JPH0668848B2 - Optical recording / reproducing device - Google Patents

Description

The present invention relates to an optical recording / reproducing apparatus using an optical recording medium capable of optically writing and reading data, such as a magneto-optical disk.

SUMMARY OF THE INVENTION The present invention is an optical recording / reproducing apparatus such as an optical disk provided with an APC circuit (automatic power control circuit), in which the current flowing through the laser diode is independent of the APC circuit depending on the recording or reproducing mode. By performing the control in this manner, the current is quickly controlled at the time of mode switching.

[Conventional technology]

The magneto-optical disk can write, read, and erase data by using a laser diode.
FIG. 3 shows the light output characteristic a with respect to the current of the laser diode.
Indicates.

In the case of a magneto-optical disk, predetermined optical outputs are determined in each of writing, reading and erasing modes. If the optical output during reading is P _R , the optical output during erasing is P _E , and the optical output during writing is P _W , then in general P _R
<P _E <P _W. For example, P _R = 2mW, P _E = 2
0 mW and P _W = 30 mW.

The laser diode has a temperature characteristic, and in general, the optical output tends to decrease as the temperature rises. The characteristic a in FIG. 3 is translated in the direction of the current axis indicated by the arrow A due to the temperature change. Therefore, in the optical disc recording / reproducing apparatus, an APC circuit is provided in order to obtain predetermined optical outputs P _R , P _E and P _W regardless of temperature changes. In this APC circuit, the pin diode built in the laser diode detects the current flowing through the laser diode, and based on the detected value, the current is controlled so that the optical output has a predetermined magnitude. . In this case, since the current change mainly due to the temperature change is controlled, the time constant of the APC loop is made relatively large to make the response characteristic gentle.

On the other hand, when writing data in the optical disk recording / reproducing apparatus, first, the designated address is searched in the read mode from the addresses previously recorded in the disk. When the designated address is detected, the write mode is immediately switched to write the desired data in the data area of the address. When switching from the read mode to the write mode, it is necessary to increase the light output from P _R to P _W. Also, when switching between read, write, and erase modes, it is necessary to increase or decrease the optical output, respectively.

[Problems to be solved by the invention]

When performing the above-mentioned mode switching, it is necessary to raise or lower the light output to a predetermined value as quickly as possible, but since the conventional APC circuit has a relatively long time constant as described above,
It took time until the light output reaches a predetermined value after the mode switching was instructed. That is, since the APC circuit has a configuration in which the mode change is included in addition to the temperature change as a factor of the disturbance in the APC circuit, it is not possible to cope with the mode change requiring a quick response.

Therefore, the length of the gear tape from the end of the area where the address on the disk is recorded to the start of the data area,
Also, the length of the gap from the end of the data area to the start of the next address area is increased, and the data recording density is reduced accordingly.

[Means for solving problems]

In the present invention, means for changing the current of the laser diode according to the mode switching is provided.

[Action]

The APC circuit responds slowly to temperature changes, etc., and the current of the laser diode can be changed quickly for mode switching. As a result, the gear gap between the address area and the data area on the disk can be shortened, and the recording density can be improved.

〔Example〕

 FIG. 1 shows a first embodiment of the present invention.

In the figure, an input signal Si such as data to be written or an erase signal is input to an input terminal 1. This signal Si is applied to the amplifier 2, the output signal from its inverting terminal is applied to the base of the transistor Q ₁ , and the output signal from the positive terminal is applied to the base of the transistor Q ₂ . The transistors Q ₁ and Q ₂ are differentially configured, and the transistor Q ₃ is commonly connected to the emitters. The collector of the transistor Q ₁ is connected to the power supply V _CC via the load resistor R ₁ . The collector of the transistor Q ₂ is connected to the power supply V _CC via the laser diode LD, and is also connected to the collector of the shunt transistor Q ₄ via the resistor R ₂ .

The base voltage of the transistor Q ₁ is V _B1 , the transistor Q is
_When the base voltage of ₂ is V _B2 , the transistor Q ₁ is non-saturated and turned on when V _B1 > V _B2 . When V _B1 <V _B2 , the transistor Q ₂ is unsaturated and turned on, and at this time, the current i ₀ flows through the laser diode LD.

The transistor Q ₃ determines the current i ₀ according to the mode, and the base voltage of the transistor Q ₃ is V
_B3 , base-emitter voltage is V _BE , and emitter resistance is R
If it is ₃ , It is represented by.

On the other hand, the optical output of the laser diode LD is detected by the built-in pin diode PD. This detection output is the amplifier 3
After being converted into a current by, it is added to the sample circuit 4,
Sampled. This sampling is read,
This is performed only in one of the writing and erasing modes, for example, the reading mode, and the sampling output is held in the other modes. Therefore, the sample circuit 4 is provided with the read mode signal S _R. The sampled signal is applied to the comparison circuit 5 and compared with the reference voltage V _S.
The output signal of the comparator circuit 5 is applied to the base of the transistor Q ₄ to control its collector current i ₂ . This current i ₂ is shunted from the current i ₀ of the laser diode LD, and when the collector current of the transistor Q ₂ is i ₁ , there is a relationship of i ₀ = i ₁ + i ₂ .

According to the above, the output of the comparison circuit 5 shows that the characteristic a in FIG.
It indicates whether or not there is a deviation in the direction. Since the temperature changes gently, it is possible to know the deviation amount of the characteristic a by sampling only at the time of reading. Then, by controlling the current i ₀ according to this deviation, it is possible to obtain the characteristic a required under the current temperature conditions.

The sampling circuit 4 may be configured to constantly perform sampling, and the reference voltage V _S may be changed according to the mode.

On the other hand, digital mode selection signals S _R , S _W and S _E are selectively applied to the input terminal 6, and this signal is applied to the D / A converter 7 and converted into an analog voltage V _B3. It As a result, this voltage V _B3 becomes the signal S _R ,
The current i ₀ gradually increases in this order according to _SW and S _E , and the current i ₀ increases accordingly. That is, in the current characteristics a, optical main output according to the mode _{P R, P} W, P
Changed to _E.

According to the above, the current i ₀ is controlled according to the temperature change by the sampling performed in the comparison circuit 4 in the APC loop at a relatively long cycle, and the mode selection signal S
_R, S _W, can be Yotsute to S _E, rapidly change the magnitude of the current i ₀ obtain a predetermined light output. That is, since the means for changing the current i ₀ according to the mode change is provided in a circuit different from the APC loop, it is possible to make a quick response to the mode change and a gentle response to the temperature change.

Therefore, the gear gap between the address area and the data area on the disk can be shortened.

It is also known that noise is generated by the return beam of the laser beam reflected on the disk when reading the optical disk. As a countermeasure against this, a method of superposing a high frequency current on the above current has been conventionally used. According to the embodiment of the present invention, when superposing the high frequency current, it is sufficient to supply the high frequency current to the input terminal 1, so that there is an advantage that the circuit configuration is simplified.

FIG. 2 shows a second embodiment, in which parts corresponding to those in FIG. 1 are designated by the same reference numerals.

In this embodiment, the APC circuit 8 having a relatively long time constant is used to detect the detection signal corresponding to the optical output from the amplifier 3.
Is added to the multiplication type D / A converter 9 through. This APC
The circuit 8 operates according to the signal S _R only in the read mode and is held in the other modes. The multiplication type D
In the / A converter 9, one of the signals S _R , S _W and S _E selectively applied from the input terminal 6 is multiplied by the control signal obtained from the APC circuit 8. Therefore, control signals having different levels for each mode are obtained as this multiplication output. This control signal is applied to the base of the transistor Q _3, which by connexion current i ₀ is controlled according to the mode and temperature changes. In this case, the mode selection signals S _R , S _W , and S _E promptly respond to the mode switching,
The APC circuit 8 responds flexibly to changes in temperature. At the same time, it is possible to obtain the operation and effect described above for the embodiment of FIG.

The case where the present invention is applied to the recording / reproducing apparatus of a magneto-optical disk has been described above. However, the present invention can be applied to a recording / reproducing apparatus of a recording medium such as an optical disk in which a signal is optically recorded. it can.

〔The invention's effect〕

In the present invention, the second power control circuit for changing the light output of the laser diode at least when switching between the recording mode and the reproducing mode is an APC circuit for compensating the temperature characteristic of the laser diode. It is provided separately. The second power control circuit is configured to be able to control the current flowing through the laser diode independently of the APC circuit according to a mode selection signal obtained by mode switching, and It is configured to have a response characteristic faster than a predetermined response characteristic. Therefore, not only the temperature characteristics of the laser diode can be well compensated, but also the light output of the laser diode can be changed promptly according to the mode switching, so that the gap between the address area and the data area on the recording medium can be prevented. It is possible to reduce the size, and thus it is possible to improve the recording density.

In addition, the second power control circuit can control the current flowing through the laser diode independently of the APC circuit,
Also, since it has a response characteristic faster than the predetermined response characteristic of the APC circuit, it is possible to satisfactorily compensate for the temperature characteristic of the laser diode, and the optical output of the laser diode can be promptly changed according to the mode switching. Although it can be changed, the circuit configuration is simple.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention, FIG. 2 is a circuit diagram showing a second embodiment of the present invention, and FIG. 3 is a characteristic diagram of a laser diode. In the reference numerals used in the drawings, Q ₁ , Q ₂ ... transistors (switch means) Q ₃ , Q ₄ ... transistor LD ... laser diode PD ... pin diode (detection means) 4 ... sample circuit (APC circuit) ) 5 ... Comparison circuit (APC circuit) 7 ... D / A converter (second power control circuit) 8 ... APC circuit.

Claims (2)

[Claims] 1. A switch means for performing a switching operation according to an input signal, a laser diode to which a current is applied according to the switching operation of the switch means, a detecting means for detecting an optical output of the laser diode, and at least a recording. In order to perform the control according to the temperature characteristic of the laser diode with a predetermined response characteristic in the mode and the reproduction mode, the current flowing through the laser diode can be controlled according to the detection signal from the detecting means. In order to change the light output of the laser diode at the time of switching to at least one of the recording mode and the reproducing mode by the power control circuit, the current flowing through the laser diode is changed according to the mode selection signal obtained by the mode switching. It can be controlled independently of the above automatic power control circuit and A second power control circuit having a response characteristic faster than the predetermined response characteristic of the automatic power control circuit. 2. The second power control circuit is configured to control a current flowing through the laser diode by a control signal obtained by multiplying the mode selection signal by a power control signal from the automatic power control circuit. The optical recording / reproducing apparatus according to claim 1.