Patent Publication Number: US-2007097827-A1

Title: Method and apparatus for detecting saw-tooth wobble signal to reproduce information recorded on an optical disk

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION  
      This application claims all benefits accruing under 35 U.S.C. §119 from Korean Patent Application No. 2005-104935, filed on Nov. 3, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated by reference herein.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an optical disk, and more particularly, to a method and apparatus for detecting a saw-tooth wobble (STW) signal to reproduce information recorded on an optical disk.  
      2. Related Art  
      An STW signal is a wobble signal having a saw-tooth shape recorded on an optical disk may be expressed as one of cos(at)−0.25 sin(2at) and cos(at)+0.25 sin(at) depending on whether recorded information is “0” or “1”. An apparatus for detecting an STW signal is configured to determine whether an input signal is cos(at)−0.25 sin(2at) or cos(at)+0.25 sin(at) in order to detect digital information recorded using the wobble signal, and detect whether recorded information represents “0” or “1” according to such a determination.  
       FIG. 1  is a schematic view of an apparatus for detecting a STW signal. Referring to  FIG. 1 , the apparatus  100  includes a multiplier  110 , a phase locked loop (PLL)  120 , an accumulator  130 , a memory device  140 , a comparator  150 , and a zero signal source  160 .  
      The PLL  120  selects a carrier of an input wobble signal. The multiplier  110  multiplies an input wobble signal by an output signal from the PLL 120 . The accumulator  130  accumulates output signals from the multiplier  110 . The memory device  140  stores an output signal from the accumulator  130 , and the comparator  150  compares an output signal from the memory device  140  with a zero signal from the zero signal source  160 .  
      An input signal of the apparatus  100  for detecting the STW signal may be expressed as one of cos(at)−0.25 sin(2at) and cos(at)+0.25 sin(at) depending on whether recorded information represents “0” or “1”. When the recorded information is “1”, an input signal can be expressed as cos(at)+0.25 sin(at), whose waveform is shown in  FIG. 2A . Referring to  FIG. 2A , the waveform of information “1” has edges that fall steeply from a region (+) to a region (−), and rise gently from a region (−) to a region (+). When the recorded information is “0”, the input signal can be expressed as cos(at)−0.25 sin(2at). In that case, the waveform of information “0” has edges that fall gently from a region (+) to a region (−), and rise steeply from a region (−) to a region (+), unlike the waveform shown in  FIG. 2A . The apparatus  100 , as shown in  FIG. 1 , analyzes the waveform of the input signal, in order to detect whether recorded information is “0” or “1”.  
      The frequency of an output signal from the PLL  120  is 2ω. This signal is generated by a controllable oscillator of the PLL  120 . An output signal from the controllable oscillator is not ideal because such an output signal contains high-order harmonics.  
      Assuming that an input signal of the apparatus for detecting the STW signal is cos(at)+0.25 sin(at), a plot of this input signal is shown in  FIG. 2A . Also, a plot of an output signal of the PLL is shown in  FIG. 2B . A multiplication result of a wobble input signal and an output signal from the PPL  120  is shown in  FIG. 2C . An output signal from the multiplier  110 , as shown in  FIG. 2C , contains a DC component and a selective component. Useful information is contained in the DC component, and the selective component does not have any effective information.  
      The accumulator  130  accumulates the DC component, and particularly, suppresses a selective component of an input signal. Of course, noises are actually included in all of signals but noise is not shown in  FIGS. 2A-2C . When signals as shown in  FIG. 2C  are accumulated, the size of signals is relatively large in regions (+) (e.g., regions  210 ,  230 , and  250 ) and the size of the signals is relatively small in regions (−) (e.g., regions  220 ,  240 , and  260 ). Therefore, a (+) result is obtained when theses signals are accumulated. As a result, the apparatus for detecting a STW signal, as shown in  FIG. 1 , may judge recorded information as “1”. However, this is true of an ideal case. In actuality, since output signals from the multiplier  110  contain both a (+) component and a (−) component, an accumulated signal may have a different sign when a signal is twisted a little.  
      An input reset signal may reset the accumulator  130  at the beginning of each cycle of reading information. The memory device 140  stores an output signal of the accumulator  130  at the end of each cycle of reading the information. The stored output signal is then compared with a zero level signal provided from a zero signal source  160  by the comparator  150 .  
      However, an error may occur in an output of the apparatus for detecting a STW signal, as shown in  FIG. 1 . Such an error depends on a noise level of an input signal and a quality of an output signal from the PLL  120 , as shown in  FIG. 1 . Particularly, existence of PLL signal harmonics together with frequencies 4ω, 6ω, and 8ω generates an additional DC component to an output of the accumulator  130  and finally increases the possibility of an error.  
      Moreover, known apparatus for detecting a STW signal, as shown in  FIG. 1 , has additional disadvantages, including being very sensitive to noise included in an input signal and receiving an incompleteness of a PLL output signal. Therefore, the input noise and the incompleteness of the PLL output signal increase the possibility that recorded information can be falsely detected.  
     SUMMARY OF THE INVENTION  
      Several aspects and example embodiments of the present invention provide an apparatus and method for detecting a STW signal in a system for reproducing information recorded on an optical disk, while guaranteeing reduction of an error possibility.  
      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.  
      In accordance with an embodiment of the present invention, a method for detecting a STW signal to reproduce information recorded on an optical disk, comprises: extracting a sine component from an input wobble signal containing a sine component and a cosine component; multiplying the sine component by a sine component having the same period as that of the sine component; accumulating the multiplied results; and detecting a sign of the accumulated results.  
      According to an aspect of the present invention, the extracting of the sine component may include: removing a DC component from the input wobble signal; and delaying the DC component-removed signal as much as a predetermined degree such that a cosine component is removed from the DC component-removed signal and adding the DC component-removed signal and the delayed signal to extract the sine component.  
      According to an aspect of the present invention, the multiplying of the sine component may include providing the sine component having the same period as that of the sine component on the basis of a counter synchronized by passing the input wobble signal through a phase locked loop (PLL).  
      In accordance with another embodiment of the present invention, an apparatus for detecting a STW signal to reproduce information recorded on an optical disk, comprises: a sine component extracting unit for extracting a sine component from an input wobble signal containing a sine component and a cosine component; a sine component multiplication unit for multiplying the sine component by a sine component having the same period as that of the sine component; an accumulator for accumulating the multiplied results; and a sign detector for detecting the sign of the accumulated results.  
      According to an aspect of the present invention, the sine component extracting unit may include: a subtractor for subtracting an input wobble signal-accumulated signal from the input wobble signal in order to remove a DC component of the input wobble signal; a delayer for delaying the DC component-removed signal as much as a predetermined degree such that a cosine component is removed from the DC component-removed signal outputted from the subtractor; and an adder for adding the DC component-removed signal from the subtractor and the delayed signal from the delayer to extract the sine component.  
      According to an aspect of the present invention, the sine component multiplication unit may include: a phase locked loop (PLL) for receiving the input wobble signal; a counter for receiving a signal from the PLL to perform synchronization; and a sine component memory for providing the sine component having the same period as that of the sine component on the basis of counting by the counter.  
      In addition to the example embodiments and aspects as described above, further aspects and embodiments of the present invention will be apparent by reference to the drawings and by study of the following descriptions. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      A better understanding of the present invention will become apparent from the following detailed description of example embodiments and the claims when read in connection with the accompanying drawings, all forming a part of the disclosure of this invention. While the following written and illustrated disclosure focuses on disclosing example embodiments of the invention, it should be clearly understood that the same is by way of illustration and example only and that the invention is not limited thereto. The spirit and scope of the present invention are limited only by the terms of the appended claims. The following represents brief descriptions of the drawings, wherein:  
       FIG. 1  is a schematic view of a typical apparatus for detecting information carried by a STW signal from an optical disk;  
       FIGS. 2A through 2C  are waveform diagrams illustrating signals at different stages of the apparatus for detecting information carried by a STW signal shown in  FIG. 1 ;  
       FIG. 3  is a schematic view of an apparatus for detecting information carried by a STW signal according to an embodiment of the present invention;  
       FIGS. 4A through 4D  are waveform diagrams illustrating signals at different stages of the apparatus for detecting information carried by a STW signal shown in  FIG. 3 ; and  
       FIG. 5  is a flowchart of a method for detecting information carried by a STW signal according to an embodiment of the present invention.  
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
      Reference will now be made in detail to the present 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 in order to explain the present invention by referring to the figures.  
      As describe above, the apparatus for detecting a STW signal analyzes an input signal and determines the input signal as digital information “0” or “1” depending on whether recorded information is cos(at)−0.25 sin(2at) or cos(at)+0.25 sin(at).  
      The difference between a signal expressed as cos(at)−0.25 sin(2at) for the recorded information is “0” and a signal expressed as cos(at)+0.25 sin(at) for the recording information is “1” is that a sine component is different. To detect an input STW signal, the present invention removes a cosine component from the input STW signal and extracts only a sine component to analyze the sine component, so as to detect whether the STW signal is “0” or “1”.  
      Turning now to  FIG. 3 , a schematic view of an example apparatus for detecting a STW signal according to an embodiment of the present invention is illustrated. Referring to  FIG. 3 , the apparatus for detecting a STW signal  300  comprises a sine component extracting unit  310  arranged to remove a cosine component and extract only a sine component from an input wobble signal containing a sine component and a cosine component; a sine component multiplication unit  320  arranged to multiply the sine component extracted from the sine component extracting unit  310  by a sine component having the same period as that of the extracted sine component; and a detection unit  330  arranged to accumulate the multiplied results and detect a sign of the accumulated results.  
      The sine component extracting unit  310  includes a subtractor  312 , a first accumulator  314 , a delayer  316 , and an adder  318 . The subtractor  312  subtracts an output of the first accumulator  314  from an input STW signal, in which the first accumulator  314  selects a DC component of an output signal from the subtractor  312 . This way the subtractor  312  can subtract an accumulated signal from the input STW signal so as to remove a DC component from the input STW signal. The delayer  316  is used to shift the phase of an input STW signal from the subtractor  312  such that a cosine component is removed from the DC component-removed signal output from the subtractor  312 . The adder  318  is used to add the DC component-removed signal output from the subtractor  312  and the delayed signal from the delayer  316  so as to compensate for first harmonics of the delayed signal from the delayer  316  and extract the sine component from the delayed signal.  
      The sine component multiplication unit  320  includes a phase locked loop (PLL)  322 , a synchronization counter  324 , a sine wave memory device  326  and a multiplier  328 . The PLL  322  obtains a carrier signal from an input STW signal. The synchronization counter  324  is arranged to receive an output signal from the PLL  322  to perform synchronization. The sine wave memory device  308  provides a sine component having the same period as that of the sine component extracted from the sine component extracting unit  310  on the basis of the synchronization counter  324 . The multiplier  307  is arranged to multiply an output signal from the adder  318  of the sine component extracting unit  310  by an output signal from the sine wave memory device  308 .  
      The detection unit  330  includes a second accumulator  332 , a sign detector  334  and a D type of flip-flop  336 . The second accumulator  332  accumulates output signals from the multiplier  328  of the sine component multiplication unit  320 . The sign detector  334  then detects the sign of an output signal from the second accumulator  332 , and the D-type of flip-flop  336  stores an output signal from the sign detector  334 .  
      Operation of the apparatus  300  shown in  FIG. 3  will now be described with reference to waveforms shown in  FIGS. 4A-4D  herein below.  
      An input of the apparatus  300  is connected to an input of the subtractor  301   
      In an ideal case, the input signal of the apparatus  300  may be expressed as one of cos(at)−0.25 sin(2at) and cos(at)+0.25 sin(at). The waveform according to cos(at)+0.25 sin(at) is shown in  FIG. 4A .  
      However, actually, an input signal of the apparatus  300  may include a low frequency component and may contain a DC component and a noise component. The DC component and the noise component are accumulated at the first accumulator  314 , and an output signal from the first accumulator  314  is subtracted from an input STW signal by the subtractor  312 . As a result, an output signal from the subtractor  312  does not contain a DC component.  
      A DC component-removed output signal from the subtractor  312  is provided to an input of the delayer  316 . A delay time is π/ω.  
      When an input signal of the delayer  316  is expressed as: U 1 =cos(at)+0.25 sin(at), an output signal of the delayer  316  may be expressed as:
 
 U   2 =cos(ω( t−π/ω ))+0.25 sin(2ω( t−π/ω ))=−cos( at )+0.25 sin(2 at )
 
      Therefore, an output signal of the adder  318  may be expressed as
 
 U   3   =U   1   +U   2 =0.5 sin(2 at ).
 
      A comparison of an input signal and an output signal of the delayer  316  shows that cosine components, i.e., meaningless first harmonics have phases opposite to each other. That is, the cosine component cos(at) of U 1  and the cosine component −cos(at) of U 2  cancel each other, so that the cosine component is removed by the adder  318 .  
      The sine components, i.e., second harmonics having information have the same phase. That is, the sine component 0.25 sin(2at) of U 1  and the sine component 0.25 sin(2at) of U 2  are added by the adder  318 , so that the amplitude of second harmonics increases twice. An output signal of the adder  318  is illustrated in  FIG. 4B .  
      An input and an output noise of the delayer  316  are added by the adder  318 . The phase of a noise is infinite, so an increase of a noise contained in an output from the adder  318  is √{square root over (2)}. A resultant improvement of a signal-to-noise (R/N) ratio contained in an output signal from the adder  318  is √{square root over (2)}/2 when compared with an output signal of the subtractor  312 .  
      The sine wave memory device  326  is used to generate an ideal symmetric sine wave having a frequency  2 •. A control code for the sine wave memory device  326  is generated by the synchronization counter  324 .  
      An output signal from the PLL  322  is used to synchronize the synchronization counter  324 . An output signal of the sine wave memory device  326  is shown in  FIG. 4C . That is, the output signal of the sine wave memory device  326  has the same period as that of an output signal of the adder  318 , as shown in  FIG. 4B , and has an amplitude of 1, as shown in  FIG. 4C .  
      An output signal from the multiplier  328  multiplying an output signal from the adder  318  by a signal from the sine wave memory device  326  is shown in  FIG. 4D . A s shown in  FIG. 4D , the output signal from the multiplier  328  has always a positive value. Therefore, when the output signal from the multiplier  328  is accumulated, a positive value is always outputted. Absence of a negative component in an output signal from the multiplier  328  improves linearity of an output signal from the second accumulator  332 . A reset signal is used to reset the second accumulator  332  at the moment when a wobble signal having information starts.  
      Also, since an input wobble signal is expressed as cos(at) +0.25 sin(at) as shown in  FIG. 4A , a resultant output signal from the multiplier changes from  0  to  0 . 5 . However, when an input wobble signal is expressed as cos(at)−0.25 sin(at), a resultant output signal from the multiplier changes from 0 to −0.5. Therefore, even when an output signal of the multiplier is twisted more or less, an output signal from the multiplier  328  always has a positive value in the case where an input wobble signal is expressed as cos(at) +0.25 sin(at). Also, an output signal from the multiplier  328  always has a negative value in the case where an input wobble signal is expressed as cos(at)−0.25 sin(at). This fact reduces the possibility that a signal is falsely outputted from positive to negative, or from negative to positive.  
      The sign detector  324  and the D-type of flip-flop  336  are used for detecting and storing the sign of an output signal from the second accumulator  332  at an ending time of an input wobble signal. The ending time is determined by a synchronization signal when a clock is input by the D-type of flip-flop  336 .  
       FIG. 5  is a flowchart of a method for detecting a STW signal according to an embodiment of the present invention.  
      First, a sine component is extracted from an input wobble signal containing a sine component and a cosine component at operation  510 .  
      A sine component having the same period as that of the sine component is multiplied to the sine component at operation  520 . After that, signals obtained by the multiplication are accumulated at operation  530 .  
      Next, the sign of the accumulated results is detected at operation  540 . When the sign is positive, information of a recorded wobble signal is determined as “1”. When the sign is negative, information of a recorded wobble signal is determined as “0”.  
      As described in the foregoing, the present invention advantageously provides a circuit for detecting an accurate shape of a reference sinusoidal signal and improving a signal-to-noise ratio. As a result, better detection accuracy is achieved, and a DC component and a low frequency component of an input signal can be suppressed.  
      While this invention has been particularly shown and described with reference to exemplary 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. For example, elements of the sine component extracting unit  310 , the sine component multiplication unit  320  and the detection unit  330 , as shown in  FIG. 3 , can be arranged differently as long as their functionalities are achieved. In addition, the apparatus shown in  FIG. 3 , can be incorporated as part of a recording apparatus, or alternatively a single apparatus for performing recording and/or reproducing functions with respect to a storage medium. Similarly, the CPU can be implemented as a chipset having firmware, or alternatively, a general or special purposed computer programmed to perform the methods as described, for example, with reference to  FIG. 5 . Accordingly, it is intended, therefore, that the present invention not be limited to the various example embodiments disclosed, but that the present invention includes all embodiments falling within the scope of the appended claims.