Abstract:
A power calibrating method includes steps of: determining a target value for a front monitor diode signal; outputting light with a power having a writing power level and an erasing power level, durations of the writing power level being identical to durations of the erasing power level; obtaining multiple values of the front monitor diode signal and an average of the multiple values of the front monitor diode signal; and adjusting the writing power level until the average of the multiple values of the FMD signal equals to the target value.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to data recording apparatuses and, more particularly, to a method for calibrating a writing power of a data recording apparatus. 
       DESCRIPTION OF RELATED ART 
       [0002]    In recent years, data storage media that are capable of being written data thereon, such as rewritable digital versatile discs (DVD-RW) or rewritable compact discs (CD-RW) have become more and more popular. Accordingly, related data recording apparatus are developed to record data onto the data storage medium. A typical data recording apparatus employs an optical pick-up unit (OPU) to emit a laser beam onto a data storage medium to form a spot on the data storage medium. When a laser beam power reaches a first predetermined level, a position where the spot is formed is changed from a first state to a second state, a recording mark is thus formed on the data storage medium. That is, data are recorded on the data storage medium. When the laser beam power reaches a second predetermined level, the position in the second state is restored to the first state and the recording mark is cleared from the data storage medium. That is, the data recorded on the data storage medium is erased. 
         [0003]    Before recording data onto the medium, the laser beam power should be calibrated in order to ensure accuracy of the recording. In general, the laser beam power includes three power levels: a writing power level for writing data onto the data storage medium, an erasing power level for erasing data from the data storage medium, and a biasing power level for reading data from the data storage medium. Each of the erasing power level and the biasing power level can be automatically calibrated via a separate automatic power control (APC) loop of the data recording apparatus. Each APC loop uses a sample/hold circuit connected to a front monitor diode (FMD) of the OPU to sample an output voltage of the FMD. The FMD is used for sensing the laser beam power and outputting a FMD signal to the APC loop to indicate the power of the laser beam. The APC loop adjusts the laser beam power based on the FMD signal. However, there is no APC loop specifically for adjusting the writing power level. The writing power level is adjusted by many calculations based on the FMD signal, the erasing power level, and a ratio between the writing power level and the erasing power level. Such calculations are time-consuming and accuracy of the adjustment is difficult to control. 
         [0004]    Therefore, a writing power calibrating method is desired. 
       SUMMARY OF THE INVENTION 
       [0005]    A power calibrating method includes steps of: determining a target value for a front monitor diode signal; outputting light having a writing power level and an erasing power level, durations of the writing power level being identical to durations of the erasing power level; obtaining multiple values of the front monitor diode signal and an average of the multiple values of the front monitor diode signal; and adjusting the writing power level until the average of the multiple values of the FMD signal equals to the target value. 
         [0006]    A data recording apparatus includes a laser diode, a laser diode driver, and a digital signal processor. The laser diode driver is used for driving the laser diode to emit a laser beam. The digital signal processor is used for controlling a duration of the laser beam. The digital signal processor controls the laser diode driver to drive the laser diode to emit the laser beam with a power in a predetermined wave form. The power in the predetermined wave form has alternate writing power levels and erasing power levels. A duration of each writing power level equals to a length of a corresponding pit included in eight-to-fourteen modulate data to be recorded. 
         [0007]    A controlling processor for controlling a laser diode driver to drive a laser diode to emit a laser beam with a power in a predetermined wave form during a power calibrating procedure, the power in the predetermined wave form wave form comprising a first power level for forming recording marks on a medium and a second power level for erasing recording marks from the medium, a duration of the first power level being equal to a length of a corresponding pit in eight-to-fourteen modulate data to be recorded on the medium. 
         [0008]    Other advantages and novel features will become more apparent from the following detailed description of preferred embodiments when taken in conjunction with the accompanying drawings, in which: 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Many aspects of the writing power calibrating method and the data recording apparatus using the writing power calibrating method can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, the emphasis instead being placed upon clearly illustrating the principles of the present writing power calibrating method and the present data recording apparatus. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
           [0010]      FIG. 1  is a block diagram of a data recording apparatus in accordance with a first exemplary embodiment, the data recording apparatus including a laser diode (LD) and a front monitor diode (FMD); 
           [0011]      FIG. 2  is an exemplary general wave form of a laser beam power outputted by LD of  FIG. 1 , the laser beam power in the general wave form including three power levels: a writing power level Pw, an erasing power level Pe, and a biasing power level Pb; 
           [0012]      FIG. 3  is an exemplary characteristic curve illustrating relationship between the laser beam power outputted by the LD of  FIG. 1  and an output voltage of the FMD of  FIG. 1 ; 
           [0013]      FIG. 4  are exemplary wave forms of the laser beam power outputted by the LD of  FIG. 1  and the output voltage of the FMD of  FIG. 1 ; 
           [0014]      FIG. 5  is an exemplary circuit diagram of an APC loop in the data recording apparatus of  FIG. 1 ; 
           [0015]      FIG. 6  is an exemplary diagram illustrating structures of the three power levels in  FIG. 2 ; 
           [0016]      FIG. 7  is an exemplary curve illustrating relationships between an average of the output voltage of the FMD and a ratio of the erasing power level Pe to the writing power level Pw; 
           [0017]      FIG. 8  are exemplary wave forms outputted by different LDs; 
           [0018]      FIG. 9  is an exemplary diagram illustrating a contrast between the general wave form in  FIG. 2  and a specific wave form in accordance with an exemplary embodiment; 
           [0019]      FIG. 10  is a flow chart illustrating a calibrating procedure for calibrating the writing power level of a power calibrating method in accordance with an exemplary embodiment; and 
           [0020]      FIG. 11  is a block diagram of a data recording apparatus in accordance with a second exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    Reference will now be made to the drawings to describe the preferred embodiments of the present writing power control apparatus and the present writing power control method, in detail. 
         [0022]    Referring to  FIG. 1 , a data recording apparatus  1  includes an optical pick-up unit (OPU)  10 , a digital signal processor (DSP)  12 , and an analog signal processor (ASP)  14 . The OPU  10  includes a laser diode driver (LDD)  100  connected to the ASP  14 , a laser diode (LD)  102 , and a front monitor diode (FMD)  104 . The LDD  100  is used for driving the LD  102  to emit a laser beam onto a data storage medium (not shown) to record data onto the data storage medium and/or reproduce data from the data storage medium. Referring also to  FIG. 2 , an exemplary wave form of a laser beam power outputted by the LD  102  is illustrated. The laser beam power includes three power levels: a writing power level Pw, an erasing power level Pe, and a biasing power level Pb. When the laser beam is emitted at the writing power level Pw, data is recorded on the data storage medium. When the laser beam is emitted at the erasing power level Pe, data recorded on the data storage medium is erased. When the laser beam is emitted at the biasing power level Pb, data recorded on the data storage medium is read. 
         [0023]    The FMD  104  is used for detecting the laser beam power and for outputting an FMD signal indicating the laser beam power to the DSP  12  and the ASP  14 . Referring also to  FIG. 3 , an exemplary characteristic curve illustrating relationship between an input power and an output voltage of the FMD  104 . The laser beam power outputted by the LD  102  serves as the input power of the FMD  104 , and the output voltage of the FMD  104  is the FMD signal. If the laser beam power is lower than a given value N, the FMD  104  outputs a constant voltage. If the laser beam power exceeds the given value N, the greater the laser beam power is, the lesser the output voltage of the FMD  104 . The output voltage of the FMD  104  has three voltage levels: FMD Pb , FMD Pe , and FMD Pw  respectively corresponds to the writing power level Pw, the erasing power level Pe, and the biasing power level Pb (referring to  FIG. 4 ). 
         [0024]    The DSP  12  is used for controlling a duration of each power level of the laser beam power and for controlling operations of the ASP  14 , and includes an analog-to-digital converter (ADC)  120  connected to the FMD  104  for sampling the FMD signals. The ASP  14  is used for adjusting the laser beam power based on the FMD signal. The OPU  10 , the DSP  12 , and the ASP  14  collectively form an automatic power control (APC) loop. In the APC loop, the DSP  12  controls the ASP  14  to output driving signals to the LDD  100  to drive the LD  102  to emit a laser beam at a predetermined power level. The FMD  104  detects the laser beam power and outputs the FMD signal to the ASP  14 , the ASP  14  then adjusts the laser beam power based on the FMD signal. 
         [0025]    The data recording apparatus  1  further includes a memory  16  such as a read only flash memory for storing a write strategy table  160 . The write strategy table  160  stores values of the erasing power level and a ratio ε of the erasing power level Pe to the writing power level Pw. Because different data storage media have different properties, when the laser beam is applied on different data storage media, the laser beam power should be calibrated to be consistent with the different properties of the data storage media. In order to provide an appropriate power for recording information on the different data storage medium, some data recording apparatuses predefine the write strategy table  160  in the memory  16 . When the data recording apparatus  1  starts recording, the OPU  10  reads specific information from the data storage medium, such specific information are usually recorded in a lead-in area of the data storage medium. Based on the specific information read from the data storage medium, corresponding values of the erasing power level Pe and the ratio ε can be obtained by searching in the write strategy table  160 . 
         [0026]    The DSP  12  controls the duration of each power level of the laser beam power based on the information stored in the write strategy table  160 . 
         [0027]    Referring to  FIG. 5 , an exemplary circuit diagram of the APC loop is illustrated. The ASP  14  includes two parts, one for reading information from the data storage medium, the other one for writing information onto the data storage medium. Each part includes a digital-to-analog converter (DAC)  140  that is connected to the DSP  12 , a subtracter  142 , and a sample/hold (S/H) unit  144  that is connected to the FMD  104  via an amplifier  106 . The DAC  140  is used for receiving commands from the DSP  12  and for outputting a specified voltage based on the commands received from the DSP  12 . The FMD signal outputted by the FMD  104  is first amplified by the amplifier (AMP)  106 , and then the AMP  106  transmits the FMD signal amplified to the S/H unit  144 . The S/H unit  144  samples the amplified FMD signal and holds the samples for a predetermined time period to provide enough time for the subtracter  142  to perform a subtraction operation. The DSP  12  controls operation and non-operation of the S/H unit  144 . The subtracter  142  subtracts the amplified FMD signal from the output of the DAC  140  to obtain error signals. The error signals are then amplified by corresponding amplifiers (not labeled) to be driving signals to be fed to the LDD  100  to control the laser beam power. 
         [0028]    The driving signals generated in the ASP  14  include a first driving signal CH_R, a second driving signal CH_W, and a third driving signal CH_A. The first driving signal CH_R is used for adjusting the magnitude of the biasing power level Pb, the second driving signal CH_W is used for adjusting the magnitude of the erasing power level Pe, and the third driving signal CH_A is used for adjusting the magnitude of the writing power level Pw. The second driving signal CH_W is multiplied by a gain  145  to get the third driving signal CH_A. Each of the three driving signals CH_A, CH_W, and CH_R is transmitted to the LDD  100  via a separate channel, and then amplified by corresponding amplifiers (not labeled) in the corresponding channel before fed to an adder (not labeled). The three driving signals amplified are identified as G 1 (CH_A), G 2 (CH_W), and G 3 (CH_R), respectively. Each of G 1 , G 2 , and G 3  represents a gain function of a corresponding channel. The adder adds up the three driving signals amplified G 1 (CH_A), G 2 (CH_W), and G 3 (CH_R) before the three driving signals amplified are fed to the LD  102 . Referring to  FIG. 6 , the writing power level Pw equals to a sum of the three driving signals amplified (that is Pw=Σ(G 1 (CH_A), G 2 (CH_W), G 3 (CH_R))), the erasing power level Pe equals to a sum of G 3 (CH_W) and G 2 (CH_R) (that is Pe=Σ(G 2 (CH_W), G 3 (CH_R))), and the biasing power level Pb equals to G 3 (CH_R). 
         [0029]    Because each of the first driving signal CH_R and the second driving signal CH_W can be adjusted by a corresponding APC loop, the CH_A is obtained by multiplying CH_A by the gain  145 , and the writing power level Pw equals to Σ(G(CH_A), G(CH_W), G(CH_R)), the writing power level Pw can be calibrated by adjusting the value of the gain  145 . 
         [0030]    An exemplary general procedure for adjusting the value of the gain  145  is as follows. First, the DSP  12  controls the LDD  100  to drive the LD  102  to output a laser beam with a power in a predetermined wave form. Second, the ADC  120  of the DSP  12  samples the output voltage of the FMD  104  to obtain more than one thousand sampled values of the FMD signal. An average FMD AVG  of the values of the FMD signal is obtained by averaging the sampled values. Third, a relationship among the FMD AVG , the erasing power level Pe, and the ratio ε is established and stored in the data recording apparatus  1 . An exemplary relationship among the FMD AVG , the erasing power level Pe, and the ratio ε is illustrated in  FIG. 7 . Fourth, a corresponding value of the FMD AVG  corresponding to given values of the erasing power level Pe and the ratio ε is obtained according to the relationship among the FMD AVG , the erasing power level Pe, and the ratio ε. The corresponding valued of the FMD AVG  is used as a target value FMD TGT  of the FMD signal. Sixth, the DSP  12  controls the LDD  100  to drive the LD  102  to output the laser beam with the power in the predetermined wave form and the ADC  120  samples the output voltage of the FMD  104  more than one thousands times to obtain a new average FMD AVG . If the newly obtained FMD AVG  equals to the FMD TGT , the adjustment of the value of the gain  145  is finished. Otherwise, the procedure loops back to the sixth step to adjust the value of the gain  145 . 
         [0031]    However, different LDs  102  may output laser beams with powers in different wave forms even if being given same commands by the DSP  12  due to their different inherent characteristics. The wave form shown in  FIG. 2  is an ideal wave. In fact, a real wave form of the laser beam power outputted by the LD  102  is not as ideal as the wave form shown in  FIG. 2 . At an ascending edge or a descending edge of the real wave form, an overshoot may be generated due to inherent properties of the LD  102 . Because different LDs  102  have different inherent properties, different overshoots may be generated (Referring to  FIG. 8 ). The wave forms A) and B) corresponds to two different LDs. It is clear that the overshoot in wave form A) is smaller than the overshoot in the wave form B). Because the FMD signal is dependent on the laser beam power outputted by the LD  102 , the FMD signal may be biased due to the overshoots. Therefore, the value of the FMD AVG  is badly influenced. When different LDs  102  are applied in the data recording apparatus  1 , the relationships among the FMD AVG , the erasing power level Pe, and the ratio ε may be modified according to the different LDs  102 . It may be a troublesome task to modify the relationship among the FMD AVG , the erasing power level Pe, and the ratio ε. If the overshoots cause the value of FMD AVG  to bias away from an ideal value too much, an accuracy of calibration of the writing power level Pw is degraded. 
         [0032]    In order to reduce the deviation of the FMD AVG  caused by the different inherent properties of the different LDs  102 , a specific wave form is proposed. The specific wave form has less ascending/descending edges than the wave form shown in  FIG. 2  (hereinafter referred as to general wave form). Referring to  FIG. 9 , a contrast between the specific wave form and the general wave form is illustrated. In general, the information to be recorded onto the data storage medium is firstly converted to eight-to-fourteen modulate (EFM) data. The EFM data employs a shift between a “pit” and a “land” to represent a bit “ 1 ”. Each “pit” represents a recording mark recorded on the data storage medium. Corresponding to each “pit”, there is more than one pulse in the general wave form, whilst only one pulse in the specific wave form. It can be seen that each pulse has the ascending edge and the descending edge. Since the number of the pulses in the specific wave form is less than the number of the pulses in the general wave form, the number of the ascending edges and the descending edges is reduced. Accordingly, the number of the overshoots is also decreased and the deviation placed on the FMD AVG  by the overshoots is reduced. 
         [0033]    Since the power in the specific wave form has only two power levels: the writing power level Pw and the erasing power level Pe, the FMD only has only values that include FMD Pw  and FMD Pe , according to the relationship between the laser beam power and the FMD signal shown in  FIG. 3 . In general, with respect to the EFM wave form, a duty ratio of the “pits” is 50%. That is, the number of the “pits” is identical to the number of the “lands”. Because there is only one pulse in the specific wave form corresponding to each “pit”, a total duration of the writing power level Pw equals to that of the erasing power level Pe. That is, a duty ratio of the writing power level Pw is 50%. Accordingly, a total duration of the FMD Pw  is also identical to that of the FMD Pe . The FMD AVG  can be obtained by averaging the FMD Pw  and the FMD Pe . 
         [0034]    Referring to  FIG. 10 , a calibrating procedure for calibrating the writing power level Pw of a power calibrating method in accordance with an exemplary embodiment is illustrated. The calibrating procedure includes following steps. 
         [0035]    First, in step  60 , two different values of the FMD signal are obtained. The DSP  12  controls the LDD  100  to drive the LD  102  to output the laser beam with two different static direct current (DC) powers PW_DC 1  and PW_DC 2 . Then, the ADC  120  samples the output voltage of the FMD  104  under each DC power to get two different values FMD DC1  and FMD DC2  of the FMD signal. 
         [0036]    Second, in step  62 , corresponding values of the ratio ε and the erasing power level Pe are read from the write strategy table  160 . Based on the values of the ratio ε and the erasing power level Pe, the value of the writing power level Pw is obtained. 
         [0037]    Third, in step  64 , values of the FMD Pe  and FMD Pw  are obtained by interpolation, based on the two different values of the FMD signal. 
         [0038]    Fourth, in step  66 , the value of the FMD TGT  is calculated by averaging the value of the FMD Pe  and FMD Pw . 
         [0039]    Fifth, in step  68 , the DSP  12  controls the ASP  14  to drive the LD  102  to output the specific wave form. 
         [0040]    Sixth, in step  610 , the ADC  120  samples the output voltage of the FMD  104  for more than one thousand times to get more than one thousand values of the FMD signal. Then, the value of the FMD AVG  is obtained by averaging the more than one thousand values of the FMD signal. 
         [0041]    Seventh, in step  612 , a conclusion is made as to whether the value of the FMD AVG  equals to that of the FMD TGT . 
         [0042]    Eighth, if the value of the FMD AVG  is concluded to not be equal to that of the FMD TGT  in step  612 , the value of the writing power level Pw is calibrated by adjusting the value of the gain (step  614 ). 
         [0043]    Ninth, if the value of the FMD AVG  is concluded to be equal to that of the FMD TGT  in step  612 , the calibration of the writing power level Pw is accomplished and the DSP  12  controls the ASP  14  to drive the LD  102  to output the general wave form to perform recording operations (step  616 ). 
         [0044]    It should be noted that in order to reduce the number of the overshoots, a writing rate of the data recording apparatus  1  is preferably low, such as a double of a base recording rate (know as 2×). The base recording rate is specified for each type of data storage medium. For example, a base recording rate of a compact disc audio (CD_DA) disc is specified to be 150 Kbps. Furthermore, a low pass filter  18  can be added between the ADC  120  and the FMD  104  in order to further lower the deviation on the value of the FMD signal caused by the overshoots (referring to  FIG. 11 ). 
         [0045]    The embodiments described herein are merely illustrative of the principles of the present invention. Other arrangements and advantages may be devised by those skilled in the art without departing from the spirit and scope of the present invention. Accordingly, the present invention should be deemed not to be limited to the above detailed description, but rather by the spirit and scope of the claims that follow, and their equivalents.