Abstract:
When performing OPC, data including a plurality of first sequences and second sequences with specified contents are written onto the optical disk. A read result corresponding to the written data is then read. The read result is high-pass filtered such that effects corresponding to the second sequences are contained in a portion of the read result corresponding to the first sequences. Since the first sequences have specified contents, the portion of the read result corresponding to the first sequences are detected, and the beta-parameter is evaluated only according to the portion of the read result corresponding to the first sequences.

Description:
BACKGROUND OF INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention provides a method and related apparatus for performing optimal power control, and more particularly, a method and related apparatus for evaluating a beta-parameter according to a read result of portion of write-in data with specific content.  
         [0003]     2. Description of the Prior Art  
         [0004]     In modern information society, small, light, high-density, and low-cost optical disks have become one of the most popular non-volatile storage devices. With development of CD-R drives and Compact Disk Recordable drives, users can store personal data in an optical disk. Since technologies for writing (burning) data into an optical disk need high precision and high accuracy, developmental issues of information technologies have focused on how to store data with an optimal write-in power.  
         [0005]     In general, when writing data into an optical disk, a CD-R drive emits laser beams with a specific power onto the optical disk, so as to bring about specific physical or chemical reactions for the optical disk to form a plurality of pits and lands. Owing to different reflection coefficients of the pits and the lands corresponding to a laser beam, an optical disk drive can read data stored in the optical disk by detecting reflection intensity of the pits and lands after emitting proper power laser beams onto the optical disk. However, optical disks made by different manufacturers usually have different physical/chemical characters while optical disk drives with different brands and models also have different laser emitters, rotational speeds, etc. Therefore, a proper power degree used for forming pits and lands onto the optical disk is a key issue during associated data writing operation.  
         [0006]     In order to choose a preferred write-in power, the optical disk drive performs optimal power control before writing data onto the optical disk. When performing optimal power control, the optical disk drive employs different write-in powers to write default write-in data onto the optical disk, and then reads back the just write-in data from the optical disk, so as to determine whether the currently used write-in power is an optimal power. Please refer to  FIG. 1 , which illustrates a waveform-timing diagram of a write-in data  10  and two possible corresponding read results  12 A,  12 B during relative performing optimal power control procedure, wherein the X- and Y-axis indicates time scale and waveform amplitude, respectively. The read result  12 A is a result when writing the write-in data  10  into the optical disk with a preferred write-in power, while the read result  12 B is a result when writing with an improper power.  
         [0007]     As those skilled in the art recognize, digital data is properly coded before being written into the optical disk. Generally, in protocols of CD-R/RW, Compact Disk Recordable/ReWriteable, or DVD-R/RW, DVD+R/RW, Digital Versatile Disk R/RW, specific streams of coded data include bits with the same content. For example, in protocols of CD-R/RW, a stream of the coded data includes at most 11 bits with the same content, but at least 3 bits with the same content, while in the DVD protocol, a stream of the coded data includes at most 14 bits with the same content. Owing to original data after coding includes different streams with different numbers of bits, a write-in data should include streams with different numbers of bits for simulating data writing with different degree of write-in powers.  
         [0008]     In  FIG. 1 , the write-in data  10  includes streams with different numbers of bits. For example, a stream  14 A includes three digital “0”s between time points ta6 and ta1, which continues for a 3T duration Ta, where T is a bit duration. Also, a stream  14 B with the duration Ta includes three “1”s between time points ta1 and ta2. Besides, a stream  16 A includes  14  “0”s between time points ta5 and ta6, which continues with a 14T duration Tb, while a stream  16 B with the duration Tb includes  14  “1”s between time points ta4 and ta5.  
         [0009]     Because of different reflection coefficients, the pits and the lands of the optical disk can properly represent “0” and “1”. Therefore, the optical disk drive can decide each bit whether “0” or “1” by comparing the read result with a zero level. When writing data with a preferred write-in power, the read signal should be the read result  12 A. For example, the write-in data  10  changes data status (which means the data changes from “0” to “1”, or vice versa) at time points ta1, ta2, ta3, ta4, ta5, ta6, and ta7, while the read result  12 A corresponding to the time points responds to zero-crossings (which means a signal level changes from a level greater than a zero level L0 to a level smaller than the zero level L0, or vice versa). In other words, the read result  12 A can be decoded as “1” streams during a duration Ta from time points ta2 to ta3, a duration Tb from time points ta4 to ta5, and a duration Ta from ta6 to ta7, where the level of the read result  12 A is greater than the zero level L0. Also, the read result  12 A can be decoded as “0” streams during a duration Ta from time points ta1 to ta2, a duration Ta from time points ta3 to ta4, and a duration Tb from ta5 to ta6, where the level of the read result  12 A is smaller than the zero level L0.  
         [0010]     However, if the write-in power deviates from an ideal power, the read signal should be the read result  12 B in  FIG. 1  because the optical disk drive cannot form proper pits and lands with improper laser power. In this case, the read result  12 B cannot represent original data in that the read result  12 B crosses the zero level L0 at time points tb1, tb2, tb3, tb4, tb5, tb6, and tb7, which can not respond to the write-in data  10  from time points ta1 to ta7 when changing data status. For example, a duration of the read result  12 B between time points tb1 and tb2, which level is smaller than the zero level L0, is obviously smaller than a duration between time points tb2 and tb3, which level is greater than the zero level L0. However, the fact is that the streams  14 A and  14 B corresponds to the two durations of the read result  12 B respectively with the same length. Therefore, when the write-in power deviates from the ideal power, the read result  12 B cannot represent the length of stream  14 A is equal to the length of stream  14 B.  
         [0011]     Besides, in  FIG. 1 , lengths of the streams affect the read result corresponding to the streams. For example, when an optical disk drive writes a longer “0” stream onto an optical disk with laser beams of larger power, deeper pits are formed. Relatively, when writing a shorter “0” stream, the laser beam has a shorter duration and forms shallower pits. Since different pit depths have different reflection coefficients, when reading the “0” streams with different lengths, portions of the read result corresponding to the “0” streams have different signal values.  
         [0012]     For example, in  FIG. 1 , because the “0” stream  16 A between time points ta5 and ta6 is longer than the “0” stream  14 A between time points ta1 and ta2, a portion of the optical disk corresponding to the stream  16 A reflects weaker laser beams with deeper pits. Even if both the streams  14 A and  16 A represent “0”, the signal level of the read result  12 A between time points ta5 and ta6 is lower than that between time points ta1 and ta2. As  FIG. 1  illustrates, the lowest levels of the read result  12 A between time points ta5 and ta6 and between time points ta1 and ta2 are levels Ln1 and Ln0 respectively, wherein the level Ln1 is lower than the level Ln0. Similarly, as to the “1” streams  14 B and  16 B, the signal level of the read result  12 A corresponding to the longer stream  16 B can reach a level Lp1between time points ta4 and ta5, while the signal level of the read result  12 A corresponding to the stream  14 B reaches a lower level Lp0between time points ta1 and ta2.  
         [0013]     The write-in power also affects waveforms of the read result. The absolute value of the lowest level Ln0 of the read result  12 A between time points ta1 and ta2 is equal to the absolute value of the highest level Lp0 of the read result  12 A between time points ta2 and ta3, which means that the stream  14 A of the write-in data  10  between time points ta1 and ta2 has the same length (or number of bits) as the stream  14 B between time points ta2 and ta3. Similarly, the absolute value of the highest level Lp1 of the read result  12 A between time points ta4 and ta5 is equal to the absolute value of the lowest level Ln1 between time points ta2 and ta3, which means that the streams  16 B and  16 A have the same lengths.  
         [0014]     Contrarily, in the real case as the read result  12 B shows, the waveform is not so symmetric as the ideal read result  12 A. For example, the read result  12 B has a lowest level Ln3 between time points tb1 and tb2 corresponding to the stream  14 A, and a highest level Lp3 between time points tb2 and tb3 corresponding to the stream  14 B. However, the absolute value of the level Lp3 is larger than the absolute value of the level Ln3; that is, the read result  12 B cannot represent the equal length of the streams  14 A and  14 B. Also, the absolute value of the highest level Lp2 of the read result  12 B corresponding to the stream  16 B between time points tb4 and tb5 is not equal to the absolute value of the lowest level Ln2 corresponding to the stream  16 A between time points tb4 and tb5.  
         [0015]     In summary, after writing the write-in data onto the optical disk with an ideal power, each portion of the read result corresponding to the streams with the same lengths should have the same durations during two zero-crossing time points and should also have the same amplitude. On the other hand, if the write-power deviates from the ideal power, pits and lands with incorrect depths cannot represent streams with correct lengths and content. Furthermore, even if streams have the same length, the corresponding read signals do not keep the same duration and amplitude. In other words, according to durations of zero-crossings and amplitudes of the read result, the optical disk drive determines whether the write-in data is written onto the optical disk with a preferred write-in power. In general, a prior art optical drive with burn function sets a beta-parameter for responding to the read result quantitatively. When performing optimal power control, the optical disk drive writes with different write-in powers, calculates beta-parameters corresponding to the read result with the write-in powers, and then compares each beta-parameter. In this way, the optical disk drive chooses a preferred power approximating the ideal power from these write-in powers.  
         [0016]     Please refer to  FIG. 2 , which illustrates a schematic diagram of a prior art optical disk drive  20  when performing optimal power control. The optical disk drive  20  includes a motor  22 , a pick-up head  24 , an access circuit  28 , and a control module  30 . The optical disk drive  20  further includes a peak hold circuit  32 A, a bottom hold circuit  32 B, and an analog to digital converter  34  for performing optimal power control. The motor  22  rotates an optical disk  26 . The pick-up head  24  emits laser beams onto the optical disk  26  and receives reflections for data access. The control module  30  controls operations of the optical disk drive  20 . The access circuit  28  drives the pick-up head  24  to write coded data onto the optical disk  26  under control of the control module  30 . The pick-up head  24  transmits signals corresponding to the reflections through the access circuit  28  to the control module  30  after receiving the reflections from the optical disk  26 . The peak hold circuit  32 A generates an output signal after receiving an input signal and makes the output signal track to peaks of the input signal, while the bottom hold circuit  32 B makes its output signal track to bottoms of its input signal. The converter  34  converts analog signals to digital signals under control of the control module  30 .  
         [0017]     When performing optimal power control, the access circuit  28  transmits the write-in data to the pick-up head  24 , and the pick-up head  24  writes the write-in data onto the optical disk  26  with a default write-in power. Then, the pick-up head  24  reads the written data from the optical disk  26 , and transmits a read result  36  through the access circuit  28  to the peak and the bottom hold circuits  32 A and  32 B. The peak hold circuit  32 A tracks to peaks of the read result  36  and generates a corresponding signal  38 A, while the bottom hold circuit  32 B tracks to bottoms of the read result  36  and generates a corresponding signal  38 B. The converter  34  converts the signals  38 A and  38 B alternatively to digital signals. According to the digital signals corresponding to the signals  38 A and  38 B, the control module  30  can calculate a beta-parameter corresponding to the write-in power. Please refer to  FIG. 3  (also  FIG. 2 ), which illustrates an amplitude-versus-time diagram of each signal of the optical disk drive  20  in  FIG. 2  when performing optimal power control, where the X-axis is time scale, and the Y-axis is signal amplitude. As  FIG. 3  illustrates, the signal  38 A provided by the peak hold circuit  32 A tracks to peaks of the read result  36  (a dotted line shown in  FIG. 3 ), while the signal  38 B provided by the bottom hold circuit  32 B tracks to bottoms of the read result  36 . The level of the signal  38 A provided by the converter  34  at time point tc1 is a level LP0, and at time point tc2 is a level LB0. Considering the levels LP0 and LB0, the beta-parameter of the read result  36  can be calculated.  
         [0018]     As mentioned above, whether the write-in power deviates from the ideal value can be determined whether amplitudes of the read result are symmetric to the zero level L0. In the prior art optical disk drive  20 , the peak and the bottom hold circuits  32 A and  32 B track peaks and bottoms of the read result  36  for calculating amplitude of the read result  36 , allowing calculation of the beta-parameter.  
         [0019]     Nevertheless, as  FIG. 3  illustrates, the peak/bottom hold circuits track extreme values of signals with capacitors, where electric leakage is inevitable, such that both the peak and the bottom hold circuits cannot keep tracking the extreme values stably, thereby affecting amplitude calculations of the read result  36 . Take the signal  38 A provided by the peak hold circuit  32 A for example. When the peak hold circuit  32 A starts tracking a peak level LP of the read result  36  at time point tc0, owing to electric leakage, the signal level of the signal  38 A provided by the peak hold circuit  32 A decreases gradually. Until at time point tc5 the signal level of the signal  38 A is lower than the signal level LP0 of the read result  36 , the peak hold circuit  32 A starts to track the peak level LP again. That is, the converter  34  samples a level LP0 of the signal  38 A at time point tc1, but the level LP0 is not the real peak level LP of the read result. Similarly, the extreme level of the signal  38 B provided by the bottom hold circuit  32 B should be a level LB, but actually, the converter  34  samples a level LB0 at time point tc2 instead of the extreme level LB. In other words, the sampling values of the signals  38 A and  38 B provided by the converter  34  cannot indicate the amplitude of the read result  36  exactly. Besides, sampling results provided by the converter  34  at different time points also cannot indicate the amplitude of the read result because of the same reason. For example, sampling results provided by the converter  34  at time points tc3 and tc4 are different from those at time points tc1 and tc2, with the result that the corresponding beta-parameters calculated by the control module  30  are also different. That is, the beta-parameters are not stable.  
         [0020]     In addition, the converter  34  cannot sample the signals  38 A and  38 B at the same time, that is, the extreme values of the signals  38 A and  38 B are the values in different sampling times. It is correct to compare the peak value with the bottom value corresponding to the same length of the stream. If the peak extreme value of the signal  38 A is sampled by the converter  34  corresponds to the short data stream, but the bottom value of the signal  38 B is sampled corresponds to the long data stream because of the different sampling time, the beta-parameter will not be accurate.  
         [0021]     Please refer to  FIG. 4 .  FIG. 4  illustrates functional blocks of another well-known optical disk drive performing optimal power control. The optical disk drive  40  comprises a pick-up head  44 , an access circuit  48 , a control module  50 , a high pass filter  42 , a slicer  46 , a charger  52 A, a discharger  52 B, a resistor R 0 , and a capacitor C 0 . The control module  50  controls the operation of the optical disk drive  40 . When performing optimal power control, the control module  50  controls the access circuit  48  to transmit write-in data to the pick-up head  44 . The pick-up head  44  writes the write-in data with a predetermined power onto the optical disk  26 . The write-in data that was written in the optical disk  26  is sent back to the access circuit  48 , which generates a read result  56 A. The high-pass filter  42  filters the read result  56 A and generates a filtered read result  56 B. The slicer  46  slices the parts of the read data  56 b which are higher or lower than a zero level L0 to sliced signals having fixed high and low levels, which are used to control the charger  52 A and the discharger  52 B. The charger  52 A and the discharger  52 B can be the controlled current sources. The charger  52 A is able to charge the capacitor C 0  through the resistor R 0  to increase the voltage of the node N 0 . The discharger  52 B is able to discharge the capacitor C 0  through the resistor R 0  to decrease the voltage of the node N 0 . Finally, the control module  50  calculates the beta-parameter according to the voltage of the node N 0 .  
         [0022]     To further describe the principles of an optical disk drive performing optimal power control, please refer to  FIG. 5  (as well as  FIG. 4 ).  FIG. 5  illustrates a waveform timing diagram of each relative signal of the optical disk drive  40  calculating the beta-parameter. The X-axis represents time, and the Y-axis represents the amplitude of each waveform. As described in  FIG. 1 , the write-in power deviates from the ideal value, the corresponding read result deviate from the zero level too. Accordingly, the periods between zero-crossing points do not represent the time period of the data streams of the same length. As for the case of the short data stream, the deviation from the zero level is more obvious. In  FIG. 5 , the read result  56 A deviates from the zero level, especially the parts corresponding to short data streams between time intervals td1 to td4, and td6 to td8. The purpose of the high-pass filter  42  is to filter out DC corresponding to deviation of the read result  56 A from the zero level. For example, the high frequency part of the read result  56 A between td1 to td4 and td6 to td8 deviates from the zero level L0, so two parts larger and smaller than the zero level L0 in the read result  56 A have no symmetric amplitude. After high-pass filtering, the high frequency part of the read result  56 B has a more symmetric waveform, which results from the reservation of high frequency signals and blocking of low frequency signals during filtering. Equivalently speaking, the high-pass filter  42  removes the deviation of the high frequency part of the read result  56 A corresponding to short data streams from the zero level L0.  
         [0023]     In contrast to the high frequency part, the high-pass filter  42  adjusts the deviation of the low frequency part of the read result  56 A to a larger degree. For example, between td4 and td5, the part of the read result  56 A corresponding to a long data stream originally maintains two zero-crossing periods Tp0 and Tp1, but after being high-pass filtered, the read result  56 B has similar DC shifting due to the effect of the reservation of high frequency part (the read result  56 A in  FIG. 5  is vertically shifted). Thus, the zero-crossing points, td4 and td5, of the read result  56 B will be changed to td2 and td3. In other words, the deviation of the high frequency part (corresponding to the short data stream) of the read result  56 A from the zero level L0 will be transformed to the change of the low frequency part (corresponding to the long data stream) of the read result  56 B. Therefore, in the read result  56 B, even for different data streams (especially the long data stream) with the same length, zero-crossing periods are different. The optical disc drive  40  of prior art calculates the beta-parameter according to the read result  56 B to indicate if the write-in power deviates from the ideal value.  
         [0024]     After the read result  56 B is generated, the slicer  46  generates the sliced signal  58  according to the zero-crossing points of the read result  56 B, letting the H level part of the sliced signal  58  correspond to the part of the result  56 B which is higher than the zero level L0, and letting the L level part of the sliced signal  58  correspond to the part of the result  56 B which is lower than the zero level L0. Therefore, the H level part and the L level part of the sliced signal  58  represent the zero-crossing periods of the read result  56 B. According to the sliced signal  58  of the slicer  46 , the charger  52 A and the discharger  52 B will charge and discharge the capacitor C 0  in different times. The timing diagrams of  59 A and  59 B in  FIG. 5  represent the charging time and the discharging time of the charger  52 A and the discharger  52 B, respectively. During the time when the sliced signal  58  maintains the level H, such as the time td2 to td3 and the time td4 to td5 in the timing diagram  59 A, the charger  52 A will charge the capacitor with a predetermined current. On the other hand, during the time when the sliced signal  58  maintains the level L, such as the time td1 to td2, the time td3 to td4 and the time td5 to td6 in the timing diagram  59 B, the discharger  52 B will discharge the capacitor with a predetermined current (usually the same as the predetermined charging current). Therefore, the charges stored in the capacitor CO are relative to the difference of zero-crossing periods of the read signal  56 B. As the capacitor C 0  is charged and discharged according to the sliced signal  58 , the accumulated charges in the capacitor C 0  are equivalent to the difference between the period when the read result  56 B is larger than the zero level L0 and the period when the read result  56 B is smaller than the zero level L0.  
         [0025]     When the write-in power is closer to the ideal degree of power, the read results  56 A and  56 B should have almost perfect oscillation waveforms, and the period when the waveform is larger than the zero level L0 and the period when the waveform is lower than the zero level L0 should be almost equal, resulting in that the charges of the capacitor C 0  are close to zero. In this situation, the write-in power is near the ideal value. Otherwise, if the write-in power further deviates from the ideal value, the read result  56 A deviates from the zero level L0, as shown in  FIG. 5 . The deviation of read result  56 A from the zero level L0 leads to the differences in the zero-crossing periods. The larger the differences in the zero-crossing periods, the more charges the capacitor C 0  accumulates.  
         [0026]     A disadvantage of the above prior art is that the accumulated charges in the capacitor C 0  cannot sensitively and definitely indicate the difference of the zero-crossing periods of the read result  56 B. Generally speaking, it is much easier for the deviation of the write-in power from the ideal value to result in shifting of the zero level in the high frequency part of the read result  56 A. However, in the prior art technique shown in  FIG. 4  and  FIG. 5 , both the high-frequency part and the low-frequency part of the read result  56 B keep accumulating the difference of the zero-crossing periods. Because the purpose of high pass filtering is to reserve the AC (alternating current) part of the read result  56 B, and an AC signal has equal positive and negative parts, the accumulation of the high-frequency zero-crossing periods and the low-frequency zero-crossing periods of the read result  56 B after some time will cancel each other. In other words, the charges of the capacitor C 0  are closer to zero after accumulation of the high-frequency zero-crossing periods and the low-frequency zero-crossing periods of the read result  56 B even when the write-in power deviates from the ideal value, making the optimal control more difficult.  
         [0027]     In summary, high-pass filtering transforms the deviation of the high-frequency part of the read result  56 A to the differences of the zero-crossing periods of the low-frequency part of the read result  56 B. If both high-frequency zero-crossing periods and the low-frequency zero-crossing periods are accumulated, the beta-parameter cannot definitely express the deviation of the write-in power.  
       SUMMARY OF INVENTION  
       [0028]     This invention provides a method and an apparatus for performing optimal power control of an optical disk drive based on a beta-parameter for determining whether a default power is equal to an optimal write-in power for writing data onto an optical disk.  
         [0029]     Briefly described, a method for performing optimal power control includes: (a) setting a write-in data, which includes a plurality of first sequences and second sequences; (b) writing the write-in data onto the optical disk with the default power, then reading the write-in data from the optical disk and generating a corresponding read result, the read result including a first read signal and a second read signal each corresponding to the first sequence and the second sequence; (c) processing an evaluation step according to a portion of the first read signal, instead of the second read signal, with signal level greater or smaller than a default level for summing the beta-parameter.  
         [0030]     These and other objectives of 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  
       [0031]      FIG. 1  illustrates a waveform versus time diagram of a read result provided by a prior art optical disk drive.  
         [0032]      FIG. 2  illustrates a block diagram of a prior art optical disk drive.  
         [0033]      FIG. 3  illustrates a waveform versus time diagram of the optical disk drive in  FIG. 2  while performing optimal power control.  
         [0034]      FIG. 4  illustrates a block diagram of a prior art optical disk drive.  
         [0035]      FIG. 5  illustrates a waveform versus time diagram of the optical disk drive in  FIG. 4  while performing optimal power control.  
         [0036]      FIG. 6  illustrates a block diagram of a present invention optical disk drive.  
         [0037]      FIG. 7  illustrates a waveform versus time diagram of the optical disk drive in  FIG. 6  while performing optimal power control.  
         [0038]      FIG. 8  illustrates an implementation of a write-in data and related signals. 
     
    
     DETAILED DESCRIPTION  
       [0039]     Please refer to  FIG. 6 , which illustrates a schematic diagram of a present invention optical disk drive  60 . The optical disk drive  60  includes a motor  62 , a pick-up head  64 , an access circuit  68 , a control module  70 , a high-pass filter  72 , a slicer  74 , a write-in data arrangement module  71  and an evaluation module  80 . The evaluation module  80  includes a charger  76 A, a discharger  76 B, a decision module  78 , a switch  82  and a storage unit  84 . In  FIG. 6 , the storage unit  84  includes a resistor R and a capacitor C. The motor  62  rotates an optical disk  66 . The pick-up head  64  emits laser beams onto the optical disk  66  and receives reflections for data access. The control module  70  controls operations of the optical disk drive  60 . The access circuit  68  connects to the high-pass filter  72 , and the slicer  74  slices a filtered signal provided by the high-pass filter  72 , and then transmits a sliced signal to the decision module  78 . According to the sliced signal, the optical disk drive  60  determines whether the charger  76 A and the discharger  76 B should charge or discharge. In the evaluation module  80 , the switch  82  is between the storage unit  84  and the charger  76 A or the discharger  76 B for controlling connection between the storage unit  84  and the charger  76 A or the discharger  76 B. A control signal  90  provided by the decision module  78  controls the open or closed state of the switch  82 . In addition, data stored in the storage unit  84  represents charge amount of the capacitor C. When the switch  82  is open, electricity provided by the charger  76 A can be transmitted to the storage unit  84  for charging the capacitor C, which is equivalent to increasing a data amount stored in the storage unit  84 , while the discharger  76 B acts to decrease the data amount. When the switch  82  is closed, the connection between the charger  76 A or the discharger  76 B and the storage unit  84  is shut down, so as to prevent from electricity exchange; moreover, the data amount of the storage unit  84  is prevented from changing, and charge stored in the capacitor C returns to the control module  70  at a node N 1 .  
         [0040]     In the present invention, the write-in data arrangement module  71  can arrange or record the write-in data  92  with specific content. In a preferred embodiment, the write-in data includes a plurality of sequences (each named a long sequence) comprising long streams, and a plurality of sequences (each named a short sequence) comprising short streams. Each long sequence includes two long streams with the same length (the same number of bits) and different content, while each short sequence includes two short streams with the same length and different content.  
         [0041]     When the present invention optical disk drive  60  performs optimal power control, the control module  70  controls the pick-up head  64  to write the write-in data  92  provided by the write-in data arrangement module  71  onto the optical disk  66  with a default write-in power through the access circuit  68 . Then, the pick-up head  64  reads the write-in data  92  from the optical disk  66 , and generates a corresponding read result  86 A through the access circuit  68  to the filter  72 . The filter  72  outputs a read result  86 B after high-pass filtering the read result  86 A. The slicer  74  generates a slice signal  88  according to whether the signal level of the read result  86 B is greater than a zero level. Moreover, the slicer  74  controls the charger  76 A and the discharger  76 B with the slice signal  88 . Besides, the slice signal  88  is transmitted to the decision module  78  for determining which portions of the read result  86 B (and the slice signal  88 ) corresponds to the long sequence. According to the decision result, the decision module  78  outputs the control signal  90  for controlling the switch  82 , so that the connection between the charger  76 A or the discharger  76 B and the storage unit  84  is closed only when the slice signal  88  corresponds to the long sequence, while the control signal  90  controls the switch  82  to be open when the slice signal  88  corresponds to the short sequence, so as to prevent the charger  76 A and the discharger  76 B from changing the data amount of the storage unit  84 . Finally, according to the data amount of the storage unit  84 , the control module  70  can calculate a beta-parameter corresponding to the default write-in power.  
         [0042]     Please refer to  FIG. 7  (also  FIG. 6 ), which illustrates a waveform-time diagram of the write-in data  92  and related signals when the present invention optical disk drive  60  performs optimal power control. The X-axis in  FIG. 7  is time scale, while the Y-axis is amplitudes of the read results  86 A,  86 B, the slice signal  88 , and the control signal  90 . As mentioned above, the write-in data  92  includes a block SL comprising a plurality of long sequences Sa, and a block SS comprising a plurality of short sequences Sb, wherein each long sequence Sa includes a “1” long stream S 1  and a “0” long stream S 2 , while each short sequence Sb includes a “1” short stream S 3  and a “0” short stream S 4 . Additionally, data to be written into the optical disk is coded to a plurality of streams with different lengths. In DVD-R/RW protocols, the longest stream includes 14 bits (14T) of the same content (0 or 1), while the shortest stream includes three bits (3T) of the same content, so that the long streams S 1  and S 2  of the present invention include 14 “1” bits and 14 “0” bits respectively, while the short streams S 3  and S 4  of the present invention include three “1” bits and three “0” bits respectively. Similarly, in protocols of CD-R/RW, the longest and the shortest streams include 11 and three bits (11T and 3T) respectively, so that the long streams S 1  and S 2  of the present invention should be 11 bits, and the short streams S 3  and S 4  should be three bits.  
         [0043]     As mentioned regarding  FIG. 1 , two streams of a sequence with the same length and different contents correspond to a cycle of a read result. For example, in  FIG. 7 , the three sequences Sa provided by the streams S 1  and S 2  of the write-in data  92  correspond to three low-frequency cycles of the read result  86 A from time points t0 to t2, from time points t2 to t4, and from time points. t4 to t6, while each short sequence Sb corresponds to a high-frequency cycle of the read result  86 A, such as the read result  86 A from time points t6 to t7 or from time points t7 to t8. In addition, when the write-in power deviates from the ideal power, the read result  86 A deviates from the zero level L0, especially in the short sequences or the high-frequency cycles. After the read result  86 A is high-pass filtered with the filter  72 , deviation of the read result  86 A from the zero level corresponds to the low-frequency portion of the read result  86 B, so that durations of the low-frequency portion of the read result  86 B greater than the zero level are different from durations of the low-frequency portion of the read result  86 B smaller than the zero level.  
         [0044]     After the slicer  74  slices the read signal  86 B into the slice signal  88 , level H portions of the slice signal  88  correspond to portions of the read result  86 B greater than the level L0, while level L portions of the slice signal  88  correspond to portions of the read result  86 B smaller than the level L0. In other words, the level L portions of the slice signal  88  are the portions of the read result  86 B smaller than the zero level L0, while the level H portions of the slice signal  88  are the portions of the read result  86 B greater than the zero level L0. Therefore, the charger  76 A can charge the storage unit  84  during the level H portions of the slice signal  88 , while the discharger  76 B can discharge the storage unit  84  during the level L portions of the slice signal  88 .  
         [0045]     In addition, according to the slice signal  88 , the decision module  78  of the present invention determines which portion of the write-in data  92  corresponds to the slice signal  88  and generates the control signal  90  for controlling the open or closed state of the switch  82 . As mentioned above, main difference of duration between portions of the read result  86 B (and the slice signal  88 ) greater than the zero level L0 and portions of the read result  86 B (and the slice signal  88 ) smaller than the zero level L0 appears in the low-frequency portion of the read result  86 B. Besides, the difference becomes unapparent after filtering, caused by accumulating of differences of durations of the low-frequency portion and high-frequency portion, so that the filtered read result cannot accurately indicate deviation of the original read result from the zero level. Therefore, the decision module  78  of the present invention determines the low-frequency portion of the read result  86 B (and the slice signal  88 ) corresponding to the long sequence, and makes the switch  82  closed when the slice signal  88  corresponds to the long sequence, but open when the slice signal  88  corresponds to the short sequence. Therefore, the present invention indicates deviation of the read result  86 A from the zero level L0 according to the low-frequency portion of the read result  86 B, and performs optimal power control with the data amount of the storage unit  84  corresponding to each write-in power under control of the control module  70 .  
         [0046]     The decision module  78  can be achieved according to whether the signal level of a portion of the slice signal  88  keeps the same level over a default duration, which means that the portion of the slice signal  88  corresponds to the long sequence or equivalently the low-frequency portion of the read result  86 B. The default duration can be longer than the duration of the short stream, but shorter than the duration of the long stream. For example, if a long stream and a short stream have  14  and three bits (14T and 3T), the default duration can be 5T or 6T. Therefore, if the signal level of a portion of the slice signal  88  keeps at the same level over the duration of which a short stream should be, the slice signal  88  corresponds to a long stream.  
         [0047]     In  FIG. 7 , the long sequence Sa of the block SL corresponds to the “1” stream S 1  with the level H, and the decision module  78  determines whether the long sequence Sa starts according to whether a portion of the slice signal  88  keeps at the level H over a default duration Te. For example, after the slice signal  88  jumps from the level L to the level H at time point t0, the decision module  78  calculates the level H duration of the slice signal  88 . At time point te (also the time point from time point t0 plus the default duration Te), a portion of the slice signal  88  still keeps in the level H, so that the decision module  78  determines that the portion of the slice signal  88  corresponds to a long stream at time point te. Additionally, the write-in data arrangement module  71  arranges a default number of the sequences Sa of the write-in data  92  in the block SL, and the decision module  78  determines that the slice signal  88  has a specific length corresponding to the long sequence from time point te. As a result, after the slice signal  88  falls from the level H to the level L at time point t1, the decision module  78  determines that the slice signal  88  is corresponding to the “0” long stream, so that the decision module  78  changes the signal level of the control signal  90  from the level L to the level H for closing the switch  82 , so as to charge or discharge the storage unit  84 . As a discharge sequence  91  in  FIG. 7  illustrates, while the control signal  90  changes from the level L to the level H at time point t1, the discharger  76 B discharges the capacitor C between time points t0 and t2, where the slice signal  88  is corresponding to a long stream S 2 . Then, the charger  76 A charges the capacitor C between time points t2 and t3, where the slice signal  88  is corresponding to a long stream S 1 . Therefore, from time point t1 to t3, increased charge of the capacitor C is directly proportional to different duration between the streams S 1  and S 2  (or Td-Tc). Similarly, from time point t3 to t5, increased charge of the capacitor C is directly proportioned to Tg-Tf.  
         [0048]     In addition, after the switch  82  is closed at time point t1, the decision module  78  continues the recording level difference of the slice signal  88  between the level H and the level L. Owing to the fixed default number of the long sequences of the write-in data provided by the write-in data arrangement module  71 , the decision module  78  can determine how many long streams have passed by way of calculating alternation times between the level H and the level L of the slice signal  88 , so as to control the switch  82  with the control signal  90 . Moreover, because the short sequences Sb of the block SS continue with the last long sequence Sa of the block SL in the write-in data  92 , the decision module  78  makes the switch  82  open at the end of the long “1” stream S 1  of the last long sequence Sa, so as to stop increasing the data amount of the storage unit  84  while the slice signal  88  corresponds to the short streams. Therefore, the present invention determines whether the write-in power for the write-in data  92  is a preferred power according to the low-frequency portion of the filtered read result  86 B.  
         [0049]     In  FIG. 7 , because the block SL of the write-in data  92  has three long sequences Sa, or six long streams, the decision module  78  determines a duration corresponding to the b  6  long streams by means of detecting five level alternations (or time points t1, t2, t3, t4, and t5) of the slice signal  88  after time point te. Additionally, the level alternation of the slice signal  88  at time point t5 indicates that the last long stream of the block SL is starting, so that the decision module  78  makes the switch  82  open with the changing of the control signal  90  from high to low at time point t5. The present invention does not increase the data amount of the storage unit  84  during the duration corresponding to the last long stream of the block SL, which can prevent negative effects on the data amount when the signal level is alternating from low to high. The block SL includes six long streams with alternative “1”s and “0s. Deducting the first and the last long streams, the charger  76 A and the discharger  76 B calculate two zero-crossing differences between two cycles during time points t1 to t5.  
         [0050]     The present invention can arrange the write-in data  92  into a plurality of blocks SL, SS, SL, SS, etc. The decision module  78  makes the switch  82  closed during durations of the blocks SL. In this case, the decision module  78  continues detecting durations of the slice signal  88  staying at the same level after making the switch  82  open, so as to determine a start of a first long stream of the next block SL. For example, in  FIG. 7 , the decision module  78  determines whether the duration of the slice signal  88  staying at the level H is greater than the default duration Te after time point t5, so as to determine the start of the next block SL. Certainly, the duration of the slice signal  88  maintaining the level H is very short during a duration of the block SS, so that the decision module  78  does not make the switch  82  closed until a block SS ends and the next block SL starts.  
         [0051]     Please refer to  FIG. 8  (also  FIG. 6  and  FIG. 7 ), which illustrates a data format of a write-in data  96  of the present invention with a waveform-time diagram of a filtered read result  100 , a slice signal  104 , and a control signal  98 , where the X-axis is time scale. The write-in data  96  includes a plurality of blocks SL and SS; each block SL includes M long sequences Sa, while each block SS includes N short the sequences Sb; each long sequence Sa includes “1” and “0” long streams S 1  and S 2  with the same length (such as a 14-bit long stream), while each short sequence Sb includes “1” and “0” short streams S 3  and S 4  with the same length (such as a 3-bit short stream). Portions of the read result corresponding to the long sequences have greater amplitude and cycle than the short sequences, so that the block SL corresponds to a low-frequency portion of the read result  100 , or a read signal  102 A, while the block SS corresponds to a read signal  102 B.  
         [0052]     In the present invention, a proportion of M to N is for adjusting effect of the high-pass filter when high-pass filtering an original read signal. For example, if the proportion of M to N is an inverse proportion of number of bits of the long stream to number of bits of the short stream (that is, M:N=3:14), the duration of the block SL is equal to the duration of the block SS. After high-pass filtering, deviation of zero level in high-frequency portions of the original read result corresponding to the block SS causes the same deviation of zero level in low-frequency portions of the filtered read result. If the proportion of M to N is decreased (such as to 3:17), the duration of the block SL is greater than the duration of the block SS while the deviation of zero level in low-frequency portions of the filtered read result becomes more serious.  
         [0053]     Furthermore, unlike the embodiment in  FIG. 7 , after detecting a first long stream of the block SL, the decision module  78  can still make the switch  82  open while the next long stream starts. For example, in  FIG. 8 , the decision module  78  detects a start of a long stream corresponding to a read result at time point tk0, and changes the control signal  98  from the level L to the level H at time point tk2 (where the signal level of the slice signal  104  changes again), instead of at time point tk1. Similarly, time points for the decision module  78  to change the control signal  98  to low can be chosen at any point corresponding to the long stream. For example, in  FIG. 8 , the decision module  78  makes the switch  82  on at time point tk3, instead of at time point tk4. Nevertheless, a duration Tt (from time point tk2 to time point tk3) for the decision module  78  keeping the switch  82  closed should correspond to an even number of the “1 0 ” and “0” long streams S 1  and S 2  in that combination of a “0” and a “1” long streams S 1  and S 2  can form a cycle corresponding to the read result, so as to generate a zero-crossing difference. That is, the decision module  78  determines that the evaluation module  80  has evaluated zero-crossing differences of the read signal  102 A during the duration Tt by means of detecting an odd number of level alternation of the slice signal  104  during the duration Tt.  
         [0054]     The decision module  78  of the present invention can be a state machine or a firmware with program codes. The evaluation module  80 , the filter  72 , the slicer  74 , and the control module  70  can be included into a circuit or a chip. In addition, the decision module  78  can determine whether durations of the slice signal staying at a level are greater than the default duration Te with a high-frequency timer. For example, if the default duration Te is set to ST and a timer with a cycle 0.01T is set for calculating durations of the slice signal  88  staying at the level H, the decision module  78  calculates a cycle number of the cycle 0.01T after the signal level of the slice signal  88  changes from the level L to the level H. If the cycle number of the cycle 0.01T is 500 (or 5/0.01), the decision module  78  determines that the slice signal has corresponded to a long stream. Additionally, the charger and the discharger of the present invention can be digital counters with summing and subtracting functions in place of power supplies and capacitors C, and the storage unit can be a register. In this case, the digital counters can function based on the high-frequency timer, wherein only the digital counter in place of the charger sums data stored in the register, while the digital counter in place of the discharger subtracts the data. Therefore, data stored in the register can be a basis for calculating the beta-parameter.  
         [0055]     In all, the decision module  78  of the present invention is set for the specific format of the write-in data. The decision module  78  can determine the zero-crossing difference of the high-pass filtered read result only corresponding to the long stream of the write-in data. Therefore, the data amount of the storage unit  84  is prevented from being affected by high-frequency portions of the read result, so as to increase sensitivity of the beta-parameter corresponding to the write-in power. In comparison with the prior art, the present invention can determine a portion of the high-pass filtered read result corresponding to the long stream, and calculate a beta-parameter based on such portion, so that the beta-parameter can correspond to the write-in power provided by the optical disk drive more precisely. Finally, the optical disk drive can write onto a optical disk with a preferred power to perform optimal power control.  
         [0056]     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.