WO2008139406A1

WO2008139406A1 - Method of recording over defects

Info

Publication number: WO2008139406A1
Application number: PCT/IB2008/051860
Authority: WO
Inventors: Yu Zhou; Tek Seow Loi
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2007-05-11
Filing date: 2008-05-09
Publication date: 2008-11-20
Also published as: TW200912909A

Abstract

A method comprising controlling recording of data on an optical record carrier based on the detection of at least one defect on the optical record carrier at a moment in time before actual recording of the data on the optical record carrier is disclosed. The method can perform an early detection of defects during recording and take suitable corrective measures to handle the defects. This can reduce the recording problems such as loss of data, unable to read recorded information. The technique is useful for all optical disc recording devices such as CD, DVD, HD-DVD and Blu-ray disc recorders.

Description

Method of recording over defects

FIELD OF THE INVENTION

The subject matter relates to a method of recording data on an optical disc and more specifically to recording of the data over defects present on the optical disc.

BACKGROUND OF THE INVENTION

WO2003044794 discloses a method of recording data on a rewritable optical recording medium. The method scans the optical recording medium by reading at least a portion of the recorded data to find out the defects and based on the defects the recording strategy is adapted. It would be advantageous to have a recording method that detects defects without writing and adapts the recording strategy based on the detected defects. It would be also advantageous to have an optical drive that detects defects without writing and adapts the recording strategy based on the detected defects.

SUMMARY OF THE INVENTION

A method comprising controlling recording of data on an optical record carrier based on the detection of at least one defect on the optical record carrier at a moment in time before actual recording of the data on the optical record carrier is disclosed.

An optical drive comprising a control unit arranged to control recording of data on an optical record carrier based on the detection of at least one defect on the optical record carrier at a moment in time before actual recording of the data on the optical record carrier is disclosed.

Furthermore, the method could be implemented with a computer program.

BRIEF DESCRIPTION OF THE DRAWINGS

The above mentioned aspects, features and advantages will be further described, by way of example only, with reference to the accompanying drawings, in which the same reference numerals indicate identical or similar parts, and in which: Fig. 1 shows an exemplary optical drive; Fig. 2 shows example defects on an exemplary optical record carrier; Fig. 3a and Fig. 3b schematically shows the signal characteristics of an exemplary blank optical record carrier with fingerprints and with localized dye media or black dots; Fig. 4a - Fig. 4d schematically shows variation of the normalized mirror signal and the wobble signal for a blank optical record carrier having a fingerprint and a black dot defect; and

Fig. 5 shows a schematic block diagram of defect detection according to an embodiment of the subject matter;

Referring to Fig. 1, the optical record carrier 10 (Cf. Fig. 1) is constant angular velocity (CAV) controlled or constant linear velocity (CLV) controlled by a spindle motor 52. An optical pick-up unit 54 records data on the optical record carrier 10 by using laser light (at a recording power value) emitted form a laser diode. When the data is to be recorded, it is supplied to an encoder unit 58 and the data encoded by the encoder unit 58 is supplied to a laser diode-driving unit 56. The laser diode-driving unit 56 generates a drive signal based on the encoded data and supplies the drive signal to the laser diode of the optical pick-up unit 54. In addition, a control signal from a control unit 54 is supplied to the laser diode-driving unit 56 so that the recording strategy and recording power are determined by the control signal. However, when the data is read from the optical record carrier 10, the laser diode of the optical pick-up unit 54 emits laser light of a read power (read power < record power), and the reflected light is received. The received reflected light is converted into an electrical signal and a read RF signal is obtained. The read RF signal is supplied to an RF signal-processing unit 50. The RF signal-processing unit 50 comprises an equalizer, a binarizing unit, a phase-locked loop (PLL) unit, and binarizes the read RF signal, generates a synchronous clock, and supplies these signals to a decoder unit 57. The decoder unit 57 decodes data based on these supplied signals and outputs the decoded data as read data.

The optical drive 500 also includes a circuit (for data read-out) for controlling the focus servo or tracking servo by producing a tracking error signal or a focus error signal respectively, and a wobble signal formed on the optical record carrier 10 (e.g. for use in address demodulation or for controlling the number of rotations). The servo control structures are identical to those in conventional drive systems and therefore are not described in detail. The construction shown in Fig. 1 only illustrates portions related to the general operation of the optical drive 500. The description and detailed explanation of servo circuits for controlling the optical pick-up unit, the spindle motor, the slide motor, and the control circuits are omitted, because they are constructed in a similar manner as in conventional drive systems.

A large number of optical record carriers (e.g. CD, DVD, HD-DVD, Blu-ray discs) available in the market marginally meet with the specifications prescribed by the standards (e.g. DVD Standards, Blu-ray disc standards) or fails to meet the specifications prescribed by the standards. This may give rise to disc defects such as dye media defects, a black dot, a white dot, a fingerprint, and a scratch as shown in Fig. 2. The defects can cause problems such as unable to read the disc after recording or loss of data on the recorded disc. Furthermore, the defects can introduce sudden high amplitude peaks in the error signal that can easily steer the laser beam off the track. This can affect the recording performance and can lead to recording failure. Referring now to Fig. 3a and Fig. 3b, chl shows the normalized mirror signal

MIRN, ch2 shows the radial error signal, ch3 shows the wobble signal and ch4 shows the focus error signal. It can be seen that disc defects of fingerprints usually have a larger area on the disc and the influence to the recording quality is not as high compared to the rest of them.

DETAILED DESCRIPTION OF THE EMBODIMENTS

A method comprising controlling recording of data on an optical record carrier based on the detection of at least one defect on the optical record carrier at a moment in time before actual recording of the data on the optical record carrier is disclosed. On inserting the optical record carrier into the optical drive for recording of data, a defect detection function is turned on and the actuator is moved to the next recording area. The defect detection function examines the optical record carrier for various types of defects and detects the defects. Once the defect is detected, the optical drive can take appropriate measures to handle defects and then adapt recording accordingly. This can improve the overall recording quality. The method does not make use of the recorded data to find the defects. Hence, the method does not require the optical drive to record the data before being able to detect the presence of defects. The disclosed method detects the defects while recording the data on the optical record carrier. In an embodiment, the method includes detecting the at least one defect on the optical record carrier using a measured mirror signal and a measured wobble signal.

The amplitude of the mirror signal (i.e. the central diode signal) which represents the optical record carrier reflectivity is monitored along with the wobble signal to detect the occurrence of defect. The mirror signal used here is the normalized mirror signal. For instance in a conventional four quadrant photo-detector (including four quadrants A, B, C, D with respective photo-detectors on which the reflection light from the laser beam is irradiated) a normalized mirror signal can be generated as the sum of the signals coming from all the photo-detectors and can be used as a measure of the reflected laser light. When there are defects on the optical record carrier, the normalized mirror signal level changes. These changes can be used to detect the defects.

The grooves of a track (in an optical record carrier) are provided in the form of a wave or undulating pattern. The undulating pattern of a groove may be detected to generate a wobble signal at a wobble frequency. The detected wobble signal can be used as track position information and also as a basic signal in generating a timing signal. The defects present on the optical record carrier can cause disturbance in the wobble signal that can be used to detect the defects.

In a further embodiment, the method includes:

- determining whether the measured mirror signal is within lower and upper pre-defined mirror signal threshold values;

- if so, determining whether disturbance in the measured wobble signal is above a pre-defined wobble signal threshold value, wherein the disturbance is a difference between a maximum peak value and a minimum peak value obtained from the measured wobble signal; and

- if so, declaring that a fingerprint defect is present on the optical record carrier. Generally, the fingerprint defect area is large compared to other defect areas caused due to black dots, scratches, dye media etc. If in case the recording of the data is skipped in the fingerprint area and the data are to be relocated to an other defect free area, the relocated data needs large space. On the other hand, if recording of the data is carried out as usual without distinguishing the fingerprint defect area, then the read back of the recorded data in the fingerprint defect area can be affected due to bad recording quality and can result in uncorrectable errors. Hence distinguishing the fingerprint defect can help the drive in taking necessary action to record on the fingerprint area (e.g. increase the recording power and record the data on the fingerprint defect area without relocating the data). In a further embodiment, the method includes: - determining whether the measured mirror signal is below the lower pre-defined mirror signal threshold value;

- if so, determining whether the disturbance in the measured wobble signal is above the predefined wobble signal threshold value; and - if so, declaring that at least one of a black dot, a white dot, a scratch, an air bubble and a dye defect is present on the optical record carrier.

The defects such as black dot, white dot, air bubbles or dye defects are defects on which recording of the data has to be avoided, since it results in poor recording quality (or may result in unrecoverable errors) and reading the recorded data from these defect areas is difficult. When such defects are detected, the optical drive has the necessary information to skip recording the data in the defect areas. Further, the data can be relocated to an other defect free area and the recording can be continued.

Referring now to Fig. 4a and Fig. 4b, the horizontal axis represents the time (in milli seconds) and the vertical axis represents the amplitude of the measured normalized mirror signal on an optical record carrier having a fingerprint (Cf. Fig. 4a) and a black dot (Cf. Fig. 4b) respectively. It can be seen in Fig. 4a and Fig. 4b that the drop in the level of the normalized mirror signal on the fingerprint is much smaller as compared to that on black dot, scratches, dye defects etc. The upper and lower pre-defined mirror signal threshold values can be set taking into consideration the variations in the normalized mirror signal levels.

Referring now to Fig. 4c and Fig. 4d, the horizontal axis represents the time (in milli seconds) and the vertical axis represents the amplitude of the measured wobble signal on an optical record carrier having a fingerprint and a black dot respectively. When there is no defect on the optical record carrier, the wobble disturbance (wobble dis = max_peak - min_peak) is almost zero. When there is a defect, the wobble disturbance can increase as shown in Fig. 4c and Fig. 4d. Hence, the wobble signal threshold value can be set in such a way that the wobble_dis>= disturbance limit indicates the occurrence of defects

In a still further embodiment, determining the at least one defect on the optical record carrier is done during idle time. The idle time is a time period between the start of the filling of recording data buffer and the start of the recording of the data on the optical record carrier. During real time recording of the data to the optical record carrier, the optical drive will normally be recording at a higher speed (2.4x or higher) than video being encoded into MPEG data. This means that the data will be filled incrementally into the optical drive's recording buffer until it reaches a certain threshold before actually recording the data onto the optical record carrier. In between the actual recording of the data onto the optical record carrier and waiting for the recording buffer to fill up, the optical drive will be idle. This idle time is effectively used to detect defects on the optical record carrier. In other words, the disclosed method takes into account the characteristics of real time direct recording to the optical record carrier that allows idle time due to data encoding latency. Further, this early detection of defect can be carried out for certain period of time depending on the recording data buffer size and seek time. Furthermore, the method can detect defects without writing on the optical record carrier.

In a still further embodiment, the data is recorded on the optical record carrier by initiating a defect handling mechanism that depends on a type of the defect detected. The defects can affect the recording quality in many ways and needs to be handled differently. In other words, each defect (e.g. dye defect, scratch, air bubble, and fingerprint) needs a different correction mechanism to overcome the defect and continue with recording. Hence, recording data by initiating a defect handling mechanism that can take appropriate measures based on the type of the defect can improve the recording quality. In other words, the disclosed method can improve recording robustness by doing early defect detection and recording correction (i.e. over correctable detected defects).

In an embodiment, the defect handling mechanism adjusts recording parameters during actual recording of the data based on the detected position of the fingerprint defect. When the fingerprint defect is detected, the optical drive can increase the writing power by certain percentage e.g. 20% of the optimum power to write on the defect area with fingerprints. In this way, fingerprint defect can be corrected. The increase of power can be varied depending on the optical record carrier types, and can be stored in the optical drive EEPROM according to the optical record carrier type or media ID. In a further embodiment, the defect handling mechanism skips detected defect area during actual recording of the data based on the detected position of at least one of the black dot, the white dot, the scratch, the air bubble or the dye defect. Once the defect is detected, the optical drive can generate a defect flag and set the defect flag to high until exiting the defect area. Based on the defect flag, the optical drive can flag the corresponding physical block address where the defect is started and ended. This defect area of the optical record carrier can be remembered and can be handled by the optical drive's defect management implementation. This early defect detection can be done during every recording. The disclosed method detects defects and adapts recording of the data on the defects based on the type of the detected defect. Hence, the method improves recording efficiency. Furthermore, the disclosed method detects defects based on the variations in the normalized mirror signal and the wobble signal and hence the defect detection is accurate. Additionally, other defect management approaches such as i) pre-allocation of defect data storage area and moving the affected data to the pre-allocated area and ii) skipping of defective area with address translation can be adapted.

In a still further embodiment, the method is performed on a blank optical record carrier. This saves the recording time since the defect detection can be carried out before recording of the data on the defect area. Further, in case the defect detection is carried out after recording, there are chances of increasing the defect area. This happens because the distorted servo error signal in the defect area (during recording) can steer the actuator to the neighboring tracks which doesn't have any defects resulting in corrupting the data in those neighboring tracks. This implies that recording in the defect area having defects such as black dots can lead to corrupted data around the black dots. Hence, the actual defect area while detecting the defects after recording may increase. The disclosed method avoids this by carrying out early defect detection before recording on the blank optical record carrier. The optical drive 500 (Cf. Fig. 1) can be adapted to perform the method as disclosed in the embodiments. To this end, the optical drive includes a control unit 59 arranged to control recording of data on an optical record carrier based on the detection of at least one defect on the optical record carrier at a moment in time before actual recording of the data on the optical record carrier.

In an embodiment, the optical drive 500 (Cf. Fig. 1) includes a defect detection unit 400 arranged to detect the at least one defect on the optical record carrier using a measured mirror signal and a measured wobble signal.

Referring now to Fig. 5, the defect detection unit 400 receives the measured normalized mirror signal MIRn and the measured wobble signal and processes them to find the defects on the optical record carrier. The defect detection unit 400 for processing the measured normalized mirror signal MIRn includes: i) an analog to digital converter 402 ii) a high pass filter 404 iii) an averaging FIR filter 406 iv) a comparator 408 and v) a logic AND circuit 410

In operation, the analog to digital converter 402 receives the measured MIRn signal and outputs a normalized digital mirror signal which is passed through a high pass filter 404 and an averaging filter 406 in order to filter out the DC component and obtain MIRN out signal. The averaging filter 406 can be anti-causal and can have zero phase delay. The comparator 408 receives as input the MIRN out signal and compares the MIRN out signal with the pre-defined mirror signal threshold values. The comparator checks whether the MIRN out signal is within the upper and the lower pre-defined mirror signal threshold values and if so sets the first input FP to the logic AND circuit 410 as 1. The second input DD to the logic AND circuit 410 is set to 1 (by the comparator 450) if the wobble signal disturbance is above a pre-defined wobble signal threshold value. Based on the status of FP and DD, the logic AND circuit 410 detects the presence of the fingerprint defect and sets the FP flag to 1. An exemplary pseudo-code representation of the defect detection is given below: If (mirror signal upper threshold <MIRN_out < mirror signal lower threshold) and If (wobble disturbance > pre-defined wobble signal threshold value) Then declare that a fingerprint defect is present.

Further, the defect detection unit for processing the measured wobble signal includes: i) an analog to digital converter 442 ii) a high pass filter 444 iii) an averaging FIR filter 446 iv) a digital slope detector 448 v) a comparator 450 and vi) a logic AND circuit 452

In operation, the analog to digital converter 442 receives the measured wobble signal and outputs a digital wobble signal which is then passed through a high pass filter 444 and an averaging filter 446 to filter high frequency components of noise and wobble signal (the wobble modulation frequency= N* 818KHz where N is the optical record carrier rotation speed. The defect induced disturbances in the wobble signal has at least 12 times lower frequency as compared to wobble frequency.) The output of the averaging filter 446 is received by the digital slope detector 448 to generate a wobble out signal. The comparator 450 receives as input the wobble out signal and compares the wobble out signal with the pre-defined wobble signal threshold value. When the slope rate is higher than the predefined wobble signal threshold value, the first input DD to the logic AND circuit 452 is set to 1 (indicating the occurrence of disturbance in the wobble signal). The second input BD to the logic AND circuit 452 is set to 1 (by the comparator 408) if the MIRN out signal is less than the lower mirror signal threshold level. Based on the status of DD and BD, the logic AND circuit 452 detects the presence of a black dot, a white dot, a scratch, an air bubble or a dye defect and sets the BD flag to 1. An exemplary pseudo-code representation of the defect detection is given below: If (MIRN out < mirror signal lower threshold) and

If (wobble disturbance > pre-defined wobble signal threshold value) Then declare that a defect such as dye defect, a black dot, a scratch and an air bubble is present.

A recorder comprising the optical drive as disclosed in the embodiments can perform an early detection of defects during recording and take suitable corrective measures to handle defects during recording. This can also reduce the recording problems such as loss of data, unable to read recorded information. Although the present subject matter has been explained by means of embodiments using exemplary optical discs, the present subject matter is applicable to all types of optical record carriers (CD, DVD, HD-DVD, Blu-ray discs). It is not limited to a two-layer one side disc, i.e., a dual layer disc, and to a two-layer double side disc, i.e. a dual layer double-sided disc. A person skilled in the art can implement the described embodiments of the method in software or in hardware or in both hardware and software. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art of practicing the claimed subject matter, from a study of the drawings, the disclosure and the appended claims. The use of the verb "comprise" does not exclude the presence of elements other than those listed in a claim or in the description. The use of the indefinite article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The figures and description are to be regarded as illustrative only and do not limit the subject matter.

Claims

CLAIMS:

1. A method comprising: controlling recording of data on an optical record carrier based on the detection of at least one defect on the optical record carrier at a moment in time before actual recording of the data on the optical record carrier.

2. The method as claimed in claim 1, further comprising: detecting the at least one defect on the optical record carrier using a measured mirror signal and a measured wobble signal.

3. The method as claimed in claim 2, further comprising: determining whether the measured mirror signal is within lower and upper predefined mirror signal threshold values; if so, determining whether disturbance in the measured wobble signal is above a pre-defined wobble signal threshold value, wherein the disturbance is a difference between a maximum peak value and a minimum peak value obtained from the measured wobble signal; and if so, declaring that a fingerprint defect is present on the optical record carrier.

4. The method as claimed in claim 3, further comprising: determining whether the measured mirror signal is below the lower predefined mirror signal threshold value; if so, determining whether the disturbance in the measured wobble signal is above the pre-defined wobble signal threshold value; and if so, declaring that at least one of a black dot, a white dot, a scratch, an air bubble or a dye defect is present on the optical record carrier.

5. The method as claimed in any one of the claims 1 - 4, further comprising: determining the at least one defect on the optical record carrier during idle time, wherein the idle time is a time period between the start of the filling of recording data buffer and the start of the recording of the data on the optical record carrier.

6. The method as claimed in any one of the claims 1 - 5, wherein controlling the recording of the data on the optical record carrier comprises controlling the recording of the data on the optical record carrier by initiating a defect handling mechanism that depends on a type of the defect detected.

7. The method as claimed in claim 6, wherein the defect handling mechanism adjusts recording parameters during actual recording of the data based on the detected position of the fingerprint defect.

8. The method as claimed in claim 6, wherein the defect handling mechanism skips the detected defect area during actual recording of the data based on the detected position of at least one of the black dot, the white dot, the scratch, the air bubble or the dye defect.

9. The method as claimed in any one of the claims 1 - 8, wherein the method is performed on a blank optical record carrier.

10. An optical drive (500) comprising: a control unit (59) arranged to control recording of data on an optical record carrier based on the detection of at least one defect on the optical record carrier at a moment in time before actual recording of the data on the optical record carrier.

11. A recorder comprising the optical drive as claimed in claim 10.

12. A computer program comprising code means arranged to perform a method, the method comprising: controlling recording of data on an optical record carrier based on the detection of at least one defect on the optical record carrier at a moment in time before actual recording of the data on the optical record carrier.