JP3958673B2 - Multilevel recording servo signal detection method and optical information recording / reproducing apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a servo signal detection method for multilevel recording and an optical information recording / reproducing apparatus.
[0002]
[Prior art]
CD drives and DVD drives have begun to be recognized as optical information recording devices for recording data on optical information recording media such as CDs and DVDs. In addition, the data size of the file to be handled has become huge, and further increase in capacity of the optical information recording apparatus is desired.
As one method for increasing the capacity, there is a multi-value recording technique in which recording marks are recorded one by one in a virtual cell divided into a specific length in a circumferential direction on a track formed on an optical information recording medium. . In this multilevel recording technique, the circumferential length of a cell, which is an information recording unit on an optical information recording medium, is approximately equal to or less than the optical resolution of the spot. Information is embedded in the area of the mark recorded in the cell. Multi-level information can be extracted by determining the reflection signal level corresponding to the area of the mark in multiple stages.
[0003]
In the binary information recording system for CDs, DVDs, etc., information is embedded in the length of the recording mark larger than the optical resolution, so the limit of spot diameter reduction has become a bottleneck for increasing the capacity. Since the spot is physically determined from the laser wavelength and the degree of lens narrowing (NA), the spot has to be relied upon to shorten the laser wavelength or increase the NA of the lens. On the other hand, in multi-value recording, since multi-value information can be recorded in a cell having an optical resolution or less, it has been attracting attention as a technology capable of increasing the capacity without relying on a spot diameter reduction.
[0004]
The typical laser emission waveform of multi-value information recording using a phase change recording medium (media) is a light pulse with high light intensity for melting the film of the optical information recording medium and a mark formed by rapid cooling. This comprises an off pulse having a low light intensity for the purpose of forming a space, and a space pulse for forming a space (for erasing an existing mark). In this case, most of the time during the formation of the mark is an off-pulse, and since the light is emitted with a very weak intensity during the off-pulse period, it is difficult to detect a signal. Further, since the write pulse is short, stable signal detection cannot be performed.
[0005]
[Problems to be solved by the invention]
However, since there are servo signals and wobble signals that must be detected even during recording, the conventional off-pulse period that determines the size of the mark is the off-pulse period that maintains the rapid cooling effect necessary for mark formation, and signal detection There has been proposed a technique for improving the quality of the detection signal while solving the above-mentioned problems and maintaining the recording performance as it is by emitting light by changing the power in the bias pulse period during which the recording can be performed.
[0006]
However, such a technique has a problem that a servo signal suitable for recording multilevel information using a write pulse, an off pulse, a space pulse, and a bias pulse cannot be detected.
The present invention has been made to solve the above-described problems, and is intended to enable detection of a servo signal suitable for recording multilevel information using a write pulse, an off pulse, a space pulse, and a bias pulse. Objective.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a servo signal detection method for multilevel recording (1) to (8).
(1) When forming recording marks having different sizes according to information to be recorded on cells equally divided in a specific area on the optical information recording medium, a write pulse set to a predetermined high light intensity; An off-pulse set to a predetermined low light intensity, a space pulse set smaller than a light pulse capable of forming a space and larger than the off-pulse, and a light intensity smaller than the space pulse and larger than the off-pulse. And a wobble signal from a source servo signal detected from the optical information recording medium, wherein the servo signal is detected by using laser emission comprising a bias pulse output following the off pulse. Alternatively, a servo signal detection method for multilevel recording that extracts a servo signal by removing a high frequency component of a cell frequency component.
[0008]
(2) In the servo signal detection method for multilevel recording of (1), at least the bias pulse is used as a gain to be applied to a signal obtained by removing a high frequency component of a wobble signal or a cell frequency component from the source servo signal. A servo signal detection method for multilevel recording, wherein a servo signal is extracted using a set value calculated based on the light intensity and the light intensity of the space pulse.
(3) In the servo signal detection method for multi-value recording of (1), the wobble signal or cell is generated from the source servo signal with the same gain as the gain for maintaining the sum signal level from which the high frequency component is removed at a preset target voltage. A servo signal detection method for multilevel recording, in which a servo signal is extracted by amplifying or attenuating a signal from which high frequency components of frequency components have been removed.
[0009]
(4) In the servo signal detection method for multilevel recording of (1), a gain for maintaining the sum signal level acquired during the laser emission period with the bias pulse or the laser emission period with the space pulse at a preset target voltage. A servo signal detection method for multi-level recording, in which a servo signal is extracted by amplifying or attenuating a signal obtained by removing a wobble signal or a high frequency component of a cell frequency component from the source servo signal with the same gain.
(5) In the servo signal detection method for multilevel recording of (1), a signal obtained by removing a high frequency component of a wobble signal or a cell frequency component from the source servo signal acquired only during the laser emission period with the bias pulse. A servo signal is extracted by synthesizing a signal to which a specific gain is applied and a signal obtained by removing the high frequency component of the wobble signal or cell frequency component from the source servo signal acquired only during the laser emission period with the space pulse. Servo signal detection method for multi-value recording.
[0010]
(6) In the servo signal detection method of multi-value recording of (1), the sum signal level acquired during the laser emission period with the bias pulse is the same gain as the gain for maintaining the preset target voltage. A signal obtained by amplifying or attenuating a signal obtained by removing the high frequency component of the wobble signal or cell frequency component from the source servo signal acquired only during the laser emission period, and the sum signal level acquired during the laser emission period in the space pulse. A signal obtained by removing the wobble signal or the high frequency component of the cell frequency component from the source servo signal acquired only during the laser emission period with the space pulse with the same gain as the preset target voltage is synthesized. A servo signal detection method for multi-level recording that extracts servo signals.
[0011]
(7) In the servo signal detection method of multilevel recording of (1), a gain for maintaining the sum signal level acquired during the laser emission period with the bias pulse at the sum signal level acquired during the laser emission period with the space pulse; A signal obtained by amplifying or attenuating a signal obtained by removing a high frequency component of a wobble signal or a cell frequency component from the source servo signal acquired only in the laser emission period with the bias pulse with the same gain, and laser emission with the space pulse. A multilevel recording servo signal detection method for extracting a servo signal by synthesizing a wobble signal or a signal obtained by removing a high frequency component of a cell frequency component from the source servo signal acquired only in a period.
(8) The servo signal detection method for multilevel recording according to any one of (1) to (7), wherein the servo signal is subjected to phase compensation.
[0012]
In addition, an optical information recording / reproducing apparatus (9) is also provided.
(9) Recording of information by determining the position of the laser beam irradiated on the optical information recording medium based on the servo signal detected by the servo signal detection method for multilevel recording of any one of (1) to (8) An optical information recording / reproducing apparatus comprising means for performing reproduction.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be specifically described below with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of an optical disc apparatus according to an embodiment of the present invention.
This optical disk apparatus is an optical information recording apparatus such as a CD drive or a DVD drive, and an optical pickup 1 equipped with an optical system, and an optical disk (medium) 15 that is an information recording medium such as a movement of the optical pickup 1 or a CD or DVD. The motor drive circuit 6 controls the rotational drive of the motor 14 that rotates the motor 14 and various electric circuits.
[0014]
The optical pickup 1 includes a laser light source 2, an optical component that guides a laser beam emitted by the laser emission of the laser light source 2 to each element (not shown and detailed description is omitted since it is known), and a laser beam on the optical disk 15. An objective lens 3 for condensing the spot, an actuator 4 for controlling the lens position to cause the spot to follow a desired position, and a light receiving element (PD) 5 are mounted.
The various electric circuits include a laser drive circuit 7 including a laser drive unit 8 that determines a current for causing the laser light source 2 to emit laser light and a strategy generation unit 9 that determines a laser emission waveform. Since the current-to-light output characteristics of the laser light source 2 vary greatly depending on the temperature, the laser driving unit 8 is generally equipped with an output control function that detects the output light intensity and stabilizes the output. For light intensity detection, a light receiving element built in the laser light source 2 may be used, or a dedicated optical system may be constructed.
[0015]
User data transmitted from the outside as recording data is converted into multi-value information in an encoder circuit (not shown because it is well known), which is controlled by a CPU (not known), and then transferred to the laser drive circuit 7. And recorded on the optical disk 15.
Reflected signals from the optical disk 15 received by the light receiving element 5 as other circuits are subjected to current / voltage conversion by the I / V circuit 10 and transferred to several detection circuits.
The I / V circuit 10 is positioned as a first-stage circuit, and is set with conversion efficiency (gain) suitable for reproduction and recording.
The RF detection circuit 11 extracts a multi-value information component recorded on the optical disk 15 and transfers it to a decoder circuit (not shown because it is well known) to be converted into user data.
[0016]
The wobble detection circuit 12 extracts the servo signal component carved on the track based on the push-pull signal which is the difference between the outputs of the light receiving element 5 divided into two by the dividing line in the track tangent direction on the optical disc 15 and extracts the address signal from the servo signal component. The data is transferred to a clock generation circuit (not shown because it is publicly known) and used for clock generation in synchronization with the rotation of the medium and media rotation control. A timing signal necessary for detecting the servo signal is mainly supplied from the laser driving circuit 7.
The servo detection circuit 13 extracts spot position information, issues an instruction to the motor drive circuit 6 to cause the spot to follow the desired position, and moves the optical pickup 1 and the actuator 4.
[0017]
That is, this optical disc apparatus corresponds to the optical information recording / reproducing apparatus according to claim 9 of the present invention, and the laser drive circuit 7 or the wobble detection circuit 12 performs multilevel recording according to claims 1 to 7 of the present invention described later. This corresponds to control means for performing control based on the servo signal detection method.
[0018]
FIG. 2 is a diagram for explaining the outline of multi-value recording on the optical disc 15.
As shown in FIG. 3A, virtual cells (virtual cells) are arranged at substantially equal intervals on the track formed on the optical disk 15. One recording mark is formed in the center of the virtual cell. For example, (a) in the figure shows the case where marks of level 3 (L3), level 4 (L4), and level 1 (L1) are recorded in three consecutive virtual cells, respectively (b) in the figure. Shows an example of the shape of each recording mark.
(C) of the figure shows an example of a laser emission waveform during recording, and the laser emission waveform is composed of a write pulse Pw, an off pulse Pof, a bias pulse Pb, and a space pulse Ps.
[0019]
At the time of reproduction, information is reproduced by estimating the area of the recording mark in the virtual cell by discriminating the reproduction signal intensity level obtained from the reflected light of the virtual cell portion. (D) of the same figure is a figure which shows the waveform of the reproduction | regeneration signal corresponding to each recording mark when the said virtual cell is reproduced | regenerated.
For example, if recording marks of three types (L1 to L3) of area can be recorded and reproduced in the virtual cell, four-value (2-bit (bit)) information including no recording mark can be stored. Further, if seven types (L1 to L7) of recording marks can be separated, eight-value information (three bits (bit)) including no recording mark can be stored.
[0020]
Multi-value information recording is established in a state where the area of the recording mark and the amplitude of the reproduction signal are in a certain relationship in a region below the optical resolution. When the cell length is shortened, the difference between the levels of the multi-value information recorded in the virtual cell becomes small and separation becomes difficult. Conversely, if the cell length increases and the area is increased beyond the optical resolution, the amplitude will saturate and multi-value information cannot be separated, so the relationship between the spot diameter and the cell length (cell width) There are limitations. However, the virtual cells do not need to be completely equidistant over the entire surface of the medium, and may be slightly longer or shorter than the cell length that can withstand the separation of multi-value information.
For example, when the recording area of the optical disk 15 is divided into several zones in the radial direction and a CAV format with a constant medium rotational angular velocity is adopted in each zone, the cell length becomes longer toward the outer periphery in that zone. However, by increasing the number of zones, the difference in cell length between the inner and outer peripheral sides in the zone is reduced, and the multi-value information can be sufficiently separated.
[0021]
Next, the servo signal detection process for the first multi-value recording according to claim 1 of the present invention will be described.
FIG. 3 is a block diagram showing a circuit configuration for executing the first multi-value recording servo signal detection process according to claim 1 of the present invention.
FIG. 4 is an explanatory diagram for explaining servo signal detection processing of the first multi-value recording by the circuit shown in FIG.
As a circuit configuration for executing the first multi-value recording servo signal detection process, a light receiving element (PD) 5 that receives reflected light from the optical disk 15 is divided into four in a shape as shown in FIG. The case of the light receiving element 5 will be described. The four light receiving portions of the light receiving element 5 divided into 5A to 5D, respectively, and the signals obtained by converting the outputs from the light receiving portions 5A to 5D by the I / V circuits 10a to 10d are referred to as VA to VD.
[0022]
The source focus error signal is (VA + VD)-(VB + VC), and the source track error signal is (VA + VC)-(VB + VD). The source focus error signal and the source track error signal are called source servo signals because they are only calculated and not subjected to signal processing. The source servo signal contains a wobble signal if it is an unrecorded area, and a high frequency component such as a data signal (cell frequency component) if it is an already recorded area. Unnecessary noise components are cut by 16 and 17.
Thereafter, the signal is amplified or attenuated by gain control (GC) circuits 18 and 19 to obtain a desired signal amplitude, and servo signals such as a focus error signal and a track error signal are obtained. The calculation method of the source focus error signal and the source track error signal is not limited to this because it depends on the light receiving mode. Although not shown, a track cross signal of (VA + VB + VC + VD) as other servo signals can be detected by the same process.
[0023]
That is, when the optical disc apparatus forms recording marks having different sizes according to information to be recorded on cells equally divided in a specific area on the optical information recording medium, the optical disc apparatus is set to a predetermined high light intensity. A light pulse, an off pulse set to a predetermined low light intensity, a space pulse set smaller than a light pulse capable of forming a space and larger than the off pulse, and smaller than the space pulse and smaller than the off pulse The filter 16 and 17 perform wobble from a source servo signal detected from the optical information recording medium. The filter 16 and 17 perform a recording function using laser light emission composed of a bias pulse output following the off pulse. The GC circuits 18 and 19 perform the function of removing the high frequency component of the signal or cell frequency component. Signal functions to extract the servo signal from the high-frequency component removed signal of the wobble signal or cell frequency components from.
[0024]
However, the servo signal quality deteriorates during recording because the laser output is intensity modulated.
In particular, in recording light emission without a bias pulse, when a large recording mark continues, an effective detection period cannot be ensured. On the other hand, recording light emission with a bias pulse can be detected because it is effective during the bias pulse period.
Since the servo signal is a difference, ideally, the laser intensity modulation component only affects the amplitude change of the servo signal component.
However, in reality, an intensity difference appears between the four-divided light receiving elements due to the axis deviation of the lens and the light beam and the inclination of the medium, so that the laser intensity modulation component is directly superimposed on the servo signal and the servo signal deteriorates.
[0025]
This will be described more specifically with reference to FIG.
In the virtual cell shown in (a) of the figure, recording marks of various sizes are formed, but here, for the sake of easy understanding, half the cell length of the virtual cell as shown in (b) of the figure. Let us consider a case where recording marks of a size are continuously recorded. FIG. 4C is a waveform diagram showing the laser emission waveform during the recording.
The laser emission waveform is modulated with a plurality of emission intensities, but the signal “rounding” occurs due to the limit of the transfer characteristics of the light receiving element and the circuit, and the reflected signal at the time of recording is shown in FIG. It becomes a waveform in which the transition between the space pulse and the bias pulse is noticeable.
The frequency in this case is the same frequency as the cell. When an intensity difference appears between the four-divided light receiving elements due to some variation, the reflected signal at the time of previous recording remains in the source servo signal, which causes noise for the servo signal component.
[0026]
As described above, in the case of multilevel information recording, cell frequency components are easily superposed on each other. Therefore, in the circuit configuration for executing the servo signal detection processing of the first multilevel recording, a filter for removing the cell frequency in particular. 16 and 17 are inserted.
Further, depending on the format of the optical disk (recording medium) 15, the wobble signal obtained from the meandering of the track for controlling the rotational speed of the medium may be superimposed and become noise, so the component is also removed.
Note that in a system that supports high speed, a light pulse and an off pulse also appear remarkably in the reflected signal, and therefore a filter characteristic that removes components higher than the cell frequency is desirable. That is, a low-pass filter that cuts over the wobble frequency that is the lowest frequency is desirable. Further, GC circuits 18 and 19 are provided after the outputs of the filters 16 and 17, respectively, and gain correction is performed so that the amplitude of the servo signal is appropriate.
In this way, because the high frequency component of the wobble signal or cell frequency component is removed, servo signal deterioration due to laser emission of multi-value information recording with a short effective signal period is suppressed, and high-quality servo signal detection is performed. Can be done.
[0027]
Next, a second multi-value recording servo signal detection process according to claim 2 of the present invention will be described.
FIG. 5 is a block diagram showing a circuit configuration for executing a second multi-value recording servo signal detection process according to claim 2 of the present invention.
In the circuit configuration for executing the second multi-value recording servo signal detection process, a certain level of servo signal quality can be obtained with a simple circuit configuration.
In general, in order to record high-quality multi-value information, laser light emission intensity is optimized by performing test writing or the like before recording user data. Therefore, the optimum gain of the wobble signal may be changed if the light intensity of the laser beam changes.
[0028]
The circuit configuration for executing the second multi-value recording servo signal detection process includes a laser drive circuit 7 and a wobble detection circuit 12 shown in FIG. 1, a filter 20 and a gain control (GC) circuit 21 as shown in FIG. To.
In the GC circuit 21, a laser drive circuit 7, a CPU 30, a D / A converter 31, and a VCA 32 are provided.
That is, the GC circuit 21 shown in FIG. 5 applies at least the light intensity of the bias pulse and the space as a gain applied to the signal obtained by removing the high frequency component of the wobble signal or cell frequency component from the source servo signal. The servo signal is extracted using the set value calculated based on the light intensity of the pulse.
[0029]
In this circuit, the light intensity of laser emission is managed by the CPU 30, and an optimum value is set in the laser drive circuit 7. Alternatively, the current light intensity setting can be read from the laser driving circuit 7.
The CPU 30 calculates an average laser emission amount obtained by virtually smoothing the light intensity modulation component based on the light intensity setting, and sets an appropriate value to the D / A converter 31 to determine the gain of the VCA 32.
The VCA 32 has a gain that changes according to the output voltage value of the D / A converter 31. The average laser light emission amount can be obtained from the width of each pulse managed by the CPU 30, the light intensity, and the occurrence frequency of multi-value information.
In this way, since the gain is changed and optimized with respect to the recording light intensity that is sequentially changed for the purpose of ensuring recording quality with a simple circuit configuration, proper servo signal detection can be performed.
[0030]
Next, a third multi-value recording servo signal detection process according to claim 3 of the present invention will be described.
FIG. 6 is a block diagram showing a circuit configuration for executing a third multi-value recording servo signal detection process according to claim 3 of the present invention.
In the circuit configuration for executing the third multi-value recording servo signal detection process, stable servo signal detection is performed in conjunction with the average change in the reflected signal (sum signal) during recording.
The sum signal changes at a low frequency due to variations in reflectance within the surface of the medium and within the circumference and fluctuations in the intensity of the laser beam (lower than the modulation component of each pulse). Furthermore, it varies depending on the continuity of the multi-value information. These wide band fluctuations also affect the servo signal as gain fluctuations.
[0031]
Therefore, this is avoided by a circuit that executes the servo signal detection process of the third multi-value recording.
In the circuit configuration for executing the third multi-value recording servo signal detection process, the wobble detection circuit 12 shown in FIG. 1 is replaced with a filter 20 and a gain control (GC) circuit 21 as shown in FIG.
In the GC circuit 21, a VCA 40, a filter 41, a VCA 42, an amplitude detection circuit 43, and a comparator 44 are provided.
That is, the GC circuit 21 shown in FIG. 6 uses the same gain as the gain for maintaining the sum signal level from which the high-frequency component is removed at a preset target voltage, from the source servo signal to the high frequency of the wobble signal or cell frequency component. It functions to extract the servo signal by amplifying or attenuating the signal from which the frequency component has been removed.
[0032]
In this circuit, a high frequency component is removed from the sum signal by a filter 41, and an output signal from the filter 41 is amplified or attenuated by a voltage gain control amplifier (VCA). The amplitude detection circuit 43 measures the amplitude of the output signal from the VCA 42, compares it with a target voltage signal set in advance by the comparator 44, outputs a voltage corresponding to the difference, and changes the gain of the VCA 42.
By this loop, the gain of the VCA 42 is controlled so that the output signal amplitude of the VCA 42 becomes the target voltage. On the other hand, high frequency components (high frequency components) such as cell frequency components and wobble signals (wobble frequency components) are removed from the source servo signal by the filter 20 and amplified or attenuated by the VCA 40. The gain of the VCA 40 is the same as that of the VCA 42.
In this way, the gain is sequentially changed and optimized for fluctuations in laser light emission intensity and fluctuations in the media's peripheral reflectance during recording of multi-valued recording information with periodicity. Can be done.
[0033]
Next, fourth servo signal detection processing for multi-value recording according to claim 4 of the present invention will be described.
FIG. 7 is a block diagram showing a circuit configuration for executing a fourth multi-value recording servo signal detection process according to claim 4 of the present invention, and the same reference numerals are given to portions common to FIG.
The circuit configuration for executing the servo signal detection processing for the fourth multi-value recording is similar to the circuit for executing the servo signal detection processing for the third multi-value recording, but as shown in FIG. A sample hold (S / H) circuit 45 is newly provided before the filter 41, and the sample signal sampled during the bias pulse or space pulse period is used as the reference signal instead of the average of the sum signal.
[0034]
That is, the GC circuit 21 shown in FIG. 7 has the same gain as the gain for maintaining the sum signal level acquired during the laser emission period with the bias pulse or the laser emission period with the space pulse at a preset target voltage. The servo signal is extracted by amplifying or attenuating a signal obtained by removing the high frequency component of the wobble signal or cell frequency component from the source servo signal.
Since the circuit configuration for executing the servo signal detection processing for the fourth multi-value recording is largely the same as the circuit configuration for executing the servo signal detection processing for the third multi-value recording, the S of the different portions Only the signal input to the / H circuit 45 and the filter 41 will be described.
[0035]
As described above, the sum signal includes fluctuations related to the continuity of the multilevel information. For example, when the multi-value information of 10 consecutive cells is “0, 0, 0, 0, 0, 4, 4, 4, 4, 4”, the sum signal has a frequency component that is 1/10 of the cell frequency. There are fluctuations. Ideally, in consideration of frequency separation, the modulation rule should be limited at the stage of multi-level modulation so as to avoid the fluctuation of the sum signal near the servo signal frequency. The limitation of the modulation rule is to eliminate the use of a specific pattern after adding redundant bits (redundant bits) to increase the amount of information.
That is, since the recording density is lowered, the merit of increasing the density of the multi-value recording method is reduced. In addition, in the case of multilevel recording, unlike binary recording, complete frequency separation due to modulation rule restrictions is difficult.
[0036]
For example, in the case of “0, 1, 0, 1, 0, 7, 6, 7, 6, 7”, the multi-value information is not continuous, but it looks like the pattern of “0” and “4”. The frequency component of 1/10 of the cell frequency exists in the same manner as described above. To completely eliminate a desired frequency component, a large number of redundant bits are added, and many combinations (patterns) are eliminated.
Actually, the sum signal fluctuation of the servo band cannot be completely removed, and it is expected to remain.
When fluctuations close to the servo band are superimposed on the sum signal, it is conceivable that gain correction of the servo signal using the VCA 40 adversely affects depending on the control loop band (phase delay) centered on the VCA 42.
[0037]
For example, it is assumed that the sum signal and the servo signal have a variation of 1/10 of the cell frequency. Assuming that the phase delay of the control loop centered on the VCA 42 is 1/5 of the cell frequency, the gain correction of the VCA 42 and VCA 40 is out of phase with the input, and the output is output when the amplitude of the input sum signal or servo signal is large. It is amplified and attenuated when the amplitude is small.
Actually, since the high-frequency component is removed by the filter 41, it does not become as remarkable as this example, but the same thing can occur even at a frequency lower than the wobble frequency.
[0038]
In order not to follow the change of the sum signal due to the continuation of such multi-value information, the sum signal of the bias pulse or the space pulse period is acquired (sampled) by the S / H circuit 45. The sampling may be limited to the recording timing of specific multilevel information in order to improve signal quality.
For example, since the space pulse is long when recording at level “0” and the bias pulse is long when recording at level “7”, the sampling error affected by the “round” of the signal is reduced.
Sampling noise is also removed from the output signal of the S / H circuit 45 by a filter 41 that removes high frequency components in the same manner as described above.
In this way, since the gain is sequentially changed and optimized with respect to fluctuations in the reflectance of the medium within the circumference, proper servo signal detection can always be performed.
[0039]
Next, a fifth multi-value recording servo signal detection process according to claim 5 of the present invention will be described.
FIG. 8 is a block diagram showing a circuit configuration for executing a fifth multi-value recording servo signal detection process according to claim 5 of the present invention.
In the circuit configuration for executing the fifth multi-value recording servo signal detection process, the source servo signals in the bias pulse period and the space pulse period are obtained by sampling, and the two signals are combined to obtain a wobble signal.
The circuit configuration for executing the fifth multi-value recording servo signal detection process is the same as the wobble detection circuit 12 shown in FIG. 1 except that the filter 20, the sample circuits 50 and 51, and the gain control (GC) as shown in FIG. An a circuit 52, a gain control (GC) b circuit 53, and an adder 54 are provided.
[0040]
That is, the signal shown in FIG. 8 is obtained by applying a specific gain to the signal obtained by removing the wobble signal or the high frequency component of the cell frequency component from the source servo signal acquired only during the laser emission period with the bias pulse. And the function of extracting the servo signal by synthesizing the wobble signal or the signal obtained by removing the high frequency component of the cell frequency component from the source servo signal acquired only during the laser emission period with the space pulse.
[0041]
In this circuit, the wobble signal or the high frequency component of the cell frequency component is removed from the source servo signal by the filter 20, and only the bias signal in the bias pulse period and the space signal in the space pulse period are acquired by the sample circuits 50 and 51, respectively. . A sampling signal (including all other sample signals in this embodiment) represented as a bias signal and a space signal may be a bias pulse or a space pulse itself, or the timing may be shifted or the width may be changed in order to wait for the stability of the source servo signal. You may process it.
A signal sampled at each timing is amplified or attenuated by a GCa circuit 52 and a GCb circuit 53 capable of changing the gain, and then synthesized by an adder 54 to extract a servo signal.
[0042]
The purpose of providing the GCa circuit 52 and the GCb circuit 53 is to correct the gain difference between the servo signal component acquired during the bias pulse period and the servo signal component acquired during the space pulse period. In the circuit that executes the wobble signal detection process, only the GCa circuit 52 is changed to eliminate the signal difference therebetween. Therefore, the GCb circuit 53 may be omitted.
The gain changing method of the GCa circuit 52 may be a circuit configuration of the D / A converter and the VCA used in the circuit for executing the above-described second multi-value recording wobble signal detection process, or a plurality of resistance values. Either of the configurations may be adopted.
Further, the same function can be obtained even if all the adders of this embodiment are changed to selectors. Although the sample circuits 50 and 51 are used in the subsequent stage of the filter 20 in FIG. 8, this order may be reversed. In that case, one more filter circuit is required.
In this way, the bias pulse period with a low light intensity and a small wobble signal component is amplified in the same way as the signal level of the space pulse period. Quality servo signal can be detected.
[0043]
Next, a sixth multi-value recording servo signal detection process according to claim 6 of the present invention will be described.
In the circuit configuration for executing the sixth multi-value recording servo signal detection process, the servo signal component is also amplified or attenuated by a gain that keeps the sum signal level obtained by sampling in each of the bias pulse period and the space pulse period constant. .
The circuit configuration for executing the sixth multi-value recording servo signal detection process is the same as the circuit for executing the fifth multi-value recording wobble signal detection process shown in FIG. The internal configuration is the same as that of the GC circuit 21 shown in FIG.
[0044]
That is, the source acquired by the circuit only during the laser emission period with the bias pulse with the same gain as the gain for maintaining the sum signal level acquired during the laser emission period with the bias pulse at a preset target voltage. A signal that amplifies or attenuates a signal obtained by removing the high frequency component of the wobble signal or cell frequency component from the servo signal, and a gain that keeps the sum signal level acquired during the laser emission period in the space pulse at a preset target voltage. The servo signal is extracted by synthesizing the wobble signal or the signal obtained by removing the high frequency component of the cell frequency component from the source servo signal acquired only during the laser emission period with the space pulse with the same gain as the above.
[0045]
In the circuit configuration for executing the sixth multi-value recording servo signal detection process, the sample timing is set to the bias pulse period in the GCa circuit 52 and the space pulse period in the GCb circuit 53. The sample signal indicating the sample timing may be either a pulse itself or a processed signal as described above. Each target voltage is made equal.
In this way, the wobble signal component with low light intensity is optimized by sequentially changing the gain with respect to fluctuations in the laser emission intensity during recording of multi-valued recording information with periodicity and fluctuations in the reflectance of the medium within the circumference. Since the signal component of the low-power bias pulse period is effectively used by amplifying the same bias pulse period as the signal level of the space pulse period, a proper and high-quality servo signal can always be detected.
[0046]
Next, a seventh multi-value recording servo signal detection process according to claim 7 of the present invention will be described.
FIG. 9 is a block diagram showing a circuit configuration for executing a seventh multi-value recording servo signal detection process according to claim 7 of the present invention, and parts common to FIG. 8 are given the same reference numerals. .
The circuit configuration for executing the seventh multi-value recording servo signal detection processing is a circuit configuration in which the internal configuration of the GCa circuit 52 of the circuit for executing the fifth multi-value recording servo signal detection processing shown in FIG. 8 is changed. The difference is that the sum signal level acquired during the space pulse period is used as the target voltage signal of the GCa circuit 52.
[0047]
That is, the circuit shown in FIG. 9 has the same gain as that for maintaining the sum signal level acquired during the laser emission period with the bias pulse at the sum signal level acquired during the laser emission period with the space pulse. A signal obtained by amplifying or attenuating a signal obtained by removing the high frequency component of the wobble signal or cell frequency component from the source servo signal acquired only in the laser emission period, and the source servo acquired only in the laser emission period in the space pulse. The servo signal is extracted by synthesizing the wobble signal or the signal obtained by removing the high frequency component of the cell frequency component from the signal.
[0048]
In this circuit, the servo signal detection during the bias pulse period is the same as the circuit for executing the above-described sixth multi-value recording servo signal detection process, but the target voltage signal of the GCa circuit 52 is generated as follows.
A sum signal is acquired at the timing of the space signal indicating the space pulse period by the S / H circuit 60, and the target voltage signal is obtained by performing smoothing to remove high frequency components from the sum signal by the filter 62, and the target voltage is obtained. The signal is sent to the comparator 66.
[0049]
The S / H circuit 61 acquires (samples) a sum signal at the timing of the bias signal in the bias pulse period, removes the frequency component of the signal by the filter 63, and converts the output signal from the filter 63 into a voltage gain control amplifier ( VCA) 65 amplifies or attenuates. The amplitude detection circuit 64 measures the amplitude of the output signal from the VCA 65, compares it with the target voltage signal by the comparator 66, outputs a voltage corresponding to the difference, and changes the gain of the VCA 67.
Therefore, the GCb circuit 53 that determines the gain of the servo signal in the space pulse period may be a fixed gain and can be omitted, and the circuit scale can be reduced.
[0050]
In this way, the servo signal component with low light intensity is optimized by sequentially changing the gain with respect to fluctuations in the laser emission intensity during recording of periodic multi-level recording information, fluctuations in the media's internal reflectance, etc. A small bias pulse period is amplified to the same level as the signal level of the space pulse period, and the circuit scale for always detecting a proper and high-quality servo signal by effectively using the signal component of the low output bias pulse period is reduced. can do.
[0051]
Next, an eighth multi-value recording servo signal detection process according to claim 8 of the present invention will be explained.
FIG. 10 is a block diagram showing a circuit configuration for executing the eighth multi-value recording servo signal detection process according to claim 8 of the present invention.
FIG. 11 is an explanatory diagram for explaining a servo signal detection process of the eighth multi-value recording by the circuit shown in FIG.
[0052]
In the circuit configuration for executing the eighth multi-value recording servo signal detection process, the phase characteristic obtained in the closed loop for controlling the position of the laser beam on the medium is taken into consideration, and the subsequent stage of the wobble detection circuit 12 is shown in FIG. Such a phase compensation circuit 70 is provided, and phase compensation is performed on the servo signal obtained by any one of the first to seventh multi-value recording servo signal detection processes.
[0053]
That is, the phase compensation circuit 70 has a function of performing phase compensation on the servo signal obtained by any one of the first to seventh servo signal detection processes for multilevel recording.
In laser beam position control, the setting of the crossing frequency (the frequency at which the closed-loop gain characteristic becomes 0 dB) cannot be set too high due to the limitations of the mechanical system.
Here, as shown in FIG. 11A, the simplest gain characteristic at the crossover frequency ω1 is a line indicated by [a]. On the other hand, since the tracking accuracy to the low frequency fluctuation such as the media rotation component is required from the point of control accuracy, the gain characteristic of the closed loop requires a high gain in the low frequency. A simple gain characteristic satisfying this is a line indicated by [b], but in this case, the crossing frequency is as high as ω2, which is outside the constraints of the mechanical system.
[0054]
In such a case, the phase compensation circuit 70 is used. As shown in FIG. 11B, the single characteristic of the phase compensation circuit 70 changes the gain only in the Δω band. At this time, the phase is delayed around that band, but otherwise no delay occurs.
By passing through such a phase compensation circuit 70, the crossing frequency can be suppressed to ω1 while ensuring a high gain in a low frequency range. Although a phase delay circuit is shown here as the phase compensation circuit 70, a phase advance circuit may be used for the purpose of ensuring a phase margin near the crossover frequency.
Since the servo signal is phase-compensated in order to control the position of the laser beam on the medium in this way, servo signal characteristics satisfying both the constraints of the mechanical system and the control accuracy can be obtained.
[0055]
Further, the multi-value information is recorded on the optical disk 15 by the optical disk device described above, and the multi-value information recorded on the optical disk 15 is reproduced, so that the recording / reproducing system can be stabilized.
[0056]
【The invention's effect】
As described above, according to the multi-value recording servo signal detection method and optical information recording / reproducing apparatus of the present invention, it is suitable for recording multi-value information using a write pulse, an off pulse, a space pulse, and a bias pulse. The servo signal can be detected.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an optical disc apparatus according to an embodiment of the present invention.
FIG. 2 is a diagram for explaining the outline of multi-value recording on the optical disc 15 shown in FIG. 1;
FIG. 3 is a block diagram showing a circuit configuration for executing a first multi-value recording servo signal detection process according to claim 1 of the present invention;
4 is an explanatory diagram for explaining servo signal detection processing of first multi-value recording by the circuit shown in FIG. 3; FIG.
FIG. 5 is a block diagram showing a circuit configuration for executing a second multi-value recording servo signal detection process according to claim 2 of the present invention;
FIG. 6 is a block diagram showing a circuit configuration for executing third multi-value recording servo signal detection processing according to claim 3 of the present invention;
FIG. 7 is a block diagram showing a circuit configuration for executing a fourth multi-value recording servo signal detection process according to claim 4 of the present invention;
FIG. 8 is a block diagram showing a circuit configuration for executing a fifth multi-value recording servo signal detection process according to claim 5 of the present invention;
FIG. 9 is a block diagram showing a circuit configuration for executing a seventh multi-value recording servo signal detection process according to claim 7 of the present invention;
FIG. 10 is a block diagram showing a circuit configuration for executing an eighth multi-value recording servo signal detection process according to claim 8 of the present invention;
FIG. 11 is an explanatory diagram for explaining a servo signal detection process for eighth multi-value recording by the circuit shown in FIG. 10;
[Explanation of symbols]
1: Optical pickup 2: Laser light source
3: Objective lens 4: Actuator
5: Light receiving element 6: Motor drive circuit
7: Laser drive circuit 8: Laser drive unit
9: Strategy generator 10, 10a to 10d: I / V circuit
11: RF detection circuit 12: Wobble detection circuit
13: Servo detection circuit
14: Motor 15: Optical disk
16, 17, 20, 41, 62, 63: Filter
18, 19, 21: GC circuit
30: CPU 31: D / A converter
32, 40, 42, 65, 67: VCA
43 and 64: amplitude detection circuit
44, 66: Comparator 45, 60, 61: S / H circuit
50, 51: Sample circuit
52: GCa circuit 53: GCb circuit
54: Adder 70: Phase compensation circuit

Claims (9)

When forming recording marks of different sizes according to information to be recorded on cells equally divided in a specific area on an optical information recording medium, a write pulse set to a predetermined high light intensity and a predetermined low Off-pulse set to light intensity, space-pulse set smaller than light pulse that can form a space and larger than the off-pulse, and light intensity smaller than the space pulse and larger than the off-pulse. And a servo signal detection method for multi-value recording that records using laser light emission composed of a bias pulse output following the off-pulse,
A servo signal detection method for multilevel recording, wherein a servo signal is extracted by removing a high frequency component of a wobble signal or a cell frequency component from a source servo signal detected from the optical information recording medium. As a gain to be applied to a signal obtained by removing a high frequency component of a wobble signal or a cell frequency component from the source servo signal, a setting value calculated based on at least the light intensity of the bias pulse and the light intensity of the space pulse 2. The servo signal detection method for multi-value recording according to claim 1, wherein the servo signal is extracted using the servo signal. Amplifies or attenuates the signal obtained by removing the high frequency component of the wobble signal or cell frequency component from the source servo signal with the same gain as the gain for maintaining the sum signal level from which the high frequency component is removed at a preset target voltage. 2. The servo signal detection method for multi-value recording according to claim 1, wherein a servo signal is extracted. A high wobble signal or cell frequency component from the source servo signal with the same gain as the gain for maintaining the sum signal level acquired during the laser emission period with the bias pulse or the laser emission period with the space pulse at a preset target voltage. 2. The servo signal detection method for multi-level recording according to claim 1, wherein the servo signal is extracted by amplifying or attenuating the signal from which the frequency component has been removed. A signal obtained by applying a specific gain to a signal obtained by removing a high frequency component of a wobble signal or a cell frequency component from the source servo signal acquired only in the laser emission period with the bias pulse, and a laser emission period with the space pulse 2. A servo signal for multi-level recording according to claim 1, wherein a servo signal is extracted by synthesizing a wobble signal or a signal obtained by removing a high frequency component of a cell frequency component from the source servo signal acquired only by Detection method. The wobble signal or cell frequency from the source servo signal acquired only during the laser emission period with the bias pulse with the same gain as the gain for maintaining the sum signal level acquired during the laser emission period with the bias pulse at a preset target voltage. A signal obtained by amplifying or attenuating a signal obtained by removing the high frequency component of the component, and the space pulse with the same gain as the gain for maintaining the sum signal level acquired during the laser emission period in the space pulse at a preset target voltage. A servo signal is extracted by synthesizing a signal obtained by amplifying or attenuating a signal obtained by removing a high frequency component of a wobble signal or a cell frequency component from the source servo signal acquired only during the laser emission period of Item 4. The servo signal detection method for multilevel recording according to Item 1. The source acquired only during the laser emission period with the bias pulse with the same gain as the gain for maintaining the sum signal level acquired during the laser emission period with the bias pulse at the sum signal level acquired during the laser emission period with the space pulse. A signal obtained by amplifying or attenuating a signal obtained by removing the high frequency component of the wobble signal or the cell frequency component from the servo signal, and the wobble signal or the cell frequency component from the source servo signal acquired only during the laser emission period with the space pulse. 2. The servo signal detection method for multi-level recording according to claim 1, wherein the servo signal is extracted by synthesizing the signal from which the high frequency component has been removed. 8. The servo signal detection method for multilevel recording according to claim 1, wherein phase compensation is performed on the servo signal. Recording or reproducing information by deciding the position of the laser beam irradiated on the optical information recording medium based on the servo signal detected by the servo signal detection method for multi-level recording according to any one of claims 1 to 8. An optical information recording / reproducing apparatus characterized by comprising:

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