Abstract:
This disc reproducing apparatus comprises an optical pickup for reproducing a signal recorded in a disc from the disc, an amplifier for amplifying the signal outputted from this optical pickup at a predetermined gain, a focus servo circuit for matching the focus of the optical pickup with the disc using the signal outputted from this amplifier, and control means. The control means executes focusing of the optical pickup using the gain of the amplifier as a predetermined gain when starting reproduction of the signal from the disc, starts reproduction of the signal from the disc when this focusing is successful, and executes the second focusing of the optical pickup by setting the gain of the amplifier to a higher gain than the predetermined gain and starts reproduction of the signal when the focusing is unsuccessful.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a disc reproducing apparatus and a disc reproducing method.  
           [0003]    2. Description of the Related Art  
           [0004]    An optical pickup is used to reproduce a signal recorded on a CD. However, when regenerating the signal, the focus of the optical pickup needs to match the signal plane (reflection surface) of the CD. Therefore, a focus servo circuit is provided in a CD player. A focusing error of the optical pickup is detected, and at the same time servo control is executed so that the focusing error can be eliminated.  
           [0005]    In this case, an astigmatism method and the Foucault method are known as methods of detecting the focusing error. According to these detection methods, a focusing error voltage V FE of such characteristics as shown in FIG. 5 can be obtained.  
           [0006]    To be specific, FIG. 5 shows the relationship between the opposed interval d between the object lens of the optical pickup and the signal plane of a CD, and a focusing error voltage V FE. The focusing error voltage V FE is set to V FE=0 when the lens is in focus (this occurs when d=d0) . Further, the focusing error voltage V FE changes in an S—shaped form against the change of the opposed interval d centering around the interval d 0  at the time of exact focusing. Accordingly, a focus servo circuit will servo-control the opposed interval d so that V FE=0 can be obtained within a proportional range Δd between the maximum point and the minimum point of its S-shaped characteristics.  
           [0007]    However, in this case, as also shown in FIG. 5, V FE=0 is obtained even within the outside range of S-shaped characteristics. So in a practical CD player, when reproducing a CD is started, first, the opposed interval d is driven within the proportional range Δd of the S-shaped characteristics, and then an attempt is made to perform focus servo control. Besides, in the following, the processing in which the opposed interval d is driven into the proportional range Δd of the S-shaped characteristics when starting reproducing the CD is called a “focus search.” 
           [0008]    [0008]FIG. 4 shows a voltage waveform of each portion when executing the focus search. In this case, the object lens of the optical pickup is mounted on a moving coil that deflects the object lens in the direction of the optical axis, and when a drive voltage supplied to the moving coil is 0, the object lens is constituted so as to be located in the vicinity of d=d0. Further, in general, a CD is arranged horizontally, and is arranged so that the signal plane can face downward, and the optical pickup is located under the CD.  
           [0009]    When the playback button is pressed at an optional time t 0 , as shown in FIG. 4A, the focus drive voltage V FD reaches the minimum value from 0 V at the time t 0 , for example. Then, consequently, the object lens descends to the lower limit position at a time slightly delayed from the time t 0 . At this time, the opposed interval d for the signal plane of a CD is maximized (the scale of the interval d is shown at the right side of FIG. 4A).  
           [0010]    Subsequently, when a time ti is reached, the focus drive voltage V FD gradually rises from the minimum value. As this focus drive voltage rises, the object lens gradually ascends and the opposed interval d will be reduced.  
           [0011]    As shown in FIG. 4B, when a time t 2  is reached, a playback signal S PB of the CD is outputted from the optical pickup. By discriminating the level of this signal S PB using a predetermined value V TH1, a regenerative detection signal S OK that rises at a time t 3  is acquired, as shown in FIG. 4C.  
           [0012]    Further, as shown in FIG. 4D, from almost the time t 3 , the focusing error voltage V FE starts an S-shaped change, and rises as shown in FIG. 4D. Then by discriminating the level of this focusing error voltage V FE using a predetermined value V TH2, a focus check signal S FZC that rises at a time t 4  is acquired, as shown in FIG. 4E.  
           [0013]    The focusing error voltage V FE rises with the rise of the focusdrivevoltageVFD. When the maximum point is exceeded, the focusing error voltage gradually decreases later. When V FE=V TH2 is reached at a time t 5 , the signal S FZC falls. Then at this time, as clearly shown in FIG. 4 and FIG. 5, the opposed interval d will be located within the proportional range Δd.  
           [0014]    Then the focus servo circuit is set on at the falling edge of this signal S FZC, and at this fall time t 5  or later, a focused state for a CD is held by focus servo control. Accordingly, the CD can be reproduced from the time t 5 . Besides, after the time t 5  or later, although the focus drive voltage V FD and the focusing error voltage V FE reach almost zero after both the voltages fluctuate to some extent, they slightly change corresponding to the focused state.  
           [0015]    When a CD is loaded on a CD player, TOC data is reproduced from the CD. Also at this time, first, a focus search is executed, and then focus servo control is set on. Then another servo control is set on, and the TOC data is read. That is, both when the CD is loaded on the CD player and when the playback button is pressed, the focus search is executed, and after the focus servo control is validated, a signal (TOC data or musical data) is reproduced from the CD.  
           [0016]    Hereupon, CDs are classified into a CD-R to which data can be written only once and a CD-RW to which data can be written about 1,000 times besides a read-only CD-ROM (generically called “CD” when CD-ROM, CD-R, and CD-RW are not discriminated).  
           [0017]    For a CD-ROM, when the laser beam outputted from the optical pickup is reflected by the signal plane of the CD-ROM and returns to the optical pickup, an optical path difference occurs depending on the presence of a pit. So a signal is reproduced using this optical path difference.  
           [0018]    For a CD-R, too, since an optical path difference occurs depending on the presence of a pit, a signal is reproduced using this optical path difference. Further, for a CD-RW, since the amount of reflected laser beam depends on the presence of a pit, a signal is reproduced by detecting the difference of this reflection amount.  
           [0019]    For a CD-ROM, when the laser beam outputted from the optical pickup is reflected by the signal plane and returns to the optical pickup, it returns with the same or equivalent amount of light as for a CD-ROM. So a CD-R can be reproduced in an unchanged state by a CD-ROM reproducing apparatus.  
           [0020]    However, for a CD-RW, since the amount of reflected laser beam that returns from the signal plane to the optical pickup is about one quarter that for a CD-ROM, the CD-RW cannot normally be reproduced by a CD-ROM reproducing apparatus.  
           [0021]    Hence, in a reproducing apparatus that reproduces a CD-ROM, CD-R, and CD-RW, the following actions are usually taken:  
           [0022]    (1) The type of CD is discriminated by checking the reflectivity of the CD.  
           [0023]    (2) When the discrimination result of (1) indicates a CD-ROM or CD-R, the gain of an RF amplifier that amplifies the output signal of the optical pickup is set as the reference gain.  
           [0024]    (3) When the discrimination result of (1) indicates a CD-RW, the gain of the RF amplifier is set to four times the reference gain, for example.  
           [0025]    However, performing this will execute a focus search for checking the reflectivity of a CD, and will execute a focus search for focus servo control also when reproducing the CD is started.  
           [0026]    However, when a CD is reproduced, it takes a long time to execute a focus search twice until playback is actually started.  
         SUMMARY OF THE INVENTION  
         [0027]    An object of the present invention is to solve such problems.  
           [0028]    In the present invention, for example, a disc reproducing apparatus is obtained, comprising:  
           [0029]    an optical pickup that reproduces a signal recorded in a disc from the disc;  
           [0030]    an amplifier that amplifies the signal outputted from this optical pickup at a predetermined gain;  
           [0031]    a focus servo circuit that matches the focus of the optical pickup with the disc using the signal outputted from this amp; and  
           [0032]    a control circuit that executes predetermined control, wherein the control circuit  
           [0033]    executes focusing of the optical pickup using the gain of the amplifier as a reference gain when starting reproduction of the signal from the disc;  
           [0034]    validates the focus servo circuit and starts the reproduction of the signal from the disc when this focusing is successful;  
           [0035]    executes the second focusing of the optical pickup by setting the gain of the amplifier to a higher gain than the reference gain when the focusing is unsuccessful; and  
           [0036]    validates the focus servo circuit and starts the reproduction of the signal from the disc when this second focusing is successful.  
           [0037]    Accordingly, when a disc has the first optical characteristics, playback starts in the first focusing, and when a disc has the second optical characteristics, playback starts in the second focusing.  
           [0038]    According to the present invention, even if a CD is any of a CD-ROM, CD-R or CD-RW, reproduction can be started at the shortest time. Further, even if the CD is any of the CD-ROM, CD-R or CD-RW, signal processing is executed at a normal signal level. So the reproduction and various types of servo control can appropriately be performed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0039]    [0039]FIG. 1 is a flow diagram showing one embodiment of the present invention;  
         [0040]    [0040]FIG. 2 is a flow chart showing one embodiment of the present invention;  
         [0041]    [0041]FIG. 3 is a flowchart showing one yet another embodiment of the present invention;  
         [0042]    [0042]FIG. 4 is a waveform chart for describing the present invention; and  
         [0043]    [0043]FIG. 5 is a characteristic diagram for describing the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0044]    [0044]FIG. 1 shows the case where the present invention applies to a CD player for audio discs. First, the basic configuration and operation are described as follows.  
         [0045]    That is, a symbol  10  indicates a CD. This CD  10 , as described above, is any of a CD-ROM, CD-R or CD-RW, and, for example, is horizontally set so that the signal plane forms the underside. Further, the CD  10  is rotated at a predetermined speed by a spindle motor  21  when reproducing it, and the optical pickup  22  is arranged facing the signal plane of the CD  10 .  
         [0046]    This optical pickup  22 , as clearly described above, has a laser diode for reading the pits of the CD  10 , a photosensor, and the object lens, and has a moving coil for changing the focus position of the object lens. Then a signal S PB recorded on the CD  10  is reproduced by this optical pickup  22 , and this playback signal S PB is supplied to a reproduction processing circuit  24  via an RF amplifier  23 .  
         [0047]    This reproduction processing circuit  24  is composed of an IC called a CD-DSP. This circuit has an A/D converter circuit  241  that A/D-converts an input playback signal S PB, a decoding DSP  242 , a D/A converter circuit  243  that D/A-converts decoded digital audio data, and a digital servo processor  244 .  
         [0048]    In this case, the DSP  242  executes reproduction processing, such as EFM demodulation, de-interleaving, and error correction for a playback signal S PB converted to a digital signal by the A/D converter circuit  241  and digital audio data is decoded. Further, the digital servo processor  244  produces control voltages and control signals necessary for the focus servo, tracking servo, sled servo, spindle servo, and focus search of the CD  10 .  
         [0049]    In the reproduction processing circuit  24 , audio signals L, R of the left and right channels are decoded from the playback signal S PB outputted from the RF amplifier  23  and these signals L, R are supplied to speakers  26 L,  26 R of the left and right channels via output amps  25 L,  25 R.  
         [0050]    At this time, a spindle error signal that indicates an error of the rotational speed of the CD  10  is acquired from the reproduction processing circuit  24 , and this spindle error signal is supplied to the spindle motor  21  via a drive amplifier  27 . Thus, the rotational speed of the spindle motor  21  is controlled, and the CD  10  is servo-controlled so that the linear velocity of the rotation can be set to a specified constant value.  
         [0051]    Further, the focus drive voltage V FD that corresponds to a focusing error of the optical pickup  22  is acquired from the reproduction processing circuit  24 . This voltage V FD is supplied to the moving coil of the optical pickup  22  and focus servo control of the object lens is executed.  
         [0052]    A tracking error voltage that corresponds to a tracking error of the optical pickup  22  is acquired from the reproduction processing circuit  24 . This voltage is supplied to the moving coil of the optical pickup  22  via a drive amplifier  28  and tracking servo control of the object lens is executed. Then at this time, the direct current component of the tracking error voltage is supplied to a sled mechanism (not shown) of the optical pickup  22  and sled servo control is executed.  
         [0053]    Further, a microcomputer  31  is provided as control means, that is, a system control circuit. Various operation buttons (control switches)  32  are connected to this microcomputer  31 , and, for example, a display  33  consisting of an LCD is connected. Then various control signals are supplied from the microcomputer  31  to the reproduction processing circuit  24 , and various data are supplied from the reproduction processing circuit  24  to the microcomputer  31 .  
         [0054]    The basic configuration and operation of a CD player are described above, and the present invention is further constituted for such CD player as follows.  
         [0055]    That is, the RF amplifier  23  uses a variable gain amplifier that can switch the gain into a reference gain AL [double] and a high gain AH [double] (for example, AH=4×AL) . Further, a switching control signal S GAIN of the gain is supplied from the microcomputer  31  to the amplifier  23 .  
         [0056]    Further, for example, a focus search routine  100  shown in FIG. 2 is provided in the microcomputer  31  as part of the program the microcomputer executes, and, for example, a routine  200  shown in FIG. 3 is prepared in the DSP  244  of the reproduction processing circuit  24  as part of the routine the DSP  244  executes. Besides, in FIG. 2 and FIG. 3, only the parts of the routines  100 ,  200  related to the present invention are selected and shown.  
         [0057]    The CD  10  refers to a CD-ROM, CD-R, or CD-RW, and in general, many of the CDs to be reproduced are CD-ROMs. (By far the largest number of CDs worldwide are CD-ROMs.) Hereupon, in the routines  100 ,  200 , when reproducing the CD  10  is started, a focus search is executed assuming the CD  10  is a CD-ROM. When this focus search is successful, playback of the CD  10  is started. When it is unsuccessful, a focus search is re-executed assuming the CD  10  is a CD-RW, and playback of the CD  10  is started.  
         [0058]    That is, when regenerating TOC from the CD  10  (loading the CD  10  on a CD player) or when pressing the playback button among the operation buttons  32 , the processing in the microcomputer  31  starts from step  101  of the routine  100 .  
         [0059]    Next, in step  102 , the gain of the RF amplifier  23  is a basic gain AL [double] with a control signal S GAIN, that is, is a gain that assumes the CD  10  is a CD-ROM or CD-R. Subsequently, in step  103 , the execution of the routine  200  is instructed from the microcomputer  31  to the DSP  244 , and, accordingly, the routine  200  is executed by the DSP  244 .  
         [0060]    Hereupon, although the details will be described later, according to the DSP  244  and the routine  200 , a focus search is executed. When the focus search is successful, a focus flag FSFLG is set to “H” and focus servo control is set on. When the focus search is unsuccessful, the flag FSFLG is set to “L”.  
         [0061]    When the processing of the routine  200  terminates, the processing in the routine  100  advances from step  103  to step  104 . In this step  104 , the result of a focus search is discriminated by checking the flag FSFLG. When the focus search is successful (FSFLG=“H”), the processing advances from step  104  to step  107 , and this routine  100  terminates.  
         [0062]    On the other hand, as a result of the check of step  104 , when a focus search is unsuccessful (FSFLG=“L”) the CD  10  may be a CD-RW. Hereupon, in this case, the processing advances from step  104  to step  105 . In this step  105 , the gain of the RF amplifier  23  changes to a high gain [double] with a control signal S GAIN, that is, a gain that assumes the CD  10  is a CD-RW. Next, in step  106 , a direct current offset component contained in an output signal S PB of the RF amplifier  23  is canceled, and then the processing returns to step  103 .  
         [0063]    Subsequently, in step  103  (routine  200 ) , a focus search is executed in the same manner as the case where the CD  10  is a CD-ROM and a CD-R. When the focus search is successful, the routine  100  terminates as described above.  
         [0064]    Besides, if this routine  100  is executed when loading the CD  10  on a CD player, each servo control is sequentially set on following the routine  100  and reproduction of TOC data is started from the CD  10 . Further, if the routine  100  is executed when pressing the playback button among the operation buttons  32 , each servo control is sequentially set on following the routine  100  and reproduction of an audio signal is started from the CD  10 .  
         [0065]    On the other hand, in step  103 , when the execution of the routine  200  is instructed from the microcomputer  31  to the DSP  244 , the routine  200  is executed by the DSP  244  as follows.  
         [0066]    That is, the processing of the DSP  244  starts from step  201  of the routine  200 . Next, in step  202 , the focus drive voltage V FD supplied from the DSP  244  to the optical pickup  22  is once set to the minimum value, as shown at the time t 0  of FIG. 4A. Accordingly, the object lens of the optical pickup drops to the lower limit position and the opposed interval d between the object lens and the signal plane of the CD  10  is maximized.  
         [0067]    Subsequently, when the time t 1  is reached, in step  203 , the measurement of a waiting time timer T TMR for assigning a predetermined time limit T LIM to a focus search is started. Next, in step  204 , the focus drive voltage V FD is set from the time t 1  so as to gradually rise from the minimum value. Accordingly, as this focus drive voltage V FD rises, the object lens gradually rises and the opposed interval d is reduced.  
         [0068]    Besides, in this case, a time limit T LIM is, for example, as shown in FIG. 4A by a dashed line, the time until the object lens rises to the upper limit position (from the time t 1 ) when a focus drive voltage V FD successively rises at the time t 5  or later, too.  
         [0069]    The processing of the DSP  244  advances to step  211  following step  204 . In this step  211 , whether a reproduction detection signal S OK rises is discriminated. Since the signal does not rise before the time t 3 , the processing advances from step  211  to step  212 . Then in this step  212 , whether the waiting time timer T TMR whose measurement is started in step  203  reaches the time limit T LIM is discriminated. When the timer T TMR does not reach the time limit, the processing returns from step  212  to step  211 .  
         [0070]    Accordingly, after the time t 1  or later, until a regenerative detection signal S OK rises or the waiting time timer T TMR reaches the time limit T LIM, steps  211 ,  212  will be repeated.  
         [0071]    When a regenerative detection signal S OK rises at the time t 3 , this signal is discriminated according to step  211 , and the processing advances from step  211  to step  213 . In this step  213 , whether a focus check signal S FZC is successively rising over a predetermined fixed period τ is checked.  
         [0072]    Since a signal S FZC does not rise before the time t 3 , the processing advances from step  213  to step  214 . In this step  214 , whether the waiting time timer T TMR of which the measurement is started in step  203  reaches the time limit T LIM is discriminated. When the timer T TMR does not reach the time limit, the processing returns from step  214  to step  213 .  
         [0073]    Accordingly, after the time t 3  or later, until a focus check signal S FZC is successively rising over a predetermined fixed period τ or the waiting time timer T TMR reaches the time limit T LIM, steps  213 ,  214  will be repeated.  
         [0074]    At the time t 4 , while a focus check signal S FZC is successively rising over a predetermined fixed period τ, this signal is discriminated according to step  213  and the processing advances from step  213  to step  215 . In this step  215 , whether the focus check signal S FZC rises is checked.  
         [0075]    Before the time t 5 , since a signal S FZC does not fall, the processing advances from step  215  to step  216 . In this step  216 , whether the waiting time timer T TMR of which the measurement is started in step  203  reaches the time limit T LIM is discriminated. When the timer T TMR does not reach the time limit, the processing returns from step  216  to step  215 .  
         [0076]    Accordingly, after the time t 4  or later, until a focus check signal S FZC falls or the waiting time timer T TMR reaches the time limit T LIM, steps  215 ,  216  will be repeated.  
         [0077]    At the time t 5 , while a focus check signal S FZC falls, this signal is discriminated according to step  215  and the processing advances from step  215  to step  221 . The focus check signal S FZC falls at the time t 5  when a focus search is successful. Accordingly, in this step  221 , the focus search flag FSFLG is set to “H” that indicates a success.  
         [0078]    Subsequently, in step  222 , the DSP  244  enters the state where focus servo control is executed, and the routine  200  terminates according to step  225 . Accordingly, after the time t 5  or later, a focused state for the CD  10  is held by focus servo control.  
         [0079]    On the other hand, in step  212 ,  214  or  216 , when it is detected that the waiting time timer T TMR reaches the time limit T LIM, this indicates that a focus search is unsuccessful.  
         [0080]    Accordingly, instep  212 ,  214  or  216 , when it is detected that the waiting time timer T TMR reaches the time limit T LIM, the processing advances from step  212 ,  214  or  216  to step  223 . In this step  223 , the focus search flag FSFLG is set to “L” that indicates a failure. Next in step  224 , a focus drive voltage is once set off, and, subsequently, the routine  200  terminates according to step  225 .  
         [0081]    Thus, when the CD  10  is a CD-ROM or CD-R, it is discriminated in the first focus search that the CD  10  is a CD-ROM or CD-R. At the same time, focus servo control is validated and playback of the CD  10  is started. Further, when the CD  10  is a CD-RW, it is discriminated in the first focus search that it is a CD-RW. Focus servo control is validated in the second focus search and playback of the CD-RW is started.  
         [0082]    Therefore, according to the CD player of FIG. 1, for a CD-ROM and CD-R which use many CDs  10 , playback can be started in the first focus search and the time to playback can be shortened. Further, even if the CD  10  is a CD-RW, the playback can be started in the second focus search.  
         [0083]    Regardless of the fact that the CD  10  is any of a CD-ROM, CD-R or CD-RW, if the gain of the RF amplifier  23  is set to a high gain AH, the level of the playback signal S PB of the optical pickup  22  is high when the CD  10  is a CD-ROM and CD-R. So the dynamic range of the playback signal S PB outputted from the RF amplifier  23  exceeds the dynamic range of the A/D converter circuit and normal A/D conversion is disabled. As a result, neither focus servo control nor tracking servo control can appropriately be performed.  
         [0084]    However, in the CD player of FIG. 1, since the RF amplifier  23  is switched to a reference gain AL or a high gain AH in accordance with the fact that the CD  10  is a CD-ROM, CD-R or CD-RW, the dynamic range of a playback signal S PB will not exceed the dynamic range of the A/D converter circuit  241 . Consequently, both focus servo control and tracking servo control can appropriately be performed.  
         [0085]    Besides, in the aforementioned, even if the processing of steps  103  to  106  is executed the predetermined number of times, the CD  10  may not be loaded when a focus search is unsuccessful, so it is desirable that the routine  100  be terminated. Further, in the aforementioned, the present invention applies to a CD player, and can also apply to a CD-ROM drive and an optical type disc (such as a DVD) reproducing apparatus.  
                                         [List of abbreviations used in this specification]                                A/D:   Analog to Digital       CD:   Compact Disc       CD-DSP:   CD Digital Signal Processor       CD-R:   CD Recordable       CD-ROM:   CD Read Only Memory       CD-RW:   CD Rewritable       D/A:   Digital to Analog       DSP:   Digital Signal Processor       DVD:   Digital Versatile Disc       EFM:   Eight to Fourteen Modulation       IC:   Integrated Circuit       LCD:   Liquid Crystal Display       TOC:   Table of Contents       RF:   Radio Frequency       laser:   Light Amplification by Stimulated Emission of           Radiation