Abstract:
A circuit and a method of detecting a mirror signal for an optical disc apparatus, the method includes detecting a bottom envelope from a radio frequency signal and providing a bottom envelope signal thereof, amplifying the bottom envelope signal according to a center level of the bottom envelope signal, and comparing the amplified bottom envelope signal with a predetermined comparison voltage to detect the mirror signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims the benefit of Korean Patent Application No. 2002-38878, filed on Jul. 5, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a circuit and a method of detecting a mirror signal for an optical disc apparatus, and more particularly, to a circuit and a method of accurately detecting a mirror signal during a high-speed seek or a seek, for a high density disc or a poor quality disc.  
           [0004]    2. Description of the Related Art  
           [0005]    Generally, in an optical disc apparatus which reproduces data recorded on an optical disc, signals generated when a servo jumps tracks to seek a predetermined position include a track cross signal and a mirror signal. The number of tracks is counted using these two signals. Also, the velocity of seeking a track is controlled and the accurate position of the track is sought by using a phase difference between these two signals.  
           [0006]    [0006]FIG. 1 shows a block diagram of a conventional circuit which detects a mirror signal for an optical disc apparatus. Referring to FIG. 1, a mirror signal detecting circuit  20  selects an RFSUM signal from a signal picked up by a pickup  10 , detects a mirror signal by using the RFSUM signal, and supplies the mirror signal to a servo processor  30 .  
           [0007]    The mirror signal detecting circuit  20  includes an RFSUM signal selector  21 , a top envelope detector  22 , a bottom envelop detector  23 , a top holding unit  24 , a bottom holding unit  25 , an amplifier and low-pass filter (AMP &amp; LPF)  26 , a comparison voltage determiner  27 , and a comparator (COMP)  28 .  
           [0008]    The RFSUM signal selector  21  selects the RFSUM signal. The top envelope detector  22  detects a top envelope of the RFSUM signal. The bottom envelope detector  23  detects a bottom envelope of the RFSUM signal. The top holding unit  24  detects a top level of the top envelope. The bottom holding unit  25  detects a bottom level of the bottom envelope. The AMP &amp; LPF  26  amplifies and low-pass filters the bottom envelope. The comparison voltage determiner  27  determines a comparison voltage. The comparator  28  compares an output of the AMP &amp; LPF  26  with the comparison voltage to output a mirror signal.  
           [0009]    The operation of the mirror signal detecting circuit  20  shown in FIG. 1 will be described with reference to FIGS.  2 A- 2 F.  
           [0010]    The RFSUM signal selector  21  receives a signal picked up by the pickup  10  and provides the signal in a form of an RFSUM signal shown in FIG. 2A to the top envelope detector  22  and the bottom envelope detector  23 . The top envelope detector  22  detects a top envelope of the RFSUM signal and outputs a top envelope signal shown in FIG. 2B. The bottom envelope detector  23  detects a bottom envelope of the RFSUM signal and outputs a bottom envelope signal shown in FIG. 2C. The top holding unit  24  holds the top envelope signal to detect a top level and outputs a top hold signal shown in FIG. 2D. The bottom holding unit  25  holds the bottom envelope signal to detect a bottom level and outputs a bottom hold signal shown in FIG. 2E.  
           [0011]    The bottom envelope signal, shown in FIG. 2C, output from the bottom envelope detector  23  is input to the AMP &amp; LPF  26 . The bottom hold signal, shown in FIG. 2E, output from the bottom holding unit  25  is input as a reference voltage level to the AMP &amp; LPF  26 . The AMP &amp; LPF  26  amplifies and low-pass filters the bottom envelope signal based on the bottom hold signal. At the same time, the comparison voltage determiner  27  controls the top hold signal and the bottom hold signal output from the top holding unit  24  and the bottom holding unit  25  at a predetermined level, respectively, and provides the predetermined level as a comparison voltage of the comparator  28 , i.e., a slice level. The comparator  28  compares a voltage output from the AMP &amp; LPF  26  with the comparison voltage determined by the comparison voltage determiner  27  and provides a mirror signal of a digital signal shown in FIG. 2F to the servo processor  30 .  
           [0012]    In a case where a high density disc or a poor quality disc (a disc that is deflected, eccentric, tilted, has a defect, or the like) is used, the high density disc or the poor disc may be defocused or degraded. In this case, where a seek operation is performed, a deteriorated RFSUM signal is generated as shown in FIGS. 3A through 3D. FIGS. 3A and 3B show the actual waveform of an RFSUM signal deteriorated where a disc is deflected and tilted, FIG. 3C shows the actual waveform of an RFSUM signal deteriorated by fingerprints, and FIG. 3D shows the actual waveform of an RFSUM signal deteriorated due to defects of a disc.  
           [0013]    A bottom envelope signal also deteriorate s due to the deteriorated RFSUM signal, i.e., the intensity of the bottom envelope signal is reduced and inconstant. Accordingly, a glitch occurs where the comparator  28  generates a digital signal (logic “high” or logic “low”), and therefore the duty cycle is distorted. As a result, an accurate seek is difficult. To solve these problems, the AMP &amp; LPF  26  has to perform a proper signal amplification and a low-pass filtering. However, since the glitch cannot be completely removed only by a low-pass filtering, the comparator  28  has to properly control the hysteresis and the level of the comparison voltage.  
           [0014]    In other words, where a deteriorated RFSUM signal shown in FIG. 4A passes through the top envelope detector  22  and the top holding unit  24 , a top envelope signal and a top hold signal are generated as shown in FIG. 4B. Where the deteriorated RFSUM signal passes through the bottom envelope detector  23  and the bottom holding unit  25 , a bottom envelope signal and a bottom hold signal are generated as shown in FIG. 4C. The AMP &amp; LPF  26  amplifies the bottom envelope signal according to the voltage level of the bottom hold signal. The comparator  28  slices the amplified bottom envelope signal to a proper reference voltage (slice level) determined by the comparison voltage determiner  27  to detect a mirror signal MIRR.  
           [0015]    However, where the bottom envelope signal is low, the bottom envelope signal has to be amplified by a high amplification degree. Where a difference in the bottom envelope signal occurs due to the deviation of a reflectance, depending on types of discs, the amplification degree of the AMP &amp; LPF  26  and the reference voltage level of the comparator  28  have to be set to predetermined values. In the former case, the possibility that the bottom envelope signal is saturated is high. In the latter case, the amplification degree and the reference level have to be fixed to predetermined values.  
           [0016]    Only where a signal is amplified based on the center value thereof, the signal is not saturated and can be greatly amplified. Since the mirror signal detecting circuit  20  shown in FIG. 1 amplifies the bottom envelope signal according to a voltage level of the bottom hold signal, a center level of the amplified bottom envelope signal differs greatly from a comparison voltage level (slice level) of the comparator  28 . Thus, the amplified bottom envelope signal cannot be properly sliced, as shown in FIG. 4D. Therefore, the comparator  28  cannot detect a proper mirror signal, as shown in FIG. 4E. Also, where the AMP &amp; LPF  26  does not amplify a signal and the comparator  28  does not induce hysteresis to prevent this phenomenon, an inaccurate mirror signal is detected due to noise.  
         SUMMARY OF THE INVENTION  
         [0017]    Accordingly, it is an aspect of the present invention to provide a mirror signal detecting circuit and a detecting method for an optical disc apparatus, which detects an accurate mirror signal during a high-speed seek.  
           [0018]    Another aspect of the present invention is to provide a mirror signal detecting circuit and a detecting method for an optical disc apparatus, which detects an accurate mirror signal during a seek so as to cope with a high density disc or a poor disc.  
           [0019]    Yet another aspect of the present invention is to provide a mirror signal detecting circuit and a detecting method for an optical disc apparatus, which detects an accurate mirror signal by amplifying a bottom envelope signal detected from a radio frequency signal, using a center level of the bottom envelope signal.  
           [0020]    Additional aspects and 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.  
           [0021]    To achieve the above and/or other aspects of the present invention, there is provided a mirror signal detection circuit for an optical disc apparatus having a servo that moves a pickup to a target track of a disc by using a mirror signal detected from a radio frequency signal picked up by the pickup, comprising a first detector which detects a bottom envelope of the radio frequency signal and provides a bottom envelope signal, a processor which amplifies the bottom envelope signal based on a center level of the bottom envelope signal, and a second detector which compares the amplified bottom envelope signal with a predetermined comparison voltage and detects the mirror signal.  
           [0022]    The radio frequency signal may be an RFSUM signal that is a sum signal of signals picked up by the pickup, and the comparison voltage level may be set to a proper level that is within a range of a top level of the bottom envelope signal and a bottom level of the bottom envelope signal.  
           [0023]    To achieve the above and/or other aspects of the present invention, there is a method of detecting a mirror signal for an optical disc apparatus which moves a pickup to a target track of a disc using the mirror signal detected from a radio frequency signal picked up by the pickup, the method comprising detecting a bottom envelope of the radio frequency signal and providing a bottom envelope signal, amplifying the bottom envelope signal based on a center value of the bottom envelope signal, and comparing the amplified bottom envelope signal with a predetermined comparison voltage and detecting the mirror signal.  
           [0024]    The radio frequency signal may be an RFSUM signal that is a sum signal of signals picked up by the pickup, and the comparison voltage level may be set to a proper level that is within a range of the top level of the bottom envelope signal and the bottom level of the bottom envelope signal. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]    These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which:  
         [0026]    [0026]FIG. 1 is a block diagram of a conventional mirror signal detecting circuit for a known optical disc apparatus;  
         [0027]    [0027]FIGS. 2A through 2F are views illustrating output waveforms of the mirror signal detecting circuit shown in FIG. 1;  
         [0028]    [0028]FIGS. 3A through 3D are views illustrating actual waveforms of a deteriorated RFSUM signal;  
         [0029]    [0029]FIGS. 4A through 4E are views illustrating output waveforms of the mirror signal detecting circuit shown in FIG. 1 where a deteriorated RFSUM signal is input thereto;  
         [0030]    [0030]FIG. 5 is a block diagram of a mirror signal detecting circuit for an optical disc apparatus according to an embodiment of the present invention; and  
         [0031]    [0031]FIGS. 6A through 6E are views illustrating output waveforms of the mirror signal detecting circuit shown in FIG. 5. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0032]    Reference will now be made in detail to the present preferred 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.  
         [0033]    [0033]FIG. 5 shows a mirror signal detecting circuit for an optical disc apparatus according to an embodiment of the present invention. Referring to FIG. 5, a mirror signal detecting circuit  200  receives a signal that a pickup  100  picks up from an optical disc, on which data is recorded, for example, only on groove tracks, detects a mirror signal, and supplies the detected mirror signal to a servo processor  300 .  
         [0034]    The mirror signal detecting circuit  200  includes an RFSUM signal selector  210 , a bottom envelope detector  220 , a top holding unit  230 , a bottom holding unit  240 , a center level detector  250 , an amplifier and low-pass filter (AMP &amp; LPF)  260 , a comparison voltage determiner  270 , and a comparator (COMP)  280 . The RFSUM signal selector  210  selects an RFSUM signal. The bottom envelope detector  220  detects a bottom envelope of the RFSUM signal and outputs a bottom envelope signal. The top holding unit  230  detects a top level of the bottom envelope signal. The bottom holding unit  240  detects a bottom level of the bottom envelope signal. The center level detector  250  detects a center level between the top level and the bottom level. The AMP &amp; LPF  260  amplifies and low-pass filters the bottom envelope signal according to the center level. The comparison voltage determiner  270  determines the level of a comparison voltage. The comparator  280  compares the level of a voltage output from the AMP &amp; LPF  260  with the level of the comparison voltage and outputs a mirror signal MIRR as a digital signal.  
         [0035]    An operation of the mirror signal detecting circuit  200  shown in FIG. 5 will be described with reference to FIGS.  6 A- 6 E.  
         [0036]    The RFSUM selector  210  provides a signal picked up by the pickup  100  in a form of an RFSUM signal (as shown in FIG. 6A where the RFSUM signal is deteriorated) to the bottom envelope detector  220 . In an event that the pickup  100  has a quadrant photodiode (not shown), the signal picked up by the pickup  100  may be an RFSUM signal that may be a signal expressed by a photodiode piece A on a left top, a photodiode piece B on a right top, a photodiode piece C on a right bottom, and a photodiode D on a left bottom, that is, a differential output signal of two channels (RFIN(+):(A+D)−(B+C); a difference signal between a sum signal of two electrical signals by the photodiode pieces A and D and a sum signal of two electrical signals by the photodiode pieces B and C, RFIN(−):(B+C)−(A+D); a difference signal between a sum signal of two electrical signals by the photodiode pieces A and D and a sum signal of two electrical signals by the photodiode pieces A and D), or a sum signal (A+B+C+D) of four channels.  
         [0037]    The bottom envelope detector  220  detects a bottom envelope of the RFSUM signal shown in FIG. 6A and outputs a bottom envelope signal as shown in FIG. 6B. Where the bottom envelope signal passes through the top holding unit  230  and the bottom holding unit  240 , the bottom envelope signal is output as a top hold signal and a bottom hold signal shown in FIG. 6C. The center level detector  250  detects a center level between the top hold signal of the bottom envelope signal output from the top holding unit  230  and the bottom hold signal of the bottom envelope signal output from the bottom holding unit  240 , as shown in FIG. 6C. The AMP &amp; LPF  260  amplifies a signal according to a center value of a reference signal so as not to saturate the signal and greatly amplify the signal. Thus, the bottom envelope signal is amplified according to the center level of the bottom envelope signal detected by the center level detector  250 .  
         [0038]    In other words, the bottom envelope signal, shown in FIG. 6B, detected by the bottom envelope detector  220 , is input to the AMP &amp; LPF  260 . A reference voltage level of the AMP &amp; LPF  260  is the center level between the top hold signal and the bottom hold signal, shown in FIG. 6C, output from the center level detector  250 . The AMP &amp; LPF  260  amplifies and low-pass filters the bottom envelope signal according to the center level and outputs an amplified bottom envelope signal shown in FIG. 6D.  
         [0039]    The comparison voltage determiner  270  controls a level of the top hold signal of the bottom envelope signal output from the top holding unit  230  and a level of the bottom signal of the bottom envelop signal output from the bottom holding unit  240  at predetermined levels and provides the predetermined levels as a comparison voltage of the comparator  280 , i.e., a slice level shown in FIG. 6D. The level of the comparison voltage is set to a proper level that is within a range of the level of the top hold signal and the level of the bottom hold signal. The comparator  280  compares the amplified envelope signal output from the AMP &amp; LPF  260  with a comparison voltage level provided from the comparison voltage determiner  270 , detects a mirror signal MIRR of a digital signal shown in FIG. 6E, and outputs the mirror signal MIRR to the servo processor  300 .  
         [0040]    The servo processor  300  counts the number of tracks which are jumped in accordance with the mirror signal MIRR output from the mirror signal detecting circuit  200  in seeking or jumping tracks of a disc and generates a servo control signal necessary to move the pickup  100  to a target track. A servo driving unit (not shown) is driven based on the servo control signal of the servo processor  300  to move the pickup  100  to the target track. Here, the servo processor  300  and the servo driving unit may be referred to as a servo.  
         [0041]    The present invention may be widely used in a servo signal processing of a recording and/or reproducing system of an optical disc.  
         [0042]    As described above, in the present invention, by using data recorded on an optical disc, a mirror signal can be accurately detected during a high-speed seek. Also, mis-detecting of a mirror signal due to noise can be reduced. Furthermore, an accurate mirror signal can be detected during a seek in order to cope with a high density disc and a poor disc (a disc that is deflected, eccentric, tilted, has a defect, or the like) or a defocused and deteriorated disc. As a result, the seek efficiency can be increased and the performance of a system using the same is improved.  
         [0043]    Although a few preferred 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 this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.