Patent Publication Number: US-2005122859-A1

Title: Method and apparatus of mirror signal auto-calibration for optical disk drive

Description:
FIELD OF THE INVENTION  
      The present invention relates to a method and apparatus of mirror signal auto-calibration, and more particularly, to a method and apparatus of mirror signal auto-calibration for optical disk drive capable of effectively generating correct mirror signals for enabling the optical head to locate a correct track without sliding during seeking.  
     BACKGROUND OF THE INVENTION  
      During readout, the optical head of an optical disk drive needs to focus the laser beam thereof to a diffraction-limited spot, and onto an optical disk so as to perform the track-seeking and track-following operations between tracks of the optical disk. However, since the tracks of the optical disk is not an exact circle or due to the assembly of a loader, a considerable amount of extra electronics wizardry is needed to ensure that the laser stays in focus on the optical disk surface and that it follows the track it is reading. The forgoing condition is referred as “run out”. Therefore, a detection mechanism of the optical disk drive is used for detecting the “run out” and feedbacks the signal thereof for ensuring the optical head to perform track-seeking, track-following, and focusing normally.  
      Please refer to  FIG. 5 , which is a block diagram showing a track-seeking and track-following architecture of a conventional optical disk drive. Such architecture comprises an optical head  110 , a preamplifier  125 , a seek controller  150 , a tracking controller  170 , and a driver  160 . Taking a seeking operation for example, while the optical head  110  is performing the seeking operation, some parameters are provided by software to a direction detection/hysteresis protection/remaining tracks controller  151  so as to assure the direction and the track number for the seeking.  
      The optical head  110  corresponds to the seeking action of the optical disk to output certain signals  115  to the preamplifier  125 , and accordingly the preamplifier  125  will generate signals as following: track-error (TE) signal  143 , mirror (MIRR) signal  145 , track-error-zero-cross (TEZC) signal  146 , and so on, and the TE signal  143  is being fed into the track controller  170 , and the MIRR signal  145  along with the TEZC signal  146  is being fed into the direction detection/hysteresis protection/remaining tracks controller  151 , and further the TEZC signal  146  is being fed into a speed calculator  175  of the seek controller  150 .  
      Therefore, a seek speed controller  177  in the seek controller  150  will receive velocity error signal  185  formed by combining a signal  181  produced by a velocity profile generator  179  with an zero-cross-speed signal  183  produced by the speed calculator  175  according to the TEZC signal  146 , and use the same as the feedback for controlling the velocity error while the optical head  110  is seeking.  
      However, the seeking direction of the optical head  110 , the remaining number of track, and the hysteresis protection during slip is controlled by the direction detection/hysteresis protection/remaining tracks controller  151  based on both the phase of the MIRR signal  145  and the phase of the TEZC signal  146 . In this regard, the direction detection/hysteresis protection/remaining tracks controller  151  outputs a corresponding output signal  153  to the seek speed controller  177 .  
      Such that, the seek speed controller  177  can drive the driver  160  to control the optical head  110  to seek track at specific speed and direction, and carry out the hysteresis protection when sliding according to the velocity error signal  185  and the signal  153 .  
      The focus of the present invention is the MIRR signal generated by a preamplifier  125 . Please refer to  FIG. 1 , which is a schematic diagram depicting how a MIRR signal is generated. As seen in  FIG. 1  with reference to  FIG. 5 , a signal  115  is being fed into the preamplifier  125  for enabling a MIRR source signal generator  126  to produce a MIRR source signal  136 , and a MIRR slice level generator to produce a MIRR slice level signal  137 , such that a MIRR signal  145  can be formed by synthesizing the MIRR source signal  136  and the MIRR slice level signal  137  using a comparator  128 .  
      However, the nature of each optical disk and the carrying mechanism of the same will have affects on the signal  115  which is also the inputs of the MIRR source signal generator  126  and the MIRR slice level signal generator  127 . Therefore, when the MIRR source signal  136  generated by the MIRR source signal generator  126  is sliced by the MIRR slice level signal  137  generated by the MIRR slice level signal generator  127  while both passing through the comparator  128 , the slice level of the MIRR source signal  136  is inaccurate most of the time, and thus forming a MIRR signal  145  with phase error, i.e. the asymmetry duty cycle.  
      Therefore, in the condition that no feedback is being provided to the preamplifier  125  for forming the MIRR signal  145 , an erroneous MIRR signal  145  is being outputted more than often while the optical head  110  is being used for reading different optical disk since the slice level of the MIRR source signal  136  generated by the MIRR source signal generator  126  is usually inaccurate. If the direction detection/hysteresis protection/remaining tracks controller  151  receives the erroneous MIRR signal  145  during optical head  110  is seeking, the seeking direction will be misjudged, a wrong track number is calculated, or a slide occurs at the end of the seeking while the hysteresis protection can not stop the slide, that is, the optical head  110  will jiggle unceasingly.  
      In view of the above description, the present invention discloses a method and an apparatus of mirror signal auto-calibration for optical disk drive to effectively generate correct mirror signals, such that the optical head can locate the correct track without sliding during seeking.  
     SUMMARY OF THE INVENTION  
      The primary objective of the present invention is to provide an apparatus of mirror signal auto-calibration for optical disk drive, which comprises a preamplifier and a MIRR signal calibrator. The preamplifier is used for receiving the signal outputted from an optical head to produce a MIRR signal and feeds the MIRR signal to a seek speed controller for controlling the seeking of the optical head. The MIRR signal calibrator is used for receiving and evaluating the MIRR signal so as to output a calibration signal to a MIRR signal generator as the basis for generating the MIRR signal.  
      In a preferred embodiment of the present invention, the MIRR signal calibrator further comprises a detector and a calibrator. The detector is used for receiving and detecting the MIRR signal so as to output a result signal. The calibrator is used for receiving the result signal to output a calibrated signal. The detector could be a low pass filter or a counter.  
      Another objective of the present invention is to provide a method of mirror signal auto-calibration for optical disk drive, which comprises the step of: reading a MIRR signal; calibrating the MIRR signal while the upper and lower cycles of the same are not symmetric; and outputting the MIRR signal whose upper and lower cycles are symmetric as the basis for the optical head to perform a seeking operation.  
      Since the MIRR signal is formed from a MIRR source signal sliced with a slice level provided by a MIRR slice level signal, therefore, the method according to the preferred embodiment of the present invention further comprises the step of: calibrating the slice level for ensuring a MIRR signal to be formed with symmetric cycle, that is, if a slice level signal is too high that causes an asymmetry of the upper and lower cycles of the resulting MIRR signal, the slice level is adjusted to a lower level; and vice versa.  
      Accordingly, the method of the present invention further comprises a step of: Raising the waveform level of the MIRR source signal while a slice level signal is too high in order to enable the MIRR source signal to be sliced appropriately by the slice level; and vice versa.  
      Further, if the slice level is still high and has exceeded a certain limit after the same has been calibrated, then the calibrating process is terminated; or the calibration times of the slice level is larger than a threshold, the calibrating process is terminated.  
      In view of the description above, the present invention discloses a method and an apparatus of mirror signal auto-calibration for optical disk drive capable of using a feedback control mechanism for MIRR signal to effectively produce accurate MIRR signals, such that the optical head can locate the correct track without sliding during seeking. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a block diagram depicting a conventional apparatus of mirror signal generation for optical disk drive.  
       FIG. 2  is a block diagram depicting an apparatus of mirror signal auto-calibration for optical disk drive according to a preferred embodiment of the present invention.  
       FIGS. 3A  is waveforms of the MIRR source signal and the tracking error signal of a preamplifier of  FIG. 1 .  
       FIG. 3B  is waveforms of the MIRR signal and TEZC signal of a preamplifier of  FIG. 1 .  
       FIG. 4  is a flow chart of an apparatus of mirror signal auto-calibration for optical disk drive as depicted in  FIG. 2  according to a preferred embodiment of the present invention.  
       FIG. 5  is a conventional seeking and tracking architecture of an optical disk drive. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
      For your esteemed members of reviewing committee to further understand and recognize the fulfilled functions and structural characteristics of the invention, several preferable embodiments cooperating with detailed description are presented as the follows  
      Please refer to  FIG. 2 , which is a block diagram depicting an apparatus of mirror signal auto-calibration for optical disk drive according to a preferred embodiment of the present invention. In FIG.  2 , the apparatus  200  of mirror signal auto-calibration for optical disk drive comprises a preamplifier  210  and a MIRR signal calibrator  230 , wherein the MIRR signal calibrator  230  receives a MIRR signal  211  generated by the preamplifier  210  and feeds back a calibration signal to be used for calibrating the MIRR signal  211  to an correct phase, that is, the upper and lower cycles are symmetrical.  
      Please refer to  FIG. 3A  and  FIG. 3B  for the waveforms of a MIRR source signal  136  and a TEZC signal  146  of an amplifier  125  and the waveforms of a MIRR signal  145  and a TEZC signal  146  of the amplifier  125  respectively. In  FIG. 3A , while comparing the MIRR signal  136  of  FIG. 1  with a MIRR slice level signal  137  using a comparator  128 , it is equivalent to pass the MIRR source signal  136  through a direct current level, e.g. levels a, b, and c as seen in  FIG. 3B , and be sliced.  
      The MIRR signals  145  formed by a same MIRR source signal  136  being sliced respectively by levels a, b, and c is shown in  FIG. 3B . If the MIRR slice level such, as level a, is too high, the period t 1  of the upper half cycle of the formed MIRR signal  145  will be smaller than the period t 2  of the lower half cycle of the MIRR signal  145 . Similarly, if the MIRR slice level, such as level c, is too low, the period t 3  of the upper half cycle of the MIRR signal  145  will be larger than the period t 4  of the lower half cycle of the MIRR signal  145 . Therefore, when the MIRR signal  145  and the TEZC signal  146  formed by using either level a or level c is used for controlling the seeking operation of the optical head  110  of  FIG. 1 , the unmatched phase problem happened between the MIRR signal  145  and the TEZC signal  146  will degrade the seeking operation.  
      If the MIRR slice level is correct, such as level b of  FIG. 3B , the period t 5  of the upper half cycle of the corresponding MIRR signal  145  will be equal to the period t 6  of the lower half cycle, and the MIRR signal  145  formed by slicing the MIRR source signal  136  with level b is then a correct MIRR signal  145 . Therefore, when the MIRR signal  145  and the TEZC signal  146  formed by using the level b is used for controlling the seeking operation of the optical head  110 , the seeking operation can be performed accurately since the phase of the MIRR signal  145  matches that of the TEZC signal  146 .  
      Please refer to  FIG. 2 , is a block diagram depicting an apparatus  200  of mirror signal auto-calibration for optical disk drive according to a preferred embodiment of the present invention. In this architecture, the foregoing issue of having an excessively high or low slice level is handled by using the MIRR signal calibrator  230  of the apparatus  200  to receive a MIRR signal  211  generated by the preamplifier  210  so as to produce calibration signals  240 ,  250  as feedback for controlling the calibration of the MIRR signal  211 .  
      The method of mirror signal auto-calibration for optical disk drive using the apparatus  200  comprises the steps of: reading a MIRR signal  211 ; calibrating the MIRR signal  211  while the upper and lower cycles of the same are not symmetric; and outputting the calibrated MIRR signal whose upper and lower cycles are symmetric to a seek controller  220  as the basis for the optical head  210  to perform a seeking operation.  
      The MIRR signal  211  outputted from the preamplifier  210  is formed as following: a signal  203  outputted from an optical head  201  is being fed into the preamplifier  210  for enabling a MIRR source signal generator  215  therein to produce a MIRR source signal  216 , and a MIRR slice level generator  217  to produce a MIRR slice level signal  218 , such that a MIRR signal  211  can be formed by synthesizing the MIRR source signal  216  and the MIRR slice level signal  218  using a comparator  219 . Therefore, the method of mirror signal auto-calibration for optical disk drive using the apparatus  200  for calibrating the MIRR signal  211  further comprises: If the MIRR slice level provided by the MIRR slice level signal  218  is too high or too low for slicing the MIRR source signal while compared the signals  216  and  218  by the comparator  219  and thus forms a MIRR signal  211  with asymmetric upper and lower half cycles, the MIRR signal calibrator  230  will produce calibration signals  250 ,  240  respectively for the MIRR slice level signal generator  217  and the MIRR source signal generator  215  to adjust some internal parameters thereof, and further calibrate the slice level of the MIRR slice level signal  218  outputted from the MIRR slice level signal generator  217  and the waveform level of the MIRR source signal  216  outputted from the MIRR source signal generator  215 , such that the MIRR slice level provided by the MIRR slice level signal  218  is right for the MIRR source signal  216 .  
      In view of the method of mirror signal auto-calibration for optical disk drive using the apparatus  200  as described above, the MIRR signal calibrator  230  comprises a detector  260  for detecting the upper and lower half cycles of the MIRR signal  211  and a calibrator  270  for evaluating and adjusting the symmetry of the upper and lower half cycles of the MIRR signal  211 . In a preferred embodiment of the present invention, the detector can be a low pass filter consisted of resistors and capacitors or digital counter which outputs a result signal  280  to the calibrator  270  after detecting the MIRR signal  211 . The low pass filter will rectify the waveform of the MIRR signal  211  into a voltage signal to reflect the symmetry of the upper and lower half cycles of the MIRR signal  211 . The counter can directly count the upper and lower half cycles of the MIRR signal  211  to reflect the symmetry of the upper and lower half cycles of the MIRR signal  211 . The calibrator  270  controls and outputs the calibration signals  240 ,  250  respectively to the slice level signal generator  217  and the MIRR source signal generator  215  according to the result signal  280 .  
      Please refer to  FIG. 4 , which is a flow chart of an apparatus  200  of mirror signal auto-calibration for optical disk drive as depicted in  FIG. 2  according to a preferred embodiment of the present invention. Flow begins at block  401  where a MIRR signal  211  is being produced by the preamplifier  210 . Flow then proceeds to block  402 . At block  402 , the detector  260  arranged inside the MIRR signal calibrator  230  starts to read the MIRR signal  211  outputted from the preamplifier  210 .  
      At decision block  403 , an evaluation is made to determine if the slice level of the MIRR source signal  216  is too high according to the following operations: the upper and lower half cycles of the MIRR signal  211  are computed by a low pass filter  260  and a counter  290  in the detector  260  so as to be used by the calibrator  270  to check if the upper and lower half cycles of the MIRR signal  211  are symmetric or not. If the slice level for the MIRR source signal  216  is too high, then flow is directed to block  404 . If not, then flow proceeds to decision block  405 . At block  404 , a calibration signal  250  is being outputted from the MIRR signal calibrator  230  to the MIRR slice level generator  217  for decreasing the MIRR slice level of the MIRR slice level signal  218  and providing the same to the MIRR source signal  216 . Flow then proceeds to decision block  406 . At decision block  406 , an evaluation is made to determine if the criteria for terminating the calibration are fulfilled, i.e. the upper and lower cycles of the MIRR signal  211  are symmetric. If yes, then flow is directed to block  407  and stopped. If not, then flow is directed to block  408 . At block  408 , a calibration signal  250  is being outputted from the calibrator  270  to the preamplifier  125  that is used for adjusting the MIRR slice level of the MIRR source signal  216  provided by the MIRR slice level signal  240 .  
      At decision block  405 , an evaluation is made to determine if the slice level of the MIRR source signal  216  is too low. If the MIRR slice level is too low, then flow is directed to block  409 . If not, then flow is directed to block  407  and stop. At block  409 , a calibration signal  250  is being outputted from the MIRR signal calibrator  230  to the MIRR slice level generator  217  for raising the MIRR slice level of the MIRR slice level signal  218  and providing the same to the MIRR source signal  216 . Flow then proceeds to decision block  411 . At decision block  411 , an evaluation is made to determine if the criteria for terminating the calibration are fulfilled, i.e. the upper and lower cycles of the MIRR signal  211  are symmetric. If yes, then flow is directed to block  407  and stopped. If not, then flow is directed to block  412 . At block  412 , a calibration signal  250  is being outputted from the calibrator  270  to the preamplifier  125  that is used for adjusting the MIRR slice level of the MIRR source signal  216  provided by the MIRR slice level signal  240 .  
      Further, the termination criteria of the whole process are not limited to the above. For example, when the number of calibration reaches an threshold, or when the MIRR slice level reaches a certain limit, the whole process can be terminated to prevent the process from being continued unceasingly, which will affect the seeking operation of the optical disk drive.  
      By the above-mentioned procedure, an apparatus  200  of mirror signal auto-calibration for optical disk drive can effectively calibrate the MIRR slice level signal  240  to produce an accurate MIRR signal  21   1  for the optical head  201  to perform the seeking operation on an optical disk  205 , and such apparatus  200  also has a complete set of operation mechanism.  
      To sum up, the present invention discloses a method and an apparatus of mirror signal auto-calibration for optical disk drive capable of using a feedback control mechanism for MIRR signal to effectively produce accurate MIRR signals, such that the optical head can locate the correct track without sliding during seeking.  
      While the preferred embodiment of the invention has been set forth for the purpose of disclosure, modifications of the disclosed embodiment of the invention as well as other embodiments thereof may occur to those skilled in the art. Accordingly, the appended claims are intended to cover all embodiments which do not depart from the spirit and scope of the invention.