Abstract:
A method and the related apparatus for performing optimal power control of an optical disk drive includes reading a write-in data from an optical disk and generating a corresponding read result after the write-in data is written onto the optical disk with the default power, and accumulating a beta parameter according to a portion of the filtered read result whose level is higher than a first level and lower than a second level. The first level is substantially higher than the second level.

Description:
BACKGROUND OF INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a method and related apparatus for performing optimal power control in an optical disc drive, and more particularly, to a method and related apparatus for evaluating a beta-parameter according to sliced signals of read results in different levels.  
         [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, Compact Disk Recordable drives, users can store personal data in an optical disk with an optical disk drive. 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 into 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 the lands with proper power laser beams emitting into the optical disk. However, optical disks from different manufacturers have different physical/chemical characters, also optical disk drives with different brands and models have different laser emitters, rotational speeds, etc. Therefore, with which power writing into the optical disk for forming proper pits and lands is a key point when writing into the optical disk.  
         [0006]     In order to choose a preferred write-in power, the optical disk drive performs optimal power control before writing data into the optical disk. When performing optimal power control, the optical disk drive writes a default write-in data into the optical disk with different write-in powers, and then reads the write-in data from the optical disk, so as to determine whether the write-in power is an optimal power. Please refer to  FIG. 1 , which illustrates a waveform-time diagram of a write-in data  10  and two possible corresponding read results  12 A,  12 B when performing optimal power control, where X-axis is time scale, and Y-axis is waveform amplitude. 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 recognized, 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 contents. For example, in protocols of CD-R/RW, a stream of the coded data includes at most 11 bits with the same contents, but at least 3 bits with the same contents, while in protocol of DVD, a stream of the coded data includes at most 14 bits with the same contents. Owing to different bit numbers of different streams, a write-in data should include streams with different bit numbers for simulating data writing with different write-in powers.  
         [0008]     In  FIG. 1 , the write-in data  10  includes streams with different bit numbers. For example, a stream  14 A includes 3 digital “0” between time points ta0 and ta1, where continues with a 3T duration Ta, and T is a bit duration. Also, a stream  14 B with the duration Ta includes 3 “1” between time points ta1 and ta2. Besides, a stream  16 A includes 14 “0” between time points ta5 and ta6, where continues with a 14T duration Th, while a stream  16 B with the duration Th includes 14 “1” between time points ta4 and ta5.  
         [0009]     Because of different reflection coefficients corresponding to a laser beam, the pits and the lands of the optical disk can properly represent “0” and “1”. Therefore, when reading data corresponding to the read result from the optical disk, the optical disk drive compares 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: contents of the data change 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 responses 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 are 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 are 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 pits and lands with proper lengths. 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 is smaller than the zero level L0, is smaller than a duration between time points tb2 and tb3, which is greater than the zero level L0. But, in practical, the two durations of the read result  12 B corresponds to the streams  14 A and  14 B with the same lengths. Therefore, when the write-in power deviates from the ideal power, the read result  12 B cannot represent that the durations corresponding to the streams  14 A and  14 B of the write-in data  10  are the same.  
         [0011]     Besides, in  FIG. 1 , lengths of the streams affect the read result corresponding to the streams. For example, provided that a optical disk drive writes a “0” stream into an optical disk with laser beams comprising larger power to form pits. When the optical disk drive writes a longer “0” stream into the optical disk, laser beams with larger power keep a longer duration and form deeper pits consequently. Relatively, when writing a shorter “0” stream, the laser beams keep a shorter duration and form shallower pits. Owing to different deepnesses comprising different reflect coefficients corresponding to a laser beam, 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 point 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 point 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 Ln1. 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 Lp1 between 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 Lp0 between time points ta1 and ta2.  
         [0013]     The write-in power also affects waveform 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 bit number) as the stream  14 B between time points ta2 and ta3 has. 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 (or bit numbers)  
         [0014]     In contrast, in real case as the read result  12 B shows, the waveform is not so symmetric as the ideal read result  12 A shows. For example, the read result  12 B comprises 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. 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 unequal 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 into the optical disk with an ideal power, each portion of the read result corresponding to the streams with the same lengths should have same durations during two zero-crossing time points and have same amplitude. On the other hand, if the write-power deviates from the ideal power, pits and lands with incorrect lengths cannot represent streams with different lengths and contents. 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 into 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. Therefore, the optical disk drive chooses a preferred power approximating to 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 into 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 into 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 the optical disc drive  20  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 into 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 Y-axis is signal amplitudes. 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 is 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 are to track peaks and bottoms of the read result  36  for calculating amplitude of the read result  36 , and then calculate 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, which affects amplitude calculation 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 of the read result  36 . 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 . 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 are different. That is, the beta-parameters are not stable.  
         [0020]     Because the converter  34  samples one of the signals  38 A and  38 B in each sampling, the read results  36  are the values in different sampling times. The read results  36  have different extreme values when data strings of the write-in data have different lengths. If the amplitude of the write-in data is determined correctly, write-in data of the same length should be compared by checking the extreme values of these write-in data. If the signal  38 A is sampled by the converter  34  at the low extreme value of the short data stream, but the signal  38 B is sampled at the bottom value of the long data stream, 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 CD  26 . The write-in data that was written in the CD  26  is sent back to the access circuit  48 , which generates a read result  56 A. The filter  42  high-pass 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 NO. 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 , when write-in power deviates from the ideal value, the corresponding read result will deviate from the zero level. 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 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 reservation of 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 L0will 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 C 0  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 value, 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]     It is therefore an objective of the claimed invention to provide a method for performing optimal power control of an optical disk drive in order to solve the above-mentioned problems.  
         [0029]     According to the claimed invention, a method 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 comprises: reading a write-in data from the optical disk and generating a corresponding read result after the write-in data is written onto the optical disk with the default power; setting a first level and a second level, wherein the first level is higher than the second level; and processing an evaluation step according to a portion of the read result whose level is higher than the first level and lower than the second level for accumulating the beta-parameter.  
         [0030]     These and other objectives of the present 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-timing diagram of read result versus write-in power.  
         [0032]      FIG. 2  illustrates a block diagram of an optical disk drive according to the prior art.  
         [0033]      FIG. 3  illustrates a waveform-timing diagram of the optical disk drive in  FIG. 2  while performing optimal power control.  
         [0034]      FIG. 4  illustrates a block diagram of another optical disk drive according to the prior art.  
         [0035]      FIG. 5  illustrates a waveform-timing diagram of the optical disk drive in  FIG. 4  while performing optimal power control.  
         [0036]      FIG. 6  illustrates a block diagram of an optical disk drive according to the present invention.  
         [0037]      FIG. 7  illustrates a waveform-timing diagram of the optical disk drive in  FIG. 6  while performing optimal power control.  
         [0038]      FIG. 8  illustrates a waveform-timing diagram of a write-in data and related signals in another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0039]     Please refer to  FIG. 6 , which illustrates a schematic diagram of an optical disk drive  60  according to the present invention. The optical disk drive  60  comprises a motor  62 , a pick-up head  64 , an access circuit  68 , a control module  70 , a high-pass filter  72 , a write-in data arrangement module  71  and an evaluation module  80 . The evaluation module  80  includes two slicers  74 A and  74 B, a charger  76 A, a discharger  76 B, a level setting module  82  and a storage unit  84 . In  FIG. 6 , the storage unit  84  includes a resistor R a capacitor C. The motor  62  rotates an optical disk  66 . The pick-up head  64  emits laser beams into the optical disk  66  and receives reflections for data access. The access circuit  68  connects to the high-pass filter  72 . The control module  70  controls operations of the optical disk drive  60 .  
         [0040]     In the evaluation module  80 , the level setting module  82  sets a high level LH and a low level LL. The slicer  74 A slices the signals filtered after the filter  74  to generate a corresponding signal  88 A according to the high level LH and controls the charger  76 A to charge the storage unit  84  according to the corresponding signal  88 A. Similarly, the slicer  74 B slices the signals filtered after the filter  72  to generate a corresponding signal  88 B according to the low level LL and controls the discharger  76 B to discharge the storage unit  84  according to the corresponding signal  88 B. In the preferred embodiment of the present invention, the high level LH and the low level LL have the same absolute value but opposite sign (LL=−LH).  
         [0041]     The stored data in the storage unit  84  is represented by the charges of the capacitor C. The charger  76 A increases the charges of the capacitor C or increases the data in the storage unit  84  when charging, while the discharger  76 B decreases the charges of the capacitor C or decreases the data in the storage unit  84 . The charge amount of the capacitor C is sent to the control module  70  with the voltage of the node N 1 . The write-in data arrangement module  71  is used to arrange the write-in data  92 .  
         [0042]     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 A generates a sliced signal  88 A according to whether the signal level of the read result  86 B is larger than the high level LH. According the sliced signal  88 A, the slicer  74 A controls the charger  76 A to charge the storage unit  84 . Similarly, the slicer  74 B generates a sliced signal  88 B according to whether the signal level of the read result  86 B is smaller than the low level LL to control the discharger  76 B to discharge the storage unit  84 . According to the stored data in the storage unit  84 , the control module  70  obtains the beta-parameter.  
         [0043]     Please refer to  FIG. 7  (also  FIG. 6 ), which illustrates a waveform-time diagram of the write-in data  92 , the read results  86 A and  86 B (shown as a dotted line and a solid line respectively), the sliced signals  88 A and  88 B and related signals when the optical disk drive  60  of the present invention performs optimal power control. The X-axis in  FIG. 7  represents time, while the Y-axis represents amplitudes of the read results  86 A and  86 B, and the sliced signals  88 A and  88 B. The write-in data  92  includes long sequences Sa and 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 . In addition, data to be written to the optical disk is coded to a plurality of streams with different lengths. In the DVD-R/RW specification, the longest stream has 14 bits (14T) with the same content, while the shortest stream includes three bits (3T) with the same content, so that the long streams S 1  and S 2  of the present invention have 14 “1” bits and  14  “0” bits respectively, while the short streams S 3  and S 4  of the present invention have three “1” bits and three “0” bits respectively. Similarly, in the specification of CD-R/RW, the longest and the shortest streams have 11 and three bits (also 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.  
         [0044]     As mentioned regarding  FIG. 1 , two streams in a data sequence with the same length and different contents correspond to a cycle of a read result. For example, in  FIG. 7 , the three long data sequences Sa formed by the long 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 t6, t6 to t12, and from time points t12 to t18, 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 t25 to t26 and time points t26 to t27. Of course, when the write-in power deviates from the ideal power, the read result  86 A deviates from the zero level L0, especially for 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.  
         [0045]     After the slicer  74  slices the read signal  86 B into the sliced signal  88 A, the level H portions of the sliced signal  88 A correspond to the portions of the read result  86 B greater than the level LH, while the level L portions of the slice signal  88  correspond to the portions of the read result  86 B smaller than the level LH. For example, as shown in  FIG. 7 , the levels of the read result  86 B during time points t1 to t2 and time points t7 to t8 are higher than the level LH, so the sliced signal  88 A changes from the level L to the level H during this time. Similarly, for the slicer  74 B the levels of the read result  86 B during time points t4 to t5 and time points t10 to t11 are lower than the level LH, so the sliced signal  88 B changes from the level L to the level H.  
         [0046]     The portions of the read result corresponding to long streams not only have low frequency but also have larger amplitude. In contrast, the portions corresponding to short streams have smaller amplitude. In fact, in the specification of a rewritable CD, the amplitude of the waveforms corresponding to the short stream 3T is usually 15% of that corresponding to the long stream 14T. The present invention utilizing the above principles, the slicers  74 A and  74 B in the invention slice the read result  86 B according to the levels LH and LL. Therefore, the sliced signal  88 A and  88 B show the parts of the read result having the larger amplitude, or the low frequency parts of the read result  86 B which correspond to the long streams. Notice that to achieve the above effects, the level setting module  82  should carefully set the levels LH and LL. The absolute values of the level LH and LL range between a typical value of the amplitude of the low frequency part and a typical value of the amplitude of the high frequency part.  
         [0047]     As shown in  FIG. 7 , the difference of the zero-crossing periods of the read signal  86 B also causes the difference of the durations in which the read signal  86 B is higher than the level LH and the durations in which the read signal  86 B is smaller than the level LL. For example, during the time points t6 to t9, the portion of the read signal  86 B larger than the zero level L0 maintains the zero-crossing period Ta1, and during the time points t9 to t12, the portion of the read signal  86 B smaller than the zero level L0 maintains the zero-crossing period Ta2. During the time points t6 to t12, the deviation of the zero level of read result  86 B makes the total signal shift downward, so the positive portion and the negative portion of the zero-crossing periods are unbalanced and Ta2 is longer than Ta1. Meanwhile, the down shifting of the read signal  86 B results during the duration when the read signal  86 B is higher than the level LH is shorter than the duration when the read signal  86 B is lower than the level LL. If the down shifting of the read signal  86 B is larger, the difference between zero-crossing durations Ta2 and Ta1 is larger.  
         [0048]     In other words, for the read result  86 B, the portions exceeding the level LH and the level LL not only represent the read signal  86 B corresponding to the low frequency part of long streams and durations when the signal exceeds the levels LH and LL, but also represent the length of the zero-crossing periods of the low frequency parts which are larger or smaller than the zero level L0 in the read signal  86 B. Therefore, the present invention uses the difference between the durations when the result signal  86 B exceeds the levels LH and LL to estimate the beta-parameter of the write-in result. In comparison, the high-frequency part of the read result  86 B completely ranges between the levels LH and LL. Equivalently speaking, the high frequency part of the read result  86 B is filtered out. Therefore, the present invention obtains a more definite beta-parameter according to only the low-frequency part of the read result.  
         [0049]     To implement the above principle, the charger  76 A charges the storage unit  84  when the sliced signal  88 A maintains the level H. The discharger  76 B discharges the storage unit  84  when the sliced signal  88 B maintains the level H. In  FIG. 7 , the timing diagram  91  represents the charger  76 A and the discharger  76 B charging or discharging the capacitor C. For example, the read result  86 B is larger than the high level LH during the time points t6 to t12, and the sliced signal  88 A drives the charger  76 A to charge with the voltage H, illustrated as the cross-hatched durations in the timing diagram  91 . The increased charges in the capacitor C are proportional to Tb1. In contrast, the read result  86 B is lower than the low level LL during the time points t10 to t11, and the sliced signal  88 B drives the discharger  76 B to discharge with the voltage H, as illustrated by the single-hatched durations. During the times t6 and t12, the increased charges in the capacitor C are proportional to (Tb1-Tb2), corresponding to the difference of the zero-crossing periods of the read signal  86 B. Notice that during time points t18 to t19, the capacitor C will not be charged or discharged due to the small amplitude of the high part of the read result  86 B which does not exceed the level LH and LL. Therefore, the accumulated charge in the capacitor C can reflect the difference of the zero-crossing periods of the low frequency part of the read result  86 B, and the write-in optimal power control is performed more accurately accordingly.  
         [0050]     In the preferred embodiment of the present invention, the write data can include a plurality of connected long data sequences, and a plurality of connected short data sequences. As for this situation, please refer to  FIG. 8  (also  FIG. 6  and  FIG. 7 ).  FIG. 8  illustrates a data format of a write-in data  96  and a waveform-timing diagram of a (high-pass filtered) read result  100 , sliced signals  104 A and  104 B, and a driving sequence  105  representing the charge or discharge of the capacitor C by the charger  76 A or the charger  76 B according to the present invention. The X-axis is time scale. In the driving sequence  105 , the cross-hatched part represents the charging period and the single-hatched part represents the discharging period. 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 period 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.  
         [0051]     In the block SL and SS, the number of the long data sequence is represented by M, and the number of the short data sequence is represented by N. A proportion of M to N is for adjusting the effect of the high-pass filter 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, the 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 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. Accordingly, the durations when the read result  100  exceeds the level LH and LL have more differences.  
         [0052]     In implementing the evaluation module  80 , each circuit, the filter  72  and the control module  70  of the evaluation module  80  can be integrated by a chip in hardware or by program codes in firmware. Besides the charger, discharger and the storage unit of the present invention being implemented with a fixed current source and a capacitor, the present invention can use counters to implement the charger and the discharger and use a register to implement the storage unit. In this case, the counter counts the time that the sliced signal maintains the levels H and L and the counted result is stored in the storage unit. The combination of the count of the H level duration and the count of the L level duration represents the difference of the time when the read result exceeds the H and L levels. For example, in  FIG. 7  suppose that the optical disc drive  60  uses a high-frequency clock whose period is 0.01T (1T is the time of one bit in the read data). If the duration Tb1 between t7 to t8 is 3.3T, the counter will increase 330 counts during the period (3.3T/0.01T). Comparatively, if the duration Tb2 between t10 to t11 is 4.2T, the counter will decrease 440 counts during the period. Therefore, the accumulated counts can be used to calculate the write-in result.  
         [0053]     In conclusion, to perform write-in power control in the present invention is to calculate the write-in result parameter, beta-parameter being according to the difference of the durations when the high-pass filtered read result exceeds a high level and a low level. Therefore, the present invention accumulates the data of the storage unit  84  according to only a low-frequency part of the read result so that the present invention obtains a more accurate beta-parameter, and reflects the deviation of the write-in power more definitely by removing the effect of a high-frequency part of the read result.  
         [0054]     In the prior art, it is difficult to choose the proper sampling time when calculating the beta-parameter by using the extreme value of the read result. On the other hand, using accumulation of both high frequency zero-crossing periods and low frequency zero-crossing periods to calculate the beta-parameter cannot definitely express the deviation of 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 that portion, so that the beta-parameter can better correspond to the write-in power provided by the optical disk drive. Finally, the optical disk drive can write onto an optical disk with a preferred power to perform optimal power control.  
         [0055]     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.