JP2903782B2 - Optical spot position control method and optical recording / reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tracking method for an optical disk file device, and more particularly to a method effective for stabilizing the tracking characteristics of a perforated optical disk device and an optical recording / reproducing device.

[0002]

2. Description of the Related Art Accurate control of the position of a light spot for recording and reproduction on a disk is very important for high density and high reliability of an optical disk file device. As a tracking method in an optical disc device, a continuous track guide groove is scanned by one beam, a diffracted light from the guide groove is received by a two-segment type photodetector, and an actuator is operated so that the difference between the two becomes zero. A driving method is known. This method is called a push-pull method. In a compact disk device that is a read-only optical disk, a tracking method using three beams is used. This method arranges sub-beams before and after the main beam for data reproduction by displacing them in opposite directions with respect to the data track, and prevents the difference in reflected light amount between the data pit portion and the no-data portion. In this method, reflected light from each of the two sub-beams is received, and the actuator is driven so that the difference between the two beams becomes zero.
Similar to the tracking control, in principle, with respect to the follow-up of the vertical vibration of the disk, that is, the automatic focus control, a method is generally used in which control is performed so that the difference between the amounts of light received by a plurality of photodetectors becomes zero.

In order to accurately control the position of the spot as described above, the influence of the data pattern in various operation modes, for example, a recording mode and a reproduction mode, is minimized as much as possible, and furthermore, it occurs in a circuit system and a mechanical system. It is necessary to reduce the deviation (offset). In particular, a recording medium having a large change in the disk reflectance due to the presence or absence of pits is advantageous from the viewpoint of data reproduction because a large S / N ratio can be obtained, but disadvantageous in tracking control and automatic focus control due to a large gain fluctuation. It may be. Basically, the tracking control and the automatic focus control can be similarly discussed as a servo system. Therefore, here, the prior art will be described using the tracking control as an example.

[0004] With respect to gain fluctuations caused by differences in operation modes, a method of uniformly changing the gain of the amplifier system in the recording mode and the reproduction mode so that the amplifier system is not saturated even when recording light is irradiated. Has been adopted. As a light spot position control means described in Japanese Patent Application Laid-Open No. 52-80802, a method of switching the gain of a control circuit between reproduction and recording has been proposed.

[0005] As a method of reducing the gain fluctuation,
In the method described in Japanese Patent Application Laid-Open No. 54-115883, the level on the unrecorded side is always held by using the peak hold during reproduction and the bottom hold during recording.
The gain is stabilized.

[0006] With respect to gain fluctuation caused by a difference in data pattern, a method of setting a servo system gain for a random pattern and operating within a dynamic range of an amplifier system is generally adopted. I have.

As for the offset generated in the circuit system and the mechanical system, measures such as adoption of an amplifier with low offset and low drift, and adjustment of the offset to zero at the time of manufacturing the device have been adopted.

[0008]

With the conventional tracking control method, it has been difficult to eliminate the effects of gain fluctuations over a wide range and changes in the physical properties of the recording film during recording. In particular, when pit edge recording is applied to a perforated recording medium, in addition to gain fluctuation due to a difference in operation mode, gain fluctuation due to sparse and dense data patterns is large. Furthermore,
Variations in the distribution of diffracted light from the track guide grooves when the recording film is in the process of melting have a large effect, making it difficult to keep track offset small. This effect is particularly remarkable in the case of a data pattern in which the longest pit and the shortest gap are alternately repeated in the applied modulation method. When a peak hold is used during reproduction and a bottom hold is used during recording, it is necessary to switch between operation modes, and the circuit configuration becomes complicated.

The problem to be solved by the present invention is to propose a method for reducing the influence of a long hole recording which is susceptible to gain fluctuation and offset. In the present invention, a case where a pit edge recording method is used as a target for a perforated recording film is described as an example, but it is a method that can be widely applied to other recording films and recording methods.

[0010]

In order to perform stable light spot position control even during recording, an error signal is generated and controlled based on the peak value (high level side) of the reflected light level of the recording light pulse. The method is effective.

As means for solving the problem, a resistance value for converting a detection current into a voltage at the time of irradiating the reproduction light and at the time of irradiating the recording light by utilizing a nonlinear current-voltage characteristic of a diode in a tracking amplifier system. A circuit to make it variable, a peak hold circuit to recover a decrease in gain at the time of reproduction, and to hold the peak level of reflected light at the time of long hole recording, and a reflected light at the time of delete light irradiation at the time of delete and before and after the delete light irradiation By using a delete mask circuit for preventing a signal from being seen, stable tracking control with little gain change and offset can be realized.

In the current-voltage conversion resistance variable circuit using a diode, the gain is automatically selected depending on the magnitude of the detected current, as compared with a method in which the gain is uniformly changed for each reproduction or recording mode. Is unnecessary, and the gain does not decrease even during the non-irradiation period of the recording pulse light in the recording mode, that is, during the reproduction light irradiation period.
Further, the gain at the time of irradiation of the reproduction light can be large, so that the allowable value of the offset of the circuit system can be increased, and the gain at the time of irradiation of the recording light can be reduced, so that the saturation of the circuit system can be avoided.

[0013]

In the current-voltage conversion variable circuit using a diode, the value of the conversion gain resistance can be set large in the reproduction light irradiation range where the irradiation power is low, so that the allowable value of the circuit offset of the amplifier system can be expanded. In addition, since the value of the conversion gain resistance can be automatically reduced in the recording light irradiation range where the irradiation power is high, saturation of the amplifier system can be prevented. In addition, in the method in which the gain is switched uniformly between the reproduction mode and the recording mode, the level during the reproduction light irradiation period in which the recording pulse light is not irradiated in the recording mode is extremely reduced. However, such a problem does not occur because the gain changes depending on the magnitude of the detected current.

The peak hold circuit can suppress a decrease in gain at a position where a pit exists during reproduction by maintaining the level of a gap portion (unrecorded portion) between the pits. In the case of a perforated recording film, the distribution of diffracted light from the guide groove tends to be biased in the process of melting and breaking the recording film. For this reason, the influence on the track offset can be reduced by maintaining and using the reflected light level in the bulging process in which the recording film has not yet entered the breaking process.

The delete operation is an operation of overwriting a certain pattern (delete pattern) on an unrecorded portion or a recorded portion to invalidate the recorded data. Therefore, this is a function unique to the write-once optical disc. As described above, since the reflected light signal fluctuates according to the data pattern already recorded, and the servo operation needs to be performed in the reproduction mode, the delete pulse is irradiated from the disk before and after irradiation with the delete pulse light. It is desirable not to see the reflected light. The delete mask has a function of holding the signal level immediately before the delete mask for the period. Thus, it is possible to prevent an increase in the track offset and to stabilize the servo gain.

[0016]

Embodiments of the present invention will be described below. FIG. 1 is a configuration diagram of an example of the tracking circuit of the present invention.
In the tracking by the push-pull method, the diffraction light distribution from the disk guide groove is received by the split-type photodetector, and the actuator for tracking is operated so that the amount of light received by each photodetector is equal, The light spot is always located on or between the guide grooves. 3
Basically, the same operation as the push-pull method is performed in the tracking by the spot method. That is, reflected light from each of the two sub-beams positioned before and after the main beam is received by the photodetector, and control is performed so that the respective light amounts become equal. In FIG. 1, TR-A and TR-B are two series of tracking signals for which the amounts of received light should be equal. For convenience of explanation, the operation of this circuit will be described for a signal sequence on the TR-A side. The reflected light from the disk received by the photodetector 101 is converted into a current here. Generally, a PIN-type photodiode is used as a photodetector, and a current proportional to the amount of light is generated. This detection current is
At 03, it is converted to a voltage. Here, the resistor 105 is a current-voltage conversion resistor in the reproduction mode, and the resistor 107 is a current-voltage conversion resistor connected in parallel with the resistor 105 in the recording mode. The diode 109 is for controlling the value of the current-voltage conversion resistor by using a so-called non-linear characteristic of a diode in which a forward voltage changes according to the magnitude of a forward current. About this nonlinear characteristic,
It will be described later.

The transistor 111 constitutes a diode for determining the charging direction of the peak hold circuit.
Here, the transistor 140 is for adding an offset to the reference voltage of the amplifier 103 and the amplifier 104 in advance in order to cancel the potential difference between the emitter and the base in the transistor 111 and the transistor 112. Therefore, it is necessary to ensure uniformity of the temperature characteristics by using a pair having a good pair characteristic and by bringing the pair closer to each other in mounting. Similarly, the diodes 109 and 110 are TR-A
It is necessary to use a pair having good pair characteristics for the side and the TR-B side to minimize the offset generated in the circuit system. The resistor 113 and the capacitor 115 are elements for determining a time constant for peak hold. Normally, when an operational amplifier is used as the amplifier 103, the output impedance can be extremely small (several ohms). Further, the amplifier 117 has an effect of making the input impedance extremely large, whereby the time constant of the hold can be substantially determined by the product of the resistor 113 and the capacitor 115. The charging time constant is determined by the product of the conduction resistance of the transistor 111 and the capacitor 115. For example,
When the conduction resistance of the transistor is 10Ω and the capacitance of the capacitor is 1000 pF, the charging time constant is 10 ns. On the other hand, the discharge order constant is determined by the resistance 113 and the capacitor 11
Determined by the product of five. For example, when the resistance value is 1 kΩ and the capacitance of the capacitor is 1000 pF, the discharge time constant is 1
μs. The output of the amplifier 117 is input to the amplifier 119 and amplified to an appropriate level. FIG. 1 shows an example of an inverting amplifier using an operational amplifier, but a non-inverting amplifier may be used depending on the polarity of a signal.

When recording the delete pattern, the analog switch 121 opens the switch for a certain period including the irradiation period of the recording light of the delete pattern, thereby controlling the influence of the reflected light of the delete light in the period. It is to avoid feeling. In other words, it is unclear what pattern has been recorded by the time of the delete operation, and the level of the reflected light when the delete pulse is irradiated varies depending on the recorded pattern. In order to suppress this, the detection signal of the delete period is not used. In the following description, this period will be referred to as a delete mask period. The analog switch is opened by the control signal 123 during the delete mask period, and is short-circuited during other periods. The signal level immediately before the delete mask is held by a hold circuit including a resistor 125 and a capacitor 127. Amplifier 12
Reference numeral 9 denotes a voltage follower, which receives a signal with a high input impedance to change the time constant by the resistor 125 and the capacitor 127.
Is to be determined by Thus, the charging time constant is determined substantially by the product of the resistor 125 and the capacitor 127, and the discharging time constant is determined by the product of the input impedance of the amplifier 129 and the capacitor 127.

The delete means an operation of invalidating the information of the sector by overwriting the pattern in a certain cycle while an unrecorded portion or some data pattern is already recorded in the form of pits. That is. As conditions for the delete pattern, after the delete is performed, the sector is always determined to be the deleted sector (no undetection occurs), and the original data string cannot be restored even by the error correction code of the data. And a pattern that does not affect the servo characteristics. In the case where the leading end and the trailing end of a pit are respectively made to correspond to data "1" by using a pit edge recording method by 2-7 modulation, a delete mark longer than the longest pattern (4T) existing in the data pattern Is repeated in a cycle that cannot be corrected even by an error correction code. As a specific example, there is a pattern in which the delete mark length is 8T and this is repeated at a cycle of 64T. Here, T is a time interval of one bit of data.

At the subsequent stage of the circuit shown in FIG.
Amplifier for generating a difference signal between the signals of the two channels TR and TR-B, a phase compensation circuit for compensating the mechanical characteristics of the actuator, a driver circuit for driving the actuator, and a jump for a track jump A pulse application circuit and the like are added. Further, in order to suppress the influence of the variation in the reflectivity of the disk, the TR-A side and the TR-B
A method is conceivable in which a sum signal on the side is generated, and a gain control circuit for normalizing the level of the difference signal is provided based on the sum signal. For the purpose of the present invention, since a conventional circuit may be used after the circuit for generating the difference signal or the sum signal, a detailed description is omitted.

FIG. 2 shows the optical power and signal waveforms of TR-A and TR-B when a dense data pattern is recorded on the unrecorded disk recording film by the pit edge recording method.
FIG. 4 is a diagram showing a recording process of a perforated recording film. The pit edge recording method is a recording method in which the ends of the pits correspond to data, and is a method capable of achieving a higher density than a pit center recording method in which data is corresponded to the center of a round hole even with a light spot having the same resolution. In FIG. 2, considering the case where 2-7 modulation is used as the modulation method, the recording power irradiation period is the longest in terms of duty from 4T.
During the period of 1.5T, a pattern in which the recording light pulse is irradiated to the reproducing power is repeated. When the data 4T length itself is used for the recording pulse width, the duty becomes about 72%. Generally, the pit length formed by the recording pulse width is longer than the recording pulse width. Therefore, recording is performed by shortening the recording pulse width by a certain width. In the following description, such a dense data pattern will be referred to as a closest data pattern. In FIG.
When the recording pulse is irradiated, the signal waveforms of both channels reach the levels of A1 and B1, respectively. During this period, the recording film is in the process of swelling, and the recording film itself has not been broken yet. For this reason, since the reflectance of the recording film is almost the same as that in the unrecorded state, the reflected light level changes by the ratio of the reproducing power to the recording power. Further, this period does not depend much on the data pattern length, and this bulging process exists for almost the same time even with the recording pulse width shown in FIG. Further, in this period, the shape distortion due to the aberration of the light spot and the influence of the track offset hardly appear, so that the peak values A1 and B1
The difference is not so large. Next, when the recording film enters a period in which sufficient heat is applied, the recording film starts to be broken. This period is longer for a pattern having a longer recording pulse width. Also,
The pause period between recording pulses is in the state of reproducing power irradiation. During this reproduction period, there is no level change due to a change in the state of the recording film. During the melting period of the recording film, since the recording film is in a molten state, the level of reflected light in each channel tends to be different. This is because the diffracted light pattern from the track guide groove is easily disturbed. On the other hand, in the conventional tracking method, since processing is performed in a transmission system of a servo band of about several tens of kHz, the servo operation is performed at an average level including the area of the breaking process. Therefore, the area where the difference between the signal levels A2 and B2 in the breaking process is large is strongly affected. In particular, the influence is great in the densest data pattern as shown in FIG. From the above, it is desirable from the viewpoint of track offset reduction that tracking control be performed by relying on the reflected light level in the bulging process at the start of recording pulse irradiation as much as possible.
The peak hold is also a method of detecting and holding the level of the peak value so as to be less susceptible to the breaking process.

FIG. 3 is a diagram showing characteristics of a diode used in the nonlinear current-voltage conversion gain circuit of FIG. The forward voltage changes with respect to the forward current flowing through the diode. In FIG. 3, the resistances 105 and 106 are set to 10 kΩ and the resistance 1
The case where 07 and 108 are 1 kΩ is shown.
The region where the forward current is 40 μA or less is a region corresponding to the detection current of the reflected light in the reproduction light power irradiation, and since the diode is not in a conductive state yet, the value of the resistors 105 and 106 is the value of the current-voltage conversion resistor as it is. become. On the other hand, in the region corresponding to the detection current of the reflected light in the irradiation of the recording light power, about 2
A detection current of 00 μA or more is obtained, and the value of the current-voltage conversion resistor becomes the value of the parallel resistance of the resistors 105 and 107, that is, about 900Ω. In FIG. 3, the value of the current-voltage conversion resistance changes non-linearly between the reproducing light area and the recording light area. However, if the recording power is set to five times or more the reproducing power, this non-linear area will not cause any problem. As described above, the conversion gain variable circuit using the diode can achieve both the gain of the amplifier system in the reproduction light power region and the avoidance of the saturation of the amplifier system in the recording light power region. Since the gain in the reproduction light power region can be increased, the allowable value of the offset voltage of the circuit system in the subsequent stage can be increased. For example, considering that the gain of the first-stage amplifier does not saturate at the reflected light level at the time of recording pulse irradiation, 5
Assuming that the allowable value of the offset of the post-stage amplifier is 10 mV in the case of setting to double, if the gain of the first-stage amplifier can be increased by a factor of 10, the same tracking offset occurs when the offset of the post-stage amplifier is 20 mV. And the allowable offset value of the post-stage amplifier can be doubled.

FIG. 4 shows another embodiment for changing the value of the current-voltage conversion resistor in the reproducing mode and the recording mode. FIG. 4 shows only the first-stage amplifier on the TR-A side. The analog switch 401 is opened in the reproduction mode and short-circuited in the recording mode by the switch control signal 402. Therefore, in the reproduction mode, the value of the resistor 403 becomes the current-voltage conversion resistance value, and in the recording mode, the value of the parallel resistance of the resistor 403 and the resistance 404 becomes the value of the current-voltage conversion resistance. The switching of the gain in the reproduction mode and the recording mode in the circuit form of FIG. 4 is different from the operation of the gain switching shown in FIGS. In the gain switching by the diode shown in FIG. 3, the gain (the ratio of the output voltage to the detection current) automatically changes depending on the detection current regardless of the reproduction mode or the recording mode. On the other hand, when the gain is switched between the reproduction mode and the recording mode as shown in FIG. 4, the same gain is fixed during the pause period of the irradiation of the recording pulse light in the recording mode. Therefore, when the data pattern to be recorded is the densest data, the average detected current is relatively large. Conversely, the average detected current is small in the sparse data pattern in which the relationship between the pit length and the gap length is reversed from the densest data pattern. Becomes smaller. Thus, the influence of the change in the data pattern is more remarkable in the case of the circuit configuration of FIG. However, a circuit for selecting a resistor by a switch as shown in FIG. 4 is more stable with respect to a change in an external factor such as temperature. Is valid.

FIG. 5 is an example showing the relationship between the detected current and the output voltage in the reproduction mode and the recording mode. Here, the case where the resistance 403 is selected to be 10 kΩ and the resistance 404 is selected to be 1 kΩ is shown. Compared with FIG. 3, the relationship (slope) of the output voltage with respect to the detected current in each operation mode matches each other.

FIG. 6 is a diagram showing TR-A and TR-B signal waveforms when the current-voltage conversion gain resistance is fixed and when the current-voltage conversion gain resistance is nonlinearly varied by a diode. Here, the waveforms of TR-A and TR-B shown in FIG. 2 are shown as rectangular approximations. That is, in the period of about 100 ns immediately after the irradiation of the recording light pulse, the amount of reflected light is large because the recording film is in the process of swelling, and then, when the recording film enters the tearing process and melts, the reflected light level decreases in the swelling process. The level you have followed. Thereafter, when the power returns to the reproduction light power, the reflected light level also decreases correspondingly. In the case of (a) where the gain resistance is constant, the area of the recording light pulse irradiation period occupies a large proportion in one pattern period. Therefore, the recording film is particularly affected by the melting process. On the other hand, in the case of the variable gain resistance shown in FIG. 4B, the ratio of the area of the recording light pulse irradiation period to one cycle of the pattern decreases. The dotted line in FIG. 6 shows the waveform decay when the discharge time constant is set to 1 μs. The actual track offset amount is
It can be estimated by the area ratio between the waveforms of TR-A and TR-B. That is, the areas of the channel waveforms A and B in one cycle of a certain data pattern are Sa and S, respectively.
Assuming b, the track offset amount α is given by Equation 1.

[0026]

(Equation 1)

The conversion from α to the track offset distance Δ is obtained from Equation 2.

[0028]

(Equation 2)

In Equation 2, δ is a numerical value determined by the track interval, β is a numerical value determined by the light spot-track interval, the shape of the guide groove, and the like, and is experimentally obtained as a relative amount when an unrecorded state is set to 100%. It is a numerical value. For example, in the case of a guide groove having a track interval of 1.5 μm, a V-shaped width of about 0.4 μm, and a light spot diameter of about 1.4 μm, the value of β obtained from an experiment was about 50%. Using Equations 1 and 2 and FIG. 6, the results of trial calculation of the track offset for the case where the gain resistance is changed by the diode, the case where it is constant as in the past, and the case where peak hold is used and the case where it is not used are shown below. Show. In the following description, for the sake of convenience, a nonlinear current-voltage conversion
V and the peak hold circuit are abbreviated as PH.

In the conventional method (without NIV and without PH),
From FIG. 6, α = 23.4%, that is, ΔTR = 0.12
This results in a track offset of 2 μm. On the other hand, the hold time constant is set to 1 μs, Δ = 0.083 μm when there is no NIV and there is PH, and NI
In the case where V is present and PH is present, a calculation result has been obtained in which track offset can be suppressed to Δ = 0.033 μm. That is, the track offset can be suppressed to about 1/4 by using the NIV and the PH.

The non-linear gain resistance variable circuit using the diode or the peak hold circuit alone has a track offset suppressing effect at the time of recording. Since the nonlinear gain resistance variable circuit compresses the ratio of the reflected light level at the time of recording to the reflected light level at the time of reproduction, the influence of the melting period of the recording film, which is a main factor of track offset during recording, is reduced. It is thought to be.

The recording mode has been mainly described as the operation mode. Next, the delete mode will be described. FIG. 7 is a diagram showing a state in which the delete pattern is overwritten on the existing data. The meaning of the delete and an example of the pattern have been described above, and the description is omitted here. The upper part of FIG. 7 is a diagram showing the relationship of the optical power with respect to time. The width of the delete pulse is T _1. Before and after the delete pulse irradiation period, the signal level immediately before the mask signal is held by the delete mask signal (DELMASK-P), whereby tracking control is performed. Therefore, the period of T ₃ only, tracking control is performed using a reflected light level signal directly. In FIG. 7, the levels of TR-A and TR-B at the time of reproducing light irradiation are a and b, and the levels at the time of delete light irradiation are ka and lb. Also, the period of light emission at the delete pulse width, that is, the delete light power is T ₁ , the period from the end of the delete pulse to the end of the delete mask period is T ₂ , and the next delete mask from the end of the delete mask period the period up to the start of the period to T _3. The area of each of the TR-A and TR-B in the period T ₃ Sa, S
Assuming that b, they are described by Equations 3 and 4, respectively.

[0033]

(Equation 3)

[0034]

(Equation 4)

In the above equation, τ ₁ and τ ₂ are respectively TR-
It is the discharge time constant of the peak hold on the A side and TR-B side. By substituting Equations 3 and 4 into Equations 1 and 2, the track offset amount α or Δ can be calculated. FIG. 8 to FIG. 1 show calculation results when parameters are changed with respect to Equations 3 and 4.
0. Hereinafter, the relationship between each parameter and the track offset will be described based on the calculation results.

FIG. 8 is an example showing the relationship between the discharge time constant and the track offset under the following conditions.

(1) TR-A and TR-B during reproduction light irradiation
Are equal. That is, the discharge time constant of a = b (2) TR- A side and TR-B side is equal, further providing a time constant T ₂ criteria. That is, τ =
τ ₁ = τ ₂ = qT ₂ (3) The levels of TR-A and TR-B at the time of irradiating the delete pulse light are set to 10 times those at the time of irradiating the reproduction light. That is, (k
+ L) / 2 = 10 (4) The relationship between the levels on the TR-A side and the TR-B side based on the reproduction is different from each other by p times. That, k = pl (5) Delete unmasked period T ₃ is four times the period T ₂ of the from the end irradiated Delete pulsed light to delete the mask ended. That is, based on T ₃ = 4T ₂ and the bit period T, this corresponds to, for example, setting T ₃ = 44T and T ₂ = 11T.

The track offset α when the above conditions are used is shown in Expression 5.

[0039]

(Equation 5)

FIG. 8 shows the result of calculating the change in the track offset amount using the gain ratio p between TR-A and TR-B as a parameter with respect to the discharge time constant τ (= qT ₂ ). The smaller the gain ratio between the A side and the B side, that is, p =
The closer to 1, the smaller the track offset amount. Also, the smaller the discharge time constant is, the smaller the track offset amount is. However, if the discharge time constant is too small, the tracking gain becomes small especially when reproducing the densest data string, so that it is necessary to optimize between the delete time and the reproduction time. Changes in the gain at the time of reproduction with respect to the discharge time constant will be described with reference to FIGS.

FIG. 9 shows that the gain ratio p between the A side and the B side is 10%.
As if different, that take p = 1.1 as an example, the ratio of the period T ₂ of the from Delete unmasked period T ₃ and delete pulse irradiation until the end delete the mask end parameter,
It is a result of calculating a track offset amount with respect to a discharge time constant q. The results, for the same discharge time constant, the longer the track offset as compared to the non-mask period T ₃ is T ₂ are seen to be smaller.

FIG. 10 shows the result when (k + 1) / 2 = 2 in FIG. This corresponds to a case where the signal level during the irradiation of the delete pulse is suppressed due to the effect of the nonlinear conversion gain resistance circuit using the diode. As described above, if the detection level is lowered during irradiation with the delete pulse, the track offset amount can be reduced even for the same discharge time constant. For example, in FIG. 9, q = 1 and u =
In the case of 2, α = 3, but in FIG.
And u are reduced to α = 1.

9 and 10 were derived by the following equations.

[0044]

(Equation 6)

[0045]

(Equation 7)

In the above, the examination of the discharge time constant and the delete mask period in the delete mode has been described. In the delete mode and the recording mode, a track offset caused by various parameters has been an evaluation criterion. Here, a gain change in the reproduction mode, which is another evaluation criterion, will be described.

FIG. 11 is a diagram showing signal changes of TR-A and TR-B when a repeated portion of the densest data pattern is read. Holes (pits) for perforated recording film
Is generally smaller in reflectance than the unrecorded area,
The detected light level for the servo decreases. In particular, when a long hole pattern such as the pit edge recording method is used, the average amount of reflected light decreases, and becomes severest when the densest data pattern is repeated. In FIG. 11, a solid line indicates a signal change when the peak hold is not performed. In the figure, a rectangular approximation is used. A dotted line indicates a signal change when a peak hold of a certain discharge time constant is performed. By holding the level of the unrecorded portion during the period in which the pit is present by the peak hold, the influence of the presence or absence of the pit can be reduced, and the servo control can be made as if the unrecorded portion is being performed. FIG. 12 is a diagram illustrating the relationship between the time constant τ and the gain change γ. The derivation was performed by the following equation.

[0048]

(Equation 8)

Here, the time constant τ is expressed as a ratio based on the pit period T ₄ . That is, τ = wT ₄
And When considering the gain reduction may be a period corresponding to the longest pit length in the modulation scheme to be used with T _4. FIG. 12 shows that the discharge time constant may be set to infinity in order to eliminate the gain reduction. However,
Considering that the same discharge time constant is used at the time of recording or delete, it is necessary to select a time constant that can achieve both the recording mode and the delete mode. Further, when the discharge time constant is extremely large, it becomes impossible to follow the level fluctuation of the mixed data pattern, so that the unrecorded level may not be detected accurately. Therefore, a certain degree of gain reduction is expected, and a time constant is set in a range that follows such a change in the reproduction signal level. For example, based on the reproduction signal amplitude in the case of the repetition pattern of the longest pit and the longest gap allowed for the modulation method, the reproduction signal amplitude of the repetition gap portion of the densest data pattern decreases. If the amount of gain decrease is adjusted to this decrease, it is possible to follow and hold the signal level of the unrecorded portion even for a mixed data pattern. In FIG. 12, as an example, the gain change amount γ is set to −2 dB.
This shows a case in which prediction is made, and at this time, w = 2. Now, assuming that T ₄ = 4T and T ₂ = 11T, w
= 2 is q = 2 × 4T / 1 in FIGS. 8 to 10 described above.
This corresponds to 1T = 0.73. As a specific numerical example, the gain ratio between the A side and the B side is suppressed to within 10%, and T ₃
= 4T ₂ and (k + 1) / 2 = 2 by a non-linear conversion gain circuit using a diode, the track offset is 0.00 with respect to tracks at 1.5 μm intervals.
It can be suppressed within 3 μm.

[0050]

According to the present invention, it is possible to effectively suppress the influence of the gain fluctuation and offset of the spot position control signal during reproduction and during recording. In particular, by using the nonlinear effect of the forward current and voltage of a semiconductor such as a diode, it is not necessary to switch the gain between reproduction and recording. In the case of a perforated medium, the effect of offset can be reduced by performing servo control using the level of the head of reflected light in the recording process.

[Brief description of the drawings]

FIG. 1 is a light spot position control circuit diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram of various signal waveforms in a recording process.

FIG. 3 is a diagram showing a relationship between a forward current and a forward voltage of a diode.

FIG. 4 is another embodiment of the gain switching means between the reproduction mode and the recording mode.

FIG. 5 is a diagram illustrating a relationship between an output voltage and a detection current in FIG. 4;

6 is a diagram illustrating an example of a difference in tracking signal waveform between a case where a conversion gain to an output voltage with respect to a detection current is constant and a case where the nonlinear current-voltage conversion gain shown in FIG. 1 is used.

FIG. 7 is an explanatory diagram of a state in which a delete pattern is overwritten on already recorded data pits.

FIG. 8 is a diagram illustrating a relationship between a discharge time constant of a hold circuit and a track offset amount.

FIG. 9 is a diagram showing a relationship between a discharge time constant and a track offset amount when a non-mask period during delete and a period from the end of delete pulse irradiation to the end of delete mask are used as parameters.

FIG. 10 is a diagram showing a result in a case where the peak value of the reflected light level in FIG. 9 is reduced by a nonlinear current-voltage conversion circuit including a diode.

FIG. 11 is a diagram showing how a tracking signal waveform changes at the time of reading a densest data pattern.

FIG. 12 is a diagram showing a relationship between a time constant and a gain change in FIG. 11;

[Explanation of symbols]

101, 102: photodetector, 109, 110: diode, 111, 112: transistor, 113, 114 ...
Resistors, 115, 116 ... capacitors, 121, 122 ...
Analog switch, 125, 126 ... resistance, 127, 1
28: capacitor, A1: peak value on the tracking signal A side when forming a pit, B1 ... peak value on the tracking signal B side when forming a pit, A2: peak value on the tracking signal A side when forming a long pit, B2: a peak value on the tracking signal B side when a long pit is formed, α: ratio of a difference signal to a sum signal, Δ: track offset amount.

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Masahiro Takasago 2880 Kozu, Odawara-shi, Kanagawa Prefecture Odawara Plant, Hitachi, Ltd. (56) References JP-A-2-276024 (JP, A) (58) Fields investigated (Int.Cl. ⁶ , DB name) G11B 7/09-7/095 G11B 7/00

Claims (6)

(57) [Claims] 1. An optical recording / reproducing apparatus for recording, reproducing, and erasing data by irradiating a recording medium with a light beam, wherein an output value changes nonlinearly according to the amount of received light. An optical recording / reproducing apparatus for generating an error signal for controlling the position of the light beam on a disk, using a means for holding the peak value of the output value. 2. The optical recording / reproducing apparatus according to claim 1, wherein the nonlinear conversion means uses nonlinear characteristics of a semiconductor. 3. The optical recording / reproducing apparatus according to claim 1, wherein a circuit constituted by a capacitance and a resistance is used as the means for holding the peak value. 4. A method according to claim 1 , wherein a signal passing through the non-linear conversion means and the means for holding the output value is irradiated with a light pulse of specific data for invalidating the recording area, and In the period before and after the light pulse irradiation period,
An optical recording / reproducing apparatus, comprising means for preventing the amount of reflected light of the specific data light pulse from the medium from being sensed. 5. The optical recording / reproducing apparatus according to claim 4, wherein a signal in a period other than the sensing period is used as a signal for controlling a light spot position. 6. An optical disk according to claim 1, wherein an optical disk medium is used as a recording medium, a mark length is recorded, and a recording method is used in which an end of said mark corresponds to data, and an output value corresponding to the amount of reflected light from said optical disk is used. An optical recording / reproducing apparatus, wherein a peak value of an output value of the conversion means is held by using a conversion means whose value changes.