An optical recording/reproducing system 1 reads, based on a predetermined reproduction clock, information associated with a recording track of a recording medium by irradiating frequency light. The frequency light is scanned at a predetermined scan velocity. The optical recording/reproducing system includes a computer 13, a DSP 49, and a LD driver that modulate light by a drive signal on which a frequency signal is superimposed to thereby output the frequency light, and synchronizes a frequency of the frequency signal with a frequency of the reproduction clock according to the scan velocity.

This application is the U.S. national phase of International Application No. PCT/JP2007/062272 filed 19 Jun. 2007 which designated the U.S. and claims priority to Japanese Patent Application No. 2006-170664 filed 20 Jun. 2006, the entire contents of each of which are hereby incorporated by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to methods, systems, and programs for reproducing data optically recorded on a recording medium, such as a CD (Compact Disc), a DVD (Digital Versatile Disc), a Blu-ray Disc, a HD (High Definition) DVD, or the like.

BACKGROUND ART

Optical recording/reproducing systems are designed to irradiate a laser beam to a recording medium, such as a CD, a DVD, or a next generation DVD (Blu-ray DISC or HD DVD). This writes, into the recording medium, data to be written as a recorded signal by a state change in a recording layer of the recording medium due to the heat of the irradiated laser beam. The optical recording/reproducing systems are also designed to reproduce data corresponding to a beam reflected from a plurality of recorded marks (also referred to as ‘recorded pits’) constituting the recorded signal. Such optical recording/reproducing systems have rapidly become common as data recording/reproducing systems.

In such a data recording/reproducing system, an acceleration of a linear velocity of the laser beam from 1× to 2×, . . . , 32× allows a rate or time of reproduction and/or recording to be reduced. The linear velocity represents a velocity of a laser beam travelling on a medium during recording and/or reproducing.

In such a data recording/reproducing system designed set forth above, a single-mode laser with a comparatively low operating current is used as a light source; this single-mode laser has a single longitudinal mode. A laser light outputted from a single-mode laser has very high coherency. For this reason, for reproducing data, it is required to maintain, at a high level, a ratio of a laser beam to noise, that is, CNR (Carrier to Noise Ratio); this noise may cause power fluctuations in a laser light outputted from the single-mode laser.

The noise that fluctuates the power of a laser beam includes external feedback noise and laser noise. The external feedback noise is due to interference with optical feedback from a recording medium and/or optical components. The laser noise is due to the fluctuations in temperature As described above, data writing (data recording) into a recording medium is carried out by a state change in a recording layer of the recording medium due to the heat of an irradiated laser beam. For this reason, there is a limit to the power of the irradiated laser beam during reproduction from the standpoint of the prevention of deterioration of the recording layer

In this respect, Patent Documents 1 and 2 change an optical coupling efficiency, which is a ratio of the quantity of part of a laser beam focused on a recording medium to the total of the laser beam to be irradiated from an optical source, according to its mode (recording mode and/or reproducing mode), the kind of the recording medium and/or its recording layer (single layer and/or multiple layer). This can maintain the CNR at a higher level while reducing the power of the irradiated laser beam.

As another method for reducing the external feedback noise, as disclosed in Patent Document 3, a high-frequency current of the order of hundreds of megahertz is superimposed on a drive current (direct current) for a laser beam outputted from a single-mode laser so that the outputted laser beam flashes (on and of). This changes the longitudinal mode of the laser beam to a multimode. This method will be referred to as “high-frequency superimposing method” hereinafter.

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

FIG. 1illustrates an example of a relationship between recorded signals written to a part of a recording track and the waveform of a laser beam output obtained by the high-frequency superimposing. Note that the run length (mark length) of a recorded signals along a recording track is commonly modulated. However, inFIG. 1, to facilitate the description, the recorded signals each with a minimum run length are written to a part of the recording track. The part of the recording track is linearly developed in the track direction.

In addition, inFIG. 1, an intermittent high-frequency current in the form of a sine wave with its positive duty (on-duty) being less than 50% is used as the high-frequency current.

When a reproducing linear velocity is increased so that the time required for the minimum run length of a recorded signal to pass through a scanning position of the laser beam approaches the period of the intermittent high-frequency current, as illustrated inFIG. 1, the recorded signal may pass through the scanning position of the laser beam in a high-frequency current off period, in other words, a laser-beam off period, making it difficult to read the recorded signal.

The present invention has been made in light of the circumstances provided above, and has an object of reliably reading a signal recorded in a recording medium to reproduce data corresponding to the recorded signal even if a reproducing linear velocity is increased.

Means for Solving the Problems

A first aspect of the present invention is an optical recording/reproducing system for reading, based on a predetermined reproduction clock, information associated with a recording track of a recording medium by irradiating frequency light. The frequency light is scanned at a predetermined scan velocity. The optical recording/reproducing system includes a modulating unit that modulates light by a drive signal on which a frequency signal is superimposed to thereby output the frequency light, and a synchronizing unit that synchronizes a frequency of the frequency signal with a frequency of the reproduction clock according to the scan velocity.

A second aspect of the present invention is a program readable by a computer installed in an optical recording/reproducing system that reads, based on a predetermined reproduction clock, information associated with a recording track of a recording medium by irradiating frequency light. The frequency light is scanned at a predetermined scan velocity. The optical recording/reproducing system includes a modulating unit that modulates light by a drive signal on which a frequency signal is superimposed to thereby output the frequency light. The program instructs the computer to execute an operation to synchronize a frequency of the frequency signal with a frequency of the reproduction clock according to the scan velocity.

A third aspect of the present invention is an optical recording/reproducing method for reading, based on a predetermined reproduction clock, information associated with a recording track of a recording medium by irradiating frequency light. The frequency light is scanned at a predetermined scan velocity. The optical recording/reproducing method includes modulating light by a drive signal on which a frequency signal is superimposed to thereby output the frequency light, and synchronizing a frequency of the frequency signal with a frequency of the reproduction clock according to the scan velocity.

DESCRIPTION OF CHARACTERS

5Optical pickup unit

11Record and reproduction data processing unit

19Light control element

45Modulator and demodulator

49Digital signal processor

49alinear-velocity setting unit

BEST MODES FOR CARRYING OUT THE INVENTION

First Embodiment

FIG. 2is a block diagram illustrating a schematic structure of a data recording/reproducing system1according to a first embodiment of the present invention.

InFIG. 2, reference numeral3represents a recording medium including, for example, a disc-like protective layer and a disc-like recording layer including spiral or concentric recording tracks. For example, as the recording medium3, a CD, a DVD, a Blu-ray Disc, a HD DVD, or the like can be used.

The data recording/reproducing system1according to the first embodiment has a function of recording information on the recording tracks of the recording medium3rotating at a desired velocity and a function of reproducing information recorded on the recording tracks of the recording medium3.

For example, in the First embodiment, the recording tracks, as one structural example, include at least one of lands and grooves alternately arranged in a radial direction. The at least one of the lands and grooves are wobbled at a predetermined frequency, and part of the at least one of the lands and grooves is for example phase-modulated to include information such as address informant of the recording tracks.

Specifically, the data recording/reproducing system1is equipped with an optical pickup unit (optical head unit)5for recording/reproducing information on/from the recording tracks of the rotating recording medium by irradiating a light spot on the recoding tracks. The data recording/reproducing system1is equipped with a power adjusting unit7for adjusting power of the irradiated light on the recording medium3.

The data recording/reproducing system1is also equipped with a servo driver9as a servo-control system for carrying out: rotating-velocity controls of the recording medium3, focus-position controls of the spot beam to be irradiated on the recording tracks of the recording medium3by the optical pickup unit5, and tracking controls of the beam spot with respect to the recording tracks.

Moreover, the data recording/reproducing system1is equipped with a record and reproduction data processing unit11having a function of producing data (referred to as “record data” hereinafter) corresponding to information to be recorded on the recording medium3and a function of producing data (referred to as “reproduction data” hereinafter) corresponding to information recorded on the recording medium3.

The data recording/reproducing system1is equipped with a computer13that controls the optical pickup unit5, the power adjusting unit7, the servo driver9, and the record and reproduction data processing unit11.

The computer13includes a first memory13a, such as a HDD (Hard Disc Drive), a FLASH MEMORY, or the like, for storing therein data representing processed results and the like, and a second memory13bserving as a main memory of the computer13for storing therein a plurality of programs P loaded from the first memory13a. The plurality of programs P cause the computer13to carry out the control operations.

The computer13has installed therein a crystal oscillator13c, and is configured to carries out operations according to a clock (crystal clock) issued from the crystal oscillator13c.

Referring toFIG. 2, the optical pickup unit5includes a laser diode (LD) unit15, an LD driver17, and a light control element19. The LD unit15irradiates a laser beam as light for information recording and/or information reproducing. The LD driver17controls the waveform of the laser beam outputted from the LD unit15. The light control element19serves as an element for adjusting the quantity of the laser beam outputted from the LD unit15. The light control element19is made up of a liquid crystal device with a light transmittance that changes with change in an applied voltage from a LC (Light Control) driver described hereinafter.

For example, in the first embodiment, the LD unit15and the light control element19of the optical pickup unit5are arranged such that the optical axis of the laser beam guided by the components15and19is parallel to the surface of the transparent layer of the recording medium3.

Note that, in the first embodiment, the light control element19has the light transmittance of a substantially 100% (decay rate of 0%) in an initial condition

The optical pickup unit5also includes a beam splitter21disposed on an optical path of the laser beam outputted from the LD unit15and transferred through the light control element19. The beam splitter21is operative to transmit therethrough the laser beam travelling through the light control element19and to reflect a light beam sent from a stand-up mirror described hereinafter.

The optical pickup unit5further includes a stand-up mirror23arranged on an optical path of the laser beam passing through the beam splitter21. The stand-up mirror23is configured to reflect the laser beam passing through the beam splitter21in a direction perpendicular to the optical axis of the passing laser beam toward the recording medium3.

The optical pickup unit5includes a spindle motor25. The spindle motor25supports the recording medium3such that the recording medium3faces the stand-up mirror23and the optical axis of the laser beam reflected by the stand-up mirror23is orthogonal to the surface of the protective layer of the recording medium3. The spindle motor25also rotatably drives the recording medium3.

The optical pickup unit5includes an objective lens27interposed between the stand-up mirror23and the protective layer of the recording medium3. The objective lens27is operative to focus the laser beam reflected by the stand-up mirror23onto a recording track of the recording medium3to thereby irradiate the laser beam thereto as a spot beam.

The optical pickup unit5includes an actuator29. The actuator29is allowed to move the objective lens27in at least a radial direction of the recording medium3and a direction close to and away from the recording medium3. The actuator29is electrically connected to the servo driver9. The actuator29is configured to move the objective lens27under control of the servo driver9to thereby adjust a focusing position and a tracking position of the beam spot.

The objective lens27is operative to, during reproduction, receive light reflected from a recording track of the recording medium3and to output the received light as a parallel beam with a predetermined beam diameter. The stand-up mirror23is operative to reflect the reflected beam transferred through the objective lens27so as to transfer the reflected beam to the beam splitter21.

The beam splitter21works to reflect the reflected beam transferred from the stand-up mirror23.

The optical pickup unit5includes a receiver30. The receiver30is arranged on the optical path of the reflected beam reflected by the beam splitter21. The receiver30receives the reflected beam and converts the received beam into an electric signal (referred to as “RF signal” hereinafter).

The power adjusting unit7includes a monitor photodiode, referred to as “monitor diode”,31and an amplifier33. The monitor diode31is arranged on an optical path of a laser beam outputted from a back surface in a package of the LD unit15; this back surface is opposite to a normal output end of the LD unit15. The laser beam outputted from the back will be referred to as “backside laser beam”. The backside laser beam has the same power as that of the laser beam outputted from the normal output terminal of the LD unit15.

The monitor diode31continuously monitors the power (intensity) of the backside laser beam and outputs the result of the monitoring as a monitor signal (monitor electric signal, such as a monitor current).

The amplifier33is electrically connected to the monitor diode31. The amplifier33amplifies the monitor signal outputted from the monitor diode31.

The amplifier33is electrically connected to the computer13. The computer13is allowed to monitor the power of the laser beam irradiated on the recording medium3based on the monitor signal amplified by the amplifier33and the actually set light transmittance of the light control element19.

The power adjusting unit7includes a sample-hold circuit (S/H)35electrically connected to the amplifier33and the computer13. The sample-hold circuit35is operative to sample a value of the monitor signal outputted from the amplifier33and to hold the sampled value during the execution of APC (Automatic Power Control) by the computer13.

The power adjusting unit7also includes an APC circuit37electrically connected to the sample-hold circuit35and the LD driver17. During the execution of the APC by the computer13, the APC circuit37is operative to control a driving current from the LD driver17to the LD unit15based on the sampled and held value of the monitor signal by the sample-hold circuit35such that:

the sampled and held value of the monitor signal is substantially matched with a predetermined value corresponding to a predetermined power level of the laser beam irradiated on the recording medium3.

This carries out feedback control of the output waveform of the laser beam outputted from the LD unit15including the putout power level.

The power adjusting unit7includes a light control element driver (LD driver)38. Under control of the computer13, the LC driver38works to control a voltage to be applied therefrom to the light control element13to thereby control the light transmittance of the light control element19.

The record and reproduction data processing unit11includes an interface41that receives record data (bit-string data) inputted from a connection device during recording. The record and reproduction data processing unit11includes a buffer43electrically connected to the interface41and operative to hold the record data received by the interface41. The record and reproduction data processing unit11includes a modulator and demodulator45electrically connected to the buffer43. Each of the interface41, buffer43, and modulator and demodulator45is electrically connected to the computer13. The operations of each of the interface41, the buffer43, and the modulator and demodulator45are configured to be controlled by the computer13.

To the computer13, an input unit47is connected. The input unit47is allowed to input, to the computer13, various pieces of information and instructions including: setting information of a linear velocity of the recording medium3. The linear velocity represents a velocity of a laser beam traveling on a medium during recording and/or reproducing, such as 1×, 2×, . . . , 32×.

To the computer13, servo driver9, and modulator and demodulator45, a DSP (Digital Signal Processor)49is connected. The DSP49operates under control of the computer13.

The modulator and demodulator45is operative to, during recording, append an error-correcting code, such as a PI (Parity Inner) correcting code and/or a PO (Parity Outer) correcting code to the record data stored in the buffer43for each predetermined unit of the record data. In the first embodiment, the modulator and demodulator45is operative to, during recording, append the error-correcting code to the record data for each ECC (Error Correction Code) block of the record data.

Note that the ECC block represents a unit of data to be stored in the recording medium3.

For example, the recording medium3according to the first embodiment is a DVD, the ECC block is configured by 280 rows of 182 bytes each. 280 rows consist of 192 rows and 16 rows of the PO correcting code, and 182 bytes consist of 172 bytes of data and 10 bytes of the PI connecting code. Specifically, 12 rows of 172 bytes constitutes one data frame, and 16 date frames constitute one ECC block.

For example, in the first embodiment, the recode data of each data frame of each ECC block to which the error-correcting code has been appended is converted into a signal according to a clock (wobble clock) with a wobble frequency of the recording tracks such that the signal is changed from a high level to a low level or the low level to the high level at each bit of “1” of the record signal. The wobble clock is extracted from a wobble signal obtained by scanning the wobbled recording tracks by the computer13.

The converted data, such as NRZI data (Non Return to Zero Inverted) data, corresponds to recorded signals (recorded marks, recorded pits) to be written to the record tracks of the recording medium3.

Note that, in the first embodiment, a bit length (run length or recorded-signal length) of the NRZI data until its edge changes depending on an encoding or the like. For example, the bit lengths of the NRZI data are set to be NT. The reference character N varies depending on the type of the recording medium3. For example, when the recording medium3is a DVD, the N is set to be equal to or greater than 3, and when the recording medium3is a Blu-ray Disc, the N is set to be equal to or greater 2. The reference character T represents the period of the wobble clock.

Specifically, in the first embodiment, on a recording track of the recording medium3, the laser beam, which has a power level on the recording medium3being automatically feedback-controlled to a recording power level and has a modulated output waveform, such as a multipulse-modulated output waveform, is irradiated. This allows recorded signals corresponding to respective run length of the NRZI data to be written onto a recording track of the recording medium3.

The output-waveform control (multipulse control of the laser beam is called “Write Strategy”. Proper setting of the width of each of independent multi-pulses of the output waveform of the laser beam according to the power level of the laser beam on the recording medium3prevents deterioration of the recorded signals that results from continuous irradiation of a laser beam with a constant power level.

During reproduction, the LD driver17has a function F1. The function F1is to set a superimposed frequency of the order of hundreds of megahertz according to a superimposition-frequency control command indicative of a superimposed frequency of current on the drive current sent from the computer13. The function F1is also to superimpose, on the drive current, an intermittent high-frequency current with the superimposed frequency on the controlled drive current. For example, the intermittent high-frequency current is in the form of a sine wave with its on-duty being less than 50%.

Light reflected from a corresponding recorded signal based on the irradiated laser beam is detected through the receiver30as the RF signal by operations of the optical pickup unit5.

The modulator and demodulator45, during reproduction, has a function of:

amplifying the RF signal obtained by the receiver30; and

producing a wobble-modulated signal, a tracking error signal indicative of an error caused by the tracking control, and a focusing error signal caused by the focusing control.

The modulator and demodulator45also has a function of demodulating (decoding) reproduction data (bit-string data) from the RF signal according to an RF clock obtained by the DSP49described hereinafter. The demodulated playback data is sent to the computer13. The computer13carries out an error detecting task, a determining task to determine whether a detected error is allowed to be corrected, a correcting task to carry out error-correction when it is determined that the detected error is allowed to be corrected. The reproduction data after the correction task is stored in the buffer43by the computer13.

The interface41works to, during reproduction, output the reproduction data stored in the buffer43to an information output device connected to the interface41under control of the information output device.

The DSP49includes a liner-velocity setting unit49a. The linear-velocity setting unit49aworks to send, to the servo driver9, a liner-velocity command corresponding to the setting information of the linear velocity determined by the input unit47and passed via the computer13.

The DSP49also includes a PLL (Phase Locked Loop) module49bfor outputting a clock properly synchronized with an input signal.

The PLL module49bincludes a PLL circuit49b1that extracts the RF clock from inputted NRZI data, a PLL circuit49b2that produces a multiple wobble clock from the wobble clock inputted thereto, and a PLL circuit49b3that produces a multiple crystal clock from the crystal clock inputted thereto.

For example, the PLL circuit49b1includes a digital phase comparator, a digital loop filter, a digital VCO (Voltage Controlled Oscillator), and a frequency divider.

According to the PLL circuit49b1, a phase difference between the NRZI data inputted to the digital phase comparator and feedback digital data outputted from the digital VCO with its frequency being divided by the frequency divider to 1/m (m is a positive integer) is calculated by the digital phase comparator. The phase difference data is inputted to the digital VCO via the loop filter.

By the digital VCO, a clock with its frequency being adjusted to cancel the inputted phase difference data to zero is fed back to the digital phase comparator via the frequency divider. Repeat of the feedback loop allows the clock (RF clock) synchronized with the phase of the NRZI data to be outputted. The RF clock can be multiplied after being outputted from the PLL circuit49b1.

The PLL circuits49b2and the49b3each substantially have the same structure as that of the PLL circuit49b1. Thus, the multiple crystal clock and the multiple wobble clock are respectively outputted from the PLL circuits49b2and49b3.

The DSP49includes a selector49cfor selecting any one of the RF clock, the multiple wobble clock, and the multiple crystal clock produced by the PLL module49b.

Specifically, the servo driver9is operative to drive the spindle motor25according to the linear-velocity command from the linear-velocity setting unit49a:

turn the recording medium3with the set linear velocity being kept constant (CLV: Constant Linear Velocity); or

turn the recording medium3with an angular velocity being kept constant based on the set liner velocity (CAV: Constant Angular Velocity).

In addition, the servo driver9is operative to control the actuator29based on the tracking error signal and the focusing error signal obtained by the modulator and demodulator45to thereby carry out the focusing position control and the tracking control of the spot light to be irradiated on a recording track of the recording medium3.

In the first embodiment, as the light control element19configured to change the quantity of the output laser beam according to control information applied from the computer13via the LC driver38, the liquid crystal device with the light transmittance that changes with change in control information applied from the computer13via the LC driver38is used, but the present invention is not limited to the structure.

For example, as a light control element according to the present invention, a variable light attenuator with a light attenuation quantity, in other words, a volume of light to be transmitted therethrough can be used; this light attenuation changes with change in a voltage applied from the computer13via a driver. As an example of the variable light attenuator, a variable ND (Neutral Density) filter or the like is used. A polarizer, such as a wavelength plate or a crystal liquid element, and an element designed by a beam splitter can be used as a light control element according to the present invention.

For example, the polarizer is disposed in place of the light control element19illustrated inFIG. 2, and the polarizer is used in combination with the beam splitter21. The structure can constitute a light control element according to the present invention.

According to the structure, an optical axial direction (polarization direction) of the polarizer is changed according to control information applied from the computer13via a driver by a predetermined angle from a polarization direction of the incident laser beam. This allows the beam splitter21to split the laser beam transferred through the polarizer into a predetermined percent of the laser beam and the remaining percent thereof in light-volume. This can change the light transmittance of the incident laser beam transmitted through the polarizer and the beam splitter21.

The computer13according to the first embodiment is configured to carry out a control task of the LD driver17and the light control element19, a control task of the power adjusting unit7, a control task of the servo driver9, an error detecting and/or correcting task in accordance with programs P loaded to the second memory13b.

Next, specific operations of the data recording/reproducing system1according to the first embodiment will be described with a particular emphasis on the control tasks of the power adjusting unit7, the LD driver17, and the light control element19by the computer13.

In the data recoding/reproducing system1according to the first embodiment, when reproducing data recorded on the recording tracks of the recording medium3, the computer13carries out the operations illustrated inFIG. 3in accordance with at least one of the programs P loaded in the second memory13b.

First, in step S1, the computer13carries out a recording-medium playback operation while the light transmittance of the light control element19is set to an initial percentage of 100%.

Note that 100% of the light transmittance of the light control element19means the light transmittance of the light control element19during no voltage being applied to the light control element19.

Specifically, as the recording-medium playback operation, the computer13controls the spindle motor25through the DSP49and the servo driver9to thereby:

turn the recording medium3at the linear velocity inputted from the input unit47;

set the power level of the laser beam irradiated on the recording medium3to a predetermined reproducing power level;

control the sample-hold circuit35based on the set reproducing power level during the execution of the APC; and

send, to the LD driver17, the superimposition-frequency control command indicative of a predetermined frequency as the superimposed frequency of current (referred to as a superimposed frequency f1of the order of hundreds of megahertz).

Based on the control during the execution of the APC in step S1, the sample-hold circuit35samples and holds a value of the monitor signal outputted from the amplifier33and measured by the monitor diode31, and outputs the held value of the monitor signal to the APC circuit37.

At that time, the APC circuit37sends, to the LD driver17, the power control command to substantially match the monitored power level corresponding to the sampled and held value of the monitor signal with the reproduction power level.

Based on the power control command sent from the APC circuit37, the LD driver17controls the drive current, and superimpose, on the drive current, an intermittent high-frequency current Iout10with the superimposed frequency f1corresponding to the superimposition-frequency control command indicative of the superimposed frequency of current. The LD driver17provides the intermittent high-frequency current Iout10to the LD unit15to thereby drive the LD unit15. For example, the intermittent high-frequency current Iout10is in the form of a sine wave with its on-duty being less than 50%. This causes the LD unit15to output the high-frequency superimposed laser beam having the on-duty less than 50%.

As a result, the high-frequency superimposed laser beam is irradiated on the recorded signals written to a recording track of the recording medium3by operations of the optical pickup unit5. The power of the laser beam irradiated on the recording medium3is substantially kept constant at the reproducing power level by the APC control.

The laser beam irradiated on a recording track of the recording medium3searches a playback start point based on address information by operations of the optical pickup unit5under control of the computer13; this address information is recognized by the wobble signal obtained by scanning of wobbled-recording tracks by the computer13.

In parallel with the operation in step S1, the computer13monitors the linear velocity of the recording medium3from the servo driver9, and determines whether the monitored liner velocity is equal to or greater than the predetermined velocity in step S2.

When a result of the determination in step S2is NO, that is, the monitored linear velocity is less than the threshold velocity, the computer13determines that a recorded signal does not pass through the scanning position of the laser beam during a laser-beam off period, terminating the operations.

Otherwise, when the result of the determination in step S2is YES, that is, the monitored linear velocity is equal to or greater than the threshold velocity, the computer13determines that a recorded signal may pass through the scanning position of the laser beam during a laser-beam off period. In other words, the computer13determines that the readout of a recorded signal by the laser beam may be impossible, proceeding to step S3.

In step S3, the computer13carries out any one of:

an operation to send, to the LD driver17a superimposition-frequency increasing command to change the superimposed frequency f1to a superimposed frequency f2higher than the superimposed frequency f1as the superimposition-frequency control command; and

an operation to send, to the LD driver17and the DSP49, a reproduction-clock synchronizing command to synchronize the superimposed frequency with the multiple wobble clock or the multiple crystal clock as a reproduction clock.

When the superimposed-frequency increasing command is sent from the computer13, the LD driver17increases the frequency f1of the intermittent high-frequency current Iout10to the frequency f2corresponding to the superimposition-frequency increasing command while controlling the drive current based on the power control command sent from the APC circuit37(see the superimposed-frequency setting function F1).

Otherwise, when the reproduction-clock synchronizing command is sent from the computer13, the DSP49selects via the selector49cthe multiple wobble clock or the multiple crystal clock, and sends, to the LD driver17, the selected clock as the reproduction clock.

When the reproduction-clock synchronizing command is sent from the computer13, the LD driver17synchronizes the frequency f1of the intermittent high-frequency current Iout10superimposed on the drive current with the frequency of the reproduction clock (multiple wobble clock or the multiple crystal clock) sent from the DSP49while controlling the drive current based on the power control command sent from the APC circuit37.

Next, the computer13determines whether the laser beam is actually searching the playback start address, in other words, whether an RF signal corresponding to reflected light from the recording medium3is sent in step S5.

When a result of the determination in step S4is NO, that is, no RF signals are sent, the computer13determines that the laser beam is actually searching the playback start address, proceeding to step S5. In step S5, the computer13maintains unchanged the frequency of the intermittent high-frequency current Iout10determined in step S3.

When the irradiated position of the laser beam is matched with the playback start address by the playback-start address searching operation by the optical pickup unit5, light reflected from the playback start address of a corresponding one of the recorded signals based on the irradiated laser beam is detected through the receiver30as the RF signal by operations of the optical pickup unit5.

The detected RF signal is decoded by the modulator and demodulator45as reproduction data (bit-string data) of the ECC blocks, and thereafter, the reproduction data is sent to the computer13. After the error-correcting task has been applied to the reproduction data, the reproduction data is outputted to an information output device or the like via the buffer43and the interface41.

At that time, when a result of the determination in step S4is YES, that is, the RF signal is sent, the computer13proceeds to step S6and carries out an RF-clock synchronizing task in step S6.

The RF-clock synchronizing task in step S6is illustrated inFIG. 4Specifically, the computer13controls the DSP49to carry out PLL pull-in for the NRZI data, and determines whether the NRZI data is PLL locked, in other words, input and output of the PLL49bis synchronized in phase with each other) in step S6a1.

when a result of the determination in step S6a1is NO, that is, the NRZI data is unlocked, the computer13controls the DSP49to adjust the frequency of the clock in the digital VCO in step S6a2, and thereafter proceeds to step S6a1, carrying out again the PLL-lock determining operation in step S6a1.

As a result of the repetitions of the operations in steps S6a1and S6a2, when it is determined that the NRZI data is PLL locked, the computer13sends, to the DSP49and the LD driver17, a reproduction-clock synchronizing command to synchronize the superimposed frequency f1with the frequency of the RF clock in step S6a3.

The DSP49selects via the selector49cthe RF clock outputted from the PLL49b1, and sends, to the LD driver17, the selected RF clock as the reproduction clock.

When the reproduction-clock synchronizing command is sent from the computer13, the LD driver17synchronizes the frequency f1of the intermittent high-frequency current Iout10superimposed on the drive current with the frequency f3of the reproduction clock (RF clock) sent from the DSP49while controlling the drive current based on the power control command sent from the APC circuit37.

FIG. 5is a view illustrating a relationship among:

intermittent high-frequency currents Iout10and Iout11to be superimposed on the drive current Id from the APC circuit37in steps S2and S6(S6a1to S6a3);

laser-beam outputs Pout10and Pout11outputted from the LD unit15and corresponding to the respective intermittent high-frequency currents Iout10and Iout11;

a plurality of recorded marks (recorded pits) of the recorded signals written from the playback start address in the travelling direction of the recording tacks; and

the NRZI data obtained by the plurality of recorded marks.

Specifically, as a result of the determination in step S2, when the monitored liner velocity is equal to or greater than the threshold velocity (YES in step S2), as clearly understood by comparison between the recorded signals (recorded marks) and the laser-beam output waveform illustrated inFIG. 1, a recorded signal may pass through the scanning position of the laser beam in a laser-beam off period.

At that time, in the first embodiment, referring toFIG. 5, the frequency f1of the high-frequency current Iout10being synchronized with the frequency f3of the reproduction clock (RF clock) is superimposed on the drive signal as the high-frequency current Iout11while the power of the laser beam irradiated on the recording medium3is substantially maintained constant by the APC-on control.

The RF clock is extracted from the NRZI data obtained based on the edges of the recorded marks of the recorded signals. For this reason, as illustrated inFIG. 5, it is possible to synchronize each of the laser-bema output timings from the LD unit15with the timing at which a corresponding edge of a corresponding one of the recorded marks of the recorded signals.

As a result, referring toFIG. 5, each of the recorded marks of the recorded signals each pass through the scanning position of the laser beam during the laser-beam output being on at all times, making it possible to reliably read the recorded signals.

As described above, it is assumed that the reproducing linear velocity of the recording medium3is so set to a desired velocity that a recorded signal may pass through the scanning position of the laser beam in a laser-beam off period. In this assumption, in the first embodiment, the synchronization of the superimposed frequency of the intermittent high-frequency current with the frequency of the RF clock extracted from the RF signal obtained by the recorded signals can reliably read the recorded signals.

As a result, it is possible to provide the data recording/reproducing system1that, while improving the reproduction performance with increase in the reproducing linear velocity, prevents the skip of a recorded signal.

According to the first embodiment, in addition to during which the recorded signals are actually read from the playback start address in a recording track, during the playback start address is searched, the frequency of the intermittent high-frequency signal to be superimposed on the drive current is increased, or synchronized with the frequency of the reproduction clock (multiple wobble clock and/or multiple crystal clock) sent from the DSP49.

In a case where the former superimposed-frequency increasing method is used, when it is shifted from the searching mode to the reading mode, it is possible rapidly transfer the superimposed frequency to the mode in which the superimposed frequency is synchronized with the RF clock. This results in rapidly changing the intermittent high-frequency current to be superimposed on the drive current when it is shifted from the address searching mode to the reading mode for each of the recorded signals.

In a case where the latter frequency-synchronizing method is used, when it is shifted from the searching mode to the reading mode, it is possible rapidly and smoothly transfer the superimposed frequency from the mode in which the superimposed frequency is synchronized with the multiple wobble clock or the multiple crystal clock to the mode in which the superimposed frequency is synchronized with the RF clock.

This results in rapidly and stably oscillating the intermittent high-frequency current to be superimposed on the drive current when it is shifted from the address searching mode to the reading mode for the recorded signals.

Second Embodiment

A data recording/reproducing system according to a second embodiment of the present invention will be described hereinafter with reference to the corresponding drawings. Note that the hardware structural elements of the data recording/reproducing system according to the second embodiment is substantially identical to those of the data recording/reproducing system1according to the first embodiment. For this reason, like reference characters are assigned to the identical elements in the data recording/reproducing systems according to the first and second embodiments so that descriptions of the elements of the data recording/reproducing system of the second embodiment will be omitted or simplified.

In the data recoding/reproducing system1according to the second embodiment, when reproducing data recorded on the recording tracks of the recording medium3, the computer13carries out the operations illustrated inFIG. 6in place of inFIG. 3in accordance with at least one of the programs P loaded in the second memory13b. In the second embodiment, the operations illustrated inFIG. 6are executed for each ECC block of the recorded data as a target for reproduction.

The operations in steps S1to S4by the computer13are identical to those in steps S1to S4ofFIG. 3, and therefore, the descriptions of those are omitted.

When a result of the determination in step S4is NO, the computer13carries out the operation in step S5illustrated inFIG. 3.

Otherwise, when a result of the determination in step S4is YES, that is, the RF signal is sent, the computer13proceeds to step S10illustrated inFIG. 6.

In step S10, the computer13computes the error rate as the reproducing characteristic based on the reproduction data of an ECC block sent thereto. Moreover, in step S10, the computer13determines whether the computed error rate is equal to or greater than a predetermined threshold value.

Note that the reproducing characteristic according to the second embodiment is an index for evaluating the reproduction data obtained by the record and reproduction data processing unit11and the computer13. For example, in the second embodiment, the percentage of PI error representing the number of error bytes in all of the rows of each ECC block, which corresponds to the division of the number of error bytes by the number of normal bytes in each ECC block, is used as the reproducing characteristic.

When a result of the determination in step S10is NO, that is, the error rate is less than the predetermined threshold value, the computer13determines that the corresponding ECC block can be reproduced, exiting the operations.

Otherwise, when a result of the determination in step S10is YES, that is, the error rate is equal to or greater than the predetermined threshold value, the computer13determines that the readout of the corresponding ECC block is difficult, proceeding to step S6. Thereafter, the computer13executes the RF-clock synchronizing task set forth above (see step S6ofFIG. 3) to thereby synchronize each of the laser-bema output timings from the LD unit15with the timing at which a corresponding edge of a corresponding one of the recorded marks of the recorded signals (seeFIG. 5).

As described above, it is assumed that the reproducing linear velocity of the recording medium3is so set to a desired velocity that a recorded signal may pass through the scanning position of the laser beam in a laser-beam off period. In this assumption, in the second embodiment, the synchronization of the superimposed frequency of the intermittent high-frequency current with the frequency of the RF clock extracted from the RF signal obtained by the recorded signals can reliably read the recorded signals.

As a result, like the first embodiment, it is possible to provide the data recording/reproducing system1that, while improving the reproduction performance with increase in the reproducing linear velocity, prevents the skip of a recorded signal.

Third Embodiment

A data recording/reproducing system according to a third embodiment of the present invention will be described hereinafter with reference to the corresponding drawings. Note that the hardware structural elements of the data recording/reproducing system according to the third embodiment is substantially identical to those of the data recording/reproducing system1according to the first embodiment. For this reason, like reference characters are assigned to the identical elements in the data recording/reproducing systems according to the first and third embodiments so that descriptions of the elements of the data recording/reproducing system of the third embodiment will be omitted or simplified.

In the data recoding/reproducing system according to the third embodiment, when reproducing data recorded on the recording tracks of the recording medium3, the computer13carries out the operations illustrated inFIG. 7in place of inFIG. 3in accordance with at least one of the programs P loaded in the second memory13b.

The operations in steps S1and S2by the computer13are identical to those in steps S1and S2ofFIG. 3, and therefore, the descriptions of those are omitted.

When a result of the determination in step S2is YES, that is, the monitored linear velocity is equal to or greater than the threshold velocity, the computer13determines that a recorded signal may pass through the scanning position of the laser beam during a laser-beam off period. In other words, the computer13determines that the readout of a recorded signal by the laser beam may be impossible, proceeding to step S20ofFIG. 7.

In step S20, the computer13controls the voltage applied to the light control element19via the LC driver38while executing the APC control, that is, while maintaining constant the power of the laser beam irradiated on the recording medium3to thereby reduce the light transmittance of the light control element19to a preset value, such as 50%.

Note that 50% of the light transmittance of the light control element19means that the percentage of the monitored power level during control of the voltage being applied to the light control element19to the monitored power level during no voltage being applied thereto (100% of the light transmittance) becomes substantially 50%.

The reduction in the light transmittance of the light control element19and the APC control (the irradiated-power constant control) allow the output power of the laser beam outputted from the LD unit15to increase.

Thereafter, execution of the operations in steps S3to S6by the computer13allows each of the laser-bema output timings from the LD unit15to be synchronized with the timing at which a corresponding edge of a corresponding one of the recorded marks of the recorded signals (seeFIG. 5).

As described above, in the third embodiment, in addition to the effect of improving the reproduction performance by maintaining the reliability of reading the recorded signals, it is possible to, while the power of the irradiated laser beam on the recording medium3, increase the output power of the LD unit15, thus reducing the laser noise, and to intermittently turn on and off the laser beam through the LD unit15.

This makes it possible to improve the reproduction performance while preventing the protective layer of the recording medium3from being deteriorated.

Fourth Embodiment

A data recording/reproducing system according to a fourth embodiment of the present invention will be described hereinafter with reference to the corresponding drawings. Note that the hardware structural elements of the data recording/reproducing system according to the fourth embodiment is substantially identical to those of the data recording/reproducing system1according to the first embodiment. For this reason, like reference characters are assigned to the identical elements in the data recording/reproducing systems according to the first and fourth embodiments so that descriptions of the elements of the data recording/reproducing system of the fourth embodiment will be omitted or simplified.

In the data recoding/reproducing system according to the fourth embodiment, when reproducing data recorded on the recording tracks of the recording medium3, the computer13carries out the operations illustrated inFIG. 8in place of inFIG. 3in accordance with at least one of the programs P loaded in the second memory13b.

The operations in steps S1and S2by the computer13are identical to those in steps S1and S2ofFIG. 3, and therefore, the descriptions of those are omitted.

When a result of the determination in step S2is YES, that is, the monitored linear velocity is equal to or greater than the threshold velocity, the computer13determines that a recorded signal may pass through the scanning position of the laser beam during a laser-beam off period. In other words, the computer13determines that the readout of a recorded signal by the laser beam may be impossible, proceeding to step S20ofFIG. 8.

In step S20, the computer13controls the voltage applied to the light control element19via the LC driver38while executing the APC control, that is, while maintaining constant the power of the laser beam irradiated on the recording medium3to thereby reduce the light transmittance of the light control element19to a preset value, such as 50%.

The reduction in the light transmittance of the light control element19and the APC control (the irradiated-power constant control) allow the output power of the laser beam outputted from the LD unit15to increase.

Thereafter, the computer13executes the operations in steps S3and54illustrated inFIG. 3.

When a result of the determination in step S4is NO, the computer13carries out the operation in step S5illustrated inFIG. 3.

Otherwise, when a result of the determination in step S4is YES, that is, the RF signal is sent, the computer13proceeds to step S10illustrated inFIG. 8.

In step S10, the computer13computes the error rate as the reproducing characteristic based on the reproduction data of an ECC block sent thereto. Moreover, in step S10, the computer13determines whether the computed error rate is equal to or greater than the predetermined threshold value.

When a result of the determination in step S10is NO, that is, the error rate is less than the predetermined threshold value, the computer13determines that the corresponding ECC block can be reproduced, exiting the operations.

Otherwise, when a result of the determination in step S10is YES, that is, the error rate is equal to or greater than the predetermined threshold value, the computer13determines that the readout of the corresponding ECC block is difficult, proceeding to step S6. Thereafter, the computer13executes the RF-clock synchronizing task set forth above (see step S6ofFIG. 3) to thereby synchronize each of the laser-bema output timings from the LD unit15with the timing at which a corresponding edge of a corresponding one of the recorded marks of the recorded signals (seeFIG. 5).

As described above, it is assumed that the reproducing linear velocity of the recording medium3is so set to a desired velocity that a recorded signal may pass through the scanning position of the laser beam in a laser-beam off period. In this assumption, in the fourth embodiment, the synchronization of the superimposed frequency of the intermittent high-frequency current with the frequency of the RF clock extracted from the RF signal obtained by the recorded signals can reliably read the recorded signals. As a result, like the first embodiment, it is possible to provide the data recording/reproducing system1that, while improving the reproduction performance with increase in the reproducing linear velocity, prevents the skip of a recorded signal.

In addition to the effect, it is possible to increase the output power of the LD unit15, thus reducing the laser noise and to intermittently turn on and off the laser beam through the LD unit15while the power of the laser beam irradiated on the recording medium3.

This makes it possible to improve the reproduction performance while preventing the protective layer of the recording medium3from being deteriorated.

In the first to fourth embodiments, according to the superimposition-frequency increasing command and/or the reproduction clock synchronizing command, the LD driver17changes the superimposed frequency of the intermittent high-frequency current to be superimposed on the drive current of the LD unit15, but the present invention is not limited to the structure.

For example, in the first embodiment, the computer13has stored in the first memory13adata representing a frequency characteristic of current-attenuation associated with current transfer between the LD driver17A and the LD unit15. For example, the current-attenuation frequency characteristic is a current-attenuation frequency characteristic of wiring between the LD driver17and the LD unit15.

At that moment, as step S3A corresponding to step S3, referring toFIG. 9, based on the superimposed frequency increase from the frequency f1to the frequency f3, the computer13obtains a current attenuation during current transfer from the LD driver17to the LD unit15from the current-attenuation frequency characteristic data stored in the memory13a. Then, the computer13, as step S3B, sends, to the LD driver17, a correction command indicative of a correction current to cancel the obtained current attenuation in addition to the superimposition-frequency increasing command and/or the reproduction clock synchronizing command.

While controlling the drive current based on the power control command sent from the APC circuit37, the LD driver17changes the frequency f1of the intermittent high-frequency current Iout10based on the superimposition-frequency increasing command and/or the reproduction clock synchronizing command. In addition, the LD driver17increases the amplitude of the intermittent high-frequency current Iout10by the correction current contained in the correction command.

As a result, it is possible to continuously maintain on the level of the high-frequency superimposed laser beam outputted from the LD unit15, and to correct the attenuation of the intermittent high-frequency current being transferred from the LD driver17to the LD unit15.

In the operations identical to the operation in step S6a3and that in the step S3according to the other embodiments, the operations in steps S3A and S3B can be carried out.

Note that, in the first to fourth embodiments, as the reproducing characteristic that is an index for evaluating the reproduction data obtained by the record and reproduction data processing unit11and the computer13, the PI error rate for each ECC block is used, but the present invention is not limited to the structure.

Specifically, various pieces of data that are responsible for reproducing-data evaluating index, such as jitter representing the rate of variation between the reproduction data and a clock extracted from the reproduction data, can be used as the reproducing characteristic.

In the first to fourth embodiments, the control task for the light control element19in the optical pickup unit5, the control task for the power adjusting unit7, the control task for the servo driver9, and the process associated with the error-detecting and/or error-correcting tasks are configured to be carried out by the computer13in accordance with the corresponding programs P. The present invention is however not limited to the structure.

Specifically, these tasks can be shared by two or more computers.

In the first to fourth embodiments, the superimposition-frequency setting function F1can be carried out, as the superimposition magnitude setting process and the superimposition-frequency setting process, by a computer circuit, such as a microcomputer, installed in the LD driver in accordance with programs externally loaded from, for example, a computer or the like.

In the first to fourth embodiments, when the monitored linear velocity is less than the threshold velocity corresponding to the minimum mark length, the computer13determines that the recorded signals can be read by the laser beam, but the present invention is not limited to the structure.

For example, during the CAV reproduction, the computer13can continuously monitor the actual reproducing liner velocity via the serve driver9. This configuration allows, even if the reproducing linear velocity increases toward the outer periphery of the recording medium3during the CAV reproduction up to a threshold velocity, such as 4× corresponding to 3T and over, the computer13to detect the increase in the reproducing linear velocity equal to or greater the threshold velocity to thereby carry out the frequency-increasing task and/or the reproduction-clock synchronizing task (see step S3), and the RF-clock synchronizing task (see step S6).

This prevents the skip of a recorded signal.

In the first to fourth embodiments, as the operation in step S6, the intermittent high-frequency current to be superimposed on the drive current is synchronized with the frequency of the RF clock, but the present invention is not limited to the structure. For example, as set forth above, the wobble clock is used as the recording clock, so the wobble clock is identical to the RF clock. Thus, as the operation in step S6, the intermittent high-frequency current to be superimposed on the drive current can be synchronized with the frequency of the wobble clock in place of the RF clock.

In the first to fourth embodiments, during reproduction, the LD driver is configured to superimpose the sinusoidal intermittent high-frequency current with its on-duty being less than 50% on the drive current to the LD unit to thereby drive the LD unit, but the present invention is not limited to the structure.

Specifically, the LD driver can use, as the high-frequency current to be superimposed on the drive current, a cyclically waved current except for a sinusoidally waved current. Moreover, the LD driver can set the on-duty of the high-frequency current to a desired percentage.

In the first to fourth embodiments, the monitor diode is arranged on the optical path of the backside laser beam outputted from the back surface opposing the normal output end in the package of the LD unit15. The monitor diode is configured to monitor the backside laser beam. The present invention is not however limited to the arrangement. For example, the monitor diode can be configured to continuously monitor the power of part of the laser beam passing through the beam splitter21and the stand-up mirror23illustrated inFIG. 2. The monitor diode can be arranged on an optical path between the light control element19and the objective lens27, or on an optical path branched from an optical system between the light control element19and the objective lens27, and configured to monitor reflected light on the corresponding optical path.

The present invention is not limited to the aforementioned embodiments and their modifications, and can be implemented as variations of the aforementioned embodiments and their modifications within the scope of the present invention.