JPH10228652A - Optical disk reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a jitters amount from increasing rapidly even when the detective error of the jitters amount exists at a focus bias amount setting time and to enhance reliability in data read by setting an allowable jitters amount based on a minimum value of the jitters amount and setting the focus bias amount becoming its middle value. SOLUTION: When an optical disk 1 is exchanged, a bias operation part 10 obtains the jitters amount that the jitters amount outputted from a jitters detection circuit 8 becomes minimum while changing the focus bias amount. The bias amount answering to the allowable jitters amount set by adding the prescribed jitters amount to this minimum jitters amount is detected in the increase/decrease directions, and its middle value is set in a bias register 9 as the bias amount. Thus, even when the detection error of the jitters amount is incorporated at the focus bias amount setting time, the matter that the jitters amount is kept within the allowable range becomes possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a CD or a CD-RO.
More particularly, the present invention relates to an optical disk reader that detects a relationship between a focus bias amount and a jitter amount and obtains an optimal focus bias amount from a detection result. .

[0002]

2. Description of the Related Art In an optical disk reader for reading data from an optical disk such as a CD or a CD-ROM, it is necessary to adjust a focus bias amount of a pickup so that a jitter amount of read data is minimized. For this reason, a semi-fixed resistor or the like for adjusting the focus bias amount is provided, and the semi-fixed resistor is adjusted in the adjustment step so that the jitter amount is minimized. However, the amount of focus bias depends on the optical disc to be reproduced.
The best bias amount changes. Further, if the amount of focus bias is adjusted using a semi-fixed resistor, the manufacturing process becomes complicated. For this reason, there has been proposed an optical disc reader having a function of automatically setting the best focus bias amount.

In this optical disk reader, as shown in FIG. 9, a range 91 in which the amount of focus bias is changed is set in both positive and negative directions with 0 as a reference value. Then, the jitter amount corresponding to each focus bias amount is detected while gradually changing the focus bias amount within the set range 91. The detected jitter amount is stored in association with the focus bias amount. When the detection of the jitter amount corresponding to each focus bias amount within the setting range 91 and the storage of the detected jitter amount are completed, the minimum jitter amount is searched from the stored data. Then, the focus bias amount B15 corresponding to the searched minimum jitter amount is set in the register holding the bias amount as the best focus bias amount.

[0004]

However, when the above technique is used, the following problems have occurred. That is, in the vicinity of the bias amount B15 where the focus bias amount becomes the best, the change in the jitter amount only slightly changes even when the focus bias amount is changed. Therefore, the jitter amount when the focus bias amount is B16 may be detected as the minimum jitter amount due to the influence of the vibration of the optical disk, noise, or the like. In this case, the focus bias amount set as the best value is
The bias amount becomes B16. Focus bias amount B16
Is set as the best value, when the focus error signal at the time of the data reading operation greatly changes in the direction of increasing the current value of the actuator, a situation occurs in which the jitter amount sharply increases. As a result, an error is likely to occur in data reading, which causes a problem that reliability of data reading is reduced.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to set an allowable jitter amount obtained by adding a predetermined value to a minimum value of the jitter amount. By detecting the maximum value and the minimum value of the focus bias amount at which the jitter amount to be performed becomes an allowable jitter amount, and setting the intermediate value between the maximum value and the minimum value as the focus bias amount, the focus bias amount can be set. It is an object of the present invention to provide an optical disk reading apparatus capable of suppressing an increase in the amount of jitter during a reading operation even when an error is included in the detection of the amount of jitter.

Another object of the present invention is to limit the change range of the focus bias amount for detecting the jitter amount so that the change rate of the jitter amount with respect to the change of the focus bias amount is reduced. Optical disk capable of preventing unnecessary increase in time required for setting the amount of jitter even when a small amount of occurrence occurs, and avoiding the risk of giving a bias amount greatly deviating from the focus bias amount at which the amount of jitter is minimized. A reading device is provided.

According to a third aspect of the present invention, in addition to the above object, a maximum value of the jitter amount is set, and a range in which the jitter amount does not exceed the maximum value is defined as an effective range of the focus bias amount. It is an object of the present invention to provide an optical disk reading apparatus which can set the focus bias amount to the best value even when reading an optical disk having a large amount of jitter by finding the best focus bias amount in (1).

[0008]

According to an aspect of the present invention, there is provided an optical disk reading apparatus, comprising: a focus bias amount for shifting a reference position of a focus of a pickup; and a jitter of data read by the pickup. By applying this method to an optical disc reading device that determines the focus bias amount corresponding to the optical disc to be read by detecting the corresponding relationship with the amount, the jitter amount corresponding to each focus bias amount is changed while changing the focus bias amount. By detecting, a minimum value of the jitter amount is obtained, and a jitter amount obtained by adding a predetermined value to the obtained minimum value of the jitter amount is set as an allowable jitter amount, and a focus bias corresponding to the optical disc to be read is set. When the amount is the set bias amount, the corresponding jitter amount is the allowable jitter. Is detected in each of two directions of a direction in which the focus bias amount is increased and a direction in which the focus bias amount is decreased, and an intermediate value of the detected focus bias amounts in the two directions is defined as the set bias amount. Configuration. That is, the allowable jitter amount is a value obtained by adding a predetermined value to the minimum value of the jitter amount when the focus bias amount is changed. Therefore, if the predetermined value is set to a value within the allowable range of the increase in the jitter amount, the allowable jitter amount indicates a limit value of the jitter amount at which data can be read from the optical disk. Therefore, when the jitter amount is equal to or less than the allowable jitter amount, it may be considered that the data can be read without any trouble. Now, it is assumed that the maximum value of the focus bias amount at which the corresponding jitter amount becomes the allowable jitter amount is bmax, and the minimum value is bmin. When the set bias amount is indicated by C, C = (bmax + bmin) / 2. Therefore, the change range of the focus error amount that can be regarded as being able to read data without hindrance is ± (b
(max-bmin) / 2. This means that the change range of the focus error amount in which the data can be read without any trouble is the widest.

In addition to the above configuration, the optical disk reading apparatus according to the present invention can cope with a case where a change range of the focus bias amount is set in advance and the focus bias amount is changed to the limit value of the change range. When the amount of jitter to be performed does not reach the allowable amount of jitter, the set bias amount is obtained using a focus bias amount that is a limit value of the change range. That is,
The change range of the focus bias amount for detecting the jitter amount is limited. Therefore, even if the focus bias amount is changed and the corresponding jitter amount does not reach the allowable jitter amount, the focus bias amount is not unnecessarily increased.

According to a third aspect of the present invention, in addition to the above configuration, the maximum jitter amount indicating the maximum value of the allowable range of the jitter amount is set in advance, and the allowable jitter amount exceeds the maximum jitter amount. Sometimes, the focus bias amount at which the corresponding jitter amount becomes the maximum jitter amount is detected,
The set bias amount is obtained based on the detected focus bias amount. That is, when the minimum value of the amount of jitter becomes large, even when the amount of jitter is within the range of the allowable amount of jitter, data reading may be hindered. Therefore, if the set bias amount is obtained based on the focus bias amount that is the allowable jitter amount, the allowable range of the focus error amount may be extremely narrow. However, when the set bias amount is obtained based on the focus bias amount that is the maximum jitter amount, the possibility of narrowing the allowable range of the focus error amount is reduced.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below.
This will be described with reference to the drawings. FIG. 5 is a block diagram showing the electrical configuration of an embodiment of the optical disk reading device according to the present invention.

In FIG. 1, a pickup 15 is a block for optically reading data from an optical disk (CD or CD-ROM, etc.) 1 and outputs the read data to a signal processing circuit 2. For this purpose, an optical lens group for forming a focal point on the data surface of the optical disc 1, a light emitting element and a light receiving element for laser light, an actuator for tracking and an actuator for focusing are provided inside.

The signal processing circuit 2 is a block for restoring recorded data by decoding data output from the pickup 15. And
The restored data is sent to a block (not shown) with an output 12. Further, it amplifies data output from the pickup 15 and outputs the amplified signal to the jitter detection circuit 8 as a clock signal. Further, it generates a focus error signal indicating an error amount of the focus error, and outputs the generated focus error signal to the A / D converter 3.

The A / D converter 3 converts the error amount indicated by the focus error signal output from the signal processing circuit 2 into a digital value and outputs the digital value to the adder 4. The bias register 9 is a memory for holding the focus bias amount, and outputs the held focus bias amount to the adder 4. The adder 4 adds the focus error amount converted into the digital value and the focus bias amount, and outputs the addition result to the focus filter 5.

The focus filter 5 is a block for correcting the phase of a focus error signal in order to prevent unnecessary oscillation of a control circuit forming a loop. For this purpose, an input register that holds input data, a digital filter that performs phase correction, and an output register that holds data to be output are provided. D / A converter 6
Converts the digital signal (the addition signal of the focus error amount and the focus bias amount) output from the focus filter 5 into an analog signal, and outputs the analog signal to the drive circuit 7.

The drive circuit 7 is a block that amplifies the analog signal 13 output from the D / A converter 6. Then, the focus actuator provided on the pickup 15 is driven by the amplified signal 14. The jitter detection circuit 8 is a block that detects the amount of jitter of the clock signal detected by the pickup 15 and output from the signal processing circuit 2 as a digital value. Then, the detected jitter amount is output to the bias value calculator 10.

The bias value calculation unit 10 is a block for obtaining an optimum focus bias amount for each of the optical disks 1 and sets the obtained focus bias amount in the bias register 9. That is, the optical disk 1
Is replaced, the focus bias amount set in the bias register 9 is changed. Further, the amount of jitter output from the jitter detection circuit 8 is read in accordance with the changing focus bias amount. Then, an optimum focus bias amount is obtained based on the relationship between the read jitter amount and the focus bias amount. Next, the obtained focus bias amount is set in the bias register 9.

FIG. 6 is a circuit diagram showing a detailed electrical connection of the drive circuit 7. As shown in FIG. The amplifier 21 whose amplification factor is determined by the resistors R1 and R2 amplifies the voltage of the analog signal 13 output from the D / A converter 6 to a predetermined level. The voltage-amplified signal is current-amplified by an amplifier circuit including the transistor Q1 and the transistor Q2. Then, the pickup 1 is provided with the current-amplified signal 14.
5 is driven. It should be noted that the amplifier 21 for performing voltage amplification and the amplifier circuit including the transistors Q1 and Q2 are amplifier circuits covering two quadrants, positive and negative. Therefore, a current flows through the actuator 22 in two directions, positive and negative.

FIGS. 1 to 4 are explanatory diagrams showing the relationship between the focus bias amount and the jitter amount, and FIGS. 7 and 8 are flowcharts showing the main operation of the embodiment. The operation of the embodiment will be described with reference to these drawings as necessary. When the optical disk 1 is replaced, the bias value calculation unit 1
A value of 0 determines a focus bias amount that is optimal for the replaced optical disc 1 and sets the calculated focus bias amount in the bias register 9.

More specifically, referring to FIG. 1, FIG. 7, and FIG. 8, when the optical disk 1 is replaced, the bias value calculator 10 sets the focus bias amount B set in the bias register 9 to a reference value. Is set to 0. At this time, the jitter amount J2 output from the jitter detection circuit 8
Is read (step S1). Then, the read jitter amount J2 is stored internally as the minimum value jm. Further, a value obtained by adding ΔJ which is a predetermined amount set in advance to the minimum value jm is internally stored as an allowable jitter amount js (step S2).

When the above operation is completed, the focus bias amount B is increased by a specified amount, and the jitter amount J output from the jitter detection circuit 8 is read (step S3). Next, it is determined whether or not the focus bias amount B has exceeded a preset limit value BMAX (step S4). In this case, since it does not exceed, the read jitter amount J is compared with the allowable jitter amount js (step S5). The read jitter amount J is the allowable jitter amount j
If it is smaller than s, the operation moves to step S6,
The read jitter amount J is compared with the minimum value jm.

If the read jitter amount J is smaller than the minimum value jm, it is determined that a new minimum value jm has been detected, and the read jitter amount J is stored internally as the minimum value jm. Also, based on the updated minimum value jm,
A new allowable jitter amount js is calculated and stored (step S7). Next, the process proceeds to step S3. On the other hand, in the determination in step S6, the read jitter amount J is
If it is larger than the minimum value jm, the already stored minimum value j
The process proceeds to step S3 without changing m and the allowable jitter amount js.

When the operations in steps S3 to S7 are repeated, the minimum value jm and the allowable jitter amount js eventually become the minimum value jm = J1 and the allowable jitter amount js = J3. When the focus bias amount B becomes B1, the jitter amount J becomes equal to the allowable jitter amount js. Therefore, the operation moves from step S5 to step S8. The focus bias amount B1 when the jitter amount J becomes equal to the allowable jitter amount js becomes a corresponding value bmax in the increasing direction of the focus bias amount. For this reason, the bias value calculation unit 10 internally stores the focus bias amount B1 as the corresponding value bmax. Also, the already stored minimum value jm and allowable jitter amount js
And are kept as they are.

When the above operation is completed, the bias value calculator 10 sets the focus bias amount set in the bias register 9 to 0, which is a reference value. Further, the update flag F is set to 0 (step S10). Then, the focus bias amount B is reduced by a specified amount, and the jitter amount J output from the jitter detection circuit 8 is read (step S1).
1). Next, it is determined whether or not the focus bias amount B has exceeded a preset limit value BMIN (step S12). In this case, since it does not exceed, the read jitter amount J is compared with the allowable jitter amount js. If the read jitter amount J is smaller than the allowable jitter amount js, the operation shifts from step S13 to step S14 to read the jitter amount J and the minimum value jm.
Compare with

If the read jitter amount J is smaller than the minimum value jm, it is determined that a new minimum value jm has been detected, and the read jitter amount J is stored internally as the minimum value jm. Also, based on the updated minimum value jm,
A new allowable jitter amount js is calculated and stored. Also,
The value of the update flag F is set to 1 (step S15).
After that, the operation moves to step S11. On the other hand, in the determination of step S14, the read jitter amount J
Is larger than the minimum value jm, the already stored minimum value j
The process proceeds to step S11 without changing m and the allowable jitter amount js.

Now, the focus bias amount B and the jitter amount J have the relationship shown in FIG. Therefore, step S1
The operations of 1 to S14 are repeated. When the operations of steps S11 to S14 are repeated and the focus bias amount B becomes B2, the jitter amount J becomes equal to the allowable jitter amount js (specifically, J3). Therefore, the operation moves from step S13 to step S16. The focus bias amount B2 when the jitter amount J becomes equal to the allowable jitter amount js (J3) becomes the corresponding value bmin in the decreasing direction of the focus bias amount. Therefore, the bias value calculation unit 10 internally stores the focus bias amount B2 as the corresponding value bmin. Next, the process proceeds to step S17 to determine whether or not the value of the update flag F is 1.

Generally, when the value of the update flag F is 1, it means that the minimum value jm of the jitter amount J is detected when the focus bias amount B is changed in the decreasing direction. Therefore, the corresponding value bmax does not become a value corresponding to the allowable jitter amount js. On the other hand, when the value of the update flag F is 0, it means that the minimum value jm is detected when the focus bias amount B increases. Therefore, the corresponding value bm
ax means a value corresponding to the allowable jitter amount js.

Since the relationship between the amount of jitter and the amount of focus bias is as shown in FIG. 1, the value of the update flag F is 0 as a result of the above operation. Therefore, the corresponding value bmax
Indicates a correct value corresponding to the allowable jitter amount js. Therefore, the operation is performed from step S17 to step S17.
Move to 19. When the process proceeds to step S19,
The corresponding value bmax (B1) already obtained and the corresponding value bmin
From (B2), a set bias amount C1, which is an intermediate value, is obtained by an operation of C1 = (B1 + B2) / 2. Further, the determined set bias amount C1 is set in the bias register 9.

The description of the operation in the case where the relationship between the jitter amount and the focus bias amount is the relationship shown in FIG. 1 has been completed, and the relationship between the focus bias amount B and the jitter amount J is as follows.
The operation when the relationship is as shown in FIG. 2 will be described below.

At this time, after the operation of step S1,
When the operation of steps S2 to S7 is repeated, and then the operation of step S8 is performed, the minimum value jm = J6 the allowable jitter amount js = J8 and the corresponding value bmax = B3. After the operation in step S10, the operations in steps S11 to S15 are repeated, and then in step S1
6, the minimum value jm = J5, the permissible jitter amount js = J7, and the corresponding value bmin = B4.

At this time, the value of the update flag F becomes 1. Therefore, the operation moves from step S17 to step S18. Therefore, an operation of detecting the corresponding value bmax is performed with the allowable jitter amount js = J7. With this operation, the focus bias amount B5 is detected. Next, the operation moves to step S19. In step S19, the obtained focus bias amount B
The set bias amount C2 is calculated by calculating C2 = (B4 + B5) / 2 based on 4, B5. The calculated set bias amount C2 is set in the bias register 9.

With the above, the description of the operation in the case where the relationship between the jitter amount and the focus bias amount becomes the relationship shown in FIG. 2 is finished, and the relationship between the focus bias amount B and the jitter amount J becomes
The operation when the relationship shown in FIG. 3 is satisfied, that is, when the change rate of the jitter amount with respect to the change of the focus bias amount is small, will be described below.

At this time, after the operation of step S1,
If the operations of steps S2 to S7 are repeated, the focus bias amount B may exceed the limit value BMAX.
Therefore, the operation moves from step S4 to step S8. When the operation of step S8 is performed, the minimum value jm = J10 and the allowable jitter amount js = J11, but the corresponding value bmax becomes the limit value BMAX.

When the operations of steps S11 to S15 are repeated after the operation of step S10, the focus bias amount B may exceed the limit value BMIN.
Therefore, the operation is performed from step S12 to step S1.
Move to 6. When the operation in step S16 is performed, the minimum value jm = J10 and the allowable jitter amount js = J11, but the corresponding value bmin is the limit value BMIN.
Therefore, the set bias amount is limited to the limit value BMAX and the limit value B.
It is an intermediate value with MIN, and specifically, the value is 0. That is, the value 0 as the reference value is set in the bias register 9 as the best value of the set bias amount.

In FIG. 3, the relationship between the focus bias amount and the jitter amount is indicated by a broken line 51 when the focus bias amount is positive, and is indicated by a solid line when the focus bias amount is negative. And In this case, when the operation goes to step S19, the corresponding value bmax = B7 and the corresponding value bmin = BMIN. As a result, the set bias amount C4 is calculated by an operation expressed as C4 = (B7 + BMIN) / 2. Further, the calculated set bias amount C4 is set in the bias register 9.

The description of the operation in the case where the relationship between the jitter amount and the focus bias amount is as shown in FIG. 3 has been completed, and the relationship between the focus bias amount and the jitter amount is shown in FIG.
The following describes the operation when the relationship shown in (1), that is, when the situation occurs in which the jitter amount becomes a large value on average. The following operation is not shown in the flowchart.

Even if a situation occurs where the jitter amount J becomes a large value on average, when the operation in step S19 is completed, the minimum value jm = J13 and the permissible jitter amount js = J14, and the corresponding value bmax and the corresponding value bmin Will be obtained. However, the allowable jitter amount J14 is
Is too large, and if the set bias amount as an intermediate value is obtained from the corresponding value bmax and the corresponding value bmin based on the allowable jitter amount J14, the reliability of the obtained set bias amount decreases.

Therefore, it is safe to set the maximum value also for the allowable jitter amount js. For this reason, the allowable jitter amount js
Is set as a maximum value of JMAX. The maximum jitter amount JMAX is desirably set to a small value if possible. However, if the value is too small, the set meaning is lost. For this reason, an error generated due to an increase in the amount of jitter can be corrected by the error correction executed by the signal processing circuit 2,
The occurrence of an error is allowed, and the amount of jitter corresponding to this allowable range is defined as the maximum amount of jitter JMAX.

Returning to the description of the operation, when step S16 ends, it is determined whether the allowable jitter amount js does not exceed the maximum jitter amount JMAX. If it is determined in this determination that the allowable jitter amount js does not exceed the maximum jitter amount JMAX, step S17
To S19.

On the other hand, the allowable jitter amount js is equal to the maximum jitter amount J.
If it exceeds MAX, the corresponding jitter amount J becomes
Focus bias amount B that becomes maximum jitter amount JMAX
Between the increasing direction and the decreasing direction of the focus bias amount.
Detect in both directions. Referring to FIG. 4, the focus bias amount B10 and the focus bias amount B11 are detected as the focus bias amounts at which the jitter amount J becomes the maximum jitter amount JMAX. For this reason,
The bias value calculator 10 performs a calculation represented by C7 = (B10 + B11) / 2 from the detected focus bias amounts B10 and B11 to calculate a set bias amount C7. Further, the calculated set bias amount C7 is set in the bias register 9.

[0041]

According to the first aspect of the present invention, the optical disk reading apparatus detects the correspondence between the focus bias amount for shifting the reference position of the focus of the pickup and the jitter amount of the data read by the pickup. , Applied to an optical disk reading device for obtaining a focus bias amount corresponding to an optical disk to be read,
By detecting the jitter amount corresponding to each focus bias amount while changing the focus bias amount,
The minimum value of the jitter amount is obtained, the jitter amount obtained by adding a predetermined value to the obtained minimum value of the jitter amount is defined as the allowable jitter amount, and the focus bias amount corresponding to the optical disc to be read is set as the set bias amount. In this case, the focus bias amount at which the corresponding jitter amount becomes the allowable jitter amount is detected in each of two directions of a direction in which the focus bias amount is increased and a direction in which the focus bias amount is decreased, and the detected focus in the two directions is detected. The intermediate value of the bias amount is set as the set bias amount. That is, the allowable jitter amount is obtained by adding a predetermined value to the minimum value of the jitter amount, and the maximum value and the minimum value of the focus bias amount at which the corresponding jitter amount becomes the allowable jitter amount are detected. Is an intermediate value of the focus bias amount. Therefore, even when an error is included in the detection of the jitter amount when the focus bias amount is set, the allowable range in which the jitter amount remains at a small value is determined by the difference between the plus side and the minus side of the set focus bias amount. Since both are equally secured, it is possible to suppress an increase in the amount of jitter during the reading operation.

In addition to the above configuration, the optical disk reading apparatus according to the second aspect of the present invention can cope with a case where the change range of the focus bias amount is set in advance and the focus bias amount is changed to the limit value of the change range. When the amount of jitter to be performed does not reach the allowable amount of jitter, the set bias amount is obtained using a focus bias amount that is a limit value of the change range. That is,
Since the change range of the focus bias amount for detecting the jitter amount is limited, even when the change amount of the jitter amount with respect to the change of the focus bias amount is small, the time required for setting the jitter amount is unnecessary. In addition to preventing the increase, it is possible to avoid the danger of giving a bias amount greatly deviating from the focus bias amount at which the jitter amount is minimized.

According to a third aspect of the present invention, in addition to the above configuration, the maximum jitter amount indicating the maximum value of the allowable range of the jitter amount is set in advance, and the allowable jitter amount exceeds the maximum jitter amount. Sometimes, the focus bias amount at which the corresponding jitter amount becomes the maximum jitter amount is detected,
The set bias amount is obtained based on the detected focus bias amount. That is, the maximum value of the jitter amount is set, the range in which the jitter amount does not exceed the maximum value is set as the effective range of the focus bias amount, and the best focus bias amount within the effective range is obtained. Therefore, it is possible to set the focus bias amount to the best value even when reading an optical disk having a large amount of jitter.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a relationship between a focus bias amount and a jitter amount.

FIG. 2 is an explanatory diagram showing a relationship between a focus bias amount and a jitter amount.

FIG. 3 is an explanatory diagram showing a relationship between a focus bias amount and a jitter amount.

FIG. 4 is an explanatory diagram showing a relationship between a focus bias amount and a jitter amount.

FIG. 5 is a block diagram showing an electrical configuration of an embodiment of an optical disk reading device according to the present invention.

FIG. 6 is a circuit diagram showing detailed electrical connections of a drive circuit.

FIG. 7 is a flowchart showing a main operation of the embodiment.

FIG. 8 is a flowchart showing a main operation of the embodiment.

FIG. 9 is an auxiliary diagram showing a method of determining a focus bias amount according to the related art.

[Explanation of symbols]

Reference Signs List 1 optical disk 15 pickup B1, B2, B4, B5 Focus bias amount corresponding to allowable jitter amount B10, B11 Focus bias amount corresponding to maximum jitter amount BMAX, BMIN Limit value of focus bias amount C1, C2, C4, C7 Setting bias Amount J1, J5, J10, J13 Minimum value of jitter amount J3, J7, J11, J14 Allowable jitter amount JMAX Maximum jitter amount ΔJ Predetermined value added to minimum value of jitter amount

Claims (3)

[Claims] 1. A focus bias amount corresponding to an optical disk to be read by detecting a correspondence between a focus bias amount for shifting a reference position of a focus of the pickup and a jitter amount of data read by the pickup. In an optical disc reader that seeks, the jitter amount corresponding to each focus bias amount is detected while changing the focus bias amount,
The minimum value of the jitter amount is determined, the jitter amount obtained by adding a predetermined value to the determined minimum value of the jitter amount is defined as the allowable jitter amount, and the focus bias amount corresponding to the optical disk to be read is set as the set bias amount. Then, a focus bias amount at which the corresponding jitter amount becomes an allowable jitter amount is detected in each of two directions of a direction in which the focus bias amount is increased and a direction in which the focus bias amount is decreased, and the detected focus is detected in the two directions. An optical disc reading apparatus, wherein an intermediate value of the bias amount is set as the set bias amount. 2. A method according to claim 1, wherein a change range of the focus bias amount is set in advance, and when the corresponding jitter amount does not reach the allowable jitter amount even if the focus bias amount is changed to the limit value of the change range, the change is not performed. 2. The optical disk reading device according to claim 1, wherein the set bias amount is obtained by using a focus bias amount that is a limit value of the range. 3. A maximum jitter amount indicating a maximum value of an allowable range of the jitter amount is preset, and when the allowable jitter amount exceeds the maximum jitter amount, a focus bias amount at which the corresponding jitter amount becomes the maximum jitter amount is detected. 3. The optical disk reading device according to claim 1, wherein the set bias amount is obtained based on the detected focus bias amount.