Patent Publication Number: US-8115661-B2

Title: Automatic power control system for optical disc drive and method thereof

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of U.S. patent application Ser. No. 12/603,762, now U.S. Pat. No. 7,948,409 filed on Oct. 22, 2009, which is a Continuation-In-Part of U.S. patent application Ser. No. 12/273,601, filed on Nov. 19, 2008, issued as U.S. Pat. No. 7,903,006, which is a Continuation application of U.S. patent application Ser. No. 11/758,119, filed on Jun. 5, 2007, issued as U.S. Pat. No. 7,474,235, which claims the benefit of U.S. Provisional Application No. 60/811,017, filed on Jun. 5, 2006, the entirety of which are incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to optical disk drives, and more particularly to automatic power control for optical disc drives. 
     2. Description of the Related Art 
     A pickup head of an optical disk drive projects a laserbeam onto a data layer of an optical disk to write data thereto or read data therefrom. When the pickup head emits the laserbeam with a high power level, the laserbeam melts the data layer of the optical disk or changes the phase of the data layer, scarfing data patterns thereon, thereby recording data onto the optical disk. When the pickup head emits the laserbeam with a low power level which can not melt/change the data layer of the optical disk, the pickup head decodes data according to the pattern of the reflection of the laserbeam from the disk, thereby reading data from the optical disk. A pickup head of an optical disk therefore must be capable of generating laserbeams with different power levels corresponding to the different functions of the optical disk drive. 
     A pickup head generates a laserbeam with a laser diode. The power level of the laserbeam emitted by the laser diode is controlled by a driving current. When the pickup head continues to generate the laserbeam, the laserbeam gives off heat which increases the temperature of the pickup head. Along with increasing temperature of the pickup head, driving current must be increased, thus controlling the laser diode to emit the laserbeam with a constant power level. Referring to  FIG. 1 , a schematic diagram of a relationship between a driving current level and a laserbeam power level is shown. When the pickup head is operated in a temperature T 1 , the relationship between the driving current level and the laserbeam power level is depicted by a line L 0 . When the temperature of the pickup head is changed to T 2 , the relationship between the driving current level and the laserbeam power level is changed to lines L 1  or L 2 . The lines L 0  and L 1  have different offset levels Ith(T 1 ) and Ith(T 2 ) for generating a laserbeam with a minimum power level, and the lines L 0  and L 2  have different slopes s(T 1 ) and s(T 2 ). 
     To prevent the power level of the laserbeam from decreasing when the temperature of the pickup head increases, the optical disk drive must comprise an automatic power control mechanism to adjust the driving current of the laser diode according to the temperature, thus maintaining the laserbeam at a constant power level. Referring to  FIG. 2 , a schematic diagram of signals generated by a conventional automatic power control mechanism is shown. The conventional automatic power control mechanism is a closed-loop control mechanism. When a pickup head writes data to an optical disk with a laserbeam, the pickup head generates a driving current for controlling a laser diode (LD) to generate the laserbeam, and a front monitor diode (FMD) detects the power of laserbeam and generate an FMD output signal. The FMD output signal is sampled as references for adjusting the driving current of the laser diode. In  FIG. 2 , the laserbeam generated by the laser diode comprises multiple power levels, such as cooling power, erase power, write power, and over drive power, etc., in order to write data onto disk. Two power levels including for example a write power level and an erase power level are respectively sampled according to corresponding sample pulses for power level adjustment. 
     When the optical disk is a blu-ray disk, data density is increased. The laserbeam for writing data onto the blu-ray disk therefore has power levels that last for a shorter duration which is becoming smaller as recording speed getting higher. Referring to  FIG. 3 , a schematic diagram of signals generated by an automatic power control mechanism corresponding to a blu-ray disk is shown. There are two different writable area in a blu-ray disk, the data area and the APC area. APC area is utilized to perform automatic power control and data area is utilized to write the normal data. When a pickup head writes data (such us NRZ (Non-Return to Zero) signal in  FIG. 3 ) to the blu-ray disk with a high recording speed, each power level of the laserbeam only lasts for a short duration. Because a front monitor diode requires a longer time period to appropriately generate a stable output signal, the FMD output signal does not converge to a real amplitude during the period for each power level and cannot be taken as feedback for correct automatic power control. The APC area is being set to solved this problem, but the APC area is relative smaller to the data area and the drive may not have enough time to get a stable write power in the beginning of the data writing. A method for automatic power control for an optical disk drive is therefore required. 
     BRIEF SUMMARY OF THE INVENTION 
     A method for calibrating an initial driving signal for driving an optical pick-up head of an optical disk drive is provided. On one embodiment, said optical disk drive is utilized for reading or writing data on an optical disk, the optical disk includes a plurality of auto power control areas (APC areas) and a plurality of data areas, and the APC areas and the data areas are interleaved in between. In at least one of the APC areas that before the data areas for a normal data writing, an initial driving signal is used for the normal data writing to drive the optical pick-up head to emit laserbeam. A detected level of the laserbeam is then obtained. An update initial driving signal is then calibrated according to the detected level and a target level. 
     The invention also provides an automatic power control system of an optical disk drive having a pick-up head with a front monitor diode. In one embodiment, said optical disk drive is utilized for reading or writing data on an optical disk. The optical disk includes a plurality of auto power control areas (APC areas) and a plurality of data areas. The APC areas and the data areas are interleave in between. The system comprises a power initialization unit and a compensator. In at least one of the APC areas that before the data areas for a normal data writing, an initial driving signal is used for the normal data writing to drive the optical pick-up head to emit laserbeam. The compensator is for obtaining a detected level of the laserbeam detected by the front monitor diode, and calibrating an update initial driving signal according to the detected level and a target level. 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1  is a schematic diagram of a relationship between a driving current level and a laserbeam power level; 
         FIG. 2  is a schematic diagram of signals generated by a conventional automatic power control mechanism; 
         FIG. 3  is a schematic diagram of signals generated by an automatic power control mechanism corresponding to a blue-ray disk; 
         FIG. 4  is a block diagram of an embodiment of an automatic power control system according to one of the embodiments; 
         FIG. 5  is a flowchart of a method for automatic power control for an optical disk drive according to one of the embodiments; 
         FIG. 6  is a schematic diagram of an embodiment of sampling of the detector output signal generated by the photo detector; 
         FIG. 7  is a schematic diagram of an embodiment of operations of the analog-to-digital converter and the compensator of  FIG. 5 ; 
         FIG. 8  is a flowchart of an operation method of a compensator according to one of the embodiments; 
         FIG. 9  is a flowchart of a method for making selection between a normal control mode and an APC control mode; 
         FIG. 10  is a block diagram of another embodiment of an automatic power control system of an optical disk drive according to one of the embodiments; 
         FIG. 11  is a schematic diagram of signals of an embodiment of an automatic power control process; 
         FIG. 12  is a block diagram of an automatic power control system of an optical disk drive according to one of the embodiments; 
         FIG. 13  is a flowchart of a method for automatic power control for an optical disk drive according to one of the embodiments; 
         FIG. 14  is a block diagram of a laser diode driver according to one of the embodiments; 
         FIG. 15  is a schematic diagram of a relationship between a power level of a laserbeam and corresponding driver enable signals; 
         FIG. 16  is a block diagram of an embodiment of a compensator according to one of embodiments; 
         FIG. 17  is a schematic diagram of an embodiment of a test power pattern of a laser beam emitted by the laser diode according to one of the embodiments; 
         FIG. 18  is a schematic diagram of another embodiment of a test power pattern of a laser beam emitted by the laser diode according to one of the embodiments; 
         FIG. 19  is a schematic diagram of an embodiment of automatic power initialization with a pre-recording process according to one of the embodiments; and 
         FIG. 20  is a schematic diagram of another embodiment of automatic power initialization with a pre-recording process according to one of the embodiments. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best-contemplated mode of carrying out embodiments. This description is made for the purpose of illustrating the general principles of the embodiments of the invention and should not be taken in a limiting sense. The scope of the embodiments of the invention is best determined by reference to the appended claims. 
     An automatic power control (APC) system controls a power level of a laserbeam emitted by a pickup head for an optical disk drive. Referring to  FIG. 4 , a block diagram of an optical disk drive  400  comprising an automatic power control system  406  according to one of the embodiments is shown. In one embodiment, the optical disk drive  400  comprises a front monitor diode  410 , the automatic power control (APC) system  406 , a laser diode driver (LD driver)  416 , and a laser diode (LD)  418 . The laser diode driver  416  generates a driving signal I according to a plurality of driving component signals I 1 ˜I 4  and a plurality of driver enable signal OE 1 ˜OE 4 . The laser diode  418  then emits a laser beam with a power level determined by the driving signal I. Because the power level of the laserbeam reduces with the various operation condition (such as temperature increase or rotational speed increase). The APC system  406  therefore performs an automatic power control process to adjust the driving current I of the laser diode  418  in response to the various operation conditions, thus keeping the power level of the laser beam emitted by the laser diode  418  constant. 
     The front monitor diode  410  first samples a laser diode output power to obtain an analog input signal R. The automatic power control system  406  then adjusts the driving component signals I 1 ˜I 4  according to the analog input signal R. In one embodiment, the automatic power control system  406  comprises a write pulse generator  402 , a sampling pulse generator  404 , a controller  430 , two sample and hold circuits  412   a  and  412   b , two low pass filters (LPF)  411   a  and  411   b , an analog-to-digital converter (ADC)  413 , a compensator  414 , and a digital to analog converter (DAC)  415 . In this embodiment, although the laser diode  418  emits a laserbeam with a plurality of probable power levels, the automatic power control system  406  only uses two of the power levels to control the whole power levels. In this embodiment, using a write power level and an erase power level as an example. Referring to  FIG. 5 , a flowchart of a method for automatic power control for an optical disk drive  400  according to an embodiment of the invention is shown. First, the sample and hold circuits  412   a  and  412   b  respectively sample the analog input signal R according to sampling pulse signals SH 1  and SH 2  to obtain two analog input signals Sa 1  and Sb 1  respectively corresponding to the write power level and erase power level (step  902 ). The sampling pulse signals SH 1  and SH 2  are generated by the sampling pulse generator  404  to indicate which segment of the analog input signal R respectively corresponds to the power levels. The low pass filters  411   a  and  411   b  then respectively filter the analog input signals Sa 1  and Sb 1  to obtain signals Sa 2  and Sb 2 . 
     When the low pass filters  411   a  and  411   b  initially generates the filtered analog input signals Sa 2  and Sb 2 , the filtered analog input signals Sa 2  and Sb 2  are not stable and not available for further processing. The controller  430  then determines the timings for enabling a digitizing trigger signal AD_trig and a compensating trigger signal Ctrl_trig (step  904 ). In one embodiment, the controller  430  enables the digitizing trigger signal AD-trig when the filtered analog input signals Sa 2  and Sb 2  are stable. In one embodiment, the controller  430  will base on a signal APC_area to generate the digitizing trigger signal AD_trig and the compensating trigger signal Ctrl_trig. A disk surface read or written by the optical disk drive  400  is assumed to be divided into a plurality of auto power control areas (APC areas) and a plurality of data areas, wherein the APC areas and the data areas are spaced in between. The data areas are used for common data storage, and the APC areas are reserved for performing automatic power control processes. The APC-area signal indicates whether a laserbeam is projected on the APC areas of the disk surface. 
     When the digitizing trigger signal AD-trig is enabled, the analog-to-digital converter  413  then converts the filtered analog input signals Sa 2  or Sb 2  from analog to digital to obtain digital data Sa 3  or Sb 3  (step  906 ). Similarly, when analog-to-digital converter  413  initially generates the digital data Sa 3  or Sb 3 , the digital data Sa 3  or Sb 3  are not stable and not available for further processing. The controller  430  therefore enables the compensating trigger signal Ctrl-trig when the digital data Sa 3  or Sb 3  is stable. When the compensating trigger signal Ctrl-trig is enabled, the compensator  414  then generates component current signals d 1 , d 2 , d 3 , and d 4  according to the digital data Sa 3  or Sb 3  and a target level (step  908 ). In one embodiment, the compensator  414  compares the digital data Sa 3  (detected from the write power level) with a target write power level to generate a power level offset, and then adjusts the driving component signal d 3  (which use to drive the laser diode to emit write power level) to obtain an updated driving component signal d 3  according to the power level offset. Because the power levels are proportional, in one embodiment, the other updated driving component signals can be calculated base on the proportional and the power level offset. 
     The digital to analog converter  415  then converts the component current signals d 1 , d 2 , d 3 , and d 4  from digital to analog to obtain component current signals I 1 , I 2 , I 3 , and I 4  (step  910 ). The laser diode driver  416  then generates a driving current I according to the component current signals I 1 , I 2 , I 3 , and I 4  (step  912 ) and OE 1 ˜OE 4 . The write pulse generator  402  generates driver enable signals OE 1 , OE 2 , OE 3 , and OE 4  respectively corresponding to the component current signals I 1 , I 2 , I 3 , and I 4 . When a driver enable signal OEi is enabled, the laser diode driver  416  adds a corresponding component current signal Ii to the driving current I. Finally, the laser diode  418  generates the laserbeam with a power level determined by the driving current I, thus completing the automatic power control process. Thus, even if the temperature of the laser diode  118  changes, the laser diode  118  can still generate the laserbeam with an accurate power level P after the automatic power control process is performed. The optical disk drive  400  can then continue data writing. 
     Referring to  FIG. 6 , a schematic diagram of an embodiment of sampling of the analog input signal generated by the front monitor diode (FMD) is shown. When an automatic power control process is performed. The laser diode  418  projects a laserbeam on an APC area according to the control of write pulse generator, which is represent in signal WSR in  FIG. 6 . The power level of the laserbeam is alternately changed between two power levels I 2  and I 1 . In one embodiment, each power level has a duration of 20 T which is a minimum time period to make FMD output stable. The front monitor diode  410  needs time T 1  to stably detect the power level  12 , and needs time T 2  to stably detect the power level I 1 . After each segment of the analog input signal is stable, the sampling pulse generator  404  generates the sampling pulses SH 1  and SH 2  to trigger the sample and hold circuits  412   a  and  412   b  to sample the analog input signal, thus obtaining the analog input signals Sa 1  and Sb 1 . 
     Referring to  FIG. 7 , a schematic diagram of an embodiment of operations of the analog-to-digital converter  413  and the compensator  414  is shown. When the laser diode  418  is on APC areas of the disk surface, the automatic power control system  400  performs automatic power control processes. After the front monitor diode  410  generates an analog input signal, the sampling pulse generator  404  generates a sampling pulse signal SH 1  indicating the segment of the analog input signal corresponding to a first power level, and the sample and hold circuit  412   a  samples the analog input signal according to the sampling pulse signal SH 1  to obtain the analog input signal Sa 1 . When the analog input signal Sa 1  is stable, the controller  430  enables the digitizing trigger signal AD_trig, and the analog-to-digital converter  413  starts to convert the analog input signal Sa 1  from analog to digital to obtain an ADC data stream Sa 3 . When the ADC data stream Sa 3  is stable, the controller  430  enables the compensating trigger signal Ctrl_trig, and the compensator  414  starts to adjust the component driving current I 1  according to the ADC datastream Sa 3 . The digitizing trigger signal has a delay D 1  in comparison to an ADC_area signal indicating whether the disk surface illuminated by the laserbeam is an APC area, and the compensating trigger signal Ctrl_trig has a delay D 2  in comparison to the digitizing trigger signal D 2 . In one embodiment, the delay values D 1  and D 2  are zero. In addition, the APC system  400  can normally operate according to merely the compensating trigger signal Ctrl_trig even if no digitizing trigger signal AD_trig is generated. In one embodiment, the controller  430  only generates the compensating trigger signal Ctrl_trig to trigger compensation operations of the compensator  414 , and the analog-to-digital converter  413  directly converts the analog signals Sa 2  and Sb 2  to digital signals Sa 3  and Sb 3  without limiting of the digitizing trigger signal AD_trig. 
     Referring to  FIG. 8  a flowchart of an operation method of the compensator  414  according to one of the embodiments is shown. When the sampling and hold circuits  412   a  and  412   b  samples new sampled data Sa 1  and Sb 1 , and the analog-to-digital converter  413  generates new digital data Sa 3  and Sb 3  according to the new sampled data Sa 1  and Sb 1  (step  502 ), the compensator  414  adjusts the component driving currents I 1 ˜I 4  according to the new digital data Sa 3  and Sb 3  (step  504 ). Otherwise, when the sampling and hold circuits  412   a  and  412   b  samples no data Sa 1  and Sb 1 , the analog-to-digital converter  413  generates no data Sa 3  and Sb 3  (step  502 ), and the compensator  414  makes no adjustment to the component driving currents I 1 ˜I 4  (step  506 ). In other embodiment, the ADC can directly sample the analog input signal without the sample and hold circuit, and compensator will be controlled by the control signal Ctrl_trig to calculate the component driving current I 1 ˜I 4 . 
     The aforementioned automatic power control process provided by one of the embodiments is performed when the laserbeam emitted by the laser diode  418  is projected on an APC area. The aforementioned automatic power control process is therefore referred to as an APC area control mode automatic power control process. A conventional automatic power control process, however, is performed in companion with normal data writing on a data area. The conventional automatic power control process is therefore referred to as a normal control mode automatic power control process. The normal control mode automatic power control process operates with errors when a recording speed of the automatic power control system  400  surpasses a high speed level. A method for making a selection between the normal control mode and the APC control mode is therefore provided. Referring to  FIG. 9 , a flowchart of a method  600  for making selection between the normal control mode and the APC control mode is shown. When the recording speed of the automatic power control system  400  is greater than a threshold (step  602 ), the APC area control mode is determined (step  604 ). Otherwise, when the recording speed of the automatic power control system  400  is lower than the threshold (step  602 ), the normal control mode is determined (step  606 ). 
     Referring to  FIG. 10 , a block diagram of another embodiment of an optical disk drive  700  comprising an APC system  706  according to one of the embodiments is shown. The optical disk drive  700  shown in  FIG. 10  is similar to the automatic power control system  400  shown in  FIG. 4 , except for a digitizer  713 , a compensator  714 , and a controller  730 . In one embodiment, the digitizer  713  comprises an analog-to-digital converter  722  and two filters  724  and  725 . The analog-to-digital converter  722  converts analog input signals Sa 2  and Sb 2  from analog to digital to obtains digital data Sa 3  and Sb 3 . When the analog-to-digital converter  722  initially generates the digital data Sa 3  and Sb 3 , the digital data Sa 3  and Sb 3  are not stable and not suitable for further processing. When the digital data Sa 3  and Sb 3  are stable, the controller  730  enables filtering trigger signals F_trig_a and F_trig_b, and the filters  724  and  725  then start to filter the digital data Sa 3  and Sb 3  to obtain the filtered digital data Sa 4  and Sb 4 . 
     The filtered digital data Sa 4  and Sb 4  are then delivered to the compensator  714 . In one embodiment, the compensator  714  comprises two subtractors  726  and  727  and a compensating filter  728 . The subtractors  726  and  727  respectively subtract the digital data Sa 4  and Sb 4  from target levels Sa* and Sb* to obtain power level offset signals Sa 5  and Sb 5 . The compensating filter  728  then filters the power level offset signals Sa 5  and Sb 5  to generate component driving signals d 1 , d 2 , d 3 , and d 4 . When the substractors  726  and  727  initially generate the power level offset signals Sa 5  and Sb 5 , the power level offset signals Sa 5  and Sb 5  are not stable and not suitable for further processing. After the power level offset signals Sa 5  and Sb 5  are stable, the controller  730  enables the compensating trigger signal Ctrl_trig to trigger the compensating filter  414 , and the compensating filter  414  starts filtration of the power level offset signals Sa 5  and Sb 5 . In addition, the APC system  700  can normally operate according to merely the compensating trigger signal Ctrl_μg even if no filtering trigger signals F_trig_a and F_trig_b are generated. In one embodiment, the controller  730  only generates the compensating trigger signal Ctrl_μg to trigger compensation operations of the compensator  714 , and the filters  724  and  725  directly filter the digital signals Sa 3  and Sb 3  to obtain the filtered digital signals Sa 4  and Sb 4  without using the filtering trigger signals F_trig_a and F_trig_b. In one embodiment, the compensating filter  728  is an integrator, When the compensating trigger signal Ctrl_μg is disabled, the compensating filter  728  does not integrate the signals Sa 5  and Sa 6 , and the component current signals d 1 , d 2 , d 3 , and d 4  are therefore held at original levels. 
     Referring to  FIG. 11 , a schematic diagram of signals of an embodiment of an automatic power control process is shown. When the pickup head is on an non-APC area such as a data area, the write pulse generator  402  generates driver enable signals OE 1 ˜OE 4  to control the laser diode driver  416  to generate the driving current I, and a power curve of the laser beam is shown on the upper half of  FIG. 11 . When the pickup head writes the normal data on the data area, the driving current is changed very fast and the APC system is difficult to have a stable detected level to be used to calculate an updated driving signal. When the pickup head is on an APC area, the write pulse generator  402  can generate driver enable signals OE 1 ˜OE 4  by a predetermined condition to control the laser diode driver  416  to generate the driving current I, in addition, the durations of each enabled segment of the driver enable signals OE 1 ˜OE 4  can be setup to extend. For example, in comparison with the duration periods t 1  and t 2 , the duration periods t 3  and t 4  corresponding to the two power levels are extended. The front monitor diode  410  can therefore generate a stable analog input signal R, and the sample and hold circuits  412   a  and  412   b  can then sample the analog input signal R to obtain reliable data Sa 1  and Sb 1  as reference for compensation. 
     When a conventional APC controller adjusts a laser power of a pickup head, the APC power controller requires a predetermined transient time period to stabilize the laser power, and the laser power is unstable during the transient time period. In addition, a high temperature of the laser diode may increase the transient time period of the laser power. When data is recorded at a high speed, because a laser beam is projected on APC areas with a lower frequency, the sampling rate of a reflection power is lowered, and the APC controller requires a longer transient time period to stabilize the laser power. To reduce the transient time period for stabilizing the laser power, a method for setting the laser power with an accurate initial value is provided. If the laser power is set with an accurate initial value, the transient time period required by the APC controller to adjust the laser power is reduced. 
     Referring to  FIG. 12 , a block diagram of an optical disk drive  100  comprising an automatic power control system  106  according to one of the embodiments is shown. In one embodiment, the optical disk drive  100  comprises the automatic power control (APC) system  106 , a laser diode driver  116 , a laser diode (LD)  118 , and a front monitor diode (FMD)  110 . In one embodiment, the automatic power control system  106  comprises a controller  101 , a write pulse generator  102 , a sampling pulse generator  104 , a sample and hold circuit  112 , a compensator  114 , and a power initialization module  120 . The laser diode driver  116  generates a driving signal I according to a plurality of driving component signals di and a driver enable signal OEi. The laser diode  118  then emits a laser beam with a power level P determined by the driving signal I. In this embodiment, the power initialization module  120  is used to set an initial driving current for each component current signals I 1 , I 2 , I 3 , and I 4 , in the beginning of data writing or recording. According to this embodiment, the optical disk drive has to determine the initial driving currents to overcome the problems mentioned above. 
     Referring to  FIG. 13 , a flowchart of a method  800  of automatic power control for an optical disk drive  100  according to an embodiment of the invention is shown. A disk surface read or written by the optical disk drive  100  is assumed to be divided into a plurality of auto power control areas (APC areas) and a plurality of data areas, wherein the APC areas and the data areas are spaced in between. The data areas are used for common data storage. The APC areas are reserved for performing automatic power control processes. In one embodiment, the optical disk is a blu-ray disk (BD) and the optical disk drive utilizes the APC areas for determined the initial driving currents for a normal data writing/recording. First, the controller  101  determines whether the laser diode  118  is projecting the laserbeam on an APC area of the optical disk (step  802 ). When the laserbeam is projected on an APC area of the optical disk, the controller  101  directs the write pulse generator  102  to generates a driver enable signal OEi corresponding to a test area pattern. Otherwise, the controller  101  directs the write pulse generator  102  to generates a driver enable signal OEi corresponding to a data area pattern. 
     When the laserbeam is projected on the APC area of the optical disk, the automatic power control system  106  starts to perform an initial driving signal calibration process, thereby setting an initial driving signal for driving an optical pick-up head of the optical disk drive to emit laserbeam. When the laser beam is projected on one of the APC areas, the power initialization module  120  generates the initial component driving signals for the LD driver  114  to drive the laser diode  118  of the pickup head to emit a laserbeam corresponding to the laser power P (step  804 ). The laser diode  118  then projects a laserbeam with the at least one power level P onto the APC area according to the driving current I. In one embodiment, the at least one power level is selected from a read power, a cooling power (or someone called bias power), an erase power, a write power, and an over drive power. 
     The front monitor diode  110  then detects level of reflection of the laserbeam to obtain a detected signal R corresponding to the at least one power level P in each operation period (step  806 ). After the detected signal R is substantially stable, the sampling pulse generator  104  then generates a sampling pulse signal SH. The sample and hold circuit  112  then samples the level of the at least one detected signal R in the corresponding operation period according to the sample pulse signal SH to obtain a plurality of detected signal levels pi respectively corresponding to the power levels P. Because the detected signal levels pi are proportional to the power levels P, the compensator  114  then calibrates an update initial driving signal di according to the detected signal level pi and a target level. In one embodiment, the compensator  114  compares the detected signal level pi with a target level to generate a power level offset, and then adjusts the initial driving signal to have the update driving signal di according to the power level offset. The update driving component signal di is stored in the power initialization module for the normal data writing or next initial driving signal calibration. In one embodiment, the initial driving signal stored in the power initialization module is updated at each time the initial driving signal calibration performed. In the other embodiment, the initial driving signal stored in the power initialization module is updated when the initial driving signal calibration has a stable result which means the initial driving signal is stable. 
     In one embodiment, calibration of the update initial driving signal di comprises the following steps. First, the compensator  114  compares the detected level pi with the target level to generate a intermediated power level offset (step  808 ). The compensator  114  then adjusts the initial driving signal to have an intermediated initial driving signal according to the intermediated power level offset di (step  810 ). After the laser diode  118  generates a laser power P corresponding to the intermediated power level offset di, the front monitor diode  110  then detects a detected signal R, and the sample and hold circuit  112  samples the detected signal R to obtain an intermediated detected level pi (step  812 ). In one embodiment, after at least two detected levels are obtained, the compensator 114  performs an interpolated algorithm to get the updated driving signal di. The APC system  106  then determines whether the power level offset of the detected level and the target level is in a predetermined range (step  814 ). When the power level offset of the detected level and the target level is not in the predetermined range, the steps  808 ,  810 , and  812  are recursively performed until the power level offset of the detected level and the target level is in the predetermined range, thus stabilizing the laser power. 
     Referring to  FIG. 14 , a block diagram of a laser diode driver  200  according to one of the embodiments is shown. The laser diode driver  200  comprises a plurality of current amplifiers  202 ,  204 ,  206 ,  208 ,  210  and an adder  212 . Each current amplifier corresponds to a specific power level. For example, the current amplifiers  202 ,  204 ,  206 ,  208 , and  210  respectively correspond to a read power, a cooling power, an erase power, a write power, and an over drive power. The compensator  114  generates component current signals d 0 , d 1 , d 2 , d 3 , and d 4  corresponding to the different power levels. When a driver enable signal OE 0  corresponding to the read power is enabled, the current amplifier  202  then amplifies a component current signal d 0  corresponding to the read power to obtain an amplified component driving current i 0  corresponding to the read power. The current amplifiers  204 ,  206 ,  208 , and  210  similarly operate with the current amplifier  202 . The adder  212  then sums up the amplified component driving currents i 0 , i 1 , i 2 , i 3 , and i 4  to form a driving current I. The laser driver  214  then generates a laserbeam with a power level P determined by the driving current I. The subsequent embodiments shown in  FIGS. 17˜20  illustrates details of an APC control method provided by the invention. The embodiments therefore only comprises a less number of power levels than the power levels shown in  FIG. 14 . 
     Referring to  FIG. 15 , a schematic diagram of a relationship between a power level P of a laserbeam and corresponding driver enable signals OE 0 ˜OE 4  is shown. Assume that the laserbeam is sequentially emitted with a read power level P 0 , an over drive power P 4 , a write power level P 3 , the over drive power P 4 , a cooling power level P 1 , and an erase power level P 2 . The read power P 0  requires a driving current equal to the amplified component driving current i 0 , and the driver enable signal OE 0  is first enabled for generating the laserbeam with the read power level P 0 . The over drive power P 4  requires a driving current equal to a sum of the amplified component driving currents i 1 , i 2 , i 3 , and i 4 , and the driver enable signals OE 1 , OE 2 , OE 3 , and OE 4  are then enabled for generating the laserbeam with the over drive power P 4 . The write power P 3  requires a driving current equal to a sum of the amplified component driving currents i 1 , i 2 , and i 3 , and the driver enable signals OE 1 , OE 2 , and OE 3  are then enabled for generating the laserbeam with the write power level P 3 . The cooling power P 1  requires a driving current equal to the amplified component driving current i 1 , and the driver enable signals OE 1  is then enabled for generating the laserbeam with the cooling power level P 1 . Finally, the erase power P 2  requires a driving current equal to a sum of the amplified component driving currents i 1  and i 2 , and the driver enable signals OE 1  and OE 2  are then enabled for generating the laserbeam with the erase power level P 2 . 
     Referring to  FIG. 16 , a block diagram of an embodiment of a compensator  300  according to one of the embodiments is shown. The compensator  300  comprises a subtractor  302  and a compensating filter  304 . The compensator may have different forms. To make the steady state error zero, one simple method is by adopting an integrator described hereafter for easy description. The substractor  302  subtracts a detected signal level pi generated by the sample and hold circuit  112  from a target power level Pi* to obtain a power level offset. The compensating filter  304  then integrates the power level offset to obtain a component current signal di. The detected signal level pi, the target power level Pi*, and the component current signal di correspond to a read power, a cooling power, an erase power, a write power, or an over drive power. Since the APC control loop has bandwidth limit, there&#39;re some transient time for the laser beam to become stable with APC control. The transient time could make zero, if a proper initial di (for the integrator form is the initial value of it) is given. However, this initial di value not only depends on the target power, Pi, but also the laser diode temperature characteristics. So a method of finding this initial value before issuing disk recording is necessary. The power initialization module  120  therefore generates an initial value delivered to the compensator, and the compensating filter  304  start outputing from the initial value as the component current signal di after issuing disk recording. The subsequent laser driver  116  can then generate a driving current I according to the component current signal di to control generation of the laserbeam in the laser diode  118 . 
     Referring to  FIG. 17 , a schematic diagram of an embodiment of a test power pattern of a laser beam emitted by the laser diode  118  according to one of the embodiments is shown. When the APC system  106  starts to perform an automatic power control process, the optical disk drive  100  moves a pickup head containing the laser diode  118  to an APC area of the optical disk. The laser diode  118  then sequentially projects a laserbeam with four power levels P 4 , P 3 , P 2 , and P 1  onto the APC area. The first power level is the over drive power P 4  and lasts for a duration period Tp 4 . The second power level is the write power level P 3  and lasts for a duration period Tp 3 . The third power level is the erase power level P 2  and lasts for a duration period Tp 2 . The fourth power level is the cooling power level P 1  and lasts for a duration period Tp 1 . The front monitor diode  110  then detects the laserbeam to output a detected signal, wherein the duration periods Tp 1 , Tp 2 , Tp 3 , and Tp 4  are greater than the settling time of the front monitor diode  110  to generate a stable detected signal. Because the front monitor diode  110  can generate a detected signal that accurately representing the power level of the laserbeam, the compensator  114  can generate component current signals according to the detected signal to make a laserbeam output a precise power level. The sample and hold circuit  112  then samples the detected signal according to sampling pulses generated by the sampling pulse generator  104  to obtain the detected signal levels p 4 , p 3 , p 2 , and p 1  respectively corresponding to the power levels P 4 , P 3 , P 2 , and P 1 . The compensator  114  can then generate the component current signals d 0 , d 1 , d 2 , d 3 , and d 4  according to the detected signal levels p 4 , p 3 , p 2 , and p 1  to calibrate the driving current I of the laser diode deriver  116 , thus making the laser diode  118  generate a laserbeam with a constant power level. 
     Referring to  FIG. 18 , a schematic diagram of another embodiment of a test power pattern of a laser beam emitted by the laser diode  118  according to one of the embodiments is shown. In the embodiment, the laser diode  118  sequentially projects a laserbeam with three power levels P 2 , P 3 , and P 1  onto the APC area. The first power level is the erase power level P 2  lasting for a duration period Tp 2 . The second power level is the write power level P 3  lasting for a duration period Tp 3 . The third power level is the cooling power level P 1  lasting for a duration period Tp 1 . After the front monitor diode  110  detects reflection of the laserbeam to output a detected signal, the sample and hold circuit  112  samples the detected signal according to sampling pulses generated by the sampling pulse generator  104  to obtain the detected signal levels p 2 , p 3 , and p 1  respectively corresponding to the power levels P 2 , P 3 , and P 1 . The compensator  114  can then generate the component current signals d 0 , d 1 , d 2 , d 3 , and d 4  according to the detected signal levels p 2 , p 3 , and p 1  to calibrate the driving current I of the laser diode deriver  116 , thus making the laser diode  118  generate a laserbeam with a constant power level. 
     In the embodiments shown in  FIGS. 17 and 18 , the optical disk drive  100  respectively generates laserbeams with four power levels and three power levels for driving current calibration. The sample and hold circuit  112  therefore respectively obtains four detected signal levels and three detected signal levels corresponding to the power levels. The compensator  114 , however, has to generate five component current signals d 0 , d 1 , d 2 , d 3 , and d 4  according to the four detected signal levels or the three detected signal levels. Referring to  FIG. 4 , an approximate relationship line between a driving current and a laserbeam power level at a specific temperature T is determined by an offset current Ith(T) and a slope s(T). The APC system  106  can therefore determine the offset current Ith(T) and the slope s(T) according to the detected signal levels sampled by the sample and hold circuit  112 , and then estimate all five component current signals d 0 , d 1 , d 2 , d 3 , and d 4  of a driving current corresponding to a specific power level according to the offset current Ith(T) and the slope s(T). An embodiment of power level equations for estimating power levels according to the offset current Ith(T) and the slope s(T) is shown as following:
 
 P 0=( i 0 −Ith ( T ))× s ( T );
 
 P 1=( i 1 −Ith ( T ))× s ( T );
 
 P 2 =P 1 +i 2 ×s ( T );
 
 P 3 =P 2 +i 3 ×s ( T ); and
 
 P 4 =P 3 +i 4 ×s ( T ),
         wherein P 0  is a read power level, P 1  is a cooling power level, P 2  is an erase power level, P 3  is a write power level, P 4  is an over drive power, and i 0 , i 1 , i 2 , i 3 , and i 4  are amplified component driving currents shown in  FIG. 15 .       

     When the optical disk drive is powered on, the optical disk drive  100  does not know the temperature of the laser diode  118 . The laser diode driver  116  therefore cannot determine an amplitude of the driving current I for controlling the laser diode  118  to generate a laserbeam with a desired power level. The optical disk drive  100  therefore performs an automatic power initialization process to calibrate the driving current I before the optical disk drive  100  formally writes data. The automatic power initialization process before normal data writing is also referred to as a pre-recording process where APC area are used for calibrating initial driving signal di while data area are leaving as normal data reading (i.e. laser beam outputting read power). Referring to  FIG. 19 , a schematic diagram of an embodiment of a pre-recording process according to one of the embodiments is shown. In this embodiment, before an optical disk drive records data on a target address of an optical disk, the optical disk drive performs the pre-recording process to write test data on APC areas near and prior to the target address. In other embodiments, the optical disk drive may perform the pre-recording process to write test data on any APC areas and then seek to the target address after completing the pre-recording process. For simplification, a ordinary APC control structure is used to illustrate implementation of the automatic power initialization of the invention, but the APC control structure does not limit the application range of the invention. When the pre-recording process is started, the APC system  106  performs a first automatic power control process (i.e. APC) on a first APC area, thus making a first adjustment di according to a detected signal level pi of the laserbeam. After a projection spot of the laserbeam leaves the first APC area, the APC system then halts emission of the laserbeam until the pickup head reaches a second APC area. The APC system  106  then sequentially performs another three automatic power control processes on subsequent three APC areas, thus making another three adjustments to the detected signal level pi of the laserbeam. The three automatic power control processes performed on subsequent three APC areas are only for illustration. When the APC bandwidth gets lower or the current laser power has a greater offset in comparison with a target laser power, the APC system  106  must performs a greater number of automatic power control processes on a greater number of APC areas to obtain a converged laserbeam power level. Finally, the detected signal level pi is equal to a target power level, and calibration of the driving current is completed. The optical disk drive  100  then performs normal data recording process with correct laser power when the target address is met. 
     Referring to  FIG. 20 , a schematic diagram of another embodiment of a pre-recording process is shown. In the pre-recording process, the optical disk drive  100  moves the pickup head containing the laser diode  118  to an APC area of the optical disk, and performs four automatic power control processes on the APC area to make four adjustments to a power level of the laserbeam. In one embodiment, the APC area is an APC area or an optimal power control (OPC) area of the optical disk. After calibration of the power level Pi is completed, the optical disk drive  100  then moves the pickup head containing the laser diode  118  to a target address for normally recording data. 
     While one of the embodiments has been described by way of example and in terms of preferred embodiment, it is to be understood that one of the embodiments is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.