JPH03245327A - Light emission power control circuit for semiconductor laser - Google Patents

Abstract

PURPOSE:To attain correct pit formation and recording by high speed switching by using bias power, for which driving at the time of recording is set weaker than the reproducing power, as a base and superimposing prescribed power to this bias power as recording power. CONSTITUTION:At the time of recording, a recording current value I3 determined by a current setting circuit 16 flows through a third constant current source 15 to a semiconductor laser 2 so that a switch element 8 can be turned off and prescribed recording power can be outputted, and a switch element 14 is turned on/off corresponding to a recording information signal. In such a way, the bias power, for which driving at the time of recording is set weaker than the reproducing power, is used as the base and the prescribed power is superimposed to this bias power and defined as the recording power. Thus, the correct pit formation is attained in the case of recording and recording is enabled by high-speed switching as well.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a light emitting power control circuit for a semiconductor laser used as a light source for recording, reproducing, or erasing in an optical disk device.

2. Description of the Related Art In general, optical disk devices use a semiconductor laser as a light source, and the light beam emitted from the semiconductor laser is focused onto an information recording medium such as an optical disk or magneto-optical disk using an objective lens to record, reproduce, or erase information. I try to do this. In this case, it is common to irradiate light with a power equal to or higher than a predetermined value during recording (including erasing, if necessary; hereinafter, erasing will not be discussed in particular, but the same will apply).

Therefore, the light emission pattern of the semiconductor laser in the recording mode is generally as shown in FIG. 4(a) at the recording power Pw.
It is assumed that a predetermined light emitting power is superimposed on the reproduction power PR. That is, the base of the emission power of the semiconductor laser is set to the reproduction power PR, and a predetermined power is superimposed on the portion to be recorded to obtain the recording power Pw. As a semiconductor laser drive circuit for causing such a power change, there is one disclosed in Japanese Patent Laid-Open No. 6.3-129537. This drive method samples and holds the semiconductor laser drive current during playback and during recording.
This method involves superimposing recording currents. Figure 3(a)
The semiconductor laser drive current corresponding to is as shown in FIG. 1w indicates the recording drive current, and 3 indicates the reproduction drive current.

However, in this method, since light is irradiated with the reproduction power PR between the bits to be recorded on the optical disc, it may not be possible to form bits correctly.

In order to eliminate such drawbacks, there is also a semiconductor laser power control method as shown in FIG. 5(a). This uses a bias power P11 that is weaker than the reproduction power P11, and the normal level is set to the bias power PB, and in the part to be recorded, a predetermined power is superimposed on this to set the recording power Pw. . FIG. 5B shows the corresponding semiconductor laser drive current. Such a bias power P6 emission control method is described in Japanese Patent Application Laid-Open No. 59-542.
There is one shown in Publication No. 81. In this method, the bias current IB for outputting the bias power PB is measured in advance at each temperature of the semiconductor laser, and the bias current 8 corresponding to the temperature change is caused to flow to output the bias power PB.

Incidentally, as shown in FIG. 6(a), there is also a method in which the recording power PW is applied to the portion to be recorded in the recording mode, but the power is completely set to 0 in the portion not to be recorded. FIG. 5B shows the corresponding semiconductor laser drive current.

Problems to be Solved by the Invention However, the method disclosed in Japanese Unexamined Patent Publication No. 59-5428 cannot cope with deterioration of the semiconductor laser, and the bias power PB becomes weaker over time. Further, it takes time and effort to measure temperature-dependent changes in characteristics of a semiconductor laser in advance, resulting in high costs. That is, there is a problem in setting or stabilizing the bias current or bias power.

Furthermore, according to the method shown in FIG. 6, the driving current required for switching at the portion to be recorded is large, making high-speed switching difficult.

Means for Solving the Problem The semiconductor laser is driven with a drive current in which a recording current is superimposed on a bias current that causes the semiconductor laser to emit light with a bias power set to be weaker than the reproduction power of a reproduction current, so that the semiconductor laser emits light with a recording power. In the light emitting power control device for a semiconductor laser in an optical disk device, which records information by condensing a light beam of this recording power onto an information recording medium by an objective lens, a first constant current connected to the semiconductor laser; a photodetector for detecting the amount of light emitted by the semiconductor laser; a current-voltage converter for converting the photocurrent output obtained from the photodetector into a voltage signal; and sampling the output voltage of the current-voltage converter. a sample-and-hold circuit for holding the sample-and-hold circuit; and a comparator for comparing the output voltage of the sample-and-hold circuit with a predetermined first reference voltage corresponding to the reproduced current value. A control circuit for controlling a first current value of the source forms a first control loop, and the output voltage of the current-voltage converter and a predetermined second reference voltage corresponding to the bias current value are set at a predetermined timing. A comparator to compare,
An up/down counter that operates up or down according to the output of this comparator, a digital-to-analog converter that converts the output of this up/down counter into an analog signal, and a switching element that is switched at a predetermined timing to control the semiconductor laser. A second constant current source is connected to the digital-to-analog converter and the second current value is controlled according to the output of the digital-to-analog converter to form a second control loop. The first current value of the current source is controlled to control the emission power of the semiconductor laser to the reproduction power, and then the switch element is turned on to generate a superimposed current of the first current value and the second current value. While controlling the emission power of the semiconductor laser to the reproduction power by controlling only the first current value by the first control loop in the semiconductor laser drive state according to the current value, the switch element is turned off at a predetermined timing to control the first current value at that time. The second current value is controlled by the second control loop so that the semiconductor laser has the bias power based only on the current value.

Basically, the drive during recording is based on a bias power set to be weaker than the reproduction power, and a predetermined power is superimposed on this to obtain the recording power, which allows correct bit formation and high speed. Recording by switching becomes possible. At this time, the bias current for bias power emission is set based on the reproduction power in addition to the essential reproduction power control, so it is accurate to cope with the deterioration of the semiconductor laser, and it is possible to set the This eliminates the trouble of measuring changes in characteristics due to

Embodiment An embodiment of the present invention will be described with reference to FIGS. 1 to 3. First, a semiconductor laser 2 driven by a first constant current source 1 with a first current value 1 is provided. A photodiode 3 is provided as a photodetector for receiving and detecting the amount of light emitted from the semiconductor laser 2. Photodiode 3
A current-voltage converter 4 is connected to convert the photocurrent output into a voltage signal. A sample-and-hold circuit (S/H circuit) 5 is connected to the current-voltage converter 4 for sampling the output voltage at a predetermined timing according to a sample-and-hold signal and holding the result. A control circuit 6 for controlling the current value 1 of the first constant current source 1 is connected to the S/I-f circuit 5. This control circuit 6 has a comparison section, and compares the output voltage of the S/H circuit 5 with a predetermined first reference voltage VRREF (corresponding to the reproduction current value), so that the output voltage becomes the first reference voltage vIIR.
The current value of the first constant current source l is adjusted to match EF.
It controls the A first control loop 7 is formed by these loops.

On the other hand, a second constant current source 9 is connected to the semiconductor laser 2 in parallel with the first constant current source 2 via a switching element 8 that is switched by an auto laser power control A LPC signal. Further, a comparator 10 is provided which compares the output voltage of the current-voltage converter 4 with a predetermined second reference voltage VBREF (corresponding to a bias current value). This comparator 10 has an up/down counter 11 that performs an up or down operation depending on the comparison result.
is connected. The count output of this up/down counter 11 is input to a digital/analog converter (D/A converter) 12. The output of the D/A converter 12 controls the second current value (2) of the second constant current source 9, and a second control loop 13 is formed.

Further, in the semiconductor laser 2, a third constant current source 15 with a recording current value of 3 is connected in parallel with the 1°2 constant current source 2.9 via a switch element 14 that is closed according to recording information in the recording mode. It is connected. The recording current value of the third constant current source 15 is set by the current setting circuit 6.

In such a configuration, the initial reproduction power control is
This is done by the control loop 7. That is, the switch element 8 is turned on, but the current value (2) of the second constant current source 9 connected thereto is set to I,=OmA, and the switch element 14 is turned off.

In this state, since the drive current {circle around (2)} flowing through the semiconductor laser 2 is caused only by the first constant current source 1, I=1. This is controlled so that it becomes the reproduction power PR regulated by the first base voltage VREF. In such a situation,
1-2- playback operations are possible for optical discs. Therefore, the I on the optical disk is
It is also possible to discriminate information such as D, and it is also possible to detect an A L PC area provided on an optical disc.

Therefore, when the ALPC region is detected by such a reproducing operation, the switch element 8 is turned off by the ALPC signal, and the output voltage of the current-voltage converter 4 at this time (that is, the output voltage of the semiconductor laser 2 Comparator 10
is compared with the second reference voltage VBREF. The up/down operation of the up/down counter 11 is determined based on the comparison result, and one counting operation is performed in one ALPC area. This count value is converted into analog by the D/A converter 12, and the current value of the second constant current source 9 is determined according to this analog output.
2 to change the amount of light emitted from the semiconductor laser 2.

At this time, the comparator 10 outputs a counter 11 when the amount of light emitted in the ALPC region is larger than the predetermined bias power P8.
The up signal is outputted to count up, the output of the D/A converter 12 becomes thicker, and as a result, the current value (7) increases. Then, when the ALPC region ends, the drive current flowing through the semiconductor laser 2 becomes I −I, +
However, the current value ■1 is automatically reduced by the reproducing power control of the first control loop 7, and the overall reproducing power is maintained at PR.

By sequentially repeating such operations, the amount of light emitted by the semiconductor laser 2 in the ALPC region approaches the bias power PB, and finally becomes equal to or less than the bias power P. At this time, the comparator 10 outputs a down signal to the counter 11 to count down and decrease the current value 2.

Thereafter, current values I and T are determined by repeating such up/down operations. Here, the amount of light emitted only by the current value ■1 becomes the bias power P.

Through such a series of operations in the ALPC region, the semiconductor laser 2 is adjusted to read power PR and bias power -1.
, i) 8, the current value II2 for emitting light is determined. The current value 11 corresponds to the bias power P[1, and the current value (I, +T2) corresponds to the reproduction power I), %t I;
i; Do 6. Also, in normal reproduction power control, in addition to the current value ■2 determined by the counter 11, a current 4+'f T, which corresponds to the light emitting area, is added! l', is realized by flowing into the conductive laser 2.

During actual recording, the switch element 8 is turned off, and the recording current value 1.0 is determined by the current setting circuit 16 so that a predetermined recording power pH is output. is applied to the semiconductor laser 2 through the third constant current source 15, and the switch element 14 is turned on/off in accordance with the recording information signal. As a result, the drive current 1 flowing through the semiconductor laser 2 is 11
and (1, +1.,) alternately. That is, the bias power P,3 is used as a base, and the power state becomes the recording power Pw in the recording portion, resulting in the recording method shown in FIG.

In addition, in the operation described in -1-, the timings of the sample-and-hold signal to the sample-and-hold circuit 5, the ALI) signal to the switch element 8, and the count pulse to the counter 11 are shown in FIG. That is, in the initial reproduction power control, since the ALPC signal and count pulse are not output, the first control loop 7 performs normal control.

Thereafter, when the A L PC signal and the count pulse are output, the bias power P5 is also controlled at the same time.

In the above description, the sampling and hold operation is performed even during the initial control, but the sampling mode may be continuous in the initial stage. In addition, bias power control is performed at the timing of ALPC area utilization, but if bias power control is performed, for example, when the power is turned on or when idle due to temperature changes, regardless of the presence or absence of an optical disk and the focus/tracking state. , the power can be controlled 5 6 .

Effects of the Invention Since the present invention is configured as described above, basically,
Because the drive during recording is based on a bias power set weaker than the reproduction power, and a predetermined power is superimposed on this to obtain the recording power, it is possible to form correct bits during recording, and it is also possible to record with high-speed switching. At this time, the bias current for bias power emission is set based on this reproduction power in conjunction with the essential reproduction power control by the predetermined first and second control loops. It is accurate enough to cope with deterioration of the laser, allows reliable recording operation, and does not require the trouble of measuring changes in characteristics due to temperature.

[Brief explanation of drawings]

1 to 3 show an embodiment of the present invention,
Fig. 1 is a block diagram, Fig. 2 is a semiconductor laser drive current-emission power characteristic diagram, Fig. 3 is a timing chart, and Figs. 4, 5, and 6 each show conventional examples of different control methods. FIG. 3 is a light emission power drive current characteristic diagram. 1... First constant current source, 2... Semiconductor laser, 3...
- Photodetector, 4... Current-voltage converter, 5... Sample and hold circuit, 6... Control circuit, 7... First control loop, 8... Switch element, 9... 2nd constant current source, 10... Comparator, 11... Up/down counter, 12... Digital-to-analog converter, 13... Second control loop

Claims (1)

[Claims] The semiconductor laser is driven with a drive current in which a recording current is superimposed on a bias current that causes the semiconductor laser to emit light with a bias power set to be weaker than the reproduction power of the reproduction current, and the semiconductor laser is made to emit light with a recording power, and the luminous flux of this recording power is A light emitting power control device for a semiconductor laser in an optical disk device configured to record information by condensing light onto an information recording medium using an objective lens, comprising: a first constant current source connected to the semiconductor laser; and a first constant current source connected to the semiconductor laser; A photodetector that detects the amount of photocurrent, a current-voltage converter that converts the photocurrent output obtained from the photodetector into a voltage signal, and a sample-and-hold circuit that samples and holds the output voltage of the current-voltage converter. , further comprising a comparator for comparing the output voltage of the sample and hold circuit with a predetermined first reference voltage corresponding to the reproduced current value, and the first current value of the first constant current source is determined according to the output of the comparator. a comparator that forms a first control loop with a control circuit and compares the output voltage of the current-voltage converter with a predetermined second reference voltage corresponding to the bias current value at a predetermined timing;
An up/down counter that operates up or down according to the output of this comparator, a digital-to-analog converter that converts the output of this up/down counter into an analog signal, and a switching element that is switched at a predetermined timing to control the semiconductor laser. A second constant current source is connected to the digital-to-analog converter and the second current value is controlled according to the output of the digital-to-analog converter to form a second control loop. The first current value of the current source is controlled to control the emission power of the semiconductor laser to the reproduction power, and then the switch element is turned on to generate a current value based on the superimposed current value of the first current value and the second current value. While the semiconductor laser is being driven, the first control loop controls only the first current value to control the emission power of the semiconductor laser to the reproduction power, and turns off the switch element at a predetermined timing to obtain a first current value at that time. 1. A light emission power control circuit for a semiconductor laser, characterized in that a second current value is controlled by a second control loop so that the semiconductor laser has the bias power only when the semiconductor laser has the bias power.