JP2003218455A - Semiconductor laser driving apparatus and optical disk device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To automatically adjust a pulse width of emitted laser light to a desired value in a semiconductor laser driving apparatus. <P>SOLUTION: Laser light emitted from a laser diode LD is detected by a photo detector PD and is converted into a voltage signal by means of an I/V 14. An average level of the voltage signal is extracted by a low pass filter 16. The average level of the emitted laser light is compared with a target pulse level by means of a comparator 18. Based on the differential signal, a threshold level in a laser diode driver LDD 10 is increased or decreased. When the threshold level is changed and the pulse width becomes smaller than the desired value, the average level becomes smaller than the target pulse level. As a result, the threshold level is downwardly corrected to increase a pulse width of a driving current. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser driving device and an optical disk device, and more particularly to a technique for adjusting the pulse width of laser light emitted from a semiconductor laser (laser diode).

[0002]

2. Description of the Related Art Conventionally, a semiconductor laser (laser diode) for recording / reproducing is mounted on an optical disk device such as a CD drive or a DVD drive, and a driving device for controlling the power and pulse width of laser light emitted from the semiconductor laser ( Laser diode driver) is used for adjustment.

FIG. 5 is a block diagram showing the configuration of a drive unit mounted on an optical disc device. A laser diode driver (LDD) 10 that supplies a driving current to a semiconductor laser (laser diode) LD and a controller 12 that supplies a control signal to the LDD 10 to control the LDD 10 are provided. When recording data on an optical disk such as a CD-R or a DVD-R, the controller 12 supplies the LDD 10 with a recording pulse modulated based on the recording data supplied from a higher-level device such as a personal computer, and the LDD 10 records this recording. A drive current pulse corresponding to the pulse is generated and supplied to the LD.

On the other hand, a photodetector PD for monitoring is provided near the LD and outputs a current signal proportional to the amount of laser light emitted from the LD. The current signal from the PD is supplied to the current / voltage converter I / V 14, and is fed back to the controller 12 as a voltage signal according to the laser light amount. The controller 12 sets the power control signal APC to L based on the voltage signal level according to the laser light amount.
This is supplied to the DD 10, and the LDD 10 adjusts the drive current level up or down based on the APC signal to maintain the emission laser power at the reference value.

Since the recording pulse supplied from the controller 12 to the LDD 10 has a certain finite rise time and fall time, it is not exactly rectangular but trapezoidal.
In the LDD 10, the trapezoidal recording pulse is sliced at a predetermined threshold level, and the drive current is LDed.
Supply to.

FIG. 6 shows a drive current generation timing chart in the LDD 10. 6A shows a waveform of 6T (T is a reference period of the track direction length) as an example of the recording pulse. In an optical disk device such as a DVD drive, data recording is performed by multi-pulse. That is, there are 3T to 11T and 14T as recording data, and the shortest pulse length of 3T is recorded by a single pulse, but for the pulse of 4T or more, the data is recorded by a multipulse of a head pulse and a subsequent pulse. A pulse waveform of such a multi-pulse is shown in (b). There are a leading pulse and subsequent multi-pulses, and each pulse waveform is trapezoidal due to the finite rise time and fall time as described above. LDD10
Generates a drive current pulse for such a recording pulse with a hysteresis characteristic using two thresholds of H level and L level. That is, the level of the recording pulse is H
When the level reaches the level, the drive current pulse is raised, and when the recording pulse reaches the L level, the drive current pulse is lowered. (C) shows a drive current pulse waveform obtained by slicing at the H level and the L level in this way.

[0007]

However, the LDD 10
The slice level changes due to fluctuations in the power level of
When the H level increases to the H ′ level and the L level increases to the L ′ level, the drive current pulse waveform as shown in (d) is generated, and the original drive current shown in (c) is generated. The pulse width becomes smaller than the pulse.
Such a change in pulse width causes a change in recording strategy, which may cause a problem that data cannot be accurately recorded.

Even if the threshold level of the LDD 10 does not fluctuate, the controller 12 depends on the power supply voltage and the temperature.
Even if the rising time and the falling time of the recording pulse itself output from the pulse width change, the pulse width also changes.

The present invention has been made in view of the above problems of the prior art, and an object thereof is to obtain a pulse width of a laser beam emitted from a semiconductor laser (laser diode) even if a power supply voltage fluctuates. The object is to provide a device capable of automatically adjusting to a desired value.

[0010]

In order to achieve the above object, the present invention is a drive device for slicing a pulse signal at a threshold level to generate a drive pulse and driving a semiconductor laser. Detecting means for detecting the pulse width of the laser light emitted from, the output means for comparing the pulse width with the target pulse width and outputting the difference signal, and the threshold level is increased or decreased based on the difference signal. Adjusting means for adjusting the pulse width of the laser light.

Here, the detecting means detects the amount of laser light emitted from the semiconductor laser as a current signal, a current-voltage converter for converting the current signal into a voltage signal, and an average level of the voltage signal. A filter for extracting, the output means has a comparator for comparing the reference level corresponding to the target pulse width and the average level, and outputs the difference signal, the adjusting means, the average When the level is higher than the reference level, the threshold level is increased to reduce the pulse width of the laser light, and when the average level is lower than the reference level, the threshold level is decreased. It is preferable to increase the pulse width of the laser light.

As described above, the semiconductor laser drive device of the present invention detects the pulse width of the laser beam emitted from the semiconductor laser, compares the detected pulse width with the reference value, and generates the drive current signal using the difference signal. Adjust the threshold level for doing. By dynamically feedback controlling the threshold level instead of a fixed value, the semiconductor laser can be driven by setting the optimum threshold level regardless of the fluctuation of the power supply voltage. Specifically, if the pulse signal from the host device is trapezoidal,
The pulse width of the drive current signal can be reduced by increasing the threshold level (slice level), and the pulse width of the drive current signal can be increased by decreasing the threshold level. The amount of increase or decrease of the pulse width is adjusted by the correction amount of the threshold level.

The semiconductor laser driving device of the present invention is an optical disk device, particularly CD-R, CD-RW, DVD-R, D.
It can be mounted on a recordable optical disk device such as a VD-RW or a DVD-RAM. In this case, the recording starting current pulse width for recording data can be automatically adjusted to a desired value, and the recording quality can be maintained constant.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings, taking an optical disk device as an example.

FIG. 1 is a block diagram showing the configuration of the semiconductor laser driving device according to this embodiment. Like the conventional device shown in FIG. 5, an LD that supplies a drive current to the LD
Controller 1 for controlling the operation of D10 and LDD10
2, and a photodetector PD that outputs a current signal proportional to the amount of laser light emitted from the LD, and a current-voltage converter I / V1 that converts the current signal from the photodetector PD into a voltage signal and feeds it back to the controller 12.
4 are provided. When recording data on the optical disc, a drive current corresponding to the recording power is supplied from the LDD 10 to the LD, 3T data is recorded with a single pulse, and 4T or more data is recorded with multiple pulses. Further, when reproducing data, a drive current corresponding to the reproduction power is supplied to the LD. The laser power is feedback-controlled by comparing the voltage signal level from the current-voltage converter I / V 14 with a reference value (voltage signal level at which the reference laser power is obtained).

In addition to the conventional device, the semiconductor laser driving device of this embodiment has a current-voltage converter I / V1.
The low-pass filter LPF16 for inputting the voltage signal from the No. 4 and extracting the average level thereof, and the comparator 18 for comparing the output level from the LPF16 with the target pulse level and outputting the difference signal. The difference signal from the comparator 18 is adjusted to be increased or decreased by the amplifier 19 and is adjusted to L as a correction level signal.
It is supplied to the DD 10. The gain of the amplifier 19 is adjusted by the gain switching circuit 20 in consideration of the sensitivity of the PD and the like.

In the LDD 10, basically the controller 1
The drive current pulse is generated by slicing the recording pulse from 2 at two threshold levels, H level and L level.
The threshold level of H level and L level is increased / decreased by the correction level signal supplied from the comparator 18 to generate a drive current pulse. That is, the threshold level of the LDD 10 is not fixed but feedback controlled.

The operation of the comparator 18 and the LDD 10 is shown in FIG. (A) is a current-voltage converter I / V1
4 is an example of a voltage signal output from the No. 4 to the LPF 16.
This voltage signal has a voltage signal waveform when the LD is driven by a 5T recording pulse. In the case of a 5T recording pulse, there are two subsequent pulses in addition to the head pulse, and laser light is emitted according to this recording pulse. The photodetector converts such multi-pulse laser light amount into an electric signal and outputs it to the I / V 14. LPF16
Generates an average level voltage signal from the voltage signal waveform and outputs the voltage signal to the non-inverting input terminal (+) of the comparator 18.

FIG. 2B shows the output level (solid line) from the LPF 16 and the target pulse level (dotted line). The target pulse level is a reference level that will be output from the LPF 16 when laser light is emitted with a desired laser pulse width. The power of the emitted laser light is assumed to be adjusted to the reference value by APC.
If the laser power is adjusted to the reference value, LPF1
The output level from 6 varies depending on the pulse width of the voltage signal. Specifically, when the pulse width is smaller than the desired width, the output level also becomes smaller than the target pulse level, and the pulse width is larger than the desired width. Then, the output level becomes higher than the target pulse level. (B) shows the case where the output level from the LPF 16 is smaller than the target pulse level by ΔL. The target pulse level is input to the inverting input terminal (−) of the comparator 18, and the difference value ΔL between the output level from the LPF 16 and the target pulse level is appropriately adjusted by the amplifier 19 and supplied to the LDD 10 as a difference signal.

FIG. 2C shows the correction of the threshold level in the LDD 10. LDD10 is comparator 1
The threshold level is increased / decreased based on the sign of the differential signal from 8 and its absolute value. Specifically, the difference signal is positive,
That is, when the output level from the low-pass filter 16 is higher than the target pulse level, the threshold level is increased by the amount corresponding to its absolute value. When the differential signal is negative, that is, when the output level from the low-pass filter 16 is smaller than the target pulse level, the threshold level is corrected to be smaller by the amount corresponding to its absolute value. Figure 2
In (c), since the output level from the LPF 16 is smaller than the target pulse level, the threshold level (slice level) is corrected to be small from the alternate long and short dash line to the solid line.

FIG. 3 shows changes in the pulse width of the drive current supplied from the LDD 10 to the LD when the threshold level is increased or decreased. As shown in FIG. 3 (a),
When a trapezoidal recording pulse is supplied from the controller 12 to the LDD 10, when the threshold level is corrected downward (decreased) from the level indicated by the alternate long and short dash line to the level indicated by the solid line, L
The pulse width of the drive current pulse supplied from the DD 10 to the LD increases from the pulse shown in FIG. 3B to the pulse shown in FIG. 3C. On the contrary, when the threshold level is corrected upward (increased), the pulse width of the drive current pulse decreases. It is understood that the pulse width of the drive current pulse can be adjusted to a desired value by increasing / decreasing the threshold level by an amount corresponding to the difference value of the difference signal.

Since the LDD 10 generates the drive current pulse at two threshold levels of H level and L level, the H level and the L level are simultaneously set on the basis of the difference signal from the comparator 18 as shown in FIG. It is preferable to correct. In the figure, both the H level and the L level are reduced and corrected from the one-dot chain line level to the solid line level. The H level and L level correction amounts may be the same, or the H level and L level may be different correction amounts. Comparator 1
It is also possible to increase / decrease only one of the H level and the L level based on the difference signal from 8.
It is also possible to compare the difference value with a predetermined value, correct only one of the H level and the L level if the difference value is less than the predetermined value, and correct both the H level and the L level if the difference value exceeds the predetermined value. .

Thus, in this embodiment, the LPF
When the output of 16 is larger than the target pulse, LDD 10
LDD when the output level from the LPF 16 is smaller than the target pulse level by increasing the threshold level at
The drive current pulse width is adjusted by reducing the threshold level of 10. Even if the pulse width of the emitted laser light changes due to the power supply voltage or temperature, the pulse width is automatically adjusted to a desired value and the recording strategy is adjusted. Can be stabilized.

Although the embodiment of the present invention has been described above, the present invention is not limited to this, and various modifications can be made. For example, in the present embodiment, the LDD 10 generates the drive current pulse at two threshold levels. However, when the drive current pulse is generated using one threshold level, the one threshold level is differentiated. The increase / decrease may be adjusted based on the signal.

Further, in the present embodiment, the voltage signal from the I / V 14 is supplied to the LPF 16 and the pulse width of the emitted laser light is evaluated by the average level value of the voltage signal. However, the pulse width of the laser light is evaluated. However, any configuration in which the LDD 10 is feedback-controlled based on the difference value from the reference pulse width can be adopted.

[0026]

As described above, according to the present invention, the pulse width of the laser beam emitted from the semiconductor laser (laser diode) can be automatically adjusted to a desired value. As a result, it is possible to stabilize the recording strategy and the recording quality in the recordable optical disk device.

[Brief description of drawings]

FIG. 1 is a configuration block diagram of an embodiment.

FIG. 2 is an explanatory diagram of correction of a threshold level in LDD.

FIG. 3 is an explanatory diagram of drive current pulse waveform adjustment by threshold level correction.

FIG. 4 is an explanatory diagram of correction of an H level threshold and an L level threshold.

FIG. 5 is a configuration block diagram of a conventional device.

FIG. 6 is an explanatory diagram of fluctuations in the drive current pulse waveform associated with threshold level fluctuations.

[Explanation of symbols]

10 laser diode driver (LDD), 12 controller, 14 current-voltage converter (I / V), 16
Low-pass filter (LPF), 18 comparator.

Continued front page    F-term (reference) 5D119 AA23 BA01 BB01 BB02 BB04                       DA01 FA05 HA12 HA47 HA60                       HA68                 5D789 AA23 BA01 BB01 BB02 BB04                       DA01 FA05 HA12 HA47 HA60                       HA68                 5F073 BA05 BA06 EA29 GA04 GA12                       GA18 GA38

Claims (3)

[Claims] 1. A drive device for driving a semiconductor laser by slicing a pulse signal at a threshold level to generate a drive pulse, the detection means detecting a pulse width of a laser beam emitted from the semiconductor laser, Output means for comparing the pulse width with a target pulse width and outputting a difference signal thereof, and adjusting means for adjusting the pulse width of the laser light by increasing / decreasing the threshold level based on the difference signal. A semiconductor laser drive device characterized by: 2. The device according to claim 1, wherein the detection means includes a photodetector that detects the amount of laser light emitted from the semiconductor laser as a current signal, and a current-voltage converter that converts the current signal into a voltage signal. A filter for extracting an average level of the voltage signal, and the output means compares the reference level corresponding to the target pulse width with the average level, and outputs the difference signal. However, the adjusting means increases the threshold level to reduce the pulse width of the laser light when the average level is larger than the reference level, and the average level is smaller than the reference level. In some cases, the semiconductor laser driving device is characterized in that the threshold level is reduced to increase the pulse width of the laser light. 3. An optical disk device comprising the semiconductor laser drive device according to claim 1.