KR100256645B1 - Method for controlling focus bias in optical disc system - Google Patents

Abstract

PURPOSE: An adjusting method for a focus bias in an optical disk system is provided to perform focus bias adjustment based on a focus bias voltage having a minimum jitter amount. CONSTITUTION: An established focus bias voltage is applied to a focus servo circuit(S2). Jitters of a reproducing signal read from an optical unit are sampled based on the focus bias voltage(S3). Then, the jitter having minimum jitter amount is detected(S4). In case of the jitter amount the same of lower than an established jitter amount, focus bias adjustment is completed(S12). In case of the detected minimum jitter amount over the established jitter amount, the focus bias voltage is increased or decreased to sampling jitters of the reproducing signal.

Description

How to Adjust Focus Bias in Optical Disc System

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disc system, in particular to a method of adjusting the focus bias of a focus servo circuit which controls the signal plane of the disc to be located within the depth of focus of the laser beam.

In general, an optical disk system reads data on a disk by injecting a laser beam into a signal surface of the disk and converting light reflected from the signal surface of the disk into an electrical signal.

At this time, data can be read correctly only if the signal plane of the disc is located within the depth of focus of the laser beam. The operation of controlling the signal plane of the disc to be located within the depth of focus of the laser beam is called focus servo.

1 is a block diagram for such a focus servo.

In FIG. 1, digital information is recorded along a track in the optical disc 100, and the optical pickup unit 110 enters the laser beam focused by the objective lens 100a onto the signal surface of the disc 100. After that, the light reflected from the signal surface of the disk 100 is converted into an electrical signal and output. Here, the focus error signal detector 120 detects the focus error signal from the signal output from the optical pickup unit 110 and provides it to the phase compensator 130. At this time, the focus error signal is an electrical signal indicating the degree of deviation of the signal plane of the disk 100 within the depth of focus of the laser beam. On the other hand, the phase compensation amplifier 130 phase compensates and amplifies a focus error signal to provide it to the focus driver 140, and the focus driver 140 corresponds to the output voltage level of the phase compensation amplifier 130. The actuator coil 150 is driven, and accordingly, the focus actuator coil 150 adjusts the objective lens 110a in the optical pickup unit 110 in the up and down directions to perform the focus servo.

Ideally, the focus error signal should have a value of zero if such a signal servo accurately positions the disk's signal plane within the laser's depth of focus. However, even if the disk's signal surface is precisely located within the depth of focus of the laser beam due to the limitations of mechanical assembly or defects, the focus error signal may have a certain level. Therefore, if the signal surface of the disk is located exactly within the depth of focus of the laser beam, the focus error signal should be adjusted so that it does not have a certain level. Such adjustment is called focus bias adjustment.

In general, focus bias adjustment is performed by applying a certain level of focus bias voltage to a focus error signal. In the past, such a focus bias voltage was determined through an experiment or the like, and the determined focus bias voltage was set. However, in the case of performing the focus bias adjustment in this manner, it is difficult to adaptively cope with the unique characteristics of each system, it is difficult to expect accurate focus bias adjustment.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and focus bias adjustment is performed based on a focus bias voltage of which the jitter amount is minimized by referring to the jitter amount of the reproduction signal read out from the optical pickup unit, and thus the system inherent characteristics. The purpose is to provide a focus bias adjustment method that can be more adaptively coped.

In order to achieve the above object, the present invention provides a focus bias adjustment method of an optical disc system in which a focus bias of a focus servo circuit is adjusted with reference to the jitter amount of a reproduction signal read out from an optical pickup unit. A first step of applying a set focus bias voltage; A second step of sampling the jitters of the reproduction signals read out from the optical pickup unit based on the focus bias voltage applied to the focus bias circuit, and detecting the jitter of the m jitters with the minimum amount of jitter; A third step of completing the focus bias adjustment if the jitter amount of the minimum jitter detected in the second step is less than or equal to a preset jitter amount; When the jitter amount of the minimum jitter detected in the second step is larger than the preset jitter amount, the fourth step of performing the second step after increasing or decreasing the focus bias voltage is characterized in that it comprises.

1 is a view showing a general focus servo device,

2 is a hardware configuration diagram for performing a focus bias adjustment method of the present invention;

3 is a detailed flowchart according to a preferred embodiment of the present invention.

<Explanation of symbols for main parts of drawing>

200: disk 210: optical pickup unit

220: focus servo unit 230: bias adjustment unit

240: jitter detection unit 250: sampling unit

260 control unit

Hereinafter, with reference to the accompanying drawings will be described in detail the present invention.

FIG. 2 is a hardware configuration diagram for performing the focus bias adjustment method of the present invention. The optical pickup which reads and outputs a radio frequency (RF) signal from the disk 200 and the disk, and outputs an electrical signal for focus servo control. A focus servo unit 220 for detecting a focus error signal from an electrical signal for focus servo control output from the unit 210 and the optical pickup unit 210 and performing focus servo corresponding to the level of the focus error signal; Preset the jitter provided from the bias adjustment unit 230 for adjusting the focus bias of the unit 220, the jitter detector 240 for detecting jitter of the RF signal output from the optical pickup unit 210, and the jitter detector 230 Focus bar in a direction in which the jitter amount is reduced based on the jitter provided from the sampling unit 250 and the sampling unit 250 to sample and output at a time interval. It consists of a controller 260 for controlling the bias adjusting unit 230 so that the ground is adjusted.

3 is a detailed flowchart illustrating a preferred embodiment of the focus bias adjustment method of the present invention. The focus bias adjustment method of FIG. 3 is performed using the hardware of FIG.

Therefore, hereinafter, the focus bias adjustment method of FIG. 3 will be described with reference to FIG. 2.

First, when the disk 200 is loaded in the optical disk system (S1), the bias adjusting unit 230 is controlled to apply the first bias voltage (V _t , t = integer) to the focus servo unit 220 (S2). The pickup unit 210 is controlled to drive the optical pickup unit 210.

The focus servo unit 220 adjusts the focus bias based on the first bias voltage V _t , and in such a situation, the optical pickup unit 210 is driven by the control of the controller 260 to provide the RF from the disk 200. The signal is detected and output.

The jitter detector 240 receives an RF signal from the optical pickup unit 210, measures jitter from the RF signal, and provides the same to the sampling unit 250. When the sampling start signal is input from the controller 260, the sampling unit 250 samples the jitter provided from the jitter detector 240 at predetermined time intervals and provides the same to the controller 260.

When m (m; integer) sampled jitter is input from the sampling unit 250, the controller 260 provides a sampling end signal to the sampling unit 250 (S3), and then, among the m sampled jitters, the jitter amount is the highest. The small value J _k , k = integer is detected (S4) and stored in the internal memory (S5). Then, the controller 260 compares whether J _k is less than or equal to the reference jitter amount J _t (S6).

In this case, the above-described first bias voltage (V _t ) is determined through experiments, and based on the general characteristics of the optical disk system, after measuring the voltage that can minimize the jitter amount through the experiment, the inside of the control unit 260 It is stored in memory and applied. Thus, if the optical disc system is in a state not departing from general system characteristics like other optical disc systems, the jitter amount J _k based on the above-described first bias voltage may be lower than or equal to the reference jitter amount J _t . If the optical disc system has its own characteristics beyond the general characteristics due to mechanical assembly limitations or defects, even if the first bias voltage V _t is input to the focus servo unit 220, It will have a value higher than the jitter amount J _k .

On the other hand, if J _k in S6 process is greater than the reference jitter amount (J _t), control unit 260 is the second bias voltage to control the bias adjusting unit 230 is higher than the first bias voltage (V _t) (V _{t + 1} = V _t + V _n is applied to the focus servo unit 220 (S7).

Therefore, the bias adjuster 230 provides the second bias voltage V _{t + 1} to the focus servo unit 220 under the control of the controller 260, and the focus servo unit 220 is provided by the bias adjuster 230. The focus servo is performed based on the second bias voltage V _{t + 1} .

In this state, the optical pickup unit 210 detects the RF signal and provides it to the jitter detector 240, and the jitter detector 240 measures the jitter from the RF signal and provides it to the sampling unit 250. The control unit 260 provides a sampling start signal to the sampling unit 250. Accordingly, the sampling unit 250 samples the jitter provided from the jitter detecting unit 240 at predetermined time intervals and provides the sampling unit 250 to the control unit 260.

When the m (m; integer) sampled jitter is input from the sampling unit 250, the controller 260 provides the sampling end signal to the sampling unit 250 (S8), and the jitter amount among the m sampled jitters is the highest. The small value J _{k + 1} is detected (S9) and stored in the internal memory (S10). Then, the controller 260 compares whether J _{k + 1} is less than or equal to the reference jitter amount J _t (S11). As a result of the comparison, if J _{k + 1} is less than or equal to the reference jitter amount J _t , the control unit 260 determines that the focus bias adjustment is completed, and ends the focus bias adjustment (S12), but J _{k + 1} is the reference. When larger than the jitter amount J _t , J _{k + 1} and J _k are compared again (S13).

Here, if J _{k + 1} is smaller than J _k , the focus bias adjustment by the S7 process is approaching more accurately, but if J _{k + 1} is larger than J _k , the focus bias adjustment will be wrong.

Thus, the J _{k + 1} is smaller than J _k controller 260 is a bias adjustment unit 230 to be applied with the high third bias voltage (V _{t + 1} + V _n = V _{t + 2)} than V _{t + 1} After the control (S14), the above-described t → t + 1, k → k + 1 is set (S15, S16), the S8 process and the following processes are repeated. Also J _{k + 1} is large, the control unit 260 has a lower fourth bias voltage higher than V _t than the J _k - and then the control of the bias adjuster 230 such that the (V _t V _n = V _t-1) is applied (S17) In the above-described t → t-1, k → k + 1 is set (S18, S16), and the process S8 and the like are repeated.

At this time, in the above-described steps S4 and S9, the detection of the smallest jitter amount among the m sampled jitters is because the amount of jitter increases instantaneously due to a defect in a predetermined section on the disc. It is for detecting.

In other words, even if the focus bias adjustment is made correctly, the amount of jitter can be instantaneously increased due to dots or scratches on the disc. Therefore, if the focus bias adjustment is made based on the instantaneously increased jitter amount due to the above-described causes, the correct focus bias adjustment will not be made. After detecting m jitters, the focus is based on the minimum detected jitter. By performing the bias adjustment, more accurate focus bias adjustment can be performed.

As described above, according to the present invention, the focus bias adjustment is performed based on the focus bias voltage of which the jitter amount is minimized by referring to the jitter amount of the reproduction signal read out from the optical pickup unit, thereby more adaptively coping with the characteristics peculiar to the system. In addition, after sampling the j jitter, by performing the focus bias adjustment based on the minimum amount of jitter in the m jitter, it is possible to perform a more accurate focus bias adjustment.

Claims (1)

A focus bias adjustment method of an optical disc system for adjusting a focus bias of a focus servo circuit by referring to the jitter amount of a reproduction signal read out from an optical pickup unit: A first step of applying a preset focus bias voltage to the focus servo circuit; A second step of sampling the jitters of the reproduction signals read out from the optical pickup unit based on the focus bias voltage applied to the focus bias circuit, and detecting the jitter of the m jitters with the minimum amount of jitter; A third step of completing the focus bias adjustment if the jitter amount of the minimum jitter detected in the second step is less than or equal to a preset jitter amount; If the jitter amount of the minimum jitter detected in the second step is greater than the predetermined jitter amount, the method of adjusting the focus bias of the optical disc system comprising the fourth step of increasing or decreasing the focus bias voltage, and performing the second step. .

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