WO2008096333A1 - Réduction de bruit - Google Patents

Réduction de bruit Download PDF

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Publication number
WO2008096333A1
WO2008096333A1 PCT/IB2008/050495 IB2008050495W WO2008096333A1 WO 2008096333 A1 WO2008096333 A1 WO 2008096333A1 IB 2008050495 W IB2008050495 W IB 2008050495W WO 2008096333 A1 WO2008096333 A1 WO 2008096333A1
Authority
WO
WIPO (PCT)
Prior art keywords
focus
disc
error signal
optical pick
actuator
Prior art date
Application number
PCT/IB2008/050495
Other languages
English (en)
Inventor
Marcel Rieck
Original Assignee
Philips Intellectual Property & Standards Gmbh
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 Philips Intellectual Property & Standards Gmbh, Koninklijke Philips Electronics N.V. filed Critical Philips Intellectual Property & Standards Gmbh
Publication of WO2008096333A1 publication Critical patent/WO2008096333A1/fr

Links

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
    • G11B20/24—Signal processing not specific to the method of recording or reproducing; Circuits therefor for reducing noise
    • 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
    • G11B7/0908—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 for focusing only

Definitions

  • the invention relates to the field of optical pick-up units (OPU) for reading out an optical data storage medium, e.g. a compact disc (CD) or digital video disc (DVD).
  • OPU optical pick-up units
  • CD compact disc
  • DVD digital video disc
  • the US Patent Application No. US 2004/0208092 Al discloses a focus position adjustment method for adjusting the focus position of the optical beam by which an optical storage device reads an optical storage medium.
  • the optical storage medium comprises a header and a recording area.
  • the optical storage device generates a focus error signal as reading the medium and utilizes the focus error signal to control the focus of the optical pickup head.
  • a method is performed according to the deviation value between the levels of focus error signals of the header and the recording area to adjust the focus position to make the deviation value fall in a predetermined range.
  • the referenced system comprises a deviation value detection module for determining the deviation value and a focus control module for adjusting the focus position.
  • a light source in combination with a detector are used in order to illuminate the disc surface to be read out and detect the light reflected from the surface of the disc providing the information encoded on the disc.
  • a two-stage electromechanical system is provided in order to control both the focus position of the focusing element (lens) with respect to the data layer on the disc and the radial spot position of the optical pick-up unit on the disc.
  • This system consists of a carriage or sledge, on which the optical pick-up unit including a radial electromechanical actuator for the focusing element is mounted.
  • the electromechanical actuator operating in a radial direction is responsible for the fast positioning of the focused reading spot in a radial direction with respect to the target track and keeps it in the middle of the track.
  • the spiral track slowly moves outwards.
  • the carriage or sledge slowly moves outwards, following the path of the track.
  • an optical pick-up unit for a disc comprising a light source, a focusing element, a focus actuator for providing a motion perpendicular with respect to a surface of a disc, wherein the focusing element is mounted on the focus actuator, a detector for detecting light emitted from the light source and reflected by the disc and a detector circuit in communication with a detector for determining a focus error signal, wherein a filter is provided for filtering the focus error signal.
  • the lens of the optical pick-up unit is positioned using two electromechanical actuators, one in focus direction (perpendicular to the disc) and the other in radial direction (along the radius of the disc).
  • the former focuses the reading spot in the plane of the data layer of the disc whereas the later provides the fast short stroke tracking of the track in the data layer.
  • the radial carriage/sledge on which the optical pick-up unit is mounted provides for the slow long stroke tracking of the track. Its main goal is to keep the radial actuator the in the middle of its operating range, i.e. in the middle of the optical pick-up unit.
  • two error signals are generated from the reflected light.
  • the focus error signal which is a measure for the distance (perpendicular to the disc) between the focal point of the lens and the data layer of the disc.
  • the radial error signal is a measure for the distance between the centre of the reading spot and the middle of the track on which the reading spot is currently positioned (along the radius of the disc).
  • the focus error is used by the focus controller to position the focus actuator such that the focal point of the lens coincides with the data layer of the disc, whereas the radial controller controls the radial actuator using the radial error signal in order to keep the centre of the reading spot in the middle of the track being read.
  • the sledge controller controls the sledge/carriage, it moves the sledge/carriage in such a way that the DC value of the radial controller output becomes zero, in that case the radial actuator positions the lens radially in the middle of the operating range of the optical pick-up unit.
  • an access to the information stored on the disc involves a controlled jump from a first position on the disc to a second position on the disc, during which the track on the disc is crossed several times in a radial direction. During this crossing, the number of tracks crossed is counted.
  • the lens actuator providing a movement in a radial direction is actuated. Aside from relatively short acceleration and deceleration periods at the beginning and the end of the jump, respectively, the lens actuator moves radially over the disc, crossing the tracks at constant velocity.
  • the second stage of the electromechanical system i.e. the sledge, just follows and keeps the lens actuator in the middle of its working range.
  • the spot position of the optical pick-up unit is moved in a radial direction with respect to the disc, the track crossing frequency during the jump lies typically in the kHz range.
  • the reflectivity of a disc is different when spot positions on the track and on all other parts of the disc are compared.
  • a radial movement of the reading spot across the disc generates a repeated change in intensity of the light reflected from the optical disc.
  • the changes in intensity of the reflected light are thus also in the kHz range.
  • the difference in the amount of reflected light between spot positions on the track and on other areas of the disc is used to control the spot position such that it follows the track on the disc.
  • the light reflected from the disc is used to generate a focus error and a radial error signal, the former indicates the difference between the actual focal point position and the optimal focussing position, whereas the latter is a measure for the difference between the reading spot centre and the middle of the track to be followed .
  • the focus error signal is used to provide a feedback to the focus controller controlling the electromechanical actuators of the Optical Pick-up Unit.
  • the focus controller is a PID element (Proportional Integral Differential element).
  • the above changes in the amount of light reflected from the disc surface during a jump result in a distortion and modulation of the focus error signal.
  • the gain of the focus error signal changes and an offset is introduced as well.
  • the distortion introduced in the focus error signal by a crossing of the spot position over the disc with constant velocity is amplified by the focus controller and actuates the focus actuator with an additional oscillatory movement in the kHz range.
  • An embodiment of the present invention preferably suppresses the distortion in the focus error signal, thereby suppressing the high frequency actuation of the focus actuator which generates the whistling noise. Also, the high actuator current might be reduced.
  • filtering of the focus error signal means the focus error signal as computed by a detector circuit or any signal derived thereof, containing the information carried by the focus error signal.
  • the distortion suppression in the focus error signal in an embodiment of the present invention can be implemented by means of a band-stop filter.
  • the band-stop filter operates at a fixed frequency corresponding to the track-crossing frequency.
  • the track crossing frequency is defined as the number of tracks crossed per second during a movement of the spot in a radial direction. This embodiment is particularly useful once the track-crossing frequency, i.e. the constant velocity provided by the actuator during a jump is the same for each jump occurring in the system.
  • the filter is arranged such that its filtering frequency can be adjusted to the track-crossing frequency, i.e. to the velocity provided by the actuator moving in a radial direction.
  • the filter provides a filtering in a range from 2 to 5 kHz, in particular at 3.7 kHz.
  • the bandwidth of the stop-band should be wide enough to suppress deviations in the track-cross frequency over the complete jump and narrow enough not to make the focus control loop instable, i.e. not to lose too much phase at the bandwidth frequency of the focus control loop.
  • the optical pick-up unit comprises a focus controller to drive the electromechanical actuator, wherein the focus controller is designed to receive the focus error signal.
  • the filter is arranged between the detector circuit and the focus controller. As the output of the focus controller in an embodiment is amplified to drive the focus actuator, any distortions received with the focus error signal will be amplified. Therefore, a filtering according to an embodiment of the present invention before the focus error signal enters into the focus controller enables a more efficient filtering of the signal at the track-crossing frequency when compared to a signal filtering after an amplification of the distortions.
  • the filtering could also be provided on the output signal of the focus contr oiler as the distortion of this output signal corresponds to the distortion of the focus error signal.
  • optical pick-up unit could advantageously be employed in a play back module for a data medium or a disc.
  • a play back module in the sense of this application could be a simple play back unit and/or a recording equipment, preferably for a CD or DVD or any disc- shaped optical data medium.
  • a play back module according to an embodiment of the present invention could be employed in an audio or video system, advantageously in a portable or car audio or video system.
  • the play back module according to the present invention could also be employed in any type of system for optically storing and reading data on or from an optical data storage medium.
  • the method for the reduction of noise generated by the optical pick-up unit could be implemented as a computer program enabling a processor to carry out the method according to an embodiment of the present invention.
  • the computer program could be run on a DSP (Digital Signal Processing) board.
  • DSP Digital Signal Processing
  • the respective computer program could advantageously be stored on a computer-readable medium such as an optical disc or a magnetic tape.
  • the information which represents a computer program corresponding to an embodiment of the present invention could also be provided as an electromagnetic signal, preferably via a computer network, e.g. the internet.
  • Figure 1 shows a cutaway top view of a disc and a spot location of an optical pick-up unit thereon.
  • Figure 2 shows a schematic view of an optical pick-up unit according to an embodiment of the present invention.
  • Figure 3 shows the frequency characteristics of the band- stop filter according to an embodiment of the present invention.
  • Figure 4 shows a schematic view of an embodiment of the present invention implemented in a software run on a digital signal processing board.
  • Figure 1 schematically shows a cutaway view of the surface of an optical compact disc.
  • the different sections 1 belong to a single track provided for data storage in the surface of the disc.
  • the track is spirally arranged around the center of the disc such that the distances between the sections 1 of the track when considered in a radial direction are equal.
  • the optical spot 2 provided by the Optical Pick-up Unit moves along the track, following its spiral shape.
  • jumps of the spot position 2 over the surface 3 of the disc in a radial direction are necessary to access different parts of the track.
  • a movement of the spot position 2 in a radial direction is provided by the lens actuator moving the lens or any other focusing element providing a focusing of the optical readout beam onto the disc. This movement occurs in essentially three phases 4, 5, 6.
  • the three distinguishable phases 4, 5, 6 are schematically sketched in figure 1.
  • a phase 4 of acceleration is followed by a phase 5 of constant radial velocity and a phase 6 of deceleration between a first spot position 2 and a second spot position 7 on the disc.
  • phase 5 with constant velocity the sections 1 of the spirally shaped track are crossed at regular time intervals. Each crossing of a section 1 of the track leads to a change in the intensity of the light reflected from the surface 3 of the disc. Therefore the reflected intensity is modulated with a frequency depending on the velocity of the radial movement of the spot 2 as well as the radial distance between the different sections 1 of the track.
  • the light reflected from the surface 3 (data layer) of the disc is used to generate a focus error signal that is used to control the focus position of the lens such that the laser beam (reading spot) is kept focussed on the disc's data layer. Therefore the focus error signal during a movement of the spot in a radial direction is modulated corresponding to the crossing of the sections 1 of the track. The crossing of each radial section of the track leads to a variation in the reflected intensity.
  • FIG 2 a schematic view of an embodiment according to the present invention is shown.
  • the data layer 11 below the surface of a disc 10 is illuminated by an optical pick-up unit 12 comprising a light source 13 and detector 14.
  • the light generated by the light source 13 is focused by a lens 15 onto the data layer 11 of the disc 10.
  • an electromechanical actuator (not shown) enables a movement of the lens 15 in a radial direction keeping the position of the spot 17 in the middle of the track 19.
  • the light reflected from the data layer 11 of the disc 10 is detected by the detector 14.
  • the signal generated by the detector 14 is further processed by a detector circuit 18 in order to determine a focus error signal providing an indication for the distance between the focal point of the lens 17 and the data layer 11 (perpendicular to the disc).
  • the focus error signal 20 is communicated to a focus controller 21 which in the shown embodiment is a proportional plus integral plus derivative (PID) element.
  • the PID element 21 computes the focus error signal 20 providing an output signal to control the focus actuator 16 in order to enable a correct positioning of the focal spot 17 on the data layer 11 of the disc 10.
  • the output signal of the PID element 21 is further amplified by an amplifying element 22.
  • a radial movement of the spot position on the disc leads to a modulation of the overall intensity reflected from the data layer 11 of the disc 10.
  • This also leads to a modulation or distortion of the focus error signal 20 and thus via the focus controller 21 and the driver circuit 22 to a modulated actuation of the focus actuator 16.
  • the modulation frequency and thus the modulated actuation occurs at approximately 3.7 kHz. Therefore the modulated actuation of the focus actuator 16 lies in the audible frequency range.
  • the mounting of the focusing element 15 as well as the focus actuator 16 provide a resonance body and therefore the modulated actuation would clearly be audible for the user.
  • a band-stop filter 23 is introduced between the detector circuit 18 and the PID element 21.
  • the band- stop filter provides a stop-band at 3.7 kHz, filtering out the modulation of the focus error signal 20 due to the track- crossing of the focal spot 17.
  • FIG. 2 describes the focus control loop of the system.
  • a focus actuator 16 positioning a focussing element, i.e. lens 15, which focuses the laser beam radiating from laser 13 to a reading spot 17 on the track 19 on the data layer 11 (some distance below the surface) of the disc.
  • the light reflected back from the disc (modulated by the data layer) to the detector 14, from which the focus error signal 20 is generated by a detector circuit 18.
  • the focus error signal 20 filtered by the band-stop filter 23 and computed by the PID element 21 is used to actuate the focus actuator 16 via the driver circuit 22.
  • Figure 3 shows the Bode diagram for the band-stop filter 23 as used in the embodiment schematically shown in figure 2.
  • the upper section of the diagram shows the magnitude in dB, whereas the lower part of the diagram shows the phase in degrees versus frequency.
  • FIG. 4 is a schematic diagram of an embodiment of the PID element 50 as well as the band-stop filter 51, implemented in the embedded software of a digital signal processing board.
  • the focus error signal 52 is first passed through a band-stop filter 51 before being communicated to the PID element 50 which drives a corresponding focus actuator providing a movement of the focusing element in a direction perpendicular to the disc to be read out.

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  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • Optical Recording Or Reproduction (AREA)

Abstract

Afin de réduire le bruit produit par un mouvement radial d'un point de lecture d'une unité de capture optique pour un support de stockage optique, l'invention suggère de prévoir un filtrage du signal d'erreur de mise au point ou de tout autre signal issu de celui-ci et d'éviter ainsi un actionnement modulé de l'actionneur de mise au point.
PCT/IB2008/050495 2007-02-09 2008-02-12 Réduction de bruit WO2008096333A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EP07102021.8 2007-02-09
EP07102021 2007-02-09

Publications (1)

Publication Number Publication Date
WO2008096333A1 true WO2008096333A1 (fr) 2008-08-14

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ID=39433885

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/IB2008/050495 WO2008096333A1 (fr) 2007-02-09 2008-02-12 Réduction de bruit

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TW (1) TW200849231A (fr)
WO (1) WO2008096333A1 (fr)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
TWI597723B (zh) * 2016-03-11 2017-09-01 Pei-Yu Liao Filter CD music pieces noise device

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS60160033A (ja) * 1984-01-28 1985-08-21 Seiko Instr & Electronics Ltd 光情報検出装置
EP0469617A1 (fr) * 1990-08-01 1992-02-05 Mitsubishi Denki Kabushiki Kaisha Système de régulation en boucle fermée avec filtre adaptatif
EP0757345A2 (fr) * 1995-08-04 1997-02-05 Sony Corporation Enregistrement et lecture optique
EP0833310A2 (fr) * 1996-09-25 1998-04-01 Deutsche Thomson-Brandt Gmbh Dispositif de reproduction ou d'enregistrement pour la reproduction ou l'enregistrement sur un support d'enregistrement optique
EP0992987A2 (fr) * 1998-10-06 2000-04-12 Pioneer Corporation Appareil de lecture optique
US20010026507A1 (en) * 2000-03-29 2001-10-04 Sanyo Electric Co., Ltd. Control apparatus for optical pickup and optical disc apparatus
US20020048236A1 (en) * 2000-10-25 2002-04-25 Hitachi, Ltd. Optical disc apparatus and focus jump method
US6519496B1 (en) * 1999-02-19 2003-02-11 Fujitsu Limited Feedback controller, digital filter device, and storage device

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS60160033A (ja) * 1984-01-28 1985-08-21 Seiko Instr & Electronics Ltd 光情報検出装置
EP0469617A1 (fr) * 1990-08-01 1992-02-05 Mitsubishi Denki Kabushiki Kaisha Système de régulation en boucle fermée avec filtre adaptatif
EP0757345A2 (fr) * 1995-08-04 1997-02-05 Sony Corporation Enregistrement et lecture optique
EP0833310A2 (fr) * 1996-09-25 1998-04-01 Deutsche Thomson-Brandt Gmbh Dispositif de reproduction ou d'enregistrement pour la reproduction ou l'enregistrement sur un support d'enregistrement optique
EP0992987A2 (fr) * 1998-10-06 2000-04-12 Pioneer Corporation Appareil de lecture optique
US6519496B1 (en) * 1999-02-19 2003-02-11 Fujitsu Limited Feedback controller, digital filter device, and storage device
US20010026507A1 (en) * 2000-03-29 2001-10-04 Sanyo Electric Co., Ltd. Control apparatus for optical pickup and optical disc apparatus
US20020048236A1 (en) * 2000-10-25 2002-04-25 Hitachi, Ltd. Optical disc apparatus and focus jump method

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
GLOVER J R: "Adaptive noise canceling applied to sinusoidal interferences", IEEE TRANSACTIONS ON ACOUSTICS, SPEECH AND SIGNAL PROCESSING, IEEE INC. NEW YORK, vol. ASSP-25, no. 6, 1 December 1977 (1977-12-01), pages 484 - 491, XP002402297, ISSN: 0096-3518 *

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