JPH0837331A - Semiconductor laser controller - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to enable a reduction in current consumption and a reduction in chip size when integrated into an IC, and to enable high-speed semiconductor laser output control. According to the present invention, an error amplifier 13 that amplifies a difference current between a light emission command signal and a monitor signal, a current driver 15 that outputs a current proportional to a light emission command signal, and an error amplifier 1 are provided.
A current amplifier 14 that amplifies a signal obtained by adding the output of No. 3 and the output of the current driver 15 is provided, and the semiconductor laser 11 is controlled by the output current of this current amplifier 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser control device for controlling the optical output of a semiconductor laser used as a light source for laser printers, digital copying machines, optical disk devices, optical communication devices and the like.

[0002]

2. Description of the Related Art A semiconductor laser is extremely small and
In addition, since it is possible to directly perform high-speed modulation with a drive current, it has been widely used as a light source for laser printers, optical disk devices, digital copying machines, etc. in recent years. However, the relationship between the drive current of the semiconductor laser and the light output changes remarkably depending on the temperature, which poses a problem when the light intensity of the semiconductor laser is set to a desired value. In order to solve this problem and utilize the advantages of the semiconductor laser, various APC (Automatic Power Control) circuits have been conventionally proposed. This APC circuit can be roughly classified into the following three types.

(1) The optical output of the semiconductor laser is desired by an optoelectronic negative feedback loop that monitors the optical output of the semiconductor laser with a light receiving element and controls the light receiving current proportional to the optical output of the semiconductor laser generated in the light receiving element. Method to control the value of.

(2) During the power setting period, the light output of the semiconductor laser is monitored by the light receiving element, and a signal proportional to the light receiving current (proportional to the light output of the semiconductor laser) generated in this light receiving element and the light emission command. The forward current of the semiconductor laser is controlled so that the signal becomes equal to that of the signal, and the value of the forward current of the semiconductor laser set in the power setting period is held outside the power setting period to obtain the desired optical output of the semiconductor laser. A method in which information is added to the optical output of the semiconductor laser by controlling the value to the value and modulating the forward current of the semiconductor laser set during the power setting period based on the information outside the power setting period.

(3) The temperature of the semiconductor laser is measured, and the forward current of the semiconductor laser is controlled by the measured temperature signal, or the temperature of the semiconductor laser is controlled to be constant so that the semiconductor laser is controlled. A method of controlling the light output to a desired value.

The method (1) is desirable in order to set the optical output of the semiconductor laser to a desired value, but the operating speed of the light receiving element, the operating speed of the amplifying element forming the optoelectronic negative feedback loop, etc. Limits cause control speed limits. For example,
When considering the crossover frequency in the open loop of the photoelectric negative feedback loop as a measure of this control speed, this crossover frequency is f
_{When set to 0} , the step response characteristic of the optical output of the semiconductor laser can be approximated as follows.

Pout = P ₀ {1-exp (-2πf ₀ t)} Pout: Optical output of semiconductor laser P ₀ : Set light velocity of semiconductor laser t: Time For many purposes of the semiconductor laser, the semiconductor laser is used. The total amount of light (integral value of light output ∫Pout) from immediately after changing the light output of the light source until the set time τ ₀ elapses is required to be a predetermined value. Becomes

∫Pout = P ₀ · t ₀ {1- [1-exp (-2
πf ₀ τ ₀ )] / 2πf ₀ τ ₀ } If τ ₀ = 50 nS and the allowable range of error is 0.4%, then f ₀ > 800 MHZ, which is extremely difficult.

In the method (2), the above-mentioned problems of the method (1) do not occur and the semiconductor laser can be modulated at a high speed, and therefore it is widely used. However, in the method (2), since the light output of the semiconductor laser is not always controlled, the light quantity of the semiconductor laser easily changes due to disturbance or the like. The disturbance has, for example, a dow loop characteristic of a semiconductor laser, and the light amount of the semiconductor laser easily causes an error of about several percent due to the dow loop characteristic.

As an attempt to suppress the droop characteristic of the semiconductor laser, a method has been proposed in which the frequency characteristic of the semiconductor laser drive current is matched with the thermal time constant of the semiconductor laser and the compensation is performed. There is a problem that there are variations among the semiconductor lasers, and the semiconductor lasers vary depending on the surrounding environment. In addition, there are other problems such as fluctuations in the light amount due to the influence of the return light of the semiconductor laser, which is a problem in optical disk devices and the like.

To solve these problems, for example, a semiconductor laser control device disclosed in Japanese Patent Laid-Open No. 205086/1990 has been proposed. In this semiconductor laser control device,
An optical electrical negative feedback loop that constantly controls the forward current of the semiconductor laser so that the optical output of the semiconductor laser is monitored by the light receiving element and the output and the light emission command signal are equal.
And a conversion means for converting the light emission command signal into a forward current of the semiconductor laser, and the optical output of the semiconductor laser by the sum or difference current of the control current of the photoelectric negative feedback loop and the current generated by the conversion means. To control
By adding the converting means, the control amount of the control current of the opto-electric negative feedback loop is reduced, and high-speed modulation of the semiconductor laser is enabled.

In this semiconductor laser control device, as shown in FIG. 13, the light emission command signal is input to the comparison amplifier 1 and the current converter 2, and a part of the optical output of the driven semiconductor laser 3 is monitored by the light receiving element 4. It The comparison amplifier 1, the semiconductor laser 3, and the light receiving element 4 form a photoelectric negative feedback loop,
The comparison amplifier 1 compares the light receiving signal, which is induced in the light receiving element 4 and is proportional to the photocurrent which is proportional to the optical output of the semiconductor laser 3, with the light emission command signal, and the semiconductor laser 3
The forward current is controlled so that the light reception signal and the light emission command signal are equal.

Further, the current converter 2 outputs a current preset according to the light emission command signal so that the light receiving signal and the light emission command signal become equal to each other. The sum or difference of the output current of the current converter 2 and the control current output from the comparison amplifier 1 becomes the forward current of the semiconductor laser 3. In this semiconductor laser control device, the comparison amplifier 1 and the current converter 2 directly drive the semiconductor laser 3, respectively.
An output circuit having a current driving capability of about 100 mA was required for each.

FIG. 14 is a rewrite of FIG. 13 in more detail. The comparison amplifier 1 includes a comparison amplification section 5 for comparing a light reception signal output from the light reception element 4 with a light emission command signal, and this comparison amplification section 5. Is divided into a current amplification section 6 for amplifying the output of the current converter 2, and the current converter 2 is divided into a current conversion section 7 for outputting a signal proportional to the light emission command signal and a current amplification section 8 for amplifying the output thereof. It

[0015]

In the semiconductor laser control device as shown in FIG. 14, the current amplifying units 6 and 8 are required to have a driving ability to output a large current, so that they are constructed by using a large-sized transistor. However, it has been insufficient to reduce the current consumption and the chip size at the time of forming an IC.

It is an object of the present invention to provide a semiconductor laser control device capable of reducing the current consumption and the chip size at the time of forming an IC and enabling high-speed semiconductor laser output control.

[0017]

In order to achieve the above object, the invention according to claim 1 is proportional to the output intensity of the semiconductor laser by monitoring a part of the optical output of the driven semiconductor laser by a light receiving section. In a semiconductor laser control device that obtains a monitor signal and controls the forward current of the semiconductor laser so that the monitor signal and the light emission command signal are equal, an error that amplifies the difference current between the light emission command signal and the monitor signal An amplifier, a current driver that outputs a current proportional to the light emission command signal, and a current amplifier that amplifies a signal obtained by adding the output of the error amplifier and the output of the current driver, and the output of the current amplifier The semiconductor laser is controlled by an electric current.

According to a second aspect of the present invention, in the semiconductor laser control device according to the first aspect, the current amplifier comprises a transistor and a resistor connected to the emitter of the transistor, and the output of the error amplifier and the current A signal obtained by adding the output of the drive unit is applied to the base of the transistor and converted into a forward current of the semiconductor laser by the resistor.

According to the third aspect of the present invention, a part of the optical output of the driven semiconductor laser is monitored by the light receiving section to obtain a monitor signal proportional to the output intensity of the semiconductor laser, and the monitor signal and the light emission command signal are supplied. In a semiconductor laser control device for controlling the forward current of the semiconductor laser so that the values become equal to each other, a first transistor whose emitter current is changed by a current proportional to the light emission command signal and a collector of the first transistor are connected. A first resistor, and a second transistor whose base is connected to the first resistor,
A second resistor having one end connected to the emitter of the second transistor, an error amplifier for amplifying a difference current between the light emission command signal and the monitor signal, and an output side of the error amplifier connected to the base. A third transistor, a third resistor having one end connected to the emitter of the third transistor, a fourth transistor having a collector and a base connected to the other end of the third resistor, and a fourth transistor A fourth resistor whose one end is connected to the emitter of the transistor, a fifth transistor whose base is connected to the base of the fourth transistor, and a fifth resistor whose one end is connected to the emitter of this fifth transistor. The semiconductor device includes a resistor and a current amplifier whose input side is connected to the other end of the second resistor and the collector of the fifth transistor. It is intended to control the over The.

According to a fourth aspect of the present invention, in the semiconductor laser control device according to the third aspect, the second resistor, the third resistor, the fourth resistor and the fifth resistor are respectively arranged in parallel with each other. The first capacitance, the second capacitance, the third capacitance, and the fourth capacitance are connected.

According to a fifth aspect of the present invention, a part of the optical output of the driven semiconductor laser is monitored by the light receiving section to obtain a monitor signal proportional to the output intensity of the semiconductor laser, and the monitor signal and the light emission command signal are supplied. In a semiconductor laser control device for controlling the forward current of the semiconductor laser so that the values become equal to each other, a first transistor whose emitter current is changed by a current proportional to the light emission command signal and a collector of the first transistor are connected. A first resistor, and a second transistor whose base is connected to the first resistor,
A sixth resistor having one end connected to the emitter of the second transistor and a fifth resistor connected in parallel with the sixth resistor.
Capacitance, a seventh resistor having one end connected to the other end of the sixth resistor, a sixth capacitance connected in parallel with the seventh resistor, the light emission command signal, and the monitor signal. Error amplifier for amplifying the differential current of the third amplifier, a third transistor whose output side is connected to the base, and one end of which is connected to the emitter of the third transistor and whose resistance value is equal to that of the sixth resistor. 3 resistance,
A second capacitance connected in parallel with the third resistor and having the same capacitance as the fifth capacitance;
A fourth transistor having a collector and a base connected to the other end of the resistor; a fourth resistor having one end connected to the emitter of the fourth transistor and having a resistance value equal to that of the seventh resistor; A third capacitance connected in parallel to the resistance of the third capacitance and having the same capacitance as the sixth capacitance, a fifth transistor having a base connected to the base of the fourth transistor, and one end of an emitter of the fifth transistor. An input side is connected to a fifth resistance connected to the fifth resistance, a fourth capacitance connected in parallel to the fifth resistance, the other end of the seventh resistance and the collector of the fifth transistor. A current amplifier is provided, and the semiconductor laser is controlled by the output current of the current amplifier.

According to a sixth aspect of the present invention, in the semiconductor laser control device according to the fourth aspect, a value obtained by multiplying the resistance value of the second resistor and the capacitance of the first capacitance is input to the current amplifier. The value is equal to or almost equal to the value obtained by multiplying the resistance component and the capacitance component of the impedance.

According to a seventh aspect of the present invention, a part of the optical output of the driven semiconductor laser is monitored by the light receiving section to obtain a monitor signal proportional to the output intensity of the semiconductor laser, and the monitor signal and the light emission command signal are supplied. In a semiconductor laser control device that controls the forward current of the semiconductor laser so that the values become equal, an error amplifier that amplifies a difference current between the light emission command signal and the monitor signal, and a current proportional to the light emission command signal is output. A current driver, a compensator for generating a differential signal from a value proportional to the light emission command signal of the output signal of the current driver, an output of the error amplifier, an output of the current driver and the compensator. And a current amplifier for amplifying a signal obtained by adding the output to the semiconductor laser. The semiconductor laser is controlled by the output current of the current amplifier.

According to an eighth aspect of the present invention, in the semiconductor laser control apparatus according to the seventh aspect, the compensator has a first means for multiplying the light emission command signal by a constant, and the light emission command is generated by the first means. And a second means for generating a differential waveform signal of a signal obtained by multiplying the signal by a constant.

According to a ninth aspect of the present invention, a part of the optical output of the driven semiconductor laser is monitored by the light receiving section to obtain a monitor signal proportional to the output intensity of the semiconductor laser, and the monitor signal and the light emission command signal are supplied. In the semiconductor laser control device for controlling the forward current of the semiconductor laser so that the light emission command signals are equal to each other, an error amplifier for amplifying a difference current between the light emission command signal and the monitor signal and the light emission command signal are (1 + 2 /
K) third means for multiplying, a current drive section for outputting a current proportional to the light emission command signal using the output of the third means as an input signal, and a fourth means for multiplying the light emission command signal by 1 / K. Means, fifth means for generating an integrated waveform signal of the output of the fourth means, and sixth means for adding the output of the fifth means and the output of the fourth means Compensator for generating a difference signal from a value of the output signal of the unit proportional to the light emission command signal, seventh means for subtracting the output of the sixth means from the output of the current driver, and the seventh means And a current amplifier for amplifying a signal obtained by adding the output of the means and the output of the error amplifier, and the semiconductor laser is controlled by the output current of the current amplifier.

[0026]

According to the first aspect of the present invention, a part of the optical output of the driven semiconductor laser is monitored by the light receiving section to obtain a monitor signal proportional to the output intensity of the semiconductor laser, and the error amplifier outputs a light emission command signal. Amplifies the difference current with the monitor signal. The current driver outputs a current proportional to the light emission command signal, the current amplifier amplifies the signal obtained by adding the output of the error amplifier and the output of the current driver, and the semiconductor laser is controlled by the output current of this current amplifier. .

According to a second aspect of the present invention, in the semiconductor laser control device according to the first aspect, a signal obtained by adding the output of the error amplifier and the output of the current driver is applied to the base of the transistor and the resistance of the semiconductor laser is applied by the resistance. Converted to forward current.

According to the third aspect of the present invention, a part of the optical output of the driven semiconductor laser is monitored by the light receiving section, and a monitor signal proportional to the output intensity of the semiconductor laser is obtained.
The current proportional to the light emission command signal changes the emitter current of the first transistor to change the voltage across the terminals of the first resistor, and the second transistor outputs an output according to the voltage across the terminals of the first resistor. Input to the amplifier. The error amplifier amplifies the difference current between the light emission command signal and the monitor signal, and the output of this error amplifier is the third transistor, the fourth transistor, the fifth transistor, the fourth resistor, and the fifth resistor. Is input to the current amplifier via the current mirror circuit configured by. The semiconductor laser is controlled by the output current of the current amplifier.

According to a fourth aspect of the present invention, in the semiconductor laser control device according to the third aspect, a first capacitance is provided in parallel with each of the second resistor, the third resistor, the fourth resistor and the fifth resistor, By connecting the second capacitance, the third capacitance, and the fourth capacitance, the influence of the parasitic capacitance is improved and high-speed operation becomes possible.

According to the fifth aspect of the present invention, a part of the optical output of the driven semiconductor laser is monitored by the light receiving section, and a monitor signal proportional to the output intensity of the semiconductor laser is obtained.
The current proportional to the light emission command signal changes the emitter current of the first transistor to change the voltage across the terminals of the first resistor, and the second transistor outputs an output according to the voltage across the terminals of the first resistor. Input to the amplifier. The error amplifier amplifies the difference current between the light emission command signal and the monitor signal, and the output of this error amplifier is the third transistor, the fourth transistor, the fifth transistor, the fourth resistor, and the fifth resistor. Is input to the current amplifier via the current mirror circuit configured by. The semiconductor laser is controlled by the output current of the current amplifier. Further, between the emitter of the second transistor, the collector of the fifth transistor, and the input side of the current amplifier, a parallel circuit of a sixth resistor and a fifth capacitance, a seventh resistor and a sixth capacitance are connected. A parallel circuit is connected in series, the third resistor and the sixth resistor have the same resistance value, the fourth resistor and the seventh resistor have the same resistance value, and the second capacitance and the fifth capacitance have the same capacitance value. Are equal to each other and the capacitances of the third capacitance and the sixth capacitance are equal to each other, the frequency characteristic is improved.

According to a sixth aspect of the present invention, in the semiconductor laser control device according to the fourth aspect, a value obtained by multiplying a resistance value of the second resistor and a capacitance of the first capacitance is a resistance of an input impedance of the current amplifier. By making the value equal to or substantially equal to the value obtained by multiplying the capacitance value by the capacitance value, the deviation of the output signal of the current driver from the value proportional to the light emission command signal is almost eliminated.

In the seventh aspect of the invention, a part of the optical output of the driven semiconductor laser is monitored by the light receiving section to obtain a monitor signal proportional to the output intensity of the semiconductor laser, and the error amplifier outputs the light emission command signal. The current difference between the monitor signal and the monitor signal is amplified. The current driver outputs a current proportional to the light emission command signal, and the compensator generates a difference signal from a value proportional to the light emission command signal of the output signal of the current driver. The current amplifier amplifies a signal obtained by adding the output of the error amplifier, the output of the current driver and the output of the compensator, and the semiconductor laser is controlled by the output current of this current amplifier.

According to an eighth aspect of the present invention, in the semiconductor laser control device according to the seventh aspect, the compensator multiplies the light emission command signal by a constant by the first means and the compensator by the second means.
The differential waveform signal of the signal obtained by multiplying the light emission command signal by a constant is generated by the means.

In a ninth aspect of the present invention, a part of the optical output of the driven semiconductor laser is monitored by the light receiving section to obtain a monitor signal proportional to the output intensity of the semiconductor laser, and the error amplifier outputs a light emission command signal. Amplifies the difference current with the monitor signal. The third means multiplies the light emission command signal by (1 + 2 / K) and uses it as an input signal to the current driver, and the current driver outputs a current proportional to the light emission command signal. The compensator multiplies the light emission command signal by 1 / K by the fourth means and the fourth means by the fifth means.
An integrated waveform signal of the output of the means is generated, and the output of the fifth means and the output of the fourth means are added by the sixth means.
The seventh means subtracts the output of the sixth means from the output of the current driver, and the current amplifier amplifies a signal obtained by adding the output of the seventh means, the output of the error amplifier and the output of the current driver, The semiconductor laser is controlled by the output current of this current amplifier.

[0035]

FIG. 1 shows a first embodiment of the present invention. This first
The embodiment is an embodiment of a semiconductor laser control device to which the invention according to claim 1 is applied. A part of the optical output P ₀ of the driven semiconductor laser 11 is received by the light receiving section 12 and monitored. The light receiving section 12 is composed of a light receiving element including a photodiode, and a light receiving signal (monitor current Im) proportional to the light intensity of the semiconductor laser 11 is induced. The error amplifier 13 receives the light emission command signal Isig and the photodiode 1.
The difference current (Isig-Im) from the monitor current Im from 2 is amplified. The output current ΔI ₁ of this error amplifier 13 is ΔI ₁ = A, where A ₁ is the current amplification factor of the error amplifier 13.
It becomes ₁ (Isig-Im). The output current ΔI ₁ of the error amplifier 13 is amplified by the current amplifier 14 and supplied to the semiconductor laser 11 as a forward current. Current amplifier 14
The current amplification factor of A is A ₀ .

Semiconductor laser 11 and photodiode 1
2. The error amplifier 13 and the current amplifier 14 form a photoelectric negative feedback loop, and control the forward current of the semiconductor laser 11 so that the light emission command signal Isig and the monitor current Im become equal. Further, the current driver 15 supplies a current proportional to the light emission command signal Isig to the semiconductor laser 1 via the current amplifier 14.
1 is supplied as a forward current.

Here, the output current ΔI ₂ of the current driver 15
Is ΔI ₂ = κ · Isig. κ is a proportional constant and is set in advance. Output current [Delta] I ₂ output current [Delta] I ₁ and the current driving portions 15 of the error amplifier 13 is input is summed with a current summing point a current amplifier 14, converted by the current amplifier 14 in the forward current I _LD of the semiconductor laser 11 Then, the semiconductor laser 11 is controlled. The forward current I _LD of the semiconductor laser 11 is given by the following equation.

I _LD = A ₀ · (ΔI ₁ + ΔI ₂ ) = A ₀ · (A ₁ (Isig−Im) + κ · Isig) (1) Generally, the optical output P ₀ of the semiconductor laser 11 is as follows. Is approximated as follows. P ₀ = η · (I _LD −Ith) η: Differential quantum efficiency, Ith: Threshold current of semiconductor laser 11 Further, the monitor current Im is α, the coupling coefficient between the semiconductor laser 11 and the photodiode 12, and the photodiode 12.
If the radiation sensitivity of S is S, it can be expressed as follows.

Im = αSP ₀ = αSη · (I _LD −Ith) = αSη · (A ₀ · (ΔI ₁ + ΔI ₂ ) −Ith) Therefore, the current driver 15 proportional to the light emission command signal Isig.
The magnitude of the output current _{ΔI 2, A 0 · ΔI 1} = when the Ith, emission command signal Isig and monitor current Im are equal so as to advance the proportionality constant κ of the semiconductor laser 11 the light output, a forward current Characteristics, semiconductor laser 11 and photodiode 1
It may be set based on the coupling coefficient with 2 and the light input / received signal characteristics of the photodiode 12 (that is,
κ = 1 / αSηA ₀ ).

[0040] In this first embodiment, since the conversion in the forward current I _{L D} of the semiconductor laser 11 by the output current [Delta] I ₁ and the current amplifier 14 by adding the output current [Delta] I ₂ of the current driving portions 15 of the error amplifier 13 , The output current ΔI ₁ of the error amplifier 13
And the output signal ΔI ₂ of the current driver 15 (ΔI ₁ +
ΔI ₂ ) may be I _LD / A ₀ , and the current value of the sum signal (ΔI ₁ + ΔI ₂ ) may be small. Therefore,
It is not necessary to provide separate current amplifiers for the output sections of the error amplifier 13 and the current driver 15, and the error amplifier 13 and the current driver 15 can share a current amplifier for driving the semiconductor laser 11 with a large current. Like For this reason, it is possible to reduce the current consumption when integrated into an IC, in addition, it is possible to reduce the number of transistors having a large transistor size, reduce the chip area, and reduce the chip size. Further, since the current adding portion is easily incorporated in the IC, the influence of the parasitic element is reduced, and high-speed current adding can be performed.

FIG. 2 shows a second embodiment of the present invention. The second embodiment is an embodiment of a semiconductor laser control device to which the invention according to claim 2 is applied, and in the first embodiment,
The current amplifier 14 is composed of a transistor 16 and a resistor 17. The semiconductor laser 11 is connected between the collector of the transistor 16 and the DC power supply, and the emitter of the transistor 16 is grounded via the resistor 17.

The summed output current [Delta] I ₁ and output current [Delta] I ₂ and the current summing point a of the current driving portions 15 of the error amplifier 13, the semiconductor laser 11 current and the addition is by resistor 17 is applied to the base of the transistor 16 Is converted to a forward current of. Here, the transistor 16 and the resistor 1
The current amplification factor A ₀ of the current amplifier 14 composed of 7 is A _{0 to} h _fe -100. In the second embodiment, parts other than the current amplifier 14 are the same as in the first embodiment. In the second embodiment, since the current amplifier 14 is composed of the transistor 16 and the resistor 17, the same effect as that of the first embodiment can be obtained with a simple structure, and the transistor 16 and the resistor 17 can be formed as an IC into external parts. Then, the current consumption in the IC can be reduced.

FIG. 3 shows a third embodiment of the present invention. The third embodiment is an embodiment of a semiconductor laser control device to which the invention described in claim 3 is applied. The light receiving section 12 is composed of a light receiving element composed of a photodiode, and the cathode of the photodiode 12 is connected to a DC power supply of a voltage V _LD . The anode of the photodiode 12 is the error amplifier 13
A current source 18 for generating a light emission command signal Isig and a capacitance 19 are connected in parallel between the anode of the photodiode 12 and the ground point.

The output terminal of the error amplifier 13 is connected to the base of the NPN transistor 20, and the collector of the transistor 20 is connected to the DC power source of the voltage Vcc. The emitter of the transistor 20 is a diode 22 via a resistor 21.
Connected to the anode of the diode 22 and the cathode of the diode 22 is N
NPN and collector and base of PN transistor 23
Connected to the base of the transistor 24. The emitters of the transistors 23 and 24 are grounded via the resistors 25 and 26, respectively, and the transistors 23 and 24 and the resistor 25 and
26 constitutes a current mirror circuit.

A predetermined voltage V ₄ is applied to the base of the NPN transistor 27 by a circuit (not shown), and the collector of the transistor 27 is connected through a resistor 28 to a DC power source of voltage Vcc. The emitter of the transistor 27 is grounded via a current source 29 that generates a current Isig ₂ proportional to the light emission command signal Isig, and the emitter of the transistor 27 and the collector of the NPN transistor 30 are connected.
A predetermined voltage V ₅ is applied to the base of the transistor 30 from a circuit (not shown), and the emitter of the transistor 30 is grounded via the resistor 31.

The collector of the transistor 27 is connected to the base of the NPN transistor 32, and the transistor 32
Is connected to a DC power source of voltage Vcc. The emitter of the transistor 32 is connected to the collector of the transistor 24 and the base of the NPN transistor 34 via the resistor 33, and the collector of the transistor 34 is connected to the DC power source of the voltage Vcc.

The emitter of the transistor 34 is a resistor 35,
36 is grounded in series and connected to the base of an NPN transistor 37, and the emitter of the transistor 37 is connected to the connection point of the resistors 35 and 36. The collector of the transistor 37 is connected to the cathode of the semiconductor laser 11, and the anode of the semiconductor laser 11 is connected to the DC power supply of the voltage V _LD . The transistors 34 and 37 and the resistors 35 and 36 form the current amplifier 14.

Next, the operation of the third embodiment will be described.
The current source 29 is a current Isig ₂ proportional to the light emission command signal Isig _2.
Is generated, and the current Isig ₂ becomes Isig ₂ = −γκ · Isig. Here, the proportional constant γκ is set in advance as described above. Transistor 27 emitter current changes by a current Isig _2, the change [Delta] V ₂ voltage V ₂ is generated across the resistor 28. This ΔV ₂ is ΔV ₂ = R ₅ · Isig ₂ when the resistance value of the resistor 28 is R ₅ .

On the other hand, the optical output P of the driven semiconductor laser 11
A part of ₀ is received and monitored by the photodiode 12, and a light reception signal (monitor current Im) proportional to the light intensity of the semiconductor laser 11 is induced. The input impedance of the error amplifier 13 is high impedance,
Difference current (Isig-Im) between the light emission command signal Isig from the current source 18 and the monitor current Im from the photodiode 12.
Is charged and discharged by the capacitance 19 to generate a voltage Vi. This Vi is amplified by the error amplifier 13 and applied to the base of the transistor 20.

The output signal ΔV ₃ of the error amplifier 13 is ΔV ₃ = A · Vi = −A · ((Isig−Im) / jωCf, where Cf is the capacitance of the capacitance 19 and A is the voltage amplification factor of the error amplifier 13. The transistors 23 and 24 and the resistors 25 and 26 form a current mirror circuit, and here, for simplification of description, the resistance value R ₃ of the resistance 25 and the resistance value R _{2 of the} resistance 26 are equal. , The transistors 23 and 24 have the same size, and the diode 22 is the transistor 2
Assuming that the transistors 3 and 24 are formed of the same transistor and the variations in the characteristics are the same, the collector current I of the transistor 24 is as follows.

I = (Vcc−V ₃ −3Vbe) / (R ₃ + R ₄ ) where V ₃ is the difference between Vcc and the output voltage of the error amplifier 13, Vbe is the base-emitter voltage of each transistor,
R ₄ is the resistance value of the resistor 21. Therefore, the potential Va at the addition point a, to which the resistor 33, the collector of the transistor 24 and the base of the transistor 34 are connected, is Va = Vcc−V ₂ −Vbe− (Vcc− when the resistance value of the resistor 33 is V _1. V ₃ -3Vbe) R ₁ /
(R ₃ + R ₄ ), so that R ₁ = R ₃ + R ₄
When the resistance values R ₁ , R ₃ and R ₄ of 33 are selected, Va = V ₃ −V ₂ + 2Vbe, and the influence of the fluctuation of the power supply voltage Vcc disappears.

This addition point a is the current addition point a of the first embodiment.
In this embodiment, the current amplifier 14 is composed of transistors 34 and 37 and resistors 35 and 36. Therefore, the potential Vb at the point b where the resistors 35 and 36 and the emitter of the transistor 37 are connected is Vb = V ₃ −V ₂ . This Vb also cancels out the Vbe term, and V ₃ and V ₂
If the bias voltage is set from a stable reference power source, a stable potential can be obtained that is independent of fluctuations in the power supply voltage Vcc, temperature changes in Vbe, and variations in characteristics. Therefore, the semiconductor laser 11 has a stable offset current Ioff (=
Vb / R _E, R _E: resistance value of the resistor 36) flows. Also,
The voltage change ΔVa at point a is ΔVa = − (ΔV ₃ −ΔV ₂ ), and the control current I _LD flowing through the semiconductor laser 11 is as follows.

[0053] _{I LD = - (ΔV 3 -ΔV} 2) / R E = - (- A · (Isig-Im) / jωCf + R 5 · Isig 2) / R E = (A · (Isig-Im) / jωCf + R 5 · γκ · Isig) / R _E Accordingly, the control current of the semiconductor laser 11 becomes a similar form therewith ((1)) of the first embodiment, the first embodiment can be realized a structure similar to that of the first embodiment The same effect as the example is obtained.

Although the current amplifier 14 is composed of the transistors 34 and 37 and the resistors 35 and 36 here,
The current amplifier 14 is provided with a transistor 16 as in the second embodiment.
In the case of using the resistor 17 and the resistor 17, the diode 22 may be removed. The transistor 30 and the resistor 31 to which the voltage V ₅ is applied as a base are for allowing a constant emitter current to flow in the transistor 27 as an offset current, and improve the linearity when Isig ₂ is small. As described above, in the third embodiment, the same effect as that of the first embodiment can be obtained with a simple structure, and the semiconductor is provided with a stable current that does not depend on the fluctuation of the power supply voltage Vcc, the temperature change of Vbe and the characteristic variation. The laser 11 can be driven.

FIG. 4 shows a fourth embodiment of the present invention. The fourth embodiment is an embodiment of a semiconductor laser control device to which the invention described in claim 4 is applied. In the third embodiment, the resistor 33 is a parasitic capacitance C such as the collector capacitance of the transistor 24.
It becomes a low-pass filter with _X , which hinders the speedup. In order to improve this problem, the fourth embodiment uses the third embodiment described above.
In the embodiment, the capacitance 38 of the capacitance C ₁ (>> C _X ) is connected in parallel with the resistor 33, and the influence of the parasitic capacitance can be ignored, and high speed operation becomes possible. In addition, in the fourth embodiment, similarly, the resistors 26, 25, and 21 are respectively connected in parallel with the capacitances 39 to 41 to increase the speed. The other parts of the fourth embodiment are similar to those of the third embodiment.

FIG. 5 shows a fifth embodiment of the present invention. The fifth embodiment is an embodiment of a semiconductor laser control device to which the invention described in claim 5 is applied. In the fourth embodiment, the impedance of the circuit in which the resistance 33 and the capacitance 38 are connected in parallel is Z ₁ , the resistance 26 and the capacitance 39 are
The impedance of the circuit connected in parallel is Z ₂ , resistance 2
When the impedance of the circuit in which 5 and the capacitance 40 are connected in parallel is Z ₃ , and the impedance of the circuit in which the resistor 21 and the capacitance 41 are connected in parallel is Z ₄ ,
The potential Va at the point a is given by the following equation.

[0057] _{Va = Vcc-V 2 -Vbe- (} Vcc-V 3 -3
_{Vbe) Z 1 / (Z 3} + Z 4) Therefore, in order to improve the frequency characteristic, Z ₁ = Z ₃ +
It should be Z ₄ . Therefore, in the fifth embodiment, in place of the circuit in which the resistor 33 and the capacitance 38 are connected in parallel in the fourth embodiment, the resistor 33 and the capacitance 38 are used.
A circuit in which the circuit is connected in parallel and a circuit in which the resistor 42 and the capacitance 43 are connected in parallel are used in series, and the frequency characteristic can be improved.

Here, when the resistance value of the resistor 42 is R ₈ and the capacitance of the capacitance 43 is C ₅ , Z ₁ = R ₁ / (1 + jωR ₁ C ₁ ) + R ₈ / (1 + jωR ₈ C
₅ ) Z ₃ + Z ₄ = R ₄ / (1 + jω R ₄ C ₄ ) + R ₃ / (1 + jω
R ₃ C ₃ ), so in the fifth embodiment, R ₁ = R ₄ , C ₁ = C ₄ , R ₈
= R ₃ and C ₅ = C ₃ so that Z ₁ = Z ₃ + Z ₄ is established. The other parts of the fifth embodiment are similar to those of the fourth embodiment.

In the fourth embodiment of FIG. 4, the addition point a
The AC equivalent circuit based on can be modeled as shown in FIG. In FIG. 6, a resistor 33, a capacitance 38, points a and c (the point where the emitter of the transistor 32, the resistor 33 and the capacitance 38 are connected)
Corresponds to FIG. R ₀ is a resistance component of the input impedance of the current amplifier 14, and C ₀ is a capacitance component of the input impedance of the current amplifier 14. Where c
When the voltage signal applied to the point is V ₁ and the input impedance of the current amplifier 14 is Z ₀ , the voltage V _{0 at the} point a is given by the following equation.

V ₀ = V ₁ · Z ₀ / (Z ₀ + Z ₁ ) In this formula, the term Z ₀ / (Z ₀ + Z ₁ ) is R ₀ / (R ₀ + R ₁ ) in the low frequency region, In the range C ₀ / (C ₀ +
It can be approximated as C ₁ ). R ₀ / (R ₀ + R ₁ ) ≠ C ₀ / (C ₀ +
At C ₁ ), even if a rectangular wave is applied as the voltage signal V _{1 to the} point c, the voltage V _{0 at the} point a does not become a perfect rectangular wave. For example, in the case of R ₀ / (R ₀ + R ₁ )> C ₀ / (C ₀ + C ₁ ), V ₀ has a waveform as shown in FIG. 7, and the difference Δ from the desired value of V ₀ (halftone dot Part) can be expressed as follows.

Δ = Δ ₀ · exp (−t / τ ₀ ) · V ₁ Δ ₀ = R ₀ / (R ₀ + R ₁ ) −C ₀ / (C ₀ + C ₁ ) τ ₀ : time constant t: time , When this Δ ₀ increases, at the time of rising (t = 0
The voltage difference (1 / K) V ₀ (= Δ ₀ · V ₁ ) at the time of ( ₁ ) increases, and there arises a problem that a desired waveform cannot be obtained.

Therefore, the sixth embodiment of the present invention is the same as the fourth embodiment.
In the example, R ₀ / (R ₀ + R ₁ ) = C ₀ / (C ₀ +
C ₁ ), that is, R ₀ · C ₀ = R ₁ · C ₁ , or R ₀ / (R ₀ + R ₁ ) ≈C ₀ / (C ₀ +
C ₁ ), that is, R ₁ and C ₁ are determined so that R ₀ · C ₀ ≈R ₁ · C _1, and there is almost no difference Δ from the desired value of V ₀ . A deviation from a value of V ₀ proportional to the light emission command signal can be almost eliminated.

Further, when the above Δ is added to the point a or the point c in FIG. 6 to compensate Δ, that is, by the compensation signal that decreases with the time constant τ ₀ at the amplitude of 1 / K times the input signal, Δ By compensating for the above, the problem of the deviation from the value proportional to the light emission command signal of V ₀ can be greatly improved. FIG. 8 shows a seventh embodiment of the present invention in which a compensator for performing such compensation is added. The seventh embodiment is an embodiment of the invention described in claim 7, and is a semiconductor laser control device according to the first embodiment to which a compensator 44 is added.

The compensator 44 uses the current driver 1 as a compensation signal.
A difference signal from a value proportional to the light emission command signal of the output signal of 5 is obtained from the light emission command signal, and the current amplifier 14 including the transistor 16 and the resistor 17 outputs the output of the error amplifier 13, the output of the current driver 15, and the compensator 44. Output of and addition point h
The semiconductor laser 11 is driven by amplifying the signal added in. Therefore, it is possible to compensate the deviation of V ₀ from the value proportional to the light emission command signal.

FIG. 9 shows a part of the eighth embodiment of the present invention.
FIG. 10 shows each signal waveform of the eighth embodiment. This eighth embodiment is an embodiment of the invention as set forth in claim 8, and in the seventh embodiment, the compensator 44 is provided with a constant multiplication circuit 45 for multiplying the light emission command signal V ₁ by a constant (1 / K). 46 and this first
And a differentiator 47 for generating a differential waveform signal of a signal obtained by multiplying the light emission command signal V ₁ by a constant.

The light emission command signal V ₁ is multiplied by a constant (1 / k) by a constant multiplication circuit 45 and differentiated by a differentiator 47,
It is multiplied by a constant (1 / k ') by the constant multiplication circuit 46. Here, 1 / k × 1 / k ′ = 1 / K. Constant multiplication circuit 46
The compensation signal Ve from is added to the output of the current driver 15 at the addition point h, added to the output Vd of the error amplifier 13 at the addition point a, and then input to the current amplifier 14. The other parts of the eighth embodiment are similar to those of the seventh embodiment. In the eighth embodiment, since the compensator 44 is composed of the constant multiplication circuits 45 and 46 and the differentiator 47, the same effect as that of the seventh embodiment can be obtained with a simple structure. Although the constant multiplication circuit is configured by combining the two constant multiplication circuits 45 and 46, the input signal may be 1 / K in either one of the constant multiplication circuits.

FIG. 11 shows a part of the ninth embodiment of the present invention, and FIG. 12 shows each signal waveform of the ninth embodiment. This 9th
The seventh embodiment is an embodiment of the invention according to claim 9, and in the seventh embodiment, the compensator 44 is replaced by a constant multiplication circuit 45, 46.
And an integrator 48, and a constant multiplication circuit 49 is provided. The light emission command signal V ₁ is a constant multiplication circuit 45.
The constant (1 / k) is multiplied is integrated by the integrator 48, a constant by the output signal Ve ₁ and an output signal Ve ₂ and is summed at summing point f constant multiplication circuit 46 of the constant multiplication circuit 45 of the integrator 48 It is multiplied by (1 / k '). Further, the light emission command signal V ₁
Is multiplied by (1 + 2 / K) by a constant multiplication circuit 49 and a current proportional to the light emission command signal is output by the current driver 15.
The compensation signal Ve from the constant multiplication circuit 46 is subtracted from the output Vd of the current driver 15 at the subtraction point g, added to the output of the error amplifier 13 at the addition point a, and then input to the current amplifier 14. The other parts of the ninth embodiment are similar to those of the seventh embodiment.

In the ninth embodiment, since the compensator 44 is composed of the constant multiplication circuits 45 and 46 and the integrator 48 and the constant multiplication circuit 49 is provided, it is generated based on the integrated waveform signal Ve _1. Since the compensation signal does not include high frequency components, the compensator can be easily designed. Although the constant multiplication circuit is configured by combining the two constant multiplication circuits 45 and 46, the input signal may be 1 / K in either one of the constant multiplication circuits. Further, the compensation signal is only an integrated waveform signal obtained by multiplying the light emission command signal V ₁ by 1 / K, and the light emission command signal V ₁ is multiplied by a constant (1 + 1 / K) by a constant multiplication circuit 49 to obtain a current at the subtraction point g. Similar compensation can be performed by subtracting from the output of the driving unit 15.

[0069]

As described above, according to the first aspect of the present invention, a part of the optical output of the driven semiconductor laser is monitored by the light receiving section to obtain a monitor signal proportional to the output intensity of the semiconductor laser. In a semiconductor laser control device that controls the forward current of the semiconductor laser so that the monitor signal and the light emission command signal are equal to each other, an error amplifier for amplifying a difference current between the light emission command signal and the monitor signal, and the light emission. The semiconductor laser includes a current driver that outputs a current proportional to a command signal, and a current amplifier that amplifies a signal obtained by adding the output of the error amplifier and the output of the current driver. Therefore, it is not necessary to provide a separate current amplifier for each output section of the error amplifier and the current driver, and the error amplifier and the current driver need not be provided with the current amplifier. Can common, current consumption can be reduced during an IC, it is possible to reduce the number of large transistor transistor size can be reduced chip size can reduce the chip area. Further, the current addition portion can be incorporated in the IC, the influence of the parasitic element can be reduced, high-speed current addition can be performed, and high-speed semiconductor laser control can be performed.

According to a second aspect of the present invention, in the semiconductor laser control device according to the first aspect, the current amplifier is composed of a transistor and a resistor connected to the emitter of the transistor, and the output of the error amplifier is provided. A signal obtained by adding the output of the current driver is applied to the base of the transistor and converted into the forward current of the semiconductor laser by the resistor, so that the same effect as that of the invention according to claim 1 can be obtained with a simple configuration. can get.

According to the third aspect of the present invention, a part of the optical output of the driven semiconductor laser is monitored by the light receiving section to obtain a monitor signal proportional to the output intensity of the semiconductor laser. In a semiconductor laser control device for controlling the forward current of the semiconductor laser so that the signal becomes equal to the signal, a first transistor in which an emitter current is changed by a current proportional to the light emission command signal;
A first resistor connected to the collector of the transistor of
A second transistor whose base is connected to the first resistor, a second resistor whose one end is connected to the emitter of the second transistor, and a difference current between the light emission command signal and the monitor signal are amplified. Error amplifier, and a third transistor whose output side is connected to the base,
A third resistor having one end connected to the emitter of the third transistor, a fourth transistor having a collector and a base connected to the other end of the third resistor, and one end connected to the emitter of the fourth transistor. A fourth resistor connected to
A fifth transistor whose base is connected to the base of the fourth transistor, a fifth resistor whose one end is connected to the emitter of the fifth transistor, the other end of the second resistor and the fifth transistor. The semiconductor laser is controlled by the output current of the current amplifier, and the same effect as that of the invention of claim 1 is obtained with a simple configuration. In addition, the semiconductor laser can be driven with a stable current that does not depend on the fluctuation of the power supply voltage, the temperature change of the base-emitter voltage of the transistor, and the characteristic variation.

According to the invention of claim 4, in the semiconductor laser control device of claim 3, the second resistor,
Since the first capacitance, the second capacitance, the third capacitance, and the fourth capacitance are connected in parallel with the third resistor, the fourth resistor, and the fifth resistor, respectively, the influence of parasitic capacitance is reduced. It can be ignored, and high-speed semiconductor laser control becomes possible.

According to the fifth aspect of the present invention, a part of the optical output of the driven semiconductor laser is monitored by the light receiving section to obtain a monitor signal proportional to the output intensity of the semiconductor laser. In a semiconductor laser control device for controlling the forward current of the semiconductor laser so that the signal becomes equal to the signal, a first transistor in which an emitter current is changed by a current proportional to the light emission command signal;
A first resistor connected to the collector of the transistor of
A second transistor whose base is connected to the first resistor, a sixth resistor whose one end is connected to the emitter of the second transistor, and a fifth resistor which is connected in parallel with the sixth resistor. A capacitance, a seventh resistance having one end connected to the other end of the sixth resistance, a sixth capacitance connected in parallel with the seventh resistance, the light emission command signal, and the monitor signal. An error amplifier that amplifies the difference current,
A third transistor whose output side is connected to the base, a third resistor whose one end is connected to the emitter of the third transistor and which has a resistance value equal to that of the sixth resistor, and the third resistor. A second capacitance connected in parallel with the fifth capacitance and having the same capacitance as the fifth capacitance, a fourth transistor having a collector and a base connected to the other end of the third resistor, and an emitter of the fourth transistor. A fourth resistor having one end connected to the seventh resistor and having a resistance value equal to that of the seventh resistor, and the fourth resistor connected in parallel to the fourth resistor.
A third capacitance having a capacitance equal to the capacitance of, a fifth transistor having a base connected to the base of the fourth transistor, and a fifth resistor having one end connected to the emitter of the fifth transistor, A fourth capacitance connected in parallel to the fifth resistor and a current amplifier whose input side is connected to the other end of the seventh resistor and the collector of the fifth transistor are provided. Since the semiconductor laser is controlled by the output current, the frequency characteristic can be improved and the semiconductor laser can be controlled at higher speed.

According to a sixth aspect of the present invention, in the semiconductor laser control device of the fourth aspect, a value obtained by multiplying the resistance value of the second resistor and the capacitance of the first capacitance is used as the current amplifier. The value obtained by multiplying the resistance component and the capacitance component of the input impedance is equal to or substantially equal to the value. Therefore, the semiconductor laser control can be performed so that there is almost no deviation from the value proportional to the light emission command signal.

According to the seventh aspect of the present invention, a part of the optical output of the driven semiconductor laser is monitored by the light receiving section to obtain a monitor signal proportional to the output intensity of the semiconductor laser. In a semiconductor laser control device that controls the forward current of the semiconductor laser so that the signals become equal, an error amplifier that amplifies a difference current between the light emission command signal and the monitor signal, and a current proportional to the light emission command signal. A compensator for generating a difference signal from a value proportional to the light emission command signal of the output signal of the current driver, an output of the error amplifier, an output of the current driver and the compensation A current amplifier that amplifies a signal obtained by adding the output of the device and the semiconductor laser is controlled by the output current of the current amplifier. It is possible to compensate for the deviation.

According to an eighth aspect of the present invention, in the semiconductor laser control device according to the seventh aspect, the compensator has a first means for multiplying the light emission command signal by a constant number, and the first means.
And a second means for generating a differential waveform signal of a signal obtained by multiplying the light emission command signal by a constant number.
With a simple structure, the same effect as the invention according to claim 7 can be obtained.

According to the ninth aspect of the present invention, a part of the optical output of the driven semiconductor laser is monitored by the light receiving section to obtain a monitor signal proportional to the output intensity of the semiconductor laser. In a semiconductor laser control device that controls the forward current of the semiconductor laser so that the signals become equal, an error amplifier that amplifies the difference current between the light emission command signal and the monitor signal and the light emission command signal (1
+ 2 / K) times the third means, a current drive unit that outputs a current proportional to the light emission command signal using the output of the third means as an input signal, and a first means that multiplies the light emission command signal by 1 / K. 4 means, 5th means for generating an integrated waveform signal of the output of the 4th means, and 6th means for adding the output of the 5th means and the output of the 4th means. A compensator for generating a difference signal from a value proportional to the light emission command signal of the output signal of the current driver, and a seventh means for subtracting the output of the sixth means from the output of the current driver, A current amplifier for amplifying a signal obtained by adding the output of the seventh means and the output of the error amplifier is provided. Since the semiconductor laser is controlled by the output current of this current amplifier, it is generated based on the integrated waveform signal. The compensation signal does not contain high frequency components and Vessel design becomes easy.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a block diagram showing a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a third embodiment of the present invention.

FIG. 4 is a circuit diagram showing a fourth embodiment of the present invention.

FIG. 5 is a circuit diagram showing a fifth embodiment of the present invention.

FIG. 6 is a circuit diagram showing a part of an AC equivalent circuit of the fourth embodiment.

FIG. 7 is a waveform diagram showing a signal waveform of the fourth embodiment.

FIG. 8 is a block diagram showing a seventh embodiment of the present invention.

FIG. 9 is a block diagram showing an eighth embodiment of the present invention.

FIG. 10 is a waveform diagram showing each signal waveform of the eighth embodiment.

FIG. 11 is a block diagram showing a ninth embodiment of the present invention.

FIG. 12 is a waveform diagram showing each signal waveform of the ninth embodiment.

FIG. 13 is a block diagram showing a conventional semiconductor laser control device.

FIG. 14 is a block diagram showing the semiconductor laser control device in detail.

[Explanation of symbols]

11 Semiconductor Laser 12 Photodiode 13 Error Amplifier 14 Current Amplifier 15 Current Driver 16, 20, 23, 24, 27, 30, 32, 3437
Transistors 17, 21, 25, 26, 28, 31, 33, 35, 3
6,42 Resistance 18,29 Current source 19,38-41,43 Capacitance 22 Diode 44 Compensator 45,46,49 Constant multiplication circuit 47 Differentiator 48 Integrator

Claims (9)

[Claims] 1. A part of the optical output of a driven semiconductor laser is monitored by a light receiving portion to obtain a monitor signal proportional to the output intensity of the semiconductor laser, and the monitor signal and the light emission command signal are equalized. In a semiconductor laser control device that controls the forward current of a semiconductor laser, an error amplifier that amplifies a difference current between the emission command signal and the monitor signal,
A current driver that outputs a current proportional to the light emission command signal; and a current amplifier that amplifies a signal obtained by adding the output of the error amplifier and the output of the current driver. A semiconductor laser control device characterized by controlling a semiconductor laser. 2. The semiconductor laser control device according to claim 1, wherein the current amplifier is composed of a transistor and a resistor connected to the emitter of the transistor, and the output of the error amplifier and the output of the current driver are formed. A semiconductor laser control device, wherein the added signal is applied to the base of the transistor and converted into a forward current of the semiconductor laser by the resistor. 3. A part of the optical output of the driven semiconductor laser is monitored by a light receiving part to obtain a monitor signal proportional to the output intensity of the semiconductor laser, and the monitor signal and the light emission command signal are equalized. In a semiconductor laser control device for controlling a forward current of a semiconductor laser, a first transistor whose emitter current is changed by a current proportional to the light emission command signal, and a first resistor connected to a collector of the first transistor. A second transistor whose base is connected to the first resistor, a second resistor whose one end is connected to the emitter of the second transistor, and a difference current between the light emission command signal and the monitor signal. An error amplifier for amplifying, a third transistor whose output side is connected to the base, and one end connected to the emitter of the third transistor A fourth resistor having a collector and a base connected to the other end of the third resistor, a fourth resistor having one end connected to the emitter of the fourth transistor, and A fifth transistor whose base is connected to the base of the fourth transistor, a fifth resistor whose one end is connected to the emitter of this fifth transistor, the other end of the second resistor and the fifth transistor. A semiconductor laser control device comprising: a collector of a transistor; and a current amplifier whose input side is connected, wherein the semiconductor laser is controlled by an output current of the current amplifier. 4. The semiconductor laser control device according to claim 3, wherein the second resistance, the third resistance, the fourth resistance and the fifth resistance are respectively parallel to a first capacitance and a second capacitance. 3. A semiconductor laser control device, wherein the third capacitance, the third capacitance, and the fourth capacitance are connected. 5. A part of the optical output of the driven semiconductor laser is monitored by a light receiving part to obtain a monitor signal proportional to the output intensity of the semiconductor laser, and the monitor signal and the light emission command signal are equalized. In a semiconductor laser control device for controlling a forward current of a semiconductor laser, a first transistor whose emitter current is changed by a current proportional to the light emission command signal, and a first resistor connected to a collector of the first transistor. A second transistor whose base is connected to the first resistor; a sixth resistor whose one end is connected to the emitter of the second transistor;
A fifth capacitance connected in parallel with the resistance of, and a seventh resistance having one end connected to the other end of the sixth resistance,
A sixth capacitance connected in parallel with the seventh resistor, an error amplifier for amplifying a difference current between the light emission command signal and the monitor signal, and a third amplifier having an output side of the error amplifier connected to the base. A transistor, a third resistor whose one end is connected to the emitter of the third transistor and has a resistance value equal to that of the sixth resistor, and a transistor and a third resistor which is connected in parallel with the third resistor and has the same capacitance as the fifth capacitance. Second
And a fourth transistor whose collector and base are connected to the other end of the third resistor, and
A fourth resistor having one end connected to the emitter of the transistor and having a resistance value equal to that of the seventh resistor; and a third capacitance connected in parallel to the fourth resistor and having the same capacitance as the sixth capacitance, A fifth transistor having a base connected to the base of the fourth transistor, a fifth resistor having one end connected to the emitter of the fifth transistor, and a fifth resistor connected in parallel to the fifth resistor. And a current amplifier whose input side is connected to the other end of the seventh resistor and the collector of the fifth transistor, and the semiconductor laser is controlled by the output current of the current amplifier. And a semiconductor laser control device. 6. The semiconductor laser control device according to claim 4, wherein a value obtained by multiplying a resistance value of the second resistor and a capacitance of the first capacitance is used as a resistance component and a capacitance of an input impedance of the current amplifier. A semiconductor laser control device, characterized in that it is equal to or approximately equal to a value obtained by multiplying by minutes. 7. A part of the optical output of the driven semiconductor laser is monitored by a light receiving part to obtain a monitor signal proportional to the output intensity of the semiconductor laser, and the monitor signal and the light emission command signal are equalized. In a semiconductor laser control device that controls the forward current of a semiconductor laser, an error amplifier that amplifies a difference current between the emission command signal and the monitor signal,
A current driver that outputs a current proportional to the light emission command signal, a compensator that generates a difference signal from a value of the output signal of the current driver that is proportional to the light emission command signal, an output of the error amplifier and the A current amplifier for amplifying a signal obtained by adding the output of the current driver and the output of the compensator,
A semiconductor laser control device characterized in that the semiconductor laser is controlled by an output current of the current amplifier. 8. The semiconductor laser control device according to claim 7, wherein the compensator has a first means for multiplying the light emission command signal by a constant, and the light emission command signal is multiplied by a constant by the first means. And a second means for generating a differential waveform signal of the signal. 9. A part of the optical output of the driven semiconductor laser is monitored by a light receiving part to obtain a monitor signal proportional to the output intensity of the semiconductor laser, and the monitor signal and the light emission command signal are equalized. In a semiconductor laser control device that controls the forward current of a semiconductor laser, an error amplifier that amplifies a difference current between the emission command signal and the monitor signal,
A third means for multiplying the light emission command signal by (1 + 2 / K), a current drive section for outputting a current proportional to the light emission command signal using the output of the third means as an input signal, and the light emission command signal Fourth means for multiplying by 1 / K, fifth means for generating an integrated waveform signal of the output of the fourth means, and fifth means
A sixth means for adding the output of the means and the output of the fourth means
Compensator for generating a difference signal from a value proportional to the light emission command signal of the output signal of the current driver, and subtracting the output of the sixth means from the output of the current driver. 7 means and a current amplifier for amplifying a signal obtained by adding the output of the seventh means and the output of the error amplifier, and the semiconductor laser is controlled by the output current of the current amplifier. Semiconductor laser control device.