Method for performing servo defect compensating operation by compensating servo-related signal derived from reading optical medium and related optical disc drive system with DSP

A method for performing a servo defect compensating operation by compensating a servo-related signal in an optical disc drive and a related optical disc drive system with a DSP is provided. The method comprises: reading an optical medium by an optical pick-up unit; detecting whether a defect exists by monitoring a side beam signal; when the defect on the optical medium is detected, determining a new compensation value based on a servo error signal; and compensating the servo-related signal with the new compensation value during defect crossing to adjust servo control when the optical pick-up unit passes the defect.

BACKGROUND

The present invention relates to servo defect compensating operation of an optical disc drive, and more particularly, to a method of servo defect compensation for a scratch disc and a related optical disc drive system with a digital signal processor (DSP).

In a conventional optical disc drive comprising an optical pick-up unit for reading an optical medium having defects such as a scratch, there is no defect compensation scheme when the optical pick-up unit passes through the defect. The focusing and tracking servo is in a close loop control while reading data from the optical medium, and after the optical pick-up unit passes through the defect, the focusing and tracking servo will probably point at somewhere far from the desired focus/tracking point due to factors such as spindle rotating speed, clamp direction, size of the defect, defect detect level, and digital equalizer design. The focusing and tracking servo traces back using a larger transient response, but the RF quality of data read from the optical medium is typically deteriorated. This issue becomes more serious in high resolution discs such as Blu-ray

SUMMARY OF THE INVENTION

It is therefore one of the objectives of the present invention to provide a method for performing a servo defect compensating operation by compensating a servo-related signal in an optical disc drive and a related optical disc drive system with a DSP, so as to solve the above problem.

In accordance with an embodiment of the present invention, a method for performing a servo defect compensating operation by compensating a servo-related signal in an optical disc drive is disclosed. The method comprises reading an optical medium by an optical pick-up unit; detecting whether a defect exists by monitoring a side beam signal; when the defect on the optical medium is detected, determining a new compensation value based on a servo error signal; and compensating the servo-related signal with the new compensation value during defect crossing to adjust servo control when the optical pick-up unit passes the defect.

In accordance with an embodiment of the present invention, an optical disc drive system for performing a servo defect compensating operation by compensating a servo-related signal is disclosed. The optical drive system comprises an optical pick-up unit and a digital signal processor (DSP). The optical pick-up unit is for reading an optical medium. The DSP is for detecting whether a defect exists by monitoring a side beam signal, and determining a new compensation value based on a servo error signal when the defect on the optical medium is detected, and compensating the servo-related signal with the new compensation value during defect crossing to adjust servo control when the optical pick-up unit passes the defect.

The method and the optical disc drive system with the DSP disclosed by the present invention can perform the servo defect compensating operation in real time for an optical disc drive comprising an optical pick-up unit for reading an optical medium having at least a defect, so as to let the focus/tracking servo approach the focus/tracking point and thereby improve the RF quality.

DETAILED DESCRIPTION

FIG. 1shows a simplified block diagram of an optical disc drive system1000in accordance with an embodiment of the invention. As shown inFIG. 1, the optical disc drive system1000comprises an optical medium10, an optical pick-up unit12, an RF signal processor14, a power driver16, a spindle motor18, and a digital signal processor (DSP)100.FIG. 2shows a simplified block diagram of the DSP100in the optical disc drive system10in accordance with a first embodiment of the invention. As shown inFIG. 2, the DSP100comprises a first adder110, a second adder120, and a digital equalizer130. The first adder110receives and combines the focus error signal FE or tracking error signal TE and an electrical offset FE_OFFSET or TE_OFFSET to generate an output signal. The second adder120is coupled to the first adder110, which receives and combines the output signal, an intentional bias FE_BAL or TE_BAL, and a compensating signal FEOFT_DEFECT or TEOFT_DEFECT to generate an input signal FE_INPUT or TE_INPUT. The digital equalizer130is coupled to the second adder120, which receives the input signal FE_INPUT or TE_INPUT to generate a focusing servo output signal FOO or tracking servo output signal TRO.

FIG. 3shows a simplified timing diagram of a focus servo ON OK indicator FOK, a sub-beam addition signal SBAD, a defect signal DEFECT, and the previously mentioned compensating signal FEOFT_DEFECT or TEOFT_DEFECT. The sub-beam addition signal SBAD may be a summation of the four light detectors detecting light intensity of the side beams (SBAD=E+F+G+H). As shown inFIG. 2, when the servo is successful focused on and a defect on the optical medium10is detected, SBAD is lower than a threshold FLEVEL (SBAD<FLEVEL) and the indicator FOK is high (FOK=1), the compensating signal FEOFT_DEFECT is set to a predicted compensation value FEOFT_PROT or the compensating signal TEOFT_DEFECT is set to a predicted compensation value TEOFT_PROT. When the servo is not yet focused on, FOK is low (FOK=0), or when no defect has been detected, which means FOK is high but SBAD exceeds the threshold FLEVEL (SBAD>FLEVEL), the compensation signal FEOFT_DEFECT or TEOFT_DEFECT is set to 0.

In some embodiments, the optical medium10as shown inFIG. 4is segmented into a plurality of circular zones Z1, Z2, . . . , Zi, for example, 15 zones in total. During playback, a current zone of a current data accessing location is checked and compared to a previous zone of a previous data accessing location to determine whether the servo defect compensation needs to be triggered. If the current zone is different from the previous zone, the system performs servo defect compensation, for example, a predicted compensation value FEOFT_PROT and TEOFT_PROT is utilized to compensate the focus error signal and tracking error signal.

FIG. 5shows a simplified timing diagram of the focus error signal FE or tracking error signal TE, the defect signal DEFECT, and the compensating signal FEOFT_DEFECT or TEOFT_DEFECT. As shown inFIG. 5, after the optical pick-up unit12inFIG. 1detects a defect, a servo peak bottom detection is enabled for calculating an offset of FE or TE of the optical disc drive system1000. When FEOFT_DEFECT or TEOFT_DEFECT signal changes to low, the servo peak bottom detection is continued for a predetermined delay srvdft_pk_bt delay. The servo peak bottom detection results are obtained for computing the offset caused by the defect. In some embodiments, a deviation result FE_DEV or TE_DEV is calculated according to the peak value or the bottom value of FE or TE and the intentional bias FE_BAL or TE_BAL by the following formula (1):
FE_DEV/TE_DEV=(Peak or Bottom) atT1−FE_BAL/TE_BAL  (1)

Next, a new compensation value FEOFT_PROT_new or TEOFT_PROT_new of the embodiment is derived from a current compensation value FEOFT_PROT_now or TEOFT_PROT_now, the deviation result FE_DEV or TE_DEV, and a gain GAIN_FE or GAIN_TE by the following formulae (2) and (3):
FEOFT_PROT_new=FEOFT_PROT_now+FE_DEV/GAIN_FE  (2)
TEOFT_PROT_new=TEOFT_PROT_now+TE_DEV/GAIN_TE  (3)

The new compensation value FEOFT_PROT_new or TEOFT_PROT_new is then updated to the DSP command to compensate FE or TE after passing the detected defect. The servo defect compensation method of the embodiments detects and predicts a direction or/and an amount of FE or TE offset caused by a disc defect based on the focus error signal FE or tracking error signal TE. When crossing the disc defect, FE or TE is compensated by combining with a predicted FE or TE compensation value to make the servo control approaches the actual focusing point or tracking point after passing the defect area. In comparison to the system without the servo defect compensation method, the servo control needs a greater transient response to track the actual focusing or tracking point after crossing the defect on the disc.

In a second embodiment, a method for performing the servo defect compensating operation is conducted by compensating a focus error DC signal FEDC or tracking error DC signal TEDC in the optical disc drive system1000.FIG. 6shows a simplified block diagram of a DSP200for replacing the DSP100in the optical disc drive system1000in accordance with the second embodiment. Compared with the DSP100inFIG. 2, the DSP200further comprises a first non-unity gain digital equalizer140; the remaining elements of the DSP200may be the same as those of the DSP100, thus further explanation of the configuration details of these elements are omitted herein for the sake of brevity. The first non-unit gain digital equalizer140, we designed the DC gain of TE_LPF or TE_LPF (equalizer140) as non-unit gain that called as FEDC/TEDC. The first non-unity gain digital equalizer140equalizes FE_LPF or TE_LPF derived by the digital equalizer130during a defect crossing period. The signals FEDC or TEDC that from FE_LPF or TE_LPF can be compensated by varying magnitudes and direction of the signals to allow the focus or tracking servo locates at somewhere closer to the actual focusing and tracking point.

The second embodiment may utilize formulae (4) and (5) to derive the compensated focus error DC signal and tracking error DC signal similar to formulae (2) and (3) of the first embodiment.
FEDC_new=FEDC_now+FE_DEV/GAIN_FEDC  (4)
TEDC_new=TEDC_now+TE_DEV/GAIN_TEDC  (5)

In a third embodiment, a method for performing the servo defect compensating operation is conducted by compensating a focus servo output hold signal FOO_HOLD or tracking servo output hold signal TRO_HOLD in the optical disc drive system1000.FIG. 7shows a simplified block diagram of a DSP300for replacing the DSP100in the optical disc drive system1000in accordance with the third embodiment. Compared with the DSP100inFIG. 1, the DSP300further comprises a second non-unity gain digital equalizer150; the remaining elements of the DSP300may be the same as those of the DSP100, and thus further explanation of the configuration details of these elements are omitted herein for the sake of brevity. The second non-unity gain digital equalizer150compensates the focus servo output hold signal FOO_HOLD or tracking servo output hold signal TRO_HOLD. The second non-unity gain digital equalizer150equalizes (FOO_HOLD_LPF or TRO_HOLD_LPF) the servo output FOO_HOLD or TRO_HOLD during a defect crossing period. FOO_HOLD or TRO_HOLD that from FOO_HOLD_LPF or TRO_HOLD_LPF can be compensated by varying magnitudes and direction of the signals to allow the focus or tracking servo locates at somewhere closer to the actual focusing and tracking point.

The third embodiment may utilize formulae (6) and (7) to derive the compensated focus servo output hold signal and tracking servo output hold signal similar to formulae (2) and (3) of the first embodiment.
FOOHOLD_new=FOOHOLD_now+FE_DEV/GAIN_FOOHOLD  (6)
TROHOLD_new=TROHOLD_now+TE_DEV/GAIN_TROHOLD  (7)

Please note that the above embodiments are only for illustrative purposes and are not meant to be limitations of the present invention. In other embodiments, for example, the methods of the first embodiment, the second embodiment, and the third embodiment can be combined for performing the servo defect compensating operation.

Briefly summarized, the method and the optical disc drive system with the DSP disclosed by the present invention can perform the servo defect compensating operation in real time for an optical disc drive system comprising an optical pick-up unit for reading an optical medium having at least a defect, so as to let the focus/tracking servo approach the focus/tracking point and thereby improve the RF quality.