Abstract:
An apparatus includes a first circuit and a second circuit. The first circuit may be configured to generate status signals and an error signal in response to accessing a storage medium. The error signal provides a first value based on an accuracy of accessing the storage medium. The second circuit may be configured to offset the first value of the error signal to a second value to increase the accuracy of accessing said storage medium. The status signals include one or more of a data signal and a differential signal. In a first mode, an offset signal is generated in response to the data signal. In a second mode, the offset signal is generated in response to the differential signal.

Description:
[0001]    This is a continuation of U.S. Ser. No. 11/450,846, filed Jun. 9, 2006, which is incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to optical storage generally and, more particularly, to a method and/or apparatus for optimizing a focus point for optical disc. 
       BACKGROUND OF THE INVENTION 
       [0003]    In a conventional optical disc system, to sense the position of the laser beam in relation to the track on the disc, a main laser beam creates a reflection from the disc. The reflection from the main laser beam is picked up by 4 photo-diode sensors within a photo-diode sensor assembly.  FIG. 1  is a conceptual diagram illustrating how such a photo-diode sensor assembly  10  is laid out in relation to the track direction. The outputs of the 4 photo-diodes within the photo-diode assembly  10  (when the laser beam is focused on the disc) are shown as signals A, B, C and D, respectively. 
         [0004]    Referring to  FIG. 2 , a conventional optical disc system  20  is shown. A focus actuator (not shown) will keep a laser beam  22  focused on a surface of the disc  23  by adjusting the vertical position of a lens  24 . A focus controller (not shown) controls the focus actuator. To control the focus actuator to keep the laser beam  22  focused on the surface of the disc  23 , a signal focus error (FE) is controlled to zero and a signal beam strength (BS) is controlled to a high value. The signal FE provides information related to the vertical position of the lens  24 . The signal BS provides information related to the strength of the laser beam  22 . Due to the alignment of the photo-diode sensor  10  when the signal FE is controlled to zero, the focus point of the laser beam  22  may not be optimally positioned on the surface of the disc  23 . It is necessary to adjust the signal FE slightly off of a zero level in order to optimally establish the focus point of the laser beam  22  on the surface of the disc  23 . Conventional methods fail to provide an optimal focus point of the laser beam on the surface of the disc when the signal FE is slightly off a zero level (or at an optimized focus offset level). Since conventional methods fail to provide an optimal focus point of the laser beam on the disc, the overall quality of reading and writing data from and to the disc will be decreased. 
         [0005]    It would be desirable to provide a method and/or apparatus to optimize the focus point for an optical disc. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention concerns an apparatus including a first circuit and a second circuit. The first circuit may be configured to generate status signals and an error signal in response to accessing a storage medium. The error signal provides a first value based on an accuracy of accessing the storage medium. The second circuit may be configured to offset the first value of the error signal to a second value to increase the accuracy of accessing said storage medium. The status signals include one or more of a data signal and a differential signal. In a first mode, an offset signal is generated in response to the data signal. In a second mode, the offset signal is generated in response to the differential signal. 
         [0007]    The objects, features and advantages of the present invention include providing a method and/or apparatus for optimizing the focus point for an optical disc that may (i) provide for a reliable method of optimizing the focus point of a laser beam, (ii) optimize the focus point of a laser beam to read and write data on an optical disc, (iii) increase quality in the read/write process, (iv) be inexpensive to implement and/or (v) be easy to implement. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    These and other objects, features and advantages of the present invention will be apparent from the following detailed description and the appended claims and drawings in which: 
           [0009]      FIG. 1  illustrates a photo-diode sensor distribution; 
           [0010]      FIG. 2  illustrates a lens and a lens housing in relation to a position of a laser beam; 
           [0011]      FIG. 3  is a diagram of a system incorporating the present invention; 
           [0012]      FIG. 4  is a more detailed diagram of the data circuit in the context of the present invention; 
           [0013]      FIG. 5  is a diagram illustrating a data signal creation circuit; 
           [0014]      FIG. 6  is a diagram illustrating a main beam push-pull signal creation circuit; 
           [0015]      FIG. 7  is a diagram illustrating a focus error signal creation circuit; 
           [0016]      FIG. 8  is a flow diagram for finding the optimal focus point to read data from an optical disc; 
           [0017]      FIG. 9  is a diagram illustrating the peak-to-peak value of the signal DS as the focus offset is changed; 
           [0018]      FIG. 10  is a flow diagram for finding the optimal focus point to record data on an optical disc; and 
           [0019]      FIG. 11  is a diagram illustrating the peak-to-peak value of the main beam peak-to-peak signal. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]    Referring to  FIG. 3 , a block diagram of a system  100  is shown in accordance with a preferred embodiment of the present invention. The system  100  generally comprises an optical pick-up unit (OPU)  102 , an optical disc  104 , a number of disc tracks  105   a - 105   n , a block (or circuit)  106 , a block (or circuit)  108 , a block (or circuit)  110 , a block (or circuit)  112 , a block (or circuit)  114  and a laser source  120 . The circuit  106  may be implemented as data circuit. The circuit  108  may be implemented as a focus error creation circuit. The circuit  110  may be implemented as a focus offset circuit. The circuit  112  may be implemented as an adder circuit. The circuit  114  may be implemented as a focus controller. The circuits  110 ,  112  and  114  may be implemented via hardware or software. In one example, the circuits  110 ,  112  and  114  may be implemented as hardware circuits. Depending on the particular hardware design, the circuits  110 ,  112  and  114  may be analog and/or digital circuits. In one example, the circuits  110 ,  112  and  114  may each be implemented as a software block (e.g., a digital signal processing software structure) without the use of a hardware circuit. The implementation of the circuits  110 ,  112  and  114  as software or hardware may be varied to meet the design criteria of a particular implementation. The OPU  102  generally comprises a photo-diode sensor  122 , a lens  126 , a sled housing  128  and a focus actuator  130 . 
         [0021]    The photo-diode sensor  122  may present any combination of signals A, B, C and D on a signal (e.g., PD_ 1 ) to the data circuit  106 . The photo-diode sensor  122  may present any combination of signals A, B, C, and D on a signal (e.g., PD_ 2 ) to the data circuit  106 . The photo-diode sensor  122  may present any combination of signals A, B, C and D on a signal (e.g., PD_ 3 ) to the focus error creation circuit  108 . The data circuit  106  may present a data signal (e.g., DS) to the focus offset circuit  110 . The data circuit  106  may present a signal (e.g., MBPP) to the focus offset circuit  110 . The focus offset circuit  110  may present a signal (e.g., OFFSET) to the adder  112 . The focus error creation circuit  108  may present the signal FE to the adder circuit  112 . The adder circuit  112  may present a signal (e.g., FE_AFTER_OFFSET) to the focus controller  114 . The focus controller  114  may control the vertical position of the lens  126  with a signal (e.g., CTRL). 
         [0022]    In a first state, the data circuit  106  may present the signal DS to the focus offset circuit  110  when reading data from the disc  104 . The focus offset circuit  110  may generate the signal OFFSET in response to the signal DS. In a second state, the data circuit  106  may present the signal MBPP to the focus offset circuit  110  when writing or rewriting (recording) data to the disc  104 . The focus offset circuit  110  may generate the signal OFFSET in response to the signal MBPP. The signal FE may be at zero (or at a first value) when the focus controller  114  keeps the laser beam  124  focused on the surface of the disc  104 . The focus offset circuit  110  may offset the signal FE to a level off of zero (or to a second value) to ensure that the focus point of the laser beam  124  is at an optimal position. The focus offset circuit  110  may adjust (or increase) the focus point of the laser beam  124  when (i) reading data from any one of a particular tracks  105   a - 105   n  and (ii) writing data to any one of a particular tracks  105   a - 105   n.    
         [0023]    Referring to  FIG. 4 , a more detailed diagram of the data circuit  106  in the context of the present invention is shown. The data circuit  106  generally comprises a block (or circuit)  116  and a block (or circuit)  118 . The circuit  116  may be implemented as a data signal creation circuit. The circuit  118  may be implemented as a push-pull signal creation circuit. The focus offset circuit  110  may generate the signal OFFSET when (i) data is read from any one of a particular tracks  105   a - 105   n  and (ii) data is written to any one of a particular tracks  105   a - 105   n.    
         [0024]    In the first state, when reading data from the disc  104 , the data signal creation circuit  116  may generate the signal DS. The signal DS may be a radio frequency signal. The signal DS may be generated from data on the optical disc  104 . The focus offset circuit  110  may generate the signal OFFSET based on the value of the signal DS. The signal FE may be zero when the focus actuator  130  adjusts the focus point of the laser beam  124  on the surface of the disc  104  (e.g., the focus actuator  130  adjusts the vertical position of the lens  126  with respect to the laser beam  124 ). The focus actuator  130  may be positioned within the sled housing  128 . The focus actuator  130  may be implemented as a voice coil motor. The focus actuator  130  may act as a spring and move the lens  126  vertically. The focus actuator  130  may adjust the vertical position of the lens  126  by controlling the amount of current that flows through a coil when in the presence of a magnetic field. The focus actuator  130  may be integrated as a hardware device within the OPU  102 . 
         [0025]    The adder circuit  112  may add the signal OFFSET to the signal FE to generate the signal FE_AFTER_OFFSET. In general, the system  100  may not obtain an optimal focus point of the laser beam  124  when the signal FE is equal to zero. The focus controller  114  may control the focus actuator  130  such that the signal FE_AFTER_OFFSET is always at zero. When the signal FE_AFTER_OFFSET is zero, an optimal focus point of the laser beam  124  may be achieved. If the signal OFFSET is zero, such a condition may illustrate that the signal FE is at zero (e.g., the signal FE_AFTER_OFFSET may be set to zero) and an optimal focus point of the laser beam  124  has been achieved. If the signal OFFSET is not zero, the focus actuator  130  (via control of the focus controller  114 ) may adjust the vertical position of the lens  124  such that the focus error creation circuit  108  may generate the signal FE to be at a reverse level (or value) of the signal OFFSET. The sum of the signal OFFSET and the signal FE (which is at a reverse level of the signal OFFSET) may ensure that the signal FE_AFTER_OFFSET is set to zero. In general, the signal OFFSET may control the focus actuator  130  to adjust the focus point of the laser beam  124  in order to achieve the optimal focus point. While in the first state, the laser beam  124  may be (i) focused on the surface of the disc  104  and (ii) controlled (by a tracking actuator (not shown)) to stay on any one of a particular tracks  105   a - 105   n.    
         [0026]    In the second state, when the disc  104  is recordable (e.g., data is written to the disc  104 ), the beam push-pull signal creation circuit  118  may generate the signal MBPP. The signal MBPP may be a low frequency signal. The focus offset circuit  110  may generate the signal OFFSET based on the value of the signal MBPP. The signal FE may be zero when the focus actuator  132  adjusts the focus of the laser beam  124  on the surface of the disc  104 . The adder circuit  112  may add the signal OFFSET to the signal FE to generate the signal FE_AFTER_OFFSET. In general, the system  100  may not obtain an optimal focus point of the laser beam  124  when the signal FE is equal to zero. The focus controller  114  may control the focus actuator  130  such that the signal FE_AFTER_OFFSET is always at zero. When the signal FE_AFTER_OFFSET is zero, an optimal focus point of the laser beam  124  may be achieved. If the signal OFFSET is zero, such a condition may illustrate that the signal FE is at zero (e.g., the signal FE_AFTER_OFFSET may be set to zero) and an optimal focus point of the laser beam  124  has been achieved. If the signal OFFSET is not zero, the focus actuator  130  (via the control of the focus controller  114 ) may adjust the vertical position of the lens  124  such that the focus error creation circuit  108  may generate the signal FE to be at a reverse level of the signal OFFSET. The sum of the signal OFFSET and the signal FE (which is at a reverse level of the signal OFFSET) may ensure that the signal FE_AFTER_OFFSET is set to zero. While in the second state, the laser beam  124  may be focused on the surface of the disc  104 . The laser beam  124  may not be controlled to stay on any one of a particular tracks  105   a - 105   n.    
         [0027]    Referring to  FIG. 5 , a more detailed diagram of the data signal creation circuit  116  is shown. The data signal creation circuit  116  generally comprises a circuit  130 , a circuit  132 , a circuit  134 , and a circuit  136 . The circuit  130 , the circuit  132  and the circuit  136  may be implemented as summing circuits. The circuit  136  may be implemented as a radio frequency filter. The circuit  130  may (i) receive the signal B and the signal D and (ii) present a signal equal to B+D. Similarly, the circuit  132  may (i) receive the signal A and the signal C and (ii) present an output signal equal to A+C. The summing circuit  134  may (i) receive the signal A+C and the signal B+D and (ii) present a signal equal to (A+C)+(B+D). The signal (A+C)+(B+D) may be presented to the radio frequency filter  136 . The radio frequency filter  136  may generate the signal DS. The signal DS or (radio frequency signal) may be a high frequency signal. The radio frequency filter  136  may be implemented as a high pass filter that is combined with one or more low pass filters. The data signal creation circuit  116  may generate the signal DS from data on the optical disc  104  as the laser beam  124  is focused on the surface of the disc  104  while the disc  104  is spinning. 
         [0028]    Referring to  FIG. 6 , a more detailed diagram of the beam push pull creation circuit  118  is shown. The beam push pull creation circuit  118  generally comprises a circuit  150 , a circuit  152 , a circuit  154 , and a circuit  156 . The circuit  150  and the circuit  152  may be implemented as summing circuits. The circuit  154  may be implemented as a differential circuit (e.g., a comparator, etc.). The circuit  156  may be implemented as a low pass filter. The circuit  150  may (i) receive the signal A and the signal D from the photo-diode sensor  122  and (ii) present a signal equal to A+D. Similarly, the circuit  152  may (i) receive the signal B and the signal C from the photo-diode sensor  122  and (ii) present an output signal equal to B+C. The differential circuit  154  may (i) receive the signal A+D and the signal B+C and (ii) present a signal equal to (A+D)−(B+D). The signal (A+D)−(B+C) may be presented to the low pass filter  156 , which may generate the signal MBPP. The signal MBPP may be a low frequency signal. The signal MBPP may be generated when (i) the laser beam  124  is focused on the surface of the disc  104  and (ii) the disc  104  is spinning. The disc  104  may (i) be independent of data (e.g., a blank disc) or (ii) include data (e.g., a rewrittable disc). Due to differences between the read and write processes, the optimal focus point of the laser beam  124  may be different. 
         [0029]    Referring to  FIG. 7 , a more detailed diagram of the focus error creation circuit  108  is shown. The focus error creation circuit  108  generally comprises a circuit  170 , a circuit  172 , a circuit  174  and a circuit  176 . The circuit  170  and the circuit  172  may be implemented as summing circuits. The circuit  174  may be implemented as a differential circuit (e.g., a comparator, etc.). The circuit  176  may be implemented as a low pass filter. The circuit  170  may (i) receive the signal B and the signal D and (ii) present a signal equal to B+D. Similarly, the circuit  172  may (i) receive the signal A and the signal C and (ii) present an output signal equal to A+C. The differential circuit  174  may (i) receive the signal A+C and the signal B+D and (ii) present a signal equal to (A+C)−(B+D). The signal (A+C)−(B+D) may be presented to the low pass filter  176 , which generates the signal FE. 
         [0030]    Referring to  FIG. 8 , a method  200  for optimizing the focus point to read data from an optical disc is shown. The method  200  generally comprises a state (or step)  202 , state (or step)  204 , a state (or step)  206 , a state (or step)  208 , a state (or step)  210 , a state (or step)  212 , a state (or step)  214 , a state (or step)  216  and a state (or step)  218 . The state  202  may be a start state. The state  218  may be an end state. 
         [0031]    The state  204  may control the lens  126  to keep the laser beam  124  focused on the surface of the disc  104 . When the lens  126  is controlled by the focus controller  114  so that the laser beam  124  is focused on the disc  104 , the laser beam  124  may be controlled to lock to any one of a particular tracks of data  105   a - 105   n  on the disc  104 . The state  206  may apply a predetermined amount of constant offset in the signal OFFSET. The predetermined amount of offset in the signal OFFSET may be added to the signal FE to generate the signal FE_AFTER_OFFSET. The state  208  may measure the peak-to-peak value of signal DS as the signal OFFSET is added to the signal FE to generate the signal FE_AFTER_OFFSET. 
         [0032]    The state  210  may gradually adjust (by increasing or decreasing) the signal OFFSET by a fixed predetermined amount. The state  212  may repeat states  206 ,  208 , and  210  a number of times (e.g., N). The step  208  may collect Xi and Yi values (where i=1, 2, . . . , N). The Yi value may correspond to the measured peak-to-peak values of the signal DS when the states  206  and  208  are repeated N-times. The Xi value may correspond to the adjusted values of the signal OFFSET when the state  210  is repeated N times. 
         [0033]    The state  214  may find a second order curve from the N points (Xi, Yi) (where i=1, 2, . . . , N) collected in the state  212 . The second-order curve may be defined by Y=A*X 2 +B*X+C (with i=1, 2, . . . , N) which goes through N points (Xi, Yi) so that the sum of (Y−Yi) 2  is minimal. 
         [0034]    The state  216  may find the optimal value of the signal OFFSET from the second order curve Y=A*X 2 +B*X+C. The optimal value of the signal OFFSET may be found when the signal OFFSET allows the peak-to-peak value Y of the signal DS to become maximal. The optimal value of the signal OFFSET may be applied to signal FE via the adder  112  to obtain the best (or increased) focus point for the laser beam  124  to read data on the disc  104 . 
         [0035]      FIG. 9  illustrates the peak-to-peak value of the signal DS as the signal OFFSET is changed.  FIG. 9  illustrates a measurement plot  220  and a curved plot  222 . The optimal value of the signal OFFSET is shown as a point  224 .  FIG. 9  illustrates that the point  224  may be at the second value which is slightly off of the first value (or zero). The point  224  may correspond to the optimal focus point of the laser beam  124  on the disc  104 . 
         [0036]    Referring to  FIG. 10 , a method  250  for optimizing the focus point to record data on an optical disc is shown. The method  250  generally comprises a state (or step)  252 , a state (or step)  254 , a state (or step)  256 , a state (or step)  258 , a state (or step)  260 , a state (or step)  262 , a state (or step)  264 , a state (or step)  266 , and a state (or step)  268 . The state  252  may be a start state. 
         [0037]    The state  254  may control the lens  126  to keep the laser beam  124  focused on the surface of the disc  104 . When the lens  126  is controlled so that the laser beam  124  is focused on the disc  104 , the laser beam  124  may not be controlled to lock on a particular one of a number of physical tracks  105   a - 105   n  of the disc  104 . The state  256  may apply a predetermined amount of constant offset in the signal OFFSET. The predetermined amount of offset in the signal OFFSET may be added to the signal FE to generate the signal FE_AFTER_OFFSET. 
         [0038]    The state  258  may measure the average peak-to-peak value of the signal MBPP based on revolutions (e.g., R) of the spinning disc  104 . The number of revolutions R used by the method  250  to measure the average peak-to-peak value of the signal MBPP may be varied to meet the design criteria of a particular implementation. 
         [0039]    The state  260  may gradually adjust (by increasing or decreasing) the signal OFFSET by a fixed predetermined amount. The state  262  may repeat states  256 ,  258  and  260  a number of times (e.g., N). The step  258  may collect Xi and Yi values (where i=1, 2, . . . , N). The Yi value may correspond to the measured peak-to-peak values of the signal MBPP when the states  256 - 258  are repeated N-times. The Xi value may correspond to the adjusted values of the signal OFFSET when the state  260  is repeated N-times. 
         [0040]    The state  264  may find a second order curve from the N points (Xi, Yi) (where i=1, 2, . . . , N) collected in the state  260 . The second-order curve may be defined by Y=A*X 2 +B*X+C (with i=1, 2, . . . , N) which goes through N points (Xi, Yi) so that the sum of (Y−Yi) 2  is minimal. 
         [0041]    The state  266  may find the optimal value of the signal OFFSET from the second order curve Y=A*X 2 +B*X+C. The optimal value of the signal OFFSET may be found when the signal OFFSET allows the peak-to-peak value Y of the signal MBPP to become maximal. The optimal value of the signal OFFSET may be applied to the signal FE via the adder  112  to obtain the best (or increased) focus point for the laser beam  124  to record data on the disc  104 . 
         [0042]      FIG. 11  illustrates the peak-to-peak value of the signal MBPP as the signal OFFSET is changed.  FIG. 11  illustrates a measurement plot  270  and a curved plot  272 . The optimal value of the signal OFFSET is shown as a point  274 .  FIG. 11  illustrates that the point  274  may be at a second value which is slightly off of the first value (or zero). The point  274  may correspond to the optimal focus point of the laser beam  124  to record data on the disc  104 . 
         [0043]    The present invention may (i) optimize the focus point of the laser beam  124  on the optical disc  104  based on whether (a) data is being read from the disc  104  or (b) data is being written to the disc  104 , (ii) provide a high degree of reliability by using a curved-fit technique to find the optimal value of a focus offset, (iii) be easily implemented within hardware and/or firmware or completely with firmware, and (iv) ensure a high degree of quality in optimizing the focus point of the laser beam  124  to either read or record data on the optical disc  104 . 
         [0044]    The function performed by the flow diagram of  FIGS. 8 and 10  may be implemented using a conventional general purpose digital computer programmed according to the teachings of the present specification, as will be apparent to those skilled in the relevant art(s). Appropriate software coding can readily be prepared by skilled programmers based on the teachings of the present disclosure, as will also be apparent to those skilled in the relevant art(s). 
         [0045]    The present invention may also be implemented by the preparation of ASICs, FPGAs, or by interconnecting an appropriate network of conventional component circuits, as is described herein, modifications of which will be readily apparent to those skilled in the art(s). 
         [0046]    The present invention thus may also include a computer product which may be a storage medium including instructions which can be used to program a computer to perform a process in accordance with the present invention. The storage medium can include, but is not limited to, any type of disk including floppy disk, optical disk, CD-ROM, magneto-optical disks, ROMs, RAMs, EPROMs, EEPROMs, Flash memory, magnetic or optical cards, or any type of media suitable for storing electronic instructions. The present invention may be particularly useful in an optical disc system (e.g., CD type, DVD type, etc.). The present invention may be useful in newly developing formats such as Blue-ray and HD-DVD systems. 
         [0047]    While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the scope of the invention.