JP2834920B2 - Control method of optical information recording / reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling an optical information recording / reproducing apparatus, and more particularly to a method for controlling an optical information recording / reproducing apparatus characterized by a method for controlling a light output of a laser diode used as a light source. It is.

[0002]

2. Description of the Related Art Conventionally, a light output control circuit of a laser diode of an optical information recording / reproducing apparatus is configured as shown in FIG. First, the configuration will be described. In the figure, 1 is a laser diode as a light source, 2 is a photodiode for monitoring the optical output of the laser diode 1, 3 is a CPU, 4, 7
Is a register whose value can be rewritten by the CPU 3,
5, 8 are DA converters for converting the values of the registers 4, 7 into analog values, and 6, 9 are the DA converters 5, 8
A current source controlled by an output voltage of a high-speed switch for generating a write pulse light and an erase light;
Reference numeral 11 denotes a gain adjustment circuit that adjusts the gain of the output current of the photodiode 2 and converts it to a voltage, 12 denotes an AD converter that converts the output voltage of the gain adjustment circuit 11 to a digital value, and 13 to 15 denote the registers and the like. Is a memory for temporarily storing the value of the laser diode 1, 16 is a thermistor for detecting the temperature of the laser diode 1, and 17 is an AD converter for converting the output voltage of the thermistor 16 to a digital value.

The components of the optical information recording / reproducing apparatus other than the light output control circuit, such as the spindle motor and the actuator servo system, will not be described in order to explain the present invention, so that the description is omitted.

[0004] Next, the operation will be described, but before that, the characteristics of the laser diode will be described to help understanding of the operation. FIG. 3 is a diagram showing the relationship between the forward current and the light output of the laser diode. As shown in the figure, the laser diode does not emit laser light until a current of a certain value (Ith), and thereafter the light output increases linearly. In the figure, “a” is a representative one, but there are some such as “b” and “c” due to individual variations. Change. Therefore, when it is necessary to accurately obtain a predetermined optical output as in an optical information recording / reproducing apparatus, the optical output is monitored and the forward current for driving the laser diode is adjusted so that the optical output becomes a predetermined value. A possible light output control circuit is required. In the drawing, IB is a forward current required to obtain a readout optical output, and IP is a forward current required to be added to IB and flow to obtain a write and erase optical output. The reason for using two current sources in this way will be described later. Returning to FIG. 2, the description will be continued.

In the figure, the output current of the photodiode 2 and the optical output of the laser diode 1 are in a proportional relationship, but since the laser diode passes through several optical components from the recording medium, the optical efficiency of this optical component And the variation of the photodiode 2, the proportional coefficient between the laser power on the recording medium and the output current of the photodiode varies. The gain adjustment circuit 11 is adjusted so as to correct this variation so that the CPU 3 can detect the absolute value of the laser power on the recording medium via the AD converter 12. The procedure for lighting the laser diode 1 with the read light output is as follows. First, the register B is cleared and the switch 10 is off.

Therefore, the current value of the current source (B) 9 is 0, and the laser diode 1 does not emit light. Next, the CPU 3 gradually increases the value of the register (B) 7 and increases the drive current of the laser diode 1. Then, when it is detected through the AD converter 12 that a predetermined optical power has been obtained, the increase of the register (B) 7 is stopped. As described above, even when a constant current is supplied to the laser diode due to a temperature change or deterioration due to energization, the light emission output changes, so that the CPU 3 constantly monitors the output of the laser 1 via the AD converter 12. When the value becomes larger than the predetermined value, the value of the register (B) 7 is decreased. On the contrary, when the value becomes smaller than the predetermined value, the value of the register (B) 7 is increased so that the output of the laser 1 becomes the predetermined value. Control to maintain.

As described above, a current corresponding to IB in FIG. 3 is supplied by adjusting the current source (B) 9 and lighting is performed with a readout light output. Hereinafter, such automatic control will be referred to as APC (A
autoPower Control).

The procedure for lighting the laser diode 1 with the write and erase light outputs is as follows.
The register (B) 7 holds a value that gives a read light output immediately before starting writing and erasing. A value is set in the register (A) 4 so that a predetermined write and erase light output can be obtained by a method described later. Then, the high-speed switch 10 is turned on and off in accordance with the write pulse and the erase timing.
As described above, the current corresponding to IP in FIG.
Is adjusted, added to the current corresponding to IB, and given to the laser diode 1 to obtain an optical output for writing and erasing. Since the current sources (A) 6 and (B) 9 cannot change the current value at high speed, high-speed pulse lighting requires such a configuration as “two current sources and one high-speed switch”. Take.

[0009] Even when the light output for writing and erasing is turned on (hereinafter, when the high output is turned on), current control is required to keep the light output at a predetermined value in consideration of the temperature characteristics of the laser diode. This is performed by adjusting the value of the register (A) 4 so that the optical output (in writing, an average value of a portion where the duty is constant is often used) becomes a predetermined value.
It is more important to control the register A to set a value that can be a predetermined light output before the high-power lighting described above, rather than the APC performed during the high-power lighting. It is for the following two reasons.

Since the response speed of the APC is slow, if the APC is started after the high-power lighting is started, the time during which a predetermined light output is not obtained may be long.

Since the high output lighting time is relatively short, even if APC is not performed, the light output fluctuation during that period is small.

The value for high output lighting is stored in a register (A).
A relatively easy and typical prior art method of presetting to 4 is as follows.

1. A test track that can be arbitrarily erased is provided on the recording medium in advance.

2. After the power is turned on and the laser spot is focused on the recording medium, the laser spot is sought to the test track.

3. After setting an appropriate value in the register (A) 4, high-power lighting is started and APC is performed so as to attain the first laser power.

4. When the APC is performed at the first laser power, the CPU 3 stores the value of the register (A) 4 in the memory (A).
13 is stored.

5. Subsequently, the CPU 3 performs APC so as to have the second laser power.

6. When the APC is performed at the second laser power, the CPU 3 stores the value of the register (A) 4 in the memory (B).
Save to 14.

[7] The high output lighting ends.

8. The CPU 3 measures the temperature of the laser diode 1 at this time via the thermistor 16 and the AD converter 17 and stores the value in the memory (C) 15.

As described above, a series of steps in which the laser spot is sought on the test track, the value of the register (A) 4 capable of emitting light with the first and second laser powers is obtained by APC, and stored in the memory. The operation is hereinafter called a write test.

9. At the time of the next high output lighting, the CPU 3 first measures the temperature of the laser diode 1 via the thermistor 16 and the AD converter 17 and compares it with the value stored in the memory (C) 15.

10. If the difference between the two is equal to or greater than the predetermined value,
The write test is performed again, and the memories (A) 13 and (B) 1
4 and the value of (C) 15 is updated.

11. The value of the register (A) 4 corresponding to the desired high output power is stored in the memory (A) 13 corresponding to the first laser power and the value of the memory (B) 14 corresponding to the second laser power. And set in the register (A) 4. As shown in FIG. 3, the IP current and the emission power of the laser have a linear relationship. In general, the relationship between the resistor (A) 4 and the current source (A) 6 is made linear to correspond to the desired power. When the value of the register (A) 4 is obtained, linear interpolation (or external measurement) is performed based on the values of the memory (A) 13 and the memory (B) 14.

As described above, the laser diode 1
When the temperature of the laser diode 1 changes by a predetermined value or more, a write test is performed, and the value of the register (A) 4 is set in advance. A desired laser power can be obtained accurately from the start of lighting.

This concludes the description of the entire operation of the laser diode light output control circuit.

[0027]

The conventional method of setting the value of the register A in advance has the following disadvantages.

That is, conventionally, a thermistor and an AD converter for measuring the temperature of the laser diode were required, which was disadvantageous in cost and mounting area. In particular, with respect to the thermistor, it has been extremely difficult to simplify and reduce the size of the laser diode around the mechatronics for miniaturization.

It is an object of the present invention to provide a method for controlling an optical information recording / reproducing apparatus which solves the above problems.

[0030]

According to the present invention, there is provided an optical information recording / reproducing apparatus for recording, reproducing and erasing information by irradiating a recording medium with light emitted from a laser diode. A first register for setting a current value at the time of reproducing information, a first current source for supplying a current to the laser diode based on the value set in the first register, and recording / erasing A second register for setting a current value at the time, and a current based on the value set in the second register is supplied to the laser diode while being superimposed on the current supplied from the first current source. The light emitted from the second current source and the laser diode is monitored, and the light is supplied from the first and second current sources to the laser diode via the first and second registers so that the light has a predetermined output. The current Optical information recording apparatus comprising: an auto power control circuit for adjusting the current value; a memory for storing a current value set in the first and second registers; and a control means for controlling the memory and the first and second registers. In the control method of the reproducing apparatus, a recording test in which a current supplied to the laser diode is adjusted by an auto power control circuit so that the light has a predetermined output while irradiating a predetermined area of the recording medium with light having a recording power. Performing, a step of storing the current values set in the first and second registers in the memory at the time of the recording test, and an auto power control circuit for irradiating the recording medium with light of a predetermined reproduction power. The current value set in the first register is updated, and information is reproduced while adjusting the current supplied from the first current source to the laser diode. And superimposing the current output from the second current source based on the current value of the second register stored in the memory on the current from the first current source adjusted at the time of the reproduction. And recording and erasing information, and the current value of the first register stored in the memory and the updated first current value.
And if the difference between the current values is equal to or more than a predetermined value, the recording test is performed again.

[0031]

According to the present invention, the change in temperature is detected by utilizing the fact that the optical output of the reproduction power of the laser diode changes with the change in temperature, and the timing for performing the recording test again is determined. This makes it possible to appropriately control the laser diode light output without requiring a thermistor and an AD converter for detecting the temperature of the laser diode as in the related art.

[0032]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, in which a thermistor for measuring the temperature of the laser diode 1 and an AD converter are omitted from the circuit of FIG. Since other configurations are the same as those in FIG. 1, the following description focuses on the operation of detecting the temperature change of the laser diode 1, which is a feature of the present invention.

As described above, the current-light output characteristics of the laser diode 1 change as shown in FIG. 3, but the IB current at this time approximately follows the following equation.

[0035] _{IB (T1) = IB (T0} ) exp {(T 1 -T 0) / T k} IB (T1): IB IB at the temperature T _{1 (T0):} IB T at the temperature T _{0 k:} if a characteristic temperature (constant) the same type of laser diode, IB _(T0) and the individual variations in the value of T _k, since falling within a certain value, laser by detecting a change in the IB The temperature change of the diode 1 can be known. T _k is generally 1
Since the temperature is 30 ° K to 160 ° K, which is a sufficiently large value with respect to the temperature change of the laser diode 1, the change of the IB current with respect to the temperature change may be regarded as substantially linear.

The write test according to the present invention is performed as follows.

1. After the power is turned on, the first write test is the same as the conventional one. However, the memory (C) 15 stores not the temperature of the laser diode 1 via the thermistor and the AD converter but the register (B) 7 immediately before the write test. The value is saved.

2. At the time of high output lighting, first, the CPU 3 compares the value of the register (B) 7 at that time with the value of the previous register (B) 7 stored in the memory (C) 15.

3. If the difference between the two is equal to or greater than the predetermined value, a write test is performed again to update the values of the memories (A) 13, (B) 14, and (C) 15. If not, go to the next step.

4. A value is set in the register (A) 4 in the same manner as in the prior art, and high-output lighting is started.

(Other Embodiments) To simplify the explanation,
In the description of the conventional example, a series of APC operations are performed by the CPU. However, the present invention can be applied in exactly the same manner even if this is configured by a comparator and an up / down counter. Usually, a high-frequency current is superimposed on an applied current to reduce laser noise during lighting with a readout output. Even in such a case, the present invention can be applied within a range in which the high-frequency current does not largely fluctuate.

[0042]

As described above, according to the present invention, the laser light output can be appropriately controlled without the need for a temperature detecting thermistor and an AD converter, and the cost can be reduced. It has a great effect on miniaturization.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a block diagram of a conventional example.

FIG. 3 is a diagram showing characteristics of a laser diode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser diode 2 Photodiode 3 CPU 4 Register A 5 DA converter A 6 Current source A 7 Register B 8 DA converter B 9 Current source B 10 High-speed switch 11 Gain adjustment circuit 12 AD converter 13 Memory A 14 Memory B 15 Memory C

Claims (1)

(57) [Claims] 1. An optical information recording / reproducing apparatus for recording, reproducing and erasing information by irradiating a recording medium with light emitted from a laser diode, wherein the apparatus is used for setting a current value at the time of reproducing information. A first register, a first current source for supplying a current to the laser diode based on the value set in the first register, and a second register for setting a current value during recording and erasing. A second current source that supplies a laser diode with a current based on the value set in the second register superimposed on the current supplied from the first current source, and light emitted from the laser diode. An auto power control circuit for monitoring and adjusting a current supplied from the first and second current sources to the laser diode via the first and second registers so that the light has a predetermined output; as well as In a control method for an optical information recording / reproducing apparatus, comprising: a memory for storing a current value set by a second register; and control means for controlling the memory and the first and second registers. Performing a recording test in which a current supplied to the laser diode is adjusted by an auto power control circuit so that the light has a predetermined output while irradiating the predetermined area with light having a recording power; Storing the current value set in the second register in the memory; and setting the current value set in the first register by the auto power control circuit so that the recording medium is irradiated with light of a predetermined reproduction power. Updating and reproducing the information while adjusting the current supplied from the first current source to the laser diode; and reproducing the information from the first current source adjusted during the reproduction. The flow, the based on the current value of the second register which is stored in the memory 2
Superimposing the current output from the current source and supplying the superposed current to the laser diode to record and erase information; and the current value of the first register stored in the memory and the updated value of the first register. Comparing the current values with each other, and when the difference between these current values is equal to or more than a predetermined value, performing a recording test again.