Abstract:
A wobble signal reproducing device and method. The wobble signal reproducing device may include a computation unit for outputting a push-pull signal by use of a signal picked up by wobbling an optical disc; a wobble band pass filter (BPF) unit for applying band pass filtering to the push-pull signal based on a first control signal, applying low pass filtering to the band pass filtering-applied signal based on a second control signal, and outputting a wobble signal; a wobble phase locked loop (PLL) unit for generating a channel clock signal based on the wobble signal, wherein the first and second control signals correspond to the channel clock signal, the wobble BPF unit applies the band pass filtering at a center frequency varying based on the first control signal, and applies the low pass filtering at a cutoff frequency varying based on the second control signal. Accordingly, the wobble signal reproducing device and method can effectively reproduce a wobble signal in the CLV mode as well as in the CAV mode in which the spindle motor rotates at a constant speed.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims benefit under 35 U.S.C. § 119 from Korean Patent Application No. 2004-3996, filed on Jan. 19, 2004, the entire content of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an optical reproducing device, and more particularly, to a wobble signal reproducing device for reproducing a wobble signal recorded on writable optical discs.  
         [0004]     2. Description of the Related Art  
         [0005]     Optical discs are classified into once-writable discs such as CD-R, DVD-R and the like, and re-writable discs such as CD-RW, DVD-RW, DVD-RAM, and the like, in addition to read-only discs such as CD-ROM and DVD-ROM. Unlike such existing read-only discs, as for the re-writable discs, a channel clock signal cannot be generated from a reproducing signal. Thus, the re-writable discs have grooves wobbled in a certain period having information, and a wobble signal is detected so that a channel clock signal necessary for writing data is generated.  
         [0006]     Furthermore, the CD/DVD read/write modes are divided into the constant linear velocity (CLV) mode and the constant angular velocity (CAV) mode depending on a spindle motor control method, and, in general, the CLV mode is employed for a low speed operation, and the CAV mode is employed for a high speed operation. The CLV mode causes the spindle motor to spin fastest in the innermost of a disc and to spin slowest in the outermost of the disc, and has the same frequency characteristics in the innermost and outermost of the disc. However, the CAV mode spins the spindle motor at a constant speed regardless of which portion of the disc information is accessed from, and the innermost and outermost of the disc has a 2.4 times difference in frequency.  
         [0007]      FIG. 1  is a block diagram for showing a conventional wobble signal reproducing device, and  FIGS. 2A-2C  explain a wobble signal reproducing process for the wobble signal reproducing device shown in  FIG. 1 .  
         [0008]     As shown in  FIG. 1 , as for the light amount corresponding to the wobble signal measured in the portions A, B, C, and D on the disc, the adders  11  and  13  add the light amounts corresponding to the portions A and D and the light amounts corresponding to the portions B and C, and, as shown in  FIG. 2A  and  FIG. 2B , the adders  11  and  13  output a (A+D) signal and a (B+C) signal, respectively, that have an RF signal in phase and a wobble signal in 180° phase difference. The (A+D) signal and the (B+C) signal are filtered through high-pass filters (HPFs)  21  and  23  each having a cut-off frequency sufficient to pass the wobble signal, so that a DC offset is removed.  
         [0009]     Next, automatic gain controllers (AGC)  31  and  33  maintain the amplitude of the RF signal constant, so as to prevent the RF signal from being missed due to the wobble signal.  
         [0010]     The subtractor  41  performs the subtraction between the gain-controlled (A+D) and (B+C) signals, and outputs a wobble signal as shown in  FIG. 2C . The narrow-band pass filter (BPF)  45  filters the output wobble signal to detect a wobble signal having a high signal-to-noise (S/N) ratio, the automatic gain controller  47  amplifies its gain, and the comparator  49  quantizes the wobble signal, and then outputs a wobble clock signal.  
         [0011]     The above existing wobble signal producing device has the band-pass filter  45  consisting of an active RC filter for a center frequency, and varies the center frequency of the band-pass filter  45  under controls of a system controller according to the variations of read/write speeds. The above control approach of the band-pass filter  45  has a disadvantage that the system controller controls the band-pass filter  45  every time the speed changes.  
         [0012]     Furthermore, with signal reproducing speeds increasing, the above approach has a problem of deviating the pass band of the band-pass filter owing to an access limit of the system controller in case that the wobble signal is reproduced in the CAV mode. Thus, this causes the S/N ratio of the wobble signal to be reduced as well as the jitter in the wobble clock signal to be increased.  
       SUMMARY OF THE INVENTION  
       [0013]     Embodiments of the present invention have been developed in order to solve the above drawbacks and other problems associated with the conventional arrangement. An aspect of the present invention is to provide a wobble signal reproducing device capable of effectively reproducing a wobble signal even when the CAV mode is used to reproduce a signal coping with a signal reproducing speed becoming faster.  
         [0014]     Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.  
         [0015]     The forgoing and other objects and advantages are substantially realized by providing a computation unit for outputting a push-pull signal by use of a wobbled signal picked up by wobbling an optical disc; a wobble band pass filter (BPF) unit for applying band pass filtering to the push-pull signal based on a first control signal, applying low pass filtering to the band pass filtering-applied signal based on a second control signal, and outputting a wobble signal; a wobble phase locked loop (PLL) unit for generating a channel clock signal based on the wobble signal, wherein the first and second control signals correspond to the channel clock signal, the wobble BPF unit applies the band pass filtering at a center frequency varying based on the first control signal, and applies the low pass filtering at a cutoff frequency varying based on the second control signal.  
         [0016]     The wobble BPF unit may include a band pass filter having a switched capacitor filter (SCF) varying the center frequency according to a switching frequency being the first control signal, and for applying the band pass filtering at the varied center frequency; and a smoothing filter having a gm-C low pass filter for varying the cutoff frequency according to a control voltage signal being the second control signal, and applying the low pass filtering at the varied cutoff frequency according to an embodiment of the present invention.  
         [0017]     The wobble PLL unit may include a phase detector for outputting a signal corresponding to a phase difference between a wobble clock signal corresponding to the wobble signal and a clock signal obtained by dividing the channel clock signal by a factor; a low pass filter for applying the low pass filtering to the output signal of the phase detector; and a voltage control oscillator for outputting the channel clock signal, according to an oscillating frequency being controlled based on the low pass filtering-applied signal, the first control signal being generated based on an output signal of the voltage control oscillator, and the second control signal being generated based on an input signal of the voltage control oscillator according to an embodiment of the present invention.  
         [0018]     A wobble signal reproducing device, according to another embodiment of the present invention, may include an automatic gain controller for amplifying a gain of the wobble signal output from the wobble BPF unit; and a comparator for quantizing an output signal of the automatic gain controller and outputting a wobble clock signal.  
         [0019]     In the meantime, a wobble signal reproducing device may further include a computation unit for outputting a push-pull signal by use of a signal picked up by wobbling an optical disc; a wobble band pass filter (BPF) unit for applying band pass filtering to the push-pull signal based on a first control signal, applying low pass filtering to the band pass filtering-applied signal based on a second control signal, and outputting a wobble signal; a wobble phase locked loop (PLL) unit for generating a channel clock signal based on the wobble signal; a first control signal generator for generating a clock signal proportional by a factor to the channel clock signal, and generating the first control signal corresponding to the clock signal proportional to the channel clock signal; and a second control signal generator for generating the second control signal corresponding to the channel clock signal.  
         [0020]     Accordingly, in embodiments of the present invention, the wobble signal reproducing device can effectively reproduce a wobble signal in the CAV mode in which the spindle motor spins at a constant speed as well as in the CLV mode. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]     These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments taken in conjunction with the accompanying drawings in which:  
         [0022]      FIG. 1  is a block diagram for schematically showing an existing wobble signal reproducing device;  
         [0023]      FIGS. 2A-2C  show a wobble signal reproducing process for the wobble signal reproducing device shown in  FIG. 1 ;  
         [0024]      FIG. 3  is a block diagram for schematically showing a wobble signal reproducing device according to an embodiment of the present invention;  
         [0025]      FIG. 4  is a block diagram for showing a wobble signal reproducing device shown in  FIG. 3 , according to another embodiment of the present invention;  
         [0026]      FIGS. 5A-5C  explain operations of the control voltage generator  393  of  FIG. 4 ; and  
         [0027]      FIG. 6  is a view for showing the band pass filter  351  of  FIG. 4 , according to another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]     Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the present invention by referring to the figures.  
         [0029]      FIG. 3  is a block diagram for schematically showing a wobble signal reproducing device that reproduces a wobble signal embedded on an optical disc according to an embodiment of the present invention.  
         [0030]     The optical recording/reproducing device forms optical spots on the recording surface of a disc by use of laser beams output from a light source for recording and reproducing an information signal. The reflected laser beams corresponding to a wobble signal on the recording surface of the disc are received by a light-receiving device, and the light-receiving device divides the received optical spots into portions A, B, C, and D, and measures light amounts for outputs. As stated above, the wobble signal is reproduced by using the light amounts corresponding to the optical spots measured on the portions A, B, C, and D of the disc.  
         [0031]     The wobble signal reproducing device may include adders  311  and  313  for adding light amounts A and D and light amounts B and C, respectively, as for light amounts A, B, C, and D measured on the portions A, B, C, and D on the disc, high-pass filters (HPFs)  321  and  323  for removing a DC offset in a (A+D) signal and a (B+C) signal, automatic gain controllers (AGCs)  331  and  333  for maintaining constant the amplitude of an RF signal contained in the (A+D) signal and the (B+C) signal, and a subtractor  341  for subtracting the gain-controlled (A+D) signal and (B+C) signal and outputting a push-pull signal, that is, a (A+D)−(B+C) signal.  
         [0032]     The wobble BPF unit  350  can employ a band pass filter having a switched capacitor filter (SCF) for varying and filtering the center frequency, and a smoothing filter having a gm-C low pass filter for varying and filtering a cutoff frequency in association with the center frequency with respect to a signal output in a track-and-hold form according to the characteristics of the switched capacitor filter.  
         [0033]     The wobble signal filtered by the switched capacitor filter (SCF) and the gm-C low pass filter is amplified to have a constant amplitude in the automatic gain controller (AGC)  361 , and output as a wobble clock signal through the comparator  371 .  
         [0034]     The wobble PLL unit  380  uses the wobble clock signal output from the comparator  371  to output a channel clock signal synchronized with the wobble clock signal. The wobble PLL unit  380  generates a switching frequency fsw for controlling the center frequency of the band pass filter (SCF) and a control voltage Vctrl for controlling the cutoff frequency of the smoothing filter (gm-C LPF) to be associated with the center frequency, based on the channel clock signal output from wobble PLL unit  380 . A detailed description will be later made on the switching frequency fsw (hereinafter, referred to as a control frequency) and a control voltage Vctrl that are provided by the wobble PLL unit  380 .  
         [0035]     Accordingly, the wobble signal can be precisely detected in the CLV mode in which the innermost and outermost of a disc have the same frequency characteristics as well as in the CAV mode in which the innermost and outermost of the disc have different frequency characteristics.  
         [0036]      FIG. 4  is a block diagram for showing in detail a wobble signal reproducing device according to an embodiment of the present invention, and, referring to  FIG. 4 , the present invention will be described in more detail.  
         [0037]     As shown in  FIG. 4 , the wobble signal reproducing device, according to an embodiment of the present invention, includes the wobble BPF unit  350  for filtering the center frequency adaptively varied to the push-pull signal, that is, the (A+D)−(B+C) signal inputted, the wobble PLL unit  380  for outputting a channel clock signal CLK synchronized with the wobble clock signal corresponding to the wobble signal output from the wobble BPF unit  350 , and a control frequency generator  391  and a control voltage generator  393  for generating the control frequency fsw and the control voltage Vctrl, respectively, based on the channel clock signal of the wobble PLL unit  380 .  
         [0038]     First, the wobble PLL unit  380  has a phase detector (PD)  381 , a low pass filter  383 , a voltage controlled oscillator (VCO)  385 , and a frequency divider  387 . The phase detector  381  obtains a phase difference between an input wobble clock signal and a channel clock signal divided in the frequency divider  387 , and outputs a signal corresponding to the phase difference. The low pass filter  383  filters the output signal of the phase detector  381 , and outputs the filtered output signal to the voltage controlled oscillator  385 , and the output signal of the low pass filter  383  controls the oscillation frequency of the voltage controlled oscillator  385 . Thus, the voltage controlled oscillator  385  outputs a channel clock signal synchronized to the wobble clock signal.  
         [0039]     Here, the output and input signals of the voltage controlled oscillator  385  can be processed in the control frequency generator  391  and a control voltage generator  393 , and supplied to the wobble BPF unit  350  as a control signal.  
         [0040]     The control frequency generator  391  generates a clock signal proportional to the frequency by a factor of the channel clock signal being the output signal of the voltage controlled oscillator  385 , with the generated clock signal being provided to the switched capacity filter (SCF) of the wobble BPF unit  350  as the control frequency fsw. For example, a ratio of a wobble clock signal frequency to a channel clock signal frequency in DVD-R/RW and DVD-RAM discs is 1:186. Therefore, the channel clock signal output from the voltage controlled oscillator  385  has to be lowered to a frequency that is processable by the switched capacity filter  351  (SCF). Accordingly, the switched capacitor filter  351  has the center frequency varied in association with the change of the channel clock signal.  
         [0041]     The control voltage generator  393  generates the control voltage Vctrl to the gm-C low pass filter  353  of the wobble BPF unit  350  based on a certain voltage being an input signal of the voltage controlled oscillator  385 . That is, the control voltage Vctrl varies the cutoff frequency of the gm-C low pass filter  383 .  
         [0042]     In  FIGS. 5A and 5C , for example, as for the innermost and outermost of a disc,  FIG. 5A  shows an oscillation frequencies Fvco corresponding to voltages Vctrl input to the voltage controlled oscillator  385 , and, when the cutoff frequencies f 1 ˜f 2  of the gm-C low pass filter are designed corresponding to the input voltages V 1 ˜V 2  of  FIG. 5A , accordingly, the control voltage generator  393  applies the input voltages V 1 ˜V 2  of the voltage controlled oscillator to the gm-C low pass filter as control voltages. Further, as shown in  FIG. 5C , if the input voltages V 1 ˜V 2  are proportional to the cutoff frequencies f 1 ˜f 2  but not equal to the input voltages V 1 ˜V 2  of  FIG. 5A , the control voltage generator  393  adjusts the input voltages V 1 ˜V 2  so as to obtain the satisfied cutoff frequencies f 1 ˜f 2 .  
         [0043]     The wobble BPF unit  350  has the band pass filter  351  and the smoothing filter  353 .  
         [0044]     The band pass filter  351  is a filter having a pass band proportional to the channel clock signal output from the wobble PPL unit  380 , and implemented with a switched capacitor filter (SCF). That is, as expressed in Equation 1, the center frequency f 0  of the band pass filter  351  has the relation with the frequency fsw and capacitors C 1  and C 2 , as below:  
               f   o     =       fswEC   2       2   ⁢   π   ⁢           ⁢     EC   1                 Equation   ⁢           ⁢   1             
 
         [0045]     As in Equation 1, the center frequency f o  of the switched capacitor filter (SCF) is proportional to the control frequency. Accordingly, if the frequency of a reproduced wobble signal varies as in the CAV mode, the switched capacitor filter (SCF) varies its center frequency f o  in proportion to the channel clock signal corresponding to the frequency of the varied wobble signal, to thereby obtain a pass band adaptive to an input signal.  
         [0046]     The wobble signal output from the switched capacitor filter (SCF) is output in a track-and-hold form due to the control frequency fsw. The smoothing filter  353  is implemented to smoothly process a signal in the track-and-hold form. The smoothing filter  353  is implemented with the gm-C low pass filter having the cutoff frequency fc varying with the control voltage in order to solve the problem that a low pass filter having a fixed cutoff frequency fc can not adaptively compensate for the phase difference between the innermost and outermost of a disc like the CAV mode (gm is referred to the mutual conductance being a ratio of input current to output voltage).  
         [0047]     That is, the smoothing filter  353  implemented with the gm-C low pass filter has a cutoff frequency fc depending on the control voltage Vctrl corresponding to the channel clock signal output from the wobble PLL unit  380 , so the cutoff frequency fc is varying with the center frequency fo.  
         [0048]      FIG. 6  is a view for showing a detailed circuit for the band pass filter  351  implemented with the switched capacitor filter (SCF), according to an embodiment of the present invention. As shown in  FIG. 6 , the center frequency f o  of the band pass filter is determined by a ratio between the capacitors C 1  and C 2  (refer to Equation 1).  
         [0049]     The band pass filter  351  is inputted with a push-pull signal, that is, a (A+D)−(B+C) signal from the subtractor  341  of  FIG. 3  through a V i  terminal, and filters the push-pull signal by varying a center frequency f 0  and outputs the filtered signal through a V o  terminal.  
         [0050]     The center frequency f 0  of the band pass filter  351  is obtained by use of switches phy 1  and phy 2  which perform switching operation according to the frequency fsw inputted from the control frequency generator  391  and the capacitors C 1  and C 2  based on the equation 1.  
         [0051]     In general, a ratio of a wobble clock signal frequency to a channel clock signal frequency in DVD-R/RW and DVD-RAM discs is 1:186, and a ratio of a wobble clock signal frequency to a channel clock signal frequency in CD-R/RW is 1:196. Accordingly, the center frequency f o  can be determined by a multiplexer mux 2  controlled based on the control signal DISKSEL to select a capacitor depending on a CD or a DVD.  
         [0052]     Further, the pass bandwidth of the band pass filter can be varied by the multiplexer mux 1  controlled based on a control signal Q to select a capacitor C 3  or C 4 .  
         [0053]     A detector is disposed on an outer portion of the band pass filter  351  to detect the kind of disk. According to the detected kind of disk, the band pass filter  351  is inputted with the control signal DISKSEL and the control signal Q. The multiplexer mux 1  and the multiplexer mux  2  are controlled based on the control signal DISKSEL and the control signal Q to select capacitors (C 1 , C 2 , C 3  or C 4 ) corresponding to the kind of disk.  
         [0054]     The wobble signal filtered through the switched capacitor filter (SCF) shown in  FIG. 6  is output in the track-and-hold form, and then the wobble signal is filtered smooth by the smoothing filter  353  that can be diversely designed with the gm-C low pass filter to have the cutoff frequency associated with the center frequency.  
         [0055]     Thus, in the CLV mode, the center frequency of a wobble signal is always constant so that the smoothing filter has a constant cutoff frequency, and, in the CAV mode, the center frequencies of the wobble signals between the innermost and outermost of a disc have a 2.4 times difference therebetween, so that the cutoff frequency fc of the smoothing filter is also varied by the difference with respect to the center frequency.  
         [0056]     Accordingly, the wobble signal can be effectively reproduced in the CLV mode as well as in the CAV mode in which the spindle motor rotates at a constant speed.  
         [0057]     According to embodiments of the present invention, the band pass filter (SCF) can be implemented to have its center frequency vary with a channel clock signal of the wobble PLL circuit, and a smoothing filter (gm-C LFH) can be implemented to have its cutoff frequency vary with the channel clock signal in order to compensate for distortions of a signal filtered in the band pass filter (SCF), so that a wobble signal can be precisely reproduced in the CLV mode as well as in the CAV mode in which the spindle motor rotates at a constant speed.  
         [0058]     Further, embodiments of the present invention can be effectively implemented since control signals applied to the switched capacitor filter (SCF) for the band pass filter and to the gm-C low pass filter, for the smoothing filer, can be, generated by use of a wobble PLL circuit provided in an existing optical recording/reproducing device.  
         [0059]     Foregoing 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. Also, the description of the embodiments of the present invention is intended to be illustrative, and not to limit the scope of the claims, and many alternatives, modifications, and variations will be apparent to those skilled in the art.  
         [0060]     Thus, although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.