WO2008023319A1

WO2008023319A1 - Optical drive and integrated calibration method

Info

Publication number: WO2008023319A1
Application number: PCT/IB2007/053309
Authority: WO
Inventors: Yu Zhou
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2006-08-21
Filing date: 2007-08-20
Publication date: 2008-02-28
Also published as: TW200822088A

Abstract

A method of calibrating an optical drive (1) is described here. The method comprises performing calibration of a focus offset and a tilt offset simultaneously after a record carrier (2) is inserted in the optical drive (1). The above technique generally improves the optical drive's overall recording and reading performance and is useful for all optical disc recording and playing devices.

Description

Optical drive and integrated calibration method

FIELD OF THE INVENTION:

The invention relates to optical drives, and more specifically to focus offset and tilt offset calibration methods for optical drives.

BACKGROUND OF THE INVENTION:

US 2002/0031060 discloses a method of calibrating tilt offset, focus offset and radial offset of an optical disk drive apparatus wherein the focus offset and the tilt offset calibrations are carried out separately. The tilt offset calibration is carried out by setting different tilt calibration points and measuring the Jitter signal. Similarly, the focus offset calibration is performed. This method does not yield optimal calibration results and the calibration lasts for approximately more than 1 second. This generally increases the start-up time of the optical disk drive and the optimum power calibration time, which in turn affects the drive's response time to user commands.

It would be advantageous to have a calibration method that reduces the time required for calibrating the focus offset and the tilt offset of an optical drive. It would also be advantageous to have an optical drive that reduces the time required for calibrating the focus offset and the tilt offset.

SUMMARY OF THE INVENTION:

A method of calibrating an optical drive is described here. The method comprises performing calibration of a focus offset and a tilt offset simultaneously after a record carrier is inserted in the optical drive. In an optical drive described here, the optical drive comprises an optical system for scanning tracks (T₁, T₂, ..T_n) of a record carrier. The optical system comprises a light beam generator that generates a light beam, an objective lens for focusing the light beam on the record carrier. The optical drive further comprises an optical detector for detecting a reflected light beam, a controllable focus actuator for axially displacing the objective lens with respect to a recording reference plane of the record carrier, and a controllable tilt actuator for pivoting the objective lens with respect to the record carrier. The optical drive further comprises a first memory arranged to store calibration data points. The optical drive further comprises a second memory arranged to store an optimal focus offset value and an optimal tilt offset value. The optical drive further comprises a control circuit having inputs for receiving signals from the optical detector and having outputs coupled to a control input of the focus actuator and the tilt actuator. The control circuit further includes an integrated calibration unit arranged to perform calibration of a focus offset and a tilt offset simultaneously after the record carrier is inserted in the optical drive.

Furthermore, the method of calibrating the optical drive could be implemented with a computer program.

BRIEF DESCRIPTION OF THE DRAWINGS: These and other aspects, features and advantages will be further explained by means of the following description, by way of example only, with reference to the accompanying drawings, in which same reference numerals indicate same or similar parts, and in which:

Fig. 1 schematically illustrates an exemplary DVD drive; Figs. 2a and Fig. 2b schematically illustrate calibration results obtained by performing focus offset and tilt offset calibration separately in an exemplary DVD drive; Fig. 3 schematically shows the calibration points selected for performing focus offset and tilt offset calibration simultaneously in an exemplary DVD drive;

Fig. 4 schematically illustrates read calibration results obtained by performing focus offset and tilt offset calibration simultaneously in an exemplary DVD drive; and

Fig. 5 schematically illustrates write calibration results obtained by performing focus offset and tilt offset calibration simultaneously in an exemplary DVD drive.

DETAILED DESCRIPTION OF THE EMBODIMENTS:

Fig. 1 schematically illustrates one example of an optical drive 1 (e.g. DVD drive) suitable for writing information on and/or reading information from a record carrier 2 (typically a DVD). For rotating the record carrier 2, the optical drive 1 comprises a motor 4. The motor 4 is typically fixed to a frame defining a rotation axis 5. For receiving and holding the record carrier 2, the optical drive 1 may comprise a turntable or clamping hub 6, which in the case of a spindle motor 4 is mounted on the spindle axis 7 of the motor 4. The optical drive 1 further comprises an optical system 30 for scanning tracks

(Ti₅T₂,...T_n) of the record carrier 2. More specifically, the optical system 30 comprises a light generator 31 (e.g. a laser diode) that generates a light beam 32a. The light beam 32a passes through a beam splitter 33 and an objective lens 34. The objective lens 34 focuses the light beam 32b (on a focal spot F) on the record carrier 2. The light beam 32b reflects from the record carrier 2 (reflected light beam 32c) and passes through the objective lens 34 and the beam splitter 33 (beam 32d) to reach an optical detector 35. A rectangular co-ordinate system XYZ is used. The rotation axis 5 is the Z- axis. The radial direction is the X-axis (perpendicular to the Z-axis, such that the focal spot F lies in the XZ plane). The tangential direction is the Y-axis (perpendicular to the X-axis and the Z-axis). A polar co-ordinate system, r, Φ is also used to define the co-ordinates of the record carrier 2. For achieving and maintaining correct focusing of the light beam 32b on a desired location (on the record carrier 2), the objective lens 34 is mounted so as to be axially displaceable (Z-direction). Furthermore, the actuator system 40 of optical drive 1 comprises a focus actuator 42 arranged for axially displacing the objective lens 34 with respect to the recording reference plane of the record carrier 2. Due to spherical aberration (refractive index of the substrate), the focal spot F of the light beam on the record carrier 2 is shifted by an offset value. To eliminate these influences, a focus offset calibration is carried out to bring back the focus offset to a suitable position.

The record carrier 2 may also suffer from tilt. Tilt of the record carrier 2 is defined as a condition where the recording reference plane of the record carrier 2 is not perpendicular to the rotation axis. A record carrier 2 that is tilted as a whole with respect to the laser beam (e.g. because the motor axle is tilted with respect to the frame and as a consequence the amount of tilt depends on the location on the record carrier) may cause tilt. Especially DVD systems, which have a relatively large numerical aperture (NA), are sensitive to disc tilt. Typically, in an optical drive 1 having tilt correction, the objective lens 34 is pivotable, and the optical drive 1 comprises a tilt actuator that controls the tilt position of the objective lens 34. To this end, the objective lens 34 is mounted so as to be pivotable about a pivot axis which is directed parallel to the Y-axis, such that an optical axis 36 of the objective lens 34 is located in the XZ- plane. Preferably, the pivot axis coincides with the optical center of the objective lens 34. A pivot angle Φ will be defined as the angle between the Z- axis and the optical axis 36 of the objective lens 34. Furthermore, the actuator system 40 of the optical drive 1 comprises a tilt actuator 43, arranged for pivoting the objective lens 34 with respect to the record carrier 2. Principally, the angle Φ should be zero. However, due to manufacturing process variations, the record carrier 2 is generally not flat. The record carrier 2 curves in both radial and circumferential directions. Therefore, the optical system 30 cannot scan the recording tracks with its optical axis 36 perpendicular to the recording surface of the record carrier 2. This deviation of the pivot angle Φ from the optical axis 36 of the objective lens 34 is referred to as tilt offset. To eliminate these influences, a tilt offset calibration is carried out to bring back the tilt offset to a suitable position. The optical drive 1 further comprises a control circuit 90 having a first output

92 connected to a control input of the motor 4, a second output 93 coupled to a control input of the radial actuator 41, a third output 94 coupled to a control input of the focus actuator 42, and a fourth output 95 coupled to a control input of the tilt actuator 43. The control circuit 90 is designed to generate: - at its first output 92, a control signal Sc_M for controlling the motor 4, at its second output 93, a control signal S_CR for controlling the radial actuator 41, at its third output 94, a control signal S_CF for controlling the focus actuator 42, and - at its fourth output 95, a control signal S_CT for controlling the tilt actuator 43.

The control circuit 90 further has a read signal input 91 for receiving a read signal S_R from the optical detector 35.

It is necessary to achieve a good focusing and tracking performance while reading data from the record carrier 2 (Cf. Fig. 1) or while writing data onto the record carrier 2 (Cf Fig. 1). In order to achieve this, focus offset and tilt offset calibrations are carried out. The focus offset and tilt offset calibrations for reading are generally based on Jitter. The focus offset and tilt offset calibrations for writing are generally based on a radial tracking error signal. US 2002/0031060 discloses a calibration procedure wherein the focus offset and tilt offset calibration are carried out separately. The tilt offset calibration is carried out by setting different tilt calibration points and measuring the Jitter signal. Similarly, the focus offset calibration is performed. This method takes more time and is generally inaccurate, since the tilt offset and the focus offset are not independent variables. The tilt offset calibration result will affect the focus offset calibration result and vice-versa.

Fig. 2a and Fig. 2b schematically illustrate calibration results obtained by performing the focus offset and tilt offset calibration seperately in the DVD drive (Cf. Fig. 1). First, the tilt offset calibration is performed and next the focus offset calibration is performed. It can be seen from Fig. 2a and Fig. 2b that the best focus offset and the best tilt offset obtained using this method is not the actual optimal focus offset and the actual optimal tilt offset. Furthermore, this method generally takes about 1 second. The method generally requires more time for start-up and for carrying out an optimum power calibration (OPC) procedure for recording. This generally affects the drive's response time to user commands. For example, during an OPC procedure, radial-tracking-error-signal based focus offset and tilt offset calibrations are performed to obtain the best tracking performance during recording. After recording, in order to improve the readback performance on the OPC area, Jitter-based focus offset and tilt offset calibrations are performed. In all, the focus offset and the tilt offset calibration will generally take more than 2 seconds, which increases the overall OPC time for record calibration. This generally affects the playing and recording continuity. A method that reduces the time required for performing the focus offset and tilt offset calibration is described here. The method performs calibration of the focus offset and the tilt offset simultaneously. The method performs both the focus offset and the tilt offset calibration at the same time in a 3-dimensional space. The focus offset and tilt offset calibration points are set in the first and second dimension respectively, while the calibration signal is measured in the third dimension. The method performs one integrated calibration instead of two separate calibrations, and hence reduces the calibration time. For example, for OPC, instead of performing 4 calibrations during OPC, the disclosed method performs only 2 calibrations (one for reading and one for recording) and reduces the total calibration time to about less than 1 second. The optical drive's overall reading and recording performance is generally improved. Additionally, the method improves the optical drive's playback and recording response time to a user's command.

Fig. 3 schematically shows the calibration points selected for performing focus offset and tilt offset calibration simultaneously in an exemplary DVD drive 1 (Cf. Fig. 1). The drive 1 (Cf. Fig. 1) generally has an actuator to move the objective lens and adjust the focus offset, the tilt offset and the radial offset. Based on the maximum allowable displacement of the actuator, the calibration points are selected. These calibration points are stored in a memory of the drive. Fig. 3 shows 17 calibration points, but a minimum of 6 stable points are generally needed to be able to do a surface fitting and to calculate the required parameters. If the number of stable measurement points is below 6, then the calibration method cannot be carried out. In order to get good and accurate calibration results, generally more than 6 points are used, and that is one of the considerations in choosing 17 calibration points. If all 17 points are stable, then all 17 points are used for surface fitting to obtain the parabolic surface. The stable points here mean that the measurement of the calibration signal (Jitter or radial tracking error signal) is stable after the offset values are set. The 6 stable points could be any 6 points of the 17 points shown in fig. 3. The stable points are generally around the center points. But these stable points could be around a certain phase and depend on the optical pickup unit and the drive mechanism. The selection of stable points is carried out such that there is no phase locked loop locking problem during Jitter or radial tracking error signal measurement. If the focus offset and the tilt offset are set too far away from the optimum point, this will result in a bad tracking performance and thus a bad read back HF signal quality for a read disc or a bad wobble signal quality for a blank disc. This leads to HF phase locked loop locking failure. Another factor to be considered is the Jitter level. If the Jitter level is too high, i.e., higher than 16%, (which is the current decoder system's reliable measurement limit) then the calibration point will be considered as an unstable point. In the case of a blank disc, there is a possibility of radial off-track if the focus offset and the tilt offset are set too far away from the optimum point which is to be considered.

In one possible embodiment, a 3-dimensional relationship between the focus offset, the tilt offset and a Jitter signal is obtained. An optimal read focus offset value and an optimal read tilt offset value is found at which the Jitter signal is substantially at a minimum. The step of finding the 3-dimensional relationship between the focus offset, the tilt offset and the Jitter signal comprises the following: obtaining a focus offset step size, a tilt offset step size, a maximum allowable focus offset value and a minimum allowable focus offset value. The selection of the focus offset and tilt offset adjustable range depends on the optical pickup unit. The focus offset calibration range is determined by the focus S-curve (focus offset adjustable range). The tilt offset calibration range depends on the optical pickup unit's adjustable tilt angle, which is usually ± 12 to 15 mrad. The maximum step sizes for the calibration are then calculated by dividing the adjustable range by the points (i.e. 6 points) as described in Fig. 3. A smaller step size is used when there are not enough valid stable points to perform surface fitting, (i.e., if the number of valid stable points are less than 6). This procedure is also referred to as adaptive calibration step size. In an example disclosed here, half of the previous calibration step size is used. The reason for doing this is that for some disc and/or drive, the tilt offset and focus offset stable adjustable range is very small as compared to the optical pickup unit's allowed range. In some cases, the optical pick up unit's adjustable tilt range is at a lower limit, and the quality of the disc played or tracked is poor. The minimum Jitter is very high, for example 12%. In such cases, a large offset in focus offset and/or tilt offset will cause the Jitter to go up to 16%. In order to achieve a minimum of valid calibration points, a smaller offset stepsize is used. In other words, the calibration coverage is decreased. The first 17 calibration are chosen to cover the typical tilt and focus offset adjustable range according to the product physical adjustable range specification. In order to get 6 valid stable points and to find the optimum focus offset and optimum tilt offset for the drive and the disc, the calibration step size generally cannot be too large. Hence, an adaptive step size is introduced by reducing the step size by half, or even more, if the number of calibration points is below 6.

The Jitter signal at different focus offset and tilt offset values is determined. The procedure for performing read calibration and obtaining the optimal read focus offset value and the optimal read tilt offset value is described below. A possible result of this procedure is schematically illustrated in Fig. 4 and involves the following steps: 1. Start with phase N = I.

2. Preset the focus offset and tilt offset mode to ramping up mode.

3. Set ramping mode to phase N.

4. Set the focus offset and the tilt offset to default value.

5. Set focus offset = focus offset + focus-step size; tilt offset = tilt offset + tilt-step size;

6. Read Jitter signal.

7. Check if all the calibration points in phase N are complete. If they are complete, go to step 8, otherwise repeat steps 5 to 7.

8. Check if N > 4. If so, go to step 10, otherwise go to step 9. 9. Set phase N = N + 1; Check if N > 4, if so, go to step 10, otherwise repeat steps 3 to 8.

10. Form a vector of the read Jitter signal.

11. Calculate 2^nd order surface model co-efficient.

12. Curve fit the values of the focus offset, the tilt offset and the Jitter signal values and obtain the 3 -dimensional relationship.

It is to be noted that, phase N = I means that both the focus offset and the tilt offset are in ramping up mode, phase N = 2 means that the focus offset is in ramping down mode and the tilt offset is in ramping up mode, phase N = 3 means that both the focus offset and the tilt offset are in ramping down mode and phase N = 4 means the focus offset is in ramping up mode and the tilt offset is in ramping down mode. The phase can be varied suitably depending on the parameters to be calibrated and the definition of ramping direction. It is noted that the measuring time is substantially equal to the time necessary to perform one disc revolution, so that the measured result of Jitter signal value is an average value over one disc revolution. Fig. 4 schematically illustrates an example of read calibration results obtained using the above procedure. The procedure is carried out on the DVD drive 1(Cf. Fig. 1). The DVD drive used is a DVD recorder with a focus offset adjustable range of ± 860 nm, and a tilt angle of ± 9 mrad. The coded focus offset value and the coded tilt offset value are plotted against the Jitter signal values. The reason to use coded value is to make the implementation more general (so that it can be applied to different types of optical recording devices).

As should be clear to a person skilled in the art, a 2^nd order model can be represented as,

Z = CI_y +a₂x + a_iy + a_Λx² +a₅y² + a₆xy (1)

Using the coded variables, the matrix X and Vector Z for the Jitter-based calibration should be (See Table 1)

The estimated / predicted co-efficient can be calculated as:

A = (X^TXy^lX^TZ (2) where X^τ is the transpose of matrix X (X¹X)^"1 is the inverse matrix of (X^TX) and

A = [ ^Qi Cl2 CI3 CI4 ^Qs ^Qe]. In real implementation, the component (X¹ X) ^l X^τ is determined by the pre-defined calibration points and is referred to as matrix B. This matrix value is stored in the memory of the optical drive 1. Z is the measured Jitter value. After completing all the measurements, a simple multiplication of B x Z is performed to calculate the 2^nd order surface model co-efficients.

Fig. 4 illustrates one example of a 2^nd order surface relationship. With the calibration data of X (coded focus offset values), Y (coded tilt offset values), and Z (measured Jitter signal), the coefficients aι, a 2, cii, 0,4, as and aβ are calculated. The optimum read focus offset value and the optimum read tilt offset value are then calculated as:

X ^L o,ptii e optimumreadfocusoffset) = (2a₂a₅ - a₃a₆)/(a₆ ² - 4a₄a₅) (3)

*- opt(ι e ophmumreadhltoffset) ~ \^3<^4 ^"" ^2^6 // V²6 ~~ 4<2₄<2₅ ) (4)

The optimum read focus offset value and the optimum read tilt offset value are coded values and are to be decoded before being used for reading data from the DVD.

Table 1

Table 1 shows an example of the read calibration results obtained for the DVD drive 1 (Cf. fig. 1). The total calibration points are set (in the DVD drive) to a total of 17 points as shown in Fig. 3. The calibration points and the focus offset and the tilt offset step sizes are determined in such a way that the system is generally stable in the whole calibration process. This is performed to guarantee accurate surface fitting and prediction of Jitter versus focus offset and tilt offset surface so that the optimal settings can be found accurately. Due to sensitivity of the focus offset and tilt offset influence on the drive system, which affects the tracking performance, a smaller than allowable focus offset and tilt offset adjustment range is used. An unstable state may be reached when the focus offset and/or tilt offset is set too far away from the optimum point, in which case the radial tracking or HF signal quality can be badly affected, ( e.g. when the disc quality is very bad, such as in the case that the disc substrate layer thickness varies substantially from the disc standard). In order to overcome this, the focus offset step size is reduced by half ( the action of reducing the step size could be repeated even if the half step size still can not collect enough stable calibration points) if i. the measured HF Jitter level is > 13% ii. there is some phase locked loop locking failure due to poor HF signal quality.

Phase locked loop failure generally occurs when the system clock is not able to lock to the bad HF signal. This generally occurs when the HF signal is bad ( bad eye pattern, bad HF signal asymmetry, modulation or when the focus offset and tilt offset values are away from the optimum focus offset and tilt offset values. )

The optimum focus offset for the data shown in Table 1 is 255.18 nm and the optimum tilt offset is 1.21 mrad. The minimum Jitter is 8.2%. Under similar conditions, when using separate calibration method, the following values are obtained: optimum focus offset at 277.73 nm, optimum tilt offset at -9.04 mrad. The minimum Jitter is 9.2%. It can be observed that the HF signal Jitter performance is increased by 1% using the disclosed 3- dimensional read calibration method.

During the manufacture of the optical drive 1 (Cf. Fig. 1) focus offset and tilt offset calibrations are performed and the calibrated values are stored in the optical drive 1 , depending on the disc type and speed. These values which are stored in the optical drive, are used as default values. During subsequent start-up, the 3 dimensional read calibration is carried out. The obtained optimal read focus offset value and optimal read tilt offset value are stored in a memory in the optical drive 1 according to regions. The stored values are used for reading data.

In essence, the disclosed read calibration procedure is based on performing the focus offset and the tilt offset calibration simultaneously. A 3-dimensional relationship between the focus offset, the tilt offset and a Jitter signal is obtained. The optimum read focus offset value and the optimum read tilt offset value are obtained from the 3-dimensional relationship. The 3-dimensional read calibration method generally improves the calibration accuracy and finds the system read tilt offset and read focus offset. The optical drive's overall reading performance can generally be improved.

In a still further embodiment, a 3-dimensional relationship between the focus offset, the tilt offset and a radial tracking error signal is obtained. An optimal write focus offset value and an optimal write tilt offset value are found at which the radial tracking error signal is substantially at a maximum. The step of finding the 3-dimensional relationship between the focus offset, the tilt offset and the radial tracking error signal comprises the following: obtaining a focus offset step size, a tilt offset step size, a maximum allowable focus offset value and a maximum allowable tilt offset value as described in the previous paragraphs. A possible result of this procedure is schematically illustrated in Fig. 4 and involves the following steps:

1. Start with phase N = 1.

2. Preset the focus offset and tilt offset mode to ramping up mode. 3. Set ramping mode to phase N.

4. Set the focus offset and the tilt offset to default value.

6. Measure peak-to-peak radial tracking error signal. 7. Check if all the calibration points in phase N are complete. If they are complete, go to step 8, otherwise repeat steps 5 to 7.

8. Check if N > 4. If so, go to step 10, otherwise go to step 9.

9. Set phase N = N + 1; Check if N >4, If so, go to step 10, otherwise repeat steps 3 to 8. 10. Form a vector of the measured radial tracking error signal.

11. Calculate 2^nd order surface model co-efficient.

12. Curve fit the values of the focus offset and the tilt offset and the radial tracking error signal values and obtain the 3-dimensional relationship.

It is noted that the measuring time is substantially equal to the time necessary to perform one disc revolution, so that the measured result of radial tracking error signal is an average value over one disc revolution.

It is also possible to measure the wobble signal amplitude instead of the radial tracking error signal and then perform the calibration. Fig. 5 schematically illustrates an example of write calibration results obtained using the above procedure. The procedure is carried out on the DVD drive 1 (Cf. Fig. 1). The coded focus offset value and the coded tilt offset value are plotted against the radial tracking error signal values. Fig. 5 illustrates one example of a 2^nd order surface relationship. With the calibration data of X (coded focus offset values), Y (coded tilt offset values), and Z (normalised radial tracking error), the coefficients a^ ci2, cii, 0,4, as and aβ are calculated. The optimum write focus offset value and the optimum write tilt offset value are then calculated as, X_Opt(, _{e op}n_mumvntef_ocusoffi_et) = (

²^₅ - Ut₃Ut₆ - Aa₄ ^Q ₅ ) (5)

*opt(i e optimumwntetiltoffset) ^~ \

^3<^4 ^{~ ~} 4<2₄ύ!₅ ) [ O)

The optimum write focus offset value and the optimum write tilt offset value are coded values and are to be decoded before being used for recording data on the DVD. The calibration points and the focus offset and tilt offset step sizes are determined in such a way that the system is stable in the whole calibration process in most cases. This is performed to guarantee accurate surface fitting and prediction of radial tracking error signal or wobble signal amplitude versus focus offset and tilt offset surface so that the true optimal settings can be found accurately. Due to the sensitivity of the focus offset and tilt offset influence on the drive tracking performance, a smaller than allowable focus offset and tilt offset adjustment range is used. An unstable state of radial off-track may occur when the focus and/or tilt offset is set too far away from their optimum point. In order to overcome this, the focus offset step size is reduced by half if i. the number of valid calibration points is lower than 6 for recording, or ii. there is detected some radial off-track. During the manufacture of the optical drive 1, focus offset and tilt offset calibrations are performed and the calibrated values are stored in the optical drive depending on the disc type and speed. These values which are stored in the optical drive are used as default values. During subsequent start-up, the 3 dimensional write calibration is carried out. The obtained optimal write focus offset value and optimal write tilt offset value are stored in a memory in the optical drive according to regions. The stored values are used for recording data.

In essence, the disclosed write calibration procedure is based on performing the focus offset and tilt offset calibration simultaneously. A 3 -dimensional relationship between the focus offset, the tilt offset and a radial tracking error signal is obtained. The optimum write focus offset value and the optimum write tilt offset value are obtained from the 3-dimensional relationship. The 3-dimensional write calibration method generally improves the calibration accuracy and finds the system write tilt offset and write focus offset. The optical drive's overall recording performance can generally be improved.

Now referring to Fig. 1 , the optical drive 1 can be adapted to perform the calibration method as disclosed in the embodiments. To this end, the optical drive 1 includes a first memory 2000 arranged to store the calibration data points. Furthermore, the optical drive 1 includes a second memory 2100 arranged to store the optimal read focus offset value, the optimal read tilt offset value, the optimal write focus offset value and the optimal write tilt offset value. The component (X^TX) ^-1 X^τ is calculated from the stored calibration data points and stored in the first memory 2000 of the optical drive. The control circuit 90 (Cf. Fig. 1) includes an integrated calibration unit 1000 arranged to perform calibration of the focus offset and tilt offset simultaneously after the record carrier is inserted in the optical drive as described in the embodiments.

A recorder or a player having the optical drive 1 can perform calibration of the focus offset and the tilt offset simultaneously, thereby improving the overall recording/reading performance of the recorder/player. It is also possible that the optical drive 1 is capable of recording and/or playing the record carrier 2. Furthermore, among recording, reproducing and erasing, the recorder may perform at least a recording operation.

Although the calibration method has been explained by embodiments using DVD drives and DVD discs, the calibration method is applicable to all types of optical disc media and optical drives, e.g. write-once media and write-many recordable types (CD-RW, DVD-RW, DVD+RW, Blu-ray discs). A person skilled in the art can implement the described embodiments of the calibration method in software 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 invention, 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 stated in a claim or in the description. The use of the indefinite article "a" or "an" preceding an element or step does not exclude the presence of a plurality of such elements or steps. The Figures and description are to be regarded as illustrative only and do not limit the invention. In summary, a method of calibrating an optical drive is described. The method comprises performing calibration of a focus offset and a tilt offset simultaneously after a record carrier is inserted in the optical drive.

Claims

CLAIMS:

1. A method of calibrating an optical drive (1), the method comprising: performing calibration of a focus offset and a tilt offset simultaneously after a record carrier (2) is inserted in the optical drive (1).

2. The method as claimed in claim 1, wherein performing calibration of the focus offset and the tilt offset simultaneously further comprises: finding a 3 -dimensional relationship between the focus offset, the tilt offset and a Jitter signal; and finding an optimal read focus offset value and an optimal read tilt offset value at which the Jitter signal is substantially at a minimum.

3. The method as claimed in claim 2, wherein the method further comprises: reading data from the record carrier using the optimal read focus offset value and the optimal read tilt offset value.

4. The method as claimed in claim 3, wherein reading the data from the record carrier comprises: reading the data from a DVD or a CD or a blu-ray disc.

5. The method as claimed in claim 1, wherein performing calibration of the focus offset and the tilt offset simultaneously further comprises: finding a 3 -dimensional relationship between the focus offset, the tilt offset and a radial tracking error signal; and finding an optimal write focus offset value and an optimal write tilt offset value at which the radial tracking error signal is substantially at a maximum.

6. The method as claimed in claim 5, wherein the method further comprises: recording data on the record carrier using the optimal write focus offset value and the optimal write tilt offset value.

7. The method as claimed in claim 6, wherein recording the data on the record carrier comprises: recording the data on a DVD or a CD or a blu-ray disc.

8. The method as claimed in claim 2, wherein the method further comprises: storing the optimal read focus offset value and the optimal read tilt offset value.

9. The method as claimed in claim 5, wherein the method further comprises: storing the optimal write focus offset value and the optimal write tilt offset value.

10. An optical drive (1) comprising: an optical system (30) for scanning tracks (T₁, T₂, ...T_n) of a record carrier (2), which optical system comprises a light beam generator (31) that generates a light beam (32a), an objective lens (34) for focusing the light beam on the record carrier (2), an optical detector (35) for detecting a reflected light beam, a controllable focus actuator (42) for axially displacing the objective lens with respect to a recording reference plane of the record carrier, a controllable tilt actuator (43) for pivoting the objective lens with respect to the record carrier; a first memory (2100) arranged to store calibration data points; a second memory (2000) arranged to store an optimal focus offset value and an optimal tilt offset value; and a control circuit (90) having inputs for receiving signals from the optical detector and having outputs coupled to a control input of the focus actuator and the tilt actuator, wherein the control circuit further comprises: an integrated calibration unit (1000) arranged to perform calibration of a focus offset and a tilt offset simultaneously after the record carrier (2) is inserted in the optical drive (1).

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

12. The recorder as claimed in claim 11, wherein the recorder is a DVD recorder or a CD recorder or a Blu-ray disc recorder.

13. A player comprising the optical drive as claimed in claim 10.

14. The player as claimed in claim 13, wherein the player is a DVD player or a CD player or a Blu-ray disc player.

15. A computer program comprising program code means to perform a method of calibrating an optical drive (1), wherein the method comprises performing calibration of a focus offset and a tilt offset simultaneously after a record carrier (2) is inserted in the optical drive (1).