WO2008001317A2 - Device and method for retrieving information - Google Patents

Device and method for retrieving information Download PDF

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Publication number
WO2008001317A2
WO2008001317A2 PCT/IB2007/052490 IB2007052490W WO2008001317A2 WO 2008001317 A2 WO2008001317 A2 WO 2008001317A2 IB 2007052490 W IB2007052490 W IB 2007052490W WO 2008001317 A2 WO2008001317 A2 WO 2008001317A2
Authority
WO
WIPO (PCT)
Prior art keywords
jitter
region
control parameter
rate
data errors
Prior art date
Application number
PCT/IB2007/052490
Other languages
French (fr)
Other versions
WO2008001317A3 (en
Inventor
Yu Zhou
Original Assignee
Koninklijke Philips Electronics N.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Koninklijke Philips Electronics N.V. filed Critical Koninklijke Philips Electronics N.V.
Publication of WO2008001317A2 publication Critical patent/WO2008001317A2/en
Publication of WO2008001317A3 publication Critical patent/WO2008001317A3/en

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Classifications

    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/10—Digital recording or reproducing
    • G11B20/10009—Improvement or modification of read or write signals
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/10—Digital recording or reproducing
    • G11B20/10009—Improvement or modification of read or write signals
    • G11B20/10018—Improvement or modification of read or write signals analog processing for digital recording or reproduction
    • G11B20/10027—Improvement or modification of read or write signals analog processing for digital recording or reproduction adjusting the signal strength during recording or reproduction, e.g. variable gain amplifiers
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/10—Digital recording or reproducing
    • G11B20/10009—Improvement or modification of read or write signals
    • G11B20/10046—Improvement or modification of read or write signals filtering or equalising, e.g. setting the tap weights of an FIR filter
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/10—Digital recording or reproducing
    • G11B20/10009—Improvement or modification of read or write signals
    • G11B20/10046—Improvement or modification of read or write signals filtering or equalising, e.g. setting the tap weights of an FIR filter
    • G11B20/10212—Improvement or modification of read or write signals filtering or equalising, e.g. setting the tap weights of an FIR filter compensation for data shift, e.g. pulse-crowding effects
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/10—Digital recording or reproducing
    • G11B20/10009—Improvement or modification of read or write signals
    • G11B20/10481—Improvement or modification of read or write signals optimisation methods
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/10—Digital recording or reproducing
    • G11B20/10527—Audio or video recording; Data buffering arrangements
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/094—Methods and circuits for servo offset compensation
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/0948—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following specially adapted for detection and avoidance or compensation of imperfections on the carrier, e.g. dust, scratches, dropouts
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/095—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following specially adapted for discs, e.g. for compensation of eccentricity or wobble
    • G11B7/0953—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following specially adapted for discs, e.g. for compensation of eccentricity or wobble to compensate for eccentricity of the disc or disc tracks
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/095—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following specially adapted for discs, e.g. for compensation of eccentricity or wobble
    • G11B7/0956—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following specially adapted for discs, e.g. for compensation of eccentricity or wobble to compensate for tilt, skew, warp or inclination of the disc, i.e. maintain the optical axis at right angles to the disc
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/10—Digital recording or reproducing
    • G11B20/10527—Audio or video recording; Data buffering arrangements
    • G11B2020/10537—Audio or video recording
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/10—Digital recording or reproducing
    • G11B20/10527—Audio or video recording; Data buffering arrangements
    • G11B2020/1062—Data buffering arrangements, e.g. recording or playback buffers
    • G11B2020/10814—Data buffering arrangements, e.g. recording or playback buffers involving specific measures to prevent a buffer underrun

Definitions

  • the invention relates to a device for retrieving information from a disc-like optical record carrier, the information represented by optically readable marks along a substantially spiral track on the record carrier, the information organized into information units comprising main data and error correction data, the device comprising: a rotation unit for rotating the record carrier; a reading head for scanning the track by a radiation beam and generating a high-frequency signal on the basis of the marks; a reading head control unit for controlling generation and positioning of the radiation beam using signals representing control parameters; a decoding unit for processing the high-frequency signal into the main data and the error correction data; an error correction unit for finding and correcting data errors using the error correction data; and - a memory buffer for transitionally storing the main data.
  • the invention further relates to a method of retrieving information from a disc-like optical record carrier, the information represented by optically readable marks along a substantially spiral track on the record carrier, the information organized into information units comprising main data and error correction data, the method comprising steps of: a) rotating the record carrier and scanning the track by a radiation beam generated by a reading head; b) controlling positioning of the radiation beam using signals representing control parameters; c) generating a high-frequency signal by the reading head on the basis of the marks; d) processing the high-frequency signal into the main data and the error correction data; e) finding and correcting data errors using the error correction data; and f) transitionally storing the main data in a memory buffer.
  • the invention also relates to a computer program product for use in retrieving information from a disc-like optical record carrier by a reading device.
  • US 6,747,924 tackles this problem by performing test reproduction with respect to a plurality of testing radial locations of the optical disc, prior to actual reproduction of the disc.
  • the apparatus adjusts a focus balance/offset and an equalizer of the high-frequency signal to optimal settings, which are then used during the actual reproduction.
  • no disc errors will appear leading to time consuming corrective actions or even interruption of reproduction.
  • the device for retrieving information further comprises a disc error determination and correction unit for determining disc errors and controlling the reading head control unit, the disc error determination and correction unit comprising following sub-units: - a monitoring unit for selecting regions of the track, for monitoring position of the radiation beam along the track and for checking for occurrence of uncorrected data errors; a sampling unit for sampling a rate of data errors and a jitter a first predefined number of times in each region entered by the radiation beam, the jitter representing time variations of the high-frequency signal; a computing unit for calculating a region jitter as average value of the jitter corresponding to the first predefined number of times and for calculating a region rate of data errors as average value of the rate of data errors corresponding to the first predefined number oftimes; - a verification unit for checking a first predefined condition for the region jitter and the region rate of data errors in case the region jitter is different from any other region
  • the method of retrieving information further comprises steps of: g) checking for occurrence of uncorrected data errors ; h) selecting regions of the track; i) monitoring position of the radiation beam along the track; j) for each region entered by the radiation beam, out of the selected regions, sampling a jitter and a rate of data errors a first predefined number oftimes, the jitter representing time variations of the high-frequency signal; k) calculating a region jitter as average value of the jitter corresponding to the first predefined number of times;
  • a computer program product for use in retrieving information, as described in the opening paragraph, is provided, the computer program comprising program code means for causing a processor of the reading device, to perform the method as described in relation to the second aspect of the invention, when the computer program is run on the processor.
  • the measures according to the invention have the effect that different types of disc errors are determined during the reproduction/on the fly and effective corrective actions, calibrations are applied based on such determination. This adaptive disc error determination and correction improves performance of the device.
  • the disc error determination and correction unit is adapted to repeat within the same region actions of the sub-units with the actuator tilt substituted by the focus offset. This allows for more optimized focus offset calibration after a tilt correction.
  • the requested calibration being the calibration of the control parameter based on the jitter
  • the disc error determination and correction unit is adapted to repeat within the same region at least actions of the calibration unit and the adjustment unit with the control parameter substituted by a radial offset .
  • the jitter-based calibration of the radial offset in addition to standard calibrations, can further improve performance. This is specifically useful for the asymmetry type of disc.
  • the disc error determination and correction unit is adapted so that in case of absence of the high-frequency signal the requested calibration is substituted by a calibration comprising measuring of a radial error signal at different values of the control parameter and determining the region adjusted value of the control parameter corresponding to an optimal value of the radial error signal, the radial error signal being generated by the reading head on the basis of a pre-embossed track structure indicating the track.
  • the disc error determination and correction unit comprises an asymmetry and unbalance detection unit for: in case of occurrence of an uncorrected data error in the main data, sampling an asymmetry of the high-frequency signal a second predefined number of times; - calculating an average asymmetry as average value of the asymmetry of the high-frequency signal corresponding to the second predefined number of times; and correcting the asymmetry of the high-frequency signal in case the average asymmetry is outside a predefined asymmetry range, otherwise testing unbalance of the record carrier.
  • This facilities determination of the asymmetry disc and setting a corrective action.
  • the asymmetry and unbalance detection unit is adapted to correct the asymmetry of the high-frequency signal by: sampling the jitter and the rate of data errors a third predefined number of times and calculating corresponding average values of the jitter and the rate of data errors; - checking a second predefined condition for the average values of the jitter and the rate of data errors; in case the second predefined condition is fulfilled, measuring the rate of data errors for different settings of an equalizer of the high-frequency signal and determining optimal settings of the equalizer corresponding to a minimal value of the rate of data errors, otherwise measuring the jitter for different settings of the equalizer and determining optimal settings of the equalizer corresponding to a minimal value of the jitter.
  • This corrects performance problems due to asymmetry of the high-frequency signal.
  • the asymmetry and unbalance detection unit is adapted to correct the asymmetry of the high-frequency signal by measuring the jitter at different values of a radial offset and determining an optimal value of the radial offset corresponding to a minimal value of the jitter. This can be used as alternative or additional (improving) measure to correct performance problems due to asymmetry of the high- frequency signal.
  • the asymmetry and unbalance detection unit is adapted to test unbalance of the record carrier by: sampling a radial integrator a fourth predefined number of times; calculating an average radial integrator as average value of the radial integrator corresponding to the fourth predefined number of times; - calculating a unbalance indicator as ratio of the average radial integrator to the square of a rotational frequency of the record carrier; in case the unbalance indicator is outside a predefined unbalance range, reducing the rotational frequency of the record carrier. This makes it possible to detect unbalanced discs and to apply a corrective action.
  • processing the high-frequency signal comprises a first and a second stage of amplification of the high-frequency signal, the second stage gain being controlled automatically within a range
  • the disc error determination and correction unit is adapted for: monitoring values of the second stage gain; - adjusting the first stage gain in dependence of measured values of the second stage gain so as to keep the second stage gain away from the limits of the range. This allows for elimination or prevention of errors caused by the bifringence disc.
  • Figure Ia shows an example of a disc-shaped optical record carrier
  • Figure Ib shows a cross-section taken of the record carrier
  • Figure Ic shows an example of a wobble of the track
  • Figure 2 shows a reading device, in accordance with the invention
  • Figure 3 shows an example of focus/radial control loop for controlling radial and focus actuators
  • Figures 4a and 4b show an example of a procedure performed by the disc error determination and correction unit 32, in accordance with the invention.
  • Figure 5 shows an example of a procedure performed by the calibration unit
  • Figure 6 shows dependence of HF jitter and PI BLER on the actuator tilt.
  • Figure 7 shows dependence of HF jitter on the focus offset.
  • Figure 8a shows dependence of the radial error push-pull signal on the focus offset.
  • Figure 8b shows dependence of the radial error push-pull signal on the actuator tilt.
  • Figure 9 shows definition of the asymmetry of the HF signal.
  • Figure 10 shows an example of a procedure to measure asymmetry of HF signal by the asymmetry and unbalance unit 42, in accordance with the invention.
  • Figure 11 shows an example of a procedure to measure and correct the HF signal asymmetry, in accordance with the invention.
  • Figure 12 shows an example of a digital equalizer.
  • Figure 13 shows an example of the bathtub shape of jitter dependence on the equalizer settings.
  • Figure 14 shows an example of a procedure for testing unbalance of the record carrier, performed by the asymmetry and unbalance detection unit 42, in accordance with the invention.
  • Figure 15 shows an example of a procedure to correct for the effect of bifringence, in accordance with the invention.
  • Figure 16 shows an example of a block diagram of a part of the read processing unit 30 and the front-end unit 31.
  • Figure 17 shows an example of a procedure performed by the disc error determination and correction unit 32, in accordance with the invention. Corresponding elements in different Figures have identical reference numerals/symbo Is .
  • Figure Ia shows a disc-shaped record carrier 11 having a track 9 and a central hole 10.
  • the track 9 is arranged in accordance with a spiral pattern of turns constituting substantially parallel tracks on an information layer.
  • the record carrier may be optically readable, called an optical disc.
  • Recorded information is represented on the information layer by optically detectable marks recorded along the track.
  • the marks are constituted by variations of a physical parameter and thereby have different optical properties than their surroundings, e.g. variations in reflection.
  • the marks on the information layer can be pre- embossed, like in read-only discs, such as CD-ROM or DVD.
  • the information layer, or at least a part of it can be of a recordable type, on which marks can be recorded.
  • Examples of a recordable disc are the CD-R, CD-RW, and writable versions of DVD, such as DVD+RW, and the high-density writable optical disc called Blu-ray Disc, BD.
  • the track 9 on the recordable type of record carrier is indicated by a pre-embossed track structure provided during manufacture of the blank record carrier, for example a pregroove.
  • Figure Ib is a cross-section taken along the line b-b of the record carrier 11 of the recordable type, in which a transparent substrate 15 is provided with a recording layer 16 and a protective layer 17.
  • the track structure is constituted, for example, by a pregroove 14, which enables a read/write head to follow the track 9 during scanning.
  • the pregroove 14 may be implemented as an indentation or an elevation, or may consist of a material having a different optical property than the material surrounding it.
  • a track structure may also be formed by regularly spread sub-tracks, which periodically cause servo signals to occur.
  • the record carrier may be intended to carry real-time information, for example video or audio information, or other information, such as computer data.
  • Figure Ic shows an example of a periodic variation of the transversal position of the track of the (recordable) disc, also called wobble.
  • the variations cause an additional signal to arise in auxiliary detectors, for example in a push-pull channel generated by sub detectors or partial detectors in the central spot in a head of a scanning device.
  • the wobble is, for example, frequency modulated and position information is encoded in the modulation.
  • FIG. 2 shows an example of a device for retrieving information from a record carrier 11 such as CD-ROM, DVD, CD-R, CD-RW, DVD+RW or BD, according to the invention.
  • the device is provided with scanning means for scanning the track of the record carrier 11, which means include a rotation unit 21 for rotating the record carrier 11, a reading head 22 for scanning the track by a radiation beam 24 and a reading head control unit 25 for controlling generation and positioning of the radiation beam.
  • the head 22 comprises an optical system of a known type for generating the radiation beam 24 guided through optical elements to generate the radiation spot 23 on a track of the information layer of the record carrier.
  • the radiation beam 24 is generated by a radiation source, e.g. a laser diode.
  • the head further comprises (not shown) a focusing actuator for focusing the beam to the radiation spot 23 on the track by moving the focus of the radiation beam 24 along the optical axis of said beam, and a sledge and a tracking actuator for positioning the radiation spot 23 in a direction transverse to the scanning direction of the track on the center of the track.
  • the transverse direction is called radial direction and the tracking actuator is called radial actuator.
  • the tracking actuator may comprise coils for radially moving an optical element or may alternatively be arranged for changing the angle of a reflecting element.
  • the focusing actuator may comprise coils for moving the focus of the radiation beam 24.
  • the focusing and radial actuators may be constructed in the form of one actuator for positioning an optical element such as a lens and performing functions of said actuators.
  • the tracking and focusing actuators are driven by actuator signals, RA and FA in Figure 3, from the reading head control unit 25. For reading the radiation reflected by the information layer is detected by a detector of a usual type, e.g.
  • a four-quadrant diode in the reading head 22 for generating detector signals coupled to a front- end unit 31 for generating various scanning signals, including a main detector signal 33 and sub detector signals 35 for tracking and focusing.
  • the main detector signal 33 is also called a high-frequency, HF, signal.
  • the sub detector signals 35 are coupled to the reading head control unit 25 for controlling said focusing actuators. Examples of the sub detector signals 35 are a focusing error signal and a radial error signal, FEN and REN in Figure 3, respectively.
  • Figure 3 shows an example of so-called focus/radial control loop for controlling radial and focus actuators.
  • the main detector signal 33 is processed by a read processing unit 30 of a usual type including a decoding unit and an error correction unit and output unit to retrieve the information.
  • the decoding unit is for processing the high-frequency signal into the main data and the error correction data comprised in the information.
  • the error correction unit is for finding and correcting data errors using the error correction data.
  • the read processing unit may comprise a memory buffer for transitionally storing the main data. Alternatively, the memory buffer can be a separate unit.
  • reading means for reading information include the rotation unit 21, the reading head 22, the reading head control unit 25 and the read processing unit 30.
  • the reading head 22 is also referred to as the Optical Pickup Unit, OPU.
  • the device comprises a control unit 20, which is connected via control lines 26, e.g. a system bus, to the other units in the device, for controlling these units.
  • the control unit 20 comprises control circuitry, for example a microprocessor, a program memory and interfaces for performing different control procedures and functions.
  • the control unit 20 may also be implemented as a state machine in logic circuits.
  • the control unit 20 controls the scanning, for example for recording or reading of information, and may be arranged for receiving commands from a user or from a host computer.
  • the device may be provided with recording means for recording information on a record carrier of a writable or re-writable type, for example CD-R or CD-RW, or DVD+RW or BD.
  • the reading head 22 is adapted for recording marks on a record carrier.
  • the recording means cooperate with the head 22 and the front-end unit 31 for generating a write beam of radiation, and comprise write processing means for processing the input information to generate a write signal to drive the head 22, which write processing means comprise an input unit 27, a formatter 28 and a modulator 29.
  • the power of the beam of radiation is controlled by the modulator 29 to create optically detectable marks in the recording layer.
  • the marks may be in any optically readable form, e.g.
  • the device is a storage system only, for example an optical disc drive for use in a computer.
  • the control unit 20 is arranged to communicate with a processing unit in the host computer via a standardized interface (not shown).
  • Digital data is interfaced to the formatter unit 28 and from the read processing unit 30 directly. In this case, the interface acts as an input unit and an output unit.
  • the device is arranged as a stand alone unit, for example a video playback/recording device for consumer use.
  • the control unit 20, or an additional host control unit included in the device is arranged to be controlled directly by the user.
  • the device includes application data processing, for example audio and/or video processing circuits.
  • the information presented to the input unit 27 may comprise analog audio and/or video, or digital uncompressed audio/video signals; in this case the input unit 27 may comprise compression means for these signals.
  • the read processing unit 30 may comprise suitable audio and/or video decompression units.
  • the reading head control unit 25 applies a set of beam control parameters for controlling various aspects of the radiation beam.
  • a first example of a beam control parameter is related to achieving a correct focus, and is called a focus offset.
  • the focus offset is used to provide an adjusted set point for the sub detector signals and/or actuator signals that control the focus.
  • the focus offset may for example compensate deviations of the optical system or detector location in the head.
  • a similar example of a beam control parameter is called a radial offset, and compensates the transverse position of the scanning spot.
  • Another example of a beam control parameter is an actuator tilt, which is used to actively compensate for tilt in drive, for example the reading head unit or the rotation unit, or disc tilt.
  • beam control parameters may be related to the power of the beam, timing of certain signal elements in the beam, etcetera.
  • beam control may be (partly) implemented in a software or in other units, such as a laser power control unit or a signal pattern from a recording unit. It is noted that the beam control parameters may require calibration or measurements during manufacture of the device, or may be affected by ageing, temperature, or other actual operational conditions during use of the device.
  • the device for retrieving information comprises a disc error determination and correction unit 32 for determining disc errors and controlling the reading head control unit 25.
  • disc errors are disc deviation, disc unbalance, disc tilt, differences in a disc substrate layer thickness, bifringence disc, variable beta/asymmetry disc and other, leading to, for example, changes in a quality (characteristics) of the high-frequency signal derived from the disc.
  • the disc error determination and correction unit 32 controls the reading head control unit 25 in dependence on detected disc errors by adjusting a selected beam control parameter of the reading head control unit 25 to a calibration value obtained from a calibration procedure. This procedure can be based for example on a jitter of the High- Frequency signal, HF jitter, which jitter represents time variations of this signal.
  • the jitter can be presented as a standard deviation of the time variation of the digitized data passed through the equalizer of the decoding unit; the jitter of the leading and trailing edges of the signal is measured relative to the Phase-Locked Loop (PLL) clock and normalized by the channel bit clock, as known in the art.
  • PLL Phase-Locked Loop
  • a calibration procedure can be based also on a parameter measuring quality of data retrieval by means of rate of data errors in the information processed by the read processing unit 30. For example, so-called PI BLER,
  • Parity of the Inner code BLock Error Rate can be used as known from the DVD system.
  • PI BLER is also known as "PI Sum 8", which is a moving average sum of the Parity Inner errors over 8 Error Correction Code blocks.
  • Cl a corresponding parameter
  • PI BLER can also denote Cl BLER, PI Sum 8 or a more general term - the rate of data errors.
  • the above two quality parameters, the jitter and the rate of data errors can be measured only in presence of the high-frequency signal, which is generated on the basis of the marks in the track.
  • the disc error determination and correction unit 32 monitors scanning of the record carrier, evaluates quality parameters in order to identify different disc errors and, if necessary, takes corrective actions.
  • the disc error determination and correction unit 32 includes the following sub units: - a monitoring unit 36 for selecting regions of the track, for monitoring position of the radiation beam along the track and for checking for occurrence of uncorrected data errors; a sampling unit 37 for sampling a rate of data errors and a jitter a first predefined number of times in each region entered by the radiation beam, the jitter representing time variations of the high-frequency signal; a computing unit 38 for calculating a region jitter as average value of the jitter corresponding to the first predefined number of times and for calculating a region rate of data errors as average value of the rate of data errors corresponding to the first predefined number oftimes; a verification unit 39 for checking a first predefined condition for the region jitter and the region rate of data errors in case the region jitter is different from any other region jitter by a predefined jitter difference, said other region jitter calculated for any previously scanned region, and for requesting a calibration of a control parameter based on the rate of data
  • the sub units of the disc error determination and correction unit 32 perform a method comprising steps of: g) checking for occurrence of uncorrected data errors ; h) selecting regions of the track; i) monitoring position of the radiation beam along the track; j) for each region entered by the radiation beam, out of the selected regions, sampling a jitter and a rate of data errors a first predefined number of times, the jitter representing time variations of the high-frequency signal; k) calculating a region jitter as average value of the jitter corresponding to the first predefined number of times;
  • the disc tilt or substrate layer thickness across the disc can be different from inner side of the disc to the outer side of the disc.
  • (actuator) tilt calibration and focus offset calibration are done by the disc error determination and correction unit 32 at the start-up, at the inner side of the disc, and the best tilt and focus offset is set to achieve minimum jitter point, the HF signal quality (jitter and PI BLER) can be worsen off, if the disc tilt or substrate layer thickness is changed when playing from the inner side of the disc to the outer side of the disc.
  • the detectable symptom is increase of HF jitter and/or PI BLER.
  • the whole disc is divided into several regions from the inner side to the outer side by the monitoring unit 36.
  • the calibration is done in regions across the whole disc from the inner side to the outer side, during scanning of those regions.
  • the measured HF jitter in region (k) is 1.0% higher/lower than in region (k-1), region (k-2), ...etcetera, and the calibration in region k has not been done before, the calibration will be done in this region.
  • HF jitter and PI BLER are monitored by the sampling unit 37. This is done by sampling values of the jitter and PI BLER for each region entered by the radiation beam.
  • the number of sampling points is predefined. For example, said values can be measured 25 times during one rotation of the record carrier by reading them from a decoder register. Then, the measured values of HF jitter and PI BLER at different sampling points are averaged by the computing unit 38.
  • the verification unit 39 checks the first predefined condition for the average HF jitter and the average PI BLER.
  • the jitter difference of less than 0.5% can be caused by the measurement noise.
  • the difference of more than 1% across the region usually means that the present system settings are not the best for this region. Therefore, in an embodiment of the device, the given jitter difference is 1%.
  • experimental data show that a condition with HF jitter lower than about 13% and PI BLER > 130 can be used to decide which type of adjustment should be applied.
  • Other condition can be applied depending on a particular system; the above condition is optimized mainly for the DVD system. If this condition is fulfilled, the verification unit 39 sets request for a calibration based on PI BLER, otherwise the jitter based calibration will be requested.
  • a calibration is performed when the memory buffer occupancy is above the predefined level corresponding to a time necessary for performing the calibration. That means the calibration can be done without any interruption of video/audio playback.
  • the occupancy level of 80% may correspond to about 2 seconds of video playback, a time to do engine level calibrations or adjustments.
  • a calibration can be executed also in case of presence of uncorrectable data error(s), "read error", as this leads to interruption of data retrieval, anyway.
  • Figures 4a and 4b show an example of a procedure performed by the sub units of the disc error determination and correction unit 32.
  • the requested calibration is the tilt calibration and after this calibration is done the above measurements and checks are repeated and the focus offset calibration is executed, if relevant conditions described above are fulfilled.
  • the required buffer time is 1 second for Constant Angular Velocity, CAV, 40Hz DVD playback. Same conditions as for the tilt calibration are used to decide whether the jitter based or the PI BLER based focus offset calibration is to be done.
  • Figure 5 shows an example of a procedure performed by the calibration unit 40 and the adjustment unit 41 in case of the calibration of the focus offset based on the jitter. See also Figure 7.
  • the PI BLER based focus offset calibration or the jitter/PI BLER based tilt calibration follow the same procedure.
  • the disc error determination and correction unit is adapted to perform each type of the calibration of each control parameter no more than one time in the same region. In other words, a specific calibration is performed only once in the same region, if successful.
  • a successful calibration is a calibration for which it was possible to find optimal, the region adjusted value of a control parameter. This value is saved in memory for using during scanning the same region again.
  • the disc error determination and correction unit is adapted to perform a radial offset calibration based on HF jitter, after first performing the actuator tilt or focus offset calibration based on HF jitter.
  • the jitter based calibration is repeated, but with the actuator tilt or focus offset substituted by the radial offset. This can be done by simply repeating actions of the calibration unit 40 and the adjustment unit 41 without any precondition or by repeating the whole procedure described above, but sampling only HF jitter and checking only the condition related to the jitter difference, in order to request the radial offset calibration.
  • Figure 6 shows dependence of HF jitter and PI BLER on the actuator tilt, which dependences are used in respective calibrations. The second order polynomials fitted to the measured values are also shown.
  • Figure 7 shows dependence of HF jitter on the focus offset. "Default setting” and “ramp down/up” modes are as used in Figure 5.
  • the region adjusted value of the control parameter is determined simply by taking this value of the control parameter applied during measurements, for which a minimal value of HF jitter or PI BLER was measured.
  • the calibration unit 40 is adapted to determine the region adjusted value of the control parameter by calculating a minimum of a function fitted to the measured values.
  • the function may be the second or higher order polynomial; the second order one requires simpler computations.
  • the disc error determination and correction unit is adapted so that in case of absence of the high-frequency signal the requested calibration is substituted by a calibration comprising measuring of a radial error signal at different values of the control parameter and determining the region adjusted value of the control parameter corresponding to an optimal value of the radial error signal, the radial error signal being generated by the reading head on the basis of a pre-embossed track structure indicating the track.
  • the device may use for example a radial error push- pull signal, a radial error signal based on so-called sampled tracking, or other radial error signals known in the art.
  • Figures 8a and 8b show dependence of the radial error push-pull on the focus offset and the actuator tilt, respectively.
  • the calibration unit is adapted to determine the region adjusted value of the control parameter by calculating a maximum of a function fitted to the measured values of the radial error signal. This maximum defines the optimal value of the radial error.
  • the function may be the second or higher order polynomial; the second order one requires simpler computations.
  • the disc error determination and correction unit comprises an asymmetry and unbalance detection unit 42 for: in case of occurrence of an uncorrected data error in the main data, sampling an asymmetry of the high-frequency signal a second predefined number of times; calculating an average asymmetry as average value of the asymmetry of the high-frequency signal corresponding to the second predefined number of times; and - correcting the asymmetry of the high-frequency signal in case the average asymmetry is outside a predefined asymmetry range, otherwise testing unbalance of the record carrier.
  • the values of Ai, A 2 , and CALF can be read from the decoder register. They are sampled the second predefined number of times after the monitoring unit 36 detects the uncorrected error, "read error". For example, in an embodiment of the device, the asymmetry is sampled/calculated 16 times during one rotation of the disc. Then, the asymmetry is averaged over the second predefined number. For the purpose of classifying the disc as asymmetry disc, the averaged calculated asymmetry is compared against the predefined asymmetry range. This range can have different values for different types of discs. For example, for DVD+R, DVD+RW discs, the range is set to (-5%, 15%). This means that a disc with the asymmetry outside this range is considered to be the asymmetry disc; corrective action is necessary.
  • Figure 10 shows an example of a procedure performed by the asymmetry and unbalance detection unit 42 for detecting the HF signal asymmetry.
  • checking the asymmetry can be done on more regular basis, for example when entering a new region of the disc, so not only after detection of "read error".
  • the asymmetry and unbalance detection unit 42 is adapted to correct the asymmetry of the high-frequency signal by measuring the jitter at different values of a radial offset and determining an optimal value of the radial offset corresponding to a minimal value of the jitter. Again, this optimal value can be determined simply by taking this value of the control parameter applied during measurements, for which the minimal value of HF jitter was measured. Another option is to fit a function, for example the second order polynomial, to the measured values of HF jitter and to calculate a minimum of such function.
  • Another way of correcting the asymmetry of the HF signal is done by the asymmetry and unbalance detection unit 42, by: sampling the jitter and the rate of data errors a third predefined number of times and calculating corresponding average values of the jitter and the rate of data errors; checking a second predefined condition for the average values of the jitter and the rate of data errors; - in case the second predefined condition is fulfilled, measuring the rate of data errors for different settings of an equalizer of the high-frequency signal and determining optimal settings of the equalizer corresponding to a minimal value of the rate of data errors, otherwise measuring the jitter for different settings of the equalizer and determining optimal settings of the equalizer corresponding to a minimal value of the jitter.
  • the third predefined number of times can be the same as the first predefined number of times, that is 25 times during one rotation of the disc.
  • the second predefined condition can be same as the first predefined condition, that is HF jitter lower than 13% and PI BLER greater than 130.
  • the second condition requires that PI BLER > 130. In this case, it is sufficient to sample only the rate of data errors.
  • Figure 11 shows an example of a procedure to measure and correct the HF signal asymmetry.
  • the determination of optimal settings of the equalizer can be done as follows in the case of the DVD disc. If so-called limit equalizer with adaptive clipping level is used to amplify the HF signal components like 3T, it is turned off. Then, settings of the HF high pass filter, HF HPF, are checked. If the HF high pass filter cut-off frequency is higher than about 1/10 of the frequency of 14T, set it to 1/10 of the frequency of 14T.
  • T is a measure of a length of a mark in the track. For the DVD system, 14T is the longest mark and 3T is the shortest mark.
  • the HF HPF cut-off frequency is set to a value, which is as high as possible and at the same time does not lead to too much phase distortion. This is done in order to filter out lower frequency noise caused by disc scratches, etcetera. For the asymmetry disc, one should reduce the phase distortion introduced by the HF HPF into a level as small as possible. Therefore, the HF HPF cut-off frequency is corrected to 1/10 of the frequency of 14T, if necessary.
  • HF jitter and/or PI BLER are sampled as described above.
  • jitter based or PI BLER based equalizer settings adjustments are performed. These adjustments are can be done by changing gain taps A and/or B of the equalizer as shown in Figure 12.
  • Figure 13 shows an example of the bathtub shape of jitter dependence on the equalizer settings.
  • the asymmetry and unbalance correction unit 42 can be modified to determine the optimal settings of the equalizer by calculating a minimum of a function fitted to the measured values of the jitter or the rate of data errors, in accordance with the second predefined condition.
  • the simple function is the second order polynomial.
  • Disturbances caused by most unbalance discs can be compensated well enough by the servo control loop.
  • unbalance disc for example caused by sticker/marker put by a user on the disc by himself, normal servo control loop are unable to handle it.
  • the disturbances can be so high that they can affect normal tracking performance, causing read problem or error.
  • a general way to handle this kind of error is to spin down the drive and do playback at lower speed.
  • the asymmetry and unbalance detection unit 42 is adapted to test unbalance of the record carrier by: sampling a radial integrator during a predefined number of revolutions; calculating an average radial integrator as average value of the radial integrator corresponding to the predefined number of revolutions; calculating a unbalance indicator as ratio of the average radial integrator to the square of a rotational frequency of the record carrier; - in case the unbalance indicator is outside a predefined unbalance range, reducing the rotational frequency of the record carrier.
  • the radial integrator (peak-to-peak) output is measured a number of times over the predefined number of revolutions, for example over one revolution, and averaged. The ratio of this averaged radial integrator output and the square of disc rotational speed is monitored. If it is outside the predefined range/value, the disc is detected as high unbalance disc. Consequently, action to spin down to lower playback speed is activated.
  • Figure 14 shows an example of a procedure for testing unbalance of the record carrier, performed by the asymmetry and unbalance detection unit 42.
  • Another kind of a disc error is caused by so-called bifringence disc.
  • Bifringence is a property of a material, which causes incident light waves of different polarizations to be refracted differently by the material.
  • the amplitude of the HF signal increases greatly from inner side of the disc to the outer side of the disc, so that HF Automatic Gain Control, HF AGC, in the decoder IC is no effective anymore, which leads to saturation of the HF AGC adjustable range in the decoder path.
  • the solution to this problem is to monitor the HF AGC gain while playing.
  • the disc error determination and correction unit when processing the high-frequency signal comprises a first and a second stage of amplification of the high-frequency signal, the second stage gain being controlled automatically within a range, the disc error determination and correction unit is adapted for: monitoring values of the second stage gain; - adjusting the first stage gain in dependence of measured values of the second stage gain so as to keep the second stage gain away from the limits of the range.
  • FIG 15 shows an example of a procedure performed by the disc error determination and correction unit to correct for the effect of bifringence.
  • the front gain, a refers to the front signal processing DC gain for HF signal, performed by the front-end unit 31, front IC.
  • the HF AGC gain, agc gain refers to the HF AGC block in the decoder.
  • Figure 16 shows an example of a layout of relevant parts of the front IC and the decoder IC.
  • the disc error determination and correction unit 32 is adapted to perform a procedure as shown in Figure 17.
  • the disc error determination and correction unit 32 is included in the control unit 20.
  • the disc error determination and correction unit 32 can be implemented in firmware.
  • Embodiments of the method according to the invention correspond to functions/ procedures performed by the disc error determination and correction unit 32 and its sub units as described above in reference to different embodiments of the device.
  • each type of the calibration of each control parameter is requested no more than one time in the same region.
  • control parameter is the actuator tilt and thereafter steps from j) to p) are repeated within the same region with the actuator tilt substituted by the focus offset.
  • requested calibration is the calibration of the control parameter based on the jitter and thereafter at least steps o) and p) are repeated within the same region with the control parameter substituted by a radial offset .
  • the jitter is the standard deviation of time variations of the high-frequency signal and the predefined jitter difference is substantially 1%.
  • the first predefined condition requires that the region jitter is lower than substantially 13% and the region rate of data errors is greater than substantially 130 data errors per one information unit.
  • the region adjusted value of the control parameter is determined by calculating a minimum of a function fitted to the measured values of the jitter or the rate of data errors as in the request.
  • the requested calibration is substituted by a calibration comprising measuring of a radial error signal at different values of the control parameter and determining the region adjusted value of the control parameter corresponding to an optimal value of the radial error signal, the radial error signal being generated by the reading head on the basis of a pre- embossed track structure indicating the track.
  • the radial error signal is a radial error push- pull signal.
  • the region adjusted value of the control parameter is determined by calculating a maximum of a function fitted to the measured values, said maximum defining the optimal value of the radial error signal.
  • the following steps are executed: sampling an asymmetry of the high-frequency signal a second predefined number of times; calculating an average asymmetry as average value of the asymmetry of the high-frequency signal corresponding to the second predefined number of times; and - in case the average asymmetry is outside a predefined asymmetry range, correcting the asymmetry of the high-frequency signal, otherwise testing unbalance of the record carrier.
  • correcting the asymmetry of the high- frequency signal comprises measuring of the jitter at different values of a radial offset and determining an optimal value of the radial offset corresponding to a minimal value of the jitter.
  • the optimal value of the radial offset is determined by calculating a minimum of a function fitted to the measured values of the jitter.
  • correcting the asymmetry of the high- frequency signal comprises steps of: sampling the jitter and the rate of data errors a third predefined number of times and calculating corresponding average values of the jitter and the rate of data errors; checking a second predefined condition for the average values of the jitter and the rate of data errors; - in case the second predefined condition is fulfilled, measuring the rate of data errors for different settings of an equalizer of the high-frequency signal and determining optimal settings of the equalizer corresponding to a minimal value of the rate of data errors, otherwise measuring the jitter for different settings of the equalizer and determining optimal settings of the equalizer corresponding to a minimal value of the jitter.
  • the optimal settings of the equalizer are determined by calculating a minimum of a function fitted to the measured values of the jitter or the rate of data errors, accordingly.
  • testing unbalance of the record carrier comprises steps of: sampling a radial integrator a fourth predefined number of times; calculating an average radial integrator as average value of the radial integrator corresponding to the fourth predefined number of times; - calculating a unbalance indicator as ratio of the average radial integrator to the square of a rotational frequency of the record carrier; in case the unbalance indicator is outside a predefined unbalance range, reducing the rotational frequency of the record carrier.
  • processing the high-frequency signal comprises a first and a second stage of amplification of the high-frequency signal, the second stage gain being controlled automatically within a range
  • the method comprising steps of: monitoring values of the second stage gain; adjusting the first stage gain in dependence of measured values of the second stage gain so as to keep the second stage gain away from the limits of the range.
  • Different embodiments of a computer program for use in retrieving information from a disc-like optical record carrier by a reading device are operative to cause a processor of the reading device, and in particular the control unit 20, to perform functions/procedures as described in reference to embodiments of the device and/or the method presented above, when the computer program is executed by the reading device.
  • the invention may be implemented by means of a general purpose processor executing a computer program or by dedicated hardware or by a combination of both, and that in this document the word “comprising” does not exclude the presence of other elements or steps than those listed and the word “a” or “an” preceding an element does not exclude the presence of a plurality of such elements, that any reference signs do not limit the scope of the claims, that "means” may be represented by a single item or a plurality and that several "means” may be represented by the same item of hardware.

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Abstract

A device for retrieving information from a disc-like optical record carrier (11). The device comprises reading means (21, 22, 25, 30) for reading the information recorded on the record carrier and control means (20) for controlling the reading. Further, the device comprises disc error determination and correction means (32, 36, 37, 38, 39, 40, 41, 42) for determining disc errors and taking corrective actions by adjusting beam control parameters on the fly, during scanning of the record carrier. The disc errors handled by the disc error determination and correction means include tilt, unbalance, variable high-frequency signal asymmetry disc, bifringence disc, etcetera.

Description

A device for and a method of retrieving information
FIELD OF THE INVENTION:
The invention relates to a device for retrieving information from a disc-like optical record carrier, the information represented by optically readable marks along a substantially spiral track on the record carrier, the information organized into information units comprising main data and error correction data, the device comprising: a rotation unit for rotating the record carrier; a reading head for scanning the track by a radiation beam and generating a high-frequency signal on the basis of the marks; a reading head control unit for controlling generation and positioning of the radiation beam using signals representing control parameters; a decoding unit for processing the high-frequency signal into the main data and the error correction data; an error correction unit for finding and correcting data errors using the error correction data; and - a memory buffer for transitionally storing the main data.
The invention further relates to a method of retrieving information from a disc-like optical record carrier, the information represented by optically readable marks along a substantially spiral track on the record carrier, the information organized into information units comprising main data and error correction data, the method comprising steps of: a) rotating the record carrier and scanning the track by a radiation beam generated by a reading head; b) controlling positioning of the radiation beam using signals representing control parameters; c) generating a high-frequency signal by the reading head on the basis of the marks; d) processing the high-frequency signal into the main data and the error correction data; e) finding and correcting data errors using the error correction data; and f) transitionally storing the main data in a memory buffer. The invention also relates to a computer program product for use in retrieving information from a disc-like optical record carrier by a reading device.
BACKGROUND OF THE INVENTION: Compared to a hard disc drive, the most challenging part for an optical disc drive is its robustness requirement of being able to play all kinds of discs. It is very common that same batch of same type of disc can have totally difference playback quality even on the same drive. This could be caused by localized disc defects like finger-prints, scratches and dust, but also by special disc errors like disc deviation, disc unbalance, disc tilt, differences in a disc substrate layer thickness, bifringence disc, variable beta/asymmetry disc and other, leading to, for example, changes in a quality of the high-frequency signal derived from the disc. This issue becomes more significant with the wide usage of all kinds of optical recorders. Large spread of the high-frequency signal recorded on different media and by different recorders can lead to serious playback problems. The optical disc reproduction apparatus disclosed by the United States Patent
US 6,747,924 tackles this problem by performing test reproduction with respect to a plurality of testing radial locations of the optical disc, prior to actual reproduction of the disc. During said test reproduction the apparatus adjusts a focus balance/offset and an equalizer of the high-frequency signal to optimal settings, which are then used during the actual reproduction. However, there is no guarantee that during the actual reproduction no disc errors will appear leading to time consuming corrective actions or even interruption of reproduction.
SUMMARY OF THE INVENTION:
Therefore, it is an object of the present invention to provide an efficient way of handling disc errors during the actual reproduction of data from the disc.
For this purpose, according to a first aspect of the invention, the device for retrieving information, as described in the opening paragraph, further comprises a disc error determination and correction unit for determining disc errors and controlling the reading head control unit, the disc error determination and correction unit comprising following sub-units: - a monitoring unit for selecting regions of the track, for monitoring position of the radiation beam along the track and for checking for occurrence of uncorrected data errors; a sampling unit for sampling a rate of data errors and a jitter a first predefined number of times in each region entered by the radiation beam, the jitter representing time variations of the high-frequency signal; a computing unit for calculating a region jitter as average value of the jitter corresponding to the first predefined number of times and for calculating a region rate of data errors as average value of the rate of data errors corresponding to the first predefined number oftimes; - a verification unit for checking a first predefined condition for the region jitter and the region rate of data errors in case the region jitter is different from any other region jitter by a predefined jitter difference, said other region jitter calculated for any previously scanned region, and for requesting a calibration of a control parameter based on the rate of data errors in case the first predefined condition is fulfilled, otherwise requesting a calibration of the control parameter based on the jitter, the control parameter being an actuator tilt or a focus offset ; a calibration unit for performing the requested calibration comprising measuring of the jitter or the rate of data errors as in the request at different values of the control parameter and determining a region adjusted value of the control parameter corresponding to a minimal value of the jitter or the rate of data errors, respectively, in case the memory buffer occupancy is above a predefined level or in case of occurrence of an uncorrected data error in the main data; and an adjustment unit for saving the region adjusted value of the control parameter for use during scanning the region and setting the control parameter to the region adjusted value, in case the requested calibration is successful.
For this purpose, according to a second aspect of the invention, the method of retrieving information, as describe in the opening paragraph, further comprises steps of: g) checking for occurrence of uncorrected data errors ; h) selecting regions of the track; i) monitoring position of the radiation beam along the track; j) for each region entered by the radiation beam, out of the selected regions, sampling a jitter and a rate of data errors a first predefined number oftimes, the jitter representing time variations of the high-frequency signal; k) calculating a region jitter as average value of the jitter corresponding to the first predefined number of times;
1) calculating a region rate of data errors as average value of the rate of data errors corresponding to the first predefined number oftimes; m) in case the region jitter is different from any other region jitter by a predefined jitter difference, said other region jitter calculated for any previously scanned region, checking a first predefined condition for the region jitter and the region rate of data errors; n) in case the first predefined condition is fulfilled, requesting a calibration of a control parameter based on the rate of data errors, otherwise requesting a calibration of the control parameter based on the jitter, the control parameter being an actuator tilt or a focus offset ; o) in case the memory buffer occupancy is above a predefined level or in case of occurrence of an uncorrected data error in the main data, performing the requested calibration comprising measuring of the jitter or the rate of data errors as in the request at different values of the control parameter and determining a region adjusted value of the control parameter corresponding to a minimal value of the jitter or the rate of data errors, respectively; and p) in case the requested calibration is successful, saving the region adjusted value of the control parameter for use during scanning the region and setting the control parameter to the region adjusted value.
For this purpose, according to a third aspect of the invention, a computer program product for use in retrieving information, as described in the opening paragraph, is provided, the computer program comprising program code means for causing a processor of the reading device, to perform the method as described in relation to the second aspect of the invention, when the computer program is run on the processor.
The measures according to the invention have the effect that different types of disc errors are determined during the reproduction/on the fly and effective corrective actions, calibrations are applied based on such determination. This adaptive disc error determination and correction improves performance of the device.
In an embodiment of the device, the control parameter being the actuator tilt, the disc error determination and correction unit is adapted to repeat within the same region actions of the sub-units with the actuator tilt substituted by the focus offset. This allows for more optimized focus offset calibration after a tilt correction. In another embodiment of the device, the requested calibration being the calibration of the control parameter based on the jitter, the disc error determination and correction unit is adapted to repeat within the same region at least actions of the calibration unit and the adjustment unit with the control parameter substituted by a radial offset . The jitter-based calibration of the radial offset, in addition to standard calibrations, can further improve performance. This is specifically useful for the asymmetry type of disc.
Advantageously, the disc error determination and correction unit is adapted so that in case of absence of the high-frequency signal the requested calibration is substituted by a calibration comprising measuring of a radial error signal at different values of the control parameter and determining the region adjusted value of the control parameter corresponding to an optimal value of the radial error signal, the radial error signal being generated by the reading head on the basis of a pre-embossed track structure indicating the track. This makes it possible to perform corrective actions at instances when the high-frequency signal is not present.
It is advantageous, if the disc error determination and correction unit comprises an asymmetry and unbalance detection unit for: in case of occurrence of an uncorrected data error in the main data, sampling an asymmetry of the high-frequency signal a second predefined number of times; - calculating an average asymmetry as average value of the asymmetry of the high-frequency signal corresponding to the second predefined number of times; and correcting the asymmetry of the high-frequency signal in case the average asymmetry is outside a predefined asymmetry range, otherwise testing unbalance of the record carrier. This facilities determination of the asymmetry disc and setting a corrective action.
In an embodiment of the device, the asymmetry and unbalance detection unit is adapted to correct the asymmetry of the high-frequency signal by: sampling the jitter and the rate of data errors a third predefined number of times and calculating corresponding average values of the jitter and the rate of data errors; - checking a second predefined condition for the average values of the jitter and the rate of data errors; in case the second predefined condition is fulfilled, measuring the rate of data errors for different settings of an equalizer of the high-frequency signal and determining optimal settings of the equalizer corresponding to a minimal value of the rate of data errors, otherwise measuring the jitter for different settings of the equalizer and determining optimal settings of the equalizer corresponding to a minimal value of the jitter. This corrects performance problems due to asymmetry of the high-frequency signal.
In a further embodiment of the device, the asymmetry and unbalance detection unit is adapted to correct the asymmetry of the high-frequency signal by measuring the jitter at different values of a radial offset and determining an optimal value of the radial offset corresponding to a minimal value of the jitter. This can be used as alternative or additional (improving) measure to correct performance problems due to asymmetry of the high- frequency signal. In another embodiment of the device, the asymmetry and unbalance detection unit is adapted to test unbalance of the record carrier by: sampling a radial integrator a fourth predefined number of times; calculating an average radial integrator as average value of the radial integrator corresponding to the fourth predefined number of times; - calculating a unbalance indicator as ratio of the average radial integrator to the square of a rotational frequency of the record carrier; in case the unbalance indicator is outside a predefined unbalance range, reducing the rotational frequency of the record carrier. This makes it possible to detect unbalanced discs and to apply a corrective action. In an embodiment of the device, processing the high-frequency signal comprises a first and a second stage of amplification of the high-frequency signal, the second stage gain being controlled automatically within a range, and the disc error determination and correction unit is adapted for: monitoring values of the second stage gain; - adjusting the first stage gain in dependence of measured values of the second stage gain so as to keep the second stage gain away from the limits of the range. This allows for elimination or prevention of errors caused by the bifringence disc.
Further preferred embodiments of the device and the method according to the invention are given in the appended claims, disclosure of which is incorporated herein by reference.
BRIEF DESCRIPTION OF THE DRAWINGS:
These and other aspects of the invention will be apparent from and elucidated further with reference to the embodiments described by way of example in the following description and with reference to the accompanying drawings, in which:
Figure Ia shows an example of a disc-shaped optical record carrier, Figure Ib shows a cross-section taken of the record carrier, Figure Ic shows an example of a wobble of the track, Figure 2 shows a reading device, in accordance with the invention, Figure 3 shows an example of focus/radial control loop for controlling radial and focus actuators,
Figures 4a and 4b show an example of a procedure performed by the disc error determination and correction unit 32, in accordance with the invention. Figure 5 shows an example of a procedure performed by the calibration unit
40 and the adjustment unit 41, in accordance with the invention.
Figure 6 shows dependence of HF jitter and PI BLER on the actuator tilt.
Figure 7 shows dependence of HF jitter on the focus offset.
Figure 8a shows dependence of the radial error push-pull signal on the focus offset.
Figure 8b shows dependence of the radial error push-pull signal on the actuator tilt.
Figure 9 shows definition of the asymmetry of the HF signal.
Figure 10 shows an example of a procedure to measure asymmetry of HF signal by the asymmetry and unbalance unit 42, in accordance with the invention.
Figure 11 shows an example of a procedure to measure and correct the HF signal asymmetry, in accordance with the invention.
Figure 12 shows an example of a digital equalizer.
Figure 13 shows an example of the bathtub shape of jitter dependence on the equalizer settings.
Figure 14 shows an example of a procedure for testing unbalance of the record carrier, performed by the asymmetry and unbalance detection unit 42, in accordance with the invention.
Figure 15 shows an example of a procedure to correct for the effect of bifringence, in accordance with the invention.
Figure 16 shows an example of a block diagram of a part of the read processing unit 30 and the front-end unit 31.
Figure 17 shows an example of a procedure performed by the disc error determination and correction unit 32, in accordance with the invention. Corresponding elements in different Figures have identical reference numerals/symbo Is . DETAILED DESCRIPTION OF EMBODIMENTS:
Figure Ia shows a disc-shaped record carrier 11 having a track 9 and a central hole 10. The track 9 is arranged in accordance with a spiral pattern of turns constituting substantially parallel tracks on an information layer. The record carrier may be optically readable, called an optical disc. Recorded information is represented on the information layer by optically detectable marks recorded along the track. The marks are constituted by variations of a physical parameter and thereby have different optical properties than their surroundings, e.g. variations in reflection. The marks on the information layer can be pre- embossed, like in read-only discs, such as CD-ROM or DVD. Alternatively, the information layer, or at least a part of it, can be of a recordable type, on which marks can be recorded.
Examples of a recordable disc are the CD-R, CD-RW, and writable versions of DVD, such as DVD+RW, and the high-density writable optical disc called Blu-ray Disc, BD. The track 9 on the recordable type of record carrier is indicated by a pre-embossed track structure provided during manufacture of the blank record carrier, for example a pregroove. Figure Ib is a cross-section taken along the line b-b of the record carrier 11 of the recordable type, in which a transparent substrate 15 is provided with a recording layer 16 and a protective layer 17. The track structure is constituted, for example, by a pregroove 14, which enables a read/write head to follow the track 9 during scanning. The pregroove 14 may be implemented as an indentation or an elevation, or may consist of a material having a different optical property than the material surrounding it. A track structure may also be formed by regularly spread sub-tracks, which periodically cause servo signals to occur. The record carrier may be intended to carry real-time information, for example video or audio information, or other information, such as computer data.
Figure Ic shows an example of a periodic variation of the transversal position of the track of the (recordable) disc, also called wobble. The variations cause an additional signal to arise in auxiliary detectors, for example in a push-pull channel generated by sub detectors or partial detectors in the central spot in a head of a scanning device. The wobble is, for example, frequency modulated and position information is encoded in the modulation. A comprehensive description of the prior art wobble as shown in Figure Ic in a writable CD system comprising disc control information encoded in such a manner can be found in US
4,901,300 and US 5,187,699. It is noted that other transversal variations are known which are intended to be detected by variations of reflected radiation by (sub) detectors in a scanning head, such as variations in the width of the track, prepits adjacent to the track, and other. Figure 2 shows an example of a device for retrieving information from a record carrier 11 such as CD-ROM, DVD, CD-R, CD-RW, DVD+RW or BD, according to the invention. The device is provided with scanning means for scanning the track of the record carrier 11, which means include a rotation unit 21 for rotating the record carrier 11, a reading head 22 for scanning the track by a radiation beam 24 and a reading head control unit 25 for controlling generation and positioning of the radiation beam. The head 22 comprises an optical system of a known type for generating the radiation beam 24 guided through optical elements to generate the radiation spot 23 on a track of the information layer of the record carrier. The radiation beam 24 is generated by a radiation source, e.g. a laser diode. The head further comprises (not shown) a focusing actuator for focusing the beam to the radiation spot 23 on the track by moving the focus of the radiation beam 24 along the optical axis of said beam, and a sledge and a tracking actuator for positioning the radiation spot 23 in a direction transverse to the scanning direction of the track on the center of the track. For a disc shaped medium the transverse direction is called radial direction and the tracking actuator is called radial actuator. The tracking actuator may comprise coils for radially moving an optical element or may alternatively be arranged for changing the angle of a reflecting element. Analogously, the focusing actuator may comprise coils for moving the focus of the radiation beam 24. It should be noted that the focusing and radial actuators may be constructed in the form of one actuator for positioning an optical element such as a lens and performing functions of said actuators. The tracking and focusing actuators are driven by actuator signals, RA and FA in Figure 3, from the reading head control unit 25. For reading the radiation reflected by the information layer is detected by a detector of a usual type, e.g. a four-quadrant diode, in the reading head 22 for generating detector signals coupled to a front- end unit 31 for generating various scanning signals, including a main detector signal 33 and sub detector signals 35 for tracking and focusing. The main detector signal 33 is also called a high-frequency, HF, signal. The sub detector signals 35 are coupled to the reading head control unit 25 for controlling said focusing actuators. Examples of the sub detector signals 35 are a focusing error signal and a radial error signal, FEN and REN in Figure 3, respectively. Figure 3 shows an example of so-called focus/radial control loop for controlling radial and focus actuators.
The main detector signal 33 is processed by a read processing unit 30 of a usual type including a decoding unit and an error correction unit and output unit to retrieve the information. The decoding unit is for processing the high-frequency signal into the main data and the error correction data comprised in the information. The error correction unit is for finding and correcting data errors using the error correction data. The read processing unit may comprise a memory buffer for transitionally storing the main data. Alternatively, the memory buffer can be a separate unit. Hence reading means for reading information include the rotation unit 21, the reading head 22, the reading head control unit 25 and the read processing unit 30.
The reading head 22 is also referred to as the Optical Pickup Unit, OPU. The device comprises a control unit 20, which is connected via control lines 26, e.g. a system bus, to the other units in the device, for controlling these units. The control unit 20 comprises control circuitry, for example a microprocessor, a program memory and interfaces for performing different control procedures and functions. The control unit 20 may also be implemented as a state machine in logic circuits. The control unit 20 controls the scanning, for example for recording or reading of information, and may be arranged for receiving commands from a user or from a host computer. The device may be provided with recording means for recording information on a record carrier of a writable or re-writable type, for example CD-R or CD-RW, or DVD+RW or BD. In this case, the reading head 22 is adapted for recording marks on a record carrier. The recording means cooperate with the head 22 and the front-end unit 31 for generating a write beam of radiation, and comprise write processing means for processing the input information to generate a write signal to drive the head 22, which write processing means comprise an input unit 27, a formatter 28 and a modulator 29. For writing information the power of the beam of radiation is controlled by the modulator 29 to create optically detectable marks in the recording layer. The marks may be in any optically readable form, e.g. in the form of areas with a reflection coefficient different from their surroundings, obtained when recording in materials such as dye, alloy or phase change material, or in the form of areas with a direction of polarization different from their surroundings, obtained when recording in magneto -optical material. Writing and reading of information on/from optical discs and formatting, error correcting and channel coding rules are well-known in the art, for example from the CD and DVD systems. In an embodiment the device is a storage system only, for example an optical disc drive for use in a computer. The control unit 20 is arranged to communicate with a processing unit in the host computer via a standardized interface (not shown). Digital data is interfaced to the formatter unit 28 and from the read processing unit 30 directly. In this case, the interface acts as an input unit and an output unit. In an embodiment the device is arranged as a stand alone unit, for example a video playback/recording device for consumer use. The control unit 20, or an additional host control unit included in the device, is arranged to be controlled directly by the user. The device includes application data processing, for example audio and/or video processing circuits. The information presented to the input unit 27 may comprise analog audio and/or video, or digital uncompressed audio/video signals; in this case the input unit 27 may comprise compression means for these signals. The read processing unit 30 may comprise suitable audio and/or video decompression units.
In operation the reading head control unit 25 applies a set of beam control parameters for controlling various aspects of the radiation beam. A first example of a beam control parameter is related to achieving a correct focus, and is called a focus offset. The focus offset is used to provide an adjusted set point for the sub detector signals and/or actuator signals that control the focus. The focus offset may for example compensate deviations of the optical system or detector location in the head. A similar example of a beam control parameter is called a radial offset, and compensates the transverse position of the scanning spot. Another example of a beam control parameter is an actuator tilt, which is used to actively compensate for tilt in drive, for example the reading head unit or the rotation unit, or disc tilt. Further beam control parameters may be related to the power of the beam, timing of certain signal elements in the beam, etcetera. In practice beam control may be (partly) implemented in a software or in other units, such as a laser power control unit or a signal pattern from a recording unit. It is noted that the beam control parameters may require calibration or measurements during manufacture of the device, or may be affected by ageing, temperature, or other actual operational conditions during use of the device.
The device for retrieving information comprises a disc error determination and correction unit 32 for determining disc errors and controlling the reading head control unit 25. Examples of disc errors are disc deviation, disc unbalance, disc tilt, differences in a disc substrate layer thickness, bifringence disc, variable beta/asymmetry disc and other, leading to, for example, changes in a quality (characteristics) of the high-frequency signal derived from the disc. The disc error determination and correction unit 32 controls the reading head control unit 25 in dependence on detected disc errors by adjusting a selected beam control parameter of the reading head control unit 25 to a calibration value obtained from a calibration procedure. This procedure can be based for example on a jitter of the High- Frequency signal, HF jitter, which jitter represents time variations of this signal. For example, the jitter can be presented as a standard deviation of the time variation of the digitized data passed through the equalizer of the decoding unit; the jitter of the leading and trailing edges of the signal is measured relative to the Phase-Locked Loop (PLL) clock and normalized by the channel bit clock, as known in the art. A calibration procedure can be based also on a parameter measuring quality of data retrieval by means of rate of data errors in the information processed by the read processing unit 30. For example, so-called PI BLER,
Parity of the Inner code BLock Error Rate, can be used as known from the DVD system.
Here, a unit of information can be a single block or a group of blocks. PI BLER is also known as "PI Sum 8", which is a moving average sum of the Parity Inner errors over 8 Error Correction Code blocks. In case of CD discs, a corresponding parameter is so-called Cl
BLER. It should be noted that hereinafter PI BLER can also denote Cl BLER, PI Sum 8 or a more general term - the rate of data errors.
Of course, the above two quality parameters, the jitter and the rate of data errors, can be measured only in presence of the high-frequency signal, which is generated on the basis of the marks in the track.
However, dependence of the radial error signal on the wobble of the track can be used at locations with no marks. Hence, calibrations based on the radial error signal can be used during Optimal Power Control procedures for recordable discs and during recordings on such discs. The disc error determination and correction unit 32 monitors scanning of the record carrier, evaluates quality parameters in order to identify different disc errors and, if necessary, takes corrective actions.
For this purpose, the disc error determination and correction unit 32 includes the following sub units: - a monitoring unit 36 for selecting regions of the track, for monitoring position of the radiation beam along the track and for checking for occurrence of uncorrected data errors; a sampling unit 37 for sampling a rate of data errors and a jitter a first predefined number of times in each region entered by the radiation beam, the jitter representing time variations of the high-frequency signal; a computing unit 38 for calculating a region jitter as average value of the jitter corresponding to the first predefined number of times and for calculating a region rate of data errors as average value of the rate of data errors corresponding to the first predefined number oftimes; a verification unit 39 for checking a first predefined condition for the region jitter and the region rate of data errors in case the region jitter is different from any other region jitter by a predefined jitter difference, said other region jitter calculated for any previously scanned region, and for requesting a calibration of a control parameter based on the rate of data errors in case the first predefined condition is fulfilled, otherwise requesting a calibration of the control parameter based on the jitter, the control parameter being an actuator tilt or a focus offset ; a calibration unit 40 for performing the requested calibration comprising measuring of the jitter or the rate of data errors as in the request at different values of the control parameter and determining a region adjusted value of the control parameter corresponding to a minimal value of the jitter or the rate of data errors, respectively, in case the memory buffer occupancy is above a predefined level or in case of occurrence of an uncorrected data error in the main data; and an adjustment unit 41 for saving the region adjusted value of the control parameter for use during scanning the region and setting the control parameter to the region adjusted value, in case the requested calibration is successful.
Thus, the sub units of the disc error determination and correction unit 32 perform a method comprising steps of: g) checking for occurrence of uncorrected data errors ; h) selecting regions of the track; i) monitoring position of the radiation beam along the track; j) for each region entered by the radiation beam, out of the selected regions, sampling a jitter and a rate of data errors a first predefined number of times, the jitter representing time variations of the high-frequency signal; k) calculating a region jitter as average value of the jitter corresponding to the first predefined number of times;
1) calculating a region rate of data errors as average value of the rate of data errors corresponding to the first predefined number of times; m) in case the region jitter is different from any other region jitter by a predefined jitter difference, said other region jitter calculated for any previously scanned region, checking a first predefined condition for the region jitter and the region rate of data errors; n) in case the first predefined condition is fulfilled, requesting a calibration of a control parameter based on the rate of data errors, otherwise requesting a calibration of the control parameter based on the jitter, the control parameter being an actuator tilt or a focus offset ; o) in case the memory buffer occupancy is above a predefined level or in case of occurrence of an uncorrected data error in the main data, performing the requested calibration comprising measuring of the jitter or the rate of data errors as in the request at different values of the control parameter and determining a region adjusted value of the control parameter corresponding to a minimal value of the jitter or the rate of data errors, respectively; and p) in case the requested calibration is successful, saving the region adjusted value of the control parameter for use during scanning the region and setting the control parameter to the region adjusted value.
The disc tilt or substrate layer thickness across the disc can be different from inner side of the disc to the outer side of the disc. Although, in an embodiment of the device, (actuator) tilt calibration and focus offset calibration are done by the disc error determination and correction unit 32 at the start-up, at the inner side of the disc, and the best tilt and focus offset is set to achieve minimum jitter point, the HF signal quality (jitter and PI BLER) can be worsen off, if the disc tilt or substrate layer thickness is changed when playing from the inner side of the disc to the outer side of the disc. For both, tilt disc and different substrate layer thickness, the detectable symptom is increase of HF jitter and/or PI BLER. The whole disc is divided into several regions from the inner side to the outer side by the monitoring unit 36. For the tilt or focus offset calibrations, the calibration is done in regions across the whole disc from the inner side to the outer side, during scanning of those regions. In particular, if the measured HF jitter in region (k) is 1.0% higher/lower than in region (k-1), region (k-2), ...etcetera, and the calibration in region k has not been done before, the calibration will be done in this region.
During playback, HF jitter and PI BLER are monitored by the sampling unit 37. This is done by sampling values of the jitter and PI BLER for each region entered by the radiation beam. The number of sampling points is predefined. For example, said values can be measured 25 times during one rotation of the record carrier by reading them from a decoder register. Then, the measured values of HF jitter and PI BLER at different sampling points are averaged by the computing unit 38. When the average value of HF jitter for a particular region is different from the average jitter value measured in any other region by a given jitter difference, the verification unit 39 checks the first predefined condition for the average HF jitter and the average PI BLER. The jitter difference of less than 0.5% can be caused by the measurement noise. The difference of more than 1% across the region usually means that the present system settings are not the best for this region. Therefore, in an embodiment of the device, the given jitter difference is 1%. As for the first predefined condition, experimental data show that a condition with HF jitter lower than about 13% and PI BLER > 130 can be used to decide which type of adjustment should be applied. Other condition can be applied depending on a particular system; the above condition is optimized mainly for the DVD system. If this condition is fulfilled, the verification unit 39 sets request for a calibration based on PI BLER, otherwise the jitter based calibration will be requested. Under normal conditions, a calibration is performed when the memory buffer occupancy is above the predefined level corresponding to a time necessary for performing the calibration. That means the calibration can be done without any interruption of video/audio playback. For example, the occupancy level of 80% may correspond to about 2 seconds of video playback, a time to do engine level calibrations or adjustments. A calibration can be executed also in case of presence of uncorrectable data error(s), "read error", as this leads to interruption of data retrieval, anyway.
Figures 4a and 4b show an example of a procedure performed by the sub units of the disc error determination and correction unit 32.
In an embodiment of the device, the requested calibration is the tilt calibration and after this calibration is done the above measurements and checks are repeated and the focus offset calibration is executed, if relevant conditions described above are fulfilled. In other words, if the HF signal jitter difference is still higher than 1% after the tilt set, a further, focus offset calibration will be requested and activated when the buffer time is long enough. For example the required buffer time is 1 second for Constant Angular Velocity, CAV, 40Hz DVD playback. Same conditions as for the tilt calibration are used to decide whether the jitter based or the PI BLER based focus offset calibration is to be done.
Figure 5 shows an example of a procedure performed by the calibration unit 40 and the adjustment unit 41 in case of the calibration of the focus offset based on the jitter. See also Figure 7. The PI BLER based focus offset calibration or the jitter/PI BLER based tilt calibration follow the same procedure. In an embodiment of the device, the disc error determination and correction unit is adapted to perform each type of the calibration of each control parameter no more than one time in the same region. In other words, a specific calibration is performed only once in the same region, if successful. A successful calibration is a calibration for which it was possible to find optimal, the region adjusted value of a control parameter. This value is saved in memory for using during scanning the same region again.
In order to further minimize HF jitter, in another embodiment of the device, the disc error determination and correction unit is adapted to perform a radial offset calibration based on HF jitter, after first performing the actuator tilt or focus offset calibration based on HF jitter. In other words, the jitter based calibration is repeated, but with the actuator tilt or focus offset substituted by the radial offset. This can be done by simply repeating actions of the calibration unit 40 and the adjustment unit 41 without any precondition or by repeating the whole procedure described above, but sampling only HF jitter and checking only the condition related to the jitter difference, in order to request the radial offset calibration.
Figure 6 shows dependence of HF jitter and PI BLER on the actuator tilt, which dependences are used in respective calibrations. The second order polynomials fitted to the measured values are also shown. Figure 7 shows dependence of HF jitter on the focus offset. "Default setting" and "ramp down/up" modes are as used in Figure 5.
In an embodiment of the device, the region adjusted value of the control parameter is determined simply by taking this value of the control parameter applied during measurements, for which a minimal value of HF jitter or PI BLER was measured. However, as the measured values are only discrete points, taking the point with the minimal value might not always render the optimal value of the parameter. This can be seen in Figure 7. Therefore, in a further embodiment of the device, the calibration unit 40 is adapted to determine the region adjusted value of the control parameter by calculating a minimum of a function fitted to the measured values. The function may be the second or higher order polynomial; the second order one requires simpler computations.
In an embodiment of the device, the disc error determination and correction unit is adapted so that in case of absence of the high-frequency signal the requested calibration is substituted by a calibration comprising measuring of a radial error signal at different values of the control parameter and determining the region adjusted value of the control parameter corresponding to an optimal value of the radial error signal, the radial error signal being generated by the reading head on the basis of a pre-embossed track structure indicating the track. Depending on a disc type, the device may use for example a radial error push- pull signal, a radial error signal based on so-called sampled tracking, or other radial error signals known in the art.
Figures 8a and 8b show dependence of the radial error push-pull on the focus offset and the actuator tilt, respectively.
Based on this dependence, in an embodiment of the device, the calibration unit is adapted to determine the region adjusted value of the control parameter by calculating a maximum of a function fitted to the measured values of the radial error signal. This maximum defines the optimal value of the radial error. The function may be the second or higher order polynomial; the second order one requires simpler computations.
Figure 9 shows definition of the asymmetry of the HF signal. Peak values, Ai and A2, and an average value of the HF signal, CALF, are measured. The asymmetry, also called beta, is calculated as ratio of (Ai -(CALF - A2)) to (Ai +(CALF - A2)).
In an embodiment of the device, the disc error determination and correction unit comprises an asymmetry and unbalance detection unit 42 for: in case of occurrence of an uncorrected data error in the main data, sampling an asymmetry of the high-frequency signal a second predefined number of times; calculating an average asymmetry as average value of the asymmetry of the high-frequency signal corresponding to the second predefined number of times; and - correcting the asymmetry of the high-frequency signal in case the average asymmetry is outside a predefined asymmetry range, otherwise testing unbalance of the record carrier.
This facilitates detection of variable HF signal asymmetry across the disc. The values of Ai, A2, and CALF can be read from the decoder register. They are sampled the second predefined number of times after the monitoring unit 36 detects the uncorrected error, "read error". For example, in an embodiment of the device, the asymmetry is sampled/calculated 16 times during one rotation of the disc. Then, the asymmetry is averaged over the second predefined number. For the purpose of classifying the disc as asymmetry disc, the averaged calculated asymmetry is compared against the predefined asymmetry range. This range can have different values for different types of discs. For example, for DVD+R, DVD+RW discs, the range is set to (-5%, 15%). This means that a disc with the asymmetry outside this range is considered to be the asymmetry disc; corrective action is necessary. Figure 10 shows an example of a procedure performed by the asymmetry and unbalance detection unit 42 for detecting the HF signal asymmetry.
It should be noted that checking the asymmetry can be done on more regular basis, for example when entering a new region of the disc, so not only after detection of "read error".
In an embodiment of the device, the asymmetry and unbalance detection unit 42 is adapted to correct the asymmetry of the high-frequency signal by measuring the jitter at different values of a radial offset and determining an optimal value of the radial offset corresponding to a minimal value of the jitter. Again, this optimal value can be determined simply by taking this value of the control parameter applied during measurements, for which the minimal value of HF jitter was measured. Another option is to fit a function, for example the second order polynomial, to the measured values of HF jitter and to calculate a minimum of such function.
Another way of correcting the asymmetry of the HF signal is done by the asymmetry and unbalance detection unit 42, by: sampling the jitter and the rate of data errors a third predefined number of times and calculating corresponding average values of the jitter and the rate of data errors; checking a second predefined condition for the average values of the jitter and the rate of data errors; - in case the second predefined condition is fulfilled, measuring the rate of data errors for different settings of an equalizer of the high-frequency signal and determining optimal settings of the equalizer corresponding to a minimal value of the rate of data errors, otherwise measuring the jitter for different settings of the equalizer and determining optimal settings of the equalizer corresponding to a minimal value of the jitter. The third predefined number of times can be the same as the first predefined number of times, that is 25 times during one rotation of the disc. Analogously, the second predefined condition can be same as the first predefined condition, that is HF jitter lower than 13% and PI BLER greater than 130.
In another embodiment of the device, the second condition requires that PI BLER > 130. In this case, it is sufficient to sample only the rate of data errors.
Figure 11 shows an example of a procedure to measure and correct the HF signal asymmetry.
The determination of optimal settings of the equalizer can be done as follows in the case of the DVD disc. If so-called limit equalizer with adaptive clipping level is used to amplify the HF signal components like 3T, it is turned off. Then, settings of the HF high pass filter, HF HPF, are checked. If the HF high pass filter cut-off frequency is higher than about 1/10 of the frequency of 14T, set it to 1/10 of the frequency of 14T. Here, T is a measure of a length of a mark in the track. For the DVD system, 14T is the longest mark and 3T is the shortest mark. For normal HF HPF design, the HF HPF cut-off frequency is set to a value, which is as high as possible and at the same time does not lead to too much phase distortion. This is done in order to filter out lower frequency noise caused by disc scratches, etcetera. For the asymmetry disc, one should reduce the phase distortion introduced by the HF HPF into a level as small as possible. Therefore, the HF HPF cut-off frequency is corrected to 1/10 of the frequency of 14T, if necessary. In a next step, HF jitter and/or PI BLER are sampled as described above. Next, depending on the second condition, jitter based or PI BLER based equalizer settings adjustments are performed. These adjustments are can be done by changing gain taps A and/or B of the equalizer as shown in Figure 12.
Figure 13 shows an example of the bathtub shape of jitter dependence on the equalizer settings.
The asymmetry and unbalance correction unit 42 can be modified to determine the optimal settings of the equalizer by calculating a minimum of a function fitted to the measured values of the jitter or the rate of data errors, in accordance with the second predefined condition. The simple function is the second order polynomial. Some times, even after optimizing the equalizer settings to boost the 3T component of the HF signal, the asymmetry is still too high, leading to persisting "read errors" and/or being outside the allowed range. In this case, further adjustments like radial offset calibration and/or tilt calibration can be performed in order to further reduce the asymmetry of the HF signal. Another type of the disc error is unbalance disc. Disturbances caused by most unbalance discs, say unbalance lower than 1O g, can be compensated well enough by the servo control loop. For some very high unbalance disc, for example caused by sticker/marker put by a user on the disc by himself, normal servo control loop are unable to handle it. The disturbances can be so high that they can affect normal tracking performance, causing read problem or error. A general way to handle this kind of error is to spin down the drive and do playback at lower speed.
In an embodiment of the device, the asymmetry and unbalance detection unit 42 is adapted to test unbalance of the record carrier by: sampling a radial integrator during a predefined number of revolutions; calculating an average radial integrator as average value of the radial integrator corresponding to the predefined number of revolutions; calculating a unbalance indicator as ratio of the average radial integrator to the square of a rotational frequency of the record carrier; - in case the unbalance indicator is outside a predefined unbalance range, reducing the rotational frequency of the record carrier.
To differentiate the read error caused by high disc unbalance from other reasons, the radial integrator (peak-to-peak) output is measured a number of times over the predefined number of revolutions, for example over one revolution, and averaged. The ratio of this averaged radial integrator output and the square of disc rotational speed is monitored. If it is outside the predefined range/value, the disc is detected as high unbalance disc. Consequently, action to spin down to lower playback speed is activated.
Figure 14 shows an example of a procedure for testing unbalance of the record carrier, performed by the asymmetry and unbalance detection unit 42. Another kind of a disc error is caused by so-called bifringence disc. Bifringence is a property of a material, which causes incident light waves of different polarizations to be refracted differently by the material. For the bifringence disc, the amplitude of the HF signal increases greatly from inner side of the disc to the outer side of the disc, so that HF Automatic Gain Control, HF AGC, in the decoder IC is no effective anymore, which leads to saturation of the HF AGC adjustable range in the decoder path. The solution to this problem is to monitor the HF AGC gain while playing. When the HF AGC gain is close to the adjustable limit, a increase/decrease of the signal pre-processing gain is done in order to avoid saturation as a consequence of the HF AGC gain being too close to the limit. The HF signal is monitored all the time when doing PLL locking checking. In another embodiment of the device, when processing the high-frequency signal comprises a first and a second stage of amplification of the high-frequency signal, the second stage gain being controlled automatically within a range, the disc error determination and correction unit is adapted for: monitoring values of the second stage gain; - adjusting the first stage gain in dependence of measured values of the second stage gain so as to keep the second stage gain away from the limits of the range.
Figure 15 shows an example of a procedure performed by the disc error determination and correction unit to correct for the effect of bifringence. The front gain, a, refers to the front signal processing DC gain for HF signal, performed by the front-end unit 31, front IC. The HF AGC gain, agc gain, refers to the HF AGC block in the decoder.
Figure 16 shows an example of a layout of relevant parts of the front IC and the decoder IC. In an embodiment of the device, the disc error determination and correction unit 32 is adapted to perform a procedure as shown in Figure 17.
In an embodiment of the device, the disc error determination and correction unit 32, or any part of it, is included in the control unit 20.
The disc error determination and correction unit 32, or any sub unit comprised within, can be implemented in firmware.
Embodiments of the method according to the invention correspond to functions/ procedures performed by the disc error determination and correction unit 32 and its sub units as described above in reference to different embodiments of the device.
In particular: In an embodiment of the method, each type of the calibration of each control parameter is requested no more than one time in the same region.
In an embodiment of the method, the control parameter is the actuator tilt and thereafter steps from j) to p) are repeated within the same region with the actuator tilt substituted by the focus offset. In an embodiment of the method, the requested calibration is the calibration of the control parameter based on the jitter and thereafter at least steps o) and p) are repeated within the same region with the control parameter substituted by a radial offset .
In an embodiment of the method, the jitter is the standard deviation of time variations of the high-frequency signal and the predefined jitter difference is substantially 1%.
In an embodiment of the method, the first predefined condition requires that the region jitter is lower than substantially 13% and the region rate of data errors is greater than substantially 130 data errors per one information unit.
In an embodiment of the method, the region adjusted value of the control parameter is determined by calculating a minimum of a function fitted to the measured values of the jitter or the rate of data errors as in the request.
In an embodiment of the method, in case of absence of the high-frequency signal, the requested calibration is substituted by a calibration comprising measuring of a radial error signal at different values of the control parameter and determining the region adjusted value of the control parameter corresponding to an optimal value of the radial error signal, the radial error signal being generated by the reading head on the basis of a pre- embossed track structure indicating the track.
In an embodiment of the method, the radial error signal is a radial error push- pull signal.
In an embodiment of the method, the region adjusted value of the control parameter is determined by calculating a maximum of a function fitted to the measured values, said maximum defining the optimal value of the radial error signal.
In an embodiment of the method, in case of occurrence of an uncorrected data error in the main data the following steps are executed: sampling an asymmetry of the high-frequency signal a second predefined number of times; calculating an average asymmetry as average value of the asymmetry of the high-frequency signal corresponding to the second predefined number of times; and - in case the average asymmetry is outside a predefined asymmetry range, correcting the asymmetry of the high-frequency signal, otherwise testing unbalance of the record carrier.
In an embodiment of the method, correcting the asymmetry of the high- frequency signal comprises measuring of the jitter at different values of a radial offset and determining an optimal value of the radial offset corresponding to a minimal value of the jitter.
In an embodiment of the method, the optimal value of the radial offset is determined by calculating a minimum of a function fitted to the measured values of the jitter.
In an embodiment of the method, correcting the asymmetry of the high- frequency signal comprises steps of: sampling the jitter and the rate of data errors a third predefined number of times and calculating corresponding average values of the jitter and the rate of data errors; checking a second predefined condition for the average values of the jitter and the rate of data errors; - in case the second predefined condition is fulfilled, measuring the rate of data errors for different settings of an equalizer of the high-frequency signal and determining optimal settings of the equalizer corresponding to a minimal value of the rate of data errors, otherwise measuring the jitter for different settings of the equalizer and determining optimal settings of the equalizer corresponding to a minimal value of the jitter. In an embodiment of the method, the optimal settings of the equalizer are determined by calculating a minimum of a function fitted to the measured values of the jitter or the rate of data errors, accordingly.
In an embodiment of the method, the function is the second order polynomial. In an embodiment of the method, testing unbalance of the record carrier comprises steps of: sampling a radial integrator a fourth predefined number of times; calculating an average radial integrator as average value of the radial integrator corresponding to the fourth predefined number of times; - calculating a unbalance indicator as ratio of the average radial integrator to the square of a rotational frequency of the record carrier; in case the unbalance indicator is outside a predefined unbalance range, reducing the rotational frequency of the record carrier.
In an embodiment of the method, processing the high-frequency signal comprises a first and a second stage of amplification of the high-frequency signal, the second stage gain being controlled automatically within a range, the method comprising steps of: monitoring values of the second stage gain; adjusting the first stage gain in dependence of measured values of the second stage gain so as to keep the second stage gain away from the limits of the range. Different embodiments of a computer program for use in retrieving information from a disc-like optical record carrier by a reading device, according to the invention, are operative to cause a processor of the reading device, and in particular the control unit 20, to perform functions/procedures as described in reference to embodiments of the device and/or the method presented above, when the computer program is executed by the reading device.
Whilst the invention has been described with reference to preferred embodiments thereof, it is to be understood that these are not limitative examples. Thus, various modifications may become apparent to those skilled in the art, without departing from the scope of the invention, as defined by the claims and the embodiments. Further, the invention lies in each and every novel feature or combination of features described above. It is noted, that the invention may be implemented by means of a general purpose processor executing a computer program or by dedicated hardware or by a combination of both, and that in this document the word "comprising" does not exclude the presence of other elements or steps than those listed and the word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements, that any reference signs do not limit the scope of the claims, that "means" may be represented by a single item or a plurality and that several "means" may be represented by the same item of hardware.

Claims

CLAIMS:
1. A method of retrieving information from a disc-like optical record carrier, the information represented by optically readable marks along a substantially spiral track on the record carrier, the information organized into information units comprising main data and error correction data, the method comprising steps of: - rotating the record carrier and scanning the track by a radiation beam generated by a reading head; controlling positioning of the radiation beam using signals representing control parameters; generating a high-frequency signal by the reading head on the basis of the marks; processing the high-frequency signal into the main data and the error correction data; finding and correcting data errors using the error correction data; transitionally storing the main data in a memory buffer; - checking for occurrence of uncorrected data errors ; selecting regions of the track; monitoring position of the radiation beam along the track; for each region entered by the radiation beam, out of the selected regions, sampling a jitter and a rate of data errors a first predefined number of times, the jitter representing time variations of the high-frequency signal; calculating a region jitter as average value of the jitter corresponding to the first predefined number of times; calculating a region rate of data errors as average value of the rate of data errors corresponding to the first predefined number of times; - in case the region jitter is different from any other region jitter by a predefined jitter difference, said other region jitter calculated for any previously scanned region, checking a first predefined condition for the region jitter and the region rate of data errors; in case the first predefined condition is fulfilled, requesting a calibration of a control parameter based on the rate of data errors, otherwise requesting a calibration of the control parameter based on the jitter, the control parameter being an actuator tilt or a focus offset ; in case the memory buffer occupancy is above a predefined level or in case of occurrence of an uncorrected data error in the main data, performing the requested calibration comprising measuring of the jitter or the rate of data errors as in the request at different values of the control parameter and determining a region adjusted value of the control parameter corresponding to a minimal value of the jitter or the rate of data errors, respectively; and in case the requested calibration is successful, saving the region adjusted value of the control parameter for use during scanning the region and setting the control parameter to the region adjusted value.
2. A method as claimed in claim 1, wherein each type of the calibration of each control parameter is requested no more than one time in the same region.
3. A method as claimed in claim 1, wherein the control parameter is the actuator tilt and thereafter steps from j) to p) are repeated within the same region with the actuator tilt substituted by the focus offset.
4. A method as claimed in claim 1, wherein the requested calibration is the calibration of the control parameter based on the jitter and thereafter at least steps o) and p) are repeated within the same region with the control parameter substituted by a radial offset .
5. A method as claimed in claim 1, wherein the jitter is the standard deviation of time variations of the high-frequency signal and the predefined jitter difference is substantially 1%.
6. A method as claimed in claim 5, wherein the first predefined condition requires that the region jitter is lower than substantially 13% and the region rate of data errors is greater than substantially 130 data errors per one information unit.
7. A method as claimed in claim 1, wherein the region adjusted value of the control parameter is determined by calculating a minimum of a function fitted to the measured values of the jitter or the rate of data errors as in the request.
8. A method as claimed in claim 1, wherein in case of absence of the high- frequency signal, the requested calibration is substituted by a calibration comprising measuring of a radial error signal at different values of the control parameter and determining the region adjusted value of the control parameter corresponding to an optimal value of the radial error signal, the radial error signal being generated by the reading head on the basis of a pre-embossed track structure indicating the track.
9. A method as claimed in claim 8, wherein the radial error signal is a radial error push-pull signal.
10. A method as claimed in claim 9, wherein the region adjusted value of the control parameter is determined by calculating a maximum of a function fitted to the measured values, said maximum defining the optimal value of the radial error signal.
11. A method as claimed in claim 1 , wherein in case of occurrence of an uncorrected data error in the main data the following steps are executed: sampling an asymmetry of the high-frequency signal a second predefined number of times; - calculating an average asymmetry as average value of the asymmetry of the high-frequency signal corresponding to the second predefined number of times; and in case the average asymmetry is outside a predefined asymmetry range, correcting the asymmetry of the high-frequency signal, otherwise testing unbalance of the record carrier.
12. A method as claimed in claim 11, wherein correcting the asymmetry of the high-frequency signal comprises measuring of the jitter at different values of a radial offset and determining an optimal value of the radial offset corresponding to a minimal value of the jitter.
13. A method as claimed in claim 12, wherein the optimal value of the radial offset is determined by calculating a minimum of a function fitted to the measured values of the jitter.
14. A method as claimed in claim 11, wherein correcting the asymmetry of the high-frequency signal comprises steps of: sampling the jitter and the rate of data errors a third predefined number of times and calculating corresponding average values of the jitter and the rate of data errors; - checking a second predefined condition for the average values of the jitter and the rate of data errors; in case the second predefined condition is fulfilled, measuring the rate of data errors for different settings of an equalizer of the high-frequency signal and determining optimal settings of the equalizer corresponding to a minimal value of the rate of data errors, otherwise measuring the jitter for different settings of the equalizer and determining optimal settings of the equalizer corresponding to a minimal value of the jitter.
15. A method as claimed in claim 14, wherein the optimal settings of the equalizer are determined by calculating a minimum of a function fitted to the measured values of the jitter or the rate of data errors, accordingly.
16. A method as claimed in any of claims 7, 10, 13 or 15, wherein the function is the second order polynomial.
17. A method as claimed in claim 11, wherein testing unbalance of the record carrier comprises steps of: sampling a radial integrator a fourth predefined number of times; calculating an average radial integrator as average value of the radial integrator corresponding to the fourth predefined number of times; - calculating a unbalance indicator as ratio of the average radial integrator to the square of a rotational frequency of the record carrier; in case the unbalance indicator is outside a predefined unbalance range, reducing the rotational frequency of the record carrier.
18. A method as claimed in claim 1, wherein processing the high-frequency signal comprises a first and a second stage of amplification of the high-frequency signal, the second stage gain being controlled automatically within a range, the method comprising steps of: monitoring values of the second stage gain; adjusting the first stage gain in dependence of measured values of the second stage gain so as to keep the second stage gain away from the limits of the range.
19. A device for retrieving information from a disc-like optical record carrier, the information represented by optically readable marks along a substantially spiral track on the record carrier, the information organized into information units comprising main data and error correction data, the device comprising: a rotation unit 21 for rotating the record carrier; a reading head 22 for scanning the track by a radiation beam and generating a high-frequency signal on the basis of the marks; a reading head control unit 25 for controlling generation and positioning of the radiation beam using signals representing control parameters; a decoding unit 30 for processing the high-frequency signal into the main data and the error correction data; - an error correction unit 30 for finding and correcting data errors using the error correction data; a memory buffer for transitionally storing the main data; a disc error determination and correction unit 32 for determining disc errors and controlling the reading head control unit, the disc error determination and correction unit comprising following sub-units: a monitoring unit 36 for selecting regions of the track, for monitoring position of the radiation beam along the track and for checking for occurrence of uncorrected data errors ; a sampling unit 37 for sampling a rate of data errors and a jitter a first predefined number of times in each region entered by the radiation beam, the jitter representing time variations of the high-frequency signal; a computing unit 38 for calculating a region jitter as average value of the jitter corresponding to the first predefined number of times and for calculating a region rate of data errors as average value of the rate of data errors corresponding to the first predefined number oftimes; a verification unit 39 for checking a first predefined condition for the region jitter and the region rate of data errors in case the region jitter is different from any other region jitter by a predefined jitter difference, said other region jitter calculated for any previously scanned region, and for requesting a calibration of a control parameter based on the rate of data errors in case the first predefined condition is fulfilled, otherwise requesting a calibration of the control parameter based on the jitter, the control parameter being an actuator tilt or a focus offset ; a calibration unit 40 for performing the requested calibration comprising measuring of the jitter or the rate of data errors as in the request at different values of the control parameter and determining a region adjusted value of the control parameter corresponding to a minimal value of the jitter or the rate of data errors, respectively, in case the memory buffer occupancy is above a predefined level or in case of occurrence of an uncorrected data error in the main data; and - an adjustment unit 41 for saving the region adjusted value of the control parameter for use during scanning the region and setting the control parameter to the region adjusted value, in case the requested calibration is successful.
20. A device as claimed in claim 19, wherein the disc error determination and correction unit 32 is adapted to perform each type of the calibration of each control parameter no more than one time in the same region.
21. A device as claimed in claim 19, the control parameter being the actuator tilt, wherein the disc error determination and correction unit 32 is adapted to repeat within the same region actions of the sub-units with the actuator tilt substituted by the focus offset.
22. A device as claimed in claim 19, the requested calibration being the calibration of the control parameter based on the jitter, wherein the disc error determination and correction unit 32 is adapted to repeat within the same region at least actions of the calibration unit and the adjustment unit with the control parameter substituted by a radial offset .
23. A device as claimed in claim 19, wherein the jitter is the standard deviation of time variations of the high-frequency signal and the predefined jitter difference is substantially 1%.
24. A device as claimed in claim 23, wherein the first predefined condition requires that the region jitter is lower than substantially 13% and the region rate of data errors is greater than substantially 130 data errors per one information unit.
25. A device as claimed in claim 19, wherein the calibration unit 40 is adapted to determine the region adjusted value of the control parameter by calculating a minimum of a function fitted to the measured values of the jitter or the rate of data errors as in the request.
26. A device as claimed in claim 19, wherein the disc error determination and correction unit 32 is adapted so that in case of absence of the high-frequency signal the requested calibration is substituted by a calibration comprising measuring of a radial error signal at different values of the control parameter and determining the region adjusted value of the control parameter corresponding to an optimal value of the radial error signal, the radial error signal being generated by the reading head on the basis of a pre-embossed track structure indicating the track.
27. A device as claimed in claim 26, wherein the radial error signal is a radial error push-pull signal.
28. A device as claimed in claim 27, wherein the calibration unit 40 is adapted to determine the region adjusted value of the control parameter by calculating a maximum of a function fitted to the measured values, said maximum defining the optimal value of the radial error signal.
29. A device as claimed in claim 19, wherein the disc error determination and correction unit 32 comprises an asymmetry and unbalance detection unit 42 for: in case of occurrence of an uncorrected data error in the main data, sampling an asymmetry of the high-frequency signal a second predefined number of times; calculating an average asymmetry as average value of the asymmetry of the high-frequency signal corresponding to the second predefined number of times; and correcting the asymmetry of the high-frequency signal in case the average asymmetry is outside a predefined asymmetry range, otherwise testing unbalance of the record carrier.
30. A device as claimed in claim 29, wherein the asymmetry and unbalance detection unit 42 is adapted to correct the asymmetry of the high-frequency signal by measuring the jitter at different values of a radial offset and determining an optimal value of the radial offset corresponding to a minimal value of the jitter.
31. A device as claimed in claim 30, wherein the asymmetry and unbalance detection unit 42 is adapted to determine the optimal value of the radial offset by calculating a minimum of a function fitted to the measured values of the jitter.
32. A device as claimed in claim 29, wherein the asymmetry and unbalance detection unit 42 is adapted to correct the asymmetry of the high-frequency signal by: - sampling the jitter and the rate of data errors a third predefined number of times and calculating corresponding average values of the jitter and the rate of data errors; checking a second predefined condition for the average values of the jitter and the rate of data errors; in case the second predefined condition is fulfilled, measuring the rate of data errors for different settings of an equalizer of the high-frequency signal and determining optimal settings of the equalizer corresponding to a minimal value of the rate of data errors, otherwise measuring the jitter for different settings of the equalizer and determining optimal settings of the equalizer corresponding to a minimal value of the jitter.
33. A device as claimed in claim 32, wherein the asymmetry and unbalance detection unit 42 is adapted to determine the optimal settings of the equalizer by calculating a minimum of a function fitted to the measured values of the jitter or the rate of data errors, accordingly.
34. A device as claimed in any of claims 25, 28, 31 or 33, wherein the function is the second order polynomial.
35. A device as claimed in claim 29, wherein the asymmetry and unbalance detection unit 42 is adapted to test unbalance of the record carrier by: - sampling a radial integrator a fourth predefined number of times; calculating an average radial integrator as average value of the radial integrator corresponding to the fourth predefined number of times; calculating a unbalance indicator as ratio of the average radial integrator to the square of a rotational frequency of the record carrier; in case the unbalance indicator is outside a predefined unbalance range, reducing the rotational frequency of the record carrier.
36. A device as claimed in claim 19, processing the high-frequency signal comprising a first and a second stage of amplification of the high-frequency signal, the second stage gain being controlled automatically within a range, wherein the disc error determination and correction unit 32 is adapted for: monitoring values of the second stage gain; adjusting the first stage gain in dependence of measured values of the second stage gain so as to keep the second stage gain away from the limits of the range.
37. A computer program product for use in retrieving information from a disc-like optical record carrier by a reading device, the computer program comprising program code means for causing a processor of the reading device, to perform the steps of the method as claimed in any of claims 1 - 19, when the computer program is run on the processor.
PCT/IB2007/052490 2006-06-29 2007-06-27 Device and method for retrieving information WO2008001317A2 (en)

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