1. Field of the Invention
The present invention relates to a method of controlling an optical drive to write data, more specifically, a method of adjusting a write-in strategy and a write-in power according to a linear velocity of an optical disc operating on the optical drive.
2. Description of the Prior Art
With the rapid development of computer technology, most data can be transformed into digital form for convenience of transmitting and storing.
In order to help users store data more conveniently, various data storage devices, such as CD recorders, are being introduced. A CD-R drive, due to a low price, small volume, and large capacity of a disc, can record data onto the CD, letting the user store data more easily.
The conventional CD-R drive rotates at a zone constant linear velocity (ZCLV). When a pickup head of the CD-R drive is passing through different zones of a disc, for keeping a constant linear velocity, the angular velocity of the operating CD-R drive also changes so as to accurately record the data on the disc. In addition, a fixed-angular-velocity-operated CD-R drive does not need to frequently adjust the motor turns, and has also become a widely used drive in recent years.
Please refer to FIG. 1, which shows a schematic diagram of the CD-R drive 10 recording data onto an optical disc 20. The disc 20 has a spiral track 22 covered by a photoresist layer from the center outward. The drive 10 comprises a pickup head 12. While the drive 10 writes data onto the disc 20, the pickup head 12 makes the photoresist layer of the track 22 on the disc 20 be intermittently exposed to an on-and-off laser according to the data. The exposed photoresist layer of the track 22 will cause pits to form. On the contrary, the unexposed photoresist layer will be kept as lands. Reflections of the pits and the lands are not similar, in this way, the different data (for example, the digital “0” or “1”) can be represented by the pits and the lands respectively, and stored in the disc 20. While reading the data stored in the disc 20, the drive 10 can receives reflecting laser from the disc 20 to read the data stored in the disc 20.
The extended length of the pit and the land represent the times of the particular repetition bit in disc 20, a length for continuing representative data. For example, if the pit represents bit “1”, the three repetition bits “1 1 1” is represented by longer extended pits. As above-mentioned, when the disc 20 passes through the pickup head 12, the pickup head 12 will apply energy onto the disc 20 with a laser so as to write data onto the disc 20. Both the applied energy (that is, the laser power) and the applied time of the energy can affect the extended length of the pits and further affect the precision of the written data on the disc 20.
Please refer to FIG. 2, which shows a relation plot of an amount of exposure of the photoresist layer against the fragment position relative to the pickup head 12 while the disc 20 is rotating. When the drive 10 is going to write data into the disc 20, the pickup head 12 begins to emit a laser while passing through the fragment of p0. At this moment, the received energy of the disc 20 is not enough to form a pit. As the disc 20 is rotating, the pickup head 12 constantly supplies energy onto the disc 20. While the fragment of p1 is passing through the pickup head 12, a temperature of the photoresist layer of the fragment reaches a threshold temperature Eth and a pit is formed. While passing through the fragment of p2, the pickup head 12 stops emitting a laser and the temperature of the disc 20 decreases gradually. While the pickup head 12 is passing through the p3, the temperature of the photoresist layer is lower than threshold temperature Eth and a pit is no longer formed. In other words, a real extended length of the pit is from position p1 to p3. From FIG. 2, a length from p0 to p1 is obviously different from a length from p2 to p3, that is, if a pit intends to be formed from p1 to p3, the pickup head 12 of the drive 10 must begin/stop emitting a laser while passing through the position p0 and p2 respectively. In addition, the energy applied from the pickup head 12 affects the formed pit as well. For instance, the larger energy the pickup head 12 applies to the disc 20, the closer to the initial position, where the pickup head 12 begins to apply energy, the reaching threshold temperature Eth position of the photoresist layer is. Generally speaking, while writing data into the disc 20, the drive 10 can determine a position and a length of a pit, i.e. the position of p1 and p3, according to the data. As to the position where the pickup head 12 actually applies energy, i.e. the position of p0 and p2, are determined by a specific write-in strategy along with an optimal write-in power based on the position p1 and p3. Because the data within the disc 20 has direct relation to the extended length of the pit, an over-length or an under-length of the pit is incapable of correctly recording data onto the disc 20.
Please refer to FIG. 3. FIG. 3 is an enlarged plot according to a dotted line section of the disc 20 shown in FIG. 1. For a rewritable disc 20, its track 22 can be divided into two kinds of tracks, one is a data track 26 for use to record data, and the other is a wobble track 28 for use to record relative information of each frame on the disc 20. The data track 26 is an arc along the disc 20 and around the center of the disc 20, like the track 22. Because FIG. 3 is an enlarged plot of a tiny part of the arc track, the data track 26 shown in FIG. 3 is a straight line. However, the wobble track 28 is not only an arc along the disc 20 and around the center of the disc 20, from a view of FIG. 3, but also appears as crawl-shaped with small amplitude along the track 22. The pickup head 12 of the drive 10 can receive reflected light from the wobble track 28 and forms a wobble signal. The drive 10 can detect which part of data on the disc 20 is being read by the pickup head 12 based on the wobble signal.
According to the orange book regulating the specification of the disc 20, while the emitted laser power from the pickup head 12 has optimal power, the reflected signal measured by the pickup head 12 is an AC coupled high frequency (HF) signal with a perfect symmetrical amplitude. Please refer to FIG. 4 which shows a waveform of the HF signal reflected from the disc 20 while the pickup head 12 of the drive 10 writes data onto the disc 20 based on an optimal write-in power, where the horizontal axis represents time, the vertical axis represents amplitude, and the place marked as level dc represents a corresponding amplitude of a long-term average of the waveform. If a laser is reflected from a pit, the HF signal shows an upper amplitude A1 over the level dc. If a laser is reflected from a land, the HF signal shows a lower amplitude A2 below the level dc. A measurement amplitude parameter β=(A1−A2)/(A1+A2) is for use to compare the A1 and A2. During writing data into the disc 20, the drive 10 will encode the data, resulting in a total extended length of pits equaling to a total extended length of lands. In other words, a total spent time of the laser reflecting from pits and a total spent time of the laser reflecting from lands are the same, which causes a long-term average level dc of the reflected HF signal to be exactly in the middle of the upper amplitude A1 and the lower amplitude A2, that is β=0. If the laser power emitted from the pickup head 12 is lower than the optimal power or if the laser-emitting time is too short, either causes the insufficient extended pits, which makes the waveform of the HF signal move downward and causes A1 to be less than A2, leading to β<0. On the contrary, if the laser power emitted from the pickup head 12 is higher than the optimal power or if the laser-emitting time is too long, either forms an over-length of an extended pit, which makes the waveform of the HF signal move upward and causes A1 to be more than A2, leading to β>0. In other words, β represents an amount of the pits matching an amount of the lands during encoding. When β does not equal to 0, it means either the length of the pit or that of the land is incorrect, resulting in errors during encoding. Besides β, a signal jitter in the duration of data-reading also can be used to judge a correction of data-writing. If there is something wrong when the disc 20 is written, even identical bits, the last time of signal-reading (that is, the extended length of the pits or the lands), are not the same, which increases the signal jitter.
Please again refer to FIG. 1. The drive 10 further includes an absolute time in pregroove decoder (ATIP decoder) 14 for decoding the absolute time code acquired from pickup head 12 and an eight-to fourteen modulator (EFM) 16 for modulating the data into EFM data. The drive 10 includes a table 18, which shows write-in strategies corresponding to write-in powers. The drive 10 adjusts the write-in strategy and the write-in power based on both a time code and the table 18. The drive 10 can be a constant-angular-velocity-operated drive. While the drive 10 rotates the disc 20, the rotation angular velocity of the drive 10 stays constant. Due to the fixed angular velocity of the drive 10, when the drive 10 is operating, a linear velocity of an inner orbit of the disc 20 is smaller, but a linear velocity of an outer orbit of the disc 20 is larger. If intending to write data into the inner orbit of the disc 20, due to a smaller linear velocity of an inner orbit, the pickup head 12 has enough time to emit a laser exposing the photoresist layers on the inner orbits, therefore the emitted laser power from the pickup head 12 is not too large. On the other hand, if intending to write data into the outer orbit of the disc 20, due to a larger linear velocity of an outer orbit, the pickup head 12 has to augment the laser power or increase the heating time so that the photoresist layer on the outer orbit of the disc 20 can complete exposure in a predetermined time. As a result, the write-in strategy and the write-in power have to be adjusted adequately along with the process of data-writing.
Please refer to FIG. 5, FIG. 6, and FIG. 7. FIG. 5 is a schematic diagram of distribution frames along the disc 20. FIG. 6 is a relation plot showing the linear velocity of the rotating disc 20 against the record time of the drive 10 while the pickup head 10 is passing through the disc 20. FIG. 7 is a relation diagram showing the value of β against time. The track for recording data on the disc 20 can be divided into a plurality of frames, each having identical data capacity. In CD-R/CD-RW, a linear length of each frame (an arc along the track) is identical. Two frames FA and FB are marked in FIG. 5, where the inner frame FA is from Fa0 to Fa1 and the outer frame FB is from Fb0 to Fb1. In the prior art, the drive 10 adjusts the laser power emitted from the pickup head 12 according to the frames, that is, the emitted laser powers from the pickup head 12 are the same in an identical frame. The emitted laser powers from the pickup head 12 changes as a change of frames.
As a curve 50 shows in FIG. 6, while the pickup head 12 is moving from the inner part of the disc 20 outward, the linear velocity of the disc 20 skipping the pickup head 12 is increasing. On the other hand, even though the linear length of each frame is identical, the spread angle of the center of the disc 20 corresponding to the frame distributed in the inner disc 20 (like frame FA) is also larger and each point within the frame corresponding to the radius of the center of the disc 20 has a larger difference. As inner frame FA shows in FIG. 5, the radius from the center to the start point of Fa0 is different from that from the center to the end point of Fa1. Relatively, the spread angle of the center of the disc 20 corresponding to the frame FB distributed in the outer disc 20 is smaller, and the radius from the center to the point Fb0 and Fb1 are almost the same. That the radius from each point to the center has a larger difference means while the pickup head 12 passes through different points within the frame FA, the linear velocity changes more greatly. As shown in FIG. 6, where an interval between the time t0 and t1 represents the spent time of the pickup head 12 passing through the inner frame FA, an interval of the time t5 and t6 represents the spent time between the pickup head 12 passing through the outer frame FB. Despite the change of the linear velocity among different points within the inner frame of the disc 20 being larger, the write-in strategy and the write-in power are adjusted according to the frames in prior art, resulting in the same write-in strategy and the write-in power are used to write data into the inner frame. In this way, the linear velocity at the end fragment of the inner frame is faster than that at the start fragment of the inner frame during writing data into the inner frame. For the end fragment of the frame, the write-in strategy and the write-in power adapted to the start fragment of the frame can cause a lack of absorption energy, which leads to too short a length of the pits. Similarly, for the start fragment of the frame, the write-in strategy and the write-in power adapted to the end fragment of the frame can cause over-absorption energy, which leads to too long a length of the pits. From FIG. 7, while the pickup head 12 writes data into the end of the inner orbit, the absolute value of β being maximum, that is, the laser power emitted from the pickup head 12 at this moment is most far from the optimal power, meaning that the pickup head 12 is prone to generate errors at this position of the disc 20.
While writing data into the outer frame of the disc 20, owing to little linear velocity change at each position of the outer frame, the pickup head 12 is unable to make mistakes, even when writing data into a sequence of two or three frames with the same write-in strategy and the write-in power. From FIG. 7, β is approximate to 0 when the pickup head 12 writes data into the outer orbit of the disc 20. As a result, it is not necessary to store too many write-in strategies and the write-in powers in the table 18 in prior art.
In addition to the above defect, a change of the drive 10 operation speed makes the table 18 useless. For example, the table 18 adapted to the two-times drive is not suitable for the four-times drive. Even at the same frame, while the operation speed of the drive changes, the linear velocity of the pickup head passing the frame changes, and the corresponding write-in strategy and the write-in power also change. In this way, arising from a promotion of the drive operation speed, the conventional drives have to test new write-in strategies and write-in powers again, resulting in a wasted time and a cost increase of the drive development.