JPH0563846B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical disc device, and more particularly to a recording protection device in an optical disc device that additionally records information.

In an optical disk device capable of recording and reproducing, both recording and reproduction are performed using the same optical head. Semiconductor lasers are suitable as light sources because they are easy to modulate and are small and lightweight.

In the recording mode, the laser output is pulsed in accordance with the recorded information, and a light spot narrowed down by an _optical head is applied to the recording film on the disk in a pulsed manner, and the recording film is thermally melted. Recording is done by making tiny holes. On the other hand, in the reproduction mode, the laser power is set to a constant value _PR . lead power
The energy of _PR is controlled by a focused light spot to an extent that thermal deformation of the recording film does not occur.

In other words, the difference between recording and reproduction is simply the difference in the magnitude of the laser power. Therefore, if the laser power becomes excessive compared to the normal read power due to some reason such as a failure or malfunction of the logic circuit or element in the playback mode, it may result in erroneous recording or the loss of information that has already been recorded. It may be misleading. Therefore, in the reproduction mode, it is necessary to limit the laser power so that it does not increase beyond a certain value, and in the recording mode, it is necessary to control the range of recording power to a predetermined value. For example, as an optical disk device that performs recording and playback using one light source,
- Proposed in No. 120505. Furthermore, stabilization of the output of a semiconductor laser in the reproduction mode is proposed in Japanese Patent Laid-Open No. 51-29821.

On the other hand, recordable/reproducible optical disk devices are not provided with conventional protection means. Further, in the case of a read-only disk device, the above problem does not occur. Furthermore, the same applies to other devices using semiconductor lasers. Therefore, the above-mentioned problem can be said to be a new problem unique to optical disk devices for recording and reproducing.

The present invention provides for recording mode and playback mode.
It is an object of the present invention to provide a protection device that prevents erroneous recording due to the power of a semiconductor laser for each of them deviating from an appropriate value.

In the present invention, a protection element is connected in parallel to a semiconductor laser. The protection element has a characteristic of becoming short-circuited when a predetermined input is applied to its control input. The control input is set with a constant power threshold for each read and write mode, such that when the read or write power exceeds this threshold, a control signal is generated to the protection element. This prevents erroneous recording by reducing the laser power to zero or a small value in the event of an abnormality.

The present invention will be explained in detail below with reference to Examples. Figure 1 shows the semiconductor laser current I _L and laser output power P.
A summary of the characteristics is shown below. The current applied to the element is the threshold
When I _th is exceeded, a laser output proportional to the exceeded current is obtained. When reading, set the current to I _R ,
Let the laser power be P _{R. PR} can perform all the processing and control necessary to reproduce recorded information without causing any deformation to the recording film of the optical disc. During writing, the laser current is modulated in pulses based on the recording signal to generate a current I _W and a power P _W . When the above ride power is generated, the recording film
The portion hit by the light spot is deformed to form an information pit and writing is performed. FIG. 2 is an explanatory diagram showing the current applied to the laser and the appearance of pits recorded thereby.

Accurate control of laser current is required to perform accurate read and write operations. That is, at the time of reading, it is necessary to secure the power necessary for the read process and to ensure stable power sufficiently lower than the deformation threshold power of the recording film. In order to keep the recording pits formed constant during writing, it is necessary to correctly control the pulse width, amplitude, waveform, etc. of the write current. On the other hand, when a situation deviates from the above conditions due to variations in element characteristics, malfunctions, or erroneous operations occurs, protective measures are required immediately. By the way, in both read and write cases, it is safer to reduce the laser power to zero in case of an abnormality, at least in the sense that erroneous information will not be written. Therefore, by connecting a device in parallel with the laser that has the characteristic that the input/output terminal is short-circuited in response to an abnormality detection signal, the current to the laser can be bypassed in the event of an abnormality, and the current can be kept below the threshold current.

FIG. 3 shows the basic configuration of the present invention. 1 is a semiconductor laser which is incorporated into the read/write head. Read current I _R and write current I _W are provided from current sources 3 and 4, respectively. Note that the generation and control circuits for I _R and I _W are omitted. A protection element 5 bypasses the current of the laser 1, and normally has a sufficiently high resistance so as not to affect the current flowing to the laser 1. When control input 50 is applied, a short circuit condition bypasses the current to the laser. 6 is an abnormal state detection circuit that monitors the laser power and generates an abnormal signal 50. Here, input 60 is a laser power monitor signal, and 30 is a mode signal such as read or write. Note that the resistor 2 connected in series to the semiconductor laser 1 is for stable operation of the protection element 5 and can be omitted.

FIG. 4 shows the configuration of the abnormality detection circuit. The power monitor signal 60 of the semiconductor laser has an average value of 61.
Obtain the temporal average value and use this value and the set value of the read power.
A comparator circuit 65 compares it with P _R 64 and generates a logic "1" output if the allowable range is exceeded. The other side of the power monitor signal is the write power setting value.
_PW 62 is compared with comparator circuit 63, and if the allowable range is exceeded, a logic "1" is generated. The above two signals pass through an OR circuit 66 and set a flip-flop 67. The output 50 becomes a control signal for driving a protection element connected in parallel to the laser. In FIG. 4, an average value circuit 61, comparison circuits 63, 65,
The OR circuit 66, flip-flop 67, etc. do not need to have all special characteristics, and ordinary circuit means are sufficient. For semiconductor laser power monitors,
A portion of the optical output of the laser may be received by a photodetector, such as a photodiode, and the output current may be used, or simply, a current applied to a semiconductor laser may be used. The outputs from the comparison circuits 63 and 65 are set to output logic "1" at a point where the power of the laser increases and does not exceed a level at which the possibility of erroneous recording occurs. In addition, in FIG. 4, the protection circuit 6 at the time of writing
2, 63 and protection circuit when reading 61, 64, 65
Even if either one is used, it has a certain effect. In particular, when using the protection circuits 61, 64, and 65 during reading, the response speed is not fast, but it also has a protection function during writing.

FIG. 5 is a circuit diagram showing a specific embodiment of the present invention. In FIG. 5, the write protection circuits 62 and 63 in FIG. 4 are omitted. As the laser power monitor signal 60, an output proportional to the drive current to the laser 1 is used. The average value circuit 61 is a resistor 61
1,612, and a circuit consisting of a capacitor 612. An SCR 5 is used as a protection element, and its anode and cathode are connected in parallel with the semiconductor laser circuits 1 and 2. The average value circuit output is applied to the gate 501 of the SCR through a diode 502.
The output of the average value circuit, that is, the voltage at the terminal of the parallel circuit of resistor 613 and capacitor 612 is maintained at a value corresponding to the normal read power. When the read power increases, or when the pulse peak value or pulse width during writing increases, the output voltage of the average value circuit increases. When this voltage exceeds a trigger threshold consisting of diode 502 and the gate of SCR5, SCR5 becomes conductive. Once conductive, the SCR 5 maintains that state even if the trigger input is removed, so the SCR 5 also includes the function of the flip-flop 67 in FIG. Due to conduction of SCR5, the current to semiconductor laser 1 is bypassed to the SCR circuit,
To prevent erroneous recording due to excessive power.
When the SCR 5 becomes conductive, that is, when the output of the flip-flop 67 in FIG. 4 becomes "1", this is transmitted to a display or other means and appropriate measures are taken. When the countermeasure is completed, a reset signal 68 is applied to the flip-flop 67 in FIG. 4 to return to normal operation. In the case of FIG. 5, it is reset by reducing the current of SCR 5 to below the self-holding current in the conducting state. Diode 50 in the SCR gate circuit
Since 2 increases the trigger threshold of the SCR as described above, it may be a resistor, or it may not be related to other constants. As is clear from the above description, this portion has the function of the comparison circuit 65 in FIG. 4. Note that the circuit consisting of the resistor 503 and switch 504 connected to the SCR gate 501 in FIG.
This is to make the SCR conductive.

Although the SCR is used as a protection element in the embodiment shown in FIG. 5, it can be used as a protection element except for mechanical contacts that may generate surge voltage during on/off operation. However, it is undesirable for the protection element to have characteristics that would hinder the high-speed modulation operation of the laser, such as having a very large resistance.

As described above, according to the present invention, it is possible to prevent the occurrence of errors such as recording in areas that should not be recorded due to some cause such as failure or malfunction. In a high-performance read/write capable disk device using a semiconductor laser as a light source, both reading and writing are performed using the same head, so the problems posed by the present invention may occur, such as excessive laser power during reading and erroneous recording, and write power reduction during writing. The problem of not being able to record proper information due to excessive size cannot be avoided. Particularly in the case of optical disk devices in which recorded contents cannot be erased once, the above-mentioned problem can be said to be an essential function in maintaining system reliability. The protection system according to the present invention exhibits great effects in a practical system in that it can solve the above problems without requiring parts with special characteristics or precision.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the relationship between the current and optical output of the semiconductor laser, Fig. 2 is an explanatory diagram showing the modulation current of the semiconductor laser and information recorded on the disk, and Fig. 3 is a diagram showing the basic configuration of the present invention. 4 are block diagrams showing one embodiment of the abnormality detection circuit in the present invention, and FIG. 5 is a circuit diagram showing a specific embodiment.

Claims (1)

[Scope of Claims] 1. A semiconductor laser, and an abnormality detection means for detecting an abnormality in the semiconductor laser, which receives a monitor signal corresponding to the optical output of the semiconductor laser as an input signal, and is connected in parallel to the semiconductor laser. and a protection means that short-circuits the two terminals when a control signal output from the abnormality detection means is input, and the abnormality detection means is configured to control the respective optical outputs of the semiconductor laser during recording or reproduction. a comparison means for individually comparing a signal corresponding to the threshold value with the monitor signal and generating an abnormal signal when the monitor signal exceeds the threshold value; An optical disk device characterized in that it is switched into a control state by inputting a signal and has means for constantly generating a control signal. 2 A semiconductor laser, a thyristor connected in parallel to the semiconductor laser, and a monitor signal corresponding to the optical output of the semiconductor laser are input to an average value circuit, and when the output of the average value circuit exceeds a predetermined value, ,
An optical disk device comprising an average value circuit and a diode placed between the thyristors so as to keep the thyristors in a steady conductive state.