Abstract:
An optical disk drive has a pick-up head for emitting laser beams, and an analog front-end circuit controlled by a microprocessor for controlling the operation of the pick-up head. An automatic control method for generating stable laser power of the optical disk drive includes getting a power reference function measured by a fixed quantity of optical disk sample drives, establishing the relationship between the laser power control signal of pick-up head from the analog front-end circuit by the microprocessor, and calculating the difference amount from a feedback signal minus a reference voltage on pick-up head side to generate a first function. When the analog front-end circuit receives this feedback signal, this method will be enabled automatically and adjust the first function of the laser power control signal to approach the reference function so as to adjust the intensity of the laser power generated by the pick-up head.

Description:
BACKGROUND OF INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a method for controlling laser power of an optical disk drive, and more particularly, to an automatic control method using a feedback mechanism to steady laser power of an optical disk drive.  
           [0003]    2. Description of the Prior Art  
           [0004]    Management of documents is an important concern for both companies and individuals. In the past, all documents were printed or written on paper. This method is very inconvenient as the number of documents continues to increase. As computer technology develops day-by-day, digital data is widely used and stored in computer storage media. In order to make storing digital data more convenient, many data storage devices have been developed such as writable compact disk drives. The optical disk drive has a low cost and a light volume, but a high storage capacity, making storing data more convenient.  
           [0005]    Please refer to FIG. 1. FIG. 1 is a perspective view of a laser power control device  10  according to a prior art optical disk drive. The laser power control device  10  comprises a microprocessor  12 , a digital to analog converter (DAC)  14 , an analog front end (AFE) circuit  15 , and an optical pick-up unit  18 . The microprocessor  12  outputs a control signal  20  to the DAC  14 . The DAC  14  converts the digital control signal  20  into an analog control signal and then transmits the converted analog control signal to the analog front end circuit  15 . The initial control signal  20  is a reference signal that is used to control the optical pick-up unit  18  to generate a suitable laser power. The analog front end circuit  15  generates a corresponding writing voltage  22  according to the control signal  20  so as to control the laser power outputted from the optical pick-up unit  18 . That means the optical pick-up unit  18  can output different laser power levels according to different writing voltages  22 . When the optical pick-up unit  18  outputs laser beam, the laser beam is bisected by a prism. A greater part of the laser beam goes through the prism along the original optic path and then outputs to an optical disk. The smaller part of the laser beam is refracted by the prism and then arrives to a front photo diode. The front photo diode converts the laser beam into a watching signal  24 . The watching signal  24  is used to monitor a status of the laser power outputted from the optical pick-up unit  18 . If the optical pick-up unit  18  outputs a greater laser power, the power of the laser beam that is refracted by the prism will also be greater. Therefore, users can know the variation of the laser power outputted from the optical pick-up unit  18  according to the variation of the watching signal  24 . The analog front end circuit  15  provides a reference voltage  26  to be a reference voltage of the watching signal  24 . The analog front end circuit  15  comprises a automatic power control (APC) circuit  16 . The automatic power control circuit  16  adjusts the writing voltage  22  according to a difference amount between the watching signal  24  and the reference voltage  26  so as to steady the laser power outputted from the optical pick-up unit  18 . For example, the decided value of the laser power outputted to the optical disk from the optical pick-up unit  18  is X. When laser power of X is outputted, a watching signal  24  of VI voltage is generated at the same time. If the reference voltage  26  provided by the analog front end circuit  15  is V 2 , then the difference amount between the watching signal  24  and the reference voltage  26  is V 1 -V 2 . When the analog front end circuit  15  receives a watching signal  24  which has a voltage greater than V 2  for the instable output of the optical pick-up unit  18 , that means the laser power outputted from the optical pick-up unit  18  is greater than the decided value X at that time. Therefore, the analog front end circuit  15  use the automatic power control circuit  16  to decrease the writing voltage  22  so as to decrease the laser power outputted from the optical pickup unit  18  at the same time. Therefore, the laser power control device  10  of the prior art optical disk drive uses the difference amount between the watching signal  24  and the reference voltage  26  to finely tune the writing voltage  22  so as to make the optical pick-up unit  18  output stable laser power.  
           [0006]    However, the laser power control device  10  only forms a feedback mechanism between the analog front end circuit  15  and the optical pick-up unit  18  to steady the laser power outputted from the optical pick-up unit  18 . When the optical pick-up unit  18  outputs the unsuitable writing power, it is unable to adjust the writing voltage  22  generated by the analog front end circuit  15  through the feedback mechanism. For example, when error caused by the laser power control device  10  makes interference, the optical pick-up unit  18  will output undesirable writing power. However, the laser power control device  10  can only use the feedback mechanism formed between the analog front end circuit  15  and the optical pick-up unit  18  to stably output the undesirable writing power. Therefore, the laser power control device  10  is unable to use the undesirable writing power to adjust the writing voltage  22  and to control the optical pick-up unit  18  to output suitable writing power.  
           [0007]    In general, the optical disk drive must use an optimum power control (OPC) before writing data onto a disk so as to find out the most suitable writing power for the disk. The orange book has detailed description about the practice of the optimum power control, which is briefly described below.  
           [0008]    Please refer to FIG. 2. FIG. 2 is a perspective view of using the optimum power control according to the prior art. When using the optimum power control, the optical pick-up unit  18  of the optical disk drive will first read an indicative optimum writing power P from a lead-in area  29  on the optical disk  28 . The indicative optimum writing power P is a writing power suggested by the manufacturer of the optical disk. The optical pick-up unit  18  tests the writing operation in fifteen continuous test blocks  31  inside the test area  30  on the optical disk  28  by using seven writing powers P 1 ˜P 7  that are smaller than the indicative optimum writing power P, the indicative optimum writing power P, and the seven writing powers P 8 ˜P 14  that are greater than the indicative optimum writing power. In total, fifteen different writing powers are used.  
           [0009]    Continuously, the optical pick-up unit  18  reads back the result of writing data into the test blocks  31 . The read back signal is an alternating current coupled high frequency signal. The orange book has defined a symmetrical parameter β with regard to the read back signal. If the symmetrical parameter β of the read back signal conforms with the decided demands, the corresponding writing power can be the optimum writing power of the optical disk  28 . Fifteen symmetrical parameter values (β) of the fifteen read back signals corresponding to the fifteen writing powers are generated after the optical pick-up unit  18  has read back the writing result of the fifteen writing powers. Then, the optical disk drive compares the fifteen symmetrical parameter values of the read back signals with a target β stored in the lead-in area  29  of the optical disk. The writing power corresponding to a symmetrical parameter value of a read back signal, which has a minimum difference amount from the target β in the fifteen symmetrical parameter values of the read back signals, is the optimum writing power. If all the difference amounts between the fifteen read back signal parameters and the target β are greater than a decided value, none of the fifteen writing powers is suitable to be the practical writing power. In this case, the optical disk drive will use a preset value to be the writing power and write data into the writing area  32  of the optical disk  28 .  
           [0010]    However, errors are generated between the output laser power of the optical pick-up unit  18  and the writing voltage  22  and the deviation of the laser power is caused due to errors in optical elements and fabricating process. Besides, the resistance effect and noise interference generated by the electronic elements on the printed circuit board of the optical disk drive will influence the actual output voltage. Therefore, an error exists between the output voltage and the original decided value designed by the circuit. The errors generated by the optical pick-up unit  18  and the electronic elements make the optical pick-up unit  18  output a laser power that is too large or too small and exceeds the optimum power control range of the optical disk. The inefficacy of the optimum power control will not only influence the burning efficiency, but also calculate an unsuitable writing power. For example, when using the optimum power control, the optical pick-up unit  18  of the optical disk drive will first read an indicative optimum writing power P from a lead-in area  29  on the optical disk  28 . The optical pick-up unit  18  tests the writing operation in fifteen continuous test blocks  31  inside the test area  30  on the optical disk  28  by using seven writing powers P 1 ˜P 7  which are smaller than the indicative optimum writing power P, the indicative optimum writing power P, and seven writing powers P 8 ˜P 14  which are greater than the indicative optimum writing power. All together, fifteen writing powers are used. However, the error generated by the optical disk drive makes the optical pick-up unit  18  emit a laser beam which deviates from the indicative optimum writing power P. The optical pick-up unit  18  is unable to get a suitable writing power from the fifteen test writing powers. Therefore, the optical pick-up unit  18  must use the heterodyne method or repeat to do the optimum power control to get the writing power. However, it is difficult to get a suitable writing power for the error of the output laser power. If the optical pick-up unit  18  outputs the unsuitable writing power, it will damage the chemical dyes on the optical disk and increase the error rate when reading data from the optical disk, or make the optical disk unusable for storing any further data. In order to calibrate the error, the prior art optical disk drive uses detecting instruments to calibrate the output laser power of the optical disk drive by manpower, through the procedure of testing and recombining the optical pick-up unit  18  many times, so as to make the laser power outputted from the optical disk drive lie inside the optimum power control range. Therefore, not only the production yield cannot be improved, but also the total production cost is increased.  
         SUMMARY OF INVENTION  
         [0011]    It is therefore a primary objective of the claimed invention to provide an automatic control method for generating stable laser power of an optical disk drive, using the feedback mechanism to automatically calibrate the laser power so as to lower production cost and increase yield.  
           [0012]    The claimed invention, briefly summarized, discloses an automatic control method for generating stable laser power of an optical disk drive. The optical disk drive comprises an optical pick-up unit for emitting laser beams, a microprocessor for generating control signals, and an analog front end (AFE) circuit. The analog front end circuit is used to receive the control signals generated by the microprocessor, generating a writing voltage for the optical pick-up unit according to the control signals so as to make the optical pick-up unit emit laser beams, to receive watching signals generated when the optical pick-up unit emits laser beams, and to adjust the writing voltage according to a difference amount between the watching signals and a reference voltage so as to adjust a magnitude of the laser beams emitted by the optical pick-up unit. The control method is to generate a first function according to a relationship between the control signals transmitted from the microprocessor to the analog front end circuit and the difference amount between the watching signals and the reference voltage. When the analog front end circuit receives the watching signal, the analog front end circuit adjusts the writing voltage according to the first function and a reference function so as to adjust the magnitude of the laser beams emitted by the optical pick-up unit.  
           [0013]    It is an advantage of the claimed invention that the laser power control device of the claimed invention optical disk drive reduces the deviation of the output laser power caused by the error of the output laser power of the optical pick-up unit and the voltage drift of the electronic circuit, increasing the stability of output laser power control. In addition, the claimed invention optical pick-up unit uses automatic manner to adjust the output laser power. Therefore, it can decrease the error caused by using manpower to adjust the output laser power, resulting in cost decreases and yield increases.  
           [0014]    These and other objectives of the claimed invention will be apparent to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment, which is illustrated in the various figures and drawings. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0015]    [0015]FIG. 1 is a perspective view of a laser power control device according to a prior art optical disk drive.  
         [0016]    [0016]FIG. 2 is a perspective view of using the optimum power control according to the prior art.  
         [0017]    [0017]FIG. 3 is a perspective view of a laser power control device of the present invention optical disk drive.  
         [0018]    [0018]FIG. 4 is a perspective view of a reference function according to the present invention.  
         [0019]    [0019]FIG. 5 is a flow chart of the laser power control device shown in FIG. 3.  
         [0020]    [0020]FIG. 6 is a perspective view of the first function of the present invention optical disk drive.  
         [0021]    [0021]FIG. 7 is a perspective view of the deviation function of the present invention optical disk drive. 
     
    
     DETAILED DESCRIPTION  
       [0022]    Please refer to FIG. 3. FIG. 3 is a perspective view of a laser power control device  40  of the present invention optical disk drive. The laser power control device  40  comprises a microprocessor  42 , a digital to analog converter (DAC)  44 , an analog to digital converter (ADC)  46 , an analog front end circuit  47 , a differential amplifier  49 , and an optical pick-up unit  50 . The microprocessor  42  outputs a control signal  51  to the DAC  44  and then the DAC  44  converts the digital control signal  51  into the analog control signal and transmits the converted analog control signal into the analog front end circuit  47 . The control signal  51  is a reference signal which is used to control the optical pick-up unit  50  to emit laser beams. The analog front end circuit  47  generates a writing voltage  52  according to the control signal  51  so as to control the laser power outputted from the optical pick-up unit  50 . The optical pick-up unit  50  generates a watching signal  53  and outputs different laser power according to the different writing voltage  52 . The analog front end circuit  47  provides a reference voltage  54  of the watching signal  53 . The analog front end circuit  47  comprises a automatic power control (APC) circuit  48  for adjusting the writing voltage  52  by using a difference amount between the watching signal  53  and the reference voltage  54  so as to steady the laser power outputted from the optical pick-up unit  50 . The watching signal  53  and the reference voltage  54  are inputted into the differential amplifier  49  at the same time and then a difference amount  55  between the watching signal  53  and the reference voltage  54  is generated. The ADC  46  converts the difference amount  55  into the digital signal and feeds back the converted digital signal to the microprocessor  42  for further adjusting the control signal  51 . The optical disk drive of the present embodiment is a rewritable compact disk drive or a recordable compact disk drive.  
         [0023]    Please refer to FIG. 4. FIG. 4 is a perspective view of the reference function  56  according to the present invention. The horizontal axle represents the value of the control signal  51 . The vertical axle represents test values of the output power (the difference amount between the watching signal  53  and the reference voltage  54 ). Before the laser power control device  40  of the present invention optical disk drive performs the output power control of the optical pick-up unit  50 , the laser power control device  40  must get a reference function  56  to be the reference value for adjusting the laser power. At first, the microprocessors of the plurality of optical disk drives generate the plurality of control signals. Then, the difference amounts between the watching signals and the reference voltages corresponding to the plurality of control signals are measured. Then second functions corresponding to the plurality of the optical disk drives are generated according to the control signals and the corresponding difference amount between the voltages. Therefore, each optical disk drive generates a different second function after testing. Finally, the reference function  56  is generated by averaging the plurality of second functions. Therefore, the present invention uses the plurality of optical disk drives to be the optical disk sample drive, and then calculates the average value of the corresponding output power test value according to the control signal  51 . The reference function  56  corresponding to the control signals  51  and the average value of the output power test values is generated last.  
         [0024]    Please refer to FIG. 5. FIG. 5 is a flow chart of the laser power control device  40  shown in FIG. 3. The operation procedure is described as below:  
         [0025]    Step  101 : The microprocessor  42  outputs a first control signal Y 1  so as to make the optical pick-up unit  50  emit the laser beams;  
         [0026]    Step  102 : The differential amplifier  49  generates a first output power test value X 1  according to the watching signal  53  and the reference voltage  54 ; Step  103 : The microprocessor  42  outputs a second control signal Y 2  so as to make the optical pickup unit  50  emit the laser beams;  
         [0027]    Step  104 : The differential amplifier  49  generates a second output power test value X 2  according to the watching signal  53  and the reference voltage  54 ; Step  105 : Generate the first function of the optical disk drive according to the first control signal Y 1  and the first output power test value X 1 , and the second control signal Y 2  and the second output power test value X 2 ;  
         [0028]    Step  106 : Generate a deviation function according to the first function and the reference function  56 ; Step  107 : Calculate a difference amount according to the deviation function; and  
         [0029]    Step  108 : Adjust the output power of the optical pick-up unit  50  according to the difference amount.  
         [0030]    Please refer to FIG. 5, FIG. 6, and FIG. 7. FIG. 6 is a perspective view of the first function  57  of the present invention optical disk drive. FIG. 7 is a perspective view of the deviation function  58  of the present invention optical disk drive. In the present embodiment, the first control signal Y 1  is an initial value that makes the optical pickup unit  50  start to generate laser beams. As shown in FIG. 6, when the microprocessor  42  outputs the first control signal Y 1  to make the optical pick-up unit  50  output the first laser power, the differential amplifier  49  generates the first output power test value X 1  corresponding to the first laser power according to the watching signal  53  and the reference voltage  54  at the same time. Similarly, when the microprocessor  42  outputs the second control signal Y 2  to make the optical pick-up unit  50  output the second laser power, the differential amplifier  49  generates the second output power test value X 2  corresponding to the second laser power according to the watching signal  53  and the reference voltage  54  at the same time. Therefore, the first function  57  can be calculated by using the first control signal Y 1  and the first output power test value X 1 , and the second control signal Y 2  and the second output power test value X 2 . When the control signal is Y 1 , a output power test value X 3  can be obtained from the reference function  56 . Therefore, the laser output power of the optical pickup unit  50  of the optical disk drive is greater than the output power test value X 3 , and the difference amount is X 1 -X 3 . When the control signal is Y 2 , an output power test value X 4  can be obtained from the reference function  56 . Therefore, the laser output power of the optical pick-up unit  50  of the optical disk drive is smaller than the output power test value X 4 , and the difference amount is X 2 -X 4 . The deviation function  58  can be obtained according to the relationship between the difference amounts Z 1  (X 1 -X 3 ), Z 2  (X 2 -X 4 ), and the control signals Y 1  and Y 2 . As shown in FIG. 7, for each control signal, a corresponding difference amount can be obtained. The analog front end circuit  47  adjusts the writing voltage  52  according to the difference amount so as to change the output power of the optical pick-up unit  50 . Therefore, the first function  57  of the optical disk drive can conform the laser power characteristic of the reference function  56  after suitable adjusting. The optical disk drive can use a write strategy corresponding to the reference function  56  to write data onto the optical disk so as to make more accurate when writing data onto the optical disk.  
         [0031]    In addition, the optimum power control uses the test area on the optical disk to do the laser power test. The size of the test area is limited. The number of times the optimum power control is performed is limited by the capacity of the test area. Therefore, there is a limitation to using the optimum power control to adjust the laser power range. However, the error of the output laser power of the optical pick-up unit and the voltage drift of the electronic circuit always causes large deviations of the laser power so that the suitable writing power cannot be obtained by using the optimum power control. In order to reduce the difference among the different optical disk drives and to control the stability of the output laser power of the optical pick-up unit effective, the laser power control device  40  of the present invention optical disk drive uses the differential amplifier  49  to feedback the output status of the optical pick-up unit  50  to the microprocessor  42 . A difference amount can be obtained after comparing the output status with the reference function  56 . Using the difference amount to change the writing voltage  52  of the analog front end circuit  47 . The feedback mechanism is used to automatically adjust the output power of the optical pick-up unit  50  so as to compensate the error of the output power caused by the optical pick-up unit  50  and the electronic circuit. Then the automatic power control (APC) circuit  48  of the front end circuit  47  is used to further steady the output power of the optical pick-up unit  50 . The different optical pick-up unit and the different electronic circuit will give the different influence level to the output laser power, so that the different optical disk drive has the different laser power characteristic. However, the laser power control device  40  of the present invention optical disk drive uses the feedback mechanism to automatically adjust each optical disk drive, which has the different first function  57 , to the laser power output characteristic represented by the reference function  56 . After suitable adjusting, the laser output power range of the optical pick-up unit of each optical disk drive is fixed (decided by the reference function  56 ). Therefore, the laser power control device  40  of the present invention optical disk drive can reduce the deviation of the output laser power caused by the error of the output laser power of the optical pick-up unit and the voltage drift of the electronic circuit. When doing the optimum power control, the laser power control device  40  can use the output laser power range defined by the reference function  56  to calibrate the writing power so as to save the time and space of testing on the optical disk and find a suitable writing power quickly.  
         [0032]    In contrast to the prior art, the laser power control device of the present invention optical disk drive reduces the deviation of the output laser power caused by the error of the output laser power of the optical pick-up unit and voltage drift of the electronic circuit, increasing the stability of output laser power control. The successful rate of the optimum power control can be increased inside a stable output laser power range so as to avoid selecting an unsuitable writing power and causing the optical disk cannot be read or read correctly after burning data onto the disk, increasing the efficiency of the optical disk drive. Moreover, the present invention optical pick-up unit automatically adjusts the output laser power. Therefore, it can decrease the error caused by using manpower to adjust the output laser power, so that costs are decreased and yield is increased.  
         [0033]    Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.