JPS63124482A - Device for driving semiconductor laser - Google Patents

Abstract

PURPOSE:To write information in an optical disk at an optimum write level even when the conditions of the outside air change by monitoring emission power projected from a semiconductor laser, comparing the result of the monitor and a specified value previously set to a current control means and varying and controlling driving currents fed to the laser. CONSTITUTION:The voltage value of a radiant power output at the time of a record level is sampled by a sampling hold circuit 1 in response to a recording signal 25, and difference between a voltage value output from the circuit 1 and a reference voltage value 3a transmitted from a reference voltage source 3 is amplified by an error amplifier 2. Error voltage is evaluated at steps such as three steps of +, 0 and - from the amplifier 2 by using a detector 4, the signals of the evaluation are added to a counter 5, and the count values of +, 0 and - are determined on the basis of an output from the level detector 4. The signals are output to an adder 7 to which the reference voltage value 3a is applied, and the result of the output is fed back to a constant current circuit 23 and currents from the circuit 23 are controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a driving device for a semiconductor laser serving as a means for writing and reading information into and from a recording medium such as an optical disk.

[Conventional technology]

Conventionally, as this type of device, a device as shown in FIG. 3 has been proposed.

FIG. 3 is a block diagram illustrating the configuration of a conventional semiconductor laser driving device, in which 21 is a semiconductor laser, the optical output during reproduction is controlled by a constant current circuit 22, and a constant current circuit 23
controls the optical output during recording. 24 is a switch which is closed based on the input recording signal 25, and the semiconductor laser 21 is closed by increasing the current applied to the constant current circuit 23.
increase the light emission output of the device to a recording level. 26 is a photodiode that monitors the light emission output of the semiconductor laser 21, and the voltage value corresponding to the light emission output is sent to the sample and hold circuit 28.
Enter. The sample hold circuit 28 receives the recording signal 25
A voltage value corresponding to the light emission output value is sampled and held based on. A current-voltage conversion resistor 27 converts the current value flowing through the photodiode 26 into a voltage value based on the light emission output input to the photodiode 26. Reference numeral 29 denotes an error amplifier that amplifies the difference between the light emission output during reproduction held in the sample and hold circuit 28 and a preset reference voltage, and applies a difference signal to the constant current circuit 22.

The optical output of the semiconductor laser 21 during reproduction is controlled by a constant current circuit 22, and when the recording level is reached, the constant current circuit 23 is closed by closing the switch 24 in response to the recording signal 25.
The optical output of the semiconductor laser 21 is increased to the recording level by the increasing portion of the current supplied to the semiconductor laser 21 .

In addition, the photodiode 26. Current voltage conversion resistor 27
The voltage value of the light emission output of the semiconductor laser 21 detected by the sample and hold circuit 28 is sampled at the reproduction level, and the value at the reproduction level is held at the recording level.
2 is controlled to keep the optical output of the semiconductor laser 21 constant at the reproduction level.

[Problem that the invention seeks to solve]

Next, problems with the semiconductor laser driving device will be explained with reference to FIG.

FIG. 4 is a diagram for explaining the characteristics of the semiconductor laser 21 shown in FIG. 3, in which the vertical axis shows the light emission output P and the horizontal axis shows the laser drive current I.

In this figure, a is the light emission characteristic, which shows the relationship between the light emission output and the laser drive current when the temperature is tl. b shows luminescence characteristics, and the temperature is tl (tl>t+)
This figure shows the relationship between the way light is emitted and the laser drive current in the case of .

As can be seen from this figure, the threshold current value for laser oscillation of the semiconductor laser 21 increases as the temperature rises.
Unit light emission output/unit drive current (ΔP) in the laser oscillation region
It is known as a general characteristic that the value of

Now, assuming that the temperature changes from tl to tl,
The laser drive current is controlled from Ilt+ to lR2 so that the light emission output PR during reproduction remains constant, but since the constant current circuit 23, which is responsible for the current increase during recording, is conventionally fixed, The drive current is IRI + I + lR2, and since I R1 - I R2 < I2 - Iga l, Iw + + lR2 - IH < In2, and the light emission output P during recording will not reach the light emission output FW. There was a problem.

In view of the current situation where accurate control of recording power is required as recording density increases in the future, there is a strong desire to improve the above-mentioned problems.

This invention was made to solve the above-mentioned problems, and it is possible to write information by monitoring the light emission power emitted from the semiconductor laser during information writing and by connecting the drive current supplied to the semiconductor laser. An object of the present invention is to obtain a semiconductor laser driving device that can maintain the light emission level at a prescribed writing level without being affected by external influences.

[Means for solving problems]

The semiconductor laser driving device according to the present invention includes a monitor means for monitoring the light emission power emitted from the semiconductor laser during information writing, and a comparison between the light emission power monitored by the monitor means and the light emission power during information writing with a specified value set in advance. A current control means for variably controlling the drive current supplied to the semiconductor laser is provided.

[Effect]

In this invention, the monitor means monitors the power of light emitted from the semiconductor laser. The current control means compares this monitoring result with the preset value,
Variably controls the drive current supplied to the semiconductor laser.

Embodiment C] FIG. 1 is a block diagram illustrating the configuration of a semiconductor laser driving device showing an embodiment of the present invention, and the same components as in FIG. 3 are given the same reference numerals.

In this figure, reference numeral 1 denotes a sample and hold circuit which samples the voltage value of the light emission output at the recording level in accordance with the recording signal 25, and holds the voltage value at the recording level at the reproduction level. Reference numeral 2 denotes an error amplifier that amplifies the difference between the reference voltage 3a supplied from the reference voltage source 3 and the voltage value output from the sample and hold circuit 1. 4 is a level detector that detects the output of the error amplifier 2, that is, the error voltage, for example, +
,0. - is evaluated in three stages, and a signal indicating the evaluation is output to the counter 5. The counter 5 receives the input recording signal 25
Count up (+), stop counting (0), count down (-) based on the output from level detector 4
I do. 6 is a D/A converter which converts the count value counted by the counter 5 into an analog signal and outputs it to the adder 7. Since the reference voltage 3a supplied from the reference voltage source 3 is applied to the adder 7, the addition result of the reference voltage 3a and the count value of the counter 5 is fed back to the constant current circuit 23, and the result is fed back to the constant current circuit 23. The current applied to the is controlled. Note that the operations 21 to 29 described above are the same as those of the conventional example, so the explanation thereof will be omitted.

When the recording signal 25 is input, the sample and hold circuit 1 samples the voltage value corresponding to the light emission output at the recording level, and holds the voltage value sampled at the recording level at the reproduction level. Accordingly, the error amplifier 2
amplifies the difference with the reference voltage 3a supplied from the reference voltage source 3 and outputs the difference signal to the level detector 4. The level detector 4 evaluates the difference signal into three levels, for example, + and O9-, based on a preset value, and outputs a signal indicating this to the counter 5. As a result, the counter 5 counts up, stops counting, and counts down the input recording signal 25, and outputs the count result to the D/A converter 6.

Note that the counter 5 holds a count value when the optical output is at the reproduction level. The D/A converter 6 D/A converts the value outputted from the counter 5 and outputs it to the adder 7. For this reason, the adder 7 adds the reference voltage 3a supplied from the reference voltage source 3 and the count value, and increases, maintains, or decreases the current applied to the constant current circuit 23, thereby changing the signal to a constant current. It is fed back to the circuit 23.

For this reason, if the necessary light emission output at the recording level cannot be obtained due to a rise in temperature, the evaluation of the level detector 4 will be "+".
”, the count is increased in synchronization with the recording signal 25 input to the counter 5, and the count value is input to the D/A converter 6, so the adder 7 outputs the count value to the reference voltage 3a. As a result of the addition of the converted values, a signal is fed back to the power failure flow path 23, the current for driving the semiconductor laser 21 is increased, and the control is performed so that a specified recording level is obtained.

FIG. 2 is a block diagram illustrating a semiconductor laser drive circuit showing another embodiment of the present invention, and the same components as in FIG. 1 are given the same reference numerals.

In this figure, 11 is an A/D converter which A/D converts the voltage value of the light emission output of the semiconductor laser 21 based on the input recording signal 25. Reference numeral 12 denotes an error calculator that calculates the difference between the set value supplied from the reference value setter 17 and the A/D conversion output from the A/D converter 11. A level comparator 13 compares the error level calculated by the error calculator 12 with a preset reference level and outputs the comparison result to the counter 5. The counter 5 has a clock generator 14
A gate circuit 16 is provided so that a clock signal (having a higher frequency than the recording signal 15) generated from the recording signal 15 is inputted only when the single recording signal 15 is inputted.

As can be seen from this figure, if the count value is set in advance in the counter 5 by the reference setter 17, the optical output level can be controlled according to the count value, and when a single recording signal 15 is input. It also outputs light and can control the bell.

In the above embodiment, the case where the optical output level control is executed based on the input recording signal 15 has been explained, but the optical output level control is executed when the power is turned on, and the optical output level control is executed based on the input recording signal 15 thereafter. It may be configured to finely control the output level.

〔Effect of the invention〕

As explained above, the present invention includes a monitor means for monitoring the light emitting power emitted from a semiconductor laser when writing information, and a comparison between the light emitting power monitored by the monitor means and the light emitting power during writing the information with a predetermined value. hand,
Since a current control means for variably controlling the drive current supplied to the semiconductor laser is provided, the emission power of the semiconductor laser can be varied when writing information, and even if the outside air conditions change due to temperature information, the optimum It has the excellent advantage of being able to write information on optical discs at a high writing level.

[Brief explanation of the drawing]

FIG. 1 is a block diagram explaining the configuration of a semiconductor laser driving device showing one embodiment of the invention, FIG. 2 is a block diagram explaining a semiconductor laser driving circuit showing another embodiment of the invention, and FIG. 3 4 is a block diagram illustrating the configuration of a conventional semiconductor laser driving device, and FIG. 4 is a diagram illustrating the characteristics of the semiconductor laser shown in FIG. 3. In the figure, 1 is a sample hold circuit, 2 is an error amplifier, and 3
is a reference voltage source, 4 is a level detector, 5 is a counter, 6 is a D/A converter, 7 is an adder, 11 is an A/D converter, 12
13 is a level comparator, 14 is a clock generator, 15 is a recording signal, 16 is a gate circuit, 21 is a semiconductor laser, and 22.23 is a constant current circuit.

Claims (1)

[Claims] In a semiconductor laser drive device that irradiates a recording medium while varying the light emitting power of a laser beam emitted from a semiconductor laser during information reproduction or information writing, the light emitting power emitted from the semiconductor laser during information writing is monitored. and current control means for variably controlling the driving current supplied to the semiconductor laser by comparing the light emission power during information writing monitored by the monitoring means with a preset standard value. A semiconductor laser drive device characterized by: