Abstract:
The present invention discloses an apparatus for generating a tracking error signal in an optical disc drive. The disclosed apparatus includes: an analog-to-digital conversion module for receiving a plurality of analog signals generated by accessing an optical disc and for converting the plurality of analog signals into a plurality of digital signals with a sampling rate; a frequency control module coupled to the analog-to-digital conversion module for adjusting the sampling rate according to the plurality of digital signals; and a signal generation module coupled to the analog-to-digital conversion module for generating the tracking error signal according to the plurality of digital signals.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This is a continuation-in-part of U.S. application Ser. No. 11/160,820, which was filed on Jul. 12, 2005, and is included herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an optical disc drive, and more particularly, to an apparatus and related method for generating a tracking error signal in the optical disc drive.  
         [0004]     2. Description of the Prior Art  
         [0005]     A servo system in an optical disc drive needs to utilize a tracking error signal TE for dynamically controlling a laser diode of a pick-up head (PUH) to output a laser beam to an optical disc track. The conventional method utilizes an optical sensor on the PUH to sense a reflected beam from the optical disc to generate a plurality of analog signals, utilizes an ADC to convert the plurality of analog signals to a plurality of digital signals with a specific sampling rate, and then generates the tracking error signal for the servo system.  
         [0006]     However, quality of the tracking error signal relates to the sampling rate of the ADC. If the ADC converts the plurality of analog signals to a plurality of digital signals with a fixed sampling rate, quality of the tracking error signal is not always the same when different tracks on the optical disc are read or the reading condition changes.  
         [0007]     Additionally, the conventional method generates the tracking error signal according to four signals A, B, C, D detected from the optical sensor. For example, the tracking error signal can be generated by subtracting a phase difference between the signals A and B from a phase difference between the signals C and D.  
         [0008]     However, the phase difference value between the signals A and B and the phase difference value between the signals C and D are not equally important in every situation. When one is more important than the other, the synthesis method with equal weighting factors for generating the tracking error signal is not the optimal method to represent the tracking error information.  
       SUMMARY OF THE INVENTION  
       [0009]     One objective of the claimed invention is therefore to provide an apparatus for dynamically adjusting a sampling rate utilized by an ADC when a tracking error signal is being generated, to solve the above-mentioned problems.  
         [0010]     According to an exemplary embodiment of the claimed invention, an apparatus is disclosed for generating a tracking error signal in an optical disc drive. The apparatus comprises: an analog-to-digital conversion module for receiving a plurality of analog signals generated by accessing an optical disc and for converting the plurality of analog signals to a plurality of digital signals according to a sampling rate; a frequency control module coupled to the analog-to-digital conversion module for adjusting the sampling rate according to the plurality of digital signals; and a signal generation module coupled to the analog-to-digital conversion module for generating the tracking error signal according to the plurality of digital signals.  
         [0011]     According to another exemplary embodiment of the claimed invention, a method is disclosed for generating a tracking error signal in an optical disc drive. The method comprises: receiving a plurality of analog signals generated by accessing an optical disc and converting the plurality of analog signals to a plurality of digital signals according to a sampling rate; adjusting the sampling rate according to the plurality of digital signals; and generating the tracking error signal according to the plurality of digital signals.  
         [0012]     According to another exemplary embodiment of the claimed invention, an apparatus is disclosed for generating a tracking error signal in an optical disc drive. The apparatus comprises: an analog-to-digital conversion module for receiving a plurality of analog signals generated by accessing an optical disc and converting the plurality of analog signals to a plurality of digital signals according to a sampling rate; a frequency control module coupled to the analog-to-digital conversion module for adjusting the sampling rate according to the plurality of digital signals; a signal generation module coupled to the analog-to-digital conversion module for generating an error signal according to the plurality of digital signals; a quality detection module coupled to the signal generation module for generating a quality detection signal according to the error signal; and a signal mix module coupled to the signal generation module and the quality detection module for generating the tracking error signal according to the error signal and the quality detection signal.  
         [0013]     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a diagram of an apparatus according to an embodiment of the present invention.  
         [0015]      FIG. 2  is a detailed diagram illustrating the operation of the frequency control module of  FIG. 1 .  
         [0016]      FIG. 3  is a detailed diagram illustrating the operation of the envelope generation unit of  FIG. 2 . 
     
    
     DETAILED DESCRIPTION  
       [0017]      FIG. 1  shows a diagram of an apparatus according to an embodiment of the present invention. The present embodiment apparatus can be applied to an optical disc drive for generating a tracking error signal TE. The apparatus of this embodiment includes an optical detection module, an analog-to-digital conversion module (ADC module), a frequency control module  150 , and a signal generation module. The optical detection module comprises a first optical sensor  112  and a second optical sensor  114  for respectively generating a first analog signal A and a second analog signal B according to a light beam reflected off an optical disc. The analog signals A and B can first be processed by AC coupling capacitors, equalizers, and low pass filters (LPF), and then be inputted into the analog-to-digital conversion module. The analog-to-digital conversion module includes a first ADC  122  and a second ADC  124  for respectively converting the analog signals A and B into a first digital signal A 0  and a second digital signal B 0  by a sampling rate 1/Ts, which is a frequency of a clock signal CLK′ of  FIG. 1 . The signal generation module includes a delay module with a first delay chain  132  and a second delay chain  134 , a third digital logic module  140 , and a charge pump  170  for generating the tracking error signal TE according to digital signals A 0  and B 0 . The digital apparatus  160  of the present embodiment apparatus can operate under the clock signal CLK′ provided by a frequency conversion module  180  such as a phase locked loop. In other words, the frequency of the clock signal CLK′ is the operation frequency of the digital apparatus  160  and the sampling rates of the ADCs  122  and  124 . The frequency control module  150  can control the frequency conversion module  180  to dynamically change the frequency of the clock signal CLK′. Then the ADCs  122  and  124  can utilize a better sampling rate 1/Ts to convert digital data into analog data.  
         [0018]     In the present embodiment, the delay chain  132  delays the digital signal A 0  by times Ts,  2 Ts,  3 Ts respectively to generate a first delay signal A 1 , a second delay signal A 2 , and a third delay signal A 3 . The delay chain  134  delays the digital signal B 0  by times Ts,  2 Ts,  3 Ts respectively to generate a fourth delay signal B 1 , a fifth delay signal B 2 , and a sixth delay signal B 3 . The digital logic module  140  generates a charging signal UP and a discharging signal DOWN according to the digital signals A 0 , B 0  and the delay signals A 2 , B 2 . The charge pump generates the tracking error signal TE according to the charging signal UP and the discharging signal DOWN.  
         [0019]     The digital signals A 0  and B 0  and the delay signals A 1 , A 2 , A 3 , B 1 , B 2 , B 3  of the present embodiment are all 1-bit digital signals. For the digital logic module  140 , if the value of a signal among the four signals A 0 , B 0 , A 2 , B 2  differs from the values of the other three signals, the digital logic module  140  determines that there is a phase difference between the analog signals A and B. At this moment, the level of the tracking error signal TE can be adjusted through the charging signal UP or the discharging signal DOWN. In other words, when the value of the signal A 0  differs from values of the signals A 2 , B 0 , and B 2 , or when the value of the signal B 2  differs from the values of signals A 0 , A 2 , and B 0 , the digital logic module  140  triggers the charging signal UP to increase the level of the tracking error signal TE through the charge pump  170 . When the value of the signal A 2  differs from values of the signals A 0 , B 0 , and B 2 , or when the value of the signal B 0  differs from the values of signals A 0 , A 2 , and B 2 , the digital logic module  140  triggers the discharging signal DOWN to decrease the level of the tracking error signal TE through the charge pump  170 . In the present embodiment, the digital logic module  140  can operate according to a truth table satisfying the above-mentioned conditions.  
         [0020]      FIG. 2  shows a detailed diagram illustrating the operation of the frequency control module  150  of  FIG. 1 . The frequency control module  150  includes a first detection module consisting of a first digital logic module  312  and a first envelope generation unit  322  and a second detection module consisting of a second digital logic module  314  and a second envelope generation unit  324 . The first detection module generates a first detection value TEL_env according to the first and second digital signals A 0  and B 0  as well as the first and fourth delay signals A 1  and B 1 . The second detection module generates a second detection value TER_env according to the first and second digital signals A 0  and B 0  as well as the third and sixth delay signals A 3  and B 3 .  
         [0021]     The operation of the digital logic module  312  is similar to the above mentioned digital logic module  140 . The first control signal UPL or the second control signal DOWNL is triggered when the value of a signal among the four signals A 0 , B 0 , A 1 , B 1  differs from the other three signals. In other words, when the value of the signal A 0  differs from values of the signals A 1 , B 0 , and B 1 , or when the value of the signal B 1  differs from the values of signals A 0 , A 1 , and B 0 , the digital logic module  312  triggers the control signal UPL. When the value of the signal A 1  differs from values of the signals A 0 , B 0 , and B 1 , or when the value of the signal B 0  differs from the values of signals A 0 , A 1 , B 1 , the digital logic module  312  triggers the control signal DOWNL.  
         [0022]     If the control signal UPL and the control signal DOWNL are utilized to control an extra charge pump, the charge pump will generate a signal TEL, which is similar to the tracking error signal TE. The functionality of the envelope generation unit  322  is to generate an envelope of possible signal TEL, which is the first detection value TEL_env, according to the control signal UPL and the control signal DOWNL.  FIG. 3  shows a detailed diagram illustrating the operation of the envelope generation unit  322  of  FIG. 2 . The operation of the envelope generation unit  322  comprises an up/down counter  410 , a first decimator  420 , a first register  430 , a first adder  440 , an absolute value apparatus  450 , a second adder  460 , a mixer  470 , a second register  480 , and a second decimator  490 . As the operation of the apparatus shown in  FIG. 3  is known to those skilled in the art, further discussion is omitted for the sake of brevity. The functionality of the envelope generation unit  324  is similar to the envelope generation unit  322  and the architecture can also be shown as  FIG. 3  but is not meant to be taken as a limitation of the present invention.  
         [0023]     When the first detection value TEL_env is larger than the second detection value TER_env, the quality of the tracking error signal TE generated from the signal generation module can be improved by increasing the operation frequency 1/Ts of the digital apparatus  160  (i.e. increasing the frequency of the clock signal CLK′). At this moment, the frequency control unit  330  of  FIG. 2  triggers a fifth control signal SUP to increase the frequency of the clock signal CLK′ by the frequency conversion module  180  in  FIG. 1 . When the first detection value TEL_env is smaller than the second detection value TER_env, the quality of the tracking error signal TE generated from the signal generation module can be improved by decreasing the operation frequency 1/Ts of the digital apparatus  160 . At this moment, the frequency control unit  330  of  FIG. 2  triggers a sixth control signal DOWNS to decrease the frequency of the clock signal CLK′ by the frequency conversion module  180  in  FIG. 1 .  
         [0024]     Please note that in the embodiment shown in  FIG. 1 , the signals inputted into the ADC  122  and the ADC  124  are the signals A and B respectively from the optical sensor. In fact, the two signals can also be the signal C and the signal D from the optical sensor respectively, or be the signal (A+C) and the signal (B+D). Additionally, the present invention apparatus and related method can also be utilized in TAIWAN Application No. 93121904, apparatus for generating a tracking error signal in an optical disc drive, which was filed on September, 2004. Besides dynamically adjusting the sampling rate utilized by the ADC, generating a first candidate tracking error signal TEAB according to the signal A and the signal B, and generating a second candidate tracking error signal TECD according to the signal C and the signal D, an extra quality detection module is utilized to determine respectively the quality of the first and second candidate tracking error signals TEAB, TECD to generate the tracking error signal TE needed according to the first and second candidate tracking error signals TEAB, TECD. Please refer to the above-mentioned TAIWAN Patent to obtain the detailed description of the quality detection module.  
         [0025]     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.