Abstract:
A method and a related apparatus for diagnosing crosstalk within an optical pick-up unit by utilizing firmware. The method includes calculating a tracking driving signal and a focusing driving signal according to a tracking error signal and a focusing error signal respectively, adding a noise to the focusing driving signal to form a test focusing driving signal through executing firmware, driving an optical pick-up unit by the tracking driving signal and the test focusing driving signal, and diagnosing characteristics of the pick-up unit through observing the tracking error signal.

Description:
BACKGROUND OF INVENTION 
     1. Field of the Invention 
     The present invention relates to a method and a related apparatus for diagnosing an optical disk drive. In particular, the present invention discloses a method and a related apparatus for diagnosing crosstalk within an optical pick-up unit by utilizing firmware of the optical disk drive. 
     2. Description of the Prior Art 
     Please refer to  FIG. 1 , which is a block diagram of a prior art optical disk drive  10 . The optical disk drive  10  is used for reading data stored on an optical disk  11 . The optical disk drive  10  has an optical pick-up unit (OPU)  12 , a spindle motor  14 , a motor controller  16 , a focusing controller  18 , a tracking controller  20 , a microprocessor  22 , a servo system  24 , and a signal converter  26 . The OPU  12  emits a laser Li with a predetermined wavelength and predetermined power to the optical disk  11 . It is well-known that spiral track  28  is formed on the optical disk  11 . In addition, the track  28  records a plurality of lands and pits with different lengths for storing eight-to-fourteen modulation (EFM) data. For example, the land corresponds to the low logic value “0”, and the pit corresponds to the high logic value “1”. In addition, when the laser Li spots the pits and lands on the track  28 , the laser Li is modulated by the pits and lands to generate a reflecting laser Lr. The magnitude of the reflecting laser Lr generated from the laser Li spotting the land is greater than the magnitude of the reflecting laser Lr generated from the laser Li spotting the pit. Therefore, the OPU  12  is capable of detecting the reflecting laser Lr to generate a corresponding analog electric signal EFMa. Then, the signal converter  26  transforms the analog electric signal EFMa into a digital electric signal EFMd. In the end, the microprocessor  22  decodes the received digital electric signal EFMd to obtain wanted data DATA stored on the optical disk  11 . 
     In addition, when the optical disk  11  is loaded into the optical disk drive  10 , the microprocessor  22  drives the motor controller  16  to adjust rotation speed associated with a spindle of the spindle motor  14 , and the microprocessor  22  also drives the servo system  24  to control the position of the OPU  12  corresponding to the optical disk  11 . As mentioned above, the OPU  12  adopts the optical means to retrieve the data recorded by the track  28 . Therefore, if the laser Li cannot be precisely focused on the track  28 , the electric signal EFMa generated from the OPU  12  contains erroneous information. Similarly, if the laser Li forms a spot on the optical disk  11 , and the location of the spot is deviated from the target track  28 , the electric signal EFMa generated from the OPU  12  contains incorrect information. Therefore, when the OPU  12  is operating, the OPU  12  generates a focusing error signal FEO and a tracking error signal TEO. Then, the focusing controller  18  calculates a focusing driving signal FOO to the servo system  24  according to the focusing error signal FEO, and the tracking controller  20  calculates a tracking driving signal TRO to the servo system  24  according to the tracking error signal TEO. Thus, the servo system  24  is capable of moving the OPU  12  vertically for adjusting a vertical gap between the OPU  12  and the optical disk  11  through the focusing driving signal FOO, and is capable of moving the OPU  12  horizontally for adjusting a horizontal displacement of the OPU  12  above the optical disk  11  through the tracking driving signal TRO. 
     From the above description, it is understood that the focusing operation and the tracking operation for the OPU  12  greatly affect accuracy of the final electric signal EFMa. If the signal quality of the electric signal EFMa is bad, the wanted data DATA cannot be correctly obtained even if the microprocessor  22  enables an error correction mechanism. Therefore, the OPU  12  has to accurately generate the focusing error signal FEO and the tracking error signal TEO. Otherwise, the focusing controller  18  and the tracking controller  20  are unable to figure out the wanted tracking driving signal TRO and the focus driving signal FOO. In other words, the servo system  24  cannot move the OPU  12  to a correct position for retrieving data recorded on the track  28  of the optical disk  11 . 
     Before the optical disk drives  10  leave the factory, component characteristic of the OPU  12  need to be carefully tested to filter out optical disk drives  10  having abnormal OPUs  12 . Please refer to  FIG. 2 , which is a diagram of a prior art optical disk drive diagnosing system  40 . The diagnosing system  40  includes the optical disk drive  10  shown in  FIG. 1 , a dynamic signal analyzer  42  (HP35670A for example), and a mixer  44 . The optical disk drive  10  shown in  FIG. 2  only contains the OPU  12 , the focusing controller  18 , the tracking controller  20 , and the servo system  24  for simplicity. Input ports A, B of the dynamic signal analyzer  42  are respectively connected to the OPU  12  and the focusing controller  18 . That is, the tracking error signal TEO outputted from the OPU  12  is passed to the input port A of the dynamic signal analyzer, and the focusing driving signal FOO calculated by the focusing controller  18  is delivered to the input port B of the dynamic signal analyzer  42 . In addition, an output port C of the dynamic signal analyzer  42  outputs a testing signal TEST to the mixer  44 . The testing signal TEST functions as a noise to interfere with the focusing driving signal FOO calculated by the focusing controller  18 . As shown in  FIG. 2 , the mixer  44  finally mixes the focusing driving signal FOO and the testing signal TEST, and outputs a test focusing driving signal FOO″ to the servo system  24 . The testing signal TEST generated from the dynamic signal analyzer  42  is used for simulating a noise, and is generally a sine wave with a frequency gradually increased from an initial value toward a target value. At the same time, the test focusing driving signal FOO″ influenced by the testing signal TEST is inputted into the servo system  24 . Then, the servo system  24  adjusts a vertical gap between the OPU  12  and the target track  28  of the optical disk  11  according to the test focusing driving signal FOO″. With an appropriate adjustment, the laser emitted from the OPU  12  is capable of focusing on the track  28  of the optical disk  11 . When the frequency of the testing signal TEST varies from the initial value toward the target value for affecting the focusing driving signal FOO, a user can use the tracking error signal TEO and the focusing driving signal FOO respectively received at input ports A, B of the dynamic signal analyzer  42  for analyzing a frequency response associated with the focusing driving signal FOO and the tracking error signal TEO. 
     Please refer to  FIG. 3  in conjunction with  FIG. 4 .  FIG. 3  is a first frequency response diagram associated with the focusing driving signal FOO and the tracking error signal TEO, and  FIG. 4  is a second frequency response diagram associated with the focusing driving signal FOO and the tracking error signal TEO. In  FIG. 3  and  FIG. 4 , the horizontal axis stands for the frequency, and the vertical axis stands for the gain. The response curve L 2  shown in  FIG. 4  corresponds to a standard OPU  12 , and the response curve L 1  shown in  FIG. 3  corresponds to a flawed OPU  12 . It is obvious that when the frequency of the testing signal TEST is greater than 10 KHz, the gains corresponding to the response curve L 1  are greatly deviated from the gains corresponding to the response curve L 2 . Taking the frequency F for example, the gain, which corresponds to the frequency F, is equal to 25 through the response curve L 1 . However, the gain, which corresponds to the frequency F, is equal to 45 through the response curve L 2 . In other words, the crosstalk inherent to the flawed OPU  12  seriously affects the tracking error signal TEO and the focusing error signal FEO. Therefore, the tracking error signal TEO generated from the OPU  12  is introduced to the focusing error signal FEO generated from the OPU  12 , and the unwanted interference couples with the focusing error signal FEO. Similarly, the focusing error signal FEO generated from the OPU  12  is introduced to the tracking error signal TEO generated from the OPU  12 , and the unwanted interference couples with the tracking error signal TEO. The OPU  12  with serious crosstalk effect can be filtered out through observing the frequency response associated with the focusing driving signal FOO and the tracking error signal TEO or observing the frequency response associated with the tracking driving signal TRO and the focusing error signal FEO. 
     In order to diagnose characteristics of the OPU  12 , a tester needs an external dynamic signal analyzer  42  and an external mixer  44  shown in  FIG. 2 . In addition, the dynamic signal analyzer  42  needs to be connected to the OPU  12  and the focusing controller  18 , and the mixer  44  needs to be connected to the dynamic signal analyzer  42 , the focusing controller  18 , and the servo system  24 . Concerning the optical disk drivers  10  waiting to be tested, the complicated connection shown in  FIG. 2  is repeatedly established for diagnosing the characteristic of the OPU  12  within each optical disk driver  10 . When mass production of the optical disk drive  10  begins, the prior art quality assurance (QA) procedure greatly slows actual yield of the optical disk drive  10  owing to the above-mentioned complicated testing mechanism. 
     SUMMARY OF INVENTION 
     The invention provides a method and a related apparatus for diagnosing crosstalk within an optical pick-up unit by utilizing firmware of the optical disk drive. 
     Briefly summarized, a preferred embodiment of the present invention provides a method for diagnosing an optical disk drive. The claimed method includes utilizing an optical pick-up unit for outputting an incident laser to a track on an optical disk and reading a reflecting laser modulated by the track for generating a tracking error signal and a focusing error signal, calculating a tracking driving signal according to the tracking error signal, calculating a focusing driving signal according to the focusing error signal, utilizing a firmware of the optical disk drive for mixing a noise with the focusing driving signal to generate a test focusing driving signal, adjusting a position of the optical pick-up unit corresponding to the optical disk according to the test focusing driving signal and the tracking driving signal, and determining whether the focusing error signal outputted from the optical pick-up unit interferes with the tracking error signal outputted from the optical pick-up unit according to the tracking error signal. 
     A preferred embodiment of the present invention also provides a method for diagnosing an optical disk drive. The claimed method includes utilizing an optical pick-up unit for outputting an incident laser to a track on an optical disk and reading a reflecting laser modulated by the track for generating a tracking error signal and a focusing error signal, calculating a tracking driving signal according to the tracking error signal, calculating a focusing driving signal according to the focusing error signal, utilizing a firmware of the optical disk drive for mixing a noise with the tracking driving signal to generate a test tracking driving signal, adjusting a position of the optical pick-up unit corresponding to the optical disk according to the test tracking driving signal and the focusing driving signal, and determining whether the tracking error signal outputted from the optical pick-up unit interferes with the focusing error signal outputted from the optical pick-up unit according to the focusing error signal. 
     The preferred embodiment of the present invention provides an optical disk drive. The claimed optical disk drive comprises an optical pick-up unit for outputting an incident laser to a track on an optical disk and reading a reflecting laser modulated by the track for generating a tracking error signal and a focusing error signal, a focusing controller for calculating a focusing driving signal according to the focusing error signal, a tracking controller for calculating a tracking driving signal according to the tracking error signal, a memory for storing a noise processing program, a microprocessor electrically connected to the memory for running the noise processing program to mix a noise with the focusing driving signal to generate a test focusing driving signal, and a servo system electrically connected to the microprocessor and the tracking controller for adjusting a position of the optical pick-up unit corresponding to the optical disk according to the test focusing driving signal and the tracking driving signal. 
     The preferred embodiment of the present invention provides an optical disk drive. The optical disk drive comprises an optical pick-up unit for outputting an incident laser to a track on an optical disk and reading a reflecting laser modulated by the track for generating a tracking error signal and a focusing error signal, a focusing controller for calculating a focusing driving signal according to the focusing error signal, a tracking controller for calculating a tracking driving signal according to the tracking error signal, a memory for storing a noise processing program, a microprocessor electrically connected to the memory for running the noise processing program to mix a noise with the tracking driving signal to generate a test tracking driving signal, and a servo system electrically connected to the microprocessor and the tracking controller for adjusting a position of the optical pick-up unit corresponding to the optical disk according to the test tracking driving signal and the focusing driving signal. 
     It is an advantage of the present invention that the claimed optical disk drive utilizes the digital signal processing means to impose the noise upon either the focusing driving signal or the tracking driving signal. Because the generic optical disk drive commonly has a firmware, the claimed invention only needs to modify the firmware, and adds the noise processing program and other programs that process the noise to the firmware. In addition, when the behavior of the optical pick-up unit is being diagnosed, the microprocessor embedded in the optical disk drive is capable of running the noise processing program of the firmware. Therefore, the claimed optical disk drive does not need to establish complicated connections to connect external diagnosing equipment. Therefore, the claimed optical disk drive is capable of diagnosing its installed optical pick-up unit quickly. 
     These and other contents 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, which is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram of a prior art optical disk drive. 
         FIG. 2  is a diagram of a prior art optical disk drive diagnosing system. 
         FIG. 3  is a first frequency response diagram associated with a focusing driving signal and a tracking error signal. 
         FIG. 4  is a second frequency response diagram associated with the focusing driving signal and the tracking error signal. 
         FIG. 5  is a block diagram of a first optical disk drive according to the present invention. 
         FIG. 6  is a flow chart illustrating a first diagnosing process for an optical pick-up unit shown in  FIG. 5 . 
         FIG. 7  is a flow chart illustrating a second diagnosing process for the optical pick-up unit shown in  FIG. 5 . 
         FIG. 8  is a block diagram of a second optical disk drive according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 5 , which is a block diagram of a first optical disk drive  50  according to the present invention. The optical disk drive  50  includes an optical pick-up unit (OPU)  52 , a focusing controller  54 , a tracking controller  58 , a microprocessor  60 , a memory  62 , a servo system  64 , two multiplexers  66   a ,  66   b , two analog-to-digital converters (ADCs)  68   a ,  68   b , and two digital-to-analog converters (DACs)  70   a ,  70   b . The OPU  52  is used for outputting a laser to an optical disk and receiving a reflecting laser modulated through the optical disk. At the same time, the OPU  52  generates a focusing error signal FEO and a tracking error signal TEO according to the received reflecting laser. The focusing controller  54  is capable of generating a focusing driving signal FOO according to the focusing error signal FEO, and the tracking controller  58  is capable of generating a tracking driving signal TRO according to the tracking error signal TEO. For example, each of the focusing controller  54  and the tracking controller  58  has an amplifier and a compensator. Concerning the focusing controller  54 , its amplifier amplifies the amplitude of the focusing error signal FEO. Because the amplitude of the focusing error signal FEO corresponds to a vertical gap error between the OPU  52  and the optical disk, the compensator determines how to adjust the vertical location of the OPU  52  according to a predetermined mapping function and the amplitude of the focusing error signal FEO, and outputs a focusing driving signal FOO. Regarding the tracking controller  58 , it operates according to the same means mentioned above. That is, its amplifier amplifies the amplitude of the tracking error signal TEO. Because the amplitude of the tracking error signal TEO corresponds to horizontal location error of the OPU  52  above the optical disk, the compensator determines how to adjust the horizontal location of the OPU  52  according to a predetermined mapping function and the amplitude of the tracking error signal TEO, and outputs a tracking driving signal TRO. Then, the servo system  64  is capable of moving the OPU  52  vertically and horizontally according to the tracking driving signal TRO and the focusing driving signal TRO. The microprocessor  60  is used to control operations of the optical disk drive  50 . For instance, the microprocessor  60  is a digital signal processor (DSP) that is capable of reading the firmware  72  stored in the memory  62 . In the preferred embodiment, the memory  62  is a non-volatile memory (a flash memory for example). Therefore, after the power feeding the optical disk drive  50  is cut, the firmware  72  is still kept in the memory  62  without being flushed. Suppose that the optical disk drive  50  is installed on a computer host. The computer host itself only needs to output high-level control commands to the microprocessor  60  within the optical disk drive  50 , and then the microprocessor  60  is capable of executing the received control commands to control corresponding operations of the optical disk drive  60  with the help of the firmware  72 . 
     It is noteworthy that the focusing controller  54  in the preferred embodiment is electrically connected to a multiplexer  66   a  and an ADC  68   a . In addition, the tracking controller  58  is similarly connected to a multiplexer  66   b  and an ADC  68   b . The ADC  68   a  is used to convert the focusing driving signal FOO into a corresponding digital focusing driving signal S 1 , and delivers the digital focusing driving signal S 1  to the microprocessor  60 . Similarly, the ADC  68   b  is used to convert the tracking driving signal TRO into a corresponding digital tracking driving signal S 2 , and delivers the digital tracking driving signal S 2  to the microprocessor  60 . The firmware  72  in the preferred embodiment has a noise processing program  74  for imposing a predetermined noise (a sine wave for example) on the digital focusing driving signal S 1  to generate a test focus driving signal S 1 ′. In addition, the noise processing program  74  also can impose a predetermined noise such as a sine wave on the digital tracking driving signal S 2  to generate a test tracking driving signal S 2 . 
     As shown in  FIG. 5 , after the microprocessor  60  computes the test focusing driving signal S 1 ′, a DAC  70   a  converts the digital test focusing driving signal S 1 ′ into an analog test focusing driving signal FOO′, and passes the test focusing driving signal FOO′ to the multiplexer  66   a . Similarly, after the microprocessor  60  computes the test tracking driving signal S 2 ′, a DAC  70   b  converts the digital test tracking driving signal S 2 ′ into an analog test tracking driving signal TRO′, and passes the test tracking driving signal TRO′ to the multiplexer  66   b . The multiplexer  66   a  has two input ports A 1 , B 1 , and an output port C 1 . In addition, a control signal SW 1  is used to control the output port C 1  being electrically connected to either the input port A 1  or the input port B 1 . Another multiplexer  66   b  also has two input ports A 2 , B 2 , and an output port C 2 . In addition, a control signal SW 2  is used to control the output port C 2  being electrically connected to either the input port A 2  or the input port B 2 . 
     When the characteristic of the OPU  52  is diagnosed, the microprocessor  60  reads the noise processing program  74 , runs the retrieved noise processing program  74 , and outputs appropriate control signals SW 1 , SW 2  to multiplexers  66   a ,  66   b  for adjusting internal transmission routes of the multiplexers  66   a ,  66   b . In other words, with the control of the transmission routes within the multiplexer  66   a , the vertical movement of the OPU  52  is driven by one driving signal selected from the focusing driving signal FOO and the test focusing driving signal FOO′. By the same means, the horizontal movement of the OPU  52  is driven by one driving signal selected from the tracking driving signal TRO and the test tracking driving signal TRO with the control of the transmission routes within the multiplexer  66   b.    
     Please refer to  FIG. 6 , which is a flow chart illustrating a first diagnosing process for the OPU  52  shown in  FIG. 5 . The process of diagnosing the OPU  52  includes following steps. 
     Step  100 : Start. 
     Step  102 : After the optical disk drive  50  is powered on, and an optical disk is loaded into the optical disk drive  50 , the microprocessor  60  enables the servo system  64 . 
     Step  104 : The microprocessor  60  reads the noise processing program  74  and runs the noise processing program  74 . 
     Step  106 : The microprocessor  60  determines initial values of the amplitude and frequency of a noise through the noise processing program  74 . 
     Step  108 : The microprocessor  60  runs the noise processing program  74  to mix the noise with the focusing driving signal S 1  inputted into the microprocessor  60 , and generates the test focusing driving signal S 1 . 
     Step  110 : Measure a peak-to-peak voltage of a tracking error signal TEO outputted from the OPU  52 . 
     Step  112 : Determine if the peak-to-peak voltage is greater than a voltage threshold. If so, go to step  118 ; otherwise, go to step  114 . 
     Step  114 : Update the frequency of the noise. 
     Step  116 : Determine if the frequency of the noise is greater than a target value. If yes, go to step  118 ; otherwise, go back to step  110 . 
     Step  118 : End. 
     The detailed operation of diagnosing the OPU  52  is described as follows. When the optical disk drive  50  is powered on, operating voltages are successfully delivered to components (the OPU  52  and the microprocessor  60  for example) within the optical disk drive  50 . Then, each of the components can function normally. After putting a test optical disk into the optical disk drive  50 , a tester is capable of inputting a control command to the microprocessor  60  for moving the OPU  52  to a predetermined track location on the inserted optical disk. Therefore, the microprocessor runs the firmware  72  according to the received control command for enabling the servo system  64  to move the OPU  52  (step  102 ). Please note that the OPU  52  outputs the focusing error signal FEO and the tracking error signal TEO for further tuning position of the OPU  52  after the OPU  52  is moved to the predetermined track location. At the same time, the focusing controller  54  and the tracking controller  58  are also enabled to generate the focusing driving signal FOO and the tracking driving signal TRO. In addition, the microprocessor  60  outputs control signals SW 1 , SW 2  for controlling the input port A 1  of the multiplexer  66   a  electrically connected to the output port C 1  of the multiplexer  66   a  and controlling the input port A 2  of the multiplexer  66   b  electrically connected to the output port C 2  of the multiplexer  66   b . Therefore, the servo system  64  still uses the focusing driving signal FOO and the tracking driving signal TRO to adjust the position of the OPU  52 . 
     Then, the tester inputs another control command to the microprocessor  60  for commanding the microprocessor  60  to run the noise processing program  74 . After the microprocessor  60  reads the noise processing program  74 , and runs the noise processing program  74 , the control signals SW 1 , SW 2  outputted from the microprocessor  60  now is used for driving the multiplexers  66   a ,  66   b  to make the input port B 1  electrically connected to the output port C 1  and the input port A 2  still electrically connected to the output port C 2  (step  104 ). 
     The noise processing program  74  sets parameters associated with a noise. The noise is mixed with the focusing driving signal S 1 , which corresponds to the focusing driving signal FOO. The preferred embodiment utilizes a sine wave to function as the noise used for diagnosing the OPU  52 . That is, when the noise processing program  74  is run, the noise processing program  74  initializes the amplitude and frequency of the sine wave first (step  106 ). In addition, the preferred embodiment tests characteristics of the OPU  52  with the frequency of the noise limited within a frequency range. Therefore, the initial value for the frequency of the noise can be set to a minimum value of the frequency range, and a target value for the frequency of the noise can be set to a maximum value of the frequency range. Please note that the initial value for the frequency of the noise is capable of being set to the maximum value of the frequency range, and the target value for the frequency of the noise capable of being set to the minimum value of the frequency range. In addition, the noise used in the present invention is not limited to being a sine wave. Therefore, signals with any waveforms can be used to simulate the noise except the D.C. signal with fixed amplitude. 
     The noise processing program  74  mixes the sine wave with the focusing driving signal S 1  through prior art digital signal processing, and then outputs the test focusing driving signal S 1 ′ (step  108 ). The DAC  70   a  further converts the test focusing driving signal S 1 ′ into the test focusing driving signal FOO′. Because the output port C 1  of the multiplexer  66   a  is connected to the output port B 1  of the multiplexer  66   a , and the output port C 2  of the multiplexer  66   b  is connected to the output port A 2  of the multiplexer  66   a , the test focusing driving signal FOO′ and the tracking driving signal TRO are inputted into the servo system  64  finally. Please note that the test focusing driving signal FOO′ is influenced with the noise provided by the noise processing program  74 , and the servo system  64  utilizes the test focusing driving signal FOO′ and the tracking driving signal TRO to control the position of the OPU  52 . Therefore, the crosstalk interference of the tracking error signal TEO outputted from the OPU  52 , which is caused by the noise imposing on the focusing error signal FEO, is capable of being determined through detecting the tracking error signal TEO outputted from the OPU  52 . In other words, the tester can measure the peak-to-peak voltage of the tracking error signal TEO to determine the magnitude of the induced interference (step  110 ). It is known from experiments that if the OPU  52  is seriously affected by the crosstalk, the generated tracking error signal TEO oscillates so that its peak-to-peak voltages becomes greater than a voltage threshold. On the contrary, concerning the ideal OPU  52 , the outputted tracking signal TEO does not oscillate to make its peak-to-peak voltage greater than the voltage threshold. Therefore, the goal of filtering out the flawed OPU  52  is achieved through comparing the measured peak-to-peak voltage with the voltage threshold (step  112 ). That is, if the peak-to-peak voltage of the tracking error signal TEO becomes greater than the voltage threshold, the behavior of the tested OPU  52  is bad. Otherwise, the noise processing program  74  updates the frequency of the noise for re-testing the behavior of the OPU  52  (step  114 ). 
     If the initial value for the frequency of the sine wave is set to the minimum value of the frequency range, the noise processing program  74  increases the frequency of the sine wave. On the contrary, if the initial value for the frequency of the sine wave is set to the maximum value of the frequency range, the noise processing program  74  decreases the frequency of the sine wave. The preferred embodiment diagnoses the OPU  52  with the sine wave having the frequency within the frequency range. When the frequency of the sine wave is outside the frequency range, it means that the diagnosing process for the OPU  52  is finished. However, if the frequency of the sine wave is still inside the frequency range, the noise processing program  74  continuously updates the frequency of the noise to interfere with the focusing driving signal S 1  until the frequency of the sine wave is outside the frequency range. 
     Please refer to  FIG. 7 , which is a flow chart illustrating a second diagnosing process for the OPU  52  shown in  FIG. 5 . The process of diagnosing the OPU  52  includes following steps. 
     Step  200 : Start. 
     Step  202 : After the optical disk drive  50  is powered on, and an optical disk is loaded into the optical disk drive  50 , the microprocessor  60  enables the servo system  64 . 
     Step  204 : The microprocessor  60  reads the noise processing program  74  and runs the noise processing program  74 . 
     Step  206 : The microprocessor  60  determines initial values of the amplitude and frequency of a noise through the noise processing program  74 . 
     Step  208 : The microprocessor  60  runs the noise processing program  74  to mix the noise with the tracking driving signal S 2  inputted into the microprocessor  60 , and generates the test tracking driving signal S 2 . 
     Step  210 : Measure a peak-to-peak voltage of a focusing error signal FEO outputted from the OPU  52 . 
     Step  212 :Determine if the peak-to-peak voltage is greater than a voltage threshold. If so, go to step  218 ; otherwise, go to step  214 . 
     Step  214 : Update the frequency of the noise. 
     Step  216 : Determine if the frequency of the noise is greater than a target value. If so, go to step  218 ; otherwise, go back to step  210 . 
     Step  218 : End. 
     The operation of diagnosing the OPU  52  shown in  FIG. 7  is similar to the operation of diagnosing the OPU  52  shown in  FIG. 6 . The main difference is that operations of the steps  204 ,  208 ,  210  are different from operations of the steps  104 ,  108 ,  110 . The operations for the steps identical to that shown in  FIG. 6  are not repeatedly described for simplicity because they have been described above. Regarding the step  204 , the control signals SW 1 , SW 2  outputted from the microprocessor  60  now are used for driving the multiplexers  66   a ,  66   b  to make the input port B 2  electrically connected to the output port C 2  and the input port A 1  still electrically connected to the output port C 1  after the microprocessor  60  reads and runs the noise processing program  74 . In other words, after the noise processing program  74  runs, the servo system  64  controls the position of the OPU  52  according to the focusing driving signal FOO outputted from the focusing controller  54  and the test tracking driving signal TRO′ outputted from the DAC  70   b . In addition, concerning the steps  208 ,  210  shown in  FIG. 7 , the noise processing program  74  run by the microprocessor  60  mixes a noise (a sine wave for example) with the tracking driving signal S 2  through prior art digital signal processing. Therefore, the test tracking driving signal TRO′ is influenced with the noise provided by the noise processing program  74 , and the servo system  64  utilizes the test tracking driving signal TRO′ and the focusing driving signal FOO to control the position of the OPU  52 . Therefore, the crosstalk interference of the focusing error signal FEO outputted from the OPU  52 , which is caused by the noise imposing on the tracking error signal TEO, is capable of being determined through detecting the focusing error signal FEO outputted from the OPU  52 . In other words, the tester can measure the peak-to-peak voltage of the focusing error signal FEO to determine the magnitude of the induced interference. Therefore, the goal of filtering out the flawed OPU  52  is achieved through comparing the measured peak-to-peak voltage with the voltage threshold. 
     Please refer to  FIG. 8 , which is a block diagram of a second optical disk drive  80  according to the present invention. The optical disk drive  80  has an OPU  82 , a microprocessor  84 , a memory  86 , a servo system  88 , two ADCs  89   a ,  89   b , and two DACs  90   a ,  90   b . In addition, a firmware  92  is stored in the memory  86 , and the firmware  92  includes a noise processing program  94 , a focusing program  96 , and a tracking program  98 . The optical disk drive  80  shown in  FIG. 8  is similar to the optical disk drive  50  shown in  FIG. 5 . The components in the optical disk drives  50 ,  80  having identical names correspond to the same functionality, and repeated description for the component in the optical disk drive  80  is skipped. The main difference between the optical disk drive  80  and the optical disk drive  50  is that the optical disk drive  80  utilizes software or so-called firmware (the focusing program  96  and the tracking program  98 ) to replace the hardware (the focusing controller  54  and the tracking controller  58 ) originally used in the optical disk drive  50 . As shown in  FIG. 8 , the ADC  89   a  converts the focusing error signal FEO into a digital focusing error signal S 3 , and the ADC  89   b  converts the tracking error signal TEO into a digital tracking error signal S 4 . Therefore, the microprocessor  84  runs the focusing program  96  and the tracking program  98  in the firmware  92  to process the focusing error signal FEO and the tracking error signal TEO through digital signal processing, and then outputs corresponding focusing driving signal S 3 ′ and the tracking driving signal S 4 ′. The DAC  90   a  is capable of converting the digital focusing driving signal S 3 ′ into a corresponding analog focusing driving signal FOO, and the DAC  90   b  is capable of converting the digital tracking driving signal S 4 ′ into a corresponding analog tracking driving signal TRO. In other words, when the optical disk drive  80  is activated, the microprocessor  84  loads the focusing program  96  and the tracking program  98 . The focusing program  96  functions as the focusing controller  54 , and the tracking program  98  functions as the tracking controller  58 . The position of the OPU  82  through driving the servo system  88  is successfully controlled. For the optical disk drive  80 , it adopts the digital signal processing means to control the focusing operation and the tracking operation associated with the OPU  82 . Similarly, the optical disk drive  80  also adopts the digital signal processing means to diagnose the crosstalk inherent to the OPU  82 . In other words, the diagnosing process for the OPU  82  is identical to the diagnosing process of the OPU  52  shown in  FIG. 6  or  FIG. 7 . Therefore, the description for the diagnosing process of the optical disk drive  80  is not repeated. 
     In contrast to the prior art, the claimed optical disk drive utilizes the digital signal processing means to impose the noise upon the focusing driving signal. Then, the peak-to-peak voltage of the tracking error signal is measured to determine if the optical pick-up unit is critically affected by the well-known crosstalk. In addition, claimed optical disk drive also can utilize the digital signal processing means to impose the noise upon the tracking driving signal. Then, the peak-to-peak voltage of the focusing error signal is measured to determine if the optical pick-up unit is critically affected by the well-known crosstalk. Because the generic optical disk drive commonly has a firmware, the claimed invention only needs to modify the firmware, and adds the noise processing program and other programs that process the noise to the firmware. Then, The noise to the focusing driving signal or the tracking driving signal during diagnosing the optical disk drive is imposed. In addition, when the behavior of the optical pick-up unit is being diagnosed, the microprocessor embedded in the optical disk drive is capable of running the noise processing program of the firmware. Therefore, the claimed optical disk drive does not need to establish complicated connections to connect external diagnosing equipment (the dynamic signal analyzer for example). To sum up, the claimed optical disk drive is capable of diagnosing its installed optical pick-up unit quickly. The influence of the quality assurance (QA) on the yield of optical disk drives is alleviated owing to the greatly reduced diagnosing time. 
     The above description provides a full and complete description of the preferred embodiments of the present invention. Various modification, alternate construction, and equivalent may be made by those skilled in the art without changing the scope or spirit of the invention. Accordingly, the above description and illustrations should not be construed as limiting the scope of the invention which is defined by the following claims.