Method and apparatus for recording and reproducing data on and from optical disk

Abstract: A method and apparatus for recording and reproducing data on and from an optical disk. Data is recorded on an optical disk exhibiting a difference in an optical absorption rate between wavelengths by a light beam having a wavelength of a first standard. The data recorded on the optical disk is reproduced by a light beam having a wavelength of a second standard.

Description: The present invention relates to a method and apparatus for recording and reproducing data on and from an optical information recording medium, and in particular, to a method and apparatus for recording and reproducing data by irradiating a light beam to an optical disk having a wavelength characteristic. Optical information recording media such as an optical disk have widely been used to record and reproduce various information as well as audio and video. Generally, optical disks may be classified into a read-only type disk, a recordable or write-once type disk, a rewritable or overwritable type disk, etc. The read-only type disk can not write data but can read data. For example, there are a digital audio compact disk (CD-DA), a read only memory compact disk (CD-ROM), and a digital video disk (DVD) which are commercially available. For the recordable or write-once type disk which can write data only once, there are known a recordable compact disk (CD-R) and a recordable digital video disk (DVD-R). The rewritable or overwritable type disk can write data several times by an magneto-optical or phase-change method. As examples, a rewritable compact disk (CD_RW) and a power disk (PD) are commercially available, and a random access memory compact disk (DVD-RAM) is known. Data is recorded and reproduced on and from the optical disk by irradiating a light beam. A laser is used as light, and a semiconductor laser such as a laser diode is used as a light source for generating the laser. In order to record data on the optical disk, an optical output of the light source should be approximately several tens of mW in consideration of the optical efficiency of an optical pickup. Generally, a higher the optical output, allows a faster a recording speed. However, the light source having the optical output higher than such several tens of mW is expensive and generates heat due to a loss of light. Therefore, there is a limit to the light source of a very high output in use. EP-A-0 463 550 and JP-A-5120727 disclose optical recording media having a large light absorption ratio at light wavelengths shorter than those used for data reproduction from a CD, which enable high speed recording within a short time. EP-A-0 463 550 forms the pre-characterising portion of the claims appended hereto. EP-A-0 789 354 discloses an optical disk device suitable for use with both CD-ROM or DVD-ROM, wherein the amount of light reflected from the optical disk is used to select the amount of laser light output and the frequency of oscillation of the laser light. The CD-R and CD-RW of a CD series are standardized to use the light source having a wavelength of 780 nm which is an infrared wavelength band. Meanwhile, the DVD-ROM, DVD-R and DVD-RAM of a DVD series are standardized to use the light source having a wavelength of 635-650 nm which is a red wavelength band. Among theses disks, the CD-R and DVD-R have a wavelength characteristic. Since the material of a recording layer of the CD-R or DVD-R containing a coloring matter, the absorption rate differs according to the waveform band and the reflectance of the disk varies. The characteristic of the reflectance as a function of the wavelength of the CD-R is illustrated in Figure 1. As shown in Figure 1, the recording layer of the CD-R is formed such that the reflectance at the wavelength of 780 nm is 70% or more, and the reflectance at the wavelength of 650 nm is 10% or less. In the CD standard, since the rotating speed of the disk during recording and reproducing is low (about 1.2 m/s), it takes a long time to record and reproduce a large amount of data. This speed problem can be overcome by rotating the disk at high speed during recording. Thus, in a CD-R drive, the speed problem has been solved by rotating the disk at high speed, and the CD-R drive which can record and reproduce 2 or 4 times a reference speed of the CD has been announced. However, as the recording speed increases, the optical output needed to record data, that is a recording optical power, increases as shown in Figure 2 although it varies according to the sensitivity of the recording layer of the disk. The CD-R drive which can record and reproduce data on and from the CD-R uses a high output semiconductor laser having the wavelength of 780 nm. When recording data, the CD-R drive uses the semiconductor laser to produce a high output, and when reproducing data, it uses the semiconductor laser to generate a low output. As noted above, since the optical output needed to record data increases as the recording speed becomes faster, the high output semiconductor laser is more required for high speed recording than low speed recording. However, since the high output semiconductor laser raises the cost of the drive and generates heat, its performance may be degraded. As described previously, since the optical disk such as the CD-R having the wavelength characteristic is used to record and reproduce data at the wavelength of 780 nm of a high reflectance, few problems are encountered in recording and reproducing data in the CD-R drive using the wavelength of 780 nm. However, if the recording optical power increases by speeding up the rotating speed in order to shorten the recording time, there are problems such as the generation of heat and a rise in cost. That is, in the CD-R driver using a single wavelength of 780 nm, there is a limit to the increase in recording speed. It is an object of the present invention to provide a recording/reproducing method and apparatus which can efficiently improve a recording speed for an optical disk having a wavelength characteristic, preferably without generating heat or without raising the cost. It is an aim of at least preferred embodiments of the present invention to provide a recording/reproducing method and apparatus which can record and reproduce data in a CD-R at high speed and also can be applied to a drive using a rewritable optical disk of a DVD series. According to the present invention there is provided an apparatus and method as set forth in the appended claims. Preferred features of the invention will be apparent from the dependent claims, and the description which follows. For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings, in which: Figure 1 is a graph showing the characteristic of an optical reflectance of a general CD-R; Figure 2 is a graph showing a recording optical power as a function of a recording linear velocity when recording data in a general optical disk; Figure 3 is a block diagram of an optical disk data recording and reproducing apparatus according to a preferred embodiment of the present invention; Figure 4 is a flow chart showing a processing procedure of a controller illustrated in Figure 3 when an optical disk is a CD-R type; and Figure 5 is a flow chart showing a processing procedure of a controller illustrated in Figure 3 when an optical disk is a DVD-RW type. In the following description, numerous specific details, such as kinds of an optical disk, wavelengths, etc., are set forth to provide a more thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practised without these specific details. In other instances, well known functions and constructions have not been described so as not to obscure the present invention. In general, if a laser of a red wavelength, 650 nm for example, which is a reference wavelength of the DVD standard is irradiated to the CD-R, the reflectance is lowered to 10% or less, as shown in Figure 1. Hence, the absorption is high and the quantity of light returned from the disk is reduced. If the quantity of reflected light decreases, a signal level is reduced, thus to cause a problem in reproducing data from the CD-R. That is, in a DVD system using light of the red wavelength, the reflectance is very low so that it is difficult to reproduce data from the CD-R. In order to reproduce data from the CD-R, it is essential to use the light source of an infrared wavelength of 780 nm. A DVD-ROM drive utilizes an optical pickup using two wavelengths of 650 nm and 780 nm. When reproducing data from the CD-R, the wavelength of 780 nm is used, and when reproducing data from the DVD, the wavelength of 650 nm is used, thereby reproducing data from the CD-R as well as the DVD. A preferred embodiment of the present invention is applied to an example for reproducing data from the optical disk of a CD series, recording data on the CD-R, and recording and reproducing data on and from a rewritable optical disk of a DVD series. An optical disk data recording and reproducing apparatus of Figure 3 shows the construction in which it is possible to reproduce data from the optical disk of the CD series, record data on the CD-R, and record and reproduce data on and from the rewritable optical disk of the DVD series. In the following description, the rewritable optical disk of the DVD series is called DVD-RW. A first standard is used to designate the DVD standard and a second standard is used to represent the CD standard. In this case, the wavelength of the first standard is 635-650 nm, which is a red wavelength band, typically 650 nm. The wavelength of the second standard is of the order of 780 nm. An optical disk drive basically consists of an optical pickup, a circuit part and a mechanical part. In Figure 3, the mechanical part which is not directly related to the present invention is not shown. In the circuit part, other portions including portions related to a servo are not shown and only a recording/reproducing signal processor 14 and a controller 16 are illustrated. An optical pickup 12 records or reproduces a signal provided from the recording/reproducing signal processor 14 on an optical disk 10 and supplies the recorded or reproduced signal to the recording/reproducing signal processor 14. The recording/reproducing signal processor 14 generates a signal to be recorded through the optical pickup 12 or processes a signal reproduced by the optical pickup 12. The optical pickup 12 includes two light sources, that is, first and second light sources 18 and 20, and one optical system 22. One optical detector 24 is contained in the optical pickup 12. The first and second light sources 18 and 20 each use a semiconductor laser and produce light beams of different wavelengths. In a preferred embodiment of the present invention, the first light source 18 uses the semiconductor laser oscillating a laser of 650 nm of a red wavelength of a high absorption that is, a low reflectance in the CD-R. The second light source 20 uses the semiconductor laser oscillating a laser of 780 nm of a red wavelength of a low absorption rate, that is, a high reflectance in the CD-R. The first light source 18 is a high output light source of about 40 mW which is a rewritable output. The second light source 20 is a low output light source of about 5 mW which can not record data but can reproduce data. The optical system 22 converts lights generated from the first and second light sources 18 and 20 into beams and irradiates the beams to the optical disk 10. The optical system 22 also condenses light reflected from the optical disk 10 and supplies the condensed light to the optical detector 24. The optical disk 10 is an optical disk mounted in an optical disk drive including the recording/reproducing apparatus of Figure 3, and it may be one of optical disks of the CD series including the CD-R, or optical disks of the DVD series including the DVD-RW. In this optical system 22, the light generated from the first light source 18 is converted into a parallel beam by a collimator lens 26 which is suitably designed for the wavelength of 650 nm, and irradiated onto the optical disk 10 via a beam splitter 30 and an object lens 32. The light generated from the second light source 20 is converted into a parallel beam by a collimator lens 28 which is suitably designed for the wavelength of 780 nm, and irradiated to a data recording surface of the optical disk 10 via the beam splitter 30 and the object lens 32. The light beam irradiated to the optical disk 10 is reflected with a difference in the reflection between a recording portion and a non-recording portion of the data recording surface of the optical disk 10. Thus, the light reflected from the optical disk 10 is applied to the optical detector 24 through the object lens 32, the beam splitter 30 and a condenser lens 34. The optical detector 24 detects the light condensed by the optical system 22 and converts the detected light into an electric signal. As this optical detector 24, a photo diode which is a photoelectric conversion element is used. In Figure 3, although the optical pickup 12 has one optical detector 24 and one optical system 32, it may use two optical detectors and two optical systems for use in the CD standard and the DVD standard. Thus, one or two optical detectors and optical systems may be used, like a typical optical disk drive sharing the CD standard and the DVD standard. The recording/reproducing signal processor 14 includes first and second reproducing processors 52 and 54 and first and second processors 36 and 38 which are connected to the optical pickup 12 and to a controller 16. The first processor 36 has a first modulation circuit 40, a first recording waveform generating circuit 42 and a first laser driving circuit 44 and is operated by the control of the controller 16. The first recording processor 36 drives the first light source 18 by data to be recorded on the CD-R, that is, CD recording data according to the second standard, and drives the second light source 20 when reproducing data from the CD-R. The first modulation circuit 36 modulates the CD recording data to a signal of a format to be suitably recorded on the optical disk of the CD series. The first recording waveform generating circuit 42 generates, when recording data on the optical disk 10 by driving the first light source 18, a recording waveform signal corresponding to the signal modulated by the first modulation circuit 40. The first recording waveform generating circuit 42 also generates, when reproducing data from the optical disk 10 by driving the second light source 20, a preset reproducing waveform signal. The first laser driving circuit 44 drives the first light source 18 according to the recording waveform signal provided from the first recording waveform generating circuit 42 and drives the second light source 20 according to the reproducing waveform signal. The second processor 38 has a second modulation circuit 46, a second recording waveform generating circuit 48 and a second laser driving circuit 50 and is operated by the control of the controller 16. The second processor 38 drives the first light source 18 by data to be recorded on the DVD, that is, DVD recording data according to the first standard, and drives the first light source 18 even when reproducing data from the DVD. The second modulation circuit 46 modulates the DVD recording data to a signal of a format to be suitably recorded on the optical disk of the DVD series. The second recording waveform generating circuit 48 generates, when recording data on the optical disk 10 by driving the first light source 18, a recording waveform signal corresponding to the signal modulated by the second modulation circuit 46. The second recording waveform generating circuit 48 also generates, when reproducing data from the optical disk 10 by driving the first light source 18, a preset reproducing waveform signal. The second laser driving circuit 50 drives the first light source 18 according to the recording waveform signal or the reproducing waveform signal provided from the second recording waveform generating circuit 48. The first reproducing processor 52 has a first amplifying circuit 56 and a first demodulation circuit 58. If the optical disk 10 is an optical disk of the CD series, the first reproducing processor 52 is operated by the control of the controller 16. The first reproducing processor 52 reproduces data from the electric signal generated from the optical detector 24 according to the second standard. The first amplifying circuit 56 amplifies the electric signal generated from the optical detector 24. The first demodulation circuit 58 demodulates a signal amplified by the first amplifying circuit 56 to CD reproducing data. The second reproducing processor 54 has a second amplifying circuit 60 and a second demodulation circuit 62. If the optical disk 10 is an optical disk of the DVD series, the second reproducing processor 54 is operated by the control of the controller 16. The second reproducing processor 54 reproduces data from the electric signal generated from the optical detector 24 according to the first standard. The second amplifying circuit 60 amplifies the electric signal generated from the optical detector 24. The second demodulation circuit 62 demodulates a signal amplified by the second amplifying circuit 60 to DVD reproducing data. The controller 16 uses a system controller of the optical disk drive including the recording/reproducing apparatus of Figure 3. The controller 16 controls the operation of the first and second recording processors 36 and 38 and the first and second reproducing processors 52 and 54 according to the kind of the optical disk 10 and an operating mode, that is, a recording mode, a reproducing mode or an erasing mode. In the recording and reproducing apparatus of Figure 3, an operation for reproducing data recorded on the CD-R is substantially identical to an operation for reproducing data from the CD-R in a general CD-R drive. An operation for recording and reproducing data on and from the DVD-RW is substantially identical to an operation for recording and reproducing data on and from the DVD-RW in a typical DVD drive. However, when recording data by increasing the rotating speed in order to shorten the recording time for the optical disk such as the CD-R having the wavelength characteristic, data is recorded by the light beam having the wavelength of 650 nm instead of the wavelength of 780 nm. In such a case, since the absorption when the light of the wavelength of 650 nm is used is higher than the absorption when the light of the wavelength of 780 nm is used by 5 times or more, data can be recorded with a low output. For example, the recording optical power is 15 mW when the light of the wavelength of 780 nm is used, whereas the recording optical power of 3 mW is sufficient to record data when the light of the wavelength of 650 nm is used. Generally, since the DVD-RW has the recording optical power of about 15 mW, a drive for recording data on this optical disk is designed to generate the recording optical power of 15 mW by the output of the light source of the wavelength of 650 nm. That is, the DVD drive having the semiconductor laser of 650 nm which can generate the recording optical power of 15 mW can sufficiently record data on the CD-R at high speed. Since the recording speed can be improved by speeding up the linear velocity of the optical disk, a problem such as the generating of heat or a rise in cost can be prevented. When reproducing data recorded on the optical disk such as the CD-R, the data is reproduced by the light beam having the wavelength of 780 nm, like a general case. If the optical disk 10 is mounted in the drive having the recording/reproducing apparatus of Figure 3, the controller 16 determines the kind of the optical disk 10 and performs an operation suitable for the kind of the optical disk 10. To determine the kind of the optical disk 10 is known to the art and therefore will not be described. Figure 4 is a flow chart showing a processing procedure of the controller 16 shown in Figure 3 when the optical disk 10 is the CD-R. If the optical disk 10 is mounted and the kind of the optical disk 10 is the CD-R, the controller 16 checks a current operating mode at step 100. At steps 102 and 104, it is checked whether the operating mode is a recording mode, a reproducing mode or other modes. If the operating mode is set to the recording mode, the controller 16 records, at step 106, the CD recording data on the optical disk 10 by driving the first light source 18 by the first recording processor 36. In this case, the controller 16 does not drive the second light source 20 and does not operate the second processor 38 and the first and second reproducing processors 52 and 54. Therefore, the CD recording data is recorded on the CD-R by the laser of the wavelength of 650 nm of the first light source 18, and thus the recording speed is increased. If the operating mode is set to the reproducing mode, the controller 16 drives, at step 108, the second light source 20 by the first processor 36 and operates the first reproducing processor 52, thereby generating the CD reproducing data from the optical disk 10. This is the same technique as a general CD-R reproducing technique. If the operating mode is set to other modes except the recording and reproducing mode, the controller 16 executes a corresponding operating mode at step 110. If the above operation is ended, the controller 16 returns a typical control routine. Figure 5 is a flow chart showing a processing procedure of the controller 16 shown in Figure 3 when the optical disk 10 is the DVD-RW. If the optical disk 10 is mounted and the kind of the optical disk 10 is the DVD-RW, the controller 16 checks a current operating mode at step 200. At steps 202, 204 and 206, it is checked whether the operating mode is a recording mode, a reproducing mode, an erasing mode or other modes. Unlike the CD-R, the DVD-RW has the erasing mode since it is possible to erase data. If the operating mode is set to the recording mode, the controller 16 records, at step 208, the DVD recording data on the optical disk 10 by driving the first light source 18 by the second processor 38. In this case, the controller 16 does not drive the second light source 20 and does not operate the first processor 36 and the first and second reproducing processors 52 and 54. If the operating mode is set to the reproducing mode, the controller 16 drives, at step 210, the first light source 18 by the second processor 38 and operates the second reproducing processor 54, thereby generating the DVD reproducing data from the optical disk 10. If the operating mode is set to the erasing mode, the controller 16 erases, at step 212, data recorded on the optical disk 10 by driving the first light source 18 by the second processor 38. If the operating mode is set to other modes except the recording, reproducing and erasing modes, the controller 16 executes a corresponding operating mode at step 214. If the above operation is ended, the controller 16 returns a typical control routine. The operation of Figure 5 is identical to a technique for recording, reproducing or erasing data in the general DVD-RW. Hence, the recording speed for the optical disk having the wavelength characteristic can be efficiently improved without generating heat. Meanwhile, the light source of the wavelength of 780 nm is used in order to reproduce data from the CD-R, in the DVD system normally using the wavelength of 650 nm. When reproducing data from the CD-R in a 2-wavelengths system, the wavelength of 780 nm is used. When recording data on the CD-R, the wavelength of 650 nm is used. Therefore, it is possible to record data on the CD-R at high speed. In the drive sharing the CD-R and the rewritable optical disk of the DVD series, the present invention may be effectively used. If the optical disk 10 is the CD-R, the absorption is high when recording data by the light beam of the wavelength of 650 nm. Therefore, the optical quantity reflected from the optical disk 10 is smaller than the optical quantity when the wavelength of 780 nm is used. The smaller quantity of the reflected light is undesirable for servo control when considering the fact that the servo control for the optical pickup 12 uses the light reflected from the optical disk. If the optical disk 10 is the CD-R, when recording data by the light beam of the wavelength of 650 nm generated from the first light source 18, the light beam of the wavelength of 780 nm is transmitted to the optical disk 10 together with the light beam of the wavelength of 650 nm by driving the second light source 20 by the first recording processor 36. Then the quantity of the reflected light increases and the servo control for the optical pickup is effectively performed. Even if the optical disk 10 is the DVD-RW, the same principle is applicable during recording. As noted above, the recording speed for the optical disk having the wavelength characteristic can be efficiently improved without any problem of the generation of heat or a rise in cost. Further, the present invention may be more effectively used in the drive sharing the CD-R and the rewritable optical disk of the DVD series. While the invention has been shown and described with reference to a certain preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein. Especially, although the present invention has been applied to the drive using the CD-R and the rewritable optical disk of the DVD series, it may be identically applied to the drive for recording and reproducing optical disks having the wavelength characteristic like the CD-R. If the drive uses a new DVD standard utilizing the light of a wavelength shorter than 600 nm, the same principle is applied. In such a case, one light source is used to oscillate a wavelength shorter than 600 nm, that is, a blue or green laser. Another light source is used to oscillate a wavelength of 780 nm or between 635 nm and 650 nm, that is, an infrared or red laser. Therefore, it is intended that the present invention is not limited to the particular embodiment disclosed as the best mode contemplated for carrying out the present invention, but that the present invention includes all embodiments falling within the scope of the appended claims. Although a few preferred embodiments have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims.

Claims: A method for recording and reproducing data by irradiating an optical disk (10) with a light beam, said disk exhibiting a difference in absorption depending on the wavelength of said light beam, said method comprising the steps of: recording data on an optical disk (10) by a light beam (18) having a first wavelength for which said optical disk (10) has a high absorption; and reproducing said data recorded on said optical disk (10) by a light beam (20) having a second wavelength for which said optical disk has a low absorption; characterised by the steps of: recording data on a first type of optical disk (10) by a light beam (18) having said first wavelength which is of a first standard, and reproducing said data recorded on said first type of optical disk by said light beam (18) having said first wavelength of said first standard; recording data on a second type of optical disk by said light beam (18) having said first wavelength of said first standard, and reproducing said data recorded on said second type of optical disk by a light beam (20) having said second wavelength which is of a second standard, wherein said second type of optical disk has a high absorption for said first wavelength and a low absorption for said second wavelength. The method as claimed in claim 1, wherein said wavelength of said first standard is shorter than said wavelength of said second standard. The method as claimed in claim 1 or 2, wherein said first standard is a digital video disk standard and said second standard is a compact disk standard. The method as claimed in any of claims 1 to 3, wherein light of said first standard is a red laser and light of said second standard is an infrared laser. The method as claimed in any of claims 1 to 3, wherein light (18) of said first standard is a blue or green laser and light (20) of said second standard is a red or infrared laser. The method as claimed in any preceding claim, wherein said data recorded on said optical disk is erased by said light beam (18) of said first standard. The method as claimed in any preceding claim, wherein said light beam (20) of said second standard is transmitted to said optical disk (10) together with said light beam (18) of said first standard during recording. An apparatus for recording and reproducing data by irradiating an optical disk (10) with a light beam, said disk exhibiting a difference in absorption depending on the wavelength of said light beam, said apparatus comprising: a first light source (18) for generating light having a first wavelength for which said optical disk (10) has a high absorption; a second light source (20) for generating light having a second wavelength for which said optical disk has a low absorption; an optical system (24, 26, 34) for converting said light generated from said first and second light sources (18, 20) into beams to be transmitted to said optical disk and condensing light reflected from said optical disk (10); an optical detector (24) for detecting reflected light condensed by said optical system (24, 26, 34) and converting the detected light into an electric signal; characterised by : said first light source (18) generating light of said first wavelength being of a first standard; said second light source (20) generating light of said second wavelength being of a second standard; a first processor (36) for driving said first light source (18) by recording data according to said second standard, and driving said second light source (20) when reproducing data from a second type of optical disk; a second processor (38) for driving said first light source (18) by recording data according to said first standard, and driving said first light source (18) when reproducing data from a first type of optical disk; a first reproducing processor (52) for reproducing data by said electric signal generated from said optical detector (24) according to said second standard; a second reproducing processor (54) for reproducing data by said electric signal generated from said optical detector (24) according to said first standard; and a controller (16) for recording data on said second type of optical disk by driving said first light source (18) by said first processor (36), and reproducing data from said second type of optical disk by driving said second light source (20) by said first processor (36) and simultaneously by operating said first reproducing processor (52), and said controller (16) for recording data on said first type of optical disk by driving said first light source (18) by said second processor (38), and reproducing data from said first type of optical disk by driving said first light source (18) by said second processor (38) and simultaneously by operating said second reproducing processor (54), wherein said second type of optical disk has a high absorption for said first wavelength and a low absorption for said second wavelength. The apparatus as claimed in claim 8, wherein said wavelength of said first standard is shorter than said wavelength of said second standard. The apparatus as claimed in claim 8 or 9, wherein said first standard is a digital video disk standard and said second standard is a compact disk standard. The apparatus as claimed in claim 8, 9 or 10, wherein said light of said first standard is a red laser and said light of said second standard is an infrared laser. The apparatus as claimed in claim 8, 9 or 10, wherein said light of said first standard is a blue or green laser and said light of said second standard is a red or infrared laser. The apparatus as claimed in any of claims 8 to 12, wherein said controller erases data recorded on said optical disk by a light beam of said first standard by driving said first light source by said recording processor (36). The apparatus as claimed in any of claims 8 to 13, wherein said controller irradiates said second type of optical disk with a light beam of said second standard by driving said second light source (20) by said first processor (36), together with a light beam of said first standard during recording.

Inventors: PARK IN-SIK, PARK, IN-SIK
Applicants: SAMSUNG ELECTRONICS CO LTD, SAMSUNG ELECTRONICS CO., LTD.
Application year: 1998
Main classification: G11B7
IPC codes: G11B7