Method of detecting a reproduction signal and circuit therefor

Abstract: A method of detecting a reproducing signal, and a circuit therefor are provided. A detector (214-224) detects the outputs (R1,R2) of an optical detection device (204-212) corresponding to a combination of signals from sections (A-D) of a photodetector (204) arranged in the track direction, the outputs (T1,T2) for the radial direction, and/or the outputs (X1,X2) arranged diagonally. A control unit (226) provides a selection control signal and a compensation signal on the basis of data conditions on the optical recording medium, optical interference and/or various system states such as tilting or detracking. The compensator selects (228) some of the outputs of the optical detection device provided via the detector in response to the selection control signal, and adaptively compensates (230-240) for the selected outputs in response to the compensation signal. Only the least degraded signals are used as a reproducing signal, depending on the system states, the data conditions and/or optical interference. Thus, the jitter of a detected signal is reduced, and the performance of the system can be improved.

Description: The present invention relates to detection of a reproduction signal, and more particularly, to a method of detecting only some of the outputs of an optical detection device, which are the least distorted or degraded, in an optical recording/reproduction system, and a circuit thereof. US 5,701,283, which is used for the two-part delimitation, discloses a method and apparatus for an optical storage device. In the recording/reproduction system of optical recording media such as compact discs (CDs) and digital versatile discs (DVDs), data is manifested on a disk in the form of pits on a substrate or modifications of a recording film. Data on a disk is detected by illuminating the disk with a laser, and detecting light reflected back. In the recording/reproduction system, a signal is degraded due to a time delay between the outputs of an optical detection device caused by the geometry (for example, the width, the length, the depth and the angle) of a data pit and a recording domain, and due to a time delay caused by the interference between data in a tangential direction. When a time delay is caused between the outputs of an optical detection device, a reproduction signal is distorted. When the amplitude of a reproduction signal is not properly detected, the performance of the system is degraded. Optical discs are being developed for high-density recording and high-speed reproduction, to record and/or reproduce a high definition (HD) image. As recording/reproduction systems are developed for high-density and high-speed recording/reproduction, the inter-symbol interference increases, causing time delays between adjacent data and distortion of a signal, leading to deterioration of a signal. Accordingly, the performance of a reproduction signal is degraded, requiring a considerable effort and an extra cost during implementation of the system. The principle of conventional reproduction signal detection is shown in Figure 1. First, in order to detect information recorded on a disc 100, a pickup unit (P/U) 102 radiates a beam emitted from a light source (for example, a laser diode) to the disc 100, and a multi-section optical detection device 104 (which can also be called a detection sensor), which is usually made up of a photodetector (PD), receives and divides an optical signal reflected by the disc 100 into multiple signals. First, second, third and fourth current/voltage (I/V) converters 106, 108, 110 and 112 convert current signals A, B, C and D output by the optical detection device 104 into voltage signals. An arithmetic unit 114 sums the voltage signals output by the first, second, third and fourth I/V converters 106, 108, 110 and 112, and outputs the sum as a radio frequency reproducing signal RF SUM. In the prior art, a method of detecting a reproducing signal by simple addition of the outputs of the I/V converters 106, 108, 110 and 112 is adopted, so that a reproducing signal is degraded due to the data conditions recorded on a disc, crosstalk, the interference between optical signals reflected/diffracted from pits in close proximity and from adjacent tracks on a recording medium, and other problems with a system (for example, defocusing, detracking and tilting). Therefore, the quality of a reproducing signal and the performance of a system are degraded. As described above, as recording/reproduction systems using optical recording media are designed for high-density and high-speed recording/reproduction, the degradation of a signal due to the data conditions recorded on a disc, the interference between optical signals reflected/diffracted from pits in close proximity and from adjacent tracks on a recording medium, or other problems with a system (for example, defocusing, detracking or tilting) becomes serious, which results in many problems during implementation of the system. An aim of the present invention is to provide a method of detecting an optimal reproducing signal while overcoming problems caused by data conditions, crosstalk, and the interference between optical signals reflected/diffracted from pits in close proximity and from adjacent tracks on a recording medium. Preferred embodiments of the invention aim to provide a method of detecting an optimal reproducing signal while overcoming defocusing and/or detracking and/or radial tilting and/or tangential tilting. Another aim of the present invention is to provide a method of detecting an optimal reproducing signal by adaptively compensating for signal interference caused by data conditions, crosstalk, the interference between optical signals reflected/diffracted from pits in close proximity and from adjacent tracks on a recording medium, defocusing, detracking, radial tilting and/or tangential tilting. A further aim of the present invention is to provide a circuit for detecting a reproducing signal, in which only some of the outputs of an optical detection device, that are the least degraded, are reproduced depending on data conditions, the interference between optical signals reflected/diffracted from pits in close proximity and from adjacent tracks on a recording medium, and/or the state of the system. According to the present invention there is provided a method of detecting a reproducing signal as set forth in claim 1 appended hereto. Also according to the present invention there is provided a device for detecting a reproducing signal, as set forth in claim 13 appended hereto. Preferred features of the invention will be apparent from the dependent claims and the description which follows. For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings in which: Figure 1 is a block diagram illustrating the principle of conventional reproducing signal detection; Figure 2 is a circuit diagram of a reproducing signal detection circuit according to an embodiment of the present invention; Figure 3 shows an example of a 8-section photodetector that can be used as the optical detection device shown in Figure 2; Figure 4 is a graph showing the results of detection of reproducing signals during detracking to explain the effects of the present invention; and Figure 5 is a graph showing the results of detection of reproducing signals during tangential tilting to explain the effects of the present invention. Referring to Figure 2, which shows a reproducing signal detection circuit according to an embodiment of the present invention, a pickup unit (P/U) 202 moves to a location from which information recorded on a disc 200 is detected, and projects a beam emitted from a light source (laser diode) to the disc 200. An n-section optical detection device 204 receives and divides an optical signal reflected back from the disc 200 into multiple signals. Here, the optical detection device 204 groups multiple outputs into two parts by combining the multiple outputs in the radial direction, the track direction or diagonally depending on the data conditions, the interference between optical signals reflected/diffracted from pits in close proximity and from adjacent tracks on a recording medium, or the state of a system (for example, problems with focusing, tracking, or tilting). Hence, the multiple outputs of the optical detection device 204 are grouped into degraded output signals and less degraded output signals. Using this characteristic, only one group of outputs among the outputs of the optical detection device 204, that is the less degraded output signal group, can be reproduced depending on the state of the system, the data conditions or the interference between optical signals reflected/diffracted from pits in close proximity and from adjacent tracks on a recording medium. Here, a signal used as a reproducing signal is automatically selected by a system state detector 226 for detecting the state of a system (for example, focusing or defocusing, tracking or detracking, and tilting), the data conditions, or the interference between optical signals reflected/diffracted from pits in close proximity and from adjacent tracks on a recording medium. Some detection signals of the optical detection device 204, which are selected to compensate for abnormal operating conditions, detected data conditions, or detected interference between optical signals reflected/diffracted from pits in close proximity and from adjacent tracks on a recording medium, are adaptively equalized, so that an optimal reproducing signal is detected. That is, first, second, third and fourth current/voltage (I/V) converters 206, 208, 210 and 212 convert current signals A, B, C and D output by the optical detection device 204 into voltage signals. A first adder 214 adds a voltage signal output from the first I/V converter 206, which corresponds to the output A of the optical detection device 204, to a voltage signal output from the second I/V converter 208, which corresponds to the output B of the optical detection device 204, and outputs the sum (A+B) as a signal R1. A second adder 216 adds a voltage signal output from the third I/V converter 210, which corresponds to the output C of the optical detection device 204, to a voltage signal output from the fourth I/V converter 212, which corresponds to the output D of the optical detection device 204, and outputs the sum (C+D) as a signal R2. Here, the outputs A and B of the optical detection device 204 having the same distance from the center of the disk, and the outputs C and D of the optical detection device 204 having the same distance from the center of the disk. A third adder 218 adds a voltage signal output from the first I/V converter 206, which corresponds to the output A of the optical detection device 204, to a voltage signal output from the fourth I/V converter 212, which corresponds to the output D of the optical detection device 204, and outputs the sum (A+D) as a signal T1. A fourth adder 220 adds a voltage signal output from the second I/V converter 208, which corresponds to the output B of the optical detection device 204, to a voltage signal output from the third I/V converter 210, which corresponds to the output C of the optical detection device 204, and outputs the sum (B+C) as a signal T2. Here, the outputs A and D of the optical detection device 204 are on the same level in a track direction, and the outputs B and C of the optical detection device 204 are on the same level in a track direction. Accordingly, a time delay is generated between the output of the optical detection device 204 supplied via the third adder 218 and the output of the optical detection device 204 supplied via the fourth adder 220, in a track direction, due to data conditions, crosstalk, or the interference between optical signals reflected/diffracted from pits in close proximity and from adjacent tracks on a recording medium. A fifth adder 222 adds a voltage signal output from the first I/V converter 206, which corresponds to the output A of the optical detection device 204, to a voltage signal output from the third I/V converter 210, which corresponds to the output C of the optical detection device 204, and outputs the sum (A+C) as a signal X1. A sixth adder 224 adds a voltage signal output from the second I/V converter 208, which corresponds to the output B of the optical detection device 204, to a voltage signal output from the fourth I/V converter 212, which corresponds to the output D of the optical detection device 204, and outputs the sum (B+D) as a signal X2. Here, the outputs of the fifth and sixth adders 222 and 224 are used when defocusing occurs, since they are obtained by adding diagonally-aligned outputs among the outputs of the optical detection device 204. The system state detector 226 detects not only the system state (for example, defocusing, detracking and tilting) but also the data conditions and the interference between optical signals reflected/diffracted from pits in close proximity and from adjacent tracks on a recording medium, and provides a selection control signal to a selector 228 so that at least one good-performance signal is selected from among the outputs of the first through sixth adders 214 through 224 depending on a detected system state, detected data conditions and/or detected interference between optical signals reflected/diffracted from pits in close proximity and from adjacent tracks on a recording medium. Also, the system state detector 226 calculates an adaptive equalization amount for compensating for the detected system state, the detected data conditions and/or the detected interference between data, and provides the adaptive equalization amount to first through sixth equalizers 230 through 240. The selector 228 selects at least one signal from among the outputs of the first through sixth adders 214 through 224 in response to the selection control signal of the system state detector 226, and provides the selected signal to the corresponding first through sixth equalizers 230 through 240. The first through sixth equalizers 230 through 240 (EQ1 through EQ6) equalize the outputs of the optical detection device 204 selected by the selector 228 according to the adaptive equalization amount provided from the system state detector 226, thereby detecting an optimal reproducing signal. Here, the first through fourth I/V converters 206 through 212, and the first through sixth adders 214 through 224 are referred to as detectors for detecting the outputs of the optical detection device 204 combined in the track direction, the outputs combined in the radial direction, and the outputs combined diagonally. The system state detector 226 is referred to as a control unit for detecting the data conditions, the interference between optical signals reflected/diffracted from pits in close proximity and from adjacent tracks on a recording medium, and/or various system states, and providing a selection control signal and a compensation signal on the basis of the results of the detection. The selector 228 and the first through sixth equalizers 230 through 240 can be referred to as a compensator for compensating for unequal levels of some of the outputs of the optical detection device supplied from the detector in response to the compensation signal (adaptive equalization amount) provided from the system state detector 226. In the present invention, the selector 228 can be installed at the rear of the first through sixth equalizers 230 through 240, so that the signal having the best quality is selected as an optimal reproducing signal from among the equalized results RFR1, RF2, RFT1, RFT2, RFX1 and RFX2 obtained by equalizing the signals R1, R2, T1, T2, X1 and X2 detected by the first through sixth adders 214 through 224 using the first through sixth equalizers 230 through 240. The detection of a reproducing signal when the system state detector 226 detects data conditions or the interference between optical signals reflected/diffracted from pits in close proximity and from adjacent tracks on a recording medium, when it detects defocusing, when it detects detracking, when it detects radial tilting, and when it detects tangential tilting, will now be described on the basis of the operations of the selector 228 and the first through sixth equalizers 230 through 240. (1) Detection of a reproducing signal depending on the data conditions or during the interference between optical signals reflected/diffracted from pits in close proximity and from adjacent tracks on a recording medium. As for a signal reproduced from data on a disc, one of the output signals T1 and T2 of the optical detection device 204 shown in Figure 2 is less degraded than the other, depending on the data conditions or the state of the interference between optical signals reflected/diffracted from pits in close proximity and from adjacent tracks on a recording medium. The selector 228 selects one of the detected signals T1 and T2 in response to a selection control signal provided from the system state detector 226. The third or fourth equalizer 234 or 236, which receives the selected detected signal, equalizes the selected detected signal according to the adaptive equalization amount that can compensate for the amount of signal interference caused due to the data conditions or the interference between optical signals reflected/diffracted from pits in close proximity and from adjacent tracks on a recording medium, which are detected by the system state detector 226. In this way, an optimal RF reproducing signal is provided. In the case of the optical detection device 204 used in Figure 2, which is a four-section photodetector, track-directional sum signals A+D and B+C are represented as T1 and T2. However, the present invention is not limited to the four-section photodetector. In another embodiment, when the eight-section photodetector shown in Figure 3 is used, T1 can indicate the sum of B1, B2, B3 and B4, and T2 can indicate the sum of A1, A2, A3 and A4. (2) Detection of a reproducing signal upon defocusing As for a signal reproduced from data on a disc, one of the detected signals X1 and X2 output by the optical detection device 204 is better than the other due to the direction of defocusing. The selector 228 selects the better quality signal from the detected signals X1 and X2 in response to a selection control signal provided from the system state detector 226. The fifth or sixth equalizer 238 or 240, which receives the selected detected signal, equalizes the selected detected signal according to the adaptive equalization amount that can compensate for the amount of signal interference caused due to the defocusing detected by the system state detector 226. In this way, an optimal RF reproducing signal is provided. (3) Detection of a reproducing signal upon detracking As for a signal reproduced from data on a disc, one of the detected signals R1 and R2 output by the optical detection device 204 is better than the other due to the direction of detracking. The selector 228 selects one of the detected signals R1 and R2 in response to a selection control signal provided from the system state detector 226. The first or second equalizer 230 or 232, which receives the selected detected signal, equalizes the selected detected signal according to the adaptive equalization amount that can compensate for the amount of signal interference caused due to the detracking detected by the system state detector 226. In this way, an optimal RF reproducing signal is provided. (4) Detection of a reproducing signal upon radial tilting As for a signal reproduced from data on a disc, one of the detected signals R1 and R2 output by the optical detection device 204 is better than the other due to radial tilting. The selector 228 selects one of the detected signals R1 and R2 in response to a selection control signal provided from the system state detector 226. The first or second equalizer 230 or 232, which receives the selected detected signal, equalizes the selected detected signal according to the adaptive equalization amount that can compensate for the amount of signal interference caused due to the radial tilting detected by the system state detector 226. In this way, an optimal RF reproducing signal is provided. (5) Detection of a reproducing signal upon tangential tilting As for a signal reproduced from data on a disc, one of the detected signals T1 and T2 output by the optical detection device 204 is better than the other due to tangential tilting. The selector 228 selects one of the detected signals T1 and T2 in response to a selection control signal provided from the system state detector 226. The third or fourth equalizer 234 or 236, which receives the selected detected signal, equalizes the selected detected signal according to the adaptive equalization amount that can compensate for the amount of signal interference caused due to the tangential tilting detected by the system state detector 226. In this way, an optimal RF reproducing signal is provided. As described above, the n outputs of an optical detection device, which can be an n-section photodetector, are combined and grouped into two parts, depending on the data conditions recorded on a disc, the state of the interference between optical signals reflected/diffracted from pits in close proximity and from adjacent tracks on a recording medium, or system states. When two signals obtained by the combination are compared, one detection signal is less degraded than the other. If two detected signals having opposite properties are simply combined, the characteristics of an inferior signal are included in the result, which prevents a good reproducing signal from being obtained. To be more specific, when radial tilting occurs in the positive direction of a disc, the detected signal R1, which is one of the outputs of sections of the photodetector having the same distance from the center of the disk, is better than the detected signal R2, which is another signal output from sections of the photodetector having the same distance from the center of the disk. Conversely, when radial tilting occurs in the negative direction of the disc, the detected signal R1 is more degraded than the detected signal R2. The detected signal that improves the reproducing signal is selected from the two detected signals, in order to prevent degradation of the reproducing signal, resulting in an improvement in reproduction. The effects of the present invention described above will now be described referring to Figures 4 and 5. In Figure 4, which shows the results of detection of a reproducing signal during detracking, the jitter values of reproducing signals according to the present invention are compared to that in the prior art. Upon negative detracking, the detected signal R2 has less jitter than the prior art and the detected signal R1. Thus, in this case, it is preferable that the detected signal R2 is used as a reproducing signal. Upon positive detracking, the detected signal R1 has less jitter than the prior art and the detected signal R2. Thus, in this case, it is preferable that the detected signal R1 is used as a reproducing signal. That is, in the prior art, when a reproducing signal is detected using the sum of the outputs of a 4-section photodetector upon detracking within a range of ±0.08 µm, jitter is about 15.6% (data to data). However, in the present invention, when the detected signal R2 is used upon detracking of -0.08 µm, jitter of about 9.22% is obtained. When the detected signal R1 is used upon detracking of +0.08 µm, jitter of about 9.22% is obtained. Therefore, the present invention can obtain a reproducing signal having good characteristics and a wide margin, compared to the prior art. In Figure 5, which shows the results of detection of a reproducing signal during tangential tilting, the jitter values of reproducing signals according to the present invention are compared to that in the prior art. Upon negative tilting, the detected signal T1 has less jitter than the prior art and the detected signal R2. Thus, in this case, it is preferable that the detected signal T1 is used as a reproducing signal. Upon positive tilting, the detected signal T2 has less jitter than the prior art and the detected signal T1. Thus, in this case, it is preferable that the detected signal T2 is used as a reproducing signal. In the present invention, only some of the outputs of an optical detection device, which are the least degraded, are used to reproduce a signal, depending on the system states, the data conditions and/or the interference between optical signals reflected/diffracted from pits in close proximity and from adjacent tracks on a recording medium. Thus, the jitter of a detected signal is improved, and the performance of the system can be improved. Also, in the present invention, the demodulation degree of a signal, which is the most important factor in signal processing, is improved. Hence, signal distortion and signal degradation are reduced, and the performance of the system can be improved. Furthermore, the use of a reproducing signal according to the present invention increases the defocusing margin, the detracking margin, the radial tilting margin, and the tangential tilting margin, so that the performance of the system can be improved.

Claims: A method of detecting a reproducing signal using an optical detection device (204) for receiving an optical signal reflected from an optical disc recording medium (200) having adjacent tracks and dividing the received signal into multiple signals (A,B,C,D) corresponding to sections of the optical detection device (204), the method comprising the steps of: (a) selecting (228) some signals (e.g. R1,T1) which are less degraded than other signals (e.g. R2,T2), derived from among the output signals (A-D) of the optical detection device (204); and (b) obtaining (230-240) a reproducing signal (RFR1,RFT1) from the selected signals (R1,T1); characterised by : wherein the selecting step comprises selecting among signals (R1,T1) derived from sections (A,B,C,D) of the optical detection device (204) arranged in a matrix to all receive light from a single track of the optical recording medium (200) with rows in the tangential direction and columns in the radial direction of the optical recording medium (200). A method of detecting a reproducing signal using an optical detection device as in claim 1, wherein the selection in step (a) is performed on the basis of: data conditions recorded on the optical recording medium; interference between optical signals reflected/diffracted from pits in close proximity and from adjacent tracks on a recording medium; and/or system states. A method of detecting a reproducing signal using an optical detection device as in claim 1 or 2, wherein the reproducing signal obtained in step (b) is obtained by compensating (230-240) for the amount of signal interference caused due to: the data conditions; the interference between optical signals reflected/diffracted from pits in close proximity and from adjacent tracks on a recording medium; and/or system states. The method of claim 1, 2 or 3, wherein in the step (a), one (T1,T2) among the outputs of the optical detection device (204-212) corresponding to a combination of signals (A+D,B+C) corresponding to sections (A-D) of the optical detection device (204) arranged in the radial direction is selected depending on signal interference caused due to data conditions or the interference between optical signals reflected/diffracted from pits in close proximity and from adjacent tracks on a recording medium. The method of claim 1, 2 or 3, wherein in the step (a), one (X1,X2) among the outputs of the optical detection device (204-212) corresponding to a combination of signals (A+C,B+D) corresponding to sections (A-D) of the optical detection device arranged diagonally is selected depending on signal interference caused due to defocusing. The method of claim 1, 2 or 3, wherein in the step (a), one (R1,R2) among the outputs of the optical detection device (204-212) corresponding to a combination of signals (A+B,C+D) corresponding to sections (A-D) of the optical detection device (204) arranged in the track direction is selected depending on signal interference caused due to detracking. The method of claim 1, 2 or 3, wherein in the step (a), one (R1,R2) among the outputs of the optical detection device (204-212) corresponding to a combination of signals (A+B, C+D) corresponding to sections (A-D) of the optical detection device (204) arranged in the track direction is selected depending on signal interference caused due to radial tilting. The method of claim 1, 2 or 3, wherein in the step (a), one (T1,T2) among the outputs of the optical detection device (204-212) corresponding to a combination of signals (A+D,B+C) corresponding to sections (A-D) of the optical detection device (204) arranged in the radial direction is selected depending on signal interference caused due to tangential tilting. The method of any of claims 1 to 8, wherein in the step (b), the selected outputs of the optical detection device are adaptively equalized (230-240) according to the amount of signal interference caused due to the data conditions, the interference between optical signals reflected/diffracted from pits in close proximity and from adjacent tracks on a recording medium, and/or system states. The method of any of claims 1 to 9, wherein the reproducing signal is used to increase the defocusing margin of a system and/or is used to increase the detracking margin of a system and/or is used to increase the radial tilting margin of a system and/or is used to increase the tangential tilting margin of a system. A method of detecting a reproducing signal using an optical detection device as in claim 1, 2 or 3 comprising: (a) detecting the outputs (R1,R2) of the optical detection device (204) corresponding to a combination of signals corresponding to sections (A-D) of the photodetecting means (204) arranged in the track direction, the outputs (T1,T2) corresponding to a combination of signals corresponding to sections of the photodetecting means arranged in the radial direction, and/or the outputs (X1,X2) corresponding to a combination of signals corresponding to sections of the photodetecting means arranged diagonally; and (b) detecting (226) a less degraded signal among output signals obtained by reproducing the outputs detected in the step (a), as a reproducing signal. The method of claim 11, further comprising (c) controlling a good signal to be detected as a reproducing signal in the step (b), by detecting the data conditions recorded on the optical recording medium, the interference between optical signals reflected/diffracted from pits in close proximity and from adjacent tracks on a recording medium, and/or various system states. A device for detecting a reproducing signal using an optical detection device including a photodetecting means (204) for receiving an optical signal reflected from an optical disc recording medium (200) having adjacent tracks and dividing the received signal into multiple signals (A-D), the device comprising: a control unit (226); characterised by : a detector (226) for detecting the outputs (R1,R2) derived from the optical detection device, the optical detection device having sections arranged in a matrix to all receive light from a single track of the recording medium, corresponding to a combination of signals corresponding to sections of the photodetecting means arranged in the track direction, the outputs (T1,T2) corresponding to a combination of signals corresponding to sections of the photodetecting means arranged in the radial direction, and/or the outputs (X1,X2) corresponding to a combination of signals corresponding to sections of the photodetecting means arranged diagonally; the control unit (226) being arranged to provide a selection control signal and a compensation signal on the basis of the results of detection of the data conditions recorded on the optical recording medium, the interference between optical signals reflected/diffracted from pits in close proximity and from adjacent tracks on a recording medium, and/or various system states; and a compensator (228,230-240) for selecting some of the outputs of the optical detection device provided via the detector in response to the selection control signal, and adaptively compensating for the selected outputs in response to the compensation signal. The device of claim 13, wherein the compensator (228,230-240) comprises: a selector (228) for selecting some of the outputs of the optical detection device provided via the detector (214-224) in response to the selection control signal; and an equalizer (230-240) for adaptively equalizing the selected outputs of the optical detection device in response to the compensation signal.

Inventors: JOO SEONG-SIN, LEE KYUNG-GEUN, OTSUKA TATSUHIRO, JOO, SEONG-SIN, LEE, KYUNG-GEUN, OTSUKA, TATSUHIRO
Applicants: SAMSUNG ELECTRONICS CO LTD, SAMSUNG ELECTRONICS CO., LTD.
Application year: 2000
Main classification: G11B7
IPC codes: G11B20, G11B7