JPH04102238A - Semiconductor laser control circuit - Google Patents

Abstract

PURPOSE:To reduce the fluctuation of a light emitting power due to self-heating by detecting the light emitting power in erasure, and controlling the light emitting power by correcting a current value for the acquisition of a reproducing power from an error with an erasing power. CONSTITUTION:Such control is performed that not only the erasing power in the erasure but the reprducing power after completing the erasure can be kept at appropriate values by detecting the error with the erasing power and correcting a first current driving circuit 4 to control the emitted light quantity of a semiconductor laser 1 at the reproducing power. To perform them above control, the output of an I-V converter 3 is compared with a reference voltage Vref equivalent to the erasing power by a comparator 12 in an erasure operation, and out-out in accordance with the error is obtained. The output of the comparator 12 is held with a peak holding circuit 13, and the current value of the first current driving circuit 4 is corrected. Also, the light emitting power is always kept at the reproducing power by a reproducing power control circuit 11.

Description

DETAILED DESCRIPTION OF THE INVENTION The above invention relates to a control circuit for a light source in an optical disk device, an optical card device, etc., and in particular, the present invention relates to a control circuit for a light source in an optical disk device, an optical card device, etc. This invention relates to a semiconductor laser control circuit with improved operational reliability.

In optical disk devices, it is necessary to control the current of the semiconductor laser, which is the light source, to a predetermined value during recording, playback, or erasing. Various proposals have been made.

For example, in a conventional semiconductor laser control method for recording or erasing in an optical disk device, just before recording or erasing, the semiconductor laser is made to emit light, and the current value and emitted light power that flowed at this time are determined. A method is known in which the differential efficiency is determined and the required recording or erasing power is output.

However, the I-L characteristics (current-light characteristics) of semiconductor lasers change significantly depending on temperature.

Therefore, in devices that use semiconductor lasers, it is necessary to accurately control the emission power of the semiconductor laser also with respect to temperature.

For example, a laser control area is provided in a part of each track of an optical disc, and in this area, the power of the semiconductor laser during recording or erasing is controlled.

FIG. 3 is a diagram showing an example of the sector format of each track of an optical disc.

As shown in FIG. 3, the laser control area is provided in a part of the address field located in the center, and is left blank in order to cause the semiconductor laser to emit light on a test basis.

In this conventional method of controlling light emitting power, the laser control area shown in Figure 3 is used to superimpose a predetermined current on the current value that was previously flowing for the semiconductor laser to emit light, thereby increasing the light emitting power. Calculate the differential efficiency from .

Then, from the calculated differential efficiency, the current value until the target light emission power is obtained is determined, and control is performed so that the desired light emission output is obtained.

However, with this control method, before recording or erasing,
It is necessary to measure the I-L characteristic (current-light characteristic). For example, when a semiconductor laser is caused to emit light continuously at high output during erasing, the I-L characteristic changes.

As a result, the light emission power also fluctuates, reducing the reliability of the optical disk device and the like. There is a problem.

In addition, since the optimum current value is different during reproduction and erasing, during erasing, control is performed to obtain erasing power by adding a predetermined current IE to current IR for obtaining reproduction power. Methods are also conventionally known.

Even in this control method, since no particular consideration is given to temperature changes, there is a problem in that the single light emission power similarly fluctuates and the reliability of the optical disk device etc. decreases.

However, this invention aims to overcome the disadvantages of conventional semiconductor laser control circuits, especially when erasing, the current 1. In addition, by adding a predetermined current ■E, the inconveniences of the control method for obtaining erasing power are solved, and the reliability of the optical disk is improved by reducing fluctuations in the light emitting power even with temperature changes. The purpose of the present invention is to provide a semiconductor laser control circuit with improved performance.

Means for Solving the Problems This invention provides a light emitting power control circuit for a semiconductor laser in a device that records, reproduces, or erases information by condensing a beam from a semiconductor laser onto an information recording medium using an objective lens. And at the time of erasing, the semiconductor laser.

A predetermined current value E is added to the current value R for obtaining reproduction power.
The light emitting power control circuit obtains the erasing power by adding and flowing the light emitting power.The light emitting power control circuit detects the light emitting power at the time of erasing, and corrects the current value for obtaining the above playback power from the error with the erasing power. I try to control the power.

Next, embodiments of the semiconductor laser control circuit of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows the semiconductor laser control circuit of the present invention.
1 is a functional block diagram showing an example of the configuration of its main parts;
In the drawing, 1 is a semiconductor laser, 2 is a light receiving element, 3 is an IV (current-voltage) converter, 4 is a first current drive circuit, 5 is a switch element, 6 is a second current drive circuit, 7 is D
/A converter, 8 is a CPU, 9 is an A/D converter, 10 is a sample hold circuit, 11 is a reproduction power control circuit, 12
is a comparator, 13 is a peak hold circuit, 14 is an adder circuit, and ■, , l are reference voltages.

The semiconductor laser control circuit of the present invention also uses a laser control area.

First, during normal reproduction, a part of the light emitted from the semiconductor laser 1 is received by the light receiving element 2, photoelectrically converted, and then passed through the next stage IV converter 3. Generates a voltage corresponding to

Further, the sample-and-hold circuit 10 is set to sample mode, and a voltage corresponding to this amount of light emission is applied to the sample-and-hold circuit 10, and is inputted to one side of the adder circuit 14 via the reproduction power control circuit 11.

The other manual input of this adder circuit 14 has OV as an initial value.
I will give you.

Then, the first current drive circuit 4 is controlled by the output of the adder circuit 14, and the amount of current of the semiconductor laser 1 is controlled by the output thereof.
Controls the amount of light emitted by the reproducing power.

Next, in the laser control area, C
A predetermined value is set in the D/A converter 7 by the PU 8,
A signal is applied to the second current drive circuit 6, the sample and hold circuit 10 is set to the sample mode, and the switch element 5 is turned on, thereby causing the semiconductor laser 1 to emit light more strongly than during reproduction.

The voltage corresponding to the amount of light emitted at this time is converted from analog to digital by the A/D converter 9, and the data is provided to the CPUa.

Here, the current value given via the D/A converter 7 is 11
and the playback power is P. , the power generated in the laser control area is Pl, then the differential efficiency η is given by η=(P knee P,)/I□ (1).

Next, when actually erasing, change the erasing power to PE.
Then, the current IE applied via the D/A converter 7 at this time can be found as follows: 1E=.(PEP−)η (2).

That is, by setting the current IE of the above equation (2) in the second current drive circuit 6, erasing becomes possible.

However, as described above, when the erasing operation is performed to some extent continuously (continuously in the case of the sample servo method), the emission power decreases due to self-heating of the semiconductor laser 1.

The reason for this is that the IL characteristics of the semiconductor laser 1 cause this second
This is because it changes as shown in the figure.

FIG. 2 is a characteristic diagram showing an example of the relationship between current and light emission amount in a semiconductor laser control circuit. In the drawings, the horizontal axis shows the current (I), the vertical axis shows the amount of light emitted (L), and ■ indicates the normal state, ■ indicates the time when self-heating occurs, and ITH indicates the threshold current.

As shown in FIG. 2, the IL characteristics of the semiconductor laser change rapidly when the current exceeds a threshold value.

Furthermore, the threshold value changes due to the occurrence of self-heating of the semiconductor laser.

In this way, the I-L characteristic of a semiconductor laser is expressed by the above equation (
From the differential efficiency obtained in 2), the threshold current (IT) I
) is more dominant.

Therefore, it is not possible to maintain the erasing power or the reproduction power after erasing at an appropriate value simply by controlling the current using differential efficiency.

In this invention, we focus on such characteristics in the I-L characteristics of a semiconductor laser, detect the error with the erasing power,
By correcting the first current drive circuit 4, not only the erase power during erasing but also the reproduction power after erasing is controlled so as to be maintained at an appropriate value.

Therefore, during the erase operation, the output of the IV converter 3 is compared with a reference voltage v1 corresponding to the erase power by the comparator 12, and an output corresponding to the error is obtained.

The output of the comparator 12 is held in a peak hold circuit 13 to correct the current value of the first current drive circuit 4.

After the erase operation is completed, the output of the comparator 12 is turned off, the hold time of the peak hold circuit 13 is set to a predetermined value, and the output of the peak hold circuit 13 is gradually brought to OV.

In this case, the light emission power is always maintained at the reproduction power by the reproduction power control circuit 11.

Such control makes it possible for the semiconductor laser 1 to suppress fluctuations in light emission power caused by self-heating during erasing.

According to the semiconductor laser control circuit of the present invention, the current value flowing through the semiconductor laser during erasing is the sum of the current value IR for outputting reproduction power and the current IE for producing erasing power. Moreover, the current value IR for outputting reproduction power is corrected based on power fluctuations during erasing.

Therefore, fluctuations in not only the erasing power but also the reproduction power after the erasing operation are suppressed, and the reliability of the operation of the optical disk device and the like is significantly improved, which is an excellent effect.

[Brief explanation of the drawing]

FIG. 1 shows the semiconductor laser control circuit of the present invention.
FIG. 2 is a characteristic diagram showing an example of the relationship between the current and the amount of light emitted in the semiconductor laser control circuit. FIG. 3 is a diagram showing the sector format of each track of the optical disc. A diagram showing an example. In the drawing, 1 is a semiconductor laser, 2 is a light receiving element, 3 is an IV (current-voltage) converter, 4 is a first current drive circuit, 5 is a switch element, 6 is a second current drive circuit, 7 is D
/A converter, 8 is a CPU, 9 is an A/D converter, 10 is a sample hold circuit, 11 is a reproduction power control circuit, 12
is a comparator, 13 is a peak hold circuit, and 14 is an adder circuit.

Claims (1)

[Claims] A semiconductor laser light emitting power control circuit in a device that records, reproduces, or erases information by condensing a beam from a semiconductor laser onto an information recording medium using an objective lens, and at the time of erasing. is a light emitting power control circuit that obtains erasing power by adding a predetermined current value I_E to a current value I_R for obtaining reproduction power to flow through the semiconductor laser, detects the light emitting power at the time of erasing, and determines the erasing power. A semiconductor laser control circuit, characterized in that the emission power is controlled by correcting the current value I_R for obtaining the reproduction power from the error between the two.