Abstract:
Disclosed is a disc player for obtaining a read signal from an optical disc having sectors including land and groove tracks and ID regions, preformatted at given angular spatial intervals, which demarcate the sectors and are segmented, in the track extending direction, into two regions, each segmented region including a plural number of recording regions and non-recording regions, which are alternately and radially arrayed while being radially shifted by approximately half a track pitch from the tracks of the sectors adjacent to the segmented regions, each recording region containing record position information recorded therein having predetermined time durations. The disc player comprises: optical read means for projecting a light beam onto the optical disc and receiving a light beam reflected from a recording surface of the optical disc; first and second signal generating means for generating first and second signals which are dependent on the record position information recorded in the recording regions of the first and second segmented regions by use of a signal output from the optical read means; and ID region detecting means for outputting a detecting signal indicating that the ID region is detected when the first and second signals are both present.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a disc player for reading information from an optical disc having ID regions, segmented into two regions in the direction of the track, in which record position information are preformatted and recorded. 
     A spindle control system as shown in FIG. 14 is known as the technique for driving an optical disc to rotate in a CAV (constant angular velocity) mode in an optically readable, disc player. Information is read out of a disc  1  being rotated by a spindle motor  2 , by a pick-up (not shown). The spindle motor  2  includes means to generate a pulse signal (FG pulse signal) of which the frequency corresponds to a rotation speed of the motor. The FG pulse signal generated is applied to an error generating circuit  3 . A reference clock signal of a predetermined frequency corresponding to a target angular speed of the motor is supplied to the error generating circuit  3 . The error generating circuit  3  detects frequency and phase errors through the comparison of the clock signal and the FGpulse signal, and applies error signals dependent on the detection errors to a pulse width modulator (PWM)  4 . The output signal of the PWM  4  passes through a low-pass filter (LPF)  5  and reaches a drive circuit  6 . 
     Thus, the error signal is PWM processed and only its low frequency component is filtered out. The drive circuit  6  applies a drive signal, which is based on the error signal of the low frequency component, to the spindle motor  2 . The spindle motor  2  is controlled so as to reduce the error detected by the error generating circuit  3  to zero (0), viz., so as to maintain the target angular velocity of the motor. 
     To read the disc  1  in a CLV (constant linear velocity) mode, it is required that the disc  1  is driven to rotate in accordance with a read signal (or a read position) To realize such a drive of the motor, a synchronizing (sync) signal is extracted from the read signal, and the angular velocity of the spindle motor  2  is controlled so that the sync signal has a predetermined frequency. 
     In connection with the sync-signal basis motor control, the Examined Japanese Patent Application Publication No. Hei 4-71269 discloses the following technique. In a situation where no sync signal is produced, e.g., when the disc player is started or when the pick-up is moved at high speed, the maximum value of the time interval (maximum reversal interval) from the leading edge of a data signal of the read signal to the next trailing edge is detected, and the angular velocity of the spindle motor is controlled so that the maximum reversal interval reaches a predetermined value. 
     At present, a high density recording disc, called a DVD (digital versatile disc), is increasing its market share. Some type of the DVD has a plural number of formats for recording information therein. A typical example of those DVDs is a DVD-RAM (DVD-random access memory) allowing information to be rewritten into the DVD itself. 
     The DVD-RAM, or a RAM type DVD, has the following disadvantage when no information is recorded therein or a small amount of information is recorded in a part thereof. In the RAM type DVD, data signals to be used for the control of the spindle motor are absent or, if present, are insufficient for the control. Therefore, the disc player frequently fails to detect the maximum reversal interval or the maximum/minimum time period. 
     ID regions are preformatted at predetermined angular spatial intervals in the surface of the DVD-RAM. Address information on the disc and information indicative of a groove track or a land track are stored in the ID regions. (The ID region will be described in detail later.) It is required that the disc player accurately detects the ID regions. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to provide a disc player capable of performing a good spindle control of a disc-like recording medium of the DVD-RAM type having no information recorded therein or information recorded in a part thereof in accordance with a signal read out of the disc, and hence of exactly recording information into or playing back the same from the disc. 
     According to a first aspect of the present invention, there is provided a disc player for obtaining a read signal from an optical disc having sectors including ID regions, preformatted at given angular spatial intervals, which demarcate the sectors and are segmented, in the track extending direction, into two regions, each segmented region including a plural number of recording regions and non-recording regions, which are alternately and radially arrayed while being radially shifted by approximately half a track pitch from the tracks of the sectors adjacent to the segmented regions, each recording region containing record position information recorded therein having predetermined time durations. The disc player comprises: optical read means for projecting a light beam onto the optical disc and receiving a light beam reflected from a recording surface of the optical disc; first and second signal generating means for generating first and second signals which are dependent on the record position information recorded in the recording regions of the first and second segmented regions by use of a signal output from the optical read means; and ID region detecting means for outputting a detecting signal indicating that the ID region is detected when the first and second signals are both present. 
     According to a second aspect of the present invention, a disc player, based on the first aspect, is constructed such that the ID region detecting means in the disc player produces a detecting signal when the first and second signals continue for a predetermined time. 
     According to a third aspect of the present invention, a disc player modifies the first aspect or the second aspect such that the first signal generating means generates a first signal by use of a signal formed by binarizing an output signal of the optical read means in accordance with a first threshold value, and the second signal generating means generates a second signal by use of a signal formed by binarizing an output signal of the optical read means in accordance with a second threshold value. 
     According to a fourth aspect of the present invention, a disc player modifies any of the first to third aspects such that information is recorded in the land tracks and the groove tracks every sector demarcated by the ID regions. 
     According to a fifth aspect of the present invention, a disc player modifies any of the first to fourth aspects such that the optical disc is controlled in rotation thereof in accordance with the detecting signals. 
     According to a sixth aspect of the present invention, a disc player, based on the fourth or fifth aspects, further comprises means for judging if the track being currently scanned is a land track or a groove track depending on the first and second signals, and the detecting signals. 
     The thus constructed disc player is capable of performing a good spindle control of a disc-like recording medium of the DVD-RAM type having no information recorded therein or information recorded in a part thereof in accordance with a signal read out of the disc, and hence of exactly recording information into or playing back the same from the disc. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a recording format in a recording surface of a DVD-RAM used in a disc player, which is an embodiment of the present invention. 
     FIG. 2 is a diagram typically showing the detail of ID regions in the recording format shown in FIG.  1 . 
     FIG. 3 is a block diagram showing an information reading system for the disc player. 
     FIG. 4 is a block diagram showing an arrangement of an ID region detecting system in the disc player. 
     FIG. 5 is a timing chart showing an operation of the ID region detecting system. 
     FIG. 6 is a timing chart showing another operation of the ID region detecting system. 
     FIG. 7 is a block diagram showing an L/G judging section contained in the ID region detecting system of FIG.  4 . 
     FIG. 8 is a timing chart showing in particular a variation of a PP-L/G signal output from a flip-flop circuit. 
     FIG. 9 is a block diagram showing a selector for selecting a PP-L/G signal or a DEC-L/G signal in accordance with a CRC basis error signal. 
     FIG. 10 is a block diagram showing a selector for selecting a PP-L/G signal or a DEC-L/G signal in accordance with a LOCK signal. 
     FIG. 11 is a block diagram showing another L/G judging section contained in the ID region detecting system of FIG.  4 . 
     FIG. 12 is a timing chart showing the waveforms of signals FP, RP 1 , RP 2 , and a PP-L/G signal in the L/G judging section of FIG. 11, together with the signal waveforms shown in FIG.  5 . 
     FIG. 13 is a timing chart showing the waveforms of signals FP, RP 1 , RP 2 , and a PP-L/G signal in the L/G judging section of FIG. 11, together with the signal waveforms shown in FIG.  6 . 
     FIG. 14 is a block diagram showing a basic arrangement of a conventional spindle control system for driving an optical disc by the CAV control. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments of the present invention will be described with reference to the accompanying drawings. 
     An example of a recording format of the DVD-RAM will be described. 
     FIG. 1 shows a track structure of the DVD-RAM. The DVD-RAM employs a land/groove (L/G) recording system in which data is stored into groove portions  1 G within guide grooves and portions between grooves (land portions)  1 L. In FIG. 1, the groove tracks  1 G are hatched, while the land tracks  1 L are not hatched. The DVD-RAM employs a single spiral land/groove (SS-L/G: single spiral land-groove) recording system in which the land and the groove are interconnected every revolution of the disc to form a single track, spirally configured, in the entire surface of the disc. For the SS-L/G recording system, reference is made to “Access Method for the Single Spiral Land/Groove Recording Method”, written by Nakane et al., in “Technical Report of IEICE. MR95-88. CPM95-126 (1996-02)”. 
     The land tracks and the groove tracks are grouped into a plurality of sectors. Those sectors are demarcated by ID regions S 0  to S 7 . The address information (referred to as ID), e.g., physical position and the sector numbers or positions, which substantially define the recording position on the disc, are preformatted and stored in each ID region. Those ID regions are angularly and equidistantly arrayed on the disc, and the recording rates and the reading rates of the ID regions are set to be equal. 
     The detail of the ID regions is illustrated in FIG.  2 . 
     In the figure, an ID region S 0  and another ID region S 1  are exemplarily illustrated. As shown, in the ID region S 0 , the groove tracks confront the land tracks. In the ID region S 1 , the groove tracks confront each other and the land tracks confront each other. As shown, each of the ID regions S 0  and S 1  includes recording regions and non-recording regions, arrayed radially and alternately. The length of the ID region is the half of the full width of the ID region (when viewed in the read direction, i.e., the direction of track), and the width or height of the ID region is equal to that of the land (groove) track. The recording and non-recording regions, radially arrayed, are radially shifted by approximately half a track pitch from the tracks of the sectors adjacent to the segmented regions. 
     A sequence of pits representative of an ID pattern are formed in the major surface (each recording region) of the ID region. The non-recording regions are formed of mirror-like surfaces, and on the level of the surfaces of the lands. 
     In the ID region S 0 , a virtual track T 1  is present interconnecting a groove track (located preceding to the virtual track T 1 ) and a land track (located succeeding thereto). In the virtual track T 1 , a recording region, which first appears (when viewed in the read direction), is shifted radially inward by half a track pitch with respect to the preceding groove track, and another recording region, which then appears, is shifted radially upward by half a track pitch with respect to the succeeding land track. Also in the ID region S 0 , a virtual track T 2  is present interconnecting a preceding land track and a succeeding groove track. In the virtual track T 2 , a recording region, which first appears, is shifted radially outward by half a track pitch with respect to the preceding land track, and another recording region, which then appears, is shifted radially inward by half a track pitch with respect to the succeeding groove track. 
     In the ID region S 1 , a virtual track T 3  is present interconnecting a groove track (located preceding to the virtual track T 3 ) and a groove track (located succeeding thereto). In the virtual track T 3 , a recording region, which first appears, is shifted radially outward by half a track pitch with respect to the preceding groove track, and another recording region, which then appears, is shifted radially inward by half a track pitch with respect to the succeeding groove track. Also in the ID region S 1 , a virtual track T 4  is present interconnecting a preceding land track and a succeeding land track. In the virtual track T 4 , a recording region, which first appears, is shifted radially inward by half a track pitch with respect to the preceding land track, and another recording region, which then appears, is shifted radially outward by half a track pitch with respect to the succeeding land track. 
     Thus, in the ID region S 0 , the land track is switched to the groove track and the groove track is switched to the land track. An occurrence pattern in the recording region (already stated) is switched to another pattern. 
     Description will be given about a disc player for recording information into and playing back or reading the same from the thus formatted DVD-RAM. FIG. 3 shows an outline of an information reading system for the disc player. In the figure, a pickup drives a light source (not shown) to emit a light beam toward the disc, and receives a light beam reflected from a recording surface of the disc by a photo-sensor  21 . As shown, a surface of the photo-sensor  21  is equally divided into four photo-sensing areas  21   a ,  21   b ,  21   c  and  21   d  by two dividing lines orthogonally intersecting each other. 
     Those photo-sensing areas  21   a  to  2   d  are separated, with respect to the horizontal dividing line  21 L, into two groups; one group consists of photo-sensing areas  21   a  and  21   b , which are symmetrical with respect to the vertical dividing line  2 L (?), and the other group consists of the photo-sensing areas  21   c  and  21   d . The photo-sensing areas  21   a  and  21   b  of the first group independently perform light-to-electric conversion processes in accordance with the quantities of received light and states of light receiving, and apply the conversion results to an adder  31 . Similarly, the photo-sensing areas  21   c  and  21   d  of the second group independently perform light-to-electric conversion processes in accordance with the quantities of received light and states of light receiving, and apply the conversion results to an adder  31 . 
     The output signals of those adders  21  and  32  are applied to an adder  33 . The adder  33  generates a total sum signal that depends on the quantity of received light and the light receiving state in the entire photo-sensing area, and outputs it as a read signal RF to a data demodulator  40 . The data demodulator  40  performs a given demodulation process to generate playback data, and sends the playback data to other systems (not shown), e.g., a data processing system and an information playback system. The demodulation process includes the processing of the read signal for wave shaping and A/D (analog/digital) conversion, the removal of the RLL (run length limited) coding, and others. 
     The output of the adders  31  and  32  are also applied to a subtractor  34 . The subtractor  34  produces a signal, called a push-pull signal PP, which depends on a difference between the output signals from the photo-sensing areas symmetrical with respect to the vertical dividing line  2 L. The push-pull signal is input to the noninverting input terminals of differential amplifiers  51  and  52  as comparators. 
     Signals, which depend on threshold values TH 1  and TH 2 , are input to the inverting input terminals of the differential amplifiers  51  and  52 , respectively. The differential amplifier  51  compares the received push-pull signal with the corresponding threshold value TH 1 , and produces a signal binarized in accordance with the comparison result in the form of a read address signal ID 1  to an address demodulator  60  and an ID region detecting system to be given later. Similarly, the differential amplifier  52  compares the received push-pull signal with the corresponding threshold value TH 2 , and produces a signal binarized in accordance with the comparison result in the form of a read address signal ID 1  to the same. The address demodulator  60  executes a given demodulation process of the read signal to generate a playback address data, and transfers the playback address data to an address processing system and a system control system. The ID region detecting system receives the read address signals ID 1  and ID 2 , and executes the following process on the basis of those signals; a process of controlling the rotation of the disc and a process of judging if the current track (being currently scanned) is a land track or a groove track. 
     Next, description will be given about a spindle control using the ID region detecting system in the disc player. 
     FIG. 4 is a block diagram showing an arrangement of an ID region detecting system of the disc player. The ID region detecting system includes an ID region detector  100  and a spindle control section  200 . In accordance with an ID-region detecting signal output from the ID region detector  100 , the spindle control section  200  controls the rotation of a spindle motor  2 . 
     In the ID region detector  100 , read address signals ID 1  and ID 2  as the output signals of differential amplifiers  51  and  52  are respectively input as trigger signals to monostable multivibrators (MMVs)  71  and  72 . Each of the MMVs  71  and  72  produces a signal (high level signal), which is higher in level than the trigger signal, for a preset time. When another trigger signal comes in during the high level signal, the MMV  71  ( 72 ) continues the generation of the high level signal for another preset time. In this way, the MMVs  71  and  72  produce a first signal MVID 1  and a second signal MVID 2  which in turn are input to an OR gate  73   a  and an AND gate  73   b  simultaneously. 
     The OR gate  73   a  logically sums the first and second signals MVID 1  and MVID 2  and produces a signal CAPA for transfer to the inputs of a counter  74   a  and an AND gate  73   d . The AND gate  73   d  ANDs the first and second signals MVID 1  and MVID 2  and produces a gate signal GATE for transfer to an AND gate  73   c . The counter  74   a  performs a counting operation of a clock signal CK received from a 1/N frequency divider  92  when the signal CAPA supplied thereto is in a high level, and outputs a pulse signal to the AND gate  73   c  when its count value reaches a first count value QTH 1 . 
     The AND gate  73   c  logically multiplies the supplied gate signal and the output signal of the counter  74   a  to generate a gate sync signal (GTSYNC) and transfers it to a counter  74   b . In response to the gate sync signal (GTSYNC), the counter  74   b  starts a counting operation of a clock signal CK received from the 1/N frequency divider  92 . When the count value of the counter  74   b  reaches a second count value QTH 2 , the counter  74   b  produces a pulse signal to the AND gate  73   d . The AND gate  73   d  logically multiplies the count outputs from the CAPA and the counter  74   b  to generate a sync signal (SYNC) indicating the detection of ID region, and supplies to a frequency/phase comparator  76 . 
     On the contrary, the spindle control section  200  has a reference signal generating system including a crystal oscillator (OSC)  91 , a 1/N frequency divider  92  and a 1/M frequency divider  93 . An output signal of the crystal oscillator  91  is frequency divided into a signal having a 1/N frequency (N: integer of 1 or larger). The frequency divided signal is applied as a clock signal CK to the counters  74   a  and  74   b . The output signal of the 1/N frequency divider  92  is output to the 1/M frequency divider  93  where it is frequency divided into a signal having a 1/M frequency (M : integer of 1 or larger), and applied as a reference signal to a frequency/phase comparator  76  where it is compared in frequency and phase with a synchronizing signal SYNC. 
     The frequency/phase comparator  76  compares the frequency and phase of the reference signal (the frequency divided signal output from the 1/M frequency divider  93 ) with those of the synchronizing signal SYNC from the ID region detector  100 , and produces signals representative of the frequency and phase errors, and applies a rotation drive signal that depends on the error signals to the spindle motor  2 . 
     Therefore, the number of revolutions of the spindle motor  2  can be controlled so that a synchronizing signal SYNC that is generated every time the ID region is read out appears at fixed time intervals. 
     FIG. 5 shows waveforms of the signals at the key points in the ID region detecting system of FIG. 4 when a light beam scans a track including a virtual track T 1  (FIG. 2) of the ID region S 0 , which interconnects a groove track preceding to the virtual track and a land track succeeding to the same. A push-pull signal PP represents an inward or outward shift of the land/groove from the center of the track at a read point (position of a beam spot on the recording disc). In this respect, the push-pull signal PP is equivalent to a called tracking error signal. 
     When the read point scans the virtual track T 1  (FIG.  2 ), the push-pull signal PP takes a waveform having the upper and lower peaks corresponding to a series of pits arrayed on the virtual track T 1  of the ID region S 0 . The push-pull signal PP shown in FIG. 5 is produced by scanning the virtual track T 1  of the ID region S 0 , segmented half as already mentioned, with the read point in such a manner that the first recording region (the lower left half of the virtual track T 1 ) and the first non-recording region (the upper left half of the virtual track T 1 ) are first read, and then the second recording region (the upper right half of the virtual track T 1 ) and the second non-recording region (the lower right half of the virtual track T 1 ) are read. 
     A threshold value TH 1  that is applied to the noninverting input terminal of the differential amplifier  51  (FIG. 4) is much higher than the reference level of the push-pull signal PP. When receiving a push-pull signal PP having positive peak values higher than the threshold value THi 1 , the differential amplifier  51  produces a high level signal ID 1 . A threshold value TH 2  that is applied to the noninverting input terminal of the differential amplifier  52  is much lower than the reference level of the push-pull signal PP. When receiving a push-pull signal PP having negative peak values much lower than the threshold value TH 2 , the differential amplifier  52  produces a low level signal ID 2 . 
     Thus, the push-pull signal PP consisting of successions of small sinusoidal waveforms, which are read out from the preceding and succeeding recording regions of the ID region, are converted into read address signals ID 1  and ID 2  (FIG. 5) consisting of successions of small rectangular waveforms by the differential amplifiers  51  and  52 . The MMVs  71  and  72  are triggered at the leading or trailing edges of the rectangular waves of the read address signals ID 1  and ID 2 . 
     The MMV  71  produces a high level signal MVID 1  which keeps a high level over a period of time ranging from the leading edge of the first rectangular wave of the read address signal ID 1  to a time point after a preset time elapses from the leading edge of the last rectangular wave. The MMV  72  produces a high level signal MVID 2  which keeps a high level over a period of time ranging from the trailing edge of the first rectangular wave of the read address signal ID 2  to another time point after a preset time elapses from the trailing edge of the last rectangular wave. 
     The first and second signals MVID 1  and MVID 2  are applied to the OR gate  73   a  which in turn produces a signal CAPA. The signal CAPA is high in level over a period of time ranging from the leading edge of the first rectangular wave of the read address signal ID 1  to a time point after a preset time elapses from the trailing edge of the rectangular wave of the read address signal ID 2 . The signal CAPA output from the OR gate  73   a  is applied to the counter  74   a  and the AND gate  73   d.    
     The counter  74   a  is arranged so as to be reset to 0 (zero) when the signal CAPA is at 0 level. Then, when the first or second signal MVID 1  or MVID 2  goes high (in level), the counter  74   a  is ready for its counting operation. Accordingly, when the first or second signal MVID 1  or MVID 2  is in high level, he counter  74   a  counts a clock signal (consisting of clock pulses) at a relatively high frequency CK received from the 1/N frequency divider  92 . 
     In this case, the counter  74   a  increases its count value Q and supplies it to the input terminal of the AND gate  73   c  till the count value Q reaches a first count value QTH 1  (corresponds to a time longer than a time taken for reading the preceding ID recording region in the ID region S 0  at a given linear speed). When the count value Q reaches the first count value QTH 1 , the counter  74   a  resets its count value to 0 (zero), and a gate sync signal GTSYNC is generated and transferred to the counter  74   b.    
     The first and second signals MVID 1  and MVID 2  are logically processed into a gate signal GATE. The gate signal GATE goes high in a time period where the first and second signals MVID 1  and MVID 2  are both logically high, and is transferred to the AND gate  73   c . The fact that the gate signal GATE of high level is generated indicates that the read point has read the preceding recording and non-recording regions in accordance with a reading direction (FIG. 2) in the ID region S 0 , and the succeeding recording and the non-recording regions. 
     When receiving a count value signal from the counter  74   a  and a high level gate signal GATE from the AND gate  73   b , the AND gate  73   c  generates a gate sync signal (GTSYNC) as a high level pulse signal, and transfers it to the counter  74   b . The gate sync signal GTSYNC is generated at a time point where the counter  74   a  is reset to have its count value of 0 (zero). 
     In response to a high level gate sync signal GTSYNC, the counter  74   b  counts a clock signal (consisting of clock pulses) CK of a relatively high frequency. In this case, the counter  74   b  increases its count value Q and continues the supply of the count value Q to the input terminal of the AND gate  73   d  till the count value Q reaches a second count value QTH 2 . When the count value Q reaches the second count value QTH 2 , the resets its count value Q to 0 (zero). 
     When a high level signal CAPA from the OR gate  73   a  is applied to the AND gate  73   d  and the counter  74   b  is reset to have the count value Q of 0 (zero) the AND gate  73   d  produces a synchronizing signal SYNC as a high level pulse signal to the frequency/phase comparator  76  and an L/G judging section  300  to be given later. The synchronizing signal SYNC is generated when the contents of the counter  74   b  is reset to zero. 
     In this way, the ID region detecting system generates a synchronizing signal SYNC positionally synchronized with the ID region S 0 . 
     FIG. 6 shows waveforms of the signals at the key points in the ID region detecting system of FIG. 4 when a light beam scans a track including a virtual track T 2  (FIG. 2) of the ID region S 0 , which interconnects a land track preceding to the virtual track and a groove track succeeding to the same. As seen from the figure, the spindle control system operates as shown in FIG.  5  and produces a synchronizing signal SYNC corresponding in position to the ID region S 0 . 
     In the remaining ID regions S 1  to S 7 , the ID region detecting system generates synchronizing signals SYNC which are positionally synchronized with those ID regions, in similar manners. 
     As described above, the ID region detecting system produces a gate signal GATE by the AND gate  73   b  to show that the preceding and succeeding recording regions, which are radially arrayed shifted by approximately half a track pitch from the related tracks, are present. The ID region detecting system produces a gate sync signal GTSYNC by the AND gate  73   c  to show that the recording portion is switched from the preceding recording region to the succeeding recording region. Further, the ID region detecting system generates a synchronizing signal SYNC every ID region, and controls a rotation angle of the optical disc that is rotating together with the spindle motor  2 . 
     The ID region detecting system includes an L/G judging section  300  as shown in FIG.  7 . The L/G judging section  300  judges whether or not the track preceding or succeeding to each ID region is a land track or a groove track. 
     In the L/G judging section  300 , an AND gate  73   e  ANDs a synchronizing signal SYNC and a first signal MVID 1  to generate a reset signal R; an AND gate  73   f  ANDs a synchronizing signal SYNC and a second signal MVID 2  to generate a set signal S; and a flip-flop circuit (FF)  74   c  receives those signals R and S and produces a PP-L/G signal. The PP-L/G signal of high level indicates that the track is a land track, while the PP-L/G signal of low level indicates that the track is a groove track. Thus, the ID region detecting system recognizes if the succeeding track is a land track or a groove track on the basis of the level of the PP-L/G signal. The flip-flop circuit  74   c  operates while being timed by a clock signal CK received from the 1/N frequency divider  92 . 
     FIG. 8 is a timing chart showing in particular a variation of a PP-L/G signal output from the flip-flop circuit  74   c  shown in FIG.  7 . As seen, before and after an ID region of which the virtual track follows the land track and is followed by the same kind of track, i.e., land track, the PP-L/G signal maintains a high level. At the ID region S 0  where the track being currently scanned, i.e., the current track, is switched from the land track to the groove track, the level of the PP-L/G signal is switched from high level to low level. Before and after an ID region of which the virtual track follows the groove track and is followed by the same kind of track, i.e., groove track, the PP-L/G signal maintains a high level. 
     The current track (corresponding to the virtual track T 2 ) which follows the land track and is followed by the groove track is illustrated in FIG.  8 . In the case of the current track (corresponding to the virtual track T 1  of FIG. 2) which follows the groove track and is followed by the land track, the PP-L/G signal is switched from low level to high level, as a matter of course. 
     Thus, the ID region detecting system recognizes if the current track is a land track or a groove track without decoding the information recorded in the ID region, by the utilization of the SYNC-basis rotation angle control and the groove/land judgement by the L/G judging section  300  (the judgement is made on the current track, or the track being currently scanned). 
     Therefore, the disc player drives the spindle motor at the number of revolutions suitable for the playing back or recording information from and to the disc. The disc player performs the playback and recording operations in the condition most suitable for the current track since it makes the land/groove(L/G) judgement. 
     The ID recording region stores the information indicative of the kind of track (i.e., a land track or a groove track). Therefore, the ID region detecting system can recognize a kind of the current track by decoding the push-pull signal PP and extracting the track kind information from the signal PP. 
     In this case, if the information stored in the ID region is defective or cannot be read out because of disturbance, the extraction of the track kind information is impossible. 
     A selector to be given hereunder may be used for selecting the L/G judgement by the L/G judging section  300  or the L/G judgement based on the track kind information (DEC-L/G) that is produced through the decoding of the push-pull signal PP, in accordance with a playback condition. 
     FIG. 9 is a block diagram showing a selector for selecting a PP-L/G signal or a DEC-L/G signal by use of an error detecting signal produced through a CRC (Cyclic Redundancy Check) contained in the address demodulator  60  of FIG.  3 . 
     A selector  75  shown in FIG. 9 selects a PP-L/G signal derived from the L/G judging section  300  or a DEC-L/G signal derived from the FIG. 3 address demodulator  60 . A CRC-basis error detecting signal (referred to as a CRC signal) is also applied to the selector  75 , from the address demodulator  60 . When the CRC signal is received, viz., an error is detected through the CRC, the selector  75  selects the PP-L/G signal from the L/G judging section  300 . When it is not received, the selector  75  selects a DEC-L/G signal read out of the ID region with the aid of the address demodulator  60 . 
     When the information of the ID region is defective, the PP-L/G signal is used for the L/G judgement. Therefore, an accuracy of the L/G judgement is improved. 
     FIG. 10 is a block diagram showing as elector for selecting a PP-L/G signal or a DEC-L/G signal in accordance with a LOCK signal that is output from a PLL for demodulating the information of the ID region, which is contained in the FIG. 3 address demodulator  60 . 
     A selector  77  shown in FIG. 10 selects a PP-L/G signal derived from the L/G judging section  300  or a DEC-L/G signal derived from the FIG. 3 address demodulator  60 . A lock signal LOCK is also applied to the selector  77 , from the PLL of the address demodulator  60 . 
     When the PLL is locked, the selector  77  recognizes that the information of the ID region has been demodulated and selects a DEC-L/G signal. When it is not locked, the selector  77  recognizes that the information of the ID region is not demodulated and selects a PP-L/G signal. 
     When the ID region information is not demodulated, the PP-L/G signal is used for the L/G judgement. Therefore, an accuracy of the L/G judgement is improved. 
     FIG. 11 is a block diagram showing another example of the L/G judging section  300  which makes the L/G judgement by use of the push-pull signal PP (FIG.  7 ). 
     In FIG. 11, an L/G judging section  301  is made up of a first polarity judging means  80 , a second polarity judging means  81  and a comparing means  82 . The first polarity judging means  80  includes AND gates  791  and  792 , and a flip-flop  793 . The AND gate  791  receives a leading edge of a signal CAPA, a first signal MVID 1  and an inverted second signal MVID 2 ; ANDs the first signal MVID 1  and the inverted second signal MVID 2  at the leading edge of the signal CAPA to generate a set signal S; and transfers it to the S input terminal of the flip-flop  793 . 
     The AND gate  792  receives a leading edge of a signal CAPA, an inverted first signal MVID 1  and a second signal MVID 2 ; ANDs the inverted first signal MVID 1  and the second signal MVID 2  at the leading edge of the signal CAPA to generate a reset signal R; and transfers it to the R input terminal of the flip-flop  793 . The flip-flop  793  performs a flip-flop operation in accordance with the set signal S and the reset signal R from those AND gates  791  and  792  to generate a binarized signal FP, and transfers it to the comparing means  82 . 
     The polarity of the signal FP produced by the first polarity judging means  80  thus arranged remains unchanged in the ID region (any of S 1  to S 7 , FIG. 1) where its virtual track interconnects the groove tracks or the land tracks. The polarity of the signal FP is inverted in the ID region (S 0 , FIG. 1) where its virtual track interconnects the groove track and the land track. 
     The second comparing means includes AND gates  794  and  795 . The AND gate  794  receives a first signal MVID 1  and an inverted second signal MVID 2 ; ANDs those signals at the leading edge of a signal CAPA to generate a signal RP 1 ; and transfers it to the comparing means  82 . The AND gate  795  receives an inverted first signal MVID 1  and a second signal MVID 2 ; ANDs those signals at the leading edge of a signal CAPA to generate a signal RP 2 ; and transfers it to the comparing means  82 . 
     The comparing means  82  is made up of AND gates  796  and  797 , and a flip-flop  798 . As shown, the AND gate  796  receives a synchronizing signal SYNC, a signal FP from the first polarity judging means  80 , and a signalRP 2  from the second polarity judging means  81 ; logically multiplies the signal FP and the signal RP 2  at the timing of the synchronizing signal SYNC to generate a binarized signal S; and transfers it to the terminal S of the flip-flop  798 . 
     The AND gate  797  receives a synchronizing signal SYNC, an inverted signal FP from the first polarity judging means  80 , and a signal RP 1  from the second polarity judging means  81 ; logically multiplies those signals at the timing of the synchronizing signal SYNC to generate a binarized signal R; and transfers it to the terminal Rof the flip-flop  798 . The flip-flop  798  performs a flip-flop operation in accordance with the set signal S and the reset signal R from those AND gates to generate a PP-L/G signal. 
     FIG. 12 is a timing chart showing the waveforms of signals FP, RP 1 , RP 2 , and a PP-L/G signal in the L/G judging section of FIG. 11, together with the signal waveforms shown in FIG.  5 . FIG. 13 is a timing chart showing the waveforms of signals FP, RP 1 , RP 2 , and a PP-L/G signal in the L/G judging section of FIG. 11, together with the signal waveforms shown in FIG.  6 . 
     The waveforms of the signals shown in FIG. 12 appear at the related points in the ID region detecting system including the L/G judging section  301  (FIG. 11) when the light beam scans the virtual track T 1  of the ID region S 0  which follows the groove track and is followed by the land track. At this ID region, the track is switched from the groove track to the land track. Therefore, the signal FP switches its level from low level to high level. 
     The signal FP exhibits a high level when the first half in the ID region is shifted radially outward, and a low level when it is shifted radially inward. The fact that the signal FP is in high level indicates that the first half of the ID region is shifted radially outward, and hence it is readily conjectured that the second half of the ID region will be shifted radially inward. Therefore, it is readily preestimated that this ID region is for the land track. 
     Where the signal FP is in low level, the first half of the ID region is shifted radially inward. On this fact, it is conjectured that the second half of the ID region is shifted outward, and hence that this ID region is for the land track. In this sense, the first polarity judging means  80  is means for determine if the first half of the ID region is shifted radially inward. 
     The second polarity judging means  81  produces the signals RP 1  and RP 2  indicative of the inward or outward shift of the second half of the ID region. Specifically, a high level of the signal RP 1  indicates that the second half of the ID region is shifted radially outward. A high level of the signal RP 2  indicates that the second half of the ID region is shifted radially inward. Therefore, in the ID region of the land track, the signal RP 1  goes high and then the signal RP 2  goes high as shown in FIG.  12 . 
     The comparing means  82  judges if the track being currently scanned is a land track or a groove track on the basis of the synchronizing signal SYNC from the ID region detector  100  (FIG.  4 ), the signal FP from the first polarity judging means  80 , and the signals RP 1  and RP 2  output from the second polarity judging means  81 . When a synchronizing signal SYNC is generated at the ID region S 0  where the groove track is switched to the land track, the signal FP is in high level, the signal RP 1  is in low level, and the signal RP 2  is in high level. Therefore, the output signal of the AND gate  796  is in high level. And the output signal of the AND gate  797  is in low level. 
     Under this condition, the set signal S to the flip-flop  798  goes high and the reset signal R to the same goes low, so that the output signal Q of the flip-flop  798  is inverted from low level to high level. Accordingly, the signal level of the PP-L/G signal output from the flip-flop  798  is switched from a low level representing a groove track to a high level representing a land track. 
     The waveforms of the signals shown in FIG. 13 appear at the related points in the ID region detecting system including the L/G judging section  301  when the light beam scans the virtual track T 2  of the ID region S 0  which follows the land track and is followed by the groove track. At this ID region, the track is switched from the land track to the groove track. Therefore, the signal FP switches its level from high level to low level, as already stated. 
     In this case, in the second polarity judging means  81 , as shown in FIG. 13, the signal RP 2  goes high in the ID region of the groove track, and then the signal RP 1  goes high. 
     In the comparing means  82 , when a synchronizing signal SYNC is generated at the ID region S 0  where the land track is switched to the groove track, the signal FP is in low level, the signal RP 1  is in high level, and the signal RP 2  is in low level, and hence the AND gate  796  produces a low level signal. And the AND gate  797  produces a high level signal. 
     Under this condition, the set signal S to the flip-flop  798  is in low level, the reset signal R thereto is in high level, and the output signal Q thereof is switched from high level to low level. Therefore, a PP-L/G signal output from the flip-flop  798  is switched from a high level indicating a land track to a low level indicating a groove track. 
     At the ID regions (S 1  to S 7 , FIG. 1) where the virtual tracks interconnect the groove tracks or the land tracks, the signal levels at the output of the flip-flop  798  follows. At the ID region interconnecting the land tracks, the terminal S of the flip-flop  798  is always at high level and the terminal R thereof is always at low level, and hence the output terminal thereof is always at high level. At the ID region interconnecting groove tracks, the terminal S of the flip-flop  798  is always at low level and the terminal R thereof is always at high level, and hence the output terminal thereof is always at low level. Therefore, at the ID region interconnecting the same kind of tracks, the signal level of the PP-L/G signal is invariable. 
     The disc player thus constructed is capable of performing a good spindle control of a disc-like recording medium of the DVD-RAM type having no information recorded therein or information recorded in a part thereof in accordance with a signal read out of the disc, and hence of exactly recording information into or playing back the same from the disc.