JPH09265642A - Tracking error detecting circuit and method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tracking error detecting circuit and a method therefor capable of exactly obtaining a tracking error signal whose offset component is canceled for both MD and CD by the simple constitution. SOLUTION: An outer pushpull signal PP0 is obtained in a subtractor 11 based on signals A, D from an outer PD and an inner pushpull signal PPi is obtained based on signals B, C from an inner PD. The inner pushpull signal PPi is multiplied by a prescribed coefficient K in a coefficient multiplier 13, the inner pushpull signal PPi multiplied by the coefficient K is subtracted from the inner pushpull signal PPi in a third subtractor 14 and a tracking error signal TE is obtained. By making the coefficient K a ratio O0 /Oi of the change O0 of the outer pushpull signal PP0 to the change Oi of the inner push-pull signal PPi for spot movement due to the offset, the offset component is canceled and a tracking error signal having only the amplitude component is extracted.

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 applied to an optical disc device such as a compact disc (CD) or a mini disc (MD), and a method thereof.

[0002]

2. Description of the Related Art Recording / recording on so-called optical disks such as compact disks (CD) and mini disks (MD)
In a recording / reproducing apparatus for reproducing, as a tracking servo method for appropriately following a track, a three-spot method is mainly used in which the amounts of reflected light from two sub-beams sandwiching the main beam are compared. ing. But,
A push-pull method that can detect a tracking error with one spot is drawing attention from the viewpoints of simplification, downsizing of a 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. As a method capable of canceling the DC offset and appropriately detecting the tracking error, for example, there is the following method.

With respect to the lens variation and the disk skew as described above, the fact that the envelope of the RF signal is slightly modulated is used to detect the change in the peak value of the envelope, and the change and the predetermined value are detected. There is a method of multiplying by a coefficient to obtain a DC offset and canceling. This tracking error detection method is based on TPP (Top holdPu
It is called sh-Pull) and is a method usually used for a CD reproducing device.

Further, when the tracking servo is applied to the disk-shaped recording medium in which the wobble (the state where the track meanders) is formed on the track, the amplitude of the wobble frequency component included in the output signal of the photodetector is changed. There is a method of detecting the amplitude of the wobble frequency component by utilizing the fact that it changes depending on the position of the objective lens, obtaining the position of the objective lens, and canceling the offset value generated in the tracking error. This tracking error detection method is called WPP (Wobble Push-Pull) and is often used in MD devices capable of recording / reproducing.

The WPP method is a method for detecting the wobble frequency component contained in the signal detected by the photodetector of the optical pickup, so that it is correct if the rotation of the disk is not locked at a constant linear velocity by applying the tracking servo. Do not work. Therefore, it is necessary to use together with a method capable of canceling the offset in the off-track state. As such a circuit, there is a track-on circuit. The track-on circuit is a method of canceling the offset value from the tracking error signal by detecting the peak level and the bottom level of the tracking error signal at the moment when the tracking servo is turned on and using the average value thereof as the offset value. .

[0007]

As described above, there are various methods for canceling the offset value of the tracking error signal, but the offset value that can be effectively used according to the recording medium to be tracked, the tracking state, and the like. There is a problem that the versatility is low because the cancellation method is fixed. That is, there has been a demand for a tracking error signal detection circuit capable of obtaining a tracking error signal whose offset value is appropriately canceled in any of a track formed by pits and a track provided with a guide groove. Further, each of the tracking error offset value canceling circuits as described above has a problem that the configuration is complicated and the circuit scale becomes large, and a simpler circuit has been desired.

Therefore, the object of the present invention is a simple circuit structure, which can be applied to both MD and CD, and a tracking error detection in which a tracking error signal with an offset value canceled can be obtained. To provide a circuit. Another object of the present invention is to provide such a tracking error detection method.

[0009]

In order to solve the above-mentioned problems, two types of push-pull signals having different fluctuation ratios with respect to a DC component which is an offset signal and fluctuation ratios with respect to an AC component which is an original tracking error signal. The offset error signal is canceled out by using the above, and a tracking error signal in which the offset signal is substantially canceled can be obtained.

Therefore, the tracking error detection circuit of the present invention receives the reflected light of the beam of one spot applied to the disk-shaped recording medium, and outputs two types of push-pull signals, which are generated by the spot movement due to the offset. The rate of change in each type of push-pull signal,
Push-pull signal detecting means for detecting the first push-pull signal and the second push-pull signal, respectively, which have different rates of change in the two types of push-pull signals due to the spot movement due to the amplitude; ,
The ratio of the change caused in the first push-pull signal due to the spot movement due to the offset to the change caused in the second push-pull signal due to the spot movement,
It has a multiplication circuit for multiplying the second push-pull signal, and a subtraction circuit for detecting the tracking error signal by subtracting the first push-pull signal from the multiplication result.

Specifically, the push-pull signal detecting means has a four-divided photodetector that is divided in parallel and receives the reflected light, and the push-pull signal detecting means detects the photodetection signals detected by the two outer photodetectors. Either the detected outer push-pull signal or the inner push-pull signal detected based on the photodetection signals detected by the two inner photodetectors is detected as the first push-pull signal, and the first push-pull signal is detected. The outer or inner push-pull signal detected based on the photodetection signals detected by the two inner or outer photodetectors different from the pull signal is detected as the second push-pull signal.

Further, according to the tracking error detecting method of the present invention, the reflected light of the beam of one spot irradiated on the disk-shaped recording medium is received, and two kinds of push-pull signals are received, and the spot movement by the offset causes the above-mentioned two. A first push-pull signal and a second push-pull signal in which the rate of change that occurs in each of the types of push-pull signals and the rate of change that occurs in each of the two types of push-pull signals due to spot movement due to amplitude are different. The second detected push-pull signal is the ratio of the change detected in each of the first push-pull signals due to the spot movement caused by the offset to the change generated in the second push-pull signal caused by the spot movement. To the tracking error by subtracting the first push-pull signal from the multiplication result. To detect the signal.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram showing the configuration of a tracking error detection circuit according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a photodetector PD that supplies a photodetection signal to the tracking error detection circuit 10. The tracking error detection circuit 10 includes a photo detector PD, a first subtractor 11, a second subtractor 12,
It has a coefficient multiplier 13 and a third subtractor 14.

First, the configuration and operation of the tracking error detection circuit 10 will be described. Photo detector P
D 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 amount of light. Photodetector P of the present embodiment
As D, a four-division PD in which four photodetectors PD-A to PD-D are arranged as shown is used. Of the four photo detectors PD-A to PD-D, two photo detectors PD-A and PD-B detect the first-order diffracted light reflected to the left side of the data track, and the remaining two photo detectors PD-C and PD-C. The PD-D detects the -1st order diffracted light reflected on the right side of the data track.

The first subtractor 11 is an outer photodetector P of the four photodetectors PD-A to PD-D.
The first push-pull signal is obtained based on the photodetection signals from D-A and PD-D. That is, from the output signal D from the photo detector PD-D, the photo detector PD
-Outer push-pull signal P by subtracting the output signal A from A
Get P _O. The second subtracter 12 is an inner photodetector P among the four photodetectors PD-A to PD-D.
A second push-pull signal is obtained based on the photodetection signals from D-B and PD-C. That is, from the output signal C from the photodetector PD-C, the photodetector PD
-The output signal D from B is subtracted, and the inner push-pull signal P
Get P _i .

The coefficient multiplier 13 is obtained by the second subtractor 12.
Inner push-pull signal PP _iIs a predetermined coefficient K
And the multiplication result K × PP_iTo the third subtractor 14
Output to This coefficient K is the spot due to the offset
Outer push-pull signal PP for movement_OSignal change
O_OAnd the inner push-pull signal PP_iSignal change O
_IRatio of_O/ O_IIs measured and set in advance
Good. The third subtractor 14 receives the input from the coefficient multiplier 13.
Inner push-pull signal PP multiplied by the coefficient K_iYo
The outer push-pull signal obtained by the first subtractor 11.
Issue PP_OTo obtain the tracking error signal TE,
Output. In this way, the tracking error detection circuit 1
From 0, the tracking error signal T as shown in equation 1
E is required.

[0017]

[Equation 1] TE = K (C−B) − (D−A) (1)

Next, how the tracking error detection circuit 10 obtains the offset signal with the offset component canceled will be described. Position of the spot and the outer push-pull signal PP _O and the inner push-pull signal P
The change of each signal of P _i is shown in FIG. In FIG.
(A) is a diagram showing that the spots are not displaced, (B)
Shows a state where the spots are deviated, (C) shows an inner push-pull signal PP _i when the spots are not deviated, and (D) shows an outer push-pull signal PP _O when the spots are deviated. FIG. 6E is a diagram showing the inner push-pull signal PP _i when the spots are not displaced,
(F) is a diagram showing the outer push-pull signal PP _O when the spot is displaced.

The offset component of the inner push-pull signal PP _i is O _I , the amplitude component corresponding to the actual tracking error signal is A _I , the offset component of the outer push-pull signal PP _O is O _O , the actual tracking error signal. When the amplitude component corresponding to A 0 is A _O , the respective fluctuations associated with the spot movement are shown in FIG. In FIG.
(A) is a diagram showing the relationship between the spot position and the offset component, and (B) is a diagram showing the relationship between the spot position and the amplitude component.

Now, the tracking error signal TE obtained by the tracking error detection circuit 10 and represented by the equation 1 is shown.
Is expressed as in Equation 2 when each push-pull signal is divided into an offset component and an amplitude component.

[0021]

[Equation 2] TE = K (O _I + A _I ) − (O _O + A _O ) ... (2)

As mentioned above, K = O _O / O _I ,
Further, when K '= A _O / A _I , the tracking error signal TE is expressed by the equation 3.

[0023]

[Equation 3] TE = K × O _I + K × A _I −O _O + A _O = (1 + K / K ′) × A _O (3)

Therefore, if K <K ', then (1 + K /
K ′)> 0, the offset component is canceled, and only the amplitude component remains. And K and K'are P
Since it varies depending on the division width of D, if the PD is divided so that K <K ′, the offset component will be canceled by the tracking error detection circuit 10.

As described above, in the tracking error detection circuit 10 of the present embodiment, the 4-division PD whose division width is appropriately adjusted is used, and its external PD and internal PD are used.
By detecting the two types of push-pull signals that are more detected, the offset component is well cancelled between them, leaving only the amplitude component, and as a result, the tracking error signal with the offset value canceled can be obtained. it can.

The present invention is not limited to this embodiment, but various modifications can be made. For example, PD
In this division method, in the present embodiment, the division is performed so that the coefficients K and K ′ as described above are K <K ′. However, if K ≠ K ′, the amplitude component can be detected and may be divided so that K> K ′. In such a case, TE = (D−A) − (C−
B), and the polarities of the tracking drive may be reversed.

Further, the present invention is not limited to the use of 4-division PD. If two types of push-pull signals having different rates of change in the signal due to the offset component and the amplitude are obtained, the tracking error detection circuit 10 shown in FIG. The acquisition method may be arbitrary. Further, the shape and arrangement of the divided sensor are not limited to the shapes shown in the present embodiment, and the divided sensor having any configuration may be used.

[0028]

According to the present invention, a tracking error detection circuit and its method capable of accurately obtaining a tracking error signal with an offset component canceled for both MD and CD with a simple structure. Could 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 diagram illustrating a photo detector that supplies a photo detection signal to the tracking error detection circuit shown in FIG.

3A and 3B are diagrams showing changes in the position of a spot and a push-pull signal, FIG. 3A showing a state where the spot is not displaced, and FIG. 3B showing a state where the spot is displaced,
(C) is a diagram showing an inner push-pull signal when the spot is not displaced, (D) is a diagram showing an outer push-pull signal when the spot is displaced, and (E) is an inner face when the spot is not displaced. Diagram showing push-pull signal,
(F) is a diagram showing an outer push-pull signal when the spots are displaced.

4A and 4B are diagrams showing changes in an offset component and an amplitude component due to movement of a spot. FIG. 4A is a diagram showing a relationship between a spot position and an offset component, and FIG. 4B is a diagram showing a relationship between a spot position and an amplitude component. FIG.

[Explanation of symbols]

PD ... Photo detector, 10 ... Tracking error detection circuit, 11 ... First subtractor, 12 ... Second subtractor, 1
3 ... Coefficient multiplier, 14 ... Third subtractor

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[Procedure amendment]

[Submission date] April 7, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction contents]

[0007]

As described above, there are various methods for canceling the offset value of the tracking error signal, but the offset value that can be effectively used according to the recording medium to be tracked, the tracking state, and the like. There is a problem that the versatility is low because the cancellation method is fixed. That is, even properly canceled tracking error signal tracking <br/> error signal detection circuit is a desire as obtained the offset value in any of the tracks track or guide groove formed by the pit is provided It had been. Further, each of the tracking error offset value canceling circuits as described above has a problem that the configuration is complicated and the circuit scale becomes large, and a simpler circuit has been desired.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0015

[Correction method] Change

[Correction contents]

The first subtractor 11 is an outer photodetector P of the four photodetectors PD-A to PD-D.
The first push-pull signal is obtained based on the photodetection signals from D-A and PD-D. That is, from the output signal D from the photo detector PD-D, the photo detector PD
-Outer push-pull signal P by subtracting the output signal A from A
Get P _o . The second subtracter 12 is an inner photodetector P among the four photodetectors PD-A to PD-D.
A second push-pull signal is obtained based on the photodetection signals from D-B and PD-C. That is, from the output signal C from the photodetector PD-C, the photodetector PD
-The output signal B from B is subtracted, and the inner push-pull signal P
Get P _i .

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction contents]

The coefficient multiplier 13 uses the inside push-pull signal PP _i obtained by the second subtractor 12 as a predetermined coefficient K.
And the multiplication result K × PP _i is multiplied by the third subtractor 14
Output to The factor K is for spot movement by the offset, between changes O _o of the signals of the external push-pull signal PP _o, the signal of the inner push-pull signal PP _i changes O
The ratio of _i is O _o / O _i, which is measured and set in advance. The third subtractor 14 subtracts the outer push-pull signal PP _o obtained by the first subtracter 11 from the inner push-pull signal PP _i multiplied by the coefficient K input from the coefficient multiplier 13, Obtain the tracking error signal TE,
Output. In this way, the tracking error detection circuit 1
From 0, the tracking error signal T as shown in equation 1
E is required.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction contents]

Next, how the tracking error detection circuit 10 obtains the offset signal with the offset component canceled will be described. Spot position and outer push-pull signal PP _o and inner push-pull signal P _o
The change of each signal of P _i is shown in FIG. In FIG.
(A) is a diagram showing that the spots are not displaced, (B)
Shows the state that shift the spot, (C) is a diagram showing the inner push-pull signal PP _i when no shift spot, (D) the inner push <br/>-pull when are shifted spot Signal PP _i , (E) diagram showing outer push-pull signal PP _o when the spot is not displaced,
(F) is a diagram showing the outer push-pull signal PP _o when the spot is displaced.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0019

[Correction method] Change

[Correction contents]

The offset component of the inner push-pull signal PP _i is O _i , the amplitude component corresponding to the actual tracking error signal is A _i , the offset component of the outer push-pull signal PP _o is O _o , the actual tracking error signal. When the amplitude component corresponding to is represented by A _o , the respective fluctuations associated with the spot movement are shown in FIG. In FIG.
(A) is a diagram showing the relationship between the spot position and the offset component, and (B) is a diagram showing the relationship between the spot position and the amplitude component.

[Procedure correction 6]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction contents]

[0021]

[Equation 2] TE = K (O _i + A _i ) − (O _o + A _o ) ... (2)

[Procedure amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0022

[Correction method] Change

[Correction contents]

As mentioned above, K = O _o / O _i ,
Further, when K ′ = A _o / A _i , the tracking error signal TE is expressed by the equation 3.

[Procedure amendment 8]

[Document name to be amended] Statement

[Correction target item name] 0023

[Correction method] Change

[Correction contents]

[0023]

## EQU3 ## TE = K × O _i + K × A _i −O _o −A _o = (K / K′−1) × A _o (3)

[Procedure amendment 9]

[Document name to be amended] Statement

[Name of item to be corrected] 0024

[Correction method] Change

[Correction contents]

Therefore, if K> K ' , then (K / K'
-1) > 0, the offset component is canceled and only the amplitude component remains. And K and K'are P
Since D is thus changed to the division width of, if dividing the PD such that K> K ', so that the offset component is canceled by the tracking error detection circuit 10.

[Procedure amendment 10]

[Document name to be amended] Statement

[Correction target item name] 0026

[Correction method] Change

[Correction contents]

The present invention is not limited to this embodiment, but various modifications can be made. For example, PD
In this division method, in the present embodiment, the division is performed so that the above-mentioned coefficients K and K ′ are K> K ′ . However, if K ≠ K ′, the amplitude component can be detected and may be divided so that K <K ′ . In such a case, TE = (D−A) − (C−
B), and the polarities of the tracking drive may be reversed.

Claims (3)

[Claims] 1. A reflected light of a beam of one spot applied to a disc-shaped recording medium is received, and two types of push-pull signals are generated, and changes in each of the two types of push-pull signals caused by spot movement due to an offset. Of the
Push-pull signal detection means for detecting a first push-pull signal and a second push-pull signal, respectively, which have different rates of change in the two types of push-pull signals caused by the spot movement due to the amplitude; A multiplying circuit for multiplying the second push-pull signal by a ratio of a change of the first push-pull signal caused by the spot movement due to the offset to a change of the second push-pull signal caused by the spot movement; And a subtraction circuit for detecting the tracking error signal by subtracting the first push-pull signal from the result. 2. The push-pull signal detecting means has a four-divided photodetector divided in parallel for receiving the reflected light, and the outside detected based on the photodetection signals detected by the two outside photodetectors. Either the push-pull signal or the inner push-pull signal detected based on the photodetection signals detected by the two inner photodetectors is detected as the first push-pull signal, and the first push-pull signal The tracking error detection circuit according to claim 1, wherein the outer or inner push-pull signal detected based on the light detection signals detected by the two inner or outer photodetectors is detected as the second push-pull signal. 3. A reflected light of a beam of one spot applied to a disk-shaped recording medium is received, and two types of push-pull signals are generated, and changes in the two types of push-pull signals caused by spot movement due to offset. Of the
By detecting the first push-pull signal and the second push-pull signal, which have different rates of change in the two types of push-pull signals due to the amplitude-based spot movement, respectively, The second push-pull signal is multiplied by the ratio of the change occurring in the first push-pull signal to the change occurring in the second push-pull signal due to the spot movement, and the first push-pull signal is obtained from the multiplication result. A tracking error detection method that detects the tracking error signal by subtracting.