Abstract:
An apparatus for generating tracking error signals including: an optical detection unit having a plurality of divided light receiving elements to allow beams reflected from a recording surface of the optical disks to be incident; a comparator for outputting after comparing the signals from light receiving elements, which correspond to the set group of the optical detection unit, with the reference signals set for the each group; an error correction unit for correcting and outputting errors if there are any errors after mutual comparison with signals of the groups output from the comparator; a phase-difference detection unit for outputting the signals for each group that correspond to a phase-difference after mutual comparison of the signals of the groups output from the error correction unit; a subtractor for mutually subtracting the signals for each group from the phase-difference detection unit and outputting the tracking error signals.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an apparatus for generating tracking error signals, and more particularly to an apparatus for generating tracking error signals from a reflected and received light from a recording surface of optical disks.  
         [0003]     The present application is based on Korean Patent Application No. 2002-45139, filed Jul. 31, 2002, which is incorporated herein by reference in its entirety  
         [0004]     2. Background of the Related Art  
         [0005]     Optical disks, for example, a compact disk(CD) and a digital video disk(DVD), include tracks of spiral shape. Disk players which read out information recorded on these disks emit a light on the optical disks. In order for an optical pickup apparatus, which receives a light reflected from the recording surface, to extract data with no errors, it is necessary to follow tracks with precision. To do this, tracking error signals are generated by using information of optical distribution incident upon a quarterly-divided optical detector which usually receives a light reflected by the recording surface of an optical disk.  
         [0006]     For example, optical disk players for DVD generate tracking error signals by using a phase-difference detection method. Korean Patent Laid-Open Publication No. 1998-082277 discloses an apparatus for generating tracking error signals by means of a phase-difference detection method. This apparatus, however, has some problems in that it cannot correct errors of some distortions of the optical detector when a light is received by the optical detector after being reflected from the optical disks. Particularly, when the pit/land length is short, the amplitude of the pick-up signals is very much decreased due to the modulation transfer function(MTF) of the optical pickup, so the effect of noise becomes great. With the MTF, if either the pit/land length gets shorter or the reading speed gets larger, the frequency of the output signals will increase, and as a result, the amplitude of the pick-up signals will decrease. Accordingly, to increase the recording density and speed, it is required to find a method for correcting these signal distortions.  
         [0007]     On the other hand, U.S. Pat. No. 6,317,396 B1 discloses an apparatus for generating tracking error signals to reduce problems from these signal distortions. However, an apparatus as suggested in U.S. Pat. No. 6,317,396 B1 uses signals directly from the optical detector and distinguishes errors. Further, its circuit embodiment gets very complicated.  
       SUMMARY OF THE INVENTION  
       [0008]     An object of the invention is to solve at least the above problems and/or disadvantages and to provide an apparatus for generating tracking error signals which can simplify the circuit architecture to correct signal distortion.  
         [0009]     To accomplish the object, the apparatus for generating tracking error signals followed by the present invention includes: an optical detection unit equipped with divided light receiving elements to allow beams reflected from a recording surface of the optical disks to be incident; a comparator for outputting comparison signals resulting from comparing the signals from light receiving elements, which correspond to groups of the optical detection unit, with the reference signals set for each group; an error correction unit for correcting and outputting signals, if there are any errors, after mutual comparison with signals of the groups output from the comparator; a phase-difference detection unit for outputting the signals for each group that correspond to a phase-difference after mutual comparison of the signals of the groups output from the error correction unit; a subtractor for outputting tracking error signals by making a mutual subtraction of the signals of the groups output from the phase-difference detection unit.  
         [0010]     Desirably, the optical detection unit is a quarterly-divided light receiving element.  
         [0011]     In addition, the optical detection unit includes: a first adder for adding up the signals of two light receiving elements disposed in one diagonal direction of the four quarterly-divided light receiving elements, and outputting the added signals to the comparator as the first group signals; a second adder for adding up the signals of two light receiving elements not included in the first group, placed in another diagonal direction of the four quarterly-divided light receiving elements, and outputting the added signals to the comparator as the second group signals.  
         [0012]     The comparator includes: a first comparator for comparing the signals of the first adder with reference signals and outputting the results; and a second comparator for comparing the signals of the second adder with reference signals and outputting the results.  
         [0013]     The error correction unit includes: a first switching unit for outputting the signals of the first comparator and the first reference signals selectively to the phase-difference detection unit; a second switching unit for outputting the signals of the second comparator and the first reference signals selectively to the phase-difference detection unit; a XOR gate for performing an exclusive logical adding operation of signals of the first and the second comparators; an OR gate for performing a logical adding operation of signals of the first and the second comparators; a pulse comparator for comparing signals of the XOR gate and the OR gate, and controlling the first and second switching units so that the first reference signals are output for those signals corresponding to the same level.  
         [0014]     In addition, an apparatus for generating tracking error signals followed by another embodiment of the present invention includes: an optical detection unit equipped with divided light receiving elements to allow beams reflected from the recording surface of optical disks to be incident; a plurality of comparators for outputting comparison signals resulting from comparing the signals from each light receiving element of the optical detection unit with the set reference signals; an error correction unit for determining if there are any errors after mutually comparing the signals of the compared results from the comparators associated with groups of light receiving elements of the optical detection unit oppositely disposed, and thereby correcting and outputting the signals; a phase-difference detection unit for mutually comparing the signals corresponding to each light receiving element from the error correction unit within the associated group, and outputting signals corresponding to the phase-difference respective to each light receiving element; an adder for mutually adding up the signals output from the phase-difference detection unit corresponding to light receiving elements placed in the diagonal direction of the optical detection unit; a subtractor for outputting tracking error signals by making a mutual subtraction of the signals of the groups output from the adder.  
         [0015]     The error correction unit includes: a first error correction unit for comparing the signals from the comparator corresponding to the first and second light receiving elements oppositely disposed of the quarterly-divided light receiving elements applied by the optical detection unit, determining if there are any errors, correcting and outputting signals; a second error correction unit for comparing the signals from the comparator corresponding to third and fourth light receiving elements oppositely disposed of the quarterly-divided light receiving elements applied by the optical detection unit, determining if there are any errors, correcting and outputting signals.  
         [0016]     In addition, the phase-difference detection unit includes: a first phase-difference detection unit for comparing the signals corresponding to the first and second light receiving elements output from the error correction unit, outputting the signals corresponding to the phase-difference with respect to the first and second light receiving elements; a second phase-difference detection unit for comparing the signals corresponding to the third and fourth light receiving elements output from the error correction unit, outputting the signals corresponding to the phase-difference with respect to the third and fourth light receiving elements; a first OR gate for making a mutual logical adding of the signals output from the first phase-difference detection unit corresponding to the first light receiving element and signals output from the second phase-difference detection unit corresponding to the third light receiving element, and then outputting the result to the subtractor; a second OR gate for making a mutual logical adding of signals output from the first phase-difference detection unit corresponding to the second light receiving element and signals output from the second phase-difference detection unit corresponding to the fourth light receiving element, and then outputting the result to the subtractor.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The invention will be described in detail with reference to the following drawings in which like reference numerals refer to like elements wherein:  
         [0018]      FIG. 1  is a block diagram of an apparatus for generating tracking error signals in accordance with a first preferred embodiment of the present invention;  
         [0019]      FIG. 2  is a waveform diagram of signals outputted from elements of  FIG. 1 ;  
         [0020]      FIG. 3  is a drawing of input and output waveforms of the error correction unit of  FIG. 1 ;  
         [0021]      FIG. 4  is a circuit diagram in accordance with a preferred embodiment of the error correction unit in  FIG. 1 ;  
         [0022]      FIG. 5  is a waveform diagram of signals outputted from elements of  FIG. 4 ; and  
         [0023]      FIG. 6  is a block diagram of an apparatus for generating tracking error signals in accordance with the second preferred embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0024]     The following detailed description will present an apparatus for generating tracking error signals in accordance with a first preferred embodiment with reference to the accompanying drawings.  
         [0025]      FIG. 1  is a block diagram of an apparatus for generating tracking error signals in accordance with a first preferred embodiment of the present invention.  
         [0026]     Referring to  FIG. 1 , an apparatus for generating tracking error signals includes first and second adders  21 ,  22 , first and second comparators  41 ,  42 , an error correction unit  50 , a phase-difference detection unit  60 , and a subtractor  80 .  
         [0027]     The first adder  21  outputs signals resulting from the mutual adding of the first and third light receiving elements P 1 , P 3 , which are placed in one diagonal direction of the quarterly-divided optical detector  11 . The signals from the first adder  21  correspond to signals of a first group.  
         [0028]     The second adder  22  outputs signals resulting from the mutual adding of the second and fourth light receiving elements P 2 , P 4 , which are placed in another diagonal direction of the quarterly-divided optical detector  11 . The signals from the second adder  22  correspond to signals of a second group.  
         [0029]     A first gain control amplifier  31  controls the output signals from the first adder  21  to a predetermined amplitude.  
         [0030]     A second gain control amplifier  32  controls the output signals from the second adder  22  to a predetermined amplitude.  
         [0031]     The first comparator  41  outputs signals from the first gain control amplifier  31  as binary signals after comparing them with a reference level.  
         [0032]     The second comparator  42  outputs signals from the second gain control amplifier  32  as binary signals after comparing them with a reference level.  
         [0033]     An error correction unit  50  compares signals from the first comparator  41  with signals from the second comparator  42 , determines if there are any signal distortions, corrects the signals if there are any distortions, and outputs the resulting signals.  
         [0034]     A phase difference detection unit  60  compares signals corresponding to the first group from the error correction unit  50  with signals corresponding to the second group and outputs signals corresponding to the phase-difference by each group.  
         [0035]     A first and a second low pass filter  71 ,  72  convert signals from the phase-difference detection unit  60  into voltage signals proportional to the phase-difference and output the resulting signals.  
         [0036]     A subtractor  80  subtracts signals mutually from the first and second low pass filters  71 ,  72  and outputs the resulting signals as tracking error signals(TES).  
         [0037]     When signal distortions occur in the apparatus for generating tracking error signals, an error correction unit  50  will correct them. The diagram of  FIG. 2  describes the process in which tracking error signals are generated by disclosing waveforms of each unit.  
         [0038]      FIG. 2  teaches waveforms A 1 , A 2  from the first and second adders  21 ,  22 , respectively. In addition, the waveform from the second adder  22  illustrates that reduced and abnormal signals are output in the section(X) where signal distortions are assumed to occur.  
         [0039]     In this case, the error correction unit  50  decides that the section X, where signals B 2  from the second comparator  42  compared to signals B 1  from the first comparator  41  maintains a low level for more than a predetermined time, has errors due to signal distortions, and outputs the signal level for the related section after converting them into the same level. As a result, even though signal distortions take place, it is possible to generate normal tracking error signals.  
         [0040]     A desirable example of this error correction unit  50  is shown in  FIG. 4 . Also, output waveforms of some of the elements of  FIG. 4  are shown in  FIG. 5 .  
         [0041]     Referring to  FIGS. 4 and 5 , the error correction unit  50  includes a first MUX  51 , a second MUX  52 , a XOR gate  53 , an OR gate  54 , and a pulse comparator  55 .  
         [0042]     The first and second MUXs  51 ,  52  output signals in accordance with controlling signals from the pulse comparator  55 . Specifically, either signals B 1 , B 2  from the first and second comparator  41 ,  42  are output unchanged or low signals are output, which are the set first reference signals.  
         [0043]     The XOR gate  53  performs an exclusive logical adding operation on the signals B 1  from the first comparator  53  and the signals B 2  from the second comparator B 2 , and outputs the results to the pulse comparator  55 .  
         [0044]     The OR gate  54  performs a logical adding operation on the signals B 1  from the first comparator  41  and the signals B 2  from the second comparator  42 , and outputs the results to the pulse comparator  55 .  
         [0045]     The pulse comparator  55  compares signals (K) from the XOR gate  53  with signals(L) from the OR gate  54 . As a result, when the signals (K) and (L) correspond to the mutually same level, the pulse comparator controls the first MUX  51  and the second MUX  52 , which are the first and second switching units, according to the first reference signals. For example, when the signals (K) and (L) correspond to the mutually same level, low signals are output.  
         [0046]     The pulse comparator  55  includes two serial-parallel converters  55   a,    55   b  and a parallel comparator  55   c.    
         [0047]     The serial-parallel converter  55   a  converts signals (K) from the XOR gate  53  and the serial-parallel converter  55   b  converts signals(L) from the OR Gate  54 , where signals (K) and signals (L) are input in series. A shift register can be applied to the serial-parallel converters  55   a,    55   b.    
         [0048]     A parallel binary comparator  55   c  compares signals which are made to be parallel in the serial-parallel converter  55   a,    55   b.  In the section where two signals correspond to the same level, the parallel binary comparator  55   c  outputs signals for controlling MUXs  51 ,  52  so that the first reference signals are output. In comparing signals, the number of bits compared by the parallel binary comparator  55   c  corresponds to the number of bits contained in the section X.  
         [0049]     According to this error correction unit, if mutual logical adding or exclusive logical adding is performed on the signals from each comparator  41 ,  42 , the signals which have distortions, as illustrated in  FIG. 2  and  FIG. 5 , can be converted into the same waveforms of signals.  FIG. 2  and  FIG. 5  illustrate waveforms from each unit in  FIG. 4  and the section (X), which has signal distortions as seen through sections marked with S 1  and S 2 . So errors can be corrected in the phase-difference detection process later.  
         [0050]      FIG. 6  illustrates another preferred embodiment where the output signals from light receiving elements of an optical detection unit are grouped. However, the error correction method on signal distortions of the error correction unit  50  is applied in the same way.  
         [0051]     Referring to  FIG. 6 , an apparatus for generating tracking error signals includes first to fourth comparators  141 - 144 , an error correction unit  150 , a phase-difference detection unit  160 , and a subtractor  180 .  
         [0052]     In  FIG. 6 , the first group signal corresponds to signals from the first and second light receiving elements P 1 , P 2  placed closely together on opposite sides in the clockwise direction of the signals from a quarterly-divided optical detector  111 , and the second group signal corresponds to signals from the third and fourth light receiving elements P 3 , P 4 .  
         [0053]     First to fourth gain control amplifiers  131 - 134  control and output signals from light receiving elements P 1  to P 4  of the optical detector  111 , respectively, in a predetermined amplitude.  
         [0054]     The first to fourth comparators  141 - 144  compare signals from corresponding gain control amplifiers  131 - 134  with reference levels, and output them as binary signals.  
         [0055]     An error correction unit  150  includes a first error correction unit  151  which corrects the first group signal and a second error correction unit  152  which corrects the second group signal.  
         [0056]     The first error correction unit  151  corrects and outputs signals from the first light receiving element P 1  and the second light receiving element P 2  of the optical detector  111  by means of the signal correction method described in  FIG. 4 .  
         [0057]     The second error correction unit  152  corrects and outputs signals from the third light receiving element P 3  and the fourth light receiving element P 4  of the optical detector  111  by means of the signal correction method described in  FIG. 4 .  
         [0058]     In other words, the same circuit in  FIG. 4  is applied to the first error correction unit  151 , but the input signals are the signals b 1  from the first comparator  141  and the signals b 2  from the second comparator  142 .  
         [0059]     Similarly, the same circuit in  FIG. 4  is applied to the second error correction unit  152 , but the input signals are the signals b 3  from the third comparator  143  and the signals b 4  from the fourth comparator  144 .  
         [0060]     A phase-difference detection unit  160  includes the first phase-difference detection unit  161  which processes the signals of the first group and the second phase-difference detection unit  162  which processes the signals of the second group.  
         [0061]     The first phase-difference detection unit  161  compares signals corresponding to the first light receiving element P 1  and second light receiving element P 2  which are output from the first error correction unit  151 , and outputs each signal corresponding to the phase-difference to correspond to each light receiving element.  
         [0062]     The second phase-difference detection unit  162  compares signals corresponding to the third light receiving element P 3  and fourth light receiving element P 4  which are output from the second error correction unit  152 , and outputs each signal corresponding to the phase-difference to correspond to each light receiving element.  
         [0063]     A first OR gate  221  performs a mutual logical adding of the signals from the first phase-difference detection unit  161  corresponding to the first light receiving element P 1  and the signals from the second phase-difference detection unit  162  corresponding to the third light receiving element P 3 , and outputs the result into a subtractor  180 .  
         [0064]     A second OR gate  222  performs a mutual logical adding of the signals from the first phase-difference detection unit  161  corresponding to the second light receiving element P 2  and the signals from the second phase-difference detection unit  162  corresponding to the fourth light receiving element P 4 , and outputs the result into the subtractor  180 .  
         [0065]     A subtractor  180  performs a mutual subtraction of the signals from the first OR gate  221  and signals from the second OR gate  222 , and outputs the resulting signals.  
         [0066]     Signals from the subtractor  180  go through a low pass filter(LPF)  270  and are output as tracking error signals(TES).  
         [0067]     While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. For example, while the invention has been described in the specific content of an apparatus for generating tracking error signals, it has an advantage that it has simple circuit construction as it is made to perform a correction of signal distortions by using signals from comparators which convert signals from light receiving elements into binary signals.  
         [0068]     The embodiments and advantages are merely exemplary and are not to be construed as limiting the present invention. The present teaching can be readily applied to other types of apparatuses. The description of the present invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures.