JPH0221433A - Semiconductor laser output detector - Google Patents

Abstract

PURPOSE:To prevent output from being controlled at a light quantity state different from a targeted value by providing an amplifier circuit to output a reproducing level signal by connecting capacitors in parallel with a load resistor via switching devices and detecting respective potential generated on each of the capacitors. CONSTITUTION:When both two switching devices 10R and 10W are turned off, a voltage corresponding to the light output of a semiconductor laser 2 from an optical sensor 5 is generated on the load resistor. Here, when the switching device on one side is turned on at a reproducing level timing, a charge corresponding to a reproducing level is charged on a corresponding capacitor CR, and finally, it is converged to a voltage value equivalent to reproducing output. It is amplified at an amplifier circuit, and goes to the reproducing level signal. Meanwhile, when the switching device 10W on the other side is turned on at a recording level timing, the charge corresponding to a recording level is charged on a corresponding capacitor CW, and finally, it is converged to the voltage value equivalent to recording output, and is amplified, then, goes to a recording level signal. In such a way, it is possible to obtain a level signal accurately by making a device hard to receive a noise, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a semiconductor laser output detection device in an optical disk drive device (optical pickup) or the like.

2. Description of the Related Art In recent years, many optical disk drive devices use a semiconductor laser (LD) as a light source.

In this case, when the semiconductor laser records information on the optical disk, the output of the semiconductor laser is modulated according to the written information (modulation signal) as shown in FIG. PR is the reproduction output, and I)w is the recording output, which changes in binary depending on the modulation. Here,
Semiconductor lasers have optical output characteristics that vary greatly due to temperature changes, etc., so generally the optical output can be increased by detecting a portion of the optical output and feeding it back to control the semiconductor laser's driving current. I always try to reach the target value.

By the way, as a method of obtaining the optical output of a semiconductor laser for information writing as shown in FIG. 3, as shown in FIG. Alternatively, a recording level current ■W corresponding to the recording output PW is superimposed. Here, in order to control the reproduction level current IR and the recording level current Iw, a part of the output of the semiconductor laser is electrically detected by a photo sensor, etc., but in order to control each current, P It is necessary to obtain electrical signals corresponding to each of Rr P W.

For this reason, conventionally there is a detection device using a peak hold circuit as shown in FIG. First, the reproduction current drive circuit 1 applies a reproduction level current IR to the semiconductor laser 2 according to a reproduction current control signal. - On the other hand, the recording current drive circuit 3 sets the current to 0 when the modulation signal is "O", and the recording current drive circuit 3 sets the current to 0 when the modulation signal is "O".
”, the recording level current IW follows the recording current control signal.
is superimposed on the semiconductor laser 2. Here, in the laser unit 4, a part of the optical output of the semiconductor laser 2 is detected by the photodetector 5, and a current proportional to the previous output is generated. The current detected by this photodetector 5 is converted into a voltage by a current-voltage conversion circuit 6 using an OP amplifier, and outputted to two peak hold circuits 7 and 8, respectively. Second, one peak hold circuit 7 detects the minimum peak value of the absolute value of the input voltage, that is, the electrical signal 9 (reproduction level signal) corresponding to the reproduction output PR. The other peak hold circuit 8 detects the maximum peak value of the absolute value of the input voltage, that is, the electrical signal (recording level signal) corresponding to the recording output PW.

Note that these separated and extracted playback level signals and recording level signals are compared with their respective target voltages and then fed back as playback current control signals and recording current control signals, respectively, so that the playback output and recording output are always at their respective levels. It is controlled to reach the target value.

FIG. 6 also shows a similar conventional example using peak hold circuits 7 and 8, but the difference is that the current generated in the photodetector 5 is converted into a voltage by a series load resistor Rt, and the current generated in the photodetector 5 is converted into a voltage by an OP amplifier. The point is that the signal is input to these peak hold circuits 7 and 8 after being amplified by the amplifier circuit 9.

Problems to be Solved by the Invention As described above, according to the conventional system as shown in FIGS. and an amplifier circuit 9 are required. In an optical disk drive device, the modulation signal is several M
It has a frequency of Hz, and in order for the OP amplifier used in these circuits to accurately output changes in the semiconductor laser output, it needs to have an extremely high band, making the device expensive.

Furthermore, since the circuit operates in a high frequency band, it is easily affected by noise and the like, causing an error in the peak hold value, and the output of the semiconductor laser may be controlled to a light amount state different from the target value. In such a state, errors occur that make it impossible to record accurate information.

Means for Solving the Problem First, a load resistor is connected in series with an optical sensor that generates a current approximately proportional to the optical output of the semiconductor laser. At the midpoint of the connection between the load resistor and the optical sensor, there is provided a regeneration level switch element that is turned on during part or all of the period when the optical output of the semiconductor laser is at the regeneration level, and A recording level switch element that is turned on during part or all of the period during which the output is at the recording level is connected to each of the recording level switch elements. Then, capacitors are connected in parallel to the load resistors via these switch elements, and an amplifier circuit that detects each potential generated in these capacitors and outputs a playback level signal, and an amplifier that outputs a recording level signal. A circuit is provided.

If both switching elements are off, a voltage corresponding to the optical output of the semiconductor laser from the optical sensor is generated in the load resistor. Therefore, when one switch element is turned on at the reproduction level timing, the corresponding capacitor is charged with a charge corresponding to the reproduction level, and the voltage value finally converges to a voltage value corresponding to the reproduction output.

This is amplified by an amplifier circuit and becomes a reproduction level signal. On the other hand, if the other switch element is turned on at the recording level timing, the corresponding capacitor is charged with a charge corresponding to the recording level, and the voltage value finally converges to the voltage value corresponding to the recording output. This is amplified by an amplifier circuit and becomes a recording level signal. Here, the voltage obtained at each capacitor changes extremely smoothly, and the amplifier circuit for amplifying this can be an inexpensive OP amplifier. At the same time, since these voltages change smoothly according to the CR time constant,
It is also less susceptible to the effects of noise and the like.

Embodiment An embodiment of the present invention will be explained based on FIGS. 1 and 2. Components that are the same as those shown in FIGS. 3 to 6 are indicated using the same reference numerals. In this embodiment, first, a load resistor RL is connected in series to the photodetector 5 as an optical sensor, similar to the one in FIG. Here, the photodetector 5 which detects a part of the optical output of the semiconductor laser 2 generates a current approximately proportional to this optical output. Further, at the midpoint of connection between the photodetector 5 and this load resistor RL, an analog switch I is provided as two switching elements in parallel.
OR and IOW are connected. In addition, a capacitor CR is connected to the other end of these analog switches IOR and Low.
, CW are connected to each other.

Therefore, the load resistance RL and the capacitor CR are connected in parallel via the analog switch IOR, and similarly, the load resistance R
L and capacitor Cw are connected in parallel via an analog switch 10w. And these capacitors CR+ c
Amplifying circuits 11R and l1w each having an OP amplifier configuration are connected to w.

Here, the analog switch IOR is turned on by the control signal SR during a part (or the entire period) of the period when the optical output of the semiconductor laser 2 is at the reproduction level. Also,
The analog switch 1ow is turned on by the control signal Sw during a part (or the entire period) of the period when the optical output of the semiconductor laser 2 is at the recording level.

In such a configuration, the detection operation will be explained with reference to the timing chart of FIG. First, a current proportional to the optical output of the semiconductor laser 2 generated in the photodetector 5 flows through the load resistor RL.

At this time, if the two analog switches IOR and LOW are both off, a voltage vL proportional to the optical output is detected at the load resistor RL. On the other hand, analog switch IO
R and Low are turned on by control signals SR+Sw as shown in FIGS. 2(C) and (b), respectively.

For example, when the analog switch IOR is turned on, a charge corresponding to the playback level is gradually charged to the capacitor CR as shown in FIG. The voltage converges to the voltage value at the reproduction output PR. Analog switch 10. The same is true when ・ is turned on, and the charge corresponding to the recording level is the second
As shown in Figure (e), the capacitor Cw is gradually charged, and the charging voltage Vw eventually converges to the voltage value when the semiconductor laser 2 is at the recording output PW.

As can be seen from Fig. 2, these voltages VR+vw change extremely smoothly compared to the voltage V, which is proportional to the optical output of the semiconductor laser 2, so these voltages
The OP amplifier used in the amplifier circuit llR111w for amplifying the signal does not need to be a high-bandwidth one as in the past, and an inexpensive one will suffice. Also, these voltages V
Since R+vw changes smoothly according to the time constants of RL and CR, and RL and Cw, it is less susceptible to the effects of noise and the like, and it is possible to accurately obtain a reproduction level signal and a recording level signal.

Effects of the Invention The present invention connects a load resistor in series to the optical sensor as described above, and also connects a capacitor and an amplifier circuit for the reproduction level signal via a switch element that is turned on at the reproduction level. Since the capacitor for the recording level signal and the amplifier circuit are connected through a switch element that is turned on, the voltage obtained at each capacitor changes smoothly when the reproduction output and recording output of the semiconductor laser are detected separately. The amplifier circuit can be configured with inexpensive OP amplifiers, and is less susceptible to noise and other influences.
Accurate detection of reproduction level signals and recording level signals is possible, and output control of semiconductor lasers can be performed appropriately.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a timing chart showing its operation, Fig. 3 is a modulation waveform diagram of a general semiconductor laser output, and Fig. 4 is a characteristic showing the superimposition method. 5 is a circuit diagram showing a conventional example, and FIG. 6 is a circuit diagram showing a different conventional example. W: Semiconductor laser, Switch element, Optical sensor, 10R2 1R, l1w: Amplifier circuit, RL: Load resistance, CR+ Cw: Capacitor

Claims (1)

[Claims] A semiconductor laser is driven by superimposing a reproduction level current and a recording level current corresponding to a modulation signal, a part of the optical output of this semiconductor laser is detected by an optical sensor, and the optical output of the semiconductor laser is determined to be at the reproduction level and the recording level. A reproduction level signal and a recording level signal each proportional to the optical output at the time of In a semiconductor laser output detection device that controls current, a load resistor is connected in series to an optical sensor that generates a current approximately proportional to the optical output of the semiconductor laser, and a load resistor is connected in series to the optical sensor at a midpoint between the load resistor and the optical sensor. , a reproduction level switch element that is turned on during part or all of the period when the optical output of the semiconductor laser is at the reproduction level;
A recording level switch element that is turned on during a part or all of the period during which the optical output of the semiconductor laser is at the recording level is connected to each, and a capacitor is connected in parallel to the load resistor through these switch elements. 1. A semiconductor laser output detection device comprising: an amplifier circuit connected to each other, an amplifier circuit for detecting each potential generated in these capacitors and outputting a reproduction level signal, and an amplifier circuit for outputting a recording level signal.