Abstract:
A laser beam power studying system for studying laser power in a reproducing mode and a recording mode of an optical recording apparatus. A laser beam having different powers in the recording mode and the reproduction mode is emitted and a first part of the laser beam is measured. A second part of the laser beam is measured by a front photo diode and a signal corresponding to the measurement by the front photo diode is amplified by a single amplifier in both reproducing recording study operations. Relational expression between measurements of the first part of the laser beam and the second part of the laser beam at different power levels of the laser beam is developed for both the recording and reproducing modes.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of Korean Patent Application No. 2005-44365, filed on May 26, 2005 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a system for studying power of a laser beam, and, more particularly, to a laser beam power studying system for presetting references for control of power of a laser beam in a manufacturing process of an optical recording/reproduction apparatus.  
         [0004]     2. Description of the Related Art  
         [0005]     In general, an optical recording/reproduction apparatus includes a recording automatic power control (APC) circuit controlling power of a laser beam in a recording operation, and a reproduction APC circuit controlling power of a laser beam in a reproduction operation, and is adapted to maintain the power of the laser beam at a predetermined value through the use of the recording or reproduction APC circuit when recording or reproducing data on an optical disc.  
         [0006]     Such a conventional optical recording/reproduction apparatus is disclosed in Korean Patent Laid-open Publication No. 2004-2232. As disclosed in the Korean publication 2004-2232, the conventional optical recording/reproduction apparatus includes a radio frequency (RF) unit including recording and reproduction APC circuits, a read only memory (ROM) storing offset values of the recording and reproduction APC circuits for outputs of optimum recording laser beam power and optimum reproduction laser beam power, a voltage value of the optimum recording laser beam power, and a voltage value of the optimum reproduction laser beam power, a microcomputer setting offsets of the recording and reproduction APC circuits, a voltage of recording laser beam power and a voltage of reproduction laser beam power on the basis of the values stored in the ROM, respectively, when the optical recording/reproduction apparatus is powered on, and an optical pickup adjusting the voltage of the recording or reproduction laser beam power in response to an output signal from a front photodiode fed back to the optical pickup in a recording or reproduction mode. With this configuration, the conventional optical recording/reproduction apparatus is adapted to properly control the laser beam power in the reproduction or recording mode.  
         [0007]     The conventional optical recording/reproduction apparatus utilizes the offset values and voltage values stored in the ROM as references for the control of the reproduction and recording laser beam powers. Although not disclosed in detail in the above publication, these values are obtained by studying the reproduction and recording laser beam powers in advance in a manufacturing process of the optical recording/reproduction apparatus. At this time, a reproduction laser beam power studying operation and a recording laser beam power studying operation are performed separately from each other, thus involving separate studying paths.  
         [0008]     In the reproduction laser beam power studying operation, the optical pickup outputs photovoltage signals of different levels depending on different powers of a laser beam. The photovoltage signals are amplified by a first amplifier of an analog signal processor (ASP) and then input to the microcomputer. Then, the microcomputer stores the laser beam powers and the levels of output voltages from the first amplifier of the ASP and controls the reproduction laser beam power using the stored values.  
         [0009]     Similarly, in the recording laser beam power studying operation, the optical pickup outputs photovoltage signals of different levels depending on different powers of a laser beam. The photovoltage signals are amplified by a second amplifier of the ASP and then inputted to the microcomputer. Then, the microcomputer stores the laser beam powers and the levels of output voltages from the second amplifier of the ASP and controls the recording laser beam power using the stored values.  
         [0010]     However, such a conventional laser beam power studying system is disadvantageous in that, because the different amplifiers are used in the recording laser beam power studying operation and the reproduction laser beam power studying operation, the accurate setting of references for laser beam power control may be difficult due to gain and offset differences between the amplifiers. In addition, the recording laser beam power studying path and the reproduction laser beam power studying path must be controlled separately from each other, thereby increasing load on the microcomputer.  
         [0011]     Moreover, the use of inaccurate references for laser beam power control may cause the laser beam power control to be performed inaccurately or for a longer time.  
       SUMMARY OF THE INVENTION  
       [0012]     Therefore, an aspect of the invention is to provide a laser beam power studying system wherein a same amplifier is used in a recording laser beam power studying operation and a reproduction laser beam power studying operation, thus raising reliability of the laser beam power studying results and simplifying the circuit configuration of the system.  
         [0013]     The above and/or other aspects are achieved by providing a laser beam power studying system comprising: a laser diode emitting a laser beam having different powers in a recording mode and a reproduction mode; a front photodiode receiving a part of the laser beam from the laser diode and converting the received laser beam part into a photocurrent signal; an analog signal processor amplifying a photovoltage signal obtained by performing a current/voltage conversion operation with respect to the photocurrent signal, with reference to a reference voltage signal, to provide an output voltage signal; and a microcomputer deriving an output voltage signal-to-laser beam power relational expression in a reproduction laser beam power studying operation or a recording laser beam power studying operation by repeatedly varying the laser beam power in the reproduction or recording mode, wherein the analog signal processor includes a single amplifier amplifying the photovoltage signal in the reproduction laser beam power studying operation and the recording laser beam power studying operation.  
         [0014]     The single amplifier may be set to different gains and different offsets in the reproduction laser beam power studying operation and the recording laser beam power studying operation.  
         [0015]     The analog signal processor may further include: a gain storage unit storing a reproduction gain and a recording gain to be applied to the amplifier in the reproduction laser beam power studying operation and the recording laser beam power studying operation, respectively; and a first multiplexer selecting one of the reproduction gain and the recording gain stored in the gain storage unit according to whether the system is in the reproduction laser beam power studying operation or the recording laser beam power studying operation, and applying the selected gain to the amplifier as the gain to be set in the amplifier in the reproduction laser beam power studying operation or the recording laser beam power studying operation. As used in this application, an expression of the form one of A and B and expression of the form A or B have a same meaning.  
         [0016]     The analog signal processor may further include: an offset storage unit storing a reproduction offset and a recording offset to be applied to the amplifier in the reproduction laser beam power studying operation and the recording laser beam power studying operation, respectively; and a second multiplexer selecting one of the reproduction offset and the recording offset stored in the offset storage unit according to whether the system is in the reproduction laser beam power studying operation or the recording laser beam power studying operation, and applying the selected offset to the amplifier as the offset to be set in the amplifier in the reproduction laser beam power studying operation or the recording laser beam power studying operation.  
         [0017]     The analog signal processor may further include a level shifter set to different levels in the reproduction laser beam power studying operation and the recording laser beam power studying operation, and the level shifter may shift the photovoltage signal to the different levels in the reproduction laser beam power studying operation and the recording laser beam power studying operation and supply the level-shifted photovoltage signal to the amplifier.  
         [0018]     The analog signal processor may further include: a level storage unit storing a reproduction level and a recording level to be applied to the level shifter, respectively, in the reproduction laser beam power studying operation and the recording laser beam power studying operation; and a third multiplexer selecting one of the reproduction level and the recording level stored in the level storage unit according to whether the system is in the reproduction laser beam power studying operation or the recording laser beam power studying operation, and applying the selected level to the level shifter as the level to be set in the level shifter in the reproduction laser beam power studying operation or the recording laser beam power studying operation.  
         [0019]     Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:  
         [0021]      FIG. 1  is a block diagram showing a configuration of a laser beam power studying system according to an embodiment of the present invention; and  
         [0022]      FIG. 2  is a detailed block diagram of an analog signal processor shown in  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0023]     Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the present invention by referring to the figures.  
         [0024]      FIG. 1  shows a configuration of a laser beam power studying system according to an exemplary embodiment of the present invention. As shown in  FIG. 1 , the laser beam power studying system comprises a pickup  10 , a laser beam power meter  20 , an analog signal processor (ASP)  30 , a microcomputer/digital signal processor (DSP) unit  40 , and a studying control personal computer (PC)  50 .  
         [0025]     The pickup  10  includes a laser diode  11  emitting a laser beam, a laser diode driver  12  driving the laser diode  11 , an objective lens  13  focusing the laser beam from the laser diode  11  on an optical disc to form a spot thereon, a photodiode  14  receiving a laser beam reflected from the optical disc and converting the received laser beam into a current signal, and a front photodiode (FPD)  15  receiving a part of the laser beam from the laser diode  11  and converting the received laser beam part into a photocurrent signal corresponding to an amount of the received laser beam. The laser beam emitted from the laser diode  11  is fed mostly to the objective lens  13 , and partially to the FPD  15 .  
         [0026]     The laser diode driver  12  includes a register (not shown) storing laser diode drive voltage values of multiple levels to enable the laser diode  11  to emit laser beams with multiple power levels in a laser beam power studying operation. These drive voltage values are set by the microcomputer/DSP unit  40 . In the laser beam power studying operation, the laser diode driver  12  sequentially supplies the laser diode drive voltage values stored in the register to the laser diode  11  to vary power of the laser beam to be emitted from the laser diode  11 .  
         [0027]     The photocurrent signal from the FPD  15  is converted into a photovoltage signal Vfpdo by a current to voltage (I/V) converter  17  and then input to the ASP  30 . A reference voltage signal Vref is also applied to the ASP  30 . The FPD  15  has a characteristic of outputting a photocurrent signal of a lower level when receiving a laser beam with larger power.  
         [0028]     The laser beam power meter  20  measures power of a laser beam passed through the objective lens  13 .  
         [0029]     Referring now to  FIG. 2 , the ASP  30  includes a level shifter  32 , a level storage unit  37 , a first multiplexer  34 , an amplifier  31 , a gain storage unit  33 , a second multiplexer  36 , an offset storage unit  35 , and a third multiplexer  38 .  
         [0030]     The level shifter  32  shifts the photovoltage signal Vfpdo from the pickup  10  to different levels in a reproduction laser beam power studying operation and a recording laser beam power studying operation. For example, in a playback-only system, the pickup  10  outputs a photovoltage signal Vfpdo higher than a specific voltage in a reproduction mode. In contrast, in a recording/reproduction system, the pickup  10  outputs a photovoltage signal Vfpdo lower than the specific voltage in a recording mode. The level shifter  32  adjusts the photovoltage signal Vfpdo from the pickup  10  to the specific voltage.  
         [0031]     The level storage unit  37  is a register, and stores a reproduction level that is the level to which the photovoltage signal Vfpdo from the pickup  10  is to be shifted by the level shifter  32  in the reproduction laser beam power studying operation, and a recording level that is the level to which the photovoltage signal Vfpdo from the pickup  10  is to be shifted by the level shifter  32  in the recording laser beam power studying operation.  
         [0032]     The third multiplexer  38  selects one of the reproduction level and the recording level stored in the level storage unit  37  in response to a switching signal from the microcomputer/DSP unit  40  and applies the selected level to the level shifter  32 .  
         [0033]     The amplifier  31  has a plus terminal receiving the reference voltage signal Vref and a minus terminal for receiving the level-shifted photovoltage signal Vfpdo. The amplifier  31  is also set to different gains and different offsets in the reproduction laser beam power studying operation and the recording laser beam power studying operation. As a result, in the reproduction laser beam power studying operation and the recording laser beam power studying operation, the level-shifted photovoltage signal Vfpdo is amplified with the different gains and different offsets and then provided as an output voltage signal Vout.  
         [0034]     The gain storage unit  33  is a register, and stores a reproduction gain to be applied to the amplifier  31  in the reproduction laser beam power studying operation, and a recording gain to be applied to the amplifier  31  in the recording laser beam power studying operation.  
         [0035]     The first multiplexer  34  selects one of the reproduction gain and the recording gain stored in the gain storage unit  33  in response to the switching signal from the microcomputer/DSP unit  40  and apply the selected gain to the amplifier  31  such that the amplifier  31  is set to the reproduction gain in the reproduction laser beam power studying operation and to the recording gain in the recording laser beam power studying operation.  
         [0036]     The offset storage unit  35  is a register, and stores a reproduction offset to be applied to the amplifier  31  in the reproduction laser beam power studying operation, and a recording offset to be applied to the amplifier  31  in the recording laser beam power studying operation.  
         [0037]     The second multiplexer  36  selects one of the reproduction offset and the recording offset stored in the offset storage unit  35  in response to the switching signal from the microcomputer/DSP unit  40  and applies the selected offset to the amplifier  31  such that the amplifier  31  is set to the reproduction offset in the reproduction laser beam power studying operation and to the recording offset in the recording laser beam power studying operation.  
         [0038]     The microcomputer/DSP unit  40  stores the output voltage signal Vout from the ASP  30  and derives a correlation between the stored output voltage signal Vout and the corresponding laser beam power. The microcomputer/DSP unit  40  also receives analog signals other than the output voltage signal Vout from the ASP  30 , converts the received analog signals into digital signals, processes the converted digital signals, and controls the pickup  10  and ASP  30  depending on the processed signals. The studying control PC  50  controls the entire operation of the laser beam power studying system. Although the microcomputer/DSP unit  40  is disclosed in the present embodiment to be a single block, the microcomputer and the DSP may be implemented as separate blocks.  
         [0039]     A description will hereinafter be given of the operation of the laser beam power studying system described above with reference to  FIGS. 1 and 2 . Notably, it is impractical to actually measure and control power of a laser beam passed through the objective lens  13  of the pickup  10  in a recording or reproduction mode of an optical recording/reproduction apparatus. For this reason, references for control of power of a laser beam are preset through the recording or reproduction laser beam power studying operation in a manufacturing process of the optical recording/reproduction apparatus and the laser beam power is controlled in the recording or reproduction mode on the basis of the preset references.  
         [0040]     The reproduction laser beam power studying operation is performed by acquiring a plurality of sets of data. First, the microcomputer/DSP unit  40  supplies the switching signal to the first multiplexer  34  and second multiplexer  36  such that the amplifier  31  is set to the reproduction gain and reproduction offset. The microcomputer/DSP unit  40  also supplies the switching signal to the third multiplexer  38  such that the reproduction level is applied to the level shifter  32 . Then, for a first set of data, the microcomputer/DSP unit  40  applies a first one of n (where n is a natural number&gt;2) reproduction laser diode drive voltage values stored in the register of the laser diode driver  12  to the laser diode  11  such that the laser diode  11  emits a laser beam of power corresponding to the first reproduction laser diode drive voltage value.  
         [0041]     The laser beam emitted from the laser diode  11  is passed through the objective lens  13  and the power thereof is then measured by the laser beam power meter  20 . The FPD  15  receives a part of the laser beam from the laser diode  11  and converts the received part into a photocurrent signal, which is in turn converted into a photovoltage signal Vfpdo and input to the level shifter  32 . The level shifter  32  shifts the photovoltage signal Vfpdo to the reproduction level and outputs the level-shifted photovoltage signal Vfpdo to the amplifier  31 . The amplifier  31  amplifies the level-shifted photovoltage signal Vfpdo input thereto by the reproduction gain and outputs the amplified signal as an output voltage signal Vout. The output voltage signal Vout from the amplifier  31  is transferred to the microcomputer/DSP unit  40 , which stores the transferred output voltage signal Vout and a corresponding reproduction laser beam power value. The Vout and the corresponding laser beam power level value are included in the data set.  
         [0042]     Thereafter, the microcomputer/DSP unit  40  determines whether a predetermined number of data sets have been acquired. Upon determining that the predetermined number of data sets have not been acquired, the microcomputer/DSP unit  40  repeats the data acquisition using another one of the stored reproduction laser diode drive values. However, if it is determined that the predetermined number of data sets have been acquired, the microcomputer/DSP unit  40  obtains an output voltage signal-to-reproduction laser beam power relational expression based on a plurality of stored output voltage signals Vout and a plurality of stored reproduction laser beam powers (i.e., the plurality of the data sets) and stores the obtained relational expression. Note that the reproduction laser diode drive voltage values stored in the register of the laser diode driver  12  are sequentially applied to the laser diode  11  so that a laser beam with different power is emitted from the laser diode  11  during the acquisition of each data set.  
         [0043]     The output voltage signal-to-reproduction laser beam power relational expression, obtained in the above manner, becomes a reference for control of reproduction laser beam power in the optical recording/reproduction apparatus with the pickup  10  shown in  FIGS. 1 and 2 .  
         [0044]     The recording laser beam power studying operation is performed by acquiring a second plurality of sets of data. First, the microcomputer/DSP unit  40  supplies the switching signal to the first multiplexer  34  and second multiplexer  36  such that the amplifier  31  is set to the recording gain and recording offset. The microcomputer/DSP unit  40  also supplies the switching signal to the third multiplexer  38  such that the recording level is applied to the level shifter  32 . Then, for a first set of the second plurality of sets of data, the microcomputer/DSP unit  40  applies a first one of n (where n is a natural number&gt;2) recording laser diode drive voltage values stored in the register of the laser diode driver  12  to the laser diode  11  such that the laser diode  11  emits a laser beam of power corresponding to the first recording laser diode drive voltage value.  
         [0045]     The laser beam emitted from the laser diode  11  is passed through the objective lens  13  and the power thereof is then measured by the laser beam power meter  20 . The FPD  15  receives a part of the laser beam from the laser diode  11  and converts the received part into a photocurrent signal, which is in turn converted into a photovoltage signal Vfpdo and then inputted to the level shifter  32 . The level shifter  32  shifts the photovoltage signal Vfpdo to the recording level and outputs the level-shifted photovoltage signal Vfpdo to the amplifier  31 . The amplifier  31  amplifies the level-shifted photovoltage signal Vfpdo inputted thereto by the recording gain and outputs the amplified signal as an output voltage signal Vout. The output voltage signal Vout from the amplifier  31  is transferred to the microcomputer/DSP unit  40 , which then stores the transferred output voltage signal Vout and the corresponding recording laser beam power.  
         [0046]     Subsequently, the microcomputer/DSP unit  40  determines whether a predetermined number of data sets of the second plurality of data sets have been acquired. If it is determined that the predetermined number of the second plurality of data sets has not been acquired, the microcomputer/DSP unit  40  repeats the data acquisition using another one of the stored recording laser diode drive values. However, if it is determined that the predetermined number data sets have been acquired, the microcomputer/DSP unit  40  obtains an output voltage signal-to-recording laser beam power relational expression based on a plurality of stored output voltage signals Vout and a plurality of stored recording laser beam powers (i.e., the second plurality of the data sets) and stores the obtained relational expression. Note that the recording laser diode drive voltage values stored in the register of the laser diode driver  12  are sequentially applied to the laser diode  11  so that a laser beam with different power can be emitted from the laser diode  11  during the acquisition of each data set. The predetermined number of times the data acquisition is repeated determines a quality of the relational expression. For better results, the predetermined number should be at least three in the reproducing mode and at least three in the recording mode.  
         [0047]     The output voltage signal-to-recording laser beam power relational expression, obtained in the above manner, becomes a reference for control of recording laser beam power in the optical recording/reproduction apparatus with the pickup  10  shown in  FIGS. 1 and 2 .  
         [0048]     As set forth in the above description, aspects of the present invention provide a laser beam power studying system wherein the same amplifier is used in a recording laser beam power studying operation and a reproduction laser beam power studying operation. Therefore, it is possible to prevent references for laser beam power control from being inaccurately set due to the use of separate amplifiers with different gains and different offsets in the recording laser beam power studying operation and the reproduction laser beam power studying operation.  
         [0049]     In addition, the use of one amplifier in an analog signal processor, not two amplifiers as in the conventional system, simplifies the circuit configuration of the present system.  
         [0050]     Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.