Patent Application
20090010143
The present invention generally relates to a power control system and a method of same for controlling an optical disk drive, which are capable of generating an optimized output power of the optical disk drive under a variation of operational environment.
In power control of an optical disk drive during a high-speed recording procedure, a power waveform of single level often causes a bad formation of the pits (or marks) on a recordable disk. As a result, conventional optical disk drive introduces a power control of composite waveform for increasing the writing performance, such as an over-drive power control to a CD-R media or a multi-pulse power control to a CD-RW media.
The main power of the laser generated by a laser diode of the optical disk drive is controlled by a write power control unit, for example. The write power of the laser is detected by a photodetector and then sampled by a sample and hold device according to a main power sample hold pulse. The sampled write power signal is fed back to the write power control unit as a feedback power signal. Then the write power control unit can adjust the write power of the laser using the feedback power signal. The above operations are similar to the read power. However, for an over drive power or multipulse power signal of the laser, the sampled period is very short Hence, the sampled feedback signal will be incorrect if the sampling bandwidth of the laser power feedback signal is not sufficient to support such short sampled period power signals. Further, the laser power control will be inconstant or incorrect if a high-frequency noise is induced.
As mentioned, since the sampled period of the over-drive power signal or the multi-pulse power signal are much shorter than that of the writing pulse or reading pulse, a higher bandwidth of the feedback signal of laser power and power control circuit is required, especially in a high-speed recording condition. Consequently and undoubtedly, the higher bandwidth induces a higher cost.
Some conventional arts adopt an open DAC (Digital to Analog Converter) control instead of the APC methods of the over-drive power control or the multi-pulse power control. The open DAC control means to control the OD power or the multipulse power at a constant level. Nevertheless, the optimized write power cannot be achieved by the open DAC control when the characteristic of laser diode varies under variation of operation environment, such as operation temperature. Therefore, the recording performance of the optical disk drive by open DAC control will be degraded under a varied operation environment.
As shown, relationships of the DAC value relative to the laser power at different temperatures are different. It is obvious that the two characteristic relationship lines have different slopes under different temperatures, i.e. the relationship of the DAC value relative to laser power would be varied with the temperature variation. The optical disk drive can adjust the laser power by determining a proper DAC value in accordance with the different characteristic relationships which are stored in the memory.
The characteristic relationship of the DAC value relative to the laser power can be explained clearly by following equations with detailed explanation. Referring to
wherein rDAC represents a reading DAC value of the digital to analog converter, ΔrDAC represents a reading DAC variation of the digital to analog converter, and ΔrP represents a read power variation of the laser emitting unit.
Then, we can derive the proper reading DAC value rDAC from equation (2).
wherein rPw represents a current read power, rOffset represents a read power offset of the laser emitting unit.
Similarly, the writing DAC value can be derived from the equations (3) and (4).
wherein wDAC1 and wDAC2 represent two reference reading DAC values with respect to two write power wPw1 and wPw2 respectively under a specific temperature, ΔwDAC represents a writing DAC variation of the digital to analog converter, ΔwP represents a write power variation of the laser emitting unit, wPw represents a current write power, wOffset represents a write power offsets of the laser emitting unit, wDAC represents a proper writing DAC value of the digital to analog converter.
Further, we can also obtain two output voltage signals VO1 and VO2 of a reading channel of the APC circuit, with respect to the read powers rPw1 and rPw2 respectively. Accordingly, the characteristic relationship of the output voltage signal relative to the read power can be explained by the equation (5).
wherein the value of ΔP/ΔV represents a variation parameter of output power to output voltage of the APC circuit under different temperatures.
We may assume that the output voltage signal of reading channel of the APC circuit is VRO1 at a specific temperature. The characteristic of laser power will be varied by the variation of environment temperatures due to a temperature-rising environment or the high heat capacities produced during the recording operation of the optical dick drive. Therefore, the output voltage signal of APC circuit will be changed to VRO2 in order to maintain a constant output of laser power. Accordingly, we can obtain the characteristic relationship of the variation of the read power due to the variation of temperatures by comprehending equation (5), shown as equation (6).
wherein ΔPr represents the variation of read power of the laser emitting unit under the temperature variation.
Although the varied temperatures can be detected by using a temperature sensor, the usage of the temperature sensor by aforementioned power control methods of laser power will increase the cost of the optical disk drive. Further, conventional control methods would be easily invited within incorrect sampling signals by using a high-speed APC circuit in a high-speed recording condition. Also, that will increase the manufacturing cost of the optical disk drive to raise the sampling rate of signals.
According to the present invention, a power control system of an optical disk drive is provided to effectively and dynamically control over drive or multipulse power of the optical disk drive. The optical disk drive has a laser diode for generating laser of multiple power levels and a detecting unit for detecting laser powers to generate power feedback signals correspondingly. In the power control system, a first power control unit is used to control the read or write power of the laser. The first power control unit generates an original first power control signal to control the laser diode to emit laser with a predeteremined power level. The first power control unit receives a first power feedback signal from the defecting unit. The first power feedback signal corresponds to the power level of the laser generated corresponding to the original first power control signal. The first power control unit generates a modified first power control signal according to the original power feedback signal and a desired power level to control the laser diode to emit laser corresponding to the modified first power control signal. A second power control unit is used to control over drive power and/or a multipulse write power for the laser diode. The second power control unit receives the original and modified first power control signals from the first power control unit, and generates a modified second power control signal according to a predetermined ratio, the modified and original first power control signals, and an original second power control signal to control the laser diode to emit laser with a desired power level.
The present invention also provides a method for maintaining the output power of a laser diode of an optical disk drive to improve the recording performance of the optical disk drive. In addition to the laser diode, the optical disk drive has a detecting unit for detecting laser powers of the laser diode to generate power feedback signals correspondingly. The power control method comprises generating an original first power control signal to control the laser diode to emit laser; generating a first power feedback signal corresponding to the laser generated corresponding to the original first power control signal; generating a modified first power control signal according to the first power feedback signal and a desired power level to control the laser diode to emit laser corresponding to the modified first power control signal; and generating a modified second power control signal according to a predetermined ratio, the modified and original first power control signals, and an original second power control signal to control the laser diode to emit laser with a desired power level.
The advantages of the present invention include: (a) generating a compensating DAC signal to adjust the output power of the laser emitting of an optical disk drive, especially to adjust a write power of the laser emitting, for maintaining the write power in a constant state; (b) providing a high recording performance of the optical disk drive with a reduced cost by compensating the power variation due to the temperature variation without a high-speed APC circuit.
By equation (6), we can introduce a characteristic index δ under different temperatures to calculate a compensating power ΔPwc for adjusting a write power of a writing channel of the APC circuit, shown as equation (7).
ΔPwc=δ×ΔPr (7)
Consequently, a compensating DAC value wDACc can be derived by introducing the equation (4) for compensating the output power of the laser emitting unit, shown as equation (8).
Finally, we can obtain the compensating DAC value by realizing the above-mentioned equations to generate a compensating power for maintaining the output power of the laser emitting unit in a constant level.
The photo detecting unit 10 detects current laser power of the laser diode and transmits the power feedback signals to the sample and hold circuits 14, 16. The sample and hold circuits 14, 16 sample the current read power feedback signal and current writing feedback power signal then transmit a sampled read power feedback signal and a sampled write power feedback signal to the read and write power control units 18, 20, respectively. The read and write power control units 18 and 20, each of which can be referred to as “a first power control unit”, generate and output a power control signal (VRDCO or VWDC1O as shown in
The power control signals VRDCO and VWDC1O are voltage values, which are converted into digital signals by the ADC 25 and transmitted to the OD/MP power control unit 30. The advance power control unit 30, which can also be referred to as a second power control unit, receives original and modified read or write power control signals (also referred to as first power control signals) from the ADC 25 and generates a modified (second) power control signal according to a predetermined relationship among the read or write power control signals and an original second power control signal so as to control the over drive power or multipulse write power of the laser diode.
The laser drive 50 receives the modified second power control signal, VWDC2O, which indicates a modified control value, to control the laser power. The laser driver 50 drives the laser emitting unit 12 by a proper power in accordance with the read power control signal VRDCO, write power control signal VWDC1O and OD/MP power control signal VWDC2O.
It is noted that equation (9) or (10) is set to approach the required DAC curve. The power signals can be read or write power signals. The term ΔDAC/ΔP can utilize the read power related value (equation (1)) or the write power related value (equation (3)). Furthermore, the terms ΔP/ΔV and ΔDAC/ΔP may even incorporated into the term “Ratio” in some circumstances.
By utilizing the method of the present invention, an optimized write power of the laser emitting unit of the optical disk drive can be determined by introducing the current reading or write power signals of the laser emitting unit with a predetermined relationship of the output power of the laser emitting unit relative to the DAC value.
The advantages of the present invention include: (a) generating a modified DAC signal to adjust the output power of the laser emitting of an optical disk drive, especially to adjust a write power of the laser emitting, so that the write power is maintained in a constant level; (b) providing a high recording performance of the optical disk drive with a reduced cost by compensating the power variation due to the temperature variation without a high-speed APC circuit.
As is understood by a person skilled in the art, the foregoing preferred embodiments of the present invention are illustrative rather than limiting of the present invention. It is intended that they cover various modifications and similar arrangements be included within the spirit and scope of the appended claims, the scope of which should be accorded the broadest interpretation so as to encompass all such modifications and similar structure.
