Abstract: In an optical disc drive, the read channel electronics and the wobble channel electronics are combined into one common channel, for reduced cost. When the drive is reading, the common channel is used for primary data and a read clock. When the drive is writing, the common channel is used for wobble data and a write clock. Two example embodiments are provided. In each example, a single front end amplifier, without automatic gain control, is used. In each example, a single PLL and a single data detector are used.

Abstract: The present invention is applicable to a recording apparatus of a CD or DVD, a recording method thereof and a recording medium, and an object of the present invention is to clearly record a second information such as characters and figures between two recording levels in an optical disk. The second information is recorded in a predetermined area in a radius direction and a angular direction on the optical information recording medium, and further, the second information is recorded according to a change of a pit width based on a change of power of the laser beam, a change of a pit length based on an on/off control of the laser beam, or a change of depression or bulge of the pit based on a change in the vicinity of the on/off control of the laser beam. Whereby it is possible to record the second information such as a watermark pattern or a visible image, which is capable of being confirmed by seeing a disk.

Abstract: In the case of a method of detecting a signal edge in a signal with temporally successive signal edges, there are performed, after triggering by an interrupt signal (IS) generated in an analog/digital converter (13), detection of a rise-representing rise value between two detected amplitude values with subsequent assessment of the rise value together with detection of signal edge direction information and signal edge occurrence information. Further use of this signal edge information is dependent on an additionally detected and assessed signal strength value, which signal strength value is formed from a sum of further amplitude values.

Abstract: A pre-pit detecting apparatus which, when a light beam is radiated onto an optical recording medium having a recording surface with pre-pits repeatedly formed between tracks, receives light reflected by the recording surface with first and second light receiving faces, obtains the push-pull signal corresponding to the light receiving signals for the first and second light receiving faces, samples the push-pull signal to collect sample data for a predetermined period, and sets a threshold value between the maximum value of data corresponding to a track and the minimum value of data corresponding to a pre-pit, of the collected sample data.

Abstract: A reproduction signal evaluation method of this invention includes the step of obtaining a reproduction signal from an information recording medium on which digital information is recorded with record marks having different sizes, the step of obtaining the amplitude of a first reproduction signal, of the signals contained in the reproduction signal, which reflects digital information recorded with a record mark having the maximum size, the step of obtaining the amplitude of a second reproduction signal, of the signals contained in the reproduction signal, which reflects digital information recorded with a record mark having the second smallest size, the step of obtaining an evaluation value from the ratio of the amplitudes of the first and second reproduction signals, and the step of evaluating a characteristic of the reproduction signal on the basis of the evaluation value.

Abstract: A method of increasing data extraction compatibility for an optical disc drive is disclosed. The method first provides extraction parameter sets, wherein the extraction parameter sets comprise a first extraction parameter set and a second extraction parameter set. The optical disc drive then uses the first extraction parameter set to extract data from an optical disc. Finally, the optical disc drive uses the second extraction parameter set to extract data from the optical disc if a data extraction error occurs.

Abstract: A data slicer capable of removing current mismatch between internal current pumps and its operating method is proposed. The data slicer includes a comparator for comparing an analog signal with a slice reference level to convert the analog signal into a digital signal, a counter electrically connected to the comparator for calculating a digital sum value according to logic values carried by the digital signal, and a voltage-adjusting circuit electrically connected to the comparator for adjusting the slice reference level. The voltage-adjusting circuit has two current pumps for shifting the slice reference level. The current generated by the current pumps can be adjusted according to the calculated digital sum value to reduce a difference between a first and a second binary values which are used to increase and decrease the slice reference level respectively.

Abstract: An equalizer and an equalizing method of optical recording/reproducing apparatus capable of enhancing equalizing performance and equalizing speed are disclosed. The equalizer includes a FF unit having a feedforward filter for removing pre-cursor from inter-symbol interference of input signal, a FB unit having a feedback filter for predicting post-cursor of the inter-symbol interference and outputting it, a first adder and a second adder for adding the signal from the FF unit and the signal from the FB unit, to remove the inter-symbol interference, a slicer for deciding the level of the signal from the first adder to be a predetermined level and feeding back the level-decided signal to the FB unit, and a signal detection unit for outputting the signal having the inter-symbol interference removed by the second adder as a predetermined signal using at least one of a trellis structure method and a tree structure method.

Abstract: In a signal detection circuit for an optical disk, a comparator converts an analog HF signal into a digital HF signal by using a slice level. A dropout detection circuit detects a dropout of the digital HF signal. A charge-pump circuit feeds back a slice-level control voltage to the comparator based on a result of the detection by the dropout detection circuit. A voltage follower holds and outputs a voltage stored in the capacitor. A switch is turned OFF when a dropout signal has been detected, and outputs to the voltage follower the voltage that has been stored in the capacitor during an ON state of the switch. A second switch is turned ON when a dropout signal has been detected, and applies an output of the voltage follower to the comparator.

Abstract: A circuit arrangement including means for determining a slicer level from incoming signal levels for slicing the incoming signal levels on the basis of the slicer level thus determined, includes a first and a second register circuit, which register circuits are connected to an output of a discriminator circuit. The discriminator circuit compares an incoming signal level with a set discrimination level and is adapted to apply an incoming signal level to the first register circuit if the incoming signal level is higher than the set discrimination level and to apply and incoming signal level to the second register circuit if the incoming signal level is lower than the set termination level. The first and the second register circuit are adapted to determine a register value of a least two different incoming signal levels consecutively applied to the register circuit. The circuit supplies a signal having a level which is a value determine from register values determined by the first and second register circuit.

Abstract: A composite signal in which pre-pit signal components are piggypacked onto frequency components of wobbling, is extracted from an optical recording medium. The composite signal is binarized, so that pre-pit signals are generated. The pre-pit signals pass through a first gate when the gate is open. The gate is periodically opened only in a period during which the amplitude of the wobbling becomes a maximum one. The number of the pre-pit signals passing through the gate is counted, so that a binarizing level for generating the pre-pit signal is set based on the relationship between the counted number per a reference time and a predetermined reference number.

Abstract: A data reproduction apparatus for adjusting filter coefficients of an equalizer including a digital filter, and connected before a Viterbi detector and a method therefor. A level of the output value of the equalizer is detected based on a reference level set in the Viterbi detector, and a level error of the detected level with respect to a predetermined reference value is detected. The filter coefficients of the equalizer are adjusted such that the level error is minimized, thereby improving the detection performance of the Viterbi detector.

Abstract: An apparatus for detecting a pre-pit signal at different laser power intensities of an optical disk drive. The apparatus includes an amplifier for receiving a push-pull signal acquired from an optical disk to generate an adjusted signal, a multiplexer for receiving the push-pull signal and the adjusted signal and selecting the push-pull signal or the adjusted signal as a slicing signal for output according to a power state signal, and a slicer for receiving the slicing signal and slicing the slicing signal according to a slicing level to generate the pre-pit signal. Thus, the apparatus only needs one set of slicer to correctly slice the pre-pit signal.

Abstract: A method and apparatus in an optical disk system employing a decision feedback equalization (DFE) technique to provide a boosted signal resolution at a data slicer input while minimizing noise. In one embodiment, an optical equalizer includes a feed forward equalizer (FFE) that equalizes the signal from the optical disk and provides an equalized signal and a feedback equalizer (FBE) that generates a feedback signal. The feedback signal is subtracted from the equalized signal to provide a signal having increased resolution and low noise, which is then applied to a data slicer. In one embodiment, the boost provided by the FFE is lower than in conventional equalizers to minimize noise. As the boost of the FFE is reduced, the number of taps in the FBE is increased to provide optimized system performance.

Abstract: In a data slicer and data slicing method for an optical disc system, the data slicer for converting an analog input signal into a digital signal includes a comparator, a duty detector, and a low pass filter. The comparator compares the analog input signal with a feedback signal to generate the digital signal. The duty detector detects the duty of the digital signal. If the detected duty is longer than a preset duration, the duty detector converts the detected signal into a signal having the preset duration, and outputs the converted signal. The low pass filter integrates the output signal of the duty detector to generate the feedback signal.

Abstract: A disk is placed into a disk drive device to be held therein. Then, a laser pickup is moved to the inner edge of the disk in step S1, various servos are automatically adjusted in step S2, TOC information of the disk is read in step S3, and a DBAL adjustment is performed in step S4. Here, the DBAL adjustment refers to an adjustment of a balance of a slice value for data. It is then determined whether or not the disk is recorded with information in multisession in step S5. If the disk is recorded in multisession, the DBAL adjustment for the session proceeds to a DBAL adjustment for a subsequent session in step S7. In other words, if the disk is a multisession disk, the DBAL adjustment is performed for each session.

Abstract: An apparatus for driving a record carrier according to the invention comprises a transducer for generating a read signal in response to patterns recorded at the record carrier and displacement means for displacing the transducer and the record carrier with respect to each other. Out of the read signal an auxiliary signal having a relatively low frequency content is generated. The apparatus comprises binary signal generating means for generating a binary signal out of the auxiliary signal including first hold means for generating a first hold signal, second hold means for generating a second hold signal, signal combination means for generating a slicing signal out of the first hold signal and the second hold signal, and comparing means for comparing the auxiliary signal with the slicing signal and outputting a binary output signal. The first hold means are adapted for temporarily maintaining the first hold signal at a value substantially corresponding to a top value of the auxiliary signal.

Abstract: A combined signal Spc in which a pre-pit signal is superposed on a wobble signal is generated based on a radial push-pull signal Spp with a noise component having been removed therefrom. Based on the combined signal Spc, a wobble signal SWB with the phase &thgr;0 not having time fluctuation and a pre-pit signal SPD are generated with the phases compared to each other, and then a phase adjustment signal SCNT corresponding to a phase difference &thgr;e is generated. The phase differences &thgr;e are stored, and an average value &thgr;r thereof generated, the phase difference &thgr;e is compared to the average value &thgr;r, the phase &thgr;0 is shifted according to only by the phase difference &thgr;e only when the phase difference &thgr;e is within the range of (&thgr;r±W), and then a wobble signal SWB with the phase &thgr;1 synchronized to the pre-pit signal SPD is generated.

Abstract: The present invention is applied to an optical disk apparatus which records data on and/or plays back data from one of a variety of DVD optical disks. The present invention generates a binarization threshold S3 by offsetting an envelope S2 of a playback signal RF by an offset voltage V1, and binarizes the playback signal RF (S4) according to the binarization threshold.

Abstract: An optical disk device reproduces an RF signal by projecting a light beam on an optical disk and detecting a reflected light therefrom. On the optical disk, information is recorded by forming a pit on a track determined according to a groove having a wobble signal recorded thereon. The optical disk device comprises a comparator comparing the RF signal with a threshold value so as to output a binary signal, a first band-pass filter filtering a frequency band of the wobble signal from the binary signal so as to extract a wobble signal component, and a first adder obtaining a value by adding the wobble signal component to a fixed reference value so as to supply the value to the comparator as the threshold value.

Abstract: This invention relates to an optical disk apparatus for optically reproducing information recorded on an information carrier by an optical beam emitted by a light source, the optical disk apparatus comprising: a converging section for directing the optical beam to the information carrier in a converged state; a light detection section for generating a reproduction signal corresponding to the optical beam reflected by or transmitted through the information carrier; a waveform equalization section for varying a frequency characteristic of the reproduction signal generated by the light detection section; a jitter measuring section for measuring a jitter of a signal output from the waveform equalization section; and a minimum jitter value searching section for determining a minimum value of the jitter in an initial area of an X-Y plane defined by a variable x and a variable y which can vary the jitter measured by the jitter measuring section. A PLL circuit is disclosed.

Abstract: In an initial operation of an optical disc apparatus for reading out information data recorded in the innermost data recording area on the optical disc, a main processor judges whether periods between adjoining two pits are normal or not from signals outputted from an optical pickup. When the periods of the pits are normal, a light beam emitted from the optical pickup is on the present data recording track, and the information data is read out from the optical disc. Alternatively, when the periods of the pits are abnormal, the optical pickup is moved inwardly with sensing the periods of the pits and judges whether the periods are normal or not. When the periods of the pits become normal, the light beam is precisely tracked on the present data recording track, and reproduces the information data from the optical disc.

Abstract: An optical disc playback apparatus capable of signal processing so that the above-noted new jitter does not appear even when a waveform equalizer is used is provided. A trimmer is inserted before the waveform equalizer, the maximum amplitude in the positive direction of the playback signal waveform and the maximum amplitude in the negative direction are limited so that amplitude in the positive direction and amplitude in the negative direction are substantially equal. Jitter in the playback signal can be improved as a result.

Abstract: A circuit and method for protecting the run length in RLL (run length limited) code is proposed to correct the illegal run length in an EFM (eight to fourteen modulation) signal. The proposed circuit comprises a sampling unit for sampling a RF signal with a high frequency sampling clock, and generating a high frequency sampling signal. The frequency of the high frequency sampling clock is higher then the frequency of the EFM signal. A detector is employed to receive and to detect the high frequency sampling signal whether there is any illegal run length in the EFM signal, and to generate control signals. Two reference signal generators are employed to generate an ideal front reference signal and an ideal rear reference signal, respectively, corresponding to the control signals. A first difference generator and a second difference generator are employed to generate a first difference and a second difference according to the front and rear reference signals and the high frequency sampling signal, respectively.

Abstract: An optical information reproducing method for reproducing information recorded at at least one mark on an optical information medium. The method includes irradiating a laser to the optical information medium, detecting a reflected beam reflected from the optical information medium, and reproducing information recorded on the optical information medium from an output signal of a detector which detects the reflected beam. The step of reproducing information is changed in dependence upon a length of the mark of the optical information medium.

Abstract: The present invention relates to a disk recording medium such as a CD or a DVD in which data is recorded in high-density, and method and apparatus for reproducing data recorded in the high-density disk recording medium. The data reproducing method and apparatus according to the present invention converts a high-frequency signal reproduced from the disk into a plurality of binary signals through comparing the reproduced signal with two or more slicing levels which are different each other, selects one of the plurality of binary signals or a periodic pulse signal based on the difference magnitude between the plurality of binary signals, synchronizes a reference clock with the selected signal, and restores the selected signal into bit stream using the synchronized reference clock.

Abstract: An information recording medium for recording main information and auxiliary information is provided. The auxiliary information is recorded on the information recording medium in a manner that edge positions of the pits or the recording marks indicating the main information are shifted either in a phase advancing direction or in a phase delaying direction along the track direction. A predetermined frequency is used to determine whether the edge position is shifted in the phase advancing direction or in the phase delaying direction in order to record the auxiliary information. The predetermined frequency is substantially consistently lower than ½of a reference frequency of a recording clock for creating the pits or the recording marks and is higher than a response frequency of a PLL for generating a reproduction clock for reproducing the main information.

Abstract: A radio frequency ripple zero crossing signal calibration method for an optical disk reader undergoing a track following to track seeking transition is disclosed. The method utilizes sampling to obtain radio frequency ripple peak level during a track seeking operation and radio frequency ripple DC level during a track following operation and using their differences as a calibrated value. Through the calibrated value, the radio frequency ripple zero crossing slice level is modified so that a correct radio frequency ripple zero crossing signal is obtained during a track following to track seeking transition. In a track following to seeking transition, this arrangement prevents distortion of the radio frequency ripple signal and corresponding drift in the radio frequency zero crossing signal that may lead to errors in computing moving speed and counting tracks of the pickup head. Hence, search capacity of the optical disk reader is improved and the pickup head is better controlled.

Abstract: Device and method for detecting a non-writable region of an optical recording medium, wherein a read channel 1 signal and a read channel 2 signal are sliced at respective slice levels to produce header mask signals, and a header region which is a non-writable region is determined for the header mask signal taking the slice levels and written/unwritten regions ion the disk, whereby permitting stabilization of servos because servo error signals, such as a tracking error signal, and a focus error signal can be held exactly at a header region even if the servos are not stable, that prevents deterioration of a data quality in writing and reading, and permitting to shift an optical pickup to a desired position and accurate measurement of an amount of eccentricity because there is no influence of the header in a track jump and a disk eccentricity measurement.

Abstract: An optical information reproducing method for reproducing information recorded at at least one mark on an optical information medium. The method includes irradiating a laser to the optical information medium, detecting a reflected beam reflected from the optical information medium, and reproducing information recorded on the optical information medium from an output signal of a detector which detects the reflected beam. The step of reproducing information is changed in dependence upon a length of the mark of the optical information medium.

Abstract: In the context of a DVD-RAM read-type architecture in which an optical storage medium (20) makes use of an eccentric wobble (164) to attain synchronisation information, a wobble PLL (179) is held in an acquired state whenever header regions (32, 33) embossed at regular intervals across the optical storage medium (20) are detected. More specifically, large dc variations associated with voltage spikes caused by header regions (32, 33) are scaled (260) relative to a dynamically varying amplitude envelope of the extracted wobble signal (164), such as to identify a start location (300) for each header region. The wobble PLL (179) is effectively allowed to free-run and hold state during periods of header, thereby mitigating the likelihood that the wobble PLL will loose lock during the header regions.

Abstract: A slicing apparatus for slicing a pre-pit signal is disclosed. The slicing apparatus utilizes a reference signal with a dynamical voltage to slice a pre-pit signal. The slicing apparatus includes a peak detector, a low-pass filter, a calculating unit, and a comparator. The peak detector detects the peak value of the pre-pit signal to generate a peak signal. The low-pass filter filters out the high-frequency components of the pre-pit signal to generate a DC signal. The calculating unit sums up the peak signal and the DC signal, and then divides the sum value by a predetermined value, so as to generate the reference signal. The comparator compares the pre-pit signal with the reference signal to generate an output signal. Accordingly, even though the amplitude of the pre-pit signal is not always the same, the voltage of the reference signal may also be dynamically adjusted to make the comparator generate a correct output signal.

Abstract: In this optical disk device, a reflected light of a light beam reflected from a pre-pit-formed side of a track wobbled on a disk is detected as a first detection signal. A reflected light of the light beam reflected from the other side of the track is detected as a second detection signal. The first detection signal and/or the second detection signal are/is amplified with a gain(s) so set that a peak value of a wobble signal component of the first detection signal coincides with a bottom value of a wobble signal component of the second detection signal.

Abstract: The present invention relates to an apparatus and method for analyzing the read-out signal of an optical storage media and is especially suitable for the HF signal read from the digital video disk (DVD), wherein the HF signal comprises many different signals whose periods are integer times of the system period. The present apparatus can be used to record the maximum or minimum values of specific period of signals for further statistical analyses. Furthermore, the AC and DC components of the HF signal can be processed independently and the results will be combined together for further processes. Therefore, it only takes moderate memory capacity and acquisition time to obtain accurate maximum or minimum values of the specific period of signals.

Abstract: An information recording/reproducing apparatus irradiates a light beam on an optical disc on which pre-pits are formed, and performs recording and/or reproduction of information with respect to the optical disc according to a recording clock produced based on a wobble signal and a pre-pit signal. When recording information onto the optical disc having the pre-pits, a light beam is radiated to thereby extract the wobble signal and pre-pit signal. Then, according to the wobble signal and the pre-pit signal, a recording clock signal is produced, and information is recorded based on the recording clock signal. When producing a pre-pit signal, a push-pull signal is produced from the reflected light from the optical disc, and this signal is compared with a reference level to thereby detect a pre-pit. Here, when a pre-pit is not detected, the reference level is changed and the detection processing of the pre-pits is executed again.

Abstract: An equalizer for producing an equalized signal from an input signal. The input signal has a DC component. The equalizer includes a programmable filter and equalizer. A detector for generating a threshold signal from a preprocessed signal. The preprocessed signal is generated from the equalized signal. A comparator for comparing the preprocessed signal to the threshold signal to produce an output signal. A tracking device for tracking the DC component from the output signal.

Abstract: The present invention provides a binarization device that realizes reproduction with a low error rate, even where optimum recording conditions such as recording power have not been set in the recording device, or where optimum recording has not been carried out for the reproducing device. The binarization device includes a binarization unit, a slice level setting unit, and a weight adding function. The binarization unit binarizes a reproduction signal obtained by reproducing information recorded by mark length recording on a recording medium to output high-level signals and low-level signals based on a slice level. The slice level setting unit calculates the average value of the high-level signals output from the binarization unit, and determines the slice level from the average value. The determined slice level is set to the binarization unit. Either the binarization unit or the slice level setting unit adds a predetermined weight to each signal having a short high-level time among the high-level signals.

Abstract: An optical pickup includes a laser output section to emit a laser beam onto a recording medium, a photodetector to receive the light reflected by the recording medium, an amplifier to output a signal corresponding to the strength of the reflected light output from the photodetector, and a control circuit which can receive a signal which changes for data recording and playback, and suppresses the amplifier gain during recording.

Abstract: An information recording method for recording information by irradiating an information recording medium with light, including steps of providing the information recording medium with a physical identification field (PID) and a data field, and utilizing a head amplifier for amplifying a detection signal in the PID field with a first gain and amplifying a detection signal in the data field with a second gain different from the first gain to record the information to the data field.

Abstract: An optical disk provided with a land region and a groove region that are formed on a substrate, the land region and groove region being used as a recording track that is the medium of the recording/playback of information signal, and a pre-pit region that is formed at the boundary part of neighboring land region and groove region and is disposed every other boundary part, the pre-pit region including specific information. Characteristically, the specific information's in neighboring pre-pit regions are not aligned in the radius direction of the optical disk.

Abstract: This optical receiving device for discriminating and recovering a data signal, which results from converting an optical signal input through a dispersion equalizer into an electrical signal and amplifying it to a pre-determined amplitude, by using a clock and data recovery circuit for discriminating a data signal at the decision point controlled to achieve the optimum position controls the dispersion characteristics of a dispersion equalizer so that the error count in the recovered data signal by using a clock and data recovery circuit will be minimized by controlling the eye pattern of the data signal which has been amplified to a pre-determined amplitude.

Abstract: A calibration method for a slice level of zero cross signal and a method of producing zero cross signal are disclosed. In this invention, the positive cycle and the negative cycle of the zero cross signal are sampled to obtain an error value related to the slice level due to asymmetry of the zero cross signal. By this invention, the asymmetry between the positive cycle and the negative cycle of the zero cross signal can be adjusted.

Abstract: An optical read/write apparatus causes a read/write light beam from illuminating means to strike only one side of an optical storage medium including stacked data storage layers each of which is readable/writeable separately from the other layers. In this case, the optical read/write apparatus operates so that data is read/written from/into a second data storage layer after fully recording a recordable area of a first data storage layer. Thus, light can be shone with uniform intensity across the substantially entire recordable area of the second data storage layer without using a complex read/write system even under such conditions that the transmittance to light of the first data storage layer in the recordable area may vary depending on whether any data is recorded in the recordable area.

Abstract: A data restoring apparatus of an optical disk reproducing system restores data recorded on an optical disk from an RF signal read from the optical disk.

Abstract: An optical disk drive reads and/or writes data from/on an optical disk on which a pre-pit has been formed on at least one side edge of a data recording track. The disk drive includes light-emitting element, photodetector section, subtractor and amplifier. The light-emitting element emits a light beam and irradiates the track with the light beam. The photodetector section receives and detects the light beam reflected from the track, thereby generating first and second detection signals, carrying information about shapes of the track at the one and the other side edges thereof, respectively, based on the reflected light beam. The subtractor generates a differential signal representing a difference between the first and second detection signals. The amplifier amplifies the differential signal, output from the subtractor, by a variable amplification factor. The optical disk drive detects the pre-pit in accordance with the amplified differential signal.

Abstract: An optical information reproducing method for reproducing information recorded at at least one mark on an optical information medium. The method includes irradiating a laser to the optical information medium, detecting a reflected beam reflected from the optical information medium, and reproducing information recorded on the optical information medium from an output signal of a detector which detects the reflected beam. The step of reproducing information is changed in dependence upon a length of the mark of the optical information medium.

Abstract: A pre-pit detecting apparatus which, when a light beam is radiated onto an optical recording medium having a recording surface with pre-pits repeatedly formed between tracks, receives light reflected by the recording surface with first and second light receiving faces, obtains the push-pull signal corresponding to the light receiving signals for the first and second light receiving faces, samples the push-pull signal to collect sample data for a predetermined period, and sets a threshold value between the maximum value of data corresponding to a track and the minimum value of data corresponding to a pre-pit, of the collected sample data.

Abstract: A pre-pit detecting apparatus which, when a light beam is radiated onto an optical recording medium having a recording surface with pre-pits repeatedly formed between tracks, receives light reflected by the recording surface with first and second light receiving faces, obtains the push-pull signal corresponding to the light receiving signals for the first and second light receiving faces, and binarizes the push-pull signal by using a threshold value to generate a pre-pit detection signal. It is judged which area of a plurality of areas including at least a not-yet-recorded area corresponds to a position of the recording surface where the light beam is radiated is performed to judge. Then the threshold value is set in accordance with the judgement result.

Abstract: When first and second read signals generated on the basis of the outputs of electrical signals from a light receiving portion are input to an amplitude correcting circuit, the first and second read signals are added to generate an addition signal. Then the amplitudes of the first and second read signals are corrected for the each RF signal component corresponding to each recording pit, which is contained in the first and second read signals on the basis of the addition signal. Finally, the difference between the first and second read signals is computed to generate a difference signal so that a pre-pit signal will be detected on the basis of the difference signal.

Abstract: A composite signal in which pre-pit signal components are piggypacked onto frequency components of wobbling, is extracted from an optical recording medium. The composite signal is binarized, so that pre-pit signals are generated. The pre-pit signals pass through a first gate when the gate is open. The gate is periodically opened only in a period during which the amplitude of the wobbling becomes a maximum one. The number of the pre-pit signals passing through the gate is counted, so that a binarizing level for generating the pre-pit signal is set based on the relationship between the counted number per a reference time and a predetermined reference number.