Abstract:
A method and related apparatus for feedback control of laser power provided by a pick-up head of an optical disk drive. The pick-up head can adjust a cross-voltage of a laser generator according to a signal level of a control signal such that the laser power is changed correspondingly. The method includes updating the signal level of the control signal according to feedback of the cross-voltage or the control signal, such that the laser power is adjusted accordingly.

Description:
BACKGROUND OF INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a method and related apparatus for controlling a pickup head of an optical disk drive in a feedback manner, and more particularly, to a method and related apparatus for controlling the powers of laser beams emitted by the pickup head in the feedback manner according to a cross-voltage of a laser diode or a laser control signal.  
           [0003]    2. Description of the Prior Art  
           [0004]    The advantages of light weight, low cost, easy to store, and great data-storing capacity have made an optical disk a most important non-volatile memory media in modern information ages. Data stored in an optical disk is read by an optical disk drive and designing an optical disk drive of good data-reading capability is becoming a popular concern for the information industry.  
           [0005]    Please refer to FIG. 1, which is a function block diagram of an optical disk drive  10  according to the prior art. The optical disk drive  10  comprises a motor  14  for rotating a disk  12 , a pickup head  16 , a control circuit  18 , and a processor  20  for controlling functionalities of the optical disk drive  10 . The optical disk drive  10  emits laser beams onto the disk  12  with the pickup head  16  and reads data of the disk  12  according laser beams reflected by the disk  12 . The control circuit  18  is a pre-amplifier capable of controlling powers of laser beams emitted by the pickup head  16 . A laser diode  24 , installed in the pickup head  16  as a laser generator, generates the laser beams to project onto the disk  12 . A power-adjusting circuit  22  is used to adjust a cross-voltage V between two ends of the laser diode  24  at nodes Np 1 , Np 2 . As the cross-voltage V is changed, the powers of laser beams emitted by the laser diode  24  change accordingly. A reference signal end  17 A, a cross-voltage output end  17 B and a control end  17 C are installed in the pickup head  16  for controlling powers of laser beams emitted from the pickup head  16 . The power-adjusting circuit  22  receives a control signal  38  transmitted from the control end  17 C and adjusts the cross-voltage V according to the voltage level of the control signal  38 . A voltage level of the cross-voltage V at node Np 1  is determined by a bias voltage  34 A output from the reference voltage end  17 A. Since the cross-voltage V is controlled by the power-adjusting circuit  22 , a voltage level of the cross-voltage V at node Np 2  is equivalently determined by the power-adjusting circuit  22 . The pickup head  16  outputs a voltage at f3 node Np 2  as an output voltage  34 B at the cross-voltage output end  17 B.  
           [0006]    The control signal  38  to control the power-adjusting circuit  22  is generated by the control circuit  18 . The control circuit  22  comprises two sub-controllers  26 A and  26 B, a digital-to-analog converter (DAC)  30 , a differential amplifier  32 , and three transmission circuits  28 A,  28 B and  28 C. The sub-controller  26 A generates a first signal  36 A. The processor generates a digital second signal  36 B. The digital second signal  36 B will be transformed into an analog second signal  36 C by the DAC  30  and transmitted to the differential amplifier  32  by the transmission circuit  28 C. After respectively receiving the first signal  36 A and the analog second signal  36 C with a pair of differential-formed input ends (indicated by labels “+” and “−” in FIG. 1), the differential amplifier  32  generates the control signal  38  according to a difference between the first signal  36 A and the analog second signal  36 C and transmits the control signal  38  to the control end  17 C of the pickup head  16  through the transmission circuit  28 B. The sub-controller  26 B generates the bias voltage  34 A. The transmission circuit  28 A is used to receive the output voltage  34 B output from the cross-voltage output end  17 B.  
           [0007]    The processor  20  controlling powers of laser beams emitted by the pickup head  16  with the control circuit  18  is described as follows. The control circuit  18  generates the bias voltage  34 A, whose voltage level is constant, with the sub-controller  26 B to control a voltage level of the pickup head  16  at node Np 1  and to keep the voltage level at node Np 1  constant. The first signal  36 A generated by the sub-controller  26 A is also constant. The processor  20  changes the second signal  36 B input to the DAC  30  and changes the analog second signal  36 C accordingly. Therefore, the control signal  38 , which is generated by the differential amplifier  32  according to the difference between the first signal  36 A and second signal  36 C, is changed according to the variation of the second signal  36 C. As the control signal  38  is changed, the power-adjusting circuit  22  adjusts the cross-voltage V accordingly and changes the powers of laser beams emitted by the laser diode  24 . In other words, the processor  20  is capable of controlling the power-adjusting circuit  22  to adjust the cross-voltage V and of further controlling the powers of laser beams emitted by the laser diode  24  with the second signal  36 B and the control signal  38 . Since the bias voltage  34 A is constant, the variation of the output voltage  34 B reflects the variation of the cross-voltage V.  
           [0008]    In the prior art, the processor  20  stabilizes the powers of laser beams emitted from the pickup head  16  by setting the second signal  36 B at a constant voltage level. However, the stabilization suffers from a mass production of the control circuit  18 . That is, control signals, as well as bias voltages, generated by control circuits in one type are different from each other even if the second signal  36 B generated by the processor  20  is kept constant. In addition, the pickup head  16  suffers from the stabilization problem too. Characteristics of the power-adjusting circuits and laser diodes in a pickup head are different from each other even if these devices are of one type. That is, powers of laser beams emitted by different but same type pickup heads are different even if the voltage level of control signal  38  and of the bias voltage  34 A are constant. The above-mentioned problem becomes more and more serious as the control circuit  18  and the pickup head  16  combine to function, with the powers of laser beams emitted by the pickup head  16  becoming dramatically unstable. Practically, a laser output power is ideally about 700 μW, but, in reality, the laser output power will raise to as high as 1,400 μW due to a drifting effect caused by the combination of the pickup head and control circuit. As known by those skilled in the art, the optical disk drive  10  not only reads data of the disk  12  according to the laser beams reflected by the disk  12 , but controls functions of track-searching, track-locking and pickup head-positioning in a feedback manner according to the reflected laser beams. If the powers of laser beams emitted by the pickup head  16  are extremely high, the powers of laser beams reflected from the disk  12  will raise accordingly. The high power-leveled laser beams will drive transistors of the control circuit  18  to work in borders of a normal-working range, thus distorting signals and malfunctioning the feedback control. On the contrary, if the powers of laser beams emitted by the pickup head  16  are extremely low, too low a power being vulnerable to noise, the optical disk drive  10  cannot function normally either.  
         SUMMARY OF INVENTION  
         [0009]    The claimed invention provides a method and related apparatus to control powers of laser beams emitted by a pickup head in a feedback manner to solve the above-mentioned problems.  
           [0010]    In the prior art, because the drifting effect of the control circuit can not compensate for that of the pickup head, the control circuit combines with the pickup head and shifts the laser output power to a power level away from the ideal range and malfunctions the optical disk drive.  
           [0011]    In the claimed invention, a processor adjusts the control signal in the feedback manner with the cross-voltage of the laser diode or the control signal of the power-adjusting circuit and keeps the laser output power at a power level within the ideal range and keeps the optical disk drive working normally.  
           [0012]    The claimed invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.  
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0013]    [0013]FIG. 1 is a function block diagram of an optical disk drive according to the prior art.  
         [0014]    [0014]FIG. 2 is a function block diagram of a first embodiment applied to an optical disk drive according to the present invention.  
         [0015]    [0015]FIG. 3 is a diagram of a function of laser output powers of a pickup head and cross-voltages of a laser diode of the optical disk drive shown in FIG. 2.  
         [0016]    [0016]FIG. 4 is a function block diagram of a second embodiment applied to an optical disk drive according to the present invention.  
         [0017]    [0017]FIG. 5 is a diagram of a function of laser output powers of a pickup head and cross-voltages of a laser diode of the optical disk drive shown in FIG. 4. 
     
    
     DETAILED DESCRIPTION  
       [0018]    Please refer to FIG. 2, which is a function block diagram of a first embodiment applied to an optical disk drive  50  according to the present invention. Similar to the optical disk drive  10 , the optical disk drive  50  also comprises a motor  54  for rotating a disk  52 , a pickup head  56  capable of emitting laser beams, a control circuit  58  for generating a control signal  78  to adjust powers of laser beams emitted by the pickup head  56 , and a processor  60  for controlling functionalities of the optical disk drive  50 . The processor  60  changes the control signal  78  generated by the control circuit  58  with a second signal  76 B and controls powers of laser beams emitted by the pickup head  56  with the control signal  78 . The structure of the optical disk drive  50  is similar to that of the optical disk drive  1   0 . That is, the control circuit  58  also comprises three transmission circuits  68 A,  68 B and  68 C for transmitting signals, two sub-controllers  66 A and  66 B for respectively generating a constant first signal  76 A and a constant bias voltage  74 A.A DAC  70  transforms the digital second signal  76 B into an analog second signal  76 C. The transmission circuit  68 C transmits the analog second signal  76 C to a differential circuit  72  and the differential circuit  72  generates the control signal  78  according to difference between the analog second signal  76 C and the first signal  76 A. A laser diode  64 , installed in the pickup head  56  and serving as a laser generator, generates the laser beams to project onto the disk  52 . A power-adjusting circuit  62  receives the bias voltage  74 A with a reference end  57 A and adjusts a cross-voltage V 1  across two ends of the laser diode at nodes N 1  and N 2  according to the control signal  78 . A cross-voltage output end  57 B outputs the voltage at node N 2  to the transmission circuit  68   a  of the control circuit  58 .A VT3190 chip, which is produced by VIA technology, Inc., adjusts laser output powers according to a direct proportional relation between difference of two voltages FVREF and FPDOLPF and the laser output powers. So the comparison between difference of FVREF and FPDOLPF with the first signal can serve as a reference to adjust the cross-voltage.  
         [0019]    Where the present invention differs from the prior art is the processor  60  is capable of controlling the laser output powers of the pickup head  56  in a feedback manner by determining an output voltage  74 B to compensate the drifting effect of the laser output power due to variations of the pickup head and the control circuit. Principles of feeding back for the present invention are described as follows: Please refer to FIG. 3, as well as to FIG. 2. A curve  94  shown in FIG. 3 demonstrates a relation of the laser output power of the pickup head  56  and the cross-voltage V 1 , an abscissa indicating power levels of the laser output power and an ordinate voltage levels of the cross-voltage V 1 . When the cross-voltage V 1  is changed by the power-adjusting circuit  62  according to the control signal  78 , because a voltage difference across two ends of the laser diode  64  is determined according to the cross-voltage V 1 , the powers of laser beams emitted by the laser diode  64  change accordingly. That is, as the power-adjusting circuit  62  raises the cross-voltage V 1  from voltage levels V 1 a, V 1 b to voltage levels V 1 c, V 1 d gradually, the laser output power of the pickup head  56  is raised from power levels Pa, Pb to power levels Pc, Pd (as indicated in FIG. 3) accordingly. In general, the laser output power of a pickup head varies within an ideal range. That is, the power level of laser signals reflected from a disk is ideal as long as the laser output power of the pickup head falls in the ideal range, thus effectively providing complete information of the disk and controlling the rotating speed for the motor and other functions, like track-locking and track-searching functions, by determining the reflected laser signals correctly. When operated within the ideal range, the pickup head enables the laser output power of the pickup head and the cross-voltage perform well linear relation with corresponding circuits. As shown in FIG. 3, a range from the power level Pb and Pb indicates the ideal range of the laser output power. Part of the curve  94  within the range is perfectly linear, the difference between the power levels Pc and Pb being approximately proportional to the difference between the voltage levels V 1 c and V 1 b. Consequently, an ideal range for the cross-voltage V 1  can be defined by the help of the ideal range for the laser output power and the curve  94 . That the cross-voltage V 1  falls into the ideal range indicates the laser output power is falling within the ideal range as well.  
         [0020]    According to the above-mentioned principles, the processor  60  is capable of controlling the second signal  76 B in the feedback manner by determining the voltage levels of the cross-voltage V 1  and of changing the control signal  78  with the control circuit  58  to enable the power-adjusting circuit  62  to update the cross-voltage V 1 . After fed back by the updated cross-voltage V 1 , the processor  60  continues changing the control signal  78  with the second signal  76 B, enabling the power-adjusting circuit  62  to adjust the cross-voltage V 1  again. The steps described above can be processed continuously until the processor  60  has determined that the cross-voltage V 1  enters the ideal range. For example, if the cross-voltage V 1  equals the voltage level V 1 a, which is smaller than the voltage level V 1 b of the ideal range, as the processor  60  receives the voltage level V 1 a for the feedback control, the processor  60  will change the second signal  76 B and enables the control circuit  58  to generate a new control signal  78 , which is greater than the old control signal  78 , with the second signal  76   c , which is greater than the second signal  76 B. If it is assumed that a control pattern for the power-adjusting circuit  62  is a large cross-voltage V 1  corresponding to a large control signal  78 , the power-adjusting circuit  72  can, therefore, raise the cross-voltage V 1  with the enlarged control signal  78 . The enlarged cross-voltage V 1  will be fed back to the processor  60  and the processor  60  can then determine whether to further raise the cross-voltage V 1  with the control circuit  58  and power-adjusting circuit  62 .  
         [0021]    Practically, since the voltage level of the cross-voltage V 1  at node N 1  will be kept at a constant level by the bias voltage  74 A, the processor  60  can only depend on the output voltage  74 B output from the cross-voltage output end  57 B at node N 2 , as well as the cross-voltage V 1  equivalently, to process the feedback control according to the present invention. A low pass filter can be used to filter high frequency components in the cross-voltage V 1 , as well as high frequency noises, to prevent related circuits from being damaged by the cross-voltage V 1  due to abrupt variation of voltages during the feedback controlling process. In FIG. 2, a low pass filter  80 , installed in the optical disk drive  50 , is used to filter out the high frequency components and to moderate the variation of the output voltage  74 B during the feedback controlling process. Furthermore, a way to gradually raise the cross-voltage from a lower voltage level to a voltage level within the ideal range is used to prevent the laser diode  64  from damage due to too large a cross-voltage. For example, referring to FIG. 3 again, the processor  60  can raise the cross-voltage V 1  by iterating the process of feedback-and-adjusting with the control circuit  58  and the power-adjusting circuit  62  from the voltage level V 1 a to a voltage level with the ideal range gradually through voltage levels V 1 a 1 , V 1 a 2 , V 1 a 3  and V 1 a 4 . The pattern of how the power-adjusting circuit adjusts the cross-voltage according to the control signal is slightly different from one power-adjusting circuit to another due to the variations of the power-adjusting circuits, so gradually raising the cross-voltage V 1  prevents the laser diode from damage due to the abrupt variation of the cross-voltage V 1 .  
         [0022]    As mentioned previously, the control circuit  58  and power-adjusting circuit  62  suffer from drifting effect due to a mass production. In other words, the control signal  78  differs even if the processor  60  controls different but same type control circuits with an identical second signal  76 B. Even if utilizing an identical control signal  78 , different but same type power-adjusting circuits can generate different cross-voltages V 1 . In the prior art, the above two drifting effects of the control circuit and power-adjusting circuit combine to become the cross-voltage for the laser diode extremely large or small, thereby shifting the laser output power away from the ideal range. In the present invention, however, the cross-voltage V 1  can be kept at a voltage level within the ideal range by updating the control signal  78  and iteratively adjusting the cross-voltage V 1  according to the voltage level of the cross-voltage V 1 . Since the processor  60  adjusts the control signal  78  by determining the cross-voltage V 1 , the processor  60  still can keep the cross-voltage V 1  at a voltage level within the ideal range by iteratively adjusting the control signal  78  according to the cross-voltage V 1  even if the control circuit and power-adjusting circuit both suffer from the drifting effect due to mass production. For example, after controlled by the processor  60 , a control circuit can combine with a power-adjusting circuit to raise the cross-voltage V 1  sequentially from the voltage level V 1 a, V 1 a 1 , to V 1 a 2 , and another control circuit, after controlled by the processor  60 , can combine with another power-adjusting circuit to raise the cross-voltage V 1  through another route, like from voltage level V 1 a, V 1 a 2 , to V 1 a 4 . The point is no matter what kind of circumstances are present, the processor  60  always can adjust the cross-voltage V 1  to a voltage level within the ideal range and the laser output power to a power level within the ideal range as well, regardless of the drifting effects of the control circuit and power-adjusting circuit. In conclusion, the combined deviations of the control circuit  58  and power-adjusting circuit  62  can not only affect the processes, but also the results of the feedback controlling process.  
         [0023]    Please refer to FIG. 4, which is a function block diagram of a second embodiment applied to an optical disk drive  90  according to the present invention. For simplicity, the components shown in FIG. 4 and whose index is as the same as an index of a component in FIG. 2 have an identical functionality as that of the components in FIG. 2. That is, the optical disk drive  90  comprises the control circuit  58  and the pickup head  56 , the processor  100  emits the second signal  76 B and controls the control circuit  58  to generate the corresponding control signal  78 , and the power-adjusting circuit  62  adjusts the cross-voltage V 1  according to the control signal  78 . Where the second embodiment differs from the first embodiment is the processor  100  of the optical disk drive  90  adjusts the second signal  76 B to updates the control signal  78  and changes the cross-voltage V 1  with the power-adjusting circuit  62 . Please refer to FIG. 5, as well as to FIG. 4. A curve  96  shown in FIG. 5 demonstrates a relation between the laser output power of the pickup head  56  and the control signal  78 , an abscissa indicating the levels of the laser output power of the pickup head  56  and an ordinate the levels of the control signal  78 . As the control signal  78  received by the power-adjusting circuit  62  is raised from a voltage level A 1  to A 4 , the laser output power of the pickup head  56  will raise from a power level P 2  to P 4  accordingly. In the curve  96 , a laser output power can be defined with the power levels P 2  and P 4 . Similarly to the curve  94  shown in FIG. 3, part of the curve  96  within the power levels P 2  and P 4  performs a perfect linear characteristic and defines a corresponding ideal range for the control signal  78  from the voltage level A 2  to A 4 . That the control signal  78  enters the corresponding ideal range represents the laser output power being falling into the ideal range too. The principle described above shows that the processor  100  can be controlled by the control signal  78  in the feedback manner and the processor  100  can adjust the second signal  76   b  according to the second signal  76 B and controls the control circuit  58  to update the second signal  76 B and to correspond the second signal  76 B with the ideal range.  
         [0024]    Practically, the optical disk drive  90  can utilize an amplifier  92  to amplify the control signal  78  so that the processor  100  can easily generate the corresponding second signal  76 B (indicating the current power level of the pickup head  56 ) and feed the second signal  76 B to the differential amplifier  72  for a further comparison operation between the first signal  76 A and analog second  76 C. Similar to the operations of the first embodiment, by iterating the feedback-and adjusting steps, the processor  100  of the second embodiment can gradually raise the second signal  76 B from a smaller voltage level, like the voltage level A 1  shown in FIG. 5, and then determines whether the control signal  78  has fallen into the ideal range according to the feedback control signal  78 . If not so, the processor  100  continues raising the control signal  78  with the control circuit  58  by further adjusting the second signal  76 B until the control signal  78  enters into the ideal range. Similar to the first embodiment, the second embodiment shown in FIG. 4 also can overcome the drifting effect of the control circuit  58 . That is, even if the control signals generated by the control circuit  58  after receiving an identical second signal  76 B are different, because the processor  100  is controlled in the feedback manner according to the control signal  78 , the control signal  78  can still be control to stay at a voltage level within the ideal range and the laser output power will stay at a power level within the ideal range, becoming neither too large nor small.  
         [0025]    In an optical disk drive, a processor controls the laser output power of a pickup head with a control circuit and a power-adjusting circuit. According to the prior art, the drifting effect of the control circuit and power-adjusting circuit combine to enable the laser output power of the pickup head out of control and to become extremely large or small, resulting in too large or too small laser signals reflected by a disk projected by laser beams having unstable power and some functions, like track-locking, track-searching or rotating speed control of the optical disk drive, functioning according to stable reflected laser signals are hard to perform. In contrast to the prior art, the present invention can provide an optical disk drive to keep the laser output power of pickup head at a power level within the ideal range according to the control signal of the power-adjusting circuit and the cross-voltage of the laser diode. Therefore, the laser signal reflected by the disk has a moderate voltage level and the optical disk drive can perform the functions of track-locking, track-searching and rotating speed control normally according to the reflected laser signal. Additionally, the optical disk drive can achieve the above goals without changing the design of the control circuit and pickup head, reducing the bulk and cost to design the optical disk drive.  
         [0026]    Following the detailed description of the present invention above, 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.