6e, for example, obtained by the second wobble amplitude detector 212. The wobble component having the dependency is represented by
It is determined so as to be corrected to have a symmetrical lens shift dependency around the lens shift 0.

The first subtractor 213 is a first coefficient multiplier.
The corrected amplitude component K obtained in 223_A× Aw,
The corrected amplitude component obtained by the second coefficient multiplier 224.
Minute K _DXDw, and the difference is calculated by the first divider 2
Output to 16.

The second subtractor 214 obtains the difference between the output signal A from the photodetector PD-A and the output signal D from the photodetector PD-D, and the difference A-D is determined by the third wobble amplitude detector 215. Output to. The third wobble amplitude detector 215 detects the wobble amplitude signal (A-D) w in the input push-pull signals A-D,
To the divider 216. The configuration and operation of the third wobble amplitude detection unit 215 are also the same as the configuration of the first wobble amplitude detection unit 211 described above. The first divider 216 divides the signal (K _A × Aw) − (K _D × Dw) input from the first subtractor 213 into the dividend, and the signal (A from the third wobble amplitude detection unit 215). -D) w
As divisor to perform the division shown in Equation 6, determine the offset signal PP _O, and outputs to the fourth subtractor 222.

[0028]

[Equation 6] PP _O = (K _A × Aw) − (K _D × Dw) / (A−D) w (6)

Further, the third subtractor 219 subtracts the output signal L corresponding to the light quantity of the total first-order diffracted light and the output signal R corresponding to the light quantity of the all-first-order diffracted light, as shown in Expression 7. Then, the push-pull signal PP = LR is obtained and output to the second divider 220. The second divider 220 has a third
The subtraction result of the subtractor 219 is used as a dividend, and the output signal Ig corresponding to the total amount of light input is divided as a divisor to obtain a push-pull signal PP / Ig normalized by the total amount of light.
Then, in the fourth subtractor 222, the offset value PP calculated by the first divider 216 is calculated from the normalized push-pull signal PP / Ig calculated by the second divider 220, as shown in Expression 7. A signal TE corresponding to a tracking error, which is a push-pull signal with offset canceled by subtracting _O , is obtained.

[0030]

[Equation 7] TE = PP / Ig−PP _O (7)

Next, the operation of such a tracking error detection circuit 100 will be described. When the recording medium is set, the rotation of the disk is immediately started under the control of a control unit (not shown), and at the same time, the tracking servo is applied.
First, the outputs of the photodetectors PD-A and PD-B on the left side and the photodetectors PD-C and PD-D on the right side are
The output signal L on the left side and the detection signal R on the right side are generated by addition in the adder 101 and the adder 102, respectively, and they are added in the adder 103 to generate a signal Ig corresponding to the total light amount. . The difference between the detection signal L on the left side and the detection signal R on the right side is obtained by a subtractor 219 to generate a push-pull signal PP, and the result is divided by a divider 220 with the signal Ig as a divisor and normalized to obtain an offset value. A tracking error signal before cancellation is required.

The first wobble amplitude detecting section 211 and the second wobble amplitude detecting section 212 wobble from the signal A from the left outer photodetector PD-A and the signal D from the right outer photodetector PD-D, respectively. Amplitude components Aw and Dw are calculated, the amplitude components Aw and Dw are respectively multiplied by the coefficients K _A and K _D to correct the dependency due to the lens shift, and the difference between the corrected amplitude components (K _A ×
Aw) − (K _D × Dw) is obtained by the subtractor 213.
Further, the difference between the signal A and the signal D is obtained by the subtracter 214, and the third result is obtained with respect to the result which is the push-pull signal.
The wobble amplitude detection unit 215 of the wobble amplitude component (A
-W) w is required. Then, in the divider 216, the offset signal PP _O = (K _A × Aw) − (K _D ×
Dw) / (A-D) w is obtained and output to the fourth subtractor 222.

Then, the subtractor 222 cancels the offset value obtained by the first divider 216 with respect to the normalized tracking error signal obtained by the divider 220 to cancel the offset value. Generated tracking error TE.

As described above, in the tracking error detection circuit of the present embodiment, as shown in FIGS.
Depends on the lens shift depending on the direction 2
By multiplying the signals of the two wobble components by a predetermined coefficient, the dependency on these lens shifts is made equal as shown in FIGS. 4a and 4b. as a result,
The calculated offset component is a signal that is symmetrical about the lens shift 0 as shown in FIG. 4C, and is substantially the same as the offset component that actually occurs in the push-pull signal shown in FIG. That is, an accurate offset component cancellation amount that is substantially equal to the actual offset component is detected without depending on the lens shift.

The present invention is not limited to the present embodiment, and various modifications are possible. For example, the actual configuration of the tracking error detection circuit may be any configuration. Further, the photodetection signal may be A / D converted into a digital signal, and a general-purpose arithmetic processing circuit such as a DSP may be used to perform the same operation as the circuit of this embodiment to obtain the tracking error signal. . Further, the shape, arrangement, etc. of the split sensor of the optical pickup are not limited to the four-split PD shown in the present embodiment, and a split sensor of any configuration may be used. Further, for example, when using two sets of four-division PDs, two corresponding PD outputs may be added to newly create A, B, C, and D.

[0036]

According to the present invention, by correcting the difference in the dependency of the detected wobble component on the lens shift, the directionality of the lens shift is also taken into consideration,
An offset component that is substantially equal to the offset component that actually occurs in the push-pull signal can be calculated. As a result, a tracking error detection circuit capable of accurately detecting the offset component and detecting the tracking error signal with higher accuracy can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a tracking error detection circuit according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a wobble amplitude detection unit of the tracking error detection circuit shown in FIG.

FIG. 3 is a diagram showing a recording medium on which tracking is performed by the tracking error detection circuit shown in FIG.

4 is a diagram showing the lens shift dependency of an offset component detected by the tracking error detection circuit shown in FIG.

FIG. 5 is a diagram showing a lens shift dependency of an offset component generated in an actual push-pull signal.

6 is a diagram showing the lens shift dependency of a wobble component detected by a wobble amplitude detection unit of the tracking error detection circuit shown in FIG.

FIG. 7 is a diagram showing a lens shift dependency of an offset component detected by a conventional tracking error detection circuit.

[Description of Codes] PD ... Photodetector, 100 ... Tracking error detection circuit, PD ... Photodetector, 101, 102,
103 ... Adder, 213, 214, 219, 222 ... Subtractor, 216, 220 ... Divider, 211, 212, 21
5 ... Wobble amplitude detector, 223, 224 ... Coefficient multiplier, 225 ... Band pass filter, 226 ... Full wave rectifier, 227 ... Low pass filter

Claims (2)

[Claims] 1. Reflected light from two directions sandwiching the guide groove of a beam of one spot applied to a track of a disk-shaped recording medium having a meandering guide groove is detected,
A push-pull signal detection circuit that obtains a push-pull signal based on a detection signal of the reflected light, and a meandering amplitude component of the guide groove included in each of the reflected lights from two directions sandwiching the guide groove is detected, and the detection is performed. Was done 2
A difference in dependence of two amplitude components on the shift direction of the beam is corrected, and based on the corrected amplitude component,
An offset component detection circuit that detects an offset component included in a detection signal of reflected light from a direction, and an offset signal cancel circuit that obtains a tracking error signal by removing the detected offset component from the obtained push-pull signal. A tracking error detection circuit having: 2. The offset component detection circuit includes detection signals E and F of reflected light from two directions sandwiching the guide groove.
In the meandering amplitude component w (E), w of the guide groove.
A first amplitude component detection circuit for detecting (F), and a coefficient multiplication circuit for multiplying the detected amplitude components w (E), w (F) by predetermined coefficients K _E , K _F , respectively. The two amplitude components K _E × w multiplied by a coefficient
(E), K _F × w (F) difference K _E × w (E) −K _F × w
A first subtraction circuit for obtaining (F), a second subtraction circuit for obtaining a difference E−F between the detection signals E and F, and a meandering of the guide groove included in the obtained difference E−F. A second amplitude component detection circuit for detecting the amplitude component w (EF) and a difference K _E × w (E) −K obtained by the first subtraction circuit
_A division circuit for performing division using _F × w (F) as the dividend and the amplitude component w (EF) detected by the second amplitude component detection circuit as the divisor, and the offset component PP shown in Equation 1 The tracking error detection circuit according to claim 1, which calculates _O. [Number 1] _{PP O = (K E × w} (E) -K F × w (F)) / w (E-F) ··· (1)