GB2391311A

GB2391311A - Apparatus and method for detecting beam power in optical drive

Info

Publication number: GB2391311A
Application number: GB0324795A
Authority: GB
Inventors: Pyong-Yong Seong; Jong-Koog Lee; Kun-Soo Kim; Yong-Jun Cho; Sung-Du Kwon
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 2001-07-18
Filing date: 2002-07-10
Publication date: 2004-02-04
Anticipated expiration: 2022-07-10
Also published as: GB0324795D0; GB2391311B

Abstract

An apparatus for detecting beam power generated by a plurality of light sources, using a single device, includes a light-receiving unit PD3 that receives the beam power generated by one of the plurality of light sources, first and second amplifying units 402,403 that amplify beam power received by the light-receiving unit according to first and second predetermined gains respectively, and outputs the amplified beam power, and a switch SW3 for selecting and outputting one of the beam power outputs from the first and second amplifying units 402,403 as the detected beam power. Detected beam power (or amplification gain) is amplified by a gain determined according to the characteristics of the respective light sources. Thus, it is possible to provide the beam power detected in consideration of a sufficient dynamic range for each light source, thereby realizing effective Auto Power Control.

Description

239131 1

APPARATUS AND METHOD FOR DETECTING BEAM

POWER IN OPTICAL DRIVE:

5 The present invention relates to an optical drive having a plurality of light sources, and more particularly, to an apparatus for detecting beam power generated by a plurality of light sources, using a single device and a method therefore.

In an optical drive having a plurality of light sources, it is possible to use optical media on which data is recorded or reproduced with different wavelengths. To record data on or reproduce data from two different discs, is e.g., a disc classified as a compact disc (CD) and a disc classified as a digital versatile disc (DVD), in one optical drive, the optical drive has a light source for a CD and a light source for a DVD. This is because the standard wavelengths required for recording data on or 20 reproducing data from CDs and DVDs are different from each other. However, the output of a light source becomes reduced when the temperature rises in the optical drive. To solve 25 this problem, the optical drives include an auto power control (APC) function of monitoring the beam power generated by a light source to control the power of the light source automatically.

30 The optical drive, however, monitors the beam power using one device. In other words, beam power generated by a plurality of light sources are detected via one monitor photo diode (MPD). Therefore, the amplification gain (or

( 2 sensitivity) of the MPD is set to be uniform for the plurality of light sources. However, if there is a difference between the maximum beam powers generated by a plurality of light sources, it is difficult to ensure a 5 sufficient dynamic range for detecting the beam power generated by each light source. For this reason, it is impossible to realize an APC that consistently provides the light power required.

lo Figure 1 is a graph explaining the relationship between the beam power required in an optical drive having light sources for a CD and a DVD and the beam power in the optical drive detected by MPD. Referring to Figure 1, the maximum beam power from the light source for a CD is seen to be twice as great as that from the light source for a DVD and the amplification gain of the MPD is the same for both light sources. In this case, the light source for a CD has a sufficient dynamic range for detecting the beam power, whereas the light source for a DVD has half of the 20 dynamic range required. To solve this problem, it was suggested that monitor photo diodes (MPDs) that have amplification gains corresponding to the respective light sources be attached to an optical drive. However, this has disadvantages in that the optical drive has to be more 25 spacious to include the MPDs, and further, the installation of the MPDs increases the manufacturing costs. It is an aim of the present invention to provide an 30 apparatus for detecting the beam power in an optical drive having a plurality of light sources, using one device which has a sufficient dynamic range for detecting the

( 3 maximum beam power in the plurality of light sources, and a method therefore.

According to the present invention there is provided 5 an apparatus and method as set forth in the appended claims. Preferred features of the invention will be apparent from the dependent claims, and the description

which follows.

lo According to a first aspect of the present invention there is provided an apparatus for detecting the beam power in an optical drive having a plurality of light sources. The apparatus includes a light-receiving unit that receives light generated by one of the plurality of 15 light sources; a first amplifying unit that amplifies beam power received by the lightreceiving unit according to a first predetermined gain and outputs amplified beam power; a second amplifying unit that amplifies beam power, which is received by the light-receiving unit according to a 20 second predetermined gain, and outputs amplified beam power; and a switch that selects and outputs one of the beam power output from the first and second amplifying units as the detected beam power.

25 Preferably, the switch is controlled in response to a selection signal that is generated differently according to the type of an optical medium used.

Preferably, the first predetermined gain is determined 30 by a first variable resistance and a first feedback gain resistance, and the second predetermined gain is determined by a second variable resistance and a second feedback gain resistance.

( 4 Preferably, the values of the first and second variable resistance are determined such that the corresponding one of the plurality of light sources has a 5 little scatter and linear characteristics.

According to another aspect of the present invention there is provided a method for detecting the beam power in an optical drive having a plurality of light sources. The 10 method includes receiving light generated by one of the plurality of light sources; amplifying the beam power received by a first predetermined gain, and outputting the same; amplifying the beam power received by a second predetermined gain and outputting the same; and selecting 15 one of the beam power amplified by the first predetermined gain and the beam power amplified by the second predetermined gain according to the type of an optical medium used, and outputting the beam power selected as the detected beam power.

For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings in which: Figure 1 is a graph of the relationship between light power provided by an optical drive having light sources for a CD and for a DVD, and the output of a monitor photo diode (MPD); Figure 2 is a diagram of a circuit of an apparatus for detecting the beam power in an optical drive according to a third embodiment of the present invention; and

( 5 Figure 3 is a graph of the relationship between optical powers provided by an optical drive having light sources for a CD and a DVD and the output of a monitor 5 photo diode (MPD) according to embodiments of the present invention. Figure 2 is a diagram of a circuit of an apparatus for detecting the beam power in an optical drive according to lo a first embodiment of the present invention. The apparatus of Figure 2 detects the beam power in an optical drive using a plurality of amplifying units that amplify light received to a predetermined level according to a predetermined gain in consideration of a plurality of 15 light sources according to the type of an optical medium used in the optical drive.

The apparatus for detecting the beam power in an optical drive shown in Figure 2 includes a photo diode 20 PD3, a current-to-voltage amplifying unit (hereinafter, "I/V amplifying unit") 401 and amplifying units 402 and 403. The photo diode PD3 functions as a light-receiving unit that receives light generated by one of a plurality of light sources (not shown) included in an optical drive.

25 If this optical drive is realized such that both a disc classified as a CD and a disc classified as a DVD operate therein, a plurality of light sources consist of a light source for the CD and a light source for the DVD, and the beam power generated by the light source for the CD or the 30 light source for the DVD is received by the photo diode PD3.

f 6 The I/V amplifying unit 401 includes an amplifier AMP1 in which resistances R1 and R2 are connected to a feedback loop and to which a reference voltage Vref is applied via an input terminal. The I/V amplifying unit 401 converts s an electric current generated according to light received by the photo diode PD3 into a voltage and outputs the same. The first amplifying unit 402 includes an amplifier 0 AMP4. In the amplifier AMP4, a bias resistance R7 is connected to an input terminal to which a reference voltage Vref is applied and a feedback gain resistance G4 is connected to a feedback loop. Also, a variable resistance VR4 is connected to an input terminal to which 15 a voltage output from I/V amplifying unit 401 is applied.

The value of the variable resistance VR4 is determined such that the corresponding light source has little scatter and linear characteristics.

20 The first amplifying unit 402 amplifies a voltage output from the I/V amplifying unit 401 to a predetermined level according to a gain which divides the feedback gain resistance G4 by the variable resistance VR4, i. e. G4/VR4, and outputs the resultant. The voltage output from the 25 first amplifying unit 402 is sent to one of terminals of the switch SW3.

Meanwhile, the second amplifying unit 403 includes an amplifier AMPS. In the amplifier AMPS, a bias resistance 30 R8 is connected to an input terminal to which a reference voltage Vref is applied, and a feedback gain resistance G5 is connected to a feedback loop. Also, a variable resistance VR5 is connected to an input terminal to which

a voltage output from the I/V amplifying unit 401 is applied. The value of the variable resistance VR5 is determined so that the corresponding light source has little scatter and linear characteristics.

Therefore, the second amplifying unit 403 amplifies a voltage output from the I/V amplifier 401 to a predetermined level according to a gain which divides the feedback gain resistance G5 by the variable resistance lo VRS, i.e., G5/VR5, and outputs the voltage. The voltage output from the second amplifying unit 402 is sent to the other terminal of the switch SW3.

The switch SW3 selects one of a signal output from the 15 first amplifying unit 402 and a signal output from the second amplifying unit 403 in response to a selection signal and outputs the selected signal. At this time, the signal output is the detected beam power. The selection signal is the same as a gain selection signal and is 20 generated differently according to the type of an optical medium used in the optical drive. The gain selection signal can be generated by a servo controller (not shown) in the optical drive.

25 In a method for detecting the beam power in an optical drive according to the present invention, when the beam power is detected by one lightreceiving device, the detected beam power may be amplified and output according to a predetermined gain by the number of the light sources 30 in the optical drive as explained in the first embodiment referring to Figure 2. For example, in the event that two light sources are included in the optical drive, the beam power received is amplified and output according to a gain

which is determined to be proper to one light source, and then the beam power received is amplified and output according to a gain which is determined to be proper to the other light source. In addition, one of these beam 5 power that are amplified and output as described above, may be selected and output as the detected beam power.

In apparatuses for detecting the beam power in an optical drive having light sources for a CD and a DVD, lo according to the embodiments of the present invention, the relationship between the beam power required in the respective light sources (which is illustrated on an axis of X of Figure 3) and the detected beam power (which is illustrated on an axis of Y of Figure 3) is as shown in 15 Figure 3. Referring to Figure 3, it is noted that a sufficient dynamic range for detecting the maximum beam power can be ensured by controlling the amplification gain of the beam power generated by different light sources 20 As described above, in an optical drive having a plurality of light sources, detected beam power is amplified by a gain determined according to the characteristics of the respective light sources when the beam power generated by a light source is detected via a 25 device. Therefore, it is possible to provide the beam power detected in consideration of a sufficient dynamic range for the each light source, thereby realizing effective APC.

30 The specific terms used here are not intended to restrict the present invention to any of the above embodiments. It will be understood by those skilled in the art that various changes in form and details may be

made without departing from the scope of the invention as defined by the appended claims.

The reader's attention is directed to all papers and 5 documents which are filed concurrently with or previous to this specification in connection with this application and

which are open to public inspection with this specification, and the contents of all such papers and

documents are incorporated herein by reference.

All of the features disclosed in this specification

(including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification

(including any accompanying claims, abstract and 20 drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any

30 accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. An apparatus for detecting the beam power generated by a plurality of light sources, the apparatus 5 comprising: a light-receiving unit for receiving light generated by one of the plurality light sources; lo a first amplifying unit for amplifying beam power received by the lightreceiving unit according to a first predetermined gain and outputting amplified beam power; a second amplifying unit for amplifying beam power, 15 which is received by the light-receiving unit according to a second predetermined gain and outputting amplified beam power; and a switch for selecting and outputting one of the beam 20 power output from the first and second amplifying units as the detected beam power.

2. The apparatus of claim 1, wherein the switch is controlled in response to a selection signal that is 25 generated differently according to the type of an optical medium used.

3. The apparatus of claim 1 or 2, wherein the first predetermined gain is determined by a first variable 30 resistance and a first feedback gain resistance, and the second predetermined gain is determined by a second variable resistance and a second feedback gain resistance.

4. The apparatus of claim 3, wherein the values of the first and second variable resistances are determined such that the corresponding one of the plurality of light sources has little scatter and linear characteristics.

5. A method for detecting the beam power in an optical drive having a plurality of light sources, the method comprising: lo receiving light generated by one of the plurality of light sources; amplifying the beam power received by a first predetermined gain, and outputting the same; amplifying the beam power received by a second predetermined gain and outputting the same; and selecting one of the beam powers amplified by the 20 first predetermined gain and the beam power amplified by the second predetermined gain according to the type of an optical medium used, and outputting the beam power selected as the detected beam power.

25

6. An apparatus for detecting the beam power in an optical drive having a plurality of light sources, substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.

30

7. A method for detecting the beam power in an optical drive having a plurality of light sources, substantially as hereinbefore described.