US20050068864A1 - Method and apparatus for tracking error detection in optical disk driver - Google Patents
Method and apparatus for tracking error detection in optical disk driver Download PDFInfo
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- US20050068864A1 US20050068864A1 US10/991,869 US99186904A US2005068864A1 US 20050068864 A1 US20050068864 A1 US 20050068864A1 US 99186904 A US99186904 A US 99186904A US 2005068864 A1 US2005068864 A1 US 2005068864A1
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- 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
- G11B7/0901—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 track following only
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- the present invention relates to a method and apparatus for tracking error detection and more particularly, to an improved method and apparatus for tracking error detection in which a phase locked loop (PLL) is introduced into a conventional differential phase detection tracking error (DPD TE) method to increase the accuracy of tracking error detection.
- PLL phase locked loop
- DPD TE differential phase detection tracking error
- phase differences are generated on the edges of pits or marks of an optical disk.
- the length of pits or marks recorded on an optical disk lies in various ranges. For example, in the case of digital versatile disk-ROM (DVD-ROM), a length ranges from 3T to 14T where T is the duration of a channel clock of the disk. If there are a lot of pits or marks having a short length, phase difference detection can be performed many times, thereby enhancing the reliability of a tracking error signal derived therefrom. Conversely, if there are more pits or marks having a long length, the number of times phase difference detection may be done is reduced, thereby degrading the reliability of a tracking error signal.
- a spectrum component according to a modulation method of signal recorded on a disk, is closely related to outputs of AC+ and BD+, and a low-frequency component of the spectrum acts on noise with regard to a tracking error signal which is used for following and determining the position of a tracking center.
- phase difference detection is supposed to be made from pits or marks at one time, so that the gain and characteristics of a detected signal deteriorate if the signal of pits or marks is adversely affected by defects or the like.
- the conventional DPD TE method has a disadvantage in that it is difficult to precisely control tracking in a high-density track structure.
- FIG. 1 the configuration of a tracking error detecting apparatus according to a conventional differential phase detection tracking error (DPD TE) method is shown. The apparatus shown in FIG.
- the apparatus detects a phase difference between the signals output from the four-section optical detection unit 102 to determine the position of a laser spot. If the laser spot deviates from a track center, then a time delay or a phase difference between A+C and B+D signals results. Thus, a tracking error signal is generated by detecting the time delay between those signals.
- the matrix circuit 104 adds optical detection signals A and B, and C and D, which are positioned along a diagonal line among the outputs (A, B, C and D) of the four-section optical detection unit 102 , and outputs AC 1 and BD 1 from A+C and B+D, respectively.
- the HPFs 106 a and 106 b reinforce the high-frequency components of AC 1 and BD 1 provided from the matrix circuit 104 , differentiate AC 1 and BD 1 , and output the results, i.e., AC 2 and BD 2 to the comparators 108 a and 108 b .
- the comparators 108 a and 108 b binarize each of AC 2 and BD 2 provided from the HPFs 106 a and 106 b , compare AC 2 and BD 2 with a predetermined level (a ground level in FIG. 1 ) to output the results, i.e., AC 3 and BD 3 to the phase comparator 110 .
- the phase comparator 110 detects a phase difference between AC 3 and BD 3 provided from the comparators 108 a and 108 b , compares the phases of AC 3 and BD 3 to output the results, i.e., AC+ and BD+ to the LPF 112 .
- AC+ is a phase difference signal generated when AC 3 leads BD 3 in phase
- BD+ is a phase difference signal generated when BD 3 leads AC 3 in phase.
- the LPF 112 filters AC+ and BD+ input from the phase comparator 110 and outputs the result as a tracking error signal.
- FIGS. 2A-2D are waveform diagrams illustrating operation of the apparatus shown in FIG. 1 .
- FIGS. 2A-2D show the case in which AC 3 leads BD 3 in phase.
- the wave forms of AC 3 , BD 3 , AC+ and BD+ signals are illustrated sequentially from FIG. 2A to FIG. 2D .
- FIGS. 2A-2D it can be found that if a laser spot deviates by a predetermined amount, there exists a phase difference between AC 3 and BD 3 , shown in FIG. 2A and FIG. 2B , respectively, which is in turn reflected into AC+ and BD+, shown in FIG. 2C and FIG. 2D , respectively.
- a tracking error signal is greater than a predetermined central value, but in the opposite case, it is less than the predetermined central value.
- the degree to which a tracking error signal deviates from the central value corresponds to the distance by which the laser spot is departed from the track center.
- the phase comparator 110 of the apparatus shown in FIG. 1 detects a phase difference at a rising or falling edge of AC 3 and BD 3 .
- the rising or falling edges of AC 3 and BD 3 correspond to the edges of pits or marks recorded on an optical disk.
- the apparatus shown in FIG. 1 detects a phase difference once on every edge of pits and marks recorded on an optical disk.
- a spectrum component according to a recording modulation method is closely connected with AC+ and BD+, and especially a low-frequency component of the spectrum works on noise with regard to a tracking error signal. Further, in the case of a tracking error signal according to the DPD TE method, the magnitude and gain are reduced as track density is increased, which makes the accurate control of tracking in a high track-density structure difficult.
- a tracking error detecting method involves generating clock signals, synchronized with each of the binarized signals AC 3 and BD 3 , to detect a phase difference between those clock signals.
- all pulses in the synchronized clock signals have the phase difference components of AC+ and BD+, so that a tracking error signal can be generated regardless of the lengths of pits or marks recorded on a disk.
- outputs of optical detectors which are disposed along a diagonal line from a track center are each binarized.
- Clock signals synchronized with each of the outputs obtained from the binarization are generated by Phase Locked Loop (PLL) circuits.
- PLL Phase Locked Loop
- the outputs AC 3 and BD 3 obtained from the binarization have a phase difference corresponding to the deviation degree of the laser spot with regard to the track center, and the clocks which are phase locked to the outputs have the same phase difference.
- a phase difference between the synchronized clock signals output in the phase locking is detected.
- All clocks in the synchronized clock signals have the phase difference components of AC+ and BD+, so that a phase difference component is detected on a clock-by-clock basis.
- the output from the phase difference detection is filtered by an LPF to obtain a tracking error signal.
- PLL phase locked loop
- DPD TE differential phase detection tracking error
- a tracking error detecting method for producing a tracking error signal as a difference signal between optical detection signals generated from more than two optical detectors which are positioned along a diagonal line from a track center.
- the method according to the present invention includes binarizing the outputs of the optical detectors, phase-locking to generate clock signals synchronized with each of the outputs obtained from the binarization, detecting phase differences between the synchronized clock signals output from the phase-locking, and low-pass filtering the output of the phase difference detection, to output the tracking error signal.
- the present invention provides a first embodiment of a tracking error detection apparatus for producing a tracking error signal based on a difference signal of optical detection signals generated from more than two optical detectors which are positioned along a diagonal line from a track center.
- the first preferred embodiment of the apparatus according to the present invention includes binarizers which binarize each of the outputs of the optical detectors, PLLs which generate clock signals synchronized with each of the outputs of the binarizers, a phase difference detector which detects a phase difference between the synchronized clock signals output from the PLLs, and a low-pass filter which filters the output of the phase difference detector to output the result as the tracking error signal.
- the present invention also provides a second embodiment of a tracking error detecting apparatus for producing a tracking error signal based on a difference signal of optical detection signals generated from two optical detectors disposed at the outside of the track center of a three-section optical detection unit.
- the second preferred embodiment of the apparatus according to the present invention includes binarizers which binarize each of the outputs of the optical detectors, a phase difference detector which detects a phase difference between the outputs of the binarizers, and a low-pass filter which filters the output of the phase difference detector to output the result as a tracking error signal.
- the tracking error detecting apparatus further includes PLLs coupled to the binarizers and to the phase difference detector, in order to generate clock signals synchronized with each of the outputs of the binarizers and to output the synchronized clock signals to the phase difference detector.
- FIG. 1 is a block diagram of a tracking error detecting apparatus according to a conventional differential phase detection tracking error (DPD TE) method;
- DPD TE differential phase detection tracking error
- FIGS. 2A-2D are waveform diagrams showing the operation of the apparatus shown in FIG. 1 ;
- FIG. 3 is a block diagram of a first preferred embodiment of a tracking error detecting apparatus according to the present invention.
- FIGS. 4A-4F are waveform diagrams showing the operation of the apparatus shown in FIG. 3 ;
- FIG. 5 is a block diagram of a second preferred embodiment of a tracking error detecting apparatus according to the present invention.
- FIG. 6 is a block diagram of a third preferred embodiment of a tracking error detecting apparatus according to the present invention.
- FIG. 7 is a block diagram of a fourth preferred embodiment of a tracking error detecting apparatus according to the present invention.
- FIG. 8 is a graph of gain versus frequency for the equalizers shown in FIGS. 3 and 5 - 7 ;
- FIG. 9 is a graph showing the result of comparing a tracking error signal generated by a tracking error detecting apparatus according to the present invention, with a tracking signal generated by a conventional DPD TE method.
- FIG. 10 is a graph showing the characteristic of gain of tracking error signals generated by a tracking error detecting apparatus according to the present invention and a conventional DPD TE method.
- FIG. 3 is a block diagram showing a first preferred embodiment of a tracking error detecting apparatus according to the present invention.
- the apparatus shown in FIG. 3 includes a four-section optical detection unit 302 , a matrix circuit 304 , equalizers (EQs) 306 a and 306 b , binarizers 308 a and 308 b , PLLs 310 a and 310 b , a phase comparator 312 , LPFs 314 a and 314 b , a differential amplifier 316 , and a frequency divider 318 .
- EQs equalizers
- the matrix circuit 304 adds optical detection signals A and C, and B and D among the outputs A, B, C and D of the four-section optical detection unit 302 , and outputs AC 1 and BD 1 corresponding to A+C and B+D, respectively. That is, the matrix circuit 304 produces summation signals of the signals generated by optical detectors which are positioned along a diagonal line from a track center.
- the EQs 306 a and 306 b strengthen the high-frequency components of AC 1 and BD 1 provided from the matrix circuit 304 and remove noise therefrom, differentiate AC 1 and BD 1 and remove noise therefrom to output the results AC 2 and BD 2 to the binarizers 308 a and 308 b .
- the outputs A, B, C and D of the four-section optical detection unit 302 have weak high-frequency components, the high-frequency components of AC 1 and BD 1 provided from the matrix circuit 304 are reinforced through the EQs 306 a and 306 b . Further, as the outputs A, B, C and D of the four-section optical detection unit 302 contain a noise component in addition to signals reflected from an optical disk, EQs 306 a and 306 b eliminate the noise component in AC 1 and BD 1 provided from the matrix circuit 304 .
- the binarizers 308 a and 308 b convert AC 2 and BD 2 provided from EQs 306 a and 306 b into binary digital signals and output the results AC 3 and BD 3 to the PLLs 310 a and 310 b .
- Binarizers 308 a and 308 b also perform binarization level compensation for AC 2 and BD 2 provided from the EQs 306 a and 306 b .
- the PLLs 310 a and 310 b accept the input signals CLK, AC 3 and BD 3 and output CLK_AC and CLK_BD, synchronized with AC 3 and BD 3 , respectively, to the phase comparator 312 .
- the phase comparator 312 detects a phase difference between CLK_AC and CLK_BD, and compares the phases of CLK_AC and CLK_BD to output the results AC+ and BD+ to LPFs 314 a and 314 b , respectively.
- AC+ and BD+ are phase difference signals generated when CLK_AC leads CLK_BD in phase and when CLK_BD leads CLK_AC in phase, respectively.
- the LPFs 314 a and 314 b filter AC+ and BD+ provided from the phase comparator 312 to output the results to the differential amplifier 316 .
- the differential amplifier 316 amplifies the difference signal of AC+ and BD+ filtered by the LPFs 314 a and 314 b to output the result as a tracking error signal (TE).
- FIGS. 4A-4F are waveform diagrams showing the operation of the apparatus shown in FIG. 3 .
- FIGS. 4A-4F show the case in which AC 3 leads BD 3 in phase, the wave forms of AC 3 , BD 3 , CLK_AC, CLK_BD, AC+, and BD+ signals are illustrated sequentially in FIGS. 4A-4F , respectively.
- FIGS. 4A-4F it can be found that if a laser spot deviates from a track center by a predetermined amount, a phase difference existing between AC 3 and BD 3 is transferred to CLK_AC and CLK_BD, doubling by a CLK frequency.
- phase difference value ⁇ t is derived as a result of comparing the phases of CLK_AC and CLK_BD.
- the conventional apparatus shown in FIG. 1 detects the phase difference ⁇ t once in an interval t 1 as shown in FIG. 2A-2D , while the apparatus according to the present invention can detect the phase difference ⁇ t once every cycle of CLKs.
- the phase difference ⁇ t can be detected once every channel clock cycle T regardless of the lengths of pits or marks recorded on an optical disk.
- the frequency divider 318 frequency divides CLK at an interval where inversion of the output signal takes place, to output the result to the PLLs 310 a and 310 b .
- Inversion of the output signal occurs when the phase difference of a clock provided to the AC 3 and the PLL 310 a or a clock provided to the BD 3 and the PLL 310 b is beyond a detection range of the PLL 310 a and 310 b .
- Divider 318 detects whether the output signal TE OUT has been inverted and performs a division operation when the output signal TE OUT is inverted as in the interval 93 of FIG. 9 . Alternately, divider 318 detects the output signals of PLLs 310 a and 310 b to determine whether TE OUT has been inverted. In the apparatus of FIG. 3 , a tracking servo control becomes unstable at the interval where inversion of the output signal happens.
- FIG. 5 is a block diagram showing a second embodiment of a tracking error detecting apparatus according to the present invention.
- the apparatus shown in FIG. 5 includes a four-section optical detection unit 502 , EQs 506 a - 506 d , binarizers 508 a - 508 d , PLLs 510 a - 510 d , phase comparators 512 a and 512 b , LPFs 514 a - 514 d , differential amplifiers 516 a and 516 b , and an adder 518 .
- outputs A, B, C and D of the four-section optical detection unit 502 have weak high-frequency components, a high-frequency component of A, B, C and D provided from the four-section optical detection unit 502 is reinforced through the EQs 506 a - 506 d . Further, as the outputs A, B, C and D of the four-section optical detection unit 502 contain noise in addition to signals reflected from an optical disk, EQs 506 a - 506 d eliminate the noise components of A, B, C and D provided from the four-section optical detection unit 502 .
- the phase comparators 512 a and 512 b detect phase differences between CLK_A and CLK_B and between CLK_C and CLK_D provided from the PLLs 510 a - 510 d .
- the phase comparator 512 a compares the phases of CLK_A and CLK_B to output the results A+ and B+ to the LPFs 514 a and 514 b , respectively, while the phase comparator 512 b compares the phases of CLK_C and CLK_D to output the results C+ and D+ to the LPFs 514 c and 514 d , respectively.
- A+ and B+ are phase difference signals generated when CLK_A leads CLK_B in phase and when CLK_B leads CLK_A in phase, respectively.
- C+ and D+ are phase difference signals generated when CLK_C leads CLK_D in phase and when CLK_D leads CLK_C in phase, respectively.
- the LPFs 514 a - 514 d filter A+, B+, C+ and D+ provided from the phase comparators 512 a and 512 b to output the results to the differential amplifiers 516 a and 516 b .
- the differential amplifiers 516 a and 516 b amplify the difference signals of A+ and B+, and C+ and D+filtered by the LPFs 514 a to 514 d to output the results to the adder 518 .
- the adder 518 adds the signals provided from the differential amplifiers 516 a and 516 b to output the result as TE.
- FIG. 6 is a block diagram showing a third preferred embodiment of a tracking error detecting apparatus according to the present invention, in which TE is produced using outputs of a three-section optical detection unit.
- the apparatus shown in FIG. 6 includes a three-section optical detection unit 602 , EQs 606 a and 606 b , binarizers 608 a and 608 b , PLLs 610 a and 610 b , a phase comparator 612 , LPFs 614 a and 614 b , and a differential amplifier 616 .
- the detection unit 602 has three optical detectors which are arranged transverse to a tangential direction of the recording track.
- the optical detectors generate electrical signals E, F and G corresponding to light reflected from the recording track.
- the EQs 606 a and 606 b strengthen the high-frequency components of signals E and G provided from optical detectors disposed at the outside of the three-section optical detection unit 602 and remove noise therefrom, differentiate E and G and remove noise therefrom to output the results to the binarizers 608 a and 608 b .
- the binarizers 608 a and 608 b convert the signals provided from EQs 606 a and 606 b into binary digital signals to output the results E 3 and G 3 to the PLLs 610 a and 610 b , respectively.
- the PLLs 610 a and 610 b receive as input CLK, E 3 and G 3 to output CLK_E and CLK_G synchronized with E 3 and G 3 to the phase comparator 612 .
- the phase comparator 612 compares the phases of CLK_E and CLK_G and outputs the results E+ and G+ to the LPFs 614 a and 614 b , respectively. In this case, E+ and G+are phase difference signals generated when CLK_E leads CLK_G in phase and when CLK_G leads CLK_E in phase, respectively.
- the LPFs 614 a and 614 b filter E+ and G+ provided from the phase comparator 612 to output the results to the differential amplifier 616 .
- the differential amplifier 616 amplifies the difference signal of E+ and G+ filtered by the LPFs 614 a and 614 b to output the result as TE.
- FIG. 7 is a block diagram showing a fourth preferred embodiment of a tracking error detecting apparatus according to the present invention in which TE is produced using the output of a three-section optical detection unit.
- the apparatus shown in FIG. 7 includes a three-section optical detection unit 702 , EQs 706 a and 706 b , binarizers 708 a and 708 b , a phase comparator 712 , LPFs 714 a and 714 b , and a differential amplifier 716 .
- the detection unit 702 has three optical detectors which are arranged transverse to a tangential direction of the recording track.
- the optical detectors generate electrical signals E, F and G corresponding to light reflected from the recording track.
- the EQs 706 a and 706 b differentiate E and G and remove noise therefrom to strengthen the high frequency component of signals E and G and output the results to the binarizers 708 a and 708 b .
- the binarizers 708 a and 708 b binarize the signals provided from EQs 706 a and 706 b into binary digital signals to output the results E 3 and G 3 to the phase comparator 712 .
- the phase comparator 712 compares the phases of E 3 and G 3 to output the results E+ and G+ to the LPFs 714 a and 714 b , respectively.
- E+ and G+ are phase difference signals generated when E 3 leads G 3 in phase and when G 3 leads E 3 in phase, respectively.
- the LPFs 714 a and 714 b filter E+ and G+provided from the phase comparator 712 to output the results to the differential amplifier 716 .
- the differential amplifier 716 amplifies the difference signal of E+ and G+ filtered by the LPFs 714 a and 714 b to output the result as TE.
- FIG. 8 is a graph showing operation of the EQs of FIGS. 3 and 5 - 7 , in which the vertical axis and the horizontal axis indicate gain and frequency, respectively.
- the EQs having the properties as shown in FIG. 8 , perform the function of controlling their properties so that an input signal can be positioned between a first frequency f 1 and a second frequency f 2 to amplify the high-frequency component which is close to the second frequency f 2 .
- FIG. 9 is a graph showing the result of comparing a tracking error signal generated by a tracking error detecting apparatus according to the present invention with a tracking signal generated by a conventional DPD TE method.
- reference numerals 91 and 92 respectively represent tracking error signals generated by a conventional DPD TE method and a tracking error detecting apparatus according to the present invention, and it can be seen that the gain of the latter is greater than that of the former.
- FIG. 10 is a graph showing the characteristic of gain of tracking error signals generated by a tracking error detecting apparatus according to the present invention and a conventional DPD TE method.
- reference numerals 94 and 95 respectively indicate the gains of tracking error signals generated by the conventional DPD TE method and the tracking error detecting apparatus according to the present invention. If both are measured under the same conditions, it can be seen that the gain of a tracking error signal generated in the apparatus according to the present invention is about 10 times greater than the gain of the other.
- An interval 96 is the section where an optical pickup jumps on an adjacent track in a normal tracking state. While the interval 96 cannot be shown clearly in a tracking error signal generated by the conventional DPD TE method, it is output as a large value in a tracking error signal generated by the present invention.
- a tracking error detecting apparatus is capable of generating a tracking error signal which does not vary depending on the lengths of pits and marks recorded on a optical disk, so that reliability of the tracking error signal can be enhanced.
Abstract
A method and apparatus for tracking error detection in an optical disk reproduction system. The tracking error detecting apparatus generates a tracking error signal as a difference signal of optical detection signals generated by more than two optical detectors positioned along a diagonal line from a track center and includes binarizers which binarize each output of the optical detectors, phase locked loops (PLLs) which generate respective clock signals synchronized with the outputs of each of the binarizers, a phase difference detector which detects a phase difference between the synchronized signals output from the PLLs, and low-pass filters which filter the output of the phase difference detector to output the result as the tracking error signal. The tracking error detecting apparatus generates a tracking error signal which is not dependent on the lengths of pits or marks recorded on an optical disk, enhancing the reliability of the tracking error signal.
Description
- This application is a divisional of prior application Ser. No. 09/613,695, filed Jul. 10, 2000, which is incorporated herein in its entirety by reference. This application claims the benefit of Korean Application No. 99-27451, filed Jul. 8, 1999, in the Korean Patent Office, the disclosure of which is incorporated herein by reference.
- 1. Field of the Invention
- The present invention relates to a method and apparatus for tracking error detection and more particularly, to an improved method and apparatus for tracking error detection in which a phase locked loop (PLL) is introduced into a conventional differential phase detection tracking error (DPD TE) method to increase the accuracy of tracking error detection.
- 2. Description of the Related Art
- In a conventional DPD TE method, phase differences are generated on the edges of pits or marks of an optical disk. The length of pits or marks recorded on an optical disk lies in various ranges. For example, in the case of digital versatile disk-ROM (DVD-ROM), a length ranges from 3T to 14T where T is the duration of a channel clock of the disk. If there are a lot of pits or marks having a short length, phase difference detection can be performed many times, thereby enhancing the reliability of a tracking error signal derived therefrom. Conversely, if there are more pits or marks having a long length, the number of times phase difference detection may be done is reduced, thereby degrading the reliability of a tracking error signal. Further, a spectrum component, according to a modulation method of signal recorded on a disk, is closely related to outputs of AC+ and BD+, and a low-frequency component of the spectrum acts on noise with regard to a tracking error signal which is used for following and determining the position of a tracking center.
- According to a conventional DPD TE method, phase difference detection is supposed to be made from pits or marks at one time, so that the gain and characteristics of a detected signal deteriorate if the signal of pits or marks is adversely affected by defects or the like. In addition, as the track density of an optical disk increases, the magnitude and gain of a tracking error signal according to the conventional DPD TE method decrease. Thus, the conventional DPD TE method has a disadvantage in that it is difficult to precisely control tracking in a high-density track structure. Referring to
FIG. 1 , the configuration of a tracking error detecting apparatus according to a conventional differential phase detection tracking error (DPD TE) method is shown. The apparatus shown inFIG. 1 includes a four-sectionoptical detection unit 102, amatrix circuit 104, high-pass filters (HPFs) 106 a and 106 b,comparators 108 a and 108 b, aphase comparator 110, and a low-pass filter (LPF) 112. The apparatus detects a phase difference between the signals output from the four-sectionoptical detection unit 102 to determine the position of a laser spot. If the laser spot deviates from a track center, then a time delay or a phase difference between A+C and B+D signals results. Thus, a tracking error signal is generated by detecting the time delay between those signals. - Specifically, the
matrix circuit 104 adds optical detection signals A and B, and C and D, which are positioned along a diagonal line among the outputs (A, B, C and D) of the four-sectionoptical detection unit 102, and outputs AC1 and BD1 from A+C and B+D, respectively. TheHPFs matrix circuit 104, differentiate AC1 and BD1, and output the results, i.e., AC2 and BD2 to thecomparators 108 a and 108 b. Thecomparators 108 a and 108 b binarize each of AC2 and BD2 provided from theHPFs FIG. 1 ) to output the results, i.e., AC3 and BD3 to thephase comparator 110. - The
phase comparator 110 detects a phase difference between AC3 and BD3 provided from thecomparators 108 a and 108 b, compares the phases of AC3 and BD3 to output the results, i.e., AC+ and BD+ to theLPF 112. In this case, AC+ is a phase difference signal generated when AC3 leads BD3 in phase, while BD+ is a phase difference signal generated when BD3 leads AC3 in phase. TheLPF 112 filters AC+ and BD+ input from thephase comparator 110 and outputs the result as a tracking error signal. -
FIGS. 2A-2D are waveform diagrams illustrating operation of the apparatus shown inFIG. 1 .FIGS. 2A-2D show the case in which AC3 leads BD3 in phase. The wave forms of AC3, BD3, AC+ and BD+ signals are illustrated sequentially fromFIG. 2A toFIG. 2D . As shown inFIGS. 2A-2D , it can be found that if a laser spot deviates by a predetermined amount, there exists a phase difference between AC3 and BD3, shown inFIG. 2A andFIG. 2B , respectively, which is in turn reflected into AC+ and BD+, shown inFIG. 2C andFIG. 2D , respectively. If AC3 leads BD3 in phase, a tracking error signal is greater than a predetermined central value, but in the opposite case, it is less than the predetermined central value. The degree to which a tracking error signal deviates from the central value corresponds to the distance by which the laser spot is departed from the track center. - The
phase comparator 110 of the apparatus shown inFIG. 1 detects a phase difference at a rising or falling edge of AC3 and BD3. The rising or falling edges of AC3 and BD3 correspond to the edges of pits or marks recorded on an optical disk. In other words, the apparatus shown inFIG. 1 detects a phase difference once on every edge of pits and marks recorded on an optical disk. Thus, as the number of pits or marks increases, the reliability of a tracking error signal increases, and as the number of pits or marks decreases, the reliability of the signal decreases. If pits or marks are affected by defects of an optical disk or other factors, the gain and characteristics of a tracking error signal become worse. A spectrum component according to a recording modulation method is closely connected with AC+ and BD+, and especially a low-frequency component of the spectrum works on noise with regard to a tracking error signal. Further, in the case of a tracking error signal according to the DPD TE method, the magnitude and gain are reduced as track density is increased, which makes the accurate control of tracking in a high track-density structure difficult. - In order to improve such drawbacks, a tracking error detecting method according to the present invention involves generating clock signals, synchronized with each of the binarized signals AC3 and BD3, to detect a phase difference between those clock signals. In this case, all pulses in the synchronized clock signals have the phase difference components of AC+ and BD+, so that a tracking error signal can be generated regardless of the lengths of pits or marks recorded on a disk.
- In the present invention, outputs of optical detectors which are disposed along a diagonal line from a track center are each binarized. Clock signals synchronized with each of the outputs obtained from the binarization are generated by Phase Locked Loop (PLL) circuits. When a laser spot deviates from a track center, the outputs AC3 and BD3 obtained from the binarization have a phase difference corresponding to the deviation degree of the laser spot with regard to the track center, and the clocks which are phase locked to the outputs have the same phase difference. A phase difference between the synchronized clock signals output in the phase locking is detected. All clocks in the synchronized clock signals have the phase difference components of AC+ and BD+, so that a phase difference component is detected on a clock-by-clock basis. The output from the phase difference detection is filtered by an LPF to obtain a tracking error signal.
- It is an object of the present invention to provide a method of improving the accuracy of a tracking error detection with the introduction of a phase locked loop (PLL) into a conventional differential phase detection tracking error (DPD TE) method.
- It is another object of the present invention to provide an apparatus using the above method.
- Additional objects and advantages of the invention will be set forth in part in the description which follows, and, in part, will be obvious from the description, or may be learned by practice of the invention.
- Accordingly, to achieve one object of the invention, there is provided a tracking error detecting method for producing a tracking error signal as a difference signal between optical detection signals generated from more than two optical detectors which are positioned along a diagonal line from a track center. The method according to the present invention includes binarizing the outputs of the optical detectors, phase-locking to generate clock signals synchronized with each of the outputs obtained from the binarization, detecting phase differences between the synchronized clock signals output from the phase-locking, and low-pass filtering the output of the phase difference detection, to output the tracking error signal.
- In order to achieve another object, the present invention provides a first embodiment of a tracking error detection apparatus for producing a tracking error signal based on a difference signal of optical detection signals generated from more than two optical detectors which are positioned along a diagonal line from a track center. The first preferred embodiment of the apparatus according to the present invention includes binarizers which binarize each of the outputs of the optical detectors, PLLs which generate clock signals synchronized with each of the outputs of the binarizers, a phase difference detector which detects a phase difference between the synchronized clock signals output from the PLLs, and a low-pass filter which filters the output of the phase difference detector to output the result as the tracking error signal. In this case, it is preferable to further include a frequency divider for dividing the frequency of a channel clock signal by n (n=2, 3, 4, . . . ) to output the signal to the PLLs in the event that the phase of an output signal is inverted.
- In order to achieve another object, the present invention also provides a second embodiment of a tracking error detecting apparatus for producing a tracking error signal based on a difference signal of optical detection signals generated from two optical detectors disposed at the outside of the track center of a three-section optical detection unit. The second preferred embodiment of the apparatus according to the present invention includes binarizers which binarize each of the outputs of the optical detectors, a phase difference detector which detects a phase difference between the outputs of the binarizers, and a low-pass filter which filters the output of the phase difference detector to output the result as a tracking error signal. In this case, it is preferable that the tracking error detecting apparatus further includes PLLs coupled to the binarizers and to the phase difference detector, in order to generate clock signals synchronized with each of the outputs of the binarizers and to output the synchronized clock signals to the phase difference detector.
- The above objectives and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which:
-
FIG. 1 is a block diagram of a tracking error detecting apparatus according to a conventional differential phase detection tracking error (DPD TE) method; -
FIGS. 2A-2D are waveform diagrams showing the operation of the apparatus shown inFIG. 1 ; -
FIG. 3 is a block diagram of a first preferred embodiment of a tracking error detecting apparatus according to the present invention; -
FIGS. 4A-4F are waveform diagrams showing the operation of the apparatus shown inFIG. 3 ; -
FIG. 5 is a block diagram of a second preferred embodiment of a tracking error detecting apparatus according to the present invention; -
FIG. 6 is a block diagram of a third preferred embodiment of a tracking error detecting apparatus according to the present invention; -
FIG. 7 is a block diagram of a fourth preferred embodiment of a tracking error detecting apparatus according to the present invention; -
FIG. 8 is a graph of gain versus frequency for the equalizers shown inFIGS. 3 and 5 -7; -
FIG. 9 is a graph showing the result of comparing a tracking error signal generated by a tracking error detecting apparatus according to the present invention, with a tracking signal generated by a conventional DPD TE method; and -
FIG. 10 . is a graph showing the characteristic of gain of tracking error signals generated by a tracking error detecting apparatus according to the present invention and a conventional DPD TE method. - Reference will now be made in detail to the present preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, where like reference numerals refer to like elements throughout.
-
FIG. 3 is a block diagram showing a first preferred embodiment of a tracking error detecting apparatus according to the present invention. The apparatus shown inFIG. 3 includes a four-sectionoptical detection unit 302, amatrix circuit 304, equalizers (EQs) 306 a and 306 b, binarizers 308 a and 308 b,PLLs phase comparator 312,LPFs differential amplifier 316, and afrequency divider 318. - The
matrix circuit 304 adds optical detection signals A and C, and B and D among the outputs A, B, C and D of the four-sectionoptical detection unit 302, and outputs AC1 and BD1 corresponding to A+C and B+D, respectively. That is, thematrix circuit 304 produces summation signals of the signals generated by optical detectors which are positioned along a diagonal line from a track center. TheEQs matrix circuit 304 and remove noise therefrom, differentiate AC1 and BD1 and remove noise therefrom to output the results AC2 and BD2 to thebinarizers optical detection unit 302 have weak high-frequency components, the high-frequency components of AC1 and BD1 provided from thematrix circuit 304 are reinforced through theEQs optical detection unit 302 contain a noise component in addition to signals reflected from an optical disk,EQs matrix circuit 304. - The
binarizers EQs PLLs Binarizers EQs PLLs phase comparator 312. Thephase comparator 312 detects a phase difference between CLK_AC and CLK_BD, and compares the phases of CLK_AC and CLK_BD to output the results AC+ and BD+ to LPFs 314 a and 314 b, respectively. In this case, AC+ and BD+are phase difference signals generated when CLK_AC leads CLK_BD in phase and when CLK_BD leads CLK_AC in phase, respectively. - The
LPFs phase comparator 312 to output the results to thedifferential amplifier 316. Thedifferential amplifier 316 amplifies the difference signal of AC+ and BD+ filtered by theLPFs -
FIGS. 4A-4F are waveform diagrams showing the operation of the apparatus shown inFIG. 3 .FIGS. 4A-4F show the case in which AC3 leads BD3 in phase, the wave forms of AC3, BD3, CLK_AC, CLK_BD, AC+, and BD+ signals are illustrated sequentially inFIGS. 4A-4F , respectively. As shown inFIGS. 4A-4F , it can be found that if a laser spot deviates from a track center by a predetermined amount, a phase difference existing between AC3 and BD3 is transferred to CLK_AC and CLK_BD, doubling by a CLK frequency.FIGS. 4A-4F indicate that CLK_AC and CLK_BD synchronized with AC3 and BD3 respectively are generated and a phase difference Δt created between AC3 and BD3 is transferred to the outputs CLK_AC and CLK_BD of thePLLs - The conventional apparatus shown in
FIG. 1 detects the phase difference Δt once in an interval t1 as shown inFIG. 2A-2D , while the apparatus according to the present invention can detect the phase difference Δt once every cycle of CLKs. When a channel clock is used as CLK, the phase difference Δt can be detected once every channel clock cycle T regardless of the lengths of pits or marks recorded on an optical disk. Thefrequency divider 318 frequency divides CLK at an interval where inversion of the output signal takes place, to output the result to thePLLs PLL 310 a or a clock provided to the BD3 and thePLL 310 b is beyond a detection range of thePLL Divider 318 detects whether the output signal TE OUT has been inverted and performs a division operation when the output signal TE OUT is inverted as in theinterval 93 ofFIG. 9 . Alternately,divider 318 detects the output signals ofPLLs FIG. 3 , a tracking servo control becomes unstable at the interval where inversion of the output signal happens. This is because inversion of the output signals causes deviation from the extent of phase difference detection by thePLLs PLLs -
FIG. 5 is a block diagram showing a second embodiment of a tracking error detecting apparatus according to the present invention. The apparatus shown inFIG. 5 includes a four-sectionoptical detection unit 502, EQs 506 a-506 d, binarizers 508 a-508 d, PLLs 510 a-510 d,phase comparators differential amplifiers adder 518. Since outputs A, B, C and D of the four-sectionoptical detection unit 502 have weak high-frequency components, a high-frequency component of A, B, C and D provided from the four-sectionoptical detection unit 502 is reinforced through the EQs 506 a-506 d. Further, as the outputs A, B, C and D of the four-sectionoptical detection unit 502 contain noise in addition to signals reflected from an optical disk, EQs 506 a-506 d eliminate the noise components of A, B, C and D provided from the four-sectionoptical detection unit 502. - The binarizers 508 a-508 d convert signals provided from EQs 506 a-506 b into binary digital signals to output the results to the PLLs 510 a-510 d. The PLLs 510 a-510 d receive as input the signal CLK and the signals provided from the binarizers 508 a-508 d to output CLKs, CLK_A, CLK_B, CLK_C and CLK_D, synchronized with the signals provided from the binarizers 508 a-508 d to the
phase comparators phase comparators phase comparator 512 a compares the phases of CLK_A and CLK_B to output the results A+ and B+ to theLPFs phase comparator 512 b compares the phases of CLK_C and CLK_D to output the results C+ and D+ to theLPFs - The LPFs 514 a-514 d filter A+, B+, C+ and D+ provided from the
phase comparators differential amplifiers differential amplifiers LPFs 514 a to 514 d to output the results to theadder 518. Theadder 518 adds the signals provided from thedifferential amplifiers -
FIG. 6 is a block diagram showing a third preferred embodiment of a tracking error detecting apparatus according to the present invention, in which TE is produced using outputs of a three-section optical detection unit. The apparatus shown inFIG. 6 includes a three-sectionoptical detection unit 602,EQs PLLs phase comparator 612,LPFs differential amplifier 616. - The
detection unit 602 has three optical detectors which are arranged transverse to a tangential direction of the recording track. The optical detectors generate electrical signals E, F and G corresponding to light reflected from the recording track. TheEQs optical detection unit 602 and remove noise therefrom, differentiate E and G and remove noise therefrom to output the results to thebinarizers binarizers EQs PLLs PLLs phase comparator 612. Thephase comparator 612 compares the phases of CLK_E and CLK_G and outputs the results E+ and G+ to theLPFs - The
LPFs phase comparator 612 to output the results to thedifferential amplifier 616. Thedifferential amplifier 616 amplifies the difference signal of E+ and G+ filtered by theLPFs -
FIG. 7 is a block diagram showing a fourth preferred embodiment of a tracking error detecting apparatus according to the present invention in which TE is produced using the output of a three-section optical detection unit. The apparatus shown inFIG. 7 includes a three-sectionoptical detection unit 702,EQs phase comparator 712,LPFs differential amplifier 716. - The
detection unit 702 has three optical detectors which are arranged transverse to a tangential direction of the recording track. The optical detectors generate electrical signals E, F and G corresponding to light reflected from the recording track. TheEQs binarizers 708 a and 708 b. Thebinarizers 708 a and 708 b binarize the signals provided fromEQs phase comparator 712. Thephase comparator 712 compares the phases of E3 and G3 to output the results E+ and G+ to theLPFs - The
LPFs phase comparator 712 to output the results to thedifferential amplifier 716. Thedifferential amplifier 716 amplifies the difference signal of E+ and G+ filtered by theLPFs -
FIG. 8 is a graph showing operation of the EQs ofFIGS. 3 and 5 -7, in which the vertical axis and the horizontal axis indicate gain and frequency, respectively. The EQs, having the properties as shown inFIG. 8 , perform the function of controlling their properties so that an input signal can be positioned between a first frequency f1 and a second frequency f2 to amplify the high-frequency component which is close to the second frequency f2. -
FIG. 9 is a graph showing the result of comparing a tracking error signal generated by a tracking error detecting apparatus according to the present invention with a tracking signal generated by a conventional DPD TE method. InFIG. 9 ,reference numerals interval 93 indicates the section where inversion of output signal occurs so that a phase difference will exceed the detection limit if the phase difference is detected using the CLKs generated from the PLLs as in the present invention. If this is the case, the frequency of the PLL CLK is divided by n (n=2, 3, 4, . . . ) and the result is output to a phase difference detector, which increases the detection extent so that intervals such as 93 will not exist. -
FIG. 10 is a graph showing the characteristic of gain of tracking error signals generated by a tracking error detecting apparatus according to the present invention and a conventional DPD TE method. InFIG. 10 ,reference numerals interval 96 is the section where an optical pickup jumps on an adjacent track in a normal tracking state. While theinterval 96 cannot be shown clearly in a tracking error signal generated by the conventional DPD TE method, it is output as a large value in a tracking error signal generated by the present invention. - As described in the foregoing, a tracking error detecting apparatus according to the present invention is capable of generating a tracking error signal which does not vary depending on the lengths of pits and marks recorded on a optical disk, so that reliability of the tracking error signal can be enhanced.
- Although a few preferred embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (17)
1. A method of producing a tracking error signal as a difference signal of optical detection signals generated by more than two optical detectors positioned along a line diagonal to a track center, the method comprising:
binarizing each of the outputs of the optical detectors;
phase locking to generate respective clock signals synchronized with each of the binarized outputs;
detecting a phase difference between the synchronized clock signals; and
low-pass filtering the detected phase difference to output the tracking error signal.
2. A tracking error detecting apparatus for producing a tracking error signal as a difference signal of optical detection signals generated by more than two optical detectors positioned along a line diagonal line to a track center, the apparatus comprising:
binarizers which binarize each of the optical detection signals;
phase locked loops which generate clock signals synchronized with each of the outputs of the binarizers;
a phase difference detector which detects a phase difference between the synchronized clock signals output from the phase locked loops; and
a low-pass filter which filters the output of the phase difference detector to output the result as the tracking error signal.
3. The tracking error detecting apparatus as claimed in claim 2 , further comprising equalizers which reinforce the high-frequency components of the optical detection signals and output the results to the binarizers.
4. The tracking error detecting apparatus as claimed in claim 3 , wherein the equalizers remove low-frequency components of a spectrum from the optical detection signals, according to a recording modulation method.
5. The tracking error detecting apparatus as claimed in claim 2 , wherein a clock signal provided to the phase locked loops is a channel clock signal.
6. The tracking error detecting apparatus as claimed in claim 5 , further comprising a frequency divider which divides the frequency of the channel clock signal by n (where n=2, 3, 4, . . . ) to output the result to the phase locked loops when a phase of an output signal is inverted.
7. The tracking error detecting apparatus as claimed in claim 2 , wherein the phase difference detector generates a first phase difference signal indicating that a first synchronized clock signal output from the phase locked loops leads a second synchronized clock signal output from the phase locked loops, and a second phase difference signal indicating that the second synchronized clock signal leads the first synchronized clock signal, and
wherein the low-pass filters include first and second low-pass filters which filter the first and second phase difference signals, respectively, and
the tracking error detecting apparatus, further comprises a differential amplifier which generates a tracking error signal corresponding to a difference signal of the outputs of the first and second low-pass filters.
8. A tracking error detecting apparatus for producing a tracking error signal as a difference signal of optical detection signals generated by two optical detectors disposed at the outside of the track center of a three-section optical detection unit, the apparatus comprising:
binarizers which binarize each of the optical detection signals;
a phase difference detector which detects a phase difference between the binarized signals; and
a low-pass filter which filters the output of the phase difference detector to output the result as the tracking error signal.
9. The tracking error detecting apparatus as claimed in claim 8 , further comprising phase locked loops which couple the binarizers and the phase difference detector, wherein the phase locked loops generate clock signals synchronized with each of the outputs of the binarizers, to output synchronized signals to the phase difference detector,
wherein the phase difference detector detects a phase difference between the synchronized signals output from the phase locked loops.
10. An apparatus for providing a tracking error signal for an optical disk recording track, comprising:
first and second optical detectors which generate first and second electrical signals, respectively;
a circuit which binarizes the first and second electrical signals and phase locks each of the binarized signals to output first and second clock signals synchronized with the first and second binarized signals; and
a phase detector which compares a phase of the first synchronized clock signal with a phase of the second synchronized clock signal to generate the tracking error signal.
11. The apparatus as claimed in claim 10 , wherein said first and second optical detectors are on a line transverse to the optical disk recording track.
12. The apparatus as claimed in claim 10 , wherein said first and second optical detectors are on a line diagonal to the optical disk recording track.
13. The apparatus as claimed in claim 10 , further comprising first and second equalizers which increase a high frequency component of the first and second electrical signals prior to binarizing said first and second electrical signals, respectively.
14. The apparatus as claimed in claim 13 , wherein each said equalizer includes a differentiator which operates on the respective electrical signal.
15. The apparatus as claimed in claim 14 , wherein each said differentiator operates on frequencies of the respective electrical signal which are less than a first value.
16. The apparatus as claimed in claim 14 , wherein each said differentiator operates on frequencies of the respective electrical signal which are greater than a first value.
17. The apparatus as claimed in claim 12 , wherein each said differentiator operates on frequencies of the respective matrixed signal which are greater than a predetermined value.
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US10/991,869 US20050068864A1 (en) | 1999-07-08 | 2004-11-19 | Method and apparatus for tracking error detection in optical disk driver |
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KR99-27451 | 1999-07-08 | ||
KR9927451 | 1999-07-08 | ||
US09/613,695 US7102967B1 (en) | 1999-07-08 | 2000-07-10 | Method and apparatus for tracking error detection in optical disk driver |
US10/991,869 US20050068864A1 (en) | 1999-07-08 | 2004-11-19 | Method and apparatus for tracking error detection in optical disk driver |
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US09/613,695 Division US7102967B1 (en) | 1999-07-08 | 2000-07-10 | Method and apparatus for tracking error detection in optical disk driver |
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US10/991,869 Abandoned US20050068864A1 (en) | 1999-07-08 | 2004-11-19 | Method and apparatus for tracking error detection in optical disk driver |
US11/044,222 Expired - Lifetime US7310291B2 (en) | 1999-07-08 | 2005-01-28 | Method and apparatus for tracking error detection in optical disk driver |
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US7310291B2 (en) | 2007-12-18 |
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Date | Code | Title | Description |
---|---|---|---|
STCB | Information on status: application discontinuation |
Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION |