KR100240342B1 - Focus servo device of optical disk player - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus servo device of an optical disc player employing a holographic optical pickup unit, wherein the amount of light used for detecting a focus error among the lights picked up from the optical pickup unit and output by being divided into three parts is detected by a current. A first photodetector A and a second photodetector B output as signals; The calculation unit adds the output signals of the first photodetector A and the second photodetector B by adding the current signals outputted from the first and second photodetectors A and B, and dividing them in two, respectively. 32); A first I / V converter 34 for converting a current signal obtained by adding the output signal of the first photodetector A and the output signal of the calculator 32 into a voltage signal; A second I / V converter 35 for converting a current signal obtained by adding the output signal of the second photodetector B and the output signal of the calculator 32 into a voltage signal; A focus error detector (37) for detecting the focus error signal by comparing the output signals of the first and second I / V converters (34, 35) and obtaining the difference signal; And a compensator 39 for providing a compensation signal for compensating for a focus error in accordance with the focus error signal detected by the focus error detector 37 to the optical pickup unit. This has the effect of making the focus servo run more smoothly.

Description

Focus Servo of Optical Disc Player

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus servo apparatus of an optical disk player, and more particularly, to an optical disk player that can execute a focus servo smoothly without an effect of noise in executing a focus servo in an optical disk player employing a holographic optical pickup unit. Relates to a focus servo device.

With the development of audio and video media, optical disc players for recording and reproducing video and audio data on semi-permanent optical discs have been developed.

Such an optical disc player reproduces an image and / or audio recorded on an optical disc and outputs it through a screen and / or a speaker, and has a higher signal-to-noise ratio than conventional image and / or audio reproducing apparatus, resulting in better image quality and / or Or it can reproduce the signal with sound quality, it does not generate noise due to irregular reproduction and modulation, very low distortion, no ghost and random access, so it is rapidly developed and widely distributed. There is a trend.

In addition, such an optical disk player includes a compact disk player (CDP), a laser disk player (LDP), a compact disk graphic player (CDGP), and a video compact disk player (VCDP: video compact disk player) has been developed and widely used. Also, recently, a digital video disk (DVD) using MPEG-2 moving picture compression technology and a digital video disk player for playing the same have been developed. It can record and play back gigabytes (GB) of data including moving images on a 12cm optical disc such as a CD, and it is also designed to be compatible to play current CDs and VCDs.

On the other hand, in such an optical disc player, optical is used to read data as described above. In order to read data accurately recorded on the optical disc, it is necessary to accurately focus the light on the data surface recorded on the optical disc. That is, it is necessary to follow the focus of the light according to the surface vibration according to the rotation of the optical disk, that is, the vertical movement of the disk.

Therefore, in such an optical disc reproducing apparatus, a focus servo apparatus is adopted to focus the light irrespective of the vertical vibration of the optical disc, which focuses the optical disc used to read data recorded on the optical disc surface. The main purpose is to read the data recorded on the optical disk accurately by moving the optical pickup, that is, the objective lens, up and down in accordance with the movement of the optical disk to focus the light accurately on the surface of the optical disk.

On the other hand, the focus servo apparatus of such an optical disc player divides the light reflected by the main beam from the optical pickup unit into equal areas, detects the amount of light reflected and picked up for each of them, and detects the detected amount of light. Is added in a diagonal direction, and then a four-segment focus servo device that detects a focus error signal by detecting a difference signal between these signals and executes focus servo has been mainly used.

FIG. 1 is a schematic block diagram illustrating a general four-segment focus servo device, including an optical detector 10, first and second I / V (current / voltage) converters 12 and 14, and a focus error detector ( 16) and the compensation unit 18.

That is, the first light detector (A), the second light detector (B), the third light detector (C) and the fourth light detector (D) constituting the light detection unit 10 reflect the amount of light picked up on the disk. Are detected and output as current signals, respectively, and the light amount signals detected by the first and third photodetectors A and C are added to each other and provided to the first I / V converter 12, and the second and fourth photodetectors The light quantity signals detected at (B, D) are added to each other and provided to the second I / V converter 14.

Then, the first and second I / V converters 12 and 14 convert the current signals, which are added together, into voltage signals, and provide them to the focus error detector 16. The focus error signal is detected by obtaining the difference signal between the voltage signals provided from the first and second I / V converters 12 and 14, and the focus error signal is provided to the compensator 18.

Then, the compensator 18 provides a focus servo by providing a compensation signal for compensating for the focus error from the focus error signal provided by the focus error detector 18 to the optical pickup unit (not shown).

However, in recent years, a device has been developed to detect a focus error and execute a focus servo by using a hologram unit to pick up light from a disc, and to perform a focus servo. While the conventional optical pickup device generally consists of six elements, the device can be composed of three elements: a hologram unit, a reflecting mirror, and an objective lens, which enables not only miniaturization and thinning, but also optical adjustment during assembly. It is easy to use, and the use thereof is gradually expanded due to advantages such as high reliability due to vibration.

However, since the focus servo device of the optical disc player is generally configured to fit into a quadrant system, a separate circuit configuration is required to apply the hologram optical pickup.

Fig. 2 is a schematic block diagram showing a focus servo device of an optical disk player employing the holographic optical pickup unit as described above.

As shown in FIG. 2, the focus servo apparatus according to the hologram method includes a light detector 20 including a first photodetector A, a second photodetector B, and a third photodetector C, and a first photodetector 20. And two I / V converters 22 and 24, a focus error detector 26 and a compensator 28.

By the way, the focus servo device using the hologram method shown in FIG. 2 uses a three-division method while the conventional focus servo device is a four-division method, and substantially, in the first and second photodetectors A and B, respectively. Only the detected light quantity signal is used for the focus servo.

That is, the current signal according to the amount of light detected by the third photodetector C is divided in half through the parallel-connected resistors R1 and R2 and output from the first photodetector A and the second photodetector B, respectively. The currents are added to the first and second I / V converters 22 and 24, respectively, and the amount of light detected by the first and second photodetectors A and B is transmitted by the focus error detector 26. This is because the focus error may be too small to be detected. In other words, the amount of light detected by the third photodetector C is used to increase the light intensity in the focused state.

However, in this case, noise flows in the path leading to the first and second I / V converters 22 and 24 by dividing the resistors R1 and R2 into two resistors R1 and R2. There was a problem that could affect.

Accordingly, the present invention has been made to solve such a problem in the related art, and an object of the present invention is to accurately focus by preventing the inflow of noise components in executing a focus servo in an optical disk player employing a holographic optical pickup unit. It is to provide an error detection and smoothly execute the focus servo accordingly.

According to a preferred embodiment of the present invention for achieving the above object, in the focus servo device of the optical disk player for smoothly executing the focus servo in the optical disk player adopting a holographic optical pickup unit, the optical pickup A first optical detector which detects an amount of light of one light used for detecting a focus error among the light picked up from the unit and outputted in three divisions, and outputs it as a current signal; A second photodetector which detects an amount of light of another light used to detect a focus error and outputs the current signal as a current signal, and divides the current signal output from the first and second photodetectors and divides the output into two and outputs the sum; Therefore, in addition to the output signal of the first photodetector and the second photodetector, respectively Is an operation unit, a first I / V conversion unit for converting a current signal obtained by adding the output signal of the first photodetector and the output signal of the operation unit into a voltage signal, an output signal of the second photodetector and the operation unit The second I / V converter converts the current signal summed with the output signal into a voltage signal, and compares the output signals of the first and second I / V converters to obtain the difference signal, thereby detecting the focus error signal. And a compensation unit for providing a focus error detection unit and a compensation signal for compensating for a focus error according to the focus error signal detected by the focus error detection unit to the optical pickup unit.

1 is a schematic block diagram showing a conventional four-focus focus servo device;

2 is a block diagram showing a focus servo device of an optical disk player employing a conventional hologram optical pickup unit;

Fig. 3 is a block diagram showing a focus servo device of an optical disc player employing a holographic optical pickup unit according to a preferred embodiment of the present invention.

* Description of the symbols for the main parts of the drawings *

30: light detector 32: calculator

34, 35: I / V converter 37: Focus error detector

39: Compensation part OP: Operational amplifier

R: resistance

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

3 is a block diagram showing a focus servo device of an optical disk player according to a preferred embodiment of the present invention.

As shown in FIG. 3, the focus servo apparatus of the optical disk player according to the preferred embodiment of the present invention includes a light detector 30, resistors R3, R4, including first and second photodetectors A and B, respectively. An arithmetic unit 32 consisting of R5, R6, R7, R8, R9 and an operational amplifier OP, first and second I / V converters 34 and 35, a focus error detector 37 and a compensator ( 39) and is configured.

The first photodetector A detects and outputs, as a current signal, an amount of light for one light used to obtain a focus error signal among the lights provided by being divided into three from a holographic optical pickup unit (not shown). In addition, the second photodetector B detects and outputs, as a current signal, an amount of light for the other light used to obtain a focus error signal among the lights provided by being divided into three from the holographic optical pickup unit.

The operation unit 32 adds the current signals output from the first photodetector A and the second photodetector B through the resistors R3, R4, R5, and R6, and then through the operational amplifier OP. By amplifying to a predetermined level and dividing the signal amplified by the resistors R8 and R9 into two, the output signal of the first photodetector A and the output signal of the second photodetector B are respectively added. On the other hand, resistors R3, R4 and resistors R5, R6, R8, and R9 each have the same resistance value, and resistor R7 has twice the resistance of resistors R5, R6, R8, and R9. Has a value.

In addition, a signal obtained by adding the output signal of the first photodetector A and the output signal of the calculator 32 is provided to the first I / V converter 34, and outputs the output signal of the second photodetector B. The signal obtained by adding the output signals of the calculator 32 is provided to the second I / V converter 35.

Then, the first I / V converter 34 converts the current signal obtained by adding the output signals of the first photodetector A and the calculator 32 into a voltage signal, and provides it to the focus error detector 37. The second I / V converter 35 converts the current signal obtained by adding the output signals of the second photodetector B and the calculator 32 into a voltage signal and provides the converted signal to the focus error detector 37.

Therefore, the focus error detector 37 compares the output signal of the first I / V converter 34 and the output signal of the second I / V converter 35 with each other and obtains the difference signal to obtain the focus error signal. The detected focus error signal is provided to the compensator 39.

Accordingly, the compensator 39 outputs a compensation signal such that the focus error signal provided by the focus error detector 37 becomes '0' to achieve the focus servo.

As described above, according to the present invention, the output signals of the first and second photodetectors A and B are used to increase the light sensitivity, and the output signals of the third photodetector C, which are noise inflow components, are used. Since it has not been done, the focus error detector 37 can obtain an accurate focus error without noise in the state where the optical sensitivity is increased.

As described above, the present invention has an effect that the focus servo can be executed more smoothly by obtaining an accurate focus error without the influence of noise components in the optical disk player employing the hologram optical pickup unit.

Claims (1)

A focus servo apparatus of an optical disk player for allowing a focus servo to smoothly execute in an optical disk player employing a hologram optical pickup unit, A first photodetector (A) which detects an amount of light of one light used for detecting a focus error among the lights picked up from the optical pickup unit and split into three parts and outputs the current signal; A second photodetector (B) which detects an amount of light of another light used for detecting a focus error among the lights picked up from the optical pickup unit and split into three parts and outputs the current signal; The calculation unit adds the output signals of the first photodetector A and the second photodetector B by adding the current signals output from the first and second photodetectors A and B, and dividing the current signals into two parts. (32); A first I / V converter 34 for converting a current signal obtained by adding the output signal of the first photodetector A and the output signal of the calculator 32 into a voltage signal; A second I / V converter 35 for converting a current signal obtained by adding the output signal of the second photodetector B and the output signal of the calculator 32 into a voltage signal; A focus error detector (37) for detecting a focus error signal by comparing the output signals of the first and second I / V converters (34, 35) and obtaining the difference signal; And a compensator (39) for providing a compensation signal for compensating for a focus error in accordance with the focus error signal detected by the focus error detector (37) to the optical pickup unit.

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