JP2000244052A - Semiconductor laser drive device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce an unwanted power consumption with no degradation in high speed which is required for switching of outgoing light quantity of a semiconductor laser. SOLUTION: An outgoing light quantity (b) of a semiconductor laser 2 is detected with a photodetector 3, coverted into a voltage signal (d), and calculated with a reference voltage signal by a differential amplifier 5 before fedback to a current source 1. A voltage signal (h) representing a forward voltage (operation voltage) of the semiconductor laser 2 is compared to a reference voltage signal (i) by a comparator 10, and imputed in a DC/DC converter 13. DC/DC converter 13 changes an output voltage to two stages according to an input signal (k). If, for example, the forward voltage is lower than the reference voltage, a voltage which is the lower of the two stages is outputted. The control speed of the control system fedback from the differential amplifier 5 is sufficiently fast even when the DC/DC converter 13 switches an output voltage, so no fluctuation in outgoing light quantity takes place. With this configuration, a reactive voltage at a power source 1 is suppressed low for a low power consumption.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor laser drive, and more particularly, to a semiconductor laser drive incorporated in an optical memory system such as a mini disk.

[0002]

2. Description of the Related Art Conventionally, an optical disk device has been known as a large-capacity information recording / reproducing device. In this optical disk device, a semiconductor laser is used as a light source.
In general, since a semiconductor laser is largely affected by temperature drift, control is performed by using a semiconductor laser driving device for controlling the amount of emitted light so as to maintain the light amount of a light beam irradiated on an optical disk at a predetermined value.

FIG. 5 is a circuit diagram for explaining an example of a conventional semiconductor laser driving device. In the drawing, reference numeral 1 denotes a current source, 2 denotes a semiconductor laser, 3 denotes a photodetector, 4 denotes a current-voltage converter, 5
Is a differential amplifier, 6 is a changeover switch, 7 is a reproduction mode reference voltage source, and 8 is a recording mode reference voltage source. The semiconductor laser driving current a output from the current source 1 is input to the semiconductor laser 2, and the semiconductor laser 2 is driven. The light beam emitted from the semiconductor laser 2 travels toward an optical disk (not shown) as an optical information recording medium, and a part of the light beam enters the photodetector 3, whereby the emitted light amount b of the semiconductor laser 2 is detected. After the output current c of the photodetector 3 is converted into a voltage signal d by the current / voltage converter 4, the differential amplifier 5
To one of the input terminals.

A reproduction mode reference voltage source 7 or a recording mode reference voltage source 8 is connected to the other input terminal of the differential amplifier 5 via a changeover switch 6. The difference between the output voltage signal d of the current-to-voltage converter 4 and the reference voltage signal e corresponding to the reproduction mode or the recording mode is calculated and amplified by the differential amplifier 5 and then output as a voltage signal f. It is fed back to the transistor Q _1. Thus, the control operation is performed so that the reference voltage signal e and the output voltage signal d of the current-to-voltage converter 4 become equal, and as a result,
The emitted light amount b from the semiconductor laser 2 is controlled to a predetermined value in both the reproduction mode and the recording mode. Such a method is disclosed, for example, in JP-A-4-364235.

Next, a prior art for reducing power consumption will be described. Many portable optical disk devices using a rechargeable battery or a dry battery as a power supply are commercially available. In a semiconductor laser driving device used in this type of device, it is desired to reduce power consumption and extend the service life of a battery.

FIG. 6 is a circuit diagram for explaining another example of a conventional semiconductor laser driving apparatus. In the figure, reference numeral 11 denotes a reference voltage source, 15 denotes a DC / DC converter, 15a denotes a smoothing circuit, and others. 5, parts having the same functions as those in FIG. 5 are denoted by the same reference numerals as in FIG. In FIG. 6, the smoothing circuit 15
The output voltage V ₁₅ smoothed by a and output from the DC / DC converter 15 is supplied to the semiconductor laser 2 via the protection resistor R ₁ . Semiconductor laser 2 current flows a corresponding to the voltage V ₁₅ which is smoothed, thereby the semiconductor laser 2 is driven. A part of the light beam emitted from the semiconductor laser 2 is incident on the photodetector 3, whereby the emitted light amount b of the semiconductor laser 2 is detected. The output current c of the photodetector 3 is converted into a voltage signal d by the current / voltage converter 4 and then input to one input terminal of the differential amplifier 5.

A reference voltage source 11 is connected to the other input terminal of the differential amplifier 5, and the difference between the output voltage signal d of the current-to-voltage converter 4 and the reference voltage signal e is calculated and amplified by the differential amplifier 5. Thereafter, the signal is output as a voltage signal f and fed back to the DC / DC converter 15. Thus DC /
Output voltage V ₁₅ from the DC converter 15 is controlled, the emission light intensity b from the semiconductor laser 2 is controlled to a predetermined value. In this semiconductor laser driving device, since the current source as shown in FIG. 5 is not used, the power consumption other than the semiconductor laser can be reduced. Such a method is disclosed, for example, in JP-A-6-275901.

[0008]

The above-described semiconductor laser driving device has a problem that the power consumption is large or a problem that the output light amount of the semiconductor laser cannot be switched at high speed. In FIG. 5, a current source 1 includes a protection resistor R ₁ and a transistor Q _1. A power supply voltage V ₁ supplied to the current source 1 includes a forward voltage (operating voltage) Vop of the semiconductor laser 2 and a transistor The emitter-collector voltage Vec of Q ₁ and the protection resistor R ₁
Is the sum of the voltage drops Vr. For example,
The forward voltage Vop is 2.2 V, the minimum emitter-collector voltage Vec required for the operation of the transistor Q ₁ is 1 V, and the voltage drop across the protection resistor R ₁ is 0.5 V (resistance 5 Ω, drive current 100 mA). Then, the power supply voltage V ₁ is required more than 3.7V.

The forward voltage Vop of the semiconductor laser 2 varies due to individual differences. For example, a semiconductor laser having a wavelength of 780 nm order generally has a forward voltage Vop
Varies in a range of about 1.6 to 2.2 V. Thus in order to drive all of the semiconductor laser varies the forward voltage Vop is, in the above example, it is necessary to set the power voltages V ₁ a forward voltage Vop as 2.2V maximum. However, the thus set power supply voltage V ₁
In, a forward voltage Vop drives the semiconductor laser of 1.6V, the voltage difference 0.6V will be consumed as reactive voltage between the emitter and the collector of the transistor Q _1.

The driving current a required to drive the semiconductor laser 2 changes by several tens mA due to individual differences of the semiconductor laser 2, temperature drift, or aging. In order to drive the semiconductor laser 2 in response to such changes, again, the voltage drop Vr on the protection resistor R ₁ as a voltage drop in the maximum drive current, it is necessary to set the power voltage V _1. In this case, the voltage drop Vr on the resistor R ₁ when the drive current a is small becomes small, reactive voltage between the emitter and the collector of the transistor Q ₁ is increased. As described above, in the conventional semiconductor laser driving device as shown in FIG. 5, unnecessary power is consumed by the invalid voltage in the current source 1 due to the variation of the semiconductor laser 2 and the like. There is a problem that the power consumption of the device increases.

The configuration shown in FIG. 6 does not use a current source as shown in FIG. 5, and thus has the advantage of low power consumption. However, when the output light amount b of the semiconductor laser 2 is changed, / DC converter 15 must change the output voltage V ₁₅ of the. Generally, a voltage is stabilized by a smoothing circuit to supply a power supply voltage.
It is difficult to change the output of the C / DC converter at high speed, and it is impossible to switch the output light amount b of the semiconductor laser 2 at high speed. Therefore, even if the reference voltage signal e from the reference voltage source 11 connected to the differential amplifier 5 is switched, the high speed of several microseconds required for switching between the reproduction mode and the recording mode cannot be realized. Problems arise.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is capable of reducing unnecessary power consumption without impairing the high speed required for switching the amount of emitted light of a semiconductor laser. It is an object to provide a driving device.

[0013]

According to a first aspect of the present invention, there is provided a semiconductor laser driving device for controlling a light emission amount of a semiconductor laser, the semiconductor laser driving device outputting a semiconductor laser driving current for driving the semiconductor laser. Current source, and a variable output voltage type D for supplying a power supply voltage to the current source.
A C / DC converter, drive current control means for controlling the semiconductor laser drive current based on the emission light amount of the semiconductor laser, and an operating voltage of the semiconductor laser or the semiconductor laser drive current regardless of the emission light amount of the semiconductor laser And a power supply voltage control means for controlling the output voltage of the DC / DC converter based on the above.

According to a second aspect of the present invention, in the semiconductor laser driving device according to the first aspect, a voltage detector for detecting a forward voltage which is an operating voltage of the semiconductor laser, and a detection value of the voltage detector and And a comparator for comparing with a set reference value, and based on the comparison result of the comparator, the D
It is characterized by controlling the output voltage of a C / DC converter.

According to a third aspect of the present invention, in the semiconductor laser driving device according to the first aspect of the present invention, a current detector for detecting a driving current output from the current source and a detection value of the current detector are preset. A comparator for comparing with a reference value,
The output voltage of the DC / DC converter is controlled based on the comparison result of the comparator.

[0016]

[First Embodiment] FIG. 1 is a circuit diagram for explaining a first embodiment of a semiconductor laser driving device according to the present invention. In FIG. 1, reference numeral 9 denotes a buffer circuit (voltage detecting means). Numeral 10 is a comparator (comparing means), 12 is a latch circuit, 13 is a DC / DC converter, and other portions having the same functions as those of the conventional example are denoted by the same reference numerals. The semiconductor laser drive current a output from the current source 1 is input to the semiconductor laser 2, and the semiconductor laser 2 is thereby driven. The light beam emitted from the semiconductor laser 2 travels toward an optical disk (not shown) as an optical information recording medium, and a part of the light beam enters the photodetector 3, whereby the emitted light amount b of the semiconductor laser 2 is detected.

The output current c of the photodetector 3 is converted into a voltage signal d by the current / voltage converter 4 and then input to one input terminal of the differential amplifier 5. The other input terminal of the differential amplifier 5 is connected to a reproduction mode reference voltage source 7 or a recording mode reference voltage source 8 via a changeover switch 6. The difference between the output voltage signal d of the current-voltage converter 4 and the reference voltage signal e corresponding to the reproduction mode or the recording mode is determined by the differential amplifier 5.
Is output as a voltage signal f after being arithmetically amplified by
It is fed back to the transistor to Q ₁ current source 1.
Here, the current-voltage converter 4, the differential amplifier 5, the switch 6, the reproduction mode reference voltage source 7, and the recording mode reference voltage source 8 constitute driving current control means.

The current source 1 includes a protection resistor R ₁ and a transistor Q _1. The relationship between the output voltage signal f from the differential amplifier 5 and the driving current a output from the current source 1 is as follows. It is expressed by the following equation. Ia = {V ₁ − (Vf + Vbe)} / R In the above equation, Ia is the amount of the drive current a, V ₁ is the output voltage of the DC / DC converter 13 supplied as the power supply voltage of the current source 1, and Vf is the voltage value of the output voltage signal f of the differential amplifier 5, Vbe is the base-emitter voltage of the transistor Q _1, R is the resistance value of the protective resistor R _1.

With the above configuration, the control operation is performed so that the reference voltage signal e and the output voltage signal d of the current-to-voltage converter 4 become equal. As a result, the light quantity b emitted from the semiconductor laser 2 is reduced to the reproduction mode. Alternatively, it is controlled to a predetermined value according to the recording mode. It is relatively easy to make the response of the current source 1 high speed, and it is sufficiently possible to realize a high speed of several microseconds required in switching between the reproduction mode and the recording mode.

The anode terminal of the semiconductor laser 2 is connected to one input terminal of a comparator 10 via a buffer circuit 9. The cathode terminal of the semiconductor laser 2 is GN
Since it is connected to D, the output voltage signal h from the buffer circuit 9 indicates the forward voltage (operating voltage) of the semiconductor laser 2. A reference voltage source 11 is connected to the other input terminal of the comparator 10, and the reference voltage signal i is set to a median of a range of variation of the forward voltage of the semiconductor laser 2. When the output voltage signal h of the buffer circuit 9, that is, the forward voltage of the semiconductor laser 2 is larger than the reference voltage signal i, the output signal j of the comparator 10 is “L”.
Level, and when the forward voltage of the semiconductor laser 2 is smaller than the reference voltage signal i, the comparator 10
Becomes the "H" level.

The output signal j from the comparator 10 passes through the latch circuit 12 and is input to the output voltage control terminal of the DC / DC converter 13 as an input signal k. DC / D
The C converter 13 outputs a two-stage voltage according to the input signal k and supplies it as a power supply voltage V ₁ to the current source 1. In this manner, the reference voltage signal i is compared with the output voltage signal h of the buffer circuit 9, and according to the result, DC /
The output voltage of DC converter 13 is controlled in two stages.

FIGS. 2A and 2B are diagrams for explaining the control operation in the configuration shown in FIG. 1. FIG. 2A shows the emission light amount of the semiconductor laser 2, FIG. 2B shows the clear signal m of the latch circuit 12, and FIG.
(C) is the clock signal 1 of the latch circuit 12, (D) is the output signal j of the comparator 10, and (E) is the latch circuit 12.
The output signal k, (F) indicates the output voltage V ₁ of the DC / DC converter 13.

When the semiconductor laser 2 is off, the latch circuit 12 outputs an "L" level in response to a clear signal m from a controller (not shown). DC / DC
When the “L” level is input, the converter 13 outputs the high voltage V ₁ h of the preset two-stage output voltage.
Is output. The high voltage V ₁ h is set so as to drive the entire range of the semiconductor laser in which the forward voltage varies. Then, the drive current control means operates according to the ON signal (not shown), and the semiconductor laser 2 is driven. At this time, the clear signal m of the latch circuit 12 is also released and goes to the “H” level. When the semiconductor laser 2 is driven, if the forward voltage is lower than the reference voltage signal i, the output signal j of the comparator 10 becomes “H” level. Next, the output signal level of the comparator 10 is latched by the clock signal 1 from the controller,
Output signal k of latch circuit 12 attains an "H" level.

The DC / DC converter 13, the "H" level is inputted, outputs a low voltage V ₁ l of the output voltage of the two stages that are set in advance. This low voltage V ₁₁ is
The setting is such that a semiconductor laser whose forward voltage is lower than the reference voltage can be driven. At this time, DC /
Since the speed at which the drive current control means controls the emission light amount b of the semiconductor laser 2 is sufficiently faster than the speed at which the output voltage V ₁ of the DC converter 13 switches to the low voltage V ₁₁ ,
The emitted light amount b does not change. Here, the forward voltage of the semiconductor laser 2 does not always change although there are variations due to individual differences. Therefore, the control of the DC / DC converter 13 does not need to be performed at all times.
It is sufficient to carry out every time the switch is turned on.

FIG. 3 is a diagram for explaining the operation of the DC / DC converter 13 and shows a more detailed configuration example of the DC / DC converter 13. DC / DC converter 13, a chopper regulator 13a for controlling the output voltages V ₁ by the switching operation, the choke coil L
₁ and a smoothing capacitor C _{1. The} smoothed output voltage V ₁ is divided by the resistor R ₂ and the resistor R ₃ or R _4, and the voltage V ₂ is fed back to the chopper regulator 13 a. By doing so, a constant voltage is output.

With the configuration as described above, the latch circuit 1
The selector switch 13b based on the second output signal k switches the the resistor R ₃ and resistor R _4, by changing the dividing ratio, it is possible to control the output voltage V ₁ of the DC / DC converter 13. Thus, the power supply voltage V of the current source 1
By controlling the _1, the emitter of the transistor Q ₁
The reactive voltage between the collectors can be kept low.

Here, the forward voltage of the semiconductor laser 2 is compared with a reference voltage by using a comparator 10.
Although the output voltage V ₁ of the DC / DC converter 13 is controlled in two stages, for example, the forward voltage of the semiconductor laser 2 is detected via an AD converter and compared with a plurality of reference voltages by a CPU, thereby obtaining a DC / DC voltage. DC converter 13
The output voltages V ₁ may be configured to control in multiple stages.

[Embodiment 2] FIG. 4 is a circuit diagram for explaining a second embodiment of the semiconductor laser driving apparatus according to the present invention. In FIG. 4, reference numeral 14 denotes a differential amplifier (current detecting means).
Other parts having the same functions as those in FIG. 1 are denoted by the same reference numerals as those in FIG. The difference between the present embodiment and the first embodiment is that, instead of detecting the forward voltage of the semiconductor laser 2, the drive current a of the semiconductor laser 2 is detected and the DC / DC is detected.
The purpose is to control the output voltage V ₁ of the converter 13.

In this embodiment, the voltage across the protection resistor R ₁ of the current source 1 is connected to one input terminal of the comparator 10 via the differential amplifier 14. Protection resistor R ₁
Is proportional to the drive current a, the current amount of the drive current a is detected. A reference voltage source 11 is connected to the other input terminal of the comparator 10,
The reference voltage signal i input to the comparator 10 is set to a value corresponding to the median of the fluctuation range of the semiconductor laser drive current a.

When the output voltage signal h of the differential amplifier 14 is larger than the reference voltage signal i, the output signal j output from the comparator 10 is at "L" level, while the output voltage signal h is lower than the reference voltage signal i. Is smaller, the output signal j of the comparator 10 becomes the “H” level. The output signal j output from the comparator 10 is latched by the latch circuit 12 every time the semiconductor laser 2 is turned on, and the DC / DC
It is input to the output voltage control terminal of converter 13. DC /
The DC converter 13 outputs a two-stage voltage according to the input signal k.

The voltage output from the DC / DC converter 13 changes according to the change in the semiconductor laser driving current.
Power supply voltage V ₁ h required to output a large current,
Power supply voltage V required for current source 1 to output a small current
It is set in two stages of ₁ l. At this time, the voltage V ₁ h,
V ₁₁ needs to be set to a voltage value at which the semiconductor laser 2 can be driven in both the reproduction mode and the recording mode. As described above, by controlling the power supply voltage V ₁ of the current source 1, it is possible to suppress the reactive voltage between the emitter and the collector of the transistor Q ₁ low.

[0032]

According to the present invention, there is provided a semiconductor laser driving apparatus which controls a semiconductor laser driving current based on a light emission amount of a semiconductor laser and outputs a semiconductor laser driving current regardless of a light emission amount of the semiconductor laser. Since the voltage is controlled, unnecessary power consumption can be reduced without impairing the high-speed switching of the emission light amount of the semiconductor laser.

Further, by controlling the power supply voltage of a current source for outputting a semiconductor laser driving current based on the forward voltage of the semiconductor laser, generation of an invalid voltage in the current source due to variation in the forward voltage of the semiconductor laser. And the power consumption of the semiconductor laser driving device can be reduced.

Further, by controlling the power supply voltage of the current source that outputs the semiconductor laser driving current based on the driving current amount of the semiconductor laser, it is possible to reduce the generation of the invalid voltage in the current source due to the change in the driving current amount. Thus, low power consumption of the semiconductor laser driving device can be realized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram for explaining a first embodiment of a semiconductor laser driving device according to the present invention.

FIG. 2 is a diagram for explaining a control operation in the configuration shown in FIG.

FIG. 3 is a diagram for explaining the operation of the DC / DC converter 13.

FIG. 4 is a circuit diagram illustrating a second embodiment of the semiconductor laser driving device according to the present invention.

FIG. 5 is a circuit diagram illustrating an example of a conventional semiconductor laser driving device.

FIG. 6 is a circuit diagram for explaining another example of a conventional semiconductor laser driving device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Current source, 2 ... Semiconductor laser, 3 ... Photodetector, 4 ... Current-voltage converter, 5 ... Differential amplifier, 6 ... Changeover switch, 7 ... Reproduction mode reference voltage source, 8 ... Recording mode reference voltage source, 9 ... buffer circuit, 10 ... comparator, 11 ...
Reference voltage source, 12 latch circuit, 13 DC / DC converter, 13a chopper regulator, 13b changeover switch, 14 differential amplifier, 15 DC / DC converter, 15a smoothing circuit, R ₁ , R ₂ , R ₃ , R ₄ …
Resistance, Q ₁ : transistor, C ₁ : smoothing capacitor.

Claims (3)

[Claims] 1. A semiconductor laser driving device for controlling a light emission amount of a semiconductor laser, comprising: a current source for outputting a semiconductor laser driving current for driving the semiconductor laser; and an output voltage for supplying a power supply voltage to the current source. Variable DC / D
A C converter, drive current control means for controlling the semiconductor laser drive current based on the amount of light emitted by the semiconductor laser, and a drive current control means for controlling the semiconductor laser drive current or the semiconductor laser drive current regardless of the amount of light emitted by the semiconductor laser. And a power supply voltage control means for controlling an output voltage of the DC / DC converter. 2. The power supply voltage control means includes: a voltage detector that detects a forward voltage that is an operation voltage of the semiconductor laser; and a comparison unit that compares a detection value of the voltage detector with a preset reference value. 2. The semiconductor laser drive device according to claim 1, further comprising a comparator, and controlling an output voltage of the DC / DC converter based on a comparison result of the comparator. 3. The power supply voltage control means includes: a current detector for detecting a drive current output from the current source; and a comparator for comparing a detection value of the current detector with a preset reference value. And based on the comparison result of the comparator,
2. The semiconductor laser driving device according to claim 1, wherein an output voltage of the DC converter is controlled.