JPH0785307B2 - Optical disc recording / reproducing device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disc recording / reproducing apparatus for recording and reading information on a disc.

2. Description of the Related Art In recent years, application of a document file disk or a still image disk file has been considered as a large-capacity memory capable of recording and reproducing using an optical disk medium.

For example, a material (for example, a Te-based metal oxide) that changes in composition with different reflectance depending on the power level of a semiconductor laser is deposited on the optical disk as a thin film.
Information is recorded as a light and shade signal having a different reflectance according to the recording signal.

FIG. 5 shows a schematic diagram of a conventional optical disk recording / reproducing apparatus. Reference numeral 1 is an optical disc, on which a track for recording information is formed and a recording film is vapor-deposited. Reference numeral 2 denotes a motor and a turntable for rotating the optical disc 1, and the optical disc 1 is mounted on the turntable. An optical head 3 is composed of a condenser lens, a beam splitter, a collimator lens and the like. Reference numeral 4 is a semiconductor laser mounted on the optical head 3, and 5 is a light receiving element for detecting the amount of light reflected from the optical disk 1. A semiconductor laser driving circuit 6 changes the power level of the semiconductor laser 4 in accordance with the write data. Reference numeral 7 is a modulation circuit that modulates write data (for example, MFM, 3PM, (2,7) RLL) by a modulation circuit, and 8 is a circuit that demodulates reproduced data. In addition, B1 indicates an optical path in which the light beam from the optical head 3 is incident on the optical disk.

The operation of the conventional optical disk recording / reproducing apparatus configured as described above will be described below.

The optical disk 1 is mounted on the turntable 2 on the motor, and rotates at a constant speed of 1800 rpm, for example. The light beam from the semiconductor laser 4 fixed to the optical head 3 is
Optical components such as a collimator lens and a condenser lens in the optical head 3 focus the light on the optical disc 1 as indicated by B1. The light reflected from the optical disk 1 is similarly applied to the light receiving element 5 by the optical component. In general, the disk 1 rotates with surface wobbling and track eccentricity. Therefore, in order to record or reproduce information on a predetermined track, the light beam follows the surface wobbling of the optical disk 1. Focus control and tracking control to follow the track are required. With the focus control and tracking control performed in this manner, the data to be written is modulated by the modulation circuit 7 by, for example, the well-known modulation method MFM (Modified Frequency Modulation). The semiconductor laser 4 emits light by the laser drive circuit 6 in accordance with the output signal of the modulation circuit 7, and is condensed on the optical disc 1 in a state of being modulated with high power, whereby data is recorded. For example, as described above, when the Te-based metal oxide film is vapor-deposited on the optical disc 1, a signal corresponding to the cycle of data to be written is recorded as a light and shade signal having different reflectance. Next, a constant low power laser beam is focused on the recorded information track, the reflected light is detected by the light receiving element 5, the signal is demodulated by the demodulation circuit 8, and the written data is read.

In the above-mentioned structure, as shown in FIG. 6, recording is performed on the information track because recording is performed by the light beam in which P _x and P _y, which are the power values of the semiconductor laser, are constantly modulated. When the sensitivity of the film to the semiconductor laser is different or when the power of the semiconductor laser is insufficient, the time when the density of the reflectance changes becomes different, and the pit period of the density becomes different from the period of the recording signal. Becomes an ingredient,
It had the drawback of being misread. Further, conventionally, as one means for solving this drawback, the one disclosed in JP-A-60-83234 discloses that before recording, a signal having a constant frequency is applied to a predetermined track different from the track to be recorded in advance. Means is used for recording and reproducing the recorded signal to control the bias value of laser power and the like during recording so that the duty ratio of the waveform becomes 50%.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, the above-described means can deal with the variations in the pit period due to the variations in the optical disc each time, but even within one optical disc, the linear velocity changes due to the difference in the rotation radius. If the laser power becomes insufficient, it is necessary to always make correction, and the recording area is reduced. For example, if the writable innermost diameter of an optical disc with a radius of 20 cm is 9.5 cm, and the outermost shape is 19 cm, the linear velocity will be greater than the outer periphery when controlled at a constant rotation (CAV control: Constant Angular Verocity). Doubles. By the way, when rotating at 1800 rpm, it is about 9 in the innermost track.
The linear velocity is about 18 m / s in the track with the outermost diameter of m / s, and the laser power per unit area is half that of the former. Therefore, when writing data near the outermost circumference with the same power, depending on the sensitivity of the recording film, as shown in FIG. 7, it is shorter and narrower than the regular light and dark pit length a.
Pits are formed. The difference in pit length causes jitter in the time axis direction, but a decrease in pit width leads to deterioration of C / N,
As a result, the quality of the reproduced signal deteriorates. Generally, in order to compensate for the deterioration, a means for changing the driving bias value of the semiconductor laser or the like to increase the power is adopted as in the above publication. FIG. 7 shows a characteristic example of the power output of the semiconductor laser when the bias current value is changed.
In FIG. 8, when the amplitude value i ₀ of the drive current is kept constant and the bias value is changed from i ₁ to i ₂ , the maximum power changes from (P ₁ + P ₀ ) to (P ₂ + P ₀ ), and (P 2 _2- P ₁ ) power increase. However, when the power is increased, the temperature is diffused by the laser not only in the line direction of the track but also in the width direction of the track, the width of the pit becomes large as shown in FIG. 7C, and the crosstalk between tracks increases. . Further, if the difference in linear velocity between the inner peripheral portion and the outer peripheral portion is large (in other words, the diameter of the disk is large), the power control width becomes large, and a higher output semiconductor laser is required. The maximum rated power of the semiconductor laser currently put into practical use is about 20 mw at a wavelength of 830 nm, and although development of a higher output laser is in progress, it will take some time before it is put into practical use. Practical use is expected to begin for a while at wavelengths in the 780 nm and 650 nm range, which are shorter than 830 nm.

In view of the above point, the present invention has an object to provide an optical disc recording / reproducing apparatus which reduces the output of a semiconductor laser and does not require a semiconductor laser having a higher output than ever before even when the disc diameter is large.

Means for Solving the Problems The present invention divides a data recording area of an optical disc into concentric circles in the radial direction, and means for controlling the power of the semiconductor laser and driving the semiconductor laser in the divided area. Means for recording data, means for reproducing the recorded signal, means for correcting the cycle of the reproduction output signal of the reproducing means, and means for selecting a signal based on the determination signal of the recording area. And an optical disk recording / reproducing apparatus.

With the above-described structure, the present invention reduces the power of the semiconductor laser in the recording of the modulated data so that the divided area of the optical disc is reproduced shorter in the outer area by the detection window width of the modulation method. Power control and record. During reproduction, the cycle of the reproduced signal is corrected by the reproduced clock (the reciprocal of the detection window width) to enable demodulation.

Embodiment FIG. 1 shows the configuration of an optical disk recording / reproducing apparatus in an embodiment of the present invention. Reference numeral 11 is a track for recording information on the optical disc, and a recording film is vapor-deposited. Reference numeral 12 is a motor and a turntable for rotating the optical disc 11, and the optical disc 11 is mounted on the turntable. An optical head 13 is composed of a condenser lens, a beam splitter, a collimator lens, and the like. Reference numeral 14 is a semiconductor laser attached to the optical head 13, and 15 is a light receiving element for detecting the amount of light reflected from the optical disk. Reference numeral 16 is a modulation circuit, and write data is described in, for example, JP-A-58-20
It is modulated by the 4/8 modulation method disclosed in the 3609 publication. Four
The / 8 modulation method consists of an algorithm that divides the original data into 4-bit units and sequentially converts them into 8-bit code data. According to the 4/8 modulation method, the number of consecutive bit “0” s (called a run length) between the bit “1” and the bit “1” of the converted code is 2 at the minimum and 7 at the maximum. Reference numeral 17 is a circuit for detecting the position of the track based on the address information or the like recorded in advance on the optical disc 11. A bias value generation circuit 18 generates a bias voltage or current for changing the power of the semiconductor laser according to the linear velocity in the divided area of the optical disk 11. Reference numeral 19 is a mixing circuit for adding a bias value to the modulation signal. Reference numeral 20 denotes a semiconductor laser drive circuit which changes the power level of the semiconductor laser 14 in accordance with write data. Reference numeral 21 denotes a waveform equalizing circuit, which is composed of a circuit for amplifying the output signal of the light receiving element 15, an equalizing circuit for compensating for a decrease in high frequency amplitude, and a zero-cross detection circuit. Reference numeral 22 denotes a control signal detection circuit which detects a signal previously recorded for each recording area and outputs a control signal. 23 is a clock recovery circuit, which is a waveform equalization circuit 21
A clock that is synchronized with the rising and falling edges of the output signal from is generated by a PLL circuit or the like. A delay circuit 24 delays the input signal in synchronization with the clock of the clock recovery circuit 23. Reference numeral 25 is an OR circuit, which takes the logical sum (OR) of two inputs and outputs it. A switch circuit 26 selects an input signal according to the output signal of the control signal detection circuit 22. A demodulation circuit 27 demodulates the reproduced data. For example, it is composed of a 4/8 modulation type demodulation circuit.

The operation of the optical disc recording / reproducing apparatus of the present embodiment having the above-described configuration will be described below with reference to FIGS. 2, 3, and 4.

The optical disk 11 is mounted on the turntable 12 on the motor, and rotates at a constant speed of 1800 rpm, for example. The light beam from the semiconductor laser 14 fixed to the optical head 13 is
Optical components such as a collimator lens and a condenser lens in the optical head focus the light on the optical disk 11 as shown by B2.
Similarly, the reflected light from the optical disk 11 is applied to the light receiving element 15 by the optical component. Similar to the conventional example, the data to be written under the focus control and tracking control is converted by the modulation circuit 16 into a data string of the known 4/8 modulation method. Waveform 51 in FIG. 2 is one example. Further, it is converted by NRZ and becomes a recording signal of waveform 52. The output signal of the modulation circuit 16 is input to the mixing circuit 19, and the signal is mixed with the bias value from the bias value generating circuit 18, which will be described later. The laser driving circuit 20 causes the semiconductor laser 14 attached to the optical head 13 to emit light only during the "H" section of the modulation signal, and as a result, bits having different reflectances such as 53 in FIG. 2 are formed on the optical disk 11. If the diameter of the optical disk 11 is 20 cm, the innermost diameter of the recording area is 9.5 cm, and the outermost diameter is 19 cm, the linear velocities of the former and latter tracks are twice as different. Even if the laser output at the innermost circumference is optimized, when the outermost track is recorded, the pit length of 53 is originally recorded as short as 54. This is because the linear velocity is twice as different as described above, so that the power per unit area is less than a value sufficient to change the reflectance of the recording film in the laser irradiation section.

Therefore, in the present invention, the third problem is solved in order to solve the conventional problems.
The recording area is divided into two areas A and B as shown
Then, the same power control as in the conventional case is performed, and different powers are controlled in the area B so that the pit length is recorded shorter than the original pit length by one clock, like the pit 55 in FIG. FIG. 4 shows a conceptual diagram of the power control.
Conventionally, the power is increased almost at a rate depending on the diameter from the innermost circumference to the outermost circumference, but in the present invention, the power is relatively decreased in the region B. This makes it possible to record the pit length as short as a predetermined length as indicated by 55 in FIG. Conventional power control requires a semiconductor laser capable of outputting the maximum power output shown by P'max in FIG.
In the present invention, a power lower than P'max (Pmax in the figure) is sufficient.

The above power control can be performed by adding the bias value from the bias value generating circuit 18 to the mixing circuit 19 in the embodiment of FIG. The power control in the area is the same as in the case of FIG. 8 used in the conventional example. region
The detection of A and area B is detected by the position detection circuit 17, and a signal for bias value control in the area is input to the bias value generation circuit 18 based on the track position information in the area.

Next, at the time of reproduction, a constant low power laser beam is focused on the recorded information track, reflected light is detected by the light receiving element 15, and a reproduction signal is input to the waveform equalization circuit 21. In the waveform equalization circuit 21, the reproduction signal is amplified to a predetermined level, frequency-compensated, and converted into digital data. The output signal of the waveform equalization circuit 21 is a control signal detection circuit 22,
It is output to the clock recovery circuit 23, the delay circuit 24, and the like. The clock recovery circuit 23 generates a clock synchronized with a rising edge and a falling edge of an input signal (waveform 57 in FIG. 2) by a PLL circuit or the like. The clock of 4/8 modulation system is the detection window width Tw
It is the reciprocal frequency of and becomes 2 / T when the transmission rate is 1 / T (T: clock cycle of data). Therefore, the output signal waveform of the clock recovery circuit 23 becomes 58 in FIG. 2, and this is input to the delay circuit 24. The delay circuit 24 uses the input signal 57
Is delayed by one clock by the clock 58 and output to the OR circuit 25. The OR circuit 25 takes the logical sum of the 1-clock delay signal 59 and the input signal 57 of the delay circuit 24, and outputs the output signal 60 to the switch circuit 26. An input signal 57 is separately input to the switch circuit 26, and selection is performed based on the control signal of the control signal detection circuit 22, and the selected signal is output to the demodulation circuit 27. The control signal detection circuit, as shown in FIG.
A control signal is output according to the distinction between the areas A and B. That is, in the case of the present invention, the pits are recorded in the area B for one clock shorter than the original data cycle, and the pits are corrected by the circuit groups 23 to 25. Therefore, the output signal 60 from the corrected OR circuit 25 is selected while the data is reproduced in the area B, and the output signal 57 (uncorrected signal) of the waveform equalization circuit 21 is selected when the area A is reproduced. By doing so, correct data can be reproduced. In this embodiment, it is assumed that a signal for distinguishing the areas A and B is recorded in advance. However, various means are conceivable for detecting the control signal, and therefore the present invention is not limited to this case. For example, the address signal is read during reproduction. When recording beforehand, the address is area A,
If the track B is registered, it can be detected during reproduction and the operation can be performed. Also,
Since the error detection code is generally recorded at the same time as the data, the data before and after the correction, that is, the input signals 60 and 57 of the switch circuit 26 are input to the error detection circuit to detect the presence or absence of an error to detect the control signal. Is possible. That is, the data recorded in the area A is naturally converted into erroneous data when the correction is performed, and conversely, the data recorded in the area B is erroneous data when the correction is not performed, so that the error can be detected. In this case, although it is different from the configuration of the present embodiment, it fits the gist of the present invention.

Finally, the output signal of the switch circuit 26 is input to the demodulation circuit 27, and demodulation of 4/8 modulation is performed.

In the above description, the 4/8 modulation method is taken as an example, but the same configuration can be applied to other modulation methods. No limitation is imposed on the area division, the number of divisions, or the division places.

EFFECTS OF THE INVENTION As described above, according to the present invention, it is possible to reduce the output of a semiconductor laser, and in particular, even if the disk diameter becomes large and the linear velocity becomes large, a semiconductor laser having a high output can be obtained. Is unnecessary, a conventional semiconductor laser can be used, and its practical effect is great.

[Brief description of drawings]

FIG. 1 is a block diagram of an optical disk recording / reproducing apparatus in an embodiment of the present invention, FIG. 2 is a waveform diagram for explaining the operation of FIG. 1, and FIG. 3 is a recording area of the optical disk in the embodiment. FIG. 4 is a plan view showing division, FIG. 4 is an explanatory view showing an example of output control of a semiconductor laser in the embodiment, FIG. 5 is a configuration diagram of a conventional optical disk recording / reproducing apparatus, and FIG. 6 is a laser drive waveform of a conventional example. FIG. 7 and FIG. 7 are explanatory diagrams of problems in the conventional example, and FIG. 8 is an explanatory diagram of laser driving. 11 …… Optical disk, 12 …… Motor and turntable, 13 …… Optical head, 14 …… Semiconductor laser, 15 …… Light receiving element, 16 …… Modulation circuit, 17 …… Position detection circuit, 18 ……
Bias value generation circuit, 19 ... Mixing circuit, 20 ... Laser drive circuit, 21 ... Waveform equalization circuit, 22 ... Control signal detection circuit, 23 ... Clock recovery circuit, 24 ... Delay circuit, 25 ...
OR circuit, 26 ... Switch circuit, 27 ... Demodulation circuit.

Claims (1)

[Claims] 1. An optical disk recording / reproducing apparatus for recording and reproducing information by a laser on an optical disk having a data recording area divided into concentric circles in a radial direction, wherein the recording area of the optical disk is from the innermost circumference to the outermost circumference. Laser control means for controlling the laser power so that the laser power rises at a rate up to, and detecting the position of the optical head in the divided area, when the optical head is located in the area on the outer peripheral side, By controlling the laser power in the area on the inner circumference side, the laser control means is controlled so as to be lower than the laser power corresponding to the area on the outer circumference side, the length of the recording pit on the optical disc is controlled, and the data is recorded on the optical disc. The recording means and the divided area in which the position of the optical head is divided at the time of reproduction are detected, and based on the detection, the laser at the time of recording is detected. And means for correcting the length of the recording pit varied by power control, the optical disc recording and reproducing apparatus being characterized in that to enable recording and reproduction at low power.