JPH0622067B2 - Semiconductor laser drive device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser driving device used in an optical information recording / reproducing device for optically recording and reproducing information on a disc.

Conventional Technology Conventional technology will be described with reference to FIGS. 2 and 3.

FIG. 2 shows the current vs. light output characteristics of the semiconductor laser, but the temperature dependence is high, and it is difficult to obtain a constant output by constant current drive. Therefore, the semiconductor laser backward light is detected and feedback is given to the drive circuit. On the other hand, the semiconductor laser drive circuit in the optical recording device operates so as to have a constant output of low power during reading and reading of information, and it is necessary to repeat high-power and low-power light emission at high speed during recording and writing of information. However, simply adding a modulation circuit to a constant output circuit having a feedback loop for temperature compensation generally makes it difficult to obtain light emission power proportional to the modulation signal because the time constant of the feedback loop is large.

A conventional example and its problems corresponding to this problem will be described below with reference to FIG.

FIG. 3 shows a block diagram of a conventional semiconductor laser drive circuit. During reproduction, the second switching circuit 5 has the terminal b.
And terminal c are closed, and the third switching circuit 10 is open. The optical output of the semiconductor laser 12 is monitored by the power detection circuit 1 for the rear light, and during reproduction, the semiconductor laser drive current is controlled by the first control circuit 4 and the first drive circuit 8, and reproduction is performed by this power control. Power is stabilized against ambient temperature. Next, at the time of recording, the terminals a and b of the second switching circuit 5 are closed, and the third switching circuit 10 is closed. The reproduction value holding circuit 7 holds the control signal 13 at the time of reproduction, and the semiconductor laser drive current corresponding to the signal flows to the semiconductor laser 12. Further, at this time, a semiconductor laser drive current corresponding to the output of the recording power setting circuit 11 is superimposed to emit light at the recording power. When the recording time is short, stable recording power can be obtained with little absorption due to temperature rise.

Problems to be Solved by the Invention In the conventional circuit configuration shown in FIG. 3, since the control loop is opened by the second switching circuit 5 during recording, the first control is performed by increasing the output of the power detection circuit 1. The circuit 4 operates like a comparator and the control signal 13, which is an output signal, is saturated. Therefore, the semiconductor laser is driven with the minimum power or the maximum power by the saturated control signal 13 at the moment when the recording is changed to the reproduction. At this time,
There is a problem that the semiconductor laser is destroyed.

The present invention has been made in view of the above points, and an object of the present invention is to provide a semiconductor laser drive circuit in which abnormal light emission of the semiconductor laser does not occur at the time of transition from recording to reproduction.

Means for Solving the Problems The present invention relates to a power detection circuit for detecting the emission intensity of a semiconductor laser, a reproduction power setting circuit, a first drive circuit for driving the semiconductor laser, and an output of the power detection circuit. A first control circuit for controlling the first drive circuit so that the outputs of the reproducing power setting circuit and the reproducing power setting circuit are equal, and a reproduction time value holding for holding the reproduction output of the first control circuit when the recording power is emitted. Circuit, a second control circuit for controlling the input of the first control circuit so that the value held by the reproduction value holding circuit when the recording power is emitted and the output of the first control circuit become equal, and a recording power setting circuit And a semiconductor laser drive device including a second drive circuit that drives the semiconductor laser by superimposing it on the output of the first drive circuit according to the output of the recording power setting circuit when the recording power is emitted.

In order to solve the above problems, the present invention adds a second control circuit for controlling the input of the first control circuit so that the first control circuit maintains the control signal output during reproduction during recording.

Action According to the present invention, the control signal output from the first control circuit has the value at the time of reproduction even at the time of recording, and the control signal becomes stable at the time of transition to the reproduction.

Embodiment FIG. 1 is a block diagram showing an embodiment of a semiconductor laser drive circuit of the present invention. In FIG. 1, reference numeral 1 is a power detection circuit for detecting the power of the rear light of the semiconductor laser.
At the time of reproduction, the terminal f and the terminal h of the first switching circuit 3 are closed, and the output of the power detection circuit 1 and the reproduction power setting circuit 2
Is added to the input of the first control circuit 4. The second switching circuit 5 has terminals c and b closed, and the first control circuit 4 controls so that the two input signals are equal to each other. The semiconductor laser 12 is set by the reproduction power setting circuit 2. It emits light stably with the generated light output. At this time, the third switching circuit 10 is open and the second drive circuit is not operating.

The reproduction value holding circuit 7 holds the control signal 13 at the time of reproduction immediately before the recording transition. The second switching circuit 5 during recording
The terminals a and b are closed, the control signal at the time of reproduction just before the recording transition which is the output of the reproduction value holding circuit 7 is input to the first drive circuit 8, and the semiconductor laser 12 is changed to the recording transition. The current just before flows. At this time, the third switching circuit 10
Is closed and the current set by the recording power setting circuit 11 is superimposed on the semiconductor laser 12 by the second drive circuit 9, and the optical output becomes a recordable level. At the time of recording, the first switching circuit 3 has terminals g and h closed, and the second control circuit 6 controls the control signal 13 held in the reproduction value holding circuit 7 just before the recording transition. The inputs of the first control circuit 4 are controlled so as to be equal. When the recording time is short, the temperature rise of the semiconductor laser can be ignored, so that stable recording power can be obtained. At the time of transition from recording to reproduction, the first switching circuit 3 closes terminals f and h, and the second switching circuit 5 closes terminals c and b. The third switching circuit 10 opens. Immediately before this, the control signal which is the output of the first control circuit 4 is controlled to the value at the time of reproduction just before the recording transition, so that the reproduction power is smoothly shifted to the stable reproduction power and controlled.

EFFECTS OF THE INVENTION As described above, according to the present invention, stable control can be performed from the time of recording to the time of reproduction with an extremely simple circuit configuration, which is extremely useful in practice.

[Brief description of drawings]

FIG. 1 is a block diagram of a semiconductor laser driving device according to an embodiment of the present invention, FIG. 2 is a characteristic diagram of current vs. optical output of a semiconductor laser, and FIG. 3 is a block diagram of a conventional semiconductor laser driving circuit. 1 ... power detection circuit, 2 ... reproduction power setting circuit, 3
...... First switching circuit, 4 ... First control circuit, 5 ...
Second switching circuit, 6 ... Second control circuit, 7 ... Reproduction value holding circuit, 8 ... First driving circuit, 9 ... Second driving circuit, 10 ... Third switching circuit , 11 ... recording power setting circuit, 12 ... semiconductor laser, 13 ... control signal, a to h ... terminals.

Claims (1)

[Claims] 1. A power detection circuit for detecting the emission intensity of a semiconductor laser, a reproduction power setting circuit, a first drive circuit for driving the semiconductor laser, an output of the power detection circuit and a reproduction power setting circuit. A first control circuit that controls the first drive circuit so that the outputs are equal to each other, a reproduction value holding circuit that holds the reproduction output of the first control circuit when recording power is emitted, and a recording power emission When the recording power setting circuit, a second control circuit for controlling the input of the first control circuit so that the value held by the reproduction value holding circuit and the output of the first control circuit become equal A semiconductor laser drive device comprising: a second drive circuit that drives a semiconductor laser by superimposing it on the output of the first drive circuit according to the output of the recording power setting circuit.