KR100223182B1 - Pit depth compensation method of optical disc system - Google Patents

Abstract

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Description

Pit Depth Correction Method of Optical Disc System

The present invention relates to an optical disc system, and more particularly, to a method for automatically correcting a change in a characteristic of a tracking error signal according to a difference in pit depth in a tracking servo method in which a tracking error signal is obtained through phase difference detection. will be.

Digital Versatile Discs (CDs) or Compact Discs (CDs) express information by grooves called pits, and the laser beam is reflected on the recording surface where the information is recorded. The beam is detected and the signal is reproduced. In optical discs such as DVDs and CDs, the tracking balance is controlled so that the laser beam tracks the pit rows accurately, especially when the laser beam is in the center of the pit. The source technology related to tracking balance correction is described in patent application No. 96-51271 (hereinafter referred to as a prior application) filed by the same applicant.

The pre-receiving source receives the light intensity distribution according to the change of the relative position of the beam and the pit reflected from the disk into the photodetector divided into four, and the tracking error is based on the phase difference of the diagonal signals A + C and B + D. It proposes a technique applied to a tracking servo method of obtaining a signal. The prior application generates a tracking balance correction voltage for setting the value of the tracking error signal to zero in a digital signal processor (DSP) that receives the tracking error signal and controls the phases of the diagonal signals to match.

On the other hand, when the tracking error signal is obtained from the optical disc, it is affected by the pit depth. The pit depth of the disc /4( : Laser wavelength), the light distribution incident on the photodiode is symmetrical with the radial direction as the axis. At this time, even if the objective lens is shifted in the tangential direction of the track, the phases of the diagonal signals A + C and B + D detected by the photodiode match to obtain a normal tracking error signal.

However, in general, the pit depth Since the incident light distribution of the photodiode is asymmetric with respect to the radial direction since it is smaller than / 4, a phase difference, or delay, occurs between the diagonal signals A + C and B + D detected by the photodiode. . Accordingly, the level of the detected tracking error signal is reduced and an offset at which the center voltage is changed is generated.

Phase delay due to the pit depth has a problem that can not be corrected by the existing tracking balance correction voltage. More specifically, the existing tracking balance correction voltage corrects only the offset of the diffraction characteristic generated between the diagonal signals, so that the phase delay occurring between the photodetection signals generated in the photodiode due to the pit depth difference, that is, A need arises for correcting the phase delay between the photodetection signals which become asymmetrical with respect to the radial direction described above, apart from the conventional tracking balance correction.

SUMMARY OF THE INVENTION An object of the present invention for solving the above-described problems is that in an optical disc system that obtains a tracking error signal through differential phase detection (DPD), the center voltage of the tracking error signal is increased due to the difference in the depth of the pit on the optical disc. The present invention provides a method for automatically correcting a characteristic change of a tracking error signal that changes and decreases in level.

1 is a configuration diagram showing a tracking servo of an optical disc system to which the present invention is applied;

2 is a view showing a variable state of the actuator driving voltage according to the present invention,

3 is a flow chart showing a pit depth correction method according to the present invention.

* Explanation of symbols for main parts of the drawings

11 disc 12 pickup circuit

13: delay 14: tracking error amplifier

15: Digital Signal Processor (DSP)

In order to achieve the above object, a pit depth correction method of an optical disc system includes an optical disc system that obtains a tracking error signal in accordance with a phase difference detection method, which is generated between diagonal signals detected at a photodiode according to a difference in pit depth on an optical disc. A method for correcting a phase difference, the method comprising: (1) measuring a level and an offset of a tracking error signal corresponding to a tracking actuator driving voltage in a reference state; (2) changing the tracking actuator driving voltage from the driving voltage in the reference state and measuring the level and offset of the tracking error signal in response thereto; (3) determine a delay amount such that an error between the level and the offset of the tracking error signal measured in the second step with respect to the level and the offset of the tracking error signal measured in the first step (1) is minimized; Correcting a phase difference generated between the diagonal signals detected by the photodiode by the amount.

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

1 is a configuration diagram showing a tracking servo of an optical disc system to which a correction method according to the present invention is applied. The apparatus of FIG. 1 has a pickup circuit (P / U) 12 which shoots a laser beam onto the optical disc 11 and detects the beam reflected from the optical disc 11 with four photodetectors and outputs the detected signal. do. The tracking error amplifier 14 is connected to the output terminal of the pickup circuit 12 to detect the phase difference between the diagonal signals A + C and B + D in the four photodetectors to generate the tracking error signal TE. The tracking error amplifier 14 performs overall servo control and receives the tracking error signal TE to correct the characteristic of the tracking error signal according to the difference of the pit depth, that is, the level is reduced and the center voltage is changed. A digital signal processor (DSP) 15 for generating a control signal for the connection is connected.

Meanwhile, the phase of the diagonal signal A + C is delayed between the pickup circuit 12 and the tracking error amplifier 14 according to the control signal (delay value TD) supplied from the digital signal processor 15 in the apparatus of FIG. 1. The retarder 13 is connected. The digital signal processor 15 is configured to supply a drive voltage TRD to an actuator not shown in the pickup circuit 12.

The operation of the apparatus of FIG. 1 configured as described above will be described with reference to the flowchart of FIG. 3.

The digital signal processor 15 which implements the servo control unit first turns on a focus (FOCUS) servo, which is not shown, and turns off the tracking servo, according to the method described in the above-mentioned prior application. Correct the tracking balance.

When the tracking balance correction is completed, the digital signal processor 15 measures the characteristic values of the tracking error signal while varying the actuator driving voltage. Here, the variable state of the actuator driving voltage is shown in FIG.

The digital signal processor 15 outputs to the tracking actuator (not shown) in the pickup circuit 12 the center value of 3 shown in Fig. 2 as the drive voltage TRD of the actuator in the reference state. When the tracking actuator driven according to the driving voltage TRD ③ moves the objective lens, the characteristics of the tracking error signal according to the depth of the pit on the optical disc are changed and detected by the photodetector, and then through the tracking error amplifier 14. Since it is supplied to the digital signal processor 15, the digital signal processor 15 measures the offset and level of the response tracking error signal TE (step 310). The digital signal processor 15 changes the actuator driving voltage TRD to a value of 1 shown in FIG. 2 and outputs it. Then, the offset and the level of the tracking error signal TE detected in response as described above are measured (step 320). When the offset and level of the tracking error signal measured in steps 310 and 320 are respectively measured, the digital signal processor 15 performs the offset and level of the tracking error signal measured in step 320 by the offset and level of the tracking error signal measured in step 320. The first amount of delay TD ₁ of the retarder 13 shown in FIG.

When the first delay amount TD ₁ is obtained in step 330, the digital signal processor 15 changes the actuator driving voltage TRD to a value of ② shown in FIG. 2 and outputs the tracking signal. The offset and level of the error signal are measured (step 340). Next, the digital signal processor 15 performs the same method as in step 330 so that the offset and level of the tracking error signal measured in step 340 are minimized to the offset and level of the tracking error signal measured in step 310. The second delay amount TD ₂ of the retarder 13 shown in FIG. 1 is obtained (step 350).

The digital signal processor 15 calculates an average value of the first delay amount TD ₁ and the second delay amount TD ₂ obtained in the above-described steps 330 and 350, respectively, and converts the obtained average value into the final value of the delay unit 13. The delay amount TD is determined (step 360) and supplied to the delay unit 13 shown in FIG. With this sequential comparison method, if the amount of change in the offset and level of the detected tracking error signal falls within the allowable error range, the digital signal processor 15 corrects and controls the characteristic change of the tracking error signal due to the pit depth on the optical disc. To exit.

When the delayed amount TD determined according to the above is supplied to the delayer 13 shown in Fig. 1, the delayer 13 is applied to the pit depth of the signals detected and output from each of the four photodetectors in the pickup circuit. Due to this, a signal component having an asymmetry occurring with respect to the radial direction of the optical disk is delayed by the delay amount TD supplied from the digital signal processor 15 and supplied to the tracking error amplifier 14 to thereby provide a depth of pit on the optical disk. By correcting the characteristic change of the tracking error signal according to the result, accurate tracking is possible.

As described above, the pit depth correction method of the optical disc system according to the present invention provides an effect of automatically correcting the characteristic change of the tracking error signal according to the difference of the pit depth on the optical disc.

Claims (3)

In an optical disc system that obtains a tracking error signal according to a phase difference detection method, a method for correcting a phase difference generated between diagonal signals detected by a photodiode according to a difference in pit depth on an optical disc, (1) measuring the level and offset of the tracking error signal corresponding to the tracking actuator drive voltage in a reference state; (2) changing the tracking actuator driving voltage from the driving voltage in the reference state and measuring the level and offset of the tracking error signal in response thereto; (3) determine a delay amount such that an error between the level and the offset of the tracking error signal measured in the second step with respect to the level and the offset of the tracking error signal measured in the first step (1) is minimized; Correcting a phase difference occurring between the diagonal signals detected by the photodiode by the amount. The method of claim 1, wherein step (2) (2a) increasing the actuator driving voltage to measure the values; (2b) obtaining a first delay amount such that an error between the values measured in the steps (2a) and (1) is minimized; (2c) reducing the actuator drive voltage to measure the values; And (2d) obtaining a second delay amount such that an error between the values measured in the steps (2c) and (1) is minimized. The method of claim 2, wherein step (3) And determining a mean value of the first delay amount and the second delay amount obtained in the steps (2b) and (2d) and determining the average value as the delay amount for the phase difference correction.