Focusing controller and method thereof for an optical disk drive

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 focusing controller and the method thereof, and more particularly to a focusing controller and the method thereof used in an optical disk drive.

2. Description of the Related Art

In conventional operation, optical disc drives are subject to the control of servo signals. Among the servo signals of an optical disk drive, the focus error signal Fe is used to control the position of its pick up head, so as to focus the laser beam emitted by the pick up head on the optical disk. FIG. 1 is a block diagram of a convention optical disk drive. Conventional optical disk drive 100 includes a focusing controller 120 and a pick up head 110 to access an optical disk 130 . The pick up head 110 outputs a focus error signal Fe according to the reflected light from the optical disk 130 . The focusing controller 120 outputs a focus control signal Foo to control the pick up head 110 according to the focus error signal Fe.

FIG. 2 is a diagram of the focusing controller, which mainly includes an analog-to-digital converter (A/D converter) 210 , a focus compensator 220 and a digital-to-analog converter (D/A converter) 230 . Functionally speaking, the A/D converter 210 is to receive and digitize the focus error signal Fe, for outputting a digital focus error signal to the focus compensator 220 . Then, in subsequence, the D/A converter then converts the output of the focus compensator 220 to generate the focus control signal Foo for controlling the position of the pick up head 110 .

However, noises inside the optical disk drive affect the servo signals, including the focus error signal, so that the laser beam cannot precisely focus on the optical disk. There includes a plurality of tracks having pits and lands thereon used to record information on the surface of an optical disk. However, the focus error signal Fe is easily coupled with the track error signal Te during tracking operations, which indicates that the pickup head may not be allocated at an accurate position during the following focusing operations since the currently derived focus error signal Fe is erroneous because of coupling low-frequency error component from the track error signal Te. FIG. 3 shows waveform diagrams of the track error signal Te and the focus error signal Fe during tracking operations. Obviously, the focus error signal Fe is usually coupled with the low-frequency component of the track error signal Te such that the actually focus status of the pickup head may not obtained due to an erroneous Fe is derived.

It is therefore an object of the invention to provide an apparatus and method of focusing control in an optical disk drive so as to focus the laser beam precisely on the surface of an optical disk.

The invention achieves the above-identified object by providing an optical disk drive which includes an optical pick-up head and a focusing controller. The optical pick-up head is for emitting a laser beam to access the optical disk and outputting a focus error signal according to the reflected light from the optical disk. The focusing controller includes a coupler and a focus compensator. The coupler couples the focus error signal with the offset signal to generate a coupled signal. The focus compensator receives the coupled signal and outputs the focus control signal to control the pick up head of the optical disk drive such that, while seeking, the position of the optical pick-up head is out of the focus point with the optical disk for reducing the coupling of the track error signal with the focus error signal and enhancing the stability of the servo system.

The invention achieves another above-identified object by providing a control method for stabilizing a servo system while an optical electronic device executing seeking. The optical electronic device includes an optical pick-up head and a focusing controller. The optical electronic device is used for outputting a focus control signal to control the optical pick-up head for accessing an optical disk. In an embodiment, the focus error signal is coupled with an offset signal to generate a coupled signal. Next, the coupled signal is input to the focusing controller for outputting the focus control signal. The offset signal is for coupling with the focus error signal such that the position of the optical pick-up head is out of the focus point with the optical disk. When the seeking has ended, the offset signal is eliminated which causes the position of the optical pick-up head and laser beam to be in the focus point with the optical disk.

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 (prior art) is a block diagram of a convention optical disk drive.

FIG. 2 (prior art) is a diagram of the focusing controller.

FIG. 3 is a waveform diagram showing the track error signal Te and the focus error signal during tracking.

FIG. 4 is a diagram of an optical disk drive according to a preferred embodiment of the invention.

FIG. 5 is a diagram showing the focusing controller of the preferred embodiment.

FIG. 6 is a diagram showing the relative position of the optical pick-up head 410 and the optical disk 430 .

FIG. 4 is a diagram of an optical disk drive according to a preferred embodiment of the invention, which includes a focusing controller 420 and a pick up head 410 for emitting a laser beam onto an optical disk 430 so as to access data recorded on the optical disk 430 . When the focus error signal Fe according to the reflected light from the optical disk 430 , the focusing controller 420 outputs focus control signal Foo according to an offset signal OF and the focus error signal Fe so as to control the position of the pick up head 410 .

FIG. 5 is a diagram showing the focusing controller of the preferred embodiment. The focusing controller 420 includes an analog-to-digital converter (A/D converter) 520 , a coupler 540 , a focus compensator 550 and a digital-to-analog converter (D/A converter) 560 . A/D converter 520 receives and digitizes the focus error signal Fe and outputs a digital focus error signal Fe′. Then, the coupler 540 receives the digital focus error signal Fe′ and the offset signal OF for coupling the digital focus error signal Fe′ with the offset signal OF to output a coupled signal Fe′_OF. Then the focus compensator 550 receives the coupled signal Fe′_OF and outputs a compensation signal Sc. The D/A converter 560 receives the compensation signal Sc from the focus compensator 550 and outputs the focus control signal Foo. The above-mentioned coupler 540 can be an adder for summing the digital focus error signal Fe′ and the offset signal OF. The externally added offset signal OF is used to couple with the digital focus error signal Fe′ so as to focus the laser beam at a position deviated from a preset focus point, such as slightly off the disk. Because the laser beam is out of focus with the disk, the intensity of the reflected light is not as strong as when the laser beam is in the normal focused position so that the coupling of track error signal Te to the focus error signal is reduced. In other words, the noise coupled to the focus error signal is reduced such that the vibration of the focus error signal is reduced and the stability of the servo system is enhanced. It is note-worthy that the offset signal OF can be a small value so as to offset the focus a little bit from the disk. In the preferred embodiment, a value of one-thirtieth of the DC component of peak-to-peak value of the focus error signal can be used for the offset signal OF. Of course, one skilled in the art can alter the value of the offset signal OF according to the actual practice, but the various modifications and similar arrangements and procedures according to the invention are still considered to be in the scope of the invention.

FIG. 6 is a diagram showing the relative position of the optical pick-up head 410 and the optical disk 430 . While seeking, the offset signal OF is used to focus the laser beam slightly off the surface of the optical disk 430 so as to let the focus error signal couple less noises, such as the track error signal. In an embodiment, the offset signal OF is a DC signal. Besides, the apparatus and method disclosed according to the preferred embodiment of the invention, the invention can be applied to any other optical electronic device, such as CD-ROM drive, CD-RW drive, DVD-ROM drive, DVD+R drive, or DVD-RAM drive. People skilled in the art can apply the disclosed approach to the desired optical electronic devices.

The focusing controller and the method thereof according the embodiment of the invention can, while seeking, stabilize the focus of the optical pick-up head regardless of the noise. The disclosed method is only used while seeking, when no data is being read, so that the out of focus laser beam does not have any undesirable effect.

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.