JPS62298938A - Optical disk device - Google Patents

Abstract

PURPOSE:To prevent erroneous recording to a recorded part or an unrecorded part even in case of the occurrence of abnormal states by driving a laser while sampling a monitor signal and comparing the monitor signal before sampling with that after sampling. CONSTITUTION:In the reproducing state, a switching circuit 11 is closed, and a resistance 10 and the emitter of a transistor TR3 are connected by a switching command 14, and the driving current I2 of a laser 1 is conducted through the TR3 to perform the control. When an optical system is moved thereafter, a sampling command 13 is inputted to a sample holding circuit 12, and a holding signal 16 is outputted after a monitor signal 17 is held. Consequently, base potentials of TR3 and TR18 are equal to each other, and the resistance 10 and the emitter of the TR18 are connected. As the result, a current approximately equal to the current I2 is conducted to the laser 1, and such state is held during the movement of the optical system, and an abnormal current is not conducted even if a negative feedback signal is not returned by some cause during movement.

Description

DETAILED DESCRIPTION OF THE INVENTION 3. Detailed Description of the Invention Field of Industrial Application The present invention relates to an optical disc device, and more particularly to laser protection and recording protection in an optical disc device for recording and reproducing information.

Conventional technology In optical disk devices that perform recording and playback, a light spot focused on the disk is pulsed to increase or decrease the laser power in accordance with the recorded information during recording mode, changing the optical properties of the recording film. Record by doing this. In the reproduction mode, a laser power that does not change the recording film is irradiated, and information is read by detecting reflected light. Therefore, in each mode, it is necessary to keep the laser power constant, and laser puff control is performed so as not to be affected by temperature or the like.

A conventional example will be explained using FIG. 4. A laser 1 and a solar cell 2, which are surrounded by broken lines in FIG. 4, are included in an optical system (not shown) that moves for data retrieval, and are connected to other circuits via connectors or the like. In response to the laser ON command 12, the switching circuit 11 is closed to enter the regeneration state, and the laser 1 emits light. the result,
Backlight enters the solar cell 2 and current flows. The current flow enters the operational amplifier 4 (current-voltage conversion) and is converted to voltage, and accordingly, the current flow for laser driving is performed by Tr3.
is washed away. That is, the laser monitor light is used as a negative feedback signal to control the laser drive current. If the laser drive current is simply controlled to a constant value, a constant output light amount cannot be obtained because the laser output light amount for the same current varies due to temperature changes. Therefore, it is necessary to change the current while monitoring the laser light that is actually being emitted.
A backlight with a power proportional to , is used for monitoring. Note that during recording, the switching circuit 7 is turned on or off according to the output of the recording signal generation circuit 5. Furthermore, the Tr 8 is driven according to the potential of the recording power setting circuit 6, and the current is adjusted.

flows.

Furthermore, during recording, the switching circuit 11 is turned off.

As described above, the monitor light (backlight, hereinafter abbreviated) is used to control the power and deceive, and in the event of an abnormality (when a current exceeding the allowable value flows through the laser), the current flowing through the laser is detected. (For example, by monitoring both ends of the resistors 9 and 10), an abnormal state was detected and the laser was turned off. An example of this is JP-A-58-189849.

Problems to be Solved by the Invention However, in the past, the laser monitor light is used as a negative feedback signal, so if the monitor light signal is not returned, negative feedback is not applied and the signal exceeds the allowable value. Current will flow. In this case, the laser power increases instantaneously, and in the detection method described above, detection is performed after the current flows (power exceeding the allowable value is output), and the laser is turned off after a delay time in the circuit. For this reason, in the reproduction mode, power exceeding the allowable value (recordable level) is irradiated, albeit momentarily, resulting in destruction of recorded data, recording in unrecorded areas, etc. Furthermore, in the recording mode, abnormal power (abnormality in reproduction power control) is added to the recording power, resulting in recording errors and damage or deterioration of the laser. Reasons for not receiving a negative feedback signal (monitor light) include metal fatigue and poor contact in the connector portion due to repeated movement of the optical system, and defects and failures in the detector 2. However, the optical system must be constantly moved to search for data, and metal fatigue and poor contact at the connector cannot be avoided. In particular, abnormalities are concentrated in the period from immediately after the movement of the optical system starts until it ends. When these occur, they not only cause destruction or deterioration of the laser, but also cause recording errors and double writing to the recording section, which greatly reduces the data error rate and causes serious defects such as destruction of recorded data. .

Therefore, these pose a huge problem in maintaining system reliability.

Means for Solving the Problems In order to solve the above problems, the present invention uses a laser as a light source and is configured to perform recording or reproduction depending on the magnitude of the output power, and also includes means for obtaining a monitor signal corresponding to the output power of the laser. a sample-hold means for holding and outputting the monitor signal; and a switching means for switching between the monitor signal and the output of the sample-hold means;
The apparatus includes a driving means for driving the laser, and an abnormality detecting means for comparing the monitor signal with a comparison level obtained by adding a DC voltage above and below the output of the sample hold means.

Function: With the above-described configuration, the present invention can detect an abnormal state by driving the laser without sampling the monitor signal and comparing the monitor signals before and after sampling.

Therefore, since the laser is always driven at the hold value before the abnormal state occurs, there is no abnormal power output.

Embodiment FIG. 1 is a diagram showing the configuration of an optical disc device in an embodiment of the present invention. , in FIG. 1, 1 to 4 degrees 16.11 are the same as the conventional example (FIG. 4). In addition, the recording circuit section indicated by the dashed line in FIG. 4 is omitted; o12 is a sample and hold circuit; 13 is a sampling command; 14 is a switching command; 15 is a switching circuit; 16 is a hold signal; 17 is a monitor signal; 18 is Tr() transistor). In a normal reproduction state, the switching circuit 11 is closed, and the switching command 14 connects the resistor 1Q and the emitter of the Tr3. In other words, laser 1
The drive current I2 is controlled by flowing through the Tr3. Thereafter, when moving the optical system, the sampling command 13 enters the sample hold circuit 12, holds the monitor signal 17, and then outputs the hold signal 16. Therefore, the pace potentials of Tr3 and Trls become equal, and the switching command 14 connects the resistor 10 and the emitter of TrlB. As a result, almost the same current flows through laser 1, and this state is maintained while the optical system is moving (driven by TrlB). Even if a negative feedback signal is not returned for some reason during movement, no abnormal current will flow. . After the movement, if there is no abnormality, the switching command 14 returns to the normal regeneration state (driven by Tr3). Second
The figure shows the detection of an abnormal state. When the current state is normal and the monitor signal 17 = V and the hold signal 16 = v2, the hold signal 16 is output to the adder circuit 20 and the subtracter circuit together with the DC voltage v3. 21, and its outputs are (■2+v3) and (v2-■3).

(■2+v3), (■2-v3) are comparator 22,
23 and is compared with the monitor signal 17 to detect an abnormal state. Here, ■4 is the offset voltage of the operational amplifier 4 (FIG. 1), and ■3 is set so that v4>(v2+■3). Also, under normal conditions, it is v1 cow v2, so
The relationship (v2-v3)kvl<(v2+v3) is established, and the outputs of both comparators 22 and 23 become L''.The third
The figure is a relationship diagram of main voltages in a normal state (v1
cov2). Therefore, under normal conditions, the output of the OR circuit 22 is "L". If an abnormality occurs and the current from the solar cell 2 does not return (work, = ○), the operational amplifier 4, which was operating as a current-voltage converter, functions as a voltage follower. Therefore, the potential (■1) of the monitor signal 17 is equal to v4, and vl>(■2+■3) holds.As a result, the output of the comparator 22 becomes "H", and the output of the OR circuit 24 also becomes "H". "can detect any abnormality. When an abnormality is detected, the laser is turned off without connecting resistor 1o and Tr3. Also, the monitor signal 1
7 is accompanied by some fluctuation, so the comparator 22.2
3 is used as a window comparator, and one 0 resistor for abnormality detection is a high resistance, and since the current flowing through this resistor is minute, it hardly affects the laser power.

Effects of the Invention As described above, according to the present invention, even if an abnormal state in which a monitor signal is not returned occurs, it is possible to prevent erroneous recording to a recording section or an undistributed section. Furthermore, by comparing the monitor signals before and after sampling, abnormal conditions can be detected and the state of the laser can be constantly monitored. Therefore, it is useful for increasing the reliability of the system, and has a great practical effect.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an optical disk device according to an embodiment of the present invention, FIG. 2 is a circuit diagram of an abnormal state detection portion of the device,
FIG. 3 is a diagram showing the relationship between the main voltages of the device, and FIG. 4 is a circuit diagram of a conventional optical disc device. 1...Laser, 2...Solar cell, 3,
8.18... Transistor, 4... Operational amplifier, 7,11゜15... Switching circuit, 12... Sample hold circuit, 16...
...Hold signal, 17...Monitor signal,
2o... Addition circuit, 21... Subtraction circuit, 22.23... Comparator. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 17 Monitor signal Figure 3 G-1111111111

Claims (1)

[Claims] A laser is used as a light source and recording or reproduction is performed depending on the magnitude of output power, and means for obtaining a monitor signal corresponding to the output power of the laser, sample and hold means for holding and outputting the monitor signal, and a means for obtaining the monitor signal. and a switching means for switching the output of the sample and hold means, a driving means for driving the laser, and an abnormality detection means for comparing the monitor signal with a comparison level obtained by adding a DC voltage above and below the output of the sample and hold means. An optical disc device comprising: an optical disc device, wherein the laser is driven by the monitor signal only when no abnormality is detected.