JPH04355223A - Semiconductor laser driving circuit - Google Patents

Abstract

PURPOSE:To stably set the light output of a semiconductor laser a high speed, in a semiconductor laser driving circuit used in an optical disk driving the semiconductor laser and recording information. CONSTITUTION:By detecting light emitted from the rear face of a semiconductor laser 1 with a light detector 1, driving current is applied to a field back loop to be controlled, and the difference of driving voltage between reproducing time and recording time is retained in a memory circuit 26 in advance, and at the time of starting the recording, the voltage is converted into current by a voltage/current converter 27 and superimposed on the driving current at the time of recording and such current is made to flow to the laser 1. Thus, the light output of the semiconductor laser can be set to a stable value at high speed when the reproducing is changed over to the recording.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser drive circuit for controlling the optical output of a semiconductor laser during recording and reproduction in a recordable optical disc device.

0002

2. Description of the Related Art FIG. 4 is a circuit diagram showing an example of a conventional semiconductor laser drive circuit. In the figure, a semiconductor laser 1 is driven by a current source 2 via a drive circuit consisting of transistors 3 and 4 and an inverter 5. The rear emitted light of the laser is detected by a photodetector 6. Photodetector 6
converts the rear emitted light of the laser beam into a monitor current IM, the output of which is given to the I/V converter 7. The I/V converter 7 converts the monitor current IM into the monitor voltage VM.
The output is given to the error amplifier 8. A low-pass filter 11 consisting of a resistor 9 and a capacitor 10 is connected to the error amplifier 8, and its output is applied to the current source 2 as a drive voltage VLD. The current source 2 converts the drive signal VLD into a drive current ILD to drive the semiconductor laser 1. Also, terminals 12 and 13 provide REC and PLAY signals during recording and playback, respectively.
is provided. The terminal 12 is connected to an analog switch 14 and an input end of an AND circuit 15. Further, the terminal 13 is connected to an analog switch 16 and an OR circuit 17. Reference voltages VR and VP are connected to the analog switches 14 and 16, respectively, and the other ends are commonly connected to the reference voltage V.
It is connected as ref to one end of resistors R1 and R2. The midpoint between resistors R1 and R2 is connected to an error amplifier 8. Also, the AND circuit 15 inputs recorded data to the OR circuit 17 during recording.
The OR circuit 17 provides a continuous signal during reproduction and a recording signal during recording to the laser drive circuit.

Now, during playback, a PLAY signal is obtained at the terminal 13 as shown in FIG. Semiconductor laser 1 is continuously driven. The optical output at this time is assumed to be WP as shown in FIG. 5(d).

During recording, the REC signal is applied to the terminal 12 as shown in FIG. 5(b), and the recorded data is sent to the AND circuit 1.
5, this signal energizes transistor 3. Also, the reference voltage VR is set by the analog switch 14.
is selected. This recording data employs the well-known EFM modulation (8-14 modulation) in the case of a compact disc modulation method for recording digital audio. In this modulation method, 3-bit margin bits are added after converting 8-bit data to 14-bit data, so when the modulation waveform is a binary signal of 1 and 0, the temporal average of the modulation waveform is 1 It is known that it takes a value of /2. Therefore, in the conventional semiconductor laser drive circuit, the monitor voltage VM of the photodetector 6 and the reference voltage Vref are compared using this, and the optical output of the semiconductor laser 1 appropriate for recording is set based on the average value. .

[0005]

[Problem to be Solved by the Invention] Now, when the mode of the optical disk device changes from playback to recording, the analog switch 14 in FIG. Information is recorded by modulating the optical output of the laser 1. However, in such a conventional EFM modulation method, the modulation signal has a relatively low frequency spectrum ram component, and this may cause ripples to occur in the optical output of the semiconductor laser 1. Therefore, in the conventional semiconductor laser drive circuit, the cutoff frequency of the low-pass filter 11 has to be set to a relatively low value of about 1 kHz. Therefore, the optical output of the semiconductor laser 1 during recording takes about 1 msec from the start of recording until it reaches the stable value WR.
It took c. Therefore, when information recorded immediately after the start of recording is reproduced, there is a problem in that the signal quality of the reproduced signal is poor.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a semiconductor laser drive circuit that can quickly set the optical output to a stable value from the start of recording and can perform accurate recording from the start of recording. purpose.

[0006]

[Means for Solving the Problems] The present invention provides a recordable optical disc device that includes a light detection means for detecting light from a semiconductor laser, and a light output control for controlling the light output of the semiconductor laser based on the output of the light detection means. drive voltage detection means for detecting the drive voltage of the semiconductor laser during recording and playback, subtraction means for subtracting the drive voltage during playback from the drive voltage during recording, and holding for holding the output of the subtraction means. means and
Voltage-current converting means for converting the output voltage of the holding means into a current, and driving the semiconductor laser by adding the output of the voltage-current converting means to the drive current of the optical output control means during recording. It is something to do.

[0007]

According to the present invention having such features, the light intensity of the semiconductor laser is detected by the light output detection means, and the output is kept constant by the light output control means. The drive voltages of the semiconductor laser during recording and reproduction are detected in advance, and the difference between them is held in a holding means. When switching from playback to recording, the output voltage of the holding means is converted into a current, and the semiconductor laser is driven in addition to the drive current by the light output control means, thereby increasing the light output of the semiconductor laser during recording at high speed. Set to a stable value.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing the configuration of a semiconductor laser drive circuit according to an embodiment of the present invention. In this figure, the same parts as those in the conventional example described above are given the same reference numerals, and detailed explanation will be omitted. In this embodiment as well, the semiconductor laser 1 is driven by the current source 2 through the transistors 3 and 4, and the rear surface emitted light is detected by the photodetector 6.
It is converted into a voltage by an I/V converter 7. Here, the photodetector 6 and the I/V converter 7 constitute a photodetection means for detecting the light from the semiconductor laser. The voltage signal converted by the I/V converter 7 is given to an error amplifier 8 including a low-pass filter 11, and a current source 2, transistors 3, 4
Driving the semiconductor laser 1 via the laser diode is the same as in the conventional example described above. These blocks and reference voltage VR
, VP and the analog switches 14 and 16 constitute a light output control means that controls the light output of the semiconductor laser based on the output of the light detection means.

In this embodiment, a recording drive voltage detection circuit 23 and a reproduction drive voltage detection circuit 24 are connected to the output side of the error amplifier 8 via analog switches 21 and 22.
is provided. Here, the analog switches 21 and 22 and the drive voltage detection circuits 23 and 24 constitute drive voltage detection means for detecting the drive voltage of the semiconductor laser during recording and reproduction, respectively. These drive voltage detection circuits 23 and 24 are constituted by sample and hold circuits, which hold the applied input voltage and transmit the output to the subtraction circuit 25. The subtraction circuit 25 is a subtraction means for calculating the difference in drive voltages, and its output is given to the memory circuit 26. The memory circuit 26 constitutes a holding means for holding the output voltage, and its output is given to the voltage-current converter 27. The voltage-current converter 27 converts the input voltage into a current, and its output is connected to the common connection terminal of the collectors of the transistors 3 and 4 via an analog switch 28. The analog switches 21, 22 and 28 have switch outputs SETR, SE obtained from the system controller 29.
This is a switch that closes the input and output terminals by TP and USREC, respectively. The other configurations are the same as those of the conventional example described above. Here, SETR and SETP are signals that control the drive voltage detection intervals during recording and reproduction, respectively, and USREC is a signal that controls the output of the voltage-current converter 23.

Next, the operation of this embodiment will be explained. First, the driving voltage is detected in advance during reproduction and recording. The drive voltage is detected immediately after the optical disk device is powered on. When detecting the drive voltage, it is necessary to make the semiconductor laser 1 emit light with optical output during reproduction and recording. FIG. 2 is a time chart and a waveform diagram of optical output when detecting drive voltages during reproduction and recording. First, when detecting the reproduction side drive voltage, as shown at time t0 in FIG. 2(a), the PLA
The Y signal is set at H level, the REC signal is set at L level, and the USREC signal is held at L level when the drive voltage is detected. When the PLAY signal is at H level, the reference voltage VP is selected by the analog switch 16 as described above, and the transistor 3 is turned on via the OR circuit 17, causing the semiconductor laser 1 to become conductive.
lights up continuously. However, as shown in FIG. 2(d), a predetermined time is required until the output of the optical waveform reaches a constant value WP. Therefore, after setting the PLAY signal to H level, at time t1 after a predetermined time, the SETP signal is set to H level as shown in FIG. In this way, the drive voltage during reproduction is maintained.

Next, when detecting the drive voltage on the recording side, the PLAY signal is set to L level and the REC signal is set to H level, as shown after time t2 in FIG.
As shown in f), the signal is a continuous H level signal. Then, the reference voltage VR is selected via the analog switch 14, and the semiconductor laser 1 is continuously driven by the recording data. Then, at time t3 after the optical waveform reaches a certain value WR, the SETR signal is set to H as shown in Fig. 2(g).
level. In this way, the analog switch 21 is closed, and the drive voltage at that time is detected by the recording side drive voltage detection circuit 2.
3 will be held.

When the drive voltages on the recording side and the playback side are detected in this manner, the difference between the drive voltages is calculated by the subtraction circuit 25 and held in the memory circuit 26. The held voltage value is then converted into a current by the voltage-current converter 27. The additional resistance of the current-voltage converter 27 is the same as that of the current source 2.

Next, the case of recording information will be explained. FIG. 3 is a time chart showing waveforms of various parts at the time of switching from reproduction to recording. In this figure, time t4
When switching from playback to recording, the PLAY signal is set to L level, the REC signal is set to H level, and the USR
Set the EC signal to H level. Then, the analog switch 14 selects the recording voltage VR. Also USR
The analog switch 28 is turned on by the EC signal. Therefore, the drive voltage difference that has already been subtracted by the subtraction circuit 25 and held by the memory circuit 26 is converted into a current via the voltage-current converter 27, and is converted into a current by the analog switch 2.
Join 8. Therefore, this drive current is added to the transistors 3 and 4 in addition to the current of the current source 2, and this added current is applied to the semiconductor laser 1. That is, the laser drive circuit of this embodiment forms a loop by monitoring the light emitted from the rear surface of the semiconductor laser 1 with the photodetector 6, as in the conventional example, but the reference voltage is set at the same time as the recording starts. Voltage-current converter 2 to switch and drive current during recording
The outputs of 7 are added. Therefore, the monitor voltage output by the current-voltage converter 7 can be set to a stable optical output WR monitor voltage at the same time as the recording starts, and the optical output of the semiconductor laser 1 can be set to a stable value quickly from the recording start. be able to.

To record information, the transistors 3 and 4 are driven according to the recording data shown in FIG. 3(d), and the drive current is modulated to cause the semiconductor laser 1 to emit light. Therefore, the optical output modulated by the semiconductor laser driving circuit of the present invention is as shown in FIG.
As shown in (e), it is possible to record correctly from the start of recording.

In this embodiment, the semiconductor laser 1 is illuminated when detecting the driving voltage during recording and reproducing, but when detecting the driving voltage during recording, the semiconductor laser 1 is emitted within the user area of the recording layer of the optical disc. A problem arises in that if the light is illuminated, information that has already been recorded by the user will be destroyed. Therefore, the drive voltage during recording is detected outside the user area of the recording layer of the optical disc. As a result, the driving voltage at the time of recording can be detected without destroying the information already recorded by the user on the recording layer of the optical disc. Furthermore, in this embodiment, the detection of the driving voltage during reproduction and recording is performed immediately after the power is turned on to the optical disc device, but the driving current of the semiconductor laser 1 during recording and reproduction differs depending on the type of recording layer of the optical disc. Therefore, the drive current may be detected immediately after the optical disc is loaded into the optical disc device.

[0016]

Effects of the Invention As described above in detail, according to the invention of claim 1 of the present application, the difference between the driving voltages during reproduction and recording is subtracted in advance and held in the holding means, and the difference between the driving voltages during reproduction and recording is subtracted and held in the holding means. When switched, a current corresponding to this voltage difference is applied in addition to the drive current of the optical output control means to drive the semiconductor laser. Therefore, the optical output of the semiconductor laser can be set to a stable value quickly from the start of recording. Therefore, recording can be performed correctly from the start of recording, and the quality of the reproduction signal of information recorded during this period can be improved.

In addition to the above-described effects, the invention of claim 2 of the present application detects the driving voltage during recording outside the user area of the recording layer of the optical disc. Therefore, there is no problem of destroying information that has already been recorded, and its practical effects are great.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the configuration of a semiconductor laser drive circuit according to an embodiment of the present invention.

FIG. 2 is a time chart and an output waveform diagram for detecting drive current during playback and drive in this embodiment.

FIG. 3 is a diagram showing a time chart and an optical output waveform when recording information in this embodiment.

FIG. 4 is a circuit diagram showing an example of a conventional semiconductor laser drive circuit.

FIG. 5 is a diagram showing a time chart and an optical output waveform when information is recorded in a conventional semiconductor laser drive circuit.

[Explanation of symbols]

1 Semiconductor laser 2 Current source 3, 4 Transistor 6 Photodetector 7 I/V converter 8 Error amplifier 11 Low-pass filter 14, 16, 21, 22, 28 Analog switch 1
5 AND circuit 17 OR circuit 23 Recording side drive voltage detection circuit 24 Reproduction side drive voltage detection circuit 25 Subtraction circuit 26 Memory circuit 27 Voltage current converter 29 System controller

Claims (2)

[Claims] Claim 1: In a recordable optical disc device,
A photodetection means for detecting light from a semiconductor laser, an optical output control means for controlling an optical output of the semiconductor laser based on the output of the photodetection means, and a drive voltage for the semiconductor laser during recording and reproduction, respectively. drive voltage detection means, subtraction means for subtracting the drive voltage during reproduction from the drive voltage during recording, holding means for holding the output of the subtraction means, and voltage-current conversion for converting the output voltage of the holding means into a current. What is claimed is: 1. A semiconductor laser drive circuit comprising: means for driving a semiconductor laser by adding an output from said voltage-current conversion means to a drive current from said light output control means during recording. 2. The semiconductor laser drive circuit according to claim 1, wherein the drive voltage detection means detects the drive voltage of the semiconductor laser during reproduction and recording outside the user area of the recording layer of the optical disc.