JPH0520706A - Control method for optical spot position and optical recording/reproducing device - Google Patents

Abstract

PURPOSE:To attain the stable position control for a light spot position control system of an optical disk file and to reduce the gain variation and the offset in a recording/reproducing state for especially in the case where the mark length (pit edge) is recorded on a boring type recording medium. CONSTITUTION:A circuit system which produces a tracking control signal is provided with a means which varies the gains needed for conversion of a detecting current into a voltage signal with irradiation of the recording and reproducing beams by making use of the non-linear current/voltage conversion characteristic, a means which holds the peak level of the reflected light, and the means 121, 125 and 127 masking the period before and after the irradiation of a deleting pulse that invalidates the existing data including the irradiation period of an optical pulse and holding a level set right before the masking period for a servo control signal.

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 holed optical disk device, and an optical recording / reproducing apparatus.

[0002]

2. Description of the Related Art It is very important to control the position of a light spot for recording / reproducing on a disc with high precision in order to achieve high density and high reliability of an optical disc file device. As a tracking method in an optical disk device, a continuous track guide groove is scanned with one beam, and the diffracted light from the guide groove is received by a two-division type photodetector, and an actuator is used so that the difference between the two becomes zero. A driving method is known. This method is called a push-pull method. Further, in a compact disc device which is a read-only type optical disc, a tracking method using three beams is used. In this method, the sub-beams are arranged before and after the main beam for data reproduction by displacing the sub-beams in opposite directions with respect to the data track, and there is a difference in reflected light amount between the data pit portion and the no-data portion. This is a system in which the reflected light from each of the two sub-beams is received and the actuator is driven so that the difference between the two is zero.
In the same way as the tracking control, also in the tracking of the vertical shake of the disk, that is, in the automatic focus control, in principle, a method of controlling so that the difference in the amount of light received by a plurality of photodetectors becomes zero is general.

In order to perform the above-described spot position control with high accuracy, the influence of the data pattern in various operation modes, for example, the recording mode and the reproduction mode is suppressed as much as possible, and further, the circuit system or the mechanical system is used. It is necessary to reduce the bias (offset). In particular, a recording medium in which the disc reflectance changes greatly depending on the presence or absence of pits is advantageous from the viewpoint of data reproduction because the S / N ratio can be large, but it is disadvantageous in tracking control and automatic focus control because the gain variation becomes large. May become. Basically, the tracking control and the automatic focus control can be discussed in the same way as the servo system, and therefore the conventional technique will be described here by taking the tracking control as an example.

With respect to the gain fluctuation caused by the difference in the operation mode, there is a method of uniformly changing the gain of the amplifier system in each of the recording mode and the reproducing mode so that the amplifier system is not saturated even when the recording light is irradiated. Has been taken. As a light spot position control means described in JP-A-52-80802, a method of switching the gain of a control circuit between reproduction and recording has been proposed.

Further, as a method of reducing the gain fluctuation,
In the method described in Japanese Patent Laid-Open No. 54-115883, the peak hold is used during reproduction and the bottom hold is used during recording, so that the level on the unrecorded side is always maintained.
We are trying to stabilize the gain.

Regarding the gain variation caused by the difference in the data pattern, a method of setting the gain of the servo system for a random pattern and operating the gain within the dynamic range of the amplifier system is generally adopted. There is.

Regarding an offset generated in a circuit system or a mechanical system, measures such as adoption of a low offset and low drift amplifier, and adjusting the offset to zero at the time of manufacturing the device have been adopted.

[0008]

In the conventional tracking control system, it was difficult to eliminate the effects of wide-range gain fluctuations and changes in the physical properties of the recording film during recording. In particular, when the pit edge recording is applied to a punching type recording medium, in addition to the gain variation due to the difference in operation mode, the gain variation due to the density of the data pattern is large. Moreover,
Since the fluctuation of the diffracted light distribution from the track guide groove when the recording film is in the melting process has a great influence, it becomes difficult to keep the 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. Further, when peak hold is used during reproduction and bottom hold is used during recording, switching in each operation mode is necessary and the circuit configuration becomes complicated.

The problem to be solved by the present invention is to propose a method of reducing the influence of gain variation and offset even in long-hole recording which is easily influenced. In the present invention, the case where the pit edge recording method is used for the perforated recording film has been described as an example, but the method is widely applicable 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 a means for solving the problem, a nonlinear current-voltage characteristic of a diode is used in a tracking amplifier system, and a resistance value for converting a detection current into a voltage during reproduction light irradiation and during recording light irradiation is set. A variable circuit, a peak hold circuit for recovering the gain reduction during playback and holding the peak level of the reflected light during slot recording, and the reflected light before and after the delete light irradiation during delete By using a delete mask circuit for not seeing the signal, 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 according to the magnitude of the detected current, as compared with the method in which the gain is uniformly changed for each reproduction or recording mode, and therefore the switching for each mode is special. Is unnecessary, and the gain does not decrease even during the recording pulse light non-irradiation period during the recording mode, that is, the reproduction light irradiation period.
Further, since the gain when the reproducing light is irradiated is large, the allowable value of the offset of the circuit system is expanded, and the gain when the recording light is irradiated can be made small, so that the saturation of the circuit system can be avoided.

[0013]

In the variable current-voltage conversion circuit using the diode, the value of the conversion gain resistance can be set to a large value 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 of high irradiation power, the saturation of the amplifier system can be prevented. Further, in the method in which the gain is uniformly switched between the reproduction mode and the recording mode, the level is extremely reduced in the reproduction light irradiation period in which the recording pulse light is not irradiated in the recording mode, but in this method, the operation mode is switched. However, since the gain changes depending on the magnitude of the detected current, this problem does not occur.

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

The delete is an operation of invalidating the recorded data by overwriting a certain pattern (delete pattern) on the unrecorded portion or the recorded portion. Therefore, it is a function peculiar to the write-once optical disc. In this way, since the reflected light signal fluctuates depending on the data pattern that has already been recorded and the servo operation needs to be performed in the reproduction mode in this way, the deletion pulse light irradiation and before and after the deletion pulse light irradiation from the disc It is desirable not to see the reflected light. The delete mask is a function of holding the signal level until immediately before the delete mask in the period. This makes it possible to prevent an increase in track offset and stabilize the servo gain.

[0016]

EXAMPLES Examples of the present invention will be described below. FIG. 1 is a block diagram of an example of a tracking circuit of the present invention.
In tracking by the push-pull method, a split type photodetector receives the diffracted light distribution from the disc guide groove, and the actuator for tracking is operated so that the amount of light received by each photodetector becomes equal, The light spot is always located on or between the guide grooves. Three
The tracking by the spot method is basically the same as the push-pull method. That is, the reflected light from each of the two sub-beams positioned before and after the main beam is received by the photodetector, and the light amounts are controlled to be equal. In FIG. 1, TR-A and TR-B are two series of tracking signals whose light receiving amounts should be equal. For convenience of explanation, the operation of this circuit will be described for the signal sequence on the TR-A side. The reflected light from the disc received by the photodetector 101 is converted into an electric current here. Generally, a PIN photodiode is used for the photodetector, and a current proportional to the amount of light is generated. This detection current is the amplifier 1
It is converted into a voltage at 03. Here, the resistor 105 is a current-voltage conversion resistor in the reproduction mode, and the resistor 107 is a current-voltage conversion resistor that is connected in parallel with the resistor 105 in the recording mode. The diode 109 is for controlling the value of the current-voltage conversion resistance by using the so-called non-linear characteristic of the diode, in which the forward voltage changes according to the magnitude of the forward current. For 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 of the transistor 111 and the transistor 112. Therefore, it is necessary to secure the uniformity of the temperature characteristics by using the one having a good pair characteristic and further bringing them close in mounting. Similarly, the diodes 109 and 110 are also TR-A.
It is necessary to use the one having good pair characteristics also for the side used for the TR side and the TR-B side, and 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 made very small (several ohms). Further, the amplifier 117 has an effect of making the input impedance very large, and thus the hold time constant can be roughly 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 constants are the resistance 113 and the capacitor 11
It is determined by the product of 5. 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. In FIG. 1, the case of an inverting amplifier using an operational amplifier is shown as an example, but a non-inverting amplifier may be used depending on the signal polarity and the like.

When the delete pattern is recorded, the analog switch 121 opens the switch for a certain period including the irradiation period of the record light of the delete pattern, so that the influence of the reflected light of the delete light is affected during the period. It's meant to prevent you from feeling it. In other words, when deleting is performed, it is unknown what pattern has been recorded up to that point, and the level of the reflected light during irradiation of the delete pulse varies depending on the recorded pattern.Therefore, it affects gain variation and offset of the tracking system. In order to suppress, the detection signal of the delete period is not used. In the following description, this period will be called a delete mask period. The analog switch is opened by the control signal 123 during the delete mask period and short-circuited during other periods. The signal level immediately before the delete mask is held by the hold circuit composed of the resistor 125 and the capacitor 127. Amplifier 12
Reference numeral 9 is a voltage follower, which receives a time constant with a high input impedance, and thus has a time constant of 125 and 125.
It is intended to be decided by. As a result, the charging time constant is substantially determined 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 is an operation of invalidating the information of the sector by overwriting the pattern in a certain period in addition to the unrecorded portion or some data pattern already recorded in the form of pits. That is. As a condition of the delete pattern, after the delete is performed, it is always determined that the sector is a deleted sector (no undetection occurs), and the original data string cannot be restored even with the error correction code of the data. That is, the pattern does not affect the servo characteristics. When the pit edge recording method by 2-7 modulation is used to associate the front end and the rear end of the pit with data "1", respectively, a delete mark longer than the longest pattern (4T) existing in the data pattern. A pattern that repeats with a cycle that cannot be corrected by the error correction code is suitable. As a specific example, there is a pattern in which the delete mark length is 8T and this is repeated in a cycle of 64T. Here, T is a time interval of 1 bit of data.

A TR-A is provided after the circuit shown in FIG.
Amplifier for generating a difference signal between the signals of both channels of 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 applying circuit and the like are added. Further, in order to suppress the influence of the fluctuation of the reflectance of the disc, the TR-A side and the TR-B side are
A method is conceivable in which a gain control circuit for generating a side sum signal and standardizing the level of the difference signal by the sum signal is provided. For the purpose of the present invention, the conventional method may be used after the generation circuit of the difference signal or the sum signal, and thus the detailed description is omitted.

FIG. 2 shows the optical power and the signal waveforms of TR-A and TR-B when a dense data pattern is recorded on the unrecorded disc recording film by the pit edge recording method.
FIG. 6 is a diagram showing a recording process of a perforated recording film. The pit edge recording method is a recording method in which the end of a pit corresponds to data, and is a method that can achieve higher density than a pit center recording method in which even a light spot having the same resolution corresponds to the center of a round hole. In FIG. 2, considering the case where 2-7 modulation is used as the modulation method, the largest recording power irradiation period is 4T in terms of duty.
The recording light pulse is radiated during the period of, and the pattern for returning to the reproducing power is repeated during the period of 1.5T. When the data 4T length itself is used for the recording pulse width, the duty is about 72%. Generally, the pit length formed by the recording pulse width is longer than the recording pulse width, so that the recording pulse width is shortened by a certain width for recording. In the following description, such a dense data pattern will be called 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. Therefore, 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 reproduction power and the recording power. Also, this period does not depend much on the data pattern length, and even in the recording pulse width shown in FIG. 2, this swelling process exists for almost the same time. Further, during this period, the distortion of the shape due to the aberration of the light spot and the influence of the track offset are unlikely to appear, so that the peak values A1 and B1
Difference is not so big. Next, in a period in which sufficient heat is applied to the recording film, the recording film starts to break. This period becomes longer as the pattern having the longer recording pulse width. Also,
During the pause period between the recording pulses, the reproduction power irradiation state is set. During this reproducing period, there is no level change due to the 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 is likely to differ. This is because the diffracted light pattern from the track guide groove is likely to be disturbed. On the other hand, in the conventional tracking method, since the processing is performed by the transmission system having the servo band of several tens of kHz, the servo operation is performed at the average level including the region of the breaking process. Therefore, it is strongly influenced by the region in which the difference between the signal levels A2 and B2 in the breaking process is large. In particular, the influence is great in the close-packed data pattern as shown in FIG. From the above, it is desirable from the viewpoint of reducing the track offset to perform the tracking control by relying on the reflected light level in the swelling process at the start of the recording pulse irradiation as much as possible.
Peak hold is also a method to detect and hold the peak level to make it less susceptible to the breaking process.

FIG. 3 is a diagram showing the characteristics of the 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 resistors 105 and 106 are 10 kΩ and the resistor 1 is
It is shown that 07 and 108 are set to 1 kΩ.
The region in which the forward current is 40 μA or less is a region corresponding to the detection current of the reflected light when the reproducing light power is irradiated, and the diode is not in the conductive state yet. Therefore, the values of the resistors 105 and 106 are the same as the value of the current-voltage conversion resistance. become. On the other hand, in the area corresponding to the detection current of the reflected light when the recording light power is irradiated, about 2
A detection current of 00 μA or more is obtained, and the value of the current-voltage conversion resistance becomes the value of the parallel resistance of the resistance 105 and the resistance 107, that is, about 900Ω. In FIG. 3, the value of the current-voltage conversion resistance changes non-linearly between the reproduction light region and the recording light region, but if the recording power is set to 5 times or more of the reproduction power, this non-linear region will not be a problem. In this way, the conversion gain variable circuit using the diode can achieve both the large 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 expanded. For example, considering that the gain of the first-stage amplifier is not saturated at the reflected light level at the time of recording pulse irradiation,
If the allowable value of the offset of the post-stage amplifier is 10 mV and the gain of the post-stage amplifier can be increased 10 times, the same tracking offset will be obtained when the offset of the post-stage amplifier is 20 mV. The offset allowable value of the latter-stage amplifier can be doubled.

FIG. 4 shows another embodiment for changing the value of the current-voltage converting resistance 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, the value of the resistor 403 becomes the current-voltage conversion resistance value in the reproduction mode, and the value of the parallel resistance of the resistors 403 and 404 becomes the current-voltage conversion resistance value in the recording mode. The gain switching between the reproduction mode and the recording mode in the circuit format of FIG. 4 is different from 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 detected current) automatically changes according to the detected 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 gain is fixed to the same during the rest period of the recording pulsed light irradiation in the recording mode. Therefore, when the data pattern to be recorded is the close-packed data, the average detection current becomes large, and conversely, in the sparsest data pattern in which the relationship between the pit length and the gap length is the reverse of the close-packed data pattern, the average detection current is Becomes smaller. As described above, the influence of the change in the data pattern is more remarkable in the case of the circuit configuration of FIG. However, since a circuit for selecting a resistance by a switch as shown in FIG. 4 is more stable with respect to changes in external factors such as temperature, in the case of a modulation method or a recording method in which a change in data pattern is small. Is valid.

FIG. 5 is an example showing the relationship between the output voltage and the detected current in the reproduction mode and the recording mode. Here, the case where the resistor 403 is selected to be 10 kΩ and the resistor 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 is the same.

FIG. 6 is a diagram showing the signal waveforms of TR-A and TR-B when the current-voltage conversion gain resistance is constant and when it is varied nonlinearly by the diode. Here, the waveforms of TR-A and TR-B shown in FIG. 2 are shown in rectangular approximation. 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 swelling process, and when the recording film melts into the breaking process thereafter, the reflected light level is lower than the reflected light level in the swelling process. The level you did continues. After this, when the power of the reproduction light is restored, the level of the reflected light also decreases correspondingly. When the gain resistance of (a) is constant, the area of the recording light pulse irradiation period occupies a large portion of one cycle of the pattern. Therefore, it is strongly affected by the melting process of the recording film. On the other hand, in the case where the gain resistance is variable as shown in (b), 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 1 μs. The actual track offset amount is
It can be estimated by the area ratio of the waveforms of TR-A and TR-B. That is, the areas of the channel waveforms of A and B in one cycle of a data pattern are Sa and S, respectively.
Assuming b, the track offset amount α is given by Equation 1.

[0026]

[Equation 1]

Further, the conversion from this α to the distance Δ of the track offset is obtained by the equation 2.

[0028]

[Equation 2]

In Equation 2, δ is a track interval, β is a numerical value determined by the light spot and track intervals, the shape of the guide groove, etc., and is experimentally determined as a relative amount when the unrecorded case is 100%. It is a numerical value. For example, in the case of a guide groove having a track interval of 1.5 μm and 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 the experiment was about 50%. Using the formulas 1 and 2 and FIG. 6, the track offset is calculated for the case where the gain resistance is variable by the diode, the case where the gain is constant as in the conventional case, and the case where the peak hold is used and not used. Show. In the following description, for convenience, a diode-based nonlinear current-voltage conversion circuit is referred to as NI.
V and the peak hold circuit are abbreviated as PH.

In the conventional method (without NIV, without PH),
From FIG. 6, α = 23.4%, that is, ΔTR = 0.12.
The calculation results in a track offset of 2 μm. On the other hand, with the hold time constant set to 1 μs, without NIV and with PH, Δ = 0.083 μm.
When V is present and PH is present, the calculation result that the track offset can be suppressed to Δ = 0.033 μm was obtained. That is, by using NIV and PH, the track offset can be suppressed to about 1/4.

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

Up to this point, 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 delete and an example of the pattern have been described above, and thus the description thereof is omitted here. The upper diagram 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 delete mask signal (DELMASK-P) holds the signal level immediately before the mask signal, whereby tracking control is performed. Therefore, the tracking control using the reflected light level signal directly is performed only during the period T ₃ . In FIG. 7, the levels of TR-A and TR-B during reproduction light irradiation are a and b, and the levels during delete light irradiation are ka and lb. Further, the delete pulse width, that is, the period during which light is emitted with the delete light power is T ₁ , the period from the end of the delete pulse until 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 until the start of the period is T ₃ . The areas of TR-A and TR-B in the period T ₃ are Sa, S
If it is assumed to be b, it is described by Equations 3 and 4, respectively.

[0033]

[Equation 3]

[0034]

[Equation 4]

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

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 when reproducing light is irradiated
Are equal in level. That is, a = b (2) The discharge time constants on the TR-A side and the TR-B side are equal, and a time constant is given to the T ₂ reference. That is, τ =
τ ₁ = τ ₂ = qT ₂ (3) The level of TR-A and TR-B at the time of irradiation of the delete pulse light is 10 times that at the time of irradiation of the reproduction light. That is, (k
+ L) / 2 = 10 (4) The relationship of the levels on the TR-A side and the TR-B side based on the time of reproduction is different from each other by p times. That is, k = pl (5) The delete non-mask period T ₃ is set to be four times the period T ₂ from the end of irradiation of the delete pulse light to the end of the delete mask. That is, when T ₃ = 4T ₂ and the bit period T are used as references, for example, T ₃ = 44T and T ₂ = 11T are set.

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

[0039]

[Equation 5]

FIG. 8 shows the results of calculating the change in the track offset amount with the gain ratio p of TR-A and TR-B as a parameter with respect to the discharge time constant τ (= qT ₂ ). The smaller the gain ratio on 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, the smaller the track offset amount. However, if the discharge time constant is too small, the tracking gain will be small especially when reproducing the densest data string, so it is necessary to optimize during delete and during reproduction. The change in gain during reproduction with respect to the discharge time constant will be described with reference to FIGS. 11 and 12.

In FIG. 9, the gain ratio p on the A side and the B side is 10%.
If they are different, that is, p = 1.1 is taken as an example, the ratio of the delete non-masking period T ₃ and the period T ₂ from the end of the delete pulse irradiation to the end of the delete mask is used as a parameter.
It is the result of calculating the track offset amount with respect to the discharge time constant q. From this result, it can be seen that for the same discharge time constant, the track offset becomes smaller as the non-masking period T ₃ is longer than T ₂ .

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

The derivation of FIGS. 9 and 10 was carried out by the following equations.

[0044]

[Equation 6]

[0045]

[Equation 7]

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

FIG. 11 is a diagram showing the signal changes of TR-A and TR-B when the repeating portion of the closest data pattern is being read. Holes (pits) for perforated recording films
In general, the reflectance is smaller than that of the unrecorded area,
The detected light level for the servo is reduced. 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 the severest when the densest data pattern is repeated. In FIG. 11, the solid line shows the signal change when the peak hold is not performed. In the figure, the rectangle is approximated. The dotted line shows the signal change when the peak hold of a certain discharge time constant is performed. By holding the level of the unrecorded portion by the peak hold even while the pit exists, the influence of the presence or absence of the pit can be reduced, and the servo control can be performed as if the unrecorded portion is being performed. FIG. 12 is a diagram showing the relationship of the gain change γ with respect to the time constant τ. The derivation was performed using the following formula.

[0048]

[Equation 8]

Here, the time constant τ is represented by a ratio based on the pit period T ₄ . That is, τ = wT ₄
And When considering the decrease in gain, the period corresponding to the longest pit length in the modulation method used may be T ₄ . It can be seen from FIG. 12 that the discharge time constant can 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 deleting, it is necessary to select a time constant that is compatible with the recording mode and the delete mode. Further, if the discharge time constant is extremely large, it becomes impossible to follow the level fluctuations of the mixed data patterns, so that the unrecorded level may not be accurately detected. Therefore, the gain is expected to decrease to some extent, and the time constant is set in a range that follows such a change in the reproduction signal level. For example, when the reproduction signal amplitude in the case of the repetitive pattern of the longest pit and the longest gap allowed in the modulation method is used as a reference, the reproduction signal amplitude of the gap portion in the repetition of the closest data pattern decreases. If the amount of decrease in gain is adjusted to this amount of decrease, it is possible to follow and hold the signal level of the unrecorded portion even for mixed data patterns. In FIG. 12, the gain change amount γ is −2 dB as an example.
This shows a case where it is expected, and at this time, w = 2. Now, considering the case where 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. To give a specific numerical example, the gain ratio between the A side and the B side is kept within 10%, and T ₃
= 4T ₂ and (k + 1) / 2 = 2 by the non-linear conversion gain circuit by the diode, the track offset is 0.00 with respect to the 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 variation and the offset of the spot position control signal during reproduction and recording. In particular, by using the non-linear effect of the forward current and voltage of a semiconductor such as a diode, it is not necessary to switch gains during reproduction and recording. Further, in the case of a punchable medium, the influence of offset can be reduced by performing servo control using the level of the leading portion of the reflected light in the recording process.

[Brief description of drawings]

FIG. 1 is a portion of 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.

5 is a diagram showing a relationship between an output voltage and a detected current in FIG.

FIG. 6 is a diagram showing an example of the difference in tracking signal waveforms when the conversion gain to the output voltage with respect to the detected current is constant and when the nonlinear current-voltage conversion gain shown in FIG. 1 is used.

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

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

FIG. 9 is a diagram showing the relationship between the discharge time constant and the track offset amount when the non-masking period during delete and the 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 when the peak value of the reflected light level is reduced by the non-linear current-voltage conversion circuit using the diode in FIG. 9.

FIG. 11 is a diagram showing how the tracking signal waveform changes when the densest data pattern is read.

FIG. 12 is a diagram showing a relationship of a gain change with respect to a time constant 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 during pit formation, B1 ... Peak value on the tracking signal B side during pit formation, A2 ... Peak value on the tracking signal A side during long pit formation, B2 ... Peak value on the tracking signal B side when forming a long pit, α ... Ratio of difference signal to sum signal, Δ ... Track offset amount.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masahiro Takasago             2880 Kozu, Odawara City, Kanagawa Stock Association             Hitachi, Ltd. Odawara factory

Claims (7)

[Claims] 1. An optical recording / reproducing apparatus for irradiating a recording medium with a light beam to record and reproduce data, when generating a control signal for controlling the position of the light beam on a disk. A light spot position control method, wherein the light spot position control method is performed by using a value on the side where the reflected light level from the disc is high during recording. 2. An optical recording / reproducing apparatus for irradiating a recording medium with a light beam to record, reproduce, and erase data, the converting means having an output value which changes non-linearly according to the amount of received light. An optical recording / reproducing apparatus, wherein an error signal for controlling the position of the light beam on the disk is generated by using a means for holding the peak value of the output value. 3. An optical recording / reproducing apparatus according to claim 2, wherein a nonlinear characteristic of a semiconductor is used as the nonlinear converting means. 4. An optical recording / reproducing apparatus according to claim 2, wherein a circuit composed of a capacitance and a resistance is used as a means for holding the peak value. 5. The method according to claim 2, wherein the signal passed through the non-linear conversion means and the means for holding the output value is irradiated with an optical 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, characterized in that means is provided for not sensing the amount of light pulse of the specific data reflected from the medium. 6. An optical recording / reproducing apparatus according to claim 5, wherein a signal in a period other than the sensing period is used as a signal for controlling a light spot position. 7. An optical disc medium as a recording medium according to claim 2, wherein a mark length recording is performed, and a recording system in which an end of the mark is associated with data is used, and an output value corresponding to an amount of reflected light from the optical disc. An optical recording / reproducing apparatus, characterized in that the peak value of the output value of the converting means is held by using the converting means that changes.