stability of a write control signal

This application claims the benefit of U.S. provisional application Ser. No. 60/520,711, filed Nov. 17, 2003, the subject matter of which is incorporated herein by reference.

1. Field of the Invention

The invention relates in general to a calibration method, and more particularly to a calibration method for improving stability of a write control signal during writing.

2. Description of the Related Art

FIG. 1 is a block diagram showing a conventional CD recorder. Referring to FIG. 1 , the CD recorder mainly has a read control device 10 , a write control device 20 and a pickup head device 30 . When a data reading process is to be performed, the read control device 10 generates a read control signal VRDC and outputs the signal VRDC to a drive IC 304 of the pickup head device 30 . The drive IC 304 generates a current i D flowing through a laser diode 301 according to the read control signal VRDC so as to generate a laser beam to read a disk 40 . When a data writing process is to be performed, the write control device 20 generates a write control signal VWDC and outputs the signal VWDC to the drive IC 304 of the pickup head device 30 . The drive IC 304 generates a current i D according to the write control signal VWDC so as to generate a laser beam to write the disk 40 .

Besides, A monitor diode 302 of the pickup head device 30 generates a current i M according to the laser beam sensed by the laser diode 301 . A third amplifier 303 processes the current i M and then generates a feedback control signal FPDO. The feedback control signal FPDO is fed back to input terminals of the read control device 10 and the write control device 20 in order to control a light-emitting power generated by the laser diode 301 during the reading/writing process.

Please refer to the Taiwan patent application number 92100819, filed on Jan. 15, 2003 and entitled “Write Control Device and Method for Optical Storage Apparatus”, which illustrates write control device 20 which has three working modes including a short-term open mode, a long-term open mode and a close-loop mode, as respectively shown in FIGS. 2 , 3 and FIG. 4 . In the short-term open mode shown in FIG. 2 , the write control signal VWDC is initialized according to a virtual ground of a first amplifier 201 , so that the potential of the write control signal VWDC become to zero. In the long-term open mode shown in FIG. 3 , an analog signal DAC 2 with a voltage level of V 1 is inputted to a second amplifier 203 . The gain G of the second amplifier 203 is V 2 /V 1 , and the second amplifier 203 outputs an output signal with a voltage level of V 2 to the first amplifier 201 such that the first amplifier 201 outputs the write control signal VWDC of which the voltage level becomes V 2 . The analog signal DAC 2 is the signal which influences the level of the write control signal VWDC. The analog signal DAC 2 may be obtained using a DAC converter to convert a digital value. The digital value may be selected from one of a plurality of digital values stored in a memory. Different values determine different levels of the write control signal VWDC. In this long-term open mode, the write control signal VWDC can be rapidly charged to a voltage level V 2 capable of performing writing toward the optical disk 40 . In the close-loop mode in FIG. 4 , after the feedback control signal FPDO is inputted to the write control device 20 , a sample/hold unit S/H samples and holds the signal FPDO and amplifies the signal FPDO by G12 times. Then, the amplified signal is inputted to a negative input terminal of the first amplifier 201 through a resistor Ri 2 , while the analog signal DAC 2 with a voltage level of V 1 is directly fed to a positive input terminal of the first amplifier 201 . The first amplifier 201 outputs the write control signal VWDC with a voltage level of V 2 ′ and feeds the signal VWDC back to the negative input terminal of the first amplifier 201 across the parallel connected resistor Rf 2 and capacitor C 2 . In this close-loop mode, the write control signal VWDC controls the pickup head device 30 to write data into the optical disk 40 .

Obviously, In an ideal state, V 2 ′ described above should be equal to V 2 . FIG. 5A shows signal waveforms of a time interval control signal WLDON and the write control signal VWDC when V 2 ′ is equal to V 2 . The time interval control signal WLDON is used to control the write control device 20 . When the time interval control signal WLDON switches to a high level, the write control device 20 switches to the close-loop mode to perform the writing operation. Therefore, in the time slot T 1 , the time interval control signal WLDON is low, the write control device 20 enters the long-term open mode, and the level of the write control signal VWDC is V 2 . In the time slot T 2 , the time interval control signal WLDON switches to the high level, the write control device 20 enters the close-loop mode, and the level of the write control signal VWDC is V 2 ′. Consequently, the write control signal VWDC is quickly charged to the voltage level V 2 capable of writing the optical disk 40 in the long-term open mode, and then the write control signal VWDC is held at the voltage level V 2 ′ capable of writing the optical disk 40 (in an ideal state, V 2 ′=V 2 ) in the close-loop mode. Thus, the write error may be avoided when the optical drive is being written.

However, if the gain of the second amplifier 203 is not well designed, or the gain G of the second amplifier 203 is changed due to the influence of the environmental factor or temperature, V 2 ′ will not be equal to V 2 . FIG. 5B shows signal waveforms of the time interval control signal WLDON and the write control signal VWDC when V 2 ′ is not equal to V 2 . When V 2 ′ is not equal to V 2 and the write control device 20 switches from the long-term open mode in the time slot T 1 to the close-loop mode in the time slot T 2 , the write control signal VWDC may have a transient of unstable voltage, which may cause write error when the optical drive is writing the disk.

Besides, the conventional method for obtaining the gain G of the second amplifier 203 will be described in the following. An OPC (Optimum Power Control) calibration is firstly performed on a test area of the disk before the disk is written. The OPC calibration is to write the test area according different light-emitting powers of the laser diode. In the OPC calibration process, a most suitable light-emitting power for writing may be obtained, and the theoretical value of the gain of the second amplifier 203 may be evaluated according to the light-emitting power. Thereafter, the fixed theoretical value of the gain serves as the gain G of the second amplifier 203 . In a CAV (Constant Angle Velocity) optical drive, however, when the writing speeds are different, different light-emitting powers have to be set. That is, different gains G have to be set to obtain different voltage levels V 2 of the write control signal VWDC. Obviously, the conventional method cannot achieve the function of changing the gain G according to the writing speed, so this method may cause the unstable voltage of the write control signal VWDC and thus cause the data write error.

It is therefore an object of the invention to provide a calibration method for improving stability of a write control signal during writing, and the method can effectively improve unstable conditions of the voltage of the write control signal when a long-term open mode is switched to a close-loop mode so that the error of the data written into the disk may be avoided.

The invention achieves the above-identified object by providing a calibration method for improving stability of a write control signal during writing which can be applied in a CD recorder is provided. The CD recorder has a pickup device and a write control device for outputting the write control signal. The calibration method according to the preferred embodiment of the invention obtains a gain of the write control device. The gain is for controlling the write control signal, and the write control signal controls the pickup device to write a disk. The calibration method according to the preferred embodiment of the invention includes the following steps. First, the pickup device switches into a de-focus state. Then, the write control device switches into a close-loop mode, and a first relationship curve showing a relationship between the write control signal and a light-emitting power generated by a laser diode is obtained. Thereafter, the write control device switches into a long-term open mode and a second relationship curve showing a relationship between the gain and the write control signal is obtained. After the calibration is completed and when the pickup device adopts a specific light-emitting power to write, the CD recorder can obtain a specific write control signal corresponding to the specific light-emitting power according to the first relationship curve and further obtains a specific gain corresponding to the specific write control signal according to the second relationship curve, such that the write control signal outputted by the write control device outputs in the long-term open mode substantially equals the specific write control signal outputted by the write control device in the close-loop mode.

Other objects, features, and advantages of the invention will become apparent from the following detailed description of the preferred but non-limiting embodiments. The following description is made with reference to the accompanying drawings.

FIG. 1 is a block diagram showing a conventional CD recorder.

FIG. 2 is a circuit diagram showing a short-term open mode.

FIG. 3 is a circuit diagram showing a long-term open mode.

FIG. 4 is a circuit diagram showing a close-loop mode.

FIG. 5 shows signal waveforms of a time interval control signal and a write control signal.

FIG. 6 is a flow chart showing a calibration method for improving stability of a write control signal during writing according to a preferred embodiment of the invention.

FIG. 7 is a curve showing a relationship between the write control signal and a light-emitting power target value.

FIG. 8 is a curve showing a relationship between the write control signal and a gain of a second amplifier.

FIG. 6 is a flow chart showing a calibration method for improving stability of a write control signal during writing according to a preferred embodiment of the invention. The invention directly changes the states of an optical pickup 30 and a write control device 20 in an optical drive so as to perform a calibration process according to an on-line operation. First, in step 602 , an optical pickup firstly switches into a de-focus state by, for example, moving the optical pickup to a lowest position such that the optical pickup cannot influence the state of the disk, that is, the data cannot be really written into the disk.

Next, in step 604 , the write control device 20 switches to a close-loop mode, and a relationship curve showing a relationship between a voltage value of a write control signal VWDC and a light-emitting power target value generated by a laser diode 301 is obtained. Then, in step 606 , the write control device 20 switches to a long-term open mode, and a relationship curve showing a relationship between a gain G of a second amplifier 203 and the voltage value of the write control signal VWDC is obtained.

FIG. 7 is a curve showing a relationship between the voltage value of the write control signal VWDC and a light-emitting power target value generated by the laser diode 301 in step 604 . The relationship curve is obtained as follows. First, several light-emitting power target values, such as 100 mW, 200 mW, 300 mW and 400 mW, are set. Then, feedback control signals FPDO corresponding to the light-emitting power target values are fed back to a write control device 20 in the close-loop mode of FIG. 4 , and voltage values of the write control signal VWDC, such as A 1 , A 2 , A 3 and A 4 , which are outputted from the write control device 20 is measured. The voltage value of the write control signal VWDC may be a digital value obtained by converting a voltage level of the write control signal VWDC using a ADC (Analog to Digital Converter).

FIG. 8 is a curve showing a relationship between the voltage value of the write control signal VWDC and a corresponding gain G of a second amplifier 203 in step 606 . The relationship curve is obtained by obtaining the corresponding gains of the second amplifier 203 , such as G 1 , G 2 , G 3 and G 4 , in the write control device 20 in the long-term open mode of FIG. 3 according to the measured voltage values of the write control signal VWDC, such as A 1 , A 2 , A 3 and A 4 , when the voltage level of an analog signal DAC 2 is a constant value such as V 1 . If the laser diode is asked to generate a specific light-emitting power to write the disk after the calibration, the voltage value of the write control signal VWDC corresponding to the specific light-emitting power in the close-loop mode may be quickly obtained according to the relationship curve of FIG. 7 . Then, the gain G corresponding to the voltage value of the write control signal VWDC in the long-term open mode is obtained according to the relationship curve of FIG. 8 .

For example, when the specific light-emitting power obtained through the OPC calibration is 200 mW, the corresponding voltage value of the write control signal VWDC can be obtained to be A 2 by utilizing the relationship of FIG. 7 . After that, the corresponding gain of the second amplifier 203 in the long-term open mode is obtained to be G 2 by utilizing the voltage value A 2 of the write control signal VWDC according to the relationship in FIG. 8 . After regulating the gain of the second amplifier 203 during writing according to the obtained gain G 2 , the voltage value of VWDC can maintain stable during writing. Besides, for CAV optical drive, the relationship of voltage value V 2 of VWDC can be generated according to different gain G (similar to FIG. 7 and FIG. 8 ), and the corresponding gain G for the needed light-emitting power can be obtained. By this way, the error during writing data can be reduced. The method according to the preferred embodiment of the invention can be performed before the optical drive leave the factory, or before writing data each time in regard to the situation. Person skilled in the art can modify that according to the factual application. All equivalent modifications or changes are in the scope of the invention.

The calibration method according to the embodiment of the invention can achieve the advantage of precisely controlling the gain G, such that when the write control device 20 switches from the long-term open mode to the close-loop mode, the write control signal VWDC still can be held at the fixed voltage level, as shown in FIG. 5A , and there is no error caused when the data is being written to the disk. In addition, when the method of the invention is applied to a CAV optical drive, different gains G may be quickly set according to different writing speeds so that different voltage levels V 2 of the write control signal VWDC can be obtained.

While the invention has been described by way of example and in terms of a preferred embodiment, it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.