OPTICAL DISC

Abstract: An optical disc which has a rewritable first recording region and a read-only second recording region. The first recording region has first tracks which are composed of group tracks and land tracks which are alternately provided on a disc substrate spirally or concentrically. Each first track is divided into a plurality of first sectors. Each first sector has a first header region where identification data by which the first sector is identified are recorded and a first data region in which user data are recorded with recording marks where the optical characteristics of the recording surface are changed. The second recording region has second tracks which are composed of a physical pit row which are provided on the disc substrate spirally or concentrically. Each second track is divided into a plurality of second sectors. Each second sector has a second header region where identification data by which the second sector is identified are recorded and a second data region in which read-only data are recorded by means of the pit row. The first header region includes a first physical pit row. Each pit of the first pit row has a width in a radial direction of the disc which is substantially equal to the width of the group track and, further, the pits are staggered along the center line of the group track radially with pitches of approximately a quarter of the pitch of the group track. The second header region includes a second physical pit row. Each pit of the second pit row has a width in a radial direction of the disc which is smaller than the width of the group track and, further, the pits are arranged generally along the center line of the second track to be tracked.

Description: TECHNICAL FIELD The present invention relates to an optical disk, more specifically relates to a data format on an optical disk having a rewritable area and a read-only area. BACKGROUND ART Optical disks are classified into a read-only type which only allows for reproduction of recorded data and a rewritable type which allows the user to record data thereon. A read-only optical disk has tracks formed in a spiral or concentric shape on a disk substrate. An array of concave and convex portions (pits) are physically formed along the tracks in accordance with information to be recorded. A rewritable optical disk has grooves formed in a spiral or concentric shape on a disk substrate and a recording film formed over the grooves. The grooves define tracks. When the user is to record data on the disk, the disk is irradiated with a laser beam along the tracks, and the intensity of the laser beam is modulated in accordance with the data to be recorded so as to form regions with different optical properties (recording marks) on the recording film. In an optical disk, generally, one track corresponding to one rotation of the optical disk is divided into a plurality of sectors as units for recording and reproducing data (data units) so as to manage the positions of necessary data on the optical disk and realize high-speed data retrieval. A read-only optical disk and a rewritable optical disk have different data. formats and modulation codes from each other. In order to allow the user to record data every sector, the data format of the rewritable optical disk requires to have, for example, a region for setting the laser power at the head of a recording region of each sector and a region for absorbing a variation of the rotation of a spindle motor at the end of the recording region. In the case of the read-only optical disk where no data is rewritten by the user, information has been recorded on the optical disk at the production of the optical disk with high precision, and no extra region for data recording by the user is required. Figure 5 shows a conventional optical disk 301 having a rewritable area and a read-only area. The optical disk 301 has a recording film formed on a disk substrate so that the user can record and reproduce data on and from the optical disk. Referring to Figure 5, the optical disk 301 includes read-only areas 302 and 303 located on the outer and inner portions thereof, respectively, and a rewritable area 305 located between the read-only areas 302 and 303 . In the read-only areas 302 and 303 , information and data have been previously recorded by forming physical concave and convex shaped pit arrays 304 . In the rewritable area 305 , groove-shaped guide tracks 306 have been previously formed so that the user can record and reproduce information and data by tracking the grooves of the tracks (groove tracks) or lands between adjacent grooves (land tracks). Figure 6 is a block diagram showing a conventional optical disk recording/reproducing apparatus 300 for recording/reproducing data on/from the optical disk 301 shown in Figure 5. Referring to Figure 6, the optical disk recording/reproducing apparatus 300 includes an optical head 307 for recording or reproducing data, a first signal processing section 320 for processing a reproduced signal supplied from the rewritable area 305 , a second signal processing section 330 for processing a reproduced signal supplied from the read-only areas 302 and 303 , and a switch 308 for connecting the reproduced signal from the optical head 307 to either the first signal processing section 320 or the second signal processing section 330 . The first signal processing section 320 includes a first digitizing circuit 309 , a first PLL (phase-locked loop) 310 , a first timing generation circuit 311 , and a first demodulator 312 . Likewise, the second signal processing section 330 includes a second digitizing circuit 313 , a second PLL 314 , a second timing generation circuit 315 , and a second demodulator 316. When data recorded on the rewritable area 305 is to be reproduced, the switch 308 is switched to a terminal A to be connected with the first signal processing section 320 . The reproduced signal is first converted into a digital signal by the first digitizing circuit 309 , and clocked by the first PLL 310. The first timing generation circuit 311 generates a gate signal for reading user data, and the user data is demodulated into binary data by the first demodulator 312. The demodulated data is output from a first output terminal 317 . In a conventional optical disk 301 , different data formats and modulation codes are used in the rewritable area 305 and the read-only areas 302 and 303 as described above. Accordingly, the second signal processing section 330 for the read-only areas is separately required when data recorded on the read-only area 302 or 303 is to be reproduced. When data on the read-only area 302 or 303 is to be reproduced, therefore, the switch 308 is switched to a terminal B to be connected with the second signal processing section 330. As in the first signal processing section 320 described above, the reproduced signal is first converted into a digital signal by the second digitizing circuit 313, and clocked by the second PLL 314 . Then, the second timing generation circuit 315 generates a gate signal for reading user data, and the user data is demodulated into binary data by the second demodulator 316 . The demodulated data is output from a second output terminal 318. Figure 7 schematically illustrates a data format of a sector 400 on the conventional rewritable optical disk 301 . Referring to Figure 7, the sector 400 includes a sector identification, data region 401 at the head thereof, followed by a gap region 402 , a VFO region 403 , an information data region 450 , and a buffer region 409 in this order. The sector identification data region 401 stores address information and the like for management of the sector. The gap region 402 absorbs signal disturbance at the start of data recording and sets a laser power for recording. Data stored in the information data region 450 is divided into a plurality of data blocks 405a, 405b, ... with data synchronous series 404a, 404b, ... prefixed to the respective data blocks. Each of the data synchronous series 404 (404a, 404b, ...) stores a specific code pattern which does not appear in data in the other regions obtained by modulating with a recording code. The VFO region 403 stores a repetition pattern of codes with a single period to stabilize the clocking at the reproduction. The VFO region 403 stores a repetition pattern of codes with a single period to stabilize the clocking at the reproduction. The buffer region 409 absorbs a variation of the rotation at the end of recording. Using the data format with the above configuration, the reproduction is conducted in the following manner. First, the clocking at the PLL circuit is stabilized by the repetition pattern stored in the VFO region 403. After the clock has been sufficiently stabilized, the data synchronous series 404a is detected and recognized to be the head of the information data region 450 . Upon recognition, the first data block 405a is reproduced. Subsequently, the next data synchronous series 404b is detected to reproduce the next data block 405b. By repeating this operation, the data on the information data region 450 can be stably reproduced. With the data synchronous series 404 prefixed to the respective data blocks 405 , even if the data reproduction at one data block becomes out of synchronization due to an error such as dropout, the synchronization can be resumed from the next data block, allowing the data reproduction to be continued. In the conventional optical disk, however, the data formats and modulation codes used in the rewritable area and the read-only area are different from each other as described above. The conventional recording/reproducing apparatus for such an optical disk needs to have two separate signal processing circuits for the rewritable area and the read-only areas, which complicates and enlarges the circuit size of the apparatus. DISCLOSURE OF THE INVENTION In view of the above-described problem, the object of the present invention is to provide an optical disk having a rewritable area and a read-only area and capable of reducing the circuit size of a recording/reproducing apparatus using the optical disk and providing stable reproduction and tracking. Another object of the present invention is to provide an optical disk which is easier to manufacture by using a single light source for cutting. Thus, the present invention concerns an optical disk as well as a corresponding reproduction apparatus as defined in the appended claims. Thus, the invention described herein makes possible the advantage of providing an optical disk having a rewritable area and a read-only area which can reduce the circuit size of a recording/reproducing apparatus using the optical disk and provide stable reproduction. These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a view illustrating an exemplary arrangement of a rewritable area and read-only areas of an optical disk according to the present invention. Figures 2A to 2H are views illustrating data formats and reproduced signals used in an optical disk of one example according to the present invention. Figure 3 is a view illustrating a reproduced signal processing section for reproducing data from the optical disk according to the present invention. Figures 4A to 4H are views illustrating data formats and reproduced signals used in another optical disk according to the present invention. Figure 5 illustrates a conventional optical disk. Figure 6 is a view illustrating a reproduced signal processing circuit for reproducing data from the conventional optical disk. Figure 7 is a view illustrating a data format of the conventional optical disk. BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described by way of example with reference to the relevant drawings. (Example 1) An optical disk of this example has a recording film formed on a disk substrate so as to allow the user to record and reproduce data on and from the optical disk. Referring to Figure 1 , an optical disk 1 of this example includes read-only areas 2 and 3 located on the outer and inner portions thereof, respectively, and a rewritable area 5 located between the read-only areas 2 and 3 . In the read-only areas 2 and 3 , concave and convex shaped pit rows physically formed in a spiral or concentric shape form tracks. The length and position of each pit in the pit rows have been determined in accordance with read-only data recorded on the read-only areas 2 and 3 . In the rewritable area 5 , guide grooves (guide tracks) 6 are formed in a spiral or concentric shape on a disk substrate. Information and data are recorded along groove tracks which are groove portions of the guide grooves or land tracks between adjacent grooves. Hereinbelow, the groove tracks and the land tracks are collectively referred to as information tracks. In Figure 1 , spiral tracks are shown on either area. Each of the information tracks in the rewritable area 5 is divided into a plurality of sectors. Each sector includes a first header region having identification data for identifying the sector and a first data region for storing user data by forming recording marks by changing the optical properties of the recording film. Likewise, each track in the read-only areas 2 and 3 is divided into a plurality of sectors. Each sector includes a second header region having identification data for identifying the sector and a second data region having read-only data recorded thereon in the form of the pit rows. In this way, by dividing each track corresponding to one rotation of the optical disk into a plurality of sectors (data units), management of the positions of necessary data on the optical disk and high-speed data retrieval can be realized. Figures 2A to 2H are views illustrating data formats of the optical disk 1 of this example. A data format in the rewritable area 5 will be first described. Figure 2A shows an exemplary data format of each sector 10 in the rewritable area 5 , and Figure 2C shows a corresponding physical configuration of the information track. Figure 2A shows data formats of two information tracks in correspondence with their physical configuration for comparison with Figure 2C. As shown in Figure 2A, the groove portion of the guide track 6 corresponds to the groove track 7 , while the inter-groove portion corresponds to the land track 8 . Accordingly, the groove track 7 and the land track 8 alternately appear in the rewritable area 5 of the optical disk 1 . The user can record desired information (user data) on both the groove track 7 and the land track 8 by tracking the groove track 7 and the land track 8 separately. Referring to Figure 2A , the sector 10 includes a first header region 11 (sector identification data PID1 and PID2) and an information region 20. A mirror mark 12 (M) and a gap region 13 (GAPa and GAPb) are formed between the first header region 11 and the information region 20. The information region 20 includes a first dummy data region 15 (VFO region (VFOa and VFOb)), a first data region 17 (DATAa and DATAb), and a guard data region 18 (GDa and GDb) as will be described later in detail. A buffer region 19 (BUFa and BUFb) is formed between the information region 20 and a first header region 11' of a next sector 10'. The affix a of the above abbreviated codes (e.g., VFOa and DATAa) indicates that the regions are formed on the groove track 7 , while the affix b (e.g., VFOb and DATAb) indicates that the regions are formed on the land track 8 . This is also applicable in the following description unless otherwise specified. Referring to Figure 2C , the first header region 11 includes a physically formed concave and convex shaped pit row 21 ( 21a and 21b ). The width of each pit of the pit row 21 in the radial direction of the optical disk is substantially equal to the width of the guide groove 6 (groove track 7 ). The pit rows 21a and 21b are displaced outward and inward from the center line of the guide groove 6 , i.e., wobbled, by about a quarter of the pitch of the guide groove 6 (i.e., groove pitch Tp). In this example, the first header region 11 is divided into a former half lla and a latter half 11b . The pit row 21a corresponding to the former half 11a is displaced outward to the periphery of the optical disk 1 , while the pit row 21b corresponding to the latter half 11b is displaced inward. With this displacement of the pit rows 21a and 21b from the center line of the guide groove 6 (groove track 7 ), the first header region 11 can be commonly used for servo tracking of both the groove track 7 and the land track 8 . Thus, separate exclusive header regions for the groove track 7 and the land track 8 are not required. If exclusive header regions are required for the groove track 7 and the land track 8 , a technique of forming pit rows with a width smaller than the width of the guide groove 6 so that the respective pit rows on the groove track 7 and the land track 8 do not overlap each other. Such a narrow pit may be formed by using a light beam different from a light beam for cutting the guide groove 6 . It is difficult, however, to keep stable the positional precision between the two beams. In this example, a light beam for cutting the guide groove 6 is wobbled rightward and leftward from the center line of the guide groove 6 (groove track 7 ) using an AO modulator and the like so as to form the first header region 11 (the pit row 21 ) on the optical disk 1 easily with high precision without using another beam for cutting. The mirror mark region 12 following the header region 11 is used to determine which track, the groove track 7 or the land track 8 , is being tracked. The gap region 13 (13a and 13b) is formed on the groove track (13a) and the land track (13b) to avoid a head 14 of the information region 20 from overlapping the mirror mark region 12 or the first header region 11 when a jitter occurs due to the rotation of the optical disk 1 . The information region 20 is a region where the user can record desired data and includes the first dummy data region 15 (VFOa and VFOb), the first data region 17 (DATAa and DATAb), and the guard data region 18 (GDa and GDb) as described above (see Figure 2A ). Information is recorded on the information region 20 by irradiating the recording film formed on the optical disk 1 with a laser beam to change the optical properties (reflectance) of the recording film. For example, an irradiated portion of the recording film may be changed from a crystalline state to an amorphous state so as to form a recording mark with a reflectance different from the other portions. As shown in Figure 2C , a recording mark array 22a is formed on the groove track 7 , while a recording mark array 22b is formed on the land track 8 . The first dummy data region 15 is a VFO region where a specific pattern is recorded so as to promptly stabilize the clocking of the PLL of the circuit for processing the reproduced signal from the optical disk 1 . More specifically, a specific pattern (a specific bit length) of modulation codes used for data modulation is sequentially recorded on the dummy data region 15. Desired user data including an error correction code is recorded on the first data region 17. The guard data region 18 is formed at the end of the first data region 17 to ensure the stability of the reproduced signal processing circuit. The buffer region 19 includes no data but is formed to avoid the end of the information region 20 from overlapping the header region 11' of the next sector 10' when a jitter occurs due to the rotation of the optical disk 1 , as in the case of the gap region 13 . Thus, in the rewritable area 5 , data is recorded on the groove track 7 and the land track 8 in accordance with the data formats described above. Then, a data format in the read-only areas 2 and 3 will be described with reference to Figures 2B and 2D. Figure 2B shows an exemplary data format of each sector 10 of the read-only areas 2 and 3 , and Figure 2D schematically illustrates a physical configuration of the track corresponding pit array. In the read-only areas 2 and 3 , a track 9 is composed of a pre-recorded pit row 29 (a pre-pit row). As shown in Figure 2D , the pit rows are formed in accordance with the same physical format over the entire data region in the read-only areas 2 and 3 . More specifically, the width of the pit row 29 in the radial direction of the optical disk 1 (pit width) is smaller than the width (groove width) of the guide groove 6 (groove track 7 ) formed in the rewritable area 5 , and all the pits are lined substantially along the center line of the track. Like the rewritable area 5 , each track in the read-only areas 2 and 3 is divided into a plurality of sectors 30 for data recording so as to manage the positions of necessary information data on the optical disk and realize high-speed data retrieval. It will be preferable at practical information recording/reproduction if the sectors in the read-only areas 2 and 3 and the rewritable area 5 can be managed in a same manner and the processing such as sector retrieval are unified. To realize this unified processing, in this example, the length of each sector and the lengths of the header region and the data region of each sector in the read-only area 2 and 3 are made equal to the length of each sector and the lengths of the header region and the data region of each sector in the rewritable area 5 , to match the data format in the read-only area with the data format in the rewritable area. A specific data format in the read-only areas 2 and 3 will be described as an example. Referring to Figure 2B , the sector 30 includes a second header region 31 (sector identification data PID1 and PID2) and a second data region 37 . A second dummy data region 35 (VFO1) is formed between the second header region 31 and the second data region 37. A third dummy data region 38 (VFO2) is formed between the second data region 37 and a second header region 31' of a next sector 30'. Referring to Figure 2D , the pit row 29 of the second header region 31 is lined substantially along the center line of the track 9 , not displaced outward or inward as in the first header region 11 in the rewritable area 5 . The width of the pit row 29 in the read-only areas 2 or 3 (the pit width in the radial direction of the optical disk 1 ) is smaller than the groove width unlike the width of the pit row 21 in the rewritable area 5 which is substantially equal to the groove width. In the second data region 37 , also, the concave and convex shaped pit row has been previously formed substantially along the center line of the track 9 on the optical disk 1 in accordance with the data for recording. As is observed from Figures 2A and 2B , the first header region 11 in the rewritable area 5 and the second header region 31 in the read-only areas 2 and 3 are the same in the data capacity, the data format (signal sequence), and the modulation codes. Also, the first data region 17 in the rewritable area 5 and the second data region 37 in the read-only areas 2 and 3 are the same in the data capacity, the data format (signal sequence), and the modulation codes. Further, as shown in Figures 2A and 2B , a head (start timing) 16 of the first data region 17 in the rewritable area 5 and a head (start timing) 36 in the second data region 37 in the read-only areas 2 and 3 are matched with each other. Thus, by using the same formats (signal sequences) for the first and second header regions 11 and 31 and for the first and second data regions 17 and 37 in the rewritable area 5 and the read-only areas 2 and 3 , one reproduced signal processing circuit can be shared by both types of areas, and thus the circuit size can be reduced. The second dummy data region 35 is formed to prevent the servo tracking from becoming unstable due to discontinuation of tracking error signals which may occur if no pit row is formed between the second header region 31 and the second data region 37 . The second dummy data region 35 includes, for example, a specific data pattern of the same modulation code as that used for the first dummy data region (VFO region) 15 in the rewritable area 5 . With this arrangement, it is possible to promptly and stably clock the PLL of the reproduced signal processing circuit. Random data or any other data may also be used to stabilize the servo tracking. The third dummy data region 38 is formed to prevent the servo tracking from becoming unstable due to discontinuation of tracking error signals, as in the second dummy data region 35. As described above, in the read-only areas 2 and 3 , the pit rows both in the second header region 31 and the second data region 37 are lined substantially along the center line of the track 9 . Further, the second and third dummy data regions 35 and 38 fill the space between the second header region 31 and the second data region 37 of the sector 30 and the space between the second data region 37 of the sector 30 and the second header region 31' of the next sector 30'. As a result, the physical arrangement of the pit row 29 is uniform along the track over the entire read-only areas 2 and 3 . Thus, according to the data format of the optical disk 1 of this example, the first header region 11 is commonly used for the tracking of both of the groove track 7 and the land track 8 . Thus, separate exclusive header regions for the groove track 7 and the land track 8 are not required. Since the first header region 11 can be easily and precisely formed on the optical disk by wobbling a light beam for cutting the guide groove 6 (groove track 7 ) rightward and leftward from the track center, a separate exclusive light source for forming the first header region is not required. Thus, the preformat in the rewritable area 5 of the optical disk 1 of this example can be easily formed by use of a single light source for cutting, reducing the circuit size of the recording/reproducing apparatus for this optical disk 1 . Figure 3 is a block diagram schematically showing a reproduced signal processing section of an optical disk recording/reproducing apparatus 100 for recording/reproducing data on/from the optical disk 1 of this example having the above-described data format. Referring to Figure 3 , the reproduced signal processing section of the optical disk recording/reproducing apparatus 100 includes a 2-part optical detector 110 , a summing amplifier 111 , a differential amplifier 112 , a switch circuit 113 , a digitizing circuit 114 , a PLL (phase-locked loop) 115 , a PID generation circuit 116 , a timing generation circuit 117 , a demodulator 118 , and an envelope detection circuit 120 . The 2-part optical detection circuit 110 ( 110a and 110b ) which is disposed in an optical head (not shown) receives reflected light from the groove track 7 and the land track 8 (the recording mark arrays 22 and the pit rows 21 ) in the rewritable area 5 of the optical disk 1 and reflected light from the track 9 (the pit row 29 ) in the read-only areas 2 and 3 , and converts the reflected light into a reproduced signal. The summing amplifier 111 generates a sum signal S1 indicating the sum of two detection signals obtained from the two parts 110a and 110b of the 2-part optical detection circuit 110 to supply to the switch circuit 113 . The differential amplifier 112 generates a difference signal S2 representing the difference between the two detection signals to supply to the envelope detection circuit 120. The switch circuit 113 switches between the sum signal S1 and the difference signal S2 to supply either signal to the digitizing circuit 114 . The envelope detection circuit 120 detects an envelope in the difference signal S2. When an amplitude exceeding a predetermined threshold is observed in the difference signal S2 , a control signal S3 is supplied to the switch circuit 113 to force the switch circuit 113 to switch to output the difference signal S2 as an output signal S4 . In the case of using the data formats shown in Figures 2A to 2D , the difference signal S2 is obtained only when the reproduced signal is obtained from the first header region 11 in the rewritable area 5 , as will be described later in detail. Accordingly, the control signal S3 output from the envelope detection circuit 120 becomes high only when the first header region 11 in the rewritable area 5 is detected (Figure 2E ). The output signal S4 from the switch circuit 113 is therefore equal to the difference signal S2 only in the first header region 11 . The output signal S4 from the switch circuit 113 is equal to the sum signal S1 in the information region 20 in the rewritable area 5 and the entire read-only areas 2 and 3 . The output signal S4 from the switch circuit 113 (the sum signal S1 or the difference signal S2 ) is digitized by the digitizing circuit 114 into a binary signal. For example, the digitizing circuit 114 digitizes the signal S4 in accordance with a threshold set for each of the sum signal S1 and the difference signal S2, and outputs a digital signal S5 to the PLL 115 . The PLL 115 extracts a reproduction clock from the digital signal S5 and outputs the reproduction clock to the PID generation circuit 116 which reproduces a sector identification signal from the header region. The timing generation circuit 117 determines the start timing (the head 16 of the recording data shown in Figure 2A and the head 36 of the recording data shown in Figure 2B ) for reading the user data recorded on the data regions 17 and 37 based on the sector identification signal from the PID generation circuit 116 , to initiate the demodulator 118 by supplying a control signal S6 . The demodulator 118 demodulates the user data and outputs the results. Hereinbelow, the waveforms of the signals obtained when recorded data on the information track in the rewritable area 5 (i.e., user data prerecorded on the information region 20 ) is reproduced until it is converted into a binary signal will be described. Figure 2G is an output waveform of the sum signal S1 obtained from the rewritable area 5 , and Figure 2F is an output waveform of the difference signal S2 . As shown in Figure 2G , the portion of the sum signal S1 corresponding to the first header region 11 in the rewritable area 5 is not detected by the digitizing circuit 114 because an amplitude 41 thereof is smaller than a predetermined threshold 40 for digitizing. The reason why the amplitude is small is that the pit row of the first header region 11 is slightly displaced outward (11a) or inward (11b) from the center line of the groove track. This causes light (a light beam from the optical head) to be diffracted by the pit rows 21a and 21b and thus reduces the light amount received by the optical detection circuit 110. On the contrary, an amplitude 42 of the sum signal S1 corresponding to the information region 20 where data has been recorded exceeds the threshold 40 for digitizing because the recording mark 22 is formed along the center line of the information track. The sum signal is therefore detected by the digitizing circuit 114 , and the reproduced signal is obtained. Figure 2F shows an output of the difference signal S2 obtained from the rewritable area 5 . Since the pit row 21a in the region 11a of the first header region 11 in the rewritable area 5 is displaced outward, a larger amount of reflected light is diffracted to the outward part 110a of the 2-part optical detection circuit 110. Accordingly, the difference signal S2 output from the 2-part optical detection circuit 110 has an amplitude 51a which exceeds a positive threshold 50a for digitizing as shown in Figure 2F. The difference signal is therefore detected by the digitizing circuit 114 , and the reproduced signal is obtained. Likewise, since the pit row 21b in the region 11b of the first header region 11 is displaced inward, a larger amount of reflected light is diffracted to the inward part 110b of the 2-part optical detection circuit 110. Accordingly, the difference signal S2 output from the 2-part optical detection circuit 110 has an amplitude 51b which exceeds a negative threshold 50b for digitizing as shown in Figure 2F. The difference signal S2 is therefore detected by the digitizing circuit 114 , and the reproduced signal is obtained. On the contrary, in the information region 20 in the rewritable area 5 , since the recording mark array 22 is formed along the center line of the information track, the light amounts received by the outward and inward parts 110a and 110b of the 2-part optical detection circuit 110 are substantially the same. Therefore, an amplitude 52 of the difference signal S2 is too small to reach the threshold 51a (51b) for digitizing as shown in Figure 2F. Likewise, in the read-only areas 2 and 3 , since the pit row 29 is formed along the center line of the track 9 , the light amounts received by the outward and inward parts 110a and 110b of the 2-part optical detection circuit 110 are substantially the same. The difference signal S2 is substantially not output. Therefore, in the regions other than the first header region 11 , the difference signal S2 is not detected by digitizing, and thus no reproduced signal is obtained. Figure 2H shows an output waveform of the sum signal S1 obtained from the read-only areas 2 and 3 . Referring to Figure 2H , since the pit row 29 is formed along the center line of the track 9 for servo tracking in the read-only areas 2 and 3 , the sum signal S1 has an amplitude 43 sufficiently large to be detected by digitizing. Therefore, signals from all the regions in the reproduction-only areas 2 and 3 including the second header region 31 and the second data region 37 can be converted into binary signals by use of the sum signal S1 . It is not necessary, therefore, to switch the switch circuit 113 for the read-only areas 2 and 3 . Thus, in the optical disk recording/reproducing apparatus 100 for reproducing information from the optical disk 1 with the above-described data formats, unlike the conventional apparatus, separate reproduced signal processing circuits for the rewritable area and the reproduction-only area are not required, but a common signal processing section can be used. This reduces the circuit size of the optical disk recording/reproducing apparatus, and realizes a reproduced signal processing circuit with a simpler circuit configuration and higher reliability. (Example 2) Figures 4A to 4H show data formats of an optical disk of Example 2 according to the present invention. The basic configuration of the optical disk of this example is the same as that of the optical disk 1 of Example 1. The same components are denoted by the same reference numerals, and the description thereof is omitted here. In this example, also, one track corresponding to one rotation of the optical disk is divided into a plurality of sectors. Each sector starts with a header region including sector identification data representing address information of the sector. In this example, the data format in the read-only area will mainly be described. Figure 4A is an exemplary data format of each sector 10 in the rewritable area 5 , and Figure 4C shows a corresponding physical configuration. As shown in Figure 4C , the groove portion of the groove-shaped guide track 6 constitutes the groove track 7 , and the inter-groove portion constitutes the land track 8 . Such groove tracks 7 and land tracks 8 alternately appear in the rewritable area 5 of the optical disk 1 . The user can record desired information (user data) on both the groove track 7 and the land track 8 by tracking the groove track 7 and the land track 8 separately. In this example, as shown in Figure 4A , the groove track 7 and the land track 8 are described collectively as an information track 6' . The sector 10 in the rewritable area 5 includes the first header region 11 at the head thereof. The first header region 11 is divided into the former half 11a (sector identification data PID1) and the latter half 11b (sector identification data PID2). The physical concave and convex shaped pit rows 21a and 21b are formed in correspondence with the former half 11a and the latter half 11b, respectively (Figure 4C). As shown in Figure 4C , the width of each pit of the pit rows 21a and 21b in the radial direction of the disk is substantially equal to the width of the guide groove 6 (groove track 7 ). The pit rows 21 are displaced (wobbled) outward or inward (i.e., in the opposite directions) from the center line of the guide groove 6 by about a quarter of the pitch of the guide groove 6 (groove pitch Tp). In this example, the pit row 21a is displaced inward, while the pit row 21b is displaced outward. Thus, by displacing the pit rows 21a and 21b from the center line of the guide groove 6 (the groove track 7 ), the first header region 11 is commonly used to track either of the groove track 7 and the land track 8 . Accordingly, separate exclusive header regions for the groove track 7 and the land track 8 are not required. Referring to Figure 4A , the mirror region 12 (M) follows the first header region 11 . The mirror region 12 is flat with no groove or pit formed thereon and used to determine an offset of the servo tracking. The gap region 13 (GAP) follows the mirror region 12 . The gap region 13 (GAP) is formed on the information track 6' to avoid a head 24 of the information region 20 from overlapping the mirror region 12 or the first header region 11 when a jitter occurs due to the rotation of the optical disk 1 . The information region 20 which stores information and data includes a first guard data region 23 (GD1), the first dummy data region 15 (VFO), the first data region 17 (DATA), and a second guard data region 18 (GD2). The buffer region 19 (BUF) is formed between the information region 20 and the first header region 11' of the next sector 10'. The first guard data region 23 is formed to ensure the stability of the reproduced signal processing circuit. The first dummy data region 15 (VFO) is a VFO region where a specific pattern (a specific bit length) of the modulation code used for modulation of data is sequentially recorded to promptly and stably clock the PLL of the reproduced signal processing circuit. Desired user data including an error correction code is recorded on the first data region 17. The second guard data region 18 is formed following the first data region 17 to ensure the stability of the production signal processing circuit. The buffer region 19 which includes no data is formed to avoid the end of the information region 20 from overlapping the header region 11' of the next sector 10' when a jitter occurs due to the rotation of the optical disk 1 , like the gap region 13 . Information is recorded on the information region 20 by irradiating the recording film formed on the disk substrate of the optical disk 1 to change the optical properties (reflectance) of the recording film. For example, an irradiated portion of the recording film may be changed from a crystalline state to an amorphous state so as to form a recording mark with a reflectance different from that of the other portions. As shown in Figure 4C , the recording mark array 22a is formed on the groove track 7 , while the recording mark array 22b is formed on the land track 8 . Thus, in the respective regions of the rewritable area 5 , the groove track 7 and the land track 8 are formed in accordance with the above-described data format to record data in the area. Referring to Figures 4B and 4D , a data format in the read-only areas 2 and 3 will be described. In this example, as in Example 1, the data format in the read-only areas is matched with the data format in the rewritable area. Figure 4B shows an exemplary data format of each sector 30 in the read-only areas 2 and 3 , and Figure 4D schematically shows a corresponding physical configuration of the track composed of the pit row. In the read-only areas 2 and 3 , the track 9 is composed of the pre-recorded pit row (pre-pit). As shown in Figure 4D , all the pit rows in the read-only areas 2 and 3 are formed in accordance with a uniform physical format as in Example 1 . More specifically, the width (pit width) of the pit row 29 in the radial direction of the optical disk 1 is smaller than the width (groove width) of the guide groove 6 (groove track 7 ) formed in the rewritable area 5 , and all the pits are lined substantially along the center line of the track for servo tracking. Referring to Figure 4B , the sector 30 in the read-only areas 2 and 3 includes the second header region 31 (sector identification data PID1 and PID2) and the second data region 37 (DATA). A second dummy data region 33 (DMyl) is formed between the second header region 31 and the second data region 37. A third dummy data region 34 (DMY2) is formed between the second data region 37 and the second header region 31' of the next sector 30' . The sector identification data PID1 and PID2 of the second header region 31 are repeatedly recorded on the former half and the latter half of the second header region 31, respectively, in compliance with the sector identification data PID1 and PID2 of the first header region 11 , so that the length of the second header region 31 becomes substantially the same as that of the first header region 11 . However, the concave and convex shaped pit row of the second header region is not wobbled as the pit rows 21a and 21b of the first header region 11 , but is lined substantially along the center line of the track 9 for servo tracking. The information amount recorded on the second data region 37 of one sector 30 is made equal to that recorded on one sector 10 in the rewritable area 5 , and the same format as that in the rewritable area 5 is used for an additional error correction code and the like. With this arrangement the length of the second data region is substantially the same as that of the first data region 17 . In general, data recording in the read-only area by embossing can be performed with high precision at the fabrication of the disk. In the read-only area, data is only reproduced and no arrangement to respond to rewriting by the user is required. Therefore, regions such as the gap region 13 , the first guard data region 23, the second guard data region 18, and the buffer region 19 formed in the rewritable area are not required in the read-only area. These regions should be deleted if the recording capacity of the optical disk is considered with priority. However, if these regions are deleted, the data format in the read-only area becomes different from that in the rewritable area. This requires to provide two separate exclusive signal processing sections each including a timing generation circuit and a demodulator for the read-only area or the rewritable area, and switch the two processing sections appropriately, as in the conventional apparatus described above. If regions corresponding to the gap region 13, the first guard data region 23, the second guard data region 18 , and the buffer region 19 in the rewritable area 5 are formed in the read-only area so as to synchronize the reproduction timing and no pit row is formed in these regions, the tracking error signal is discontinued at these regions, making the servo tracking in the read-only area unstable. In order to overcome the above problems, in this example, the second dummy data region 33 is formed between the header region 31 and the data region 37 of each sector 30, and the third dummy region 34 is formed between the data region 37 and the header region 31' of the next sector 30'. A specific pattern of the modulation code used for modulation of data (a pattern of a specific bit length corresponding to a specific pulse width and pulse interval) as in the first dummy data region 15 (VFO) in the rewritable area 5 , for example, can be sequentially recorded on the second and third dummy data regions 33 and 34. Using such a specific pattern, prompt and stable clocking of the PLL of the reproduced signal processing circuit can be realized. A mirror region may be formed between the header region 31 and the second dummy region 33 as in the rewritable area. When data recorded on the optical disk of this example is to be reproduced, the same procedure as that described in Example 1 with the optical disk recording/reproducing apparatus 100 shown in Figure 3 can be employed. In this case, the waveforms of the envelope detection signal, the difference signal obtained from the rewritable area, the sum signal obtained from the rewritable area, and the sum signal obtained from the read-only area are as shown in Figures 4E to 4H , respectively. Thus, in this example, the sector lengths and main portions of the data formats of the rewritable area and the read-only areas are made substantially equal to each other. With this arrangement, the sectors in the read-only areas and the rewritable area can be managed in the same manner, and the processing such as sector retrieval can be unified. Thus, one reproduced signal processing circuit can be commonly used for the rewritable area and the read-only areas. This reduces the circuit size. In this example, the first data region 17 in the rewritable area and the second data region 37 in the read-only area are arranged to start at the same timing as shown in Figures 4A and 4B. The unified sector management according to the present invention can also be realized in the case where these data regions are displaced with each other as long as they have the same length. INDUSTRIAL APPLICABILITY Thus, according to the optical disk of the present invention, the sector identification data of the first header region is reproduced when either of the groove track and the land track is traced. This eliminates the necessity of providing an exclusive header region for each of the groove track and the land track. Regarding the preformat of the rewritable area, the first header region can be formed on the optical disk easily with high precision by wobbling a light beam for cutting and forming guide grooves (groove tracks) outward and inward from the center line of the groove tracks. This eliminates the necessity of providing an additional exclusive light source for forming the header region in the rewritable area. Thus, according to the optical disk of the present invention, the preformat of the rewritable area can be easily formed with high precision using a single light source for cutting. This makes it possible to form the preformat using a conventional cutting machine when both the rewritable area and the read-only area are formed on one optical disk. According to the present invention, the sector length, the length of the header region, and the length of the data region in each sector in the read-only area are made equal to the sector length, the length of the header region, and the length of the data region in each sector in the rewritable area. As a result, the data format of the read-only area matches the data format of the rewritable area. This makes it possible to unify the sector managements of the read-only area and the rewritable area so as to unify the processing such as sector retrieval. According to the present invention, there are provided the dummy data regions preceding and following the information data region in the read-only area. With this arrangement, the sector length, the length of the header region, and the length of data to be recorded on the sector in the read-only area can be made substantially equal to the sector length, the length of the header region, and the length of data to be recorded on the sector in the rewritable area. This makes it possible to unify the sector managements of the read-only area and the rewritable area so as to unify the signal processing such as sector retrieval. According to the optical disk of the present invention, separate reproduced signal processing circuits for the rewritable area and the read-only area are not necessary but one reproduced signal processing circuit can be shared when the rewritable area and the read-only area are formed on one optical disk. This makes it possible to reduce the circuit size of an optical disk recording/reproducing apparatus. Thus, a reproduced signal processing circuit with a simpler circuit configuration and higher reliability can be realized.

Claims: An optical disk (1) having a rewritable first recording area and a read-only second recording area, wherein the first recording area (5) has spiral or concentric first tracks (6) in which groove tracks (7), which are groove portions, and land tracks (8), which are inter-groove portions, are alternately provided, each of the first tracks being divided into a plurality of first sectors (10), and each of the plurality of first sectors (10) including a first header region (11) having sector identification data (PID1, PID2) for identifying the first sector and a first data region (17) for recording user data, the second recording area (2, 3) has spiral or concentric second tracks (9) in which physical concave and convex shaped pit rows (29) are provided, each of the second tracks (9) being divided into a plurality of second sectors (30), and each of the plurality of second sectors (30) including a second data region (37) where read-only data is recorded, characterised in that the first header region (11) includes, as the sector identification data, a physical concave and convex shaped first pit row (21a) and a physical concave and convex shaped second pit row (21b), each of the first pit row and the second pit row having a width in a radial direction of the optical disk substantially equal to the width of the groove track (7), the first pit row (21a) being formed at a position shifted towards the outer periphery of the optical disk from the centre line of the groove track (7) by about a quarter of a pitch of the groove track, and the second pit row (21b) being formed at a position shifted towards the inner periphery of the optical disk from the centre line of the groove track (7) by about a quarter of a pitch of the groove track. An optical disk according to claim 1, wherein the data recorded In the first data region (17) and the read-only data recorded in the second data region (37) are modulated with a same modulation code. An optical disk according to claim 1. wherein the first data region (17) and the second data region (37) have a same data capacity and a same data format. An optical disk according to claim 1. wherein a data bit Interval In the first data region (17) is substantially equal to a data bit interval In the second data region (37). An optical disk according to any one of claims 1 to 4, wherein each of the plurality of first sectors (10) further includes: a mirror mark region (12). a gap region (13) and a firet dummy data region (15) which are provided between the first header region (11) and the first data region (17); and a guard data region (18) and a buffer region (19) which are provided between the first data region (17) and a header region (11) of a next first sector. An optical disk according to claim 5. wherein the first dummy data region (15) has a specific sequence pattern of a modulation code used for modulation of data to be recorded.

Inventors: DEGUCHI HIRONORI, GUSHIMA TOYOJI, ISHIDA TAKASHI, KOISHI KENJI, MITUI YOSHITAKA, OHARA SHUNJI, SATOH ISAO, TAKEMURA YOSHINARI, DEGUCHI, HIRONORI, GUSHIMA, TOYOJI, ISHIDA, TAKASHI, KOISHI, KENJI, MITUI, YOSHITAKA, OHARA, SHUNJI, SATOH, ISAO, TAKEMURA, YOSHINARI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1997
Main classification: G11B7
IPC codes: G11B27, G11B7, G11B20